Lunar lander concept on the moon.

NASA is developing rocket engine and propulsion technologies for future missions to the moon, Mars and beyond. These propulsion systems would have a lower mass than current systems and may have the potential to use reactants that are mined from lunar or Martian soil. They would also be designed to use non-toxic reactants.

To begin the first return mission to the moon, NASA plans to launch the Altair lunar lander and an Earth Departure Stage (EDS) via an Ares V cargo launch vehicle. The Altair lunar lander will orbit Earth until the Orion crew exploration vehicle is launched via an Ares I crew launch vehicle. Orion will detach from its launch vehicle and join the lander/EDS. Significant thrust from stored propellant will be needed to launch the combined spacecraft to its destination – the moon.

Diagram of NASA's next mission to the moon.

Lunar lander ascent module concept.

NASA’s Propulsion and Cryogenic Advanced Development (PCAD) Project is performing experimental and analytical evaluation of several areas of green propulsion systems to enable safe and cost effective exploration missions. Green propulsion represents a class of propellants considered non-toxic, such as oxygen, hydrogen or methane. 

PCAD is sponsored by the Exploration Technology and Development Program Office. The project is led by NASA’s Glenn Research Center who has partnered with Marshall Space Flight Center and Johnson Space Center/White Sands Test Facility.

Through a combination of experimental testing and analysis, PCAD is assessing the potential performance increases of green propellants, which if successful, could lead to reduced overall system mass. Lowering the vehicle system mass could reduce the cost of vehicle development or allow more payload delivery to the lunar surface. Green propellants are being considered for use on the next lunar mission because they are thought to have high performance and are safer than hypergolic propellants that ignite on contact with each other.

Through testing and analysis, the project team must prove that green propulsion is a viable propellant alternative. If the project’s goals are realized, green propellants could be used by the lunar lander and become the NASA standard for future exploration vehicles.

PCAD has focused its efforts on liquid oxygen/liquid methane reaction control system (RCS) thruster designs, integrated testing, and liquid oxygen/liquid methane ascent and liquid oxygen/liquid hydrogen descent main engine technology development.

Reaction Control System

Completed 100 lbf thrust oxygen/methane RCS engine.

The PCAD team is developing small, 100 lbf (pound-force) thrust reaction control engines that use liquid oxygen and liquid methane as propellants. The engines are being developed under two contracts with Aerojet and Northrop Grumman to meet specified performance goals identified from system studies. One of the key technology areas in development is the ignition system of the RCS. The system must provide safe, reliable ignition at varying propellant temperatures, pressures and mixture (oxidizer-to-fuel) ratios. The ignition must also operate in an instant while being exposed to the extreme temperatures in space and a high number (50,000+) of engine pulses. The team is evaluating a number of ignition concepts such as spark torch igniters, catalytic igniters and exciters, which provide voltage to the igniter’s spark plugs.

Testing of an 870 lbf thrust liquid oxygen/liquid methane reaction control engine at White Sands Test Facility.

Integrated Tests

Integrated testing has been performed using 870 lbf thrust reaction control engines previously used with oxygen/ethanol propellants and modified for use with oxygen/methane. Testing is also being conducted with 100 lbf thrust reaction control engines designed for oxygen/methane propellants to demonstrate how the thrusters and the feed system work together under simulated operating conditions. Tests will be conducted in a vacuum environment at White Sands Test Facility using four RCS thrusters and a mock-up feed system on the Auxiliary Propulsion System Test Bed. This activity will be used to determine how well the propellants can be delivered to the engines and how the engines operate together during the mission profile.

Descent Main Engines

Pratt & Whitney Rocketdyne CECE engine vacuum test.

While landing on the moon, the lander’s descent main engine must be able to throttle and remain controlled by the crew to provide a soft landing or to maneuver the vehicle to a different landing site. Standard rocket engines typically have a fixed point design that does not allow the engine’s power level to throttle over a wide operating range. If not designed properly, throttling a rocket engine can create instability in engine pressure, which can cause a reduction in performance or even damage the engine or vehicle.

The PCAD team is focused on demonstrating stable combustion at low power levels to determine the performance of the throttling engine and eliminate instability. An accurate assessment of engine performance determines how much propellant is needed, which in turn helps determine the total weight of the vehicle. Reducing the total weight of the vehicle increases the affordability of the lunar mission because fewer resources could be launched from Earth. A lower vehicle weight also could mean that there is more room inside the vehicle for the crew and their cargo. NASA is evaluating both the Pratt & Whitney Rocketdyne Common Extensible Cryogenic Engine (CECE) and the Northrop Grumman Pintle descent engine technologies.

Ascent Main Engines

Liquid oxygen/liquid methane concept ablative engine.

Once the lunar mission is complete, the lunar lander will use an ascent main engine to propel itself off of the moon’s surface. PCAD is developing technologies for liquid oxygen/liquid methane engine concepts.

PCAD is currently working with Aerojet to design, build and test a workhorse engine at sea level and in vacuum conditions. The engine concept will use high temperature ablative materials to cool the combustion chamber. These materials slowly erode (char) as the engine fires and heats up. The concept is being evaluated for overall combustion efficiency, specific impulse, engine life, and thrust-to-weight ratio.

Oxygen/methane torch igniter test in vacuum at Glenn.