Explain: Why the Apollo lander was done "Apollo style"

[mellojoe]

Why did the capsule have to detach, flip around, and reattach? Could the capsule and lander not just be built in the correct positioning? What decisions went into this process? I've honestly wondered this for years, since I was a kid, throughout college, and long after, but I've never really found out. I see all the information and reports THAT they did it, but I still can't quite find out WHY it had to be done.

[Firov]

I rather expect it was done for aerodynamic and weight savings reasons. The aft end of the service module wasn't exactly aerodynamic, so if they would have flipped the Command Module/Service Module upside down they would have needed to hide the Service Module's engine under an aerodynamic and structural fairing, which would have added additional weight (beyond what the boost protective cover took on the CM). Additionally, it wouldn't have really resulted in an easy to enter CM.

And related to that last point, having the SM sitting on the CM would have made the launch escape system VASTLY more complex, or maybe even impossible, which is a huge strike against it. Having the CM sit on top meant the launch escape system only had to pull the command module away from the rest of the stack.

Since the maneuver to dock with the Lunar Module was relatively simple, it made more sense to have the CM/SM undock, flip around, grab the LM, and pull both free.

At least that's my theory. I haven't read if that's the actual reasoning.

[Canopus]

Where would you put the escape tower then?

[TerLoki]

I can think of a couple reasons off the top of my head. Firstly, with the command module on top the launch escape system can be built smaller, since it just has to pull away a three-man capsule. Secondly, the LM only had to operate in space, so it was better to put it under a protective fairing rather than add more weight by designing it to survive the aerodynamic forces of take-off directly. And finally, if you're going to have to dock in lunar orbit to retrieve the lander anyway, then why not use a simpler lighter lander under a fairing and dock with it en-route to the Moon.

Side note: Been playing KSP too long, I had to stop myself from using "Mun" and "Munar" while typing this.

Edit: Crap, ninja'd.

[Nibb31]

The CM needed to be on top for the Launch Escape System to work properly. If the LM had been above the the CM, then the LES would have had to carry away the weight of the CM and the LM, which would mean that it would have to be more powerful and much heavier.

The CM also needed to be in the upright position with the astronauts facing upwards. If the CM was facing downward, already attached to the LM, the astronauts would have taken the Gs in an "eyeballs out" position, which is most uncomfortable and unsurvivable in case of an abort. In this case, the LES would have to carry away the entire CSM, which was even heavier than the CM+LM.

It was envisioned quite early that Apollo would require rendez-vous and docking, which is why the Gemini program was devised after Apollo started.

Edited April 16, 2014 by Nibb31

[sojourner]

The whole kit and kaboodle evolved the way it did due to weight limitations.

Edited April 16, 2014 by sojourner

[MK3424]

Watch the episode "Spider" from the HBO series "From the earth to the moon", then you will understand.

[Space Viking]

I'm quite curious over what the OP is specifically meaning with "correct positioning". Would that mean the default configuration but with the CSM upside-down, or having the LM on top upside-down?

Nevertheless, there's always other possibilities relative to design. AFAIK, the minimalistic Soviet LK lander would remain attached under the Soyuz spacecraft all the way to the Moon. It could theoretically do it Apollo style, but it would grant no benefits since the docking system didn't have a crew transfer capability and the Soyuz didn't have a mighty service module that had to be cleared. Cosmonauts had to perform an EVA in order to board the lander and then detach during Lunar orbit.

Edited April 16, 2014 by Space Viking

[Albert VDS]

Canopus said, you wouldn't be able to have an escape tower.

[Space Viking]

Canopus said, you wouldn't be able to have an escape tower.

Well, have you two actually even calculated the escape tower's thrust-to-weight ratio with a CM+LM combo and looked into important structural factors inhibiting the installation of an escape tower in such an unspecific configuration? Not saying I'm disagreeing, but nobody's gonna learn if the the answer's only gonna be "can't be done because it can't be done".

[sgt_flyer]

I'm quite curious over what the OP is specifically meaning with "correct positioning". Would that mean the default configuration but with the CSM upside-down, or having the LM on top upside-down?

