[Herra Tohtori]

None of you fans could provide sufficient cooling to fusion powered flame war. Hopefully this one can:



 

[Jeff Vader]

I never played Descent and I'am still consider myself a FreeSpace fan.

then i've got news for you.......... you're not a fan.

Who are you to decide that?

... a better and more experienced and respected fan than you...

The logic here eludes me. Does this mean that if a person has never played Flatout, he can't claim to be a Colin McRae Rally fan?

[Flipside]

Guys, let's try to keep to the physics and not trying practical applications of exothermic reactions?

[redsniper]

practical applications of exothermic reactions

[Flaser]

i figure the hardest part of rocket science is keeping your engine from melting.

i think fission + ion is the way to go for now. by the time our magnetic technology reaches a level to make fusion viable, other propulsion technologies may become feasible, such as accelerating the interstellar medium. you could probably also use magnetics to contain hotter chemical reactions than could be achieved by most materials and cooling approaches used today.

forcefields are good for technology

I guess you haven't seen one of the VASMIR designs, have you?
That's a fission engine, that replaces the reaction chamber with a fission reactor. Simply put, you cool a conventional block of fissioning material with hydrogen and use the excited matter as propulsion.

Once again: every serious sci-fi geek/enthusiast should read project rho:
http://www.projectrho.com/rocket/index.html

It's THE REFERENCE, in laymen rocket/spaceship design; and happens to be 100% scientifically accurate and damn good read at the same time.

[Nuke]

i was reading about that engine yesterday actually. if it has gears does it have a clutch too?

anyway that was essentially what i was talking about. the list of theoretical ion/plasma engines is actually quite long, vasmir is just one among many. up till now most ion engines have a limit on the output of their power source and therefore also a limit on the size of your engine, so to speak. more power such as that from a nuclear reactor, would allow for ion engines to produce more thrust, run more efficiently/longer or both (or neither ).

not that you can plug a 10kw engine into a 100kw reactor and expect it to perform 10 times better. in all likelihood all you would do is fry your engine. but better space reactors, means more energy, means you can power more powerful engines. there are many theoretical drives that require much larger power supplies to operate than are currently available. im sure many engine concepts are still being tested in labs because their waiting for a better power plant to fly it with.

i recall visiting projectrho many times before, pretty cool site. i was skimming through looking for engines which make use of the interstellar medium, not necessarily "burning" it or storing it as fuel. but engines that can accelerate it through magnetic means and thus produce tiny thrust over the course of several decades without the trouble of carrying propellant on board. projectrho seems to be void of information on such an engine (probably because its too far off from convention).

[Flaser]

i was reading about that engine yesterday actually. if it has gears does it have a clutch too?

anyway that was essentially what i was talking about. the list of theoretical ion/plasma engines is actually quite long, vasmir is just one among many. up till now most ion engines have a limit on the output of their power source and therefore also a limit on the size of your engine, so to speak. more power such as that from a nuclear reactor, would allow for ion engines to produce more thrust, run more efficiently/longer or both (or neither ).

not that you can plug a 10kw engine into a 100kw reactor and expect it to perform 10 times better. in all likelihood all you would do is fry your engine. but better space reactors, means more energy, means you can power more powerful engines. there are many theoretical drives that require much larger power supplies to operate than are currently available. im sure many engine concepts are still being tested in labs because their waiting for a better power plant to fly it with.

i recall visiting projectrho many times before, pretty cool site. i was skimming through looking for engines which make use of the interstellar medium, not necessarily "burning" it or storing it as fuel. but engines that can accelerate it through magnetic means and thus produce tiny thrust over the course of several decades without the trouble of carrying propellant on board. projectrho seems to be void of information on such an engine (probably because its too far off from convention).

Project Rho mainly focuses on rocket designs that fulfill a high delta-v requirement. It's also a giant shrine to Stanislaw Lem and Robert Heinlein, both of whom proposed the first realistic nuclear rockets.

You got one thing wrong though: ion engines do have propellants, they typically use noble gases. They have very high specific impulse compared to other existing engine designs. Although their thrust is very low, so they can't act against a strong gravity field (high delta-v requirement); but once you're in orbit, you're halfway to anywhere, so you can simply accelerate perpendicularly to whatever grav well you're sitting in.

Once there, and once you actually want to stretch your legs, you need to be very prudent with your propellant. Hence, why NASA and everybody else is so interested in these ion engine designs.

