How much lighter could Apollo be today?

[YNM]

2 hours ago, Nuke said:

composites

May as well you make a new rocket...

 

IMO a "realistic" option would be like the Soyuz. Soyuz-MS and Soyuz 7K-OK doesn't differ much in structural, only in technology.

Edited April 27, 2018 by YNM

[kerbiloid]

If a modern composite capsule with lightweight electronics were significantly (say, twice) lighter than Apollo capsule, would it even make sense to build Apollo?
Direct land/ascent scheme would be more effective, without lunar module and other. Land the lightweight capsule instead of bothering with LEMs, lunar rendez-vous, etc.
This in turn means that an orbital person would be not required. Crew of 2, both land.

So, today this would be absolutely not Apollo.

Spoiler

http://www.astronautix.com/g/geminilunargemini.html

Edited April 27, 2018 by kerbiloid

[zolotiyeruki]

6 hours ago, YNM said:

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.

That's a good point--with the miniaturization of electronics (and other systems), you'd free up space, which you could use by either giving the astronauts more room, or by shrinking the CSM diameter, which would further reduce mass.  Surface area, and therefore structural mass, increases roughly as the square of the diameter or the 2/3 power of the internal volume, if I'm remembering my math correctly.  A smaller capsule would also mean decreased forces from containing atmospheric pressure in the capsule, which might enable further weight reduction in the structure.

Edited April 27, 2018 by zolotiyeruki

[sevenperforce]

1 hour ago, kerbiloid said:

If a modern composite capsule with lightweight electronics were significantly (say, twice) lighter than Apollo capsule, would it even make sense to build Apollo?
Direct land/ascent scheme would be more effective, without lunar module and other. Land the lightweight capsule instead of bothering with LEMs, lunar rendez-vous, etc.
This in turn means that an orbital person would be not required. Crew of 2, both land.

So, today this would be absolutely not Apollo.

  Hide contents

http://www.astronautix.com/g/geminilunargemini.html

Anything that would make Apollo smaller would just make LOR more efficient.

[kerbiloid]

9 minutes ago, sevenperforce said:

Anything that would make Apollo smaller would just make LOR more efficient.

Until the orbital part gets heavier than direct flight.
You cannot decrease the mass of additional human (+ lifesupport for him) and docking systems.

Say, the lowest limit. Ships weight nothing. Just spacemen in suits fly from LEO to the Moon. 
Will the 2 on the Moon need the 3rd in LMO?
So, the intersection point is somewhere  between Apollo and bare suits.

Additional mechanisms of the 3rd stage (whale's jaws), additional cabin, etc.
When they were designing Apollo, LOR scheme was absolutely not obvious. Most of projects afaik were direct flight.

Edited April 27, 2018 by kerbiloid

[sevenperforce]

9 minutes ago, kerbiloid said:

Until the orbital part gets heavier than direct flight.
You cannot decrease the mass of additional human (+ lifesupport for him) and docking systems.

Say, the lowest limit. Ships weight nothing. Just spacemen in suits fly from LEO to the Moon. 
Will the 2 on the Moon need the 3rd in LMO?
So, the intersection point is somewhere  between Apollo and bare suits.

Au contraire. The spacemen in suits still need fuel to get from LLO to LEO, and they need a heat shield, and they need parachutes.

So it will always be more efficient to leave a bottle of fuel, the heat shield, and the parachute in LLO while they go down the the lunar surface and do their surface mission than it would be to drag the fuel, the heat shield, and the parachute down to the lunar surface and back.

[wumpus]

1 hour ago, kerbiloid said:

If a modern composite capsule with lightweight electronics were significantly (say, twice) lighter than Apollo capsule, would it even make sense to build Apollo?
Direct land/ascent scheme would be more effective, without lunar module and other. Land the lightweight capsule instead of bothering with LEMs, lunar rendez-vous, etc.
This in turn means that an orbital person would be not required. Crew of 2, both land.

So, today this would be absolutely not Apollo.

http://www.astronautix.com/g/geminilunargemini.html

I doubt that an orbital person would be required for a modern lunar rendezvous.  The direct approach still requires taking 680m/s of fuel to the surface that isn't otherwise needed.  While it might be worthwhile to take a single habitable module (heat shield and all) all  the way down to the surface and back, you still probably want to leave the last stage of return engines in orbit.

