Should we be looking at Mercury and Gemini rather than Apollo? | Mission Planning Workgroup | Forum

So far it seems to have been taken as a given that we should be trying to proceed via a stripped down version of the Apollo mission structure.  Some design decisions, such as the command module / service module division, have been taken as granted from the get go.  I am starting to think that perhaps this has been a mistake and that we should be looking more toward Mercury and Gemini.  Let me expand.

Firstly, it seems to have been very widely accepted that while CLLARE is a lunar project, we're not going to simply start trying for lunar missions from the get guy.  We'll have to build our way up to it via suborbital and orbital flights, first unmanned and then manned.  The idea so far seems to have been that we shall try to design things so that they "scale down" to these simpler missions.  Booster-wise, our OTRAG approach means this will be no problem.  The modular booster can scale from light payload suborbital flights to heavy orbital insertions.  But with regards to manned missions, we seem to have designed ourselves into a corner somewhat.

The immediately obvious way to scale down our CSM design to a simple manned suborbital flight (equivalent to Vostok/Mercury) is to just use the CM by itself.  But this actually makes very little sense.  The entire point of the CM/SM split is that the CM does not contain everything needed for the lunar mission.  Some stuff, like communications gear, gas and liquid supplies, etc. goes into the SM.  This means that for a CM-only manned test flight, we would need to put extra stuff above and beyond the CM's usual capacity into the CM, to make up for the lack of an SM.  But if the CM were big enough to allow this, then the SM becomes kind of superfluous – it would be nothing but an engine.

Note also that there has been some support for only having RCS on the SM and letting control of the CM during reentry be purely aerodynamic in nature.  This is fine for a full lunar mission with the CSM arrangement, but for a CM-only test flight it would leave us completely unable to control orientation during orbit, which would make for an even more primitive mission than Vostok 1.  Having RCS on both the CM and SM would be the only solution, but this seems contrary to our philosophy of simplicity and cheapness.

I am starting to wonder if we should take a page from the book of Mercury, which had everything except for its reentry engines inside the one main capsule.  As near as I can tell, the only things in the Apollo SM which were not related to propulsion where communication gear and fuel cell gear.  Certainly fuel cells have miniaturised incredibly since the 1960s and I have to assume that comms gear has too.  We probably could fit everything non-propulsion related into the one capsule, which would make it a lot easier to use/test the craft in simpler missions first.  Rather than a CM/SM system, this approach would lead to a single module with a propulsion system attached to the end of it (possibly two separate propulsion systems for TLI and TEI, with each being jetisonned after it was used).  By propulsion system in this case, I'm talking purely about a big engine, not RCS, which would be on the module.

I think we should give this arrangement serious consideration.

Even more than I think we should learn from Mercury, I think we can learn a lot from the Gemini project.  Tonight I learned that NASA had plans, which never eventuated, to use the Gemini spacecraft for lunar missions either as a prelude to Apollo or in place of it entirely.  The planned Gemini missions, which you can read about on Wikipedia, feel like they are much more in the spirit of our cheap and simple approach than Apollo was.  In particular, they were considering our light and open lander approach:

The initial proposal was for a Lunar orbit rendezvous mission, using a Gemini spacecraft and a lightweight, open cockpit lander, launched by a Saturn C-3 rocket. It was the first time that Lunar orbit rendezvous was proposed as part of a lunar landing concept. The spacecraft would have been tested in Low Earth orbit before the Lunar missions, using two Titan II launches. The lander, which was designed by NASA's Langley Research Center, would have had a mass of no more than 4,372 kilograms (9,640 lb). Some of the proposals had a mass as low as 1,460 kilograms (3,200 lb), with cryogenic propellants being used in place of heavier hypergolic propellant. The proposal was intended to provide a faster and lower-cost alternative to the Apollo program, which was at that time proposing a direct ascent landing.

Not only this, but everything just seems so much more feasible with the Gemini approach.  Relatively speaking, Apollo was gigantic.   The Apollo CM weighed 5,809 kg, the Service Module 24,523 kg.  In contrast, the entire Gemini vehicle weighed 3,851 kg.  This means that insted of the 3 stage, 110.6 m tall, 10.1 m wide, 3,038,500 kg Saturn V rocket, which is such an intimidating beast, Gemini modules could be launched via the 2 stage, 31.4 m tall, 3.05 m wide, 154,000 kg Titan II rocket, which actually looks and sounds like something we could hope to replicate one day.  We should definitely be looking at Gemini for estimates of craft sizes and masses rather than Apollo, it seems much closer to what we are aiming for.

Of course, the majority of the Apollo SM mass was in the service engine.  Gemini had nowhere near enough thrust to get to the moon and back.  The idea behind the lunar Gemini project was to have the module dock with a rocket stage in orbit.  One of the main purposes of the Gemini program as it did go ahead was to practice docking with things in orbit.  The Agena Target Vehicle was designed to give them something to dock with, and it was mostly a rocket engine (although not a particularly large one).  Gemini 11 used an ATV engine burn to put it into an orbit with apogee 1374.1 km – Apollo is the only manned mission to have gone further.  A larger engine would have been needed for a moon mission, the basic idea of docking with an engine in orbit was proven sound.  We could use one engine put into LEO for TLI and send another engine for TEI into lunar orbit early via low energy transfers to use for the trip home?  Docking introduces extra complexity, admittedly, but it seems like this approach would drastically decrease the mass of the sorts of payloads we would need to launch.

I welcome discussion on everything mentioned here.  Even if we decide not to emulate some aspects of Mercury and Gemini, I think all of the proposals in this post are at least sensible enough to be worth considering, and that means that we have probably rushed into an Apollo style mission structure prematurely.  There are other sensible options and we should be carefully choosing what we do and do not copy from past missions.