Whatif: Mars-built heavy lift tanker configuration

[Eer]

This is pure speculation, and a request for some number crunching for a hypothetical O2+CH4 tanker from Mars surface.

Assumptions:
1) ISRU on Mars of O2 and CH4 are "economical" given local H2O and CO2 supplies;
2) shallow gravity well of Mars makes SSTO "easy" by comparison to Earth
3) regular arrival of SS vehicles from Earth at some point in the future will allow some number of them to be "repurposed" - disassembled and reassembled into suitable Mars SSO tanker configurations, and a ready supply of working Raptor vacuum and surface optimized engines
4) The 9 meter diameter SS may not be most efficient Mars SSTO shape and size
5) energy costs for ISRU are "manageable" - that's a cop out, but whether nuclear or solar power, I don't care for this exercise - that's for some other hypothetical

Question: What is a more optimal baseline shape and size of a Mars-based tanker to deliver substantial quantities of O2 and CH4 to
a) Low Mars Orbit
b) High Mars Orbit (perhaps to refuel aerobraking SSs inbound from Earth for landing and return missions)
c) Trans Earth Injection (to deliver via slow-boat route, CH4 and O2 to Earth-Lunar L2 or other Near Earth Orbit)

My guess is that a larger diameter tanker makes sense, that raptors will have lower gravity losses (but I may be completely wrong about that) in Martian gravity, that raptors are perfectly fine engines, but a modified expansion bell tuned to martian atmosphere might be desirable.

The ultimate goal is to optimize volume delivered for least cost in fuel to launch and rendezvous.

Sorry if this seems frivolous - I'm just curious what the rocket models would say would be a "Mars-centric" tanker configuration.

[steveleach]

I was wondering in another thread...

Would Starship have sufficient delta-v to take off from Mars, get refuelled in low Mars orbit, transfer out to the asteroid belt, pick up some cargo then burn back to Earth for EDL?

But then I decided to stop wondering and start calculating.

Using a delta-v chart from Reddit

https://external-preview.redd.it/47Z8OHKj-8BImmr3bDRgrnponXxglbBbLvz0dy_3SV8.png?auto=webp&s=8f4f3021734794c6b841311f248c98b575494568

I calculate a total of 17.25 km/s of delta-v to go from low Mars orbit to the surface of Vesta, then back to Earth with aerobraking and 200 m/s left for landing.


So no, it doesn't work.

[Oersted]

Spherical, I guess!

[Slarty1080]

It seems to me that this depends on the value of power generation on Mars and balancing what it might be used for on the surface (material processing, plastic manufacture, steel manufacture etc) v the value of the propellant in orbit. IMO it will be more valuable for surface processes for a very very long time.

In the unlikely event that it is considered better to launch the propellant then the most suitable vehicle must surely be Starship as it stands.

In the very distant future the conditions on Mars such as atmospheric density and gravity would suggest a much larger vehicle could be used. But the economics of this are indeterminate at the moment.

[Eer]

Spherical, I guess!

Okay, I'll bite - spherical maximizes many good and valuable things (waves hands), but ...

Converting landed SS steel into spherical tanks from the multi-ring cylindrical steel may be more involved than simply unziping the SS rings and reassembling them into bigger diameter, maybe taller, maybe shorter cylinders.  Maybe that's not a big deal, though.

If spherical, how much aerodynamics in Martian atmosphere would be an issue? Would a non-structural skirt (or blanket) be enough to avoid too much drag until altitude makes atmosphere not an issue for the launch?

Hmmm ... I hadn't considered whether these bulk transports would ever land again (and so be themselves reusable) ... probably a gap in my imagination.

[davis_404]

A surface-to-Martian orbit tanker would work for Martian moons - water is not plentiful on Deimos or Phobos.

This would make sense if, say, Blue Origin would take my advice and instead of building trucks to space, instead concentrate on what their goal is: building spinner colonies a la Gerrard K. O'Neill and the 1975 Ames Conference - using Phobos or Deimos as material. They can buy Starships and instead of landing on Mars, land on a moon and learn the hard, hard way of building space colonies out of space materials. 

Big tankers from the Mars surface could help fill up those massive colonies with water, and bring down specialized manufactured items from zero gee factories.

Same goes for launching super Starships to the asteroids. If you drop going to Earth as a goal, a whole new world of industry and living room opens up.

[MickQ]

Spherical, I guess!

If spherical, how much aerodynamics in Martian atmosphere would be an issue? Would a non-structural skirt (or blanket) be enough to avoid too much drag until altitude makes atmosphere not an issue for the launch?

Lifting off Mars under a tarp ?    Now, where have I heard that before

[wes_wilson]

Instead of building something new; what would it look like if using a super heavy and starship both at Mars?

