View Single Post
  #11  
Old May 22nd 19, 09:02 PM posted to sci.space.policy
Fred J. McCall[_3_]
external usenet poster
 
Posts: 10,018
Default NASA's full Artemis plan revealed: 37 launches and a lunar outpost

JF Mezei wrote on Wed, 22 May 2019
15:21:39 -0400:

On 2019-05-21 22:42, Fred J. McCall wrote:

You're a bit confused. There are five LaGrange points, not just one.


https://space.stackexchange.com/ques...ear-halo-orbit


Thanks.

I take it this L2's advantage is that it gets closer to the moon from
time to time, giving opportunities to have less beefier transfer/landers?


It's covered in the cite I gave.


From a requirements perspective, would the actuial lander (without
transfer) be required to be able to rejoin the Gateway at any altitude,
or only when it makes a low pass (since we're talking direst ascent)


You've asked this before and it's been answered before. Neither the
Lander Element nor the Transfer Element could reasonably be required
to "be able to rejoin the Gateway at any altitude". I wish to God you
would learn even a little bit about orbital mechanics. Think about
what you're asking.

I'm missing something in your thought process here because the
preceding doesn't make sense. The Gateway is going to make its fast
and low north to south orbital segment around the Moon about every six
days.


I was thinking in terms of a static distance between Gateway and Moon.
If it varies, then this changes things.


You need to take notes or something. This has been explained to you
several times. At some point it ought to stick, Mayfly. Regardless,
the same thing applies if the Gateway is in a fixed lunar orbit. Once
a Transfer Element has dropped a Lander Element it is pretty much free
to return to Gateway, drop more Lander Elements, and eventually still
be available for the first Lander Element to meet with it. There is
no requirement for a Transfer Element to 'loiter' once it drops a
Lander Element.

does that because we want the Lander Element to spend roughly a month
on the surface. So they refuel it, mate with a new Lander, and 6 days
later (12 from the first Lander) it repeats and deploys a second
Lander. Another 12 days later and it deploys a third Lander. This
time instead of returning to the Gateway, it waits around. The first
Lander is 24 days into its mission.


Does this limit where the various landers can land in order to ensure a
lander can rejoin a transfer vehicle that is in the orbit that dropped
off another lander ?


No.


If the lander has to wait X time to take off so it can rejoin the
transfer element in orbit, does that make it harder to time it so that
once joined, they are in good position to ascend to Gateway?

No.


I can see why direst ascent makes sense since you don't have to wait for
the right time to launc to transfer element.


But now your Lander Element would need sufficient grunt to get from
Lunar surface into the appropriate NRHO to meet the Gateway. And you
still have to wait for the right time to Launch to Gateway.

Or you don't do that at all (remember, we're talking about L2 here),
which is why I said there was something like a 20% 'cargo penalty'


Just wanted to make sure I understood correctly. 20% is pretty
significant, isn't it ?

In terms of going to Mars and beyond, with that Gateway's L2 orbit have
any advantage over an L1 orbit ?


Yes.

Shuttle couldn't get to the Gateway orbit even if it was still flying.


Come on, I saw a documentary (Airplaine II) where the Shuttle ended up
crash landing on the moon and couldn't stop in time and hit the control
tower with Captn Kirk in it :-)


Mayfly, there are times when your output could lead someone to believe
that the preceding paragraph is about the level of your thinking.


I used the shuttle since we have experience with the main ISS resupply
vehicle being grounded for a long time.


Nope. Main ISS resupply was always Progress.


If Gateway needs to be refueled once a year, how many rockets can bring
sufficient fuel mass to an L2 orbit? Is it only SLS?


Anything that can get mass to that orbit can do the job. Gateway will
use ion engines that are pretty stingy insofar as fuel use goes. It
doesn't take huge amounts of thrust to maintain an L2 NRHO. Go read
the cite I gave again. So no, it is not only (or probably even
mainly) SLS that will be doing that job.


So if this thing gets built, doesn't it prevent SLS from ever being
cancelled?


Perhaps until Falcon Super Heavy, New Armstrong, or other vehicles are
flying, but not for the reason you're concerned with above.

Other than that you would need (and throw away) a much larger and more
capable Descent Element because now it needs the 'grunt' to get from
NRHO to LLO in addition to what it needs to get from LLO to the
surface.


So you have Gateway, designed to support multiple missions to the moon,
right? And an architecture that allows re-use of the Transfer element,
right?


Gateway is INTENDED to support both Lunar missions and deep space
missions. Other than that, essentially correct.


But if the landers ditch the descent stage when they ascend, won't they
have to ship a new descent stages for every weekend camping trip to the
moon? Seems to me like more than one resupply mission per year to Gateway.


Again you're confused. First, shipping vehicles for Lunar missions
out to Gateway is not 'resupply' any more than boosting up a new
module for ISS is 'resupply'. Second, there will be multiple types of
landers and each may (probably will) require it's own unique Elements.

And weren't you the guy proposing to just use LEM, which leaves its
descent stage on the Moon?


If this project is to support only one mission to Moon, is this Gateway
thing not only a waste of money, but also not providing any advantage to
the logistics?


If cows can fly, shouldn't you carry an umbrella? That question is
the same form as yours, above. Start with a false conditional premise
("cows can fly") and then ask a question that assumes the premise is
true. In your case, the falsehood is "this project is to support only
one mission to Moon". Since that premise is false, your question is
moot.


--
"Some people get lost in thought because it's such unfamiliar
territory."
--G. Behn