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ISS and Iridium Flares

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#1 RobT83

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Posted 13 September 2013 - 01:55 PM

So I have a question about observing the ISS and Iridium flares. I was wondering why the ISS can be seen sometimes during its entire pass, up to 5 minutes across the entire sky, while iridium flares can only be seen momentarily. Is it simply because of the size difference between the satellites and the ISS? The flip side of this is why doesn't the ISS "flare" at a specific moment when it reflects the sun's rays directly back at my location on earth, as the iridium satellites do? Thanks to all the brilliant minds that come up with an answer to this one.

#2 obin robinson

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Posted 13 September 2013 - 02:24 PM

The flare you are seeing from the Iridium satellites is caused by the MMA reflecting sunlight at a precise angle and then hitting the earth where you are standing at that moment. The Iridium satellite constellation has a highly predictable orbit and the satellites must keep an exact orientation for the system to work properly. Predicting the flares is a matter of computing the angle of the MMA in relation to the angle of the sun at that moment.

The ISS on the other hand is a large object with many surfaces which are painted bright colors. You are simply seeing a reflection of a very large object which is reflecting sunlight in every direction. The ISS and all its modules, antennas, and solar arrays is about the size of a football field. It is also not flying very high up as it is in a low earth orbit. Seeing the ISS reflect light at night is no different than seeing a bright rescue mirror reflect light across a valley. If the angles are right even a 6" mirror can reflect light which will be seen for dozens of miles away.

I hope this makes sense to you. If you have other questions feel free to ask. I am only about 10 minutes from ISS mission control and I have worked with people who actually built components for the ISS. It is truly an awesome machine.

obin :cool:

#3 Steve OK

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Posted 13 September 2013 - 02:34 PM

I would add that the Iridium satellites can be seen before and after the flare, but they are just not very bright. They look like any other run of mill satellite. Also, I did see the ISS flare once, going from bright to really bright for a few seconds. It was passing behind some high clouds at the time, and really lit them up. If the geometry is right, it can happen.

Steve

#4 obin robinson

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Posted 13 September 2013 - 02:38 PM

Good point steve. Not just Iridium satellites will flare. One of the brightest flares I ever saw was from ADEOS. I also caught a super bright flare from USA-129 while oberving with a friend one night. Tumbling satellites may also flash and flare extremely bright for a quick second if the angles are right. That is part of the reason why i enjoy observing satellites so much. Every single night and morning is completely different from the last one.

obin :jump:

#5 RobT83

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Posted 13 September 2013 - 05:08 PM

Awesome, thanks guys! Oh yeah I love watching satellites. I use a website called heavens above to find out when I can view them by inputting my gps coordinates. The iridium flares are so cool! Sometimes I use my 10/50 binoculars. I suppose it makes sense that the satellites reflect light all the way across the sky the same way the ISS does, but since theyre so much smaller its much harder to see its full pass overhead. Also, I'm glad to hear that someone has seen the ISS flare. It must happen from time to time, I just havent seen it. I can imagine its extremely bright. Must be at least -7 or -8 magnitude on a nice clear and dark dusk or dawn.

#6 obin robinson

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Posted 13 September 2013 - 05:10 PM

If you like watching satellites check the article I wrote a few weeks back. I will be adding more installments in the future.

http://www.cloudynig...hp?item_id=2903

Check out the heavensat software. It is VERY powerful and you will be able to see a lot of satellites that Heavens-above does not list.

obin :cool:

#7 Skylook123

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Posted 14 September 2013 - 09:40 AM

I first got interested in observing satellites when I was a consultant working with Motorola on the design and initial launches of the Iridium satellites. BTW, the launch of the first five Iridiums was on May 5, 1997, and I was privileged to watch the ops from the Motorola cafeteria next to Ray Leopold, the VP who came up with the idea for global telephone communications via satellite back in the late 1980s. As I was listening to range communications as the five satellites were spun off into their initial engineering orbits, I got a text page from my wife that our granddaughter Karina was born at 9:32 AM. Since I was a test director familiar with the launch timeline, that was about the time of second stage engine cutoff on the Delta II booster, so she and I chuckle over her nickname only we two use - SECO. She is very proud to have been born at the same time as the ISS architecture.

