Week 1: Inflatable Antenna Inner Workings

Inflatable Antenna

Pros:

• Much cheaper than conventional antenna
• Large surface area
• Easy to deploy
• Doesn't get jammed
• Scalable

Cons:

• Vulnerable to micrometeoroids
• Comparatively low gain due to wrinkles

How It Works:

After the satellite is launched, the satellite deploys the inflatable at an operating height.

At this point, the inflatable antenna has been evacuated of all the atmospheric gases. The only thing inside the inflatable is a chemical substrate. As you know, the reason why anything inflatable maintains its shape is because of a pressure difference.

For example, on Earth for a balloon:

As you can see the inside pressure and the outside pressure are the same.

If the pressure on the inside is greater than the outside, the balloon will inflate. Contrarily, if the pressure gradient was in the other direction, the balloon would deflate.

Remember, space is a vacuum, so the pressure is extremely low. Thus, the balloon cannot contain too much pressure, or else it would explode. Thus, the atmospheric air is evacuated from the inflatable antenna before the satellite is built.

Then how does an inflatable inflate?

Given that the inflatable is in vacuum, only a very small amount of pressure is required. Thus, scientists turned to chemical sublimates, substances that exists in the gaseous and solid stages. These substances have a low vapor pressure that can inflate the antenna without popping it. Moreover, they sublimate with a chemical equilibrium. Think about LeChatlier's principle. This is important because micro-meteoroids like dust flying at a high speed may puncture the inflatable. If there was a gas, the pressure difference would try to attain an equilibrium of 0, so the inflatable would deflate. That's bad. Luckily, sublimates maintain a chemical equilibrium that can be described by a function of pressure and temperature.  One of the most promising sublimates is benzoic acid because its rate of reaction is just right. Why does rate of reaction matter? A naïve interpretation of pressure is that it summarizes the collisions of gas molecules on the boundaries of a container. Because the rate of sublimation decreases as the pressure decreases, there will be less gas and more solid. Thus the internal pressure will decrease, so the inflatable remains inflated despite being punctured.



After the inflatable antenna inflates, it needs to keep its structure. This is solved by an UV-rigidizing resin coating. This coating will harden when exposed to UV light, which will help the antenna keep its shape.

What I'm covering:
There has been a slight change of plan. I will be doing an analysis of how we can quantify wrinkles.


For spoilers, click to -1.