39 days to Mars possible now with nuclear-powered VASIMR.

[PB666]

There is no indefinite travel, humans expire in the microgravity of space and the ship needs Argon, less so than ion drives.

The hope with VASIMR is that once they get the power they want then they can reduce the waste heat. I thonk this is were they are going. And as point of argument NASA has clearly stated that they do not have a meaningful interstellar technology, and it is clear That LFOx is not it. So they are willing to Push alternatives for the same reason the Germans pushed traditional propellants.

The critical point is to place an improved ION drive in circumstances of high payload and I agree.

Consider the problem to be solved viable interstellar is essentially 1g at 1year and the reverse. We cannot even get close to this. And I think all would agree that VASiMR is not it. But even 1/10th this would require an advanced nuclear device. And anything beyond Mars will need nuclear.

So an orbit that has significant radial velocity reaching mars with a viable payload is a major step forward in terms of efficiency per mass. If this were not tbe case we would not be arguing about it. NASA is not alone now. all the major space agencies have landed something on the moon and reached or landed on mars, The brits landed beagle but its panels failed to open. So the context makes the problem hard.

There are context specific issues that have to be defined.

1. The dV for M intercept in 39 days, this I don't think is the major problem......strictly in terms of hums on board.

2. Decellerating on martian approach, add a couple of days.

3. Orbital insertion, this will be a problem for Vasmir because the humans have to be on board, decels at peri will have to be kicks which means that time is wasted, Not smart to do Aerobraking with panels or nuclear, and the drive could be damaged.

4. LFOx carried to decel and land, which means a lander weight, which means payload doubles or triples.

So lets say you are at 50 days, you left mars, at 39 days earth was slightly ahead of Mars, now its several degress ahead, there will be know 39 day return. The ship will have to reach the Vasmir and that ship will have to kick its to a higher period. And then it have to produce double or triple the radial velocity, because simply reducing orbital velocity will slow the ship relative to earth it will not regain higher speed until close to perigee.

5. So the ship now has to maintain its orbital speed by applying alot of negative radil velocity, it will need to oeri at almost venus-mercury orbit and then intercept earth coming in, The gain is the lander can be jettisonned, but Now slowing to earth is a problem.

6. One solution is given the energy is to stop at L2 and transfer the crew to a pod for transfer back home, a second is once arriving past L2 decel into a elliptical orbit and kick back to ISS and dock, refuel the ship and recrew it, then exchange Martian crew for A soyuz pod.

7. Since the lander is not time dependent, it can be sent on a regular Hohman a year before the crewed mission and parked in a martian orbit. You could Even land a return lander on Mars if you can control the landing site lication. So niether the lander or the return launch vehicle need to transit in 39days.

8. So that leaves the essential problems

Essential problems

1. You have a free docking port, you can LFOx into a mars crossing orbit, we know we can get 100 tons x whatever of feul from the russians, this is not the problem, the problem is the time and thrust required fir an ION drive to stop at Martian Insolance. It maybe the case that only Nuclear can do this. Panels and girders and/or radiators would have to lose alot of mass per watt.

2. That venus crossing orbit is loaded with problems, there is alot of sun, but you dont need sun at least not until close to earth, you could have a shield ship that intercepts interior to venus but thats really difficult. You could reposition the panels. the dV required would mean weeks of peak acceleration off of Mars, assuming a load of argon was supplied with lander coupling. you could partially fold one panel to reduce absorption and store the others but this also adds weight.

3. The essential Mars return vessel landing is not solved. We could sky crane humans down but not the return ship, too heavy. alternative is to use indvidual command chairs in which you have a controlled ascent to an apogee that then circularizes, three ships for three nauts, the weight of each launch vehicle is cut. lol. Samples would have to be curtailed. you could land a ship and the nauts refule from separte fuel lands. You could have dead minimu weight lauch vehicle in which no food water, and minimal air to reach the vasmir. you could intercept the ship at an eccentric opa used an EM tether to quckly grab it and then pull it to a minimum orbit which vasmir intercepts.

So right now as it stands a one year Mars mission is only viable as a suicide mission. The landing mission alone begs fir two ships and 2 or more LEO fuelers.

The return ship begs for at least 1 more ship and at least 1/2 a ship for argon or a shield ship with nuclear.

So lets say we are arguing about the best of several bad alternatives.

[AngelLestat]

To achieve the "39 days to Mars" trajectory that started this whole thing, you need jet powers on the order of Gigawatts. Period. Unless your payload weights grams, of course, but we are discussing manned flights here.

I dint made the calculation, if you did or have a source to support your claim please post it.

Also I am not talking about 39 days to mars, just a vehicle that can do the trip in half of the time and can be reusable to any trip in our solar system, that will reduce the cost of all future mission.

A shame you need electricity to run electric motors, produced at a peak 50% efficiency. A shame, too, that all your ship will try to stay at the radiator operating temperature. How well do you fare at 1600ºK? I mean, I'm from Spain and we have hot summers, but even I would be a tad too warm.

HAHAHAHAHA, so lets make the calculation, imagine you have 50 or 100 mw for the reactor, you need to cool it, you have an idea how much flow you get for X power?

One example: for a 0.5 mw pump, you get 1m3 of water by second at 4 bar.

You are looking for energy loses in the wrong places.

I don't get that. Are you stating my point, that the weight of the radiator system dominates the whole thing? For a given thrust, you get a given jet power (the energy in your exhaust). And if you pick an engine, then you have a given efficiency in heat-to-thrust conversion, so you also get a set waste heat to get rid off. For nuclear-electric drives, that means at least more than half your total wattage output is waste heat.

That heat to electrical conversion is the carnot efficiency+ 5% loses in the electrical generator, and yes, you need to radiate the waste heat (that is why we have radiators, and they are responsable of the 80 to 90% of the weight from the whole system without counting payload.

So not sure what is your point more than repeat all the things that we already said.

You can get some parts of your ship to stay under the temperature of your radiator. Just like your fridge keeps part of your house slightly colder than the rest, using a boopload of energy, a convection radiator, and a complex fluid compression/expansion system. You kind of need to do it if touching the radiator would melt the crew's hands... even if they were robots.

No, you are mixing techs, here you need to move matter that carry heat (coolorant), from the core to the radiators, so you just move them with a pump (kinetic energy).

But compression and expansion, that is a heat pump!, which is different than a kinetic pump.

In that case you are moving heat, not matter or fluids.