Could a super heavy put a fully fueled (cargo fuel and fuel fuel) starship into orbit and then still land itself back on Mars?

[Oersted]

Starship can do it by itself.

[hoardsbane]

I seem to recall SuperHeavy could just about SSTO.  Could a (modified, with aeroshell and some raptor Vacs) SuperHeavy make it to orbit, be refueled in LEO/HEO and make a slow transfer to Mars orbit as contingency fuel supply for returning starships (i.e. supplementing ISRU fuel supply)

Would mean propulsive braking onto Mars orbit (but from a slow transfer).

If ISRU is successful, and sufficient fuel remained, perhaps the SuperHeavy could even make it to the surface, be stripped of some (reusable) engines and become a fuel tanker to orbit?

Fanciful?  What is stopping this?

[Robotbeat]

This is pure speculation, and a request for some number crunching for a hypothetical O2+CH4 tanker from Mars surface.

Assumptions:
1) ISRU on Mars of O2 and CH4 are "economical" given local H2O and CO2 supplies;
2) shallow gravity well of Mars makes SSTO "easy" by comparison to Earth
3) regular arrival of SS vehicles from Earth at some point in the future will allow some number of them to be "repurposed" - disassembled and reassembled into suitable Mars SSO tanker configurations, and a ready supply of working Raptor vacuum and surface optimized engines
4) The 9 meter diameter SS may not be most efficient Mars SSTO shape and size
5) energy costs for ISRU are "manageable" - that's a cop out, but whether nuclear or solar power, I don't care for this exercise - that's for some other hypothetical

Question: What is a more optimal baseline shape and size of a Mars-based tanker to deliver substantial quantities of O2 and CH4 to
a) Low Mars Orbit
b) High Mars Orbit (perhaps to refuel aerobraking SSs inbound from Earth for landing and return missions)
c) Trans Earth Injection (to deliver via slow-boat route, CH4 and O2 to Earth-Lunar L2 or other Near Earth Orbit)

My guess is that a larger diameter tanker makes sense, that raptors will have lower gravity losses (but I may be completely wrong about that) in Martian gravity, that raptors are perfectly fine engines, but a modified expansion bell tuned to martian atmosphere might be desirable.

The ultimate goal is to optimize volume delivered for least cost in fuel to launch and rendezvous.

Sorry if this seems frivolous - I'm just curious what the rocket models would say would be a "Mars-centric" tanker configuration.

Larger diameter would make sense because you'd probably not want such high cranes on Mars.

If we're optimizing for efficiency, we really should consider Phobos and Deimos tethers. They don't require exotic materials (although that helps) and they can give quite the delta-v boost for sending payloads up and away from Mars. Basically, starting at roughly low Mars orbit, you can get boosted to a Trans-Earth trajectory without using any propellant:

http://hopsblog-hop.blogspot.com/2015/12/lower-phobos-tether.html
http://hopsblog-hop.blogspot.com/2016/01/upper-phobos-tether.html
http://hopsblog-hop.blogspot.com/2016/01/deimos-tether.html

I imagine a huge, CO/O2 rocket launching from Mars. Carrying a payload of hundreds of tons of liquid water. The water is transported via Phobos lower then upper elevators to a lower then upper Deimos elevator and launched toward Earth. It does a grazing pass of the Earth's atmosphere to slow to a highly elliptical Earth orbit near escape velocity. Then loaded to a depot which splits the hydrogen from the oxygen, and subcools both of them.

(BTW, liquid water is a good form because you could engineer the system so it has zero chance of reaching the Earth's surface if there's a problem.)

[Scintillant]

This is pure speculation, and a request for some number crunching for a hypothetical O2+CH4 tanker from Mars surface.

Assumptions:
1) ISRU on Mars of O2 and CH4 are "economical" given local H2O and CO2 supplies;
2) shallow gravity well of Mars makes SSTO "easy" by comparison to Earth
3) regular arrival of SS vehicles from Earth at some point in the future will allow some number of them to be "repurposed" - disassembled and reassembled into suitable Mars SSO tanker configurations, and a ready supply of working Raptor vacuum and surface optimized engines
4) The 9 meter diameter SS may not be most efficient Mars SSTO shape and size
5) energy costs for ISRU are "manageable" - that's a cop out, but whether nuclear or solar power, I don't care for this exercise - that's for some other hypothetical

Question: What is a more optimal baseline shape and size of a Mars-based tanker to deliver substantial quantities of O2 and CH4 to
a) Low Mars Orbit
b) High Mars Orbit (perhaps to refuel aerobraking SSs inbound from Earth for landing and return missions)
c) Trans Earth Injection (to deliver via slow-boat route, CH4 and O2 to Earth-Lunar L2 or other Near Earth Orbit)

My guess is that a larger diameter tanker makes sense, that raptors will have lower gravity losses (but I may be completely wrong about that) in Martian gravity, that raptors are perfectly fine engines, but a modified expansion bell tuned to martian atmosphere might be desirable.

