ESAS draft report is out!

[JonClarke]

There is a school of throught that sees ISRU as something for later missions. I am not of this school myself. <img src="/images/icons/smile.gif" /> <br /><br />ISRU is not part of the initial lunar missions. But then lunar propellant manufacture is a bigger task than on Mars. It involves prospecting, mining and porbably smelting as well. On Mars you can process the atmosphere everywhere.<br /><br />The MTV carries its own return fuel. ISPP would fuel the return of the DAV, if it is carried out. However the proposed architecture does not seem to be ISPP friendly. <br /><br />Jon<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>

 

[najab]

I guess they are saying "let's plan the mission as if ISPP is not possible and change the plan later (after all this is 20+ years out in the future) if it is possible."

 

[gunsandrockets]

The major changes seem to revolve around improving abort conditions. The manned vehicle once it reaches Mars, does not rely upon linking up with any other element to enable return to Earth.

 

[gunsandrockets]

"Do you know the difference in m/s between a 1200 km circular orbit and a 800-1200 ellipitical one?"<br /><br />Irrelevant. The MTV orbit is described as circular, with an altitude between 800 km and 1200 km. The difference in delta V between 300 km and 800 km is about 250 m/s.<br /><br />"NASA is the one that has specified the high orbit not me."<br /><br />But why do you always use the extreme number, whatever is worst for NTR, out of the range of possibilites?<br /><br />"Remember regardless of propulsion mode you have a limited window to get to Mars from a orbital perspective. Plus if you are doing EOR you are restricted by the hydrogen boil off. For both say 30 days. "<br /><br />The active refrigeration permitted by bi-modal NTR radically alters the boiloff timescale.<br /><br />"I would be be surprised if, when the missions are actually in preparation, that serious consideration is not given to launching the crew with the Mars bound spacecraft, eliminating the need for EOR, at least for crew transfer."<br /><br />By delivering the reentry capsule of the MTV via EOR with a CEV, you gain the launch capacity of the CLV added to the launch capacity of the HLV. The mass of the CEV (with it's CM and SM) is about 20 tonnes after docking with the MTV at 800 km altitude. That's 20 tonnes the HLV doesn't have to launch. <br /><br /><br /><br />

 

[JonClarke]

Yes, a fully fueled DAV would be able to take off immediately. Or during the 30 day preliminary period.<br /><br />It could also abort back to orbit during a descent problem, at least in theory. Blasting off the ascent stage through a hypersonic or supersonic airflow is problematic through.<br /><br />The problem is it can't return to earth on its own - it still has to rendezvous with the MTV to bring the crew home. <br /><br />This approach is also not friendly for future ISRU. In semi-direct archiectures (like the DRM and its derivatives) the asecent stage is built into the module that contains the ISRU plant. Propellants are stored in the ascent stage as they are produced. Only the crew has to transfer. With a DAV and separate plant the DAV would land at least 500 m from the plant (because of debris issues). You would then have to deploy insulated hoses between the two spacecraft and pump many tonnes of cryogenic liquids across.<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]

"Is the mission mass too small? Borowski is probably the tightest NASA-related study to date, with 396 tonnes in LEO, ESAS, using current performance . This is 4% smaller on on already very tight mass budget."<br /><br />The real deal breaker in the mass budget seems to be the manned MTV. The Borowski vehicle is 140 tonnes, and it didn't have to lug the Earth reentry capsule to Mars.<br /><br />Since the ESAS manned MTV adds the mass of a docked CEV of approx. 20 tonnes, the rest of the underlying MTV will probably mass even more than 140 tonnes. 140+ tonnes is in considerable excess of the lift capability of a single HLV.<br /><br />But there is a relatively simple solution. Prior to the CEV launch, a cargo flight launched by a single CLV could EOR with the MTV. This cargo might be consumables or perhaps some part of the MTV structure such as the hab module. If the MTV will need one EOR mission to crew it, it doesn't seem like much of a stretch to use one additional EOR mission to complete the MTV before departure for Mars. <br /><br /> <br />

 

[gunsandrockets]

