Posted on 03/25/2011 12:01:39 PM PDT by LibWhacker
The way the article is written, it seems like the guy promoting the idea is saying, “We still have bugs to work out, but all we need is money from somewhere . . .”
From what little searching I did, this seems to be the method of choice -
http://www.nasa.gov/vision/space/travelinginspace/future_propulsion.html
"It runs on *water*, man!"This is a little bit interesting; Asimov's standard engine for jettin' around the Solar System was fission-based, the nuclear pile heated water to steam.
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Yep - I’m aware of that. The Mass it will use is not nearly as heavy as H2O. It can use electricity from any source solar or nuclear to do the job it’s doing. It’s estimated that a 1MW Vasimr system could get us to Mar in 13.
http://www.thespacereview.com/article/1690/1
Summary: Vasimr could get us to Mars in 39 days with direct, constant acceleration. It would use Argon as the fuel source - a LOT lighter than H2O.
I'm about 40% of the way through the faux-ars-nouveau movie Sky Captain and the World of Tomorrow. It reminds me of the children's literature I devoured a half-century ago, which echoed a forgotten motif of the 1930s -- the astonished appreciation of how fast progress could happen, and the breathless speculation about what could happen next.
There was reason for soaring optimism. A single generation had gone from clattering motorized kites to ocean-spanning aluminum monoplanes. From horse-and-buggy to the first car to travel a mile a minute (a Stanley Steamer). To the first car to travel two miles a minute (a Stanley Steamer). From telegraph to commercial radio programs. From still photos to motion pictures with sound. "The Wizard of Menlo Park" cranked out a continuous stream of new marvels from his "invention factory."
So, who slammed on the brakes? Who killed the dream? And why? Answer these questions, and maybe I will indeed get to retire on the moon.
how are you going to change that energy into something you can use for thrust?
—
Explode it against a preasure plate a ka the Orion Project from the early 60s, before the US went wimpy on nuclear power.
Steam, water - all green, which is in.
LEO per pound costs:
Low - $1672/$2341
High - $5806/$6452
Geo syc orbit per pound costs:
Low - $5051/$7071
High - $13,953/$15,504
How high you want to lift the water depends on the orbit picked for the fueling/refueling - costs are comenserate. The further into the gravity well you go for your fuel (water), the more fuel you need to enter and depart.
Exactly how much water fuel does one need to get to Mars? The faster one goes the more water one needs.
BAH ... Orion or bust.
forget about the solar BS
holding multi tonnage of water
No small step there getting that water into orbit.
this is a solar system ship...a huge non take off and landing type of vessel meant for moving large amounts of people/freight...you take off and land with separate small units...get just enough water on board to mine the ice farther out in the solar system..either from Keiper belt ice or in closer from ice moons(europa etc) that have much lower gravity to fight...
Correct. The proper term for the water would be reaction mass, not fuel.
Regarding getting the water into orbit...chemical rockets would not be the way to do it. Freezing the water and launching it with electromagnetic rail guns or ground based lasers would be the way to go. If humans don't have to go along for that ride there would be no limit on how many gees the launch system could generate.
Short term you are correct, but long term the same drive system could be attached to large chunck of ice in the outer system and boosted anywhere we need it. Short term see my earlier post about using ground based rail guns or lasers to boost to Earth orbit.
chunck = chunks
Nice thought, that stops short of the full solution. Example: rail guns cannot put anything into orbit.
Lasers would be the best choice. Rail guns would be a good solution in low gravity/thin atmo situations. When I wrote that I wasn't thinking about the problems with using rail guns out of a deep gravity well with dense atmo. I assume that is why you say rail guns can't put anything into orbit.
Lasers can't put anything into orbit, either.
Either could (theoretically, neglecting the problems with being a burning ball of plasma) launch something to orbit altitude, which is not the same as putting something into orbit. The problem is that you've got to apply another large delta-V at some point and in the right direction, to actually put the vehicle in orbit.
Best case from the flaming ball of plasma perspective is to launch straight up -- which happens also to be the worst case from the perspective of applying a delta-V to put the thing actually into orbit.
Best case from a delta-V perspective has you launching at a pretty low elevation angle, which roughly doubles the amount of atmosphere you'd have to be a flaming ball of plasma in.
Assuming you surmount that problem, there's still the problem of getting the water from where you put it in orbit, to a position where it can be loaded into your space ship (which, in a practical sense, means your target vehicle will have to do the rendezvous).
You've no doubt spotted the fly in the ointment here: how much delta-V (and how much propellant) will have to be expended just to fuel your water-powered space ship?
Note, too, this little nugget:
McConnell envisions space coaches cruising around the solar system, each individual vehicle fueling up with water in low-Earth orbit when the need arises. In the future, fuel could be sourced along a space coach's travels — for example, water could be mined from an asteroid or a Martian moon.
Yup .... all you've got to do, is just pop out of that interplanetary trajectory, down into Low Earth Orbit; or, into the orbit of an asteroid or a Martian moon.....
How? Does our author understand the orbital mechanics of his "simple" solution?
Chances are the author doesn't understand the issues. To keep the system going they will have to boost the reaction mass to match orbit with the spacecraft.
Recently read a science fiction book which described a similar concept, but I forget what the drive system was. May have been solar powered ion drive. That author called them cyclers with three cyclers continually cycling between Earth and Mars.
Done right, once the cycle is going the system won't require a lot of additional delta v. Shuttle craft would be required to boost cargo and consumables to matching orbits, but the cyclers themselves would be very efficient.
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