The ultimate goal is to optimize volume delivered for least cost in fuel to launch and rendezvous.

Sorry if this seems frivolous - I'm just curious what the rocket models would say would be a "Mars-centric" tanker configuration.

Larger diameter would make sense because you'd probably not want such high cranes on Mars.

If we're optimizing for efficiency, we really should consider Phobos and Deimos tethers. They don't require exotic materials (although that helps) and they can give quite the delta-v boost for sending payloads up and away from Mars. Basically, starting at roughly low Mars orbit, you can get boosted to a Trans-Earth trajectory without using any propellant:

http://hopsblog-hop.blogspot.com/2015/12/lower-phobos-tether.html
http://hopsblog-hop.blogspot.com/2016/01/upper-phobos-tether.html
http://hopsblog-hop.blogspot.com/2016/01/deimos-tether.html

I imagine a huge, CO/O2 rocket launching from Mars. Carrying a payload of hundreds of tons of liquid water. The water is transported via Phobos lower then upper elevators to a lower then upper Deimos elevator and launched toward Earth. It does a grazing pass of the Earth's atmosphere to slow to a highly elliptical Earth orbit near escape velocity. Then loaded to a depot which splits the hydrogen from the oxygen, and subcools both of them.

(BTW, liquid water is a good form because you could engineer the system so it has zero chance of reaching the Earth's surface if there's a problem.)

Why would anyone ever launch water from Mars to Earth? Earth has essentially unlimited water one Starship trip from LEO, and Mars needs water much more than Earth does. No matter how cheap Mars ISRU gets, I see literally no way for it to be a better method of water delivery than just launching it from Earth.

[Robotbeat]

Because it’d be cheaper.

Actually, let’s forget the whole tether thing. A Super Heavy Booster’s worth of Raptors could, because of the lower gravity and delta-v of Mars, send thousands of tons of water to a very high energy Earth orbit in a single stage launch, with reuse. To send water to the same orbit from Earth would require refueling of Starship. So effectively you’d be able to accomplish in one stage what would require three for Earth launch. And you’d require more than an order of magnitude less energy.

In a world where there’s a huge Mars city of a million people, with a pretty good spaceport and with capability to refurbish Starships (and probably assemble them like they do in Texas) and unlimited land to deploy ISRU, I think the Martians would be quite happy to export a bit of their vast water reserves to high Earth orbit.

The tethers just make it even more efficient. Potentially, they could do the whole thing without any propellant (except for fine-tuning). But I suspect it’s more efficient (since it requires less tether ratio) just use a small propulsive boost to low Mars orbit and use the tethers for going to the asteroid belt or Earth orbit.

[Robotbeat]

To explain how much more water Mars has than the Moon...
 The lunar poles have like 600 billion kg, ie 6e11kg. A single deposit on Mars has 14 teratonnes, or 1.4e16kg. A factor of 20,000 times more water in a single deposit: https://space.stackexchange.com/questions/25562/will-uncovering-the-ice-deposit-in-utopia-planitia-improve-the-climate-on-mars


Actually, let’s make it liquid hydrogen. That is more valuable than just water. Would be useful in that high orbit for sending nuclear thermal rocket versions of Starship to Mars on fast transits.

The oxygen stays on Mars to help terraforming...

[sebk]

I was wondering in another thread...

Would Starship have sufficient delta-v to take off from Mars, get refuelled in low Mars orbit, transfer out to the asteroid belt, pick up some cargo then burn back to Earth for EDL?

But then I decided to stop wondering and start calculating.

Using a delta-v chart from Reddit

https://external-preview.redd.it/47Z8OHKj-8BImmr3bDRgrnponXxglbBbLvz0dy_3SV8.png?auto=webp&s=8f4f3021734794c6b841311f248c98b575494568

I calculate a total of 17.25 km/s of delta-v to go from low Mars orbit to the surface of Vesta, then back to Earth with aerobraking and 200 m/s left for landing.


So no, it doesn't work.

Such maps are fun but are of limited usefulness because they make false assumption of additivity. Anyway the dV is too much for a single stage. You need to start fully fueled from HEMO and reduce the payload to about 25t.

More precise calculation:

Mars surface -> Vesta insertion - 5.7km/s
Transfer -> Vesta surface - 2.3km/s
Vesta -> Earth insertion - 4.5km/s

This assumes flat solar system. There's ~5° inclination diff between Mars and Vesta and then ~7° between Vesta and the Earth. This would add some more dV (the exact number would depend on the actual transfer window, on bad windows it would be significant). ​

So 2.5km/s on a very good and rare window, more on a more typical one.