Phobos First!

[gunsandrockets]

<The volume needed for hydrogen and methane are almost inverse with their LoX. In a given rocket (if the pumps and engines could do it) the LoX would be used in either tank, flying with LH in the larger tank with less LoX. When using CH4, the LoX would occupy the larger tank because methane is denser than hydrogen. This is vaguely remembered from a while ago, but would provide an interesting engine in a wider space economy.><br /><br />That volume relationship is an intriguing enough notion that I crunched the numbers myself to see if it really works out that way. It doesn't.<br /><br />Using the numbers for chilled propellant from the DunnSpace study, the volume relationships work out as follows...<br /><br />1) For LOX + methane, the LOX tank is 1.2 times larger than the methane tank.<br /><br />2) For LOX + hydrogen, the hydrogen tank is 2.7 times larger than the LOX tank. <br />

 

[keermalec]

I hate to sound like I´m defending an usubstantiated point of view but really I went to the pains of actually calculating the mass from the surface area of each tank before making my post.<br /><blockquote><font class="small">In reply to:</font><hr /><p>The numbers you use to describe both vehicle are off the mark. So of course your numbers give your hydrogen vehicle the edge -- considering your hydrogen vehicle devotes 24.5% of it's dry mass to propellant tanks and your methane vehicle only devotes 15.9% of it's dry mass to propellant tanks! Your methane vehicle suffers a 1/3 handicap. <p><hr /></p></p></blockquote><br />Obviously the LOX/LH2 vehicle has more tank mass than the LOX/LCH4 vehicle because, as you point out: Hydrogen has a very low density. To make things clear: I was comparing vehicles of equal wet mass (10 tons each, fully fuelled). I subtracted propellant mass from both to get the dry mass and did the comparison again (4 posts back). In both cases, LOX/LH2 gets more payload (in terms of ton/ton of dry mass OR in terms of ton/ton of wet mass) to LMO.<br /><br />If my calculations are incorrect I would be very happy to be proven wrong. This can be done by calculating the tank masses for LOX/LCH4 and LOX/LH from physical data (let us assume 1 square meter of tank surface is equal in mass for every propellant, and let us assume spherical tanks).<br /><br />Concerning CH4 availlability: the only source of H on Mars is water and you need H to make CH4. CH4 is therefore neither more availlable nor more easy to make than water. <--- you need 1 kg of H for every 12 kg of LOX/LCH4 produced. You actually need Oxygen too if you want to be producing the right ratio of LOX to LCH4 for combustion. <br /><br /><br />** So you need water to produce LOX/LCH4 from C02**<br /><br /><br />I am travelling right now so it is a bit difficult for me to go into lengthy calculations but for those who want to work it out for themselves and post the results:<br /><br /><br />CH4 density: 0.717 kg/m3 <div class="Discussion_UserSignature"> <p><em>“An error does not become a mistake until you refuse to correct it.” John F. Kennedy</em></p> </div>

 

[gunsandrockets]

<If my calculations are incorrect I would be very happy to be proven wrong.><br /><br />Sure! Let's beat this dead horse;-) I think it's refreshing to have a disagreement over something like this and still remain civil to each other (unlike some people who shall remain banned).<br /><br /><In both cases, LOX/LH2 gets more payload (in terms of ton/ton of dry mass OR in terms of ton/ton of wet mass) to LMO. /><br /><br />Okay lets try the dry mass exercise again. For starters I will use the numbers from your hydrogen vehicle.<br /><br /><<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<br />LOX/LH2 launcher <br />---------------------- <br />Inital mass: 10 tons <br />Isp: 465 seconds <br />Final mass from rocket equation: 3,54 tons <br />Vehicle structure: 0,4 tons <br />Tanks and tank structure: 0,59 tons <br />Engines: 1.4 tons <br />= /> Payload to LMO: 2,41 tons (or 24.1 % of inital mass) <br /> />>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>><br /><br />To make things very simple I will use the same final mass of 3.54 tonnes as the dry mass, which means your hydrogen rocket had a total of 6.46 tonnes of propellant. According to the DunnSpace numbers for chilled propellant, that is a total combined volume of 16.35 cubic meters of liquid oxygen and liquid hydrogen (at the ideal oxydizer to fuel ratio of 6 to 1).<br /><br />So for comparison I will calculate the final velocity in a free-fall envronment of your hydrogen rocket, then use the same dry mass and same volume propellant tanks for a methane rocket and calculate it's final velocity in a free-fall environment and see which rocket ends up faster.<br /><br />So a LOX/methane rocket with 16.35 cubic meters for propellant could hold 14.55 tonnes of chilled propellant at the ideal oxydizer to fuel mixture ratio

