How much lighter could Apollo be today?

[zolotiyeruki]

The SpaceX thread has included a lot of discussion about going to Mars, the moon, etc, which got me thinking:  Given the advancements we've seen in materials science, metallurgy, composites, computing, control systems, CFD, and manufacturing techniques, how much lighter could Apollo be today, given the same mission parameters?  Let's assume the rocket works the same way--2.5 stages to orbit, 3rd stage does the TLI, CSM and LM undock in lunar orbit, etc., and we've still got 3 astronauts, two of whom go to the lunar surface.

So with carbon fiber, smaller electronics, better manufacturing, etc, how much mass do you think could be saved, and by extension, how much smaller do you think the entire launch stack could be?

[Bill Phil]

Not really much. Most of the mass was propellant. The biggest benefit would be smaller electronics. But even then you'd just use the extra mass to bring more to the lunar surface, I'd think.

[KerikBalm]

Well, if you managed a 10% dry mass reduction, then you'd need 10% less propellant.

I don't know how much lighter the structure could be, but consider that the Apollo guidance computer had a mass of 32 kg

https://en.wikipedia.org/wiki/Apollo_Guidance_Computer

And the Apollo command+service module had a dry mass of 11,900 kg

https://en.wikipedia.org/wiki/Apollo_Command/Service_Module

So a smart phone could handle everything that the old guidance computer did, and comes in at far under 1 kg.... but that only saves 32 kg of 11,900 kg... so it doesn't make much difference in the end.

[NSEP]

4 hours ago, Bill Phil said:

Not really much. Most of the mass was propellant. The biggest benefit would be smaller electronics. But even then you'd just use the extra mass to bring more to the lunar surface, I'd think.

This^^ If you mass to spare, you would probably use that empty space for extra experiments/surface samples. Thats what i would do, at least.

[Hannu2]

Difficult to say, because such a project would need so much totally new technology. Costs would be more important issue than weight (for example methane as fuel of upper stages instead of hydrogen which would give lower costs even launch mass would probably be slightly larger).

I think if you assume current safety regulations modern crafts would be more massive in spite of advances in material and information technology. Any Apollo-crafts would not certainly get man rating certificates today, probably even not in Russia or China.

[zolotiyeruki]

8 hours ago, Bill Phil said:

Not really much. Most of the mass was propellant. The biggest benefit would be smaller electronics. But even then you'd just use the extra mass to bring more to the lunar surface, I'd think.

You *could* bring more to the lunar surface, but for the purposes of this thought experiment, let's assume we are trying to accomplish the same exact goals--plant a flag, take samples, take photos and video, etc.

4 hours ago, KerikBalm said:

Well, if you managed a 10% dry mass reduction, then you'd need 10% less propellant.

And the Apollo command+service module had a dry mass of 11,900 kg ... So a smart phone could handle everything that the old guidance computer did, and comes in at far under 1 kg.... but that only saves 32 kg of 11,900 kg... so it doesn't make much difference in the end.

Right, but the guidance computer is just one thing among many.  Everything is up for replacement--space suits, cameras, insulation material, fuel tanks (are COPVs lighter than whatever the Apollo tanks were made of?), life support systems, windows, seat cushions, etc.  Electric motors are smaller and more powerful than ever.  So are batteries and fuel cells.  Would solar panels be a lighter substitute for the fuel cells?  The engine could be smaller--Apollo's engine was designed to lift the CSM from the lunar surface.

[kerbiloid]

Just a brief reference

http://www.braeunig.us/space/specs/apollo.htm

Also
http://www.braeunig.us/space/specs/gemini.htm
http://www.braeunig.us/space/specs/mercury.htm
http://www.braeunig.us/space/specs/soyuz.htm
http://www.braeunig.us/space/specs/vostok.htm

[wumpus]

Bringing the third astronaut along wouldn't make much sense as I'd assume that his job can be completely automated.  The real gains would likely involve a crewless "cargo run" flight that could land supplies in orbit and on the Moon: I'm sure it was considered but was proven a bad idea by Apollo 11 (the landing computer was aimed at a bunch of boulders).  50 years of technology at least improved landers.

The lander already was extremely light and flimsy.  I'm not sure a carbon fiber skeleton would make much of a difference.  I'd guess the dry weight of any pressurized fuel tank could be improved by modern materials, but that is about it.  Don't look for much improvement in engines, and the mass ratios were already pretty good (all modern tech can do is "add [tiny bits of] lightness" and automation.  Which is one of the main reasons nobody has been on the Moon since 1972.

