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There needs to be a full scale design contract let on a low temp ( less than 1100 C )1200 megawatt interplanetary space reactor /turbo-generator coupled to a extreme high current both electron and proton operated combination klystron/linac with targeted exhaust velocities o 10e6 M/sec and exhaust masses of 10 g/sec. This would give a 50 metric ton vehicle an acceleration of about 1/5 G or about 2m/sec/sec, with a reaction propellant usage of 36 kilograms of H2 per hour. Note waste energy would be 100 to 200 megawatts and some of that would be used for internal spacecraft functions Nuclear plant thermal efficiencies would be increased to 90% in this model from the current less than 70%. If that is not possible increase the total reactor thermal output to 1500 megawatts and waste heat to 500 megawatts. That burn would make most Mars trips a twelve day cruise with just 60 hours combined acceleration and deceleration "burn time" and a reaction mass usage one way of 2.4 metric tons H2. Robot cargo ships would make the trip one way taking ten times as long with 500 ton total masses and then their reactors would be converted to surface power units. Best thing yet is that if we only achieve 50 percent of the power throughput goals the whole thing is still practical and very doable using technology that has been theoretically demonstrated today. The other thing is that the reactor radiation shielding only needs to be a 2 meter thick water tank between the crew section and the power plant and propulsion section and that the robot ships will make the flight first. you will note that this is about twice the thrust that you get per unit kilowatt than a current ion engine but the main accelerator klystron proton linac uses acceleration grids only in the preliminary low energy proton klystron stages and the target-less linac uses power only as a function of its own impedance, which using superconductors on the surface of its acceleration cavities would be quite high ( today?s commercial linacs use polished copper and have impedances in the 50 thousand ohm range. The throughput impedance on the DS1's ion drive is about 600 ohms. The high voltages and low ( comparative) frequency of this linac would enable the drift tube diameters to be quite large so that there would be no beam interaction with the accelerating current other than electrostatic. The proton klystron front end of the accelerator would be very long (50 M) because of the 1000 to one difference in the charge to mass ratio of a proton compared to an electron. and the frequency would be much lower because the initial electrostatic gun would be accelerating those protons to a much lower initial velocity, and because the system could accept virtually no out of phase beam losses both for efficiency reasons and power dissipation ones. The main source of power for the linac portion would come from the concurrent electron klystrons needed to neutralize the beam, and they of course would have no collectors just well designed Pulsed acceleration grids.and possibly quadrapole focusing magnets instead of annular windings. all current carrying surfaces would either be gold or superconductor plated and the reactor fluid waste heat and the hot side of the cryo-pumps would cool by the use of conventional space radiators, The design is doable.. all we need is for some Varian or Stanford engineer to crunch the numbers and come up with the exact specs --JJB
Can you offer links?
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"If feasible, couldn't one tack back to Earth. Sailboats use tacking to move into the wind, so wouldn't that be possible for a light sail craft?"
I don't think that it would be possible to tack back to Earth with a solar sail. Tacking is the result of the keel of the boat being pushed against by the water in response to the force of the wind pushing sideways on the sail. Like a watermelon seed squeezed between two fingers-the boat moves forward.
Unless you could construe keel-analogue that worked in space, I do not think that tacking into the light would be feasible. However, if you had a material that had alterable reflectivity and opacity, you could theoretically sail at an angle to the sun and still receive some of it's light.
In the interests of my species
I am a firm supporter of stepping out into this great universe both armed and dangerous.
Bootprints in red dust, or bust!
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Regarding the question of tacking "against" sunlight, this is easy in the sense that an object in a circular orbit around the sun is moving at right angles to the sunlight, so the solar sail needs to be aligned either to speed up or slow down the ship in its right-angle motion. If it speeds up the ship, it moves into a higher orbit; if it slows the ship down, it moves into a lower orbit.
