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Aerospace
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Propulsion Solutions for Enhancing the Small Launchers’ Competitiveness
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Propulsion Solutions for Enhancing the Small Launchers’ Competitiveness

A special issue of Aerospace (ISSN 2226-4310).

Deadline for manuscript submissions: closed (30 April 2026) | Viewed by 2458

Editor

Dr. Carmine Carmicino

E-Mail Website
Guest Editor
Propulsion and Space Research Center, Technology Innovation Institute (TII), Abu Dhabi P.O. Box 9639, United Arab Emirates
Interests: chemical propulsion; fluid dynamics
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

As we know, we are witnessing the continuous, remarkable expansion of the small-satellite market, driven by the rise of constellations and Low-Earth Orbit (LEO) applications.

Currently, the most common orbit insertion technique for nano- and micro-satellites is to take advantage of ride-share opportunities on a heavy launch rocket, typically dedicated to a primary customer.

However, dedicated launch options, where the payload owner does not have to share space with other missions, offer a more predictable and reliable schedule, as well as a customized trajectory and target orbit. This means that the payload is not subject to delays caused by other ride-share customers, which allows for a more flexible timeline.

This growing need calls for dedicated and affordable launch strategies, which can be created by improving the small-launch vehicle technology that has been in development and operation since the mid-1950s.

A small-lift launch vehicle is commonly defined as a rocket capable of launching up to a 2000 kg payload to LEO, in contrast to a heavy launcher like, for instance, the SpaceX’s Falcon 9 rocket, which brings 22800 kg to LEO.

Despite some recent signs of slowdown, the field of small launchers continues to grow; the main challenge in this area is reducing the launch cost per kilogram of payload, which, compared to the ride-share option, is still an order of magnitude higher. This effort focuses on searching for more efficient systems, which requires reducing the structural mass through advances in lightweight materials, as well as component miniaturization and integration. In this context, the propulsion system plays a key role.

Historically, on the one hand, liquid rocket engines have been well established, offering reliability and the highest performance. On the other hand, hybrid rockets, though considerably less mature, combine simplicity with inherent safety, leading to shorter development times and lower costs. By properly tailoring the configuration of both propulsion systems, significant benefits can be gained in optimizing the overall launcher architecture.

This Special Issue will explore varied topics related to advancing small-launcher technology. It will collect papers that contribute substantially to the state of the art in both propulsion systems, with a particular emphasis on methods to reduce launch costs, such as the following:

(i) The use of low-cost, green propellants;
(ii) Customized solutions for turbo or electric pumps;
(iii) The utilization of new technologies for manufacturing composite structures;
(iv) Novel 3D printing techniques.

Dr. Carmine Carmicino
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 250 words) can be sent to the Editorial Office for assessment.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-anonymized peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Aerospace is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2400 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • green propellants
  • hybrid rockets
  • liquid rockets
  • efficient propulsion systems
  • small-satellites
  • light-weight composite structures
  • 3D printing

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Published Papers (4 papers)