Heat pumps are usufull when you need to cool stuffs as super conductors, when you need to reach 60k or 3K, a radiator to the space with just little diference between source and destiny, it will have a terrible efficiency. So you move forcing that heat with a heat pump, this consume power (much more than a simple electrical pump, but it does not matter because they are two very different things.)

I'm using Lithium because it is one the best at moving amazing quantities of heat from point A to B with the minimum mass. But you touch a very good point here, the "secondary" radiators. I know they would not bother the high-temperature radiators... they would be too big to notice them, even if they only reject a fraction of the heat. It's funny how people forget that "secondary" system, which is likely to weight more than the fancy high-temperature radiators that handle the nuclear core. I mean, anything with a magnetic nozzle (and VASIMIR and every other high power, high Isp engine has one) means superconductors working at spitting distance from the main reaction chamber. In VASIMIR's case, about 40% of the the electrical power going to the engine gets wasted as low level heat. That's after you have had >50% losses in thermal-to-electric conversion, so you are dealing with heat on sensitive electronics and high-power magnets that needs to be rejecter at a MUCH lower temperature. Hence, your "secondary" radiators are likely your main radiator wings.

Lithium has low heat capacity, I read in some place that ferrofluids or other different kind of metal liquids are more promising. But well does not matter.

About the radiator and heat pump for the superconductors and engine, if they work with superconductors then not sure how they have 40% of energy loses... When most of all kind of electrical work are very efficient.

NASA is "interested", yeah. Shorta. That is tricky, they have actually built themselves the ion engines they wanted, Chang-Diaz just got a few technology development grants to work on the side on his own company. But I'll grant that. In any case, NASA is interested in a 200kW VASIMIR, to get an awesome payload fraction in a very expensive future probe, or do a crazy mission with incredible dV requirements (like putting a telescope at the sun's gravity lensing point). Certainly no NASA engineer believes they will ever use a VASIMIR to send a crew to Mars in 39 days, I hope.

They plan to use it as first application, to keep the space station in orbit.

So if that works fine, then they will use it for any other application they want. a mars mission is not discarded, more taking into account that this was their main excuse to not go to mars in all these years..

Meaning 65% of the energy is low-level heat deposited in your solar panels. Are you going to keep them at 1600ºK with liquid lithium? Because those would be some amazing photodiodes. Also, show me the operational system that gets 45%, those are lab results on very particular conditions, at best.

First the liquid lithium is your idea, nobody mentioned that before.. is just come from your head.

About solar panels, all new solar panels that goes to space has 45% efficiency.

http://sunmetrix.com/wp-content/uploads/2014/09/NREL_efficiency_chart.jpg

Also saying that I need to keep them at 1600k shows that you dont have much idea what are you talking about.

One thing is a heat engine which needs to move that heat to a radiator (where the difference of heat between the heat engine and the radiator is what matters), and another very different thing is a normal PV in the sun, when it will be able to radiate that temperature just working at 30 Celcius degree already is enoght to radiate those 65% extra. You dont need pumps or extra radiators. is just as any other PV in space.

Rune. I'm more and more a fan low Isp engines, and open cycles, the more I know about the subject.

Because clearly you still need to learn more about the subject.

You have some mixing concepts.

But dont blame the technology. Once you understand it, you will start to love it.

Edited September 4, 2015 by AngelLestat

[shynung]

Wow there! Hold on to your horses. Gas core is already difficult enough to cool, and 1,500s overkill enough for most of the solar system. Zubrin's NSWR is, shall we say, worrying (you know how the fuel is actually stored in tubes because if you let it pool it goes critical, right?), and Orion is expensive as boop, not to mention a problem to launch. I had in mind something more in the scale of the RD-0410, a very efficient design you can ground-test easily and can be used for a wide variety of applications.

Edited September 5, 2015 by shynung

[AngelLestat]

But the thrust is... close to negligible. Gas-core nuclear thermal rockets can get 1500 secs, with decent thrust.

[shynung]

Why thrust matter here? You will launch from earth surface? not..

What advantage you get to reach your speed in 10 min instead double or tripple that speed in weeks?

Military purposes. Dodging missiles would require a lot of thrust.

Also, moderately high thrust enable landing on low-gravity moons. Phobos and Deimos looks like nice places to visit.

About salt rockets we have just a paper made by zubrin.. there is not a single test on the subject.

Ayup.

At least Zubrin's rocket doesn't need finicky reactors, like these nuclear thermals and nuclear VASIMR. Most of the reaction happens just outside the nozzle. Much easier to control, too; just fuel input valves, and no such things as control rods. It works almost like a hypergolic rocket.

The same fusion, so we should ignore them by the moment, until we get some experience in earth first.

So are 1 kW/kg nuclear reactors. We shouldn't talk about them too.

Edited September 4, 2015 by shynung

[AngelLestat]

Military purposes. Dodging missiles would require a lot of thrust.

Ah, so we are dodging missiles in space now? Are you trolling?

Also, moderately high thrust enable landing on low-gravity moons. Phobos and Deimos looks like nice places to visit.

??? Since when you need to land the transfer vehicle?

Not matter what kind of propulsion your transfer vehicle use, it always remains in orbit, it will be a waste of proppelent to land it.

So are 1 kW/kg nuclear reactors. We shouldn't talk about them too.

values as 2kw/kg are for the radiator.. not the reactor.

As I said, you may have 100 mw reactors at 100kw/kg or 200kw/kg

Or something similar.

[Rune]

I dint made the calculation, if you did or have a source to support your claim please post it.

Also I am not talking about 39 days to mars, just a vehicle that can do the trip in half of the time and can be reusable to any trip in our solar system, that will reduce the cost of all future mission.

Go read Franklign's Chang-Diaz's paper. It's the thing that has the claim that is part of this thread's title.

HAHAHAHAHA, so lets make the calculation, imagine you have 50 or 100 mw for the reactor, you need to cool it, you have an idea how much flow you get for X power?

A 100MW reactor would give you a jet power of about 20MW in a VASIMR nuke-electric drive, which works out (I picked 20,000s as the Isp) as a whole 152 304N of thrust (dammit I always forget the two). To push a ship that is certainly more than a thousand tons in mass, if it has to do what you say it has to do (which it can't, of course, on account of the pitiful acceleration). That's well, shall we say, a pitiful acceleration, on the order of microgees. For comparison, NERVA ran at 200MW and 825s, and it had a thrust of 49kN for an engine TWR of 0.5, with no radiators involved. Does that answer why you need humongous reactors for manned spaceflight on electric drives?

