[HN Gopher] Large Balloon Reflector: a potentially game-changing...
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Large Balloon Reflector: a potentially game-changing antenna design
Author : foota
Score : 226 points
Date : 2023-10-27 21:08 UTC (1 days ago)
(HTM) web link (www.nasa.gov)
(TXT) w3m dump (www.nasa.gov)
| kunwon1 wrote:
| 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/
| itishappy wrote:
| buy space blanket (aluminized mylar)
|
| tape it over garbage can
|
| suck
|
| ???
|
| profit
| cwkoss wrote:
| greenpowerscience is a fun channel who did a neat version of
| this https://www.youtube.com/watch?v=-1GV3FIOR6E
| aqfamnzc wrote:
| Just need to find a parabolic garbage can!?
| eternauta3k wrote:
| No, the garbage can just supports the edges.
| ianburrell wrote:
| I don't think it would be useful for most amateur radio which
| doesn't need the gain and balloon would be huge. It would be
| useful for people who do higher frequencies and use satellite
| dishes. Portable link to 2.4GHz mesh network would be example.
| It might also be useful for cheaply making big dishes for Moon
| bounce.
| dmbche wrote:
| 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!
| smoyer wrote:
| Transparent to some portion of the electromagnetic spectrum ...
| We might not be able to see through it though.
| aimor wrote:
| 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?
| Terr_ wrote:
| I guess it depends on the odds (impacts per cross-section per
| time) for different debris size/composition/speeds in the
| planned orbit. I'm sure _somebody 's_ studying that, but I'm
| also sure it must involve a lot of complicated tables.
|
| The particular mini-satellite is slated for a 6-month mission,
| so presumably they think it'll survive at least that long.
| morcheeba wrote:
| That was my first thought, too. My ideas was to make the
| plastic UV-curable so it would become rigid and not require
| inflation. I looked it up, and that's what they're doing - UV-
| curable ribs. It's also not a sphere; it has an inflatable
| ring. Pictures & paper here:
| https://asteroid.arizona.edu/KABAND_Inflatable_v3_public.pdf
| ortusdux wrote:
| 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
| itishappy wrote:
| Also NASA's Inflatable Antenna Experiment, which looks like it
| spun off a successful commercial product.
|
| https://en.wikipedia.org/wiki/Inflatable_Antenna_Experiment
|
| https://spinoff.nasa.gov/Spinoff2010/ps_5.html
|
| https://www.cubic.com/inflatable-satellite-antenna
| uoaei wrote:
| 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.
| andreareina wrote:
| I understood it as, the structure is spherical, with one
| parabolic surface that acts as the antenna.
| teo_zero wrote:
| No, it's spherical. Instead of a transceiver placed in the
| focal point, they use array of min. 3 transceivers. It will
| definitely not have the same gain of a parabolic of similar
| size, but it will be more flexible about where the target it
| aims at must be. They are advertising it not for
| communication from fixed point to fixed point, but rather
| between vehicles that are continously moving, where a less
| directional solution will be an advantage.
| istjohn wrote:
| This page states that it is spherical.
| https://www.freefallaerospace.com/nasa-balloon/
| uoaei wrote:
| Nice, thanks for finding that.
|
| Excerpt:
|
| > FreeFall's antenna technology is unique because it is using
| a spherical reflector. In the past, antennas always used a
| parabolic antenna. A parabolic antenna focuses energy to a
| "single point" - while a spherical antenna focuses energy to
| a "focal line". Parabolic antennas are symmetric about only
| one axis which severely limits field of view. It also
| requires precise pointing for high gain and has more complex
| packaging, deployment and on-orbit operations. The spherical
| antenna provides a wider field of view for antennas and high
| gain without re-pointing of an antenna. Combining a spherical
| antennas with inflatables is the key to achieving a large
| aperture in a simple lightweight system.
| sbierwagen wrote:
| Kinda funny. Antenna gain _is_ beam width. Antennas with
| large effective apertures have narrow beam widths.
|
| I can easily buy that it could be cheaper to launch a 50m
| spherical inflatable antenna than a rigid 25m parabolic
| antenna. But it's never going to be true that a spherical
| antenna with the same gain as a parabolic will have a wider
| beam width.
| uoaei wrote:
| I assume some part of the "focal line" aspect changes
| that calculation.
| smoyer wrote:
| You can also tune the secondary a bit through the design of the
| feed horn. Even better with a phased-array and some
| electronics!
| slowhadoken wrote:
| Reminds me of the 320th Barrage Balloon Battalion.
| smeej wrote:
| 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_??
| foota wrote:
| Who would win, the space industrial complex or one shiney
| balloon boy?
|
| Given the other comment about this below
| (https://news.ycombinator.com/item?id=38044638), I'm surprised
| this hasn't been done sooner though, I wonder if there's some
| missing downside?
| jdironman wrote:
| One thing I am wondering about is SAT to SAT communication. I
| imagine the receiver / transmitter is facing "down", or is it
| maneuverable and does SAT to SAT support something like a BGP
| router network or something to ensure optimal comms.
