Author Topic: MCT Speculation and Discussion Thread 4  (Read 503178 times)

Offline Bynaus

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Re: MCT Speculation and Discussion Thread 4
« Reply #2140 on: 06/05/2016 04:24 PM »
Quote
I just don't see this happening in 9 years. You'd probably need multiple design iterations for the entire process to work, and there are only 3 transfer windows left before the process *has* to work if the 2024/5 mission date is to be met.....
Yeah, and they're going to utilize each one. 2024/5 doesn't leave a lot of margin, but that's the "if everything goes according to plan" date. When Musk gives that kind of date, usually it's the earliest it can be done, not the "we'll definitely be able to do it by then" date. Which means you should probably expect it to slip.

But again, Musk has repeatedly said they're going to mine water. I really don't think they'll mess around with liquid hydrogen. Instead, they'll double-down on getting water extraction to work. And some of that they can test here on Earth before sending it to Mars.

I agree they are going to mine water - eventually. And I am sure they will bring in some equipment towards that end as soon as possible. Some of the technology to do this can indeed be tested on Earth, but the conditions on Mars (chemistry of the water ice, extent of the ice in the ground, hardness of the ground, other reactive species present etc.) are all unknown and will likely remain so up until the first (unmanned) BFS mission is sent (even if you send a Red Dragon to scout). There are so many things that can go wrong, and if the entire process is only, say, 20% slower than thought, it means you will have to skip an entire window. However, once you have humans in place, this kind of thing (scouting for new ice, testing it, adopting the technology to account for reactants in the ice, etc.) is relatively easy to do. Developing the whole process to work completely robotically, building in all the necessary margins, for a process that will, at a later date, be supervised by humans anyway, is in my view a waste of resources.

On the other hand, the capability to bring in tanked H to jump-start fuel production can be used again whenever a new site is opened on Mars (and not all sites might have readily available ground ice). The crew bringing their own return fuel is also a more conservative approach than having to rely on locally produced fuel (what happens if there is, e.g., an explosion in the fuel factory while the first manned BFS is on its way to Mars?). Sure, something might happen to the H on the way to Mars too, but usually if there is a problem with the BFS, they are in big trouble anyway.

But of course I might be wrong. I just think it would be a way to enable a landing sooner (2024/5) rather than later, because the most cumbersome part of ISRU on Mars, robotic ice mining, can be skipped and the fuel can be produced cleanly and completely with "on board" means. We will see in September. :)

Offline mfck

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Re: MCT Speculation and Discussion Thread 4
« Reply #2141 on: 06/05/2016 05:22 PM »
The fleet aspect of MCT seems to be unduly neglected in this early ISRU discussion, imo.

Suggest that BFS will only do solo missions in cis-lunar.

Suggest that even the first BFS sent to Mars will be at least a couple of vessels, for example a cargo version (which is tasked with landing, unloading and getting back to orbit and then returning to Earth), and a tanker version (bigger built-in or maybe "as-cargo" tanks), which then could be left in Mars orbit (as a fuel depot for the cargo BFS before/after landing, a spare parts source and a comms relay) until ISRU fuel is available.

Obviously, a fleet of two leaves the cargo BFS for a solo voyage, which might be acceptable for early missions or when there's no people or precious cargo on board. Suggest that fleet is more than two, though...

"Land the whole thing" does not imply every "thing" lands, while "want them back" implies, imho, "for reuse", so if the "thing" can be "reused" at Mars... When the ISRU hits production scale at the surface (in a couple of synods?) there might be some use for BFS tankers, apart from getting themselves fueled and sent to Earth, that is.

How viable would be a rendezvous and docking between two spacecraft after their separate (coordinated, synchronised?) TMI / TEI burns?
« Last Edit: 06/05/2016 05:32 PM by mfck »

Online Lar

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Re: MCT Speculation and Discussion Thread 4
« Reply #2142 on: 06/05/2016 05:36 PM »
In line with the philosophy of reuse mfck articulated...

