Baffalo wrote:Alright, I was reading through the thread "Replace Voyager with the Enterprise-D" and I got to thinking. The entire purpose of the Warp Core is to channel the flow of matter and anti-matter to create a stream of high-energy plasma. Ok, fairly good so far. Got that. The problem I'm having is, if Starfleet uses matter and anti-matter, then why the hell does any ship ever need to stop for fuel EVER?
Because:
1) Deuterium fusion isn't actually drastically less energy-intensive than antimatter reactions; it's about an order of magnitude less. Since deuterium is free and antimatter can only be made under unusual conditions with heavy machinery, it pays to let the ship use deuterium even if that means needing more fuel (measured in kilograms).
2) Antimatter is itself a fuel that has to be manufactured. The ship can only carry so much, and when it runs out it loses its ability to use the warp core.
3) Storing antimatter is inevitably harder than storing mundane deuterium. Therefore, even if antimatter is ten times as powerful a fuel source, kilo for kilo... you end up having to spend ten (or a hundred, or a thousand) times more mass and bulk to
store a kilo of antimatter. Therefore you can't store infinite supplies of antimatter fuel aboard ship.
4) Warp travel is handwavy but may be
very power-intensive. Even a large supply of antimatter might be run down over the course of hours, days, or months at high warp speed.
Well... the problem with that is that antimatter is, inherently, not going to be found floating around. Now, here on Earth, we produce our own antimatter in two ways: nuclear reactions (where small anti-particles are released and destroyed) and particle accelerators. Now, naturally, the one that's produced naturally decays so fast that it's essentially unusable, while the other requires a huge facility to produce. Regardless, by the 24th century I'm sure they've got ways of storing enough anti-matter after producing it that they're not absolutely pressed for that at any given time.
So my question is, why does Voyager make it a point of stopping for fuel? Surely they can obtain enough in transit to keep going. And if they have the fuel covered, and they have replicators, then why would they need to stop or even limit fuel consumption? Is this just a plot device? Or is it a legitimate concern?
They don't have the means to manufacture antimatter on their own aboard the ship, presumably.
Even if they did, they might have to stop moving in order to do that. They may not be able to pour more antimatter into the warp core's storage while simultaneously running the warp core.
Or they might have the means to synthesize antimatter fuel, but not as
fast as they can consume it... in which case sooner or later the tank runs empty and they have to refill it before they can keep going.
biostem wrote:Don't Fed ships have secondary fusion reactors that actually provide a lot of the "everyday" power that the ship needs? If that is the case, then couldn't they focus on collecting usable matter, (deuterium), and converting it into antimatter as needed?
Sure. In which case they'd cruise through space collecting deuterium, and stop when they run out of antimatter. Then they'd make more antimatter from the deuterium they collected, using the fusion reactors to power antimatter synthesis. Then they'd get moving again for a while, then stop... lather, rinse, repeat.
Any opportunity to stop by a convenient gas giant (or existing Delta Quadrant fuel depot) could be desirable in that case. Because you could use such a pit-stop to collect a massive amount of deuterium
fast, and use it to synthesize an equally massive amount of antimatter.
Let me make up some numbers to illustrate. Suppose the ship's sustainable "collecting fuel" cycle involves spending 100 hours at warp and, say, 400 hours at impulse trying to scrounge up enough fuel for the next 100 hours at warp, via the Bussard scoop.
Now suppose you can spend 100 hours refueling intensively at a gas giant, which is a much higher-density fuel source. Then you travel for 1000 hours at warp continuously, while collecting further deuterium for the next 200 hours with the usual Bussard scoop technique. In 1300 hours of travel in this way, you've covered about
five times the distance you could otherwise have covered using your normal fuel cycle.
[In this case I am assuming that stopping for fuel at a fixed location is fifty times faster than scrounging it from interstellar vacuum, which seems pretty reasonable. I am also assuming the ship's "bottleneck" for producing fuel is its ability to scavenge deuterium, not its ability to synthesize antimatter, which may not be true.]
Anyway, if we make certain assumptions, the fuel stops could be very helpful and save a lot of time.
Voyager would still have the ability to 'scrounge' fuel, and Starfleet ships could still use their scrounging ability to travel normal distances inside the Federation in a pinch... but for a long range cruise it really helps if you can pick up fuel on the way in convenient, accessible locations rather than foraging
en route
SpottedKitty wrote:Found it — yes, the TNG Tech Manual, near the end of the chapter on the warp drive. The Bussard collectors only work to replenish the deuterium supply, there's an extra big, heavy gadget* that takes a deuterium feed and great big gobs of power in one end, and puts out a trickle of antimatter at the other end. And it's horribly inefficient; the book quotes ten units of deuterium needed to create one unit of antimatter.
