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posted by LaminatorX on Thursday September 03 2015, @05:05PM   Printer-friendly
from the freight-train-hopping-IN-SPAAAAAACE! dept.

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".

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  • (Score: 3, Informative) by Absolutely.Geek on Thursday September 03 2015, @10:57PM

    by Absolutely.Geek (5328) on Thursday September 03 2015, @10:57PM (#232021)

    It is a cool idea; but I have a few issues with it.

    Lets say that you want to grapple with something that is going at 10km/s; you get on an intersecting trajectory going 2km/s so your delta is 8km/s. Now we will assume that the latching onto the thing is a solved problem.

    If you somehow managed to make a 160km line you would pay that out in 20s; thus your acceleration is 400m/s^2 for 20s. Your craft has to handle approx 40g; your line and grapple point has to maintain its grip under 40 x the weight of your craft to get up to speed. This all has to happen without damage to the components that will wind the craft back into the object.

    Don't trust the police or the government - Shihad: My mind's sedate.
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  • (Score: 1) by Absolutely.Geek on Friday September 04 2015, @12:22AM

    by Absolutely.Geek (5328) on Friday September 04 2015, @12:22AM (#232049)

    Replying to myself to clarify; the 40g that I stated above is the MINIMUM acceleration achievable. It is quite likely that the actual acceleration would be much higher then 40g; if there was a failure of the unspooling mechanism half way along the craft would need to gain 4km/s is a very short amount of time....most likely outcome would be the unspooling mechanism tearing away from the craft or the teather snapping at a weak point somewhere along its length.

    Don't trust the police or the government - Shihad: My mind's sedate.
    • (Score: 2) by mhajicek on Friday September 04 2015, @02:32AM

      by mhajicek (51) Subscriber Badge on Friday September 04 2015, @02:32AM (#232095)

      Yeah, Mythbusters tried it with a car. It didn't work very well.

      The spacelike surfaces of time foliations can have a cusp at the surface of discontinuity. - P. Hajicek
    • (Score: 2) by Adamsjas on Friday September 04 2015, @04:19AM

      by Adamsjas (4507) on Friday September 04 2015, @04:19AM (#232123)

      Stretchy tether?

      Not necessarily a bungie cord, just a weave that could stretch slowly, (no rebound, its stays lengthened).
      You could soak up a lot of Gs in the cable itself.