Dale Christopher

Looking for opinions about how optimal NASA’s Lunar Gateway plan...

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I’m interested in seeing what the actual manual/mechanical requirement for getting a load of propellant from ice deposits dictates an IRSU facility look like. If we are talking tens of tons for missions, that’s a substantial amount of moon junk to haul around and process. Seems like a lot of man hours, but then I guess automation has come a long way too. 

 

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Posted (edited)
On 6/13/2019 at 3:27 PM, tater said:

Gateway is only a thing because Orion can’t do anything else.

This guy gets it.

I came to this thread to make exactly that point, but it seems my work here has been done...

Edited by natsirt721

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Posted (edited)
2 hours ago, Ol’ Musky Boi said:

Sorry if my waffling is becoming a little incoherent or inaccurate. It's all too easy to go into "armchair engineer mode" if you can call it that.

Not at all, man. I'm enjoying this conversation. :)

2 hours ago, Ol’ Musky Boi said:

 In this regard, putting ISRU directly on the lander doesn't make so much sense, carrying it with you rapidly inflates the mass of your lander. So it might make more sense to have a permanent ISRU system on the surface, fuelling the lander for a return to Earth once every month before solar power runs out, then coming back a month later to continue setting up the lunar base. This way you only have to haul the ISRU around once.

That's what I was thinking. You don't need to keep the ISRU equipment on-board. If you farm off the ISRU to an external plant, you simplify a lot of things. For example, you could put the hydrolox storage and "refinery" in a permanently shadowed crater to mitigate boiloff, while hooking it up to a solar farm on the crater rim to take advantage of the near-eternal sunlight of the south pole as a power source.

Lunar night isn't really much of an issue when NASA's identified places where there's sunlight for ~80% of it. Doing some quick math, that means you'd only have to deal with about a week of no sunlight each lunar month. That should be feasible when you're taking advantage of the previously mentioned permanently shadowed crater regions to do most of the cooling for you, so you can just pause electrolysis and conserve power until the sun comes back up.

You'd still need to beef up the descent stage though; at least, compared to the expendable version. It would have to be larger simply because the reusable version would need to handle both ascent and descent, while the expendable version would only ever handle descent. And you'd need a cryocooler and some beefier thermal insulation on the reusable stage (although you might be able to keep most of that off the lander and just handle long-term propellant storage at Gateway).

Again, these are really, really, far future, aspirational goals, but they seem to be driving NASA's lunar architecture decisions. Consider:

  • They want to land on the south pole, which is where the water ice is and where you can take advantage of the geography to get near-constant sunlight (and thus, power).
  • They want a hydrolox lander despite the boiloff problems that causes (in order to future-proof the lander design).
  • They've specified the descent stage needs to be able to handle one-way cargo landings with a payload of around 9t-10t in addition to its use in the aforementioned crewed landings (a capability that just screams "surface base").

They're not going to get there in one big leap, but they are laying down the groundwork they'll need for this stuff, and it shows. They're clearly factoring these possibilities into their planning, and it all plays into the declared goal of, "We're going to the Moon to stay."

Edited by jadebenn

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4 hours ago, Dale Christopher said:

@jadebenn

hmmm, I thought they had mentioned a permanent base on the moon was the goal, and that the high value spots were the South Pole in the areas that have both permanently shaded craters and access to sunlight.

(I think, I’m thinking of one of Bridenstine’s speaches)

No, I think you're right, it's just not what they're focusing on right now. That's something that comes down the line.

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11 hours ago, Dale Christopher said:

I’m interested in seeing what the actual manual/mechanical requirement for getting a load of propellant from ice deposits dictates an IRSU facility look like. If we are talking tens of tons for missions, that’s a substantial amount of moon junk to haul around and process. Seems like a lot of man hours, but then I guess automation has come a long way too. 