I'd like to add boosters to the thing from the Peacekeeper missile/Minotaur rocket (probably only for a crewless cargo run), but instead of making it lighter I'm sure any principle investigator (or whoever NASA puts in charge of a mission) would simply add fuel and mass to the payload.

There's also the difference in crew safety.  In 1967 Apollo killed an entire crew and NASA just did a full check for safety and kept going.  I'd expect any modern Apollo to require considerably more safety, and I don't assume that can be done without a hefty cost in mass (forget about the booster in crewed flight).

[mikegarrison]

7 minutes ago, wumpus said:

There's also the difference in crew safety.  In 1967 Apollo killed an entire crew and NASA just did a full check for safety and kept going.  I'd expect any modern Apollo to require considerably more safety, and I don't assume that can be done without a hefty cost in mass (forget about the booster in crewed flight).

I think that understates what the program went through after that incident.

[wumpus]

6 minutes ago, mikegarrison said:

I think that understates what the program went through after that incident.

It was an entire year's setback on a program with only 3 years left on the deadline, so obviously it was pretty severe (of course, so were the flaws in Apollo).  But compare that to the Columbia disaster which lead to a 15 year and counting hiatus of all manned flights by the USA.

[mikegarrison]

1 hour ago, wumpus said:

It was an entire year's setback on a program with only 3 years left on the deadline, so obviously it was pretty severe (of course, so were the flaws in Apollo).  But compare that to the Columbia disaster which lead to a 15 year and counting hiatus of all manned flights by the USA.

I think that overstates the direct effect of Columbia. In fact they were back flying not too long after Columbia, but with new rules about having a back-up orbiter ready to go. The eventual decision to stop all shuttle flights came in 2010 and the final flight was 2011, so it's only been 7 years so far. And that decision was based on program cost more than anything else.

Edited April 26, 2018 by mikegarrison

[YNM]

If the equipments can be smaller, a larger room would be a fairly good start.

[Racescort666]

The thing that would probably make the biggest gains is the fact that engine performance is now much better than what it was when the Saturn V was designed. Using existing engines rather than designing new ones, since the Saturn engines were basically designed for the rocket. Also, we have a much better grasp of long duration missions with liquid propellants, there's a chance that hydrolox could be used for the whole mission rather than hypergolics which would also save a considerable amount of mass.

[Ultimate Steve]

That's the Saturn V's instrument ring, and it weighs just shy of 2 tons. Much of that is the actual ring, but many of those instruments can be made drasticly smaller, and potentially removed entirely. If we were to clear the entire ring out, make it waaay smaller, maybe small enough to fit above in the interstage (in with the LEM) then the ring can be gotten rid of, along with a few (dozen?) cm of fuel tanks across the rocket.

The fins can go, too. A long time ago they studied making a second batch of Saturn V's, which would have improved something else, meaning that fins would not be needed - they were originally only there for stability in the event of a launch abort or engine out situation. They are probably at least a ton if not multiple.

I cannot find concrete data on the Apollo CSM blocks, but Block II added some systems necessary for lunar operation and made some other systems lighter, so the actual mass was about the same. With modern manufacturing techniques, we could reduce the mass by probably around 10%-ish? Leading to a ~7% overall reduction in rocket size.

The spacesuits are probably lighter now, too.

The LEM received upgrades in efficiency  to carry the rover. If we keep the changes but not the rover, the lander could be scaled back ~5% I think.

Engines have come a long way, the F-1's could be replaced by either a large number of or scaled up Merlins, or Raptors if you want to change the first stage to methalox. Option 2 would allow increased S1 efficiency leading to an even smaller rocket. At least on S3, you could replace the J-2 with a few RL-10's, 50s extra efficiency (!) although you would have half the thrust for the same weight (using 5 RL-10's). You could also use improved insulation to reduce boiloff.

And lastly, major tank upgrades. I have heard that the tanks as used on the F9 were way too advanced to have been built back then, so that's another couple tons off the whole rocket... Looking at payload fraction, FH has about 4.5%, the same as Saturn V, ish, despite having more tank area per volume (using 3 cores) and having lower efficiency engines, so you can probably get payload fractions up to 5-6%, which is another big chunk off the rocket, more if you switched to methalox on stage one.

Short answer: estimated at 20% smaller (but if you tried really hard you could probably (?) do better.

[Racescort666]

18 minutes ago, Ultimate Steve said:

Engines have come a long way, the F-1's could be replaced by either a large number of or scaled up Merlins, or Raptors if you want to change the first stage to methalox. Option 2 would allow increased S1 efficiency leading to an even smaller rocket. At least on S3, you could replace the J-2 with a few RL-10's, 50s extra efficiency (!) although you would have half the thrust for the same weight (using 5 RL-10's). You could also use improved insulation to reduce boiloff.

