What propulsion system should we use for Mars exploration?

[KerbonautInTraining]

On Tuesday, January 26, 2016 at 0:19 AM, shynung said:

If it ever goes into the cabin, we'd have another ASTP disaster on our hands. Definitely something not desirable to happen on a multi-month trip to Mars.

If your fuel leaks into the cabin you're dead no matter what type it is, seeing as it might be a bit more difficult to get back to earth without fuel.

Also the ASTP incident was caused by RCS fuel used for re-entry. Are you suggesting we use NERVA's for attitude control?

[/sarcasm]

[Kaos]

20 minutes ago, KerbonautInTraining said:

If your fuel leaks into the cabin you're dead no matter what type it is, seeing as it might be a bit more difficult to get back to earth without fuel.

Also the ASTP incident was caused by RCS fuel used for re-entry. Are you suggesting we use NERVA's for attitude control?

[/sarcasm]

On a free return trajectory you can get back to earth without fuel. That is why I would prefer this kind of trajectory.

[PB666]

2 hours ago, Matuchkin said:

I would go with VASIMR, because I actually know its capabilities.

Though, if anyone has a mega-laser-shark-zombie-kraken-spacecannon-warpdrive-tyrannosaurus rex-fluxcapacitor-jet-beam-shockwave-cruiser with them, I'll gladly consider it.

And your power supply? A mega toroidal dueteron-triton fusion reactor or a compact waterless fastbreeder reactor, or s superspammed 60% efficient superthin solar panel. Shrink VASMIR to 1/100th its current size, then you have enough power, just not enough thrust to go to mars in 39 days.

So from Ion drives we have a more efficient magnesium (or sulfer any number of similar atoms) that can basically run circles around the currently used (not comparing with available, because there are alot of ion drives available that are more efficient than what is being used) but n this case the magnesium drives don't destroy the electrode quite as quickly. Metals can be packed much more densly. In the image I have spammed to Xenon tanks, but limited to the size of the tank (inefficiency of tank scale ups for pressurized gases) but because of this I have permanent infrastructure for the lattice. The thing about ION drives is that you do not have to come up with a new power supply, just select the most efficient for the task versus negations from their added weight and heating.

The alternative is to shrink humans, if you could get their mass down to say 30 kilos, reduce their height and their sustenance requirments. IOW reduce the amount of mass spent on people, then you can reduce the amount of fuel, the amount of power spent on life support, while keeping power and energy constant.

I think what people are doing here is this

Someone said to mars in 39 days, but without saying how to get the humans back, so this has become the goal.
Its a false goal, simple as that Mars is one Hohmann transfer which is about 200 days. Then Earth and mars go out of phase, so you have to wait about 2 years to go back into phase again, then another 200 days to transfer back.
So if you are not talking about a plan that sustains a mission of 3 to 4 years, you are not talking serious. Taint no power supply capable of getting humans to mars in 39 days and back in 39days.

VASMIR is great I think, it could be used for trash pickup operations and shuttling supplies back and forth to the moon where you are basically bursting power for short periods. Even hauling asteroid mining stuff should be a good mission.

 

 

 

[shynung]

1 hour ago, KerbonautInTraining said:

If your fuel leaks into the cabin you're dead no matter what type it is, seeing as it might be a bit more difficult to get back to earth without fuel.

Also the ASTP incident was caused by RCS fuel used for re-entry. Are you suggesting we use NERVA's for attitude control?

[/sarcasm]

Argon or Xenon is barely harmful if it leaks into the cabin. Liquid hydrogen is a fire hazard, but not poisonous by itself. These gases, at most, excluding flammability, present little to no danger of intoxication, and a minor danger of suffocation, unlike NTO/50-50. Minor loss of deltaV is survivable in some situations.

And yes, ASTP Incident was due to RCS prop. No, I am merely suggesting that we do not use hypergolics as a main propellant. Other propulsion technologies use less-harmful propellants.

[KerbonautInTraining]

31 minutes ago, shynung said:

No, I am merely suggesting that we do not use hypergolics as a main propellant. Other propulsion technologies use less-harmful propellants.

Toxicity really isn't an issue. ASTP happened because an air vent was opened too early and let vented propellant into the cabin after the parachutes opened. 

