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Jestersage

Why is Direct Landing Beneficial for Lunar Base building?

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Posted (edited)

According to Astronautix, for Lunar Base building, Russians conclude a Direct Landing Lander is the "most practical method for emplacement and support of a lunar base, since lunar orbit rendezvous methods restrict possible base locations to a narrow band around the lunar equator." This can be seen in the Vulkan LEK

Can someone explain the reasoning behind it?

(Note: Astroantuix use "direct landing", not "direct ascend") So it's not what happen when they leave, but how they arrive. By Vulkan LEK, seems like it's just your standard DA landing profile.)

Edited by Jestersage

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You have to time your Moon intercept burn so it match the inclination of the base, that is twice an month and would even work for polar orbits. More clunky and if you get much launch delays you get to wait. 

Landing directly without an moon orbit also require precise burns but save some dV 

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Posted (edited)
8 hours ago, Jestersage said:

According to Astronautix, for Lunar Base building, Russians conclude a Direct Ascent Lander is the "most practical method for emplacement and support of a lunar base, since lunar orbit rendezvous methods restrict possible base locations to a narrow band around the lunar equator." This can be seen in the Vulkan LEK

Can someone explain the reasoning behind it?

 

(Edit* I misunderstood what direct ascent was referring too. After reading@VincentS and @Dragon01 >_<. I’ll leave my answer here anyway even though it’s about long term stuff.)

Spoiler

Hmmm, that’s weird. You don’t need to enter lunar orbit in an equatorial orbit. You can insert into any inclination and it’s better to do so because it lets you access more of the surface, so I duno what the part about being restricted is about. This is the whole idea behind NASA’s Lunar Gateway. It’s in a highly elliptical polar orbit and from there you can access virtually any part of the surface with minimal DV penalty (but I think you need to make rendezvous specifically at its apogee... not sure) 

but having said that I agree with the Russians about direct to surface being the most practical. And beyond that it’s probably better in the long term.

Gateway seems like a solution to a very temporary logistical situation. Something that could become unnecessary relatively quickly, and so may be a big waste of money depending on your viewpoint.

The reason I say this is because as soon as there is a base on the Lunar surface with an ISRU capability the logistics of exploration changes so that it would seem favourable to use the ground base as a hub and use reusable landers to make suborbital hops. A direct ascent lander should have the deltaV to access a huge percentage of the moon’s surface for less DV than it would cost to get into orbit.

(I haven’t crunched the numbers, just guesstimates but I think that’s right. Direct Ascent is a single stage lander right?)

 

Edited by Dale Christopher

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1 hour ago, Dale Christopher said:

Direct Ascent is a single stage lander right?

If so, then the obvious reason why it's better with a ground base and orbital station is, you can't make innumerable multiple trips when you drop stuff off your ship.

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Let's assume that you launch from your moon base and want to rendez-vous in orbit with some station or tug.

Case A : equatorial base. Having target on equatorial orbit makes it easy to rendez-vous because orbital plane is already the same. You launch due east to get some free velocity from moon rotation, and have one window per target orbit.

Case B : (almost) anywhere else. "Natural" orbit will have some inclination (depending on latitude), so obvious choice for target is an orbit with the same inclination. But due to moon rotation, orbit planes will match only once per month.

Case C : polar base. You can reach any polar orbit you want directly from the pole (no plane change required), so once again you have one window per target orbit.

Notices :
- Landing at your base is almost the same as launching from your base, but in reverse.
- Transfer between earth and your target orbit around the moon may require plane change too in case B and C (or waiting for the right window). In case of C, it matters only if you have some kind of station (you can always reach some polar orbit)
- Plane change is possible, but for large angles it will be very inefficient. And if you have much dv to spare, why bother to rendez-vous ? take the direct approach...
- You can test these scenarios on KSP ;)

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Orbit planes will match twice per month, since you can launch at either ascending or descending node. The problem, IIRC, is with launching to an inclined lunar orbit. KSP doesn't really do it justice, injecting into anything but a near-equatorial lunar orbit takes, like any other plane change, a lot of dV.

Direct ascent is very much not a single stage lander. In fact, as the most dV-intensive method, you'll want two stages, maybe three (crasher, landing and ascent). Vulkan's lander had two stages, and I'm not sure if Hercules wasn't supposed to perform part of the braking burn, as well. The Nova-based architecture used two stages and had a lander the size of an Atlas rocket. Direct ascent is the simplest method that allows you to reach anywhere on the Earth-facing side, but it's really dV heavy. It avoids the complexities of docking, allows the use of hydrogen stages for Earth departure without worrying about boiloff, and you get a launch window once per day. Additionaly, Baikonur is poorly situated for lunar launches, so LOR and EOR lose some of their appeal, since launching to a parking orbit is more expensive from there. 

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Posted (edited)
8 hours ago, Jestersage said:

Can someone explain the reasoning behind it?

First of all it was just because of no experience of docking at all (leave alone lunar ones), and to make the ship and ballistics as simple as possible.
Also, in the near future the LK-700 should be assisted with two more launches: of a 80 t heavy lunar base and a heavy rover/lab, spending on the Moon a month or so.

So, the Apollo-style expedition would weight less but: be more problematic after a monthly uncrewed flight (while the crew is on surface), and the lunar base anyway required a heavier than Saturn rocket, so why bother with separate landers and complicate ballistics.

5 hours ago, magnemoe said:

More clunky and if you get much launch delays you get to wait. 

And the delays are not a problem if the rocket (UR-700) is not cryogenic (hi, Saturn and N-1).
It can stay for a month ready to start.

5 hours ago, Dale Christopher said:

Direct Ascent is a single stage lander right?)

Doesn't relate to the stage count.

Edited by kerbiloid

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Posted (edited)

@kerbiloid

Thanks, I already realised it was referring to a specific thing after reading some of the other answers.

I’ll hide my answer in shame :-( 

 

Edited by Dale Christopher
Shame

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If the base is at the south pole (or north pole) then orbital rendezvous make sense again, regardless of direct ascent or orbital rendezvous return to earth windows from low polar orbit open once every 14 days, or they can fly up to L2 and swing back to earth from there at any time with small added cost in fuel and up to doubling of flight time (up to 7 days instead of 3-4) 

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Oops. I double checked. Astronautix wrote "Direct landing", not "direct ascent".

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22 hours ago, kerbiloid said:

And the delays are not a problem if the rocket (UR-700) is not cryogenic (hi, Saturn and N-1).

It can stay for a month ready to start.

I suspect that both the Saturn and N-1 could remain on the pad while being topped off for months.  Considering the Apollo budget, I'm sure the fuel bill could have come out of petty cash.  Worrying about working next to a fully fueled rocket would be significantly worse near a UR-700, as even if you survived the blast from an explosion you would have to deal with the cleanup (the size of the area in danger would be significantly larger).

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10 minutes ago, wumpus said:

Worrying about working next to a fully fueled rocket would be significantly worse near a UR-700, as even if you survived the blast from an explosion you would have to deal with the cleanup

The one who is doomed to get frozen won't get poisoned.

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