NASA adopts the best of Zubrin's ideas, eventually

[A_M_Swallow]

True but we would still want to make trips to the Moon whilst the MTV was at Mars.

You could keep a spare at L1/L2. Call that a gateway station if you will, but my point was that you don't need to design a separate station or even build a spare if you can't afford it. Similarly, a lander could be its own makeshift gateway station.

Re-usable MTV? With storables, it takes the crew to Mars for either propulsive braking into High Mars orbit (DEIMOS!!) or aerocapture. Then it waits for the crew to return and head back to Earth for propulsive braking into L-2. To do all that would take a heck of a lot of propellant, but at least between TMI windows there would be lots of time to fill it back up with a 'Propellant Railroad' from Earth. Maybe its propulsion/propellant module could be detachable; dock a new one to it between each Mars mission or when its design life is expired, whichever comes first. Engines? I suggest a quartet of AJ-110 derived motors.

The station keeping thrusters and fuel tanks on LEO and EML spacestations probably do not need to be as big as the main engine on a MTV.

However commonality between the cabins, docking systems and life support sounds like a good idea.

How big would an empty tank/engine module for a mission like this be if you had to launch it on an existing EELV? Or would it have to be launched in two separate engine & tank packages?

Since the spacecraft is in a vacuum it does not need to be thin.  Attaching drop tanks to the side provide a simple way of both fuelling the vehicle and reducing the return mass.

[Kaputnik]

Mattblack- thanks for the reply. I think we are coming at this from quite different POV on what is an achievable landed mass.
Given that current state of the art is about 1t landed, I tend to envisage anything up to 10t as a reasonably scaling up of heritage technology, with 20t as a likely upper limit before fundamentally different approaches must be taken.
A bare-bones ISRU ascent vehicle could, IMHO, be squeezed into such a mass (assuming multiple landers to fly the crew, the ISRU plant, etc). A pre-fuelled ascent vehicle clearly could not.

I should also add that the multiple small landers approach has various benefits. All of the more advanced EDLS technologies are likely to lead to a reduced landed mass fraction; therefore the IMLEO of the mission is likely to be higher. That's not to mention the costs and engineering challenges inherent in such development.

[mmeijeri]

I say make a separate, dedicated Cargo Lander by deleting the weight of the 4 ton composite crew cabin. Before Earth Departure, load it with fuel from a Prop. Depot or Propellant Delivery Modules until it contains enough hypergolics to descend to the Martian Surface.

Why before TMI (even from L1/L2 rather than LEO) instead of in high Mars orbit? You could then send the propellant by SEP and maybe be more mass-efficient than all LOX/LH2.

[MATTBLAK]

Yes! Good point.

[Robotbeat]

I say make a separate, dedicated Cargo Lander by deleting the weight of the 4 ton composite crew cabin. Before Earth Departure, load it with fuel from a Prop. Depot or Propellant Delivery Modules until it contains enough hypergolics to descend to the Martian Surface.

Why before TMI (even from L1/L2 rather than LEO) instead of in high Mars orbit? You could then send the propellant by SEP and maybe be more mass-efficient than all LOX/LH2.

Even better is to send the full, fueled lander to low Mars orbit (or high Mars orbit, whichever is where you plan on the crew getting on board) via SEP tug.

[mmeijeri]

Even better is to send the full, fueled lander to low Mars orbit (or high Mars orbit, whichever is where you plan on the crew getting on board) via SEP tug.

Maybe if you have a SEP tug that can transport a full lander, but an empty lander has lower technology requirements. The reason I was looking at high Mars orbit is because I imagined that's where the crew would leave the MTV and enter the lander. Of course that doesn't preclude additional refueling of the lander in low Mars orbit.

[MATTBLAK]

Maybe Deimos could be the staging area for arriving Earth  Return Vehicles and Ascent vehicles, sent there by SEP tugs first.

[DLR]

What's the advantage of Deimos orbit over any other Mars orbit?

[MATTBLAK]

What's the advantage of Deimos orbit over any other Mars orbit?

Low delta-vee (propellant) requirements to reach it - as you approach Mars, you would not yet be close enough to be greatly accelerated by the Martian gravity, requiring lots of fuel to thrust into Mars orbit. Also, Deimos is in direct line of sight communications with Earth most of the time and each hemisphere of Mars for a goodly portion of each Sol (Martian day). Deimos would be a good place to Tele-robotically operate Rovers, landers and sample return probes.

[Hop_David]

What's the advantage of Deimos orbit over any other Mars orbit?

Low delta-vee (propellant) requirements to reach it - as you approach Mars, you would not yet be close enough to be greatly accelerated by the Martian gravity, requiring lots of fuel to thrust into Mars orbit or heavily aerocapture. Also, Deimos is in direct line of sight communications with Earth most of the time and each hemisphere of Mars for a goodly portion of each Sol (Martian day). Deimos would be a good place to Tele-robotically operate Rovers, landers and sample return probes.