 

[gunsandrockets]

<Concerning CH4 availlability: the only source of H on Mars is water and you need H to make CH4.><br /><br />Seed hydrogen could be brought from Earth instead.<br /><br /><CH4 is therefore neither more availlable nor more easy to make than water. /><br /><br />The atmosphere can be profitably harvested anywhere the elevation is low on Mars. Wheras water ice is only profitably harvested 60 degrees or more away from the equater of Mars. And regolith processing machines are much heavier and more complicated than atmospheric compressors/cryocoolers.<br /><br /><--- you need 1 kg of H for every 12 kg of LOX/LCH4 produced. You actually need Oxygen too if you want to be producing the right ratio of LOX to LCH4 for combustion. /><br /><br />The problem of LOX production is solved by using methanol instead of methane. But even with methane the extra oxygen needed can be cracked from the martian atmosphere.<br /><br />Methane is far from the only choice or even the best choice of hydrocarbon fuel to use for In Situ Propellant Production. There is methanol, ethylene or propylene for example.<br /><br />The point is very little hydrogen is needed to harvest all the hydrocarbon propellant needed from the atmosphere of Mars, only 3.9% of the total propellant mass in the case of propylene. To get enough hydrogen for a LOX/hydrogen rocket require 14.3% of the total propellant mass in hydrogen.

 

[nexium]

Perhaps the first craft can have several options, with the decision at the last minute after analyzing the condition of the craft, the supplies, the crew and the fuel. <br />1 sling shot manuver around Mars to return to Earth as quickly as possible.<br />2 orbit Mars until an Earth return window.<br />3 Orbit or land on Demos or Phobos until an Earth return window.<br />4 Land on Mars if most everything is working.<br />Options 1 and 3 allow a gravity assist manuver around Mars. <br />5 Hope to survive on the surface until resqued years later. Neil

 

[j05h]

All of those modes are possible, but in what ways are they applicable to a Phobos mission? <br /><br />What are the reasons for and against going to the Martian Moons before Mars or Luna? There are advantages to Phobos (and Deimos) over Mars surface: predictable sunlight, somewhat familiar micro-G environment, use of some current technology, possible access to volatiles. This does not in any way mean no landings on Mars, it just puts landing off to build orbital infrastructure first. Also, see this in the context of "flotilla" operations - several entities go to Mars somewhat cooperatively. This is ideal as it creates an instant cis-Mars economy.<br /><br />What industries would be possible on these moons? Besides basing people, tele-operations and (maybe) water-mining, what do you see happening there?<br /><br />The main disadvantages to Phobos First is long-duration freefall health issues, the unknown dust environment and the limited knowledge of the moon. IMHO, if there is ice under the dust, Phobos (or Deimos) will be an immense resource hub some day. <br /><br />Orbital infrastructure, be it cached supplies and modules or ISRU fuel, even just rocket-stages-as-shelters, any of these can be a good leverage for people exploring and settling. <br /><br />In your scenario, the damaged craft from Earth would aerocapture, meet a tug and be transferred to the Phobos base. There the passengers and crew would either continue to Mars in a reusable craft, stay for a work-shift on Phobos or return on the next departing Earth-bound craft. That assumes an actual transportation system with expansion in design, not flags-n-footprints. <br /><br />My last point for now, and this goes for any Mars mission, is that they will be in 5+ year contracts. It will always be expensive to get there, both corporations and governments will have incentive to maximize the investment in their crews, and various settlers and claimstakers will trade money and labor for transport. Would you work for HydroAres <div class="Discussion_UserSignature"> <div align="center"><em>We need a first generation of pioneers.</em><br /></div> </div>

 

[j05h]

