Colonization Discussion Thread (split from SpaceX)

[kerbiloid]

10 hours ago, DAL59 said:

You can do a Mars mission with just 5 FH launches:

Even this zero-redundancy-thus-suicidal design mentioned earlier (alas, can't find someone's post) requires ~1400 t in LEO.

P.S.
ISRU flights are fantasy. ISRU fueling can be used when there is already a surface base with an administrator ready to sign the permission to use the ISRUed fuel.
Because if you can make the fuel remotely you no more need a crewed expedition.
If hope to make the fuel after landing — what if ISRU won't give enough good fuel to return?

Edited February 12, 2018 by kerbiloid

[Rakaydos]

42 minutes ago, kerbiloid said:

Because if you can make the fuel remotely you no more need a crewed expedition.

What if your billionaire bankroller WANTS crewed expeditions?

[kerbiloid]

14 minutes ago, Rakaydos said:

What if your billionaire bankroller WANTS crewed expeditions?

Spoiler

 

[Hannu2]

11 hours ago, sevenperforce said:

How hard would it be to test a Mars ISRU system in LEO with a little rotation to simulate Martian gravity?

Maybe it would be possible to make some tests for some components, but it would be no sense to test whole system. You can not test raw resource gathering in LEO and conditions are very different. Atmosphere and dust are very significant planning parameters for everything intended to work on Mars.

[Hannu2]

3 hours ago, kerbiloid said:

ISRU flights are fantasy. ISRU fueling can be used when there is already a surface base with an administrator ready to sign the permission to use the ISRUed fuel.

Because if you can make the fuel remotely you no more need a crewed expedition.
If hope to make the fuel after landing — what if ISRU won't give enough good fuel to return?

As far as I know, the idea is that ISRU unit goes first and begin to make fuels. Crew leaves at next window if telemetry tells the fuels are ready. If some problems arise during trip towards Mars, landing is aborted.

I am sure that humans can never go to Mars with current safety cavil and insane bureaucracy. We have to get the same pioneering attitude as kings had during great expeditions. We have to be ready to send spaceships to daring expeditions and accept that everyone will not come back. As far as we require that risks of astronauts can not be higher than risks of office bureaucrats, we will get only empty words, fancy "plans" and gorgeous animations.

Something must really change in out attitudes (all of us, regular taxpayers, politicians, authorities and rich entrepreneurs) and unfortunately there are no real signs of such change. Any leaps in technology will not help. We can not develop technology for manned space exploration without risking crews.

[kerbiloid]

28 minutes ago, Hannu2 said:

the idea is that ISRU unit goes first and begin to make fuels.

That's nice but who will taste the fuel and say "OK, fly here" ?
Otherwise they can get to Mars and say "Oops, do you call this fuel? How should we return?"
And who will be declared guilty? Probably that one who had allowed this adventure at all.

Omnia mea mecum porto - that's the motto for the first expeditions.

28 minutes ago, Hannu2 said:

I am sure that humans can never go to Mars with current safety cavil and insane bureaucracy. We have to get the same pioneering attitude as kings had during great expeditions. We have to be ready to send spaceships to daring expeditions and accept that everyone will not come back. As far as we require that risks of astronauts can not be higher than risks of office bureaucrats, we will get only empty words, fancy "plans" and gorgeous animations.

Retrospectively astronauts risk is 1:70, so if 1.4% bureaucrats were... hm... alternatively fired, their risks would be the same.

I think this is mostly a question of ISP and Power. (Power in watts).
When you can send a lot of useless junk you have no need to count every drink of water.

The marsonauts need at least a prepared deposit of fuel or a fueled return ship on/at Mars.
ISRU can be useful for Martian hoppers or when there is a whole planetary base on Mars with the refinery staff.

Edited February 12, 2018 by kerbiloid

[magnemoe]

7 minutes ago, kerbiloid said:

That's nice but who will taste the fuel and say "OK, fly here" ?
Otherwise they can get to Mars and say "Oops, do you call this fuel? How should we return?"
And who will be declared guilty? Probably that one who had allowed this adventure at all.

