totm nov 2023 SpaceX Discussion Thread

[sevenperforce]

1 minute ago, Nibb31 said:

Why not start a new thread on this ? Let's try to keep the SpaceX thread clean.

I think it's relevant to the ongoing discussion of BFR. I wasn't saying "let's discuss ISRU generally".

[Nibb31]

Fair enough. ISRU is IMO the less mature technology in Musk's Mars plan (the other one is the long-duration life support for 100 people). We are talking about a TRL2 or 3, when you are going to need at least TRL8 if you want to rely on it for the return trip. We are pretty certain that there is water on Mars, but we have no idea how much there is, where are the best places to look, or how deep we need to dig. Without knowing those things, I don't see how SpaceX can design a device to capture that water. The task has to be split down into a number of subtasks:

• Prospecting
• Drilling
• Collecting
• Purifying
• Converting
• Storing

It's going to require a lot trial and error to progressively develop techniques in each of these areas, and even more work to get it to work autonomously with low maintenance and high reliability in an extreme environment. Some of it can be done in a lab, but it has to be proven in the field at various scales before you can expect to refuel your ship and bring it back. It will necessarily require several iterations, and they will certainly need to survey multiple areas to find out which locations are easiest to exploit. Given that iterations will be constrained by synods and budgets, I don't see how this can be done in less than a decade or even two.

This is where Red Dragon could have come in handy. It would have be useful to carry a series proof of concept experiments with a drill or a scraping device to dig into the regolith.

Without Red Dragon, the only alternative is to send a full-blown unmanned BFR on a one-way trip, which is going to be much more expensive.

Edited October 3, 2017 by Nibb31

[kerbiloid]

9 minutes ago, Nibb31 said:

Fair enough. ISRU is IMO the less mature technology in Musk's Mars plan.

Otherwise he already had a company "Ice-Boring Hyperdrill" or so, and we had read about it.

47 minutes ago, sevenperforce said:

Since you can't be assured of getting ice the first place you dig, you'll probably need a few separate (and, probably, independently autonomous) elements:

• Drill/pump assembly
• Atmospheric collection compressor
• Power array
• Synthesis unit
• Refrigeration system
• Storage tanks
• Refueling robot

That's if you went with a drill.

And this is an optimistic view.
Because usually any gas (natural or synthesized) needs purification. And this is several huge columns more.

Edited October 3, 2017 by kerbiloid

[sevenperforce]

Cancellation of Red Dragon is a real shame. Then again, if BFR actually flies in 2022...

Are there any actual designs for a self-contained permafrost drill that have been shown to work on Earth or in simulations?

[tater]

The trick with BFR vs Red Dragon is the investment level for a single landing area. They are likely to want to pick the same sort of landing ellipse NASA would pick---virtually flat and with the smallest number of boulders possible. Such a site might be less than idea for finding water. Rovers could be dropped (several), but they face the same issues current rovers have---on the other hand if they are smaller, and cheaper, SpaceX might borrow from tesla and just let them drive themselves. If rovers were a ton or less each, they could drop rather a lot of them.

The problem with self contained ISRU units on wheels  is just that while they could test locations, they could not refill the BFR. You'd think that part of such a mission would be to have a built-in ISRU so that the vehicle could refuel itself, then return to Earth to demonstrate the entire system.

Such a mission could drop rovers with scoops, pick them up, and also be the first sample return mission (leaving a bunch of other stuff on the surface).

Edited October 3, 2017 by tater

[Rakaydos]

Or the first BFR could just land on the edge of the ice cap and drill to the h20 layer.

We've surveyed mars enough, we know where there's plenty of water. SpaceX already picked out landing sites for Red Dragon, and presumably those same sites will still be on the table for BFR.

[magnemoe]

42 minutes ago, sevenperforce said:

Cancellation of Red Dragon is a real shame. Then again, if BFR actually flies in 2022...

Are there any actual designs for a self-contained permafrost drill that have been shown to work on Earth or in simulations?

Think that would be serious overkill, an standard drill rig would work well enough you don't need an large hole. 
But yes you will need permafrost at location, then electrical heat the tip area to melt or inject steam. 

