totm dec 2023 Artemis Discussion Thread

[sh1pman]

12 minutes ago, jadebenn said:

I think you're underestimating the difficulty of building a reinforced concrete structure on another celestial body.

Look at how much effort goes into building one on Earth, then consider you have zero local infrastructure, an extremely limited amount of construction materials, and an absolutely tiny construction crew working in one of the most hazardous environments known to man.

Building the pad alone would almost certainly be a multi-year effort.

For starters, they can dig a pit with flat bottom and land Starships there. It will require some kind of bulldozer or excavator, but this equipment is likely to be used in the base construction anyway.

[Wjolcz]

1 hour ago, jadebenn said:

No. It's completely untreaded ground.

It is? You would think that after all those trips to the Moon and all those samples we would be pretty good at at least partially recreating regolith and experiment with making stuff out of it.

Edited January 4, 2020 by Wjolcz

[tater]

3 hours ago, jadebenn said:

If a 40 ton lander does that, that's yet another nail in the coffin of the boneheaded idea of bringing down an entire Starship to the Lunar surface.

It means that if the base is to be reused frequently (by anyone, for any sort of lander), you need to bring equipment to create a landing pad among the first industrial equipment you bring (ISRU on the Moon requires bringing industrial equipment).

Early steps might be to create a berm to shield the base, followup missions stabilizing the landing surface.

2 hours ago, jadebenn said:

I think you're underestimating the difficulty of building a reinforced concrete structure on another celestial body.

While lunar concrete is an option (the civil engineers have been talking about this and even experimenting since at least the late 80s, I went to the talks), I think they talk a lot now about sintering the surface in-situ, or stabilizing regolith with polymers (I wanna say there's a company here in Albuquerque doing the latter). The benefit of the former is that you don't have to deliver the polymer (though with a huge lander this is less of a problem since you can carry more polymer).

Quote

Look at how much effort goes into building one on Earth, then consider you have zero local infrastructure, an extremely limited amount of construction materials, and an absolutely tiny construction crew working in one of the most hazardous environments known to man.

You'd forget the humans and have the delivered equipment do the work by remote control anyway.

Quote

Building the pad alone would almost certainly be a multi-year effort.

Certainly in a regime where large lunar missions are every year at most, and only for a handful of days at a time, with smallish landers---and where the work is done by people instead of robots.

With more resources landed, the situation improves.

https://www.hou.usra.edu/meetings/lunarisru2019/eposter/5055.pdf

"CLPS pluming will be very minimal but this may be deceptive because scaling is a 2.5 power law of vehicle mass." (he says 40t landers (the type Artemis is considering) will have serious effects).

In short, a constructed landing pad is required for return crew missions to the same place if that is to be a thing.

 

Edited January 4, 2020 by tater

[tater]

https://ssi.org/2010/SM14-proceedings/Building-a-Vertical-Take-Off-and-Landing-Pad-using-in-situ-Materials-Hintze.pdf

https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20170002067.pdf

[Ultimate Steve]

If I understand this correctly, this is really only an issue if the Landers exhaust velocity is above lunar orbital velocity (disregarding weird compression at the surface which could result in a higher velocity) so I would imagine that the effect would be mitigated by using a low efficiency engine (200s isp, ~2km/s ev) for the final 100 or so m/s of the descent, the part that would kick up the most dust. The descent would likely have to be planned in a way that anything done before the last burn will not be low enough to kick up dust (so high above the surface that the plume will spread out). This goes both for Artemis Landers and Starship.

Unless the problem is more about the amount of exhaust than the speed of the exhaust. It's probably both as the Apollo Landers worked but didn't cause a concern (maybe it wasn't known at the time?).

[jinnantonix]

A simpler solution may be to find natural barriers, such as landing at the base of craters?  Come to think of it, isn't that the plan anyway?  To search for water in the shadows of craters?
 

[kerbiloid]

Too dangerous for pilotage, limits the abort options with walls, and all natural geological structures are by default unstable and uncomfortable to build something.
Also large craters are just plains with hills on the horizon.

[MinimumSky5]

12 hours ago, jinnantonix said:

A simpler solution may be to find natural barriers, such as landing at the base of craters?  Come to think of it, isn't that the plan anyway?  To search for water in the shadows of craters?
 