Omnia mea mecum porto - that's the motto for the first expeditions.

Retrospectively astronauts risk is 1:70, so if 1.4% bureaucrats were... hm... alternatively fired, their risks would be the same.

I think this is mostly a question of ISP and Power. (Power in watts).
When you can send a lot of useless junk you have no need to count every drink of water.

The marsonauts need at least a prepared deposit of fuel or a fueled return ship on/at Mars.
ISRU can be useful for Martian hoppers or when there is a whole planetary base on Mars with the refinery staff.

Determine that the fuel is ok is pretty simple as in sensors and chemical analyze.

You have other problems.
You need to land close to the fuel depot but not on top of it. This is an common KSP problem and harder in real world. The rocket flame and rocks expelled by it is also an major problem for the depot. 
You need to be sure you can actually transfer the fuel after landing. 

if something happens with depot before you land you can abort this is not an option after landing. 

Another issue would be that an ISRU system will be pretty large at least the power part will be, how to deploy this automatically, BFR is an fairly complex craft to deploy from to. 
This has to be done with the time delay we faces to Mars. 

 

[kerbiloid]

24 minutes ago, magnemoe said:

Determine that the fuel is ok is pretty simple as in sensors and chemical analyze.

Will they (on the Earth) buy methane on a car fuel station? Or will they deal with a specially certified vendor?
Then how can they hope on a Martian methane moonshine still?
Any measurement has its accuracy. A percent of water - and the engine will shutdown.
Until they try a small portion of ISRU methane in a marsocopter, nobody will risk and sign the permission.

24 minutes ago, magnemoe said:

You need to land close to the fuel depot but not on top of it. This is an common KSP problem and harder in real world.

Probably Falcon stages look landing enough accurately.
Though anyway they have to land not onto the ISRU head, but say in hundred meters from it. So anyway they need either a long cryo hose (looks unlikely) or a rover with cryogenic cystern.
In case of base it's not a problem, of course.

24 minutes ago, magnemoe said:

if something happens with depot before you land you can abort this is not an option after landing. 

If you see that something had happened with the depot earlier, and you have 97% methane instead of 98%, it will be oops.

Edited February 12, 2018 by kerbiloid

[Hannu2]

1 hour ago, kerbiloid said:

That's nice but who will taste the fuel and say "OK, fly here" ?
Otherwise they can get to Mars and say "Oops, do you call this fuel? How should we return?"
And who will be declared guilty? Probably that one who had allowed this adventure at all.

Omnia mea mecum porto - that's the motto for the first expeditions.

Retrospectively astronauts risk is 1:70, so if 1.4% bureaucrats were... hm... alternatively fired, their risks would be the same.

I think this is mostly a question of ISP and Power. (Power in watts).
When you can send a lot of useless junk you have no need to count every drink of water.

The marsonauts need at least a prepared deposit of fuel or a fueled return ship on/at Mars.
ISRU can be useful for Martian hoppers or when there is a whole planetary base on Mars with the refinery staff.

It is relatively easy to detect fuel quality. There are many options. For example fuel refinery can be with return craft and use return craft's tanks as a storage. When astronauts leave they remove ISRU unit and use the craft. In any case it needs much development and tests. I do not believe manned Mars expedition in my lifetime (about 40 years if it is average).

if ISRU is not used for manufacture fuel for return, mass budget explodes to ridiculous numbers. Far beyond any foreseeable technology. Such projects is possible after some (or many) sudden breakthroughs, which may take hundreds of years.

Who is guilty? That is the attitude which practically prevents manned exploration. Therefore I said, that before it changes there will not be significant steps in manned exploration. Laws must be written so that everyone know risks and no-one is accused in case of emergency and crew loss. Like no one was accused if someone died during last centuries expeditions. Every technically possible methods must also be accepted, like nuclear power in all forms. That is much slower than technological development, it is main reason why I do not believe success in many decades.

