by Lance Davis
NASA’s Marshall Space Flight Center
NASA just validated a new type of propellant, or fuel, for spacecraft of all sizes. Instead of toxic hydrazine, space missions can use a less toxic, “green” propellant and the compatible technologies designed to go along with it. In a little over a year since launch, NASA’s Green Propellant Infusion Mission (GPIM) successfully proved a never-before-used propellant and propulsion system work as intended, demonstrating both are practical options for future missions.
GPIM set out to test a monopropellant – a chemical propellant that can burn by itself without a separate oxidizer – called Advanced Spacecraft Energetic Non-Toxic (ASCENT). Formerly known as AF-M315E, the U.S. Air Force Research Laboratory invented the propellant at Edwards Air Force Base in California. It is an alternative to the monopropellant hydrazine.
“This is the first time in 50 years NASA tested a new, high-performing monopropellant in space,” said Tim Smith, GPIM mission manager at NASA’s Marshall Space Flight Center in Huntsville, Alabama. “It has the potential to supplement or even replace hydrazine, which spacecraft have used since the 1960s.” Based at Marshall, NASA’s Technology Demonstration Mission (TDM) program manages the mission.
GPIM’s effective demonstration of the propellant paved the way for NASA’s acceptance of ASCENT in new missions. The next NASA mission to use ASCENT will be Lunar Flashlight. The small spacecraft, which aims to provide clear-cut information about the presence of water deposits inside craters, will launch as a secondary payload on Artemis I, the first integrated flight test of NASA’s Orion spacecraft and Space Launch System (SLS) rocket.
Despite being pink in color, ASCENT is considered “green” for its significantly reduced toxicity compared to hydrazine, which requires protective suits and rigorous propellant loading processing procedures. It is safer to store and use, requiring minimal personal protective equipment such as lab coats, goggles, and gloves.
Besides being easier and less expensive to handle here on Earth, when loading a spacecraft with propellant, for example, ASCENT will allow spacecraft to travel farther or operate longer with less propellant in their tank, given its higher performance.
But to test the propellant on a small spacecraft, the GPIM team had to develop hardware and systems compatible with the liquid. Aerojet Rocketdyne of Redmond, Washington, designed and built the five thrusters onboard GPIM. Aerojet Rocketdyne and Ball Aerospace of Boulder, Colorado, co-designed the other elements of the propulsion system.
While in orbit, GPIM tested the propellant and propulsion system, including the thrusters, tanks, and valves, by conducting a planned series of orbital maneuvers. Attitude control maneuvers, the process of maintaining stable control of a satellite, and orbit lowering demonstrated the propellant’s pre-mission projected performance, showing a 50% increase in gas mileage for the spacecraft compared to hydrazine.
With the technology demonstration objectives almost complete, the mission proved ASCENT and the compatible propulsion system are a viable, effective alternative for NASA and the commercial spaceflight industry, Smith said.
“We can attribute GPIM’s success to a strong partnership,” Smith added. NASA’s Space Technology Mission Directorate selected Ball Aerospace to lead the mission in 2012. In addition to building the mini-refrigerator-sized spacecraft, the company integrated and tested the payloads and propulsion system before launch and provides flight operations support.
“We are excited to announce flight operations have been very smooth, with the new propulsion subsystem operating as we anticipated,” said Christopher McLean, GPIM principal investigator for Ball Aerospace. “We greatly appreciate the partnership and continuous support throughout this mission from NASA’s Space Technology Mission Directorate, and program management office at Marshall.”
GPIM approaches mission completion, and the spacecraft has started a series of deorbit burns. Approximately seven burns will lower the orbit to about 110 miles (180 kilometers) and deplete the propellant tank. The small spacecraft will burn up in Earth’s atmosphere upon reentry, anticipated in late September 2020.
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