Swedish space officials say they were able to fuel the green system on Prisma in one day, meeting Russian safety requirements for their launch on a Dnepr-1 rocket without wearing hazmat suits. During the formation-flying operations, the Mango satellite fired thrusters using hydrazine and the LMP-103S green propellant interchangeably (AW&ST Nov. 1, 2010, p. 69).
Ball's GPIM spacecraft will use all five Aerojet Rocketdyne thrusters simultaneously to demonstrate attitude control, spacecraft point and hold, orbit lowering and inclination change. It will also characterize the thruster performance in space for future improvements, which could include shipping fueled spacecraft instead of fueling them at the launch site.
The U.S. Air Force Research Laboratory developed the HAN fuel/oxidizer blend, but it wasn't until Aerojet Rocketdyne worked with AFRL to perfect the catalyst necessary for it to fire that a spacecraft propulsion system became practical.
“These are high-temperature propellants; they burn at a higher temperature than hydrazine,” says Myers. “So the catalyst lifetime is limited by the high-temperature operations, so we developed a new catalyst. That was the key breakthrough, a new catalyst material, a new catalyst processing capability to enable the catalyst to survive long life.”
For now, hydrazine remains qualified for longer service life than the U.S. green propellant. Myers says the ground test ran the thruster for 11 hr. continuously, which should qualify it for many small NASA, military and commercial missions. Basically, McLean says, the technology was designed for ESPA-class rideshare spacecraft, although it can be scaled to larger spacecraft and other applications.
“We're looking to demonstrate about 7 kg (15 lb.) of fuel out of the entire propulsion system. That really is just for a very small spacecraft. However, as part of the overall program that we're doing, we're not just testing the engines and the flight engines during the overall qualification program to those levels of fuel. We're actually testing them to 30 kg of throughput, especially on the 22N, so that we will demonstrate its compatibility with longer-life missions.”