LOGAN, Utah — As cubesats prove their ability to capture imagery and gather scientific data, developers are eager to send the miniature spacecraft on increasingly complex missions, many of which require propulsion.
“With any satellite there’s a lot of mission capability you can get when you’re able to maneuver,” said Andrew Petro, NASA’s Small Spacecraft Technology program executive. “We are trying to do more things with these satellites and that requires mobility.”
NASA is exploring a wide range of propulsion technologies to enable cubesats to change altitude, conduct proximity operations, disperse and form arrays, including cold gas, monopropellant, liquefied gas, solid rocket, Hall effect and electrospray thrusters. “We want to cast a wide net,” Petro said. “We are not looking for one solution, but for a whole set of solutions.”
NASA’s Optical Communications and Sensor Demonstration, slated for launch in 2015 as part of NASA’s Cubesat Launch Initiative, is to use cold gas thrusters to enable two 1.5-unit cubesats to maneuver and operate to within 200 meters of each other. NASA’s Small Spacecraft Technology Program has earmarked about $3.5 million over two years for the project led by the Aerospace Corp. of El Segundo, California.
The Small Spacecraft Technology Program is providing approximately $13.5 million over three years for a related effort, Cubesat Proximity Operations Demonstration. For that mission, Tyvak Nano-Satellite Systems of Irvine, California, is developing two three-unit cubesats to rendezvous, conduct proximity operations and dock with one another with the help of cold gas propulsion.
Aerojet Rocketdyne is developing liquid propulsion systems for cubesats, including MPS-100 Cubesat High-impulse Adaptable Modular Propulsion System (CHAMPS), a miniature hydrazine thruster designed to provide a change in velocity of more than 200 meters per second, and MPS-120 CHAMPS, a version that uses additive manufacturing to produce the piston propellant tank and miniature isolation system.
In August 2013, NASA’s Small Spacecraft Technology Program selected MPS-120 as one of 10 payloads for space agency-supported development. Through the project, Aerojet plans to conduct the first flight of that hydrazine-fueled engine, which it produced with additive manufacturing. “All the plumbing and a lot of the features are printed right into the tank,” said Christian Carpenter, MPS-120 principal investigator for Aerojet Rocketdyne in Redmond, Washington. “This will not only be the first test of a liquid system at this size scale but also the first test of a 3-D printed liquid system and pressurized tank.”
The MPS-120 project is designed to demonstrate that hydrazine can be safely handled and stored on cubesats. “Just like large satellites, cubesats eventually will fly pressurized systems with liquid propellants,” Carpenter said.
Busek Co. Inc. plans to demonstrate the use of an iodine-fueled Hall effect thruster on Iodine Satellite, a 12-unit cubesat scheduled for launch in 2017 by NASA Marshall Space Flight Center in Huntsville, Alabama. “The advantages of iodine is that it has three times the propulsive energy per liter as xenon,” Dan Williams, Busek business development director, said by email. In addition, Busek is developing propulsion systems based on electrospray, micro-RF ion, ammonia-fueled micro-resistojet, green monopropellant and micro-pulsed plasma thrusters.
In the past, cubesats did not include onboard propulsion because it would disqualify them from piggybacking on government flights. Now, some cubesat developers are obtaining waivers from those rules, allowing them to begin to experiment with miniature propulsion systems. “We are very interested in finding less-hazardous propulsion systems because if you are trying to fly as a secondary, you may be very limited in what the primary mission will allow you to carry,” Petro said. “Keeping the propulsion safe and simple is especially valuable when you’ve got a low-cost project to begin with and you want to keep it that way.”