41 minutes ago, kerbiloid said:

Will they (on the Earth) buy methane on a car fuel station? Or will they deal with a specially certified vendor?
Then how can they hope on a Martian methane moonshine still?
Any measurement has its accuracy. A percent of water - and the engine will shutdown.
Until they try a small portion of ISRU methane in a marsocopter, nobody will risk and sign the permission.

Probably Falcon stages look landing enough accurately.
Though anyway they have to land not onto the ISRU head, but say in hundred meters from it. So anyway they need either a long cryo hose (looks unlikely) or a rover with cryogenic cystern.
In case of base it's not a problem, of course.

If you see that something had happened with the depot earlier, and you have 97% methane instead of 98%, it will be oops.

Methane and oxygen can burn even they have much impurities. And liquefaction removes most impurities (like water). Of course ascent motor would be the type which would have large enough tolerances and the craft would have much larger marginals than normal stages. I think that would be small problem in that huge project.

[Nibb31]

1 hour ago, magnemoe said:

Determine that the fuel is ok is pretty simple as in sensors and chemical analyze.

Automated chemical and impurity testing is not as simple as it sounds. You also have to make sure that all your analysis equipment is functional and properly calibrated and doesn't go out of wack, and nothing gets into the fuel and LOX during storage and transfer.

All of this has to be highly reliable because lives will depend on the quality of the propellant, and therefore on the reliability of the test equipment as much as on the reliability of the ISRU gear and the reliability of the propellant storage transfer techniques. I don't see how you can put human lives on the line without at least TRL9 in all of these technologies, which is going to require multiple iterations of the development cycle.

 

 

 

55 minutes ago, kerbiloid said:

Probably Falcon stages look landing enough accurately.

Falcon operations rely heavily on GPS. There is no GPS on Mars.

Landing accuracy will have to rely on some sort of pre-landed beacon system, ideally with triangulation.

 

[kerbiloid]

37 minutes ago, Hannu2 said:

It is relatively easy to detect fuel quality.

I'm afraid it's not that simple even on the Earth.
I was taking part in my colleague's job when she was automating the fuel store management. Density, composition, almost everything is constantly varying.
And this is with a certified fuel delivered by a certified vendor, not ISRUed from dirt and air.

Of course, pn Mars the tanks are closed and nothing gets in or out. But at least the daily temperature on Mars oscillates between +20°C and -80°C, so all pollutions including water will freeze and vaporize all the day and night long, constantly changing the methane humidity and CO2 traces concentration.
(Or you have to keep a giant cryostate keeping your methane at -180°C, which means a large facility.)

Btw a Martian flight is 120 days long + 550 days until return. How long should the tank keep methane?

37 minutes ago, Hannu2 said:

if ISRU is not used for manufacture fuel for return, mass budget explodes to ridiculous numbers. Far beyond any foreseeable technology.

And that's why we can hardly await regular Martian fights until gaseous core reactors will be in order, with ISP 20..70 km/s.
Also such reactor will immediately change the ISRU abilities by the order of magnitude.
On another hand, without working ISRU there is nothing to do on Mars. So, gas core reactors are the reference point. They will give some sense to a Martian base, reasonable mass to the Martian ships and to the upper stages of reusable super-heavy launch vehicles.

37 minutes ago, Hannu2 said:

Methane and oxygen can burn even they have much impurities.

And water can freeze inside a pump (methalox is -180°C) and block the engine feeding.

22 minutes ago, Nibb31 said:

Falcon operations rely heavily on GPS. There is no GPS on Mars.

I mean Martian GPS as a required upfront condition of all this epic at all. As well as orbital telescope.
Humans are required to use shovels, buckets and moonshine still for fuel.

Edited February 12, 2018 by kerbiloid

[Hannu2]

5 minutes ago, kerbiloid said:

I'm afraid it's not that simple even on the Earth.
I was taking part in my colleague's job when she was automating the fuel store management. Density, composition, almost everything is constantly varying.
And this is with a certified fuel delivered by a certified vendor, not ISRUed from dirt and air.

