A Comprehensive Exploration of Contemporary Photonic Devices in Space Exploration: A Review

Abstract

Photonics plays a pivotal role in propelling space exploration forward, providing innovative solutions to address the challenges presented by the unforgiving and expansive realm of outer space. Photonic-based devices, encompassing technologies such as lasers, optical fibers, and photodetectors, are instrumental in various aspects of space missions. A notable application is in communication systems, where optical communication facilitates high-speed data transfer, ensuring efficient transmission of information across vast interplanetary distances. This comprehensive review unveils a selection of the most extensively employed photonic devices within the realm of space exploration.

1. Introduction

Photonics is poised to revolutionize spacecraft engineering, presenting a paradigm shift by either replacing or enhancing conventional electrical approaches, particularly in critical domains such as digital and radio frequency (RF) telecom payloads, sensors, micro lidars, and spectrometers [1,2,3]. The transformative potential of these photonic technologies lies in their ability to concurrently reduce the size, weight, and power consumption while enhancing the overall performance of space systems [4]. Photonic integrated circuits (PICs) are at the forefront of these advancements, emerging as a transformative force in space applications. PICs enable chip-scale integration of multiple optical elements, allowing for the realization of complex functions analogous to electrical integrated circuits [5]. The anticipation of PICs playing a pivotal role in the future of spacecraft engineering is grounded in their capacity to usher in a new era of efficiency and versatility within the field [6].

The development of PICs for space exploration requires material platforms that can withstand the unique challenges of the space environment, including extreme temperatures, radiation exposure, and vacuum conditions [7,8]. Silicon photonics is a leading material platform due to its compatibility with existing semiconductor fabrication processes and its ability to integrate both photonic and electronic components on a single chip [9]. However, for space applications, additional materials such as silicon nitride and indium phosphide are often used because of their superior optical properties, such as low propagation losses and the ability to handle higher power levels [10]. Silicon nitride, in particular, offers high thermal stability, making it ideal for harsh space environments [11,12,13]. Indium phosphide enables the integration of active components like lasers and detectors, crucial for optical communication systems [14,15]. Additionally, emerging materials like lithium niobate on insulator (LNOI) and graphene are being explored for their electro-optic modulation capabilities and radiation resistance, potentially improving the performance of PICs in space exploration [16,17]. These material platforms must also be highly durable, lightweight, and efficient to support the stringent power and size constraints of space missions [18,19].

At the crossroads of optics and electronics, optoelectronic devices captivate with their ability to leverage the distinct properties of light across a spectrum of applications [20,21]. These ingenious devices deftly manipulate and govern the flow of photons, yielding a multitude of functionalities. Among the standout examples are light-emitting diodes (LEDs) and lasers, serving as prime illustrations of optoelectronic prowess as they seamlessly convert electrical energy into light [22,23]. Their significance reverberates in diverse sectors, from revolutionizing telecommunications to enhancing the brilliance of illumination systems. Conversely, photodetectors, including photodiodes and phototransistors, undertake the reverse alchemy, transforming incoming light signals into electric currents. This transformative ability finds application in various technologies, including sensors [24], cameras [25], and sophisticated optical communication systems [26]. As a hub of modern technology, optoelectronics underscores its indispensability by propelling innovations in displays, medical imaging, and sustainable energy solutions [27,28,29]. The persistent evolution of optoelectronic devices stands as a beacon, promising even more remarkable technological breakthroughs on the horizon [30]. In essence, space-based solar panels share many fundamental features with their terrestrial counterparts [31,32,33]. Both utilize cells manufactured from conductive materials, commonly silicon, seamlessly arranged in arrays [34]. However, the key distinctions lie in the overall quality and durability of these solar modules. The space environment presents formidable challenges, exposing solar panels to extreme temperatures, ranging from scorching heat to bone-chilling cold, as well as the harsh effects of radiation [35,36,37]. Space-based solar panels are carefully designed to withstand these adversities, shaping the resilience of the hardware [38].

Notably, NASA continually explores innovative semiconductor materials to enhance solar cell performance in space [39]. Gallium arsenide stands out as one such example, displaying NASA’s commitment to pushing the boundaries of solar technology beyond conventional silicon cells [40]. It is anticipated that there will be a wave of innovations poised to redefine the landscape of space-based solar power, as ongoing research promises breakthroughs in efficiency, durability, and adaptability to the rigors of the extraterrestrial environment. The deployment of photonic devices in space has revolutionized the field of space exploration [41,42,43,44], enabling unprecedented advancements in communication, navigation, and observation. Space exploration relies heavily on the integration of cutting-edge technology to overcome the challenges posed by the harsh and vast expanse of the cosmos [45]. From communication systems to navigation instruments and observational tools, photonics/optoelectronics plays a pivotal role in shaping the success of space missions [46]. This review paper explores the key optoelectronic devices utilized in space missions, discussing their functions, applications, and the transformative impact they have had on our understanding of the cosmos.

2. Space Exploration Investment

The global photonic integrated circuits (PICs) market exhibited a valuation of USD 10.2 billion in 2022 and is poised for substantial growth, with a projected Compound Annual Growth Rate (CAGR) of 29.2% from 2023 to 2031 [47]. This optimistic trajectory is fueled by a surge in demand for cutting-edge communication technologies and the widespread adoption of photonic advancements within the space sector. Furthermore, the increasing integration of photonics into critical computing devices is expected to drive significant market progress over the coming years [48,49].

The burgeoning growth in the space, IT, and telecommunication sectors is set to unlock lucrative opportunities for the market [50,51]. PICs represent a breakthrough in integrated circuit technology, seamlessly incorporating various photonic components like modulators, lasers, waveguides, sensors, and other optical elements onto a single chip [52,53,54]. These circuits harness photons for the transfer and processing of information, marking a departure from traditional electronic circuits that rely on electrons for information transmission. This innovative approach positions PICs at the forefront of technological advancements, making them pivotal players in the evolution of communication and computing landscapes. PICs showcase a spectrum of distinctive attributes, such as elevated bandwidth and data rates, compact size, resilience to radiation, and secure communication capabilities [55]. These features are propelling their increased adoption within the space sector. Moreover, PICs provide high-performance data communication, radiation resilience, compact form factors, and energy efficiency, rendering them an ideal choice for cutting-edge space applications like Earth observation, satellite communication, and interplanetary exploration [56,57,58]. Consequently, the rising investments in space exploration are serving as a driving force behind the expansion of the market.

3. Operation in an Extreme Space Environment

Operating in the challenging space environment has been a longstanding obstacle, posing significant threats to spacecraft. Potential damages from radiation, plasma, atomic oxygen, outgassing, and contamination can risk missions and drastically curtail their lifespans. The unique conditions of space, including extreme temperatures and reduced gravity, demand advanced materials and thermal protection systems [59]. As space endeavors evolve to encompass increasingly complex missions such as establishing a permanent human presence on the Moon, on-orbit manufacturing, and repairing existing missions, the formidable challenges of the space environment persist. It is imperative to explore novel approaches, materials, and prediction methods, utilizing testing and simulation, to ensure the resilience of future space technologies against the harsh conditions necessary for comprehensive mission success while minimizing costs [60]. The graphical illustration of the harsh environment in space is shown in Figure 1.

The current strategies to shield against radiation often involve expensive measures such as heavy shielding masses or radiation-hardened components. For satellite programs operating on limited budgets, these approaches are often impractical, leading to the neglect of radiation protection and a subsequent reduction in mission lifetimes [61]. Lunar surface operations face not only direct exposure to solar wind and radiation but also grapple with drastic temperature fluctuations between day and night. The added challenges of dust contamination on surfaces and moving parts further complicate operations in this environment. The advent of on-orbit manufacturing and spacecraft servicing extends the usable duration of missions. However, the introduction of new materials and modifications to material properties in a microgravity environment necessitate thorough validation for their performance in space, given potential variations compared to currently employed materials [37]. Assurance is paramount that these novel materials and components can endure the environmental effects throughout extended mission durations [35].