If you're looking for pure propellantless designs I recommend the following designs:
-The Solar Sail is the oldest, and probably still our best bet for an interstellar mission (although it would take decades, the craft would reach .3 c, or a 1/3 of lightspeed which is nothing to scoff at).
http://en.wikipedia.org/wiki/Solar_sail
-Magnetic Sails are also another good propulsion, though their propulsion power drops a lot sharper outside the solar system than solar sails, while insystem they're a lot stronger.
http://en.wikipedia.org/wiki/Magnetic_sail

Nuclear engines, while not suited for interstellar missions (no propellant using engines is), produce the rare combination of being capable of both high specific impulse, and high thrust.
The reason why many are enamored with the design is, that these thing would be actually capable of lifting off Earth, going to another a planet, landing there, and once again lifting off. No other design can fill the insanely high delta-v requirement of such a mission.

[Nuke]

i knew that ion drives used propellant. its just the energy to drive said propellant is provided by a power system, and the output of that system has a positive effect on engine performance (or at least to the point where the mass of the system makes scaling up the power of the engine pointless). its just my last paragraph was thrown out of context (as far as that goes it belongs in another post all together). i was really trying to dig up the physics behind concepts such as the bussard ramjet with that one.

magnetic and solar sails are interesting as well. it actually seems absurd that were not using them already. solar sails would allow much longer duration missions, multiple missions, all with the expenditure of a single spacecraft. thats actually common practice. no mission has ever had its plug pulled simply because all the goals were met. if theres something more they can do with the craft, nasa is certainly gonna do it. why launch 3 probes when you can go 3 places with one probe?

[Kosh]

solar sails would allow much longer duration missions, multiple missions, all with the expenditure of a single spacecraft.

I guess it is because there is no real willingness to make such missions happen. Invading other countries is more important than making sure some of our species gets off this rock.

[Herra Tohtori]

Well, if you think about it, it will be a "stars or bust" situation to humanity at some point. Meaning that at some point, we need to either lie down and die, or leave for a new solar system.

Even before that, Earth will grow too hot - Mars and the moons of Jupiter would offer some refuge for some time, but eventually Sun will die and that'll be the story of humanity, unless interstellar travel is developed. The stage where Earth will be rendered uninhabitable (oceans vaporize into the atmosphere) will happen as "little" as 0.5-1 billion years in the future. At that point, Mars will have pretty pleasant climate as far as temperatures are considered, but the atmospheric pressure would still be a big problem. Moons of Jupiter and possibly Titan of Saturn will be the last sanctuaries for life in solar system. Of course, living in Jupiter's radiation belts would be... interesting, to say the least.

But the gist of it is that in 4-5 billion years, sun will eventually expand to red giant and then either slowly wither away or blow it's outer parts into space as a planetary nebula. AT that point at least we need to have those colonization ships at ready - although preferably sending a lot of them away during longer period of time would be smarter than making them go at the same time as one huge rag tag fleet. All that about putting all the eggs in the same basket beer to the same bag and so forth, you know... Perhaps groups of five to ten ships would deal with the travel time better than single ships, as far as psychological, social and cultural effects of generations long space travel are considered.

As to how actually construct these hundreds or even thousands of ships for the humanity (even in lessened numbers from present), I would recommend carving tunnels, living quarters, storage space, fuel tanks, facilities to repair or manufacture any part needed in the ship's tech from raw materials, hangar for maintenance ships, fighter planes (who's gonna get into outer space without a fighter complement?! ) and of course transport ships to move from ship to ship in each group, a BIG greenhouse to make food with, in asteroids of sufficient integrity... and then slap some kind of engines on it's surface, as well as radiators for the reactors needed to offer energy for high pressure natrium lamps needed for the greenhouse(s).

Basically, a Rama of sorts, but possibly without the centrifugal gravity.


Meh, I'm rambling again. But it's strangely comforting that at some day, humanity will either have to at least try and get away from solar system or lie down and die. And knowing humanity, they will at least try, which will IMHO be the greatest adventure of humanity whether or not it fails or succeeds and to what extent. Who know's, perhaps a ship will reach a new habitable world... and they're gonna call it "Kobol"...

It's just a shame we won't be there to see it.

