Sky skimmers: The race to fly satellites at the lowest orbits yet

https://www.bbc.com/future/article/20250207-sky-skimmers-the-race-to-send-satellites-into-very-low-earth-orbits

by RyanShook • 1 year ago

117 76 1 year ago

bbc.com

the8472• 1 year ago

Alas, not the tropopause-skimming Solid Osmium Sphere Satellite.

https://www.researchgate.net/publication/326153433_The_edge_...

Havoc2• 1 year ago

Theoretically, if you can generate a thrust that is the same as your drag

Is it just me or does that make no sense at all. Surely the friction will always be significant higher.

So at best such tech lets you go a little lower not go near indefinitely as article suggests. Sorta like how an energy recovery system extends a cars range

throwup2385• 1 year ago

The air molecules used by the ion engine as propellant go through channels in the satellite. The molecules aren't "caught" but instead pass through it and once they're ionized, the electromagnetic repulsion between the propellant and the satellite pushes them apart.

As long as the solar panels can supply enough energy, I don't see a problem. It isn't actually a perpetual motion machine as there's a constant energy input and there's no violation of conservation of momentum that I can see. The problem I think is more of an optimization - how big can they make the solar panels without adding too much drag? That will set a bound for how low these things can fly.

pavon2• 1 year ago

Because it is using power from solar panels to accelerate the ions, that's what makes it not a perpetual motion machine. We know we can build ion thrusters that generate enough thrust to overcome the drag at these orbits. But that is with different propellant. The question is if you can do the same using air as the propellant, and with even higher thrust to account for the additional drag a scoop would have over an aerodynamic design.

woadwarrior01• 1 year ago

I suppose solar powered aircraft count as perpetual motion machines in OP's books. They categorically aren't. :)

https://en.wikipedia.org/wiki/Solar-powered_aircraft

russdill2• 1 year ago

Universe Today has a great interview on this tech. Even optimistically, it's knifes edge, just barely enough margin to keep things going before factoring in things like solar storms.

echoangle3• 1 year ago

Why would friction always be higher? In principle, this is just like an electric RC plane. You use the surrounding air for propulsion while keeping your own mass constant.

Havoc2• 1 year ago

Any sort of energy harvesting and reuse is going to involve some sort of losses along the way. Plus not all surfaces of the craft will be energy harvesting so those parts are just straight air friction.

missedthecue• 1 year ago

Why not just a large constellation of weather balloons with a satellite payload? You have to deal with wind patterns, but that's probably a solvable problem with enough of them. Much cheaper to launch and they don't regularly and necessarily burn to ashes!

mrandish• 1 year ago

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

https://x.company/projects/loon/

throwup2385• 1 year ago

A VLEO satellite orbits the earth in under two hours, giving it visual coverage of the planet along the satellite ground track for a dozen or more orbits per day. Launching enough balloons to get that kind of coverage, especially without the ability to control their position would cost an astronomical amount. You're not going to get anywhere near the same coverage and they'll probably all end up blown by the same wind system into a vortex and get stuck there anyway.

Weather balloons are inexpensive because the radiosonde payload is very cheap and light, not requiring much power or other infrastructure. Putting a proper surveillance payload on it would dramatically increase the price mostly because it'd then have to power the payload. That role is currently mostly done by UAVs.

BalloonsInVLEO9• 1 year ago

Nope!

Weirdly, I'm probably the one person who's worked extensively with both paradigms...

There are several players in the balloon market spinning up. It's becoming very hot very fast.

The balloons in question are much smarter that radiosondes now. They are fully capable of autonomous navigation within certain limits and can even orbit a point for days at a time via some clever weather mechanics. They're also very easy to launch. Two guys and a truck can launch over a dozen in a day and they're all aggregated and flown remotely via various links.

On the payload side it's actually much easier to do optics on a balloon, you have all the same pressure and thermal issues as space but you can iterate much faster when your cost to first pixels is thousands instead of tens of millions for the same ground resolution (GSD, drives necessary aperture size). I'm not going to spell out the details on either because that's the secret sauce that pays my mortgage but it suffices to say, if you're 10x lower, you need a lens that weights a little less. It's also worth noting that a VLEO sat will only be overhead for a few minutes, balloons can stream live video as long as you want, right now (no future tech or constellations needed).

The class of UAV that can begin to compete with a balloon is two to three orders of magnitude more expensive and still has nowhere near the endurance.

There are also other sensors and phenomenologies that are wildly more capable on a balloon platform than any type of satellite or UAV but I'll get yelled at if I spell any of those out...

