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Seems to me the best way for space travel is to tap into the suns energy somehow.More efficent solar panels to boil off liquids into vapor to propel spacecraft. Just your body heat in the vacuum of space will boil water. Imagine the heat from the sun will do to water.
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There are a number of propulsion strategies that have been proposed that aim to do what you just outlined. They fall into two categories.
The first use the sun's power to heat up a propellant. However, I don't usually see this being listed when people talk about potential spacecraft ropulsion technologies. I'm not sure if it's because solar fuel heating is not very effective or whether it's just one of those thechnologies that has been forgotten about for other reasons.
The second is a reactionless drive. Solar sails, magsails and M2P2 drives fall under this category. They have the advantage of much higher performance than just about any other drive type in existence. Unforunately, they all have very low thrust so aren't good for moving people around. However, if you want to move a ton of cargo to Mars for as cheaply as possible, these are the way to go. The M2P2 technology isn't fully tested yet but looks to be the most promising of the bunch.
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yes, there is much to learn from the Sun, people have often thought about how to use its energy, solar sail designs, Ion propulsion, fusion reaction engines? plasma drive, neutrino theory...there are many things and ideas but we are behind on science and have much to learn from the Suns raw power.
Many people are trying to design faster space travel, they are trying to narrow down our time window, as on average even our quickest designs take over 6 months to reach mars. Bad if you need something delivered, or for a rescue mission. Space travel is a little slow for mankind, but we are laerning lots, Its like we have gone back in time to the days where it took weeks to cross the seas onto another land.
'first steps are not for cheap, think about it...
did China build a great Wall in a day ?' ( Y L R newmars forum member )
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The other-other way to use the sun for propulsion is to use solar photovolics to power an electric engine of some sort (probably accelerator or Hall-effect ion, perhaps VASIMR), but this would require a very large collector to power an electric engine able to move substantial masses... too large by my estimation, especially for a VASIMR plasma engine, and wouldn't be very practical very far out (even Mars is pretty far).
[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]
[i]The glass is at 50% of capacity[/i]
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Mars Direct does talk about solar thermal propulsion, and NASA has been doing research on it. A large mirror focuses sunlight on a graphite block, heating it to extremely high temperatures, and hydrogen is passed through the block. The Isp right now is about 800 seconds, but theoretically I suppose solar thermal could generate thrusts similar to solid core thermal (Isp of about 1000 seconds). The down side is that the thrust is only a few pounds (the NERVA nuclear engines generated 250,000 pounds of thrust, but their power output was in the many megawatts; mirrors can only focus some number of kilowatts on a graphite block). Thus solar thermal can only be used to transport cargo, and it would require a series of "perigee kicks" to gradually raise the apogee of a spacecraft; then a chemical engine would probaly provide the last 0.5 km/sec of delta-v to send the vehicle to Mars.
Solar thermal engines should be very cheap and reliable, though.
-- RobS
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Emphasis on "should" be... nobody has yet demonstrated such an engine, and with the giant crazy mirros would seem to be hard to navigate.
[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]
[i]The glass is at 50% of capacity[/i]
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How large of an area of solar panels in space near Earth would it take to generate 100 mws?
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With a Solar flux of around 1,400W/m^2, about 71,500 square meters.
[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]
[i]The glass is at 50% of capacity[/i]
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How much would that weigh when compared to a 100 mw nuclear reactor, and associated equipment?
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This is not a simple nor a single question to answer...
Comparing a giant Solar/Thermal rocket to "a nuclear reactor" is not apples to apples, because nuclear does different things and can propell a ship in different ways. The US NERVA rocket program made thermal rockets with high thrust and pretty good Isp, or today's Prometheous program for a nuclear/ion electic arrangement, and perhaps in the future the VASIMR nuclear electroplasma rocket. Just "nuclear" is not descriptive enough. A nuclear rocket may also be used in different missions, for instance the solar rocket will lose 75% of its power going from Earth distances to Martian distances for a pure thermal rocket.
The only reactor concept I have heard that could provide this kind of multimegwatt electric power in a flight-weight package (relativly speaking) is the far-out paper concept for a vapor-core nuclear reactor (not gas cooled, the fuel is actually vaporized) and it would be in the 50-100+ ton region probably. The largest NERVA thermal engines on the other hand hold to this day the title of the world's most powerful nuclear reactor achieving power levels of nearly 1.3 Gigawatts for a fairly small mass.
[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]
[i]The glass is at 50% of capacity[/i]
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Actually, I was comparing a 100mw solar panel combination solar sail to a 100mw nuclear reactor.Dr Chang Diaz says a Vasimr spacecraft can get to Mars in one month with a 100 mw nuclear reactor.
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Okay, then you are talking about extremely high energy nuclear electric source for a VASIMR engine... the solution of choice will probably be a vapor core nuclear reactor paired with MHD power generation.
[http://www.inspi.ufl.edu/research/gcr/]http://www.inspi.ufl.edu/research/gcr/
[http://www.spacetransportation.com/ast/ … _knigh.pdf]http://www.spacetransportation.com/ast/ … _knigh.pdf
The second link is much more technical, but also contains some very preliminary specific power figures, with 100MWe hitting around 25 tons for the reactor idealy.