That heat to electrical conversion is the carnot efficiency+ 5% loses in the electrical generator, and yes, you need to radiate the waste heat (that is why we have radiators, and they are responsable of the 80 to 90% of the weight from the whole system without counting payload.

So not sure what is your point more than repeat all the things that we already said.

So you accept that most of the power you are producing is wasted, in stark difference to a thermal engine where it is dumped on the propellant directly. Good. Now if you could only understand the implications...

No, you are mixing techs, here you need to move matter that carry heat (coolorant), from the core to the radiators, so you just move them with a pump (kinetic energy).

But compression and expansion, that is a heat pump!, which is different than a kinetic pump.

In that case you are moving heat, not matter or fluids.

Heat pumps are usufull when you need to cool stuffs as super conductors, when you need to reach 60k or 3K, a radiator to the space with just little diference between source and destiny, it will have a terrible efficiency. So you move forcing that heat with a heat pump, this consume power (much more than a simple electrical pump, but it does not matter because they are two very different things.)

You are the one not getting things. If you want to use fancy radiator concepts to save mass, and still have the cargo anywhere near 300ºK and/or the electrical engine anywhere close to its operating temperature, then you are going to need many staged coolant loops with heat pumps to make the jumps to your high-temperature radiators, or a cooler, heavier radiator system. High temperature, exotic radiator concepts only work if you engine is capable of being much, much hotter than them. That is my point.

About the radiator and heat pump for the superconductors and engine, if they work with superconductors then not sure how they have 40% of energy loses... When most of all kind of electrical work are very efficient.

Magnetic nozzles. If you want to have a plasma exhaust, you need one (else you exhaust fries your nozzle), and thus you need superconductors. Ditto for the VASIMR engine itself, that will have to be cooled too, although I don't really know it's operating temperature. I'd bet some form of liquid/gas cooling is already going on in the tests, or pulsed operation to not fry it.

They plan to use it as first application, to keep the space station in orbit.

So if that works fine, then they will use it for any other application they want. a mars mission is not discarded, more taking into account that this was their main excuse to not go to mars in all these years..

The day a VASIMR flies on ISS, I'll eat a hat. Seriously. All plans are scrapped right now, and it was never a serious thing. Just shiny acronym to flash in front of the press.

First the liquid lithium is your idea, nobody mentioned that before.. is just come from your head.

About solar panels, all new solar panels that goes to space has 45% efficiency.

http://sunmetrix.com/wp-content/uploads/2014/09/NREL_efficiency_chart.jpg

Also saying that I need to keep them at 1600k shows that you dont have much idea what are you talking about.

One thing is a heat engine which needs to move that heat to a radiator (where the difference of heat between the heat engine and the radiator is what matters), and another very different thing is a normal PV in the sun, when it will be able to radiate that temperature just working at 30 Celcius degree already is enoght to radiate those 65% extra. You dont need pumps or extra radiators. is just as any other PV in space.

Lithium is great for high temperature coolant systems, which why I mentioned it, it's used in most of the droplet radiators due to it's low vacuum pressure and a lot of other factors, not to mention it stays liquid "reasonably" cool. Obviously on solar panels it makes no sense, so we are back to low temperature cooling for your 65% inefficient super-high-tech multiple junction Gallium-Arsenide photovoltaics that are actually old as sin (see, I did click on your reference). Which means that, just like in real-life systems, you have huge, bulky, and heavy solar panels that can perhaps give you a few kws for tens of square meters of heavy panelling that incorporates high mass passive radiators. Great way to bring your powerplant weight down! Shows you really know your stuff, adn totally get where I am being sarcastic with my technologies and when I'm not.

Because clearly you still need to learn more about the subject.

You have some mixing concepts.

But dont blame the technology. Once you understand it, you will start to love it.

Said the pot to the kettle. Well, if we are going that way, I must say, you don't seem to have a very good handle on how an actual cooling system works. It's reasonable, thermodynamics is a difficult subject, took me two tries in uni (Aerospace Engineering degree, BTW). FYI, this is where I lost any hope of teaching you in this thread. Keep on dreaming, but don't wait up for anyone to actually build the stuff you dream.

Rune. You can't cheat physics.

Edited September 4, 2015 by Rune

[AngelLestat]

Go read Franklign's Chang-Diaz's paper. It's the thing that has the claim that is part of this thread's title.

Ok here it is..

http://www.adastrarocket.com/Andrew-SPESIF-2011.pdf

It said 50mw for a 39 day trip, not gigawatts as you said.... you have a word about that?

A 100MW reactor would give you a jet power of about 20MW in a VASIMR nuke-electric drive, which works out (I picked 20,000s as the Isp) as a whole 152 304N of thrust (dammit I always forget the two). To push a ship that is certainly more than a thousand tons in mass, if it has to do what you say it has to do (which it can't, of course, on account of the pitiful acceleration). That's well, shall we say, a pitiful acceleration, on the order of microgees. For comparison, NERVA ran at 200MW and 825s, and it had a thrust of 49kN for an engine TWR of 0.5, with no radiators involved. Does that answer why you need humongous reactors for manned spaceflight on electric drives?

I dint check your math, sorry, but due how wrong was your last answers, I prefer to look in better sources.

Also it does not matter if your thrust is low, meanwhile at the end of the month or week, you achieve a lot of speed.

Here, learn from these papers about vasimr ships.

http://web.mit.edu/mars/Conference_Archives/MarsWeek04_April/Speaker_Documents/VASIMREngine-TimGlover.pdf

Take a look, 12 mw, mission to mars, half of time than a nuclear thermal rocket of 1000 mw reactor.

You are the one not getting things. If you want to use fancy radiator concepts to save mass, and still have the cargo anywhere near 300ºK and/or the electrical engine anywhere close to its operating temperature, then you are going to need many staged coolant loops with heat pumps to make the jumps to your high-temperature radiators, or a cooler, heavier radiator system. High temperature, exotic radiator concepts only work if you engine is capable of being much, much hotter than them. That is my point.

But you are wrong, now I understand why you think this way..

By this paper:

http://www.adastrarocket.com/NETS2013.pdf

That use compressors as heat pumps to increase the thermal difference between the core temperature and the radiator return, they achieve to increase the carnot efficiency this way, but that extra amout of power is wasted to run the compressors.

So you reach a similar result if you dont use compressors, but you might thing that if you have a radiator working at 1000 or 1500 C close to the ship, it will heat the rest of the ship?

No, because you just need to use a plain base radiator "l" with a reflective surface bloking the crew and the engine.

Read the paper.