The other catch is that whether or not you are "upgrading a Saturn V" or not, you are making a new rocket.  Nobody has had the capability to build or launch a Saturn V since the mid 1970s.  Tweaking a Saturn V is an interesting game in realism overhaul (or possibly  Making History), but any real design would have to start from scratch and would likely be based on SLS, BFR, or New Armstrong (or possibly an extremely upgraded Soyuz or Falcon Heavy).

[kerbiloid]

17 minutes ago, sevenperforce said:

Au contraire. The spacemen in suits still need fuel to get from LLO to LEO, and they need a heat shield, and they need parachutes.

If they have enough fuel in their jetpacks to fly from Tony Stark's residence to the Moon and back, why should they need a third companion waiting in LMO?

17 minutes ago, sevenperforce said:

So it will always be more efficient to leave a bottle of fuel, the heat shield, and the parachute in LLO while they go down the the lunar surface and do their surface mission than it would be to drag the fuel, the heat shield, and the parachute down to the lunar surface and back.

If everything could be scaled.
But you can't scale down the humans.
So, an extra astronaut, his supplies, seat, additional mass of larger capsule (3 instead of 2, 5.6 t of Apollo vs ~2 t of Gemini), second cabin, 2 docking nodes, tunnel with two doors, bigger interstages, additional fuel to propel this stuff — cannot decrease. 
And at some point an unary ship will weight not much more than a splittable one, definitely less than Apollo, but LOR would still greatly increase complexity and risk.

13 minutes ago, wumpus said:

I doubt that an orbital person would be required for a modern lunar rendezvous. 

Then they don't need a capsule in orbit while they are on the Moon.

Suppose, a 2-seat capsule is as lightweight as LEM cabin. Does it still need an orbital module?

Edited April 27, 2018 by kerbiloid

[RCgothic]

If I were planning the moon landings today I would go for earth-lunar orbit rendezvous. We're just so much better at rendezvousing than we used to be.

The rocket could be much smaller which would do wonders for launch cadence, and as spacex are discovering quantity is a quality all of its own.

Edited April 27, 2018 by RCgothic

[sevenperforce]

7 minutes ago, wumpus said:

I doubt that an orbital person would be required for a modern lunar rendezvous.  The direct approach still requires taking 680m/s of fuel to the surface that isn't otherwise needed.  While it might be worthwhile to take a single habitable module (heat shield and all) all  the way down to the surface and back, you still probably want to leave the last stage of return engines in orbit.

Right. Constellation didn't plan on having any crew remain in Orion during the lunar mission on Altair. Everyone goes to the surface; Orion waits autonomously on standby.

The 680 m/s of fuel isn't going away, even if you do away with the life support in orbit.

9 minutes ago, kerbiloid said:

If they have enough fuel in their jetpacks to fly from Tony Stark's residence to the Moon and back, why should they need a third companion waiting in LMO?

The third companion waiting in lunar orbit isn't necessary. But keeping your fuel, heat shield, and anything else you can in orbit is always the more efficient option, compared to taking it down to the surface.

The most mass-efficient mission profile, assuming that you're not depending on any permanent infrastructure like a lunar space station and you're returning to Earth, will always be some sort of lunar orbit rendezvous.

The theoretically most mass-efficient mission architecture would be to have a single habitable capsule with its own vacuum engines and a docking port on the base, but with no heat shield or parachutes and only a minimal aeroshell. It would be paired with an "Earth entry module" consisting of a docking port, fuel tanks, parachutes, and a heat shield. Once in lunar orbit, the capsule would break away from the Earth entry module and descend to the lunar surface, then return and dock with the orbiting module for the homeward journey, using that module's fuel tanks for its own engine.

Of course, the complexity of such a system would make it impossible to man-rate.

7 minutes ago, RCgothic said:

If I were planning the moon landings today I would go for earth orbit rendezvous. We're just so much better at rendezvousing than we used to be.

The rocket could be much smaller which would do wonders for launch cadence, and as spacex are discovering quantity is a quality all of its own.

You'd want Earth-Lunar orbit rendezvous like Constellation, not pure Earth orbit rendezvous like the original Saturn C-1 "Jaybird" approach.