"Yes, a fully fueled DAV would be able to take off immediately. Or during the 30 day preliminary period." <br /><br />"It could also abort back to orbit during a descent problem, at least in theory. Blasting off the ascent stage through a hypersonic or supersonic airflow is problematic through."<br /><br />"The problem is it can't return to earth on its own - it still has to rendezvous with the MTV to bring the crew home."<br /><br /><br /><br />I was thinking more of the MTV than the DAV when it comes to abort scenarios, though you are right about the DAV.<br /><br />"This approach is also not friendly for future ISRU. In semi-direct archiectures (like the DRM and its derivatives) the asecent stage is built into the module that contains the ISRU plant. Propellants are stored in the ascent stage as they are produced. Only the crew has to transfer. With a DAV and separate plant the DAV would land at least 500 m from the plant (because of debris issues). You would then have to deploy insulated hoses between the two spacecraft and pump many tonnes of cryogenic liquids across."<br /><br />I don't see why the DAV couldn't bring the ISRU plant down with it. It just means the ascent fuel would be fabricated during the crews stay on Mars instead of before their arrival. <br /><br />But that may only come into play for later missions however. I suspect you are right about the DAV use of ISRU for the initial Mars missions. <br /><br /><br /><br /> <br />

 

[JonClarke]

"But why do you always use the extreme number, whatever is worst for NTR, out of the range of possibilites?"<br /><br />It's called being conservative, good engineering pratice, I am told. You should always allow for the worst case. I try to be even handed, so for example I use an Isp of 450 for LOX-LH2, even though values as high as 480 are theoretically possible.<br /><br />"The active refrigeration permitted by bi-modal NTR radically alters the boiloff timescale."<br /><br />Don't think so. As I read Borowski, the refrigeration eliminates boiloff for the relataively small (though not insignificant) amount of LH2 that is used in the later part of the mission. For the ERV this encompasses those used for propulsive capture at Mars, the TMI "burn" and of course what is needed for the disposal orbit. However refrigeration of the full tank of LH2 needed for earth departure is a different story. Here there would appear to be a 32 day limit (p13). Remember the launch window is about this long as well, so if you miss your rendezvous in this time there is no point refrigerating the fuel. It's interesting to speculate what would be done in this case. hould you send the ERV unmanned to Mars anyway, to provide a backup in Mars orbit?<br /><br />With respect to separate launching of the CEV, you are right (although I would calculate the CLV can put 27 tonnes in a 1200 km orbit). The question is what does this extra mass actually do? First it provides a means for crew escape during launch second, it provides a modest 15 m3 of extra pressurised volume (Transhab already has a volume of 300 m3), and third, it returns the crew to earth at the end of the mission. For this you only need the CEV itself (10 tonnes), plus the very small amount of propellant needed for entry. For the rest of the mission it is dead mass. Twenty seven tonnes seems excessive for this. A CEV integrated into the MTV structure would do all of this and provide a useful role as the control centre during <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]

You certainly could do the ISPP onboard. As I recall there was a study in the late 90's called the Combo lander that did precisely this. <br /><br />The problem is it means that the crew lands on Mars without an assured means of return to orbit until the fuel is manufactured. There is a risk your crew could be stranded because something happens to the ISPP system.<br /><br />On the other hand if you have the propellant manufactured ahead of time and the ascent stage fueled before the crew lands, or land in a fully fueled DAV, you have this capability to hand.<br /><br />ceratinly sending the cargo module to mars 2 years ahead of time does mean that there is time for an ISPP plant to do its stuff, if it were included.<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>

 

[centsworth_II]

Jon,<br />On the "One Way" Mars Mission thread, you seemed open to the idea of sending a crew (settlers) to Mars with no near term plan to return them to Earth. On this thread, you seem concerned with the ability to abort and return from Mars on short notice. I understand that planning for each type of Mission is different, but I'm just curious, how do you reconcile the two philosophies?<br /><br />My appologies in advance if I misunderstand your positions. <div class="Discussion_UserSignature"> </div>

 

[gunsandrockets]

