Commercial HLV and R&D

[Namechange User]

Back in the day when I was working the F-1A program, the Saturn-V was considered the standard for heavy lift. I can't even begin to tell you how many times I heard "100 tons" and "heavy lift" used in the same sentence.

OK, so let's say HLV/BFR = 100 tons.

Unlike Saturn-V, we're talking about something that won't be man-rated, and can take advantage of the technology and experience gains of the last 40 years.

The question is this:  Could it be developed for a lot less than Ares V?

Why wouldn't it be man-rated?  It's good enough to carry expensive and unique cargo.....but not people?

[Dave G]

Why wouldn't it be man-rated?  It's good enough to carry expensive and unique cargo.....but not people?

That's correct. 

Man rating requires additional margins and redundancy, which means higher cost and complexity.  So the best way to go beyond earth orbit is to launch the heavy stuff on an unmanned HLV, launch the crew on a smaller rocket, rendezvous in earth orbit, and then do TLI/TMI/whatever from there.

And that's exactly the way NASA architected it, with Ares I / Orion for crew and Ares V for cargo.  The problem was not in the architecture, but in the cost over-runs and delays in procurement.

So now they're going to try the commercial option to replace the Ares I / Orion for crew and smaller cargo missions.  I think this makes sense.  The current procurement method is essentially a slow death for human space flight.  The taxpayers won't support it.

But the commercial option doesn't seem to make as much sense for a big cargo launcher (a.k.a. HLV, BFR).  The government will probably be the only customer.  For the commercial option to be viable, you need more potential customers to justify commercial investment.

So the question is this:  Is there a cheaper viable option for the HLV/BFR than the Ares V?

[jongoff]

Chuck, you're trying to have it both ways.  The Augustine Committee specifically said that when they said "HLVs are necessary for robust exploration", they meant HLVs to mean "vehicles at least 40-50mT with fairings of at least 6.5-7.5m diameter".  You can't take their "HLVs are necessary" comment out of context of their definition of HLVs.  What they were saying in effect is that "vehicles with payloads in the 40-50mT range and 6.5-7.5m fairing diameter range are necessary for robust exploration".  If that doesn't qualify as HLVs to you, that's fine, but you can't just turn around and accuse Martijn of calling Bolden a liar.

If a vehicle in the 40-50mT range in your opinion isn't Heavy Lift, then the A-com didn't say Heavy Lift is required for robust exploration.

~Jon

You quote the Augustine Commission as defining HLV as "AT LEAST 40-50mT" and that they agreed "HLV's are necessary for robust exploration".  The "at least" is key.  Therefore, by what you just posted something that has greater than what you believe is necessary still fits the intent of the Augustine Commission. 

Umm...that seems a little logically flawed to me.  At least $5 is necessary to buy lunch at Jack in the Box, $2000 is greater than $5, so somehow $2000 is necessary for a lunch at Jack in the Box?

Buying an HLV that's bigger and more expensive than is necessary fundamentally means being able to do less in space, not more.  Payloads, operations, infrastructure, hardware to actually do stuff at destinations, all these things cost money.  Money that will be less available if we buy a bigger HLV than we need. 

I have a hard time seeing how buying an HLV that's over twice what the A-com said was necessary for spaceflight is somehow consistent with their intent.  Well, at least most of their intent--there were a few of them who felt bigger==always better, but most of them seemed more willing to go with a rocket that was big enough to get the job done.

Just my $.02

~Jon

[jongoff]

No, I'm not having it both ways. You admit yourself that the Augustine Committee said "at least" 40-50mT. That means that to those people that is at the extreme low end of what is heavy lift. Well like I said, the guys that actually invented the term and built the launch vehicle that epitomized "heavy lift" understood that term to be "in the neighborhood of 100 tons". So Augustine would be happy with anything that exceeds 40-50mT, and the guys that invented the term said it was 100 tons.

I'm not trying to have it both ways. There is agreement.

No, 40-50mT wasn't the extreme low-end.  Not if you actually were paying attention, and have listened to what the committee members said afterward.  [As an aside, I'm not just trying to appeal to authority, I thought Jeff's arguments were pretty darned valid].  25mT with 5m fairings was the "extreme low end" of the scale.  Jeff admitted you could probably do everything up to and maybe even including manned Mars EDL with existing EELV classed boosters, but that it was marginal and limited you to only a few approaches.  He said that something in the 40-50mT *max* opened up the design space to all but the most volume inefficient lunar landers, and opened up most realistic manned Mars EDL approaches even without getting clever...

