Magnetoplasma drive could make Mars transit take 39 days? | Hacker News Reader

Magnetoplasma drive could make Mars transit take 39 days?

orbitalindex.com

65 pointsblach88 comments

https://www.spaceflightinsider.com/conferences/vasimr-plasma...

"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.

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.

This boils down to theoretical vs applied. The OP approx. stated that we're basically 1/100 of the way there and this theoretical drive is currently impossible to implement.

I've changed my career path because of these problems. I was a Math Major and now EE. These are the problems we need to be focusing on. Instead of using outdated and faulty technology from the 1960s.

IMHO, humanity is an inflationary species (for lack of a better term). We want to grow, spread and thrive. We aren't using a horse and a buggy. We (mostly) aren't shipping big chunks of ice around the world. We've made massive innovations happen and we should continue. It's nice that VASIMR is trying to push the envelop. Hopefully more of us can join together and tackle these big problems together.

>>> The OP approx. stated that we're basically 1/100 of the way there

But we really aren't 1/100th of the way. That's like saying a 90miles/gallon car is 1% of the way to getting 9000 miles/gallon. Getting from one to the other cannot happen through incremental improvements. It requires totally different, as yet unexplored, areas of science.

>> That's like saying a 90miles/gallon car is 1% of the way to getting 9000 miles/gallon.

Yeah. I think that would be apt to say.

If you're able to do some napkin math about the sheer amount of R&D to get to the other 99%, start a company ASAP because that is the billion (maybe trillion) dollar question.

Getting there is different, yes, which was entirely my original point. I'd rather not shoot an idea down before we've even started. Let's stop with the nitpicking and actually build. Incremental is probably the only way that we will get there. Think like a builder, not a complainer.

Will getting the other 99% look like how we got 1%? Of course not and if it does...then we're actually very close to a major breakthrough because we have a lot of the auxiliary technology already fleshed out.

Every journey begins with one step and we already have made a few steps. Now onto making many more.

I love that we have ideas and theoretically a combination of technologies that can take us to Mars and beyond in a short timeframe. The way I see it is that while chemical rockets are un-economic, as you point out, for a large scale colony, what humanity needs is a demonstrated need and a catalyst to get us to explore the more exotic propulsion technologies like nuclear + ion drives + hydrogen.

Chemical rockets will take us from 0 to 1, and the economics will drive the next technological development to take us from 1 to n. I think it will work the same way as when telegraph wires were exploding around the US and we realized copper resources were a limiting factor. Did we give up and say "well, let's wait for the next technology"? No, we kept building the wires and other industries sprouted up to handle the demand (notably recycling).

> The basic idea is, let's attach a nuclear reactor to an ion engine.

Why do you need to attach an ion thruster to a reactor, if you can turn the reactor itself into a thruster? https://forum.kerbalspaceprogram.com/index.php?/topic/151286...

Amazing site linked a bit down in that post:

http://www.projectrho.com/public_html/rocket/enginelist.php

http://www.projectrho.com/public_html/rocket/enginelist2.php

http://www.projectrho.com/public_html/rocket/enginelist3.php

RD-600: Soviet bimodal GCNTR on page 2 is the one from that discussion

Totally agreed re: the necessity of doing what can be done [i]now[/i] within existing regulatory frameworks.

If & when we get round to allowing more exotic stuff to be used I like the look of this one.

https://www.nasa.gov/pdf/718391main_Werka_2011_PhI_FFRE.pdf

In all fairness modern naval reactors like the A1B are pushing more like 700 MW thermal (unclassified, probably higher) and float in what amounts to an infinite heatsink of excellent liquid coolant. Of course lifetimes and decades of experience produce the A1B, The First Torchship is not going to do as well.

The real problem for a spacecraft isn't generating 700 MW of thermal heat, which is pretty small and light, but radiating it away continuously. The ISS EATCS radiates about 70 KW and each radiator is in the thousands of sq ft and thousands of pounds. So four more digits would be tens of millions of sq ft and millions of pounds, VERY superficially. However the reactor probably doesn't have to be optimized for human temps, so maybe ten times to hundred times better? It would be quite large at any rate.

