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Old 12th January 2019, 01:58 PM   #41
RecoveringYuppy
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Elaborating on rjh01 it would make a lot of sense to completely divorce the payloads from the vehicles. Right now it would make sense to have "tug boats" carry satellites to circular GEOs rather than wasting fuel that could be used for station keeping. It would open up new possibilities such as doing final assembly of the satellite on the ISS or similar, avoiding deployment problems.
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Old 12th January 2019, 02:44 PM   #42
smartcooky
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Originally Posted by RecoveringYuppy View Post
We should take that seriously. It's you that should be ignored.

BTW I think they are actually understating the potential. There doesn't have to be water at every potential landing site. We got on and off the Moon without having to refuel. This technology won't need to either..
I agree.

It takes very little reaction mass to get off small planetary bodies. I seem to recall they had trouble getting the Philae lander to actually land on comet C67/P Churyumov-Gerasimenko. It bounced a kilometre off the surface and took almost 2 hours to come back down... then it bounced again - no reaction mass was involved in those bounces

Point of note - the Apollo Lunar Modules, and the Soviet Luna 16, 20 and Luna 24 landers are still the only bona-fide SSTO space craft that have ever flown, and the LM's were the only crewed ones.
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Old 12th January 2019, 02:56 PM   #43
RecoveringYuppy
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Originally Posted by smartcooky View Post
Point of note - the Apollo Lunar Modules, and the Soviet Luna 16, 20 and Luna 24 landers are still the only bona-fide SSTO space craft that have ever flown, and the LM's were the only crewed ones.

And to further the point they had already landed which also cost fuel.
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Old 12th January 2019, 04:00 PM   #44
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Originally Posted by smartcooky View Post
I agree.

It takes very little reaction mass to get off small planetary bodies.
True, but getting off the surface isn't the issue. Going from one asteroid to another is likely to require a few km/s of delta-V, and if your steam system has a poor specific impulse (Isp), you may be better off with ion thrusters (Isp ~3000) and a big never-to-be-refilled tank of some noble gas.

If the steam system is dissociating the steam to oxygen and hydrogen, then they can get a decent Isp (>400 sec) but that raises a host of other problems. If they're simply heating the steam using conventional heaters, the Isp is going to be badly limited (maybe 200 sec). And if they're using arc heating to get a decent Isp (400 to 600 sec), then the thrusters themselves will have limited life.
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Old 12th January 2019, 04:28 PM   #45
RecoveringYuppy
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Those numbers compare well against apogee kick motors in the Star family.
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Old 12th January 2019, 06:07 PM   #46
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Originally Posted by RecoveringYuppy View Post
Don't be ridiculous.
I do try not to be. So what, exactly, was I being ridiculous about? Do you think that reactors and/or solar cells last forever? Or did you think that I was seriously advocating reactor refueling/solar cell fabrication?


Quote:
True about water being the reaction mass but remember that sunshine you mentioned?
Sure I remember. Solar cells are only good out to a certain distance from the sun, and they get less useful the further out you go. After all, they have to get bigger for the same output power, so their power/weight ratio gets worse and worse. Likewise, their water-mining rate will drop in the same fashion, so the overall trip time (assuming multiple boosts) will increase.

So, could you be a bit (that is to say, a lot more) explicit about the failings you see in my argurments?

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Old 13th January 2019, 01:39 AM   #47
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Originally Posted by WhatRoughBeast View Post
I do try not to be. So what, exactly, was I being ridiculous about? Do you think that reactors and/or solar cells last forever? Or did you think that I was seriously advocating reactor refueling/solar cell fabrication?
I'm pretty sure it was taking literally the idea that the probe would last forever. That was hyperbole and no one (here anyway) is arguing that it could last forever.

What is being argued is that it could be a major improvement over current methods.
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