...do you want me to repost the discussion he left on Rand's blog?

~Jon

[jongoff]

I just read through the Summery report trying to get a handle on what they considered an HLV. As OV-106 said they consider the range of 40-50mt to be the absolute minimum needed for robust exploration. However, thats the theoretical lowest mass they were considering. Practically I think they considered HLV to be much higher. On page 5 it lists the various HLV options they identified. The lowest payload rocket class, EELV heritage, is listed at 75mt. Therefore I would make the case that they didn't consider any of the smaller EELV growth option to be heavy lift. Realistically unless we are talking about an entirely clean sheet design there are five HLV options Atlas, Delta, Ares, SD in-line, and SD side-mount. The Bolden HLV study effectively ruled out the SD side-mount and Ares. That means we are looking at the smallest HLV being 75mt. I still like the 100mt definition though

I took a look at the document that infocat13 posted. There is quite a bit there but in my limited time reading and digesting it it looks like the time tables they were giving were for human rated vehicals in the Ares I payload class. It seems to be even in this weight class that 72 month is on the low end. Yikes! Thats two times longer then the Jupiter-130. I wonder what the Delta 75mt development time looks like even without the human rating. I'm going to do some digging myself on this.

If you read through the report, there are actually a fair number of contradictions.  It was a report written by committee.  There really were some people on the committee that thought that big HLVs were the way to go.  There were others who honestly felt that while you could pull it off with existing EELVs, that a small HLV (in the 40-50mT range) was plenty enough margin to relax things substantially.  That jibes pretty well with the analysis I've done over the years--existing EELVs are a tight fit, but even going up just to a Phase 1 style EELV makes a huge difference.

I guess I just fundamentally disagree that blowing a huge chunk of our limited HSF budget on an HLV that's much bigger than we need makes sense.  I'd rather see actual missions done, new technologies developed, and new markets and commercial capabilities catalyzed, then a shiny big rocket that makes the space missions only marginally simpler at the cost of being able to afford far fewer such missions.

~Jon

[mmeijeri]

For the record, Jeff Greason - bless him - was wrong. I conjecture he got snookered by Bo Bejmuk.

[jongoff]

Now, I know most of you won't agree with it, but here's some of the best explanations I've seen from an A-com member on the sizing issues.  Note, some of his comments have actually gotten me to rethink some of my previous opinions, so this isn't just a case of "he agrees with me--that means he's smart":

Jeff Greason Says:
February 8th, 2010 at 3:30 pm

A “big enough” lifter for exploration can be built using the industrial base already in the U.S. for boosters shared with other customers (at ULA, SpaceX, and OSC).

The one piece which is missing for that is political more than technical; to do it you need a large hydrocarbon booster engine in the 750,000-1,000,000 lbf class and ideally with at least 1970’s class chamber pressure 1500+ psi). Currently the only engine in that size in U.S. use is the RD-180 which we buy from the Russians. It would be a lot easier to sell a booster like that for U.S. govt missions if there were a decent large hydrocarbon engine in U.S. production.

Personally, I don’t understand why it’s OK to buy rides on Russian spacecraft for U.S. astronauts so they can visit a station with Russian components but politically difficult to base a U.S. large booster on Russian engines (which keeps more of the value chain in U.S. hands); but the push-back against basing a booster on shared production lines with other U.S. boosters has a tendancy to fall back on that excuse.

Therefore, while I don’t have special knowledge to that effect, it seems likely to me that some of the “HLV R&D” line item is for a U.S. hydrocarbon boost engine. And public presentations to Augustine Committee were made by ULA showing that if using hydrocarbon booster engine one can derive “big enough” boosters from the existing production infrastructure. I’ve believe SpaceX can, given time, play in that arena as well, though probably not as soon as an Atlas/Delta derivative, and the engine needed would be the same. There would be benefit to other U.S. stakeholders (like DoD) in having an engine like that in U.S. production.

Fairing size does matter; you can get fairings in the 7.5m class with that approach rather than 10m. I found pieces difficult to stuff in 5m fairings but none I didn’t believe could be stuffed in a 7.5m fairing. Of course, reasonable people can disagree on this in part because they have different mission models in mind.