There are certain engineering optimizations you make if you have an infinite liquid heatsink like a naval reactor vs incredibly expensive cooling like a space reactor. If you're willing to boil sodium your condenser can radiate a lot more per sq ft than an ammonia based refrigerator for ISS HVAC. That's a little far fetched but the VHTR/HTGR design goal was a cool 1000 C, so the radiators can run quite a bit hotter and smaller than ISS HVAC systems.

Space is an infinite heatsink if, and becomes an actually very good one once your radiators can reach 2000K+

Not a problem for a glowing plutonium plasma.

Here is a quote on one project from sixties:

> a spaceborne electric powerplant dubbed EU-610, with an electric output of circa 3.3x106 kWt, specific power 0.7x105 kWt/kg/sec (sic), relative mass 18.7 g/kWt, length 10000 mm.

Space acts as a thermal insulator most of the time because radiation is the only means for a spacecraft to get rid of waste heat. Thermal radiators also only work if they can be oriented that they don't face the Sun.

The exhaust of a nuclear thermal rocket isn't waste heat. The heat from the reactor that heats everything that is not propellant is waste heat. Getting that heat to radiators without cooking people or melting/weakening load bearing structures is the challenge with nuclear reactors in space. On Earth we use literal tons of water and air to the job.

Yes, the trick there is that only MHD coils, and few chunks of tungsten carbide will be anywhere close to the plutonium jet, and most of thermal radiation will be emitted to space.

You'll need some electricity and that's a mere heat generator.

The Carnot heat engine efficiency is not nice at a cold side of 2000K and the working fluid will be a problem. Maybe gaseous helium or argon to reduce leakage, I guess.

The only place I found EU-610 was a Russian thermal rocket. Which is kind of like saying all you need for a coal electrical plant is a lightweight pile of charcoal.

Its a different type of technology, sorta like the difference between burning in a cast iron stove to boil tea, vs using a microwave oven to boil tea.

Sounds like https://en.wikipedia.org/wiki/Nuclear_lightbulb

If we are in the 700 MW range, we can go with an NTR as well and solve the cooling problem with propellant.

You gotta send the wagon trains West before you build the railway.

Physics, logic, and economics preclude interplanetary trade.

There's no realistic space propulsion that would enable interplanetary trade to be in any way economically feasible. It's economical to ship finished goods and even raw material around the surface of Earth because it costs less than a dollar per pound by sea, rail, or road. Air freight is more expensive at around two dollars a pound. SpaceX's best price to LEO (Falcon Heavy) is $750 a pound. Just to LEO. Even if it was ten times cheaper it would still be almost forty times more expensive than air freight.

Even with magic super efficient interplanetary transport the surface-LEO portion of the trip makes it ridiculously expensive. To get a Martian colonist to LEO would cost (at our magic $75 a pound) $11k just to get their body to LEO. Assuming the water and air they need can be recycled with 100% efficiency the food for the 40 day Mars trip would cost another $13k.

If every colonist needs a ton of material to support them on Mars (far too low of a number) you're looking at $175b per million colonists. That's with a bunch of magic hand waving and completely unrealistic pricing. What in the shit are Martian colonists going to produce in any quantity that will pay down the $175b capex?

For what it's worth Musk believes that Starship will bring a >10x improvement for $/kg to LEO. Not throwing away your second stage will do magical things. At any rate a Martian colony would be mostly self-sustaining with trade being a relatively small fraction of gross domestic product (like with international trade right now). On planetary scales, moving trade from 0.01% Gross Martian Product to 0.1% would more than justify the development costs for such an engine.

