Spacecraft economy of scale

[Robotbeat]

It seems to me that if the LC-39 infrastructure were used at or near its limit, SLS would be a very good use of resources, significantly more cost-effective than the EELVs even at the same upmass rate.  The complaints are mostly about the abysmal flight rate in the pre-planning documents.

Are you comparing your mythical-launch-rate SLS to current-launch-rate EELVs? Or are you comparing EELVs at an equivalent mass-to-LEO rate, at which point the various options for reuse become viable?

(several have been studied for a partially reusable EELV, and one effort is already underway to replace the first stage of EELVs with a flyback booster by 2025/2030... the same time frame that Mars missions become relevant)

You're making an unfair comparison if you compare at the same launch rate. You must compare at the same IMLEO rate (especially, but not just, for propellant).

[93143]

Yeah, and if wishes were horses we'd all be eatin' steak.

Knock off the drive-by snark and pay attention.  What does the infrastructure capacity matter if we never reach it?

@Robotbeat:  Read what you quoted again.  I said "at the same upmass rate".  Those exact words.

In fact, I probably edited the thing after you read it, so you may want to go back and check...

The point I'm making is, so what if the infrastructure limits us to a certain launch rate?  (A) we'll never reach it, and (B) if we got anywhere near it, the flight rate would be high enough that SLS' economics would look great.

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Basically, you sounded like you were claiming that SLS is too big because (presumably among other things) the launch infrastructure for such a large vehicle inherently limits the flight rate.  This is simply not true; SLS has never, to my knowledge, been criticized for poor economics at its maximum flight rate - the main complaint seems to be that the plan (such as it is) doesn't currently involve flying it anywhere near that rate.

[Robotbeat]

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The point I'm making is, so what if the infrastructure limits us to a certain launch rate?  (A) we'll never reach it, and (B) if we did, the flight rate would be high enough that SLS' economics would look great.

But then you're making a totally unfair comparison between a hypothetical SLS that runs at a high launch rate and the current EELV at its low launch rate. AT 400mT/year around 2025+, EELVs would be easily justifiably partially reusable (and there's always Blue Origin, XCOR, SpaceX), and that's still a very low SLS launch rate (~4/year).

(FWIW, Lockheed says that their flyback booster becomes superior cost-wise to current EELVs even at just 8 launches per year... 400mT/year would be around 30-40 launches per year, a launch rate which is not without precedent but also is well beyond the 8 flights per year Lockheed says is worth it.)

Another issue is that you ignore other launch vehicles which would also be used for such an effort, such as Falcon 9 and Falcon Heavy (to say nothing of a reusable Falcon 9).

At just 4 launches per year, SLS must be compared to a partially reusable EELV or at least to Falcon 9 and Falcon Heavy, not to current EELVs. In other words, in order to get to the point where SLS can defeat current launch vehicles, you have to go well past the point where the existing efforts for partially reusable launch vehicles are more than justified.

[indaco1]

The rates matter because larger launch vehicle infrastructure cannot support the same rate as smaller launch vehicle infrastructure, other things being equal.

I agree, this phenomenon is very important...  in my model it can be represented  inside the  RC(Q,S) function (recurring Fixed Costs in function of total payload and size of the veichle).   

In other words, once fixed Q the RC - S curve is very steep for high S values.

I'm sorry I haven't found a more expressive model.

[93143]

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The point I'm making is, so what if the infrastructure limits us to a certain launch rate?  (A) we'll never reach it, and (B) if we did, the flight rate would be high enough that SLS' economics would look great.

But then you're making a totally unfair comparison between a hypothetical SLS that runs at a high launch rate and the current EELV at its low launch rate. AT 400mT/year around 2025+, EELVs would be easily justifiably partially reusable (and there's always Blue Origin, XCOR, SpaceX), and that's still a very low SLS launch rate (~4/year).

(FWIW, Lockheed says that their flyback booster becomes superior cost-wise to current EELVs even at just 8 launches per year... 400mT/year would be around 30-40 launches per year, a launch rate which is not without precedent but also is well beyond the 8 flights per year Lockheed says is worth it.)

Another issue is that you ignore other launch vehicles which would also be used for such an effort, such as Falcon 9 and Falcon Heavy (to say nothing of a reusable Falcon 9).

At just 4 launches per year, SLS must be compared to a partially reusable EELV or at least to Falcon 9 and Falcon Heavy, not to current EELVs. In other words, in order to get to the point where SLS can defeat current launch vehicles, you have to go well past the point where the existing efforts for partially reusable launch vehicles are more than justified.