4. Widely Researched Photonic Devices for Space Applications

Photonic devices play a central role in advancing space exploration by providing transformative capabilities that improve communication, sensing, and data processing in the challenging environment of outer space. In contrast to traditional electronic systems, photonic devices utilize photons instead of electrons, offering benefits such as quicker data transfer rates, reduced energy consumption, and heightened resistance to radiation. Given the formidable challenges posed by vast distances and harsh conditions in space, these attributes become essential. Photonic devices facilitate high-speed optical communication between spacecraft and Earth, streamlining the transmission of substantial data volumes across interplanetary distances. They also enhance sensing technologies for remote observations, allowing for more accurate data collection and analysis. Moreover, the resilience of photonic devices in the presence of cosmic radiation ensures the dependability of critical systems, contributing to the overall success and endurance of space missions. With the escalating ambitions of space exploration endeavors, the importance of photonic devices in powering advanced communication systems and instrumentation cannot be overstressed, propelling humanity further into the cosmos with unprecedented efficiency and reliability. A few of the most important photonic devices employed in space exploration are discussed in this paper and are shown in Figure 2.

4.1. Photodetectors

Photodetectors play a pivotal role in space applications, serving as essential components in various instruments and systems designed for astronomical observations, remote sensing, and communication [62]. These detectors are crucial for capturing and converting incoming light signals into electrical signals, enabling the analysis of celestial objects and the collection of valuable data from space. In space exploration, where extreme conditions prevail, photodetectors must exhibit high sensitivity, reliability, and durability to withstand the harsh environment of outer space. Different types of photodetectors, such as charge-coupled devices (CCDs) and photodiodes, are employed in space missions to capture images, measure radiation, and facilitate communication. The development of advanced photodetector technologies has significantly enhanced our ability to explore and understand the universe, contributing to breakthrough discoveries and expanding our knowledge of the cosmos [63].

Undoubtedly, the most formidable challenges in the realm of photodetectors arise in the field of astronomy, where the spectrum of wavelengths under scrutiny spans an astonishing range. From the far IR at hundreds of microns to cosmic ray photons boasting 1020 electron volts of energy and wavelengths as minute as 10–20 µm, this encompasses an extraordinary 22 orders of magnitude. Delving into these extremes, the European Space Agency is charting its course for FIRST, the far infrared and submillimeter space telescope. This groundbreaking telescope is poised to explore the one spectral band not yet surveyed, covering a span from 60 to 670 µm [64].

The innovative design of FIRST incorporates arrays of germanium and gallium photoconductors tailored for the 100 to 200 µm range, while arrays of bolometers, meticulously cooled to a mere 0.1 K, are employed for the remaining spectrum. Venturing into the near-IR wavelengths, focal plane arrays featuring indium antinomide, mercury cadmium telluride, and platinum silicide—originally developed for military applications—are becoming standard components for telescopes both on Earth and in space. The evolution of technology is evident in the utilization of miniaturized IR and CCD cameras aboard spacecraft like Clementine. This inclusion empowered Clementine to conduct a comprehensive survey of the Moon, spanning wavelengths from the ultraviolet to 9.5 µm in the far-IR range. Such advancements underscore the dynamic constructive collaboration between technological innovation and astronomical exploration.

Detectors designed for space applications face the complex challenge of efficiently detecting, tracking, identifying, and assessing the status of both cold and hot objects. These objects may be situated in proximity or at considerable distances, and their conditions could range from being sunlit to residing in shadow. To address this diverse set of requirements, an ideal sensor must possess frequency agility, allowing it to detect a wide array of specific wavelengths. Additionally, it should exhibit optical signal enhancement capabilities. At the Space Vehicles Directorate within the Air Force Research Laboratory, innovative approaches have been explored to develop a multifunctional, monolithically integrated sensor system [65]. Their vision entails a sensor wherein each pixel is equipped with a protection layer, an amplification layer, a detection layer, and a solid-state cooling layer. These layers are seamlessly grown monolithically alongside the readout electronics and incorporate on-chip data processing capability. This groundbreaking design aims to create a self-protecting sensor with enhanced detection efficiency, expanded functionality, reduced volume and weight, heightened reliability, and decreased overall cost—both in terms of fabrication and final launch expenditures. Such a compact yet powerful sensor system holds the potential to provide detailed information about unknown objects while meeting the stringent demands of space applications [65].

A comprehensive investigation into the production and evaluation of a Ga₂O₃-based UV-C photodetector is proposed through the innovative aerosol deposition (AD) technique [66]. This approach involved meticulous optimization of both size and crystallinity parameters for the Ga₂O₃ powder, leading to the successful creation of a uniform thin film characterized by remarkable light transmittance (70–80%). Notably, this achievement was attained without resorting to additional heat treatments or the use of high vacuum environments. The resulting Ga₂O₃ film exhibited an impressive and discerning responsiveness specifically to 254 nm wavelength light, demonstrating a notable sensitivity even without any post-treatment. Furthermore, the photodetector displayed robust stability under exposure to γ-radiation. Notably, its performance endured extreme temperature variations ranging from −196 °C to 150 °C, highlighting its resilience and suitability for deployment in demanding conditions, such as those encountered in the space industry. This study underscores the considerable potential of the AD method for fabricating high-quality Ga₂O₃ thin films tailored for photodetector applications. The demonstrated properties open avenues for advancements in sensor technologies, particularly in challenging environments where stability and precision are paramount [66].

An advanced and remarkably compact thermal camera (see Figure 3), with lineage traced back to a counterpart currently deployed on NASA’s Landsat 8, has found its place within NASA’s upcoming Robotic Refueling Mission 3 (RRM3) [67]. Positioned strategically in the payload section, this cutting-edge Compact Thermal Imager (CTI) is set to capture high-resolution images and videos of Earth’s surface once the SpaceX Dragon resupply vehicle delivers it to the orbiting outpost. While RRM3 highlights specialized satellite-servicing tools crafted by NASA’s Satellite Servicing Projects Division, the hitchhiking companion, CTI, boasts the capability to image and measure a spectrum of phenomena, including fires, ice sheets, glaciers, and snow surface temperatures. Moreover, CTI will play a crucial role in measuring the transfer of water from soil and plants into the atmosphere, providing vital insights into plant growth dynamics. Many of these Earth science conditions are readily discernible in the infrared or thermal wavelength bands.

CTI owes its exceptional performance to a cutting-edge photodetector technology known as Strained-Layer Superlattice (SLS). Remarkably compact, measuring nearly sixteen inches in length and six inches in height, SLS stands out for its low power consumption, ability to operate at liquid-nitrogen temperatures, ease of fabrication in high-technology environments, and cost-effectiveness. Notably, this detector technology can be swiftly customized for various applications. The Goddard Detector Development Laboratory, responsible for CTI’s innovative SLS detectors, recently fabricated a 1024 × 1024-pixel SLS array, with plans to upscale it to 2048 × 2048 pixels soon. Another pivotal technology supporting CTI is the Goddard-developed SpaceCube 2.0, a potent hybrid computing system that will govern the instrument, processing the images and videos it captures while in orbit.

The primary goal of this demonstration is to elevate SLS’s technology-readiness level to nine (TRL-9), signifying successful deployment in space and demonstrating its robust performance under the extreme environmental conditions prevalent there. SLS, based on the Quantum Well Infrared Photodetector (QWIP) technology refined over two decades, follows in the footsteps of its QWIP predecessor, currently operational on Landsat 8 and slated for the upcoming Landsat 9 Thermal Infrared Sensor Instrument. SLS detectors are notably 10 times more sensitive, operating across a broader infrared spectral range and at substantially warmer temperatures (70 K or about −334 degrees Fahrenheit) compared to QWIP (42 K or about −384 degrees Fahrenheit). This increase in operating temperature brings several positive outcomes for future missions. Infrared radiation is sensed as heat, necessitating cooling systems to prevent heat contamination. The ability of the SLS array to operate at warmer temperatures translates to smaller and more efficient cooling systems, paving the way for smaller satellites, extended longevity, shorter build cycles, and reduced costs in future space missions, as per the researchers’ vision [67].