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23 pages, 1969 KB  
Article
Hybrid Rocket Motor Performance Dispersion and Its Mitigation Through Real-Time State Estimation and Feedback Control
by Albertus Stephanus Louw, Marco Rotondi, Landon Kamps and Toru Shimada
Aerospace 2026, 13(7), 639; https://doi.org/10.3390/aerospace13070639 - 14 Jul 2026
Viewed by 270
Abstract
Hybrid rocket motors are an attractive option for the upper-stages of low-cost small launchers, but are susceptible to variability in performance both in time and between firings. Moreover, key contributors to hybrid motors’ performance such as oxidizer-to-fuel ratio (O/F) [...] Read more.
Hybrid rocket motors are an attractive option for the upper-stages of low-cost small launchers, but are susceptible to variability in performance both in time and between firings. Moreover, key contributors to hybrid motors’ performance such as oxidizer-to-fuel ratio (O/F) are difficult to estimate, and by extension, to control. Four approaches were evaluated for the estimation and control of O/F under system uncertainty, including through on-line estimation by an Unscented Kalman Filter (UKF). A Monte Carlo analysis was conducted of a simulated hybrid kick motor, where key sources of system uncertainty such as the characteristic velocity efficiency (ηc*), fuel regression coefficients, and oxidizer flow characteristics were allowed to be variable. Feedback control of O/F informed by the UKF obtained 6.8% smaller control error than the best alternative approach. Yet the Monte Carlo analysis showed that among uncertainty sources considered, ηc* was the primary driver of performance variability, while O/F regulation had a small influence. This was because the total and specific impulses were relatively insensitive to O/F for the considered motor configuration and ranges of O/F observed during the simulated burns—highlighting the importance of system uncertainty quantification when formulating performance-regulating interventions. Further, the proposed UKF observer provided data-informed estimates of combustion efficiency and propellant residuals in time, which are valuable for the planning and execution of accurate orbital insertions in a kick motor susceptible to performance uncertainty. The developed uncertainty quantification and control modeling framework can be used also during the design and assessment of other control interventions under system uncertainty. Full article
(This article belongs to the Special Issue Propulsion Solutions for Enhancing the Small Launchers’ Competitiveness)
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20 pages, 43868 KB  
Article
Preliminary Development and Experimental Validation of a Clustering Hybrid Rocket Module for Soft-Landing Application
by Donghee Lee, Donggeun Lee, Sungwoo Park, Jungpyo Lee and Heejang Moon
Aerospace 2026, 13(6), 559; https://doi.org/10.3390/aerospace13060559 - 18 Jun 2026
Viewed by 300
Abstract
This study presents the preliminary development of a clustered hybrid propulsion module, and its experimental validation from static motor characterization to dynamic 1-D vertical drop tests to assess the feasibility of a hybrid propulsion system for soft-landing applications. The research progresses from preliminary [...] Read more.
This study presents the preliminary development of a clustered hybrid propulsion module, and its experimental validation from static motor characterization to dynamic 1-D vertical drop tests to assess the feasibility of a hybrid propulsion system for soft-landing applications. The research progresses from preliminary design of core components (such as fuel, oxidizer supply system, engine configuration), to the performance verification of the clustering module. First, the trade-off between high regression rates and mechanical integrity was evaluated for paraffin-based fuels. However, high-density polyethylene (HDPE) was utilized as the baseline to ensure predictable combustion behavior. Second, cold flow tests of the designed multi-port manifold demonstrated a highly uniform oxidizer distribution, validating the geometric design with a maximum spatial pressure deviation of 2.44% across the four engines. Third, static fire tests confirmed robust dynamic control capabilities, successfully throttling the average chamber pressure from 100% (7.00 bar) down to 43% (3.01 bar) and back to 100% (7.01 bar) with a transient response time of approximately 0.6 s. Finally, the 1-D vertical drop test validated the operational readiness of the system; the open-loop thrust modulation successfully counteracted the module’s dynamic weight, achieving a terminal descent velocity of 1.46 m/s, which strictly satisfies planetary soft-landing safety criteria. These results demonstrate the feasibility and performance of clustered hybrid propulsion systems for planetary exploration, extending to surface launch technology for sample return missions from the Moon and Mars, and precision booster recovery for small launch vehicles. Full article
(This article belongs to the Special Issue Propulsion Solutions for Enhancing the Small Launchers’ Competitiveness)
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18 pages, 2335 KB  
Article
Effects of Characteristic Chamber Length on c* Efficiency in CAMUI-Type Hybrid Rockets Using Hydrogen Peroxide
by Ryota Kinjo, Sota Watanabe, Ananda Rafi Dhaifan, Masashi Wakita and Harunori Nagata
Aerospace 2026, 13(6), 528; https://doi.org/10.3390/aerospace13060528 - 4 Jun 2026
Viewed by 365
Abstract
This study experimentally investigated the effect of characteristic chamber length, L∗, on combustion efficiency and stability in CAMUI-type hybrid rockets using 70 wt% and 80 wt% hydrogen peroxide under non-catalytic spray-injection conditions. Combustion tests were conducted by systematically varying L∗ [...] Read more.
This study experimentally investigated the effect of characteristic chamber length, L∗, on combustion efficiency and stability in CAMUI-type hybrid rockets using 70 wt% and 80 wt% hydrogen peroxide under non-catalytic spray-injection conditions. Combustion tests were conducted by systematically varying L∗ through changes in the nozzle throat diameter while maintaining the combustor volume constant. For both oxidizer concentrations, the characteristic exhaust velocity efficiency, ηc∗, increased with increasing L∗. The 70 wt% cases required a larger L∗ than the 80 wt% cases to achieve comparable efficiency, and flame blowoff occurred in the low-L∗ region. The normalized RMS pressure fluctuation was also larger for the 70 wt% cases, particularly in the low-L∗ region, indicating lower combustion stability. These results indicate that reducing the hydrogen peroxide concentration increases the L∗ required to maintain stable and efficient combustion. As a key outcome of this study, stable and efficient combustion of 70 wt% hydrogen peroxide was demonstrated without catalytic assistance when a sufficiently large L∗ was provided. These results demonstrate the capability of the CAMUI-type combustor to extend stable operation toward lower oxidizer concentrations and experimentally clarify the concentration-dependent L∗ requirement as a practical design guideline for catalyst-free hydrogen peroxide hybrid rockets. Full article
(This article belongs to the Special Issue Propulsion Solutions for Enhancing the Small Launchers’ Competitiveness)
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24 pages, 8255 KB  
Article
Further Development of a Low-Energy Arc-Ignition System for Nytrox/ABS Hybrid Propulsion Systems
by Stephen A. Whitmore, Jared S. Coen and Ryan J. Thibaudeau
Aerospace 2026, 13(4), 366; https://doi.org/10.3390/aerospace13040366 - 14 Apr 2026
Viewed by 611
Abstract
Utah State University has developed a high-performance “green” hybrid propulsion technology based on the unique electrical breakdown properties of 3D-printed acrylonitrile butadiene styrene. Using 3D-printed ABS as fuel, typical startup sequences require approximately 5–15 joules and, once started, the system can be sequentially [...] Read more.
Utah State University has developed a high-performance “green” hybrid propulsion technology based on the unique electrical breakdown properties of 3D-printed acrylonitrile butadiene styrene. Using 3D-printed ABS as fuel, typical startup sequences require approximately 5–15 joules and, once started, the system can be sequentially fired with no additional energy inputs required. The number of possible ignitions is limited only by the amount of fuel. The most technologically mature version uses gaseous oxygen (GOX) as oxidizer and 3D-printed ABS as fuel. While GOX is mass-efficient, it lacks volumetric efficiency unless highly pressurized. Nytrox, a blend of GOX and nitrous oxide, improves propellant density and volumetric efficiency, while maintaining acceptable levels of mass efficiency (specific impulse). Nytrox can safely self-pressurize, eliminating the need for a separate oxidizer pressurization system and reducing overall complexity. However, employing Nytrox as a direct substitute for GOX results in reduced ignition reliability and considerably increases cold-start ignition latency. This paper quantifies the latency, explores its sources, and analyzes expected behaviors. Solutions include raising combustion and storage pressures to boost oxygen content in Nitrox’s liquid phase and increasing combustion chamber pressure to reduce ignition delays. Full article
(This article belongs to the Special Issue Propulsion Solutions for Enhancing the Small Launchers’ Competitiveness)
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