This is also the source of your other mistake, that normal pumps consume a lot of power, but this is not a fluid pump, is a "heat pump" (compressor).

Magnetic nozzles. If you want to have a plasma exhaust, you need one (else you exhaust fries your nozzle), and thus you need superconductors. Ditto for the VASIMR engine itself, that will have to be cooled too, although I don't really know it's operating temperature. I'd bet some form of liquid/gas cooling is already going on in the tests, or pulsed operation to not fry it.

Ok, I take a look to the efficiencies, for a 200kw vasimr engine (already tested) you have a 72% of efficiency, and that efficiency increase with the power. So we might be talking of 80 or 85% efficiency for 10 or 20 mw engine.

The mass of the vasimir after 10 mw, is 1kw/kg, so 10 tons for 10 mw.

Lithium is great for high temperature coolant systems, which why I mentioned it, it's used in most of the droplet radiators due to it's low vacuum pressure and a lot of other factors, not to mention it stays liquid "reasonably" cool.

But under pressure I imagine.. not sure in vaccum. Also if you dont use compressors, just the doplet radiator, the temperature of return does not change much vs the initial.

Obviously on solar panels it makes no sense, so we are back to low temperature cooling for your 65% inefficient super-high-tech multiple junction Gallium-Arsenide photovoltaics that are actually old as sin (see, I did click on your reference). Which means that, just like in real-life systems, you have huge, bulky, and heavy solar panels that can perhaps give you a few kws for tens of square meters of heavy panelling that incorporates high mass passive radiators. Great way to bring your powerplant weight down! Shows you really know your stuff, adn totally get where I am being sarcastic with my technologies and when I'm not.

You are mad? XD

Remember that you said that 45% PV efficiency was a lie.. now you know they are very old and are used in all sattelites, but this is your answer?

About the weight, there are new PV that use the same technology that are light and kinda flexible.

Not sure what you mean by high mass passive radiators.. the same PV act as radiators.. you dont need extra radiators.. so not sure why you mention the word "mass". But I dint hear any self correction from your last post when you claim it that you will need extra radiators at 1600 C to cool the PV

Read the papers, vasimr PV are also mentioned. Yeah, they might be less effective far from sun and with big payloads, but they are the best option for low payloads and closer than mars.

Said the pot to the kettle. Well, if we are going that way, I must say, you don't seem to have a very good handle on how an actual cooling system works. It's reasonable, thermodynamics is a difficult subject, took me two tries in uni (Aerospace Engineering degree, BTW). FYI, this is where I lost any hope of teaching you in this thread. Keep on dreaming, but don't wait up for anyone to actually build the stuff you dream.

Go back to the uni. how many other things I need to correct you?

Also, there is not shame to said.. sorry I mistake.

[tater]

Quoting people who have an interest in VASIMR is hardly different than just quoting OP here. It would be like supporting Mars One by quoting... Mars One and its employees.

Regarding the adastra pdf linked, it says:

Next, we show that a 12 MW nuclear power source with a moderately aggressive technology advancement that assumes a specific mass of 4 kg/kW yields 3 month human mission to Mars with approximately the same initial mass as a chemical mission. Finally, we demonstrate that ambitious advancements in nuclear power sources at the 200 MW power level can enable 39 day human missions to Mars.

(bolding by me to reenforce the FACT that neither of the required reactor technologies actually exist, as the company itself admits in the quote above)

Note that they also say:

It is not expected that turbo-Brayton reactor systems will fall below 10 kg/kW, even for larger power output systems.

(in other words, any available reactor system that has actually been tested in space is not even close to what they need).

With no data in that paper, we can only assume that is input power (electric) to the drive. We are discussing 39 day trip parameters in this thread, BTW, read the first post. Current space reactors are about 20-25% efficient comparing thermal to electrical output. That makes the required reactor... very nearly a gigawatt (thermal). Go figure.

They are saying 40 mT of propellant, and a call it 800MWt reactor. I'm unsure (they don't say) if even their magic 4kg/kW figure is kWe or kWt. If it is electrical (lowballing to make their numbers better), the reactor mass is 800 mT. It is 200 mT for the fanciful 1kg/kW reactor that no one has ever seen.

OK, so having read that, it's more like an SBIR than anything terribly useful. Is VASIMR worth looking into? Sure. Will it be flying to Mars with people in front (at any power level) while any of us are alive? Profoundly unlikely. I'll be happy to be proved wrong.

[Rune]

Ok here it is..

http://www.adastrarocket.com/Andrew-SPESIF-2011.pdf

It said 50mw for a 39 day trip, not gigawatts as you said.... you have a word about that?

That you should read a bit better. It's 200MW electric for the manned ship, and no wonder that if you can't figure that out, you can't figure how much of a joke the whole paper is. I certainly wasn't mentioning it as a source of reliable numbers, just as the preposterous piece of disinformation that started this whole thread.

I dint check your math, sorry, but due how wrong was your last answers, I prefer to look in better sources.

Also it does not matter if your thrust is low, meanwhile at the end of the month or week, you achieve a lot of speed.

Here, learn from these papers about vasimr ships.

http://web.mit.edu/mars/Conference_Archives/MarsWeek04_April/Speaker_Documents/VASIMREngine-TimGlover.pdf

Take a look, 12 mw, mission to mars, half of time than a nuclear thermal rocket of 1000 mw reactor.

I doubt you can check it, actually, but don't worry, I did, and it's right. That paper mentions a 12MW electric. And a totally sci-fi alpha of 4kg/kw, probably taken from Chang-Diaz's paper. In fact check out the two last slides. In the next to last, an arrow to the reactor with the caption "Science fiction?", and in the next one, the actual phrase "And nobody is going anywhere without dramatic advances in space nuclear power!". Oh, and the trajectory is a 10-12 months low-energy transfer with a long spiral out of Earth orbit, nowhere near the one in the other paper.

But you are wrong, now I understand why you think this way..

By this paper:

http://www.adastrarocket.com/NETS2013.pdf

That use compressors as heat pumps to increase the thermal difference between the core temperature and the radiator return, they achieve to increase the carnot efficiency this way, but that extra amout of power is wasted to run the compressors.

So you reach a similar result if you dont use compressors, but you might thing that if you have a radiator working at 1000 or 1500 C close to the ship, it will heat the rest of the ship?

No, because you just need to use a plain base radiator "l" with a reflective surface bloking the crew and the engine.

Read the paper.

This is also the source of your other mistake, that normal pumps consume a lot of power, but this is not a fluid pump, is a "heat pump" (compressor).