 

It depends on your method of extraction, if you're scraping up regolith and putting it into an oven, assuming a water concentration of 5% (it could well be as high as 10% in places) you would have to shovel 20 tonnes of regolith for every 1 tonne of fuel. Although on the moon 20 tonnes feels more like 3.3 tonnes (tonne-force I mean), so it's feasible that you could use some kind of autonomous tractor that just trundled across the landscape. You could even put the heating system on board so you can extract the water, dump the dry regolith, and keep on driving until you've got a full tank, return to the lander, split the water and launch. The benefit of this design is that you could drive the ISRU system to new landing points whilst collecting water on the way, leaving the landing site relatively untouched. Compared to an ISRU system on the lander which would have to strip mine the surface of it's nearby landing site, contaminating the area and making it less useful for science. Assuming 16 tonnes of propellant is required and you completely remove the top 1m of regolith for fuel, you would need to mine an area of about 213m2, or a circular pit with a diameter of about 16.5m. Not impractical, but you did just destroy the closest 213m2 that you could have otherwise explored.

The beauty of microwave extraction is that it combines the excavation and the extraction of the water into one process that requires few moving parts, because moving parts don't mix well with regolith. You could set up a big plastic tent at the bottom of a crater (or anywhere else for that matter), vaporise the water-ice, collect the vapor at the top of the tent and now you've got water. This seems the most likely method in the short term, but I can imagine that far-future colonies would also want to use the dry regolith for construction, so they may favour the excavation method.

One way or another the big thing you want on the lunar surface is mobility, if your ISRU system limits you to landings only at the south pole then you're going to need a new system for landing at other locations (how about a 2001 moon bus?). Then again you could just put a bunch of ISRU systems around the moon so you could land just about anywhere, but that gets expensive quickly.

 

10 hours ago, jadebenn said:

They're not going to get there in one big leap, but they are laying down the groundwork they'll need for this stuff, and it shows. They're clearly factoring these possibilities into their planning, and it all plays into the declared goal of, "We're going to the Moon to stay."

I think you're right there, it's not so much that I don't trust NASA to pick the right architecture, it's that I don't trust politicians to fund it. So if the future plans get cut we end up with oversized and poorly optimised infrastructure for what is essentially just Apollo 2.0. I guess that's where the limits of public space exploration are and where private space exploration might have to pick up the slack. Then again if China gets really serious about a moon base I imagine that the politicians will be much more enthusiastic. Apollo certainly wouldn't have happened without the USSR.

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Posted (edited)
46 minutes ago, Ol’ Musky Boi said:

One way or another the big thing you want on the lunar surface is mobility, if your ISRU system limits you to landings only at the south pole then you're going to need a new system for landing at other locations...

I don’t think having an immobile ISRU facility located centrally to high concentrations of ice and using that as a refueling hub would have many real disadvantages compared to a refueling hub located in a polar high elliptical orbit, and the logistics and practically of shipping fuel up from the surface and storing it in orbit seem questionable. 

Also from what I’ve gathered the focus of research will be the south pole so correct me if I’m wrong but, making a sub orbital hop from a ground location to practically anywhere in the southern hemisphere would always cost far less fuel than getting into orbit not to mention no need to use fuel changing inclination as with an orbital refueling point. A reusable hopper/lander would probably be able to hop back and forth between a polar ground refueling location easily and often, not being reliant on fuel shipments or orbital windows. The benefit would also be that crews would be constantly visiting the ISRU location, which I think it will need to be run effectively... beyond that, gaining expertise with ISRU and managing ISRU experiments should probably be a high priority activity for future missions. 

Edited by Dale Christopher

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I agree, an orbital fuel depot wouldn't make sense for enabling more surface exploration, because any tanker that can get fuel from the surface into orbit and back again is capable of landing anywhere on the moon in the first place. Sub-orbital hopping is a good way to get around, and is featured prominently in Zubrin's Moon Direct plan. You could do sub-orbital hopping with the landers currently proposed by NASA, but the problem is that they have less delta-V than envisioned in the Moon Direct plan. And according to this graph:

kzD34bc.png

with only 5km/s of Delta-V you only get access to >10% of the surface. So in this case the advantages of hopping over a mobile ISRU system are only that an immobile ISRU system requires less mass to be carried around - at the expense of range. Although as long as you don't put the ISRU system on the lander the mass penalties are fairly similar, which is why I quite like the idea of a roving ISRU system. You could still utilise sub-orbital hopping, but you could slowly migrate your ISRU system to different locations to visit points of interest. Then again, if it breaks down you've just lost a crucial bit of hardware, rovers are very slow, and building a roving vehicle that can survive for long periods of time on the moon is quite a challenge, even with astronauts on site to repair things.