[Nibb31]

34 minutes ago, Rakaydos said:

Or the first BFR could just land on the edge of the ice cap and drill to the h20 layer.

The edge of the ice cap is no place to build a base. Remember what happened to Phoenix ?

Edited October 3, 2017 by Nibb31

[IncongruousGoat]

On the subject of where to find ice, I seem to remember reading that there's a large amount of underground ice in Utopia Planitia. And, as a bonus, Viking 2 landed there and operated for well over 1000 sols, so we know the region is safe for landers.

Edited October 3, 2017 by IncongruousGoat

[Elthy]

Afaik you wouldnt harvest water/ice with a drill, but by digging up soil and heating it in a heated chamber. From what i know most is closely underground anyway.

[Rakaydos]

13 minutes ago, Nibb31 said:

The edge of the ice cap is no place to build a base. Remember what happened to Phoenix ?

You said yourself, bases come after we've gotten ISRU reliable. The first dig sites dont need to be where the permanent base is established.

[Green Baron]

2 hours ago, sevenperforce said:

 

Are there any actual designs for a self-contained permafrost drill that have been shown to work on Earth or in simulations?

I can say nothing little about drilling in solid ground, but I know from the EPICA ice core project (a friend of mine participated) that you need a crew around the clock. The borer may divert (very tedious), the pipe may get blocked (frozen, that means nothing comes through and boring stops, how boring), every now and then a new segment must be added. The latter means sloppy spoken that work stops, the top segment is drawn out and a new one screwed in. Very heavy stuff. Takes many months to bore down 3km and many erratic attempts to get the whole train in line again.

But i doubt that this technology is suitable elsewhere(tm). Given the weight of the rig and all the tubes, that's a few hundred tons. They used caterpillars and sledges to get everything there in the summer months.

Flexible wouldn't work either if there is nothing to keep it straight or it'll pop out of the ground a few meters away. You can bore sideways if you know exactly what you're in. But before that several crews must scout out the ground (seismics ?) and its contents. I mean on Mars !

All in all i fear that the answer is nope, such a thing has, as everything else i dare say, yet to be invented.

Edited October 3, 2017 by Green Baron

[magnemoe]

2 hours ago, Green Baron said:

I can say nothing little about drilling in solid ground, but I know from the EPICA ice core project (a friend of mine participated) that you need a crew around the clock. The borer may divert (very tedious), the pipe may get blocked (frozen, that means nothing comes through and boring stops, how boring), every now and then a new segment must be added. The latter means sloppy spoken that work stops, the top segment is drawn out and a new one screwed in. Very heavy stuff. Takes many months to bore down 3km and many erratic attempts to get the whole train in line again.

But i doubt that this technology is suitable elsewhere(tm). Given the weight of the rig and all the tubes, that's a few hundred tons. They used caterpillars and sledges to get everything there in the summer months.

Flexible wouldn't work either if there is nothing to keep it straight or it'll pop out of the ground a few meters away. You can bore sideways if you know exactly what you're in. But before that several crews must scout out the ground (seismics ?) and its contents. I mean on Mars !

All in all i fear that the answer is nope, such a thing has, as everything else i dare say, yet to be invented.

You have plenty of drill rigs with auto feed of new segments, no I have doubt in reliability as rigs on earth always have an operator. 
Frozen is not an issue as this will be designed to melt ice, you have to drill trough the soil to get to the ice, drilling for water on earth is far closer than drilling for oil. 

And 3 KM down is very deep, I doubt you have to go so deep for permafrost. Seismic and test drilling is required, both can be automated pretty well, but yes the drill will break down after an number of holes. 

[tater]

So I was thinking while doing other stuff...

I was thinking of a first crew mission where abort modes, etc really matter.

Let's assume a nose to nose docking arrangement is possible between 2 BFS.

An idea would be to tank BFS up full, then tank up a tanker with another tanker such that the tanker in orbit gets enough propellant for ~4km/s of dv. That looks to be 2 tanks or so, so 1 tanker up and topped once with another. Dock the partially full tanker to the nose of the BFS, and use it to lift the BFS perigee quite high. Disconnect at apogee, and land tanker. At BFS perigee, do final TMI burn.