I see no way for fumes from the main propellant tanks to enter the cabin while in space. Hypergols are really our only option (for burns other than TMI) unless we develop long term cryo storage but them we'd likely use NTR. (Although it would be easier to store liquid oxygen and some form of kerosene than LH2)

Edited January 28, 2016 by KerbonautInTraining

[Elthy]

Quote

SO lets say thrust is a tenth

Actualy the thrust of real Ion drives is about 10000 times lower than in KSP.

Do we have data on the power/wheight of highly optimized solar panels?

[Streetwind]

It's super hard to find data on that. Probably in part due to the fact that the power processing unit (PPU) required to create the right voltage and current for the engine and the rest of the spacecraft usually weighs as much as, if not more, than the panels themselves. But I've seen numbers as high as 300W / kg for 2014/2015 stuff (likely panels only).

[tater]

5 hours ago, Matuchkin said:

I would go with VASIMR, because I actually know its capabilities.

Though, if anyone has a mega-laser-shark-zombie-kraken-spacecannon-warpdrive-tyrannosaurus rex-fluxcapacitor-jet-beam-shockwave-cruiser with them, I'll gladly consider it.

VASIMR has no capabilities to know right now. It has flown as much as NERVA. If they do test it, it will be a smaller scale unit at lower power.

It has some promise, but claiming you "know the capabilities" is a little odd. We know the capabilities of chemical rockets quite well. Ions are well understood, too. 

[Sanic]

VASMIR and NERVA both haven't really be tested enough to get a full scope of their abilities.

[wumpus]

6 hours ago, KerbonautInTraining said:

Toxicity really isn't an issue. ASTP happened because an air vent was opened too early and let vented propellant into the cabin after the parachutes opened. 

I see no way for fumes from the main propellant tanks to enter the cabin while in space. Hypergols are really our only option (for burns other than TMI) unless we develop long term cryo storage but them we'd likely use NTR. (Although it would be easier to store liquid oxygen and some form of kerosene than LH2)

Two issues: first if you want hypergolics as a primary fuel then you are committing to *many* heavy launches carrying nothing but hydrazine and equally nasty stuff.  If I lived in Florida I wouldn't accept such launches (and not living there I would agree with the Floridians).

Other issue: Boiloff.  First, while I don't really expect zero-boiloff to work for LH, LOX really ought to work.  The James Webb space telescope will use zero-boiloff helium cooling, that ought to prove that it can be done for helium.  Oxygen should be a walk in the park next to helium.  Pretty much any non-ultra-toxic non-cryogenic would have even worse ISPs (shuttle SRBs had 240 second ISPs, I'd expect that hybrid (rubberish/NO2) would be even worse).  Solid motors would probably require hypergolics for correction burns, but hopefully not enough for an ecological catastrophe.

I'd favor hybrids left in place by ion propulsion.  LH/LOX might work.  And I suspect that if it worked, LH4C/LOX wouldn't be significantly more difficult.

[PB666]

6 hours ago, Elthy said:

Actualy the thrust of real Ion drives is about 10000 times lower than in KSP.

Do we have data on the power/wheight of highly optimized solar panels?

The HiPep Thruster produces 0.5N of thrust with a specific impulse of ~8100 ISP the kerbal dawn thruster produces 2000N of thrust at 4200. The thust to weight ratio is 8 for dawn and .1 for HiPep, with a ratio of 80:1.

The Dawn thruster has a foot print of about 0.2 * 0.2 * pi meters or about .12 meters squared. The HiPep is 31 x 46 cm or about .12 meter squared. The Dawn produces its thrust/sa over 0.5/2000 or 1/4000 the surface area of HiPep.

So now we have major axial crossection problems. you can fit 8 0.5 N thust per meter. Thrust density of 4N per meter. So how many meter is the standard crosssection

Kerbal - FF1  = 1.2 -----> 5N
Kerbal - FF2 = 4.8 -----> 20N
Apollo service module (1.95d) = 12M^2 -----> 48N

Orion (2.5d) = 20M^2 -----> 80N (Assume 10kg  per thruster that is 160 thrusters at 1600 kg).

Orion weight 10,500 kilos, this means maximum acceleration is 0.008 m/s   This is not to much of a problem because you also need area to dissipate power heat production, so lets say we could some. The weight of the thruster is not to bad, but wait, were is that power coming from?

Breaking it down into detail, assuming HiPep numbers . . . . 70kw power input per newton. BTW current Ion drives are 60 to 70 percent efficient, so VASMIR does not lower this, VASMIR only lowers its space required and its mass required.

