Small is big again in space science
by Jeff Foust
|“You might ask the question, ‘How small can you make a satellite and still do science with it?’” Millan said.|
Months before the US launched its first satellite, Explorer 1, the Soviet Union had launched Sputnik 2, whose payloads included a cosmic ray counter. It detected anomalous spikes that Soviet scientists, led by Sergei Vernov, initially interpreted as solar flares, recounted Alexander Moiseev, a Russian scientist working today at NASA’s Goddard Space Flight Center. Later, they linked the data to particles trapped in the Earth’s magnetic field.
But James Van Allen had, months after the launch of Explorer 1, announced the discovery first, and the radiation belts would take on his name. “In the Soviet Union, it was very difficult for scientists to present something outside of the country,” he said at a January 31 symposium to mark the 60th anniversary of the Explorer 1 at the National Academies, in the same building that hosted the post-launch press conference about the launch in 1958. “Still, it was a confirmation by two independent scientific groups.”
Explorer 1 and a follow-up satellite, Explorer 3 (whose data helped nail down the existence of the radiation belts that would bear Van Allen’s name) were small spacecraft, weighing about 14 kilograms each. Since then the satellites have gotten larger and more sophisticated. NASA’s twin Radiation Belt Storm Probes, later renamed the Van Allen Probes, weighed more than 1,300 kilograms combined when launched in 2012, while the four Magnetospheric Multiscale (MMS) spacecraft, launched in 2015, weighed in at 1,360 kilograms each.
Those large spacecraft, while performing sophisticated science, also come with large price tags: the MMS mission costs NASA about $1.1 billion, including launch and operations. Even smaller missions—including those in the agency’s Explorer programs of astronomy and space science missions—routinely carry nine-figure price tags. “These Explorers have done phenomenal science,” said Robyn Millan, professor of physics and astronomy at Dartmouth. “But they still cost a couple hundred million dollars.”
At the National Academies event, Millan and others said they were increasingly looking at the other end of the spacecraft spectrum, seeing if cubesats offer a cost-effective means of doing science that is complementary to what can be done with larger satellites. “You might ask the question, ‘How small can you make a satellite and still do science with it?’” she said. “This has been a topic over the last decade or so.”
One example is the work by the National Science Foundation to fund cubesat projects for space science over the last decade. “There was a lot of skepticism in the field about doing real science with these little things,” she said, recalling discussions at an initial NSF workshop in 2007 on the topic.
However, she said that project has resulted in a wide array of innovative ideas that can use cubesat-class spacecraft, as well as supporting science and engineering education at universities supported by the NSF initiative. “This program has had a huge impact,” she said, with 25 cubesats either launched or in development. And, she added, those missions that have launched have produced noteworthy science. “There have been dozens of publications, some of them in really high impact journals.”
The success of the NSF initiative, Millan argued, has helped convince NASA to support cubesat science missions. “Prior to this program, NASA was developing cubesats, but most of that was in engineering and technology demonstration,” she said. “The success of this program really helped to fuel the NASA cubesat program we’re now seeing.”
Another factor is a 2016 National Academies study that concluded that cubesats could perform useful science, such as targeted science studies. “The conclusions of the study were that these really aren’t a replacement for those larger satellites that carry those suites of instruments,” she said. “But they are another tool that we can use for doing science.”
|“If I was you, I’d start betting on that future,” Zurbuchen said of smallsat and small launchers. “I’ve bet on worse things.”|
Cubesats also offer the opportunity to collect more data: more can be flown to provide a more complete picture of what is going on in the magnetosphere. “The future is multipoint,” said Allison Jaynes, an assistant professor of physics and astronomy at the University of Iowa who has worked on larger missions like the Van Allen Probes and MMS. “We need more launch opportunities, what we call low-cost access to space. We need options where we can piggyback on bigger missions.”
Thomas Zurbuchen, who chaired that National Academies cubesat science study and, months later, became the associate administrator for science at NASA, is working to provide such opportunities for cubesats. “In every single case when we go bid for a launch vehicle, now we’re including an option to basically get an ESPA ring that can launch cubesats and others,” he said. ESPA is a secondary payload adapter that allows cubesats and larger smallsats to fly on EELV-class rockets that have excess payload capacity.
He also emphasized NASA’s Venture Class Launch Services program, which has contracted with Rocket Lab and Virgin Orbit for launches of their smallsat launch vehicles, each carrying a cluster of cubesats, in the coming year. He argued could be a pathfinder for future low-cost launches. “For me, that’s really exciting,” he said. “For $10 million a pop, within a factor of two up or down, you could launch something.”
A week before the symposium, NASA launched its first science hosted payload, a space science instrument called Global-scale Observations of the Limb and Disk (GOLD) that is attached to the SES-14 commercial communications satellite. Zurbuchen said that also offered an option—albeit one still not utilized much by NASA—for getting payloads into orbit less expensively than dedicated larger spacecraft.
Zurbuchen said that “life changes” for scientists when they have access to low-cost launch opportunities. “If I was you, I’d start betting on that future,” he said. “I’ve bet on worse things.”
One of the next steps on this topic is completion of an ongoing study by the Committee on Space Research (COSPAR) on the use of small satellites in space science. Millan, who is co-chair of the study, said they’re considering everything from cubesats and even smaller spacecraft up to those weighing 180 kilograms, the limit of what can be launched on an ESPA ring.
|Among those concepts is a constellation with hundreds or even thousands of smallsats, for Earth observations or magnetospheric studies. “This may seem crazy, but already the commercial sector is already doing this,” Millan said|
The final report is set to be released at the COSPAR Scientific Assembly this July in Pasadena, California. The report will look at current and near-term capabilities, as well as limitations of smallsats, she said. “We’re also talking about a few different mission concepts that you might hatch, what kinds of things you could do with these small satellites.”
Among those concepts is a constellation with hundreds or even thousands of smallsats, for Earth observations or magnetospheric studies. “This may seem crazy, but already the commercial sector is already doing this,” she said, referring to proposed broadband satellite constellations. Smallsats could be used for interferometry, starting at radio wavelengths, which is less difficult.
Another issue the report will address, she said, is international cooperation in such smallsat projects. “What that looks like is still something we’re trying to figure out.”
In the meantime, more universities and space agencies are flying smallsats to do space science and other research. Moiseev said that, in 2014, Moscow State University launched a smallsat to study the radiation belts. Its name: Vernov.