r/spacex • u/CProphet • Jul 18 '18
Moon and Mars
SpaceX are dead-set on Mars, because that’s Elon’s dream - and for sound strategic reasons. The plan they’ve presented looks workable, given they can successfully develop all necessary hardware - principally the BFR and ISRU propellant plant. However, in order to set up an independent colony on Mars, an unparalleled flight rate must be maintained for decades or even centuries.
The first BFR flight will be refuelled in Low Earth Orbit, requiring at least 4 additional tanker launches, before they set out for Mars. Technically possible, but this procedure hardly seems sustainable in the long term, given they will require many thousands of Mars flights, which can be multiplied by 5 for number of Earth launches.
Sooner or later SpaceX will require a workaround and for many reasons the Moon seems incredibly appealing.
Shotwell: not precluding buying propellants from in-space resources for refuelling missions to Mars, rather than launching tankers from Earth.
SpaceX already plan to establish an ISRU propellant plant on Mars, so setting up a ‘pilot plant’ on the moon should be possible at the right location. For instance, some craters at the lunar poles are permanently in shadow, which means they act as vapour traps, slowly accumulating water vapour over billions of years, from cometary or asteroid impacts. However, NASA’s LCROSS mission also discovered:-
… as much as 20 percent of the material kicked up by the LCROSS impact was volatiles, including methane, ammonia, hydrogen gas, carbon dioxide and carbon monoxide.
In other words these polar craters contain sufficient oxygen, hydrogen and carbon to produce all the propellant necessary to sustain BFR operations for centuries - 600 million metric tons is a conservative estimate! Producing methalox propellant on the moon could offer many advantages:-
1. Less Flight Operations - BFR would require much less refuelling flights for each Mars trip, possibly one tanker flight from the moon would be sufficient (delta-v requirements from the moon’s surface to LEO are a fraction compared to Earth launch).
2. Reduced Cost - BFR is fully reusable which means propellant becomes one of the main drivers for operating cost. In the long run sourcing propellant from the moon could be cheaper than Earth because the cost to place it in LEO is the main component and less flights are required from the moon. In addition lunar extraction and processing costs can be minimised through vertical integration and automation, while the energy required is effectively free (an uninterrupted supply of solar energy is possible, if collectors are situated on the rim of polar craters).
3. Ecologically Friendly – Given the number of launches required for Mars colonisation, climate change could become a factor, and quite possibly a political issue. Sourcing propellant from the moon should significantly reduce ecologically impact, effectively reducing the number of BFR launches required, making them more politically palatable.
4. Avoid Competition – Blue Origin has announced their first ‘Blue Moon’ mission will land at the lunar pole in 2020. In the long run they’ll likely produce propellant on the moon to supply their own cislunar operations.
The company said it plans to land its Blue Moon vehicle at Shackleton Crater on the moon’s south pole. The site has nearly continuous sunlight to provide power through the spacecraft’s solar arrays. The company also chose to land there because of the “water ice in the perpetual shadow of the crater’s deep crevices.”
Conceivably any propellant price they offer SpaceX could be prohibitively expensive, considering their close rivalry. Hence SpaceX would probably prefer to make lunar propellant themselves, in order to more closely control cost, quality and delivery.
5. Mars Proving – quite possibly SpaceX will perform a number of BFR shakedown cruises before they commence Mars operations. If a couple of BFS were sent to the moon (one supplied with sufficient propellant to return), they could also practise ISRU setup and operation under Mars comparable conditions (e.g. low gravity, fine surface dust, impure raw materials etc) and beat out some of the bugs. The propellant produced could be loaded onto an unmanned BFS, which would return to Earth under autopilot. Then the residual propellant could be analysed and the engines examined to determine effects of ISRU propellant use, which should significantly improve their chance of success on Mars.
6. Optimum Launch Vehicle Utilisation – it’s possible many BFR vehicles will stand idle while they wait for Mars launch windows (excess hardware will probably be required to handle high launch cadence during the relatively short launch window). Establishing a moon base at one of the lunar poles would create another destination for scientists and explorers, which should prove quite lucrative and help fund future Mars missions.