| s1artibartfast wrote:
| There are tons of downsides and tradeoffs.
|
| Top concers I would have is working lifetime, stability, and
| percision.
|
| You don't want a dish that is continually changing shape. Gas
| and materials shrink and expand as temperature changes. The
| balloon will also leak.
| jimkoen wrote:
| These sound like manageable problems in space though.
|
| Overall the temperature of the balloon will stay pretty
| constant if it stays on a fixed orbit around the sun.
|
| The argument about precision I don't understand - the
| article talks about creating telescopes with this concept
| but NASA wants to use this for radio communication - the
| comparison with JWST doesn't apply, as it's mirrors had to
| be manufactured to a much higher tolerance.
|
| > lifetime
|
| I mean we had bigelow Aerospace with their module and it
| seems to be pretty durable. [0]
|
| [0] https://de.wikipedia.org/wiki/Bigelow_Expandable_Activi
| ty_Mo...
| s1artibartfast wrote:
| >Overall the temperature of the balloon will stay pretty
| constant if it stays on a fixed orbit around the sun.
|
| OK, so you just ruled out 99% of use cases. The world
| only has a handful of satellites in heliocentric orbits.
| squarefoot wrote:
| Space is cold; I wonder if they could find a material that
| is inflatable at room temp but would quickly harden in
| space, so they would inflate it using warm gas, then wait
| for it to cool down.
| s1artibartfast wrote:
| Space is also hot.
|
| NASA temperature conditions for flight hardware is as
| follows: LEO -65 oC to +125 oC, with 6,000 cycles/yr
| depending on orbit height. GEO is -196 oC to +128 degC,
| with 90 cycles/yr.
|
| That is some serious Thermal stress. Never mind the fact
| that it is also being blasted with UV radiation.
| Intralexical wrote:
| > That is some serious Thermal stress. Never mind the
| fact that it is also being blasted with UV radiation.
|
| This sounds like a problem that is easily solved by
| simply adding another, bigger balloon that sits between
| it and the sun.
| squarefoot wrote:
| > Space is also hot.
|
| Yes, of course. I was wondering if there are materials
| that once cooled down would harden but then remain as
| such also when temperature rises again. Assuming it's
| doable, it would likely suffer from dilation and
| contraction anyway.
| Intralexical wrote:
| > You don't want a dish that is continually changing shape.
|
| https://en.wikipedia.org/wiki/Adaptive_optics
|
| Decent ground-based telecopes have to constantly change
| shape anyway. Perhaps it would in fact be easier to manage
| with a balloon.
|
| JWST also unfolded from panels, so presumably has a way to
| calibrate itself.
| Intralexical wrote:
| > The ballon will also leak.
|
| The US solved this problem in the early Cold War for
| passive balloon communications satellites by putting a
| chunk of solid volatile material inside the balloon, so
| sublimation kept a constant internal gas pressure. I
| suppose you'd stick a cheap servo on a door to control the
| sublimation rate if you need a precise mirror.
|
| Besides, so long as you've already got the expensive
| sensors, navigation, propulsion etc. up there, why not just
| keep chucking up backpacks crammed full of new balloon
| modules for when your old one pops?
| s1artibartfast wrote:
| How many decades or years does that last?
| pmorici wrote:
| 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
| eternauta3k wrote:
| Re: wind, at what frequencies would it be ok to put them in a
| box / tent?
| MagicMoonlight wrote:
| That makes way more sense than using it somewhere fragile like
| space.
|
| You could have an emergency antenna on life rafts that suddenly
| inflates to a full size beacon.
| tigershark wrote:
| 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.
| satori99 wrote:
| In this case, the spherical shape is an advantage. See _uoaei_
| 's post (above);
|
| https://news.ycombinator.com/item?id=38043955#38045556
| h2odragon wrote:
| 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.
| mlsu wrote:
| 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.
| danboarder wrote:
| 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.
| teo_zero wrote:
| The keyword here is "focus": a spherical surface like this does
| not focus sun rays, you need a parabolic surface for that.
| While it would be possible to shape a film or another foldable
| material into a parabolic profile playing with air pressure and
| a specially crafted frame, I wonder what would be the advantage
| over a rigid parabolic mirror. The foldable/inflatable part is
| only an advantage for aerospace applications where size and
| weight are at premium.
| eternauta3k wrote:
| A balloon is not necessarily spherical, see e.g. the long
| balloons for making balloon animals.
| greesil wrote:
| Inflatables are nothing new, but still awesome.
|
| https://en.m.wikipedia.org/wiki/Inflatable_Antenna_Experimen...
| brucethemoose2 wrote:
| 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.
| incompatible wrote:
| "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.
| Scalene2 wrote:
| The rocket crane to land a rover was pretty crazy, gonna be
| hard to top that.
| ooterness wrote:
| That still blows my mind. At some point, a room full of risk-
| averse engineers all agreed that "rocket crane" is the safest
| and most practical solution to a problem.