I could see the MCT being "partially strippable"... if you had cabins for 100, but are only returning 20 people why carry all of that back? if the fittings, panels, wiring, plumbing etc was designed to be modular and reusable it could be removed by humans and used in outfitting the base.
« Last Edit: 06/05/2016 05:36 PM by Lar »
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Offline MikeAtkinson

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Re: MCT Speculation and Discussion Thread 4
« Reply #2143 on: 06/05/2016 05:56 PM »
We don't know that any water mining will be done robotically, that is an assumption based on the rather dubious proposition that SpaceX won't send a crew until there is a fully fueled return BFS waiting on the martian surface.
The idea (originating from Mars Direct) was to ensure the safety of the crew.

As Zubrin said in "The Case for Mars" (pg. 70-71):
"To ensure our Mars crew would not be stranded, the ERV would fly one launch opportunity, or twenty-six months, prior to the launch of the astronauts. Thus all the propellant would be made before the crew ever left Earth, and since the propellant plant was flown to Mars integrated with the ERV there was no question about landing 'within a hose length.' The plumbing that would deliver the Mars-manufactured propellant from the chemical synthesis unit into the ERV's fuel tanks would be hardwired, installed on Earth."

"if the ERV [Earth Return Vehicle] is sent first, the crew will know before they even leave Earth that they have a fully functional Mars ascent and Earth return system waiting for them on the Martian surface, one that has already survived the trauma of landing. In contrast, a crew that lands with their ascent system can only guess in what shape their Mars ascent vehicle will be after they've hit the surface."

SpaceX did test fire F9 engines after they've been through supersonic retropropulsion in conditions relevant to Mars EDL systems development, so the latter might not be a problem.

The ERV doesn't have to be fully fuelled before the crew leaves Earth. It merely needs to have landed safely and be producing propellant at a rate that means it will be fully fuelled by the time the crew needs to use it to launch back to Earth. No doubt there will be margins to take account of any possible breakdown after the crew has set off for Mars. Set against that is the possibility of the crew making repairs and the additional output of any further ISRU equipment they bring with them. If additional margins and/or redundancy is required you can always send two ERVs on the first trip, or perhaps an ERV and a dedicated ISRU propellant production lander.

I say dubious for several reasons. Firstly Zubrin's Mars Direct architecture is very different, you cannot throw out all the rest of the Mars Direct architecture and just kept the fully fuelled return vehicle (at least not without arguments based on the MCT architecture).

Secondly, Mars will be a very safe place for the crew, they will have access to several BFS (cargo and crew), hundreds of tonnes of supplies, equipment and habs, access to ISRU resources and the ability to be resupplied from Earth. In contract the return journey is likely to be relatively hazardous, the hab is relatively light at 25 tonnes, there are solar storms, Earth EDL and a BFS which has been sitting in the martian environment for a couple of years. Just having a fuelled BFS does not mean the crew can return in it, checkout before launch could turn up any number of problems.

Thirdly, the robotics is hard and is special purpose to the initial landing. It is probably at least an order of magnitude (perhaps two orders of magnitude) harder than Curiosity. The robotics would almost certainly be the long pole with a 2022 launch this would be really hard. The chances are that it would not work perfectly the first time. Correcting the robotics could easily take several attempts, each of which are hard to do before launch of the next synod. Worst case SpaceX could take a decade before they got the ISRU robotics correct, each year burning through a $1B or two.

Fourthly, it is likely that more than one FBS would be needed for the power supply (solar or nuclear), power supply deployment, mining robotics, ISRU, tanks etc. The FBS containing the return hab might be another craft. These BFS may have to land a considerable distance apart 100+ meters, due to landings (and even more take offs) throwing up rocks.

To sum up waiting for a fully fueled return FBS before sending crew is an assumption, the analysis above suggests it is a rather dubious assumption.

Offline docmordrid

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Re: MCT Speculation and Discussion Thread 4
« Reply #2144 on: 06/05/2016 05:57 PM »
Go back to that Max Fagin (former SpaceX intern) retropropulsion thesis defense video.

Whole vehicle lands, but only an upper portion returns to Earth. If the propulsion is in the upper portion (Dragon 2 heritage) the left behind cargo section can be used for most anything; habitation, cargo, or perhaps a dual  purpose.

