VASIMR

Why is it that Veeky Forums sees so many posts about the idiot meme-drive (you know the one I mean) while ignoring the real miracle about to revolutionize space exploration?

arstechnica.com/science/2017/02/nasas-longshot-bet-on-a-revolutionary-rocket-may-be-about-to-pay-off/

Other urls found in this thread:

en.m.wikipedia.org/wiki/Nuclear_salt-water_rocket
universetoday.com/87425/zubrin-claims-vasimr-is-a-hoax/
spacenews.com/vasimr-hoax/
twitter.com/NSFWRedditVideo

>implying this meme drive could ever be better than NSWR
en.m.wikipedia.org/wiki/Nuclear_salt-water_rocket

universetoday.com/87425/zubrin-claims-vasimr-is-a-hoax/

Then again Zubrin did propose this fucking crazy ass shit, for sci-fi but still

>arstechnica.com
Sage, hide and report.

Here have more zubrin:
spacenews.com/vasimr-hoax/

dude NSWR is like 1950s era tech, enabled by a pair of enormous testicles

meme drive getting BTFO

It hasn't been demonstrated in the lab. No reactor accidents don't count.

what is there to demonstrate?

it is just an open loop reactor

we have several hundred reactors around the planet and tons of engineers/physicists who know how to build them

That it doesn't turn into a cloud of rapidly expanding debris or pile of molten slag after being turned on.


But hey, it's not an orion drive so we could actually do it without violating international treaties

If VASIMIR was powered by nuclear fission it could take us anywhere in the solar system quickly and easily.

All you would need is a typical liquid booster rocket to leave Earth's surface first. Unfortunately this will never happen because it's a legal to launch fission reactors into space now... so keep dreaming stop following me asshole

ELECTRICAL POWER TO WEIGHT RATIO OF NUCLEAR REACTORS ISN'T THAT GOOD

the accelerations are actually a lot smaller and more controllable than orion, so you don't need a crew and spacecraft that is capable of surviving 100gs

Correct, it's absolute shit and far worse than solar until you go out past the asteroid belt.

>>it's a legal to launch fission reactors into space now
it is very legal to launch nuclear fission reactors into space. Russians launched a number of nuclear fission, not radioisotope, powered satellites during the cold war. US even launched a couple. The ruskies fucked up big time though when one reentered over canada and left a big trail of radioactive debris.

OH and guess what? pic related worked DECADES AGO and is 100% space legal.

I love me sum NERVA engine.

accelerations aren't the issue here. It's the how do you build the thing so it doesn't explode in a manner that renders it inoperable.

the lower accelerations are just another advantage over orion, agree that it needs to be verified for not exploding

eh
There are no truly modern nuclear reactors, so you can't say that
I'm sure power to weight could be massively improved

An Orion would have shock absorbers to bring the acceleration down to something manageable. The payload wouldn't see anything close to 100 gs. The main issue with Orion's acceleration is that it's pulsed and not constant.

Except it's orders of magnitude less efficient than a nuclear pulse propulsion craft
So theres zero point in it
Also yea, the rockets tested in the 60's spewed radioactive material out

i think it is far less feasible to build a gigantic shock absorber than it is to build some small pipes and a nozzle, which is all you'd need to make NSWR work

nah m8, NSWR could achieve exhaust velocities of 66 km/s, better than the 31 km/s in orion baseline

Oh I was thinking about nuclear thermal
Dnno if this NSWR is workable.
And the whole appeal of NPP is that it can be built on earth then launched into space.

you could do a single stage from earth surface to mars with NSWR, with the caveat that the launch would probably kill a fair number of people on earth

NASA cancelled the Prometheus Project for a reason.

Yea cuz Republicans are owned by coal/oil interests who kill nuclear when they are in power.

That doesn't even make sense it's not like they're planning to burn coal in space kek.

And that reason was Bush's 'return to the moon program,' which was completely underfunded.

Seriously, funding was diverted for the crew exploration vehicle, which was eventually cancelled too

it is a neat design, but how are you going to power it? VASIMR requires a fuckhuge source of electricity compared to other ion thrusters.

>Which was eventually cancelled too
You're starting to learn how NASA works.
Check out the complete list of their cancelled projects; VASIMIR should be up next.

