3 ms·

Beamed propulsion gets around the rocket equation, but trying to beam energy to something receding at exponential speeds doesn't sound that much easier. It woul

by lutorm 15y ago

Beamed propulsion gets around the rocket equation, but trying to beam energy to something receding at exponential speeds doesn't sound that much easier. It would pose an exponentially decreasing target, so to get around the diffraction limit you'd need an exponentially increasingly large collimation mechanism.

drostie 15y ago
Well that'd be a nice thing about relativity: from the point of view of the beamer, of course they're receding at a constant distance and their surface area decays like 1/t^2. ^_^
stcredzero 15y ago
Beamed propulsion gets around the rocket equation, but trying to beam energy to something receding at exponential speeds doesn't sound that much easier. If you're making a mathematical argument, be sure to do the math. Nothing's going to be receding at >exponential< speeds. (It would be nice if we could do that trick.) to get around the diffraction limit you'd need an exponentially increasingly large collimation mechanism. Yes, this gets pretty freaking huge. Robert Forward worked out the mathematics for this: http://en.wikipedia.org/wiki/Solar_sail#Interstellar_flight http://en.wikipedia.org/wiki/Solar_sail#Interstellar_flight Change targets to Proxima Centauri, use magsails to decelerate instead of jettisoning the outer mirror, and the power and lens requirements go down by a lot. I suppose your point would be that they remain freakishly huge. True, but if humanity continues to progress into the solar system, it should be feasible for the much larger and more advanced economy.
- lutorm 15y ago
  be sure to do the math. Nothing's going to be receding at >exponential< speeds Yeah, my bad. Momentary loss of order-of-magnitude sense. Speed will go as t, distance as t^2, so solid angle subtended as t^-4. That's still pretty rapidly shrinking, though nowhere near exponential of course.

by lutorm 15y ago

drostie 15y ago

Well that'd be a nice thing about relativity: from the point of view of the beamer, of course they're receding at a constant distance and their surface area decays like 1/t^2. ^_^

stcredzero 15y ago

Beamed propulsion gets around the rocket equation, but trying to beam energy to something receding at exponential speeds doesn't sound that much easier. If you're making a mathematical argument, be sure to do the math. Nothing's going to be receding at >exponential< speeds. (It would be nice if we could do that trick.) to get around the diffraction limit you'd need an exponentially increasingly large collimation mechanism. Yes, this gets pretty freaking huge. Robert Forward worked out the mathematics for this: http://en.wikipedia.org/wiki/Solar_sail#Interstellar_flight http://en.wikipedia.org/wiki/Solar_sail#Interstellar_flight Change targets to Proxima Centauri, use magsails to decelerate instead of jettisoning the outer mirror, and the power and lens requirements go down by a lot. I suppose your point would be that they remain freakishly huge. True, but if humanity continues to progress into the solar system, it should be feasible for the much larger and more advanced economy.

lutorm 15y ago
be sure to do the math. Nothing's going to be receding at >exponential< speeds Yeah, my bad. Momentary loss of order-of-magnitude sense. Speed will go as t, distance as t^2, so solid angle subtended as t^-4. That's still pretty rapidly shrinking, though nowhere near exponential of course.