Most cubesats flying today use amateur-radio frequencies to communicate with the ground, a simple approach in keeping with the low-cost origins of the satellite class. But just as military applications may require larger buses to accommodate optical and other specialized payloads, they also require higher data rates and encryption capability unavailable in the ham frequencies.
Potential military applications for cubesat-based spacecraft include inexpensive low-Earth-orbit communications with ground troops in mountainous or urban terrain where signals from geostationary orbits may be blocked.
On the civil side, NASA is pushing smallsat technology for low-cost science missions. The agency's Office of the Chief Technologist (OCT), which has funds to push the readiness levels of enabling technologies without a specific mission in mind, has just announced three space-based experiments employing cubesats to demonstrate advanced communications and control techniques.
The company receiving the largest share of the $22.6 million in OCT funding is a spin-off from the engineering school at California Polytechnic State University in San Luis Obispo, an early academic developer of cubesats. Tyvak Nano-Satellite Systems of Orange, Calif., will use two 3U cubesats in a rendezvous-and-docking experiment expected to fly in 2015. Working with Tyvak on the $13.5 million Proximity Operations Nano-Satellite Flight Demonstration project will be Applied Defense Solutions Inc. of Columbia, Md.; and 406 Aerospace of Bozeman, Mont.
Also funded by the OCT through NASA's Small Spacecraft Technology Program at Ames Research Center will be a Jet Propulsion Laboratory experiment—the integrated Solar Array and Reflectarray Antenna (Isara) for High Bandwidth CubeSat—that uses the back of a cubesat solar array as an antenna reflector to increase radio bandwidth for data communications. Richard Hodges of JPL, in partnership with Pumpkin Inc. of San Francisco, will receive about $5.5 million to launch the 3U cubesat in two years. The Aerospace Corp. will receive $3.6 million for its Integrated Optical Communications and Proximity Sensors for Cubesats experiment, a pair of 1.5U cubesats designed to demonstrate laser communications from space to Earth, as well as inexpensive radar and optical sensors for spacecraft-proximity operations.
Another hurdle for cubesat-based spacecraft is propulsion. Small satellites are typically launched as secondary payloads by launch service providers that are uncomfortable with the potential risk of extra propulsion systems. Several exhibits here featured high-specific-impulse electric propulsion systems, including variations on the electrospray thrusters engineers at the Massachusetts Institute of Technology are fabricating with micro-electromechanical systems (MEMS) techniques (AW&ST July 30, p. 36).
An alternative presented at the smallsat conference—and test-fired on an abandoned runway at the small local airport—uses additive manufacturing (AM) to create a hybrid engine that literally uses itself as fuel to generate higher thrust than the electric systems.
Those systems require “long burn times to produce significant delta V,” says Matthew Dushku, head of the Experiment Propulsion Lab, a small startup based here. “That means it's going to take longer to [reach] your desired orbit, and it's going to consume portions of useful mission life.”
Dushku and his business partner, Paul Mueller, have worked with Planetary Sciences to develop an AM motor to drive a 6U cubesat built with the same 3-D printing process. Their motor and the satellite shell are produced by race-car parts house CRP USA of Mooresville, N.C., using Windform XT 2.0, a picocarbon-reinforced nylon material that can be laid up in layers as a powder and hardened with a laser scanner.