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Post by airc777 on Oct 13, 2018 2:49:27 GMT
But you can't slow down again once you get to your destination with a laser sail You can.
You need a two-part sail. Near the destination the sail separates and discarded part acts as a mirror reflecting the beam backwards to let you brake with the remaining part.
Oh, cool.
What do you do for Reaction control? I don't imagine gyros are going to keep a vehicle straight without being overwhelmed when an outside force is propelling it to high fractions of C. I'd imagine keeping a laser perfectly straight on a mirror moving away at 80% c while that mirror is reflecting at a secondary target moving away at 40% c with four years of signal latency is going to be difficult. Would you have to set up sections of the sails as shutter screens?
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Post by bigbombr on Oct 13, 2018 6:49:20 GMT
But you can't slow down again once you get to your destination with a laser sail You can.
You need a two-part sail. Near the destination the sail separates and discarded part acts as a mirror reflecting the beam backwards to let you brake with the remaining part.
Or you could use a magnetic scoop/magsail to slow down with drag and collect remass from solarwind that you use for terminal slowing down.
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Post by AtomHeartDragon on Oct 13, 2018 11:08:49 GMT
You can.
You need a two-part sail. Near the destination the sail separates and discarded part acts as a mirror reflecting the beam backwards to let you brake with the remaining part.
Oh, cool.
What do you do for Reaction control? I don't imagine gyros are going to keep a vehicle straight without being overwhelmed when an outside force is propelling it to high fractions of C. I'd imagine keeping a laser perfectly straight on a mirror moving away at 80% c while that mirror is reflecting at a secondary target moving away at 40% c with four years of signal latency is going to be difficult. Would you have to set up sections of the sails as shutter screens?
OTOH it's all going to be rather predictable.
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Post by The Astronomer on Oct 13, 2018 12:46:11 GMT
The easiest way to go interstellar is solar sail. There, I fixed that for you. Seriously, building a ship capable of operating for a few hundred or few thousand years is plausible, but with solar sails made from conventional matter you'd need hundreds of thousands of years to get to the nearest star; it's vanishingly unlikely you could keep a ship functional for that duration. Interstellar space is just beyond heliopause, roughly 100 AU away. We have a spacecraft in interstellar space right now, and another following, so I don't see why we can't make some solar sails and send them near the sun to pick up speed and then escape the system all while being functional, too. I believe laser sails need to be really, really reflective to survive the laser.
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Post by AtomHeartDragon on Oct 13, 2018 13:07:26 GMT
There, I fixed that for you. Seriously, building a ship capable of operating for a few hundred or few thousand years is plausible, but with solar sails made from conventional matter you'd need hundreds of thousands of years to get to the nearest star; it's vanishingly unlikely you could keep a ship functional for that duration. Interstellar space is just beyond heliopause, roughly 100 AU away. We have a spacecraft in interstellar space right now, and another following, so I don't see why we can't make some solar sails and send them near the sun to pick up speed and then escape the system all while being functional, too. I believe laser sails need to be really, really reflective to survive the laser. You can always defocus the laser up close (and you should anyway - what's the point of trying to burn a tiny hole in your sail while letting almost its entire surface do nothing?) but you can't focus the Sun far away.
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Post by The Astronomer on Oct 13, 2018 13:12:27 GMT
Interstellar space is just beyond heliopause, roughly 100 AU away. We have a spacecraft in interstellar space right now, and another following, so I don't see why we can't make some solar sails and send them near the sun to pick up speed and then escape the system all while being functional, too. I believe laser sails need to be really, really reflective to survive the laser. You can always defocus the laser up close (and you should anyway - what's the point of trying to burn a tiny hole in your sail while letting almost its entire surface do nothing?) but you can't focus the Sun far away. That's exactly what I was thinking when I stare into it. Still, wouldn't it take quite a big reflective sail to not get burned anyways? Just how massive is a square meter of laser sail, anyways?
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Post by AtomHeartDragon on Oct 13, 2018 13:35:08 GMT
You can always defocus the laser up close (and you should anyway - what's the point of trying to burn a tiny hole in your sail while letting almost its entire surface do nothing?) but you can't focus the Sun far away. That's exactly what I was thinking when I stare into it. Still, wouldn't it take quite a big reflective sail to not get burned anyways? Just how massive is a square meter of laser sail, anyways? You can always adjust your beam intensity as well. You don't need your laser sail to be sturdier than your solar sail - if anything you might even be able skimp on mass if you have the right (meta)material benefitting from the fact that you will only have to reflect single band of wavelengths (although Doppler effect will stretch it up a bit) and not the entire blackbody spectrum.