"You should always allow for the worst case. I try to be even handed, so for example I use an Isp of 450 for LOX-LH2, even though values as high as 480 are theoretically possible."<br /><br />If you going for worst case, the ISP for LH2/LOX should be 430, since that is the ISP of the J2S engines proposed for the chemical Earth Departure Stage.<br /><br />"As I read Borowski, the refrigeration eliminates boiloff for the relataively small (though not insignificant) amount of LH2 that is used in the later part of the mission...However refrigeration of the full tank of LH2 needed for earth departure is a different story. Here there would appear to be a 32 day limit (p13)."<br /><br />You are misreading page 13 of the report. The 32 day limit is a specific reference to non-bimodal NTR TMI expendable stages. (The expendable TMI stages, as shown on page 20, use a 100 m/s disposal maneuver after payload separation)<br /><br />"With respect to separate launching of the CEV, you are right (although I would calculate the CLV can put 27 tonnes in a 1200 km orbit). The question is what does this extra mass actually do?"<br /><br />This is what it would do...<br /><br />http://www.spaceref.com/news/viewsr.html?pid=19067<br /><br />"The CEV departs 24 to 48 hours prior to Earth entry, and the MTV then either performs a diversion maneuver to fly by Earth or recaptures into Earth orbit. After undocking, the CEV conducts an onboard-targeted, ground-validated burn to target for the proper entry corridor, and, as entry approaches, the CEV CM maneuvers to the proper Entry Interface (EI) attitude for a direct-guided entry to the landing site."<br /><br />Now to continue our conversation...<br /><br />"...you only need the CEV itself (10 tonnes), plus the very small amount of propellant needed for entry. For the rest of the mission it [Service Module] is dead mass. Twenty seven tonnes seems excessive for this."<br /><br />Even th

 

[gunsandrockets]

"The problem is it [DAV ISRU] means that the crew lands on Mars without an assured means of return to orbit until the fuel is manufactured. There is a risk your crew could be stranded because something happens to the ISPP system. "<br /><br />Final ISRU integration will depend on things we don't know yet.<br /><br />1) How reliable is an untended-automated ISRU system? Moon testing and some unmanned direct Mars sample return missions will tell.<br /><br />2) Is subsurface ice or slush easily available on Mars? Unmanned Mars exploration will give us a clue. If there is slush we wouldn't even need to bring seed hydrogen to Mars for ISRU.<br /><br />3) Does Phobos or Deimos contain ISRU exploitable material? Unmanned exploration will give us a clue. If so than the first Mars DAV could use ISRU without landing on Mars. That would fit perfectly with the ESAS Mars plan.<br /><br /><br /><br />

 

[JonClarke]

Apologies accepted <img src="/images/icons/smile.gif" /><br /><br />I am not a great fan of either one way missions (which I think unrealistic for a long time to come), nor I am a fan of adding endless return to earth aborts (which tend add complexity and mass for miniscule and in most cases doubtful improvements in safety).<br /><br />But thinking through implications of different missions is a bit like playing a game. You have to follow the rules as given to explore the implications and (in our case) extract maximum information and guess the starting assumptions. You don't have to agree with them. For example, as you have have noticed, I have not a fan of NTR, but as it is apparently a given for this mission, I want to find out what the implications of this are.<br /><br />Hope this helps!<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>

 

[JonClarke]

Yes, MTVs are a real pain to design, whatever you do they end up massive. Landers and surface habitats are simple in comparison. <br /><br />Actually Borowski and his henchmen did lug a CEV equivalent (actually more like an Apollo capsule, it was designed to fit into a shuttle cargo bay). The crew transferred from the shuttle to the Mars bound spacecraft using the capsule. The ascent stage cabin was a duplicate capsule.<br /><br />An additional CEV flight would be a good idea, to dock a reserve consumable container. This could be the reserve consumables needed if the crew has to remain in Mars orbit for 500-600 days without landing. If not used this container can be dumped to save mass before the TMI burn. Borowsky has this, and it is a good idea inherited from earlier iterations of the DRM.<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]