I have no idea what you are going on about here. The best I can guess is that you still have no idea how this things work. Try and see if you understand the thermal diagram on page two, and why things are they way they are there (i.e: two loops at drastically different temperatures). Also note that paper assumes a never-before-built magneto-hydro-dynamic generator that sustains itself without power, and then happily proceeds to assume an alpha of 10kg/kw for the complete system. It's a step on the right direction, but still firmly inside wonderland.

Oh, and an interesting tidbit I found on it: it bases the mass of the reactor on NERVA's numbers, which is laughable to anyone that knows the slightest bit about nuclear reactors. NERVA was a fast core very highly enriched, with a lifetime measured in hours. If I can spot such glaring mistakes skimming the paper, I shudder to think what else this guy has written. What does it take to get a NASA grant these days?

Ok, I take a look to the efficiencies, for a 200kw vasimr engine (already tested) you have a 72% of efficiency, and that efficiency increase with the power. So we might be talking of 80 or 85% efficiency for 10 or 20 mw engine.

The mass of the vasimir after 10 mw, is 1kw/kg, so 10 tons for 10 mw.

I haven't even started to consider the mass of the engine. For the purposes of considering whether or not such a ship can get enough TWR to perform the fabled 39-day-to-Mars trajectory, it is completely irrelevant. You could have an engine with zero mass, and still it wouldn't cut it. The problem is in the waste heat such an engine would produce, and the waste heat the powersource for that engine would produce on top of that.

You are mad? XD

Remember that you said that 45% PV efficiency was a lie.. now you know they are very old and are used in all sattelites, but this is your answer?

About the weight, there are new PV that use the same technology that are light and kinda flexible.

Not sure what you mean by high mass passive radiators.. the same PV act as radiators.. you dont need extra radiators.. so not sure why you mention the word "mass". But I dint hear any self correction from your last post when you claim it that you will need extra radiators at 1600 C to cool the PV

Read the papers, vasimr PV are also mentioned. Yeah, they might be less effective far from sun and with big payloads, but they are the best option for low payloads and closer than mars.

Yup, and I will repeat it if you want. Ga-As cells are really old tech. And they only get those efficiencies in the lab, cooled actively and with a lens over the photodiode several times their size to concentrate the light. When you put real-life solar panels with those same cells, together with real-life electric engines, surprise surprise, you get real-life thrust to weight ratios. How fast do you think Dawn accelerates? Understand the papers you quote. You clearly don't.

Go back to the uni. how many other things I need to correct you?

Also, there is not shame to said.. sorry I mistake.

The sad part is, you probably feel proud about that post, and think that you are actually correcting me. Won't change the facts one small bit.

Quoting people who have an interest in VASIMR is hardly different than just quoting OP here. It would be like supporting Mars One by quoting... Mars One and its employees.

Regarding the adastra pdf linked, it says:

(bolding by me to reenforce the FACT that neither of the required reactor technologies actually exist, as the company itself admits in the quote above)

Note that they also say:

(in other words, any available reactor system that has actually been tested in space is not even close to what they need).

With no data in that paper, we can only assume that is input power (electric) to the drive. We are discussing 39 day trip parameters in this thread, BTW, read the first post. Current space reactors are about 20-25% efficient comparing thermal to electrical output. That makes the required reactor... very nearly a gigawatt (thermal). Go figure.

They are saying 40 mT of propellant, and a call it 800MWt reactor. I'm unsure (they don't say) if even their magic 4kg/kW figure is kWe or kWt. If it is electrical (lowballing to make their numbers better), the reactor mass is 800 mT. It is 200 mT for the fanciful 1kg/kW reactor that no one has ever seen.

OK, so having read that, it's more like an SBIR than anything terribly useful. Is VASIMR worth looking into? Sure. Will it be flying to Mars with people in front (at any power level) while any of us are alive? Profoundly unlikely. I'll be happy to be proved wrong.

It's more magical that that, actually. The ship that does it has 100mT IMLEO. Which is one third of the mass of ISS. Whose power generation is about 20kWs, if memory serves me right. Anyone has a figure for the mass of the cooling system?

Rune. I guess the astronauts are mice. That paper is priceless.

Edited September 5, 2015 by Rune

[shynung]

Ah, so we are dodging missiles in space now? Are you trolling?

A bit. High thrust is more of a handy capability than a needed feature; it's useful in certain circumstances.

??? Since when you need to land the transfer vehicle?

Not matter what kind of propulsion your transfer vehicle use, it always remains in orbit, it will be a waste of proppelent to land it.

You didn't tell me we're using a shuttle for that, so I assume the the ship simply lands on it tail-down. It's not that much of a stretch, though; Phobos and Deimos surface gravity is very small.

[tater]

I honestly have no idea for ISS, but as it is low-temp, it's likely pretty large (thanks, Stefan-Boltzman and those pesky black-bodies!).

[Exoscientist]

Gernstenmaier is a politician, and he has said many things. Don't change the fact that packing radiation shielding and a thether system for artificial gravity is a fraction of the mass of an electrical engine. And I would seriously cuestion the sanity (or honesty) of someone that tells you that sitting next to a Gigawatt-class nuclear reactor is the best way of reducing the radiation dose going to Mars.

To achieve the "39 days to Mars" trajectory that started this whole thing, you need jet powers on the order of Gigawatts. Period. Unless your payload weights grams, of course, but we are discussing manned flights here...

Actually Gerstenmaier was talking about using orbital propellant depots.

He's actually the opposite of a politician. The current White House and NASA administrator, who serves at the behest of the White House, says the Moon has no value. Gerstenmaier went out on a limb to suggest the Moon may be the best approach to get Mars in feasible way. Note this was the conclusion of the scientists of the National Academy of Sciences who recently presented a report on the best way to get to Mars.

About the VASIMR "39 days to Mars", as I recall it needed a 200 megawatt system.

IF it were easy to get a centrifugal system for artificial gravity, I would be all for it. However, NASA has had at least 5 official "Design Reference Architectures" going back at least 3 decades for getting to Mars, and they have never included artificial gravity in any of them. This while knowing the debilitating effects of long-space travel. This suggests that they don't consider it a trivial problem to get a safe artificial gravity system to work at a feasible size.

Bob Clark

[PB666]

Actually Gerstenmaier was talking about using orbital propellant depots.

He's actually the opposite of a politician. The current White House and NASA administrator, who serves at the behest of the White House, says the Moon has no value. Gerstenmaier went out on a limb to suggest the Moon may be the best approach to get Mars in feasible way. Note this was the conclusion of the scientists of the National Academy of Sciences who recently presented a report on the best way to get to Mars.

