Satellite Watching

[Armitage]

Any of you guys do it?
Alot of people don't know that you can see low earth orbit satellites with the naked eye. You need to find a dark place and watch within about an hour after sunset or an hour before dawn. What your seeing is the reflection of the sun off of low earth orbit satellites that are high enough to still be in the sun. It will generally look like a faint to medium magnitude star drifting across the rest of the starfield.

Occasionally you'll get a very bright glint from some objects ... iridium satellites are famous for this and can be predicted. You'll also see some whose brightness changes in a regular pattern ... these are tumbling objects, typically spent rocket bodies.

You can easily do this just by going out and staring up at the sky for awhile, but there are also websites that will give you pass details for your location. Here are some links:

Heavens-Above
Visual Satellite Observer's Homepage

edit...
Here are some other links for satellite elsets if you want to generate your own passes
Celestrak
NASA Orbital Information Group (registration required)

 

[tranceport]

thats cool and all...but...I guess I am not quite into it.

 

[Spacehead]

Yeah, those Iridium flares are pretty cool. I think the brightest i've seen was -7 or -8 magnitude.
Also, when the Space Shuttle is docked to the ISS it's alot brighter than normal.

 

[RossGr]

I remember watching Echo go over, must have been '58 or '59

 

[dkozloski]

Starlight, starbright,
First star I see tonight,
I wish I may, I wish I might,
Whoops! You're a satellite.

 

[dkozloski]

On a more serious note, one of the first jobs I had in the electronics racket was tracking satellites at a NASA site here in Alaska. I worked at Gilmore Creek which at the time was the largest tracking facility in the world. The Mini-Track section involved both the interferometer tracking of spacecraft transmitting on the 130-136Mhz. band and the photographic tracking of visible spacecraft using a modified Perkin-Elmer aerial camera with a sidereal drive. The process involved taking a time lapse photograph on a glass plate of the track of the spacecraft against a star background. Because the camera had a sidereal drive the stars appeared as spots but the spacecraft made a streak. The streak was broken by a time code that was caused by a solenoid jogging the glass plate in response to a precise time code produced by a time standard. After the plate was processed the image was matched up on star charts that were in the same scale as the image on the plate. The distance from the time code marks to the grid lines on the star charts was measured and a tracking message was generated and transmitted to the experimenters. The process sounds kind of crude but positions on the ground could be located to within about a meter and space craft orbital predictions to seconds of arc with multiple observations and successive messages. Some spacecraft could be RF and star tracked at the same time which could be used to calibrate the RF tracking procedure. To top it all off we got paid really good money to have all that fun.

 

[Armitage]

Very cool dk...
Haven't heard of Perkin-Elmer scopes, but I saw something recently about surviving Baker-Nunn cameras being refurbished with CCD to look for near-earth asteroids. I've been playing with the idea of setting up a small amateur scope to do this.

 

[dkozloski]

The Perkin-Elmer was chosen because it used 8x10' glass plates and with it's focal length the image on the plate exactly matched the star charts we had. The emulsion was Kodak Royal X Pan and we pushed the developement to an ASA of about 4000. We had predicted coordinates to use for pointing the camera but most often we just sighted along the camera barrel by eye because the predicts could be off and the spacecraft were highly visible anyway. We had one bird we tracked that came and went as it tumbled and we got good pictures about one try in twenty. Because the tracking facility was located in the high latitudes, in the summer we had twenty four hour daylight which wiped out the optical tracking. In the winter it often was 50deg F. below zero. The camera was kept at the outside ambient temperature to prevent fogging the lenses. Altogether it was a challenge.

 

[Armitage]

Yea, I didn't think about that ... when you're dealing with photgraphic plates you can't do all the kinds of digital image manipulation we take for granted now. So a focal length that correlates exactly with the available star charts becomes important. I always wondered why the Baker-Nunn cameras were so big.

I have sympathy on the predicted state vector issue ... they still aren't very good. That's part of my motivation to try doing it with a computer controlled amateur scope. I suspect there are significant improvements in sensor scheduling and data rduction that could be made.