Comments on: laser propulsion proposal https://habitablezone.com/2017/04/16/laser-propulsion-proposal/ Sat, 25 Apr 2026 16:17:27 -0700 hourly 1 http://wordpress.org/?v=3.3.1 By: RL https://habitablezone.com/2017/04/16/laser-propulsion-proposal/#comment-38888 RL Wed, 19 Apr 2017 02:44:52 +0000 https://www.habitablezone.com/?p=63405#comment-38888 But how good your pointing needs to be is set by your beam divergence... which, in turn, is set by your transmitted beam diameter. If your pointing is off by less than the divergence you will still hit the target, maybe not with the maximum intensity, but you will hit it. Half angle divergence for a gaussian beam is: theta=Wavelength/(pi*w) where w is the beam waist radius. So the divergence of a HeNe laser with wavelength of 632nm, transmitted with a radius at the transmitter of 10cm, is ~2micro-radian... Now consider the pointing stability of astronomical telescopes on Earth and in space- the Hubble for instance: http://www.stsci.edu/hst/HST_overview/documents/multidrizzle/ch42.html It is measured in milli-arcsec, which is on the order of nano-radians. The proposal cannot be done yet, but we understand how it could be done (unlike wormholes and warp drive). It may be impractical, and too costly- but it is possible... there will be limits it will be constrained by- there will be a maximum power density the materials on your ship can handle, space dust will be smacking into your ship- at what speed and distance of travel can you have a statistical probability of arriving at your destination in on piece? At what point will the accumulation of errors in predicted position lead to you finally missing your target with the laser? There are countless things that could make it impractical, but it IS possible. But how good your pointing needs to be is set by your beam divergence… which, in turn, is set by your transmitted beam diameter.

If your pointing is off by less than the divergence you will still hit the target, maybe not with the maximum intensity, but you will hit it.

Half angle divergence for a gaussian beam is: theta=Wavelength/(pi*w) where w is the beam waist radius.

So the divergence of a HeNe laser with wavelength of 632nm, transmitted with a radius at the transmitter of 10cm, is ~2micro-radian…

Now consider the pointing stability of astronomical telescopes on Earth and in space- the Hubble for instance:
http://www.stsci.edu/hst/HST_overview/documents/multidrizzle/ch42.html
It is measured in milli-arcsec, which is on the order of nano-radians.

The proposal cannot be done yet, but we understand how it could be done (unlike wormholes and warp drive). It may be impractical, and too costly- but it is possible… there will be limits it will be constrained by- there will be a maximum power density the materials on your ship can handle, space dust will be smacking into your ship- at what speed and distance of travel can you have a statistical probability of arriving at your destination in on piece?

At what point will the accumulation of errors in predicted position lead to you finally missing your target with the laser? There are countless things that could make it impractical, but it IS possible.

]]> By: hank https://habitablezone.com/2017/04/16/laser-propulsion-proposal/#comment-38883 hank Mon, 17 Apr 2017 23:22:41 +0000 https://www.habitablezone.com/?p=63405#comment-38883 How do you target and track a (relatively) tiny sail at semi-interstellar distances? Are we even close to being able to do this? I.e., do we have a fairly good idea about how to go about developing this? Or is this still in the wormhole/warpdrive stage of speculation? How do you target and track a (relatively) tiny sail at semi-interstellar distances? Are we even close to being able to do this? I.e., do we have a fairly good idea about how to go about developing this? Or is this still in the wormhole/warpdrive stage of speculation?

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