# Any plausible non-rocket based method to reach orbit?

#### GTOM

Recently i read, that GEO orbit actually isnt enough for a space elevator, since its weight would pull it down, either it needs constant thrust, or build it much taller than 33.000 km, so upper GEO parts pull it up.
That further lowers its plausibility level.

Any other methods?

Build a tall tower on top of Chimborazo, and an electromagnetic launchway so high, that air pressure is low?

Hypersonic skyhook? So a very long carbon nanotube hanging from a space station that has 1-2 km/s compared to surface. Of course that station also has to be lifted regularly with ion thrusters.

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#### Anachronist

Gold Member
The title of this thread uses the word "plausible" but the content discusses implausible things. With that in mind, I think a gravity repulsor would be best.

A geostationary elevator would work just fine, as long as it's center of mass is in the geostationary location. It could extend a cable down and up at the same time to keep it balanced.

#### GTOM

The title of this thread uses the word "plausible" but the content discusses implausible things. With that in mind, I think a gravity repulsor would be best.

A geostationary elevator would work just fine, as long as it's center of mass is in the geostationary location. It could extend a cable down and up at the same time to keep it balanced.
In order to achieve having a center of mass at geo, there has to be a counterweight much higher.

#### mfb

Mentor
If you can make a cable that can reach the geostationary orbit you can also extend it to the counterweight farther out - the cable thickness can decrease in that area.

StarTram (an elevated maglev tunnel) and an orbital ring sound like the most plausible options to me. The first is largely existing technology just built on a larger scale (even though the oversized plasma window would be an interesting challenge), the second one needs R&D but could launch giant masses for cheap once it is built. Both can be built with existing materials and with budgets a large country could come up with.

#### GTOM

If you can make a cable that can reach the geostationary orbit you can also extend it to the counterweight farther out - the cable thickness can decrease in that area.

StarTram (an elevated maglev tunnel) and an orbital ring sound like the most plausible options to me. The first is largely existing technology just built on a larger scale (even though the oversized plasma window would be an interesting challenge), the second one needs R&D but could launch giant masses for cheap once it is built. Both can be built with existing materials and with budgets a large country could come up with.
I fail to see how could even the largest countries build an orbital ring. Dont that require extreme amount of building material? If it spins with orbital speed, how could it lift something from the ground with cables? If it dont spin fast, it has to keep its huge weight. Until it is totally finished it has to spin fast, then it has to be decelerated.

#### russ_watters

Mentor
I fail to see how could even the largest countries build an orbital ring.
Cost estimates for highly speculative future projects are often....optomistc.
Dont that require extreme amount of building material?
Yes. It looks to me like part of the optimism is based on the hope that someone else has already paid to launch a manufacturing plant for it into space!
If it spins with orbital speed, how could it lift something from the ground with cables? If it dont spin fast, it has to keep its huge weight. Until it is totally finished it has to spin fast, then it has to be decelerated.
If it's just above geostationary orbit, it can support itself with a spin rate equal to Earth's rotation while maintaining tension on the tethers.

#### DaveC426913

Gold Member
Wiki has a list of em.

The one I was in search of was the space fountain.
A stream of massive pellets is fired up an evacuated tube and diverted back downward at the top in a loop. This can support a platform (though it contributes nothing to achieving orbital speed.)

#### mfb

Mentor
I fail to see how could even the largest countries build an orbital ring. Dont that require extreme amount of building material? If it spins with orbital speed, how could it lift something from the ground with cables? If it dont spin fast, it has to keep its huge weight. Until it is totally finished it has to spin fast, then it has to be decelerated.
It spins slightly faster than orbital speed, the additional force is used to hold up support cables, the elevator and its payloads plus some small stations where needed.

How to build it: There are proposals to launch it from the ground (make a vacuum tube around the equator, spin the ring up levitated magnetically, once it goes above orbital velocity it leads to a force upwards) but the easier construction method is just to launch everything to space.

