SpaceX: Mars Colonial Transporter "MCT" -- Speculation (not Raptor)

[tinker]

Folks:

Again, the image I used is merely a placeholder. What you see is a flow chart of operations. This is the starting point of MCT design. Everything else is secondary solution to solve the stages of this mission. In other words, no refueling anywhere, no stopping in either orbit, a 'roll on, roll off' ferry from Earth surface to Mars surface and back. Period, Finite. That's all she wrote!

Start there and you'll be on the right track. Remember what Elon says about first principles. That diagram was a first principle look at the simplest way to bring people & goods to Mars & back that's possible! Elon was acknowledging that from a first principles point of view, that's how he wants to colonize Mars.

Also, we now know methane will be SpaceX's fuel of choice for their next gen LV!

So? Get with it! If Elon says it's close, how can we make this scenario work? I left secondary aspects vague on purpose because there are multiple solutions to those parts of the overall mission (none of them include stopping, orbiting or refueling).

I've had this idea for over two years now so getting as much confirmation from Elon as I did is a pretty big thrill. 

tinker

[tinker]

Please help me to get excited here; it is revealed that MCT means something goes to Mars .. and comes back .. and .. that's it?

Actually, it was just a guess (a 'hypothesis' as someone tweeted) that only saw the light of day when Elon commented on my HyperLoop guess. So I though I'd toss some other ideas at him. The 'MCT' flowchart just stuck is all.

So, 'reveal' would be a bit of a stretch here!

tinker

[Joel]

Calm down, tinker. You draw very far-reaching conclusions from a few very vague sentences from Musk.

[Occupymars]

Folks:
In other words, no refueling anywhere, no stopping in either orbit, a 'roll on, roll off' ferry from Earth surface to Mars surface and back. Period, Finite. That's all she wrote!

But that must be wrong because MCT has a number attached to it tinker and that number is 500,000 dollar's per ticket which mean's MCT need's to transport a lot of people per trip to meet that number. Likely one hundred people per trip! and that can't be done without in space rendezvouses i.e Habitation Module.

[Jim]

Also, we now know methane will be SpaceX's fuel of choice for their next gen LV!

That has be known for quite some time.

[RocketmanUS]

Folks:

Again, the image I used is merely a placeholder. What you see is a flow chart of operations. This is the starting point of MCT design. Everything else is secondary solution to solve the stages of this mission. In other words, no refueling anywhere, no stopping in either orbit, a 'roll on, roll off' ferry from Earth surface to Mars surface and back. Period, Finite. That's all she wrote!

Start there and you'll be on the right track. Remember what Elon says about first principles. That diagram was a first principle look at the simplest way to bring people & goods to Mars & back that's possible! Elon was acknowledging that from a first principles point of view, that's how he wants to colonize Mars.

Also, we now know methane will be SpaceX's fuel of choice for their next gen LV!

So? Get with it! If Elon says it's close, how can we make this scenario work? I left secondary aspects vague on purpose because there are multiple solutions to those parts of the overall mission (none of them include stopping, orbiting or refueling).

I've had this idea for over two years now so getting as much confirmation from Elon as I did is a pretty big thrill. 

tinker

What would be the difference between the MCT returning to LEO ( aero capture with active heat shield cooling ) instead of Earth surface return, ( propellant need between the two )?

[tinker]

Also, we now know methane will be SpaceX's fuel of choice for their next gen LV!

That has be known for quite some time.

Jim:

It's the first time Elon used the word 'will'.

tinker

[tinker]

Folks:

OK, I'll let you mull this one over. I'm off to get you all some more hard data!

tinker

[Jim]

It's the first time Elon used the word 'will'.

Grasping for straws.

[meekGee]

Let's not make TOO much of it.

All Elon said was "but Mars approach is pretty close to what I have in mind", in response to a diagram that's fairly generic.

It can easily be "pretty close to what I have in mind", except part of the package stays in Mars (or Earth) orbit.

Or "pretty close to what I have in mind", except the second stage returns to Earth immediately and only the BEO portion goes to Mars and returns.

What can probably be inferred with confidence, and which we already guessed, is that there's no in-orbit assembly.  There's likely to be in-orbit refueling, and it doesn't show in the diagram.  If there is - where does it get done?

Keep watching the twitter feed.  BTW - what's Gen3?

[Avron]

Calm down, tinker. You draw very far-reaching conclusions from a few very vague sentences from Musk.

