Orbital Electromagnetic Launch System

[Fierce Wolf]

I was thinking about the possibility of constructing in the near future a magnetic train (or gun, whichever sounds cooler), launch it to LEO, and use it to accelerate crafts into deep space. Since it uses electricity (ok, gargantuan amounts of it) there's no need for propellant, said crafts would not need to carry extra weight to reach destination, just to brake around it and land.

Extra points: Is this doable in KSP?

 

Opinions?

 

[Piscator]

You shouldn't forget that each use of your cannon imparts an impulse on it (opposite to the impulse imparted on the payload). That means that you'd either have to use propellant after all or cleverly time your shots in such a manner that your orbit remains stable, for example by firing in opposite directions or firing half an orbit later.

PS The latter method (launching the payload in the same direction on opposite sides of your orbit) wouldn't work, as it would decircularize the orbit rather quickly.

Edited May 22, 2021 by Piscator
PS

[Shpaget]

Not considering the upfront cost of the system, it could be marginally beneficial, the difference being lower starting mass of the probe.

Of course, the number of such missions would need to be insane to justify such a megastructure, and mega it certainy would need to be to reach speeds needed for space exploration purposes.

[K^2]

4 hours ago, Fierce Wolf said:

Since it uses electricity (ok, gargantuan amounts of it)

Not really. You can get 1T to 1km/s for about 140kWh, which is less than $100 of electricity from outlet. (Potentially, way less, depending on where you live.) It'd be more expensive to produce that power in space, of course, but it's still not a lot of energy.

5 hours ago, Fierce Wolf said:

there's no need for propellant

Recoil still has to go somewhere. If your launch system is in orbit, you can't exactly tether it. If ships are constantly coming and going, then maybe the net impact averages out pretty well, but if you're just using it to send things to outer Sol, you'll quickly run into a problem.

[Starman4308]

Magnetic accelerators in space wind up being very similar to rocket engines: in order to deal with the recoil, you still need to eject something out the back, which means reaction mass. The energy can be obtained from solar panels, an onboard nuclear reactor, etc, but you still need to chuck something out the back.

Even ignoring that, there's another issue. A GTO transfer is, IIRC, something like 2.2 km/s. At an acceleration of 5Gs, you need a 48 km accelerator to reach that velocity. Escape velocity is roughly 3.9 km/s, so a 152 km accelerator. A higher acceleration will be very problematic for fragile cargos, especially untrained human beings. Even then, the rule-of-thumb is "5Gs for 5 seconds" for the general public, and either of these accelerators are going for much more than 5 seconds.

*I'm going off of memories from playing RO, so the figures may not be exact.

[kerbiloid]

A self-assembling mountain-like ridge of nanites, raising from the equator to sky.

Powered by the underwater layer and by the solar nano-elements.

Maybe even without a pipe, just lifting the payload from ground by the arm/legs and quickly-quickly passing it forwards until throwing away.

[wumpus]

The obvious issue is just how high  you can built your rail, which defines just how fast you need to leave so drag losses leave you with orbital velocity when you leave the atmosphere.

It is obviously far more doable in KSP, thanks to Kerbol having about 1/3 the orbital velocity of Earth.  This is why spaceplanes work at all in KSP.  You will, of course, need at least some propellant once you enter orbit (presumably after half an orbit) because your orbit will be elliptical and cross Kerbol and intersect roughly where your launch facility is.  Raising Pe out of the atmosphere should require trivial amounts of propellant (probably less than the Shuttles OMS engines), but is absolutely required.

Spinlaunch is the only group I've heard of trying to do such a thing.  It gets discussed in this thread : 

The big catches are that the rocket (and payload) have to withstand 10k gs of lateral acceleration and they also have to build something that will stop a counterweight being flung with roughly the momentum of the rocket being launch to 1km/s.

On Earth, some of the mountains of Ecuador should be ideal for this (they are further away from the center of the Earth than the Himalayas and are nearly on the Equator), but have fun with the local politics (not to mention getting Peru, Columbia, and Brazil to all agree for you to launch over them).  I think China has a launch facility on the Tibetan Plateau (not used for the big, important flights.  Presumably because the big boys barely notice the difference in drag) while the US never bothered to put a facility in Leadville, CO despite the proximity to Colorado Springs and the Air Force Academy.

[linuxgurugamer]

3 minutes ago, wumpus said:

The obvious issue is just how high  you can built your rail, which defines just how fast you need to leave so drag losses leave you with orbital velocity when you leave the atmosphere.

You missed the point that this would be in orbit, which would essentially make it unworkable for many reasons

[Fierce Wolf]

So the main problem issued are:

 

- Cost: Could make sense if missions are send in a monthly basis or so

- Reaction mass: It will end up deorbiting the station. I don't know if launching stuff retrograde would help. If rocks have to be lifted in order to just launch them up, would make zero sense. BUT, it may be useful if you deorbit spacecraft down to Earth using that method. LEO is not good/useful for that, but HEO could work.

 

Kurzgesagt (the yotube chanel) proposed a slingshot that had the same reaction problem, and same solution. I do believe humans will end up constructing infrastructure in space, the point is, exactly what

[wumpus]

2 hours ago, linuxgurugamer said:

You missed the point that this would be in orbit, which would essentially make it unworkable for many reasons

Space elevators are in orbit.  This is in space.

Of course, building something "in space / viable orbit" on the Moon would be a lot easier.  Build it on the highest mountain with a small extension and you are clear, not to mention the much lower orbital velocity.

[linuxgurugamer]

On 5/22/2021 at 2:52 PM, wumpus said:

Space elevators are in orbit.  This is in space.

Huh?

On 5/22/2021 at 1:00 AM, Fierce Wolf said:

I was thinking about the possibility of constructing in the near future a magnetic train (or gun, whichever sounds cooler), launch it to LEO,

LEO == Low Earth ORBIT.

And, FYI, anything in orbit IS in space.

The problem is that anything which fires something in one directory will be moved in the opposite direction.  

[MKI]

I feel like I watched a video on the maths of such a "electromagnetic launch system to orbit". If my memory serves me correct, to get a gun that can launch something into orbit that can provide acceleration that is manageable for humans, your looking at the gun the length of The United Kingdom North to South.

 

So we are talking a real mega-structure with completely insane requirements that need to worth flawlessly and be off the ground, and out of the atmosphere. I'm honestly not sure if that is physically possible the same way a traditional space-elevator isn't with anything but maybe carbon nano-tubes.

 

Now putting this on the Moon is a whole other story that would be much more reasonable (no atmosphere) and something I realized back in another thread I asked a number of weeks back.

 

Related thread, where I asked why we don't colonize the Moon instead of Mars, just so we can build a space elevator. An electromagnetic launch system on the surface of the Moon actually gives the space elevator a run for its money. There's also the insane prospect of possibly catching stuff from orbit using the same gun, which would be like catching a bullet back in the gun lol!