Science: Spacecraft: Propulsion: Centripetal
Ultracentrifugal satellite launcher   (+8, -5)  [vote for, against]
Impractically possible

Rockets launched from high-altitude balloons, or cannons lofted by such balloons, have both been proposed as a means of making it easier to get things up to orbital altitude and/or velocity.

I believe I have hit upon an alternative which benefits from being highly impractical.

The balloon itself can afford to carry a fairly high payload (since gas lift is cheap). Suspended beneath the balloon are two satellites, on either end of a 100m-wide arm which pivoted at its centre, so that it can rotate in the horizontal plane (so, the whole thing looks like an upside-down helicopter).

A modest electric motor (perhaps solar powered) starts to turn the rotor. Gradually, arm spins faster and faster, up to a not-unreasonable 23 revolutions per second.

At this point, the speed of the rotor tips is about 7km/s, good enough for low-earth orbit. A signal from the ground fires explosive charges on the satellites, releasing them and sending them hurtling off in opposite directions - two launches for the price of one.

Some minor problems. (1) Just before release, the satellites are experiencing a centrifugal force of about 845,000G. This will need some serious engineering, although I note that ultracentrifuges have operated up to 1 million G. Note that the centrifugal forces (for a given release velocity) become smaller as the rotor diameter increases. If the rotor were 1km across, the G-forces are only 84,000G to attain a 7km/s release speed. A 10km rotor (perhaps in the form of tethers rather than rigid arms) takes you down to 8,400G. To get down to a human- survivable 8.4G you'd need a rotor only 1000km in diameter - easy!! (2) This strategy sends the two satellites outward horizontally, with no vertical motion. It would be preferable to angle them upwards, but this means that one has to be released downwards; so, you would probably want one of the satellites to be a sacrificial counterweight. (3) Half an orbit later, the two satellites will smash into eachother at a closing speed of 14km/s. (No, not really; they'd miss by at least the diameter of the rotor.)
-- MaxwellBuchanan, Feb 23 2008

Centripetal Space Junk Drive Centripetal_20Space_20Junk_20Drive
Shares some of those minor problems [lurch, Feb 24 2008]

[xaviergisz, Feb 23 2018]

Castro fan and expert economist...
...who's never started or run a company, made payroll or balanced a business ledger. Other than that he's a genius about how all the country's businesses should be run. [doctorremulac3, Feb 23 2018]

SpinLaunch completes first test flight
[xaviergisz, Nov 10 2021]

If you tried to spin a 100m wide arm with two satellites attached to it by motor, you would just end up spinning your enormous balloon around. It's a simple comparison of rotational moments of inertia.
-- DanDaMan, Feb 24 2008

We need some mass here somewhere.....
-- WcW, Feb 24 2008

The chance of the two satellites hitting each other is so small that I wouldn't even entertain the notion. Quite imaginative.
-- WcW, Feb 24 2008

The tail would wag the dog.
-- xenzag, Feb 24 2008

//Impractically possible// [marked-for-tagline]
-- 2 fries shy of a happy meal, Feb 24 2008

// It's a simple comparison of rotational moments of inertia.//

Ah yes. Errr, glad you spotted that one. So, we have two counter-rotating rotors, and we launch 4 satellites.
-- MaxwellBuchanan, Feb 24 2008

Another minor problem: Since these arms are rotating at orbital velocity in the atmosphere, wouldn't they be cooking at around 5,000 degrees?
-- ldischler, Feb 24 2008

One could publish a line of cookbooks that exploit this effect.
-- bungston, Feb 24 2008

//Impractically possible// [marked-for-tagline]
-- wagster, Feb 24 2008

They'll be at about 50km up, the limit of balloons. Air density here is about 1/500th that at ground level and, since air resistance is proportional to air density, the tips will experience the same resistance (and heating) as if they were travelling at about 14 metres per second (31mph) at sea level.
-- MaxwellBuchanan, Feb 24 2008

It seems to me that if this was going to work then launching a large missile from a high altitude jet flying at supersonic speeds would work. Please explain what I am missing.
-- WcW, Feb 24 2008