<i>> We have mastered the technique of storing LH and LOX for long periods of time (years) using active cooling. Zubrin's LOX/CH4 idea was valid before actived cooling became reality.</i><br /><br />What kind of infrastructure is needed on Phobos or Mars for storing LH? Large-scale storage on Earth is heavy-industrial - aerospace components are generally to fragile in that context. Mars is more active in that context than Phobos, so perhaps rocket stages could be reused as orbital storage. Is the demonstrated active cooling of a few tons or 1000s of tons of active-cooled LH? What fuel is the best for scalable operations? The right fuel for a 4-person base may be much different than for settlement/mining operations.<br /><br />One interesting thing in the news the other day was bacterial production of hydrogen gas. It works, and it apparently works well. I stand corrected. It still doesn't solve LH storage cis-Mars, just production. <br /><br />One thing I posted about somewhere recently was using methane hydrate ices as storage. Solid, relatively shelf-storable fuel could be incredibly useful. If it's a wrapped slug of methane-ice fed into a fuel cell, it could be extremely safe in operation. What are other solid/storable ISRU fuels that could be made cis-Mars?<br /><br />Josh <div class="Discussion_UserSignature"> <div align="center"><em>We need a first generation of pioneers.</em><br /></div> </div>

 

[nexium]

Hi Josh: Clearly, we need more information about Deimos and Phobos. My thinking was, the first manned flight should leave Earth equally prepared for those 5 options and let the crew decide upon arrival. Clearly land on Mars has better PR value and that is important to get funding for future missions in space. The desisions for the 2nd and third manned missions depend somewhat on what the earlier missions did, but more important what is reasonably safe for the crew. 1 Land on an asteroid is my first choice, but it has poor PR value and is an unlikely alternative, if safety is marginal part of the way to Mars.<br />A hundred robotic factories can be landed on Phobos, Deimos and Mars before the manned mission. There is some doubt that humans will land close to a robot factory. Considerable doubt that the factory will function properly, or even be repairable with the help of humans. We should build some robot factories on Earth and see if they can produce useful output without humans on site. Has there been even one successful demostration so far? To keep costs low, humans could push the robotic factory off a moving truck to see if it can orient it's self and start producing from the dirt and gravel it landed on. If that works, we can then drop the facory in artifical moon dust.<br />Unless we can get a major breakthough, the early manned missons to Mars will have only tiny mass surplus for factory prototypes which may not perform usefully.<br />There is some possibility that a break though will allow emergency return to Earth less than a year after departure. Five years seems risky to me. Neil

 

[keermalec]

<blockquote><font class="small">In reply to:</font><hr /><p><If my calculations are incorrect I would be very happy to be proven wrong.> <br /><br />Sure! Let's beat this dead horse;-) I think it's refreshing to have a disagreement over something like this and still remain civil to each other (unlike some people who shall remain banned). <br /><br /><In both cases, LOX/LH2 gets more payload (in terms of ton/ton of dry mass OR in terms of ton/ton of wet mass) to LMO. /> <br /><br />Okay lets try the dry mass exercise again. For starters I will use the numbers from your hydrogen vehicle. <br /><br /><<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<< <br />LOX/LH2 launcher <br />---------------------- <br />Inital mass: 10 tons <br />Isp: 465 seconds <br />Final mass from rocket equation: 3,54 tons <br />Vehicle structure: 0,4 tons <br />Tanks and tank structure: 0,59 tons <br />Engines: 1.4 tons <br />= /> Payload to LMO: 2,41 tons (or 24.1 % of inital mass) <br /> />>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> <br /><br />To make things very simple I will use the same final mass of 3.54 tonnes as the dry mass, which means your hydrogen rocket had a total of 6.46 tonnes of propellant. According to the DunnSpace numbers for chilled propellant, that is a total combined volume of 16.35 cubic meters of liquid oxygen and liquid hydrogen (at the ideal oxydizer to fuel ratio of 6 to 1). <br /><br />So for comparison I will calculate the final velocity in a free-fall envronment of your hydrogen rocket, then use the same dry mass and same volume propellant tanks for a methane rocket and calculate it's final velocity in a free-fall environment and see which rocket ends up faster. <br /><br />So a LOX/methane rocket with 16.35 cubic meters for propellant could hold 14.55 tonnes of c</p></blockquote> <div class="Discussion_UserSignature"> <p><em>“An error does not become a mistake until you refuse to correct it.” John F. Kennedy</em></p> </div>

 

[keermalec]