S-II replace 5 J-2 engines with 2 RS-25s. Way better TWR than the RL10 and also very high ISP. You'd need 10 RL10s to match the same thrust as the J-2 but the S-IVB is 6.6 m and diameter and the RL10 is 2.13m in diameter. At most, you'd only be able to get 7 into the same area. Honestly though, a J-2X would probably be the best replacement in both cases. 

[wumpus]

17 minutes ago, Racescort666 said:

S-II replace 5 J-2 engines with 2 RS-25s. Way better TWR than the RL10 and also very high ISP. You'd need 10 RL10s to match the same thrust as the J-2 but the S-IVB is 6.6 m and diameter and the RL10 is 2.13m in diameter. At most, you'd only be able to get 7 into the same area. Honestly though, a J-2X would probably be the best replacement in both cases. 

That's more or less how I'd want to build the SLS: F1s for stage 1 and RS-25s for stage 2.  If I need solid boosters I'd use SR-118 (Peacekeeper stage 1: made by Thiokol (a political requirement) with 200 tons of thrust moving 50 tons of booster (1 minute burn)) boosters for non-crewed launch (and higher mass).  It should hit all the political notes and use up RS-25s more slowly (not that I expect enough launches to use up the supply of RS-25s).

[Racescort666]

24 minutes ago, wumpus said:

That's more or less how I'd want to build the SLS: F1s for stage 1 and RS-25s for stage 2.  If I need solid boosters I'd use SR-118 (Peacekeeper stage 1: made by Thiokol (a political requirement) with 200 tons of thrust moving 50 tons of booster (1 minute burn)) boosters for non-crewed launch (and higher mass).  It should hit all the political notes and use up RS-25s more slowly (not that I expect enough launches to use up the supply of RS-25s).

Not that this is strictly related to the discussion at hand but if you wanted to send Mir to Mars, 1 RS-25 would give you a TWR of about 0.60:1. My calculation assumes Mir as the payload and includes mass of the fuel tank to have the same kg/m2 as the ET. If you wanted to go full mega mission, hypothetically you could reuse the engine with ISRU.

[Ultimate Steve]

1 hour ago, Racescort666 said:

S-II replace 5 J-2 engines with 2 RS-25s. Way better TWR than the RL10 and also very high ISP. You'd need 10 RL10s to match the same thrust as the J-2 but the S-IVB is 6.6 m and diameter and the RL10 is 2.13m in diameter. At most, you'd only be able to get 7 into the same area. Honestly though, a J-2X would probably be the best replacement in both cases.  

1 hour ago, wumpus said:

That's more or less how I'd want to build the SLS: F1s for stage 1 and RS-25s for stage 2.  If I need solid boosters I'd use SR-118 (Peacekeeper stage 1: made by Thiokol (a political requirement) with 200 tons of thrust moving 50 tons of booster (1 minute burn)) boosters for non-crewed launch (and higher mass).  It should hit all the political notes and use up RS-25s more slowly (not that I expect enough launches to use up the supply of RS-25s). 

Well, I typed the explanation for the S-IVB stage engine choice, but then I realized that @Racescort666 was partially talking about the S-II stage... In that case RL-10s are definitely out, and RS-25 is probably a better choice than J-2X for the S-II. I won't do the math on that, though, yet, at least. Below is the math for the S-IVB engine choice, and it took me about half an hour and I need to have dinner and go in half an hour.

 

Note that this choice disregards politics. If we do bring politics and budget into play J-2X would make a lot more sense because SSME's aren't being built and both the SSME and the RL-10 are expensive.

 

Engine	Specific Impulse	Mass	Thrust
J-2	421s	1788kg	1033kN
RL-10	465s	277kg	110kN
RS-25	452s	3527kg	2279kN
J-2X	448s	2470kg	1307kN

As far as upper stage engines go, everything here seems to be better than the J-2, so any change is a good change. J-2X has the lowest isp of the three replacements but still 27s better than J-2, and a thrust upgrade, but 600kg extra mass. We could rescale it for the same efficiency but lower mass and thrust, but then we're making a new engine (which would be possible but not ideal). RS-25 is the heaviest and has the most thrust, let's say we rescale it to 50% giving 1100kN and 1750kg, which is worse than J-2 mass-wise, although it has better efficiency. And RL-10, if you sacrifice half of your TWR (5 engines, 550kN) gives you about 1400kg in mass for 465s. If TWR is a huge concern, you could potentially use more advanced insulation and split the TLI burn in two.