LEO to escape is 3.22 km/s. Any of that bought by the tanker increases the available dv of the BFS. Full BFS tanks gives 150t to Mars only for total dv<6km/s. That increases to over 7 only 100t cargo. Buying 3+ km/s from a tanker boost is a big deal. Martian surface to orbit is on the order of 4.1 km.s. So now the TMI burn might be quite low, indeed (as low as ~1.5km/s, likely more). 

This could allow (assuming it can do this) a landing with the tanks full enough to make Mars Orbit from the surface as an abort mode. It would also allow a mission to Mars orbit as a precursor (check out moons for resources) assuming they can aerocapture. The abort mode only makes sense with some prepositioned resources in LMO.

That said, if BFS could land on Mars heavy (with propellant), then the amount required via ISRU would be substantially lower.

 

[Cassel]

What about Zubrin's idea for Mars Direct to get fuel from Mars atmosphere?

[tater]

13 minutes ago, Cassel said:

What about Zubrin's idea for Mars Direct to get fuel from Mars atmosphere?

I assumed that was part of the SpaceX plan. Grab the carbon and O₂ from CO₂. To make the CH₄, they need to bring the hydrogen. Looking for water obviates the need to bring hydrogen, though, hence the drilling ideas.

[sevenperforce]

1 hour ago, tater said:

So I was thinking while doing other stuff...

I was thinking of a first crew mission where abort modes, etc really matter.

Let's assume a nose to nose docking arrangement is possible between 2 BFS.

An idea would be to tank BFS up full, then tank up a tanker with another tanker such that the tanker in orbit gets enough propellant for ~4km/s of dv. That looks to be 2 tanks or so, so 1 tanker up and topped once with another. Dock the partially full tanker to the nose of the BFS, and use it to lift the BFS perigee quite high. Disconnect at apogee, and land tanker. At BFS perigee, do final TMI burn.

LEO to escape is 3.22 km/s. Any of that bought by the tanker increases the available dv of the BFS. Full BFS tanks gives 150t to Mars only for total dv<6km/s. That increases to over 7 only 100t cargo. Buying 3+ km/s from a tanker boost is a big deal. Martian surface to orbit is on the order of 4.1 km.s. So now the TMI burn might be quite low, indeed (as low as ~1.5km/s, likely more). 

This could allow (assuming it can do this) a landing with the tanks full enough to make Mars Orbit from the surface as an abort mode. It would also allow a mission to Mars orbit as a precursor (check out moons for resources) assuming they can aerocapture. The abort mode only makes sense with some prepositioned resources in LMO.

That said, if BFS could land on Mars heavy (with propellant), then the amount required via ISRU would be substantially lower.

Nose-to-nose docking and docked burns aren't necessary.

Position two full tankers in high-elliptic Earth orbit (using as many launches as necessary to do this). Tank up your mission vehicle in LEO, then have it boost up to high-elliptic earth orbit to rendezvous with the two waiting tankers.

At perigee, all three vehicles burn to trans-martian injection together. Immediately thereafter, while still near perigee, one of the tankers docks with the mission vehicle, transfers its propellant to the mission vehicle, then decouples and burns retrograde for just long enough to bring its apogee back into Earth's SOI. It can then progressively aerobrake and eventually re-enter and land.

In transit, the mission vehicle adjusts its trajectory for EDL, while the tanker adjusts its trajectory for aerocapture.

The tanker aerocaptures into a high-elliptic Martian orbit which will be circularized slowly via aerobraking while the mission vehicle enters and descends for a landing. It will have enough reserve propellant to abort the landing and change landing sites, or to return to low Martian Orbit. Alternately, even after landing, it will have enough propellant to return to LMO if ISRU doesn't end up working out.

In nominal missions, it would refuel via ISRU and return to LMO, at which point both vehicles would return to Earth together. In abort scenarios, it would return to LMO, rendezvous with the tanker, and drain the tanker in order to get enough fuel for the trip home, leaving the tanker behind.

1 hour ago, tater said:

I assumed that was part of the SpaceX plan. Grab the carbon and O₂ from CO₂. To make the CH₄, they need to bring the hydrogen. Looking for water obviates the need to bring hydrogen, though, hence the drilling ideas.

