manned mission to Mars, favorite plans and architectures

[JonClarke]

Thanks for the feedback, much appreciated. <br /><br /><i>At first glance your plan looks very similar to the NASA DRM 1.0 except it's even more conservative, no nuclear power or nuclear propulsion. </i> <br /><br />The similarities are due to the common semi-direct architecture.<br /><br />We opted against nuclear power for three reasons. 1) the study was to be used for public outreach and we did not want to fight too many issues at once. 2) We wanted to examine the common assumption that nuclear power was necessary. 3) We wanted to minimise the amount of technology development required.<br /><br /><i>While your MTV reminds me of the MTV from the ESAS plan for Mars. Combining the MTV with Earth Return propulsion preserves certain abort options the DRM 1.0 lacks. </i><br /><br />Once again the similarities are due to the semi-direct architecture of the two studies.<br /><br /><i>I have two principle questions regarding your plan. The first is about crew size. Your payload masses appear very similar to those from the NASA DRM 1.0, but your mission is for only 4 crew while the NASA mission supports 6. The even smaller payloads of the NASA DRM 3.0 still supports a crew of 6. Are you being overly conservative with your estimates? Couldn't you easily accomodate a crew of 6? (Or alternatively cut your mass estimates by 1/3?) </i><br /><br />The size (and shape) or our lander modules were fixed, we sized the crew to what modules of this dimension could support. The landers mass ~60 tonnes in LEO and scale quite well to the ~80 tonne DRM 3.0 landers. <br /><br />The real difference is in the MTV. The DRM’s ERV massed 80 or so tonnes, ours 130. Even the difference in flight profile (we ferry the crew both ways) and design (we include an earth entry capsule) cannot account for this. We agonised over this but could find no way of reducing the mass any further using realistic numbers and margins from Larson and Pranke. Even then we cut a few corners in things like medical equipment an <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>

 

[scottb50]

Scottb50:<br />Using chemical propulsion means a pretty enormous spacecraft. It takes a lot of chemical propellants to do the job due to the limited ISP of even the best hydrogen/oxygen rocket engines.... <br /><br />I didn't say that. I may have been answering whoever wrote it.<br /><br />My point is LH2/LOX offers the highest ISp of any reasonably usable chemical propellant. If the idea is to take it with you water offers the easiest method of storage, it is easily storable, does not have to be kept crogenically cooled for extended periods or pressurized in heavy containers. Water would also be safe to launch and because water is needed for biological uses as well as propellant it is much simpler to have a single supply rather than various storage facilities and techniques.<br /><br />I also think Nuclear makes little sense as much for the reason you cite, the added mass of containment and shielding. Plus you would need a fluid to both cool the reactor and to be heated and expelled to produce the needed thrust. If you really look at the difference you would probably needed as much or more of whatever you use as you would need with water. Ideally Hydrogen would provide the best working fluid for a Nuclear engine, but the only way you could carry enough Hydrogen would be as a liquid and the amount needed for a round trip would require a pretty elaborate storage system in it's own right.<br /><br />With water you would have a source for electrical generation, using fuel cells, as well as human needs, radiation shielding and consumption. Waste water could be recycled through the fuel cells for re-use or highly contaminated water could be used to produce propellant. <div class="Discussion_UserSignature"> </div>

 

[gunsandrockets]

