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Is it physically possible to make a relay that could, magnetically or electrically, or any other form really, slingshot a spacecraft from one point and stop a spacecraft at the next? If so, could it still be energy efficient? Is there some way to absorb the energy the spacecraft had when it was shot, and therefore be able to use that energy again to sling another craft?
Question Date: 2018-03-27
Answer 1:

I think you are asking in general whether it is possible to store the kinetic energy of one spacecraft (say using something like a "slingshot"), and use the stored energy to launch another spacecraft.

Ideally this is certainly possible, but how effective it is depends on the engineering design. Let's just explore the simplest design: really using a slingshot.

The 2nd cosmic velocity , the minimum velocity for a spacecraft to escape the earth is about 11.2km/s . Assuming it carries some astronauts, in order not to kill these astronauts, the acceleration/deceleration caused by the slingshot cannot be too large. The highest acceleration that the best pilots can stand is about 7g, g being the acceleration of the earth. Let's say we just use a "7g" slingshot, so our astronauts have a chance to survive. Then a quick calculation would show that this slingshot must be 560 miles long! It seems impossible to build. But maybe there is a smarter way of doing this.

Answer 2:

I was unable to find any information about magnetic or electrical slingshots for spacecraft, but that does not mean such methods are impossible. Also, one can certainly imagine a mechanism like that used to launch and catch fighter jets on aircraft carriers, but on a larger scale. I cannot comment on the viability of such a setup, but I can imagine one.

Of the information I did find, a gravity assist ("gravitational slingshot") sounds most similar to the provided description. A gravity assist cannot be used to start a spacecraft, but can be a fuel-conserving way to change direction, speed up (relative to another object), or slow down (see this site for some math ).

Science fiction provides plenty of examples of non-rocket launching systems, such as launch/orbital loops, linear accelerators (essentially a rail gun), space elevators, and so on.

I'll go into a little more detail on a few of the more well-developed possibilities. Solar sails are one option which could work for both leaving one point and stopping at another. They essentially work by reflecting light , each photon imparting a small change in momentum. Depending on the direction in which the craft is moving and the direction of that change in momentum, the craft will either speed up or slow down. (Two related concepts are the magnetic sail, mostly for slowing down, and coupling a solar sail with a fixed laser. In the latter case, the photons would come not from a star, but from a fixed laser installation. It is certainly conceivable that such a setup could be used to send off and slow down a spacecraft. I don't think the energy of one craft could easily be captured and used to drive subsequent launches though.)

Other options to slow down are aerobraking and aerocapture , which essentially use friction with an atmosphere at the destination (obviously limiting application to destinations that have atmospheres).

Many concepts are actually under development today. However, technological possibility does not indicate economic feasibility. Even those which prove economical may have limitations on the potential applications as well. A linear accelerator might prove viable for launching payloads, but only from bodies without atmospheres (because the same atmospheric friction which enables aerobraking could also burn up the craft on launch) and for non-living cargo (because too much acceleration would kill anything on board). Regardless, there are myriad intriguing possibilities that can be explored and which may ultimately come into existence.

Answer 3:

That's an exciting question! I don't know the answer, but it reminds me of an idea from Arthur C. Clarke, who was a famous science fiction writer. He envisioned a space elevator that would take objects far above the earth and it's gravity. The top of the elevator would be where a satellite would be that stays always in the same place above the earth - i.e., it has a 'geosynchronous' orbit.

Here's a YouTube video about it, from 2012: watch the video

Arthur C. Clarke's Space Elevator - YouTube

The elevator is awfully short at the moment, and the only 'person' it can transport is one of the little Lego people [named 'Clarke']. There are other YouTube videos, too; but I didn't look at them.

A lot of the people on the video aren't scientists, but then there's at least one who's an actual scientist.

Answer 4:

Theoretically, yes. Practically, no, not with our current technology.

What you're basically describing is a magnetic spring that can recharge itself as it captures a ship landing on it. I'm not sure how you would handle that electrically.

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