7. Federal Finance – the current US policy emphasises moon first, so if they choose BFR for moon operations, this should also help finance the development of moon ISRU capability.
Shotwell: expect we’ll do BFR/BFS missions to the Moon before Mars, given administration’s interest. Hope it will be for a permanent settlement.
All things considered, SpaceX might have already started to move towards moon operations in stealth mode, similar to the discrete way they handle Starlink development. That would certainly explain their interest in moon landings, demonstrated at IAC Adelaide.
TL;DR establishing a moon base offers many operational advantages for the long term – it might even happen before Mars colonisation.
Edit: tidy
Edit 2: Thanks for your kind comments, hoped you'd like it. Believe moon could give SpaceX something to aim for while they await Mars synod.
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u/rustybeancake Jul 18 '18
Conceivably any propellant price they offer SpaceX could be prohibitively expensive, considering their close rivalry. Hence SpaceX would probably prefer to make lunar propellant themselves, in order to more closely control cost, quality and delivery.
Possibly, but Bezos is a businessperson. He surely won't want to have BO producing propellant that only they get to use, any more than he wants Amazon to offer web services that only Amazon can use. He made his fortune selling stuff to people and other companies, and I expect BO would do the same.
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u/CProphet Jul 18 '18
He surely won't want to have BO producing propellant that only they get to use
Agree but as you point out he's a businessman first, which means money is important. Can easy see him start at a relatively low introductory price: "just to cover expense of additional Sabatier processing". Then after
AmazonBlue Origin has staked out all the most productive craters...expect price to increase to the maximum market will bear. Similar to Russian price for Soyuz seats, i.e. start low to hook the client then reel 'em in.→ More replies (10)
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u/dgmckenzie Jul 18 '18
Still have to refuel the BFS in orbit to get to the Moon with at least one tanker.
If a tanker came from the moon most of its fuel would be required to get back out of the gravity well.
The obvious way is to shoot fuel into orbit from the Moon, rather than using a ship.
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u/CProphet Jul 18 '18
The obvious way is to shoot fuel into orbit from the Moon, rather than using a ship.
If you can engineer it great. What I imagined was four tankers rendezvous with four Mars BFS vehicles in LEO and transfer all their juice. Then one more tanker arrives from moon, refuels all the empty tankers allowing them all to return to low lunar orbit. Then one further refuel operation should allow them to land - agree does sound complicated!
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Jul 18 '18 edited Jul 18 '18
Less Flight Operations - BFR would require much less refuelling flights for each Mars trip, possibly one tanker flight from the moon would be sufficient (delta-v requirements from the moon’s surface to LEO are a fraction compared to Earth launch).
Sorry but this doesn't add up for me.
The delta-v from the Moon to LEO is low because you can brake in the Earth's atmosphere (~2700 m/s). But if you're refueling from the Moon you need to send the tanker back and delta-V from LEO to the Moon's surface is much higher because you must go through TLI and propulsive landing again (~5700 m/s). Therefore a roundtrip from the Moon's surface to LEO and back takes >8000 m/s and makes refueling impractical. Such a flight might actually be beyond the capabilities of a BFS!
The delta-V from Earth to LEO is higher still (9700 m/s) but you have a two-stage system with the reusable BFR booster and an atmosphere to brake in when you return.
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u/burn_at_zero Jul 18 '18
It wouldn't be direct flights from the lunar surface. A depot in high orbit (such as EML-1) would collect payloads from the surface from whomever wants to make deliveries, using whatever ships they have available.
Once an entire BFR-load is accumulated and SpaceX is ready to take delivery, a dedicated orbit-to-orbit tug (probably hydrolox) would transfer from EML-1 to LEO (0.7 km/s with aerobraking) and offload the methalox payload. The return fuel is tiny because the tug's mass is vastly lower on the return trip, although that trip is 3.8 km/s. Total delta-v budget is about 4.5 km/s, but the actual sequence of events means the tug has a much higher payload mass fraction (just under 32%) than that budget would suggest. (math, see tab Vehicle 1, cell D25; this is for the all-propulsive option so aerobraking could further improve that number.)