How about some stripped down cargo sections hauling expandable & repurposeable tanks full of distilled water (thinking Thin Red Line's expandable tank tech.) AKA, 'how to ship hydrogen and oxygen without cryocoolers', and the cargo bay volume could be repurposed for colony use later.


« Last Edit: 06/06/2016 03:20 PM by docmordrid »
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Offline MikeAtkinson

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Re: MCT Speculation and Discussion Thread 4
« Reply #2145 on: 06/05/2016 06:03 PM »
Go back to that Max Fagin (former SpaceX intern) retropropulsion thesis defense video.

Whole vehicle lands, but only an upper portion returns to Earth. If the propulsion is in the upper portion (Dragon 2 heritage) the left behind cargo section can be used for most anything; habitation, cargo, or perhaps a dual  purpose.

How about some cargo sections hauling expandable & repurposeable tanks full of distilled water (thinking Thin Red Line's expandable tank tech.) AKA, 'how to ship hydrogen and oxygen without cryocollers', and the cargo bay volume vould be repurposed for colony use later.

Maybe, but his thesis will probably be deliberately different from the MCT architecture so as to not appropriate SpaceX IPR.

Online Lar

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Re: MCT Speculation and Discussion Thread 4
« Reply #2146 on: 06/05/2016 06:04 PM »
Thirdly, the robotics is hard and is special purpose to the initial landing. It is probably at least an order of magnitude (perhaps two orders of magnitude) harder than Curiosity. The robotics would almost certainly be the long pole with a 2022 launch this would be really hard. The chances are that it would not work perfectly the first time. Correcting the robotics could easily take several attempts, each of which are hard to do before launch of the next synod. Worst case SpaceX could take a decade before they got the ISRU robotics correct, each year burning through a $1B or two.
I think this is a valid concern but I am expecting Musk thinks he can hack this in time. Asked about driving AI he called it a "solved problem" and said widespread class 4 (handless, not requiring attention) driving was 2 years away technically.  So maybe he thinks ISRU robotics won't be that hard? You'd expect a lot more visible precursor work but if there is work going already, SpaceX is very tightlipped about it!
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Offline MikeAtkinson

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Re: MCT Speculation and Discussion Thread 4
« Reply #2147 on: 06/05/2016 06:15 PM »
Thirdly, the robotics is hard and is special purpose to the initial landing. It is probably at least an order of magnitude (perhaps two orders of magnitude) harder than Curiosity. The robotics would almost certainly be the long pole with a 2022 launch this would be really hard. The chances are that it would not work perfectly the first time. Correcting the robotics could easily take several attempts, each of which are hard to do before launch of the next synod. Worst case SpaceX could take a decade before they got the ISRU robotics correct, each year burning through a $1B or two.
I think this is a valid concern but I am expecting Musk thinks he can hack this in time. Asked about driving AI he called it a "solved problem" and said widespread class 4 (handless, not requiring attention) driving was 2 years away technically.  So maybe he thinks ISRU robotics won't be that hard? You'd expect a lot more visible precursor work but if there is work going already, SpaceX is very tightlipped about it!

Autonomous driving is one of the easier ISRU robotics problems, unlike Earth the environment is very static, however Tesla are gathering 1M miles of driving data every 10 hours to use for training, spotting corner cases, etc. there is hardly any equivalent data for Mars.

Offline mfck

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Re: MCT Speculation and Discussion Thread 4
« Reply #2148 on: 06/05/2016 06:46 PM »
Why would one complicate ISRU with driving robots, excuse me my bluntness? Wouldn't it be more prudent to plan for ISRU capability be as plain and as independent of anything as possible?

Something along the lines of a self-contained chemical plant, that melts into a glacier, at landing point, brought as is by a BFS. Maybe two, one for the nuclear reactor to power it. Once you got that thing going, you can drive around all you want ;)

Offline Robotbeat

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Re: MCT Speculation and Discussion Thread 4
« Reply #2149 on: 06/05/2016 06:59 PM »
It's not as if no thought has gone into mining regolith before. There are sthudent regolith mining competitions held every year (I visited one a few weeks ago). NASA has built a bunch of prototype rovers to test mining techniques (I saw some at Glenn Research Center). Even private companies like Astrobotic have developed and tested rovers for mining regolith.