VASIMIR is more powerful than Hall effect thrusters, and since it won't be used in deep space solar power will provide enough for the low powered versions

Vasimir has been investigated for 30 years now.

in fairness, it had a fairly large budget and accomplished surprisingly little, i would guess it was canceled because of mismanagement or corruption

Or just use a simple NTR Nuclear Thermal Rocket and not have to worry about nuclear salts in the exhaust.

to put it in context, they got something like $400m over 3 years

for the same money NASA could launch 4 midex class missions or 8 smallex class missions,

but prometheus didnt even have a prototype

NTR is a fine compromise but inferior from an efficiency/complexity/cost perspective to NSWR

literally the only advantage of NTR is waste safety

What missions have used it?

NERVA =/= NSWR

A nuclear salt water rocket has enriched uranium salts dissolved in water to the point of saturation and keep in a tank with a series of walls and compartments that prevents the stored fuel from going critical. The uranium-salt bearing water is pumped out of the holding tank and into a chamber where it is allowed to build up to a critical mass, causing a nuclear chain reaction to occur and heat up the water to several million degrees, which is then expelled as propellant at high specific impulse. It's essentially a continuous, slightly less powerful nuclear bomb, kinda like an Orion drive with continuous rather than pulsed thrust, with similar efficiency of propulsion.

Some problems with NSWR is the extreme heat of the exhaust, making it difficult to imagine a nozzle material that could withstand it even considering some sort of active cooling, as well as keeping the stored fuel sufficiently isolated form itself in storage to prevent accidentally turning the entire fuel tank into a big nuclear bomb. Producing the fuel would also be expensive, because it'd require weapons grade enriched uranium to be produced in large volumes.


NERVA is a nuclear-thermal rocket design, which involved passing a light molecular weight propellant over the hot core of a nuclear reactor. The lighter the propellant molecular mass, the higher the energy per particle and the better the specific impulse. However the efficiency and thrust are limited by the power output of the nuclear reactor, which is limited by the melting point of the materials used to build the reactor. NTR engines have a specific impulse several times greater than that of the best possible chemical engines, but have comparatively high mass and low thrust, making them most useful when already in space.

Lower efficiency, higher impulse. However the thrust is still small.

You also save money on the nuclear fuel, not needing thousands of gallons of water saturated with enriched uranium salts.

None.

nope. exactly the opposite. NTR still needs reaction mass that it carries with it.(liquid hydrogen or water) But NTR has to carry its spent fuel with it, while NSWR blasts its spent fuel into space, causing the craft to lighten more as the engine runs(which actually increases NSWR craft efficiency exponentially compared to NTR craft due to the math of the rocket equation)

Is Zubrin triggered that Elon Musk did not take him up on his Mars Direct idea?

Neither = VASIMIR.

VASIMR isn't significantly better than Hall-effect thrusters. A small gain in efficiency, in exchange for a much heavier, more complex drive.

There's no plausible power source to drive VASIMR at the higher thrust levels. It would need some exotic nuclear thing, which would make more sense to design as a drive rather than a reactor (i.e. it's probably easier to build a fission fragment drive or fusion rocket).

What VASIMR's good for is giving NASA an excuse not to make a realistic plan for going to Mars. They can point at VASIMR and say, "We need this technology!"

No, he had it right. A nuclear salt-water reactor would consume far more fissile material than a closed-cycle nuclear thermal rocket.

Also, NTR is the worst fetish.

Stasis technology is real.

>NTR
Why are people still talking about this dirty cold war tech?

Just use VASIMIR.

At this point, I think Hall Effect thrusters are outpacing VASIMR's capabilities for mass, power consumption, and ISP. The only thing VASIMR has going for it at this point is the size of the impulse it can push out, and it's still worse than a chemical rocket in that respect, because the design falls so incredibly far short of being the fusion drive they originally hoped for.

you're gonna have to provide some reasoning or sources if you dont want this to devolve into a "nuh-uh" "uh-huh" level discussion, brainlet

>>prometheus didn't even have a prototype

They tested a bunch of things. They had a number of different prototypes. They demonstrated a brayton cycle heat engine powering an ion engine in a vacuum. They tested a FUCKING HUGE ion thruster for 2000 hours and demonstrated it worked.