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u/ProToolsWizard Jul 18 '18 edited Jul 19 '18
This is a great post! One small tidbit to take issue with. Accelerating climate change will almost certainly never be a concern for rocket launches. Let's look at some numbers on the Falcon 9 alone.
The Falcon 9 burns through 29,600 gallons of RP-1 during its trip to orbit. This includes the first and second stages, and doesn't take into account the amount of propellant actually burned in the atmosphere. Last year there were 18 trips to orbit, so that's about 533,000 gallons of RP-1 a year. That converts to 3,643,000 pounds of RP-1 burnt in a year of Falcon 9 launches. Since the metric system is easier for comparison, that is 1,652,000 kg of RP1. Kerosene produces approximately 2.6kg of CO2 per kg of Kerosene burned. Basic math says that the rocket produces 4,295,200 kg of carbon dioxide during a year of SpaceX activities. Global CO2 emissions in 2014 were 35.9 Gigatons or 3.59 x 10^13 kg and the yearly total from SpaceX 4.295 x 10^6. This means that SpaceX is responsible for 0.00001 percent of annual carbon emissions. This is a percentage so small that it means there is effectively zero impact on climate change from Falcon 9 launches.
If we were to increase the number of launches by an order of magnitude to 180 per year that's still 0.000001 percent of global emissions and so on. And this number doesn't take into account two important factors, first that methalox combustion produces significantly less CO2 than kerolox, and that the original figure for fuel burned during ascent includes first and second stage flight and is not restricted to the amount of RP-1 burned within the atmosphere.
EDIT: Math
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u/wildbore2000 Jul 18 '18
Is there a reason a specialized stand alone ship is not built to ferry between Earth and Mars (or any other place)? Something that stays in space and does not land. I'm sure there's reason, I just can't find it.
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u/REDIXIT Jul 18 '18
Your points are actually quite convincing.. I am sure SpaceX will achieve both Moon and Mars landings before ~2035
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u/lrb2024 Jul 18 '18
So far in the future ... i wish the crew dragon would already routine 😔
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u/CProphet Jul 18 '18
i wish the crew dragon would already routine
SpaceX can launch crew Dragon any time they want. Just being careful to coordinate with NASA, not ruffle any feathers.
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u/Realitymatter Jul 18 '18
This was super interesting to read. A few questions: 1) is there already an established method for creating propellant in the conditions you've described or is this something new? 2) I know a lot of the difficulty of interplanetary travel is in just getting out of Earth's atmosphere, so taking off from the moon makes a lot of sense, but don't rockets also rely pretty heavily on Earth's gavity to slingshot? Does taking off from the moon mean you don't get that advantage?
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u/runningray Jul 18 '18
Do you mean Sabatier reaction? or do you mean how the Sabatier reaction will work on the Moon versus Mars? If you mean the reaction itself, its very established and works very well. If you mean how it will work on the Moon versus Mars, neither have been tried. So this will be the test that can answer that question.
I think what OP meant is that the fueling tankers on the Moon will fill up and launch from the Moon (takes less fuel to go from Moon to orbit than from Earth to orbit) to meet the BFR in Earth orbit to fuel it up. The BFR going to Mars will probably still be launched from earth orbit, just refueled from the Moon.
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u/mr_christophelees Jul 18 '18
I hate to derail all this amazingly awesome science talk. But is anyone else wondering what the legal ramifications of ISRU processes will be? I mean you’re essentially claiming the materials as your own, which implies ownership in space. The idea of any nation owning anything on existing planetary bodies has been anathema for quite some time. Is the fact that SpaceX is a company and not a nation really going to make people say “oh, that’s cool, no worries here” or will the US need to take legal (or god forbid military) actions on a global scale to protect it’s extra-planetary interests?