If you going for worst case, the ISP for LH2/LOX should be 430, since that is the ISP of the J2S engines proposed for the chemical Earth Departure Stage. <br /><br />The J-2 is 60's technology, the SSME gives 453. I would judge this more reasonable. This is why when we were doing Isp for for a LOX-H2 we used a generic mid range Isp of 4.5. We did not have a specific engine in mind. <br /><br />If we wanted to be conservative one could use an Isp of under 900 for NTR as well, not the optimistic 950 the Borowski uses (for a purely conceptual engine). Where you draw the line? Judgement again. The tricky bit is trying to keep the same level of caution or optimisn through a study, and to make sure your assumptions are laid out clearly.<br /><br />I don't find that Borowski is altogether clear on the refrigeration aspect. In some places he seems to make a distinction between a resuable and disposable NTR, as you say. But a key part of the paper is also detailing a common stage shared by all spacecraft of which refrigeration is an essential part. The cargo module's TMI stage is clearly refrigerated, for example in Figure 19. The only way I can make sense of this is to say the zero-boil off refrigeration applies to the post TMI stage. this seems to be borne out on page 17 where the authors say:<br /><br /> "To minimize LH2 boiloff during the vehicle assembly phase, the cargo lander and ERV payloads are launched first, followed by the two TMI stages. Assuming 30 days between Magnum launches and ~2 days for vehicle checkout, the longest period any TMI stage is in LEO is ~32 days.<br /><br />So boil off does occur with the full tank and the period between launches must be minimised (32 days in this case)<br /><br />I thought the CLV is supposed to 29 tonnes to a 400 km orbit? My assumptions on masses for the CERV is based on that. if this is incorrect I will recalculate numbers accordingly. Incidently 15.5 tonnes to 400 km equates to 14.5 tonnes at 1200 km. Still a few mor <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]

"Final ISRU integration will depend on things we don't know yet."<br /><br />Agree<br /><br />1) "How reliable is an untended-automated ISRU system? Moon testing and some unmanned direct Mars sample return missions will tell."<br /><br />Agreed. Using ISRU for MSR is an especially good idea in this regard. It is a pity it has fallen off the agenda for such missions and indeed now MSR has been pushed back to the 2024 time frame (at least for NASA). Technologies may fly as experiments before then - a ISRU experiment was supposed to have been on the 2001 lander but got left off when reborn as Phoenix.<br /><br />Atmosphere-based ISRU can also be effective tested on earth at all scales in simulation chambers that can mimic martian atmosheric compositions, temperatures, and pressures with high fidelity.<br /><br />2) "Is subsurface ice or slush easily available on Mars? Unmanned Mars exploration will give us a clue. If there is slush we wouldn't even need to bring seed hydrogen to Mars for ISRU."<br /><br />Agreed, but I would not rely on this for the first mission. Atmospheric ISRU is the only way to go for the first mission. Also ground water or ice may not be present everywhere. It would be a useful resouce for some missions, but cannot be relied on for all.<br /><br />3) "Does Phobos or Deimos contain ISRU exploitable material? Unmanned exploration will give us a clue. If so than the first Mars DAV could use ISRU without landing on Mars. That would fit perfectly with the ESAS Mars plan."<br /><br />First we would need to develop a means of mining and extracting it. Again, not practical (IMHO) on a first mission. But finding out is a good justification for going to these moons.<br /><br />Jon<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]

Just thinking round this 32 day maximum allowable boil off period in a stage with refrigeration.<br /><br />The refrigeration is powered by the Brayton cycle generator. , which uses waste heat from the hot reactor. However, until the NTR is fired up, there is practically no waste heat to run the Brayton generator. The options seem therefore to be:<br /><br />1) Fire up the reactor just enough to run the generator (I have no idea whether this is practical)<br /><br />2) Have a non nuclear power source, such as solar panels to supply the 15 kW (p23) to run the refrigeration over the 32 day period (this would mass several tons and would be useless once the reactors went critical).<br /><br />3) Accept that there is very limited power prior to start up and factor in boil off in the 32 days prior to TMI (remember this is also about the duration of the launch window) <br /><br />I suspect that option 3 is the one chosen. This is drawn from the fact that the common stage has an internal fuel cell power source that can supply 1.5 kW for 32 days (p17). If the Brayton generator were running this would not be needed.<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]

