Riding to Mars in a capsule?

[gunsandrockets]

"You can design a perfectly adequate ISRU plant to supply a four person, 600 day mission with 14 tonnes of LOX-methane for an ascent stage, over 2 tonnes of CO-O2 propellant for a rover, 0.5 tonnes of O2 and over 7 tonnes of water for the crew, using 20 kW. This would require a 550 m2 sized flat solar array on Mars, with a 25% margin, deployable as a mat from a roll by a small rover. These would mass, using conservative estimates, 2.2, with another 0.5 tonnes for batteries. State of the art reactors for the same amount of power would mass about 4 tonnes, and would need to be deployed at least a km away, requiring complex handling and deployment systems. Compared with a reactor a solar array is simpler, much more reliable and much more mature technology."<br /><br />2.7 tonnes for a 20 kW solar power system? Why is the solar power system of the ISS so much more massive? And wouldn't your flat array only deliver 20 kW during daylight? At noon? During Summer? And when the solar power panels are clean of dust? What would the average power output be over 300 martian days? Maybe only 5 kW?<br /><br />I'm also curious about your nuclear reactor power plant numbers. If it takes a 4 tonne system to generate 20 kW, how does that compare with the JIMO spacecraft? As near as I can recall the JIMO nuclear electric powered spacecraft would have had a total mass of around 20 tonnes and a power of 100 kW. And that inlcudes all spacecraft mass including ion engines and xenon propellent, plus the extensive radiator array the JIMO reactor needed to shed excess heat in the vacuum of space.<br />

 

[j05h]

>NASA is having trouble at the moment paying for developing the CEV while operating the shuttle and ISS, so how are they ever going to be able to fund a mars mission when they are paying for the enormous costs of keeping a moon base and perhaps the ISS (or its successor) at the same time? <br /><br />I think that NASA HQ is slowly positioning itself to cancel STS and change what it does with ISS. I dont' think they are going to end participation in station, but for budgetary reasons are dropping science, new modules, etc. They have already cancelled flying complete hardware: Centrifuge and Cupola are gone, the Cupola is sitting at KSC, ready to go. A space tug like Parom (or a US equiv) being developed near-term would make this problem a lot easier/cheaper to solve.<br /><br />Moon/Mars can be done. From a survival sense, must be done. If NASA and RKS are going to be a part of it, they must, must become smarter about use of resources. I'm concerned about simple competency in both space agencies, sorry guys, but you keep screwing up. If we really want to settle Mars, I think we need to discuss a "NAFTA", at least in aerospace, between the US and Russia. It's a bit radical, sure, but would have an immense impact on commercial space over the next decades. We hold the keys to the solar system in separate hands. Do we have what it takes to unlock the door? The Vikings didn't have what it took to "unlock" the Americas, but the Portugeuse and Spanish did. Where do we stand?<br /><br />Josh <div class="Discussion_UserSignature"> <div align="center"><em>We need a first generation of pioneers.</em><br /></div> </div>

 

[JonClarke]

According to the every helpful astronautix site, the empty S-IVB massed about 13.5 tonnes. The J-2 massed 1.5 tonnes, so the shell and tankage come in at about 12 tonnes. It is the fittings of a crewed spacecraft that are massive - airlocks, consumables, attitude control, life support, power etc. etc.<br /><br />That's why I am really interested to see a mass breakdown of Nautilus, to see what weactually get for the 23 tonnes.<br /><br />That said, I hope they fly these things. people have been talking about inflatables for at neary 60 years, it's time to try them out.<br /><br />Jon<br /><br /> <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>

 

[JonClarke]

The problem with developing NTR is is that we would have to start the infrastructure almost from scratch. It has been more than 30 years since the US lasted tested an NTR, it is more than 20 years since the Russians did, although I must check this. So the expertise is now retired. The physical infrastructure is now derelict, and in the case of the US facility at Jackass Flats, completely unacceptable - tests were conducted in the open air. The Russians at least tested underground<br /><br />Alot of testing will be needed to, the demonstrated reliability of a NTR must exceed by orders of magnitude a chemical rocket. The pricture of Kiwi exploding and ejecting burning core fragments needs to be imprinted in the mind of every would be nuclear rocket scientist. As understanding the NERVAs got close to this, but this would have to be shown for a whole new system. The test facility must demonstrate complete containment for routine operations and maximum credible accidents.<br /><br />Then I can't see the community accepting anything other than complete containment of the reactor in flight for the maximum credible accident. I suggest this would include uncontrolled reentry of a malfunctioned reactor at 12 km/s. I can't see anything less than zero emissions being accepted either. While I understand that the core erosion problem was largely solved, loss of volatile fission products (the real nasties, may be unsolvable.<br /><br />Then there issue of flight containts. For safety issues NTRs would have to be started in high orbit. this immediately reduces their mass ratio advantages. Once spent, they would have to be moved into stable very high or solar orbitorbits - further inefficiency. Add the mass of even a minimum shadow shield and the advantages, once attractive, really whittle away.<br /><br />Plus the technology does not scale well, there is a minim size. This greatly reduces the range of missions the technology can be applied to.<br /><br />NEP does not suffer <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>