<blockquote><font class="small">In reply to:</font><hr /><p>Is the demonstrated active cooling of a few tons or 1000s of tons of active-cooled LH?<p><hr /></p></p></blockquote><br />Active coolling is not really that complex: your fridge does that for you every day. In the case of LH the heat exchanger is just much more powerful.<br /><br />The experiment shown here cooled only a few hundred kg of LH but the technique seems readilly adaptable to large amounts. In fact, large anounts of LH or LCH4 should be easier to keep cool as the surface to mass ratio is much smaller. <br /><br />According to numbers derived from Borowski, additional insulation and regrigeration system amount to a 21% increase in tank mass, plus a power supply providing 111 Electricity Watts per ton of LH.<br /><br />For LOX the requirements are much lower (due to increased density and higher boilling temperature) and liquid methane seems to be similar to LOX: +11% tank mass and a power supply providing 4.3 We per ton of LOX.<br /><br />Tank mass being around 14% of LH mass (for a 50-ton tank) and 2.5% of LOX mass, the additional tank mass for added insulation per ton of propellant is actually quite small.<br /><br />This study shows that boiloff in LEO (less favorable than the martian surface due to higher temperatures) is about 1% per month WITHOUT active cooling. According to the first study cited above, active cooling completely cancels all boiloff. <div class="Discussion_UserSignature"> <p><em>“An error does not become a mistake until you refuse to correct it.” John F. Kennedy</em></p> </div>

 

[keermalec]

Planned Phobos missions:<br /><br /><br />Canadian PRIME mission<br /><br />Russian-chinese Phobos-Grunt mission<br /><br /><br />No planned NASA missions to Phobos at the moment :-( ...<br /><br /><br />Should we be concerned with the fact that none of these missions involves drilling for water? Day temperatures in Mars orbit are around 40° Celsius, therefore if water exists in the moons it will necessarily be many meters down.<br /> <div class="Discussion_UserSignature"> <p><em>“An error does not become a mistake until you refuse to correct it.” John F. Kennedy</em></p> </div>

 

[gunsandrockets]

Interesting article on the PRIME mission. I had never heard of the Phobos 'monolith' before!<br /><br /><br /><Should we be concerned with the fact that none of these missions involves drilling for water? Day temperatures in Mars orbit are around 40° Celsius, therefore if water exists in the moons it will necessarily be many meters down. /><br /><br />I forget where I read it, but one source speculated that if there is ice it would lay at the shallowest depths at the polar regions of the martian moons. Maybe as little as 10 meters under the surface.<br /><br />For this reason I favor unmanned missions to Phobos and Deimos that would use the impactor + flyby observer method of the Deep Impact comet mission. The impactor would be aimed at the polar regions and hopefully would blast out signs of water or ice. <br />

 

[gunsandrockets]

<I was wrong, methane is better than hydrogen ;-) ><br /><br />Only in the very limited circumstances (dry mass etc.) described of course<br /><br />If you wanted to do a hydrogen rocket mission to the Martian surface, the polar region is the place to do it. In fact I just came across a fascinating essay describing the supposed advantages of aiming the first Mars landing at the north pole instead of more typical equatorial locations...<br /><br />Polar Landing Site for a First Mars Expedition<br /><br />... the advantages in terms of solar power (!) would have never occurred to me. I think you might find it an interesting read.

 

[gunsandrockets]

<What kind of infrastructure is needed on Phobos or Mars for storing LH?><br /><br />Interesting question.<br /><br />It occurs to me that even if Phobos/Deimos does not have the volatiles hoped for, Phobos could still provide a usefull propellant related function -- the easing of cryogenic storage (and of liquid hydrogen in particular).<br /><br />Let's say we have a vehicle in orbit around Mars which has a large tank filled with liquid hydrogen. Even as far from the Sun as Mars is, conventional passive-cooling boils off propellant thereby forcing a reliance upon active-cooling. But what if Phobos is used as a gigantic Sun-shield?<br /><br />Staying in the shadow of Phobos, the only light hitting the hydrogen tank most of the time would be sunlight reflecting off of Mars. Only during brief windows would direct sunlight fall upon the spacecraft. This advantage could reduce the mass of sunscreens needed on the vehicle and improve the efficiency of active cooling.

 

[keermalec]

<blockquote><font class="small">In reply to:</font><hr /><p>Let's say we have a vehicle in orbit around Mars which has a large tank filled with liquid hydrogen. Even as far from the Sun as Mars is, conventional passive-cooling boils off propellant thereby forcing a reliance upon active-cooling. But what if Phobos is used as a gigantic Sun-shield? <p><hr /></p></p></blockquote><br />hm, I did the check: an object orbiting Phobos would have to orbit with a period of 1.01 Earth days to stay in its shadow at all times, as this is the period of Phobos around Mars. ( corrected on 11/19/07 to 0.32 days).<br /><br />To do so it would have to orbit 54 km from the center of Phobos but... orbits around Phobos are only stable up to 17 km (Hill Sphere calculation). Therefore it would not be possible to stay in the shadow of Phobos without expending fuel continuously to do so.<br /><br />At a more advanced stage we may be able to build tanks into Phobos, thereby using its regolith as shielding material. it does seem excessive though when one considers that even without active coolling propellant loss is under 1% per month and an active cooling installation would add a mass penalty of only a few percent of propellant mass. <div class="Discussion_UserSignature"> <p><em>“An error does not become a mistake until you refuse to correct it.” John F. Kennedy</em></p> </div>