They tested everything except the reactor. IE all the important shit. We know reactors work in space, the hard part is all the moving parts that have to operate for 20 years with no maintenance

even if NWSR leaves more unreacted fuel in the exhaust, the exponential terms in the rocket equation would still leave the NWSR far more efficient in terms of fuel per delta-v

Well, a nuclear thermal rocket is great for ISRU, if you've got someplace you can scoop up a suitable working fluid. By the way they work, it's hard to use much of a nuclear reactor's fuel in a few minutes, so you can use them over and over. Using inert propellants really frees up your options.

>Just use VASIMIR.
It's VASIMR, and it's not in the same category. VASIMR is electric propulsion. It's limited by the power source.

I wasn't arguing, I was correcting. I was hoping I wasn't dealing with someone who needed to be spoonfed.

>the exponential terms in the rocket equation would still leave the NWSR far more efficient in terms of fuel per delta-v
You're confused about how this works. It isn't "the higher the specific impulse, the more energy-efficient the rocket is", that's only mass-efficiency. Energy efficiency is another story, and it's often the other way around.

For a rocket in a vacuum, specific impulse derives from exhaust velocity. Once started in motion, an ideally energy efficient rocket would leave its propellant stationary (and cold) behind it: after separation of vehicle from propellant, all the kinetic energy would go into the vehicle, and none into the propellant. So when you're moving at 5 km/s, you want your exhaust velocity to be 5 km/s. The faster you throw the propellant in the opposite direction, the more kinetic energy ends up in your expelled propellant instead of in your vehicle. (starting from a dead stop, it's impossible to leave the propellant stationary behind you, so just the bigger the mass you're pushing off of, the more efficient your start, until it gets to be so much mass you have to factor in the gravity of it)

So, for a fixed delta-v, if you have to pick your specific impulse and can't change it, and you can just get as much propellant as you need, there's an optimal choice to minimize energy consumption. The larger the delta-v, the larger the optimal specific impulse. When you go over the optimum, it gets less energy efficient very quickly, due to the energy increasing with the square of the speed.

Setting aside the waste of unreacted fuel in the NWSR exhaust, the specific impulse is far on the high side of optimal for most of the missions we'd consider within the solar system, while the NTR specific impulse is much more moderate.

>solid core NTR
>NSWR
>comparable in any way
There is a fucking orders of magnitude difference in performance, user. They're nowhere near the same class of engine. NTRs like NERVA are in the less than 1000s range, NSWR has been projected to have as much as 67 thousand seconds. Even with the low end estimates I've seeb of 14 thousand seconds, that's still ~140 kilometers per second of delta v with a mass ratio of 3. Enough to drop into a retrograde orbit around the sun. Forget Hochmann transfers, that's point and scoot territory.

The problem with NSWR is fuel storage, though. It can fail in a rather spectacular fashion.

>100s of gs
Not really. Orion deals with this quite handily by having a compressible pusher plate stage on top of a bunch of shock absorbers. Build it big enough and it will be the smoothest ride you've ever taken. NSWR requires fuel tanks made of neutron absorbing material, arranged so that the salt does not reach criticality. Far more fragile setup.

>Isp is too high
In what fucking way? Energy efficiency becomes a problem when you have to generate the power - powerplant mass, more heat to dump, etc. High Isp is also a problem since it is inversely correlated to thrust and therefore acceleration, which can complicate maneuvering or downright make the drive not feasible by taking years to get up to speed. Neither problem applies to Orions or NSWRs. You don't carry an immense reactor around, you still get plenty of acceleration. Humans have limited lifespans, so for any commerce (or military) applications involving manned interplanetary travel, faster is better. No one is going to want to sit through a decade long Hochmann transfer to the gas giants when they could be traversing the same distance in under a year.

NASA's projects have mostly been centered around exploration, but serious transportation requires travel times significantly shorter than the average human's lifespan. NERVA might be enough for Mars (in fact, so is chemical), but not for anywhere further afield.

