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  Signaling the space station from the ground

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Author Topic:   Signaling the space station from the ground
Robert Pearlman
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Posts: 27327
From: Houston, TX
Registered: Nov 1999

posted 03-06-2012 04:00 PM     Click Here to See the Profile for Robert Pearlman   Click Here to Email Robert Pearlman     Edit/Delete Message   Reply w/Quote
Spotting the International Space Station as it flies overhead is relatively easy: all you need is to do is be along its path, go outside at the projected time and hope for clear skies.

Spotting someone trying to signal you — if you are an astronaut aboard the space station — may seem equally simple, but its not. In fact, all attempts to do so have failed — until this week. Expedition 30 flight engineer Don Pettit explains:

Early Sunday morning, at 01:27 our time, the San Antonio Astronomical Association, an amateur astronomy group, succeeded in flashing the space station with a one-watt blue laser and a white spotlight as we passed overhead.

This took a number of engineering calculations. Projected beam diameters (assuming the propagation of a Gaussian wave for the laser) and intensity at the target had to be calculated.

Tracking space station's path as it streaked across the sky was another challenge. I used email to communicate with Robert Reeves, one of the association's members. Considering that it takes a day, maybe more, for a simple exchange of messages (on space station we receive email drops two to three times a day), the whole event took weeks to plan.

I was ready with cameras for the early morning San Antonio pass and can report that it was a flashing success. Here's one of the pictures to prove it:

MCroft04
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Posts: 1219
From: Smithfield, Me, USA
Registered: Mar 2005

posted 03-06-2012 07:15 PM     Click Here to See the Profile for MCroft04   Click Here to Email MCroft04     Edit/Delete Message   Reply w/Quote
Could the Astronomical Association folks see the ISS when they flashed the light?

Robert Pearlman
Editor

Posts: 27327
From: Houston, TX
Registered: Nov 1999

posted 03-06-2012 08:57 PM     Click Here to See the Profile for Robert Pearlman   Click Here to Email Robert Pearlman     Edit/Delete Message   Reply w/Quote
Yes, in fact they were manually focusing the lights on the station as they visually tracked its path across the sky.

Jay Chladek
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Posts: 2211
From: Bellevue, NE, USA
Registered: Aug 2007

posted 03-07-2012 05:13 PM     Click Here to See the Profile for Jay Chladek   Click Here to Email Jay Chladek     Edit/Delete Message   Reply w/Quote
Pretty nice to see a view of my childhood city from space (I lived in SA from 1975 to 78 and then from 1979 to 1983). I can see I-35 and Loop 410. Looks like the laser location was somewhere just west of I-10 to the north of the city (probably to get away from the light pollution).

And Pettit is the perfect one to take a picture like this, given that he perfected the art of night photography when he was part of Expedition 6. I wonder if he used the same IMAX camera mount for this shot?

Pretty cool experiment actually.

ejectr
Member

Posts: 1488
From: Brimfield, MA
Registered: Mar 2002

posted 03-07-2012 07:13 PM     Click Here to See the Profile for ejectr   Click Here to Email ejectr     Edit/Delete Message   Reply w/Quote
We need more guys like Don Pettit. He not only knows how to make things educational and useful. He knows how to have fun.

All times are CT (US)

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