And of course, there's the entire terrestrial mining community which has put billions into autonomous and remote mining tech.

We're not starting from scratch, here, it's just there hasn't been a good cheap ride to Mars before Red Dragon.
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Re: MCT Speculation and Discussion Thread 4
« Reply #2150 on: 06/05/2016 07:21 PM »
The point about driving AI is not driving per se, although that's a useful part of the overall problem... it's that they implemented something that learns.

IF SpaceX end up needing to dig for water, rather than just being able to drill into something and tap enough water via in situ heating or whatever, then I'd predict they use the learning part of the Tesla SW, but adapted to also handle things like bucket load operations, drilling, dumping, etc. Whenever a unit gets stuck or stuck on how to proceed (two different things) and phones home for help, the moves used to unstick things get high weight in learnings, but all moves even those the system comes up with, are evaluated and feed back into the routines. maybe randomize choices a bit and evaluate how well that choice did. Simulated annealing writ large.

with two years of learning time the units might be better than when they arrived...
"I think it would be great to be born on Earth and to die on Mars. Just hopefully not at the point of impact." -Elon Musk
"We're a little bit like the dog who caught the bus" - Musk after CRS-8 S1 successfully landed on ASDS OCISLY

Offline Robotbeat

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Re: MCT Speculation and Discussion Thread 4
« Reply #2151 on: 06/06/2016 01:27 AM »
If they simply install a large (but very lightweight) crane somewhere with lots of water in the soil, the crane base wouldn't need to move but could still mine thousands of tons of water. This would be pretty easy to automate.
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Online oldAtlas_Eguy

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Re: MCT Speculation and Discussion Thread 4
« Reply #2152 on: 06/06/2016 02:39 AM »
Remember Mars has a atmosphere and has water cycles (water vapor and water ice, does not have liquid phase). So to mine all the water you need, you compress the air and liquefy the water vapor in the atmosphere. Admittedly you would have to compress a lot of atmosphere for a little bit of water but the advantage is you do not have to go out and dig it up! Once the quantities needed become very high then comes the mining of water. But for the initial methalox manufacture for the return trip this method would be an easy one to implement and would not require complex equipment just plenty of power. Compressing gas takes a great deal of energy. But you need the atmosphere compressed for other parts of the methalox manufacture as well.

Online envy887

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Re: MCT Speculation and Discussion Thread 4
« Reply #2153 on: 06/06/2016 12:54 PM »
In line with the philosophy of reuse mfck articulated...

I could see the MCT being "partially strippable"... if you had cabins for 100, but are only returning 20 people why carry all of that back? if the fittings, panels, wiring, plumbing etc was designed to be modular and reusable it could be removed by humans and used in outfitting the base.

Or just have a cargo hold with multiple hab modules inside, and pull most of the modules out at Mars to live in.

Offline Paul451

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Re: MCT Speculation and Discussion Thread 4
« Reply #2154 on: 06/06/2016 01:15 PM »
If they simply install a large (but very lightweight) crane

You presumably mean a power-shovel or dragline. A crane isn't mining equipment.

This would be pretty easy to automate.

It really isn't. It takes a lot of finesse to run a bucket at the end of a flexible line. Even a basic bucket excavator would be better. But a bucket-wheel might the best option for robotic operation.

Offline Paul451

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Re: MCT Speculation and Discussion Thread 4
« Reply #2155 on: 06/06/2016 01:29 PM »
As Zubrin said in "The Case for Mars" (pg. 70-71):
"the ERV would fly one launch opportunity, or twenty-six months, prior to the launch of the astronauts.
[...]
the crew will know before they even leave Earth that they have a fully functional Mars ascent and Earth return system waiting for them on the Martian surface [...]"

...Which has been sitting idle and exposed on the surface for over a year. Fully-fuelled does not mean "fully functional". Zubrin's plan was just exchanging one risk for another.

(And the idea that pre-landing the ERV means it's somehow more "proven" than landing the ERV with the crew was always just silly.)

Thirdly, the robotics is hard

EVAs are also hard, and expensive. (And risky.)

