At relativistic speed, atmospheric braking would improve the ship into a cloud of plasma.
Relativistic Spaceship
171–180 of 500 posts
Re: Relativistic Spaceship
#172Earlier quoted context omitted.
One gee over the course of months is insane . Even if you converted the entire "fuel" reaction mass directly into momentum, you're still carrying tens or hundreds of thousands of tons of fuel for any remotely habitable spacecraft. And no engine has perfect mass conversion. Matter-Antimatter has been simulated to be maybe sixty percent efficient, fusion is around 17%, nuclear pulse propulsion a surprising 7%, fission…
What if you didn't carry the fuel? Use stationary lasers from your starting point to power your journey half way until you lasers from your destination to slow your craft down.
That's the drive of the eponymous generation ship in Kim Stanley Robinson's Aurora. It sends a mirror ahead of itself, then the Sol-Mercury lasers bounce off the mirror, back on the ship to slow it down.
I could see the light spacecraft with their matter-antimatter engines laying down "lightways", like railroads in the old west. Once a lightway is established, then it's much less of a big deal to get from system to system. Apart from the tens of thousands of years in subjective time, of course.
Re: Relativistic Spaceship
#173Earlier quoted context omitted.
Well then, it's easy: Just always face the exhaust in that direction! It's not rocket science!
> always face the exhaust in that direction! It's not rocket science! You don't see a problem with trying to accelerate with two exhaust streams at 180º to each other?
What if the front one is only a small fraction of the thrust at the rear? Would that be enough to "clear the path". Surely it would cost some efficiency but it may beat he alternative
Re: Relativistic Spaceship
#174Earlier quoted context omitted.
Every proton would have the energy of a baseball. It's bananas. Granted, space is really empty, but it's not that empty, somewhere around a hundred atoms per cubic meter. Your ship might look like a very, very long shooting star. Probably dialing the speed down a touch would be worth it for whatever your shielding material is, but who knows? We're talking miracle engines here. I think in the "Valkyrie" ship-on-a-stri…
> Every proton would have the energy of a baseball I wonder if you could capture that energy and use it to generate thrust. Most of the energy is coming from your thrust so it'd be a lossy process however if you're able to capture all of the energy then there won't be anything left to damage the ship.
Isn't this kinda like mounting a fan on your car's roof to charge the battery? You have accelerated your spaceship to 0.995C (or whatever) and now you are encountering space dust at a phenomenal rate. Some of that dust is moving away from you, some of it toward you, some of it is at rest. On average it's all just sitting there unaware that your vessel is about to smack into it. The energy is in the difference between your speed and the particle's. If you try to harness it, you slow down.
(I'm asking genuinely here. My analogy might be wrong because it's too classical!)
Re: Relativistic Spaceship
#175Earlier quoted context omitted.
Or stopping. It takes the same amount of time to slow down as it did to speed up. Presumably, you'd have to rotate 180° so you are now thrusting in the opposite direction. So at the speeds you've reached to get there in 20 years (ship time), you'd just race on by.
> takes the same amount of time to slow down as it did to speed up Assuming you're going somewhere, you can use atmospheres and gravity to slow down. Decelerating should take less time than accelerating in practical contexts.
That is doable for "normal" speeds, not one where you accelerate 1G for twenty years, reach relativistic speeds that make you travel for hundreds of thousands of light-years in merely 20 years ship time
Re: Relativistic Spaceship
#176Earlier quoted context omitted.
Of all the dangers associated with spaceflight it's a pretty interesting concept to add "lasers at the origin shut off for whatever reason" and "lasers at the destination never turn on / are misaligned / turn on too soon / turn on too late" to the list. Not sure I'd want to be in a spacecraft careening through the cosmos with no realistic way to slow it down.
There is also the question of how you get the lasers to your destination in the first place.
Send a mirror ahead, bounce the beam back toward the ship to push it backwards. Loses a lot of efficiency, though. Laser propulsion, a lot of the thrust is coming from ablation of the surface.
Re: Relativistic Spaceship
#177Great visualization of the unintuitive nature of special relativity. It's kind of mind blowing to realize that if we could accelerate our spaceship at a mere 1G continuously, we could visit the center of the Milky Way in under 20 years (spaceship time), totally do-able in a human lifespan. Of course 27900 years would have passed on Earth, so you wouldn't be able to tell anyone about your vacation.
Could use such a ship as a time machine (well, that only goes one way).
The Forever War novels have this as a key plot point, if you're interested in that sort of thing.
Re: Relativistic Spaceship
#178Great visualization of the unintuitive nature of special relativity. It's kind of mind blowing to realize that if we could accelerate our spaceship at a mere 1G continuously, we could visit the center of the Milky Way in under 20 years (spaceship time), totally do-able in a human lifespan. Of course 27900 years would have passed on Earth, so you wouldn't be able to tell anyone about your vacation.
It does not take much more years to the edge of the visible universe.
Re: Relativistic Spaceship
#179[dead]
Re: Relativistic Spaceship
#180Earlier quoted context omitted.
Every proton would have the energy of a baseball. It's bananas. Granted, space is really empty, but it's not that empty, somewhere around a hundred atoms per cubic meter. Your ship might look like a very, very long shooting star. Probably dialing the speed down a touch would be worth it for whatever your shielding material is, but who knows? We're talking miracle engines here. I think in the "Valkyrie" ship-on-a-stri…
I’d like to see a map of the known universe visualizing atomic density on a log scale. I’d never seen “a hundred atoms per cubic meter”, but it’s always been my intuition that, without some quite interesting shielding, you couldn’t make it anywhere near the speed of light. And on the other hand, I’ve seen claims that “space is really big” as you mentioned; but that claim has always seemed dubious.
100 atoms per cubic meter is on the lower end of typical densities in the interstellar medium. It can get many orders of magnitude denser than that.
Outside galaxies you have better chances of surviving high speeds. The intergalactic medium is only 1-10 particles per cubic meter in the web of gas we call the warm–hot intergalactic medium, and possibly less outside of that.