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

[Rune]

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.

Cut out the middleman. Park the ship where your tankers get to, and you save a multi-billion dollar spacecraft. Until we have some very serious regular service to a multitude of destinations, a propellant "hub" doesn't make that much sense. EML-2, BTW, would make sense if your propellant comes form off-world sources, which have to be developed before you can do so. Propellant refueling techniques can be taken advantage of much sooner, cutting out the need for costly SHLV programs for beyond-LEO manned exploration. What I'm defending is a single-item tech development: the ship.

Now the rest of what you said also makes sense, but consider that the return trip has a higher dV requirement than the way there: about 6.8km/s form Mars surface to an Earth intercept. You would need to stage the trip at LMO, and another depot would mean another multi-billon dollar project.

Rune. I know the ship I described can't make that much dV either, but I have a fancy way around that without extra hardware.

Edited September 7, 2015 by Rune

[tater]

Why a lunar source of propellant? Phobos and Deimos are actually closer in dv terms including bringing it back to an earth moon Lagrange point.

[Rune]

Why a lunar source of propellant? Phobos and Deimos are actually closer in dv terms including bringing it back to an earth moon Lagrange point.

Why an off-world source of propellant at first, besides the destination you want to go to? Refueling from the Earth in LEO would provide a fantastic market to bring launch costs down, and not that much program costs due to extra launches, at least as manned exploration programs go. And it also means that the only other big tech development is martian surface ISRU, a much more tractable technical challenge than micro-gee propellant mining.

Rune. Have you ever though about how to collect a fluid in a microgee vacuum?

[Kibble]

I think you guys missed the point - refueling at EML2 means your spacecraft don't have to have absurd amounts of delta-vee!

[tater]

I wasn't saying depots were a good idea at all, actually. I was saying that anyone who thinks that lunar mining makes sense should be willing to look at places easier (in dv terms) to get to/from. It's dubious that lunar mining would get you more than an offset in landing costs.

All the propellant still needs to get to the spacecraft. That it is already high up the gravity well is great, but it had to get there, and the propellant has to get there as well. It's like having O2 at Camp 3 on Everest. Yippee, but a bunch of Sherpas had to bring it there.

[AngelLestat]

This topic already consume me a lot of time, but here we go one more time.

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

Can you quote me in what part I seems to not understand that?

Just one time I said that you needed 12 mw without noticing that it was electric, but in the next post I said, ok, in that case is double that amount for thermal.

or a high temperature liquid droplet radiator and a low temperature ammonia one.

??? what? hahaha you are desperate.

I never mention ammonia, so not sure how you reach that conclusion? Again, please quote me to see where I am wrong.

I talk about combined cycles since my first day in this forum, you can use the advance search tool to check it.

The one you said is kalina, the order for temperature is Brayton–Rankine–Kalina in case you want a triple cycle.

But you can have just 1 cycle, which in space it is advisable due how hard is to get rid of the heat and the problem to add more complexity.

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.

20 kg by kw? really? I guess I can build something with wood using my own tools and come out with better density than that. This is the main evidence that you dont have a clue.

And of course you dont want a quote war, a compilation of your answers showing all your "knowledge" will not look nice. So you will ignore my answer and keep talking about refuelling in LEO.

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.

I already know that, I detailed here

http://forum.kerbalspaceprogram.com/threads/132918-39-days-to-Mars-possible-now-with-nuclear-powered-VASIMR?p=2178215&viewfull=1#post2178215

The 100kw electric in that point means nothing, they just need only 100kwe in that rocket, the rocket use thermal as propulsion, so why you will convert all to electric?

But that reactor produce 100mw, that is the main point, a reactor designed for electric conversion will weight a bit more, and a lot more the whole system (reactor + radiator)

100 days to mars is the best using vasimr, your reactor power may be just 50mw (depending the payload)

Take into account that a thermal nuclear rocket to transfer the same payload in the double of time will require 1000 mw.

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.

Is in the graph from one of the vasimr papers that I show, at low powers, vasimr engine density increase a lot, the best is reaching 10mwe.