And not on the development path that SpaceX is currently on. Unlike their rocket development, there's no synergies between the intermediate steps to MCT and lowering the cost/complexity/risk of EVAs. Whereas there are some synergies between robotic science missions via Red Dragon, and subsequent robotic ISRU missions.

{shrug} September.

Offline MikeAtkinson

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Re: MCT Speculation and Discussion Thread 4
« Reply #2156 on: 06/06/2016 01:58 PM »
Remember Mars has a atmosphere and has water cycles (water vapor and water ice, does not have liquid phase). So to mine all the water you need, you compress the air and liquefy the water vapor in the atmosphere. Admittedly you would have to compress a lot of atmosphere for a little bit of water but the advantage is you do not have to go out and dig it up! Once the quantities needed become very high then comes the mining of water. But for the initial methalox manufacture for the return trip this method would be an easy one to implement and would not require complex equipment just plenty of power. Compressing gas takes a great deal of energy. But you need the atmosphere compressed for other parts of the methalox manufacture as well.

Not really possible to get water by compression. Water vapour is about 0.03%, so for every kg of water you would need to compress and liquefy 3 tonnes of water air.
« Last Edit: 06/06/2016 02:17 PM by MikeAtkinson »

Offline MikeAtkinson

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Re: MCT Speculation and Discussion Thread 4
« Reply #2157 on: 06/06/2016 02:15 PM »
The point about driving AI is not driving per se, although that's a useful part of the overall problem... it's that they implemented something that learns.

...

with two years of learning time the units might be better than when they arrived...

The way that most successful AI learning works is that they use large amounts of data for training. For instance Tesla collections 1 million miles of driving data every 10 hours. This data is used to train the algorithms, but also used to evaluate how the AI does on real world data, it is also used to detect real world corner cases and allows humans to tweek the AI to handle these unusual situations better. Tesla also runs autopilot in shadow mode on customers cars, comparing what new algorithms do with what the human driver does.

For rover driving on Mars we have none of that, no large data sets, no real world data around the landing site, no ability to look at corner cases and no ability to compare AI results with what a human would do. This applies not only to driving but also to many other tasks the mining system would have to perform.

Offline lamontagne

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Re: MCT Speculation and Discussion Thread 4
« Reply #2158 on: 06/06/2016 02:15 PM »
Remember Mars has a atmosphere and has water cycles (water vapor and water ice, does not have liquid phase). So to mine all the water you need, you compress the air and liquefy the water vapor in the atmosphere. Admittedly you would have to compress a lot of atmosphere for a little bit of water but the advantage is you do not have to go out and dig it up! Once the quantities needed become very high then comes the mining of water. But for the initial methalox manufacture for the return trip this method would be an easy one to implement and would not require complex equipment just plenty of power. Compressing gas takes a great deal of energy. But you need the atmosphere compressed for other parts of the methalox manufacture as well.

Not really possible to get water by compression. Water vapour is about 0.03%, so for every kg of water you would need to compress and liquefy 3 tonnes of water <air>.
Compression requires much too much work.  It should be fairly simple to use dessicants to dry out the air, then extract the water by heating the dessicant.  This is one of the most common technologies today to dry compressed air or indoor ice rinks (and was part of the original Mars direct proposal).  alternatively you can compress a refrigerant, and use that to create a cold surface on which the water in the air will condense out.  Any of these solutions will require a minimum of about 1000 btu/lb or 2300 kJ/kg of water, the phase change energy of water.
« Last Edit: 06/06/2016 02:22 PM by lamontagne »

Offline Robotbeat

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Re: MCT Speculation and Discussion Thread 4
« Reply #2159 on: 06/06/2016 03:32 PM »
If they simply install a large (but very lightweight) crane

You presumably mean a power-shovel or dragline. A crane isn't mining equipment.
...on Earth. But sure, power-shovel or bucketwheel would work, too.

Quote
This would be pretty easy to automate.

It really isn't. It takes a lot of finesse to run a bucket at the end of a flexible line. Even a basic bucket excavator would be better. But a bucket-wheel might the best option for robotic operation.
I never said you'd use a bucket-line, you're the one who mentioned that. :)
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