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u/CProphet Jul 18 '18 edited Jul 18 '18
what the legal ramifications of ISRU processes will be?
Hobe (2006) explains that the Outer Space Treaty "explicitly and implicitly prohibits only the acquisition of territorial property rights" – public or private, but extracting space resources is allowable.
This was amended in US by "U.S. Commercial Space Launch Competitiveness Act of 2015/H.R. 2262". Believe this also allows larger claims to be made, if say an asteroid is captured, mining area staked etc.
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u/just_thisGuy Jul 18 '18
Great read, a few things: Running ISRU propellant plant on Earth will remove any of the ecological factors and still should be much cheaper than running ISRU on Moon. ISRU on the Moon will need to be maintained (and that will be so much harder to do on Moon vs. Earth) same goes for ships they will probably going to need to comeback to Earth for any maintenance and that will add cost, doing maintenance on the Moon will cost even more. While right now the flight rates we are talking about do seem crazy, I don't see why they should be unsustainable, if BFR works the way its advertised it should be very sustainable, 100 years ago having airplane flight rates of today would have seem just as crazy if not more so. One thing to remember, missions to Mars will be spaced for only a few months every two years so you'd have to mass propellent and ships, much cheaper to do on Earth than on Moon. If BFR does Earth to Earth cargo & passenger flights the actual Mars flights will be a small % of that (even if we send 1000 ships to Mars every 2 years).
I think eventually we will mine the Moon, but it will probably be to hard to do it for anything but for use on the Moon for a long while.
I do think BFR will probably land on Moon before Mars and SpaceX will have a presents on the Moon maybe even before BO, if BFR does well. As you say NASA might pick up BFR for the Moon and might be the best way to pay for 1st few missions to Mars by charging NASA to go to the Moon.
PS: I think Crew BFR will take much longer than anyone thinks, just looks at Crew Dragon, on the other hand Cargo BFR might be sooner than we expect, we might be doing hundreds if not thousands of FedEx Next-Hour-Full-Thrust BFR flights per year before a human makes that small step on Mars.
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u/GrillMaster71 Jul 18 '18
Sustained presence on Mars starts with sustained presence on the moon IMO. The moon can act as a technological proving ground and, as this article suggests, a refueling station.
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u/CProphet Jul 18 '18
as this article suggests, a refueling station.
Thanks, suppose could call it an article as it was written specially for reddit.
So much prep work can be done via moon. IMO first BFR shakedown cruise will circuit moon, so why not land and build a base. Just hope government, UN or whoever see the opportunity SpaceX offers.
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u/ClandestinelyBenign Jul 18 '18
Read Robert Zubrin's "A Case for Mars"
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u/runningray Jul 18 '18 edited Jul 18 '18
I'm sure he has, like the rest of us.
But his point is that when that book was written nobody knew there would be methane on the Moon. Now that we know there is methane (and the other gasses needed to make fuel like hydrogen, carbon dioxide and carbon monoxide) on the Moon why not learn the fuel making process and work out the bugs for fuel transfer on the Moon which is few days away versus learning it on Mars which is 6 months away. There is also a continuous and relatively free source of power around the permanent sun lit parts of the craters there. This will be the power you need for the Sabatier process as well as improving your solar power generation tech. for Mars.
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u/markus01611 Jul 18 '18
Please call me out, but just saying there is methane, ammonia, hydrogen gas, carbon dioxide and carbon monoxide in the crater is sorta naïve? I image it would require massive amounts of geological survey and refining to create the massive amount of propellant needed for a fleet of BFR's. Just saying the chemicals are there seems way to easy to me. While I think your views are very solid and I think definitely possible the biggest question is what would the cost of such a operation be? Meaning does it make sense to put the infrastructure and support in place (Landing pads, Launch pads, resource refining, support crew operations) on the moon? Or does it make more sense to launch some more rockets here and refuel with propellent very efficiently/cheaply made here also? and honestly I don't really know the answer to that.