| mannykannot wrote:
| 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
| Wingman4l7 wrote:
| There's also the old concept of spun liquid mirrors, (1994,
| Amateur Scientist column of Scientific American):
| https://optica.machorro.net/Optica/SciAm/LiquidMirror/1994-0...
| myself248 wrote:
| 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.
| prvc wrote:
| I assume this is based on a spherical cap's being "close enough"
| to a paraboloid, for the purposes of this design.
| asimpleusecase wrote:
| 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.
| Intralexical wrote:
| Reminds me of liquid-mirrored telescopes:
|
| https://en.wikipedia.org/wiki/Large_Zenith_Telescope
| tda wrote:
| 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.
| eternauta3k wrote:
| As far as I understood, it's just a balloon with a reflective
| coating from the north pole down to some latitude.
| peter_d_sherman wrote:
| 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...
| eternauta3k wrote:
| 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?
| dathos wrote:
| I think that requires a lot more pieces and engineering in
| order to work properly
| eternauta3k wrote:
| What do you mean? We can make party balloons and long
| balloons for balloon animals without any additional pieces.
| MagicMoonlight wrote:
| 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.
| denton-scratch wrote:
| > 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.
| fgeiger wrote:
| Maybe I misunderstand your point of spherical vs parabolic, but
| doesn't this paragraph explain it?
|
| > The concept turns part of the inside surface of an inflated
| sphere into a parabolic antenna. A section comprising about a
| third of the balloon's interior surface is aluminized, giving
| it reflective properties.
|
| The balloon is approximately spherical but probably not exactly
| (actually, when looking closely, hardly any beachballs are
| spherical either). What is parabolic is the part of the balloon
| which is aluminized.
|
| Edit: fixed a typo
| denton-scratch wrote:
| Yeah; I was wondering how they get the mirrored part of the
| balloon to take on a parabolic shape, rather than spherical;
| is that done by manipulating the balloon material somehow? Or
| are they settling for spherical as a good-enough
| approximation?
| persnickety wrote:
| This references the problem, but doesn't explain the big
| question: how do they turn a section of a sphere into a
| section of a parabola?
|
| Beach balls might not be spherical, but my bet would be on
| ovoid rather than parabolic.
| sandworm101 wrote:
| A few internal wires/cables might allow the final inflated
| structure to be roughly parabolic. All sorts of wacky shapes
| can be made with internal stays. Also, at low pressures the
| outer shape of the balloon could be made parabolic. Not every
| balloon need be perfectly round. When inflated a balance
| occures between internal pressure and outer structure. Just
| look at any birthday baloon. They arent spheres. And perfection
| isnt needed for a radio antenna. It just needs to be better
| than one of the same mass.
| denton-scratch wrote:
| > Just look at any birthday baloon. They arent spheres.
|
| Yeah, I wondered about that. I guess a birthday balloon is a
| pretty complicated curve; but I doubt it comes closer to a
| paraboloid than it does to a sphere or a plane, anywhere on
| its surface.
|
| But this thing isn't a telescope, it doesn't have to focus an
| image; it doesn't need to be a parabola, a sphere is fine for
| achieving highly-directional gain.
| guenthert wrote:
| Seems like an error in the article. [1] states: "FreeFall's
| antenna technology is unique because it is using a spherical
| reflector. In the past, antennas always used a parabolic
| antenna. A parabolic antenna focuses energy to a "single point"
| - while a spherical antenna focuses energy to a "focal line".
| Parabolic antennas are symmetric about only one axis which
| severely limits field of view. It also requires precise
| pointing for high gain and has more complex packaging,
| deployment and on-orbit operations. The spherical antenna
| provides a wider field of view for antennas and high gain
| without re-pointing of an antenna. Combining a spherical
| antennas with inflatables is the key to achieving a large
| aperture in a simple lightweight system."
|
| [1] https://www.freefallaerospace.com/nasa-balloon/
| Intralexical wrote:
| Arecibo is/was spherical Ftr, presumably because a paraboloid
| could only sweep a single path through space. They aimed it
| by moving the receiver.
| denton-scratch wrote:
| Thank you.
|
| I'm not up to date on telescope design (by at least 40
| years), but the Cassegrain design used a spherical mirror, I
| think. It was used for wide-field astrophotography, and
| (again, I think) it has a curved focal field, so it needs a
| curved sensor.
|
| I'm certain that Cassegrain designs have been obsoleted. I'm
| just bragging about what an anachronism I am.
|
| [Edit] The Cassegrain design also requires a refracting lens
| in front of the mirror; and the lens is a peculiar shape.
|
| [Edit again] I may be thinking of a Schmitt. I've never
| played with anything more interesting than a Newtonian; I was
| just an amateur stargazer. All these fancy designs were made
| for professional astronomers. For me, they were strictly
| theoretical.
| Daub wrote:
| 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/
| blackhaz wrote:
| 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...
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