The bottom line is that your beam fluence doesn't need to be higher than Sun's at any point, but out far it will be able to keep up as long as you can focus your lasers on the sail. Inverse square law is much less kind on the solar propulsion.
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Post by The Astronomer on Oct 13, 2018 15:24:20 GMT
That's exactly what I was thinking when I stare into it. Still, wouldn't it take quite a big reflective sail to not get burned anyways? Just how massive is a square meter of laser sail, anyways? You can always adjust your beam intensity as well. You don't need your laser sail to be sturdier than your solar sail - if anything you might even be able skimp on mass if you have the right (meta)material benefitting from the fact that you will only have to reflect single band of wavelengths (although Doppler effect will stretch it up a bit) and not the entire blackbody spectrum.
The bottom line is that your beam fluence doesn't need to be higher than Sun's at any point, but out far it will be able to keep up as long as you can focus your lasers on the sail. Inverse square law is much less kind on the solar propulsion.
I see, so laser sails will overtake solar sails as the 'easiest' way to go interstellar over time.
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Post by anotherfirefox on Oct 13, 2018 15:36:22 GMT
I suggest you stellaser: using outer layer of soon as lasing medium. You can focus sun.
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Post by AtomHeartDragon on Oct 13, 2018 16:11:40 GMT
I suggest you stellaser: using outer layer of soon as lasing medium. You can focus sun. Or just make Shkadov thruster - for when you don't want to leave your solar system when travelling to other stars.
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Post by The Astronomer on Oct 13, 2018 17:27:07 GMT
Kerr suggested using Mars' atmosphere for laser in ToughSF discord server. We could get a planetaser.
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Post by vegemeister on Oct 13, 2018 18:16:06 GMT
But you can't slow down again once you get to your destination with a laser sail You can.
You need a two-part sail. Near the destination the sail separates and discarded part acts as a mirror reflecting the beam backwards to let you brake with the remaining part.
That'd require the discarded part to be an optically flat mirror with attitude control. It might end up a lot heavier than the basic aluminized kapton sheet you could use otherwise. Plus, depending on how long the braking takes and the ratio of the masses of the main ship and the discard mirror, it might travel very far from the main ship and have to be very large to control beam divergence.
Something else that might work would be to make a close pass to the destination star and capture with a solar thermal rocket, taking advantage of the Oberth effect and high intensity radiation. Then, use the planets in the destination system to gravity assist your periapsis out of the fire.
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Post by newageofpower on Oct 13, 2018 21:48:32 GMT
That'd require the discarded part to be an optically flat mirror with attitude control. It might end up a lot heavier than the basic aluminized kapton sheet you could use otherwise. Plus, depending on how long the braking takes and the ratio of the masses of the main ship and the discard mirror, it might travel very far from the main ship and have to be very large to control beam divergence. Something else that might work would be to make a close pass to the destination star and capture with a solar thermal rocket, taking advantage of the Oberth effect and high intensity radiation. Then, use the planets in the destination system to gravity assist your periapsis out of the fire.
One of my regrets is that you don't post more. Every time you open your mouth I feel like I'm filled with more insights. Back on topic, you could turn on a magsail to increase drag against the interstellar medium. This isn't at all effective unless you're travelling at a high % of C, but it's one of the least mass intensive ways to drop from 90% C to 30% C, letting you use your AM/Fusion torch remass to complete the burn. Once your ship arrives, you can set up laser beaming and relay stations for deceleration, letting the two star systems send ships to each other without using any remass at all!
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Post by Fgdfgfthgr on Oct 13, 2018 22:02:49 GMT
Kerr suggested using Mars' atmosphere for laser in ToughSF discord server. We could get a planetaser. How can that even work? Planet atmosphere is so different to a laser pump. Does the infrastructure require will turn the red planet into a death star?
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Post by The Astronomer on Oct 14, 2018 2:03:04 GMT
Kerr suggested using Mars' atmosphere for laser in ToughSF discord server. We could get a planetaser. How can that even work? Planet atmosphere is so different to a laser pump. Does the infrastructure require will turn the red planet into a death star? Ask the person themselves, I just heard it from them and wanted to share
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