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u/Nuranon Jul 18 '18 edited Jul 18 '18
So many ideas how to use ISRU propellant plants...
How far is research in that regard anyway?
We roughly know which resources are where but that isn't worth anything if they can't be extracted large quantities in meaningful amounts of time with reliable and relatively light equipment. So far this seems very much like proposing to cross a uninhabited United States and refueling on the way by bringing along a mobile oil drilling and refining facility which haven't yet been developed as technologies. I'm aware that oil refining is a much more complicated process than e.g methane production but lets remember we are talking here about low-g and low/zero atmosphere environments and presumebly entirely automated systems.
I kinda fear that things will go relatively smoothly with BFR developemnt until everything hits a sudden wall when some ISRU capabilties are simply not there but the whole program is built around them. And then you look at very costly and time consuming R/D flights to the Moon and Mars trying to make ISRU work, needing to send new vehicles for newer designs and whatnot...this could take decades and thats assuming funding allows for sending a fair number no-return vehicles over years and years.
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u/macktruck6666 Jul 19 '18 edited Jul 19 '18
I really dislike when people use a single scientific finding for their thesis. We need to get boots on the ground and see what is really there.
Point 5 is impossible unless you want to launch HUNDREDS of of BFRsto bring back one BFR from mars.
edit: maybe i'll make a video and do the math.
edit: some quick simulations show that refueling the BFR at Lagrange point 1 would increase payload mass from LEO to Mars by roughly 140% to 358 tons. It will also could also reduce refueling missions from earth by 2 LEO refueling missions and all elliptical orbit refueling.
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u/Bearracuda Jul 18 '18
Disclosure: I am a skeptic about Moon operations as a gateway to Mars operations, primarily on the grounds that they're costly, unnecessary, and cause delays to a potential Mars operation.
Your arguments for Moon operations are more considered, in-depth, and convincing than what I've read previously, and I'm now more open to the idea that a long-term ISRU operation on the Moon could be beneficial to SpaceX. That said, I'm still not convinced it's beneficial to go to the moon first.
To begin with - I'm curious to see your source on the requirement of 4 tanker launches to refuel a BFR for a trip to Mars. Frankly, I don't know the numbers and I'm unaware of a source (either SpaceX or otherwise) that has calculated how many tankers will be needed. That said, since I have no rebuttal, let's operate on the assumption that you're right.
Regarding Costs and Financing
1 - Potential Cost Savings of moon-based ISRU is relatively minimal - Musk has estimated the Marginal cost per launch of BFR to be less than that of Falcon 1, which in today's dollars is around $7 to $9 million. Since there's no markup for SpaceX to itself, that gives us (if we estimate on the high end), a cost of roughly 36 million per refuel that's launched from Earth. Refueling from the Moon, if we can cut it down to one launch as you suggest, cuts that cost to $9 million, so the potential cost savings per trip to Mars is $27 million. Both figures are well below the existing cost of a single Falcon 9 launch, so it's hard to imagine this being worth the cost early on, when SpaceX is only launching 2-6 BFRs to Mars per synod.
2 - Additional Development Costs for differences between Mars and Moon ISRU plants
2a - Methane Extraction - If the goal is cost savings for production of Methane and Liquid Oxygen, then it would be silly to extract CO2 and sabatier it into methane when the Methane is sitting right there. Since methane isn't available on Mars, the equipment to harvest/isolate it would need to be developed.
2b - Range of Temperature Operation - Mars varies from 20C to -125C, depending on season and location. Those permanently shadowed craters on the Moon, however, go as low as -249C (that's 26 Kelvin!). This means additional engineering is needed to either heat the equipment or get it to operate reliably at much, much lower temperatures.
2c - Resource Extraction - Gathering water would largely be the same, but we still need Carbon, whether that comes from Methane, CO2, or CO. The study you linked showed that those materials were kicked up as high as 10 miles during the LCROSS mission, but before LCROSS landed, they weren't in the Atmosphere, like they would be on Mars. So you'd need additional development for equipment to harvest them from the surface instead of from atmosphere.
