Sum of their parts
Nasa’s first would-be cubesat swarm ended up in the drink. Eight cubesats equipped with space radiation sensors and software to help them cooperate were destined for low Earth orbit last November when an experimental rail-launched Super Strypi rocket broke apart shortly after launch and dumped them into the Pacific Ocean.
Definitely disappointing, but not a serious setback. NASA updated the software on two backup cubesats and sent them to the International Space Station for a more advanced swarm demonstration, said Andrew Petro, program executive for NASA’s Small Spacecraft Technology Program.
In May, astronauts plan to deploy the two-kilogram cubesats to test their ability to transmit radiation data to ground stations, exchange information with one another and decide autonomously which spacecraft should communicate with the ground as part of the Network Operations Demonstration, or Nodes, mission.
“The coolest thing is that this will be the first demonstration of autonomous control and data handling among cubesats,” said Roger Hunter, small spacecraft technology program manager at the NASA Ames Research Center in Moffett Field, California. “Each one will have an opportunity to control the other, but they will negotiate that based on how much scientific data they have on board, their state of health and which one is closest to the ground station.”
NASA is not alone in pursuing the goal of launching swarms of small satellites that communicate with each other, or in developing large constellations of satellites that satisfy a common mission but do not interact. As shoebox-size satellites become increasingly popular tools for observation, measurement and communications, engineers in government, industry and academia are exploring ways to use them to create increasingly sophisticated networks.
“We are at the precipice of being able to launch dozens of small satellites that work together,” said David Klumpar, director of Montana State University’s Space Science and Engineering Laboratory. Klumpar wants to use satellite swarms for space physics research.
The U.S. Army’s Space and Missile Defense Command is exploring whether constellations of satellites weighing 100 kilograms or less could improve voice and data communications for soldiers, or support intelligence, surveillance and reconnaissance operations by providing images of targets on the ground in multiple wavelengths.
While a single miniature satellite can’t match the capabilities of much larger spacecraft and may not be suitable for the same missions, collectively these satellites offer “unique military capabilities and advantages,” John London, chief engineer for the Huntsville, Alabamabased Space and Missile Defense Command’s Space and Strategic Systems Directorate, said by email. “These satellites are typically very low cost on a per-unit basis, allowing large numbers of satellites to be affordably deployed into typically low altitude orbits.”
Later this year, the Army plans to launch Kestrel Eye Block 2, a 50-kilogram satellite built by Seattle-based Spaceflight Inc. and designed to obtain Earth imagery with a resolution of 1.5 meters. With Kestrel Eye, the Army will test whether a soldier could send requests directly to a constellation and quickly receive imagery.
For NASA, constellations offer useful measurement tools. “Taking multiple measurements in different places at the same time allows you to gather data you couldn’t in any other way,” Petro said in March during a briefing at NASA Ames. “Even if you had the best single spacecraft possible, you will not learn as much as you might from very low cost satellites operating in a coordinated network.”
For instance, a constellation of 50 or 100 miniature satellites could monitor space weather with such high resolution that researchers could detect the type of microclimates that exist on Earth, said John Hines, former NASA Ames chief technologist and now managing director of JH Technology Associates LLC, a San Francisco- based consulting firm.
Constellations also could provide continual communications and tracking for ships at sea and aircraft in flight, which would prevent mysteries like the disappearance in 2014 of Malaysian Airlines flight 370, said Richard Hodges, NASA Jet Propulsion Laboratory’s principal investigator for Integrated Solar Array and Reflectarray Antenna (ISARA), a five-kilogram satellite aimed at transferring data to ground stations at speeds of more than 100 megabits per second.
In many cases, miniature satellites will need highgain antennas to transmit data in addition to solar cells to generate enough power for the spacecraft and on board instruments. “How do you package all that in a spacecraft the size of a loaf of bread?” Hodges asked.
ISARA, which is scheduled to launch in June on a SpaceX Falcon 9 rocket from Vandenberg Air Force Base, California, seeks to solve the problem with three panels that fold along the sides of a cubesat during launch and open into a single rectangular panel in orbit. One side of the rectangular panel is covered by solar cells. The other side transmits data through an antenna produced with printed circuits. San Francisco-based Pumpkin Inc. developed ISARA’s solar array. The Aerospace Corp. of El Segundo, California, built the ISARA spacecraft and guidance system.
NASA’s Optical Communications and Sensor Demonstration takes another approach to bolstering communications for tiny satellites. That mission, scheduled to launch on the Falcon 9 with ISARA, will use lasers mounted on two 2.5-kilogram cubesats to transmit data.
“People have demonstrated optical communications from the ground with laser terminals the size of a small refrigerator,” said Richard Welle, Aerospace Corp.’s Microsatellite Systems Department director. “We wanted to do this as a cubesat.”
Optical Communications and Sensor Demonstration satellites also are equipped with cameras, beacons and laser rangefinders to bring the two satellites close together in orbit. NASA is eager to develop that capability because it would pave the way for closely spaced satellite swarms and for individual small satellites to approach larger spacecraft.
Sending miniature satellites into their proper orbit and keeping them there remains a challenge. The Nodes mission is scheduled to conclude after two weeks because the spacecraft will drift too far apart to communicate with each other.
“The relative spacing of satellites in a given orbital ring is important,” London said. “This requires small but capable on board propulsion systems, and much progress has been made recently in this technology arena within the nanosatellite commercial sector.”
For another NASA project, the Cubesat Proximity Operations Demonstration (CPOD) slated to launch in September on an Orbital ATK Minotaur rocket, Tyvak Nano-Satellite Systems equipped two satellites with imaging sensors and cold gas propulsion systems to help the spacecraft rendezvous, move close together and dock.
The mission calls for the five-kilogram CPOD satellites to take turns acting as either a resident space object or a chaser that rendezvous and docks with the object, said Ehson Mosleh, vice president for systems and mission assurance for Tyvak Nano-Satellite Systems of Irvine, California.
In the future, this type of capability could enable orbiting spacecraft to assemble themselves autonomously. “Imagine sending up a few of these and creating larger and more sophisticated structures as they dock,” Mosleh said.