About the VASIMR "39 days to Mars", as I recall it needed a 200 megawatt system.

IF it were easy to get a centrifugal system for artificial gravity, I would be all for it. However, NASA has had at least 5 official "Design Reference Architectures" going back at least 3 decades for getting to Mars, and they have never included artificial gravity in any of them. This while knowing the debilitating effects of long-space travel. This suggests that they don't consider it a trivial problem to get a safe artificial gravity system to work at a feasible size.

Bob Clark

Because artificial gravity greatly increases the mass. To some degree tension based excercise can slow down the skeletomuscular effects of microg.

Centripedal force is omega²r. So that if you want to increase a on the brain and eyes of a six foot tall man you would need a floor at least 6 feet from the center of rotation, and so if you want acceleration at least half on the brain than on the feet it means that you would have a room 8m in diameter, plus a floor that can both support weight and pressure, so ther you have mass, and then you have disk that is 10m wide that you have to launch. The other problem is that unless you have a sophisticated gimbling system you have to despin to burn a different direction, each time burnining dV to spin up and down. Also communication, that fixed parabolic antenna wont work. The rotating crew cabin creates drag against the power units in split systems and the teflon interface will leak gas over time. They could create a gravity pod, a small biradial that could be extended and twirling the vessel at some slow speed in which the nauts workout under weights say at say third g for 30 minutes to but exercises would be limited to squats, pull ups and verticle activities. This can be compensated for by more time in the unit.

If the cannae drive actually works in space it could be used to create gravity without wasting dV of fuels and it becomes more plausible, you could have spin excercise cycles and despin navigation and communication cycles.

[SargeRho]

If you have a really long ship, such as a bimodal NTR transfer vehicle, you can spin it end over end to generate artificial gravity in the habitation section. If you have a Fusion-driven vehicle, you can forego that completely, and go brachistochrone instead.

[AngelLestat]

(bolding by me to reenforce the FACT that neither of the required reactor technologies actually exist, as the company itself admits in the quote above)

Let me translate that for you:

It does not exist, it means that never was builded or designed for that specific task.

It does not mean that we dont have the technology to build it.

Once you know what are your requirements, you design it and build it.

With no data in that paper, we can only assume that is input power (electric) to the drive. We are discussing 39 day trip parameters in this thread, BTW, read the first post. Current space reactors are about 20-25% efficient comparing thermal to electrical output. That makes the required reactor... very nearly a gigawatt (thermal). Go figure.

The efficiency of the reactor is mostly given by the radiator that you use, if you dont care about the amount of energy left after waste, because that means reduce cost in radiators and your energy needs never was big since the begining, then you are perfecty fine with 20 %.

Remember that without vasimr, nuclear reactors to produce electricity are kinda useless in space.

Ion engines does not have a good thrust and their performance is very bad when you try to scale them.

The amount of energy needs for other task can be perfectly solve with RTG or solar panels. So if we dont have a nuclear reactor already in space with good kw/kg is because we never neeed them!

They are saying 40 mT of propellant, and a call it 800MWt reactor. I'm unsure (they don't say) if even their magic 4kg/kW figure is kWe or kWt. If it is electrical (lowballing to make their numbers better), the reactor mass is 800 mT. It is 200 mT for the fanciful 1kg/kW reactor that no one has ever seen.

4kg/kw magic???? you can reach 2kg/kw with ease. The fact that the ISS still use 1960-1990 technology, is not a conclusion to think we can not improve it, when in fact we already use much better materials and tech in our common life each day.

Also 800 mwt?? ok, keep making your numbers.

That you should read a bit better. It's 200MW electric for the manned ship, and no wonder that if you can't figure that out, you can't figure how much of a joke the whole paper is. I certainly wasn't mentioning it as a source of reliable numbers, just as the preposterous piece of disinformation that started this whole thread.

The OP and the paper said 39 days to mars, it does not clarify if is manned or not. In any case, multiply that by 2 and you have your reactor power (depending the radiator you choose)

I doubt you can check it, actually, but don't worry, I did, and it's right. That paper mentions a 12MW electric. And a totally sci-fi alpha of 4kg/kw, probably taken from Chang-Diaz's paper. In fact check out the two last slides. In the next to last, an arrow to the reactor with the caption "Science fiction?", and in the next one, the actual phrase "And nobody is going anywhere without dramatic advances in space nuclear power!". Oh, and the trajectory is a 10-12 months low-energy transfer with a long spiral out of Earth orbit, nowhere near the one in the other paper.

Maybe you dont know what science fiction means, it means that is base on science and physscis laws but nobody builded yet.

I already mention and I give details and links on kw/kg for reactors and radiators designs.

You can fix the vasimr engine - radiators - reactor - (extras) at 2kw/kg (without payload)

Lets said you do it at 3 or 4.. that is still a lot better than any nuclear thermal rocket.

I have no idea what you are going on about here. The best I can guess is that you still have no idea how this things work. Try and see if you understand the thermal diagram on page two, and why things are they way they are there (i.e: two loops at drastically different temperatures). Also note that paper assumes a never-before-built magneto-hydro-dynamic generator that sustains itself without power, and then happily proceeds to assume an alpha of 10kg/kw for the complete system. It's a step on the right direction, but still firmly inside wonderland.

Ok, you are complety unable to admit any mistake or misconception.

Yesterday you was not able to difference between a normal pump from a heat pump, or the simple fact that PV does not need the same radiators than a nuclear power system. Those things are basic to know how much you understand on thermodynamics. Without even mention all your other misconceptions.

Not sure why you try to denied it, I can quote your previous post..

About your "impossible tech":

https://en.wikipedia.org/wiki/Magnetohydrodynamic_generator

These things are here since a lot of time, they never was use in big scale because there are different and more economic options for similar task in earth, for space they would work much better due microgravity.

Oh, and an interesting tidbit I found on it: it bases the mass of the reactor on NERVA's numbers, which is laughable to anyone that knows the slightest bit about nuclear reactors.

So you dint laugh I guess.

NERVA was a fast core very highly enriched, with a lifetime measured in hours. If I can spot such glaring mistakes skimming the paper, I shudder to think what else this guy has written. What does it take to get a NASA grant these days?

What errors? he is assuming a lot of weight for its reactor that he really does not need to assume.

He took a nerva reactor of 350 mw that weights 1750kg, then did an estimation of a aprox 50 mw reactor that weights 3000 kg... Really.. not sure who can laugh about that...

