Large Balloon Reflector: a potentially game-changing antenna design

I am pretty sure that something like this was conceived of by David E. H. Jones, under the pen name Daedalus, for one of his tongue-in-cheek columns in either New Scientist or Nature.

IIRC, the scheme, for creating a large space telescope in situ, went something like this: 1) create a flat film of some uncured polymer resin, polymer solution or heat-softened plastic on a large ring; 2) inflate it into a hemispherical dome by applying moderate gas pressure on one side; 3) allow the material to harden; 4) release the pressure, which will cause the bubble to adopt a parabolic shape; 5) use ion beam deposition to apply a reflective surface. I can't say whether my recollection of the geometrical claim on which this proposal is based is accurate, or, if so, whether it is correct.

Most of Jones's proposals were wildly yet entertainingly infeasible, but not always, and he is somewhat well known for conceiving of a form of 3-D printing (using a laser-polymerized monomer) before any serious proposals for the concept. There are a couple of collections of his Daedalus columns.

https://en.wikipedia.org/wiki/David_E._H._Jones

When I was a child , so a long time ago, at the Huntsville ( huntsville alabama )Space Museum they had a demo that was something that looked like a pie pan that was 10 feet across with Mylar stretched across it. And a tripod that was attached at the edge and stood over it. At the top there was a cone of metal and inside the cone was a copper tube that ran up one of the tripod legs and spiralled around the inside of the cone then ran down one of the other legs. They had a household vacuum cleaner attached to a tube at the bottom of the pie pan. When the turned on the vacuum the Mylar got sucked down and it made a parabolic surface. The sunshine was then focused into the cone and the turned on the water and it ran through the copper tube . It came out a stream of water for a few minutes but then turned to steam. Always loved that contraption.

This was in my browser history from earlier this year:

https://gizmodo.com/upcoming-cubesat-feature-inflatable-beac...

The military has used them for years on the ground, evidently this is also a nasa spinoff:

https://spinoff.nasa.gov/Spinoff2010/ps_5.html

I see the used ones for sale at ham radio flea markets sometimes.

I'm oversimplifying, but this is how I read it as a layperson, with a fair degree of joy!

NASA, for decades: Launching antennae into space is a difficult, costly procedure that requires billions of dollars.

Also NASA: Hey, what if we just...made the inside of one side of a clear balloon shiny??

I can't see a picture of the concave shape, I was under the impression that the design is that one third of the sphere is collapsed inside itself to make a nice concave antenna that's cheap and light - is this what's happenning?

Edit0: Nope! Part of the sphere is transparent, and the inside is reflective. Nothing collapsed.

And it's working very similarily to a normal parabolic antennae, but being inflatable it's way lighter/smaller, leaving more weight and room for power and instruments. Massive win!

Reminds me of Project Echo

https://en.wikipedia.org/wiki/Project_Echo

Remastered documentary: https://www.youtube.com/watch?v=19kAuAVAnDc

Scott Manley: https://www.youtube.com/watch?v=19kAuAVAnDc

> it inflates like a beachball, providing a stable parabolic-dish shape

Except the surface of a beachball is spherical, not parabolic. A parabolic surface is not closed, so you can't inflate it like a beachball.

So I'd like to know either: how they control the shape of the surface, so the mirrored portion is parabolic; or whether the antenna surface is actually spherical, and not parabolic at all.

The portion of a parabolic mirror nearest the focus approximates to a sphere. If the deviation is less than 1/4 wavelength of the signal of interest, a spherical mirror will focus the signal perfectly, as if it were a paraboloid.

A paraboloid is what you need for distortion-free imaging; this antenna is apparently used only for signalling, so perhaps accuracy doesn't matter, because only the gain is important. But this is a NASA publication, so I wouldn't expect them to say it's parabolic if it's really spherical.

I'm a little confused because the article uses 'spherical' and 'parabolic' seemingly interchangeably. I'm sure the scientists know what they're doing but just found the imprecision a bit odd for a nasa.gov article.

Is the idea here that this is new for outer space? There are ground based inflatable antennas that you can buy that have been around for a few years.

