Greetings. A long post follows, but it regards a somewhat historical event in satellite observing, so please bear with me. A while back I mentioned that Rob Matson had perfected an Iridium flare prediction program for use by the ISS crew. I reported the initial success with the program, but after that ISS Science Officer Don Pettit started reporting a long string of flare misses. I was starting to get worried, but Rob was certain of the program's functionality. The diagnosis of the problem centered on the ISS being one step ahead of the lastest orbital elements. The station had been undergoing a series of reboosts and it seems it was always a hair off from the latest elements. In spite of this, Don said he was having fun just looking for the flares and to keep the predictions coming. Things finally stabilized this morning and just before I left for work, Don sent me a note saying he had sighted flares for four out three predictions. Darn good odds, I'd say! Actually, Don had seen an unpredicted fourth flare of an in-orbit Iridium spare. Later this evening about my dinner time, Don sent me the first photo of an Iridium flare taken from orbit. The photo is embargoed by NASA, but by way of verbal description, it was taken with 50 mm f/1.2 Nikor on a Nikon D1. Assuming about a 30 X 40 degree field of view, shows a star field (after a little Photoshop work) down to about mag 5.5 or 6. The flare is trailed aproximately one degree during the exposure and is not tapered at either end, showing that the exposure began and ended at mid flare. There is a station solar panel from one corner about 1/3 the way into field of view and on the opposire side of the field is some dim, very out of focus equipment that is obviously located near the window on the outside of the Russian airlock module. The view out the station is certainly cluttered! Both Rob Matson and I have been trying to identify the star field, but it elludes us. I have been an astronomer for 40 years and this image star field mystifies me. The following is a clip from the note Don sent me about his flare observations......... ******************* Robert and Rob: Good news. We nailed nailed four out of three predictions! I took note of times which you can see below. I also saw one unpredicted flash, a bright one of mag estimated at -8 which was barely one minute before the predicted one of -1 mag. See notes below. I estimate that all times are +/- 2 seconds. We keep accurate GMT clock to less than a second and I transfer this to the digital camera and use the start image time stamp for the flash. Due to the lag between when I first can see the flash and I open the shutter (have to move my nose out of the window and place the camera on its mount), I estimate the two second uncertainty. The shutter speed was 5 seconds with automatic dark current subtraction ON so I can not take a sequential shot until 10 seconds after the first was started. I captured these flashes on two frames so the duration is at least 15 seconds each, probably more like 18 to 20 seconds with human delays. This is great fun trying to catch these. Currently I am using the windows in the Russian airlock which are on the 45 degree diagonal so they look aft-starboard and forward-port. Sometimes I can not use the port and starboard facing windows in the service module due to too much ambient light and the work schedule which will not allow the lights to be shut off. The lab window now points nadir directly at the two pointer stars in the big dipper and precesses about 1 degree per day. Attached is a small image of the -5M flash at 18:04. Looks like you can see some structure on the satellites however it may be due to shooting out the airlock window at 45 degrees (double pain with some contamination on the outside surface). I would like to try to photograph a bright flash out the lab window using a 180mm f2.8 telephoto to see if you could see any structure. I would have to have good pointing information for that. It looks like the nighttime predictions for the brighter flashes is working well. Great job on the predictions! Don ***************** And again, congratulations to Rob Matson for creating this program and taking the time to support the ISS with this "unofficial" observational experiment. Actually, I see great value in the Iridium search by the ISS, even if it isn't a real part of the ISS science progam. These guys in orbit are pretty good engineers, scientists, pilots, etc., but they usually don't have a lot of seat time just observing the sky and looking for dim transient phenomenon. I think the success rate in the flare observation program has ramped up partly because Don is now deliberately looking for different phenomena and in the process is unconsciously training training himself to see what he may have missed earlier due to inexperience. He is indeed learning to be a better observer, and this will pay dividends in other ISS programs. Robert Reeves reeves10@swbell.net 520 Rittiman Rd. www.robertreeves.com San Antonio, Texas 78209 210-828-9036 USA 29.484 98.440 200 meters ----------------------------------------------------------------- To unsubscribe from SeeSat-L, send a message with 'unsubscribe' in the SUBJECT to SeeSat-L-request@satobs.org List archived at http://www.satobs.org/seesat/seesatindex.html
This archive was generated by hypermail 2b29 : Thu Mar 20 2003 - 23:50:12 EST