Satellites come in all sizes–from the tiny ChipSats Zac is working on which are now on the ISS (see previous posts), to the massive communications satellites that bring you your favorite ball game from across the world. One particularly interesting size (at least to me) is the CubeSat size. These satellites are the size of one, two or three blocks (called U’s), each block being a 10cm x 10cm x 10cm cube. A satellite composed of three of these U’s in a row (a 3U CubeSat) is allowed to have a mass of at most 4 kg. At this scale, the satellites are just big enough to incorporate a relevant payload.
This particular shape and mass was standardized as a way to make launches cheaper and easier to attain for university-led projects. Since the standard was introduced in 1999, dozens of CubeSats have been launched into orbit. Most of these have been launched as secondary payloads, taking up some of the extra space on a larger satellite’s rocket. The spacecraft’s standard size also enables the use of readily-available off-the-shelf components, allowing developers to focus on the experimental parts instead of re-inventing routine parts.
So far, CubeSats have been confined to low Earth orbit because no propulsion system available at this scale can give the satellite the energy needed to go beyond. This may soon change, and with that change will come new missions and applications for CubeSats. What follows is a list of what I consider to be the 5 most interesting CubeSat-based missions. While the list is by no means exhaustive, it gives a good idea of the possibilities open to private researchers with relatively little cost. Feel free to post comments with your own ideas for what you’d do with a tiny spacecraft!
1. Earth Observation
The standard mission for a CubeSat in Low Earth Orbit is to communicate with ground stations and in some cases send back a few photos. As smaller and more powerful cameras become available, the resolution and detail of images taken from CubeSats will only improve. Also, with smaller components that allow the satellite to change its orientation (reaction wheels, control moment gyros, magnetic torque coils, etc.) the images will be targeted at specific locations, making them more relevant for Earth observation and studies of everything from land use to atmospheric data. Other types of sensors can be placed in CubeSats to aid in Earth remote sensing–one example of this (a CubeSat that uses magnetometers to observe earthquakes) has already flown. The general idea is that by taking advantage of the cheap, quick access to space provided by CubeSats we can learn more about the Earth.
2. Multi-body reconfiguration experiments
One of the greatest appeals of CubeSats is that they’re (relatively) cheap to launch and fast to develop, especially when compared to larger, custom-built spacecraft. So, if you want to do experiments that require long exposure to zero-gravity environments, this might be the way to go. One active area of research that can benefit from this is the development of autonomous docking and maneuvering algorithms for large groups of satellites. Having a set of three or more 1U CubeSats that can move around each other would be a great platform for validation of these experiments. Once demonstrated in small-scale on the CubeSats, the same technology can be used in larger systems with more confidence. An example of this is the docking and reconfiguration work being done using magnetic flux pinning right here at SSDS. You can see more about this here.
If you’re outfitting your CubeSat with all sorts of cameras to look at the Earth, why not point it the other way? While there are countless things you could study with a cheap telescope in orbit, one interesting proposal for astronomy that can be done with CubeSats is the ExoplanetSat, detailed in this paper.
Essentially, the plan proposed involves a cloud of CubeSats, each with a telescope, tracking bright stars in order to detect Earth-like planets orbiting other stars.
4. Orbit the Moon
This is my personal favorite. Getting a CubeSat to go to the Moon might seem pretty far off. We all remember images of the Apollo missions, with giant rockets blasting off into space, using tons of fuel in seconds. How could something the size of a milk jug get to the Moon too?
By hitchhiking part of the way on the same rocket as a larger satellite, CubeSats are able to gain much of the energy necessary to escape Earth orbit. A much smaller propulsion system, maybe even one that fits inside the small volume of a CubeSat, can then take the satellite the rest of the way to the moon. Depending on what orbit the CubeSat is released and what trajectory is chosen, the size of the propulsion system necessary can be reduced. While the Apollo spacecraft allowed astronauts to get to the moon in a matter of days, if time is not an issue, there are ways to trade time for propellant savings. This way, a CubeSat can get to the Moon in a few months, but much more efficiently than the Apollo missions. Getting anywhere near the Moon is beyond the capabilities of any propulsion system that has flown on a CubeSat to date, but here at SSDS we are hoping to soon change that.
5. Deliver ChipSats to cool places
ChipSats are far smaller than CubeSats, but their high surface area to mass ratio allows them to do things larger satellites can’t dream of. At the ChipSat scale, effects such as air drag, solar pressure and electromagnetic forces become much more important and affect the chip’s orbit significantly. Using a CubeSat as a way to deploy ChipSats can change where and how ChipSats can be deployed. From low Earth orbit, the CubeSat can time the release of the chips, which will then flutter downwards and cover a target area. If the CubeSat has propulsion, it can eject the chips in higher orbits where solar pressure forces are stronger than gravity. The chips can then use solar pressure to sail away from the Earth and explore the far reaches of the Solar System.