BalloonsInVLEO9• 1 year ago

Yup, I've worked on both and the balloons are generally just better platforms given current constraints. They can actually be steered rather accurately, if you're ever bored go look at the ADSB logs of the Aerostar balloons, they regularly can be found wandering the country and if you look at the altitude history you can start to see how they work.

They're generally more environmentally friendly too, worst case you have to go ask a farmer to retrieve the thing out of their field.

kitd• 1 year ago

worst case

Please tell me, in the industry, this is called a "rapid unscheduled descent".

If it isn't, it should be! ;)

rsynnott6• 1 year ago

and they don't regularly and necessarily burn to ashes!

_In principle_, a VLEO satellite could stay up forever (or, well, realistically until the engine wore out).

Weather balloons also don't last forever.

BalloonsInVLEO9• 1 year ago

There are atomic oxygen issues for VLEO sats, the front of the satellite slowly corrodes away from the impacts. They're longer lived than current balloons but mission lifetimes more than low single digit years aren't really feasible right now.

mcswell• 1 year ago

Sort of like a Bussard ramjet, but using solar power rather than nuclear fusion.

Something that bothered me, until I looked up some numbers: the air a VLEO satellite scoops up is presumably more or less at rest wrt the Earth below it--there could be wind and effects of the Earth's magnetic field, and so forth, but for practical purposes it would be coming at the VLEO satellite at about 18,000 mph, or 8 km/s. In order to produce thrust, it has to exit the back of the satellite at a significantly higher speed. It turns out that ion thrusters have an exit speed of 20--50 km/s. So I guess it's feasible.

More info in this Wikipedia article: https://en.wikipedia.org/wiki/Atmosphere-breathing_electric_... --which says the exit speed of this kind of ion thruster is 55 km/s (as tested in a vacuum chamber).

phire• 1 year ago

I would suspect that the conditions behind the VLEO satellite are close enough to a vacuum that vacuum chamber results are actually relevant.

throwup2385• 1 year ago

Getting to ultra high vacuum like in higher orbits requires a multistage vacuum pump. To get the right conditions for VLEO they only need to skip the final stage turbomolecular vacuum pump or run it slower to decrease its effectiveness - it's basically just a bunch of fan blades that use transfer of momentum to bump molecules out of the vacuum chamber and keep them out.

I think the harder part is simulating the relative velocities of the molecules of air. They can try to use the same mechanism as a turbomolecular pump to accelerate the remaining molecules at the test setup, but AFAIK the maximum velocities in a turbomolecular pump are on the order of 1km/s, not 8km/s like in VLEO. Quick back of the napkin math says it'd need tip velocities of 4km/s which translates to over 380,000 RPM with a 4 in blade radius. I'm not sure there any materials capable of withstanding those forces. At 0.5m diameter it's a more reasonable ~76,000 RPM but that's basically the size of a commercial jet engine that probably caps out at 10-20,000 RPM.

deepsun2• 1 year ago

In order to produce thrust, it has to exit the back of the satellite at a significantly higher speed.

Why? It can exit at 1 m/s and still be thrust. And as long as momentum from engine pushing is larger than momentum of stopping atmosphere -- it will accelerate.

In other words -- chemical engines have exit speeds way lower than 8 km/s, but are able to accelerate spaceships to and above 8 km/s.

perihelions2• 1 year ago

You're overlooking the conservation of mass constraint.

starspangled• 1 year ago

I suppose because they are catching them when they are at ~0m/s in the atmosphere so they're worth -8km/s worth of momentum to begin with. So you would have to fire them out a >8km/s to get a net +ve change in momentum.

SideburnsOfDoom• 1 year ago

It can exit at 1 m/s and still be thrust

But it won't be enough thrust to counterbalance the force of scooping up air that collides at 8 km/s

In order to produce net thrust, it has to be more than that.

jcarrano2• 1 year ago

The mass of propellant being expelled is many times higher than the mass of air colliding with the rocket.

uSoldering3• 1 year ago

I like how the article glazes over the fact that this is drone swarm delivery tech. You are naive to think otherwise.

mechagodzilla• 1 year ago

Why would I want a drone swarm in VLEO? That seems like a really hard place to effectively use drones from compared to pretty much any alternative.

tomrod2• 1 year ago

Quick deployment into a battlefield or disaster zone anywhere on earth is one idea.

