September 7, 2013
MIT Researchers Working To Develop Durable, Long-lasting Inflatable Antennae For CubeSats
April Flowers for redOrbit.com - Your Universe Online
With personal electronics, smaller is almost always better. The same is becoming true with satellite technology – which is shrinking to about the size of a shoebox. Making space exploration cheaper and more accessible, “CubeSats” and other small satellites can be launched into orbit at a fraction of the weight and cost of traditional satellites.
Miniaturization has its limitations, however, such as a satellite’s communication range. It is impossible to store large, far-ranging radio dishes in the tight quarters of a CubeSat. The small satellites are equipped with smaller, less powerful antennae. These restrict them to orbits below those of most geosynchronous satellites.
A research team from MIT has come up with a new design that might have a significant impact on the communication range of small satellites, enabling them to travel much farther into the solar system. The new design, which has been built and tested by the team, is an inflatable antenna that can fold into a compact space and inflate when in orbit.
The new antenna allows a CubeSat to transmit data back to Earth at a higher rate by significantly amplifying a radio signal. The inflatable antenna allows the satellite to transmit seven times farther than existing CubeSat communications.
“With this antenna you could transmit from the moon, and even farther than that,” says Alessandra Babuscia, who led the research as a postdoc at MIT. “This antenna is one of the cheapest and most economical solutions to the problem of communications.”
The researchers, who included graduate students Benjamin Corbin, Mary Knapp, and Mark Van de Loo from MIT, and Rebecca Jensen-Clem from the California Institute of Technology, are all part of Professor Sara Seager's research group. The findings of their studies were published in the journal Acta Astronautica.
This is not the first time an inflatable antenna has been attempted. Earlier experiments in space have been successful, though most were for large satellites. Engineers use a system of pressure valves to fill the larger, bulkier antennae with air once they are in space. The equipment is heavy and cumbersome, and would not fit within a CubeSat’s limited real estate.
An additional concern with such equipment is that the pressure valves may backfire. As most small satellites are often launched as secondary payloads aboard rockets containing other scientific missions, such a backfire could have explosive results that jeopardize everything on board. Babuscia says this is all the more reason to find a new inflation mechanism.
The team developed a lighter, safer solution. Their solution is a sublimating powder, which is a chemical compound that transforms from a solid powder to a gas when exposed to low pressure.
“It’s almost like magic,” Babuscia explains. “Once you are in space, the difference in pressure triggers a chemical reaction that makes the powder sublimate from the solid state to the gas state, and that inflates the antenna.”
The researchers built two meter-wide prototypes out of Mylar. When inflated, one is cone shaped and one cylindrical. The optimal folding configuration for each design was determined, and each antenna was packed into a 10-cubic-centimeter space within a CubeSat, along with a few grams of benzoic acid, a type of sublimating powder. The inflation of the antennae was tested in a vacuum chamber at MIT, where the team lowered the pressure to just above that experienced in space. In both cases, the powder converted to a gas and inflated the antenna to the desired shape.
The electromagnetic properties of each antenna was also tested, which gives an indication of how well an antenna can transmit data. The researchers found that the cylindrical antenna performed slightly better in radiation simulations, transmitting data 10 times faster, and seven times farther, than existing CubeSat antennae.
While potentially powerful, an antenna made of thin Mylar is vulnerable to passing detritus in space. For example, micrometeroids can puncture a balloon, which would cause leaks and affect the antenna’s performance. The sublimating powder can circumvent the problems caused by micrometeroid impacts, however, because it will only create as much gas as needed to fully inflate an antenna. This leaves residual powder to sublimate later, to compensate for any later leaks or punctures.
To test this theory, the team set up a course simulation to model the inflatable antenna’s behavior with different frequency of impacts to assess how much of an antenna’s surface may be punctured and how much air may leak out without compromising its performance. With the right sublimating powder, the team found that the lifetime of a CubeSat’s inflatable antenna may be a few years, even if it is riddled with small holes.
Babuscia, who is continuing to refine the antenna design at JPL, says future tests may involve creating tiny holes in a prototype and inflating it in a vacuum chamber to see how much powder would be required to keep the antenna inflated.
“In the end, what’s going to make the success of CubeSat communications will be a lot of different ideas, and the ability of engineers to find the right solution for each mission,” Babuscia said. “So inflatable antennae could be for a spacecraft going by itself to an asteroid. For another problem, you’d need another solution. But all this research builds a set of options to allow these spacecraft, made directly by universities, to fly in deep space.”