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It's really amazing how accurately these laser systems work. I was amazed that SpaceX Starlink uses lasers to communicate between nodes. How do they aim so acc

It's really amazing how accurately these laser systems work. I was amazed that SpaceX Starlink uses lasers to communicate between nodes. How do they aim so accurately?

exabrial 6y ago
Stepper motors and an active feedback loop most likely.
- thereisnospork 6y ago
  The positional accuracy of the motors aiming the lasers (relative to the satellite orientation) probably comes from optical encoders. I'd expect servos in an active loop as you mentioned, rather than steppers - which tend to settle at 1.8* increments. Either way I have no idea how they work out the firing solution for the comm lasers with sufficient accuracy. Hypothesizing: maybe they shoot multiple lasers, the main comm laser and a alignment pattern with auxiliary lasers which could be used for targeting feedback?
stripline 6y ago
I don't think they can yet..
cma 6y ago
Lasers still expand over time, and can expand more with lenses, so it isn't like hitting a laser pointer sized target.
- TheSpiceIsLife 6y ago
  That's right. By the time the laser reaches the target receiver it could be covering an area of tens of meters, or grater, and still be usefully detected. Think about the tiny amount of energy emitted by a mobile phone transmitter and still able to he usefully detected by an antenna on a tower kilometres away.
kevin_thibedeau 6y ago
Lasercoms has been around for decades.
walrus01 6y ago
starlink doesn't, yet, all of the satellites so far are bent pipes. They're working on it however. It may not end up using lasers, but something in the E band RF for intersatellite links.
- zaroth 6y ago
  They have a couple birds up there with lasers. As I understand it, the unit price for the necessary actuators is too high right now to deploy thousands of them.
- deleted 6y ago
  [deleted]
- richk449 6y ago
  Got links to any info about space-x using e-band inter-satellite links? I hadn’t heard that before.
  - walrus01 6y ago
    there's fcc filings where they reference V and E band.
mhh__ 6y ago
In a more regular appliance, the current Valve Lighthouse VR-tracking system works by sweeping lasers very precisely across a room and using the timing differences across the sensors on the HMD to triangulate its position in the room. There is a good talk by one of the engineers who worked on the initial prototypes, and IIRC they both require and are able to achieve something like nm accuracy when they sweep the rotating masses with the lasers on them (That is, not only is the frequency very precisely controlled, the phase cannot drift either). With the help of some custom components they can do that for a hundred bucks. I'm slightly hesitant to go into it for mostly ethical reasons, but military technology has always fascinated me if purely because of the toys they get to play with. The amount of gear even a World War 2 aircraft had by the end of still surprises me, i.e. The Mosquito had a primitive version of what we would now call a HUD displaying a radar horizon and a gunsight. Know-how and an unlimited budget go a very long way.

It's really amazing how accurately these laser systems work. I was amazed that SpaceX Starlink uses lasers to communicate between nodes. How do they aim so accurately?

exabrial 6y ago

Stepper motors and an active feedback loop most likely.

thereisnospork 6y ago
The positional accuracy of the motors aiming the lasers (relative to the satellite orientation) probably comes from optical encoders. I'd expect servos in an active loop as you mentioned, rather than steppers - which tend to settle at 1.8* increments. Either way I have no idea how they work out the firing solution for the comm lasers with sufficient accuracy. Hypothesizing: maybe they shoot multiple lasers, the main comm laser and a alignment pattern with auxiliary lasers which could be used for targeting feedback?

stripline 6y ago

I don't think they can yet..

cma 6y ago

Lasers still expand over time, and can expand more with lenses, so it isn't like hitting a laser pointer sized target.

TheSpiceIsLife 6y ago
That's right. By the time the laser reaches the target receiver it could be covering an area of tens of meters, or grater, and still be usefully detected. Think about the tiny amount of energy emitted by a mobile phone transmitter and still able to he usefully detected by an antenna on a tower kilometres away.

kevin_thibedeau 6y ago

Lasercoms has been around for decades.

walrus01 6y ago

starlink doesn't, yet, all of the satellites so far are bent pipes. They're working on it however. It may not end up using lasers, but something in the E band RF for intersatellite links.

zaroth 6y ago
They have a couple birds up there with lasers. As I understand it, the unit price for the necessary actuators is too high right now to deploy thousands of them.
deleted 6y ago
[deleted]
richk449 6y ago
Got links to any info about space-x using e-band inter-satellite links? I hadn’t heard that before.
- walrus01 6y ago
  there's fcc filings where they reference V and E band.

mhh__ 6y ago

In a more regular appliance, the current Valve Lighthouse VR-tracking system works by sweeping lasers very precisely across a room and using the timing differences across the sensors on the HMD to triangulate its position in the room. There is a good talk by one of the engineers who worked on the initial prototypes, and IIRC they both require and are able to achieve something like nm accuracy when they sweep the rotating masses with the lasers on them (That is, not only is the frequency very precisely controlled, the phase cannot drift either). With the help of some custom components they can do that for a hundred bucks. I'm slightly hesitant to go into it for mostly ethical reasons, but military technology has always fascinated me if purely because of the toys they get to play with. The amount of gear even a World War 2 aircraft had by the end of still surprises me, i.e. The Mosquito had a primitive version of what we would now call a HUD displaying a radar horizon and a gunsight. Know-how and an unlimited budget go a very long way.