Delta-V calculations, assuming 15t LM, 29t SM, 10t dry S-IVB (I subtracted the mass of the J-2) and 104t of S-IVB fuel... total of 158t, dry mass of 54t. Adding engine mass each time.

J-2 - 4382m/s

5x RL-10 - 4820m/s

10x RL-10 - 4756m/s (although 10 RL-10's would not fit as pointed out above, doing comparison for the sake of having a similar TWR)

50% RS-25 - 4666m/s

100% RS-25 - 4576m/s

J-2X - 4588m/s

 

First of all, some of these engines have different fuel mixture ratios but hopefully they all are similar enough to be used for approximate numbers. Second of all, the masses shown above are without all the other improvements we are talking about adding, they are the numbers for the original Saturn V and Apollo.

So, besides the original J-2, J-2X is probably the worst choice, although still way better. The full scale RS-25 would only be used for being available, as it is also not the best, although it is still great and semi-readily available. However, IIRC it is not restartable. A 50% RS-25 is a better option, and if you are going to the effort to make it that small you might as well add restart capability and remove unnecessary gimbal (lowering the mass) so the actual RS-25 50% Delta-V would be higher, maybe 4700m/s instead.

At that point, the RL-10 may look worse due to the TWR problems that 5 present and the space problems that 10 presents (and more failure points, but also engine out capability), however the extra 50-150m/s might be worth the cons, because they are available now rather than the 50% SSME which is not.

Plus, I checked, and boiloff between the two split TLI burns on a 5x RL-10 setup isn't actually that bad - Centaur currently boils off at about 17% per day (and they are aiming for 0.1% with ACES so that is definitely improvable), so for 2-3 extra hours in orbit that's a 2% reduction in fuel, and assuming that directly correlates to delta-V (it doesn't but it's close enough) and only half of the fuel mass is effected (the split burn) gives the 5x RL-10 4771m/s, which is better than the 50% SSME.

And you might not even need five, given the mass reductions elsewhere and the fact that you have 400m/s more Delta-V than the actual S-IVB you could probably go down to four, or even three if you were feeling adventurous.

Again, this is not counting politics. From purely a "MAKE SATURN V SMALL AND LIGHT" perspective, RL-10s seem like a pretty good choice.

 

Back to the second stage, actually the RD-120 might be better than the SSME if only slightly. 

 

As far as the first stage goes, not doing all of the math, just a table. Only the Merlin is currently in production. Specific impulse is sea level, as is thrust.

Engine	Specific Impulse	Mass	Thrust	Number needed (33850kN)
F-1	263s	8400kg	6770kN	5
RD-170	309s	10750kg	7257kN	5 (4.67)
F-1B	270	9000kg	8000kN	5 (4.23)
Merlin	282	470kg	845kN	40 (weighing about 18 tons)

Ran out of rows, Raptor - 330s Unknown 1700kN  20

 

Again, mass reductions are possible. If we're sticking with kerolox I would go with 4 (reduced mass of everything else) RD-170 (Energia core EDIT: side engine) although if you were willing to make the fuel switch Raptor looks better due to the extra efficiency.

 

EDIT: As far as S-IVB hydrolox engines go, there is also Vinci and KVD-1 which have higher efficiencies than RL-10 but also less thrust and more mass, so they probably aren't better.

EDIT: Same thing with CE-7.5 and LE-5 for the sake of being complete.

Edited April 26, 2018 by Ultimate Steve

[StrandedonEarth]

There is another area with the potential for mass savings: Power generation and storage. Newer electronics consume much less power, requiring smaller batteries, which are also lighter for a given power capacity compared to old batteries. This won't amount to much for the launch vehicle, but should have a bigger effect on the SM and LEM.

The SM used fuel cells, would modern fuel cells be lighter? Since less power is required*, they could be smaller, and less reactants would be needed. Or perhaps the SM could switch to a PV system for longer duration missions. The LM also used batteries, with the same potential for weight reduction or upgrading.

I assume Saturn was built of aluminum? Considerable weight could be saved just by switching to the Li-Al alloy used in the Super-Lightweight ET's at the end of the Shuttle program.

Personally, I wouldn't use weight saving to shrink the system, instead I would upgrade the capabilities of the mission. Newer, lighter batteries would extend the range of the rover, which is a must for science and mineral surveys, and solar charging stations could be a thing. 

*unless more power-hungry devices are added.

[Ultimate Steve]

So, I'm a techie for the play (opens tomorrow) and I don't do much, so at rehearsal tonight I made a list of optimizable things and changes. Again, IRL we would probably use the changes for extra capability, but the thread is about lightness.