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.

If we measure this according to NASA developing time, then it will take 30 years. There is nobody more slow and less efficient than NASA.

But if the money is at Elon Musk hands and someone ask him (build us a vasirm tug in space to transport cargo to mars),

he will do it at 1/3 of the cost and in 6 years.

Why? because all the things we discuss are all solvable just using the right materials and clever design, the solutions are not "hard tech" that we need to invent a new material or a new physsics law to do it, you just need to sit down in a chair and start to design it.

Edited September 7, 2015 by AngelLestat

[shynung]

I wasn't saying depots were a good idea at all, actually. I was saying that anyone who thinks that lunar mining makes sense should be willing to look at places easier (in dv terms) to get to/from. It's dubious that lunar mining would get you more than an offset in landing costs.

All the propellant still needs to get to the spacecraft. That it is already high up the gravity well is great, but it had to get there, and the propellant has to get there as well. It's like having O2 at Camp 3 on Everest. Yippee, but a bunch of Sherpas had to bring it there.

Now imagine that the cost of carrying O2 from Base Camp was much higher, in terms of energy. The hiker would have to carry a lot of food (and breathe a lot of atmospheric O2) just to carry that O2 all the way to the summit. Meanwhile, the Sherpas found a place near Camp 3 that has some O2 in a form that they could bottle (say someone airdropped an air liquiefier/separator device). This O2 source is lower than Camp 3, but higher than Base Camp, so they spent less energy (food and O2) getting that O2 to Camp 3, where people line up to get it.

Suppose that the Sherpas and the hikers work for the same company, whose mission was to mine something from the summit of Mount Everest which cannot be found somewhere else, call it Everesite for now. Suppose that the hikers and Sherpas have to use O2 all the way from base camp to the summit. Which is cheaper, in terms of energy spent: carrying their entire supply of O2 all the way from Base Camp to the summit (which means lugging around big and heavy O2 tanks), or carrying just enough O2 to get to Camp 3, refill their O2 there, and continue the rest of their journey using O2 taken from refill site?

Replace O2 with rocket propellant, hikers and Sherpas with spacecrafts, Base Camp with the launch pad, Camp 3 with EML2, O2 refilling site with the Lunar surface, and the summit with Mars.

[Rune]

I think you guys missed the point - refueling at EML2 means your spacecraft don't have to have absurd amounts of delta-vee!

Only if you need the propellant close to EML2, dV-wise. Sadly, from Mars surface, EML2 is quite far away (at least 6.8km/s using aerocapture), so you have to get creative to get back.

Rune. Dude, how off-topic are we going here.

[tater]

Your Everest analogy is wrong. The effort required (which requires a constant influx of supplies) to mine both at ~8000m and the moon might exceed the benefit. In your example, the sherpa miners would require enough O2, and other deliveries to work, that while the effort to move it to camp 3/L2 (the route would drop below camp3 to the other side of the mtn, then climb above camp 3) would be less than from basecamp/earth to the destination for a single trip, the net gain would be near zero, actually zero, or possibly worse than bringing straight up. You need to land supplies to the mine, and you need to lift the tanker. If you have cryo fuels, then you have to do all this an exceed boiloff losses into the bargain.

Obviously it depends on the material being mined. For most of the moon it's just plentiful O2. In polar areas, water is possible. Regardless, it might turn out to make more sense to drag an asteroid or comet to the Lagrange point, and just process it there.

- - - Updated - - -

T??? what? hahaha you are desperate.

To everyone else reading this thread, this describes you. You're out of your pay grade.

20 kg by kw? really? I guess I can build something with wood using my own tools and come out with better density than that. This is the main evidence that you dont have a clue.

Name some space reactors that have actually flown, or have been built and tested full-sized and quote their power densities, please. We'll wait.