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It goes back to what an ISRU operation at a scale needed to service the activities of a human presence on the moon would look like. Having astronauts sitting on their hands for months isn’t getting a lot of bang for your buck so multiple surface excursions per stay would be good. Maybe one per month to really crank out some science and exploration. I really can’t see that kind of fuel operation being mobile, but I suppose it’s also dictated by the ice deposits. If we are talking about baking subsurface dirt then I guess it’s not only possible but desirable to move around due to the area you’d need to harvest but if there are solid ice deposits at the bottoms of these polar craters? You could conceivably set up a base and hack away at it for years, never needing to move and solid ice rubble would yield a lot more water than baking dirt since it would be conceivably be mostly water, and the waste material you generate and have to deal with would be minimal compared with baking dirt where you would probably generate orders of magnitude more waste than water.

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Posted (edited)
5 hours ago, Ol’ Musky Boi said:

 

kzD34bc.png

Wow nice graph! I like how if you increase the deltaV an additional +50% from 5k to 7.5k your capability goes from 10% to 100%

That seems like good value for money! ^_^ 

(However I’m used to KSP and the thought of building a 7.5k DV anything, is daunting...)

hmmm... is that green line something like, the amount of DV needed to return to orbit?

Edited by Dale Christopher

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Posted (edited)
2 hours ago, Dale Christopher said:

Wow nice graph! I like how if you increase the deltaV an additional +50% from 5k to 7.5k your capability goes from 10% to 100%

That seems like good value for money! ^_^ 

(However I’m used to KSP and the thought of building a 7.5k DV anything, is daunting...)

hmmm... is that green line something like, the amount of DV needed to return to orbit?

The green line represents 6.1km/s, which is the delta-V Zubrin went for in his Moon Direct plan. The idea was that the lander would do direct ascent from the moon to LEO, and then once refuelled by a Falcon 9 in LEO, go back to the moon to land and refuel with ISRU. The added benefit was that with that much Delta-V you get access to much more of the lunar surface. I quite like the Moon Direct plan, but NASA doesn't seem to be heading in that direction.

2 hours ago, Dale Christopher said:

It goes back to what an ISRU operation at a scale needed to service the activities of a human presence on the moon would look like. Having astronauts sitting on their hands for months isn’t getting a lot of bang for your buck so multiple surface excursions per stay would be good. Maybe one per month to really crank out some science and exploration. I really can’t see that kind of fuel operation being mobile, but I suppose it’s also dictated by the ice deposits. If we are talking about baking subsurface dirt then I guess it’s not only possible but desirable to move around due to the area you’d need to harvest but if there are solid ice deposits at the bottoms of these polar craters? You could conceivably set up a base and hack away at it for years, never needing to move and solid ice rubble would yield a lot more water than baking dirt since it would be conceivably be mostly water, and the waste material you generate and have to deal with would be minimal compared with baking dirt where you would probably generate orders of magnitude more waste than water.

Yeah, the method that you'll want to employ does depend on wether the ice is concentrated in certain areas or not, and we won't have to wait long to find that out. Obviously NASA has stated that as part of Artemis they are going to scout out the poles with rovers first, and ESA has got its lunar "PROSPECT" mission planned for 2022. Speaking of which, ESA have also designed a "Moon Village" concept, which focuses heavily on international co-operation. Maybe this is NASA's long term goal - to collaborate with Europe on a Moon Base? That'd be cool, if all goes well I should be out of university by then and might be able to nab a job as a janitor in mission control :wink:

It's worth noting that the waste material needs not be waste at all. The ESA has experimented with building bricks by compressing and baking lunar dust, so in theory not only could the astronauts monitor the ISRU system but they could use the stuff coming out to build radiation shielding around their habitat or launch pads for their landers. You could even combine the baking and compressing processes so you can extract water and make bricks in one streamlined process. With that amount of raw material there's really no limit to what you could build. One of my favourite ideas is to build a large brick atrium, and then pile on regolith until the pressure of the regolith on top is equal to atmospheric pressure. Slap on a door, pressurise it and you've got a resilient airtight habitat made entirely from dirt. That way you don't have to send up heavy base modules every time you want to expand your capacity.

