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US: Amateur astronomers illuminate International Space Station with spotlights and 1-watt laser
Two-frame animated GIF showing bright and dim light from the Lozano Observatory (center) near the city of San Antonio (left). North is to the right in this photo from the International Space Station, taken by astronaut Don Pettit. Click on photo for a larger version.
The spotlights were flashed at the ISS by holding plywood sheets in front of the lights every two seconds. This procedure can be seen in the video below.
The animated GIF above shows a bright blue light alternating with a dim light. The bright light is almost certainly from the spotlights. The bluish tint may be an artifact of oversaturating the camera’s sensor. Astronaut Don Pettit reported that the bright light appeared white, and the dim light appeared blue. He wrote “We could only see the laser when the white light was off and not all the time.” (E.g., the white spotlights overpowered the blue laser.) He added, “It was like there were tracking issues with the laser to keep it on target.”
The dim light in the animated GIF may be the laser only, or it may be light from the spotlights that wasn’t fully blocked by the plywood sheets. The astronomers will be working with Pettit, trying to pin down exactly how visible the laser light was.
A video shows the experiment. In the first few minutes there is a mysterious thin white “beam” which is actually a guy wire being illuminated. At the very end (starting at 6:08) are still photos from space, showing the on and off cycles of the spotlights.
A screen capture taken at 1:22 into the video. This is a red 2x4 piece of wood, with deer rifle scope on top for aiming (not visible in this photo) and an unmodified Wicked Lasers Spyder III Arctic 1-watt blue laser mounted underneath it.
A Wicked Lasers Spyder III Arctic 1-watt blue laser like the one used in the ISS signaling experiment.
For the amateur astronomers, it was a difficult technical challenge to know where to aim and how to track the ISS. The experiment was done with three months of advance planning and cooperation with astronaut Pettit. During the illumination, three people were watching for aircraft.
According to Pettit, this is the first time that the ISS has been successfully flashed, at least by civilians. (The U.S. military has done experiments with lasing spacecraft. For example, on Dec. 6 1992, space shuttle astronauts saw a bright green laser dot, from a Palm Bay, Fl. Air Force observatory.) Pettit wrote that friends and well-wishers have tried to flash the station with green lasers, xenon strobes and halogen spotlights, but until March 4 2012 astronauts were not able to spot these amateur flashes.
From Universe Today and Smithsonian Air & Space magazine
Additional commentary from LaserPointerSafety.com: For general interest, here are some safety calculations. The Spyder III Arctic has an actual output of about 800 milliwatts at maximum, and a stated 1.5 milliradian divergence, and a blue beam of 445 nanometers. The nominal ocular hazard distance (NOHD) is 437 feet, the FAA flashblindness distance is 385 feet, the FAA glare distance is 1,721 feet, and the FAA distraction distance is 17,214 feet. The minimum altitude for the ISS is 1,082,400 feet (205 miles) so the astronauts were definitely not in any eye or visual interference hazard zone. However, LaserPointerSafety.com does not recommend that the general public try to replicate this experiment, by aiming lasers into the sky at the space station or any moving dot in the sky. In fact, for aiming at stars, low-powered lasers should be used (ideally 5 mW or less) and you should circle a star instead of pointing right at it, in case the “star” is really a slow-moving airplane. More info is on our Tips for outdoor use page.