Traveling around space can be hard and require a lot of fuel, which is part of the reason NASA has a spacecraft concept that would hitch a free ride on one of the many comets and asteroids speeding around our solar system at 22,000 miles per hour (on the slow end). Comet Hitchhiker, developed at NASA's Jet Propulsion Laboratory, would feature a reusable tether system to replace the need for propellant for entering orbit and landing on objects.
The spacecraft would first cast an extendable tether toward the object and attach itself using a harpoon attached to the tether. Next, it would reel out the tether while applying a brake that harvests energy while the spacecraft accelerates. This allows Comet Hitchhiker to accelerate and slowly match the speed of its ride, and keeping that slight tension on the line harvests energy that is stored on-board for later use, reeling itself down to the surface of the comet or asteroid. A comet hitchhiker spacecraft can obtain up to ~10 km/s of delta-V by using a carbon nanotube (CNT) tether, reaching the current orbital distance of Pluto (32.6 AU) in just 5.6 years.
Unfortunately rocket scientists apparently don't read SN, or they'd know from discussions last year that it simply won't work. It seems that the idea defies "basic orbital mechanics" and "makes no sense".
If you stored the energy released by spooling out the cable, and used it to wind it in again and slingshot past you could theoretically double that.
With what? A magic spring for the magic string?
This idea is completely infeasible.
This entire thing is based on ifs and buts of "future technologies that don't exist". Considering that we have enough problems slowly unfurling wires in space so they don't tangle, or failing to anchor on a comet while at 0 delta-V, well, well.... we'll sooner get reactionless drives working then this.
Did you see the word "theoretically" in there? I do not expect any system we could build soon to use the slingshot doubling, I only put in that line for completeness.
I thought the idea was ridiculous when I first saw it, but achieving a delta V of close to a km/s might be engineeringly possible, and on a large vessel could well be worthwhile.This is a technology that would actually scale well, and something to keep in mind for a manned mars mission. A large ship pulling five gees for 10 or 20 km would be able to save a lot of fuel or reduce travel time significantly.Given that you were going to do it, it might be better to have two equal mass ships with a cable strung between them and a spool on each. You could line them each side of the comet path and not have to worry about the anchor holding.The hard part would be waiting for a comet or asteroid that is going the right way at the right speed.
Also, you don't have to match the comet speed as long as you can let go at the end of the tether, but efficiency goes down as the residual speed difference goes up.