"Just thinking round this 32 day maximum allowable boil off period in a stage with refrigeration..."<br /><br />"...3) Accept that there is very limited power prior to start up and factor in boil off in the 32 days prior to TMI (remember this is also about the duration of the launch window)" <br /><br />"I suspect that option 3 is the one chosen. This is drawn from the fact that the common stage has an internal fuel cell power source that can supply 1.5 kW for 32 days (p17). If the Brayton generator were running this would not be needed."<br /><br />Page 17 does not describe the bi-modal NTR stage with refrigeration. It is instead the plain NTR expendable TMI stage with passive cooling. <br /><br />

 

[gunsandrockets]

"The J-2 is 60's technology, the SSME gives 453. I would judge this more reasonable. This is why when we were doing Isp for for a LOX-H2 we used a generic mid range Isp of 4.5. We did not have a specific engine in mind." <br /><br />Well NASA already has a very specific engine in mind. Under the ESAS plan the EDS uses 2 x J2S rocket engines. That could always change but for now it's only reasonable to plan around the performance of the J2S, not some other engine with higher ISP.<br /><br /><br />"I don't find that Borowski is altogether clear on the refrigeration aspect. In some places he seems to make a distinction between a resuable and disposable NTR, as you say. But a key part of the paper is also detailing a common stage shared by all spacecraft of which refrigeration is an essential part. The cargo module's TMI stage is clearly refrigerated, for example in Figure 19. The only way I can make sense of this is to say the zero-boil off refrigeration applies to the post TMI stage. this seems to be borne out on page 17 where the authors say:..." <br /><br /> "So boil off does occur with the full tank and the period between launches must be minimised (32 days in this case)"<br /><br />Page 17 does not describe the bi-modal NTR with active cooled tanks. Your confusion comes from the division of the paper into very detailed segements. Part of the paper is describing the standard Mars plan which uses common NTR expendable TMI stages and with the payload aerocaptured at Mars. Another part of the paper describes the advantages of bi-modal NTR as applied to the standard plan. The final part of the paper describes altered plans based on exploiting the full capabilities of bi-modal NTR.<br /><br />To be fair I suspect the BNTR might not refrigerate the 'in-line' tank which is jettisoned when empty. See page 30, figures 24 and 25 of the Borowski report. I need to do more digging to find the description of the 'in-line' tank.<br /><br /><br />"Incidently 15.5 tonnes to 400 km equat

 

[gunsandrockets]

I do like the simplicity of the Mars atmospheric ISRU. But before we ever get to Mars with a manned vehicle NASA is likely to have plenty of experience with solid material ISRU used by a lunar system.<br /><br />Time will tell.

 

[gunsandrockets]

"Actually Borowski and his henchmen did lug a CEV equivalent (actually more like an Apollo capsule, it was designed to fit into a shuttle cargo bay). The crew transferred from the shuttle to the Mars bound spacecraft using the capsule. The ascent stage cabin was a duplicate capsule."<br /><br />I was refering to the Borowski manned BNTR vehicle which masses 140 tonnes. It does not appear to carry with it a capsule to Mars as illustrated in Figure 29 on page 37 of the Borowski report.

 

[JonClarke]

"Page 17 does not describe the bi-modal NTR stage with refrigeration. It is instead the plain NTR expendable TMI stage with passive cooling."<br /><br />OK, I see where you are coming from. Yes, there is a disposable NTR stage which only has fuel cell power.<br /><br />However, as figures 19 and 20 show and it is explicity stated on page 25, BNTR is also suitable for use on the cargo and piloted lander missions. Hence the common stage approach. Table 8 shows the common stage containing both auxillary power and the Brayton generator. Likewise table 9 which is a mass breakdown of all three vehicles has both auxillary power and a Brayton generator on all three NTRs. The masses are similar: 1.63 tonnes for avionics and power in Table 6, 1.47 tonnes for avionics + power in Table 8, and 1.69 tonnes for avionics + aux power in Table 9.<br /><br />Nowhere can I find mentioned that the BNTR is capable of refrigerating the main LH2 stage before TMI.<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]