• Modern computer systems (duh)
• Modernize the instruments in the instrument ring and move them to the interstage where the LEM is stored, eliminate the instrument ring altogether.
• Modern electrical systems - less power hungry, better batteries, etc. Maybe change the interface to a touchscreen system, if the increased power requirements are worth the weight reduction.
• Update the fuel cells or get rid of them and coat the SM in lightweight solar panels.
• Lighter docking apparatus - ditch the crew tube entirely. Use the CM as an airlock and do EVA transfer, Apollo was capable of it (at least in later versions).
• Switch out the current heat shield for PICA-X
• Upgrade the spacesuits to make them lighter
• Keep the updated lander improvements but use the extra capability to remove fuel and the corresponding tankage to make the lander overall lighter. Drop the rover and most unnecessary cargo. We could go with a 1 man lander but that's outside the scope of Apollo.
• Update communications systems.
• Update Life Support Tanks.
• MAJOR: Change every single tank and structure except for possibly the S-IVB tank to carbon fiber, or Al-Li alloy as a backup if carbon fiber isn't current enough.
• Drop one of the three CM parachutes. It is redundant (for a good reason, yeah I'm getting rid of some safety features) and the lighter CM should be able to make do with 2.
• Make a better LES tower, with improved solids and make it lighter.
• Change the J-2 on the S-IVB stage to 3-5 RL-10's depending on how light the CSM/LEM end up.
• MAYBE: Switch the S-IVB to a balloon tank to lighten it, unless the CSM/LM are too heavy for the balloon tank structure.
• Add some more insulation to the S-IVB to make it last longer
• Change the whole paint scheme to mostly thermal reflective white
• MAYBE: Drop the S-IVB ullage motors, use a hot start for the first burn and pressurized gas from the stage on the others.
• Upgrade all RCS thrusters to modern efficiencies and manufacturing techniques.
• Update the SPS engine or find a replacement.
• Switch the cabin atmosphere to O2/N2, yes it adds mass but on the plus side you don't have to be as careful about fire protection.
• Lighten the boost protective cover, or if doable drop it entirely.
• Use a hot start for the S-II stage so you don't have to include ullage motors.
• You can probably get away with dropping the stage separation motors as well if you do it right.
• Switch to 2 (or maybe 1, but unlikely) RS-25's on the S-II stage.
• Don't bother with the weird S-II interstage, just leave it attached to the first stage, especially now that the nozzles are smaller and not as likely to strike the sides.
• Switch out the F-1 engines for less than 20 Raptor engines depending on how light the full stack gets OR use RD-170's if you want to stick with kerolox.
• If we use the Raptors, switch the stage 1 tankage to methalox.
• Drop the fins, they aren't needed.
• Drop the engine covers, the Raptors probably won't protrude out that far.
• 3D print many small parts and also use carbon fiber for many small parts.
• MAYBE subchill the propellants, like the Falcon 9 does.
• Get rid of most of the fuel baffles, they made them way too big because they didn't know as much about propellant slosh as we do now.
• Reduce fuel and structural margins within reason - as in, we have better computers so we can be more certain, especially the LEM's fuel margin, the computer can land it with less margin.
• MAYBE lower the first and second stage diameter by a meter or maybe 2.
• Shorten all of the fuel tanks to the necessary Delta-V requirements and drop engines as needed to preserve TWR.

 

[Nuke]

the agc was only about 32kg. a modern rad hard and ruggedized computer wouldnt be that much of a weight reduction (ive picked up modern-ish servers that heavy). unless you go with something giving you the bare minimum of computing power, something like you would find on a cube sat. i think id rather have the beefy space computer though. 

Edited April 27, 2018 by Nuke

[YNM]

IMO the best thing from modern electronics would be smaller size, not lighter mass.

Apollo CSM and LM is pretty cramped. Slightly more crew space could help with the journey i think.

Edited April 27, 2018 by YNM

[Nuke]

i think id use more composites in the structure, that would take off quite a bit of weight, at least from the parts of ship that aren't fuel. 

Edited April 27, 2018 by Nuke

[Racescort666]

@Ultimate Steve Raptor has an estimated TWR of 200 so by my guess, the mass is somewhere around 950 kg (based on vacuum thrust). Good to know I was wrong about the J-2X though.

Edited April 27, 2018 by Racescort666

[p1t1o]

At some point this starts to be more like designing a new vehicle from scratch, than "lightening" a Saturn V.

If you modernise every aspect of the Saturn V lunar shots, you probably get something much resembling the current proposed designs for new Moon missions.