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MIT's Inflatable Antennae Could Boost Small Satellite Communications
coondoggie writes "Researchers at the Massachusetts's Institute of technology say they have developed an antenna for small satellites (known as cubesats) that can fold into a compact space and inflate when in orbit. The inflatable antenna lets a CubeSat transmit data back to Earth at a distance seven times farther than that of existing CubeSat communications."
Can't they get the signal lasers working? Much better for max signal strength, bandwidth, power usage and transmitter size.
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What, like this product that's been on the market for about a decade or so?
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Tidbits for Techs Technology Blog
First line of the article: "Mylar-based attennae could inflate once launched, withstand micro-meteor threat, MIT says."
Article says it can take a number of micrometeor impacts and still stay inflated. I buy that claim. It doesn't take a lot of gas pressure to inflate a piece of mylar and they have a good mechanism for maintaining that modest gas pressure (via sublimation of a particular powdered chemical) even in the presence of a bunch of micrometeor holes (low pressure gas doesn't leak out very quickly).
OTOH, they might have a problem controlling inflation of the antenna in the first place. The sublimation triggers in the presence of vacuum. And they'll have that condition before the cubesat leaves the payload shroud.
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The bird will need an attitude detection and control system to take advantage of this antenna... decreasing the available weight, volume, and power available for other things. TANSTAAFL.
Is MIT an insect with inflatable feelers which somehow assist in satellite communications?
When referring to a radio antenna the plural is "antennas."
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The inflatable antenna lets a CubeSat transmit data back to Earth at a distance seven times farther than that of existing CubeSat communications."
When are they going to be orbiting cubesats 7x higher than they do now? No, what such an antenna can do is allow you to operate at 50x less transmitter power (or 50x the data rate at the same power). Or receive at 50x the data rate. That's all good. but we won't be sending any cubesats past the moon. Spacecraft designed for high orbits must be designed for long missions, and cubesats are designed for short missions because they must compromise something to make things fit in tiny spaces.
It doesn't take reactive chemicals. Just seal a small amount of gas in the balloon when it's on Earth, say, less than 1cc of nitrogen. When it gets to space, it will inflate as soon as you let it out of the enclosure.
Mylar has gone a long way to being shatter proof, however seeing small object traveling at say around 25 miles per second, I just don't see it resistant to that.
I find it hard to believe that the system could provide enough gas to keep it inflated for a long time in the presence of even micron-sized holes. I'd be more likely to believe that it would maintain structural integrity if they used a plastic that became stiff when struck by ultraviolet light, or became stiff as a plasticizer outgassed.
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Well, suppose they have a bag of air attached to equipment that feeds pressurized air so as to maintain the bag at standard temperature and pressure (STP which is 20 C and 1 atmosphere) and the bag is suspended in a vacuum. The speed of sound at that temperature for air (which also is the average velocity of molecules in air) is roughly 340 m/s.
For a millimeter sized hole leaking into vacuum (let's say that the hole is a square millimeter in area), that means that in the absence of friction and turbulence, roughly 3.4*10^-4 cubic meters of air leak out every second (average velocity of air times the area of the hole(s)). At a density of 1.2 kg per sq meter, that's roughly 4*10-4 kg per second of mass lost through that hole. In other words, a gram of air lost ever 2.5 seconds or so.
But mass loss is proportional to pressure. If instead, the pressure inside the bag were one ten-thousandth of an atmosphere, then the mass loss is 1 gram every 25,000 seconds, or roughly a gram lost every 7 hours.
A micron sized hole because it's a million times smaller in area would have a mass loss a millionth the rate of this. So in the one atmosphere case, you'd be losing a gram of air every four weeks, roughly.
In the absence of perturbations or vibration, such an antenna can hold its shape under extremely low pressures. But I doubt that would be the case for a normal spacecraft. At the least, you'd have perturbations from vehicle maneuvering, temperature changes should the vehicle enter shade (say the Sun is eclipsed by the Earth or Moon in the course of the spacecraft's orbit) or change orientation (different parts of the vehicle are lit means some vibration as parts of the vehicle expand or contract).
So they have to maintain some level of pressure depending on how much vibration they expect and how long they're willing to wait for the antenna to settled down to a usable level.