Sun. Mar 7th, 2021

The output of a “green” propellant, which is non-toxic, was successfully demonstrated by a recent NASA flight, providing prospects for use in a broad variety of potential spacecraft. As one of payloads which is on Space Test Program 2 flight, deployed on the SpaceX Falcon Heavy in 2019 June, the NASA agency flew Green Propellant Infusion Mission (GPIM) spaceship. The spacecraft’s mission concluded after a sequence of deorbiting motions when it re-entered in 2020 October. The goal of GPIM was to conduct an in-space demo of a green propellant called AF-M315E produced by Air Force Research Laboratory (AFRL).

The propellant was engineered to have hydrazine-like performance, which is widely used on spacecraft, however, without hydrazine-related toxicity and handling problems. The spacecraft met its efficiency targets, stated Trudy Kortes, who works at Space Technology Mission Directorate (STMD) of NASA as a program director in charge of technology demonstrations, during a discussion panel by the American Institute of Aeronautics and Astronautics on the mission at this month’s SciTech Conference. It included a “stretch objective” of pulsing over 10,000 times on the thrusters. The flight was the result of years of service on improving this green propellant and eventually flight-testing it.

“We thought that we’d do a demonstration of this propellant as early as 2002,” remembered Jeff Sheehy, STMD chief engineer who worked previously on sophisticated propellants such as AF-M315E at the AFRL. “We were far too positive in retrospect about how long it would take to have a new propellant to the level where it’s ready to show.” Part of the work included checking how different materials behaved with the propellant. “We had years of hydrazine experience with various materials, and we had no clue how this thing was going to behave,” stated Joe Cassady, the executive director in charge of space programs for the Washington office of Aerojet Rocketdyne.

The propulsion device flown on the GPIM used by AF-M315E was developed by Aerojet. To use a green propellant, certain components, he stated, had to be modified. Engineers have had to evaluate how other spacecraft technologies would communicate with the propulsion system. AF-M315E has provided a large volume of water as a by-product, unlike hydrazine. That raised concerns that the water might settle on the optical surfaces on spacecraft, such as star trackers, added Chris McLean, Ball Aerospace’s principal investigator for GPIM, requiring pre-flight ground modeling as well as testing.

Many concerned with the mission are positive about the prospects for subsequent flights, with the propellant successfully evaluated. It has a fresh, easier-to-remember identity: Energetic Non-Toxic Advanced Spacecraft, or abbreviated as ASCENT.

Adam Brand, AFRL’s advanced propellant development leader, said that his team is looking at the ASCENT versions. “We expect ASCENT to be a propellant family,” he added. “For different purposes, various kinds of missions, there are several blends.” Because ASCENT is a liquid salt, he stated that one possible application of the propellant is in a type of electrical propulsion device called an electrospray thruster.

By Adam