"However, as figures 19 and 20 show and it is explicity stated on page 25, BNTR is also suitable for use on the cargo and piloted lander missions. Hence the common stage approach. Table 8 shows the common stage containing both auxillary power and the Brayton generator. Likewise table 9 which is a mass breakdown of all three vehicles has both auxillary power and a Brayton generator on all three NTRs. The masses are similar: 1.63 tonnes for avionics and power in Table 6, 1.47 tonnes for avionics + power in Table 8, and 1.69 tonnes for avionics + aux power in Table 9."<br /><br />Yes, clearly the BNTR stages have some auxilary power. No doubt the auxilary power serves two purposes: 1) to provide emergency backup if the Brayton generators fail, and 2) (and most important) to provide system power until the stage is placed into it's 400 km orbit, therby permitting the reactors to launch while shut down. <br /><br />"Nowhere can I find mentioned that the BNTR is capable of refrigerating the main LH2 stage before TMI."<br /><br />Absence of evidence is not evidence of absence. <br /><br />Plus it makes perfect sense to run the Brayton generator before TMI. Not only is boiloff reduced, thermal stressing of the reactor (from hot/cold cycling) is eliminated (one of the important advantages of BNTR), and running the reactor up to speed for TMI is dramatically improved therby wasting less propellent (another important advantage of BNTR). <br /><br />

 

[JonClarke]

"Well NASA already has a very specific engine in mind. Under the ESAS plan the EDS uses 2 x J2S rocket engines. That could always change but for now it's only reasonable to plan around the performance of the J2S, not some other engine with higher ISP. "<br /><br />The exact performance if the J-2S is neither here nor there. the study I referred to was a generic one, not tied to either ESAS or even the US. <br /><br />"Page 17 does not describe the bi-modal NTR with active cooled tanks. Your confusion comes from the division of the paper into very detailed segements. Part of the paper is describing the standard Mars plan which uses common NTR expendable TMI stages and with the payload aerocaptured at Mars. Another part of the paper describes the advantages of bi-modal NTR as applied to the standard plan. The final part of the paper describes altered plans based on exploiting the full capabilities of bi-modal NTR."<br /><br />And as I pointed out in a previous post, all the stages, whether usable or not have similarly sized fuel cells for power. The fuels cells cannot supply the 15 kW needed to run the refrigeration. Refrigeration is only possible when the reactor is hot enough to run the Brayton generator. This only happens at the TNI burn<br /><br />"The SM needs to support the CEV for 48 hours and perform a course correction burn prior to the CM reentering the Earth's atmosphere. The SM can be sized for whatever amount of propellent is required for the job. I doubt there would be any wasted mass. "<br /><br />If you can get a very attenutated service module (11-12 tonnes) fair enough.<br /><br />"The Borowski bi-modal NTR manned MTV massed 140 tonnes at a 400 km Earth orbit. Now NASA plans to put something of similar mass into a circular orbit between 800 and 1200 km. You can't squeeze that kind of performance out of an HLV without massive changes. It's simpler and cheaper to add one or two EOR cargo missions with the pre-existing CLV and therby avoid any new launch vehic <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 was refering to the Borowski manned BNTR vehicle which masses 140 tonnes. It does not appear to carry with it a capsule to Mars as illustrated in Figure 29 on page 37 of the Borowski report."<br /><br />Figures 16, 17, and 33 all show the BNTR with the "ECRV". Either a spare ECRV can be carried from earth (allowing the possibly of a direct entry after a free return) or not, in which case the ERV must enter Mars orbit. In either case the ECRV that the crew returns home in is the one on the Mars ascent stage. <br /><br />It is not clear from the ESAS summary whether the CEV the crew returns in is one that they dock with the MTV in, or whether the DAV also has a CEV as the crew module.<br /><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>