The various “shuttle-derived” boosters are based on the same logic: use the SRB and 8.4m Shuttle ET production capacity to derive a “big enough” (and somewhat larger) booster. While such an approach is interesting and has potential for lower development cost than a “mostly new” booster like Ares V was becoming, it does not share the overhead of keeping the production lines open with any non-NASA customers. NASA is the only customer for SRB, SSME, and 8.4m tanks and is likely to remain so.

“Big enough”, in my opinion, is a cost-optimized 25-30mT booster of which you can afford to launch a lot, and occasional capacity to go to 50-75mT for, at most, a few missions a year in a “heavy” variant. A reasonable mission model has few enough of the very big launches that maintaining all-dedicated production lines for that purpose is not as cost-effective as making a “heavy” version of a somewhat smaller booster with same engines, tank tooling, etc.

The decision on whether it is worth the extra cost in dollars to maintain independent production capacity because of redundancy, which states it is in, or the labels on the personnel badges is a political decision, not an economic or technical one, and will be made by the politicians.

*****

Jeff Greason Says:
February 8th, 2010 at 3:51 pm

The fairing size debate very quickly gets too technical for a forum like this, Martin. It’s a judgement call rather than a black or white issue. Every time someone says “piece XYZ can’t fit”, someone else can say “but if you solved the problem differently it would fit”. So the bigger the fairing, the less clever you have to be in designing the pieces, and cleverness costs something in time, complexity, or because you only have so many of your best system designers to go around.

Cryogenic propulsion stages with long-duration coast capability need to be very well insulated and so even if the tanks are 5m diameter the fairing needs a lot of clearance around the tank because the insulation won’t stand aero loads. A 6.5 m fairing would probably work for that but might be a little tight.

Planetary landers can be done in a variety of overall designs and NASA did a nice study recently of all the variants. Some of them fit in 5m fairings but most of them don’t and so you’re restricting your other design options if you push the fairing too small (and we don’t know everything in advance….). As above, 6.5m might work, 7.5 covers most cases. IIRC, only very large landers that look “LEM-like” and that use LOX/LH2 tanks and that land very large payloads push in to the 10m class and it wasn’t clear to me that those had a mission need.

Mars entry, descent, and landing vehicles (EDL), are a sticky problem. Here, again, different people have different ideas about how big the “lump” is that you have to land on the Martian surface in one piece, and it makes a big difference whether or not you plan for refueling at phobos/deimos. I think its clear that by the time we do a Mars mission, the architecture will look different than DRM 5.0. Still, regardless of the details, you do need to land a fairly large piece on mars (at least 20-25mT, and some people think 40mT), and an aeroshell for that really, really doesn’t fit in 5m fairing. At 7.5m there are many solutions, at 10m fairing you can do it in a very non-clever way by brute-force scale-up of Viking style aeroshell. Given that we have …. some time to work on the problem I was convinced 7.5m fairing range was big enough, and I’d rather have 7.5m boosters that we can afford and work on the EDL problem than 10m boosters we can’t so that the EDL problem takes less work, but your mileage may vary.

Advanced in-space propulsion is (regrettably) likely to be solar-electric rather than nuclear-electric; there are paths to solar supplies light enough to do the job but they get bulky. Getting the arrays up there for a large mission will probably take multiple launches. Now you have to look at which limit do you run in to first, the throw weight of the booster or the fairing volume. 7.5m is a good match for 60-70mT booster and 10m is a good match to 125mT booster so no obvious win there. Somewhere south of 7.5m you are running in to “scale down” problems for very large deployable thin film arrays, but it’s very uncertain since those haven’t been flown yet.

Bottom line: 5m probably too small, 6.5m maybe big enough if you’re very clever, 7.5m probably big enough but a few pieces need some thought on packaging, 10m obviously fits everything with no special thought given to packaging.

And of course this isn’t a free choice; only some possible technical paths go with some fairing sizes.

Realize I’m abstracting down a very, very complex topic here!

****

Jeff also had some other interesting comments in the thread talking about Flexible Path: http://www.transterrestrial.com/?p=24710#comments

~Jon

[jongoff]

For the record, Jeff Greason - bless him - was wrong. I conjecture he got snookered by Bo Bejmuk.