>an ideally energy efficient rocket would leave its propellant stationary (and cold) behind it
the
fuck

>So when you're moving at 5 km/s, you want your exhaust velocity to be 5 km/s. The faster you throw the propellant in the opposite direction, the more kinetic energy ends up in your expelled propellant instead of in your vehicle.

wow you know zero physics. kys

newtons second law dumbass

choice of frame of reference is arbitrary in space so "propellant at rest" is fucking retarded

beyond that no one gives a crap about energy efficiency in space if you're mass efficient, time efficient, and riding the wake of a goddamn nuclear explosion

Chemical is just fine for going anywhere in the solar system
Just to land on places without an atmosphere you would need to refuel to get the delta-v needed to land aka ceres or Jupiter's moons.

Maybe with some nuclear electric propulsion for speeding up trips to the outer system.

yes magic shock absorbers solve all problems

High impulse shock absorbers aren't magic.

if building nuclear proof shock absorbers were that easy nuclear weapons would be far less of a military threat

>nukes blowing up ur tanks?
>just add high impulse shock absorbers
>problem materials scientists?

nuclear weapons are shit against hardened installations...

I, too, intend to win a hypothetical nuclear war by covering every building with massive, multi-hundred foot shock absorbers that are only designed to withstand the force of a 5 kiloton weapon.

>nuclear weapons are shit against hardened installations...
where hardened means "20 stories underground" not "high impulse shock absorber"

Are you retarded? Clearly laws of motion and thermodynamics are above you

>>Isp is too high
>In what fucking way?
We're talking about the nuclear fuel consumption, and therefore energy efficiency.

For simplicity, assume an instantaneous burn. An 800 tonne vehicle is accelerated to 10 km/s, while 100 tonnes of propellant is consumed, accelerated to 80 km/s in the opposite direction. Obviously, their momenta are equal and opposite. The vehicle's kinetic energy is 40 TJ. The propellant's kinetic energy is 320 TJ. This sets an absolute upper limit on energy efficiency of 11%, before you even start accounting for things like nozzle collimation efficiency, residual heat, and unreacted fuel. (this implies an exhaust velocity of about 85 km/s, or Isp around 8500s)

Now assume 1600 tonnes of propellant at 5 km/s. Its kinetic energy is 20 TJ. The energy efficiency limit is now 67%. (the implied exhaust velocity is about 9 km/s, or Isp around 900s)

>choice of frame of reference is arbitrary in space so "propellant at rest" is fucking retarded
Appropriate choice of frame of reference makes some things much easier to see. Obviously, I was talking about the frame in which the rocket is initially stationary. Just because you don't understand it doesn't mean it isn't useful.

>no one gives a crap about energy efficiency in space
Again: we're talking about the amount of fissile material that has to be consumed. When you have to pay for or produce things like highly enriched uranium, it starts to matter. With NSWRs, you're talking about propellant that's like 16% HEU. That's extremely expensive stuff.

With a conventional solid-fuel NTR, you retain the fission fuel in the engine, so you can tank up more propellant and fly again, for instance going back and forth between two places, and have an economical system. With NSWRs, you're spraying 99+% of the fission fuel out the back, unreacted, wasting it.

When something is fired into space, does it ever stop? Couldn't we just jury-rig a thousand fusion rockets (after inventing them), so 1000x200,000 =
200,000,000 / mph, so we could reach Tappist-1 in less than 100 years?

>Obviously, I was talking about the frame in which the rocket is initially stationary
Then it is literally impossible for the propellant to be at rest after an impulsive maneuver because of newton's second law of motion

>That's extremely expensive stuff.
It isn't *that* expensive compared to launch costs. One kg of 20% U-235 takes 11 kg of natural uranium. 11 kg of natural uranium costs $7/kg. So we're talking about $77 of feedstock per kg. It costs $20,000/kg to launch into space. Hence no one gives a shit about uranium efficiency.

>With a conventional solid-fuel NTR, you retain the fission fuel in the engine
Which is cheap as fuck, compared to the mass. which is expensive as fuck.(see above) Look up the rocket equation. Fuel mass scales exponentially for an increased delta-v. If you can reduce your dry weight by having a lighter engine because your engine discards shit as soon as it is done with it, then you have a near optimal engine. This is why rockets use staging. Even though you're throwing away high tech components that are FAR more expensive than enriched uranium, it is still cheaper than holding onto it because exponential scaling is a bitch that cucks you while you're at work trying to figure out how to build a reusable launch vehicle called STS.