I’ve heard a trade off with these is they aren’t very ridged so in windy conditions they don’t work that great. Maybe that is less of a problem in outer scpace.

https://www.cubic.com/inflatable-satellite-antenna https://spinoff.nasa.gov/Spinoff2010/ps_5.html

Makes me wonder about an inflatable balloon antenna for amateur radio. I wonder how hard it would be to do this sort of fabrication (aluminizing the inside of a balloon) as an amateur

Better pictures here https://www.freefallaerospace.com/nasa-balloon/

From TFA:

> Some 30 years ago, a young engineer named Christopher Walker was home in the evening making chocolate pudding when he got what turned out to be a very serendipitous call from his mother.

> Taking the call, he shut off the stove and stretched plastic wrap over the pot to keep the pudding fresh. By the time he returned, the cooling air in the pot had drawn the wrap into a concave shape, and in that warped plastic, he saw something – the magnified reflection of an overhead lightbulb – that gave him an idea that could revolutionize space-based sensing and communications.

I love genesis stories like this. Reminds me of Feynman's plate: https://demonstrations.wolfram.com/FeynmansWobblingPlate/

Balloons In Space are a good idea, and an antenna is not the only concept they've been proposed for:

https://www.projectrho.com/public_html/rocket/infrastructure...

https://www.projectrho.com/public_html/rocket/enginelist.php...

Even at large volumes, you get a ton of surface area for the mass, as well as a good spherical or parabolic shape for reflectors.

The article really could use a picture. If I understand correctly you can get a parabolic shape if you have a stretchy film over ring and apply a pressure differential. The spherical balloon functions as the support ring for an internal reflective third layer. If both halves of the balloon are inflated to equal pressure the reflective layer is flat, but by changing the pressure in both halves the layer takes on a parabolic shape.

I don’t think that the explanation is entirely correct. Inflating a balloon will produce a spherical antenna not a parabolic one. Now I don’t really remember the implication of using a spherical receiver for radio waves, but in case of light waves it’s necessary to use a parabolic reflector instead of a spherical one to avoid spherical aberration.

A good idea. I wonder how robust it is to small debris, I assume it won't pop but will the thin material fold up on itself if there's a hole?

Inflatables are nothing new, but still awesome.

https://en.m.wikipedia.org/wiki/Inflatable_Antenna_Experimen...

By the way, inflatable parabolic SATCOM antennas have been sold by a company called GATR for at least 10 years:

https://www.militaryaerospace.com/rf-analog/article/16715763...

The idea is that these would point to space, right?

I wonder if you could create a ground antenna as well, with a pair of these -- one acting as receiver and the other as transmitter, at a very high altitude, pointed at two different locations on the ground.

That would give you a very high gain antenna for two fixed points which might obviate the need for e.g. expensive undersea cable link.

Looks to be something easy to experiment with at home. Heat welding vinyl isn't horribly difficult or risky. use copper tape to form your antenna elements. Complicated 3d shapes that can be collapsed and reinflated should be doable.

Durability might be a concern but there's a lot of prior art in marine applications to observe.

I don't understand why the article and everyone here are talking about spheres. Balloons come in all possible shapes, and in fact the most common birthday balloons are not spherical. Can't they engineer a balloon which has a parabolic surface when inflated?

I thought of using a similar technique to build low cost concentrated solar arrays with a pump that adjusts the air pressure within to automatically focus and optimize the incoming light onto the CSP hot end.

Interesting article!

>"Now, with an assist from NASA’s Innovative Advanced Concepts (NIAC) program, funded by the agency’s Space Technology Mission Directorate, which supports visionary innovations from diverse sources, Walker’s decades-old vision is coming to fruition."

Didn't know about NIAC before reading this. It sounds like a great group of people!

https://en.wikipedia.org/wiki/NASA_Institute_for_Advanced_Co...

I assume this is based on a spherical cap's being "close enough" to a paraboloid, for the purposes of this design.

Reminds me of the idea of hiding satellite dishes in false water tanks that allow the transmission of whatever freq of radio wave.

I’d be concerned that the balloon would pop the moment it comes across some rock or dust.

Using a huge balloon to make the shape and then covering it in a material in space could be an idea. Get the ISS crew to build a mega telescope in orbit.

“At first, I was afraid to share the idea with colleagues because it sounded so crazy. You need a program within NASA that will actually look at the radical ideas, and NIAC is it.”

It doesn't seem like an even slightly crazy idea to me.

Reminds me of the 320th Barrage Balloon Battalion.