 

[keermalec]

<blockquote><font class="small">In reply to:</font><hr /><p>If you wanted to do a hydrogen rocket mission to the Martian surface, the polar region is the place to do it. In fact I just came across a fascinating essay describing the supposed advantages of aiming the first Mars landing at the north pole instead of more typical equatorial locations... <p><hr /></p></p></blockquote><br />I am totally in favor of a polar landing. For several reasons top of which is the fact that at the poles water can exist in non-protected ice form. As water ice sublimates at 198 K uner martian atmpspheric pressure and the poles have a lower temperature all year round, there is necessarilly permanent uncovered or very lightly covered ice at the poles. <br /><br />If you really want to mine for CO2 (to produce methane for example ;-)) then CO2 ice also exists there in great quantities. <div class="Discussion_UserSignature"> <p><em>“An error does not become a mistake until you refuse to correct it.” John F. Kennedy</em></p> </div>

 

[keermalec]

<blockquote><font class="small">In reply to:</font><hr /><p>I forget where I read it, but one source speculated that if there is ice it would lay at the shallowest depths at the polar regions of the martian moons. Maybe as little as 10 meters under the surface. <br /><br />For this reason I favor unmanned missions to Phobos and Deimos that would use the impactor + flyby observer method of the Deep Impact comet mission. The impactor would be aimed at the polar regions and hopefully would blast out signs of water or ice.<p><hr /></p></p></blockquote>This paper suggests that ice could exist on Phobos 100m below the surface in equatorial regions, and 20m below the surface in polar regions. I like the impact idea but a crater 20m deep requires a mother of an impactor and what about all the high speed debris we shall be placing in martian orbit? <br /><br />This 1993 project had I think the right approach to diagnosing Phobos, but it should be equiped with a longer drill. <div class="Discussion_UserSignature"> <p><em>“An error does not become a mistake until you refuse to correct it.” John F. Kennedy</em></p> </div>

 

[thereiwas]

"with a period of 1.01 Earth days"<br /><br />According to my reference the period of Phobos is 7 hours 39.2 minutes. ("The hurtling moons of Barsoom".) You may be confusing it with Mars's own rotation, which takes 1.025 days. But I suspect your conclusion still applies - a stable orbit around Phobos at <i>any</i> altitude is not stable, because Phobos is not close to spherical.

 

[keermalec]

<blockquote><font class="small">In reply to:</font><hr /><p>According to my reference the period of Phobos is 7 hours 39.2 minutes. ("The hurtling moons of Barsoom".) You may be confusing it with Mars's own rotation, which takes 1.025 days. But I suspect your conclusion still applies - a stable orbit around Phobos at any altitude is not stable, because Phobos is not close to spherical. <br /><p><hr /></p></p></blockquote><br />Perfectly right ThereIwas, I had entered a mass of 0.0107 for Mars instead of 0.107. Phobos period is 0.32 days and not 1.01. Highest "stable" orbit around Phobos would be 17 km from center, which would give an orbital period of only 0.18 days so the problem remains.<br /><br />Thanks for the correction. <div class="Discussion_UserSignature"> <p><em>“An error does not become a mistake until you refuse to correct it.” John F. Kennedy</em></p> </div>

 

[gunsandrockets]

<This paper suggests that ice could exist on Phobos 100m below the surface in equatorial regions, and 20m below the surface in polar regions.><br /><br />Ah yes, that's the same source I was thinking of. Okay so we are considering an optimum depth of 20m instead of 10m.<br /><br /><I like the impact idea but a crater 20m deep requires a mother of an impactor /><br /><br />Well the proposed THOR mission supposedly could gouge a 9m deep crater on Mars, and this from an impactor dropped from low-Mars-orbit. A flyby impactor aimed at Phobos/Deimos could hit head-on thereby adding the orbital velocity of the moon to the power of the collision. I would think 20m well within the possible depth of penetration.<br /> <br /><and what about all the high speed debris we shall be placing in martian orbit? /><br /><br />Hmmm... that's something I hadn't considered. Much of the debris would be of sub-orbital velocity since it would be the product of a head-on collision and should fall out to Mars. But some of the debris might form a dangerous lingering orbital ring.<br /><br />Perhaps such a impactor mission should be limited to only Phobos because of Phobos much lower orbit. That way any orbital debris created would decay to Mars in the least amount of time.<br /><br />I think the temporary added risk to orbiters already circling Mars from impactor debris would be worth the science return.<br /><br />One could even get more ambitious and instead of the flyby observer just watching the impact event with remote sensing devices, it could also fly through the debris cloud and collect samples with aerogel panels for return to Earth. A sort of super-cheap Phobos sample return mission! You could call it Deep Sampler;-) <br /><br />

