Spacecraft no more than an inch square will fly aboard the next (and last) Shuttle flight to the International Space Station. The work of Mason Peck (Cornell University), the micro-satellites weigh in at less than one ten-millionth of the mass of the original Sputnik, yet can accomodate all the systems we associate with a spacecraft — power, propulsion, communications — on a single microchip. We’ve looked at Peck’s work in previous Centauri Dreams essays (see this one on ‘smart dust’), but it’s great to see some of his concepts put into an actual mission plan for testing in Earth orbit.
What Peck has in mind with the spacecraft he calls ‘Sprite’ is ultimately to create a satellite with different flight dynamics from other spacecraft. Sure, we can miniaturize our electronics and create satellites with small form factors — CubeSats come to mind — but Peck’s craft call up a different analogy:
- “Their small size allows them to travel like space dust,” said Peck. “Blown by solar winds, they can ‘sail’ to distant locations without fuel. We’re actually trying to create a new capability and build it from the ground up. We want to learn what’s the bare minimum we can design for communication from space.”
Not that the three Sprite chips scheduled for launch tomorrow (April 29) are going to be making any such journeys. They will be mounted on the Materials International Space Station Experiment (MISSE-8) pallet, which will in turn be attached to the ISS. The idea is to expose the chips to space conditions to see how their systems hold up. The MISSE-8 panel will be returned to Earth after a few years, but while they are in space, the three prototypes, built by Cornell students under Peck’s direction, can be tracked individually from their transmissions.
To see what Peck has in mind for future applications, consider the behavior of dust in our Solar System. We know that for particles at these scales, solar pressure and electrostatic forces are as significant as gravity in producing unusual orbits. Some dust actually leaves the Solar System on an interstellar trajectory, while other particles achieve stable orbits around the Sun, and some particles simply fall to the surface of planets. Peck has been talking for years now about putting the orbital dynamics of extremely small bodies (up to 100 µm in size) to work on tiny spacecraft like Sprite. Such a self-sustaining spacecraft should be able to take advantage of not only photon momentum but the solar wind, unconstrained by the need to carry onboard fuel.
For now, the Sprites being sent to the ISS will have a narrower target, to collect information about the solar wind’s chemistry, radiation and particle impacts on the chips. But they are demonstrations of our ability to pack power, attitude control, communications and more onto a microchip capable of traveling in a non-Keplerian orbit. And what they point to is a different take on the solar sail, one in which it is miniaturized and integrated with onboard spacecraft systems. Such a tiny sail is capable of things that a more conventional design is not. Consider what happens in the presence of a magnetic field, as outlined on this Cornell website:
- By artificially charging a spacecraft that is orbiting a planetary magnetic field, we can achieve Lorentz Augmented Orbits (LAO). Here, a spacecraft’s rotating magnetic field transfers energy and momentum to and from a planet via the Lorentz force. LAO offers opportunities that solar-pressure propulsion does not because it requires a magnetic field to operate. This interaction enables energy change maneuvers at outer planets, notably Jupiter with its dense magnetic field, where solar-pressure is too weak to be of much benefit. We show that high charge-to-mass ratios are significantly easier to achieve and maintain at reduced length scales.
And when it comes to reaching the surface of another world, such spacecraft come into their own:
- Exogenic dust gently lands on the surface of the Earth while its larger meteorite cousins rapidly ablate in the upper atmosphere. At extremely small length scales, the surface area of the dust can efficiently radiate away the heat generated by aerodynamic friction, even at entry velocities. We seek to use similar geometries and scales to design a passive entry vehicle capable of safely gliding or fluttering down to the surface of neighboring planets.
Peck even considers interstellar possibilities for future generations of Sprites, in which a chain of the tiny spacecraft move away from the Solar System and report data back to Earth through communications relays between each subsequent craft. The tests aboard the ISS are the first chance for the Sprite concept to prove its survivability in space, and Centauri Dreams congratulates Cornell students Zac Manchester, Ryan Zhou and doctoral candidate Justin Atchison on completing the prototypes that will fly aboard Endeavour. Success there could lead to a whole new way of thinking about propellantless propulsion and micro-scale spacecraft.
Among the papers on this work, Atchison and Peck, “
A Millimeter-Scale Lorentz-Propelled Spacecraft,” AIAA 2007-6847 AIAA Guidance, Navigation and Control Conference and Exhibit (Aug 2007) is the place to begin.
