If the Apollo CSM underwent a SWIP like the LM did...

[Nikolai]

... what do you think they would cut? What could be removed quickly? What systems would take some time to re-jigger?

Keep in mind that this thing has to be able to re-enter the atmosphere and keep those onboard alive.

[Nibb31]

What's a SWIP ?

[Nikolai]

What's a SWIP ?

A Super Weight Improvement Program. It was Grumman's way of stripping all non-essential mass from the spacecraft, with a dozen experts in structures, mass property, thermodynamics, and electronics, whose task was to second-guess the whole design in order to bring the LM below weight margins. They succeeded spectacularly.

It also made the spacecraft substantially more fragile, as well as more costly and time-consuming to manufacture, but those were considered to be worth the cost.

My question is meant to pretend that that wasn't enough. How could we cut down on the CSM to save mass?

[DerekL1963]

My question is meant to pretend that that wasn't enough. How could we cut down on the CSM to save mass?

It wasn't enough in real life - SWIP was accompanied by ongoing weight control measures in the CSM and performance increases in the Saturn V. SWIP and other LM weight reduction programs just get most of the attention because the LM development program is better (publicly/popularly) documented, and because weight reduction on the LM was extremely draconian due to the hard limits on it's engine performance. Less well known, for example, is the work done on trajectory design.

Pretty much all of the lunar missions ran on the ragged edge of their performance margins. Some of this was due to the extreme difficulty of the mission (something poorly modeled in KSP). Some of it came from the fact that to a large extent they were figuring out what they were doing as they were doing it because the "end of the decade" deadline forced them onto a path of parallel and not entirely well integrated development.

[Nibb31]

Oh I see...

Well, they couldn't have diminished much the actual CM structure or skin, because it had to maintain a solid structure for reentry and landing and it was already quite minimalistic.

They did reduce the mass of the SM for the Block II lunar missions by redesigning the tanks, which allowed them to add the SIM bay and the Lunar Rover, so that was certainly possible.

Another way of reducing the weight on the CSM would be to redesign the CSM Main Engine, although this would have seriously delayed the program. The Main Engine was overengineered for when Direct Ascent was the plan, so a smaller/lighter engine would have been possible.

Other than that, they weren't stupid, and I'm pretty sure that they weren't carrying much dead weight.

[Nikolai]

SWIP was accompanied by ongoing weight control measures in the CSM and performance increases in the Saturn V.

I don't know about the CSM, obviously, but I was under the impression that the Saturn V was over-designed from the beginning to push out the mass margins. They had to do a lot of testing to remove the transient and steady-state responses to engine impulse on a case-by-case basis, I know, and that made things expensive... can you point to documentation of the need to increase performance beyond the original specifications?

[Nikolai]

Other than that, they weren't stupid, and I'm pretty sure that they weren't carrying much dead weight.

Oh, I don't mean to accuse them of stupidity or wastefulness. Just trying to tap into the cleverness of space enthusiasts who might have heard or thought of something that was overlooked.

[Xeldrak]

I think think the CSM is allready quite barebones, since this was one of the parts where is was most important so safe weight (since you lose only directly before reentry). Should they really want to cut even more weight - maybe they could fuse some of the tanks inside like they did in the second stage.

[DerekL1963]

I don't know about the CSM, obviously, but I was under the impression that the Saturn V was over-designed from the beginning to push out the mass margins. They had to do a lot of testing to remove the transient and steady-state responses to engine impulse on a case-by-case basis, I know, and that made things expensive... can you point to documentation of the need to increase performance beyond the original specifications?

No, the Saturn V was not over designed from the beginning - it originally had only four F-1's on the first stage for example. The S-II was particularly problematic because it was contracted for last, and the S-IC and S-IV were already well along in design and development and had consumed a great deal of the available weight and performance margins originally specified. Which is why in midstream it morphed from having two separate tanks to the common bulkhead scheme. (And why, in Carrying the Fire, Micheal Collins discusses the rumors of the S-II "being fragile, made of glass".) The S-IV always had the common bulkhead because it was originally designed for the extremely performance limited Saturn-I series.

Also, as the missions progressed the messed with the number of separation and ullage rockets trying to find the lightest combination that offered the best performance. They also fiddled with the amount of propellant loaded into the S-IVB because (as we all know) the closer to the top of the rocket, the more extra weight 'costs'.

The book Stages to Saturn covers some of this, the rest is scattered is a wide variety of places.

[Nikolai]

The book Stages to Saturn covers some of this, the rest is scattered is a wide variety of places.

Sorry to snip for brevity's sake, but this was all fascinating, thank you. And now I know which book I have to read next -- I've read a ton of astronaut memoirs, but not nearly enough about design.

[DerekL1963]

Sorry to snip for brevity's sake, but this was all fascinating, thank you. And now I know which book I have to read next -- I've read a ton of astronaut memoirs, but not nearly enough about design.

I'm the opposite - I've spent far more time on the technology than the biography. (Especially since most of the biographies are repetitious as hell.) I wish the NASA archives hadn't been yanked, because there's tons of good stuff in there.

[Nikolai]

I wish the NASA archives hadn't been yanked, because there's tons of good stuff in there.

You mean the NTRS? It's back online.

http://ntrs.nasa.gov/search.jsp

[Temstar]

Another way of reducing the weight on the CSM would be to redesign the CSM Main Engine, although this would have seriously delayed the program. The Main Engine was overengineered for when Direct Ascent was the plan, so a smaller/lighter engine would have been possible.

Yes this was very seriously considered and a design for a Block III CSM was even drawn up. Block III was to be a LEO only Apollo (for Apollo Applications Program, so Skylab, Apollo-Soyuz and the like) with a simplified CM with all the Lunar landing supporting gear stripped out. Instead of using the hugely overpowered SPS in the SM the engine will be a LM descent engine with the extra space and weight freed up for more cargo in the SM.

One would think that if you really wanted to go back to the moon you could take a Block II CM and mate it with a modified Block III SM. Put more fuel tanks into the Block III SM so that it the result has the same delta-V as the Block II CSM and you'll get a moon capable CSM that weight less.

Edited May 18, 2013 by Temstar

[comicbstudeo]

too... many.... acronyms......