[Kosh]

Well, if you think about it, it will be a "stars or bust" situation to humanity at some point. Meaning that at some point, we need to either lie down and die, or leave for a new solar system.

I'm not willing to wait until the sun turns into a red giant. We can at least explore our solar system now. We have the technology. Propulsion? for long term missions a solar sail can work. Gravity? Simulated through rotating sections. Life support? Submarines can stay submerged for very long periods of time, why not use that kind of technology? Long term energy source? Until fusion becomes viable, we're stuck with fission. At least the waste can be dumped in space. So what's stopping us? I guess it just isn't "cool" anymore. The Apollo program proved that if we really want to extend our reach beyond low earth orbit, we can.

[Wanderer]

Radiation is kinda big obstacle. Well probably... As there have been very few manned missions that have gone further out into the space than just into the orbit its still kinda difficult to say.

Any mission that sticks close to the Earth is relatively well protected but if you go for prolonged period outside the protective EM field of the Earth you will be exposed to cosmic and - more importantly - solar radiation. Ofcourse assuming the ship is big enough you probably could power EM field generator strong enough to keep the crew safe or then plate the ship with lead panels... But that doesnt exactly help with the heat and weight problems of the said ship.

[Kosh]

But that doesnt exactly help with the heat and weight problems of the said ship.

Heat and weight in space don't really mean that much.

[Herra Tohtori]

But that doesnt exactly help with the heat and weight problems of the said ship.

Heat and weight in space don't really mean that much.

Yes, they do.

Heat, matters a lot, because you don't want to melt your ship with excess heat, and thus if your ship's equipment produces heat (which they do), you need some way to remove the heat from your ship. And in space the only way to do that is radiate it to space, and that means you need radiators on the outside of your ship. On the other hand, you will want to insulate the living quarters (and sensitive equipment that must be kept at constant temperature to work properly) of your ship as well as possible, because you will not want to waste any more energy than necessary to try and either cool them or heat them.

So, the thing is - if your ship produces enough excess heat to require a radiator, or possibly an array of them, that brings us to another if these important issues - weight. Or rather, mass.

You will want your spaceship to have as little mass as possible and as much payload in relation to the fuelled weight of the ship as possible. This is because reduced mass improves acceleration and it means that you can manage same kind of velocity changes with less fuel - or, bigger velocity changes with same amount of fuel.

This means that you can travel from, say, Earth to Mars using either less fuel or less time with a ship with reduced mass.


On the other hand, regarding human physiology, weight is an important thing to have as well. In case you didn't know, long term exposure to weightless conditions on the orbit has some serious adverse effects on the bone density and muscle mass of astronauts - that's because both bones and muscles (and ligaments as well) are adapted to take some amount of constant abuse, develope microfractures and minuscule tears, and while repairing them they maintain the tissue and even strengthen it when the abuse increases, which is why you feel sore after exercising, but in the end you'll get stronger, faster and more resilient to damage as your muscles and tendons get stronger and more durable, and your bones do the same.

Weightlessness removes most of the abuse that human body needs to maintain it's integrity. As a result, astronauts need a lot of active exercising to apply artificial abuse to themselves, because on casual life on zero-g they wouldn't get enough of it. Of course this has an impact on their productivity if they need to do anything else than sit and monitor the ship.

On even interplanetary travel, some kind of artificial gravity would be very much appreciated in the long term because it could keep the travellers able to, you know, stand on their own legs withotu breaking their femurs under their own weight.

[perihelion]

[edit] Drat, Herra beat me to it! [/edit]

Yeah, they do.  Weight especially is a big deal.  Ignoring for a moment the horrendous problem of getting something that massive into orbit in the first place, then you need enough thrust to move it around.  Even our next-gen engines that are just now coming into use will be severely taxed by "lead shielding."

Heat dissipation is another big one because you are completely dependent on radiant heat exchange.  Convection and conduction just don't exist up there.  You need much higher thermal differentials with radiant heat exchange to get the same Q-dot you'd get with the other two modes.  Again, you can't afford to have something really massive up there, so your heat dissipation system needs to be really light-weight and efficient.  Close in to the Sun (like where we are) it is a very challenging problem because you have so much heat coming in from the Sun, but even in shadow you still have to deal with heat released from your own equipment and people.