>One kg of 20% U-235 takes 11 kg of natural uranium. 11 kg of natural uranium costs $7/kg. So we're talking about $77 of feedstock per kg. It costs $20,000/kg to launch into space.
Natural uranium costs more than $7/kg, it costs more than $20,000/kg enrich it to 20%, and less than $20,000/kg to launch it into space presently, let alone in the future when we'd be able to develop such advanced engines.

Good uranium ore is a scarce resource. If we consume a lot of uranium, we'll have to go to seawater or granite, which will make it considerably more expensive.

Furthermore, enriched uranium is a highly controlled substance. That has costs as well.

Obviously, if you're going to invest in major new technologies for space, the first places to do it are in lowering orbital launch costs from Earth and securing extraterrestrial sources of material. There's no sense in assuming that you'll be able to make some advanced nuclear drive, but orbital launch will still be done with high-cost expendable rockets.

Its complicated. You can, in theory, make yourself go but you need a more and more prohibitive amount of fuel and thrust as you add more fuel and thrust. Any significant fraction of the speed of light will be unattainable without something extremely efficient, like antimatter.

>"20 stories underground" not "high impulse shock absorber"
those terms are equivalent

I just want my own spaceship.

Cmon plasma guy gimme a spaceship.

At $40/kg it would cost $440/kg. Still a lot less than $20,000/kg.

>Good uranium ore is a scarce resource
more than 7 million metric tons discovered. Which is like 7e6/11/2700 = 236 trips to alpha centauri. Assuming we don't discover any more reserves due to new exploration. So not really all that scarce.

>There's no sense in assuming that you'll be able to make some advanced nuclear drive
If you make this not at all advanced nuclear drive, you can use it to launch directly from the earth's surface. Making other rockets somewhat unnecessary.

And if we're going to allow for advancements in technology. Then Uranium supplies are not really at issue as it should be abundant in the asteroid belts.

But the main reason to prefer NSWR over NTR is just that it is much more efficient due to

(1) the way the rocket equation works
(2) the way maximally efficient orbital transfers require high thrust

NTR is a compromise between thrust and ISP. NSWR gives high thrust and high ISP.

Not necessarily. Depends on the composition of the local rock. 20 Stories might not always be deep enough. For what it's worth when the USAF was considering deep underground basing for M-X, they were planning to bury the things close to a mile down, significantly more than 20 stories. It's a shame the plans fell through. They'd have been able to take a direct hit from a 100MT weapon and survive.

>At $40/kg it would cost $440/kg.
In terms of current price, the enrichment process is far more expensive than the material itself. It takes a lot of energy.

>236 trips
You're talking about the world's supply. When it's gone, it's gone forever.

>it is much more efficient
Specific impulse isn't the same as efficiency. Using thousands of time more rare isotopes and much more energy to get to a destination are a pretty major inefficiencies.

Look, these things aren't just better or worse. I can understand being enthusiastic for NSWR as a possible interstellar propulsion, but that doesn't make it fit to replace the things you might use solid-fuel nuclear-thermal rockets for.

When you're considering something as advanced as an interstellar trip, there are also other options, like fission fragment rockets, fusion rockets, interstellar ramjet, antimatter, and beam riding. It's a different class of competition.

>Specific impulse isn't the same as efficiency
It really is for any craft that obeys the rocket equation. (ie all rockets, but not things like jet engines, propellers, and solar sails)

>You're talking about the world's supply.
Good thing we have an asteroid belt and this sweet technology called terrestrial exploration

>When it's gone, it's gone forever.
Nah m8 we've got this sweet technology called breeder reactors.

>It takes a lot of energy.
pretty cheap on earth

> I can understand being enthusiastic for NSWR as a possible interstellar propulsion

NSWR would allow us to easily explore the solar system in a way that NTR never could. The fact that NSWR is a technology that could take us to other stars without any new exotic developments is just a demonstration of how large a capability it has.

>Chemical is just fine for going anywhere in the solar system
Not for manned travel. Unless you are fine with spending decades to get anywhere. Chemical is enough to get around the system in the same way that a rowboat is enough to traverse the oceans.
>magical shock absorbers
What exactly is magical about shock absorbers? Big and very expensive shock absorbers for sure, but no magitech involved.
Are you trolling or retarded
>energy efficiency
...doesn't really matter in space, does it? More often than not you're dealing with constant power output devices in the engines. The problem is and always has been remass, not energy.

