"30 Days to Mars using Nuke Fusion Engine" Topic

Perhaps even less, if the 30 day round-trip figure is to be believed:

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It certainly would be a great advancement over the tech we have currently available for space travel.

Now all we have to do is make a fusion engine!

It would certainly cut down on the commute, and we would not have to wait for the periods every 18 months or so when the distances are "favorable".

What about the G's this thing is going to create going that velocity? Is the crew going to be able to handle it?

Gs have nothing to do with velocity. They're acceleration.

In any case, 0.1G acceleration is so massive that space in the solar system is effectively "flat." At about 1G constant, if you have a fuel reserve you can just point at Mars' current position and head that way, adjusting as you go.

John The OFM commented "Now all we have to do is make a fusion engine! "

Well, the Bussard people have a reactor idea that has all the maths going for it – it justs needs an investment from someone who isn't hung up on massive lasers ( yes, i'm looking at you, USDoE . . . ) en.wikipedia.org/wiki/Polywell

Read that one this morning. Very exciting idea.
I can only hope I live long enough to see it put into practice!

Wouldn't a fusion engine also operate as a power plant, creating nearly limitless clean energy at a low cost?

If so, they'll never let it happen.

What about the G's this thing is going to create going that velocity? Is the crew going to be able to handle it?

As said above, it's the acceleration that gives you the G-force, not the velocity. Physics 101.
I read an article about it that said that it would be a continuous but gentle acceleration. Halfway there, turn around and decelerate.

Wouldn't slow acceleration defeat the purpose to a certain degree since most current rockets use about 2/3 of their fuel just escaping the earth & sun's gravity (ie. the beginning of the trip is costliest full consumption wise)?

Perhaps we can get the Iranians to develop it.

Seems like they've had a lot of successful projects of late, and it's about time for them to recapture some of their former glory……..

Wouldn't a fusion engine also operate as a power plant, creating nearly limitless clean energy at a low cost?

Not necessarily. A "power plant" and an engine are not the same thing. In a fusion power plant the goal is not to produce a fusion reaction— we already know how to do that— but to produce a fusion reaction that generates more energy than the energy required to cause the reaction in the first place.
That's not the goal of a rocket engine. The goal of a rocket engine is high velocity ejection of as much exhaust mass as possible, sustainable over a long period of time, summed up in the technical term ISP (for specific impulse; which is how much thrust the rocket can produce per unit of mass expelled over time (I=Ve/G, when launching from Earth, where Ve= Exhaust Velocity and G= 9.81m/sec). The concern isn't the amount of energy put into creating the reaction, the concern is how much thrust the reaction itself can generate. Chemical reactions have a theoretical upper limit of ISPs in the low thousands; actual rockets used today have ISPs around 700. A fusion rocket would have an ISP ranging anywhere from 2,500 to 200,000 (in theory). If you can produce that level of thrust, you don't care that much that the "energy in" part is unbalanced, if all you're wanting to do is get to Mars quickly. Efficiency be damned— it's still better than chemical rocket fuel!

Of course, we could just do the Orion thing and not have to do nearly as much research, but the anti-nuke crowd would have a collective shorts explosion. Bet they have one over this idea, too.

What is "the orion thing"?

Orion was a plan for a battleship sized spacecraft powered by small nuclear explosions. I could work.

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That is the video, here is the text.

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Or we could just send robots instead of squishy human beings who have absolutely no business in space.

Wow, HarmonWard, I knew about the test, but had never seen the film of it!

Yes, the Orion Project was an 1950s/1960's plan by General Atomics to built a "nuclear pulse" spacecraft— one that could be used for a mission to Saturn and back (seriously), with a projected crew of 50 (or more). The craft would be accelerated through space by a series of 0.01 kiloton shaped nuclear fission explosions ("pulse units"), which would go off in rapid succession, with the force of the explosions striking a "pusher plate" on the rear of the craft, propelling it through space. Projected ISPs range from 2,000 to 6,000, with possible extensions to 10,000 to 20,000. (Fusion pulse units could go even higher — ISP 75,000 to 1,500,000!!!)

The video shows the "Put-Put" proof-of-concept test craft, powered by chemical explosives, which reached a height of 60m.

To get US DARPA funding for the project it had to have a military purpose, so the designers created a mock-up of the spacecraft as an armed battleship that could be launched into lunar orbit, and then act as the ultimate "you play nice or we paste you" missile platform— in no small part because no one would be able to shoot it down! Alas, JFK saw the mock-up and freaked out at the thought of it (assuming the existence of such a ship, if built, would provoke a war). He never looked back at the peaceful exploration capability of the original proposed craft. The project's death nail came with the adoption of the Outer Space Treaty, which forbade nuclear explosions in space (without considering either the irony of that— hello, heard of the Sun?— or the possibility of peaceful uses). Too bad, cause we'd be on Mars and beyond by now with Orion.

What about the G's this thing is going to create going that velocity? Is the crew going to be able to handle it?