<The real difference is in the MTV. The DRM’s ERV massed 80 or so tonnes, ours 130...We agonised over this but could find no way of reducing the mass any further using realistic numbers and margins...This has massive implications for the EDS. Even switching to NTR, SEP and NEP does not make the EDS anything less than humungous. If anyone has suggestions on this we would be very attentive!><br /><br />Hmm...I might have a suggestion or two.<br /><br /><Mars Transfer Vehicle (MTV) LEO mass: 130 tonnes /> <br /><br /><It transports the crew from low Earth orbit to low Mars orbit with the crew. Capture into Mars orbit is by aerobrake and meets the Hab in low Mars orbit. The crew transfer to the Hab for landing. The MTV remains in low Mars orbit while the crew are on the surface. [MTV] transports the crew back to Earth from low Mars orbit. The crew land on direct earth in a capsule /><br /><br />Reducing the mass of the MTV is the first goal. I think I see one way that could be done. <br /><br />I see your MTV goes into Low Mars Orbit (LMO) for Mars Orbit Revendezvous (MOR); the first MOR with the Habitat lander and the second MOR with the Ascent Vehicle. After the second MOR the MTV does the Trans-Earth-Injection (TEI) burn for return to Earth.<br /><br />What if the MTV doesn't aerocapture into LMO? What if the Habitat Lander doesn't aerocapture into LMO? What if instead both vehicles aerocapture into a highly elliptical High Mars Orbit (HMO)? Instead of MOR in LMO, all the MOR would take place in HMO. This would create two important consequences, one negative and the other positive.<br /><br />The positive consequence is the MTV would not need as much propellant for the TEI burn to Earth. That saves from 1.2 to 1.4 km/s of delta-V from the TEI burn compared to a TEI burn from LMO. That could reduce the propellant load of the MTV by as much as 60%! (Aerocapture into HMO might also permit a less massive heatshield than aerocapture into LMO)<br /><br />The ne

 

[JonClarke]

Good morning, and thanks for th excellent comments to start the week with. With respect to the discussion items:<br /><br /><Mars Transfer Vehicle (MTV) LEO mass: 130 tonnes /> <br /><br /><i>Reducing the mass of the MTV is the first goal. I think I see one way that could be done. <br /><br />I see your MTV goes into Low Mars Orbit (LMO) for Mars Orbit Revendezvous (MOR); the first MOR with the Habitat lander and the second MOR with the Ascent Vehicle. After the second MOR the MTV does the Trans-Earth-Injection (TEI) burn for return to Earth. <br /><br />What if the MTV doesn't aerocapture into LMO? What if the Habitat Lander doesn't aerocapture into LMO? What if instead both vehicles aerocapture into a highly elliptical High Mars Orbit (HMO)? Instead of MOR in LMO, all the MOR would take place in HMO. This would create two important consequences, one negative and the other positive.<br /><br />The positive consequence is the MTV would not need as much propellant for the TEI burn to Earth. That saves from 1.2 to 1.4 km/s of delta-V from the TEI burn compared to a TEI burn from LMO. That could reduce the propellant load of the MTV by as much as 60%! (Aerocapture into HMO might also permit a less massive heatshield than aerocapture into LMO)<br /><br />The negative consequence is the Ascent Vehicle would have to add 1.2 to 1.4 km/s of delta-V to make a MOR with the MTV in HMO instead of LMO. But since the Ascent Vehicle derives it's propellant from ISRU the total impact on your Mars mission mass budget should be minimal. </i><br /><br />This is an excellent suggestion which would certainly help. Starting from a blank piece of paper this would be the way to go. We were constrained by 1) the chosen IRU method, and 2) the size and shape of the modules, however. <br /><br />We chose the methane – O2 production from imported hydrogen. This means a fixed amount of imported hydrogen for a certain propellant required. More propellant means more hydrogen and thus a larger tankage <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>

 

[gunsandrockets]