Jeff's one of the smartest people I've ever met or worked with.  When he disagrees with me, I tend to at least check my assumptions.  He's mortal and fallible like the rest of us, but I at least try to see if his logic holds water.  While I'm not totally on-board with his belief in 40-50mT capable vehicles as being necessary, he does have a point--sticking with existing EELVs *only* forces you in several instances to pick very marginal options, or require substantial cleverness to make the design work, and limit your options substantially.  At the end of the day, while it might be possible to do your all-hypergol approach, it might actually be less bad to go with slightly upgraded EELV-class vehicles and cryo depots to relax the constraints and allow a more open design space.

I'm sure Chuck or OV or Lee Jay will jump in and try to say "well a SDLV gives you even more flexibility, and even less constraints", but yeah, so would Orion or Sea Dragon.  The goal is global optimization not local optimization.  You want to get the best bang for the buck when it comes to flexibility vs. new launcher work, and I think that sweet spot falls well short of DIRECT.

But once again, just my $.02

~Jon

[mmeijeri]

I'm not opposed to a new hydrocarbon engine, I just don't see how it's necessary. EELV Phase 1 does not require new engines. Also bear in mind that a US hydrocarbon engine is likely to be more expensive than the Russian ones.

I am opposed to stating it's necessary when it isn't. Jeff Greason says it is, ULA says it isn't.

I'm also opposed to saying 5m fairings aren't enough and opposed to not adding 6.5m fairings are possible with current EELVs.

It seems that Jeff Greason is trying to be diplomatic, while trying to steer people away from huge HLVs. If so, this can be a very good thing. We here are not bound by such considerations however.

[jhoblik]

HLV with SPACEX components
I think SPACEX will save development cost and united their engine production, if they will create engine Merlin X with thrust ~1MN, instead of engine like F-1 (over 5MN). The reason is because the only use of this like F-1 engine will be for heavy lift.
I think it will more natural and less expensive to upgrade Merlin E to Merlin X with thrust around ~1MN(similar to upgrade of Merlin A->Merlin E).
It will give them in configuration of Falcon 9 Heavy 27 engine thrust ~ 30MN and with second stag engine LOX/LH2 give them LEO capacity around 100 tons.
This engine could be used for all their vehicles Falcon 1X …~2000kg(Mass to LEO), Falcon 9X  ~20000kg,and Falcon 9X Heavy without LH2/LOX~ 40000kg and with LH2/LOX ~100000kg. I think we could have heavy lift in 5 five years, for 0.5B.

[mmeijeri]

Jeff's one of the smartest people I've ever met or worked with.  When he disagrees with me, I tend to at least check my assumptions.  He's mortal and fallible like the rest of us, but I at least try to see if his logic holds water.

Absolutely, and I did. I don't claim my assessment of his argument is valid. It just seems to me that all the objections he mentioned (conceded to HLV proponents in my opinion) can be solved in a simpler way. I'll copy my response to Jeff Greason below. And note that I hold him in very high regard. Amicus Plato, sed magis amica veritas. I could very well be wrong about all this, in which case I'd love to be better informed. After all, I've been wrong before. I used to be OK with SDLV, and I no longer am. At least one of these positions must have been wrong.

  While I'm not totally on-board with his belief in 40-50mT capable vehicles as being necessary, he does have a point--sticking with existing EELVs *only* forces you in several instances to pick very marginal options, or require substantial cleverness to make the design work, and limit your options substantially.

I'm totally in favour of having a 50mT EELV Phase 1. But that's not the same as saying it is needed. The distinction is important. Consider your recent proposal to do exploration without any form of propellant transfer and without any HLV. If nothing else it's a good data point. It shows you what the limitations of current technology are (much less than you'd think), which allows you to assess and quantify the benefit of additional technologies. Similarly I believe it is not actually true that current EELVs would lead you to marginal solutions. That too doesn't mean we shouldn't want EELV Phase 1, but the distinction is important.

  At the end of the day, while it might be possible to do your all-hypergol approach, it might actually be less bad to go with slightly upgraded EELV-class vehicles and cryo depots to relax the constraints and allow a more open design space.