I doubt that the best first step for ISRU of water on the Moon is to blast away the insulating regolith that has kept it stable for millions of years, using superheated gases from a rocket (not to mention all of the safety problems highlighted above). 

Making your own barriers allows much more flexibility in base design, and given that permenant bases will likely be buried, you will need earthmoving equipment there to build the thing anyway. 

Also: how much ejecta is sent up in that simulation? If it isn't that much, it's not likely to be a stumbling provided that we can get a landing pad built relatively quickly. 

[kerbiloid]

The Moon is covered with impact craters. But not surrounded by their ejecta.

[tater]

16 hours ago, jinnantonix said:

A simpler solution may be to find natural barriers, such as landing at the base of craters?  Come to think of it, isn't that the plan anyway?  To search for water in the shadows of craters?

No, the plan has always been to land on the RIM of such craters. Specifically rims that are in near perpetual sunlight.

Now within that plan, you could land inside a smaller crater if there are good candidates, assuming getting out is not difficult.

[kerbiloid]

And dig through the wall to let the rovers out.

NB.
Project Horizon was to be next to the crater, not inside it.

http://www.history.army.mil/faq/horizon/Horizon_V1.pdf

http://www.history.army.mil/faq/horizon/Horizon_V2.pdf

Edited January 5, 2020 by kerbiloid

[jinnantonix]

Maybe a simple answer is to roll out and peg a large heat resistant tarp, temperature and UV resistant, and this would act as a landing pad and minimise ejecta from the lander engines.

If landing on the rim of Shackleton is the plan, maybe a Gemini style open propulsive "bike" would be a handy way of getting astronauts to and from the base of craters.  Standard rovers are going to struggle to safely negotiate the steep sides.  Although I still think landing at the crater base is  possible with today's technology.

 

 

 

 

Edited January 6, 2020 by jinnantonix

[Jestersage]

So I have a question regarding the gateway, because after 7 pages my eyes started to get dizzy.

I do understand it have multiple proposal, ranging from 4 modules inline to basically a cross (look from the side)... so what is the current modules being proposed? (ignoring the proposal by Roscosmo, who had originally threatened to do their own thing, and the relocate-ISS-module proposals.

According to the current wikipedia entry:

(PPE -- ESPIRIT) -- Int'l Hab -- US Hab -- Roscosmos Airlock/multidock
All inline
Logistic modules/supply ship dock to the Intl's Hab.
 

EDIT: According to Russian Space Web, seems what happened is that PPE split into two parts, the PPE and ESPIRIT

 

 

Edited January 6, 2020 by Jestersage

[jinnantonix]

5 hours ago, Jestersage said:

... so what is the current modules being proposed?

At the moment I understand LOP-G will start with the PPE, and then add a Minimal Habitation Module (MHM).  That will be sufficient to execute the initial Artemis missions.   The development of ESPRIT (adds xenon and hydazine refuelling facility) and the International Hab module has been commissioned, but it seems the the deployment of these remains subject to funding of beyond Artemis 4.  Logistics and Airlock modules may be added later, although development has not yet been commissioned.

Edited January 6, 2020 by jinnantonix

[tater]

12 hours ago, jinnantonix said:

Maybe a simple answer is to roll out and peg a large heat resistant tarp, temperature and UV resistant, and this would act as a landing pad and minimise ejecta from the lander engines.

This is an interesting idea. It requires more mass (like the plans to stabilize regolith with resins), but doesn't require the complex equipment for the spraying process. Wonder if they could then tile the actual landing area in the center with metal plates?

[sevenperforce]

With all of the regolith-kicking concerns, I am growing more and more fond of lander designs which use a large, non-throttleable, high-efficiency engine for descent and use the ascent stage's engines, mounted in parallel (and perhaps gimbaled outward) for final throttled landing. 

[tater]

6 minutes ago, sevenperforce said:

With all of the regolith-kicking concerns, I am growing more and more fond of lander designs which use a large, non-throttleable, high-efficiency engine for descent and use the ascent stage's engines, mounted in parallel (and perhaps gimbaled outward) for final throttled landing. 