< I guess [STP] is probably the least developed of all the propulsion options, although I know it was used in the ERV proposal that won the Kepler prize (and have a copy of that lurking somewhere). Do you have any good references on it?><br /><br />No unfortunately. I'm still digging for more information myself. Surprisingly the U.S. Air Force is (or at least was) heavily involved in STP research. I'll try to dig up one of the links I've found before.<br /><br />Ah, here's something...<br /><br />http://www.stg.srs.com/atd/STP.htm<br /><br />http://www.bmpcoe.org/bestpractices/internal/nasam/nasam_32.html<br /><br /><br /><br />Regarding the Kepler Prize for ERV design, I've been trying to find information on the winning design. I'm stunned when you say that the design employs STP. I know there is information about that ERV in a CD-ROM included with the book, "On to Mars 2", but I don't have that book and even if I did I don't have a working CD-ROM drive right now.<br /><br />http://www.amazon.com/Mars-Exploring-Settling-World-Apogee/dp/1894959302/ref=sr_1_50/002-3889742-4488855?ie=UTF8&s=books&qid=1179052638&sr=1-50<br /><br />If you could share some details of that winning ERV design, I'd be grateful. So could you please post that information over at the ERV design thread?<br />

 

[JonClarke]

Sure! if I can find it, that is.... I think its own my work computer.<br /><br />Jon <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>

 

[qso1]

Scottb50:<br />I didn't say that. I may have been answering whoever wrote it.<br /><br />Me:<br />Sorry if I attributed the comment on enormous chemically propelled vehicles to you...this discussion has been a bit confusing lately.<br /><br />The idea of bringing water along to provide propellant seems almost too good to be true. I have to wonder why with all the experience we have with H2/LOX propulsion and fuel cells, why nobody has thought of doing this before. My proposals are simply for use in stories I write so I try to get as much technical stuff as possible into them. I don't have time, or the extended abilities to actually design or build a working system.<br /><br />Nuclear thermal would have only marginal advantages the way I see it. I went with a VASIMR type design which is plasma thats technically nuclear electric propulsion IIRC. The advantage was the theoretical ability to make a three month transit to mars. <div class="Discussion_UserSignature"> <p><strong>My borrowed quote for the time being:</strong></p><p><em>There are three kinds of people in life. Those who make it happen, those who watch it happen...and those who do not know what happened.</em></p> </div>

 

[spacester]

I'm going to put this a gently as I can. I like Scott a lot, but he still doesn't understand that you can't make propellant out of water as fast as he supposes. It takes a LOT of energy and power, and both are important constraints on real-world hardware. <div class="Discussion_UserSignature"> </div>

 

[qso1]

The one thing I recall is that water was a big concern as far as up mass on mars flights. And that was just drinking water. That was one of the reasons I had doubts. That is, if its that difficult from a mass standpoint to provide crew drinking water, what will it be for propellant?<br /><br />Of course, if water could be easily converted to propellant, the whole equation changes. But for now, it appears its more difficult than what Scottb50 may realize. <div class="Discussion_UserSignature"> <p><strong>My borrowed quote for the time being:</strong></p><p><em>There are three kinds of people in life. Those who make it happen, those who watch it happen...and those who do not know what happened.</em></p> </div>

 

[JonClarke]

Yep, just about everyone has this discussion with Scott sooner or later, without much success.<br /><br />Jon <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>

 

[scottb50]

Yep, just about everyone has this discussion with Scott sooner or later, without much success.....<br /><br />I think the reason is everyone thinks I mean you produce the LH2 and LOX at the same time you consume it. That has nothing to do with what I have been saying. What I have been saying is you transport the water to Space and convert just what you need for the next event during the times you aren't using any of it. <br /><br />While a Platform is blithely orbiting the planet it could be converting water and storing the LH2 and LOX cryogenically, that propellant would be used to insert the Mars Cycler into the transit orbit. While the Cycler is coasting towards Mars the propellant needed to enter LMO would be produced, and while in LMO propellant for the return boost phase would be produced, as well as that needed to send lander/ascenders to the surface and back.<br /><br />Everyone does understand that you don't have engines running constantly don't they? You travel in Space by going really fast and coasting, then the destinations gravity pulls you in faster and you have to use power to slowdown and enter orbit.<br /><br />You would have months to convert the water and with Solar powered cooling and relatively low storage needs boil off would simply be recooled. <br /><br />Which is where using fuel cells for electrical power comes in. The LH2 and LOX would be continuously returned to water and stored, it's just a matter of storing more propellant as you get closer to the time you need it. <br /><br />When compared to huge quantities of cryogenic liquids going round trip or even larger quantities of highly corrosive materials having to be stored for long durations water it makes a lot of sense. Water is simple to store and while you need crogenics for propellant the less you store at one time greatly effects to overall weight needed.<br /><br />Looking at Zubrins plan the complexity and mass needed to take LH2 into LEO then to Mars, months before it is reacted with the Mar <div class="Discussion_UserSignature"> </div>