I still  think this is gold..  its a starting point.. much more to come..

http://twitpic.com/d1rwr6


congrats

[MikeAtkinson]

LEO to Mars surface is about 6 km/s assuming aero-braking and terminal propulsive descent. That means about 80% of IMLEO is fuel for methane/LOX.

Given the large tanks, insulation, heat shield, etc. payload is likely to be 10% or less.

It looks optimum for each mission to be topped up with 4 tanker flights. So a HLV of 100 tonnes would be able to land 40-50 tonnes of payload on Mars. Some of that would be used for the ship, and supplies for the return journey and perhaps 20 tonnes could be left on Mars.

Problems with such an architecture:
1. lots of HLV flights in a short period of time.
2. multiple docking/berthing at the ship. Multiple fuel transfers.
3. the crew spend weeks in LEO while the ship is fueled.
4. to avoid excessive boil-off in LEO some form of insulation or cryocooling  may be needed, probably not needed for transit as the heat loads are less.
5. some methane/lox needs to be stored for landing - or lower Isp storable propellants + extra engines used.
6. having the ship above the stage, leaves the payload many stories off the ground at Mars.
7. the IMLEO is about twice what an optimised (for IMLEO) architecture would be - if IMLEO is the major driver of cost, this means the architecture is more expensive.
8. the engines need to work 3 times separated by many months, the last time after exposed on dusty Mars for a long time.
9. for the return trip several hundred tonnes of propellant is required per ship. This is much more than other architectures, and drives the need for a large ISRU plant with lots of power.
10. the bootstrap problem, lots of infrastructure needed on Mars before you can start sending people - costly robotics.
11. if the main engine is optimised for vacuum, then it cannot easily be used for landing back on Earth - perhaps an extending nozzle or similar can be used.
12. a main engine suitable for landing on Earth would need to be deeply throttled to land on Mars - perhaps use 3 engines for Earth, 1 of which for Mars, or separate Mars landing engines.
EDIT: 13. it is difficult to use solar panels for either outward or return, even nuclear needs radiators [as Jim points out] - maybe SpaceX have a solution.
EDIT: 14. the whole ship has to be designed for the worst parts of the mission [as Jim points out], leading to an inefficient ship design.

Fuel depots reduce the severity of problems 1-4.

Using horizontal landing on Mars reduces the severity of 6, at the expense of another set of engines.

One way cargo missions reduce the severity of 7-10.

Using a delayed return architecture, (crews do not go for life, but cannot expect to return after a short <18 month stay on the surface) reduces the severity of 9 and 10.

Most mission architectures assume that IMLEO is the major driver of cost and so try to reduce it.

[Garrett]

Folks:
OK, I'll let you mull this one over. I'm off to get you all some more hard data!
tinker

It's a nice, simple architecture. It follows what Musk said in previous interviews (along the lines of: the whole thing should go and land on the surface of Mars).

Did you just use the FH for sketching purposes? A BFR will be needed, probably more powerful than SLS (> 150 mT maybe?).

[PlanetStorm]

The heart of the matter is that the second stage is also the Earth departure stage, and also the Mars ascend stage.

What constitutes "pretty close" is anyone's guess though.

Fair enough, that isn't what I would have drawn, I admit. As you point out, it will be interesting to see just what "pretty close" turns out to mean in this respect though.
 

[tinker]

Calm down, tinker. You draw very far-reaching conclusions from a few very vague sentences from Musk.

I still  think this is gold..  its a starting point.. much more to come..

http://twitpic.com/d1rwr6


congrats

Avron:

I did an update. Does this make clearer what I have in mind here?

http://twitpic.com/d2vj2j

tinker

[tinker]

Folks:
OK, I'll let you mull this one over. I'm off to get you all some more hard data!
tinker

It's a nice, simple architecture. It follows what Musk said in previous interviews (along the lines of: the whole thing should go and land on the surface of Mars).

Did you just use the FH for sketching purposes? A BFR will be needed, probably more powerful than SLS (> 150 mT maybe?).

Garret:

The number of boosters (or the fuel they use) is immaterial to mission success. 'Form follows function', as every architect knows (and I'm more architect than engineer). The booster's function is it to get the MCT to an altitude and velocity that matches the delta v needed to do the same job for it's return from Mars surface to Earth as a single stage.

Folks:

Anyone up to working that one out? I think you'll be surprised at the answer! Also, it is a solid number for all of you to work with. No opinion or speculations on my part. If the number fits... wear it!

tinker

[meekGee]

Folks:
OK, I'll let you mull this one over. I'm off to get you all some more hard data!
tinker

It's a nice, simple architecture. It follows what Musk said in previous interviews (along the lines of: the whole thing should go and land on the surface of Mars).

