Its pretty easy. The marginal cost is what was needed to be added to the budgets beyond the yearly sustaining costs. The Shuttle didn't fly the same number of times every year. Thus they had to budget for each mission they flew.
To bring this to SLS the question is if we fly one rocket this year how much more money will it take to fly another. That was the original question.
Quote from: arachnitect on 09/14/2015 08:07 pmSolar Probe Plus is $389 million.And even with a Delta 4-Heavy launch the mission will need seven flybys of Venus!?! Has anyone explored what SLS with an EUS could do to improve that? It's just a hypothetical... but an interesting one nonetheless.
Solar Probe Plus is $389 million.
Even with multi-year contracts NASA still has to request a budget one year at a time.
The number of manifested flights drove the yearly funding request of STS line item.
It boils down to this, either NASA can answer the question of how much more money needs to be in the yearly budget request to launch a rocket or it cannot. It has been launching a rockets and requesting budgets for a while now. NASA is perfectly capable of figuring out the difference in cost between flying one SLS or two.
You seriously think the incremental cost of the SLS is only a few hundred million dollars?
I agree with you wholeheartedly that most SLS cost estimates are ridiculously overestimated (I think $500 Million is a little too low though). I was trying to give Rocketman a range of realistically imaginable costs.
And in the absence of real cost numbers (which NASA is very behind on providing) comparisons to existing systems are one way to help estimate costs.
why make assumptions when facts exist?
So assuming that the SLS will be the same cost as the Delta IV Heavy, or even possibly less, doesn't look right.
And considering that the current human rated vehicle NASA is building (i.e. Orion MPCV) is costing $8B or more, and taking 18 years until it becomes operational, I'd guess your estimates are probably a little low.
Now if NASA uses existing ISS modules, then great, not much development needed. But no real need for the SLS either, since lower cost commercial launchers can deliver them too.
I look at the total cost, while also breaking out the development and operational portions. It's the only way to get a full up apples-to-apples cost, since "marginal cost" estimates are usually simplified too far
and ignore large classes of costs like overhead.
Figuring out marginal cost though is not easy. I've done a lot of digging to figure out marginal costs for the Shuttle program, and though I'm pretty good at it (I've done this for work purposes too), I was never able to use public records to figure it out.
Marginal cost doesn't mean a lot if you don't remember how much it took to get to unit #1.
Like all hardware programs, there were pieces and parts laying around that were mismatched purchases, so sure, the last flight could have been added without writing a check for $1.5B. But that's because the Shuttle program had over-bought, and there were pre-negoitated contracts that could be extended. And using end-of-life costing for a program just starting out doesn't make sense.
there is no possible way to accurately figure out "marginal cost"
There is no way SLS marginal costs are less than a Delta IV Heavy. SLS has more engines, more structure, more people involved, More contracts, etc. It will be closer to 1 billion than 500 million.
Is a hydrogen second stage even necessarily a bad thing when you're using solids as your main thrust/first stage?What would the performance benefits be if they used similar thrust RP1 engines on the main liquid/second stage?
You also can't just "turn off" the production line, because then you have to re-hire all your workers and retrain their rusty skills (and/or hire a lot of new people and train them from scratch, since most people don't just sit around waiting for the call for 3+ years) before you can do anything.
This also seems like a good way to never work the bugs out of your production line; the launch rate is supposed to be no less than 1 per year for a reason.
The efficiency of a high production rate is simply that you get a lot of work out of your existing facilities and personnel. Lowering the rate doesn't increase the marginal cost of a unit very much; what it does is increase that unit's share of the fixed costs.
QuoteThere is no way SLS marginal costs are less than a Delta IV Heavy. SLS has more engines, more structure, more people involved, More contracts, etc. It will be closer to 1 billion than 500 million. Apples to oranges. Unless you're trying to tell me that the Delta IV Heavy price is pure marginal cost, with all fixed costs including supplier fixed costs shoved off onto the DoD...
I suppose it's possible in principle that the marginal cost could be strongly affected by optimizing production for very low flight rates, if the changes were radical enough.
But SLS is being set up for two units per year at steady state; you can only take such a scenario so far before it becomes more expensive than just using the Shuttle infrastructure as it stood, and $1B marginal cost per launch is past that point. I don't see this as a serious possibility, not at the scale you people are talking about.
(Also, IIRC SRBs were $25M per segment pair, not per booster. Again, that's purchase price, not marginal cost.)
Apples to oranges. Unless you're trying to tell me that the Delta IV Heavy price is pure marginal cost,
Quote from: 93143 on 09/20/2015 07:36 pm(Also, IIRC SRBs were $25M per segment pair, not per booster. Again, that's purchase price, not marginal cost.)That was the cost of the SRM's and not the SRB's.
So If SLS were flying dozens of times per year the incremental cost of one additional flight might not vary much, and thus there might be a useful value to call the "marginal cost." But I would expect the incremental cost of a second flight in a given year to be different than the incremental cost of a third flight in that same year.Can anyone defend talk of a single "marginal cost" value given the actual anticipated flight rate?
Apples to oranges. Unless you're trying to tell me that the Delta IV Heavy price is pure marginal cost, with all fixed costs including supplier fixed costs shoved off onto the DoD...
Well, not dozens. They'd likely have to double or triple their manufacturing capacities. Michoud can turn out a max of 4 per year, right?