Well, yes. Basically, our ultracentrifugal launcher is a means of getting something up to orbital speeds (>7km/s) without that thing having to carry its own propulsion system. So, if you can get a high altitude jet up to 150,000 ft, and then get it up to about mach 21, it will achieve the same result.
-- MaxwellBuchanan, Feb 24 2008

Do balloons get you high enough to achieve orbit? They would need to expand with the change in pressure and even so, with a payload, we still top out in the upper atmosphere. What if we launch the payload from the high altitude (reusable) jet?
-- WcW, Feb 24 2008

//Do balloons get you high enough to achieve orbit?// No, but they can get you up to 150,000ft or so, at which point air resistance is much less.
-- MaxwellBuchanan, Feb 24 2008

//the tips will experience the same resistance (and heating) as if they were travelling at about 14 metres per second (31mph) at sea level.//
Oddly enough, meteors burn up at that altitude (ie, 150k feet). Good try, though.
-- ldischler, Feb 24 2008

//Oddly enough// Well, no. Meteors typically are travelling at >>7km/sec.
-- MaxwellBuchanan, Feb 24 2008

[Maxwell], I'm tempted to take this off to another idea, but: Make the rotor arms even more like a helicopter's blades, and fly the thing up even higher.

You'll want to build up the RPM in flat pitch, do a "jump takeoff" for maximum altitude, and wind the RPM back up while coasting upward in even thinner air.

//It would be preferable to angle them upwards// No, 'cause if you do, the one that went up will be coming down again on the other side of the planet.
-- baconbrain, Feb 24 2008

I wasn't sure if you could get much "helicopter lift". I don't know enough about helicoptering, but if the atmosphere is 1/500 as dense as at ground level, I presume you'd have 1/500th the lift, all else being equal. On the other hand, we have a high rotor speed, so maybe..
-- MaxwellBuchanan, Feb 24 2008

Maybe. I think it should work. I've a toy around somewhere that is a helicopter "rocket".
-- baconbrain, Feb 24 2008

I also considered this prior to the "blow it all up with C4" idea, but I thought that max rotor tip velocity was independant of radius (is that right?). This max tip velocity is about 1500m/s using some exotic materials. I imagined a rotor being gradually accelerated until it exploded, hurling off the mini-satellites. Anyway, the explosions thought led to C4 & etc.
-- Ling, Feb 25 2008

//since air resistance is proportional to air density, the tips will experience the same resistance (and heating) as if they were travelling at about 14 metres per second (31mph) at sea level..//
I'm assuming that this is a joke idea, and this nonsensical defense of it is also a joke. Otherwise it's very bad science.
-- ldischler, Feb 25 2008

OK, miscalculation; the equivalent speed would be 313 metres per second, or 700mph. This generates heat, but not a ludicrous amount of heat.

Air resistance (drag, to be precise) is defined as being proportional to the density of the fluid and to the square of the velocity. If I'm wrong, as frequently happens, I'd rather someone explained my mistake than simply calling it nonsense.
-- MaxwellBuchanan, Feb 25 2008

I hope this is a joke, otherwise it is terrible science. What would provide the energy to turn the arms? It would take the same about of energy to accelerate the satellites to escape velocity regardless of how you do it: in fact, more, because you are now accelerating the rotor arms. You may save a bit by launching from a higher altitude, but again, that is lost by the rotor arms.

Furthermore, the savings in fuel (ignoring the rotor arms loss) is completely negated by the added cost of such a massive piece of equipment and the cost of lift gas.
-- Agamemnon, Feb 25 2008

Agamemnon, it is intended tongue in cheek (the phrases "impractically possible" and "highly impractical" were, sort of like, clues there), but your annotation shows that you have embarrassed yourself by missing the purpose of this. bless.

The need is to get sufficient velocity in a projectile. If you do this by using a rocket, then the rocket has to carry all of its fuel, meaning that the rocket wastes most of its energy in accelerating the fuel itself that it needs for the rest of the flight. (A typical SRB is 90% propellant, and puts only a few percent of its mass into orbit.)

So, you want to get your projectile up to speed by providing an _external_ input of energy.

One way to do this is by means of a railgun or other cannon-type device, but that is inelegant. My solution achieves the same end, in a more elegant way.