It's not that high a g-force. If you could burn at 10m/s/s, that's a trip to Mars in ~96h.

15 days travel time is about .5g, if I've done the math right.

if i am not wrong, at a 1g acceleration(10m/s)… the crew would experience… well, a acceleration equal to earth gravity… so not only they could handle it, they would enjoy it! they would have artificial gravity both during acceleration and deceleration phases.
0.1g would mean a lower gravity than moon gravity.

The project's death nail

My, what a serendipitous brain glitch. My left brain was going for "death knell" (and was thinking that) and my right brain typed "nail." Or maybe, since "death knell" is a cliché, my right brain was thinking it and my left brain leapt up and said, "Oh, no, buddy, we're not gonna do the mundane expected thing," and slipped in "nail" instead. Or I could have been a complete doofus, and mangled two clichés together. Naw, I'll go with the second option, as it makes me seem more impressive.

Another great article on the Orion Project:
link

Dangnabbit. I still want to build this thing.
And I want my flying car, too!

Space:1959…the space race we should have had…DynaSoar, MOL, Gemini variants, purple-haired women on the moon…err, check that.

astronautix.com

Wouldn't slow acceleration defeat the purpose to a certain degree since most current rockets use about 2/3 of their fuel just escaping the earth & sun's gravity (ie. the beginning of the trip is costliest full consumption wise)?

Unless the engine has a TWR greater than 1 (and it won't) it's not taking off from the Earth's surface by itself anyway. Mostly likely the ship would be built from parts on Earth and then assembled in orbit (with the parts reaching orbit on conventional lift vehicles), much like the ISS. The expensive part, delta-V wise, is reaching orbit; once you're in orbit the delta-V to reach Martian orbit is really not all that high, and high acceleration isn't really an issue. The challenge has always been that conventional rockets have great acceleration but lousy fuel efficiency. Ion engines have great fuel efficiency but lousy acceleration. This fusion engine will in theory be decent in both areas, and that's what makes it so useful.

-Will

Once you're in orbit, you're halfway to ANYWHERE.

What will be interesting is if this fusion engine can actually do the single stage to orbit routine. A fission-thermal engine (Tom Corbett, Space Cadet style) is ideally suited for getting to orbit, except for the massively radioactive exhaust and unshielded reaction pointing directly at the ground.

Careful reading of the initially referenced article shows it is a pulsed thrust:

"Lab tests by Slough and his team suggest that nuclear fusion could occur by compressing a specially developed type of plasma to high pressure with a magnetic field. A sand-grain-sized bit of this material would have the same amount of energy as current rocket fuel, the team says.

To get this fuel to propel a rocket to Mars, the team says a powerful magnetic field could be used to cause large metal rings (likely made of lithium) to collapse around the plasma material, compressing it to a fusion state, but only for a few microseconds. Energy from these quick fusion reactions would heat up and ionize the shell of metal formed by the crushed rings. The hot, ionized metal would be shot out of the rocket nozzle at a high speed. Repeating this process roughly every minute would propel the spacecraft, the researchers say."

Ok, in principle this is using a theta inch magentic field to create a plasma with the temperature and pressure to create momentary fusion. The energy released by this fusion burst is turned into rocket thrust as the only opening for the plasma and vaporized metal (let's say lithium) is via the exhaust nozzle. So you get a brief burst of thrust that is followed a minute later by another brief burst and so on. It's a fusion version of the buzz bomb's pulsed jet. The mechanism for accurately placing the pellet, introducing the lithium metal bands, and creating another theta pinch magnetic field is left to the imagination. The Project Orion propulsion system used a pulsed thrust concept writ on a much larger scale and using a different thrust mechanism.

The last time I read about a fusion engine proposal like this the compressive force was to be created through a convergence of laser pulses creating simultaneous jets on the pellet's surface sufficient to compress it to fusion temperatures and pressures. See National Ignition Facility descriptions in Wikipedia or via Google.

Bottom line – way cool idea, but I'm not going to hold my breath on it happening in the next 25-30 years (assuming my life expectancy is 85-90). When I took fusion courses in my college days 40 years ago, the fusion promoters were predicting everything would be run by fusion by now as a functioning tokamak fusion power plant was right around the corner.

I somehow suspect that the Soviet scientists are laughing their butts off at the foolish Americanskii still trying to get an April Fools (or equivalent) joke to work.

Where is the equation they are using for this 30-days figure? 30 days at 1g constant? That would put you to Mars in 3 days roughly.

Of course, at that speed, hitting a grain of sand will probably equal something like 750 kj of energy – enough to shatter your spaceship. Need a shield of some sort out front methinks, heck a cloud of some debris might work.

Augustus, I used a brachistochrone equation that I pulled from Atomic Rockets (and then stuck into a spreadsheet so I can just tweak distances or thrust to get time).

I got a figure of 15 days travel time at .5g (assuming the average 225mil km Earth-Mars distance).

Requires one hell of a powerplant to do it, though.