4.2. Light-Emitting Diodes (LEDs) and Lasers

Light-emitting diodes (LEDs) and lasers are employed in space missions for various purposes. LEDs serve as reliable indicators and status lights on spacecraft, providing essential visual feedback to mission controllers. In contrast, lasers play a central role in space-based communication systems [68]. Laser communication offers high-speed data transfer between satellites and ground stations, overcoming limitations associated with traditional radio frequency communication [54].

The escalating frequency of satellite constellation and cluster launches, with a specific focus on small satellite platforms, necessitates a heightened precision and responsiveness in the currently operational tracking systems [69]. This imperative arises in the context of future Space Situational Awareness and Space Traffic Management tasks. The incorporation of active illumination payloads, such as LED-based boards, represents a transformative solution. This technology enables satellites to be optically tracked seamlessly throughout the eclipse phase, thereby eliminating constraints associated with varying light conditions and Sun phase angles [70]. The utilization of LED payloads empowers the tracking process throughout the entire orbital lifespan of a satellite. This capability extends from the initial identification upon deployment within a vast cluster to tasks involving orbit determination, attitude reconstruction, supplementary light communication, and support for Post-Mission Disposal activities. The implementation of LED technology emerges as a pivotal advancement in enhancing the efficacy and versatility of satellite tracking systems in the dynamic landscape of space exploration.

The development of an LED-based optical tracking system necessitates careful consideration of irradiance maximization within the confines of power and available volume, ensuring the involvement of small telescope stations in the ground segment. For spaceborne applications, a judicious selection of commercial LEDs, ranging from 15 to 40 diodes, should be made, maximizing quantum efficiency and irradiance while adhering to the power constraints of nanosatellite platforms’ electrical power systems. The diodes, when implementing identifier patterns for recognition and orbit determination every 25–30 s, consume a mere 5% of the energy generated by a reference 1U CubeSat EPS, rendering the LED system compatible with even the most power-constrained CubeSat platform, and establishing LEDs as a viable secondary tracking system as shown in Figure 4a [70].

Within the ground segment, cost-effective telescopes with relatively simple hardware can be employed as shown in Figure 4b. Observational techniques may involve telescope movement with sidereal rate, capturing the satellite LED signal as it traverses the stellar background, or actively tracking and maintaining the target within the Field of View (FOV) throughout the entire pass. Both arrayed (CCD and CMOS) and single-element (P-I-N or APD photodiodes) sensors offer flexibility for different tasks, each presenting unique advantages and drawbacks. Photodiodes facilitate data extrapolation from flashes, while CCD or CMOS techniques provide tracking and attitude information. In the calculation of the optical link budget, key parameters include minimum elevation, atmospheric transmittance at the LEDs’ flashing wavelength, and ground segment features such as sensor characteristics and selected observation techniques. As a general guideline, a minimum signal-to-noise ratio (SNR) of 10 and a minimum elevation of 20° are recommended for ground-based data acquisition [70].

Optimizing flashing patterns for various purposes is essential. The basic guideline for LED flashes is to incorporate both long and short flashes, facilitating satellite identification against the background stellar field and enabling the reconstruction of target celestial coordinates. Orthogonal patterns like gold codes enhance the recognition of different patterns executed simultaneously, aiding attitude determination by discriminating between different satellite sides flashing with distinct patterns. Furthermore, employing LEDs in different colors provides an additional advantage, allowing for simultaneous observations with color filters from multiple sensors and/or sites. This comprehensive approach ensures the effectiveness and versatility of LED-based optical tracking systems in diverse scenarios.

The utilization of coherent light, exemplified by the focused beams of lasers, in conjunction with the exacting prerequisites for implementing cutting-edge technologies in space, opens a myriad of possibilities across various domains. Optical communication, illumination, target designation, and active remote sensing benefit significantly from this amalgamation, displaying unprecedented outcomes compared to conventional technologies. The continual scientific progress in laser-emitting technologies not only propels these applications further but also paves the way for novel devices and functionalities.

Semiconductor lasers have been extensively researched and employed in space applications for several years, leveraging their notable advantages [72]. One key strength lies in their ability to operate under direct current injection, yielding high electrical-to-optical power conversion efficiency. Furthermore, these lasers boast extended lifetimes and offer high output power. Despite some limitations, such as divergence, beam quality, and intensity noise that may render them unsuitable for certain applications, semiconductor lasers stand out as the preferred pump element for solid-state lasers (SSLs) and fiber lasers [73]. One pivotal aspect contributing to their prominence is the semiconductor lasers’ capacity to slightly tune their wavelength. This feature enables the achievement of optimal absorption of laser media, establishing them as the cornerstone in laser technologies tailored for space applications. Various materials come into play in their construction, including GaAs, InGaAs, InP, and InGaAsP. Among the diverse semiconductor laser types, the two most prevalent are the edge-emitting laser (EEL) [74] and the vertical-cavity surface-emitting laser (VCSEL) [75].

The EEL emerges as the predominant semiconductor laser device, renowned for its diode junction structure that transforms electrical energy into light. Beyond its role in SSL pumping, EEL finds application in a spectrum of functions such as information relay (inter- and intra-satellite communication), matter–light interaction (utilized in spectroscopy and pyrotechnics), planetary exploration and monitoring, metrology, and sensor technology. Noteworthy direct applications include the autofocus system of the ChemCam laser and the rendezvous sensor facilitating the docking of the European Automatic Transfer Vehicle to the ISS. EEL has already been deployed in satellites, traversed deep space, and even operated on the Martian surface, attesting to its robust performance in real-world space scenarios.

The VCSEL distinguishes itself from the EEL not only in its manufacturing process but, more notably, in its beam emission characteristics. In contrast to the EEL, the VCSEL emits its output laser beam perpendicular to the top surface. The distinct manufacturing and packaging processes of these two types of lasers necessitate independent qualification for space missions. Additionally, VCSELs exhibit a lower threshold, resulting in a reduced requirement for electrical power. Early studies recognized VCSELs as promising candidates for space applications. Carson et al. [76] emphasized that, despite the need for careful optimization for space use, VCSELs demonstrate superior radiation resistance compared to their EEL counterparts. In-depth exploration by LaForge et al. [77] delved into the potential of VCSELs as space multi-processors, outlining both their capabilities and potential challenges when exposed to radiation. The publication focused on implementing VCSEL devices for satellite missions across various orbits, highlighting the versatility and potential applications of VCSEL technology in the space domain.

Traditionally, only formidable entities like the National Aeronautics and Space Administration (NASA), the former Soviet Union (now Russia), the European Space Agency (ESA), and more recently, the Japan Aerospace Exploration Agency (JAXA), China, and India possessed the capability to propel technology into space. However, the landscape has evolved, with Israel and private enterprises such as SpaceX, Virgin, Blue Origin, and SpaceIL entering the space race. Notably, the surge in micro- and nanosatellites, some as diminutive as one liter with weights below 1.5 kg [78], has democratized access to space. This paradigm shift has enabled new participants to launch innovative devices for applications ranging from Earth observation, communication, and the Internet of Things (IoT) to geolocation [79].

Driven by market demands and the emergence of active new players, there has been a significant upswing in the number of devices deployed in space. For instance, the United Kingdom alone envisions launching 2000 small satellites by 2030 [80]. By harnessing the intrinsic advantages of photonic applications—such as enhanced bandwidth, reduced mass, lower power consumption, and immunity to electromagnetic interference—many of these new space deployments are poised to incorporate advanced laser devices [81]. This not only underscores the transformative impact of laser technology in space but also signifies a pivotal shift towards a more inclusive and dynamic space exploration era.

