How do you put a big antenna on a tiny satellite? Make it inflatable
By Ben Coxworth
September 9, 2013
CubeSats are certainly in the process of revolutionizing the satellite industry. They can serve many of the same functions as full-sized satellites, but at a size of 10 x 10 x 10 cm (3.9 x 3.9 x 3.9 in) and a mass of under 1.33 kg (2.9 lb), they’re much cheaper to build and get into orbit. With that smaller overall size, however, comes smaller onboard antennas. These severely limit CubeSats’ communications range, restricting them to fairly low orbits. That may be about to change, though, as MIT is developing larger, inflatable antennas.
Inflatable satellite antennas have been developed and tested before, although they were designed for regular-sized satellites, and utilized compressed air systems. Given the limited payload capacity of a CubeSat, cramming in heavy, bulky metal tanks and pressure valves just wouldn’t work. There’s also a risk that the compressed air tanks could explode in transit.
Instead, the MIT team turned to benzoic acid. It’s a sublimating powder, which means that it expands into gas form when exposed to low pressure – and in outer space, the pressure is pretty darn low.
In order to test their system, the researchers constructed two inflatable one-meter-wide antennas out Mylar – one was cone-shaped, and one was cylindrical. Each one had a few grams of benzoic acid placed inside of it, then was folded down into the inside of a CubeSat. When that satellite was subsequently exposed to a low pressure environment in a vacuum chamber, each of the antennas responded by inflating to their intended shape.
The electromagnetic properties of the antennas were also tested, to see how well they would be able to transmit data. While both did well, the cylindrical antenna particularly showed promise – according to MIT, it can transmit data 10 times faster and seven times farther than traditional CubeSat antennas.
It certainly sounds impressive, although it’s rather difficult to picture a Mylar balloon standing up to the rigors of outer space. Well, that’s where another characteristic of benzoic acid comes into the picture – the powder only turns to gas as long as there’s room for it to expand. Once a space is occupied with the gas, the remainder of the powder stays in solid form.
Should a micrometeroid make a small tear in the Mylar, the escaping gas will simply be making room for more of the powder to turn into gas – this ensures that as long as there is still some powder present, and the holes aren’t too big, the antenna will remain inflated. Through more tests, the MIT scientists determined that one of the antennas could stay inflated for up to a few years, even if it contained multiple small holes.
“With this antenna you could transmit from the moon, and even farther than that,” says Alessandra Babuscia, who led the research. “This antenna is one of the cheapest and most economical solutions to the problem of communications.”