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Old 12-19-2011, 09:24 AM
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Originally Posted by eskercurve View Post
Yeah, as I said, there's LOTS of issues with interstellar travel.

You hit the nail on the head re: the energy it takes to accelerate as you start experiencing relativistic effects. As your mass increases, of course you need more energy to accelerate.
Agreed. As the energy requirement needed to actually achieve light speed approaches an infinite amount, it boggles the mind to think how it could be stored. Even though particle accelerators can fire protons at almost the speed of light, it's very different issue with individual particles than it is for a complete spacecraft. Even at that, the particles in the accelerators still don't reach the speed of light.

Newtonian and relativistic effects start to break apart when you get closer, but we can still approximate their effects for small accelerations (like 9.8 m/s^s). So I don't think there's any issues there ...
If I may expand on that, as newtonian and relativistic effects start to break down, in a sense, everything in relation to the spacecraft itself would also start to break down. Our spacecraft would be no exception to the rule. If I may use the force of Gravity as an illustration, although the effect of gravity of an object certainly weakens with distance, it probably doesn't ever reach a point where the effect never exists. For example, both the Moon and the Earth have their own points of gravity. At a given point in space between the Earth and the Moon, beyond which is where the gravitational attraction of one gets stronger than the other. However, all that really means is that the gravitational attraction of the other weakens, but it never completely ceases to exist, otherwise, there'd be no tidal effects. Gravitational waves or attraction from everything mixes, even though the results from any given object may be weakened.

Same thing goes for newtonian and relativistic effects with regard to traveling at the speed of light. As you approach the speed of light, general relativity still applies, but is greatly weakened the faster you go and the effects of special relativity becomes more apparent. It's only when you achieve light speed that general relativity completely breaks down. You'd move from general physics and enter quantum mechanics. At best, you might wobble between the two but you might not be able to actually hit light speed in any meaningful sense. Frankly, I think the atoms of the spacecraft and any passengers, would probably begin to break apart.

The bigger issue is how do you avoid stuff along the way? We don't have any way of predicting what's out there that we have to protect against. If its dust or micrometeors, we can deflect those with a shield in front of us made of a very strong material, like steel. Formed at an oblique angle to all sides (so shaped like a cone) I'm pretty sure we could simply deflect them. But that's empty weight to lug around while accelerating ... making the journey harder.
Indeed, it could be a very big issue in terms of attempting to reach the speed of light. An oblique angled cone would be fine at much lower speeds, but I'm doubtful it would help at higher speeds. The reason is any contact from hitting foreign objects, whether dust or gasses, would generate enormous energy at the moment of contact. For an oblique nosecone to be useful, it would have to be able to increasingly stretch out to near infinity to be able to continue deflect. The precision of design for such a nosecone would have to be to allow for variations at quantum scales. Otherwise, you'd eventually run into serious problems with the need to deflect atoms and subatomic particles. Particle collisions would be inevitable, especially with something as large and massive as a spacecraft.

You are right in that anything we design would have to have at least one generation whose sole job is to upkeep the thing and likely will never see their destination.

That all assumes there isn't some way to travel in an interstellar fashion. I am somewhat heartened that in the middle of the 20th century, people thought supersonic flight was impossible. In fact there was a famous equation many thought would hold .. the incompressible fluid equation. But as it turns out, as soon as you get enough energy to go supersonic, it levels out more until you get going really fast, like re-entry fast (Mach 20)
I agree, design is everything. Although we can't definitively say that 'breaking' the barrier of light speed is impossible, I'm not sure it applies to the example of supersonic flight. That's because the sound barrier is related to the density of the atmosphere. There's no sound in space, but there is the spectral frequencies of light, which includes radio frequencies. Even so, commercial jets like the SST became a reality. Reasons for its failure to continue was because it was too noisy, there weren't enough airports to accomodate them, ticket prices were very expensive, and the costs for fuel exceeded the income generated (they weren't very fuel efficient). The amount of time they could save in terms of crossing the oceans was impressive, but not overly exceptional. I guess that depends on how a person looks at it though. In the end, the more traditonal aircraft proved to be much cheaper to fly. We frequently fly between Portland, Oregon and Bangkok, Thailand. Actual flight time is around 18 hours, not including a brief stop at Narita in Japan. Much longer than the SST, but still very impressive that you can actually travel across half the planet in less than a day.

The SST was killed because of economics. It wasn't efficient enough to make it worthwhile to continue as commercial supersonic transportation. The same thing may apply to travel at light speed. If it can ever be done, it may just be for bragging rights to show it's possible. But in the end, costwise, it could be unaffordable to continue with it as an alternative to slower means of transport around the cosmos.

Right now, the point behind the idea of interstellar travel is scientific. But ultimately, it's also to determine whether or not it's feasible for humans to eventually migrate, survive and thrive elsewhere in the galaxy. Cost to construct a less than lightspeed multigenerational interstellar spacecraft would be mind numbingly expensive, not to mention take an incredibly long time to build. It would most likely have to be an extremely long term project, perhaps taking hundreds of years to complete a single craft. But it is feasible. For a smaller spacecraft to accommodate fewer people, we'd need to resolve the issue of longevity or develop a way to provide suspended animation.

If light speed is to be considered a viable alternative, it may be that converting everything associated for such a flight would be converted (disassembled) into information, transmitted to a destination and reconstructed once there. If we could do that, the transmissions could also contain information to self-assemble once it reaches its destionation. While such a project would likely be the most expensive technological project ever, it seems like it would be more feasible than to build a fleet of multigenerational spacecrafts (habitats) the size of small planets. It's all science fiction to be sure, but it might be possible to do in the future.
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Old 12-20-2011, 05:57 PM
Location: Texas
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Another thing: Suppose it doesn't have an ionosphere?
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Old 12-20-2011, 11:26 PM
5,203 posts, read 8,205,785 times
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Originally Posted by Brian.Pearson View Post
Another thing: Suppose it doesn't have an ionosphere?
You'd get one heck of a sunburn, wouldn't you? LOL! If it's a terrestrial planet and has an atmosphere, then it probably has some kind of ionosphere. As I understand it (I didn't know this before), the Moon has an an atmosphere (or exosphere) and ionosphere of sorts, albeit, about a hundred million billion times weaker than that of the Earth. So weak, that for all intents and purposes, you might as well say it doesn't have one. It's not totally airless, but not enough to explain what appears to be an ionosphere glow. A recent explanation suggests that the glow may be from high altitude partices of Moon dust that have been charged.


ScienceCast: Mystery of the Lunar Ionosphere - YouTube
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