Of course, pn Mars the tanks are closed and nothing gets in or out. But at least the daily temperature on Mars oscillates between +20°C and -80°C, so all pollutions including water will freeze and vaporize all the day and night long, constantly changing the methane humidity and CO2 traces concentration.
(Or you have to keep a giant cryostate keeping your methane at -180°C, which means a large facility.)

Btw a Martian flight is 120 days long + 550 days until return. How long should the tank keep methane?

And that's why we can hardly await regular Martian fights until gaseous core reactors will be in order, with ISP 20..70 km/s.
Also such reactor will immediately change the ISRU abilities by the order of magnitude.
On another hand, without working ISRU there is nothing to do on Mars. So, gas core reactors are the reference point. They will give some sense to a Martian base, reasonable mass to the Martian ships and to the upper stages of reusable super-heavy launch vehicles.

And water can freeze inside a pump (methalox is -180°C) and block the engine feeding.

I mean Martian GPS as a required upfront condition of all this epic at all. As well as orbital telescope.
Humans are required to use shovels, buckets and moonshine still for fuel.

Simple was compared to overall complexity of Mars mission. But certainly it is possible with enough accuracy.

Methane and oxygen must be liquified and stored in insulated tanks with small pressure. Gaseous storage would be enormous and totally impossible to land on planet. Water must be removed from air very carefully before liquefaction. Otherwise it freezes and blocks the liquifier. And if there are overpressure in tanks atmospheric water can not go in. ISRU system must be planned do that all freezing stuff is removed. It is simply necessary prerequisite for manned mission.

Probably practical time scale would be maybe 1.5-2 years of manufacturing. That would keep process in sane scale. After 26 months crew would land on planet (if telemetry tells that fuel is ready), make few months research and ascent during next return window.

Probably nuclear reactor is only suitable energy source for such resource utilization.  Unfortunately, it is currently politically impossible. I believe that all forms of nuclear propulsion are far more impossible. It is one thing which would need change of attitudes before manned Mars operations will be really feasible. Without nuclear power best option would be insanely expensive Apollo-like propaganda trick but not real long term research.

ISRU will not certainly be an easy solution and it will need much more decades and billions of dollars than some overoptimistic scenarios suggest now. It is certainly totally impossible to get ready for 2030's. But I do not see realistic choices for first missions. Nuclear propulsion would work technically, as you mentioned, but when will world's governments and safety nitpickers allow research and utilization of nuclear power for space nerds? Maybe after WW 3 when (or if) they notice that "hey, we did not extinct yet".

 

[Technical Ben]

Simulating on earth is easy. We have vacuum chambers. Gravity is lesser a concern in simulation.

If they do it here first, then they can say they can do it on Mars. But for now they can send stuff, for a certainty, up to the size of a small car...

[kerbiloid]

5 minutes ago, Hannu2 said:

Methane and oxygen must be liquified and stored in insulated tanks with small pressure. Gaseous storage would be enormous and totally impossible to land on planet. Water must be removed from air very carefully before liquefaction.

With Sabatier (or any another process) you don't get pure methane.
You get an unpredictable mixture of methane, water, carbon dioxide, carbon monoxide, occasionally appeared hydrocarbons, hydrogen and random fluids.
To separate them industrially they use several columns and additional fluids, a whole plant. They need not "mostly methane", but "exactly methane".
More or less the same with Martian ISRU oxygen.

11 minutes ago, Hannu2 said:

Probably practical time scale would be maybe 1.5-2 years of manufacturing.

And of leaking. Mars surface is -100...+30°C while methalox is -200..-180°C, i.e. is always trying to boil.
So they have either to keep freezing a cryostate for years, or have a tank-armor balloons withstanding high pressure.
Otherwise almost all they produce they will have to vent out while it's boiling.

And this doesn't remove the problem of purification.

14 minutes ago, Hannu2 said:

Probably nuclear reactor is only suitable energy source for such resource utilization.  Unfortunately, it is currently politically impossible.

It's currently technically hard even more. Solid core reactors are heavy and ineffective, while gaseous core are still a project.
Also typically a reactor needs every ~3 years to be refueled, so it's important to spend the fuel as completely as possible. Solid ones unlikely can this.