#### mfb

Mentor
Can a 25g/m ring do anything besides demonstrating that it's an orbiting ring?
Lift and accelerate smaller payloads, low tonne range. Note that 25 g/m is more than most space elevator proposals have at sea level, and a 25 g/m zylon cable can hold 10 tonnes.
(a) it is not the primary estimate, (b) it doesn't just assume it would be there, and (c) it is just a minor detail that saves a little bit of time at the end.

#### GTOM

It spins slightly faster than orbital speed, the additional force is used to hold up support cables, the elevator and its payloads plus some small stations where needed.

How to build it: There are proposals to launch it from the ground (make a vacuum tube around the equator, spin the ring up levitated magnetically, once it goes above orbital velocity it leads to a force upwards) but the easier construction method is just to launch everything to space.

You can build an initial ring system with ~1000 tonnes in space (25g/m). At $90 million per 30 tonnes to a zero inclination low Earth orbit (reusable Falcon Heavy with plane change maneuver, pessimistic) you spend$3 billion on launches. Let's double that to account for mass of delivery systems and whatever, \$6 billion. The initial payload of such a system would be in the low ton range, just enough to lift additional ring material. As the ring mass grows the payload grows as well. Launch costs are not a big deal even with existing rockets. If we use Starship cost estimates the launch costs become negligible.

There would be significant R&D cost and it is hard to estimate them - we would need some R&D to estimate that cost better. It is "just" an engineering challenge - all the materials are available, all the components have been used in many places for other purposes, the task would just be to combine them in the right way.

Why don't we have this already?
• The launch cost estimate I used was based on a rocket that first flew last year. If we would take e.g. the Space Shuttle that cost would be way higher.
• There is no "demo version" - you can't build 1/100 of an orbital ring as operational prototype. To demonstrate that the concept works you need to spend several billions.
• There is a significant risk that the first attempt fails. No government wants to justify the failure of a several billion dollar project and ask for money for the second attempt - even if that ring would pay for the launch of both attempts.
Please show an estimate that is based on such a hope.
Achieving orbital speed is the main task of rockets... you save going through the atmosphere, but it doesn't help that much. It would make a nice platform for short-term microgravity experiments (just drop stuff from the tower).
Ok, but what about the speed difference between the surface and the ring, how they attach the top of the elevator? Would it slide on a rail? And once people get up, they need to be accelerated to the speed of the ring?

#### mfb

Mentor
You ride up along one of the vertical cables suspended from the ring (just a few hundred km, there are many options how to power that), then you couple magnetically to the ring and "brake" - induction braking relative to the ring. You accelerate relative to the ground, the ring gets hot and slightly slower, the stations have to accelerate the ring to compensate for the launch of payloads.

#### Xforce

Actually, the first space elevator is probably build on the moon... existing materials can handle it
There are many ways to achieve orbit... like spaceplanes

#### Nik_2213

If you'd allow a slightly stretched definition, 'Reaction Engines' Sabre engine is a runway launching turbo-jet that progressively supplements with tank-oxidiser as it climbs out of usable atmosphere...

Disclosure: When I first read about their remarkably efficient heat-exchanger, I asked them if they could use spectrum analysis to monitor its capillaries via 'Aeolian Harping'. Constrained by NDA, they could neither confirm nor deny. But they did send me a very nice 'Smiley'...

#### Tghu Verd

Gerald Bull had a plausible concept for a cannon that could shoot objects into orbit, which got him assassinated.
You have to annoy a lot of people for your assassination to be possibly carried out by so many governments: Iran, Israel, Iraqi, Syria, USA, UK, Chile, or South Africa!

Apart from that, I'd no idea anyone had ever create a Jules Verne-like giant gun to fire objects into space. Do you know what gee force the projectiles would have been subjected to?