The 2 best designs (unflown, unbuilt) are SP-100 and SAFE-400 at ~50kg/kW and the SAFE-400 (also 100 kWe) is tricky to get the total mass of as the core is 512kg and each heat exchanger is 72kg---the design has 127 heat pipe modules hooked to exchangers, so either they share a few 72kg changers, or there are 127 of them (9144kg). I've seen a couple references to the actual total mass of the SAFE-400 being 1200kg. Regardless, it's not actually a reactor, it's just a design for a reactor.

The actually tested HOMER-15 (similar to SAFE-400) is 214kg total for 3 kWe (71kg/kW).

Edited September 7, 2015 by tater

[shynung]

Your Everest analogy is wrong. The effort required (which requires a constant influx of supplies) to mine both at ~8000m and the moon might exceed the benefit. In your example, the sherpa miners would require enough O2, and other deliveries to work, that while the effort to move it to camp 3/L2 (the route would drop below camp3 to the other side of the mtn, then climb above camp 3) would be less than from basecamp/earth to the destination for a single trip, the net gain would be near zero, actually zero, or possibly worse than bringing straight up. You need to land supplies to the mine, and you need to lift the tanker. If you have cryo fuels, then you have to do all this an exceed boiloff losses into the bargain.

For the first trip, maybe, since the Sherpas probably have to carry their mining equipment to their O2/fuel collection point. But they don't have to bring it back home; they can leave the O2 mining rig there, for future Sherpas to use them later. Sure, some things would have to be replaced, machinery oiled, consumables replaced, but the bulk of the rig mostly stays in place. The tanker that carried O2/fuel doesn't go very far, either; just back-and forth from mining spot/surface to Camp 3/EML2.

Also, the assumed mining spot shouldn't be past the summit on the other side of the mountain, otherwise that would correspond to the mining spot being farther than Mars. Lunar surface is closer to EML2 (despite going down a gravity well) than Mars orbit, taking about 2.5 km/s of deltaV, as opposed to about 5.2 km/s for going to Mars orbit.

Then again, you're right that it depends on what's being mined, Water or O2 might be close to break-even, but stuff like nuclear fuels might be something else.

Also, moving an asteroid to a stable orbit isn't an easy endeavor, because the useful (large) ones are massive. It'll take plenty of propellant to move it to EML2, but at least the tug doesn't have to carry the mining rig with it. Might be a good idea, but depends on what will the miners get from the asteroid.

[AngelLestat]

To everyone else reading this thread, this describes you. You're out of your pay grade.

To everyone else? you did a poll? I just saw Rune and you with all kind of concept issues.

Name some space reactors that have actually flown, or have been built and tested full-sized and quote their power densities, please.

Name a submarine able to transport 2000 people, you cant? then according to you: "it can not be done... we dont have the tech"

But the tech is similar, we just need to scale up, in fact a submarine so big, it will be more cost efficient by passenger. But we dont have one.. why? Because we never need it.

So first... try to fix your "logic" if you want to make a point.

The 2 best designs (unflown, unbuilt) are SP-100 and SAFE-400 at ~50kg/kW and the SAFE-400 (also 100 kWe) is tricky to get the total mass of as the core is 512kg and each heat exchanger is 72kg---the design has 127 heat pipe modules hooked to exchangers, so either they share a few 72kg changers, or there are 127 of them (9144kg). I've seen a couple references to the actual total mass of the SAFE-400 being 1200kg. Regardless, it's not actually a reactor, it's just a design for a reactor.

The actually tested HOMER-15 (similar to SAFE-400) is 214kg total for 3 kWe (71kg/kW).

Ok, I need to explain again what a reactor means? "The reactor" is the machinery component where the fission takes place.

Of course you need to connect it to the "Heat Engine", and the Heat engine to the colling system.

Now you need to move the heat from the core to the heat engine, so you may use supercritical co2 or helium, water, salt or a heat pipe that is in direct contact with the fission materials, so all that part of the system is also called Reactor, which may include a pump and a heat exchanger connected to the "Heat Engine" (which is not include in the Reactor at least is in direct contact with the fission material or through a fluid).