Do the collectors work at impulse power? They
should since it's totally possible to scoop up hydrogen from interstellar space at sublight speeds.
Baffalo wrote:Now for everyone's favorite equation, E2 = (m0c2)2 + (pc)2
Since we don't know at what velocity the atoms are traveling at when they impact, and since they would be negated simply by impact, we can safely say that p (the momentum) is zero, leaving us with E2 = (m0c2)2, or E = m0c2.
Plugging in our numbers, we get 5E19 J/s = m0(2.99792458E8 m/s)2, leaving us with m0 = 5.56325E2 kg/s, or 556.325 kg/s.
What you have just done is calculate the amount of deuterium that needs to be converted to energy. Deuterium fusion is, more realistically, limited to an efficiency such that you get, oh... about 10^15 joules per kilo of fuel. So the actual amount of fuel required is going to be something like a hundred metric tonnes of deuterium per second to supply the full 10^20 watt power output of the ship.
Alternatively, suppose the ship's power supplies are based on using antimatter at high efficiency. Theoretically, matter/antimatter fuel can get up into the range of... I don't know, 2*10^16 joules per kilo of fuel (half-and-half) would be about 20% efficiency. Roughly. In which case you need 'only' about 5000 kilograms of fuel per second to supply 10^20 watts, or 2500 kilograms of antimatter and 2500 kilograms of matter.
If you can turn 10 kilograms of deuterium into one kilogram of antideuterium, this translates into burning 2500 kilos of deuterium per second directly, and 25000 tons to produce the antimatter to run the reactor... and you
still come out ahead, because matter/antimatter reactors are converting mass into energy twenty times as efficiently as a deuterium reaction.
If matter/antimatter reactors are more efficient, this calculation becomes even more skewed in favor of using deuterium to power antimatter converters rather than using it to power a fusion reactor.
If fusion reactors are made more efficient, then the calculation shifts more to favor using the deuterium in the fusion reactor. But frankly that requires that we just drop the whole concept of
enthalpy. Deuterium fusion just
can't liberate more than a few percent of the total mass-energy of the fuel because you started with four nucleons and end with four nucleons; all you're actually doing is liberating some binding energy that ties those nucleons together.
At 14K, elemental hydrogen is a solid. Most likely, it is stored as a solid "powder" or small individual grains, with a density of 0.086 g/cm3, or 8.6E-5 kg/m3. Diving 5.56325E2 kg/s by 8.6E-5 kg/m3 gives us 6.46889535E6 m3/s.
Someone please double check me and make sure I didn't screw this up. Because that's for both feeds combined.
Denser forms of hydrogen storage exist in principle. One friend of mine likes to play with the idea of metallic hydrogen, which is quite dense, although potentially explosively unstable. But hell, it's Star Trek, having lots of stuff on the ship that explodes when you hit it too hard is par for the course.
Eternal_Freedom wrote:Napoleon the Clown wrote:The name actually kinda makes sense, from the perspective that antiparticles are the opposite charge. I don't recall the quark make-up of antiparticles relative to regular particles, but the name isn't completely absurd. At least, no more so than most of the other technobabble.
Easy enough: an anti-proton is anti-up-quarks and one anti-down quark. An anti-neutron would be two anti-downs and one anti-up. The charges on the individual quarks/antiquarks are just reversed, it doesn't change the number and type, otherwise you'd have a different particle entirely.
Note: That is going off what I remember from my 3rd year quantum physics module, I may not be correct.
Under the Standard Model, flipping quarks into antiquarks violates the conservation of "baryon number," which is a quantity as fundamental as charge. On the other hand, Star Trek is clearly predicated on the assumption that the Standard Model is very, VERY incomplete as an explanation of what is and is not possible in the universe.
Borgholio wrote:Here's the problem I had with the "always looking for fuel" thing. Converting matter to anti-matter uses a shit-ton of fuel for the fusion reactors. So while it might be hideously inefficient, if they had enough fuel there's no reason why they couldn't do it. So why don't they go find a nebula or a gas giant and start siphoning? A nebula could have several solar-masses worth of hydrogen in it. That would be plenty for them to stock up on.
Nebulae are low-density and it could take a long time to stock up enough deuterium to fill up their tanks. Gas giants are much denser sources and it's less work to fill up the tank. And if you're
really lazy you just cruise up to someone else's filler station and barter for existing, pre-refined starship fuel...