[wumpus]

16 minutes ago, kerbiloid said:

Suppose, a 2-seat capsule is as lightweight as LEM cabin. Does it still need an orbital module?

LEM (dry) : 5.4 tons (US) https://www.hq.nasa.gov/alsj/LM04_Lunar_Module_ppLV1-17.pdf
Apollo capsule: 6.1 tons (US), 5.4 tons (metric) source: infallible wiki
Dragon2 (dry): 7.0 tons (US), 6.4 tons (metric) : note this is *not* built for the >3000 m/s needed for a lunar landing. ibid wiki

Might be possible.  I'd still want the return engine in orbit.  I also suspect that using a Dragon2 would involve more mass than LEM+CSM(capsule).  You aren't building anything with a heat shield lighter than a LEM.  Those things were quite flimsy.  The real question is whether it is worth taking both spacecraft ~4000 m/s to the moon, another ~4000m/s down and back vs. a heavier system the whole ~8000m/s.  Losing the orbital module likely means a lot more mass.

Ideally I'd want the return module on the surface and passing all self-tests before launching anybody to the Moon.  From what I've read, the return engine was the weakest link expected in the whole system (it was transported the most delta-v, so was lightened the most).  Breaking a system into manned and unmanned would change the lunar mission drastically.

[kerbiloid]

39 minutes ago, sevenperforce said:

But keeping your fuel, heat shield, and anything else you can in orbit is always the more efficient option, compared to taking it down to the surface.

Of course. Until their separation/catching makes more headache than taking them to the surface, which requires just more fuel (and barrels).
If your reentry capsule weights like LEM cabin and has, say, an inflatable heatshield, will you really add the complexity and risk of its catching near another celestial body?
Or you will just take a little moar fuel and make the capsule unary, if the whole ship will mass 40 t?

Again, the IronMan sample. Should they take off the outer layer of the suit, leave it in orbit, then catch it in orbit, dress again and then return to the Earth?

39 minutes ago, sevenperforce said:

The most mass-efficient mission profile, assuming that you're not depending on any permanent infrastructure like a lunar space station and you're returning to Earth, will always be some sort of lunar orbit rendezvous.

1. Unless the docking/searching/rendezvousing equipment (which doesn't depend on your ship mass) has greater mass than your whole ship (IronMan example).
2. Most mass-efficient != optimal. It would be mass-efficient to not use LES, but they do. It would be mass-efficient to use single engine in LEM, but they used two.

27 minutes ago, wumpus said:

LEM (dry) : 5.4 tons (US) https://www.hq.nasa.gov/alsj/LM04_Lunar_Module_ppLV1-17.pdf
Apollo capsule: 6.1 tons (US), 5.4 tons (metric) source: infallible wiki
Dragon2 (dry): 7.0 tons (US), 6.4 tons (metric) :

Seats:
LEM: 2 (and its dry mass includes everything, not just cabin)
Apollo: 3 (and its mass includes the wide lower part with RCS system, while the crewed part of the capsule is the upper 2/3 of the capsule, so they made the capsule heavier than it would be if place RCS section on top, like in Gemini or VA TKS)
Dragon2: 7 (and Musk knows what it includes)

Gemini: ~1.5..2 t (depends on capsule or whole ship)
Soyuz capsule: ~ 2t

Say, that Gemini lander :

Quote

The total mass to be injected into an escape trajectory toward the moon would be no more than 13,000 kg, one fifth of the 68,000 kg planned for the Nova-boosted direct-lunar landing approach favored at that time. A

Compare it to 47 t of Apollo.

Upd. Yes, the Gemini lander should reach the Moon unmanned.
But the longest Gemini flight lasted for 2 weeks (without external supplies), so even with people onboard it would weight not much more.
Certainly the crew would reach the Moon with full diapers, but who would care at this moment of glory?

Edited April 27, 2018 by kerbiloid

[sevenperforce]

6 minutes ago, kerbiloid said:

37 minutes ago, sevenperforce said:

Keeping your fuel, heat shield, and anything else you can in orbit is always the more efficient option, compared to taking it down to the surface.

Of course. Until their separation/catching makes more headache than taking them to the surface, which requires just more fuel (and barrels).
If your reentry capsule weights like LEM cabin and has, say, an inflatable heatshield, will you really add the complexity and risk of its catching near another celestial body?
Or you will just take a little moar fuel and make the capsule unary, if the whole ship will mass 40 t?

