Solar super-sail could reach Mars in a month

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odysseus145

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Solar super-sail could reach Mars in a month<br /><br />A LICK of paint could help a spacecraft powered by a solar sail get from Earth to Mars in just one month, seven times faster than the craft that took the rovers Spirit and Opportunity to the Red Planet.<br /><br />Gregory Benford of the University of California, Irvine, and his brother James, who runs aerospace research firm Microwave Sciences in Lafayette, California, envisage beaming microwave energy up from Earth to boil off volatile molecules from a specially formulated paint applied to the sail. The recoil of the molecules as they streamed off the sail would give it a significant kick that would help the craft on its way. "It's a different way of thinking about propulsion," Gregory Benford says. "We leave the engine on the ground."<br /><br />Solar sails are in essence nothing more than giant mirrors. Photons of light from the sun bounce off the surface, giving the sail a gentle push. It was while developing a solar sail five years ago that the brothers stumbled upon their idea for enhancing the effect.<br /><br />The pair were testing a very thin carbon-mesh sail by firing microwaves at it. To their surprise, the sail experienced a force several times stronger than they expected. They eventually worked out that the heat from the microwave beam was causing carbon monoxide gas to escape from the sail's surface, and that the recoil from the emerging gas molecules was giving the sail an extra push.<br /><br />In a forthcoming issue of the journal Acta Astronautica, the Benfords explain how a sail covered with a paint designed to emit gas when it is heated might propel a spacecraft to Mars in just a month. A rocket would take the craft to low-Earth orbit, 300 kilometres up. After the craft unfurls a solar sail 100 metres across, a transmitter on Earth would fire microwaves at it to heat it up. The Benfords calculate a one-hour burst of <div class="Discussion_UserSignature"> </div>
 
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igorsboss

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Spaceter, here's your chance...<br /><br />Is there an Earth-Mars transfer orbit with a duration of 31 days or less?<br />
 
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najab

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(I'm not spacester, but I'll pretend to be)<p>><i>Is there an Earth-Mars transfer orbit with a duration of 31 days or less? </i><p> Yes. Given enough energy you can get to Mars in 15 minutes if you want. The question is, how much energy would it take? And how do you stop when you get there?</p></p>
 
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tap_sa

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I don't get it how hydrogen heated to just 1000C and released in somewhat uncontrolled fashion from some sort of hybride containing it would be better than heating it to, say, 3000C with concentrating mirrors attached to the spacecraft and then released through normal nozzle. Help, please?
 
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nexium

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Hi Tap_Sa: Except for closer to the sun than Mercury the mirrors have to be so large they produce some drag in space, to heat a gram of hydrogen per second to 3000 degrees c. 2 Sunlight does not focus into a tight beam, so a second set of mirrors (Perhaps a third) are needed to make the beam narrow enough to achieve 3000 degrees c at even 10% efficiency. 3 The 90% that is scattered overheats parts of the spacecraft creating engineering problems and possible failure. 4 The hydrogen tends to be transparent to the intense beam of light, so a minute mirror aiming error vaporizes the hydrogen holding vessel and/or the nozzle. 5 If the microwave beam (a laser beam is an alternative) is produced on Earth's surface, there is less mass to lift to orbit and it is workable small scale. I think your system is practical only very large scale, where it would, I think, be a good method. Neil
 
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tap_sa

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Hi nexium, thanks for detailed answer. Now let me try to tackle your points.<br /><br />1-3) Here is an example of terrestial solar furnace. Take a look at the specs, one megawatt, size of the parabolic reflector 1830 square meters. Total area of ISS solar panels is (or will be) 2500 square meters so it appears that drag will not be an issue, especially in interplanetary space. <br /><br />France furnace's maximum flux is 1000W/cm2 which is about 10000 times that of normal sunlight 1000W/m2. This happens to correlate very well with the fact that the parabolic mirror consists of 9130 indivual square mirror, which are probably flat and about 50x50cm in size. So efficient and relatively easy concentration of sunlight looks doable.<br /><br />Is one megawatt enough? Let's calculate how much your example needs. Hydrogen's specific heat capasity is 14304 J/kg*K. So let's assume we have a kilogram of it at it's boiling point (we probably want to store it as liquid but we can safely neglect the required heat of vaporisation, it's so small) and heat it 3300K, required energy is about 47 megaJoules, so to do the trick in a second we need 47 megawatts. Your gram needs only 47 kilowatts which is peanuts if we take the French furnace as a baseline.<br /><br />4) Yes this could be a problem. Instead of trying to contain the hydrogen in a transparent chamber and heat it directly we might have to conjure up more traditional heat exchanger, heat it with solar power and let it heat the hydrogen. How about tungsten tubing covered with graphite? Black graphite would soak solar energy like a sponge while tungsten tubing would safely contain the (high pressure?) hydrogen. Tungsten's melting point is over 3400C so it might survive the 3000C (which btw is just a nice round number which I randomly picked, maybe, say, 2500C would suffice). This would basicly be the nuclear NERVA engine with the nuclear part outsourced to the s
 
