Direct Ascent Moon landings?

[Nickmick95]

I found this article on Wikipedia about the Direct Ascent approach. Here it is: http://en.wikipedia.org/wiki/Direct_ascent

Post on this thread what you think about it.

 

[Cobalt]

So, send the whole thing to the moon and just plop it down tail first? Sounds....woefully inefficient at best, a massive catastrophe waiting to happen at worst. I think the reasons it isn't exactly feasible are listed right there.

 

[Woo482]

If nasa wants to test it I will Sit in it

 

[Belisarius]

Clearly it could only work (in manned missions) with a massive launcher and another massive return vehicle. Of course it was the method for the Surveyor landers and others, but they were never gonna come back. There are lots of reasons why it's a bad idea, but it sure looks good in Tintin.

 

[C3PO]

There are lots of reasons why it's a bad idea, but it sure looks good in Tintin.

SSTM? :rofl:

 

[Belisarius]

SSTM&B

 

[cjp]

No longer an interesting concept. It used to be interesting because people in those days didn't know whether rendez-vous would be doable. We know now that it's perfectly doable (even in lunar orbit), so we can use it to make the mission more efficient (means: smaller rocket).

 

[Andy44]

Direct ascent is technically less risky than lunar orbit rendezvous (LOR). A rendezvous is a technical problem, direct ascent skips it. Go to astronautix.com and browse the articles about Apollo. The author makes a good point: had NASA not had their hearts seton a 3-man capsule, they could have sent a direct ascent mission using a beefed-up Gemini vessel using a Saturn V: no Nova rocket required. This would have achieved Kennedy's challenge to reach the moon by 1970 and wouldn't have required mastering rendezvous techniques. It also makes abort options simpler, since you can abort at any time, even from the surface of the moon.

Another advantage to direct ascent to be considered for the future is that you can spend lots of time anywhere on the lunar surface and come home any time you like, since there is no need to dock with an orbiting spacecraft first. This is significant because for high latitude or polar landings the orbiting spacecraft's orbit plane will move with respect to both the earth and the landing site after a few days, making it necesarry to wait at least 14 days for the next fuel-efficient launch window to return home. A direct ascent vehicle can just launch into one of many planes, choosing the one that contains the best trans-Earth transfer trajectory.

 

[Belisarius]

Direct ascent is technically less risky than lunar orbit rendezvous (LOR). A rendezvous is a technical problem, direct ascent skips it. Go to astronautix.com and browse the articles about Apollo. The author makes a good point: had NASA not had their hearts seton a 3-man capsule, they could have sent a direct ascent mission using a beefed-up Gemini vessel using a Saturn V: no Nova rocket required. This would have achieved Kennedy's challenge to reach the moon by 1970 and wouldn't have required mastering rendezvous techniques. It also makes abort options simpler, since you can abort at any time, even from the surface of the moon.

Another advantage to direct ascent to be considered for the future is that you can spend lots of time anywhere on the lunar surface and come home any time you like, since there is no need to dock with an orbiting spacecraft first. This is significant because for high latitude or polar landings the orbiting spacecraft's orbit plane will move with respect to both the earth and the landing site after a few days, making it necesarry to wait at least 14 days for the next fuel-efficient launch window to return home. A direct ascent vehicle can just launch into one of many planes, choosing the one that contains the best trans-Earth transfer trajectory.

Good points. Is it really the case that DA is being considered as a mission mode for the proposed Constellation moon missions?

 

[Tschachim]

Is it really the case that DA is being considered as a mission mode for the proposed Constellation moon missions?

No, EOR + LOR: http://en.wikipedia.org/wiki/Project_Constellation#Lunar_flights

 

[Missioncmdr]

Of course, the main problem associated with the direct ascent technique that you have to bring everything you need to get home to the Lunar surface. This means that fuel need for launch and TEI would have to be carried. And that means a heavier and bigger vehicle. And a heavier vehicle means that more descent fuel would have to be carried to bring all of that to the surface. There would have to be a lot of weight compromises.

Or, as Andy44 said, you could go small and use a Gemini capsule. Of course, there are problems with that, too. Even comparing a theoretical Gemini Lunar landing to Apollo 11, Gemini is at a clear disadvantage. A Gemini capsule could not transmit live television pictures for example. Also, there are probably severe weight constaints, too. No experiments could be carried to be left on the Moon, fewer geological and other tools would have to be carried, and the amount of Lunar material that could be returned would be limited by weight and volume. And, obviously, no Lunar Rover. What you get is a classic "flags and footprints" mission.

With the LOR missions used with Apollo, less fuel and consumables would have to be brought to the Lunar surface since a lot of it was left in orbit with the CSM. This ultimately meant more science. And, with the LOR option, NASA found good uses for having a second ship in orbit. One astronaut could take pictures, operate experiments, and (on later flights) use equipment located in SIM bay.

If you look at Apollo 13, a problem in one spacecraft completely crippled it. But they had the LM which was unaffected by the problems in the SM. Having a second spacecraft is a definite advantage in this type of situtation. Something that could not be done with a direct ascent option. Unless every last component was doubly redundant, which, of course, means more weight.

LOR was probably the best option at the time, once rendezvous was proven to be practical.

 

[Andy44]

It wouldn't have been a stock Gemini, of course, it would've been a bigger version. But like I said, flags and footprints was the only reason for Apollo in the first place, and direct ascent with a 2-man mission would've been cheaper. Sounds short-sighted? Sure, but considering NASA was going to trash ALL the Apollo-Saturn hardware in 5 years, it was all pretty much a waste anyway. LOR makes better sense if you plan on building a space infrastructure, but NASA is not equipped with the political skill for that.

As for Constellation, it's even more complicated than Apollo, since it is both EOR and LOR. Which means after the first rocket launches, the second one must launch within a certain window or the whole thing gets called off. Cryogenic propellant doesn't keep for long in orbiting rocket stages bathing in sunlight. Given the delays we've seen with launches, you can see this one coming. Not to mention it's way more expensive to do two launches. All of this is good if and only if NASA, and more importantly Congress, plans on using the big moonlift capacity to actually build something lasting this time. I'm not holding my breath.

Okay, I'll stop ranting...trying to stay on topic.

 

[Jrquinlisk]

I've found that astronautix.com, while a fantastic source for technical info, is somewhat...lacking in terms of analysis. The author seems to think that Gemini is the answer to most, if not all of our problems in manned spaceflight, and while he does raise several valid points, I have to agree with Missioncmdr on this. The decision to use Apollo instead of Gemini provided the program with considerable extra scientific capability, as well as a significant emergency reserve capacity.

I do, however agree with Andy44 on Constellation. It's not worth going back to the moon if we're not going to stay this time.

Of course, this would all be a moot point if we had a well-established earth-moon infrastructure. Unfortunately, if I live long enough to see that, I'll probably be to senile to notice.