Regarding the idea of a 1200 megawatt reactor to accelerate a 50 tonne payload at 1/5 gee, the basic problem I see is the mass of the 1200 megawatt power plant. Right now, Mars Direct is talking in terms of a 100 kilowatt (0.1 megawatt!) powerplant massing 3.5 tonnes. Scale that up, and 1200 megawatts requires 42,000 tonnes. No doubt such a huge reactor would mass much less in terms of kilowatts produced per tonne of mass, but I rather doubt you could shrink it into less than 50 tonnes!
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Some thoughts.
#Do you get any benefit from adding more sails, like with sailing ships?
#Can you improve sail performance by optimizing absorption on red end of spectrum, to take advantage of Doppler?
#Can you also add magnetic sails & double your thrust without causing problems?
I'm going back to Atlantis.
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ronondexfan, more sails definitely gives you more benefit. The photon pressure equation is just flux / c (speed of light). So optimizing to one end of the spectrum won't do much good, you want to absorb the whole spectrum as much as you can. It may turn out that sails that are optimized to one end are lighter and therefore more efficient than sails that absorb more spectrum, though.
As far as adding a magnetic sail there's a wonderful concept called Dusty M2P2 that may be of interest. It uses a plasma to inflate the mag sail and if you put in little particles that reflect light it may be a successful propulsion method.
Google search for it: https://www.google.com/search?q=Dusty+M2P2
Some useful links while MER are active. [url=http://marsrovers.jpl.nasa.gov/home/index.html]Offical site[/url] [url=http://www.nasa.gov/multimedia/nasatv/MM_NTV_Web.html]NASA TV[/url] [url=http://www.jpl.nasa.gov/mer2004/]JPL MER2004[/url] [url=http://www.spaceflightnow.com/mars/mera/statustextonly.html]Text feed[/url]
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The amount of solar radiation reaching the surface of the earth totals some 3.9 million exajoules a year.
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ronondexfan, more sails definitely gives you more benefit. The photon pressure equation is just flux / c (speed of light). So optimizing to one end of the spectrum won't do much good, you want to absorb the whole spectrum as much as you can. It may turn out that sails that are optimized to one end are lighter and therefore more efficient than sails that absorb more spectrum, though.
As far as adding a magnetic sail there's a wonderful concept called Dusty M2P2 that may be of interest. It uses a plasma to inflate the mag sail and if you put in little particles that reflect light it may be a successful propulsion method.
Google search for it: https://www.google.com/search?q=Dusty+M2P2
Thx a bunch!
I ask about the optimizing because of a post elsewhere here, somewhere, about the thrust increasing at the red end. It seems like taking maximum advantage of that is a good idea.
Last edited by ronondexfan (2012-09-08 19:58:05)
I'm going back to Atlantis.
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French Firm Raises $2 Million To Sail On Sunlight
https://www.theguardian.com/science/202 … olar-space
The French aerospace company Gama has raised 2 million euros to deploy a solar sail in space. The Guardian reports:
Solar sails require no engines to move. Instead, they are pushed around by the pressure of sunlight. The angle of the sail determines the direction of motion. Gama plans to deploy a 73.3-sq-meter solar sail in a 550km-altitude orbit in October. It will be launched as an additional payload on a SpaceX rocket.
Gama hopes to demonstrate that solar sails can revolutionize access to deep space because they are cost-effective and scalable in size. After this year's deployment test, the company plans to launch a follow-up mission in 2024 to a higher orbit to demonstrate control and onboard navigation. In 2025, it hopes to emulate the Japanese and fly to Venus.
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OKEANOS Oversize Kite-craft for Exploration and Astronautics in the Outer Solar system proposed mission concept to Trojan asteroids, which share Jupiter's orbit, using a hybrid solar sail for propulsion; the sail was planned to be covered with thin solar panels to power an ion engine.
https://web.archive.org/web/20161212135 … aworkshop/
another thread
'Japan launches Solar Sail - at last someone did it!'
'Magsail'
https://ghostarchive.org/archive/V8TiB
magnetic sail is a proposed method of spacecraft propulsion that uses a static magnetic field to deflect a plasma wind of charged particles radiated by the Sun
LEO to TMI - discuss
https://newmars.com/forums/viewtopic.php?id=2516
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