On 9 May 1962, the inaugural utilization of a laser in a space experiment was documented, specifically in the Laser Lunar Ranging experiment [82]. The laser apparatus, situated on the Earth’s surface, obviated the necessity for additional specifications essential for space flights, such as mechanical stability, resistance to thermal shocks, and radiation resilience. The narrative of laser deployment in space commenced in 1971 with the Apollo 15 mission, which transported the first laser beyond Earth. This pioneering laser, a flash-lamp-pumped Q-switched Ruby laser crafted by the RCA Corporation, played a pivotal role in the Laser Altimeter experiment [83]. Fast-forward to 1992, a significant milestone was achieved with the delivery of the first diode-pumped solid-state laser (DPSSL) into space. Launched as part of the Mars Orbiter Laser Altimeter (MOLA) in 1996, this laser featured an Nd:YAG crystal as its active medium [84]. November 2001 marked another leap in space laser technology, as semiconductor laser technology was employed not just for pumping but for a direct laser application. The world witnessed the inaugural use of a laser-based optical data link, connecting the Artemis satellite from the ESA with the Centre National d’Études Spatiales (CNES) Earth observation satellite SPOT 4. This groundbreaking connection utilized GaAlAs laser diodes emitting at 0.8 µm [85]. Adding to these accomplishments, on 19 August 2012, history was made with the first laser pulse emitted on a planetary surface other than Earth. This remarkable event occurred through the laser integrated into the ChemCam device on the Curiosity Mars rover, employing an Nd:KGW crystal DPSSL [86].

The challenges inherent in operating lasers in space diverge significantly from those encountered in terrestrial applications. Consequently, lasers earmarked for space applications must adhere to specific criteria, including but not limited to prolonged operational lifespan, heightened efficiency, minimal susceptibility to optical misalignment and contamination, and the capability for unattended operation. The optimal laser selection hinges on the distinctive requirements posed by the application and the prevailing environment. Critical considerations in this selection process encompass wavelength, repetition rate, peak power, pulse length, flexibility, maintainability, manufacturing cost, and operating cost. However, the environmental context is equally paramount. Variables such as whether the laser will function in the low atmosphere, traverse deep space, operate in proximity to the Sun, or be stationed on another celestial body significantly influence the suitability and performance of the chosen laser system.

Micro-ring resonators are employed in space exploration for their ability to process and filter optical signals with high precision and efficiency [87,88]. These tiny devices, made from silicon or other photonic materials, are used in sensors to detect minute changes in light, enabling advanced spectrometry and communication systems. In space, they can help analyze the atmospheric compositions of planets, detect trace gasses, and support high-speed data transmission between spacecraft and Earth. Their compact size and low power consumption make them ideal for use in space missions, where weight and energy efficiency are critical [89,90].

While silicon photonics holds great promise as a PIC platform, the integration of lasers remains a challenging bottleneck [44]. Addressing this issue, a groundbreaking 3D hybrid integration technique was proposed under a NASA Early Career Faculty grant, aiming to seamlessly integrate lasers onto silicon substrates [91]. Illustrated in Figure 5a, this technique involves bonding an indium phosphide (InP) reflective semiconductor optical amplifier (RSOA) to silicon. The InP RSOA is equipped with a high reflectivity coated back mirror and a total internal reflection (TIR) turning mirror. Light is efficiently coupled to the silicon waveguide through a vertical grating coupler. Notably, the RSOA can be bonded P-side down to the silicon substrate, facilitating efficient heat dissipation from the active region. This configuration is particularly advantageous for high-power integrated lasers, leading to lower thermal impedance, higher efficiency, and potentially reduced relative intensity noise (RIN). Importantly, the integration is performed in a backend step, circumventing the co-fabrication of incompatible materials. Furthermore, the 3D hybrid integration approach opens the door for the bonding of III-V PICs to silicon interposers, enabling large-scale electronic–photonic integration, as depicted in Figure 5b.

The silicon chips employed in this study were fabricated at the Interuniversity Microelectronics Centre. The InP RSOAs were produced using an etched-facet process, with a gain section length of 500 µm. Thermocompression bonding was employed with a bond temperature of 350 °C and a force of approximately 20 N. Figure 5c showcases a microscope image of the fabricated bonded chip. To systematically assess the laser performance in an experimental setting, the 3D integrated laser underwent meticulous evaluation. The laser was securely affixed to a temperature-controlled stage and activated through electrical pumping facilitated by pin probes. To capture the emitted light from the Silicon Photonics External Cavity Laser (SPECL), a vertically oriented single-mode fiber probe, aligned with precision, collected the output through a fiber grating coupler. Accurate spectral measurements were conducted using an optical spectrum analyzer boasting an impressive resolution of 0.02 nm. Illustrated in Figure 5d, the lasing spectra at varying current levels near the threshold are showcased. Operating at a temperature of 20 °C, the system demonstrated single-mode continuous wave lasing, with an observable threshold current of 23 mA. The light–current–voltage (LIV) characteristic is elucidated in Figure 5e. Remarkably, at a current level of 100 mA, the optical power coupled into the silicon waveguide reached 2 mW, underscoring the laser’s robust performance under these conditions.

4.3. Optical Sensors, Fiber Optic Systems, and Modulators

Optical sensors, leveraging the principles of optoelectronics, contribute significantly to Earth observation satellites. These sensors capture light to gather data on vegetation, ocean properties, and atmospheric conditions, aiding scientific research and environmental monitoring [92]. Fiber optic systems, utilizing optical fibers for data transmission, play a crucial role in space-based communication networks, ensuring reliable and high-bandwidth data transfer over long distances. Planar photonic gyroscopes play a pivotal role in spacecraft engineering, owing to their key advantages, including compact size, lightweight design, low power consumption, and exceptional reliability and performance. These attributes make them highly attractive for space applications, driving a surge in research and development efforts in this rapidly evolving field [93].

Monitoring spacecraft is paramount for the successful execution of any space mission, necessitating a diverse array of sensors that furnish crucial information throughout fabrication, testing, and the operational lifespan of the craft. Operating in space presents a myriad of challenges, marked by microgravity, vacuum-induced outgassing, radiation (including gamma rays, protons, electrons, and heavy ions), substantial thermal fluctuations, and mechanical stresses resulting from the launch process. The specifications for spacecraft sensors are intricately derived, and primarily influenced by mission type, orbital altitude, operational lifespan, and sensor placement within the spacecraft [94].

Fiber optic sensing systems are emerging as preferred choices for space applications, owing to several inherent advantages that position them to potentially surpass traditional counterparts [95,96]. These advantages encompass (I) insensitivity to EM interference, coupled with the utilization of a passive sensor that is devoid of sparking or electrostatic discharge concerns; (II) adoption of a lightweight and flexible harness, contributing to substantial mass savings; (III) flexibility in sensor distribution across remote locations within the spacecraft’s structure; (IV) efficient multiplexing capabilities facilitating high sensor capacity and minimal power requirements per sensor; (V) high signal-to-noise ratio, ensuring exceptional measurement accuracy; (VI) multi-parameter sensing capabilities and remote interrogation functionality; and (VII) the potential for embedding within composite structures, enhancing integration possibilities.

These advantages collectively underscore the potential of fiber optic sensing systems to revolutionize spacecraft monitoring, offering reliability, versatility, and efficiency in the challenging and dynamic space environment. For over two decades, the European Space Agency (ESA) has been at the forefront of funding and driving the advancement of fiber optic sensor solutions. This sustained commitment has yielded remarkable success, with one standout achievement being the seamless integration of fiber optic gyroscopes (FOGs). Today, these FOGs have achieved widespread adoption, emerging as a cornerstone technology for high-precision rotation measurements in numerous satellite missions. The ESA’s enduring support has not only fostered technological breakthroughs but has also solidified fiber optic sensors as indispensable components in enhancing the accuracy and reliability of critical measurements within the dynamic realm of space exploration.