The Zubrin plan was to bring the hydrogen, react it with atmospheric CO₂ to make methane, and crack more atmospheric CO₂ into O₂. The latter uses solid-oxide electrolysis. SpaceX's plan is to react atmospheric CO₂ with Martian H₂O via the Sabatier process to make methane and LOX directly.

[sh1pman]

Can't you just use liquid carbon monoxide/LOX combustion on Mars? Both components can be  produced from atmospheric CO2, no drilling required. This old paper by NASA states that the specific impulse can be as high as 280 for a high pressure engine (such as Raptor). Not great, but sometimes good is good enough.

Edited October 3, 2017 by sh1pman

[sevenperforce]

48 minutes ago, sh1pman said:

Can't you just use liquid carbon monoxide/LOX combustion on Mars? Both components can be  produced from atmospheric CO2, no drilling required. This old paper by NASA states that the specific impulse can be as high as 280 for a high pressure engine (such as Raptor). Not great, but sometimes good is good enough.

I doubt Raptor could run on alt prop.

[mikegarrison]

26 minutes ago, sevenperforce said:

I doubt Raptor could run on alt prop.

Besides that, sometimes "good enough" is not good enough. If you knock down the ISP, then the whole idea behind tanking up on the surface and flying all the way back to Earth on one tank won't work.

[sh1pman]

20 minutes ago, sevenperforce said:

I doubt Raptor could run on alt prop.

Think replacing 2 SL engines on BFS heading to Mars with CO/LOX ones then. Then use the methane tank to store CO instead. Way easier to set up ISRU this way than with drilling ice and doing Sabatier.

Questionable dv though, since ISP is much lower. But it can be enough for suborbital hops and maybe orbital operations.

Anyone got any thoughts about this? Can it possibly work?

[tater]

1 hour ago, sevenperforce said:

Nose-to-nose docking and docked burns aren't necessary.

Position two full tankers in high-elliptic Earth orbit (using as many launches as necessary to do this). Tank up your mission vehicle in LEO, then have it boost up to high-elliptic earth orbit to rendezvous with the two waiting tankers.

At perigee, all three vehicles burn to trans-martian injection together. Immediately thereafter, while still near perigee, one of the tankers docks with the mission vehicle, transfers its propellant to the mission vehicle, then decouples and burns retrograde for just long enough to bring its apogee back into Earth's SOI. It can then progressively aerobrake and eventually re-enter and land.

 

That can certainly work, depending on the return dv requirements vs the partially full tanker. Makes me wonder if the tanker is different from the cargo version, or the same, just more props and no cargo. 

If there is enough dv to spare, tanker could bring some other small infrastructure.

with an automated tanker with isru on the surface, you could then tank up the orbital tanker, as well, keeping it in place as a fuel depot, so that subsequent missions have that in place.

[sh1pman]

28 minutes ago, mikegarrison said:

Besides that, sometimes "good enough" is not good enough. If you knock down the ISP, then the whole idea behind tanking up on the surface and flying all the way back to Earth on one tank won't work.

A tanker can be filled with CO/LOX on the surface and put in a low Mars orbit. Departing ships can then refuel from it like they do in LEO.

ISP difference between 280s and 375s means that the ship will have 25% less dv. Which can be mitigated by refueling in orbit.

Edited October 3, 2017 by sh1pman

[Rakaydos]

I see Co/Lox as the martian equivilant of lunar Al/Lox- a local propellant useful for local purposes, but not useful for greater transport architecture.

[kerbiloid]

A thing which I still can't understand, why

Spoiler

when

Spoiler

 

7 hours ago, sevenperforce said:

Position two full tankers in high-elliptic Earth orbit

Has this successfully happened at least once?

8 hours ago, tater said:

LEO to escape is 3.22 km/s.

Which imho means. ITS/BFS is useless here even more.
Putting a huge ship much heavier than its cargo, into high orbit to refuel another ship?..
Maybe just spiral up the lifeless and calm fuel with low thrust or long-lasting nuketug?

7 hours ago, sevenperforce said:

The tanker aerocaptures into a high-elliptic Martian orbit which will be circularized slowly via aerobraking while the mission vehicle enters and descends for a landing

Instead of just burning an aluminium barrel.

Edited October 4, 2017 by kerbiloid