The cold-gas thrusters on Tyvak's CPOD cubesats may not be the propulsion of choice for future smallsat maneuvering. While last year's conference included a hybrid rocket test banished to an abandoned runway outside of town due to safety concerns (AW&ST Aug. 20, 2012, p. 31), tiny electric and “green” propulsion systems using inert and non-toxic propellants such as Teflon were on display this year.
Those kinder, gentler characteristics, highlighted by specialty houses like Busek Space Propulsion and Systems of Natick, Mass., and Digital Solid State Propulsion (DSSP) of Reno, Nev., should allay the fears of satellite operators hoping to defray their launch costs a little by allowing smallsats to fly with them as secondary payloads.
A case in point is Spinsat, which is set for “soft stowage” launch in the pressurized portion of the SpaceX Dragon headed to the International Space Station (ISS) next April. A station crewmember will carry the 22-in. sphere, essentially packed in a fabric bag, from the Dragon into the station and leave it there until its scheduled deployment through the Japanese module's airlock. NASA safety experts approved the mission because the satellite's 12 thruster-clusters burn an inert solid fuel called Hipep, and only when an electric charge is passed across it.
In space, the Naval Research Laboratory satellite will demonstrate the DSSP thruster technology in a series of maneuvers, and also serve as a reflector for ground-based laser ranging to study atmospheric drag. It is one of two very different spacecraft that will be passed through the Japanese airlock and released from the end of one of the station's robotic arms to test a new NASA deployer known as Cyclops.
Engineers at Johnson Space Center designed Cyclops to handle as many different spacecraft shapes as possible, grappling them with a special fixture, squeezing through the airlock tunnel and attaching to the end of the Canadian or Japanese-built arms to release them down and away from the back of the station to avoid recontact. In addition to the U.S. Navy's Spinsat, the Cyclops test in April will deploy a rectangular satellite—Lonestar-2—built by Texas college students.
Neither of the first two spacecraft to be deployed with Cyclops is a cubesat, but Japan and the U.S. company Nanoracks have launched cubesats from the ISS with special spring-loaded dispensers that essentially work like a jack-in-the-box, squiring the tiny spacecraft out in stacks (see photo).
Dispensers have gone a long way beyond the standard cubesat deployer developed at California Polytechnic State University (Cal Poly) called the P-Pod. Planetary Systems of Silver Spring, Md., drew attention in the exhibit hall with noisy demonstrations of its 6U cubesat deployer, and paper presentations covered a variety of dispensing methods for smallsat packages ranging from multiple cubesats to as many as six satellites in the 180-kg (400-lb.) range riding on Moog CSA Engineering's Evolved Expendable Launch Vehicle Secondary Payload Adapter (ESPA) rings.
In the middle is an “Express” adapter for secondary payloads in the 20-50-kg class—under development at the Johns Hopkins University Applied Physics Laboratory in Columbia, Md.—to fill an unmet need.
“In talks with the community over the past few years we've noticed that a need exists for an intermediary-sized mission between cubesats and ESPA-sized vehicles,” says Clint Apland, who presented a paper on the “Express” work. “We've designed, fabricated and will begin to test this hardware next month.”