So, when a small permanent Martian base will be found and its ISRU plant will be producing methalox for years to fuel drones and hovercrafts, they can raise their bets up to the whole spaceships.

10 minutes ago, Technical Ben said:

Simulating on earth is easy. We have vacuum chambers. Gravity is lesser a concern in simulation.

And probably some of SpaceX companies would do this before planning their colony.

[PB666]

I think short term ISRU (As in BFR > Mars scheme)  is idealized and ill conceived. Find a water honey hole first and then talk about harvesting and production. As long as Space X has not disclosed a spot they intend to land and gather water from we can pretty much assume that all of this part of their future is vapor-ware.

My idea was to build space tugs now and haul stable fuels into LMO and stock pile them. Then you only have to worry about having enough dV to gain LMO, for Mars I think its 4800dV or so to orbit. Keep your transfer ship in Orbit and drop a habitation ship. Again its a good idea to bury them if you can. But honestly, if you are going to do that don't even worry about the return flight, just send a pair of mature couples to Mars.

The cost of resourcing MARS orbit IIRC about dV 1500 for orbital insertion on an Efficient-Hohmann transfer. This compares to the 5500 to 6000 dv required to land and get back to Mars orbit. However absolute cost is a matter of Payload, and even with chemical rockets you can get dV in the 11,000 range if the PL is small. So basically create a coffin sized PL with enough room for 1 crewman in a space suit. Don't even worry about docking ports, just let him space walk to the return vessel. You could even refuel the vessel from LMO if you had a small docking port and send it back for a second pickup.

The priority is on sample return, not people return, if you are going to colonize, people deciding to go back home is not something you want.

While I appreciate the effort that Musk is making to go to Mars, it is in his best interest to support the discovery missions first, discovery is about resource analysis, that is why you want geologist and chemist on the ground, not breeding pairs. The issues regarding Mars is where is 'where is it feasible to land and develop (ISRU) and after you have supplied enough resources to maintain the colony then do you have the resources for return flight. This means you need many missions to different sites and autonomous drilling vessels, etc.

My opinion is that return flight ISRU exploitation would kill the overwhelming proportion of emergent colonies.  This has nothing to do with their plan to develop BFR and send a ship to Mars, its about what you do on Mars once you get there.

 

 

 

[Hannu2]

1 hour ago, kerbiloid said:

With Sabatier (or any another process) you don't get pure methane.
You get an unpredictable mixture of methane, water, carbon dioxide, carbon monoxide, occasionally appeared hydrocarbons, hydrogen and random fluids.
To separate them industrially they use several columns and additional fluids, a whole plant. They need not "mostly methane", but "exactly methane".
More or less the same with Martian ISRU oxygen.

And of leaking. Mars surface is -100...+30°C while methalox is -200..-180°C, i.e. is always trying to boil.
So they have either to keep freezing a cryostate for years, or have a tank-armor balloons withstanding high pressure.
Otherwise almost all they produce they will have to vent out while it's boiling.

And this doesn't remove the problem of purification.

It's currently technically hard even more. Solid core reactors are heavy and ineffective, while gaseous core are still a project.
Also typically a reactor needs every ~3 years to be refueled, so it's important to spend the fuel as completely as possible. Solid ones unlikely can this.

So, when a small permanent Martian base will be found and its ISRU plant will be producing methalox for years to fuel drones and hovercrafts, they can raise their bets up to the whole spaceships.

And probably some of SpaceX companies would do this before planning their colony.

I do not want to underestimate fuel production problems. They certainly need several test missions to Mars to finalize all details before actual manned mission. But still I think that it is easier way to achieve the first manned mission than trying to overcome the terror of rocket equation by brute force.

Nuclear propulsion may be another route, but as I wrote, I do not believe that any government in the world will allow it in foreseeable future and I do not count on that.

[sevenperforce]

5 hours ago, Hannu2 said:

Maybe it would be possible to make some tests for some components, but it would be no sense to test whole system. You can not test raw resource gathering in LEO and conditions are very different. Atmosphere and dust are very significant planning parameters for everything intended to work on Mars.