There is some really autistic guy who comes all the time and starts arguing about how the only thing matters is "energy efficiency" in terms of using the nuclear fuel up

But of course he sees no problem in shooting tons of hydrogen out the back of a chemical engine, that stuff could be fused in a fusion reactor!!

It's when some Thunderfoot watching brainlet with no understanding of basic rocket stuff forgets that there is more to engineering than just getting the energy in/energy out right.

Several dozen kilograms of fissile material in a nuclear reactor costs much less than hundreds or thousands of kilograms of fissile material dissolved into water as a salt. I'm talking about cost as in dollars, highly enriched uranium (as is needed for a rocket that works using a sustained nuclear explosion) costs several million dollars per kilogram.

This is actually a niche in which NTRs make sense. However, we'd probably want to build one that used a liquid fuel in a solid heat exchanger system in order to be able to constantly clean the fuel and prevent the buildup of fission products.

Pu239 is way cheaper than enriched U235
The problem is more a question of regulation & bureaucracy, and having no free market approach

I really do think that NSWR is our only real world option for propulsion that would fit the definition of a torch drive.

>Pu239
This stuff is similarly expensive, and far more rare at the moment. 6kg of it costs $31 million according to google. Fissile nuclear fuels are expensive. Unless we find a way to easily make Thorium go critical we won't have anything close to approaching cheap nuclear propulsion.

There is no "cost" to them, they are no availible on the market

Once you got a breeder going, the costs to produce more Pu is negligible, they made thousands of tons of it back in the 60's

Hell, all civilian reactors produce tons of Pu239 just as a byproduct of operation, they are designed to contaminate it with Pu240 to ruin it though

The costs of nuclear power are 100% regulatory.

Well, to qualify as a true torchship it would have to make artificial gravity from thrust, wouldn't it? NSWRs could manage full brachistochrones within gas giant systems, but not interplanetary.

It's not expensive, nobody's making it.

>Several dozen kilograms of fissile material in a nuclear reactor costs much less than hundreds or thousands of kilograms of fissile material dissolved into water as a salt.

Yes but you only need several hundred thousand kg in an NSWR if your FLYING TO ANOTHER SOLAR SYSTEM. Protip: 10000x shorter distance requires 10000x less fuel.

>I'm talking about cost as in dollars, highly enriched uranium (as is needed for a rocket that works using a sustained nuclear explosion) costs several million dollars per kilogram.

The fuel is more expensive but when you look at the system cost it is exponentially cheaper for the same reason that it is cheaper to throw rockets away in stages than it is to carry them with you and reuse the vehicle.(even though rocket components cost millions of dollars per kg)

>The problem with NSWR is fuel storage, though. It can fail in a rather spectacular fashion.

I mean, if you store it in pipes of the right material and diameter, the physics for storing the fuel is pretty straightforward.

But I think one problem that hasn't been properly worked out is how you would feed the fuel out of the tank. There would be tremendous pressure trying to push your fuel back into your fuel tank

>10000x shorter distance requires 10000x less fuel.
actually I take that back. 10000x shorter distance requires far less than 10000x less fuel

Why not just use a fridge?

>fuel storage is ez
Not really. There are two massive problems that even pipes made of neutron poisons can't fix:
>fuel salt settling in the water, collecting a critical mass
>potential micrometeor strikes punching holes in the piping

>backpressure in the fuel injection system
Not necessarily if a pusher plate design is used. Considerable standoff can be achieved that way.

No shock absobers anywhere to be seen. No method for dealing with immense heat of conduction since it's operating within an atmosphere and the device used is considerably more powerful than the pulse propulsion units.

>fuel salt settling in the water

that isnt how aqueous solutions work, senpai

>micrometeor strike
i dont think any extant or planned spacecraft, regardless of drive type, can survive a strike without catastrophic failure

in all cases everyone dies, NSWR would just look at lot more awesome as everyone died

>pusher plate

yeah perhaps

if you're accelerating at 1g, you've basically got a 1-g gravity feed for the fuel if you design your tank right