I think we can safely say that we are very far from 1 Martian colonist, let alone 1e6. I think we would outperform expectations to set up a very small research station by the end of the century at great expense on the Martian surface. So there's clearly a lot of magical thinking going on here. If we allow for some amount of aspiration, there are a few ways to provide a return on long time scales (much more than 1 century, with capex far exceeding $175B just looking at the cost of staging the necessary propellant in LEO):

- Such a base will have a propellant depot in a much shallower gravity well than Earth and a far thinner atmosphere. This is a huge comparative advantage for launches into deep space.

- Necessity breeds ingenuity. A Mars colony would likely generate many advances useful to Earth that do not make sense to pursue terrestrially. Think hydroponics, insulation, radiation shielding, so on and so forth.

- There are plenty of completely desolate locations on the Martian surface - ideal locations for radio telescopes, neutrino observatories, and other hyper-sensitive experiments.

- ??? (We're trying to predict centuries ahead, after all!)

It wouldn’t make much economic sense to ship stuff back down a gravity well if you could make it locally.

On the other hand it might actually become cheaper to ship stuff to Earth orbit (even LEO) from Mars, simply because of the delta-v cost.

Interplanetary trade starts to make a lot more sense once a good chunk of your economy is happening outside the gravity wells of planets.

Presumably the people of the future will be much richer then we are. I think there's an idea that over time wealth doesn't grow in an absolute sense - it does. Shipping good overseas makes sense now in ways it didn't 100 years ago not just because shipping costs have fallen but also because incomes have gone up.

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.

Cooling is hard in space. It is hard and expensive to get good power to weight ratios.

There's a lot of hard problems in space, though. We've solved a few of them - enough, at least, so that talking about large nuclear reactors in space should not be dismissed as a hoax.

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.

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.

> It is 60-70% efficient

Funny - in a lot of other technology sectors, that would count as pretty good efficiency.

True, but radiating 30-40% of your waste heat isn't that easy.

Any reasonable ways to recapture?

Could you use the waste heat to boil something and then spray it out the back as extra reaction mass?

Yes, but what? You have to lift that mass to orbit. What mass boils off with greater energy than, say, mass that combusts?

You don't necessarily need to lift that mass to orbit for interstellar flight.

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

That's how nuclear thermal rockets work. Boiling and spraying is going to be much, much higher thrust than what you're getting out of the electric drive but the spray will be going much slower so the amount of boilable propellant you carry with you will end up being the limiting factor in how fast you can do. And at that point you might as well forget about the electric part.

Now, since you you can be boiling pure hydrogen rather than the water that comes out of a chemical rocket you can make the propellant faster. But you're limited in temperature by what your reactor can take without melting so that only buys you a power of 2 or so in efficiency.

I wrote a series about how the different types of rockets compare starting here: http://hopefullyintersting.blogspot.com/2015/03/rockets-some...

That's just reducing the effective exhaust velocity of your engine. Rocket equation says you will run out of propellent [your "something"] faster than you would like.

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.

Also importantly, you have to slow down at the other end.

If your ship can only handle 1G of acceleration, would that not also mean that it could only handle 1G deceleration as well? That means starting to slow down halfway to your destination.

I think it would be more like you time your arrival with the conjunction of some gas giants in the destination solar system and aerobrake multiple times to get your speed low enough so you can aerobrake on your destination planet.

Bringing enough fuel to decelerate the same way you accelerated isn't usually practical, inflating your rocket by 15x its original size or more.

One of my pet peeves about sci-fi is how ships jump out of FTL into a perfect orbit around a planet. The concept of temporal dampeners is laughable even after suspension of disbelief to allow for FTL.

Sci-fi-grade engines are always fun. If you want to jump straight into a stable orbit, just add the right velocity component to your exit point. Or select a synchronous orbit.

Any sci-fi-grade navigation computer can do that.

Even a Geo orbit is an orbit. I guess you could drop out at a Lagrange point.

Of course depending on hour your Sci-Fi FTL engines work you could build up speed by stopping up high in the gravity well, let the planet accelerate you to orbital velocity, then jump sideways into an orbit once you're moving fast enough.

