Experiments coming up on the International Space Station (ISS) early next month may someday lead to multi-spacecraft constellations that maintain formation electromagnetically, and pass electric power among themselves across open space.
The Department of Defense Spheres-Rings experiment reached the station in August on Japan’s H-II Transfer Vehicle, and underwent a successful checkout on Aug. 27. Essentially a pair of conducting coils designed to fit on two of the three Synchronized Position, Hold, Engage, Reorient, Experimental Satellites (Spheres) already on the station, the Rings experiment will be first test in microgravity of electromagnetic positioning with free-flying satellites.
“If you can maintain their position relative to each other, then you only need propulsion on one of them,” says Javier de Luis, vice president of research programs at Aurora Flight Sciences, which built the Spheres and Rings flight hardware.
The three 18-sided Spheres are free-flying software testbeds designed to operate inside one of the pressurized modules on the ISS. Each is the size of a volleyball and weighs 3.5 kg (7.7 lb.) on the ground. They use carbon-dioxide cold-gas thrusters to maneuver, and AA batteries to power their internal avionics, software, communications and measurement systems.
For the Rings experiment, two of the spheres are fitted with the 0.77-meter-dia. (2.5-ft. dia.) rings, which contain resonant coils, cooling fans, mounting structure and two lithium-ion rechargeable batteries each, plus the electronics necessary to control power to the coils. In the 3-4-hr.-long experiment, tentatively scheduled for Nov. 4, station astronauts will load test software into the Sphere/Ring rigs, position them so they are floating freely, and then activate the test.
With researchers at the University of Maryland and the Defense Advanced Research Projects Agency (Darpa) monitoring from the ground, the software will generate attractive, repulsive and shear forces between the two floating objects, while the crew and ground researchers record the resulting interactions at ranges from “decimeters to a few meters,” according to a NASA description of the test. The experiment protocol also includes attempts to transmit power from one sphere/ring to the other “via resonant inducting coupling,” NASA said.
“By advancing the knowledge base with regards to inter-satellite attitude control and wireless power transfer, future systems can expect enhanced attitude control performance between separate satellites and potentially the ability to efficiently transfer power at a distance, possibly alleviating the need for alternate or expendable (i.e., batteries) power sources,” NASA states.
The ambient-temperature station tests grew out of work done at the Massachusetts Institute of Technology for Darpa, using high-temperature superconducting coils to generate the electromagnetic fields. Using that technology on full-scale spacecraft in open space, de Luis says, it should be possible to maintain formation across multiple spacecraft at ranges of “tens to hundreds of meters.”
For the upcoming test, Ray Sedwick of the University of Maryland, where the hardware was designed, is the principal investigator. Melissa Wright of Darpa is the co-investigator.