For what I see, all those things that you Name.. produce electrical power.. so if produce electrical power then they have a Heat Engine and a colling system included. So they are not Reactors, they are "space reactors power systems"

Also, the density of a reactor, decrease with the increased power, the same as the Vasirm engine, at 100kwe has a density of 30 kg/kw, but at 10Mwe it has a density of 2kg/kw. See the difference?

[PB666]

To everyone else reading this thread, this describes you. You're out of your pay grade.

funny, being a scientist means that you are irrationally indifferent to how little you get paid. If you are testing logic and knowledge you might want to consider a different measure, such as publications on the matter.

In anycase mining everest would not be too difficult, start by using robotics driil in horizontally and but a submarine door on the entrance, pump air in and release it under pressure, will also warm the mine up. Then drill up to target. See Easy. Though this whole topic is decidely off topic and should be summarily ignored.

[peadar1987]

To everyone else? you did a poll? I just saw Rune and you with all kind of concept issues.

Name a submarine able to transport 2000 people, you cant? then according to you: "it can not be done... we dont have the tech"

But the tech is similar, we just need to scale up, in fact a submarine so big, it will be more cost efficient by passenger. But we dont have one.. why? Because we never need it.

This is actually a very good analogy, although it doesn't support your point.

To a casual observer, it may seem like the problem is as simple as scaling a current submarine up. To an engineer, it's a nightmare. A submarine is a pressure vessel. Large pressure vessels, especially those under compression, are notoriously difficult to build. There are all sorts of strange longitudinal and circumferential buckling failure modes. The stress scales linearly with the radius of the cylinder, whereas the critical buckling load scales with the square of the radius. Could we do it? Maybe. Would it be easy? No. Could we do it tomorrow without a huge research and development programme? Certainly not.

[tater]

Given how poorly science pays, being below that pay grade makes someone a McDonalds worker

We are not talking about reactor cores, we are talking about systems that create electricity. VASIMR wants electricity, not heat (a reactor core is just a heat source). Scaling up, as Rune points out is non-trivial. Also, you'll note that I provided an example, the HOMER-15, which is in miniature, very similar to SAFE-400. 70kg/kW. On top of that, SAFE-400 does't actually exist, it's a design. I actually used to host visiting students for the guy who is one of the primaries for SAFE-400 for his Space Nuclear Power meeting (ISNPS) (which resulted in some serious fun with Soviet nuke-E students), he's been working on that design for a LONG time in one form or another (possibly as long as you've been alive, depending on your age), and it is still just on paper.

[PB666]

This is actually a very good analogy, although it doesn't support your point.

To a casual observer, it may seem like the problem is as simple as scaling a current submarine up. To an engineer, it's a nightmare. A submarine is a pressure vessel. Large pressure vessels, especially those under compression, are notoriously difficult to build. There are all sorts of strange longitudinal and circumferential buckling failure modes. The stress scales linearly with the radius of the cylinder, whereas the critical buckling load scales with the square of the radius. Could we do it? Maybe. Would it be easy? No. Could we do it tomorrow without a huge research and development programme? Certainly not.

Man are we in offtopic land, floation in a submarine is govern by the ratio dry weight, balast and gas filled space. The amount of the last two squares with radius which mens the thickness can be increases with as the square of the area. However there is another option to double down on the level cross sectional bracing per doubling of radius.

The washington class of submarine if coverted from a missile launcher prolly could carry a thousand people with some added space age technology. I wouldn't neccesarily dive past 300 meters.

On the issue of why, I bet there are several thousand refugees in lybia that wish they had a sub capable of say reaching the US. And of course if you could give the mexican cartel a washington class submarine so that they could smuggle central americans into the US, sleeping on kilo wraps of cocaine they prolly would not decline the gift. Why our military would want a sub that bigger than that, they are actually going for the fast attack subs, bigger subs give a larger reflectance than smaller subs, which means i can ping you and turn head on before you can ping me and get a distance. I simply dive and you go right over me. So your best choice is to evade which means that i can ghost you.

