Great minds think alike - good to see you posting here - seems like a while since you were describing your idea for using collision to transfer momentum from a spacecraft perihelion thrust to an orbiting vehicle. I actually submitted a similar idea to NASA in an RFI solicitation and discussed it here: http://forum.nasaspaceflight.com/index.php?topic=21530.90.
As I developed the idea I proposed using small rugged vehicles based on kinetic kill type ABM vehicles carrying tethers from each vehicle that could home in on each other, slow down and latch to each other. The tow vehicle would then slowly take up the slack and tow the payload or entire launch vehicle into orbit.
IsaacKuo:Why not just exchange a cargo pod rather than tow the whole sRLV into orbit? That will save a "ton" of mass and allow the sRLV to have a faster turn around won't it?
I believe on an earlier discussion the idea of the tow vehicle collecting air as it decelerated was discussed. The tow vehicle could perhaps collect air as it made a series of skips off the upper atmosphere Sanger style and cool and liquefy it and perhaps separate the N and exhaust it, between skips. The extra drag collection requires is not a problem if you are trying to slow down anyway.
I think this concept was the basis of a long argument between Jim and a Paul Klinkman on space.com when it still had a forum.Im a bit unclear because I remember zany catches on tethers being included, but im sure the case of the orbital element also decelerating part way was also discussed.
At the time I was more interested in the concept of using an orbital atmosphere collector to get the propellant in orbit in the first place.http://forum.nasaspaceflight.com/index.php?topic=30104.0
Quote from: Solman on 01/27/2013 12:59 amI believe on an earlier discussion the idea of the tow vehicle collecting air as it decelerated was discussed. The tow vehicle could perhaps collect air as it made a series of skips off the upper atmosphere Sanger style and cool and liquefy it and perhaps separate the N and exhaust it, between skips. The extra drag collection requires is not a problem if you are trying to slow down anyway.These skips won't last very long unless you have a really good lift/drag ratio.My gut feeling is that the only way you could liquefy the oxygen quickly enough is if you were doing something like LACE, where you sacrifice LH2 to liquefy oxygen. But where would you get all this hydrogen from? Hmm...doesn't make sense.On the other hand, maybe it could work with liquid nitrogen? Atmospheric scooping could provide plenty of nitrogen.I don't know...the entire idea seems doomed to failure due to compression heating. It's one thing for LACE to operate at relatively low speeds, but this will be scooping up air at near orbital speeds.
I started thinking about this in the first place because it occurred to me that given the relatively low Dv required to bring some NEO's back to Earth orbit or the EML points, a successful asteroid mining operation might have a huge amount of water once the metals were extracted and could benefit by having a market for it. There might be few opportunities to fuel BEO vehicles ay first and so I saw taking over the job now performed by upper stages as a potential market to help jump start asteroid mining.
BTW - As I remember now, the reason for the grappling vehicles was that an objection was raised in previous discussion that the window for docking was too short to safely bring the two vehicles together but that depends i guess on how you do it.
Quote from: Solman on 01/27/2013 11:19 pmBTW - As I remember now, the reason for the grappling vehicles was that an objection was raised in previous discussion that the window for docking was too short to safely bring the two vehicles together but that depends i guess on how you do it.I imagine the two vehicles leaving the atmosphere close to each other, on an ascending trajectory around 3km/s. While in the atmosphere, the skyhitch can use aerodynamic maneuvers along with its plentiful spare speed to maneuver into a close tail chase. So, the vehicles will be ascending at perhaps a 30 degree trajectory close to each other.This implies an upward velocity component of 1500m/s, or about 5 minutes until gravity pulls them back down to the upper atmosphere.
I don't see how these tethers would help the situation. It would take extra time to deploy the tethers.I think maybe a tether might make sense if you designed around rendezvous in mid-air. That way, the LV could stay comfortably outside the shock cones of the skyhitch, and drag could keep the tether taut and trailing. However, I propose using pure rocket propulsion, so neither vehicle is airbreathing. I think it would be better to get out of the atmosphere.