How much mass was saved by using a two-stage LM in Apollo?

"Jeff Findley" wrote:

True. In addition to the mass of the landing gear is the mass of the
structure in the descent stage which was there to support and distribute the
landing loads, which was a pretty big unknown before the first landing. No
one really knew the physical properties of the lunar surface. That and no
one knew how well the astronauts would do landing the LEM with the
possibility of a lot of lunar dust being kicked up and obscuring the view.
It was a real possibility that the landing could be pretty hard if the
descent engine blew away enough dust to reveal a hard, rocky surface and the
blowing dust made the view so bad the landing was hard to begin with.

Sure, all those things were unknown before the first landing.

But after the first landing NASA chose to not disrupt LEM production
in order to update the design as the [LEM] program was already deeply
in trouble. Thus Apollo 11 was, in some regards, obsolescent even
before it flew.

D.
--
Touch-twice life. Eat. Drink. Laugh.

http://derekl1963.livejournal.com/

-Resolved: To be more temperate in my postings.
Oct 5th, 2004 JDL

are writes:


The two stage version has the safety advantage that there's a back-up
engine available should the descent engine fail during landing. In
addition, the ascent engine can be very simple, and hence reliable,
since it requires no throttle.

The later flights damaged the decent engine bell on contact, didn't they?

The seperate ascent engine was designed to be dirt-simple and discrete
from the decent systems.. for good reasons...


--
A host is a host from coast to
& no one will talk to a host that's close........[v].(301) 56-LINUX
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead....................................20915-1433

In article , says...
are writes:
The two stage version has the safety advantage that there's a back-up
engine available should the descent engine fail during landing. In
addition, the ascent engine can be very simple, and hence reliable,
since it requires no throttle.

The later flights damaged the decent engine bell on contact, didn't they?

Note that NASA required a bigger engine bell on the latter LMs. No
reason to assume an A11-sized engine bell would have suffered damage.

Once your committed to a two-stage LM, and cutting off the descent
engine while the craft is 3 feet above the surface, then a small amount
of damage to the descent engine isn't a big thing.
--
Kevin Willoughby lid

Kansas City, this was Air Force One. Will you change
our call sign to SAM 27000? -- Col. Ralph Albertazzie

Derek Lyons wrote:

Sure, all those things were unknown before the first landing.

Not completely unknown, as he had the Surveyor landings to give us some
indication of what the surface was like (the LM wasn't going to sink in
the dread hundred-foot-deep layer of Moon dust, for instance). Surveyor
6 was particularly helpful in this regard as it lifted off from the
lunar surface and then re-landed 2.5 meters away, letting the scientists
get a look at the depressions created by the landing pads during the
first landing.
But after the first landing NASA chose to not disrupt LEM production
in order to update the design as the [LEM] program was already deeply
in trouble. Thus Apollo 11 was, in some regards, obsolescent even
before it flew.


It also had the landing probes extending from the bottom of the landing
pads, to let the crew know when they were getting close to touchdown
even if they were blinded by dust. as was mentioned in another thread a
few months ago, the dust thrown up by the landing engine shot out at
very high velocity, and in the vacuum of the Moon kept right on going at
that velocity until gravity pulled it back to the surface, sandblasting
one side of the Surveyor 3 spacecraft during the landing of Apollo 12's
LM, despite the distance of the LM from the Surveyor:
http://upload.wikimedia.org/wikipedi...000-001316.jpg
During Apollo this wasn't a problem, but it will be a problem if we ever
build a permanent Moonbase and need to resupply it via cargo landers.
Every time one lands the Moonbase is going to get hit by something like
a horizontal micrometeor shower.
And you don't want to be standing outside when it hits, as it's not
going to help the clarity of your helmet's faceplate one iota.

Pat

Pat Flannery wrote:



Derek Lyons wrote:

Sure, all those things were unknown before the first landing.

Not completely unknown, as he had the Surveyor landings to give us some
indication of what the surface was like

But after the first landing NASA chose to not disrupt LEM production
in order to update the design as the [LEM] program was already deeply
in trouble. Thus Apollo 11 was, in some regards, obsolescent even
before it flew.

I thought it would be clear that Jeff was calling A11 the first
landing, while I was subtly reminding him it was not.

D.
--
Touch-twice life. Eat. Drink. Laugh.

http://derekl1963.livejournal.com/

-Resolved: To be more temperate in my postings.
Oct 5th, 2004 JDL

On Mar 24, 5:32 am, "Alan Erskine" wrote:
"Matt" wrote in message

...
On Mar 24, 6:03 am, "Alan Erskine" wrote:

Couldn't be too much - extra engine; propellant and pressurant tanks;
extra
insulation on the underside of the Ascent Stage etc, as well as the
separation mechanism and other systems.

I thought it was more about reducing the mass the ascent stage engine
had to lift back off the Moon.

Yeah, but if you had an empty 'Descent stage' (minus all the bits-and-pieces
I mentioned above), it wouldn't be _that_ much heavier. I might have to do
some heavy-duty research to find out - check out system weights etc and
deduct them from the DS structure.

Remember, it would also mean the descent stage would be lighter and
therefore use less propellant during descent; making more propellant
available for the combined ascent.

It didn't quite work anyway you'd care to cut it, so what's the
difference?
.. - Brad Guth

On Mar 24, 7:52 am, "Alan Erskine" wrote:
"Greg D. Moore (Strider)" wrote in ...

Consider you need tanks and engine. The mass of the tank compared to the
mass of the fuel probably isn't that much.

The DS tanks could have been extended - not by much either - they were
considerably greater diameter than the AS tanks. Also, the AS tanks were
spherical - basically, two domes welded together; so a small (cylindrical)
extension in the length of the DS tanks would have been much lighter than
that. Sure, as a % of propellant capacity, the saving might not have been
that great, but if all the systems _exclusive_ to the AS that were
essentially duplicates of the DS systems; the difference might be
substantial.

So extra tankage probably doesn't hurt as much there as one might think.

And then there's all the insulation panels under the AS. Think of the
increase in useable volume inside the AS. And there's all the panelling on
top of the DS - designed to prevent the thrust of the ASE from penetrating
into the DS. Wouldn't need that either.



The mass of the engine I'm guessing is a more significant issue.

According to EA (http://www.astronautix.com/engines/tr201.htm), the AS
Engine weighed 113kg. Plus all the pressurising tanks; plumbing (and the
pyrotechnics that go with stage sep) Does anyone know how much the landing
gear weighed? hmmmm....

I'm sure there's not going to be that much of a difference in total mass -
and then there's the residual prop in the DS - AS11 had 20 seconds, but the
other landings had over 60 seconds each - that adds up to quite a bit of
mass too.

You're trying to fix something that according to the lord almighty
(aka NASA/Apollo) was absolutely perfect in every possible way, that
oddly can't be replicated as of today or of any other time in order to
save their own soul.
.. - Brad Guth