 

[gunsandrockets]

<I am totally in favor of a polar landing.><br /><br />I am intrigued by the Landis proposal, but I worry about the stability of the landing zone.<br /><br />I mean, odds are Martian polar ice is as sturdy as the stuff which supports the landing of C-130 cargo planes in Antarctica. But considering the low gravity and the strange sublimation process of ice movement on Mars I would feel a lot more secure about a manned mission by littering the polar region with unmanned landers first!

 

[gunsandrockets]

<To do so it would have to orbit 54 km from the center of Phobos but... orbits around Phobos are only stable up to 17 km (Hill Sphere calculation). Therefore it would not be possible to stay in the shadow of Phobos without expending fuel continuously to do so.><br /><br />I should have been more clear. I was thinking of parking the spacecraft on the surface of Phobos rather than in orbital free-fall.<br /><br />At one time I thought maybe a spacecraft could orbit in the moon's shadow by placing itself at the Mars-Phobos-Lagrange-Point-1 position. But I discarded that notion when I realized the problem of the difference between the axial tilt of Mars vs the inclination of Phobos orbit around Mars. For a spacecraft just orbiting Mars, Phobos would hardly ever get in the way of the Sun.<br /><br />So the obvious solution is to park the spacecraft on the surface of Phobos which faces Mars. Perhaps even at the bottom of a shadowed crater?

 

[j05h]

<i>> So the obvious solution is to park the spacecraft on the surface of Phobos which faces Mars. Perhaps even at the bottom of a shadowed crater?</i><br /><br />I already called "dibs" on Stickney Crater! <img src="/images/icons/wink.gif" /> Phobos is tidally locked to Mars with this massive crater facing the planet. I want to dome it and store water there, long-term. It's not permanently shadowed but is quite deep.<br /><br />josh<br /><br />Josh <div class="Discussion_UserSignature"> <div align="center"><em>We need a first generation of pioneers.</em><br /></div> </div>

 

[scottb50]

I don't see any reason for large LH2 tanks or long term storage of Hydrogen or Oxygen as liquids. Water is a pretty benign way to keep both, either as a liquid or solid as ice.<br /><br />LH2 and LOX can be hydrolyzed and stored temporarily, as needed. Much less infrastructure needed. <div class="Discussion_UserSignature"> </div>

 

[keermalec]

<blockquote><font class="small">In reply to:</font><hr /><p>I don't see any reason for large LH2 tanks or long term storage of Hydrogen or Oxygen as liquids. Water is a pretty benign way to keep both, either as a liquid or solid as ice. <p><hr /></p></p></blockquote><br />Perfectly good point. The question is: how much would a hydrolysing station mass? And what would be its LOX/LH production rate?<br /><br />And if we're talking about shipping Phobos-mined propellant back to LEO, then water is also the best form, due to its (relatively) high density and (relatively) high boiling point. <br /><br />This actually allows me to bridge with my real idea (based on a proposal by David Kuck in 1997) which is: finance the inhabited Mars mission by selling robot-extracted Mars/Phobos/Deimos propellant in LEO. After all the cost of propellant in LEO is 10'000 USD per kg (the launch from Earth cost) and launch from Earth involves a delta-v of around 10 km/s with very high accelerations. Launch from Phobos to LEO, even if it takes longer, involves a delta-v of only 2.4 km/s and potentially very low accelerations.<br /><br />Assuming (lets be crazy) a mission that returns 100 tons of propellant from Phobos to LEO, and assuming there is a short term market for it in LEO (de-orbit propellant for shuttles to and from the ISS and Bigelow's space hotel?), the question is: can it be done for less than 1 billion USD (100'000 kg x 10'000 USD)? <div class="Discussion_UserSignature"> <p><em>“An error does not become a mistake until you refuse to correct it.” John F. Kennedy</em></p> </div>