Now, somthing I would like to note, is that a Solar/Thermal system can't hold a candle to VASIMR's fuel efficency... solar thermal tops out at 2500-3000C, because the graphite engine housing would simply burn up above this temp. VASIMR on the other hand could reach into the Millions of degrees, with similar or better thrust levels as Solar/Thermal but with an order of magnetude higher specific impulse with the higher temps... Using conventional solid-core/gas-cooled reactors though, I don't imagine making enough power with a reasonable mass easily.
Edit: Total hardware mass for the 100MWe system is theoreticly around 40,000kg.
[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]
[i]The glass is at 50% of capacity[/i]
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If you use a 100mw solar generator to run vasimr would it be lighter than a 100 mw nuclear reactor that runs vasimr?
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If a vapor core reactor can be pulled off, probably not by alot, the reactor complete package is hitting around 0.5kg/kWe, but my question is how do you manage a solar collector thats that big? If you want similar power at a Martian distance, you are talking about a solar collector with 100% efficency three hundred square kilometers big. If you factor in that solar cells are around 40% efficent you are looking at a solar collector of more than seven hundred square kilometers.
Versus a reactor thats three or four meters wide...
These are not solar sails, getting such a thing to collect energy to convert into electricity or thermal energy is unrealistic.
Edit:
Thats a square collector 16.5 miles on a side, or a disk 10 miles wide.
[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]
[i]The glass is at 50% of capacity[/i]
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No just here at Earth. Venus or Mercury gravity assist can help with the velocity. The larger the surface area the more the solar wind can also help with acceleration.
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1: Gravity assists will increase the actual distance of the journey several fold, making nuclear faster. Gravity asssit will also make launch windows much smaller and less frequent.
2: Being closer to the Sun is a BAD thing for manned spaceships, higher solar wind energies, less solar flare warning.
3: Solar sails rely on the ship being very light, which a VASIMR engine is not. The light pressure would be pretty inconsequential for 150-200+ ton spaceships like this kind.
4: Solar sails do not capture solar wind. Solar wind is predominantly a shower of charged protons, which will pass right through a solar sail, which relies on photons (light) to operate.
5: Light pressure on the giant solar collector will actually slow down the return trip from a Martian orbit, and the low amount of light beyond Mars orbital distances will make a Solar/VASIMR probe to asteroids/outter planets impossible.
[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]
[i]The glass is at 50% of capacity[/i]
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Oh yeah, and how do you intend to get BACK from Mars with only 1/4th the electricity? You must also worry about the return journey, not just boosting away from Earth.
[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]
[i]The glass is at 50% of capacity[/i]
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Great lets build one for Mars then.One month there four months back. Total five months. Doable?
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Okay, you need to figure out a way to make an opticly reflective "dish" about ten miles wide, figure out how to mount a football field or two of solar cells at the focal point, make is strong enough to resist torque from maneuvering, and figure out how to get it to operate completly independant from the orientation of the ship... Oh and don't forget inventing a battery or capacitor system for when you enter the shadow of a large body, since you won't want to power off your cooling system for the VASIMR engine every hour or two...
...or you can bring a nuclear reactor that weighs 40 tons (which will ride on an Ariane-V booster with the cryogenic 2nd stage) and fit comfortably on a flat bed truck.
No, not do-able. Just bring the reactor, you'll need them to power a Mars base anyway.
Edit: Cutting power available by 3/4ths doesnt make the trip 4 times as long, the acceleration is 1/4th as much, the trip time will probably be much longer.
[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]
[i]The glass is at 50% of capacity[/i]
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The dish can be made out of Aerogel then aluminize the surface. Very light stuff.
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Its not light enough, and would have a rough surface because of its pores, making a lousy mirror.
It would have to be made out of a "son of Mylar" metal coated polymer, which there is no such material with the characteristics required that I know of.
[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]
[i]The glass is at 50% of capacity[/i]
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You also must consider all the other things besides the giant mirror you would need... you still need a signifigant number of solar cells, which can only take 100-150 times normal sunlight brightness, and you need a structure several miles long to mount them on. And you need to cool them with somthing. And you need to have some means of keeping the dish the right shape, inflatable mirror struts 4-5mi long are impractical, which will require spinning... spinning requires a bearing of some sort you must attach to the gimbal.
The gimbal itself has to somehow operate independantly from the ship, which will need to thrust in various different directions while keeping the dish focused on the sun, which will itself require active tracking. And then you have to have some means of storing power for blackouts or maneuvering, because you can't immediatly pull the plug on an engine full of 1000000K hydrogen plasma...
The list goes on. Just bring the d**n reactor.
[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]
[i]The glass is at 50% of capacity[/i]
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Actually, it would make a great telescope mirror because of its small pore structure. The bonding would be good since it is a silca based product.
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The pores are not small enough, they are still quite large.
Also, aerogel is a solid... how do you intend to make a solid mirror only a tiny fraction of an inch thick and several miles wide? It would have to be built in orbit, and that is too much trouble, even if aerogel were low-density enough which it is not.
A reactor on the other hand, can be built in its entirety and tested on the ground, then shipped into space on exsisting rockets.
[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]
[i]The glass is at 50% of capacity[/i]
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The pores are small enough to have vapor deposition fill them in.
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