A team led by NASA and Ball Aerospace [BLL] seeks to demonstrate and test a high-performance, non-toxic “green” spacecraft propellant on orbit with a goal of launching it into space by October 2015.
The propellant, a Hydroxyl Ammonium Nitrate (HAN) fuel/oxidizer blend designated AF-M315E by the Air Force Research Laboratory (AFRL), offers 50 percent better performance than hydrazine, a traditional satellite propellant that is also extremely toxic, according to Ball Principal Investigator for GPIM Chris McLean, who is leading the demonstration of the green propellant. The program, known as the NASA Green Propellant Infusion Mission (GPIM), is powered by a three-year, $50 million NASA contract. The program is about one year into the contract.
Ball is serving as prime contractor for GPIM along with co-investigators Aerojet Rocketdyne of GenCorp [GY], NASA’s Glenn Research Center and AFRL at Edwards AFB, Calif. Air Force Space and Missile Systems Center (AFSMC), NASA’s Kennedy Space Center and NASA’s Goddard Space Flight Center provide additional mission support, according to Ball.
“This is a rare opportunity for industry to advance this state-of-the-art, in space spacecraft propulsion,” McLean told Defense Daily in a December interview.
In-space, storable liquid propulsion technologies can be broken into two main thruster types: monopropellants and bipropellants. Monopropellant is a chemical propulsion approach that only uses one propellant, such as traditional hydrazine, and the fuel can function alone without an oxidizer. Monopropellants catalytically decompose, expand with heat and energy and provide thrust as it passes through the thruster’s catalyst bed. Bipropellant propulsion subsystems use a fuel and an oxidizer, such as monomethylhydrazine (MMH) and nitrogen tetroxide (N2O4), which McLean called very complex compared to monopropellant subsystems. As they react with each other, bipropellant thrusters provide better performance than monopropellants.
The team is taking a heritage Ball BCT-100 spacecraft bus that has flown twice and is building it again to provide a platform in space for NASA to demonstrate the propellant. While AFRL developed the green propellant about 15 years ago, it was only in the last two years, McLean said, that Aerojet Rocketdyne was able to develop an engine technology that could run and operate on this propellant. Aerojet Rocketdyne developed a catalyst that could handle the extreme temperatures of this green propellant, which gets extremely hot, and provides much more energy per volume, as it catalytically decomposes. McLean said heritage catalytic technologies are not able to handle the extreme temps of the green propellant.
One challenge of the green propellant program is determining what byproducts will come out of the propellant and what effects it will have on the spacecraft and the spacecraft environment. McLean said NASA Glenn in Cleveland performed an analysis over the last year and determined that the green propellant will have very similar interactions with the spacecraft as any other types of propellant. NASA Glenn used Plume Modeling, a numerical computational fluid dynamic (CFD) method of predicting where exhaust from spacecraft engine goes to perform this analysis.
The non-toxicity of the green propellant, originally developed by AFRL, is a significant advantage over traditional hydrazine propellant. On a scale of 1-to-10, with hydrazine and other spacecraft propellants ranking as the most toxic at 10 and gasoline at 5, McLean said the green propellant ranks around “zero to one,” along with caffeine. McLean said the green propellant is even less toxic than water, which can be fatal if consumed in overly-large quantities.
The green propellant is also very benign when inhaled. McLean said the highly-toxic hydrazine and MMH have very low vapor pressure, meaning if there is a container of the propellant sitting in a room, it will evolve immediately into the air and will be inhaled. It may not necessarily be lethal, he said, but it will expose someone to cancers and carcinogens. The green propellant, on the other hand, has no vapor pressure to speak of, McLean said, making it very difficult to smell.
The reduced toxicity of the green propellant brings big savings in infrastructure, resources and training, McLean said. When scientists and handlers are filling the spacecraft with the green propellant, they need only minimum protection including rubber gloves, eye goggles and a lab suit because if they come into physical contact with the propellant, they can wash it off with soap, though it might bring a slight irritant. Traditional spacecraft propellants, on the other hand, are so toxic they can burn holes in skin with contact, McLean said. These propellants have higher safety costs as handlers need to use astronaut-like suits called Self Contained Atmospheric Protective Ensemble (SCAPE) suits to protect themselves.
The green propellant can also be disposed of in a safer manner than traditional spacecraft propellant. McLean said the green propellant can be diluted with water and disposed, unlike traditional propellants that are rated as a catastrophic hazard if leaked or spilled. The green propulsion team is still determining how exactly to dispose of non-toxic propellant, not because it’s dangerous, McLean said, but because they haven’t developed the disposal processes.
In addition to earning savings by being safer to handle and dispose, the green propellant’s price per liter is simply cheaper than hydrazine and traditional spacecraft propellants. McLean said the savings could reach as much as $500,000 per launch of a $500 million satellite. Ball was unable to provide the cost per liter of hydrazine by press time.
McLean said the GPIM team achieved an enabler with its work on NASA’s Asteroid Rendezvous Mission, which has a goal of physically capturing an asteroid and returning it to earth. The spacecraft would grab the asteroid, which spins in orbit and would make the spacecraft spin with it upon grappling. The spacecraft would use propulsion to stop the rotation, enabling it to return the asteroid to earth. McLean said the GPIM team treated that mission with the green propellant and found that if it used the green propellant, NASA could have a 60 percent reduction in the complexity of the propulsion system in addition to shaving 22 inches off the length of the spacecraft.
The green propellant also freezes at much lower temps than traditional propellants, which, like water, expand when frozen, damaging valuable spacecraft parts and components. McLean said the green propellant goes into a “glass transition phase” at -80 degrees Celsius. Other propellants, and water, freeze at zero degrees Celsius. Since the green propellant doesn’t freeze, its spacecraft can save valuable power for scientific experiments instead of using it to keep propellant warm to prevent damage to the system.
The green propellant, part of the Air Force’s Space Test Program-2 (STP-2), is scheduled to be launched by Space Exploration Technologies Corp. (SpaceX) on one of the company’s Falcon Heavy rockets. Ball anticipates 60 days of on-orbit testing including attitude control demonstrations, spacecraft pointing and hold, thruster performance characterization and mapping, inclination change and orbit lowering to begin 21 days after October 2015 launch. The green propellant is also being examined for military uses such as missiles launches and auxiliary power units that currently use hydrazine.