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| {{Move2space}} | | {{Goto space}} |
| There are many upper stages in geosynchronous transfer orbit (GTO), at perigee
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| they have a velocity of about 10.5 kilometres per second, although this
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| reduces gradually over years as they slowly decay.
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| If a suborbital vehicle could attach a [[tether]] to one of these stages at
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| perigee, it could be towed most of the way into orbit.
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| To get into LEO requires 7 km/sec.
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| If the payload and the stage are equal mass, then the payload would be
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| accelerated by 5 km/sec and the GTO stage would be decelerated the same
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| amount.
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| Accelerating by 5 km/sec requires about 50 G acceleration for ten seconds,
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| which would traverse a distance of 25 kilometres (the length of tether
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| required).
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| Alternative profile would factor by ten, e.g. 500 G for one second,
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| traverses 2.5 kilometres (shorter length of tether but higher stress).
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| The tether would be on a spool with a controlled resistance (e.g. friction
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| brake, or dashpot, or E-M brake) to soften the initial jerk at contact,
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| then, pay out the tether at the right rate to control the acceleration to
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| the planned profile.
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| The practicalities of attaching a cable to an object moving at 10.5 km/sec
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| are daunting. In this profile the suborbital vehicle would already need to boost itself to 2 km/sec, as the 5 km/sec is not enough to reach orbit. Therefore the relative speed would be 8.5 km/sec (2km/sec less).
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| <br>
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| <br>
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| Capture perhaps via a light weight structure made of a 3-D web of kevlar
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| strands (or something stronger), like a large bullet proof vest in which the
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| GTO stage becomes embedded. Size, maybe a few hundreds metres across. The
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| webbing could be within an inflatable sphere a few hundred metres diameter,
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| or alternatively shaped as a tetrahedron for simplicity of geometry.
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| <br>
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| The mechanics of high speed collisions are difficult to analyze. At such
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| speeds, the flexibility of the strands become irrelevant, they behave more
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| like solid bars. The stage would be severely damaged, one would need to
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| devise a configuration which would not shred the GTO stage into a zillion
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| fragments. The kevlar strands would probably be stronger than the stage
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| material.
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| <br>
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| Wikipedia reports that some remarkable new developments are emerging for new
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| materials being used in bullet proof vests.
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| <br>
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| http://en.wikipedia.org/wiki/Bulletproof_vest
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| <br>
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| Researchers in the U.S. and separately in the Hebrew University are on their
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| way to create artificial spider silk that will be super strong, yet light
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| and flexible.
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| <br>
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| American company ApNano have developed a nanocomposite based on Tungsten
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| Disulfide able to withstand shocks generated by a steel projectile traveling
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| at velocities of up to 1.5 km/second. During the tests, the material proved
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| to be so strong that after the impact the samples remained essentially
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| unmarred. Under isostatic pressure tests it is stable up to at least 350
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| tons/cm².
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| <br>
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| Most upper stages are composed of Aluminum alloys (softer than steel), with
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| some graphite composites.
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| <br>
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|
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| ==See Also==
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| *[[List of Propulsion Systems]]
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|
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| {{cleanup}}
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| [[Category:Transportation]]
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| [[Category:Components]]
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| [[Category:Hardware Plans]]
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