The power, as stated, comes from solar panels on the balloon. If you prefer, you can put any other power source on the balloon - bouyancy lift is dirt cheap ($37 per cubic metre of helium, if you like, which is actually cheaper than a cubic metre of good topsoil.)

So, please think at least once before annotating - it saves a great deal of embarrassment all round.
-- MaxwellBuchanan, Feb 25 2008

You could also get power from ramjet engines on the rotors, if you want to lift the fuel for them. Somewhere along the length of the blades will be a spot moving at the right speed through the air for a ramjet to work. That would also let you get back to a single rotor, perhaps.
-- baconbrain, Feb 25 2008

True. I'd originally thought of ion drives on the satellites themselves, but their impulse would be way too low. Ramjets make more sense if there's enough air for them, which I guess there would be.
-- MaxwellBuchanan, Feb 25 2008

Of course, if we could speed up the Earth's rotation by a factor of 16, the problem would be solved.
-- MaxwellBuchanan, Feb 25 2008

//you would probably want one of the satellites to be a sacrificial counterweight// Well, it's going to end up a satellite, so you may as well put some functionality in it.

//A signal from the ground fires explosive charges on the satellites// Overly complicated and could damage the satellites - suggest whistle attachment at end of arms, tone pitched so that at correct speed it excites the balloon pilot's terrier into biting the large red toggle switch that operates a servo-release.

Also if you articulate the arms at the pivot point, some interesting effects might be possible (think ice skaters twirling) Much easier to maintain balance in the whole structure by accelerating to say 600 revolutions per second with the arms folded and pointing straight down below the balloon with the two payloads close together - then release the connection between the two halves of the arm...
-- ConsulFlaminicus, Feb 26 2008

//Well, it's going to end up a satellite, so you may as well put some functionality in it. // No, because it (the sacrificial one) will be shooting downwards rather than upwards, in the situation I described.

//excites the balloon pilot's terrier into biting the large red toggle switch// If anyone manages to build a terrier that'll be happy with those centrifugal forces, I really don't want to meet it.
-- MaxwellBuchanan, Feb 26 2008

Two things about the sacrificial mass. If you do fire it downward, the other one, the intended satellite, will be going up, yes, but will be coming back down on the other side of the planet. As was understood above, the two masses must meet somewhere, theoretically, on the other side of the world. Unless the satellite has some means of circularizing its orbit, it is going to "try" to pass through its launch point again, on the same path, which means it should be coming UP out of the air.

Second, if both masses are thrown perfectly horizontally, the one thrown eastward will be going faster than the one thrown westward against the Earth's rotation. The factors I babbled about above will still apply, but differently, I think.

[MaxBun], another suggested major modification: Make the axis of rotation horizontal and north-south. Support the axis with balloons on each side. Make the rotor with two arms. On one arm, put a ramjet. On the other arm, put the satellite. Run the ramjet every time it dips down into thicker air. When the satellite is at the top, going east, have the terrier release it into orbit, and also release the ramjet to keep things balanced. Then release gas from the balloons, descend to the ground, retrieve the ramjet from its parachute, and reload for another trip.
-- baconbrain, Feb 26 2008

[Bacon] What you say is true, alas. It occurred to me the other day that, for the purposes of trajectories, you can imagine the spherical earth as being "unwrapped" into a flat sheet. Then, a circular orbit becomes a straight horizontal line above the plane. Conversely, throwing something upwards will cause it to travel in a parabola (on the "gravitationally unwrapped" earth), which will correspond to a distorted parabola (eg, a cardioid or something else weird) in the real world.

So, you're quite right. If we start with the "flat earth" model, we've got to throw something upwards but then give it a purely horizontal (flat) velocity (which corresponds to a circular orbit).

And to think they thought that thinking the earth was flat was silly.
-- MaxwellBuchanan, Feb 26 2008

I'm surprised I never saw this idea before. It's similar to an idea I've been mulling around since the start of the N- Prize. The discussion here addresses a lot of the issues I had with my idea.