Theres all kinds or reasons a group might want a big sub, and all kind of reasons for not having one. I WWii the biggest reason for bigger sub is that they could carry 3 times as many torpedos, they pushed the technology as far as they could. Balistic missle subs required bigger still, but the missiles can reach anywhere on earth, so .......

[tater]

BTW, on topic, no one is arguing that we could not make possibly arbitrarily large fission reactors for space use given time and money, but the OP states that VASIMR is ready for the 39 day journey NOW, and the document written by its own engineers says exactly the opposite (that even the slightly longer trip would take aggressive R&D for a nuclear power source, and that it would need to be very aggressive for the 200 MW version). Unless someone imagines a political change that allows NASA to blow a substantial % of their budget on a Manhattan Project push for a huge space reactor, the current development of such reactors will be no where near even the lower tier of "aggressive."

[AngelLestat]

This is actually a very good analogy, although it doesn't support your point.

Could we do it? Maybe. Would it be easy? No. Could we do it tomorrow without a huge research and development programme? Certainly not.

Heh, yeah it's just an analogy that apparently for some weird case, everybody seems to enjoy

But I dont think the stresss would be an issue, if you scale up, that is a lot more of air you add by volume, so you need to fulfill with steel and all kind of heavy stuff, but then is not easy to fit 2000 people, yeah is not easy.

But the point I want to make, is that is more an issue of will and determination, than a tech or physsics limit.

In fact you dont even need make practical test for each step and each material to see what may be the best.

Supercomputers right now are so good simulating conditions that you can test several configurations and select and discard options a lot faster and cost efficient. Also you dont need come out with the best reactor ever, you just need something that it works inside the parameters you look for.

We are not talking about reactor cores, we are talking about systems that create electricity. VASIMR wants electricity, not heat (a reactor core is just a heat source). Scaling up, as Rune points out is non-trivial.

Ok, said exactly what part of the whole system seems the most complicate and why you think it can not be done.

Then if someone of here (with our limited knowledge) come out with a possible solution, it means that even us we may have an idea of how to solve problem by problem, which a group of experts for certainly will, the devil is on the details, that takes time. But not so much as NASA always show.

Man are we in offtopic land, floation in a submarine is govern by the ratio dry weight, balast and gas filled space. The amount of the last two squares with radius ....

sub is that they could carry 3 times as many torpedos, they pushed the technology as far as they could. Balistic missle subs required bigger still, but the missiles can reach anywhere on earth, so .......

haha. that was some pro derail right there

BTW, on topic, no one is arguing that we could not make possibly arbitrarily large fission reactors for space use given time and money, but the OP states that VASIMR is ready for the 39 day journey NOW

Well I never defend that 39 day nonsense. But I guess 100 days is something that is a lot easier to achieve than 39 days, and still very promising to change and improve all our solar system activity, if we have that ship in space, we can do wherever we want, manned mission to mars, venus, titan, europa ice submarine, etc.

And you can always reduce the payload to achieve higher deltav. So the question is... we stay for always with chemical propulsion or we make once for all the obvious step?

They are planing right now fly-by to the ice giants that might take 40 years to complete, just to get some telemetry and pictures.

You really want wait that time for each new mission?

In fact, nobody takes into account the singularity, so all those long term ideas does not have a bit of logic.

[Rune]

Given how poorly science pays, being below that pay grade makes someone a McDonalds worker

We are not talking about reactor cores, we are talking about systems that create electricity. VASIMR wants electricity, not heat (a reactor core is just a heat source). Scaling up, as Rune points out is non-trivial. Also, you'll note that I provided an example, the HOMER-15, which is in miniature, very similar to SAFE-400. 70kg/kW. On top of that, SAFE-400 does't actually exist, it's a design. I actually used to host visiting students for the guy who is one of the primaries for SAFE-400 for his Space Nuclear Power meeting (ISNPS) (which resulted in some serious fun with Soviet nuke-E students), he's been working on that design for a LONG time in one form or another (possibly as long as you've been alive, depending on your age), and it is still just on paper.

