Science!! Fucking magnets, how do they work?

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scientia potentia est
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The Master_sl said:
Fuel isn't an issue for constant boost technologies, that is the point. Chemical rockets are fuel+reaction mass, rolled into one. Ion engines use solar power for fuel but still need to carry a reaction mass to ionize. But this makes a massive difference. You could carry enough reaction mass for an ion engine to last for years in the same amount of space as a few minutes of rocket burn. Solar sails use zero internal resources, but are not a good return technology (tacking against solar wind is slow). Comets in the Oort cloud have their tails pointing away from the sun still, plenty of solar radiation pressure out there. There are plans for nuclear drives going as far back as 1964 that use a vacuum (not hard to find in space) and are otherwise completely self-contained and will last for 30-40 years of constant operation. Heinlein wasn't kidding when he said if we wanted 1/1000 gee constant acceleration we could start later this afternoon (and he wrote that in 1980). There are things we know work that would just cost a fortune to build in space. That is why people are excited about the VASIMIR drive, because it is actually being tested in space. 39 days to Mars, parking orbit to parking orbit, including the flip over and slow back down maneuver.

Constant acceleration of any reasonable speed (I'll cap that at 1/1000 gee or higher, arbitrarily) is always the best choice for traveling in space. It just isn't, technologically, a choice we can make yet. Even if we have engineers who have been working on this for forty years telling us something will work, we need to get it into space and test it. Even to some place as close as the moon it'd be faster then a conventional rocket. Note the chart earlier that said Mars was 45 days away at 1/100 gee. The VASIMIR gets us to Mars in 39 days. So just a smidge faster than 1/100 gee acceleration.

Phoenix:http://www.honeysucklecreek.net/dss44/voyager.html

You might like that.
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How much reactant mass does the VASIMIR use per unit time to generate 5N from 200kw of electric power? I started to do some "how big would my spaceship be if I had an array of these... " type calculations and its impossible because I don't know the fuel consumption rate nor the weight of the engines. You got any leet beta infoz?
 
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The Master

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No idea about the VASIMIR specifically, that information hasn't been released. At best a theoretical number could be derived from some of their tests with different type of gases, but those were done more than five years ago and apparently marked increases in efficiency have been made. The term you're looking for is "specific impulse." Chemical rockets have an ISP of roughly 4.7 km/s, and need 2.6 kg of fuel per kg you want to take with you. The VASIMIR's hypothetical number would be... something like 300 km/s, needing 0.02 kg of reaction mass per kg you wanted to take with you.

Which wouldn't quite work for the Mars Direct plan at the suggested 39 days, but again there are gaps in available information.
 
Eomer

Eomer

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The Master_sl said:
Ion engines use solar power for fuel but still need to carry a reaction mass to ionize
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Small quibble here. If we're talking anything much past Mars or Jupiter's orbit, no, solar power isn't sufficient. It would have to be nuclear of some sort, like what powers Cassini, but bigger. When I was doing a bit of Googling/Wiki'ing on the RTG's use in Cassini, there was a paper somewhere that showed the progressive increase in solar arrays required to power it at various orbits. Around Earth the panels were tiny. Around Saturn the array was fucking massive, bigger than the ISS's arrays probably. Which makes sense, the Sun's light is 1/100th as powerful at Saturn as it is around Earth.
 
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The Master

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Solar panel efficiency is improving rather dramatically, but you are correct that going past Jupiter it'd be more practical to go nuclear for the power source. Or strategically station a number of giant arrays with lasers at various points in the solar system and focus the beam to a receiver on a given craft. Though if you were going to do that you may as well go with solar sails.
 
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The Master_sl said:
Solar panel efficiency is improving rather dramatically, but you are correct that going past Jupiter it'd be more practical to go nuclear for the power source. Or strategically station a number of giant arrays with lasers at various points in the solar system and focus the beam to a receiver on a given craft. Though if you were going to do that you may as well go with solar sails.
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The aversion to nuclear power on spacecraft (other than RTG's) boggles my mind.
 
Eomer

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I think there's legitimate concerns about launch failures, but yeah, it's not the HUGE DEAL that some make it out to be.
 
Void

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The VASIMIR is definitely an interesting concept and I hope it (and pretty much anything space related, really) gets the attention it deserves. If a 39 day Mars trip is really possible with something like that, then obviously we're talking about a significant change in the way we view space exploration/travel. My previous posts were basically just saying that, if it takes 5 years (just an example) for a constant acceleration system to overtake one launched with standard propulsion, the constant acceleration one isn't going to get much use for a long time to come. It's obviously still an extremely important technology, but only if something like the 39 day trip is actually a reality will it be pushed into prominence.

That being said, I hope with every fiber of my being that it is possible, and soon. I'm sure I'm too old and out of shape and worthless for a space program, but I'd give almost anything to set foot on Mars. Even to the point of knowing I'm not coming back.
 
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The Master

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The comparison was a constant acceleration ship overtaking something launched 36 years ago in 2.8 years... and that at 1/1000 gee acceleration. The VASIMIR is right around 1/100 gee acceleration. Any constant acceleration technology we get to work will open up the entire solar system.

Some reading for anyone who is curious about the Mars Direct trip.

http://www.adastrarocket.com/Andrew-SPESIF-2011.pdf
 
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The Master

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Haha, thanks for the avatar. If I ever set up a place where anyone can subscribe to my personality cult, I'll be sure to link it here. I'll try and post any relevant links for space travel in this thread though. It is something I've had a passion for since I was a kid.
 
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Well apparently it's just sensationalist journalism because we don't harvest that plutonium 238, we just make it so we just need money.

But it doesn't have to be that way. The required materials, reactors, and infrastructure are all in place to create plutonium-238. In fact, the U.S. government recently approved spending about $10 million a year to reconstitute production capabilities the nation shuttered almost two decades ago. In March, the DOE even produced a tiny amount of fresh plutonium inside a nuclear reactor in Tennessee.
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iannis

iannis

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That's my understanding. Plutonium is a manufactured substance, so "running out" is a bit deceptive. Stockpiles may be dwindling, but that's not exactly the same thing is it? I have to imagine that production is regulated by international nuclear treaty.

So it would seem the issue isn't plutonium at all, the issue is treaty obligations. That seems worse.
 
Cybsled

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Ya, we just aren't churning out plutonium 24/7 anymore like we did during the Cold War. Plutonium's primary usage, after all, is in nuclear weapons.
 
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Yea, we can totally do nuclear stuff if its for blowing people up, but for science? TOO DANGEROUS STOP IMMEDIATELY
 
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