Ionizing radiation, particularly in the complex fields of space radiation, presents a significant threat to human health [97]. This risk escalates with mission duration, especially during ventures beyond the protective confines of Earth’s magnetic field and atmosphere. Recognizing the gravity of this challenge, radiation protection stands as a paramount concern for all international space agencies engaged in human spaceflight endeavors. To address this concern comprehensively, diverse systems have been developed to analyze and ascertain the extent of exposure to ionizing radiation, both in the spacecraft environment and among the crew aboard the ISS. Beyond mere operational monitoring, ongoing efforts involve conducting experiments and technology demonstrations aimed at augmenting system capabilities. These initiatives not only prepare for exploratory missions but also anticipate events such as the Deep Space Gateway, facilitating human presence on celestial bodies beyond Earth.

The European Space Agency (ESA) has been at the forefront of proactive measures, deciding early on to support the development of an active personal dosimeter. This initiative is being pursued under the auspices of the European Space Research and Technology Center (ESTEC), in collaboration with the European Astronaut Center’s (EAC) Medical Operations and Space Medicine (HRE-OM) team. To bring this vision to fruition, a European industrial consortium was established, tasked with the development, construction, and testing of this advanced dosimetry system. The resulting ESA Active Dosimeter (EAD) technology demonstration has seen significant progress, with EAD components successfully delivered to the ISS through the ESA’s space missions “iriss” and “proxima” in 2015 and 2016. This milestone underscores ESA’s commitment to advancing space technology, ensuring the safety and well-being of astronauts, and paving the way for future missions beyond Earth’s orbit [97]. Figure 6 displays sample images of the EAD-MUs positioned in various locations, including the Columbus Laboratory (Figure 6a,d), the US segment of the ISS (Figure 6b), the Leonardo Module (Figure 6e), and the Russian Service Module (Figure 6c,f).

A groundbreaking EO imaging sensor concept is proposed which is poised to revolutionize space exploration by offering a compact, lightweight alternative to conventional optical telescopes and focal plane detector arrays as shown in Figure 7a,b [98]. This innovative imaging sensor incorporates millions of direct detection white-light interferometers densely packed onto PICs, facilitating the measurement of amplitude and phase across the entire synthetic aperture’s spatial frequencies. This visionary approach eliminates the need for bulky optics and structures inherent in traditional telescopes, replacing them with PICs based on cutting-edge photonic technologies that can be fabricated using standard lithographic techniques such as CMOS fabrication. The integration of advanced optical interferometry and photonic technologies within this EO imaging sensor concept opens avenues for transformative NASA missions. It delivers a large-aperture, wide-field EO imager at a fraction of the conventional space telescope’s cost, mass, and volume [98].

Modulators play a crucial role in space exploration by enabling the efficient transmission of data over vast distances [16,99,100]. In space communication systems, modulators are used to encode scientific data, images, and telemetry onto carrier signals, often in the form of radio waves or laser beams, for transmission back to Earth or between spacecraft [4]. The harsh conditions of space require modulators that are highly reliable, radiation-resistant, and capable of operating under extreme temperatures and vacuum conditions [101]. Advanced optical modulators, such as electro-optic or acousto-optic modulators, are particularly valuable in deep space missions, where the high bandwidth and low signal attenuation of laser communication systems can significantly improve data transfer rates [102]. As space missions become more ambitious, including interplanetary exploration and human colonization efforts, the role of modulators in enabling real-time communication, remote sensing, and data transmission will continue to expand, making them indispensable for the future of space exploration [103].

4.4. Telescopes and Imaging Devices

The Advanced Pointing Imaging Camera (APIC) is engineered to capture high-resolution images for assessing a target’s geophysical and geodetic attributes. Its development stems from NASA’s Homesteader program, which focused on advancing technology for potential New Frontiers missions. The APIC stands out for its capability to simultaneously capture images of both the target and the surrounding star field, ensuring precise camera pointing and high-resolution data. The camera is compact, measuring 28 cm × 18 cm × 24 cm, weighs only 6 kg, and operates with a maximum power consumption of 13 W, all while maintaining high performance and durability for extended deep space missions [104].

Additionally, 3D PLUS has developed an advanced CMOS camera for space applications as part of its R&D efforts [105]. The French space agency, CNES (Centre National d’Études Spatiales), was overseeing the development of this camera, as illustrated in Figure 8a. The integration of this device utilized 3D PLUS technology to achieve maximum compactness. Special emphasis was placed on enhancing radiation tolerance to support a diverse array of scientific uses, including planetology, as well as platform or launcher monitoring and star tracking. Creotech Instruments is pioneering a transformative series of sCMOS cameras [106]. The final prototype model for an astronomical camera, designed for Space Surveillance and Tracking (SST), is currently undergoing testing. The 3D view of the camera is shown in Figure 8b. This camera was engineered for SST, Near-Earth Object (NEO), and debris detection, with a versatile platform that also supports quantum technology and biological microscopy. It featured edge computing capabilities, utilizing FPGA-based SoC for real-time processing and Linux-based pre-processing. Operating autonomously, it supported on-camera machine learning algorithms, offering significant advancements in astronomy. By incorporating data pre-processing techniques such as frame stacking, it effectively reduces data load [106].

Telescopes stand as indispensable gateways to the cosmos, playing a transformative role in deepening our understanding and unraveling the mysterious tapestry of the universe [107,108,109,110]. Functioning as celestial windows, these instruments transcend the confines of the naked eye, ushering us into realms that would otherwise remain unseen [111]. Through their discerning lenses, telescopes capture the ethereal dance of celestial bodies, offering glimpses into the farthest corners of space. Their significance lies not only in unveiling the cosmic wonders that adorn the night sky but also in charting the course of cosmic evolution.

Launched into orbit by NASA in 1990, the Hubble Space Telescope stands as an unparalleled marvel in the realm of astronomical observation, marking itself as an icon of cosmic exploration and understanding. The graphical illustration of the Hubble space telescope is shown in Figure 9a [112]. Named in honor of the pioneering astronomer Edwin Hubble, this space-based observatory has not only transformed our comprehension of the universe but has also left an indelible mark on the annals of scientific achievement. Armed with a suite of cutting-edge instruments designed for ultraviolet, visible, and near-infrared observations, Hubble has consistently delivered awe-inspiring imagery and irreplaceable data. Its remarkable accomplishments include a fundamental role in refining our estimate of the universe’s age, the capture of breathtaking images highlighting distant galaxies, and the confirmation of the existence of dark energy. Hubble’s impact extends to vital contributions in the study of stellar evolution, precise measurements of the universe’s expansion rate, and the identification of exoplanets. The images unveiled by Hubble not only mesmerize the public with the sheer beauty of the cosmos but also contribute significantly to advancing scientific knowledge, establishing it as a cornerstone in the ongoing exploration of the universe. Far surpassing its initial mission lifespan, the Hubble space telescope persists as a guiding light in astronomical discovery, continuously enriching our understanding of the cosmos and inspiring future space exploration endeavors [113].

Building on this legacy, the James Webb space telescope (JWST), slated for launch in 2021, emerges as the Hubble’s successor (Figure 9b) [114]. Distinguished by a colossal primary mirror spanning 6.5 m, the JWST is a formidable infrared observatory poised to delve into the realms of the earliest galaxies and scrutinize the atmospheres of distant exoplanets. These space telescopes, epitomizing the pinnacle of optical ingenuity, continue to propel humanity’s exploration of the cosmos, revealing the universe’s secrets and expanding our understanding of the cosmos.

The JWST operates on a fundamental principle like traditional telescopes, focusing on capturing and magnifying light to extend our vision into the vast reaches of space. However, the JWST introduces distinctive features that set it apart. Unlike the human eye, which perceives visible light, the JWST specializes in the infrared portion of the electromagnetic spectrum, akin to a night vision security camera. This capability allows it to detect “heat” signatures and explore cosmic phenomena obscured by optical telescopes. With its substantial size, boasting a primary mirror of 6.5 m, the JWST excels at capturing copious amounts of light, enabling the observation of faint, distant, and colder celestial objects. Crucially, its location in space circumvents the limitations posed by Earth’s atmosphere, permitting unobstructed views and access to critical astronomical information that would otherwise be absorbed or distorted. The JWST stands as a technological marvel, poised to unravel the mysteries of the universe by providing a unique perspective on celestial bodies and events [115].