Upthread, I was discussed a reduced-complexity ISRU system, where the ascent vehicle carries its own hydrazine and merely needs to manufacture LOX to fill tanks which were used for descent. A gallium-phosphide semiconductor, combined with a nickel-based alloyed catalyst, can be used to crack CO₂ into CO and O₂ using solar power. So all you need is the solar array, a compressor/collector which can work in a 600-Pa atmosphere, and a gas liquefaction system with a small centrifuge.

This could be tested in LEO on Dragon 1. Send up the Dragon 1 and have it vent to vacuum. It would have a canister filled with 96% CO₂, 2% argon, and 2% N₂, attached to a valve. The valve would release gas at such a rate as to maintain a constant internal capsule pressure of 600 Pa, and then the Dragon 1 would use its thrusters to put itself into a steady tumble to simulate Martian gravity. The ISRU system would kick on and test everything.

Oxidizer is the majority of the propellant mass of an ascent vehicle, so if you can crack it from the atmosphere, you've cut your starting mass down considerably. 

You'd need to test it in LEO, then send a small version with a working filtration system to Mars on a Falcon Heavy for testing (this would be a good time for a Mars Sample Return mission), then send a full-scale ascent vehicle for testing, and THEN you can do your flags-and-footprints landing.

5 hours ago, Hannu2 said:

As far as I know, the idea is that ISRU unit goes first and begin to make fuels. Crew leaves at next window if telemetry tells the fuels are ready. If some problems arise during trip towards Mars, landing is aborted.

I am sure that humans can never go to Mars with current safety cavil and insane bureaucracy.

Yes, but at the same time, you do need as much mission safety and redundancy as possible.

The TMI needs to put you on a free-return, so that even if EVERYTHING goes wrong, you can still make it home as long as your life support remains functional and your entry capsule is intact. The orbiter cannot rely on ISRU fuel; it needs to carry enough propellant to brake in and out of low Martian orbit on its own. 

[Hesp]

1 hour ago, kerbiloid said:

With Sabatier (or any another process) you don't get pure methane.
You get an unpredictable mixture of methane, water, carbon dioxide, carbon monoxide, occasionally appeared hydrocarbons, hydrogen and random fluids.
To separate them industrially they use several columns and additional fluids, a whole plant. They need not "mostly methane", but "exactly methane".
More or less the same with Martian ISRU oxygen.

And of leaking. Mars surface is -100...+30°C while methalox is -200..-180°C, i.e. is always trying to boil.
So they have either to keep freezing a cryostate for years, or have a tank-armor balloons withstanding high pressure.
Otherwise almost all they produce they will have to vent out while it's boiling.

And this doesn't remove the problem of purification.

The first is a problem that could be solvable using automotive techniques (i.e. a UEGO sensor in closed loop control to adjust Fuel-LOx mixture). Needs to be engineered for a rocket engine, yes, but it removes the need for a laboratory quality fuel and allows to settle for a "good enough" mixture.

Boiloff... not sure why nobody is evaluating propane as ISRU fuel. Way more easier to keep liquid than methane, denser and more densifiable when subcooled, almost same ISP.

The biggest fraction of the propellant weight will be oxygen anyway, but you can obtain it in a "easier" way from atmosphere.

Maybe it's worth to liquify it, keep LOx cool by evaporation, use the GOx for other applications (fuel cells?) instead of going for a zero-boiloff solution.

[kerbiloid]

21 minutes ago, Hesp said:

Boiloff... not sure why nobody is evaluating propane as ISRU fuel. Way more easier to keep liquid than methane, denser and more densifiable when subcooled, almost same ISP.

To make propane you have to make methane, then use it to make propane an uncertain mixture of hydrocarbons (Fischer-Tropsch process or so) and at last separate them in similar manner. That's exactly what an oil refinery does.
And then you get a volatile propane-butane with nearly the same density and heat production as a non-volatile kerosene and have to deal with pressurized tanks.
More or less useful on Earth but requires a whole plant on Mars.

