Hybrid Mars Rockets Gain Edge with In-Situ Fuel and Smarter Trajectories

Insider Brief

• A new study in Acta Astronautica presents a multi-objective optimization framework for Mars rockets using in-situ propellants to balance payload capacity and range.
• The hybrid rocket model combines Earth-sourced paraffin and nitrous oxide with Martian magnesium and carbon dioxide for propulsion.
• Simulations showed the optimized vehicle could achieve orbital insertion or support regional hopper missions depending on mission priorities.

A new study proposes a blueprint for building Mars ascent and hopper rockets using fuel made on the Red Planet — and optimizing their flight paths to carry more cargo with less fuel, tradeoffs that are referred to as multi-objective optimization frameworks. The work is a step toward making trips to Mars more efficient and cost-effective.

Published as a pre-proof in Acta Astronautica, the study by researchers at Khalifa University and the Technology Innovation Institute in Abu Dhabi lays out a new multi-objective trajectory optimization (MOTO) framework. The method balances competing demands like downrange travel distance and payload capacity to help mission planners get more out of Mars-bound rockets, especially those using locally sourced fuel.

The researchers write: “The adoption of in-situ resources in the preparation of propellants will be a critical capability to improve the efficiency and scalability of human exploration and settlement initiatives beyond Earth. By taking advantage of Mars’ thin, carbon dioxide-rich atmosphere and locally available metals like magnesium, hybrid rocket vehicles can be optimized to support efficient point-to-point transportation and Earth return missions, facilitating inter-crater transport and logistic support for ongoing exploration efforts as well as future human settlements.”

The researchers tested their approach on a prototype hybrid rocket using 80% magnesium — extracted from Martian regolith — and 20% paraffin wax brought from Earth. The oxidizer is a mix of nitrous oxide (N₂O) and carbon dioxide (CO₂), the latter harvested from Mars’ thin, CO₂-rich atmosphere. The model vehicle, designed for Mars ascent and point-to-point “hopping” missions, was optimized across multiple performance targets, including downrange distance, fuel consumption, and payload capacity.

The study, led by Mewael Afeworki Abraham, Alessandro Gardi and Ozan Kara, arrives amid renewed global interest in Mars exploration and a growing push toward sustainable, cost-efficient interplanetary travel. Using in-situ resources — or ISRU, which refers to using resources found on Mars instead of bringing them from Earth — has become central to long-duration missions. By producing fuel on Mars, ISRU lowers the burden of carrying propellants from Earth, slashing mission mass and cost.

A Rocket Built for Mars

The hybrid rocket design investigated in the study merges a solid fuel with a liquid oxidizer. In this case, magnesium and paraffin wax serve as the fuel, while the oxidizer is a CO₂-N₂O blend. CO₂ alone can’t sustain combustion, but when combined with N₂O — which provides better ignition characteristics and is self-pressurizing — it becomes viable, the researchers indicate.

This mixture was selected not just for compatibility and storability, but also for safety. Hybrid systems keep fuel and oxidizer separate until ignition, reducing explosion risk — a useful feature for missions on remote, crewed outposts like Mars.

The propulsion system achieved a vacuum thrust of 20 kN and a specific impulse of 270 second. According to the team, these are metrics within reach for supporting both sample-return launches and regional cargo missions.

Optimizing the Climb

The study’s core innovation is a trajectory planning tool that handles multiple objectives simultaneously. Called MOTO, the tool considers both the physics of flight — including drag, thrust, gravity, and six-degree-of-freedom dynamics — and design trade-offs, like fuel use versus payload weight.

The team modeled three flight phases: an initial vertical burn, a ballistic coast, and a final thrust phase for trajectory correction. Using the open-source Pyomo library and the IPOPT solver, they computed a range of Pareto-optimal solutions. These represent the best trade-offs between objectives where improving one (e.g., carrying more payload) would worsen another (e.g., range).

In one scenario, the vehicle achieved orbital insertion at 200 km altitude with a downrange of 1,309 km and carried 13.86 kg of payload above the baseline minimum. Another configuration emphasized distance, reaching 1,531 km but leaving only 2 kg for payload. A more conservative solution minimized fuel use, saving 133 kg for cargo by flying nearly straight up, which the team suggests is a good fit for brief scientific soundings, such as a short, high-altitude flight to collect data.

Each solution offered mission planners different benefits, depending on needs: sample return, regional hopping, or high-altitude atmospheric science.

Engineering the Martian Environment

Mars’ sparse atmosphere — roughly 1% the density of Earth’s — presents unique challenges for rocket design. Aerodynamic surfaces are nearly useless, so the study excluded fins or flaps, relying entirely on thrust vectoring for control. The authors developed high-fidelity aerodynamic models using CFD tools like Ansys Fluent to characterize drag and lift during ascent.

Flight stability was managed through careful mass distribution and shape optimization. The rocket’s nose cone, for instance, used a curve optimized to reduce drag and enhance static stability. Aerodynamic coefficients were modeled as polynomial functions of Mach number and angle of attack, validated against simulations.

Constraints, Assumptions, and What’s Next

While the study’s optimization tools are robust, they come with some caveats, according to the paper. The solver depends on good initial guesses and may get stuck in local optima — a limitation of gradient-based methods. The authors suggest future work could use evolutionary algorithms or warm-start strategies to improve global performance, albeit with higher computational costs.

Atmospheric modeling relied on simplified equations, though the authors note that future versions could integrate data from more complex sources like MARS-GRAM 2010. Similarly, while CFD-based aerodynamics were used during design, integrating real-time fluid dynamics into the optimization loop could yield better results — if computational resources allow.

Planned extensions include modeling parachute-based recovery for reusable landings and expanding the descent phase simulation. Lower-altitude hopper missions may also be studied for more routine logistics or mobile science operations on Mars.

Implications for Mars Missions

By marrying trajectory science with hybrid propulsion and local resource use, the study takes a step toward a future where Mars rockets are built for Mars — and, you could say, fueled by it. The authors’ framework allows space agencies to tailor hybrid rocket missions for a variety of roles — from launching soil samples to scouting new regions, while using Martian materials to cut payload mass and increase flexibility.

The ultimate goal is to create practical tools and provide engineering to agencies planning Mars operations. As ISRU matures and Mars sample-return missions advance, the kind of modeling framework developed here may help reduce costs and broaden mission types. That could make missions to Mars are far more tenable and sustainable operation.