Your post actually took me on a very pleasant search around for nuclear power systems. Try as I might, I couldn't find a reactor that went over 3kg/kw... for the thermal production, without any electricity generation attached. I also couldn't find a power converter that went over 25% efficiency in thermal to electric conversion (using stirlings, of course), or a radiator with a cold side over 700ºK (using liquid sodium).

But, I did find the old BES-5 to power soviet radar satellites, and the TOPAZ reactors that were actually designed and built in the USSR and tested in Albuquerque. Man, the cold war was an awesome technology developer, and it has some amazing weird stories.

Rune. Has anybody not seen Rickover's quote about paper reactors vs real reactors?

Edited September 8, 2015 by Rune

[peadar1987]

Man are we in offtopic land, floation in a submarine is govern by the ratio dry weight, balast and gas filled space. The amount of the last two squares with radius which mens the thickness can be increases with as the square of the area. However there is another option to double down on the level cross sectional bracing per doubling of radius.

The washington class of submarine if coverted from a missile launcher prolly could carry a thousand people with some added space age technology. I wouldn't neccesarily dive past 300 meters.

On the issue of why, I bet there are several thousand refugees in lybia that wish they had a sub capable of say reaching the US. And of course if you could give the mexican cartel a washington class submarine so that they could smuggle central americans into the US, sleeping on kilo wraps of cocaine they prolly would not decline the gift. Why our military would want a sub that bigger than that, they are actually going for the fast attack subs, bigger subs give a larger reflectance than smaller subs, which means i can ping you and turn head on before you can ping me and get a distance. I simply dive and you go right over me. So your best choice is to evade which means that i can ghost you.

Theres all kinds or reasons a group might want a big sub, and all kind of reasons for not having one. I WWii the biggest reason for bigger sub is that they could carry 3 times as many torpedos, they pushed the technology as far as they could. Balistic missle subs required bigger still, but the missiles can reach anywhere on earth, so .......

Buoyancy in a submarine is directly proportional to its displacement, which scales with the square of the radius, so if you simply double all of the dimensions, the buoyancy to weight ratio will be the same. However, buoyancy isn't the limiting factor for the submarine, it's various buckling modes in the hull. There are ways around this, as you have said, extra transverse compression members being one of them, but a structurally optimal submarine with internal volume X will always need a greater proportion of structural mass than a structurally optimal submarine of internal volume 0.5X

The point of the whole thing is that we can't simply launch a monster submarine several times the size of all existing ones by repurposing existing designs. It will be a major technological challenge. As would be repurposing a nuclear thermal rocket to run a high-density multi-megawatt power generation cycle in the vacuum of space. It's probably possible. It's not going to happen any time soon, and it certainly isn't as simple as sticking a generator into the rocket exhaust.

[shynung]

peadar1987 said:

... It will be a major technological challenge. As would be repurposing a nuclear thermal rocket to run a high-density multi-megawatt power generation cycle in the vacuum of space. It's probably possible. It's not going to happen any time soon, and it certainly isn't as simple as sticking a generator into the rocket exhaust.

Indeed it's possible. I'd stick a large toroid MHD generator and have the rocket exhaust fly through it just after leaving the nozzle. Problem is, it works only on charged exhaust gases, and it saps a lot of thrust. Assuming identical mass flow, your thrust/weight ratio and specific impulse just went down the drain.

Edited January 3, 2016 by shynung

[Exoscientist]

Why a lunar source of propellant? Phobos and Deimos are actually closer in dv terms including bringing it back to an earth moon Lagrange point.

Yes, quite correct. Since this is on the propellant depots idea I responded on the thread, Propellant depot based Mars architecture.

Also there I noted it is surprisingly easy also to do sample return from Phobos and Deimos.

Bob Clark

Edited September 8, 2015 by Exoscientist

[tater]

Well I never defend that 39 day nonsense. But I guess 100 days is something that is a lot easier to achieve than 39 days, and still very promising to change and improve all our solar system activity, if we have that ship in space, we can do wherever we want, manned mission to mars, venus, titan, europa ice submarine, etc.

