Masten’s Green Bipropellant: MXP-351

As part of our partnership with NASA through the Lunar CATALYST (Lunar Cargo Transportation and Landing by Soft Touchdown) program, we have been actively developing a proprietary new bipropellant – MXP-351. This propellant is intended to be flown on our XL-1 lunar lander which is capable of bringing up to 100 kg (221 lb) softly to the lunar surface. MXP-351 represents the next step in Masten’s internal propulsion development program in improving our capabilities closer towards spaceflight.

MXP-351 is a nontoxic, storable and hypergolic bipropellant combination. These storable propellants, as opposed to cryogenic propellants like Liquid Oxygen or Liquid Hydrogen, are stable for long periods of time at room temperature. Hypergolic propellants mean that the fuel and oxidizer will ignite spontaneously as soon as they come into contact with each other. Storable and hypergolic systems eliminate the need for separate igniter systems and typically only need minimal thermal conditioning of the propellants, improving their reliability and performance. Consequently, such systems are favored highly for in-space missions like the XL-1 lunar lander.

Historically, spacecraft have used cocktails of Hydrazines and Nitrogen Tetroxide (NTO) as storable hypergolic propellants. These propellants have very high performance and were used in the Apollo Lunar Module Ascent and Descent engines, as well as part of the Space Shuttle’s Orbital Maneuvering System (OMS). However, they are both extremely toxic, requiring exhaustive procedures for safe procurement, handling, spill control, and disposal. The nontoxic MXP-351, by comparison, is exceptionally easy to handle. They have very low vapor pressures, meaning they don’t evaporate easily and pose inhalation hazards to any workers. Spills are easily rectified by simply diluting with water and rinsing away. These greatly reduced operational constraints have the potential to reduce recurring costs for spaceflight applications.

More importantly, it allows us to safely and thoroughly test out our propulsion systems here in Mojave with the same regularity as we fly our vehicles. In 2016, we successfully fired the first generation of our 225 lb XL-1 main engine, dubbed ‘Machete’. This simple ‘boilerplate’ engine validated our injector design, performance estimates, and applicability of MXP-351 in a rocket test environment. Future tests with MXP-351 will use additively-manufactured technology to test regeneratively-cooled thrust chambers, as well as scaling up the thrust capability up to 1,000 lb for a terrestrial testbed version dubbed (XL-1T) that is currently in manufacture.

NASA CATALYST has been instrumental in aiding our development in the program, giving advice from industry experts who have worked with similar propellants in the past, as well as providing advanced analytical capabilities to characterize engines with these propellants.