Did you just use the FH for sketching purposes? A BFR will be needed, probably more powerful than SLS (> 150 mT maybe?).

Garret:

The number of boosters (or the fuel they use) is immaterial to mission success. 'Form follows function', as every architect knows (and I'm more architect than engineer). The booster's function is it to get the MCT to an altitude and velocity that matches the delta v needed to do the same job for it's return from Mars surface to Earth as a single stage.

Folks:

Anyone up to working that one out? I think you'll be surprised at the answer! Also, it is a solid number for all of you to work with. No opinion or speculations on my part. If the number fits... wear it!

tinker

Tinker - the "equivalent delta-V" concept is clear, but it assumes equal payloads going in and out, which is not likely.  Vehicles going out will be carrying habitats, consumables, surface equipment.  Vehicles coming back will be carry people, and fewer of them then the ones going out.

Also, propulsive landing will require different dVs.

The assumption, IMO, is only that you're returning the vehicles to reduce cost.


Also:  "Anyone up to working that one out" - does that mean that you already have and are asking us to do the same calc?

[ClaytonBirchenough]

Folks:
In other words, no refueling anywhere, no stopping in either orbit, a 'roll on, roll off' ferry from Earth surface to Mars surface and back. Period, Finite. That's all she wrote!

But that must be wrong because MCT has a number attached to it tinker and that number is 500,000 dollar's per ticket which mean's MCT need's to transport a lot of people per trip to meet that number. Likely one hundred people per trip! and that can't be done without in space rendezvouses i.e Habitation Module.

No no no. $500,000 was not attached to MCT.

Read this and listen to the recording. MCT is not linked with $500,000.

http://www.bbc.co.uk/news/health-17439490

[tinker]

Folks:
OK, I'll let you mull this one over. I'm off to get you all some more hard data!
tinker

It's a nice, simple architecture. It follows what Musk said in previous interviews (along the lines of: the whole thing should go and land on the surface of Mars).

Did you just use the FH for sketching purposes? A BFR will be needed, probably more powerful than SLS (> 150 mT maybe?).

Garret:

The number of boosters (or the fuel they use) is immaterial to mission success. 'Form follows function', as every architect knows (and I'm more architect than engineer). The booster's function is it to get the MCT to an altitude and velocity that matches the delta v needed to do the same job for it's return from Mars surface to Earth as a single stage.

Folks:

Anyone up to working that one out? I think you'll be surprised at the answer! Also, it is a solid number for all of you to work with. No opinion or speculations on my part. If the number fits... wear it!

tinker

Tinker - the "equivalent delta-V" concept is clear, but it assumes equal payloads going in and out, which is not likely.  Vehicles going out will be carrying habitats, consumables, surface equipment.  Vehicles coming back will be carry people, and fewer of them then the ones going out.

Good! You can carry more payload to Mars. How does that effect the numbers? Next...

Also, propulsive landing will require different dVs.

...a minor detail to flight software and throttlable motors. Next...

The assumption, IMO, is only that you're returning the vehicles to reduce cost.

No, returning them to reuse them... many times. Next...

Also:  "Anyone up to working that one out" - does that mean that you already have and are asking us to do the same calc?

Goodness! A simple variation on the theme of F=MA? Yes, I worked it out... in my head (and I don't even like math).

Folks:

One more counter-intuitive hint on how I found out that this mission profile was not only doable, but desirable: Start at Mars!

tinker

[Jim]

One more counter-intuitive hint on how I found out that this mission profile was not only doable, but desirable: Start at Mars!

  The issue is that it is not intuitive, even though the delta V is the same going either direction. The allocation of delta V between aerobraking and propulsive landing on Mars is not the same as Earth plus throwing in Mars ascent and final LEO injection delta V's.  Not to mention aerodynamic and structural  differences for the aerobraking at the two planets.  There is no optimization. The vehicle is going to have to be designed to handle the most stressing environment or propulsive requirement at either planet with the inherent mass.  If the aero thermo heat loads are worse for earth than Mars, then the TPS will be designed for that.  The propellant load will have to be sized for either LEO injection, TMI and Mars landing or Mars ascent, TEI, and earth landing.  The optimal aero design for entry and launch is not conducive for mounting and deploying solar arrays and radiators for cruise or landed operation.  Nuclear power negates the need for solar arrays but not radiators.