In the vast expanse of the universe, the concept of cosmic redshift unveils a fascinating phenomenon: the farther an object resides from us, the more rapid its outward trajectory [116]. As objects hurtle away, they undergo redshift, causing a perceptible shift toward the red end of the spectrum. In the case of extreme distances, this shift extends beyond the visible spectrum into the infrared realm. The JWST, finely attuned to the infrared spectrum, leverages this unique attribute to peer deeper into the cosmos than any preceding telescope. As celestial objects recede, their light takes a cosmic journey to reach us, rendering the most distant entities that are also the oldest. Telescopes like Hubble and the JWST thus become cosmic time machines, allowing us to gaze back in time. The JWST’s infrared prowess affords it the capability to probe the universe’s infancy, reaching back an astonishing 13.7 billion years, a temporal vantage point that surpasses the observational capacity of its predecessors. In essence, the JWST stands at the forefront of unraveling the mysteries of the early universe, transcending the limitations of time and distance with its unparalleled infrared vision.

Figure 9. (a) Hubble space telescope [117]; (b) James Webb space telescope [118].

Figure 9. (a) Hubble space telescope [117]; (b) James Webb space telescope [118].

4.5. Optical Filters and Coatings

Optical filters and coatings are essential for enhancing the performance of photonic instruments in space [119,120]. These components selectively transmit or reflect specific wavelengths of light, improving the precision and accuracy of observations [121,122]. They protect sensors from intense solar radiation and contribute to the longevity and reliability of space-based optical systems [123]. Optical filters tailored for space applications serve as indispensable components in the realm of space exploration and observation [124,125]. These filters, designed with precision and resilience, enable scientists and engineers to selectively capture and analyze specific wavelengths of light beyond Earth’s atmosphere [126]. In the vacuum of space, where extreme temperatures, radiation, and unique environmental challenges prevail, optical filters play a pivotal role in enhancing the clarity and accuracy of data collected by space-based instruments [127].

From bandpass filters facilitating targeted spectral observations to neutral density filters mitigating overexposure risks, these optical marvels are engineered to withstand the rigors of space conditions. Their applications span astronomical observations, satellite imaging, and remote sensing, contributing crucial insights into the mysteries of the cosmos while enduring the harsh realities of the space environment. Temperature dependence is typically expressed as the maximum allowable wavelength shift due to temperature changes, or the thermal coefficient, measured in pm/°C. For Alluxa’s hard-coated filters, the temperature-induced wavelength shift usually ranges from 2 pm/°C to 5 pm/°C within the operating temperature range of most instruments (Figure 10), although this can vary depending on the substrate material and filter design [123]. Thermal stability can be enhanced by adjusting material ratios, modifying design properties, or selecting a substrate material with a higher Coefficient of Thermal Expansion (CTE) than the coating. Additionally, post-deposition annealing improves both thermal and chemical stability by thermally expanding the thin-film layers and further oxidizing the materials, which reduces coating stress.

On the other hand, optical coatings are carefully engineered to enhance the performance of optical components, such as lenses and mirrors, by mitigating issues related to reflection, transmission, and durability in the harsh conditions of outer space [128]. Space environments pose challenges such as extreme temperatures, vacuum conditions, and exposure to ionizing radiation, necessitating coatings that can withstand these adversities. Anti-reflective coatings, for instance, are designed to minimize unwanted reflections and maximize light transmission, optimizing the efficiency of optical systems [129,130]. Additionally, protective coatings act as barriers against the corrosive effects of space radiation, ensuring the longevity and functionality of optical elements [131]. The development of advanced optical coatings is integral to the success of space missions, enabling the acquisition of high-quality data and imagery critical for scientific exploration and satellite-based applications [132]. As space technology continues to evolve, the refinement of optical coatings remains pivotal in pushing the boundaries of our observational capabilities beyond Earth’s atmosphere [133].

Hostile environments encompass a spectrum of challenges, ranging from extreme temperatures, both high and low, to (bio)chemical and mechanical disruptions, including severe stresses and stress cycles. Factors such as electromagnetic noise, pressure, radiation, and vacuum further contribute to the adversities faced. Inherent to their nature, these environments pose a formidable test of the functionality of materials. The escalating complexity of components employed in engineering applications necessitates a diverse range of coating materials and methodologies tailored to specific coating applications.

The primary objective of the innovative coatings extends beyond safeguarding components exposed to harsh conditions; they also aim to introduce supplementary functionalities whenever feasible. These engineered coatings play a pivotal role in reducing production costs when compared to conventional monolithic components [134,135]. Moreover, some coatings have the added advantage of mitigating operational expenses in harsh environments by facilitating component repair. In essence, these advancements not only fortify materials against adversity but also contribute to cost-effectiveness and sustainability in challenging industrial settings [136].

Over the past two decades, the CNES Optoelectronics Detection Department, in collaboration with various partners, has conducted comprehensive assessments of the impact of space environment conditions on a diverse array of CMOS image sensors (CISs) [137]. These sensors were sourced from a broad spectrum of commercial foundries and device providers. Rigorous environmental tests have been conducted with the primary aim of shedding light on the degradation of detection chains within modern CIS designed for space applications. Remarkable advancements in CIS technology over the last decade have resulted in outstanding performance metrics, particularly in terms of quantum efficiency (QE) and spectral selectivity. These advancements are attributed to the integration of various components within the pixel’s optical stack, including but not limited to microlenses, color filters, and polarizing filters. The cumulative effect of these innovations has propelled CIS technology to achieve unprecedented levels of functionality.

Despite these strides, it is essential to underscore that these technological components were originally developed with a focus on commercial applications tailored for terrestrial environments. Therefore, a critical imperative arises in the evaluation of the resilience of these state-of-the-art technologies to the harsh conditions of space. This scrutiny is indispensable for determining the viability of incorporating these cutting-edge CIS technologies in future space imaging missions. As space exploration continues to evolve, ensuring the adaptability and durability of imaging components becomes paramount for the success of space-based endeavors [137].

The optical transmittance characteristics of nine distinct optical filters were meticulously re-evaluated following an extensive nearly six-year exposure to the space environment aboard NASA’s Long-Duration Exposure Facility [138]. Broadly speaking, a decline in transmittance was observed for most filters. Remarkably, a narrow-band filter positioned under an aluminum cover exhibited no alteration in center frequency and bandpass, highlighting the resilience of this specific configuration. Conversely, narrow-band filters directly exposed to the rigors of space exhibited a discernible shift in center frequency and an expanded bandwidth. A pair of infrared-reflecting mirrors demonstrated reduced transmittance in the visible spectrum, with the mirror shielded by an aluminum cover exhibiting less degradation compared to its counterpart exposed directly to space. Notably, the bandpass of both mirrors remained unaltered despite the reduction in transmittance. In the case of neutral density filters, a marginal increase in transmittance was noted for an uncovered filter, while essentially no change was observed for the filter shielded by an aluminum cover. These findings shed light on the nuanced effects of long-term space exposure on the optical properties of diverse filters, providing valuable insights for future space-based instrumentation design and longevity considerations [138].

Over the past decade, researchers at Lawrence Livermore National Laboratory (LLNL) have been at the forefront of designing crucial optical components for the world’s latest telescope [139]. Collaborating closely with industrial partners responsible for the fabrication process, LLNL researchers recently completed their involvement in this groundbreaking project with the delivery of the final set of six optical filters for the telescope’s camera to the SLAC National Accelerator Laboratory in Menlo Park. The culmination of this effort marks a significant milestone as the Vera C. Rubin Observatory facility, located in northern Chile, equipped with the cutting-edge Legacy Survey of Space and Time Camera (LSSTCam), is poised to commence imaging the southern sky in 2024.