Or you can just use the automatic preset that puts you in a stable orbit depending on the distance from the surface you chose. The default is synchronous (a.k.a. "standard orbit").

These functions are a hard requirement for passenger transportation anyway because you need to match orbit with the station you are docking with. Protocol is to jump to a random position a couple light seconds from the port, get authorization, then short jump to your assigned docking exit point.

I guess it comes down to the details of your fictional FTL drive. A lot of times normal space momentum is not maintained in FTL, and gaining normal space momentum requires conventional rockets where delta-V is hugely expensive in terms of mass and volume.

I don't remember any sci-fi story with a jump drive mentioning this issue. There is one book, IIRC, Cassini Division, where a devastating attack is carried out by dragging one end of a wormhole at high speed to capture icy asteroids and launch them at a high velocity from the other end against a planetary target.

I think you should check your math again.

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.

I double checked, because I originally thought you were wrong, but it looks like you're essentially right.

32mi/s * (5280ft/mi) = 168,960 ft/s

168,960 ft/s ÷ 32.17405 ft/s^2 = 5,251.4371053691s

5,251s ÷ 60 s/min ÷ 60 min/h = 1.45hr

How long do you need to accelerate at that pace to reach C? 299,792km/s / .01km/s => 29 million seconds? ~335 days?

I'm assuming a lot of things would go wrong as you get closer to C...

Or go right. Time dilation would start working in your favor. You might get there, and back, within your lifetime. Of course everyone on earth would be long dead.

Micrometeors and radiation would be the major problem. Also, it's not just time dilation that would help. At relativistic speeds, space contracts quite noticeably in the direction of travel, so the actual distance you need to cover diminishes as well.

That's because you won't be locally faster than light. You may cover 4 light years in one, but only because those light years will be much smaller from your point of view. You'll never "feel" faster than light.

I think you may have misinterpreted what I said. I didn't claim that you'd feel like you were covering the distance faster than light. I was saying that as you go faster (relative to your destination), space contracts ahead of you so the distance becomes shorter than it would if you were moving slower.

However, remember that accelerating at 1G for more than a scant few minutes is beyond the capabilities of modern rocketry.

Heh many thanks, you are correct. Somewhere in there I divided something incorrectly.

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.

If this existed I would expect it would do something similar to The Expanse where they "flip and burn" to slow down coming towards the target. On the plus side, your craft could have decent "gravity" for most of the whole trip.

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.

But usage on smaller, uncrewed probes could be much closer.

How much thin film PV is that? There's no wind and the solar constant is a lot higher in space even further from the sun.

Also remember that space is not dark. Unless you are behind something you are always in daylight if you are near a star.

The linked article also makes a comparison with the ISS solar arrays, which provide 120kW of power. They're not the most efficient panels out there, but it's hard to make up three orders of magnitude.

On Earth a commercial solar panel produces around 150W per square meter peak. I don't think you can improve this by more than an order of magnitude. Solar power drops off with the square of the distance to the sun. 200MW is a lot of solar panels.

Not by a factor of ten, but you can get 47.1% of the sunlight (which at 1 AU with no atmosphere is 1360 W/m^2), or 640 W/m^2.

Even then, 200 MW is a square 560 meters on each side.

It's a lot of solar panel. A quick search gives us a figure of 220 watts of power per square meter of space based solar panel. This would mean a 200MW solar collector would need to be almost a million square meters in size. For reference that would be a square the length of 155 NYC city blocks on each side.

Hmm... or maybe some smaller panels plus a really enormous and very very thin reflective collector for concentrating solar. Keep in mind that things can be very thin in space.

It would still weigh a lot though, and heat would be a major issue. You wouldn't want to melt the solar panels.

This would require someone much more knowledgable to determine if it's feasible.

Edit: I wonder if you'd get some amount of solar sail effect in addition to the plasma rocket? Of course this would help you one way and hurt you the other way.