First, just to get it out of the way, this isn't just about raw upmass.  Single-chunk mass and volume are important too.  So you need to include the hit to spacecraft cost (if there is any, and at that upmass rate there will be) in the cost of the smaller vehicles.

Second, READ MY POSTS.  You asked a question.  I answered it.  You then proceeded to accuse me of unfairness, in the evident belief that I had answered the question oppositely to the way I actually did.

Finally, this economic argument is getting a bit handwavy.  I see little point in continuing it.  Just don't start asserting stuff as facts when it's derived from a mix of qualitative analysis and opinion.

(And SLS still isn't that great at 4 flights per year.  Not bad, but not great.  Take it to 24 and watch the EELV unit costs eat your lunch, even with partial reusability [it occurs to me that at that flight rate, partial reusability for SLS would make sense too...].  And no, you don't get to compare it with a full RLV; that's not only apples-to-oranges but is miles off your original complaint.)

[93143]

I'll repeat my earlier final paragraph, so you don't miss it:

Basically, you sounded like you were claiming that SLS is too big because (presumably among other things) the launch infrastructure for such a large vehicle inherently limits the flight rate.  This is simply not true; SLS has never, to my knowledge, been criticized for poor economics at its maximum flight rate - the main complaint seems to be that the plan (such as it is) doesn't currently involve flying it anywhere near that rate.

[QuantumG]

That seems like a reasonable point.. Given any fixed amount of money, there is an optimum size of launch vehicle for economic operations.

[Robotbeat]

I'll repeat my earlier final paragraph, so you don't miss it:

Basically, you sounded like you were claiming that SLS is too big because (presumably among other things) the launch infrastructure for such a large vehicle inherently limits the flight rate.  This is simply not true; SLS has never, to my knowledge, been criticized for poor economics at its maximum flight rate - the main complaint seems to be that the plan (such as it is) doesn't currently involve flying it anywhere near that rate.

My original point was in the context of optimal rates under a theoretical context about if the crawler (for example) limited the launch rate, but you responded about SLS. As far as I'm aware, most domestic launch vehicles (inc. SLS and the EELVs) are operating at well under the rate the infrastructure can handle, which is to say the infrastructure is not optimal for the current launch rate. Adding SLS to the mix makes the situation worse, since the infrastructure's optimal rate is FAR higher than will ever happen. SLS is suboptimal and will always be so because it will never operate at a level which utilizes its infrastructure to the fullest.

But my second point still stands. SLS, flying at high flight rate so as to optimally use the infrastructure, would be less economical than the alternatives (which includes partially reusable launch vehicles) at the same IMLEO rate.

So consider this a criticism of SLS's economics at maximum flight rate (a complete hypothetical, mind you). I know several others have made the same criticism, that at the launch rates where HLVs start to make sense, RLVs make even more sense. (And as far as minimum sized piece, again, that gets back to the limitations of road infrastructure and size of clean rooms and thermal vacuum chambers, etc, which strongly favors EELV-sized payloads over HLV-sized ones, even if you DO decide to launch said payloads on SLS.)

[93143]

My original point was in the context of optimal rates under a theoretical context about if the crawler (for example) limited the launch rate, but you responded about SLS.

You were talking about the Shuttle pad setup specifically.  What HLV is going to be using Shuttle infrastructure other than SLS?

But my second point still stands. SLS, flying at high flight rate so as to optimally use the infrastructure, would be less economical than the alternatives (which includes partially reusable launch vehicles) at the same IMLEO rate.

You haven't even begun to prove this.  You've simply asserted it.

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Also, you're ignoring the possibility of any level of reusability of the HLV.  From what you said about the EELVs, it sounds like flyback boosters (for instance) would make sense long before the LC-39 infrastructure hit its maximum launch rate.

Finally, you're pulling a bait-and-switch, or having trouble staying on message, or both.  Your claim is that due to basic physics, infrastructure will limit the launch rate of an HLV, and thus prevent its being competitive with an MLV, all else being equal.  You then drag in RLVs when it becomes evident that the basic claim is not true.

The size of the pieces is a question of weighing facilities cost against increased complexity and mass in space, with a view towards a concrete desired capability.  The judgment simply cannot be made in the abstract; one needs more context than we have at this point.

[Robotbeat]

But my second point still stands. SLS, flying at high flight rate so as to optimally use the infrastructure, would be less economical than the alternatives (which includes partially reusable launch vehicles) at the same IMLEO rate.

You haven't even begun to prove this.  You've simply asserted it.

At 400mt/year, you're comparing an expendable launch vehicle still flying at a suboptimal rate to a (mostly) reusable launch vehicle flying at an optimal rate. This very likely changes the situation dramatically. Do you (given my assumptions) disagree? I mean, if you take my assumptions, can you see how my conclusion follows?