Inflatable heat shield saves volume, not mass. Inflatable heat shields are not significantly less massive than their rigid equivalents.

The Moon isn't small enough to just require "a little moar fuel". It requires a lot.

6 minutes ago, kerbiloid said:

Again, the IronMan sample. Should they take of  the outer layer of the suit, leave it in orbit, then catch it in orbit, dress again and then return to the Earth?

Well, that's certainly the more mass-efficient approach. And if your dV requirement is high enough (as it is with the Moon) and your Isp is low enough (as it is with chemical bipropellant fuels), then you need the mass-efficient approach. Iron Man has infinite Isp so obviously that's not a problem.

6 minutes ago, kerbiloid said:

Most mass-efficient != optimal. It would be mass-efficient to use single engine in LEM, but they used two.

Actually, because the landing engine needed high thrust to lower gravity losses along with deep throttling capability, it was more mass-efficient to use separate engines. I ran the numbers on this once. Using a crossfed drop-tank landing stage with a single engine ended up being less mass-efficient than using a separate non-throttled ascent engine, at that time.

[kerbiloid]

12 minutes ago, sevenperforce said:

The Moon isn't small enough to just require "a little moar fuel". It requires a lot.

It requires M/M~2 to start and escape (2.4 km/s delta-V / 3.5 km/s ISP) and say nearly the same to brake and land.
Say, Gemini capsule 2.5 t + 0.5 t of additional heatshield (11 km/s instead of 8).
So, 3 t.
So, the ascent stage mass = 3 * 2 * 1.1 = 6.5 t.
Landing stage = 6.5 * 2 * 1.1 = 14.3 t.
So, you need to send ~14 t from LEO. Instead of 47 t of Apollo+LEM.
As you can see, this rough estimation accurately corresponds to the real Geminin lander project mass: 13 t.

To launch this from LEO to the Moon : ~3 km/s, i.e. M/M~2.3
So, you have to put in LEO ~14.3 * 2.3 * 1.1 = 36 t.

Instead of 3000 t Saturn-5 with 140 t you could use just 1200 t UR-530 with 36 t of payload.

And no dockings (Apollo needed 2 per flight).

Edited April 27, 2018 by kerbiloid

[sevenperforce]

5 minutes ago, kerbiloid said:

It requires M/M~2 to start and escape (2.4 km/s delta-V / 3.5 km/s ISP) and say nearly the same to brake and land.
Say, Gemini capsule 2.5 t + 0.5 t of additional heatshield (11 km/s instead of 8).
So, 3 t.
So, the ascent stage mass = 3 * 2 * 1.1 = 6.5 t.
Landing stage = 6.5 * 2 * 1.1 = 14.3 t.
So, you need to send ~14 t from LEO. Instead of 47 t of Apollo+LEM.
As you can see, this rough estimation accurately corresponds to the real Geminin lander project mass: 13 t.

To launch this from LEO to the Moon : ~3 km/s, i.e. M/M~2.3
So, you have to put in LEO ~14.3 * 2.3 * 1.1 = 36 t.

Instead of 3000 t Saturn-5 with 140 t you could use just 1200 t UR-530 with 36 t of payload.

And no dockings (Apollo needed 2 per flight).

Not a good comparison because the LM+CSM combo was far, far more capable than the Gemini capsule.

[kerbiloid]

12 minutes ago, sevenperforce said:

Not a good comparison because the LM+CSM combo was far, far more capable than the Gemini capsule.

Gemini was enough capable for 2 crewmen for 2 weeks (though without pleasure).
They could anyway take a bucket of stones replacing the  bucket of wastes.
As you have 14 t instead of 47 t, then using Saturn you can scale up the ship and use ~47/14 = 3 times heavier capsule than Gemini. They call it Apollo. And in this case it is for 2 persons, not for 3.

Upd.
But of course in this case it would be more comfortable to add a 2 t lunar habitat to the Gemini capsule. See Soyuz spherical head. It is airlock, toilet, kitchen, hall 4-in-1. And it is ~1.5 t.
They can use such sphere as habitat flying to the Moon, as airlock and toilet on the Moon, then leave it there and get to the Earth inside Gemini cabin.
 

Edited April 27, 2018 by kerbiloid