Hard Sci-Fi Space Drives

[citizen]

I've been constructing a Hard Sci-fi universe recently, so I've been putting a lot of thought into advanced drive technologies. So I wanted to lay out some of my ideas, and see if anyone else has anything to add.

The upper limit I've been looking at (and one that is considerably more advanced than my Universes technology) is the Photon Drive. Basically a big laser stuck to the back of the ship providing thrust.

Assuming a Spacecraft displacing 1000tons, roughly the same as a World War II submarine, you need ~12,000,000 Newtons of thrust for 1G of acceleration, which works out to 3.6PetaWatts of power or 240 times the power used by the Human world in 2004. Assuming an Antimatter reactor power source you'd need 0.04Kg of Matter/Antimatter per second, or 76,032Kg (~76Metric Tons) for 22 days continuous thrust, or a round trip to Pluto (assuming Pluto is at it's minimum distance to Earth of ~2.6Billion Miles). It also assumes 100% efficency which is far from possible.

The actual drives I'm looking at for my Universe are Fusion based. Fusion plasma at millions of degrees Kelvin is contained by magnetic fields, and Hydrogen is flash heated, much like in an NTR-GAS rocket but hotter, by the fusion plasma. It's my thinking that this arrangment would produce (with suitably powerful magnetic fields) much more thrust than straight MC-Fusion drives, but with similar exhuast Velocities.

Any thoughts, other drive types?

[ClaysGhost]

I think there's most of what you might want to know here.

[citizen]

Originally Posted by ClaysGhost

I think there's most of what you might want to know here.

Thanks. The original version of my post actually included a link to that page though, before I shortened it! More looking too see if anyone is willing to discuss these ideas.

My idea for a Gasous Fusion Core Rocket doesn't seem to appear there though, maybe because I'm not looking hard enough, maybe because no one's really thought of it before, or maybe because it simply wouldn't work.

[Armondikov]

Hard Sci-fi.... are you some kind of masochist?

I've always thought that when you go for hard sci-fi or realistic you end up moving away from fancy theoretical drives since as soon as you start plugging in figures to real equations you get totally impractical results. It's probably best to let the craft coast through the interplanetry transport network.

[citizen]

Originally Posted by Armondikov

Hard Sci-fi.... are you some kind of masochist?

It doesn't leave behind red welts like whips and chains do.

Originally Posted by Armondikov

I've always thought that when you go for hard sci-fi or realistic you end up moving away from fancy theoretical drives since as soon as you start plugging in figures to real equations you get totally impractical results.

What do you mean? If you mean you can't flash across a solar system in five minutes, or have hour long battles with nuclear weapons then yeah, but I don't think that's necessarily 'impractical'. I could just as easily say "where's the fun in imagining a future that is impossible?". For that matter, I've never understood the whole Anime: spaceships that sail on Oceans, and fighter planes that turn into robots thing, but some people seem to like it .

[JustinDixon]

Some form of wormhole drives could work in theory. Also some that distort space-time could be considered Hard Science.... but that's iffy. If you want real hard science, go for interplanetary transit networks (pretty much highways through the solar system) and what not.

[juanxer]

Orion's Arm has a lot of post-Singularity (which complicates things but it's OK really) hard SF tech detailed in its FAQs. Ships drives and powerplants are here: Ships

Some interesting ideas for "plausible" energy sources and such come from Stephen Baxter and other hard SF authors: beyond fission and fusion as a way to liberate transitional energy, and antimatter reactions, you would have GUT (Great Unification Theory) drives in which one somehow reproduces the transtion from the original conditions of the Big Bang's "pure energy" decaying into electrons+positrons+photons+neutrinos and back hyperhot soup to ordinary matter, shedding loads of energy in the process or something like that. It gets really exotic when Baxter suggests things like supersymmetry drives, or using sails of space discontinuitie for displacement. Supossedly, these guys know what they are talking about (many of them are real Physics scientists), even if their ideas are as practicable as trying to turn a neutron star into a torus for playing spacetime games.

