Search Results (6)

This paper examines the growing adoption of laser communication (lasercom) in space missions and payloads for identifying emerging trends and key technology drivers of future optical communications satellite systems. It also presents a comprehensive overview of commercially available and custom-designed lasercom terminals, outlining their characteristics and specifications to meet the evolving demands of global satellite networks. The analysis explores the technical considerations and challenges associated with integrating lasercom terminals into LEO constellations and the Inter-satellite communications service provision in LEO due to their power, size, and weight constraints. By analyzing advancements in CubeSat lasercom technology designed to cater for the emergence of future mega constellations of interacting small satellites, the paper underscores its promising role in establishing high-performance satellite communication networks for future space exploration and data transmission. In addition, a brief overview of our ALIGN planned mission is provided, which highlights the main key operational features in terms of PAT and link budget analysis. Full article

In the near future, international space agencies have planned to achieve significant milestones in investigating the utilization of Global Navigation Satellite Systems (GNSS) within and beyond the current space service volume up to their application to lunar missions. These initiatives aim to demonstrate the feasibility of GNSS navigation at lunar altitudes. Based on the outcomes of such demonstrations, dozens of lunar missions will likely be equipped with a GNSS receiver to support autonomous navigation in the lunar proximity. Relying on non-invasive, consolidated differential techniques, GNSS will enable baseline estimation, thus supporting a number of potential applications to lunar orbiters such as collaborative navigation, formation flight, orbital manoeuvers, remote sensing, augmentation systems and beyond. Unfortunately, the large dynamics and the geometry of such differential GNSS scenarios set them apart from current terrestrial and low-earth orbit use cases. These characteristics result in an increased sensitivity to measurements time misalignment among orbiters. Hence, this paper offers a review of baseline estimation methods and characterizes the divergences and limitations w.r.t. to terrestrial applications. The study showcases the estimation of the baseline length between a lunar CubeSat mission, VMMO, and the communication relay Lunar Pathfinder mission. Notably, real GNSS measurements generated by an Engineering Model of the NaviMoon receiver in the European Space Agency (ESA/ESTEC) Radio Navigation Laboratory are utilized. A radio-frequency constellation simulator is used to generate the GNSS signals in these hardware-in-the-loop tests. The performed analyses showed the invalidity of common terrestrial differential GNSS ranging techniques for space scenarios due to the introduction of significant biases. Improved ranging algorithms were proposed and their potential to cancel ranging errors common to both receivers involved was confirmed. Full article

Satellites have been developed and operated for various purposes. The global satellite market is growing rapidly as the number of satellites and their mission diversity increase. Satellites revolve around the Earth to perform missions and communicate with ground stations repeatedly and sequentially. However, because satellites are orbiting the Earth, there is a limited time window for missions to a specific area and communication with ground stations. Thus, in an environment where multiple satellites and multiple ground stations (MS-MGs) are operated, scheduling missions and communications to maximize the utilization of satellites is a complex problem. For the MS-MG scheduling problem, this study proposes a mixed-integer linear programming (MILP) model to assign time windows for missions and communications with ground stations to individual satellites. The MILP model is based on the concept of a time-space network and includes constraints reflecting on the space mission environment of satellites. The objective function and constraints of the MILP model were validated through numerical experiments based on actual data from Korean satellites. Full article

To support the increasing number of planned lunar missions, a collaborative international initiative is underway to conceptualise and establish a lunar satellite constellation for communication and navigation. In this context, the goal of the current paper is to analyse what the obtainable performance is for a lunar lander that executes state estimation employing one-way ranging signals from such a Lunar Navigation Service (LNS). In particular, a small-sized optimised navigation constellation is considered as the main source of measurements, which, coupled with an accelerometer and an altimeter, is used to estimate the lander absolute trajectory during the main braking phase. The guidance is extracted on board by interpolation of a ground-optimised trajectory, followed by a reference-tracking regulator. Two alternative control tuning cases are presented, one targeting high performance, the other targeting low propellant mass. Nominal performance and associated sensitivity analyses assessed the feasibility of supporting such a critical phase with a reduced LNS constellation, reaching final control errors below 500$\mathrm{m}$, with the better performing one going down to 56$\mathrm{m}$. Among the two proposed alternatives, the one targeting low fuel expenditure has proven, however, to also be more robust against time and state uncertainty, providing much larger success rates. Full article

We summarize the status of the FORMOSAT-7/COSMIC-2 (COSMIC-2) mission which has completed its first three years in orbit. COSMIC-2 is a joint U.S./Taiwan program consisting of six satellites in low-inclination orbits with the following payloads: Global Navigation Satellite System radio occultation, in-situ ion velocity meter, and tri-band radio frequency beacon. The constellation is in its final orbit configuration and reached mission full operating capability in September 2021. An extensive calibration/validation campaign has to date enabled the release of all baseline neutral atmosphere products and nearly all baseline ionosphere products. The mission is providing usually more than 5000 neutral atmosphere RO profiles per day with a precision better than 2 μrad from 30–60 km altitude. Each day, nearly 12,000 combined total electron content occultations and arcs are generated with absolute accuracy of better than 3 TECU. IVM density precision is at or below the 1% requirement. Neutral atmosphere and ionosphere latency, measured from time of observation to product creation time, is below 30 min median. Data products are delivered in near real-time to operational weather and space weather centers and made available openly to the research community. New ionosphere products specifying the presence and absence of scintillation are under development and planned for future release. Full article

The wide application of satellite constellations in the field of space-based global communications and remote sensing has led to a substantial increase in small-satellite launch plans, a sharp increase in the density of space objects in low-Earth orbit (LEO), and a reduction in available orbit and frequency resources. This will further aggravate the trend of deterioration of the space debris environment. Taking the Starlink constellation as an example, this paper describes the influence of the constellation from the environmental debris flux of the satellite, the evaluation of the number of evasion maneuvers, the change of risk level, the success rate of post mission disposal (PMD) and the growth rate of space objects. The simulation results show that the collision risk of the Starlink constellation is related to the orbital parameters, and the higher success rate of post-mission disposal (PMD) can reduce the collision risk of the constellation. The large constellations increases the growth rate of space objects, and even if all the satellites are disposed of after the mission, the impact of constellations on the space environment can not be offset. Full article