 

[gunsandrockets]

<I think the reason is everyone thinks I mean you produce the LH2 and LOX at the same time you consume it.><br /><br />No, that's not it. We understand your water system.

 

[scottb50]

With a 1,000 watt/hr electrolyser it would take a year. Each array on the ISS provides 11kw/hr.<br /><br />http://www.dangerouslaboratories.org/h2homesystem.pdf <div class="Discussion_UserSignature"> </div>

 

[spacester]

Good for you Scott, that's what we're looking for, some solid numbers to chew on, actual hardware examples. If we can get you to play engineer just a bit more, you will find that I am your ally and your ideas just might gain traction. I've always liked your ideas, but my Engineering background always seems to interfere with my jumping on your bandwagon.<br /><br />Energy is force times distance<br />(newtons) * (meters) = Joules<br />N * m = J<br /><br />Power is measured in Watts and Kilowatts, it is the rate of energy delivery, energy divided by time<br />Joule / Second = Watt<br />also note that for electricity<br />Watt = Amp * Volts<br /><br />Energy is measured in Watt-hours and Kilowatt-hours, it is the accumulation of delivered power over a period of time. Since we divided energy by time to get power, we multiply power by time to get back to energy. It may seem backwards but that's the way it works.<br /><br />watt/hr and kw/hr are usually meaningless units: power divided by time is not something we are normally interested in. I have seen very experienced engineers make the exact same mistake. You need to multiply power by time to get energy.<br /><br />What you meant to say was that a 1000 watt electrolyser would take a year and that ISS arrays provide power at 11KW. Your cited paper says that operating the system at that power level will give us 170 liters / hour. <br /><br />http://www.physics.uci.edu/~silverma/units.html <div class="Discussion_UserSignature"> </div>

 

[scottb50]

What I meant to say is Solar energy can produce adequate power to electrolyse water in a reasonable time.<br /><br />As for the math I've never been patient enough with it. Just like your math on the Hohmann Transfer, I understand the concepts and the concepts involved. When it comes to laying out the math I can understand what it is showing, I just lack the patience to do the actual math. As a Chemistry Major in college I had to do it, but had to work hard at it. <div class="Discussion_UserSignature"> </div>

 

[j05h]

<i>> What I meant to say is Solar energy can produce adequate power to electrolyse water in a reasonable time. </i><br /><br />If it's for in-space transport, why bother? Just flash the water off in a solar-thermal rocket and don't worry about the Isp hit. Use the solar energy directly, with simpler, more robust systems.<br /><br />josh <div class="Discussion_UserSignature"> <div align="center"><em>We need a first generation of pioneers.</em><br /></div> </div>

 

[gunsandrockets]

<What I meant to say is Solar energy can produce adequate power to electrolyse water in a reasonable time. ><br /><br />The problem isn't time, the problem is the mass of the electric power system needed (no matter what type of power system) for cracking the water into hydrogen and oxygen propellant.<br /><br />And fuel cells do not use water to produce power; water is not an energy source. Water is merely a waste product of fuel cell power generation. Fuel cells are fed with oxygen and hydrogen, not water.<br /><br />All you accomplish by using water for propellant storage is to trade off potential boiloff for the extra mass of a super-sized power system. Instead of cracking water a smaller power system could provide active cooling of hydrogen and oxygen tanks during an entire mission. No large water-electrolyzing system would be needed either. <br /><br />

