Will tiny satellites launch a new space frontier?
An uptick in launch rates of CubeSats raises questions about how far this enabling technology could be taken.
In the world of satellites and robotic space probes, tiny is starting to make the big time.
So-called CubeSats – small, inexpensive, and increasingly capable – were initially developed as tools for training new generations of spacecraft designers in colleges and universities. Now, these miniature, box-shaped satellites are providing fresh, high-resolution close-ups of Earth daily for tracking environmental change or supporting disaster relief. Developers are laying the groundwork for using 900 CubeSat-scale satellites to provide high-speed Internet coverage worldwide.
Farther afield, CubeSats are destined for the moon, an asteroid, and perhaps Mars within the next two years. To some spaceflight visionaries, a properly designed CubeSat could become the first human object to reach the sun's nearest star, Alpha Centauri – in less than 25,000 years.
First conceived in 1999 by two university aerospace engineering professors in California, CubeSats initially appeared as boxy craft roughly 4 inches on a side. For more-ambitious projects, these modules can be combined. Without motors powerful enough for solo missions, they typically hitch rides as secondary payloads on rockets carrying much larger spacecraft.
The number of CubeSats launched hovered at less than 10 a year between 2000 and 2005, then began a relatively steady increase to 20 in 2012. Since then the number of CubeSats has vaulted from 79 in 2013 to 126 last year.
With so much growth in such a short time, “it's very difficult to predict where this is going to lead us,” acknowledges Paulo Lozano, who heads the Space Propulsion Laboratory at the Massachusetts Institute of Technology in Cambridge, Mass.
Still, he says, it hints at an exciting future for CubeSats specifically and small space hardware in general – inexpensive, increasingly capable craft whose products or services are directly available to more people than ever before.
The recent growth spurt comes with a caveat, others suggest. The outsized increases over the past two years are traceable to one start-up company, Planet Labs Inc., based in San Francisco. Founded in 2010, the firm uses its Dove satellites, typically launched from the International Space Station, to image Earth each day. It then sells the images to customers who turn the data into tools for mapping resources, changes in forest cover, the ebb and flow of farm production, or changes in a city's development patterns.
“If they were their own country, they would be moving into the top 10 of most spacecraft ever launched,” says Michael Swartwout, associate professor of aerospace and mechanical engineering at Saint Louis University in St. Louis, Mo., who maintains a database of CubeSat activity worldwide.
Almost single-handedly, the company elevated “commercial” to the single largest status of mission for CubeSats.
Without Planet Labs, the growth still would have been respectable, Dr. Swartwout says, describing the activity overall as people still trying to figure out what tasks CubeSats might best perform.
Although CubeSats are enjoying what Swartwout calls “the commercial bump” now, he says he doesn't yet see a “killer app” that would turn the bump into a long-term trend. Civilian government – alias NASA and other space agencies – may move toward the top of the user list instead.
The Obama administration's fiscal 2017 budget request for NASA seeks $15 million for the agency's CubeSat program, triple last year's amount. In January, the agency also announced that 13 CubeSats would ride to space during the first test flight of the agency's Space Launch System rocket, currently slated for November 2018.
Among the hitchhikers: a CubeSat-based craft that would use a solar sail to visit an asteroid and four craft that would either orbit or fly by the moon to look for water ice and other potential resources there.
NASA also had planned to send two CubeSats to Mars with its InSight mission. The CubeSats would have been the first to travel between planets, slated to arrive in time to relay data from InSight as it went through entry, descent, and landing. But technical problems prompted the agency to scrub the mission's March 2016 launch date. Instead, agency officials have said they expect to decide then whether to reschedule the launch for 2018 or drop the mission altogether.
For all the interest in CubeSats, they still lack an ingredient that could make them even more attractive: their own motors capable of pushing them out of Earth orbit and on to other destinations.
The CubeSats destined for Mars, for instance, would have received most of the energy they needed for the trip from the velocity of rocket stage that released them. They host miniature motors, but the motors are designed for making course adjustments along the way, not for breaking free of Earth's gravitational tug or for applying the brakes to begin orbiting a planet when the craft gets there.
Researchers at NASA's Jet Propulsion Laboratory are working on approaches for designing a motor for CubeSats that would act as such a brake. One approach uses what is essentially candle wax as a fuel, which would burn when combined with oxygen the craft brings along. Another approach would heat acrylic. The resulting gas would mix with oxygen and burn.
For powered interplanetary travel, however, researchers are looking at miniature variations of ion drive motors, similar to the motor that sent NASA's Dawn mission to Ceres and Vesta, in the asteroid belt.
But standard approaches don't shrink well. This has led researchers to explore alternate designs better matched to CubeSat scales. For instance, MIT's Dr. Lozano and colleagues have designed a motor that takes up less space than a quarter, has no moving parts, and uses an ionized liquid as its fuel, rather than a gas. Because the motor operates at room temperature, eventually it may be possible to make it from plastics.
NASA is currently testing three of the team's motors, and Lozano's lab has also been putting motors through their paces.
“We have been abusing the poor little guys,” he quips.
The motors are slated to get their first in-space test soon, he adds. The team has provided two propulsion modules for two Pentagon satellites scheduled for launch later this year.