Solar Panels
233 kg/N
233 M2/N

If you wanted 80N on your orion, you would need 18600 kg for solar panels, over about 2 hectacres of space. That 0.008 m/s now falls to about 0.003 m/s

So basically solar power at its current best is useless.

Nuclear Power
MMRTG produce 2000 watts of heat and 110 watts of power or 0.11kw. They weight about 45kg, they take up less space than a solar panel, but 1900 watts of power needs to be dissipated somewhere. You would need 636 of these per N of thrust, at a weight of 45 each adding 28600. There are thermovoltaic systems that are more efficient, but they don't last as long, you could get that down to 10000 kg per Ion N. But that orion produces 80 so thats 800,000 kg, Those 80 would produce 2000 x 636 x 80 watts of heat 101MW of heat, and thats not going to go away by passive radiation so . . . . nope.

Of course if we are more carefree, like the Russians we can use nuclear fission. A 6kw reactor weighs 1000kg and you would need 12000kg of them for each and 80 also around a million Kg. Again more efficient than RTG but you still have a megadensity of heat to dissipate. They have a relatively high failure rate, the space watchers believe that one of them actually exploded. If you have 1000 on board you cannot risk the failure of even 1. RTG are much safer.

So. . . . . . The big problem here is not the ION drives, its the energy production. Your solar panels take up about 0.7 hectacres (about an acre) for every millimeter/second of thrust, the RTGS will need more area for heat dissipation

As I said you have these big floppy launches laden with panels and decay-driven devices.

Battery Assist

Ok as seen above thruster weight and surface area is not the way major problem, the thrusters could be telescoped like panels. For making a transfer, you need a pulse at AtPG of between 200 and 160 efficiently, kicking, but driving a retrospiral orbit wastes. Since near earth orbits are on the order of an hour, and you are in that ~10 to 15 % percent of the time thrusters are active and 85 to 90% of the time they recharge (50 if in low earth orbit). The other problem is that beyond 170 degrees the earth is blocking solar panels, this means more kicks with solar panels. But once a escape trajectory is achieved, power can be ramped down to energize the transfer, it can take days. So what to power productions look like with batteries. So now assuming that the density of Lithium Ion batter is 2 a liter of battery is 2kg one can achieve a nice 650Wh/L or 325 Wh/kg of battery (higher a conservative estimate), If we are using that battery .15h then they can produce 2166 kw and we only need then 32 kg of battery per N of thruster 2560kg of battery per 80N thus we are much better off stocking up on batteries than panels. This takes now our solar panel to about 0.1 hectacre per mN of thrust, but we are going to spend many orbits kicking out our space craft. So  540 seconds at say 0.002 m/s gives us 1 m/s lol. and to break earths orbit we need to add about 7000 kicks, actuall much less because as eccentrecity grows so does time spend in the kick zone. Of Course at Mars, recharging batteries will take 3 times longer. UNfortunately if you are going to use alot of lithium Ion batteries you better have an integrated cooling system to prevent them from overheating.

Liquid fuel Oxygen assist

We can see now that adding a few dV close to earth just to get the ship away from the earths shadow is advantageous. One possibility is an ION drive LEO/HEO shuttle system, something driven by VASIMIR might pick up ships and carry them an earth radius out and then let them enjoy longer orbital periods and longer times burning, this means adding some battery weight and thruster weight. Of course VASIMR not really a prototype transport system, so for now a good kick of LfOx into say high earth orbit, then let it burn continually into escape trajectory and on to Mars.

[shynung]

11 hours ago, KerbonautInTraining said:

Hypergols are really our only option (for burns other than TMI) unless we develop long term cryo storage but them we'd likely use NTR. (Although it would be easier to store liquid oxygen and some form of kerosene than LH2)

I've got a better idea: liquid methane (CH₄). It's cryogenic, but only as much as liquid oxygen is cryogenic (CH₄ boiling point is 112 K, LOX is 90 K), as opposed to liquid hydrogen (boiling point 20 K). Specific impulse is slightly better than RP-1/kerosene (377 vs 357 seconds). It can be acquired from Martian atmospheric CO₂ and water via Sabatier reaction. And best of all, unlike LH2, liquid methane stays put in the tank; it won't boil off and disappear when you need it most.