Nevertheless, there's always other possibilities relative to design. AFAIK, the minimalistic Soviet LK lander would remain attached under the Soyuz spacecraft all the way to the Moon. It could theoretically do it Apollo style, but it would grant no benefits since the docking system didn't have a crew transfer capability and the Soyuz didn't have a mighty service module that had to be cleared. Cosmonauts had to perform an EVA in order to board the lander and then detach during Lunar orbit.

Soyuz style moon mission also needed the remaining fuel in the Block D transfer stage (on which the LK lander was attached) was also to be used as a braking stage for the moon landing - the block D was to be dropped after having slowed down the LK a lot.

[Urban_K]

Since the lander and CM has to dock once again, there's no real reason not to do it the first time too, is there?

The real questions are "why a separate lander?" and "why one launch instead of two?".

[Nibb31]

In the early stages of the Apollo program, there were two mission architectures.

- Earth Orbit Rendezvous (EOR), which involved two medium-sized rockets, and assembly of the spacecraft in orbit.

- Direct Ascent (DA), which involved one big rocket (the Nova, which was bigger than the Saturn V).

Two launches doubles the risk of failure. LOX and LH2 have a limited shelf life once on orbit. The propellant boils off if you leave it to loiter for too long. If one of the launches was scrubbed, you would lose the mission. With a single launch, you simply postpone until the next launch window. It also involved rendezvous and docking, which were technical problems that hadn't been solved yet. Some people even thought that they were unsolvable.

On the other hand, everyone knew that the Nova rocket would be a huge challenge. Saturn V was already stretching the limits of logistics and infrastructure. Nova was probably beyond those limits.

Both the EOR and DA Apollo plans had the entire CSM land on the Moon. The SPS would have served as an ascent engine (which is why it was over-engineered), but the CSM weighed 30 tons, so a descent stage would have much heavier than a separate LM that weighed only 15 tons.

There were also other problems, such as viewing the ground for the landing or getting the astronauts in clumsy EVA suits from the CM down to the surface 12 meters below (a 4-storey building) without breaking their neck. All sorts of contraptions were devised, like winches, rope ladders, and inflatable airlocks, but the whole idea was really impractical.

There were some big fights at NASA about which approach to use. Then, someone came up with the Lunar Orbit Rendezvous (LOR) architecture that we all know and all those problems were solved.

Edited April 17, 2014 by Nibb31

[MK3424]

Since the lander and CM has to dock once again, there's no real reason not to do it the first time too, is there?

The real questions are "why a separate lander?" and "why one launch instead of two?".

The key is weight:

If it's build as a single lander/spaceship you have to bring all the unnecesary parts down to the surface: that means it needs massive landing legs to support it on the surface, a massive engine to get everything on the Lunar surface and get off there,.....

(not including the lifting capacity of the Saturn V)

So, weight is the key.

[Kryten]

The single craft would also have to be aerodynamic, being at the top of the stack, which combined with the ∆v requirements would mean a relatively long, skinny vehicle: in other words, not something easy to land under rocket power.

[Nibb31]

Well, have you two actually even calculated the escape tower's thrust-to-weight ratio with a CM+LM combo and looked into important structural factors inhibiting the installation of an escape tower in such an unspecific configuration? Not saying I'm disagreeing, but nobody's gonna learn if the the answer's only gonna be "can't be done because it can't be done".

The CM weighed 5.8 tons. The fully fueled LM was 14 tons. The LES weighed 4 tons. A LES capable of carrying the CM+LM+its own weight would need need to be considerably heavier.

[KerbMav]

If there was a "best answer" function in these forums, I would select those from Nibb31.

[softweir]

There is one point that hasn't been mentioned: If the LM had been launched pre-docked to the CM, then the astronauts would have needed to perform a docking manoeuvre anyway, just to test the docking mechanism before transferring to the LM. Without a test docking manoeuvre, there would be a danger that the astronauts would discover that the docking mechanism was faulty at the worst possible moment - when they had returned from the moon and needed to get back into the CM to go home!

So launching the Apollo mission in that configuration didn't cost them an extra manoeuvre.

All the other reasons have already been explained.

Edited April 17, 2014 by softweir
Fixed clumsy wording.