21 minutes ago, Hesp said:

The biggest fraction of the propellant weight will be oxygen anyway, but you can obtain it in a "easier" way from atmosphere.

As said above, one must have onboard all necessary for return for the case if something goes wrong.
So, they anyway have to land with full tanks of oxidizer (and LOx is not the best choice to store it for years, while a bimodal engine UDMH+NTO / UDMH+LOx sounds creepy).
In this case thay won't have any use for the ISRU LOx.

But much later, when a small surface base with its small refinery plant with its engineers exists for years and produces methane/oxygen just for its own needs, it will make a great sense to refuel the ships.

Edited February 12, 2018 by kerbiloid

[Hesp]

4 minutes ago, kerbiloid said:

To make propane you have to make methane, then use it to make propane an uncertain mixture of hydrocarbons (Fischer-Tropsch process or so) and at last separate them in similar manner. That's exactly what an oil refinery does.
And then you get a volatile propane with nearly the same density and heat production as a non-volatile kerosene and have to deal with pressurized tanks.
More or less useful on Earth but requires a whole plant on Mars.

Well, commercial LPG is mostly a propane-butane mixture in uncertain proportions, and cars work reliably with it. As told before, if the engine can accept a variable HC mixture some of the ISRU complications can be ignored.

What's easier, develop a more tolerant engine or deliver a "perfect" fuel refinery to Mars? I don't have an answer to this.

Pure propane at -40°C has a vapour pressure of 1 bar, 0.1 bar at -85°C, 0.03 bar at -100°C. If you can keep it reasonably cool you don't need pressurized tanks at all. It's a tradeoff between cryo CH4 and Kerosene.

[kerbiloid]

5 minutes ago, Hesp said:

commercial LPG is mostly a propane-butane mixture in uncertain proportions, and cars work reliably with it

It's mostly not made of atmospheric CO2 but just separated from the existing natural gas, so it's cheap.
And if a car engine stops, the car stops. If an ascent vehicle engine stops, it falls down.
Car engines are more omnivorous, you can even run some of them on a rapeseed oil instead of native fuel (an insignificant adaptaion of nozzles is required afaik).

Edited February 12, 2018 by kerbiloid

[Hesp]

11 minutes ago, kerbiloid said:

It's mostly not made of atmospheric CO2 but just separated from the existing natural gas, so it's cheap.
And if a car engine stops, the car stops. If an ascent vehicle engine stops, it falls down. Car engines are more omnivorous, you can even runs some of them on a rapeseed oil instead of petrol.

Cheap or not, what I was pointing out was the uncertain mixture and the ability to work with it. Car engines are more omnivorous because they've been conceived and developed to be like that. A F1 (Formula 1) engine without its bespoke fuel won't even start up.

Oh, and if a car stops when using appropriate fuel, car manufacturer gets in trouble and loses money -> it's a critical failure as well from an engineering point of view.

Edited February 12, 2018 by Hesp
spelling

[mikegarrison]

IIRC, Kim Stanley Robinson's Mars books, one of the first things people did before colonizing Mars was set up a "APS" constellation that was a combination navsat and comsat net. That seems like a pretty reasonable thing to do for anyone planning on doing more than just a token visit.

[kerbiloid]

23 minutes ago, mikegarrison said:

That seems like a pretty reasonable thing to do for anyone planning on doing more than just a token visit.

That seems a must-have thing for the pre-human detailed orbital research of the planet.
At last, when the orbital multispectral telescopes can give nothing more, they would send humans with a shovel.

[DAL59]

14 hours ago, kerbiloid said:

ISRU won't give enough good fuel to return?

It uses the air itself to make fuel.  Thats not a risk, and their prepositioning two BFRs in advance anyway.  

8 hours ago, Hannu2 said:

ISRU will not certainly be an easy solution and it will need much more decades and billions of dollars than some overoptimistic scenarios suggest now. It is certainly totally impossible to get ready for 2030's.

The sabatier reaction has been done for decades.