Edited January 29, 2016 by shynung

[fredinno]

17 hours ago, Kaos said:

Yes, but then you need incredible many orbits and a vast amount of time. For that I would suggest low-energy transfer, it needs also a lot time, but much less than the necessary amount of orbits and can be combined with any propulsion system. Of course they are not well-suited for manned transfers, because they still need too much time, but for supplies they might help.

Time to transfer barely matters for supply/unmanned craft, as they aren't carrying the crew, which is much more vulnerable to radiation. Seriously, the only reason you'd want to choose high thrust over high efficiency is when you carry crew (which is why should always make the crewed ship as small as possible) or during the Martian style emergencies.

15 hours ago, PB666 said:

Yep I know, the kerbal ION drives are ____way____ over powered, but they are also way under ISP. It makes landing possible but it undervalues the potential dV.

However, I look at ION drives as way underpotentiated, based on latest research, even what is being used is about a half as powerful and a quarter as efficient. In fact Ion drive systems are the only deep space propulsion that actually works (proven unlike the RF resonance drive) that is as underpotentiated in terms of its current use. The Nerva, for all its worth lacks testing in a repeat use scenario, its basically been tested on a single burn, not a repetitive burn scenario after the engine is idled for 2 years.

SO lets say thrust is a tenth, and of course earth has a GM/r at minimal orbit 10 times that of kerbin, if you can break orbit in a quarter of a pass then you could break orbit in 25 passes at perigee. This lack of power has more than just inconvenience, looking at Mars entry one has to do a near perfect transfer out of earth, otherwise dV would be to high to reverse a flyby trajectory, this removes 39 day scenarios, unless alot of gas is spent on pre-SOI burning. So this basically removes ION drives from consideration from short trip scenarios, this is why I keep saying, for the technology that we currently have, a mars trip is 4 to 5 years. It gives very good reason for separating the transfer processes  Few people, lots of supplies, a small thin craft of the design I put forward. from the landing processes/reorbit processes.

You may note that I went with a single person capsule and a halfweight crew supply package, it would be about the size of a cross over SUV on the inside, which means only 1 crew. The power supplies dissipate heat at the square of the radius whereas power density increases by the cube. This also has connotations, you can not scale up in 3 dimensions, a power package can get longer, not wider, which means craft take on extremely long dimensions, or excessive weight additions for radiators. So it is not smart to send crews in one big ship but many smaller ships. This can be considered an exploit, because you may note that NASA stacks the TNGs and you would have to have huge areas of TNGs running in a wide spanning lattice to power the craft without generating so much local heat as to destroy the power unit. I have a system of piping crafted now to do this, but its an exploit to launch it, because it has impractical drag, The only way to practically use TNGs is to build the lattice in space, and each unit needs to have a shield to protect the crew. Thereare are ways to do this, you can radiate the TNGs away from the capsule. If you have to bridge the TNG over several 100 meters of axial crossection, then its better to use expandable panels.

The undeveloped technology is to embed the TNGs into the retractable radiator, the only problem there is keeping the cool until you get into space. So the basic problem is very simple, ION is great, wheres your power supply.

But the basic idea of using ION power works, but my point is that its not one ship, its multiple ships to complete a mars mission.

Not four to five years- you can use a out-of transfer window trajectory after a short thirty day Mars mission. Transit times to and fro can likely be reduced by using Ion drives to maybe five months, but more is probably stretching it.

Also, OP, isn't Solar Electric and VASMIR pretty much the same thing?

[fredinno]

13 hours ago, PB666 said:

And your power supply? A mega toroidal dueteron-triton fusion reactor or a compact waterless fastbreeder reactor, or s superspammed 60% efficient superthin solar panel. Shrink VASMIR to 1/100th its current size, then you have enough power, just not enough thrust to go to mars in 39 days.

So from Ion drives we have a more efficient magnesium (or sulfer any number of similar atoms) that can basically run circles around the currently used (not comparing with available, because there are alot of ion drives available that are more efficient than what is being used) but n this case the magnesium drives don't destroy the electrode quite as quickly. Metals can be packed much more densly. In the image I have spammed to Xenon tanks, but limited to the size of the tank (inefficiency of tank scale ups for pressurized gases) but because of this I have permanent infrastructure for the lattice. The thing about ION drives is that you do not have to come up with a new power supply, just select the most efficient for the task versus negations from their added weight and heating.