As far as space radiation (the cancer causing kind) is concerned, from what I've read, if the Apollo guys had been unlucky and been outside the van Allan belts during a solar flare, they very would very likely have died.  At the very least they would have gotten very sick.  There is no protection comparable to the double combo of the Earth's thick atmosphere and magnetic field.  The problem with setting up a comparable magnetic field aboard ship (aside from power considerations) is that it will not protect from all directions uniformly, and from some directions (north and south) it will not protect at all.  Electrostatic fields will only protect against particles of one charge or the other.

Honestly, the most promising idea I've heard so far involves strengthening humans themselves against the damage radiation can do.  I read an article just the other day about some guy at Rice who has been playing around with a nano-tube based drug that seems to be affording a good deal of resistance to radiation damage to mice.  http://www.sciencedaily.com/releases/2008/01/080128084415.htm

[Mustang19]

On even interplanetary travel, some kind of artificial gravity would be very much appreciated in the long term because it could keep the travellers able to, you know, stand on their own legs withotu breaking their femurs under their own weight.

Artifical gravity would be unecessary because space travellers aren't subjected to the stresses of gravity in the first place. The Russians have kept a guy in space for over a year. You can live fine in zero-G; the hard part is returning back to Earth.

As you said, it would be nice to have gravity during long voyages, but by the time we're talking about "even interplanetary travel" and artificial gravity, we'll have the technology to more easily solve the problem with biology. With use of growth factors, we could "force" the body to maintain muscle and bone mass in zero G.

[Herra Tohtori]

Heh, just insert the self-repair DNA code from Deinococcus badiodurans into human genome so that it actually works, and you got yourselves a space human!

By the way, if I recall correctly Van Allen belts are actually the areas of space where the charged particles (protons and electrons, mostly) guided by Earth's magnetic field end up being held - they need to go somewhere and since they are averted from Earth, they go there to hang, and during a flare/protuberance a lot more particles are released from the sun, and thus the concentration of the energetic particles in the Van Allen belts increases as well.

So I believe it's the other way round - had the astrounauts been in the Van Allen belt areas during a time when the particle winds from solar eruption reached Earth, then there would've been a lot of big trouble. But they wouldn't have had time to get cancer, they would have caught some serious radiation poisoning and ended up covering the insides of their ship with bloody vomit and diarrhoea.

A pleasant mental image indeed.

->Mustang19 - yeah, it's not a problem during the journey, but unless the astronauts are going to spend the remainder of their life up there, the journey itself would pretty much just suck all the way since they would need to dedicate a lot of mission time and effort onto exercises, whereas if there was an artificial gravity section, just moving about would offer a large portion of the exercise they needed.

[perihelion]

Re: Van Allen Belts, I don't think I was making myself clear.  I didn't mean outside versus inside the belts themselves, more like what side of the belts the astronauts would have been on.  Being inside the actual Van Allen Belts is not a good idea whether or not there is a flare because, as you say, that's where the charged particles end up getting trapped.  I may have been wrong in thinking this, but I was more thinking of the belts as defining the limit of Earth's magnetic field's influence.  As long as you are between the Earth and the belts, you should be fairly well protected.  Beyond those belts, the only shielding you get is what you take with you.

I could be wrong about the range of Earth's magnetic influence more or less ending at the Van Allen Belts.  It just makes sense to me if that's where the charged particles end up, beyond that point you aren't safe anymore.  If the Apollo astronauts had just been in open space during a flare, I don't know if the flux would have poisoned them to the point of death then and there or not.

The point I was trying to make is that in any interplanetary expedition or even just trying to get to the moon, you may as well be naked for all the protection our current technology affords.

[Admiral_Stones]

Our best bet is Gliese 581 c. First extrasolar planet with atmoshpere ever discovered.

Although one year is only 13 days (yes, 13 days for a full circle around the sun), temparature is estimated to -3 to +40 °C. Nice and comfy.

[perihelion]

I'd be more worried about flare time, personally.  At .073 AU from its sun, Gilese 581c is going to get a ****storm of x-rays at close range whenever the star flares.  And it will flare.  Gilese 581 is classified as a variable (HO Librae) based on past observations.  As a general rule, red dwarfs have significant oscillations in their output.  They aren't very bright to begin with, so oscillations that wouldn't be a big deal in a brighter, hotter star (like, say, the Sun) become more significant.

I'm not saying you couldn't make it work, but you'll weigh a bit more than twice what you are used to, and your primary will be rather punchy.