The intricate project, spanning approximately 10 years, is now entering a pivotal phase with the imminent integration of all camera components during the telescope’s commissioning. The intricate fabrication process involved sourcing raw glass material from New York State, which was then shipped to Thales Space SESO in Aix-en-Provence, southern France. Over the period from 2016 to 2020, Thales Space SESO meticulously shaped and polished the glass into the six essential optical filters. Following this, the optical filters embarked on their journey to Westford, Massachusetts, where Materion, an East Coast company, took charge of coating the glass filters. Materion not only constructed a specialized chamber for coating the filters but also developed a bespoke metrology station to measure the intricacies of the filter coatings. This collaborative effort reflects the culmination of a decade-long endeavor, promising groundbreaking observations and discoveries as the Rubin Observatory prepares to explore the celestial wonders of the southern sky [139].

The r-band filter (see Figure 11), strategically positioned to cover a spectral band near the center of the electromagnetic spectrum, stands out as a pivotal component within the suite of filters designated for frequent use with the LSSTCam. Beyond its routine application, this filter emerges as a linchpin in the comprehensive testing of the camera. Its unique placement facilitates the utilization of standard optical techniques, enabling the meticulous verification of the camera’s optical performance whenever this specific filter is engaged. This not only underscores the practicality and versatility of the r-band filter but also highlights its instrumental role in ensuring the precision and reliability of the LSSTCam through rigorous testing procedures [139].

4.6. Solar Cells

Solar cells (SCs), a quintessential optoelectronic technology, are deployed on spacecraft to generate electrical power from sunlight [140,141,142,143,144]. Space SCs, integral to the energy supply of spacecraft and satellites, have played a pivotal role for over six decades since the inaugural satellite launch in 1958 [145]. Evolving from the early days of single-junction silicon SCs with low efficiency [146], they have progressed significantly to the present state of high efficiency, exemplified by the multi-junction III-V compound SCs [147,148,149]. The primary focus of space SC development revolves around enhancing conversion efficiency, reducing the mass–power ratio, and fortifying radiation hardness [150].

There are two primary types of SCs commonly utilized in spacecraft:

(a)

Silicon Cells Covered in Thin Glass: Silicon cells coated with thin glass resemble conventional solar panels but are specially enhanced to withstand radiation and extreme temperatures. These panels, akin to those on the ISS, hold most solar panels in space [151].

(b)

Multi-Junction Cells (Gallium Arsenide and Similar Materials): Multi-junction cells, composed of materials like gallium arsenide, offer increased efficiency [152,153]. They are preferred when limited physical space is a concern, boasting up to 34% efficiency compared to the 15–20% range of most commercial solar panels. Satellites equipped with these cells can dynamically orient their solar panels to optimize sunlight absorption, as space lacks atmospheric interference, resulting in a higher abundance of solar rays. Gallium arsenide panels, being more efficient, are advantageous for spacecraft where space is at a premium [154,155,156]. Many satellites incorporate folding structures allowing the panels to expand in orbit, a feature also seen in the ISS.

Bhattarai et al. introduced an innovative deployable solar panel module designed to provide structural protection for SCs during launch [157]. The module effectively reduced vibrations transmitted through the solar panel using constrained layer damping, which was achieved through PCB-based multilayered thin stiffeners and double-sided viscoelastic tapes. A demonstration model, featuring a three-pogo pin burn wire released mechanism, was developed and tested for use in the 6U CubeSat “STEP Cube Lab-II” by Chosun University in South Korea. The release mechanism’s reliability and radiation resistance in orbit were confirmed through deployment and radiation tests. The module’s design and structural integrity were further validated through qualification-level launch vibration and in-orbit environment tests. Figure 12a illustrates the STEP Cube Lab-II in its stowed state, while Figure 12b shows it with the solar panels deployed. The CubeSat’s dimensions are 366 mm (X-axis) × 117.8 mm (Y-axis) × 238.5 mm (Z-axis), with a total weight of 9.6 kg, adhering to the 6U CubeSat standard.

The satellite primarily consisted of COTS components housed within structures developed domestically, though some interface boards and mechanical subsystems were custom-designed and assembled by the team. The main payload included three optics and sensor pairs—EOC, BBIRC, and LWIRC—that function in staring mode, enabling the simultaneous capture of images and videos from all three cameras. To ensure the stable release function of the proposed mechanism, solar panel deployment tests were conducted at a room temperature of 25 °C, using the experimental setup shown in Figure 12c. The qualification model of the P-HRM electrical system was connected to a power source for triggering and to a data acquisition (DAQ) system to monitor the solar panel’s deployment status. Additionally, an accelerometer was placed at the center of the panel to measure its acceleration responses. The results from the solar panel’s random equivalent static analysis indicated that a triple wire winding is necessary to achieve a positive margin with a safety factor of 3. Consequently, the solar panel was secured in its launch configuration using the triple wire winding method, following the prescribed wire-tightening procedure.

In space, solar panels benefit from uninterrupted exposure to sunlight. Approximately 55–60% of solar energy on Earth is either reflected or absorbed by the atmosphere, clouds, gasses, and dust. Spacecraft solar panels, therefore, harness a more consistent and abundant solar resource. Solar panels in space often include a folding structure for expansion in orbit, a design shared with the ISS. Unlike on Earth, where electronic devices run on AC power, spacecraft solar panels generate DC electricity. The absence of long-distance electricity transmission requirements in space eliminates the need for converting DC to AC. This design choice not only simplifies the system but also reduces the necessary hardware.

According to estimates from the Energy Information Agency (EIA), the Earth’s total annual electricity demand in 2050 is projected to reach approximately 5137 GW years (GW/y). Notably, about 50% of this demand, equivalent to 2569 GW/y, is anticipated to be for renewable energy sources [158]. This highlights a significant challenge for long-term energy planning. While many countries and subnational authorities are committed to policy-driven carbon targets, there remains a lack of clear alternatives to traditional carbon-emitting power stations that currently fulfill the majority of the planet’s baseload energy requirements. Despite the ongoing efforts to transition towards cleaner energy sources, the retirement of coal, gas, and nuclear power plants continues to raise the crucial question: What is the viable alternative? In addressing this challenge, one technology stands out as a promising solution capable of providing carbon-free, baseload power without necessitating revolutionary technological advancements—space-based solar power (SBSP). This innovative concept involves the deployment of a large orbital photovoltaic (PV) array that directly converts photons into electricity. The generated electricity is then transformed into microwaves, which are beamed to collectors on the Earth’s surface. These collectors, in turn, convert the microwaves back into electricity, seamlessly integrating with the local grid (see Figure 13).

While the operationalization of SBSP poses significant hurdles, notably the high cost associated with launching the materials required for a gigawatt-class plant into space, noteworthy progress has been made. Crucially, all the underlying technologies necessary for SBSP have been successfully demonstrated. Furthermore, advancements in space transport, exemplified by reusable, heavy-lift space systems like SpaceX’s Falcon Heavy and Starship, hold the potential to substantially reduce transport costs. As these technologies mature and become more cost-effective, SBSP could emerge as a transformative solution, providing a sustainable and efficient source of baseload power to meet the evolving energy needs of the future [158].

Presently, the pinnacle of SC efficiency stands at 47.1%, achieved by six-junction inverted metamorphic (6 J IMM) SCs under 143 suns [159]. The ascendancy of high-efficiency III-V triple-junction cells is also noteworthy, with research-grade multi-junction space SCs boasting 35.8% efficiency for the five-junction direct bonded SC and 33.7% for the monolithically grown 6 J IMM multi-junction SC [160]. Despite their elevated fabrication costs, these cells offer unparalleled performance and steadfast stability for space missions [161].

Among the well-established space SCs are the GaInP/GaAs/Ge (1.82/1.42/0.67 eV) lattice-matched triple-junction cells, boasting efficiencies exceeding 30% and serving various space applications over the past two decades. However, the existing disparity between its subcells poses a challenge to further improving the conversion efficiency [162]. In addressing the challenges posed by subcell mismatched space SCs, innovative approaches have been proposed, including novel structures featuring current-matched or lattice-mismatched configurations. Various fabrication methods, such as the metamorphic growth method [163], mechanical stack [164], and wafer bonding technology [165], have been introduced to surmount these issues.