The alternative is to shrink humans, if you could get their mass down to say 30 kilos, reduce their height and their sustenance requirments. IOW reduce the amount of mass spent on people, then you can reduce the amount of fuel, the amount of power spent on life support, while keeping power and energy constant.

I think what people are doing here is this

Someone said to mars in 39 days, but without saying how to get the humans back, so this has become the goal.
Its a false goal, simple as that Mars is one Hohmann transfer which is about 200 days. Then Earth and mars go out of phase, so you have to wait about 2 years to go back into phase again, then another 200 days to transfer back.
So if you are not talking about a plan that sustains a mission of 3 to 4 years, you are not talking serious. Taint no power supply capable of getting humans to mars in 39 days and back in 39days.

VASMIR is great I think, it could be used for trash pickup operations and shuttling supplies back and forth to the moon where you are basically bursting power for short periods. Even hauling asteroid mining stuff should be a good mission.

 

 

 

You can launch your manned spacecraft slightly out of transfer window while packing somewhat more fuel, land, plant a flag on Mars, come back slightly out of transfer window, then return to Earth. It's possible to do a short fifty-day mission to Mars currently- NASA makes it the baseline for a "short duration" Mars Mission. Is it worth the effort of getting there in the first place? That's the real question....

[Kaos]

5 hours ago, fredinno said:

Time to transfer barely matters for supply/unmanned craft, as they aren't carrying the crew, which is much more vulnerable to radiation. Seriously, the only reason you'd want to choose high thrust over high efficiency is when you carry crew (which is why should always make the crewed ship as small as possible) or during the Martian style emergencies.

I would prefer the faster and more efficient low energy transfers over a vast amount of orbits. Trajectories which are faster and more efficient should always be preferred. Even if time would not matter at all, the better efficiency makes it worth.

[shynung]

3 hours ago, Kaos said:

I would prefer the faster and more efficient low energy transfers over a vast amount of orbits. Trajectories which are faster and more efficient should always be preferred. Even if time would not matter at all, the better efficiency makes it worth.

I fail to see how the former and the latter can coexist. Care to enlighten me?

[KerbonautInTraining]

33 minutes ago, shynung said:

I fail to see how the former and the latter can coexist. Care to enlighten me?

"I prefer X over (rather than) Y"

Edited January 29, 2016 by KerbonautInTraining

[Kaos]

25 minutes ago, shynung said:

I fail to see how the former and the latter can coexist. Care to enlighten me?

The highlighted things do not coexist, which is my point. There were two possibilities under discussion:

Low energy transfers -- utilizing gravity assistance on complicated flight path

Low thrust propulsion with a vast amount of orbits only using short burns in each orbit for not having to pay the factor of 1.5 for the Delta-v requirements

Low energy transfers are faster and more efficient than the vast amount of orbits to compensate low thrust. Hence, I would prefer the low energy transfers.

[shynung]

Guess this is what happens when English isn't your first tongue. 

I agree with your choice.

Edited January 29, 2016 by shynung

[tater]

To be fair, the total mission efficiency is a combination of the orbital/rocket mechanics issues (least dv, etc) combined with human factors and related engineering (for the crewed component). Longer, more efficient transfers (from a dv or propellant standpoint) require larger payloads (life support, etc). Obviously there is a point where that doesn't matter, but it's a concern, certainly.

[PB666]

19 hours ago, fredinno said:

19 hours ago, fredinno said:

Time to transfer barely matters for supply/unmanned craft, as they aren't carrying the crew, which is much more vulnerable to radiation. Seriously, the only reason you'd want to choose high thrust over high efficiency is when you carry crew (which is why should always make the crewed ship as small as possible) or during the Martian style emergencies.

Not four to five years- you can use a out-of transfer window trajectory after a short thirty day Mars mission. Transit times to and fro can likely be reduced by using Ion drives to maybe five months, but more is probably stretching it.

Also, OP, isn't Solar Electric and VASMIR pretty much the same thing?

You can launch your manned spacecraft slightly out of transfer window while packing somewhat more fuel, land, plant a flag on Mars, come back slightly out of transfer window, then return to Earth. It's possible to do a short fifty-day mission to Mars currently- NASA makes it the baseline for a "short duration" Mars Mission. Is it worth the effort of getting there in the first place? That's the real question....

