Ol’ Musky Boi

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.

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.

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. 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 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.)

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: 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.

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. 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.

alt + F12, or if you are on a mac, alt + fn + F12 because function keys are locked by default.

All good points. I'm not sure how heavy an ISRU system would really be, all you need is a way to extract the water ice from the regolith (I saw an interesting proposal that involved beaming microwaves at it) a system to electrolyse the water and a system to condense the hydrogen and oxygen into fuel. I can't imagine that weighing much more than a few tonnes, then again I haven't done the math so I could be wrong... After doing some back of the envelope math using the data obtained from the microwave study, I calculated that to fill up a 17 tonne lander with 12 tonnes of hydrolox propellant in a month you would need to extract water at a rate of about 278 g/min. This would correspond to a power requirement of about 139kW (possibly overkill given how the experiment was done with literally just a commercial microwave), which could be obtained from either 3.2 tonnes worth of NASA's 10kW "kilopower" reactors, or 1.8 tonnes of solar panels (which brings it's own host of problems, namely the month long lunar night). Adding on the mass of compressors and electrolysis systems and the entire thing could mass in at several tonnes. Add, say 3 tonnes, to the dry mass of my previous estimate for a lander and it now masses in at 24.2t, so I'm starting to see where that 30t figure comes from (my bad for making silly assumptions). And this assumes that you will have the life support to sit on the surface for a month, which you probably won't if you don't have a surface base. 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. 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.

Ahh I must have missed that. All of those lander proposals seem massive to me, especially when they've not got a surface base planned that would necessitate that kind of capacity. It almost seems as if they are designed so that they can only be launched on the SLS, if you'll forgive my tinfoil hat, maybe this is an attempt to justify it's further development? If the lander was made smaller it could easily launch on commercial heavy lift LVs. One possible use of the Hydrolox boil-off is to generate power, much like in ULA's "ACES" concept and Blue Origin's "Blue Moon" lander. This could remove then need for the Gateway's power and propulsion module, although it would use up fairly significant amounts of fuel so you would need to have quite good margins (it would still be more efficient to pack a little extra fuel than launching the several tonne gateway). Speaking of which, how massive will the Gateway be? Wikipedia says 75t but I can't find anything on the updated design.

Thanks for the info, I didn't know that.

I disagree with your ~30t estimate for an ISRU lander. Assuming: -An Isp of 460s (similar to high performance hydrolox engines like the RL-10). -A delta-V expenditure of 5km/s for a single stage landing and return. Plugging those numbers into the equation edV/Ve=m0/mf gives us an approximate propellant mass fraction of 0.7, assuming a dry mass of about 5t (2t for the crew module like the LM, 1t for the ISRU system, 1t for the tankage/landing legs/etc and 1t for any extra science equipment or other payloads) this would only mean a total mass of 17 tonnes. This assumes that the lander lands empty, refuels, takes off and lands again when the next lot of astronauts arrive (this does require the propellant to not boil off too much, which is the only reason I can think off for having a gateway, so you can keep all of the heavy insulation in orbit). These are all made up numbers, but I can't imagine that they would differ by much (then again, I could've screwed up my math somewhere - please correct me if I did). The only lander design that comes close to 30t was the Altair lander (46t), but that was designed for a crew of 4 not a crew of 2 as currently envisioned in the Artemis programme.

Slightly off topic, but if we're talking about building a giant tube and detonating a bomb inside, why not build a giant nuclear cannon to get things into orbit? You have an Orion style pusher plate at the bottom of your payload, you detonate a nuke behind you that vaporises part of the pusher plate and smacks it out of the tube at horrendously high accelerations. Something similar has happened by accident before and the steel cap was propelled to 66km/s, and that was without optimisation and a relatively small 300t bomb. If you want to lower the accelerations so you can carry more delicate payloads, you could perhaps flood the chamber with sea water that, when vaporised, could act as something of a "mass beam" to push your payload into space without it's own propellant. Of course, you'd have to angle the launch tube to get enough horizontal velocity and the payload would still need it's own engines to get into orbit, so maybe this makes more sense as a weapon instead. Or maybe it doesn't make any sense at all.

Personally I don't understand the need for a lunar gateway. If you want to study the effects of deep space on the human body it's much easier to do that in simulated tests here on Earth, although as @tater points out this would still raise ethical issues, namely that blasting people with radiation to see what happens isn't going to be good for them. So excluding space biology, there's no new science that can be done at the gateway that you couldn't do on the ISS or in a capsule, all of the new science is on the lunar surface. So although the engineering challenges and the cost is greater it makes more sense to me to build a propellant depot and lunar base on the surface first. And from there you could support long duration and ranged missions with massive scientific pay-off, demonstrate the feasibility of ISRU and manufacturing, demonstrate the feasibility of long term stay on another body, and set the grounds for a permanent lunar colony later in the century. The fact that a lunar base is currently being pegged as a secondary goal to the gateway worries me, because it might be that the gateway is all we get. I could very well be mistaken, but only time will tell how this will play out.

Hard to say. It looks like tests 2-3 were very under expanded and test 4 was a over expanded, which seems counterintuitive because 2-3 were conducted at lower pressure. Maybe for tests 2-3 the throat size was too large to properly choke the flow so the exhaust exited at higher than ambient pressure, but for test 4 the pressure was high enough to choke the flow and drop the pressure. Seems like there's a sweet spot somewhere inbetween 7-8 bar for the fuel pressure and 8-9 bar for the oxygen for ideal performance. Have you considered building some sort of thrust measuring rig? Might be easier to compare performances that way.

Combustion looks really smooth, cool mach diamonds too!

Hmm, filling the propellant tanks to full does increase the chance of an explosion and is a little wasteful, but I've heard from some sources that letting a rocket engine run until it's depleted all of it's propellant can damage the engine from the sudden changes in pressure. You might want to look into that.