 

[JonClarke]

The reason the ISS solar panels are so massive is because of the support structure they need. On Mars, or the moon, large solar arrays can be unrolled and laid on the ground. The 4 kg/m2 used in the study was quite conservative.<br /><br />For reactor mass I use the most advanced design that has actually flow in space, the Topaz. This produced 6 kW on 1.25 tonnes for the entire reactor system (the core of course was much less)<br /><br />So four Topaz reactors (you would need more than one reactor for redunancy anyway would actually give you 24 kW) on 5 tonnes, so I was being generous.<br /><br />I suspect that reactors will be essential in lunar bases away from the poles because of the long lunar night. It may be that experience with these means that when we do go to mars that the issues of deploying and operating small reactors may have been solved so that they are viable for mass as well.<br /><br />However, all I am saying is that, based on what we now know to have a mass competative small ISRU plant that runs on a solar power system. Plus there are many issues with a nuclear system that this would avoid.<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>

 

[gunsandrockets]

"According to the every helpful astronautix site, the empty S-IVB massed about 13.5 tonnes."<br /><br />Rodger that.<br /><br />"That's why I am really interested to see a mass breakdown of Nautilus, to see what weactually get for the 23 tonnes. "<br /><br />I'm guessing the use of newer high-strength materials, which the Skylab did not use, and more advanced solar cell technology will give the Nautilus a significant mass advantage. Maybe the Nautilus will even make use of electric propulsion for station keeping.<br /><br /><br />

 

[gunsandrockets]

"However, all I am saying is that, based on what we now know to have a mass competative small ISRU plant that runs on a solar power system."<br /><br />Hmmm...using your figures I might agree that solar is in the ballpark but even so is still inferior to nuclear power by mass.<br /><br />Your theoretical 20 kW solar power system "with a 25% margin" masses 2.7 tonnes. This is compared to a real world power reactor from 1970's Soviet technology, "For reactor mass I use the most advanced design that has actually flow in space, the Topaz. This produced 6 kW on 1.25 tonnes for the entire reactor system".<br /><br />Your solar power system would generate 25 kW under ideal conditions. But conditions are not ideal on Mars most of the time. Since it's dark half the time the average power level is only half, 12.5 kW. And since there is no pointing or tracking system for the solar panels, even during the daylight hours the solar panels won't generate peak output most of the time. A generous estimate reduces the average power output from 12.5 kW down to 9.5 kW. Finally take another 10% off for dust obscurance of the solar power panels and that leaves you with a final average output of roughly 8.5 kW for a mass of 2.7 tonnes.<br /><br />So in the end the theoretical solar power system gives an average of about 3.2 Watts per kilogram of mass. Wheras the real world Topaz reactor gives an average of about 4.9 Watts per kilogram of mass.<br /><br />And since cooling a reactor would be easier on the surface of Mars than orbiting in the hard vacuum of low Earth orbit, I bet a purpose designed reactor to power Mars ISRU could improve on the performance of the old Topaz by quite a bit. <br /><br />"I suspect that reactors will be essential in lunar bases away from the poles because of the long lunar night."<br /><br />If you mean powering life support I agree. For powering ISRU, solar power works better on the moon than on Mars. Dust isn't as big a problem on the moon and the light is bri

 

[gunsandrockets]

I think you are loading down NTR with too many pessimistic assumptions. Many of your objections are already met by new design concepts for NTR. The new midget NTR designs are designed to ease testing needs, and the U.S. has extensive underground testing facilities for nuclear devices.<br /><br />http://www.nuclearspace.com/A_HEADNA.HTM<br /><br />http://www.nuclearspace.com/A_PWrussview_FINX.htm<br /><br /><br /><br />

 