The hypergolics and more generally noncryogenic propellants aren't necessary at all. I just advocate them because they would allow us to do this soon. This is a mostly academic point if we're not going beyond LEO soon. Even dense propellants aren't necessary, although they would remain useful for volume considerations, since EELV architectures are more constrained by volume than by mass, though not annoyingly so. Everything could be done with LOX/LH2 too. In some cases this would require some extra cleverness (such as trying to fit a single stage fully reusable LOX/LH2 lander into an EELV fairing), but it can be done. It wouldn't even be a bad idea. But I like fast progress, in tiny little steps. I'd prefer to see a program defunded after it had delivered something useful rather than before. Tiny steps help you do that.

I'm sure Chuck or OV or Lee Jay will jump in and try to say "well a SDLV gives you even more flexibility, and even less constraints", but yeah, so would Orion or Sea Dragon.

We don't even need to concede that. Nothing wet ever fits on an HLV comfortably. Everything dry fits on current EELVs comfortably. I exaggerate, but only a little.

  The goal is global optimization not local optimization.  You want to get the best bang for the buck when it comes to flexibility vs. new launcher work, and I think that sweet spot falls well short of DIRECT.

Absolutely.

[Swatch]

Wow   ... this thread got really exciting a couple pages ago...


<--- sits and listens to the edgy/interesting conversation.   

[mmeijeri]

OK, this was my reply to Jeff Greason on Rand Simberg's blog. Note that I think of Jon, Rand, Jeff Greason and Huntress as manned spaceflight prophets. Prophets don't always agree and they aren't always right, but it's a pretty darn good idea to listen to what they have to say.

Every time someone says “piece XYZ can’t fit”, someone else can say “but if you solved the problem differently it would fit”.


Heheh, so true. I’m sure Rand will warn us if he feels we are getting off-topic or too technical. Here’s my try. I believe everything can be done comfortably with existing EELVs and even without increasing complexity. I’ll agree EELV Phase 1 (but no higher) would still be nice, especially since it would reach down to commercial payload sizes.

1. Cryo stages
The problem could be avoided by using relatively small EDSs. This can be done easily if you off-load propellant from things like landers and transfer stages and use Lagrange points as staging and refueling points. As you know, ULA and our very own Jon Goff have published papers on how to do this. This has advantages for the size of the stages, the amount of thrust that is needed (no need for high thrust upper stage engines that have no commercial use) and for the thermal environment. The Augustine Commission has recommended, no doubt in large part due to your efforts, visiting Lagrange points and using depots. For best effect you would put depots at Lagrange points, which conveniently provides you with an excuse to go visit them early on, even though they are just empty points in space.

2. Landers
Here the problem can be solved without extra complications by using dense propellants, noncryogenic ones even for which propellant transfer is very mature technology. Performance would be quite acceptable. A more advanced solution might use a crasher or uncrasher stage. A refueled EDS could fill that role, so this wouldn’t really add complexity either.

3. Mars EDL
Mars EDL can be done fully propulsively, and will have to use a significant amount of propulsion anyway. Large heat shields really aren’t necessary. Some believe inflatable heat shields could be used, which would be nice if they work out but not strictly necessary. NTR, ISRU and SEP could be used to reduce the cost of orbit insertion and deorbiting.

4. SEP
SEP can be restricted to propellant which is most of the mass anyway. Current technology suffices for this. An ISS solar array would be good enough for a small propellant tug and these fit on an EELV easily. You’d just need lots and lots of them, which also gives economies of scale and redundancy.

There’s another issue that others sometimes mention:

5. Large habs
This can be solved with inflatables, which are better for MMOD and radiation shielding too.

It looks as if propellant transfer is so powerful that it actually reduces the complexity compared to some of the schemes that only work with larger payload fairings. All of this could be done with existing technology! R&D would remain very desirable of course to reduce costs, both through lowering IMLEO and by reducing launch costs.

Bottom line, just my two cents: 5m is plenty, and 6.5m would be great.

[jongoff]

Martijn,
You're making his point.  He wasn't saying you couldn't do it without going to a vehicle that could reach 50mT in its heavy configuration.  He was saying that while you *might* be able to do most of these things with smaller vehicles, they require the kind of excess cleverness, and narrow solution spaces that tend to drive up development costs.  Ie while it might be possible, relaxing the constraints just a bit without driving up the costs a bunch makes a lot of sense.  Just because we can imagine a solution doesn't say it is instantly optimal.  Going with a Phase 1 or Phase 2 EELV has a finite cost--going with hypergolic landers or doing fully-propulsive Mars EDL have finite costs as well.  It's a tradeoff, and I think that Jeff may be right that the tradeoff favors slightly bigger fairings, and boosters families that in their "Heavy" configuration reach into the 40-50mT range.