If you'll forgive for getting into really far future stuff, there's a lot of aluminium on the moon, and aluminium makes a great conductor of electricity. So in theory you could build giant coilguns or railguns and use them as mass drivers to get materials into orbit or to send things back to Earth for trade. The only materials that are inconveniently scarce on the moon are carbon and nitrogen, so unfortunately mass production of polymers is a no. That's a shame because a lunar space elevator would need something at least as strong as Kevlar to work, and Kevlar contains both nitrogen and carbon. It's like the universe is trying to crush all of our space elevator dreams.

I seriously hope we get a moon base in the next decade or two. It'll be a huge downer (to say the least) if we didn't pull it off. It's not like we can't it's just damned politics getting in the way of everything. Start a space project in one presidency, cancel it in the next, rinse and repeat. (I know expressly political topics aren't allowed on the forum, so I'll leave it at that.)

Edited by Ol’ Musky Boi

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I do like the idea of brick and mortar construction on the moon. We already have thousands of years experience with these materials and techniques and I imagine you could build relatively conventional buildings only needing some kind of internal membrane to make them air tight. (If you didn’t want to bury them, like you said)

it’s kinda disappointing actually, that we could have easily done this in the 1970s and had cities on the moon by now.

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Posted (edited)

Humanity is funny like that. We're not one connected organism so we very rarely make unanimous decisions even if they would be beneficial for us. If bees co-operated as little as we did, well there would be no bees. That being said, humanity has done a lot of stuff that we can be proud of, creating fire, building societies, inventing science, etc. So I think there's always a case for an optimistic future, one where scarcity is a thing of the past and we span the solar system and beyond, but it'll be bloomin' hard work. Best get started now.

Edited by Ol’ Musky Boi

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30 minutes ago, Ol’ Musky Boi said:

discovering fire

Fire wasn't discovered; lightning has been starting fires long before humans came around. Humans figured out how to control it and make their own. /pedant

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Posted (edited)

I suspected that someone would point that out, your pedantry will be acknowledged and rectified :)

Although, if we want to be more pedantic about it, fire must have been discovered at some point. Otherwise we would have no knowledge of it.

Edited by Ol’ Musky Boi

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I kinda just realised what a NRHO was... I had an idea that it was some species of polar orbit but it’s not, it’s orbiting empty space some distance away from the moon... 

I cant say I like the idea of this at all now. It seems like rendezvous would be overly complicated.

It would seem to not provide communication coverage to the far side... why would we need a relay between the earth facing surface of the moon and earth, and not just talk to earth directly if we are on the earth facing side...

We are planning on keeping cryogenic liquids in an environment that I would imagine gets shade considerably less than if it was in orbit of a body? 

D:

I’m sure there are some smart cookies at NASA but this idea is seeming less and less of a good solution to my untrained eye.

 

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How optimal is Gateway? For what purpose?

The current plan (lunar surface 2024 or otherwise ASAP) has Gateway as a stopping point OTW to the Moon. That's a bit like forcing all travel from San Francisco to LA to make a stop in Barstow.

The reality is that any vehicle that can make it to Gateway, AND also make it to Low Lunar Orbit could just as well go straight to LLO from LEO. The problem of course is that the lowest lunar orbit Orion can make it to and still return to Earth is something like 500km from what I have read.

Here's an idea. Dump Gateway. Make the lander (already must be in 2 parts, anyway, assembled at the Moon, for lack of a SHLV that can send it on one piece) capable of 500km lunar orbit to the surface. Send lander ahead, assemble, then send Orion. If that makes the lander descent stage unworkable, the lander could have a tug sent ahead as well that does the initial deorbit burn for the lander. Tug in this case is a docking tunnel (docking ports on both ends), with propellants around it, and a couple thrusters.

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32 minutes ago, tater said:

Tug in this case is a docking tunnel (docking ports on both ends), with propellants around it, and a couple thrusters.

I love that idea.  I use it in KSP all the time. 

There are basically 5 different stages and 3 different life support requirements.  Reentry of Earth's atmosphere requires one type of ship.  Getting from the moon surface to LEO with minimum mass and plenty of shielding against Van Allen radiation requires another type of ship.   Landing a whopping payload on the moon surface with life support for a base requires a 3rd type of ship.  And getting from Earth's surface to the Moon's surface requires at least two stages of boosters.  

Rendevous in lunar orbit is a lot less useful than rendevous in LEO.  I'd prefer to have a fleet of small ships with docking ports over a permanent station.  

 

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