If you have the opportunity, get Baxter's "Vacuum Diagrams", an anthology of short stories spanning the timeline of his Xeelee saga. Lots of hard SF ideas there.

Also, get Robert L. Forward's "Undistinguishable From Magic": a real gem providing a continuum of ideas from the practicable to the far out ones.

The Photon drive looks a bit problematic to me as a "top of the chainfood" one: it looks like any onboard drive based on expelling mass particles wins against a massless particles one. Lasers for propulsion seem better employed as stationary sail pushers. For fast propulsion drives (as opposed to slow and steady don't worry be happy ones such as ion drives), wouldn't the best matter-energy conversion always win? GUT (if doable), Matter-Antimatter or fusion? Anyway, I should add that most of times these drives, even GUT ones, are used to heat ordinary matter into eyectable gas or plasma (for in-system travel, ice is the usual source of fuel).

[Zardoz]

You think in some kind of zero point space energy source (aka vacuum power ) ??
We can think that is roughly in some weird physics theory's, a source of power in an future.

This give to your a nearly unlimited range (no need resupply fuel to generate power, but will need yet some kind of propellent).

Add to your calculations that to 74Tons of fuel used in five power to the engines (which M/AM reactor), that the ship need to spit some kind of propellent (and if the exhaust it's a very high speed and big amounts .. you wil need a lot more of propellant fuel)

[citizen]

Originally Posted by juanxer

Orion's Arm has a lot of post-Singularity (which complicates things but it's OK really) hard SF tech detailed in its FAQs. Ships drives and powerplants are here: Ships

Thanks, and thank you for your reading suggestions, I'll take a look .

Originally Posted by juanxer

The Photon drive looks a bit problematic to me as a "top of the chainfood" one: it looks like any onboard drive based on expelling mass particles wins against a massless particles one. Lasers for propulsion seem better employed as stationary sail pushers. For fast propulsion drives (as opposed to slow and steady don't worry be happy ones such as ion drives), wouldn't the best matter-energy conversion always win? GUT (if doable), Matter-Antimatter or fusion? Anyway, I should add that most of times these drives, even GUT ones, are used to heat ordinary matter into eyectable gas or plasma (for in-system travel, ice is the usual source of fuel).

The Photon drive has the lowest thrust per unit energy, but the highest exhaust velocity, meaning lowest propellant requirements and thus longest range. Chemical rockets have some of the highest thrusts possible, but use up huge amounts of fuel, so have very short range.

Originally Posted by Zardoz

Add to your calculations that to 74Tons of fuel used in five power to the engines (which M/AM reactor), that the ship need to spit some kind of propellent (and if the exhaust it's a very high speed and big amounts .. you wil need a lot more of propellant fuel)

The point of the Photon Drive is that it uses photons generated by the powerplant to propel the ship. You don't need to carry propellant, because your basically being pushed by the photon force of an incredibly powerful lightbulb

[juanxer]

I get the criteria, then . I was wondering: for a photon drive, has it got to be laser light or can it be non coherent light? It is just that laser emitters have a rather poor energy input/laser output ratio, so there must be some really big powerplant and heat dissipation requirements (I don't remember if the Atomic Rockets page studied the issue)

Vacuum Energy looks very attractive, but there is the possibility of it not being as astoundingly powerful as it has been suggested to be. Some more conservative estimations seem to make it rather irrelevant as a power source (by the way, Forward showed in his book some ways of extracting a minuscule amount of vacuum energy using the Casimir effect, not really that useful but...).

As that Baxter book goes from GUT drive to space distortion onwards, I guess the Forward one would be far more useful (it lists most traditional hard SF Newtonian drives and proposes some practical designs for each. It addresses wormhole construction and such, too, but always covering the "practical" construction issues. Also, each chapter contains a short fiction story illustrating its theme.

Forward died last year, I think. He was a member of one of those NASA idea teams. Such a loss!