<p>The guide star laser is used to adapt the optics at a specific time and location, for specific atmospheric conditions. It is not, as your question implies, used to calibrate the optics for long-term use.</p>

<p>Therefor, if order to calibrate the satellite with a laser fired from Earth, the reconnaissance target would have to provide the laser. This is useless for non-cooperative targets, which I would imagine make up the bulk of the reconnaissance targets.</p>

<p>I suppose that one could fire a laser from the satellite itself, but this would have the obvious disadvantage of making it even more obvious when a spy satellite was overhead.</p>

<p>In any case, the guide star image does not penetrate the entire atmosphere, I believe that it produces an image just a few tens of kilometers up. This is useful because it is the thicker, denser and more turbulent lower air of which is the most concern to optics. Firing the laser from above would thus see the laser energy absorbed in the thinner, stiller, more predictable upper atmosphere, thus it would have must less advantage.</p>

<p>One final reason not to use a guide star laser on a reconnaissance satellite would be power budget. These satellites are as small as possible, with as small a heat and reflectivity index as possible. The added power source, be it RTG, conventional batteries, or solar, would likely increase the reflectivity of the satellite.</p>

CC BY-SA 3.0
2015-08-02T13:49:00.380Z
2015-08-02T13:49:00.380Z
dotancohen
<p>Are sodium lasers useful for Earth observing space telescopes/spy satellites?</p>

CC BY-SA 3.0
2017-09-03T20:51:45.267Z
I suppose that for daytime observation the daylight itself (i.e. reflected sunlight) gives all the "guide star" an adaptive optics earth observing satellite needs.
JanKanis
CC BY-SA 3.0
2015-08-02T16:43:12.883Z
I'm voting to close this question as off-topic because it is about satellites and related technologies, not astronomy.
HDE 226868
CC BY-SA 3.0
2015-08-02T16:57:27.067Z
@HDE226868 Well, it is about adaptive optics used by astronomers. If astronomy isn't the right place to ask if an Earth observing space telescope could use that technology, then where?
LocalFluff
CC BY-SA 3.0
2015-08-02T16:58:09.467Z
Space Exploration, perhaps?
HDE 226868
CC BY-SA 3.0
2015-08-02T22:05:46.003Z
It could be argued both ways. I'm interested in optical hardware for astronomy, so I thought the question makes sense here. But I'm not happy with it for a different reason - it's quite speculative, exploratory and open-ended, and I don't think anybody knows the real answer. I think @dotancohen has given the best possible answer already, within reason. A speculative answer for a speculative question.
Florin Andrei
CC BY-SA 3.0
2015-08-03T10:49:05.513Z
I suggest leaving the question open. Not because it is a great _question_ per se, but rather because it addresses some incorrect notions about the technologies used in astronomy: telescopes, satellites, and guide star lasers. Also, the answer addresses these misconceptions in a way that is relevant both to the question and also in general for those who may not understand how, and why, the guide star laser is used. That is very relevant to this site.
dotancohen
CC BY-SA 3.0
2015-08-03T11:05:53.233Z
@FlorinAndrei I cut it down to one line, is that better format here?
LocalFluff
<optics><space-telescope><atmospheric-effects>
Could spy satellites use laser guide stars (for adaptive optics)?
LocalFluff
# Could spy satellites use laser guide stars (for adaptive optics)?

(Asked by: username_0 on 2015-08-01)

Are sodium lasers useful for Earth observing space telescopes/spy satellites?

**Tags:** optics, space-telescope, atmospheric-effects

> **Comments:**
> **username_2**: I'm voting to close this question as off-topic because it is about satellites and related technologies, not astronomy.  
> **username_0**: @username_2 Well, it is about adaptive optics used by astronomers. If astronomy isn't the right place to ask if an Earth observing space telescope could use that technology, then where?  
> **username_2**: Space Exploration, perhaps?  
> **username_3**: It could be argued both ways. I'm interested in optical hardware for astronomy, so I thought the question makes sense here. But I'm not happy with it for a different reason - it's quite speculative, exploratory and open-ended, and I don't think anybody knows the real answer. I think @username_4 has given the best possible answer already, within reason. A speculative answer for a speculative question.  
> **username_4**: I suggest leaving the question open. Not because it is a great _question_ per se, but rather because it addresses some incorrect notions about the technologies used in astronomy: telescopes, satellites, and guide star lasers. Also, the answer addresses these misconceptions in a way that is relevant both to the question and also in general for those who may not understand how, and why, the guide star laser is used. That is very relevant to this site.  
> **username_0**: @username_3 I cut it down to one line, is that better format here?  
> **username_1**: I suppose that for daytime observation the daylight itself (i.e. reflected sunlight) gives all the "guide star" an adaptive optics earth observing satellite needs.  

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## 1 answers

### Answer by username_4 on 2015-08-02. Score: 4

The guide star laser is used to adapt the optics at a specific time and location, for specific atmospheric conditions. It is not, as your question implies, used to calibrate the optics for long-term use.

Therefor, if order to calibrate the satellite with a laser fired from Earth, the reconnaissance target would have to provide the laser. This is useless for non-cooperative targets, which I would imagine make up the bulk of the reconnaissance targets.

I suppose that one could fire a laser from the satellite itself, but this would have the obvious disadvantage of making it even more obvious when a spy satellite was overhead.

In any case, the guide star image does not penetrate the entire atmosphere, I believe that it produces an image just a few tens of kilometers up. This is useful because it is the thicker, denser and more turbulent lower air of which is the most concern to optics. Firing the laser from above would thus see the laser energy absorbed in the thinner, stiller, more predictable upper atmosphere, thus it would have must less advantage.

One final reason not to use a guide star laser on a reconnaissance satellite would be power budget. These satellites are as small as possible, with as small a heat and reflectivity index as possible. The added power source, be it RTG, conventional batteries, or solar, would likely increase the reflectivity of the satellite.


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