Background: I was initially very surprised to hear when the Helios solar airplane set an altitude record. Considering that even flying at all is a major feat for a solar airplane, setting a new altitude record higher than the SR-71 Blackbird's "official" record seemed ludicrous. But then I realized that it has the enormous advantage that it doesn't need to carry any fuel or collect oxygen to burn the fuel. Therefore the altitude of a solar plane like the Helios is limited by how much altitude it can gain before sunset and by the thickness of the air. Now as far as lift for the main wing, I think the theoretical maximum altitude would be much higher. All you need to do to get more lift in thin air is to go faster, and I don't think the power requirements to maintain or gain altitude increase because the air resistance decreases proportionately (could be partially wrong on that). The problem is producing useful thrust in that situation. Using a propeller, the tip velocity of the propeller probably needs to be much faster than the airspeed, and for any reasonably sized propeller, that will have very high centrifugal forces.

So how do you provide thrust to the wings that can be powered by solar cells? Well since we aren't really concerned with going anywhere except up, make the wings go in circles. Specifically a pair of balanced wings going clockwise and a second set going counterclockwise, with a motor at the axis of rotation to spin them up. It seems to me that this could be made to be just as efficient as Helios in the lower atmosphere, and in the upper atmosphere it ought to be able to go much higher without relying on propellers. I think this is a good hand- waving answer to [Max]'s question about how much helicopter lift will help. I think we can depend on it entirely and skip the balloon.

It might be good to make each wing actually be a self- sufficient glider attached to the hub by an extendable tether. This would be launched from a tower slightly taller than the length of each wing with the tethers retracted. The hub will need some non-zero dimension to be able to accelerate the gliders through the tethers rather than just winding them back up around the axle when it tries to apply some torque. The hub will need to be light compared to the gliders, so the launch tower might have some infrastructure to help support the hub while the gliders are hanging from it before initial spin- up.

I expect that after spinning up on the tower, the tethers will be extended by at least one additional wingspan before takeoff so there is not a large difference in speed between the close and far parts of the wing/glider. As it gets into thinner air, the tether will be extended to allow higher wing speed without too much centrifugal G forces. Once it reaches maximum RPM and maximum tether extension, it will soon thereafter reach maximum altitude.

It may take some time at that altitude to tilt the plane of rotation (as suggested by [Max]), but we don't want to start tilting too soon or it will gain velocity in the wrong direction. Cut the tethers and let the gliders go. I assume you'll need some additional thrust from a rocket carried in the glider to boost and circularize the orbit. For the solar power to be enough for most of the trip, the rockets probably can't be a very large fraction of the mass of the glider. Since it's a comparatively small rocket, it can't do a whole lot, so you'll need to get most of the velocity from the centrifuge.

All the power for spinning needs to be transferred from the panels to the hub. I considered having motors in the gliders and transferring the power by twisting the tethers to turn a lightweight gearbox at the hub. I suspect sending electricity over the tether to a motor in the hub will be more practical. I don't know if we'll need to wait for long carbon nanotubes to get a tether that is strong enough and conductive enough, or if we might make due more conventional conductors embedded in the tether.

As an added bonus, since the solar cells are built into the wing which gets sent into orbit, you've got a very large solar cell on your satellite as part of the deal.
-- scad mientist, Nov 12 2015

//Much easier to maintain balance in the whole structure by accelerating to say 600 revolutions per second with the arms folded and pointing straight down below the balloon //

Yes, but the net energy imparted to the masses will be no greater than the energy in the lowered position. The skater thing is an indicator of that. Angular momentum is conserved, so extending the arms=slower spinning.

And yes, anything launched from earth requires a circularization burn in order to maintain orbit. Otherwise it's orbit intersects the planet somewhere. But if it already has the velocity, the circularization burn requires a relatively low delta V.
-- MechE, Nov 12 2015

Re. the link, [xav]. I can't believe they're crazy enough to try this. I think they're spinning at ground-level, too, which is doomed.
-- MaxwellBuchanan, Feb 23 2018

Ok, this has gone too far. Thirty million bucks?
-- doctorremulac3, Feb 23 2018

That's exactly what I was thinking - THIRTY MILLION??? How on earth do they expect to be taken seriously in aerospace if they're funded with loose change?
-- MaxwellBuchanan, Feb 23 2018

You know, all this funding comes from a few miles away from here up on Sand Hill Road. If you've ever been to some of these venture capital places they have frames lined up on the walls of startups they've funded. It reminds me of record companies where you walk in the big double doors (at least at Electra Records) and are greeted by a long corridor festuned with gold and platinum records from floor to ceiling. The idea is to let you know these guys make millions and millions and millions of dollars and boy does it work.