[JonClarke]

I confess I was surpised at how little the basic pressure structure of Skylab did weight. Keep in mind that this was not a pressure vessel optomised for human missions but as a LH2 tank.<br /><br />What the 12 tonne mass means is that the pressure hull was only 16% of Skylab's mass. Even if an inflatable pressure hull masses only half this it saves only 6 tonnes, leaving a Skylab equivalent wighting 71 tonnes. <br /><br />Of course a 6 tonne saving is still is very significant. However I notice that all drawings of spacecraft using inflatbale modules seem very careful to to show equipment like thrusters, radiators, solar panels, antennae, aerials, etc., attached to the inflatable part, as they would on a rigid hulled spacecraft. I assume a Bigelow style module would need some kind of additional truss structure to support these. These would detract from some of the mass savings with a ligther hull, I think.<br /><br />"I'm guessing the use of newer high-strength materials, which the Skylab did not use, and more advanced solar cell technology will give the Nautilus a significant mass advantage. Maybe the Nautilus will even make use of electric propulsion for station keeping."<br /><br />I would also guess that these innovations would equally apply to rigid hulled modules as well.<br /><br />Jon<br /><br /> <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>

 

[JonClarke]

POWER REQUIREMENTS<br /><br />To produce the reference resources needs a 110.4 mW-h. Provided the resources are available when they are needed it does matter whether they are produced by a power source operating continuously, or by one operating for a few (in the reference case 10) hours a day. <br /><br />You are quite right, a nuclear powered system could operate continuously. The reference plant consumes 200 kWh per day. Topaz produces 144 kW over 24 hours, therefore a 9 kW improvement to Topaz would be needed, massing 1.875 tonnes. BUT you need complete redundancy with uclear power, given the risk of complete failures. So two reactors are needed totallying 3.75 tonnes, still more than a solar array. Mass, complexity and reliability all points to using solar.<br /><br />ENVIRONMENTAL CONSTRAINTS<br /><br />As you say, there are environmental variables, which at the moment are poorly constrained. These are accounted for in the margins of the reference concept. These include:<br /><br />The solar array supplies 25% more power than required.<br /><br />The cells have a specified efficiency (15%) that is 33% under likely performance (20%).<br /><br />The operating period has a 28 day margin.<br /><br />The mass of the array is over engineered by a factor of 4 (according to some estimates you could supply 4 times as much power on the same mass using thinner cells). <br /><br />There is a similar margin in battery mass.<br /><br />The whole cargo module also has a 26% mass margin, allowing an extra 700 kg without eating into the margin of other components.<br /><br />Interesting you mention dust. This is as big an issue for nuclear power as solar power. A reactor generates a lot of heat, typically 20 times as much heat as electricity. This must be shed via radiators, which are highly complex surfaces both collect dust and lose efficency when they do. <br /><br />TOTAL MASS ISSUES<br /><br />It is the add on masses that really hit ractors hard. Essential items like shielding, r <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>

 

[JonClarke]

"I think you are loading down NTR with too many pessimistic assumptions."<br /><br />Maybe, but those issues are real and need to be demonstrated as unrealistic.<br /><br />" Many of your objections are already met by new design concepts for NTR."<br /><br />Not in the links you gave. There is no real discussionof containment during maximum credible accidents, safe disposal orbits, shielding for the crew, or the impact of tehse on overall efficency. There is not mention of the prevention of fission product boil off. <br /><br />The first of those links mentions that it would take over 2 billion to restore the early 70's status quo. maybe, but the status quo of 1972 with no safe recovery or disposal, no containment, and open air testing would not be acceptable today.<br /><br />"The new midget NTR designs are designed to ease testing needs, and the U.S. has extensive underground testing facilities for nuclear devices. "<br /><br />I think you will find that there is a big difference between a facility to test a NTR underground and one to test nuclear weapons.<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>

 

[dreada5]

I love the BNTR Artificial Gravity Mars Mission Architecture shown here: http://www.frassanito.com/<br /><br /><br />The artificial gravity approach using a spinning spacecraft seems the best way forward.<br /><br />But without NTR, I think NEP, VASIMR would be better...if work still continues on that.<br />http://www.nasa.gov/vision/space/travelinginspace/future_propulsion.html<br />http://www.space.com/businesstechnology/technology/vasimr_rocket_020807-1.html<br />http://ston.jsc.nasa.gov/collections/TRS/_techrep/TP-1995-3539.pdf<br />