totm dec 2023 Artemis Discussion Thread

[tater]

34 minutes ago, jinnantonix said:

OK, so thinking outside the box, how about an ultra thin wool mesh with long lightweight carbon reinforced fibreglass pegs.  Suspend your disbelief for a second, and think about it. 

Who at NASA would have (like the Chinese) chosen wood as a re-entry capsule heat shield?

Yeah, interesting.

Or graphene, maybe. Pegs are tricky (they had trouble with augers due to how compressed the lunar dust is below the surface).

[kerbiloid]

A web cocoon.

[Wjolcz]

I just had an idea: why not dig a round hole as the landing site (maybe square could work for a landing pad too). Have tilted steel panels on the outside to redirect any debris downwards and have a trench for said debris to land in (or rather redirect at these speeds). Around that make a wall out of regolith with kevlar on top to catch anything that bounces up and out of the trench.

It's kind of hard to explain for me. Just imagine a pipe under a sink, except the water flows backwards and up.

The outlet part would be inlet in this case.

How much can steel plates weigh? If SS is operational they could probably transport that with ease.

Edit: so it would be a kind of Tesla valve, I guess, except less complicated.

Edited January 7, 2020 by Wjolcz

[kerbiloid]

1. A vertical launch catapult, electromagnetic or a steam piston. To throw the lander up before ignition.

2. A steel truss on the ledge of a cliff, with rails on top and 100 m of vacuum below. Roll the lander on by rails and launch.

3. Trampoline.

Edited January 7, 2020 by kerbiloid

[jinnantonix]

4 hours ago, Wjolcz said:

I just had an idea: why not dig a round hole as the landing site (maybe square could work for a landing pad too). Have tilted steel panels on the outside to redirect any debris downwards

Great idea.  Replace steel with HDPE Plastic (High Density Polyethylene).  Half pipe, with concave facing inward.

 

[Wjolcz]

26 minutes ago, jinnantonix said:

Great idea.  Replace steel with HDPE Plastic (High Density Polyethylene).  Half pipe, with concave facing inward.

 

Steel has higher density though (almost 10x higher). So, in theory it should be way better at stopping/deflecting debris (there is a reason why combat tanks were and are being built from it). Now, I don't know much about ballistics but watching people shoot plastic bottles with shotguns makes me think HDPE is not that great at absorbing impacts. Not like steel cans of the same thickness do any better, but I assume the denser the material the lower the chances of penetration are.

Also, don't plastics degrade really quickly in vacuum and solar radiation?

Edited January 8, 2020 by Wjolcz

[tater]

If you're doing something like that, use tubes filled with regolith to build the structure. This is "earthbag" construction here.Tie off one end, and continuously fill a long, tubular bag with soil.

 

[Wjolcz]

I was talking about debris deflector panels around the landing zone. It's just that pipe cross section was the closest and most analogous I could think of when describing it.

Filling pipes with regolith using rocket exhaust from landers would be the least efficient way of filling anything lol.

Edited January 8, 2020 by Wjolcz

[jinnantonix]

And noting that landing and ascending within the area of a landing pad will require pinpoint accuracy, lots of automation, and it may in the end be easier and cheaper to just land in a crater with natural walls.

[tater]

20 hours ago, Wjolcz said:

I was talking about debris deflector panels around the landing zone. It's just that pipe cross section was the closest and most analogous I could think of when describing it.

Filling pipes with regolith using rocket exhaust from landers would be the least efficient way of filling anything lol.

I meant building the berm structure with bags.

Also:

 

[Ultimate Steve]

17 minutes ago, tater said:

I meant building the berm structure with bags.

Also:

 

Can't wait to see what they choose!

[έķ νίĻĻάίή]

On 1/8/2020 at 3:47 AM, kerbiloid said:

1. A vertical launch catapult, electromagnetic or a steam piston. To throw the lander up before ignition.

2. A steel truss on the ledge of a cliff, with rails on top and 100 m of vacuum below. Roll the lander on by rails and launch.

3. Trampoline.

GENIUS! JUST GENIUS! AMAZING!

[kerbiloid]

Spoiler

  

5 hours ago, έķ νίĻĻάίή said:

GENIUS! JUST GENIUS! AMAZING!

Thanks.

4. Swinging bar.

Spoiler

When the one lander lands on top, the starting lander gets thrown up from bottom.
So, you get at once:
1. Cold launch.
2. Saving energy,.
3. A mechanical landing system, it allows greater vertical speed to land.

 

[έķ νίĻĻάίή]

17 hours ago, kerbiloid said:

  Hide contents

  

Thanks.

4. Swinging bar.

  Reveal hidden contents

When the one lander lands on top, the starting lander gets thrown up from bottom.
So, you get at once:
1. Cold launch.
2. Saving energy,.
3. A mechanical landing system, it allows greater vertical speed to land.

 

Why

Just why

GENIUS 100

Edited January 9, 2020 by έķ νίĻĻάίή

[Kerwood Floyd]

7 hours ago, έķ νίĻĻάίή said:

Why

Is that a joke or actually 

The fact that he put it in a spoiler strongly points to it being a joke.

[tater]

 

[jinnantonix]

Dynetics lander design:  Looks like 8 engines, anyone want to guess the engine type?  Re-usable?  Tanks do not look like they are big enough to go from NRHO to lunar surface and back.  Side mounting of engines suggest that the craft initially has drop tanks mounted beneath, which are ejected during descent.  Possibly dropping engine(s) too?  Craft looks like it launches from Earth on its side, so how are drop tanks added?
 