And he took those estimations, because that mass is low in comparison with the rest of the system, so it does not matter if the reactor weights less or more.

I haven't even started to consider the mass of the engine. For the purposes of considering whether or not such a ship can get enough TWR to perform the fabled 39-day-to-Mars trajectory, it is completely irrelevant. You could have an engine with zero mass, and still it wouldn't cut it. The problem is in the waste heat such an engine would produce, and the waste heat the powersource for that engine would produce on top of that.

You dont need to consider, is all in the papers. Its around 1 or 2 kw/kg (this include the radiators needed for the engine)

You have a graph that show the mass and density depending the power.

Yup, and I will repeat it if you want. Ga-As cells are really old tech. And they only get those efficiencies in the lab, cooled actively and with a lens over the photodiode several times their size to concentrate the light. When you put real-life solar panels with those same cells, together with real-life electric engines, surprise surprise, you get real-life thrust to weight ratios. How fast do you think Dawn accelerates? Understand the papers you quote. You clearly don't.

https://www.ise.fraunhofer.de/de/veroeffentlichungen/konferenzbeitraege/konferenzbeitraege-2014/29th-eupvsec/tibbits_-4cp.2.1.pdf

40% in space, and those are not the last triple juctions made.

I honestly have no idea for ISS, but as it is low-temp, it's likely pretty large (thanks, Stefan-Boltzman and those pesky black-bodies!).

It will be great for the ISS, it does not need extra radiators, just two very little, this is because it will ignite by short amounts of time, then it cool, then again.

Edited September 5, 2015 by AngelLestat

[Rune]

Actually Gerstenmaier was talking about using orbital propellant depots.

He's actually the opposite of a politician. The current White House and NASA administrator, who serves at the behest of the White House, says the Moon has no value. Gerstenmaier went out on a limb to suggest the Moon may be the best approach to get Mars in feasible way. Note this was the conclusion of the scientists of the National Academy of Sciences who recently presented a report on the best way to get to Mars.

About the VASIMR "39 days to Mars", as I recall it needed a 200 megawatt system.

IF it were easy to get a centrifugal system for artificial gravity, I would be all for it. However, NASA has had at least 5 official "Design Reference Architectures" going back at least 3 decades for getting to Mars, and they have never included artificial gravity in any of them. This while knowing the debilitating effects of long-space travel. This suggests that they don't consider it a trivial problem to get a safe artificial gravity system to work at a feasible size.

Bob Clark

There are many camps in the political quagmire that is NASA. When the Moon-first people get their way, we get Constellation, when the Marsheads take the program back, we get to keep Ares V alive under a different name. In the meantime the usual suspects keep on living on pork. It seems the political winds may be about to change... again. Is it already eight years after the death of Constellation? Man, time flies.

As to centrifugal systems, let me direct to you to this fascinating NASA report: Preliminary Assessment of Artificial Gravity Impacts to Deep-Space Vehicle Design, where they actually find that for many things, designing for gravity actually saves weight (I.E: plumbing). As a summary, they work out how to maneuver while spinning and a bunch other real-life factors, and the final Transhab for six people and Mars missions turns out to be about 40mT, with only a few percent more mass than the one designed for free fall the whole way.

As to AngleLestat... I leave that as an impossible, since he clearly isn't listening to any of my points. He can't seem to grasp the difference between 200MW thermal and 200MW electric, or a high temperature liquid droplet radiator and a low temperature ammonia one. And he says 2kg/kw is "easy" for a full system, when 20kg/kw for the power generation equipment alone is dubious at best. Impossible to discuss such a technical issue with him, and I won't continue a quote war.

And this thread actually served at least one purpose. One of these days I will write up how you can do the whole Mars thing, with a single stage chemical reusable vehicle. And you don't even need hard cryogenics, methane/LOX is more than enough. Yesterday I had an idea spurred by this, and when I run the numbers, I surprised myself at how freaking easy the whole thing was. Did you know that with an RD-167 and a mass ratio of 4 you have 5km/s in the tanks with >80% of the (empty) vehicle not being engine nor tank? I'm getting >10% payload even fully fueled and with 25% of the mass at Mars entry devoted to aerodynamic decelerators! That should be enough to do LEO-Mars including landing, or the other way around including aerocapture into LEO.

Rune. I have a feeling Elon Musk run the same numbers when coming up with the MCT.

[Exoscientist]

Its mentioned here:

http://www.sciencedirect.com/science/article/pii/S1738573315001540

Search for "reactor total mass".

But those liquid doplet radiators does not use water! XD

They use metals which remains liquid at very high temperature and in vaccum.

Thanks for that link. Note though the quoted power is for the thermal power put out by the engine, not for the electrical. For the electrical output, they need a long-running version so they reduce the power level of the engine. This results in an electrical output of only 100 kW but that can run for 600 days. It is possible though they could reduce the power to an intermediate level to get the 90 days or so needed for the round trip of the VASIMR mission, yet still have the lightweight 1kWe/kg specific power required for the VASIMR.

Bob Clark

- - - Updated - - -

...

And this thread actually served at least one purpose. One of these days I will write up how you can do the whole Mars thing, with a single stage chemical reusable vehicle. And you don't even need hard cryogenics, methane/LOX is more than enough. Yesterday I had an idea spurred by this, and when I run the numbers, I surprised myself at how freaking easy the whole thing was. Did you know that with an RD-167 and a mass ratio of 4 you have 5km/s in the tanks with >80% of the (empty) vehicle not being engine nor tank? I'm getting >10% payload even fully fueled and with 25% of the mass at Mars entry devoted to aerodynamic decelerators! That should be enough to do LEO-Mars including landing, or the other way around including aerocapture into LEO.

Rune. I have a feeling Elon Musk run the same numbers when coming up with the MCT.

Considering it takes about 6.1 km/s delta-v to go from LEO to low Mars orbit, including a fully-propulsive Mars orbit insertion, this would not surprise me. This is well less than the delta-v needed for a SSTO to LEO for example. And if you only need the stage to do the 3.8 km/s trans-Mars insertion, with instead a full aerobraking at Mars, then the propulsive requirements are trivial. It's the aerobraking that would be a major technological challenge.

Bob Clark

[Requia]

2kg/kw is overoptimistic, but NASA estimated 1085-1954kg for the 200kWe converter being designed for Prometheus, so 20 is pretty pessimistic. Though there are also scaling issues with that tech, the largest Brayton cycle converter actually built is something like 3 MWe with 10MWe in R&D.

