Growing government interest spurs smallsat technologies
Tight budgets and small satellites are turning out to be an attractive mix, driving industrial and academic efforts to make tiny spacecraft more attractive to customers with deeper pockets than the penurious graduate students and innovative professors who pioneered the move down the size and mass scales.
Presentations at the American Institute of Aeronautics and Astronautics/Utah State University Conference on Small Satellites here show that entrepreneurs and established companies are starting to address the limitations posed by the cubesat standard to drive more capability into the 10 X 10 X 10-cm (3.9 X 3.9 X 3.9-in.) boxes originally developed as teaching tools for engineering students. And cubesats are growing beyond the three-unit, or U, limit imposed by the Poly-PicoSatellite Orbital Deployer (P-POD) dispenser they typically ride to orbit.
“The idea of 6U gives you a little more room, a little more payload space, and a little bit more room for avionics and things like that,” says James P. Marshall, director of business development at the Space Dynamics Laboratory here, which has developed operational cubesats and other small spacecraft and boasts what may be the only cubesat qualification lab in the world. “I've always guessed that we would all find the cubesat form-factor to be too constraining, and that we would all miniaturize a bunch of stuff and then get to the point of diminishing returns,” Marshall says.
Among the hardware on display here was a 6U dispenser under development by Planetary Systems of Silver Springs, Md., “in collaboration” with the Pentagon's Office of Responsive Space (ORS), according to company founder Walter Holemans. The ORS interest in cubesats as a way to meet its military mission is one of the factors shaping the direction the industry is taking, and for the second year in a row the organization held a classified workshop to discuss its requirements with industry representatives who are cleared to learn them and potentially able to meet them.
While the largest aerospace companies were represented here, some of the most promising work was presented by small startups such as Planetary Systems, which is building on its niche in mechanical separation mechanisms with the cubesat-dispenser work. Vulcan Wireless Inc. of Carlsbad, Calif., displayed a family of software-defined radios built to fit into the cubesat form that can meet some military communications requirements.
“The small satellites are starting to get more capability, so the military's starting to look at these platforms as a kind of stop-gap measure, low-cost, rapid-deployment,” says Kevin Lynaugh, president and CEO of Vulcan. “So you need to start looking into more sophisticated communications that's more applicable to military solutions and, to some extent, commercial. And those waveforms are quite a bit more sophisticated than ham radio analog modulation.”
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,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's Small Spacecraft Technology Program at will be a 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.
The motor essentially consumes itself as it burns, igniting in the presence of nitrous oxide housed in a tank space that surrounds a cylinder of the carbon-reinforced nylon that burns from the inside out. The motor configuration can only be made using the additive-manufacturing technique, which offers more flexibility than reductive machining, Dushku says.
To produce the motors, CRP uses a computer-aided design (CAD) file containing the motor's shape, and electronically divides it into layers for the 3-D printing.Corp. (SpaceX) uses the same technique to manufacture tiny impellers and other parts for its Merlin rocket engines from titanium powder, according to a SpaceX spokesman.
Dushku says the AM motors, which operate with a tank pressure of 700 psi, have been pressurized to 2,200 psi with water before failing. That margin, the inert hybrid fuel and the high temperature needed to decompose nitrous oxide into nitrogen and oxygen should reassure launch service providers with safety concerns, he says.
In their runway demonstration, Dushku and Mueller used a little of the nitrous oxide in the motor tank to fire cold-gas attitude-control thrusters to rotate the 6U spacecraft shell, and then they hot-fired the motor for 5 sec. Ultimately, they hope to produce a small AM spacecraft that can generate a delta V of 780 meters per sec. with a 60-sec. burn time.
“We can get to where we want to be very, very quickly,” Dushku says.