Both are still not happening any time soon. If the power system is not already rated for use, it's a solid 10 years away at the soonest---and that's for stuff already designed.

And you can always reduce the payload to achieve higher deltav. So the question is... we stay for always with chemical propulsion or we make once for all the obvious step?

They are planing right now fly-by to the ice giants that might take 40 years to complete, just to get some telemetry and pictures.

You cannot meaningfully reduce the payload for a manned Mars mission. NASA reference architecture in that regard is basically minimal for the required safety/redundancy.

No one is arguing that chemical is the ONLY way to explore the solar system, here, either. The question at hand is VASIMR alone, and how reality compares to the claims they are making. For VASIMR, they not only need nuclear power systems, they need them to be arbitrarily low mass. THAT is the question, really. It presents a design target for the nuke-Es, but that doesn't mean that they can hit that target, there could very well be fundamental limitations that make creating hardware to this arbitrary standard quite difficult. It's also important to remember that this is an engineering question. In the real world, engineering is not just making stuff, it's making stuff that meets the appropriate standards AND is cost-effective. It might turn out that a 1kg/kW reactor is so expensive that it would be prohibitive. Cost matters.

You really want wait that time for each new mission?

In fact, nobody takes into account the singularity, so all those long term ideas does not have a bit of logic.

What I want is irrelevant. I might want to cut "programmatic" spending by the US government by 50%, and give all that money to NASA, instead, but that won't happen. NASA exists in the real world, and they must prioritize what they pay for. It is frequently true in the real world that achieving 75% of a high-standard goal might cost X, and getting to 90% of the goal specs costs 10X, and getting to 99% costs 100X (made up numbers, but you get the idea). Making a space reactor would be expensive. Making a super light space reactor might well be possible, but prohibitively expensive to develop.

- - - Updated - - -

Your post actually took me on a very pleasant search around for nuclear power systems. Try as I might, I couldn't find a reactor that went over 3kg/kw... for the thermal production, without any electricity generation attached. I also couldn't find a power converter that went over 25% efficiency in thermal to electric conversion (using stirlings, of course), or a radiator with a cold side over 700ºK (using liquid sodium).

But, I did find the old BES-5 to power soviet radar satellites, and the TOPAZ reactors that were actually designed and built in the USSR and tested in Albuquerque. Man, the cold war was an awesome technology developer, and it has some amazing weird stories.

Rune. Has anybody not seen Rickover's quote about paper reactors vs real reactors?

I saw the Topaz delivered (the russians brought it in an Antonov, that plane was huge), then out at the lab (Sandia). The trick has always been conversion, which is why something like NERVA makes so much sense relatively speaking---it is far less challenging.

[More Boosters]

The title, "39 days to Mars possible now with nuclear-powered VASIMR." is highly misleading as there's no clear cut demonstration that it actually is possible. For all we know the power requirements are going to remain unrealistic for at least another decade.

[AngelLestat]

Both are still not happening any time soon. If the power system is not already rated for use, it's a solid 10 years away at the soonest---and that's for stuff already designed.

OF course you will not build it tomorrow !! And launch it the next week. We really need to clarify that?

I dont think so, I said that if we started now with the design and is in capable hands as Elon Musk, then you can do it in 6 or 7 years. What it starts now is the design, you dont need to wait for new tech or theories to do it.

You cannot meaningfully reduce the payload for a manned Mars mission. NASA reference architecture in that regard is basically minimal for the required safety/redundancy.

You dint read me? I said every kind of missions, maybe for mars you need 80 tons, but for a not manned mission to Titan you need just 5 tons, that will be like a 25% less dry mass. Normal missions to Titan may take a lot of years, you may do this one at 1/10 of the time or less (because you are in constant acceleration)

The question at hand is VASIMR alone, and how reality compares to the claims they are making.

The claims that the engine works? That it has that amout of ISP?