Connection, remote sensing, and mesh networking are useful.

uSoldering3• 1 year ago

You are missing the forest for the trees. This is an aerospace vehicle capable of flying in the air indefinitely. How many drones can you fit on a vehicle? How many vehicles can you fly at once? 60 miles is already reachable by the cheapest and most deadly weapon class of short-range drones. And now all they need to do is fall down. At freefall that is 140 seconds until it reaches the ground.

throwup2385• 1 year ago

What kind of drones are you thinking, other than just good ol' missiles?

Anything even remotely drone shaped would have to be covered in so many aerogel reentry tiles and thermal insulation I'm not sure there would be any usable weight left for a payload.

rsynnott6• 1 year ago

It doesn't seem terribly practical as one? The 'drones' would still have to re-enter, at, well, impressive speed. So you're not talking about terribly practical drones; more something like an ICBM warhead.

Even if this were practical, why use weird expensive highly-visible VLEO satellites rather than conventional LEO satellites? I can't see what advantage the VLEO stuff would give you here.

flanked-evergl• 1 year ago

Based.

literalAardvark• 1 year ago

As long as "based" is taken to mean "confidently wrong", yeah.

Based af

LorenDB• 1 year ago

This also has the benefit of guaranteeing that your rocket's second stage will be deorbited in a timely manner.

perihelions2• 1 year ago

- "The other major application of being in VLEO is that you are closer to the ground for communications. That is particularly useful for space internet services, like SpaceX's Starlink network, which currently beams the internet to receivers on the ground from higher orbits. By using lower satellites in VLEO, the antennas can act like mobile phone towers and beam the internet straight to your phone. "Going direct to a cell phone is a challenging task to do from space," says Tim Farrar, a satellite communications expert in California. "These lower [orbits] could enable a direct-to-cell constellation."

Starlink direct-to-cell satellites are already in a VLEO orbit shell, distinct from the rest of the constellation. They use electric propulsion (like all Starlinks) to counter drag, though it is not air-breathing electric propulsion (the theme of the OP).

- "The higher luminosity of these DTCs compared to regular Starlinks is partly because they circle Earth at just 217 miles (350 kilometers) above the surface, which is lower than traditional Starlink internet satellites, whose altitude is 340 miles (550 kilometers), the study reported. [...] There are now over 100 DTC satellites in low Earth orbit, including 13 that were launched last week. Following successful testing of the first batch of DTCs, in March SpaceX requested an amendment to their license with the U.S. Federal Communications Commission that would allow them to operate up to 7,500 DTCs in LEO."

https://www.space.com/spacex-starlink-direct-to-cell-satelli...

philipwhiuk• 1 year ago

Defining VLEO at 220km seems dumb. The ISS survives perfectly fine on periodic boosts.

sfblah• 1 year ago

When asked for use cases, they give a bunch of niche things like wildfire monitoring. What is the actual market for this stuff? Is it all spy satellites? Better versions of Street View?

verzali• 1 year ago

Lower latency communications snd more detailed Earth observation

ImHereToVote• 1 year ago

Phone to satellite communication.

rsynnott6• 1 year ago

Comms would be the big commercial one; latency reduction relative to LEO systems. High detail earth observation is also useful for weather stuff.

mppm• 1 year ago

Besides niche scientific applications, this is mostly about extremely large constellations.

The classic LEO, roughly 500km-1000km, is already quite full, and placing a lot of new satellites there increases the risk of triggering a chain reaction of collisions with orbital debris (Kessler syndrome). At these altitudes the atmosphere is thin enough that even small pieces of debris are long-lived, thus potentially creating a long-term problem for all kinds of human and non-human spaceflight.

In the VLEO band, on the other hand, the thicker atmosphere makes maintaining orbit more difficult, but also makes debris very short-lived. Due to this, it may be reasonable to risk placing a million-satellite communications network somewhere between 200-300km, which would be utterly impossible further up. Data rates, latency, mesh size, etc. also improve of course.

billfruit• 1 year ago

Perhaps real time flood water monitoring?

Despite advancements in technology, as on today it is not possible to get near real time information of flooding.

floppiplopp• 1 year ago

Not sure if it's a good idea to pollute even more orbits. We're basically one low-iq billionaire fuck-up away from creating a barrier of shrapnel around the planet.

russdill2• 1 year ago

Anything in VLEO is not going to stick around long.

rsynnott6• 1 year ago

Addressed in the article; one _advantage_ of this sort of orbit is that once the engine dies, it's not staying up there for long.

echoangle3• 1 year ago

Not for VLEO, the satellites deorbit after a short time if you just leave them.

Sky skimmers: The race to fly satellites at the lowest orbits yet

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