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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: 0) by Anonymous Coward on Thursday September 03 2015, @06:28PM

    by Anonymous Coward on Thursday September 03 2015, @06:28PM (#231889)

    The surface strength of comets is still not well constrained but believed to be in the 1 kPa – 100 kPa range [4,5]. Philae has been designed for compressive strengths between 2 kPa and 2 MPa. For a compressive strength less than 2kPa, Philae’s baseplate would touch the ground (but then effectively stopping further penetration) and the 360° rotation capability of the landing gear would be compromised. Still, all experiments could be performed. Only for compressive strengths 2 MPa (solid ice), the harpoons may not anchor safely.

    PREPARING FOR LANDING ON A COMET – THE ROSETTA LANDER PHILAE. Jens Biele and Stephan Ulamec, German Aerospace Center (DLR), RB-MUSC, Linder Höhe, 51147 Cologne, Germany. 44th Lunar and Planetary Science Conference (2013) []

    So do they know how hard the surface will be? It is just speculation with out that info, a too hard/soft comet will ruin the mission.

  • (Score: 0) by Anonymous Coward on Thursday September 03 2015, @07:20PM

    by Anonymous Coward on Thursday September 03 2015, @07:20PM (#231909)

    We suggest the minimum surface compressive strength for comet C67 to be about 1 MPa.

    HOW HARD IS THE SURFACE OF COMET NUCLEUS? A CASE STUDY FOR COMET 67P/CHURYUMOV-GERASIMENKO. A. ElShafie, E. Heggy. 46th Lunar and Planetary Science Conference (2015) []

    So to account for the bouncing they put a lower bound on compressive strength at 1 MPa, which is 10x more than expected in 2013 and at the high end of their design requirements. So how difficult is it to design a harpoon system that works with, say, 10 MPa material?