So, I got into tracking satellites, eventually bought an Atlas EQ-6 since it has slew speeds that can match most satellites, and use a variety of programs (love Heavensat), and all of my computers download the current ephemeris a couple of times a day. When I do public outreach events about ten times a month, I always do an ISS and Iridium flare prediction set for the crowd. in 2012 at the Grand Canyon Star Party we had overhead passes of the ISS and Hubble within about five minutes of each other, so I set up a program called Satellite Tracker to run my Atlas for both of them and while the other forty scopes were on the usual eye candy, Karina's sister Jessica and I nailed the ISS, then hopped over and picked up the Hubble. Dazzled our crowd! Yes, Karina (and her older sister Jessica, and one of her younger brothers Stephen) are so space happy they now run my scopes at GCSP.

Obin is such a super resource here. I never get a chance to help with the satellite questions, but he is so knowledgeable he provides great answers to folks. I'll add that the Iridium flares coming from the Main Mission Antennas that are angled to point down to cell phones, are about 6' by 3', three to a satellite, and covered in Mylar causing the specular reflection. Max flares are about 25 seconds because the angle from the sun to your eye has to be within a narrow range of potential. I use my own predictors like Heavensat, Satellite Tracker, Satspy (no longer published), and Mike McCant's Iridflare program, as well as web sites like Heavens Above and my other favorite site, CalSKY, which will send you an email when any satellite or flare is visible from a location you give it.

Here is Karina with my 18" that she ran in 2011 and 2012. This year, Jessica couldn't make the trip to the Grand Canyon due to her work schedule, so Karina switched over to the Atlas and my Mallincam Jr. setup and Stephen did super with the 18".

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#8 Skylook123

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Posted 14 September 2013 - 09:54 AM

Here is Jessica with the scope we used to track ISS and Hubble for the crowd in 2012. Scopezilla, our mascot, rode along. Table with the computer and cables are out of view.

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#9 obin robinson

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Posted 14 September 2013 - 05:06 PM

Thanks for the endorsement Jim! That's so cool that you worked at Motorola when the Iridium constellation was being designed. Being in the Houston area I have met so many people with amazing stories in the aerospace field. I've met people who worked on the Apollo mission, the Space Shuttle, the ISS, and are STILL working as consultants for NASA! What is more interesting personally are meeting the people who worked on those dozens of obscure little programs that most people never get to hear about. My neighbor nextdoor is an Air Force vet that told me about the wonderful little items they were sending up in the early 1960s. Those early programs paved the way for the magnificent satellites we have today. I love observing satellites because I feel I have a connection to them and the people who worked on them. Just today I met a gentleman who worked on some very interesting projects many years ago. We had quite an interesting conversion all composed of intentionally obfuscating lingo.

All these classic programs have been declassified by their respective agencies. It's still interesting to see how many people have either never heard of them and never taken the time to simply look up at night and watch them fly over.

obin ;)

#10 Skylook123

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Posted 14 September 2013 - 11:19 PM

Yeah, the Good Ol' Days. I was in the Air Force for 25 years, ending up as Director of Advanced Technology and have a dozen stories. I'll write a book some day.

It is so cool at a public star party to count down to when the ISS, or an Iridium Flare, or the Hubble will come into view. But most of the moving stars are space junk, old booster stages. The crowd thinks every moving star is the ISS ;)

#11 Retsub

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Posted 15 September 2013 - 08:16 PM

obin quote:>Being in the Houston area I have met so many people with amazing stories in the aerospace field.< Yes,that must be nice to hear some stories. I have machined some satellites on a CNC machine with a 66" dia. chuck that ran over 200 RPM's only at a arms length away, which is much faster that when they were launched from the Shuttle cargo bay. I could say "When I got into satellites" but in a different way. Carbide tooling was used instead of ceramic being I was cutting titanium and I once got down inside one to inspect what looked like tool marks. There are a few youtube videos of sats being launched that look like the ones I machined on. DOD stuff and you know what I mean. Great topic and info and I know you and others will keep looking up ! Thanks. *BW*

#12 obin robinson

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Posted 16 September 2013 - 07:21 AM

That's definitely cool Retsub! I only wish the general public could appreciate these objects more. I think the 1950s concept of satellites is what people people think of. They seem to imagine them as being something the size of a basketball or a refrigerator and once in a while the size of a car. People have no idea that once the antenna arrays open up satellites are as often as wide as an airliner. Speaking of the Space Shuttle people often forget the ~real~ reason for the size of the orbiter and the size of its cargo bay. Often forgetten is the reason for the MMU's existance and all the projects which paved the way for spacecraft like the Hubble Space Telescope. These things weren't born from a clean sheet nor were they just neat ideas arbitrarily designed for science experiements. You know what I mean.

In my opinion the ELINT/SIGINT birds from various nations are the most amazing ones up there. They are doing tasks in orbit that seem like James Bond science fiction. It's too bad most people don't even take the time to look when they fly over.

obin ;)






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