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nexium

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Hi tap_Sa: Tungsten and perhaps graphite evaporate significantly at 3000 degrees c, but I believe you can get about 1000 hours operating life at 2500 degrees c. Your numbers and thinking are convincing, even if the French have exagerated the specs of their solar furnace. The only additional objection is the propulsion would stop in the shadow of Earth or other planets and large moons, but I don't think that would be important to most missions, beyond LEO = Low Earth Orbit. What is delaying the building of a prototype solar furnace propulsion? The scattered light and heat could energize solar panels and/or thermal electric generation for auxillary systems. Can you give us more details on the heat exchanger including dimentions for one gram per second? For high specific impulse I think the hydrogen needs to be at high pressure as it leaves the heat exchanger. Boiling liquid hydrogen can produce extremely high pressure. Neil
 
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spacester

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<font color="yellow">>Is there an Earth-Mars transfer orbit with a duration of 31 days or less? [/yelow]<br /><br />Yes. Given enough energy you can get to Mars in 15 minutes if you want. The question is, how much energy would it take? And how do you stop when you get there? </font><br /><br />Hehehehe but we're gonna need those inertial dampeners online if you're gonna run the dilithium crystals that hot, cap'n! <br /><br />31 days to Mars the conventional way? Yeah, there's a mathematical solution. My software breaks down at 25 days because the ellipse you're calculating on is getting ridiculous.<br /><br />Speaking of ridiculous, here are the dV values (copy-n-paste):<br /><br />Delta V for away mission, burn 1 = 34.0210 km/sec<br />Delta V for away mission, burn 2 = 25.0367 km/sec<br />Delta V for away mission, Total = 59.0577 km/sec<br />Delta V for return mission, burn 1 = 29.6237 km/sec<br />Delta V for return mission, burn 2 = 30.3138 km/sec<br />Delta V for return mission, Total = 59.9374 km/sec<br /><br />It's less than 10.0 km/sec to LEO from Earth's surface, and that's plenty hard. You would need multiple stages and lots and lots of fuel.<br /><br />[BTW, arrggh! I lost a more clever post to Infopoop, that hasn't happened in a long time. Grr . . always use a text editor! Or at least copy the post text to clipboard, oops] <div class="Discussion_UserSignature"> </div>
 
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siarad

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<blockquote><font class="small">In reply to:</font><hr /><p>The deep-space communications network that NASA uses to communicate with Mars rovers and the Cassini probe now orbiting Saturn can only manage half a megawatt<p><hr /></p></p></blockquote><br />As that contains information it must be incoherent waves.<br />For the required straight power a coherent source would be used i.e. a MASER, although I don't know the power available currently.
 
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Swampcat

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<font color="yellow">"Delta V for away mission, burn 1..."</font><br /><br />I could be wrong, but didn't you say, once upon a time, that your program wasn't designed to deal with continuous boost propulsion? From the results you posted it would seem you are figuring short high-thrust burns rather than long low-thrust continuous boosting. <div class="Discussion_UserSignature"> <font size="3" color="#ff9900"><p><font size="1" color="#993300"><strong><em>------------------------------------------------------------------- </em></strong></font></p><p><font size="1" color="#993300"><strong><em>"I hold it that a little rebellion now and then is a good thing, and as necessary in the political world as storms in the physical. Unsuccessful rebellions, indeed, generally establish the encroachments on the rights of the people which have produced them. An observation of this truth should render honest republican governors so mild in their punishment of rebellions as not to discourage them too much. It is a medicine necessary for the sound health of government."</em></strong></font></p><p><font size="1" color="#993300"><strong>Thomas Jefferson</strong></font></p></font> </div>
 
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mooware

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<font color="yellow"> how do you stop when you get there </font><br /><br />That would be my question also.<br />
 