[mrfox]

It was one of the many designs that was explored. As mentioned above, the direct ascent would've required a really big rocket, but that doesn't mean it wouldn't have worked. Had that path been selected, the development effort that was expended towards rendezvous and docking would've been instead poured into rocket research. In the "anything goes" era of the space race, the technologies were developed for the mission goals defined - not the other way around.

The Soyuz, as mentioned, is a good counter-point of what else could've worked. The Soyuz orbital module, a good sized hunk of hardware, is attached to the top of the crew capsule and launched in this configuration. The Launch Escape System pulls the whole contraption clear of the rocket stack, then separates the crew capsule which lands under parachute. It was successfully used in anger back in 1983.

http://en.wikipedia.org/wiki/Soyuz_7K-ST_No._16L

[bigdad84]

There is one point that hasn't been mentioned: If the LM had been launched pre-docked to the CM, then the astronauts would have needed to perform a docking manoeuvre anyway, just to test the docking mechanism before transferring to the LM. Without a test docking manoeuvre, there would be a danger that the astronauts would discover that the docking mechanism was faulty at the worst possible moment - when they had returned from the moon and needed to get back into the CM to go home!

So launching the Apollo mission in that configuration didn't cost them an extra manoeuvre.

All the other reasons have already been explained.

Bit of an off-topic question, but when they ascended from the moon's surface did they carry space suits with them? So if they were unable to dock they could just EVA and float over to the CSM? I know it would be unguided and uncontrolled floating in space, but still! It would be the next best option.

[Nibb31]

The Soyuz, as mentioned, is a good counter-point of what else could've worked. The Soyuz orbital module, a good sized hunk of hardware, is attached to the top of the crew capsule and launched in this configuration. The Launch Escape System pulls the whole contraption clear of the rocket stack, then separates the crew capsule which lands under parachute. It was successfully used in anger back in 1983.

Agreed, but the Soyuz OM and DM weigh only 4 tons together. The Apollo CM and LM together would weigh nearly 20 tons. To lift both of them, you would need an escape rocket 4 times bigger and heavier than the one used on Apollo, i.e. over 32 tons instead of 8 tons.

[Nibb31]

Bit of an off-topic question, but when they ascended from the moon's surface did they carry space suits with them? So if they were unable to dock they could just EVA and float over to the CSM? I know it would be unguided and uncontrolled floating in space, but still! It would be the next best option.

Yes, the EVA suits had to be carried back to orbit, because:

- They were needed to transfer for a contingency EVA to transfer to the CM if the docking failed.

- They were needed on the J-missions (Apollo 15-17) for the SIM bay EVA on the way home.

- They were also needed for "critical" phases, including reentry, in case a depressurisation occured.

But mostly:

- How would you open the hatch to throw out the EVA suits without wearing them :-P

Edited April 17, 2014 by Nibb31

[mrfox]

Agreed, but the Soyuz OM and DM weigh only 4 tons together. The Apollo CM and LM together would weigh nearly 20 tons. To lift both of them, you would need an escape rocket 4 times bigger and heavier than the one used on Apollo, i.e. over 32 tons instead of 8 tons.

Yup. "Moar boosters required!"

Obviously the tradeoff was a good one, but this is only obvious in hindsight. Imagine trying to argue the reliability of multiple, mission critical dockings, beyond ground station tracking/control/coverage, with only the experience of a few Mercury/Vostok flights under your belt.

If only Korolev had won this particular argument with his original Soyuz design back in 1962 (Earth orbit rendezvous - 5x R7 launches, LEO assembly), the Soviets might've very well beaten the Americans to the moon.

Edited April 17, 2014 by mrfox

[mellojoe]

Agreed, but the Soyuz OM and DM weigh only 4 tons together. The Apollo CM and LM together would weigh nearly 20 tons.

Wow. I had no idea the difference in scale of both crafts. I mean, I knew the American system was larger but not that it was 5 times the mass.

[Nibb31]

Wow. I had no idea the difference in scale of both crafts. I mean, I knew the American system was larger but not that it was 5 times the mass.

Be careful, we are comparing apples to oranges. The Soyuz OM+DM is functionally equivalent to the Apollo CM only, so they are quite close in terms of habitable volume and mass.

If you want to compare the CSM+LM with its Russian counterpart, it would be the LOK+LK+Block D complex.