~Jon

[mmeijeri]

Martijn,
You're making his point.  He wasn't saying you couldn't do it without going to a vehicle that could reach 50mT in its heavy configuration.  He was saying that while you *might* be able to do most of these things with smaller vehicles, they require the kind of excess cleverness, and narrow solution spaces that tend to drive up development costs.

I'm trying to refine his point a bit further. I know he agrees 50mT isn't necessary. I disagree current EELVs would even lead to marginal solutions or would require excess cleverness. They may enable something that is close to being minimally complex while still being very capable, more capable than ESAS in fact. The distinction is valuable.

EELV Phase 1 would actually make the hypergolic approach easier, which is why I was first attracted to it. But now I think it's mainly important because it would be a step in the direction of cryogenic depots. ACES the upper stage as a stepping stone to ACES the EDS, ACES the depot and ACES the reusable EDS. A 50mT launch vehicle is just what falls out naturally.

  Ie while it might be possible, relaxing the constraints just a bit without driving up the costs a bunch makes a lot of sense.  Just because we can imagine a solution doesn't say it is instantly optimal.  Going with a Phase 1 or Phase 2 EELV has a finite cost--going with hypergolic landers or doing fully-propulsive Mars EDL have finite costs as well.  It's a tradeoff, and I think that Jeff may be right that the tradeoff favors slightly bigger fairings, and boosters families that in their "Heavy" configuration reach into the 40-50mT range.

It's Phase 2 that I'd have a problem with, not Phase 1. In fact I enthusiastically support Phase 1. I'm just trying to be precise about the exact reasons for it. If we disagree on the details, that's fine. If discussion can lead to a deeper understanding, that would be even better. I was surprised to see your no propellant transfer solution for example. It's a useful data point if nothing else, just like the Chinese approach.

Proposal: let's forget about hypergolics and noncryogenic propellants for now, as they seem to be getting in the way of communication. Let's assume cryogenic propellant transfer and long term storage as a given (even for LH2 and even in LEO) and focus on payload mass and fairing sizes. Let's agree EELV Phase 1 is highly desirable. Let's agree it is not strictly necessary. Let's focus on the question of whether just having current EELVs would lead to excessively complicated or suboptimal solutions. I contend they wouldn't. Knowing this for sure would give us a valuable data point.

[kkattula]

IMHO, the best solution is one that:

1) Builds multiple-use in-space infrastructure.

2) Minimizes per mission costs.

3) Creates a market for LEO propellant & cargo deliveries

4) Can be temporarily scaled back, when economically necessary, without serious damage.

I think the ULA proposal using ACES based depots and landers best fits that.

ULA seem to think a Delta IV Heavy with Aces Upper Stage (36 mt to LEO) counts as commercial HLV.

[MikeAtkinson]

I have to agree with Jeff. Although it is possible to do missions in 20T chunks and 5m fairing it seems to be far off the optimum.

Say you take a fairly standard Mars mission, 20T landed on Mars (largest chunk), 40T transhab (including supplies). The lander + descent system does not fit into 20T and probably not into 5m, so it needs to be assembled. The transhab will need to be supplied in space with food and other dry goods. Both the lander and transhab would may have to be launched dry and so would then need water and oxygen transfer and refuelling. The EDS and Mars departure stages would need refuelling and all the components docked together and checked out in a complex dance. Any problems need to be found and fixed in space with the clock ticking towards the launch window.

Most Mars mission plans have 2 or 3 departures from earth over a period of about 6 months every 2 years (1 or 2 cargo, 1 crew). So 2 or 3 stacks like the will need to be brought together. That is a similar difficulty to building the ISS which was also built using similar mass and volume constraints. 

It is difficult to see how such a complex operation can be performed without humans present, so on top there would have to be crewed launches of the fitting out teams, logistic launches for them, etc. There might need to be several crews in space at the same time fitting out the various stacks.