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najab

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><i>Hehehehe but we're gonna need those inertial dampeners online if you're gonna run the dilithium crystals that hot, cap'n! </i><p>I suppose 15 minutes is a <b>little</b> bit of an exaggeration - at closest approach that's 1/3 the speed of light! <img src="/images/icons/shocked.gif" /> I still haven't figured out how to stop when you get there though. <img src="/images/icons/smile.gif" /></p>
 
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spacester

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<font color="yellow">I could be wrong, but didn't you say, once upon a time, that your program wasn't designed to deal with continuous boost propulsion? From the results you posted it would seem you are figuring short high-thrust burns rather than long low-thrust continuous boosting. </font><br /><br />Ayup. That's what I meant by "the conventional way". It's the way we've done every interplanetary mission to date.<br /><br />The solution presented is Lambert's Solution for 31 days. Lambert's solution is the most efficient possible trajectory for a given trip time that cannot be achieved with a one-tangent trajectory. So the dV values are presented as comparison - the gravity losses associated with the Solar Super Sail would make the total dV even higher.<br /><br />I must note that the solution is not optimized for lowest possible dV. A value for the initial Mars-Sun-Earth angle (theta) must be chosen. The program selects a reasonable value for theta, but does not find the optimum theta. This is one reason why I do not often publish results for these "no-tangent" Lambert flights.<br /><br />In any case, trip times this short are IMO strictly Science Fiction. The vehicle concept described, from my quick read, still has to supply the propellant (but not the energy), and I don't see how the specific impulse can be a large value. Without very high Isp, you cannot bring enough prop (wing coating) to do anything like 31 days. <div class="Discussion_UserSignature"> </div>
 
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igorsboss

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So, this might be doable, but only if we restrict the lander to deep-impact style missions at Mars.
 
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vogon13

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Head for KBO in a flyby type mission. This technology seems more suited to quickly get you somewhere much further away than Mars. IIRC, Sagan advanced a light sail idea were a large sail went first a nd reflected laser energy back onto a trailing light sail to brake at destination. Don't suppose micrwave beam would stay tight enough for this to work at Mars to get you slowed down enough tp orbit. If technique turns out to be really efficient maybe you just take along ion drive and decelerate all the rest of the way to your destination and be at right speed to orbit when you get there. Not as fast but maybe more useful. <br /><br /><br /><br />...the firmament sheweth his handywork.<br />David <div class="Discussion_UserSignature"> <p><font color="#ff0000"><strong>TPTB went to Dallas and all I got was Plucked !!</strong></font></p><p><font color="#339966"><strong>So many people, so few recipes !!</strong></font></p><p><font color="#0000ff"><strong>Let's clean up this stinkhole !!</strong></font> </p> </div>
 
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tap_sa

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<font color="yellow">"What is delaying the building of a prototype solar furnace propulsion?"</font><br /><br />Probably the same reasons that are delaying more rapid space technology development in general. Those who would like to realize it have no money and those who have money are quite content with status quo. This technology would be clearly suited for interplanetary travel but all the stuff we send there now are relatively small probes which can be handled with existing conventional boosters.<br /><br /><font color="yellow">"Can you give us more details on the heat exchanger including dimentions for one gram per second?"</font><br /><br />Sorry, no <img src="/images/icons/smile.gif" /> Calculating and designing a real heat exchanger is out of my thermodynamical reach. But you might get some sort of picture by digging up stuff of the nuclear NERVA project:<br /><br />Wikipedia NERVA article <br /><br />That thing was seriously considered to replace the J-2 in Saturn V upper stage. Quite heavy and T/W just about one but Isp nearly 1000!<br /><br />The closed cycle gas-core engine is really interesting:<br /><br /><i> gasseous nuclear fuel is contained in a super-high-temperature quartz container, over which the hydrogen flows. The closed cycle engine actually has much more in common with the solid-core design, but this time limited by the critical temperature of quartz instead of the fuel stack. Although less efficient than the open-cycle design, the closed-cycle design is expected to deliver a rather respectable specific impulse of about 1500-2000 seconds.</i><br /><br />This got me wondering if it could be designed for solar energy source too. A quartz core, it's transparent right? We focus the solar megawatts inside it and heat the hydrogen there really, <i>really</i> hot before letting it go. Problem of hydrogen's transparenct was mentioned but what if we mix it something th
 
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