To understand why CubeSats could be the next big thing in the study of comets and asteroids, consider the story of Philae, the European Space Agency probe that recently made history with the first-ever landing on the surface of a comet. The idea was to get close enough to the comet to analyze its composition in situ—what scientists call “ground truthing.” You can only learn so much about small bodies by studying them from Earth, so scientists built and launched the first spacecraft to sample a comet directly.
Trouble is, Philae cost around $240 million, and we almost lost it. Harpoons designed to help the lander grab on to the comet in the low gravity failed to deploy. Another smidgeon of velocity in its bounce, and that $240 million would have been drifting uselessly in the comet’s wake. Philae was lucky; after another bounce it finally came to rest on the surface. But comet landings remain an inherently risky business.
That’s where CubeSats—which can cost in the tens of thousands rather than the hundreds of millions of dollars—start to look appealing. “Because CubeSat is low-cost, one can afford to tolerate more risks,” says USC’s Joseph Wang, who has been working on CubeSat engineering for the past several years. In theory, low cost means that scientists can afford to explore more small bodies, more often. The challenge is designing small, light instruments with enough capability to do serious science.
With funding from the NASA Innovative Advanced Concepts (NIAC) program—NASA’s incubator for far-out ideas—Wang and a team at the University of Southern California and the University of Utah is studying how to get the most out of CubeSat missions by using advanced nanotechnology. “If successful,” says Wang, the study “may enable an entirely new class of low-cost alternatives to small-body exploration.”
The keystone of the NIAC project is a technique called Neutron Activation Analysis (NAA). Samples of asteroid or comet material would be bombarded with neutrons, and the resulting gamma radiation would reveal what elements are present and in what concentrations. On Earth, NAA is used in archeology, soil science, geology, and environmental analysis. But the instruments in use today are too big to put on a cubesat (your average NAA takes up about a cubic meter of volume), and they lack the robust construction needed to survive launch and the harshness of space. They also require a lot of power, a precious resource on any spacecraft. Wang’s co-investigators, Swomitra Mohanty, Mano Misra and Tatjana Jevremovic at the University of Utah, aim to build an NAA instrument optimized for space and small enough to fly on a CubeSat.
The mini-version of the NAA instrument uses integrated compound semiconductor nanowires—basically insanely tiny electronic elements that weigh next to nothing and use very little power—to detect the radiation emitted by a neutron-bombarded sample. So far it’s only worked in the lab, but the Utah team is getting it ready for use in space. That will partly involve finding a portable source of neutrons to shoot at the sample, and making sure the instrument can detect a wide variety of gamma rays.
The NIAC study has an eclectic team; among other things, Jevremovic works on nuclear reactors, and Mohanty and Misra recently collaborated on using nanotechnology to diagnose tuberculosis. While they develop the NAA instrument in the lab in Utah, Wang is puzzling out how to integrate the instrument into a CubeSat, and testing the system in vacuum and radiation environments like those the instrument would encounter in space.
Like many projects from NIAC, the nano-NAA is a long way from being ready to fly. Even so, once he and his team have worked out all the details, Wang estimates it could take only a couple of years to get a CubeSat mission ready to explore a comet or asteroid. That’s partly due to one last advantage of CubeSats—because they’re so light, they’ll be easier than heavy spacecraft to land on low-gravity surfaces without bouncing off .
Move over, Philae, the cubes are on their way.