Mars missions are usually in the 600-1200T IMLEO range. Packing constraints and technology limitations due to the 20T and 5m limits probably will push that up to 700-1400T IMLEO. fuel for docking, station keeping (perhaps even orbit reboost) will push that up to 800-1600T IMLEO. Construction crew launch and their logistics will push that up to 1000-2000T (at least) [note only about half of that is propellant because construction and fitting out on orbit requires launches of crew and equipment. The effect of this is that there is little increase in the cheap propellant launch and a large increase in expensive crew launch]

If anything goes wrong with this complex operation and a earth departure window is missed, effectively 2 years of fixed cost (many billions) are added onto the project for the same return.

In contrast a 50T, 8m mission can be 3 or 4 launches per stack (one crewed), docking (no construction or fitting out) in orbit and propellant transfer.

Similar arguments can be made for other mission types, any HSF BEO would require propellant transfer and probably docking as well.

Switching to SEL, missions departing from L2, hypergolics, etc., only cause the size and mass limit problem to be moved around and IMHO add more problems elsewhere.

Jeff Greason said "“Big enough”, in my opinion, is a cost-optimized 25-30mT booster of which you can afford to launch a lot, and occasional capacity to go to 50-75mT for, at most, a few missions a year in a “heavy” variant" and I fully agree with that.

[mmeijeri]

I have to agree with Jeff. Although it is possible to do missions in 20T chunks and 5m fairing it seems to be far off the optimum.

OK, let's focus on that then. I contend this is not marginal. I'm not necessarily saying this isn't far from the optimum, just saying it would be pretty good. Seems like an important distinction.

Say you take a fairly standard Mars mission, 20T landed on Mars (largest chunk), 40T transhab (including supplies). The lander + descent system does not fit into 20T and probably not into 5m, so it needs to be assembled. The transhab will need to be supplied in space with food and other dry goods. Both the lander and transhab would may have to be launched dry and so would then need water and oxygen transfer and refuelling. The EDS and Mars departure stages would need refuelling and all the components docked together and checked out in a complex dance.

Good example. I agree with 20mT as a reasonable target for the largest piece you want to be able to land in one piece. The wet mass of the lander will obviously be much more than that. Are you saying the dry mass would have to be higher too? You seemed to be implying that it could fit if dry. If so, I agree with that too.

I would disagree with two things: I believe the lander could easily fit in 5m fairings and even more easily in 6.5m fairings. And with automated rendez-vous and docking using more flights wouldn't be a problem at all.

Any problems need to be found and fixed in space with the clock ticking towards the launch window.

You have years to fix this, so that isn't really a problem. Also, the transhab could and probably should be reused, so you'd have to do this infrequently. Every mission would still require new propellant and consumables of course. For this to work, you'd station the hab and transfer stage at a Lagrange point.

Mars missions are usually in the 600-1200T IMLEO range. Packing constraints and technology limitations due to the 20T and 5m limits probably will push that up to 700-1400T IMLEO. fuel for docking, station keeping (perhaps even orbit reboost) will push that up to 800-1600T IMLEO.

Total launch volume for near term moon and Mars missions is a better argument than fairing sizes. I do think your numbers are very high.

Construction crew launch and their logistics will push that up to 1000-2000T (at least) [note only about half of that is propellant because construction and fitting out on orbit requires launches of crew and equipment. The effect of this is that there is little increase in the cheap propellant launch and a large increase in expensive crew launch]

I dispute the need for construction. Docking should suffice. And with reusable hardware costs can be amortised over multiple missions.

If anything goes wrong with this complex operation and a earth departure window is missed, effectively 2 years of fixed cost (many billions) are added onto the project for the same return.

How so? What fixed costs?

[mmeijeri]

Jeff Greason said "“Big enough”, in my opinion, is a cost-optimized 25-30mT booster of which you can afford to launch a lot, and occasional capacity to go to 50-75mT for, at most, a few missions a year in a “heavy” variant" and I fully agree with that.

I totally agree with that, but I don't think that's what he said. It's the claim that >5m or 50mT vs 25mT makes the difference between marginal and good I disagree with. I contend it's the difference between very good and even better.

[MikeAtkinson]

Jeff Greason said "“Big enough”, in my opinion, is a cost-optimized 25-30mT booster of which you can afford to launch a lot, and occasional capacity to go to 50-75mT for, at most, a few missions a year in a “heavy” variant" and I fully agree with that.

I totally agree with that, but I don't think that's what he said. It's the claim that >5m or 50mT vs 25mT makes the difference between marginal and good I disagree with. I contend it's the difference between very good and even better.

That is exactly what he said, see Jon's quote above in the thread.