A million square metres is one square kilometre. It could be built but it would be heavy. A circular sail with a radius of just over 600 metres would do it.

wouldn't a million square metered be a megametre and not kilometre?

no. 1000m * 1000m = 1000000m^2 or 1 km^2

> A quick search gives us a figure of 220 watts of power per square meter of space based solar panel. This would mean a 200MW solar collector would need to be almost a million square meters in size. For reference that would be a square the length of 155 NYC city blocks on each side.

200MW/(220w/m2) gives us an area of 1,000,000m^2, a square 1000m on each side.

(side note: a NYC block isn't a very good length reference - they vary[1] from 250ft to 750ft depending which direction you're measuring. So the square would be 4 to 12 blocks on each side)

[1] https://streeteasy.com/blog/how-many-nyc-blocks-are-in-one-m...

That's if it's illuminated by the sun. Blast it with a 500MW space-based laser and you'll up the tempo.

If we're talking of this kind of efforts, why not to discuss this - https://toughsf.blogspot.com/2019/10/the-expanses-epstein-dr... . Seems in the realm of physics, with some more impressing results...

Yeah this sounds cool. Essentially you could design a large spacecraft and put a fusion reactor in it (we will have viable, positive yield reactors soonish). It should be possible then to power a fusion drive as well by building a sort of "half-open" fusion reactor chamber into which we dispense some of the plasma without any pressurization. It should essentially cause a massive explosion, that if somehow controlled by magnetic fields, should yield an enormous forward thrust.

Technically, does it even matter how fast we eject? Shouldn't relativity allow us to reach speed of light with any positive thrust velocity? If the speed of the shuttle was of any concern, that should directly invalidate relativity, since passengers would suddenly not perceive any acceleration anymore, even though nothing about the spaceship and its physical reaction has changed.

To my understanding of physics, there is almost no amount of thrust that would actually propel us to the speed of light, in reality. The energy costs alone would simply be too enormous.

"Folding space"/"Warping space", or shrinking the space in front of the craft while expanding the space, would seem to be the only theoretical way to achieve speeds that not only would match light speed but could surpass it and not break the laws of physics as we understand them. The drive Alcubierre proposed in the 80's, I think... maybe the 90's. I'm not sure when. A Spanish mathematician or physicist who was a fan of Star Trek.

EDIT: My understanding of physics is pretty minimal. I'm more than happy for someone to correct me and explain what I got wrong. This type of stuff is fascinating.

Alcubierre is a Mexican physicist, not Spanish.

Whoops, sorry =/ Like I said, my understanding of this stuff is very surface. Thank you.

It's actually that there is no amount of thrust that would propel you to the speed of light - no 'almost' about it.

From the perspective of an outside observer, a constantly-accelerating spaceship will approach the speed of light, but never quite get there. This will happen regardless of the level of thrust.

Alcubierre drives are pretty sweet - the only trick is they seem to require negative mass [0]... at least they've gotten down the requirement from a negative Jupiter mass to a mere -700 kg!

[0] - https://en.wikipedia.org/wiki/Alcubierre_drive#Mass%E2%80%93...

That's cartoon physics.

Even without relativity, the ejection velocity matters. To get the same change in momentum, you need to eject more mass if you have a lower ejection velocity. That means that you have to carry more mass to eject. And that means that, to accelerate that mass, you have to eject more mass. And so on. It just becomes really unworkable really quickly. (This is called the "rocket equation".)

As for the rest of your second paragraph: Look into how relativistic velocity addition works.

One would have expected a narrative published in the last decade could have featured a more felicitously named phlebotinum.

> 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.

At least 60%.

>"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...

Using nuclear bombs for propulsion was estimated to make it to Mars and back in 4 weeks. First time I heard of this, I thought it was a joke.

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

I would take the figures from Project Orion with a grain of salt. It was very much a cocktail napkin exercise.

You still need to carry reaction mass. It just gets pushed out the back faster. It's another variation on the nuclear rocket idea.

If you're into this sort of thing, we write about nerdery like this every week in The Orbital Index :)

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.

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