Lower thrust might well mitigate some of the ejecta, and gimbaled out would prevent digging a hole under the lander (something Metzger has mentioned is a thing in their test rigs). Minus some surface stabilization, however, it's still going to throw stuff, and gimbaled out, at even higher velocities, I'd imagine (on average, sideways).

All lunar base plans for decades have included landing pads, FWIW, it's not a new idea, and the techniques to do it are not novel in many cases, the tricky bit is doing it with less mass given costs to the surface. Get the landed mass up, and it ceases to be an issue.

[RCgothic]

1 hour ago, tater said:

This is an interesting idea. It requires more mass (like the plans to stabilize regolith with resins), but doesn't require the complex equipment for the spraying process. Wonder if they could then tile the actual landing area in the center with metal plates?

My team had a little bit of experience with rocket exhausts interacting with warship coatings. It's very hard to get away from "just go out and repaint whatever the exhaust just burned off".

Not saying it's impossible at a spaceflight budget level, but we certainly struggled with a frigate.

Metal plates are sturdier than tarps/coatings. But hard to ship to the moon though.

Edited January 6, 2020 by RCgothic

[tater]

It's listed as a possible solution in some of the papers. Either prefab tiles, else making tiles with ISRU (sintering them, for example).

[sevenperforce]

2 hours ago, tater said:

Lower thrust might well mitigate some of the ejecta, and gimbaled out would prevent digging a hole under the lander (something Metzger has mentioned is a thing in their test rigs). Minus some surface stabilization, however, it's still going to throw stuff, and gimbaled out, at even higher velocities, I'd imagine (on average, sideways).

It's not just about lower thrust and gimballing; it's about the distance between the engine bell and the regolith. In a vacuum, the dynamic pressure of the exhaust stream is going to be nearly inverse-squared. On a notional ten-meter-high lander (for reference, the Apollo Lunar Module came in just over 6 meters), side-mounting the ascent-stage engines and using them for the landing burn places the nozzle rim at least five meters above the surface. Compare to the original Apollo Descent Module, which had an engine bell which came to rest just 35 cm above the surface.

Of course, the Apollo descent vehicle dropped the last 1.6 meters after engine cut-off, which would put the final plume length at 2 meters and 5.6 meters, respectively. Yet that difference -- having engines mounted five meters high vs nearly flush with the ground -- would mean that the plume from top-mounted engines would have a dynamic pressure at the surface only 13% of the plume from traditional engines. If you can use gimbal to cant them out by 20 degrees or so, the increased distance to the surface means it drops to just 11%. 

The downside is that you have to make sure the lower stage material doesn't get torched by sidewash from the engine plume, but that is a fairly short pole.

[Meecrob]

A thought just occurred to me - Could they use a set up like @sevenperforce stated above with the engines gimballing outwards, only instead of throttling the engines, they used the gimbals to achieve the same effect? What I mean is that the engines would be gimballed retrograde (or 180*) when at high altitude above the moon and slowly gimbal to 90* (sort of radial out from the lander's perspective) at touchdown. Of course the cosign losses would mean more fuel spent, but the exhaust plume would be near parallel to the surface when the lander is close enough to kick up regolith.

I guess my question is what am I overlooking that kills this idea? Gimbals not reliable enough?

[tater]

Gimbal is fine, just wasteful.

I still think any base with repeat visits needs a dedicated landing area. Dangerous ejecta can be mitigated, but fines are also an issue (just because they're a mess, lunar dust is insidious).

[jinnantonix]

13 hours ago, tater said:

This is an interesting idea. It requires more mass (like the plans to stabilize regolith with resins), but doesn't require the complex equipment for the spraying process. 

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?

[Ultimate Steve]

What about spraying the surface with a sticky substance? This would provide a sort of landing pad, preventing most of the rock from flying away, and it could be done with much less work and expense than a dedicated pad.

[IncongruousGoat]

15 minutes ago, Ultimate Steve said:

What about spraying the surface with a sticky substance? This would provide a sort of landing pad, preventing most of the rock from flying away, and it could be done with much less work and expense than a dedicated pad.

It's hard to spray a liquid at something in hard vacuum and have it to keep acting like a liquid. Unless there's some epoxy formulation you know of that will stay being epoxy in vacuum long enough to set, that is.

Edited January 7, 2020 by IncongruousGoat