re: Teen builds working nuclear fusion reactor in Memphis home

TigerstuckinMS, which current fusion project do you think has the most promise?

But we're down to "fusion within the next 10-15 years". I came across one article that really drove the "carbon free" point into the ground. Well no shite, we can't build a device that creates a sustained hydrogen reaction, what makes you think we'll get to the point of fusion helium? Good thing those people wont be around when the sun starts producing carbon.

Real life Dexter’s lab? The real concern is his sister self detonating his la-bor-a-tory.

Don’t buy it. Check out the prices on vacuum pumps needed to do what they are talking about.

quote:

---

I suppose you could use the hydrogen generated in a fusion reaction to propel the craft

---

A fusion reaction consumes hydrogen. It doesn't generate it. Hydrogen nuclei are fused into helium which releases a lot of energy.

quote:

---

Well that’s not entirely where the benefit is. I suppose you could use the hydrogen generated in a fusion reaction to propel the craft, although you’d still need an oxidizer in a vacuum to gain real benefit of exponentially greater thrust in space.

---

That's not quite how they'd use it for propulsion. The hydrogen nuclear fuel would be fused in the reactor to generate heat, just like it would on Earth. The heat would be used in some way to generate electrical power for the spacecraft.

For propulsion, the fuel itself wouldn't be thrown overboard, it would be fused and the heat used to vaporize the propellant. That propellant would then be ejected overboard to push the spacecraft. No matter how you want to change your velocity in space, momentum transfer is REQUIRED, whether it be by throwing something overboard or by letting light hit big sails or whatever you can think of. No matter what the power source for propulsion is, Newton's first and third laws are still in effect. No momentum transfer, no changing course or speed. Something has to be thrown away from the spacecraft or something has to hit it.

The benefit from a nuclear propulsion system is that no oxidant is used because you're not expanding the material you're throwing overboard by burning it; you're expanding it via the energy released in the fusion reactor. This means that instead of a big hydrogen tank and a big oxygen tank, you just need a big hydrogen tank. If you can expand the hydrogen sufficiently by itself, it's WAY more efficient as a propellant than if you burn it in a rocket and use the exhaust. So, for every pound of propellant you lift into orbit, you get more change in velocity out of it with a nuclear propulsion system. In addition, oxygen is about 16 times heavier than hydrogen, so in the same volume, you can store about 16 times more molecules of hydrogen, so you can pack more propellant into the limited volume you have for storing propellant. The tradeoff is that the system won't produce the same level of thrust as a chemical rocket, though it is more efficient. So, it won't be strong enough to lift a spacecraft off a planet, but for maneuvering in space when you have the luxury to accelerate relatively slowly by throwing less material per second overboard over longer periods of time, it's hard to beat the efficiency of nuclear propulsion.

Another benefit is that any liquid that can be vaporized can be used as a propellant. Physics dictates that some are better than others (lighter molecules tend to make better propellants, which is good because they're expensive to lift), but any material that can be vaporized and ejected out of the thruster would theoretically work, making collecting gas in space to use as a propellant possible (if not technically difficult). You collect the gas, you use the fusion reaction to power the compression of it to a liquid to store it in your propellant tanks, then you vaporize it and throw it out the back when you need to maneuver. It's not like a rocket engine that requires a very specific set of propellants mixed in just the right way to not blow the frick up.

quote:

---

Thanks for elaborating. The simple point is we’re talking about incrementally increasing speed over extremely vast distances. Even with nominal levels of thrust you’re looking at an exponentially drastic cut in travel time as there is no force actively working to slow down your forward momentum.

---

Precisely. It's an exciting possibility for long voyages THROUGH space, but not really useful for getting INTO space.

quote:

---

electrocuted by the 50,000 volts of electricity he uses to warm the fusion reactor’s plasma core

---

That electric bill though

quote:

---

who was funding his hobby?

---

His dad. I’d say the expenditure has a higher chance of paying off down the road than the thousands of dollars travel ball parents sink into the pipe dream their kids will become a pro.