 

[gunsandrockets]

<If it's for in-space transport, why bother? Just flash the water off in a solar-thermal rocket and don't worry about the Isp hit.><br /><br />The ISP hit would be so bad with water that the ISP would be worse than hypergolic storable chemical propulsion. So why bother with Solar Thermal Propulsion (STP)?<br /> <br />Even ammonia propellant might only have an ISP of 375 seconds with STP. Which is no better than LOX/methane chemical propulsion, so why bother with STP?<br /><br />Methane propellant might make STP worthwhile, and methane could be produced with ISRU on Mars. Good performance with methane depends on the heat of the STP breaking the methane down into lighter molecular weight products. I'm not sure if that would work compared to ammonia which breaks down into nitrogen gas and hydrogen gas.

 

[scottb50]

All you accomplish by using water for propellant storage is to trade off potential boiloff for the extra mass of a super-sized power system. Instead of cracking water a smaller power system could provide active cooling of hydrogen and oxygen tanks during an entire mission. No large water-electrolyzing system would be needed either....<br /><br />When you include the water needed for biological and radiation protection needs your talking of massive cryogenic tanks for both LH2 and LOX as well as tanks for water. If you use smaller tanks for the LH2 and LOX and bigger tanks for water there is a bigger savings. Cryogenic storage has a lot higher structural need than does water, or ice. <br /><br />The other side of the picture is you need stable power for systems, in Space Solar power could provide it conntinuously, but in orbit or on the surface of a body you would need some sort of storage, batteries like used on the ISS. What I am suggesting is using fuel cells to provide continuous and stable electrical power, hydrolizers to break-down water and fairly modest cryogenic storage. Boil-off would be completely eliminated, simply run back through the fuel cells and stored as water. Waste water would be filtered and run through the the hydrolizers for purification as well.<br /><br />I see accomplishing at least four necessary functions with one basic system. No super-size power system would be needed and because hydrolizers and fuel cells are the same things, just wired in reverse it would be simple and cheap. <div class="Discussion_UserSignature"> </div>

 

[gunsandrockets]

Radiation shielding and life support consumables for a properly designed spacecraft are insignificant compared to the rocket engine propellant needed for a manned mission to Mars.<br /><br /><br />Let's look at a specific example of your proposed Mars spacecraft in orbit around Mars, to compare the benefits vs the costs of storing propellant in the form of water.<br /><br />One year before Mars departure, your electrolysis machine starts cracking water to fill your hydrogen and oxygen propellant tanks. The size of those tanks still must be large enough to hold enough propellant for when the rocket engine does the TEI burn. So no mass is saved in the size of the propellant tanks.<br /><br />During the one year period the propellant tanks take to fill, the contents of those tanks will be subject to boiloff losses. Which means those tanks must be highly insulated and/or employ active cooling measures to reduce boiloff. Still no mass savings.<br /><br />The potential boiloff rate for propellant tanks is not dependent on how full they are. As long as the tanks have some content they can still lose propellant. The loss rate depends on the size of the tanks, not on how full the tanks are. So during the one year period the tanks take to fill there is no advantage in potential boiloff losses.<br /><br />So much for the savings, now for the costs.<br /><br />Based on the propellant load for the ERV of NASA DRM 1.0 and 3.0 , the 'water rocket' will need anywhere from 24 to 42 tonnes of liquid hydrogen and liquid oxygen propellant. Using the more optimistic figure of 24 tonnes, for the electrolysis machine to crack 24 tonnes of water within one year means processing 66 kilograms of water per day into hydrogen and oxygen.<br /><br />According to the document ScottB50 provided, a 1000 watt power electrolysis machine can process 3.28 kilograms per day. So just to crack the water requires a power system delivering an extra 20,000 watts of electricity, in addition to all the other power n

 