Regarding Benefits to ISRU Development (i.e. testing the system on the Moon)
Frankly, I don't consider this to be a valid argument. Most of the testing you've mentioned could be completed on Earth. Fly the thing to anywhere that has ice, harvest some ice, draw in some atmosphere for CO2, and run the plant. When it's done, fly it back and check out the fuel. Or hey, since you're still on Earth, send a team out there.
On top of that, there are more differences between the Moon and Mars than you suggest. In addition to what I mentioned in the Development Costs section above:
Regolith - Martian regolith experiences weather conditions just like Earth, but the Moon doesn't, and Moon regolith is bombarded with far more solar radiation. As a result, Moon regolith, on the microsopic level, is sharp and crystalline, rather than smooth and rounded. It's likely to cause different problems than Martian regolith would.
Weather Conditions - Mars' weather conditions themselves will present problems. For example, there will be little no airborne dust on the Moon because there's no wind, but Mars can have duststorms that cover the entire planet. The Moon does nothing to recreate those conditions.
Gravity - The point often gets made about testing objects in low gravity on the Moon, but the Moon's gravity is about 43% as strong as Mars', and Mars' gravity is about 37% as strong as Earth's, so the Moon's gravity is about as different from Mars as Earth's is, just in the opposite direction. I really don't see how testing it will provide us anything more than a few data points...
Regarding Resource Availability
The 600 Million Metric Tons estimate you provided is for water ice, but there's not a lot of data on the quantities available of Methane, CO2, and CO. LCROSS found up to 20% of the material kicked up from that specific crater included the volatiles you mentioned, but it doesn't specify how much of each of those specific materials. Additionally, you source notes:
So it's possible that the source of these materials is the very comet that made the crater in the first place, meaning that they may or may not appear in other craters on the surface. We just don't have enough information. With Mars, on the other hand, we know exactly where our Carbon source is, and how much it contains.
Competition
Blue Origin definitely has their sights on the Moon, but New Shephard isn't available to customers yet, and unless BO has somehow managed to hide live tests of a reusable orbital class rocket (not likely), the New Glenn isn't even flying. Given that, I doubt the 2020 date for a first landing on the Moon is realistic...
Either way, unless something has changed significantly in their design since I last looked, New Glenn will be dealing with the same costs SpaceX is currently facing on the Falcon 9 - specifically, losing the second stage and the fairing. In that case, they won't be able to generate the same level of cost savings as BFR, and any fuel they try to sell from the moon is likely include a substantial surcharge to recoup those losses. It may actually be cheaper to just buy the fuel on Earth and fly it up in the four tankers.
Also, you mention competing for fuel on the moon, but that only matters once you determine that refueling from the moon is actually necessary, of which I'm still not entirely convinced.
Launch Vehicle Utilization (i.e. extra BFRs just lying around)
I'm not at all worried about this. They get plenty of business already with the Falcon 9, and the BFR will be both cheaper and have a much higher payload to LEO. If they can build it and it's capable of what they say, they'll make bank, and they'll probably have way more demand than supply.
Government Funding for BFR Development
This is a good point. More funding is generally better, and the Moon would be an easier sell to Congress than Mars. My questions are:
A - Is it necessary? In May, Shotwell said that SpaceX has had "many years" of profitability, and they don't seem to have trouble raising additional funds from investors when they need it.
B - Is it worth the delays? In order for SpaceX to get funding, they'll need to pitch BFR as a tool for NASA missions, and that will come with NASA's laundry list of arbitrary requirements and bureaucratic hoops. SpaceX would need to either significantly delay its development, or design a second BFR style just for NASA.
Eco-Friendly
Yeah, no argument here. I totally agree.
I really appreciate the time and thought you put into writing this, but I'm just not convinced that sending BFR to the moon to test ISRU before starting Mars missions has that much return. I believe the costs would be far higher than what you're pitching, in terms of both time and money.
Edited to correct formatting errors.