.7 km suffices for a Mars capture. If Mars periapsis is in the upper atmosphere, aerobraking will shed velocity each orbit, lowering apoapsis.

So with the use of aerobraking, a low Mars orbit can be achieved with .7 km/s. A Mars ascent vehicle could rendezvous with something in LMO much easier than a Deimos orbit.

Not including gravity loss, it'd take about 5.7 km/s for a MAV to rendezvous with Deimos. It'd take about 3.7 km/s for an MAV to rendezvous with something in LMO.

[MATTBLAK]

Sorry - my bad: I was supposed to be comparing Deimos with Phobos delta-v in terms of ease of reach. Aerobraking will always use less propellant for capture than propulsive! (previous post edited).

[MATTBLAK]

Hah! In the various posts I've been doing around Mars-based threads around here, I've often mentioned a more basic manned Mars mission with RTG & Stirling based power plants, smaller crews and mixed storable/LOX-methane propulsion - only to find somebody already did a very fine paper on the subject. The only major difference is; when this 'Austere Mars Mission' paper was authored, Ares V was still in the picture. I've been advocating uprated Delta IV-H, Atlas V & Falcon Heavy mixed launch fleets for the mission, with SLS as a 'nice-to-have-if-funding-is-there' backup option.

http://trs-new.jpl.nasa.gov/dspace/bitstream/2014/41431/1/09-3642.pdf

[Hop_David]

What's cool about it? I'm surprised I have to point it out to you: the ability to - theoretically - take a crew to Mars in about 40 days.

40 day VASIMR trip relies on an implausibly high specific power.

[MATTBLAK]

You are quite right. Er... But I'm a bit puzzled: every time I have mentioned VASIMR in this thread, a couple people seem to think I was advocating and defending it strongly! You can see from the quoted post that I bolded & italicized theoretically. And I've told Quantum more than once that I doubted a big enough nuclear reactor to power an effective VASIMR engine would ever be approved. On that basis, I have dismissed it as a contender, even in the 'nice to have' ranks.

[QuantumG]

Why can't some people spell VASIMR? I've noticed various misspellings everywhere...

[MATTBLAK]

You're quite right! I keep thinking of how I've heard it pronounced out loud so many times: "VAS-I-MEER".

I'll try not to keep subconciously typing it that way.

EDIT: There! I've gone back through this thread and changed the spelling of the word each time I used it. But I don't have time to go and change every time I typed it on this whole website: Even I'm not that pedantic!

[Patchouli]

What's cool about it? I'm surprised I have to point it out to you: the ability to - theoretically - take a crew to Mars in about 40 days.

40 day VASIMR trip relies on an implausibly high specific power.

Even with more reasonable  6 to 12MW power which should be achievable even with solar it would revolutionize the mission design.
http://www.adastrarocket.com/Andrew-SPESIF-2011.pdf
6 MW gets the round trip down to 13 months which is within the limits of what is known as far as mission duration goes.
Mass optimized Ultraflex arrays can make up to 500W per kg thin film can do even better.
http://www.sbir.gov/sbirsearch/detail/16067
Just ultraflex would put you way over the power to mass needed as the 6 MW array even accounting for Mars distance would only be a measly 33 metric tons.
Even if I double this to 66 tons to account for extra support structure power conditioning and redundancy the mass numbers still look good compared to a conventional mission.

[QuantumG]

6 MW gets the round trip down to 13 months which is within the limits of what is known as far as mission duration goes.

Do you have any idea what the largest space nuclear power source ever flown is?

[Patchouli]

6 MW gets the round trip down to 13 months which is within the limits of what is known as far as mission duration goes.

Do you have any idea what the largest space nuclear power source ever flown is?

My masses were for solar not nuclear.
BTW I know the largest space reactor flown TOPAZ 2 was only 6 KW but it used  thermal ionic conversion which was about 5.2% efficient.
A Rankine cycle turbine can easily achieve 40+% efficiency.

So if you swapped in a turbine but kept the reactor the same size you could boost the power output by a factor of up to eight bringing the power output to 48.46 KW.

Even here the reactor mass should be 143,184Kg.
Solar totally wins here but the mass numbers are good enough for Zurbin's ISRU fuel plant which only needs 80 to 100 KW as only two 1061Kg reactors would be needed this number includes the cooling system.

it should be noted they didn't really push for power to weight with TOPAZ instead reliability and simplicity were the primary goals.
A molten salt reactor would get much better numbers.

[QuantumG]

6 MW gets the round trip down to 13 months which is within the limits of what is known as far as mission duration goes.

Do you have any idea what the largest space nuclear power source ever flown is?

My masses were for solar not nuclear.

Fine.. do you have any idea what the biggest solar power source ever flown is? (and the power to mass of that system?)

If you believe in solar powered plasma rockets, you might as well believe in solar power satellites too. Zubrin calls it "an alternate universe".