[scottb50]

Radiation shielding and life support consumables for a properly designed spacecraft are insignificant compared to the rocket engine propellant needed for a manned mission to Mars.....<br /><br />I never said they were a major reason just that it makes sense to solve three different problem with a singe solution.<br /><br />One year before Mars departure, your electrolysis machine starts cracking water to fill your hydrogen and oxygen propellant tanks. The size of those tanks still must be large enough to hold enough propellant for when the rocket engine does the TEI burn. So no mass is saved in the size of the propellant tanks.....<br /><br />Again I didn't imply that. What I am saying is the same tanks can be drained and filled repeatedly. The savings would be in much simpler containment of water then required if you took alternate propellants with you. Cryogenics would require more than twice the storage and handling requirement as I'm proposing and to keep it liquid for an extended period would require a lot of energy. Even with Zubrins plan you need to take LH2 with you and take it to the surface to start the reaction. <br /><br />I would think short term minimal sized crogenic tanks would be less massive than either huge or mutiple tanks to contain the propellant for an extended period.<br /><br />During the one year period the propellant tanks take to fill, the contents of those tanks will be subject to boiloff losses. Which means those tanks must be highly insulated and/or employ active cooling measures to reduce boiloff. Still no mass savings....<br /><br />I never said it would take a year to fill the tanks, to begin with they would be in use continuously, providing LH2/LOX for the electrical system and boil off would be recycled either through the fuel cells or recooled. I would also think you would have to have an active cooling system to carry LH2 and Helium would be needed anyway to pressurize and transfer the liquids the only added mass would be in redundancy.<</safety_wrapper> <div class="Discussion_UserSignature"> </div>

 

[gunsandrockets]

I'm a glutton for punishment. Maybe if I only focus on one issue at a time I can make some headway...<br /><br /><I would think short term minimal sized crogenic tanks would be less massive than either huge or mutiple tanks to contain the propellant for an extended period. /><br /><br />No matter what scheme of filling or refilling you use, or how long it takes, you must have propellant tanks large enough to hold at least 24 tonnes of liquid hydrogen and liquid oxygen. There is no escaping that fact. You can't use smaller propellant tanks than that if you want to return to Earth.<br /><br />

 

[jimfromnsf]

I didn't see it mentioned that H2 engine mixture ratios are usually at 6 to 1 vs water's 8 to 1, which means O2 is left over for the crew

 

[gunsandrockets]

<I didn't see it mentioned that H2 engine mixture ratios are usually at 6 to 1 vs water's 8 to 1...><br /><br />How much lower would the ISP for LOX/LH2 be with a MR of 8?<br /><br />I found some information on thruster originally intended for Space Station Freedom. It is a 25 lbs thrust engine which runs on gaseous oxygen and hydrogen with a mixture ratio of 8. Highest tested ISP was only 360 seconds. <br /><br /><...which means O2 is left over for the crew /><br /><br />Based on an ERV minimum propellant load of 24 tonnes and assuming an ideal LOX/LH2 MR of 6, then using water for a storage medium means an extra 6.85 tonnes of oxygen beyond propulsion needs is carried.<br /><br />A six man crew would only consume 1.1 tonnes of oxygen during a sixth month trip from Mars to Earth. If the ERV pulled double duty by also carrying the crew from Earth to Mars, total oxygen consumption is then up to 2.2 tonnes. That's still leaves 4.65 tonnes of excess oxygen, or a deadweight of 18% of the combined propellant needs and oxygen needs.<br /><br />So if water is used as a propellant storage medium the efficiency of a LOX/LH2 rocket engine declines to the point where it is no better than a LOX/CH4 engine; or just as bad a deadweight of 4.65 tonnes has to be carried.<br /><br />Once again water strikes out as a propellant storage medium for a LOX/LH2 rocket.

 

[jimfromnsf]

But then again it had "unlimited" propellant and ISP didn't matter