#### Nik_2213

Lots.
Rail-guns/maglev aside, for a 'softer' launch, you'd need multi-charge per the WW2 'V3' guns.

#### mfb

Mentor
Do you know what gee force the projectiles would have been subjected to?
You need ~40 MJ/kg for orbital velocity, or a*s = 4000 km*g for uniform acceleration. If your cannon is 1 km long you need 4000 g, if your cannon is 2 km long this drops to 2000 g, and so on.

You can't directly shoot something to orbit from the surface (the orbit would intersect the surface), so in practice things are more complicated, but that is the general idea.

#### Tghu Verd

If your cannon is 1 km long you need 4000 g, if your cannon is 2 km long this drops to 2000 g, and so on
Right, so your not launching anything that's not structurally robust!

You can't directly shoot something to orbit from the surface
I'm struggling with this. Is the problem that you either fire the shell faster than 11.2 km/s and it leaves Earth orbit...or it has less than this and essentially falls back down? The 'intersect' orbit?

#### mfb

Mentor
Orbits that do not escape are closed ellipses. After one orbit you return to the point where you started. If you shoot an object out of a cannon and don't do anything else, the object will be at the point of the cannon again after one orbit, coming from below - through the ground. Well, that's what orbital mechanics tells you, but obviously the object won't fly though Earth.

You need to launch your payload with a small rocket stage or similar, boosting its speed close to the highest point. Some rockets do something similar - launch into a trajectory that still intersects Earth (easier to do when you actually launch from Earth), then coast for half an orbit, then fire the engine again briefly. It can look silly to see a big rocket engine fire for two seconds, but it helps saving a lot of fuel compared to a direct launch to an orbit.

(Earth rotates, so you wouldn't actually hit the place of the cannon, but something more west - but that doesn't matter as Earth is approximately rotational invariant.)

#### Tghu Verd

@mfb, I've just realized that my ignorance of orbital mechanics has just blown a huge chunk out of the plot of my first novel:

"The Egan Event had thrown so much crap into orbit that it earned its own nickname, The Girdle. The shrapnel blasted into space had cleared out low earth satellites in equatorial orbits and made launching more a chancy game of avoiding debris..."

In my novel, the Girdle is loaded with slowly decaying rubble from a cataclysmic explosion...which I now understand just can't be true

Oh well, it's published already and such a staple part of Book 2 that I'm going to have to just close my eyes to physics and go with it!!

#### DaveC426913

Gold Member
"The Egan Event had thrown so much crap into orbit that it earned its own nickname, The Girdle. The shrapnel blasted into space had cleared out low earth satellites in equatorial orbits and made launching more a chancy game of avoiding debris..."

In my novel, the Girdle is loaded with slowly decaying rubble from a cataclysmic explosion...which I now understand just can't be true
Hang on. Why can't it be true?

Explosions are chaotic, and the debris interacts with itself, altering the orbits of much of it.
Some will fall to Earth, some will get caromed into highly eccentric orbits, and some might lave Earth to orbit the Sun.

But in doing so - in transferring energy between debris components - some of it will be altered just so. Bits that were headed outward will get slowed into a more circular orbit - bits that were headed inward will get a kick of energy into a more circular orbit too. It will form a broad swath - a toroidal cloud - of debris in ever-changing orbits.

That's how the Moon coalesced (after hundreds of thousands of years).

#### hmmm27

In my novel, the Girdle is loaded with slowly decaying rubble from a cataclysmic explosion...which I now understand just can't be true
Debris will be deflected by the atmosphere, as well as other bits of debris. Some would end up in slowly decaying orbits. [edit: ie, what DaveC just said]

#### Tghu Verd

Thanks @DaveC426913 and @hmmm27, I clearly jumped the gun on @mfb's comment, misinterpreting that the context was a single projectile being fired 'into orbit', not an explosion as powerful as the Egan Event.

I am very happy to be able to utilize the Girdle in Book 2 in good conscience