"Zubrin wrote in SpaceNews: “To achieve his much-repeated claim that VASIMR could enable a 39-day one-way transit to Mars, Chang Diaz posits a nuclear reactor system with a power of 200,000 kilowatts and a power-to-mass ratio of 1,000 watts per kilogram. In fact, the largest space nuclear reactor ever built, the Soviet[-era] Topaz, had a power of 10 kilowatts and a power-to-mass ratio of 10 watts per kilogram. There is thus no basis whatsoever for believing in the feasibility of Chang Diaz’s fantasy power system.”
The idea isn't ludicrous, although the torch-ship speeds of 39-day transits are definitely out of reach for now. The basic idea is, let's attach a nuclear reactor to an ion engine. Further, let's make the propellant hydrogen so we can refuel anywhere in the solar system.
If we want to get serious about exploiting the solar system, we'll eventually have to give in and embrace nuclear technology, whether something like VASIMR or a nuclear-thermal design like NERVA. We already routinely park 100MW+ nuclear reactors in port for our navy, why not consider civilian use for space exploration? We already know many ways to mitigate risk for the launch of nuclear material.
I think Musk, Zubrin, et al. analyze propulsion technologies from the perspective of how to enable a journey to Mars now. In that light, something like Raptor makes much more sense. You still need a chemical rocket engine to lift off from Earth or Mars, so in the near term a nuclear ion thruster just adds far too much complexity to justify its inclusion. Further, it's difficult to imagine SpaceX obtaining the political backing to put nuclear tech into space as a private company. This is also why Musk would rather power Martian propellant plants with fields of solar arrays instead of the much more mass-efficient space-rated nuclear reactors that NASA has been developing.
But imagine if we actually developed a Mars colony with millions of people. The logistics of seeding a colony on Mars with chemical thrusters already boggle the mind. Economics would basically forbid meaningful interplanetary trade unless we develop new technology with much higher specific impulse. It would be even more impactful than moving from air-freight to container ships.
30 years ago as a student I tried calculating how big a space reactors cooling fins would need to be be. 1MW of power means 2 MW of heat you need to dissipate via radiation. I can't remember the numbers but I remember the result was dismal.
The problem becomes yes you can use a reactor or nuclear battery to power and ion rocket, which fuel efficient, very energy inefficient, and sloooow. Or you can use a nuclear rocket which avoids the need for a radiator by tossing your waste heat out the back end. Better fuel efficiency than a chemical rocket, can go faster, difficulty gamma radiation. Between those there isn't anything in between that makes sense because a high power thermal power reactor is too heavy.
Your source is ignoring the fact that limitations on nuclear power in space are largely political. If we could put something bigger up there without concern it would be interpreted as a nuke, we would.
From what I heard from industry people, overheating is an unsolved problem for VASIMR. It is 60-70% efficient, meaning that 60kW of thermal power has to go somewhere.
Waste heat management for 200MW system in space is firmly outside the realm of present-day technology.
I’m assuming you mean 60MW of heat, which would likely be worth recycling, especially if it’s not low grade heat. If you then are left with say 30MW of unrecoverable heat, than its only ~500x what the current largest space thermal system can handle (the one on the ISS).
It really depends on the mass budget they have for that speed for if anything new needs to be discovered.
Some quick math: 32 miles per second (see one of their linked articles, https://www.spaceflightinsider.com/conferences/vasimr-plasma...) is 155,200 miles per hour. Assume you accelerate at 21 MPH, which is about 1 g (100 KPH ~ 60 MPH, 100 KPH / 32.81 KPH/S^2 = 2.85 s, 60 MPH / 2.85 s). So at 1 g It takes you about 228 days to reach cruising speed, 2 g takes 114 days, 3 g 57 days. So I don't think this would not be useful to transport space crews? Still really cool tho.
At 1g acceleration (10m/s/s) that is 6,938 seconds.
6,938 seconds is like 2 hours.
A ship that can sustain 1g acceleration continuously for periods measured in hours, that would indeed be an interplanetary drive. Sustain that for days/weeks/months and it will take us to other stars.
And remember that you have to bleed most of that speed off before entering orbit. Even with aerobraking most orbiters try to slow down to ~2km/s before hitting the atmosphere. Hitting the Martian atmosphere at 32miles per second wouldn't be an acceptable plan in KSP, let alone in real life.
Seriously, I've been reading VASIMR press releases for the last 20 years or so. Looking into it, I get the impression it's more a livelihood (from grants) for the inventor than an ongoing technological trajectory.
"A massively scaled up version running at 200 MW could make the one-way transit to Mars in as little as 39 days, but generation of this amount of in-space energy isn’t currently anywhere near possible and would require both an advanced onboard nuclear reactor as well as super-efficient heat radiators. "
200 MW is a helluvalotta power! Disappointing to see it's so far off.
> The most recent tests of VASIMR have run at 200 kW and expelled ions at 180,000 km/h
Is this the power consumed by the device, or a measurement of the propulsion power created? It would be interesting to know the energy efficiency; i.e. what percentage of the input power is converted to thrust.