[tater]

I doubt drop tanks, frankly.

Does it need to go to Gateway? Doesn't the architecture allow (at least for the first landing) a more direct approach? Ie: comanifest a LOI stage with Orion on B1b, and send the lander ahead to LLO?

[jinnantonix]

7 hours ago, tater said:

I doubt drop tanks, frankly.

Does it need to go to Gateway? Doesn't the architecture allow (at least for the first landing) a more direct approach? Ie: comanifest a LOI stage with Orion on B1b, and send the lander ahead to LLO?

It needs to have something more than what we see in this picture to even get from LLO to Surface and back.  Something extra is needed. e.g. A transit vehicle or drop tanks.

Obviously the lander needs to be able to rendezvous at the Gateway.  The initial flight may be more direct (maybe), but NASA will not select a lander design that cannot do the Artemis mission profile including Orion rendezvous at the Gateway.  My guess is that it will be launched by two Falcon Heavy LVs, EOR docking the lander shown (ascent vehicle), with a hypergolic fueled transit vehicle, autonomously guided rendezvous with the Gateway for crew transfer from the Orion.  The transit vehicle then carries the lander to a suborbital path to the lunar landing site, and the TV is then dropped immediately prior to the AV landing on the lunar surface.  The AV is potentially re-usable - with each mission a new Transit Vehicle docks at the Gateway, refilling the AV tanks.

The engines are a mystery.  Dynetics have previously partnered with Aerojet Rocketdyne. Eight fixed 490 N model R-4D-11 auxiliary thrusters  would not have enough thrust.  Perhaps the artist left out the main engine (e.g. AJ10-190).  Alternatively Dynetics may break their AJ partnership and use SuperDRACOs, although eight engines is overkill, and compromises re-useability.

Edited January 14, 2020 by jinnantonix

[tater]

Hypergols?

I just don't think drop tanks, or even refilling tanks is ready for primetime (though the former is easier than the latter). It's gotta have a stage that gets it all but down, what are those tanks, 2.5m in diameter? As you say, fairly small.

Actually, if they have the tank a little bigger than 1m radius, they start really ramping up volume for props fast. 1.25m radius is ~2x the volume. Starts looking like 14-20 tons of props possible (hypergols, depending on which choice they made). Any density around 1 gets you there. For hypergolics, that starts getting into 4000 m/s territory.

[sevenperforce]

21 hours ago, tater said:

 

This looks remarkably similar to what I was proposing a few pages back in the thread. 

Looks like it could also serve as a bus to drop large cargo directly on the surface.

9 hours ago, tater said:

I just don't think drop tanks, or even refilling tanks is ready for primetime (though the former is easier than the latter). It's gotta have a stage that gets it all but down, what are those tanks, 2.5m in diameter? As you say, fairly small.

What if it has internal props to get back to Gateway?

[tater]

8 minutes ago, sevenperforce said:

What if it has internal props to get back to Gateway?

I was messing with tank diameters and load in tons (based on ballpark prop densities), and it might well have over 4000m/s in that image (without staging). Tank volume is very sensitive to radius, hard to tell from an image. What could the crew compartment and structure mass (how little)?

What's the total, RT dv requirement from Gateway to the lunar surface? The subway diagrams are typically overstated (they use more to and from LLO than Apollo actually used, for example).

 

[sevenperforce]

4 minutes ago, tater said:

I was messing with tank diameters and load in tons (based on ballpark prop densities), and it might well have over 4000m/s in that image (without staging). Tank volume is very sensitive to radius, hard to tell from an image. What could the crew compartment and structure mass (how little)?

What's the total, RT dv requirement from Gateway to the lunar surface? The subway diagrams are typically overstated (they use more to and from LLO than Apollo actually used, for example).

From NASA's research on NRHO it should take around 730 m/s to get between NRHO and LLO, and 1,870 m/s to get between LLO and the lunar surface. So a round trip is 5,200. That doesn't count the 430 m/s you need to brake from TLI to the gateway.

I discussed minimum crew compartment and structural mass upthread. I think 3 tonnes was a nice roomy solution.

[tater]

Looks like NASA is saying ~5800m/s total on a PDF (so your 5630 with some slop).

A 26t lander with 4t dry mass can do this. If it's just over 19 tons and 3 tons dry, it can also do this (RT from Gateway). All this assuming an I_sp of 320.

A tank with ~135cm radius seems to do the trick (times 2). Obviously just a ballpark, and that depends on the props. If you can get a higher density propellant, then smaller works.

 

 

[sevenperforce]

1 hour ago, tater said:

Looks like NASA is saying ~5800m/s total on a PDF (so your 5630 with some slop).

A 26t lander with 4t dry mass can do this. If it's just over 19 tons and 3 tons dry, it can also do this (RT from Gateway). All this assuming an I_sp of 320.

A tank with ~135cm radius seems to do the trick (times 2). Obviously just a ballpark, and that depends on the props. If you can get a higher density propellant, then smaller works.

Hypergolics are nice because you can pack them into any old nook or cranny because you don't have to worry about boiloff...yet you can't, because if you're pressure-feeding, you need a spherical tank to minimize weight.

If you are volume limited, impulse density of hypergols is 11% higher than kerolox, 34% higher than methalox, and 181% higher than hydrolox.