"Whoa! Here's the Doors, AC/DC, Queen, Metallica! We've walked into the fucking halls of Asgard!"

Same with these assholes (now I'm getting pissed) who fund all these Silicon Valley startups. Their opulent offices have these IPO plaques, the financial equivalent of the platinum record, all over the place.

"Here's Facebook, Google, Twitter!" Then you run into the classics. "Jesus Christ! Apple? Microsoft? No wonder there's not a car in the parking lot worth under $100,000! (Except mine.)"

I'm sick and tired of not getting 30 million dollars for MY startups. Every business I've ever started was funded with credit cards. CREDIT CARDS!

Fuck capitalism. I'm voting for Bernie.
-- doctorremulac3, Feb 23 2018

Hey, my business is funded out of my pocket, with a little help from the Gubment. But I like VCs. If and when they decide to give me a couple of million, I'll probably like them more. If they give other people 50 million, well, that's just something to shoot for. Metaphorically, obviously.

Also, who's Bernie?
-- MaxwellBuchanan, Feb 23 2018

//Also, who's Bernie?\\ dead guy. Sunglasses. Always has those two guys with him. Difficult to disagree with his policies.
-- bs0u0155, Feb 23 2018

Bernie is our glorious candidate for the first Premier of the People's Republic Of United States of America. (see link)
-- doctorremulac3, Feb 23 2018

umm... math ? Plugged the problem into an online calculator for an 100m arm and got 50k g, not 350... . A 600km arm yields 8.4g .

A 4k km long track isn't unreasonable. Except the $30m bit, of course. A 50g cargo track is "only" 500km in length, with a 150km diameter.
-- FlyingToaster, Feb 23 2018

//Hey, my business is funded out of my pocket, with a little help from the Gubment.//

That would have been a funny prospectus to read for my situation: "Dear Gubment, I'm in my 20s and want to be a rock star, however I need a bunch of money to buy a recording studio. Thank you in advance. P.S. Love your podiums. Are they supposed to be phallic symbols so when you do your speeches it looks like you've got a gigantic penis? P.S.S. Please ignore that last line."
-- doctorremulac3, Feb 24 2018

Well, I basically went to the Gubment and said "I've got an idea I'd like to try, can I have some money?", and they said "Oh, OK, here." So that works sometimes.
-- MaxwellBuchanan, Feb 24 2018

...original idea //two satellites outward horizontally//...//angle them upwards// [MB] had you thought of orienting the plane of spin vertically, aligned with the equator? An axle between two balloons, with the spinning arms between them. Then you could launch your payload with your preferred combination of upward and orbital velocity. You'd still be launching a sacrificial counterweight downward with a very high velocity, so you might want to warn people below.
-- Frankx, Oct 21 2019

//orienting the plane of spin vertically// Now, that is not a bad idea.
-- MaxwellBuchanan, Oct 21 2019

// you might want to warn people below. //

... or then again, depending on who they are, you might not ...
-- 8th of 7, Oct 21 2019

//not a bad idea//...thanks [MB], that’s the highest praise! Reading through the annos above I realise [Baconbrain] proposed this above, so credit to him/her.

This idea, overall, is no more insane than some of the other non-rocket space-launch proposals that are being developed. Perhaps this should be baked further.
-- Frankx, Oct 22 2019

Boy was Max a fun guy to BS with.
-- doctorremulac3, Nov 11 2021

When I first saw the photo of the SpinLaunch contraption, I thought it was about 4-5m high.
Then I noticed the tiny trucks in the corner, & this is their 1/3 scale test rig! I hope they do their material analysis carefully; it'll make a big mess if it fails...
-- neutrinos_shadow, Nov 11 2021

random, halfbakery