The step to provide and design the power energy will not depend on them, they already did the engine. So they said, now is up to you to improve the power generation in space.

They are being very proffesional and carefull with all their claims and words.

So not sure why you trash them?

Also they are not saying that you can not go mars with chemical rockets or nuclear thermal, they just are saying that if you care about the radiation doze and trip times to mars, then the only tech with the potential to solve that is vasirm (for now)

It's also important to remember that this is an engineering question. In the real world, engineering is not just making stuff, it's making stuff that meets the appropriate standards AND is cost-effective. It might turn out that a 1kg/kW reactor is so expensive that it would be prohibitive. Cost matters.

Again you are making wrong assumptions, forget about the reactor weight, you need to think in the overall density of the whole ship.

The reactor is just a 3% or 10 % (depending the design) of the ship mass. And to have sense it needs to be below to 4kg/kw.

If you have a particular concern about some part of the ship that might be impossible to solve or meet the requirements, then said it.

If you dont.. then is possible, and only depends on the will of goverments to do it.

People tend to forget the apollo missions, what they accomplish and in what year, that compared to this was even harder.

THe new NASA policy and way to do things, infect the minds of many thinking that now things are impossible to do.

[tater]

OF course you will not build it tomorrow !! And launch it the next week. We really need to clarify that?

I dont think so, I said that if we started now with the design and is in capable hands as Elon Musk, then you can do it in 6 or 7 years. What it starts now is the design, you dont need to wait for new tech or theories to do it.

The thread title says NOW.

Elon Musk? Where do you calculate 6 or 7 years? Be specific why you chose that number, and not 5 years, or 8, please.

The claims that the engine works? That it has that amout of ISP?

The step to provide and design the power energy will not depend on them, they already did the engine. So they said, now is up to you to improve the power generation in space.

They are being very proffesional and carefull with all their claims and words.

So not sure why you trash them?

They actually claim that the reactors don't exist, themselves, and would require substantial increases in reactor research. Perhaps "aggressive" doesn't click with you as a use of language? Aggressive means a very serious commitment, very aggressive means maybe Manhattan Project or Apollo. Neither will happen for reactors, period. They are being very careful about that, why aren't YOU?

Also they are not saying that you can not go mars with chemical rockets or nuclear thermal, they just are saying that if you care about the radiation doze and trip times to mars, then the only tech with the potential to solve that is vasirm (for now)

Meh. They are selling something. Really. Radiation has been well characterized in terms of what crews will be exposed to, it's a risk, but a known risk, they are hyping it to sell their product. They should think about designing their own reactor, as they seem to require one for their drive. Their drive would be like me designing a NTR, but not providing the reactor. I have a pump, and a nozzle, give me a XXXX MW reactor that masses Y, and we have a great rocket. Except the reactor doesn't exist.

Again you are making wrong assumptions, forget about the reactor weight, you need to think in the overall density of the whole ship.

The reactor is just a 3% or 10 % (depending the design) of the ship mass. And to have sense it needs to be below to 4kg/kw.

If you have a particular concern about some part of the ship that might be impossible to solve or meet the requirements, then said it.

If you dont.. then is possible, and only depends on the will of goverments to do it.

Will of governments, lol. All government money is spent via politics by definition. Do tell how NASA ends up blowing a huge chunk of budget on a novel reactor design. We'll wait. NASA is forced to buy stuff they don't even want, like SLS.

The other parts for a manned Mars mission--which is exactly what we are discussing---are pretty much fixed. The mass can drop here or there by small amounts, that's it. They have said what they require, and that reactor by their own admission DOES NOT EXIST. Period. If you say that this is easy in 6-7 years, show us an actual reactor they can use, or just admit you are making stuff up. Actual, meaning it is built and tested, or will be quite soon.

People tend to forget the apollo missions, what they accomplish and in what year, that compared to this was even harder.

THe new NASA policy and way to do things, infect the minds of many thinking that now things are impossible to do.

NASA will not again see that level of largesse heaped upon it. Not ever. Try to be realistic.