39 days is not just slightly out of the transfer window. So 40/200 is about 1/5 th. Lets see transfer from kerbin to the mun in 3 days, try to find the most efficient transfer that gets you to the Mun 3 kerbin hours compare that with the 850 dV it takes you to get in an efficient transfer. (Dont for get, to be really efficient your munar circularlization needs to be as close to periapsis as possible. Now lets make it fun, instead of using a 1g*mass thruster, lets use a 0.0001 g* mass thruster, 0.001g * mass thruster, 0.01g * mass thruster.

I actually made a ship that did this, I cut the travel time to the mun by 80%, it used 3200 dV instead of 850, it was a tiny ship, only fuel, but in required 4 ION drives to accomplish the feat, because breaking kerbin orbit would have to be done starting way before the manuevering node. When I reached the Mun SOI, I had 16 minutes until reaching the other side and 29 minutes required to circularize, most of the fuel was actually spent slowing the craft down, it missed the periapsis circularization point by about a 2000 kilometers, required extensive negative radial burning to get a periapsis, which would not have saved any time, I would have been performing a Dawn ceres like manuever to gain orbit.

To minimize the time to land I simply took out all the horizontal velocity and thrusted toward the Mun, the negative surface velocity at the suicide burn point to land. The total time took 2h 44min. Of the 7000U of fuel and 10500dV of fuel that I started with I had 38U and around 100 dV left at the end.

You guys need to sit down and actually calculate out all the dV you need to accelerate, decelerate, recircularization manuevers, etc to get to Mars. When you launch using a transfer window the planet is basically chasing the space craft, if the two planet orbits are relatively close together the craft will make a nice loop around the planet and affords a very nice window to decelerate with ION drives, if you come at the SOI at 3 or 4 times that velocity your craft is going to be heading in a strait line most of which is distal from the planets gravitational energy and therefore useless for the reverse form of the oberth effect.

This can be corrected in the game had I started decelerating short of the SOI, which I have done many time when heading to MoHo (ion drives are really good idea for inner most planets). And moho is an example where cutting corners actually can save alot of time, given that you have to power so much into the change of orbit, change of inclination, making the periapsis smaller than moho's orbit generally affords a fast intercept. But Mars is not Moho, the ion drives require alot of kW of power, the panels are not near as efficient, and Mars is far from the sun and Moho is very close to kerbol. A radical game for mars is not rational, a conservative game is however, provided the energy problem of the previous post are dealt with.

 

[magnemoe]

On 28.1.2016 at 9:48 PM, tater said:

VASIMR has no capabilities to know right now. It has flown as much as NERVA. If they do test it, it will be a smaller scale unit at lower power.

It has some promise, but claiming you "know the capabilities" is a little odd. We know the capabilities of chemical rockets quite well. Ions are well understood, too. 

We know the capabilities of both VASMIR and NERVA, we do not have an version who we know work in space and not even started on man rating. 
Its pretty likely it will be problems with the two systems. on the long burn needed to mars.

[tater]

7 minutes ago, magnemoe said:

We know the capabilities of both VASMIR and NERVA, we do not have an version who we know work in space and not even started on man rating. 
Its pretty likely it will be problems with the two systems. on the long burn needed to mars.

We know for sure only what we know from testing. I think we are in agreement that neither is an off the shelf propulsion system right now, whereas chemical and ion propulsion are well understood in actual use in space.

[KerbonautInTraining]

So I just started reading "Voyage" and they're using chemical propulsion. The propellant for the mission had to be put in LEO over the course of something like 30 Saturn VB launches (each carrying 300t to orbit) not sure how accurate that is, but I doubt it's too far off the mark.

I think NERVA will be the propulsion of choice once we get the tanks figured out. Until then? No Mars for us.

[fredinno]

1 hour ago, magnemoe said:

We know the capabilities of both VASMIR and NERVA, we do not have an version who we know work in space and not even started on man rating. 
Its pretty likely it will be problems with the two systems. on the long burn needed to mars.

VASMIR may or may not end up being used for ARM. In that sense, VASMIR has better prospects than NERVA.

25 minutes ago, KerbonautInTraining said:

So I just started reading "Voyage" and they're using chemical propulsion. The propellant for the mission had to be put in LEO over the course of something like 30 Saturn VB launches (each carrying 300t to orbit) not sure how accurate that is, but I doubt it's too far off the mark.

I think NERVA will be the propulsion of choice once we get the tanks figured out. Until then? No Mars for us.

In theory, we can use a JWST-derived Sun shield to cool the H2 pretty soon. The money to get there is another question entirely.