[tater]

Funny, the people actually making vasimr say outright that it would take aggressive pursuit of nuclear to get 4kg/kW, and very aggressive to get below that, yet angellestat seems to think 2 is "easy."

I'm sort of curious where he does nuclear engineering, since he otherwise sounds entirely against that technology.

[PB666]

Funny, the people actually making vasimr say outright that it would take aggressive pursuit of nuclear to get 4kg/kW, and very aggressive to get below that, yet angellestat seems to think 2 is "easy."

I'm sort of curious where he does nuclear engineering, since he otherwise sounds entirely against that technology.

He's invented a cold fusion reactor, and is waitng for the highest bidder? :^).

- - - Updated - - -

Elon Musk is designing essentially a suicide mission. As I stated before getting people to mars is not a problem, just set the intercept on the eqautor of the planet. In this case, here comes earth approacing the martian theta to close approach, you at L2 do a solid radial burn that then bam you run smack into mars, kersplat. Oh you want them alive. Ok so, we have no way to brake, the stuff we have right now does not stand up in testing, IOW its too heavy the surface area required is 2 mag greater than what we have used and even so our equipment either had to be sky-craned down or landed in gigantic air bags. Residual velocites are 60 m/s in thin atm. So now you have to do retrograde burns, the opposite of a liftoff, and ther is no capacity left for a return.

You think they are fools at NASA, they have stated clearly that the way to get folks there and back safely cannot be done with existing technology. We here back seat space agency program directors think we can stand on the field with the pros and send hail mary passes that are caught all the time.

If NASA Wants to get thier with resources to get back i suspect they will need Russian help moving payloads to places that can be used later.

[Rune]

Elon Musk is designing essentially a suicide mission. As I stated before getting people to mars is not a problem, just set the intercept on the eqautor of the planet. In this case, here comes earth approacing the martian theta to close approach, you at L2 do a solid radial burn that then bam you run smack into mars, kersplat. Oh you want them alive. Ok so, we have no way to brake, the stuff we have right now does not stand up in testing, IOW its too heavy the surface area required is 2 mag greater than what we have used and even so our equipment either had to be sky-craned down or landed in gigantic air bags. Residual velocites are 60 m/s in thin atm. So now you have to do retrograde burns, the opposite of a liftoff, and ther is no capacity left for a return.

You think they are fools at NASA, they have stated clearly that the way to get folks there and back safely cannot be done with existing technology. We here back seat space agency program directors think we can stand on the field with the pros and send hail mary passes that are caught all the time.

If NASA Wants to get thier with resources to get back i suspect they will need Russian help moving payloads to places that can be used later.

Actually, that is why "my" (I'm sure plenty of other people have studied it too) concept of single-staging the whole thing leaves 25% of the mass at entry interface as aerodynamic decelerators. Usually a more reasonable figure for that is 15% according to most literature (i.e: Zubrin popularized that figure), but as you point out, the mass to stop (~100mT) is so over what we have done to date, you would have to develop some pretty smart tech, like inflatable heatshields, supersonic ballutes, or something similar. Certainly a bigger heatshield that your LV's diameter is in order.

Other than that, I actually budget ~800m/s dV for terminal deceleration and touchdown, at about 10 times the martian surface gravity in acceleration since I gave the ship 1G acceleration fully loaded, and it gets to Mars almost empty of fuel. I may have overspec'ed everything because I know this is a very rough proof of concept.

The key is to trust in ISRU: the first one would drop a ~50mT ISRU factory, and test it before the flight back. Cuts your dV for the mission in roughly half, and you can imagine what that does to your single-stage mass ratio. And then you can replace the cargo module with a Transhab for a crewed mission once the gas station is up and running smoothly.

The really hard part about this plan is launching the ship to orbit. It's 500mT fully fueled, after all, or 1.6 times the mass of the ISS. But, you can launch it empty on top of a decent HLV (50mT empty weight without fuel or cargo), and then refuel it over several flights to LEO. That's about 10 launches to LEO if using a 50mT HLV, with 8 launches plus payload for every subsequent flight unitl we work out the way to have a gas station at LEO supplied from elsewhere.

Rune. I assume all propulsion is relatively-easy-to-store methane/LOX.

Edited September 6, 2015 by Rune

[Exoscientist]

...

The really hard part about this plan is launching the ship to orbit. It's 500mT fully fueled, after all, or 1.6 times the mass of the ISS. But, you can launch it empty on top of a decent HLV (50mT empty weight without fuel or cargo), and then refuel it over several flights to LEO. That's about 10 launches to LEO if using a 50mT HLV, with 8 launches plus payload for every subsequent flight unitl we work out the way to have a gas station at LEO supplied from elsewhere.

Rune. I assume all propulsion is relatively-easy-to-store methane/LOX.

That is why Gerstenmaier was arguing for orbital propellant depots. You would need then only to launch that one single 50 mT of dry mass.

Bob Clark

Edited September 7, 2015 by Exoscientist

[Rune]

That is why Gerstenmaier was arguing for orbital propellant depots. You would need then only to launch that one single 50 mT of dry mass.

Bob Clark

Yeah, orbital refueling makes a lot of sense, and the techniques should be developed like, yesterday. Depots, much less so. Basically, why would you go through the trouble of lofting an extra tank, when you can use the one in the ship you are refueling? Makes no sense. I mean, stockpiling fuel could be useful if you needed to refuel quickly, but considering the time between windows, you are going to have plenty of time to refuel/restock/refurbish between missions. And if you have the ship with the empty tanks on orbit, it just makes no sense not to dock your tankers to it and put the fuel where it's going to be used.

Note that volume is also a constraint, tough. And a seldom mentioned one at that. A 10m booster would be a godsend, frankly, and probably the bare minimum to loft this kind of behemoth, even with inflatable structures like heatshields and habs.

Rune. It's interesting how architectures come full circle to the single stage tailsitters the grandfathers of rocketry envisioned. And in case anyone thinks ion ships are new in any way, Ernst Stuhlinger.

Edited September 7, 2015 by Rune

[Kibble]

Propellant depots are pretty useful, cause you can have them at EML2, stocked with fuel cracked from Lunar ammonia and water ice. The architecture could look like this: 150 Mg wet, 50 Mg dry. Launched wet, so it can make it to EML2, around 3.5 km/s delta vee. Refueled completely or partially from the depot, the spacecraft can now make it to Mars easy!

And that's without using crazy nuclear VASIMRs or whatevs.