While the quest for enhanced efficiency remains paramount, an equally crucial consideration in space SC development is radiation resistance. SCs deployed in orbit confront irradiation damages from high-energy protons, electrons in the Earth’s radiation belt, and cosmic rays [166]. Consequently, the photoelectric performance of SCs experiences degradation, primarily attributable to radiation-induced displacement damage within the SC lattice, leading to a decline in the lifetime of photo-generated carriers [167]. Thus, exploring the degradation mechanism and performance of SCs under irradiation becomes imperative, necessitating the application of radiation-hardening methods before embarking on space missions.

The degradation of electrical performance in SCs has direct implications for the longevity of space missions. Researchers have directed their efforts towards enhancing the radiation resistance of SCs through diverse strategies, including adding a specific thickness of protective cover to shield against particle damage [168], employing back-surface (BSF) [169] or distributed Bragg reflector (DBR) [170], thinning the base layer thickness of the current-limiting subcell [171], and leveraging the p-i-n structure and diverse doping methods for multi-junction SCs [172]. Experimental observations reveal that the annealing of multi-junction SCs can restore certain electrical properties after exposure to high-energy particles [173]. This multidimensional approach underscores the ongoing commitment to advancing both the efficiency and resilience of space SCs.

Airbus- and Boeing-backed venture capital groups have joined forces to spearhead a groundbreaking initiative, injecting a substantial USD 10 million in seed funding into Solestial, an Arizona-based startup dedicated to advancing solar panel technology tailored for satellites and spacecraft [174]. In this pivotal funding round, Airbus Ventures took the helm, steering the collaboration alongside AEI HorizonX—a dynamic joint venture uniting Boeing and the esteemed private equity firm AE Industrial Partners. The consortium also includes GPVC, Stellar Ventures, Industrious Ventures, and other strategic partners. Solestial, an offshoot of Arizona State University with a decade-long focus on pioneering technology, particularly an “ultra-thin” silicon SC, stands as the recipient of this significant investment. What sets Solestial apart is its cutting-edge technology, capable of autonomously rectifying radiation damage at standard operating temperatures in space. This innovative solution is encapsulated within a flexible, lightweight panel engineered to uphold peak performance for up to a decade in Low Earth Orbit (LEO).

The infusion of funds serves a multifaceted purpose for Solestial. Primarily, it will facilitate the scaling of production capacities and deepen customer engagement initiatives. As the company expands its ground and flight testing, the financing will play a crucial role in furthering research and development efforts. Additionally, a portion of the funds will be allocated to amplify sales and marketing activities, enhancing market presence and outreach. Solestial’s technological prowess extends beyond performance benefits, as the automation-friendly manufacturing process enables mass production of solar panels. This streamlined approach not only results in a remarkable 90% reduction in costs compared to existing technologies but also boasts “virtually unlimited” manufacturing capacity, positioning Solestial as a transformative force in the realm of space-based solar energy solutions [174].

Perovskite solar cells (PSCs), positioned as a potentially transformative force in terrestrial photovoltaics, have achieved a remarkable efficiency boost to 25.2% within the past decade, marking unprecedented progress [175]. This achievement is credited to a profound understanding of charge carrier dynamics, defect physics, and interface energetics [176]. Additionally, relentless efforts in compositional engineering, crystallization control, defect passivation, and interface modification have contributed significantly [177,178]. A pivotal aspect is the potential for PSCs to emerge as cost-effective leaders in the market, contingent on module longevity, with a targeted 15-year lifespan [177]. The solar cells derived from perovskite materials possess a compelling set of characteristics: (i) they are remarkably thin and lightweight, (ii) can be manufactured through efficient solution processes, (iii) predominantly utilize cost-effective raw materials, and (iv) exhibit impressive flexibility. The amalgamation of these attributes renders perovskite solar cells uniquely intriguing for applications in space technologies. Their lightweight and adaptable nature aligns well with the demands of space missions, emphasizing the potential of perovskite solar cells to play a transformative role in advancing space-based photovoltaic systems. The most common attributes of PSCs are depicted in Figure 14 [179].

However, despite these advancements, the reported lifespan of PSCs has been limited to around 1 year, primarily due to stability issues when exposed to Earth’s atmosphere, particularly in the presence of oxygen and moisture [180,181]. This raises an intriguing question: Can PSCs endure for extended periods in space, where air density is extremely low, and water is nonexistent? Recent studies highlight the considerable advantages of PSCs, highlighting their lightweight design and resilience under high-energy particle irradiation. These attributes position PSCs as potentially viable candidates for the space market [182,183,184]. Consequently, a thorough evaluation of the prospects of deploying PSCs in space applications is imperative, considering their promising attributes and potential to overcome the challenges posed by the space environment.

5. Challenges Related to the Development of Photonic Components for Space Applications

Operating devices in space present significant challenges, especially for laser devices, photonic devices, and other equipment. While these tools may perform well in controlled laboratory environments on stable optical tables, adapting them to withstand the harsh conditions of space is a formidable task. The primary challenge lies in transforming sophisticated engineered setups into robust devices capable of enduring extreme conditions that could potentially misalign or damage optical components, leading to device failure. In the context of laser diodes, the use of indium for packaging introduces a particular vulnerability. The indium’s susceptibility to creep behavior at extreme temperatures poses a risk, potentially resulting in fatal device failure. Additionally, high vacuum conditions can induce changes in the chemical and physical properties of components due to dehydration [185]. Laser crystals and fibers face another common issue known as the photodarkening effect, caused by radiation absorption in optical components. Extensive studies have explored the impact of various types of radiation and doping ratios on laser materials [186,187], providing crucial insights for photonic space engineers to select suitable candidates for their assemblies.

While enhancing component shielding can mitigate the photodarkening issue, it introduces a trade-off [188]. The additional layers of material used for protection increase the weight, size, and cost of the integrated device. Consequently, meticulous selection of components becomes imperative to achieve an optimal balance that aligns with the mission’s radiation budgets. This ensures that the laser output maintains the required specifications throughout the mission’s extended operational period without incurring unnecessary costs associated with excessive shielding. Meeting these challenges is essential for the successful deployment and sustained functionality of devices in the demanding environment of space.

Traditional assembly techniques employed for laser components often fall short of being suitable for space applications. A notable example is the use of organic epoxies, a common choice that unfortunately gives rise to outgassing issues. This phenomenon leads to Laser-Induced Contamination and, consequently, Laser-Induced Damage [189]. To address these challenges, innovative packaging technologies offer viable solutions.

One effective approach involves the adoption of alternative packaging techniques to replace traditional adhesives. For instance, leveraging low-stress soldering techniques [190] can significantly enhance the durability and performance of diode-pumped solid-state laser devices. This transition contributes to the development of more robust devices with an extended thermal range, heightened mechanical strength, reduced outgassing, and improved resistance of bonded materials to radiation. By embracing such advanced assembly methods, space-compatible laser components can be achieved, ensuring the reliability and longevity of laser systems in the demanding conditions of space environments.

6. Concluding Remarks

Human curiosity about the universe has steadily intensified with technological advancements. Since the Soviet Union’s historic launch of the first artificial satellite in 1957, the exploration of space has witnessed a remarkable evolution. Over the years, more than 6000 spacecraft have been deployed into space, serving various purposes such as space exploration, Earth observation, communication, and military applications. This enduring quest for knowledge and the utilization of space technology underscore humanity’s persistent drive to unravel the mysteries of the cosmos and harness the vast potential that space offers. Photonic devices have become the backbone of modern space exploration, enabling a new era of discovery and connectivity. From navigating spacecraft to communicating vast amounts of data and capturing the beauty of the cosmos, these devices have transformed our ability to explore and understand the universe. As technology continues to advance, the role of integrated photonics in space exploration is set to expand, promising even more exciting discoveries and opportunities for scientific inquiry. We have provided a concise overview of some of the most crucial photonic devices and their recent advancements that play a pivotal role in space exploration.