>"VASIMR (Variable Specific Impulse Magnetoplasma Rocket) is a helicon magnetoplasma thruster designed to provide a variable thrust profile, from low-specific-impulse / high-thrust to stupidly-high-specific-impulse / low-thrust. Specific impulse could max out at ~12,000 seconds, drastically higher than the roughly 2,000 s from current hall thrusters. VASIMR creates thrust through a multi-step process. First, it bombards a neutral gas with RF energy in helical waves to ionize the gas and create plasma (it can use multiple gases: argon, hydrogen, or even CO2). Then, it uses magnetic fields and an additional RF coupler to contain and energize the plasma to a superheated state (in the neighborhood of the temperature of the Sun’s core). Finally, a magnetic nozzle ejects the plasma at exceptionally high velocity. The most recent tests of VASIMR have run at 200 kW and expelled ions at 180,000 km/h (test fire video… or a blue party light being turned on, we’re not sure). A massively scaled up version running at 200 MW could make the one-way transit to Mars in as little as 39 days, but generation of this amount of in-space energy isn’t currently anywhere near possible..."
Thoughts: We need a functioning ITER -- in space...
Everyone is missing the fact that even if this technology was available 100 years ago, and worked just like we wanted, you could not get to Mars in 39 days. It would take about twice as long, because you have to turn the ship completely around half way to the destination and slow down pretty much for the same about of time it took to get to whatever velocity.
And Mars is a rock. I am sure there are astounding discoveries to be made, but resources would be far better spent fixing ourselves and what we've done to the planet before we cause our own extinction. Maybe we can do both, but let's not ignore the fact that we have major problems, and it is unlikely we'll ever find a better home than Earth.
sandworm101|5 years ago
http://spacenews.com/vasimr-hoax/
"Zubrin wrote in SpaceNews: “To achieve his much-repeated claim that VASIMR could enable a 39-day one-way transit to Mars, Chang Diaz posits a nuclear reactor system with a power of 200,000 kilowatts and a power-to-mass ratio of 1,000 watts per kilogram. In fact, the largest space nuclear reactor ever built, the Soviet[-era] Topaz, had a power of 10 kilowatts and a power-to-mass ratio of 10 watts per kilogram. There is thus no basis whatsoever for believing in the feasibility of Chang Diaz’s fantasy power system.”
Note the word used by spacenews: Hoax.
sobellian|5 years ago
If we want to get serious about exploiting the solar system, we'll eventually have to give in and embrace nuclear technology, whether something like VASIMR or a nuclear-thermal design like NERVA. We already routinely park 100MW+ nuclear reactors in port for our navy, why not consider civilian use for space exploration? We already know many ways to mitigate risk for the launch of nuclear material.
I think Musk, Zubrin, et al. analyze propulsion technologies from the perspective of how to enable a journey to Mars now. In that light, something like Raptor makes much more sense. You still need a chemical rocket engine to lift off from Earth or Mars, so in the near term a nuclear ion thruster just adds far too much complexity to justify its inclusion. Further, it's difficult to imagine SpaceX obtaining the political backing to put nuclear tech into space as a private company. This is also why Musk would rather power Martian propellant plants with fields of solar arrays instead of the much more mass-efficient space-rated nuclear reactors that NASA has been developing.
But imagine if we actually developed a Mars colony with millions of people. The logistics of seeding a colony on Mars with chemical thrusters already boggle the mind. Economics would basically forbid meaningful interplanetary trade unless we develop new technology with much higher specific impulse. It would be even more impactful than moving from air-freight to container ships.
Gibbon1|5 years ago
The problem becomes yes you can use a reactor or nuclear battery to power and ion rocket, which fuel efficient, very energy inefficient, and sloooow. Or you can use a nuclear rocket which avoids the need for a radiator by tossing your waste heat out the back end. Better fuel efficiency than a chemical rocket, can go faster, difficulty gamma radiation. Between those there isn't anything in between that makes sense because a high power thermal power reactor is too heavy.
ColanR|5 years ago
d_silin|5 years ago
Waste heat management for 200MW system in space is firmly outside the realm of present-day technology.
extrapickles|5 years ago
It really depends on the mass budget they have for that speed for if anything new needs to be discovered.
Florin_Andrei|5 years ago
Funny - in a lot of other technology sectors, that would count as pretty good efficiency.
RandallBrown|5 years ago
adwi|5 years ago
snake_plissken|5 years ago
sandworm101|5 years ago
155,200mph = 69,380 m/s
At 1g acceleration (10m/s/s) that is 6,938 seconds. 6,938 seconds is like 2 hours.
A ship that can sustain 1g acceleration continuously for periods measured in hours, that would indeed be an interplanetary drive. Sustain that for days/weeks/months and it will take us to other stars.
ashtonkem|5 years ago
badwolf|5 years ago
pinewurst|5 years ago
blakesterz|5 years ago
200 MW is a helluvalotta power! Disappointing to see it's so far off.
avmich|5 years ago
api|5 years ago
Also remember that space is not dark. Unless you are behind something you are always in daylight if you are near a star.
tectonic|5 years ago
elihu|5 years ago
Is this the power consumed by the device, or a measurement of the propulsion power created? It would be interesting to know the energy efficiency; i.e. what percentage of the input power is converted to thrust.
d_silin|5 years ago
peter_d_sherman|5 years ago
Thoughts: We need a functioning ITER -- in space...
natcombs|5 years ago
https://en.wikipedia.org/wiki/Nuclear_pulse_propulsion
The project Orion study anticipated a one-way trip could reach Alpha Centauri in as short as 133 years
jandrese|5 years ago
Animats|5 years ago
tectonic|5 years ago
catmistake|5 years ago
And Mars is a rock. I am sure there are astounding discoveries to be made, but resources would be far better spent fixing ourselves and what we've done to the planet before we cause our own extinction. Maybe we can do both, but let's not ignore the fact that we have major problems, and it is unlikely we'll ever find a better home than Earth.