(You are, of course, welcome to question my assumptions.)

[93143]

I'm somewhat surprised at you.  That's nothing but qualitative handwaving; no conclusions can be drawn.  The phrase "very likely" betrays the fact that you realize this.

And where does 400 mT/year come from?  It has nothing to do with LC-39's launch rate limits, which are several times higher at least.  I'm sure you recall that high upmass rates tilt the economic balance towards HLVs.  Is it enough to overcome the advantage of flyback first stages (versus perhaps flyback boosters on SLS)?  No way to tell without numbers.

[Robotbeat]

I'm somewhat surprised at you.  That's nothing but qualitative handwaving; no conclusions can be drawn.  The phrase "very likely" betrays the fact that you realize this.

And where does 400 mT/year come from?  It has nothing to do with LC-39's launch rate limits, which are several times higher at least.  I'm sure you recall that high upmass rates tilt the economic balance towards HLVs.  Is it enough to overcome the advantage of flyback first stages (versus perhaps flyback boosters on SLS)?  No way to tell without numbers.

400mT/year launch rate comes from the rate at which we can be reasonably certain that at very least partial reusability for EELV-class (8-25mT) is warranted. I've heard estimates as low as 8 flights per year for partial reusability (flyback EELV first stage currently being designed and tested at subscale by Lockheed Martin) but about 40 flights or more for full reusability.

This is the point where we can say that the transition from expendable to at very least partial reusable makes sense with some certainty. That's why I chose it. You do agree that reusability is required to get where we all want to go (which is becoming truly spacefaring), right? This is, after all, why we switched to Shuttle, even if it failed its goals of low cost per kg to orbit because of several reasons which are beyond the scope of this thread. Those pioneers which pushed for Shuttle in the early days were absolutely right that reusability is essential.

Right now, reusability wouldn't require the enormous program that Shuttle was. There are several concurrent efforts underway as we speak. The only thing that is likely to cause none of them to succeed is too low of launch demand.  But the odds are tilted in their favor at 400mT, especially if that's mostly propellant. The equation then changes, because you're talking about mostly reusable launch vehicles at a high launch rate  versus at least mostly expendable (i.e. SLS still at a relatively low 4/year). Comparing at higher launch rates only tilts the odds more in favor of reusability.

[Chris Bergin]

Was away, so missed the mod report, but everyone needs to keep this thread calm. Argue the point, not the person.

[93143]

There's a big difference between partial reusability (such as flyback boosters on EELVs or SLS) and full reusability (such as Skylon or Falcon 9R).  The latter is a massive paradigm shift if it can be done cheaply enough, and your simple physics-based objection to high launch rates of an HLV seems a bit apples-to-oranges if you're comparing an expendable HLV to a reusable MLV.

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When you write that higher flight rates "tilt the odds" even more towards reusability, you seem to conflate favourable slope vs. the expendable EELV with favourable slope vs. the HLV.

Basically, you haven't demonstrated that a partially-reusable EELV would have a lower cost per kg floor than SLS at the latter's maximum upmass rate.  Remember how badly J-246 stomped the Atlas V at very high flight rates?  I know SLS is not Jupiter, but it should actually be more cost-effective per kg once development is over and if you assume you can fully utilize it, so there is probably still a significant gap to make up.  (Never mind that at SLS' maximum flight rate, flyback boosters almost certainly make sense for it too...  and perhaps an RS-25 recovery pod...)

No one has yet demonstrated that a fully-reusable launch vehicle can even be built at all, so that comparison is a bit facile.  Obviously if something like Skylon works out, servicing a LEO propellant depot with SLS would be silly.  Launching a very large and/or heavy module that needs to be ground-integrated, though, is something that Skylon flat-out can't do, so in a robust exploration program, an expendable HLV would probably still have a place unless and until a reusable one shows up...

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Okay, returning to the original point:

I don't see how your original argument regarding LC-39's maximum launch rate (the key phrase was "other things being equal") proves anything useful.  Furthermore, while the theoretical max launch rate may be lower, you don't need it to be as high to achieve the same upmass, and you didn't demonstrate that the maximum upmass would be lower, and certainly not that the cost per kg floor would be higher.  That was all I was trying to say, and as the rest of the argument is getting nowhere fast, I should probably take my own advice and back off.

[Also, I think you might have missed a few edits, judging by how things have been going...]

[93143]

Excuse me - my profuse apologies; I appear to have brought the SLS vs. EELVs fight to the Advanced Concepts board.  My bad...