Double Iridium

I had a curious experience a couple of weeks ago. The Heavens Above
website had predicted a mag -8 Iridium flare at my home. We had guests
over for the evening, so I took them out to see the show. The flare
appeared right on cue and was intensely bright. As I was explaining what
they had just seen, a second equally intense flare appeared in the exact
same spot less than a minute later. Are some of the satellites operating
in pairs? I would have expected any defunct ones to be tumbling, or at
least not nearly as bright. These two were obviously in very close orbit
and alignment.

Specifics: 40.8077N, 89.6089W, Feb 14, 19:06:45CST Iridium 43 (no idea
what the other one was, not mentioned in the prediction table)

Bryan (drop the X if you e-mail me)

Yes, this happens. Some travel a distance behind each other, some closer
than that. I happened to catch a "trailer" when photographing this -4
flare last week:

Here's the wide angle:
http://www.macnmotion.com/iridium/iriddouble.jpg

Here's a closeup with the second satellite visible (confirmed as two
satellites in Starry Night):
http://www.macnmotion.com/iridium/iriddoublecloseup.jpg

By the way, the other Iridium satellite you saw was Iridium 77.

macnmotion

wrote:
I had a curious experience a couple of weeks ago. The Heavens Above
website had predicted a mag -8 Iridium flare at my home. We had guests
over for the evening, so I took them out to see the show. The flare
appeared right on cue and was intensely bright. As I was explaining what
they had just seen, a second equally intense flare appeared in the exact
same spot less than a minute later. Are some of the satellites operating
in pairs? I would have expected any defunct ones to be tumbling, or at
least not nearly as bright. These two were obviously in very close orbit
and alignment.

Specifics: 40.8077N, 89.6089W, Feb 14, 19:06:45CST Iridium 43 (no idea
what the other one was, not mentioned in the prediction table)

Bryan (drop the X if you e-mail me)

I've also seen a second (dimmer) flare from the same Iridium after the
first bright flare. It was about 10-seconds between the two flares.

macnmotion wrote:

Yes, this happens. Some travel a distance behind each other, some closer
than that. I happened to catch a "trailer" when photographing this -4
flare last week:

Here's the wide angle:
http://www.macnmotion.com/iridium/iriddouble.jpg

Here's a closeup with the second satellite visible (confirmed as two
satellites in Starry Night):
http://www.macnmotion.com/iridium/iriddoublecloseup.jpg

By the way, the other Iridium satellite you saw was Iridium 77.

macnmotion

wrote:
I had a curious experience a couple of weeks ago. The Heavens Above
website had predicted a mag -8 Iridium flare at my home. We had guests
over for the evening, so I took them out to see the show. The flare
appeared right on cue and was intensely bright. As I was explaining what
they had just seen, a second equally intense flare appeared in the exact
same spot less than a minute later. Are some of the satellites operating
in pairs? I would have expected any defunct ones to be tumbling, or at
least not nearly as bright. These two were obviously in very close orbit
and alignment.

Specifics: 40.8077N, 89.6089W, Feb 14, 19:06:45CST Iridium 43 (no idea
what the other one was, not mentioned in the prediction table)

Bryan (drop the X if you e-mail me)


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I knew there were doubles up there (usually one out of commission), but
what really surprised me was that BOTH were mag -8 flares less than a
minute apart.

Thanks for the neat photo!

macnmotion wrote:
Yes, this happens. Some travel a distance behind each other, some closer
than that. I happened to catch a "trailer" when photographing this -4
flare last week:

Here's the wide angle:
http://www.macnmotion.com/iridium/iriddouble.jpg

Here's a closeup with the second satellite visible (confirmed as two
satellites in Starry Night):
http://www.macnmotion.com/iridium/iriddoublecloseup.jpg

By the way, the other Iridium satellite you saw was Iridium 77.

macnmotion

wrote:
I had a curious experience a couple of weeks ago. The Heavens Above
website had predicted a mag -8 Iridium flare at my home. We had guests
over for the evening, so I took them out to see the show. The flare
appeared right on cue and was intensely bright. As I was explaining what
they had just seen, a second equally intense flare appeared in the exact
same spot less than a minute later. Are some of the satellites operating
in pairs? I would have expected any defunct ones to be tumbling, or at
least not nearly as bright. These two were obviously in very close orbit
and alignment.

Specifics: 40.8077N, 89.6089W, Feb 14, 19:06:45CST Iridium 43 (no idea
what the other one was, not mentioned in the prediction table)

Bryan (drop the X if you e-mail me)

You want to see a neat one? Here's an extraordinary photo over 12
minutes by Johannes Schedler:

http://tinyurl.com/2aqyr

macnmotion



wrote:
I knew there were doubles up there (usually one out of commission), but
what really surprised me was that BOTH were mag -8 flares less than a
minute apart.

Thanks for the neat photo!

macnmotion wrote:

Yes, this happens. Some travel a distance behind each other, some closer
than that. I happened to catch a "trailer" when photographing this -4
flare last week:


Here's the wide angle:
http://www.macnmotion.com/iridium/iriddouble.jpg


Here's a closeup with the second satellite visible (confirmed as two
satellites in Starry Night):
http://www.macnmotion.com/iridium/iriddoublecloseup.jpg


By the way, the other Iridium satellite you saw was Iridium 77.


macnmotion


wrote:

I had a curious experience a couple of weeks ago. The Heavens Above
website had predicted a mag -8 Iridium flare at my home. We had guests
over for the evening, so I took them out to see the show. The flare
appeared right on cue and was intensely bright. As I was explaining what
they had just seen, a second equally intense flare appeared in the exact
same spot less than a minute later. Are some of the satellites operating
in pairs? I would have expected any defunct ones to be tumbling, or at
least not nearly as bright. These two were obviously in very close orbit
and alignment.

Specifics: 40.8077N, 89.6089W, Feb 14, 19:06:45CST Iridium 43 (no idea
what the other one was, not mentioned in the prediction table)

Bryan (drop the X if you e-mail me)

I used to work on the Iridium program, so I can tell you with
certainty that these satellites do not operate in pairs that are as
close together as you describe. However, they are crosslinked to
other Iridium satellites in the constellation, but this is not really
relevant to what you saw. There are several reasons that you might
see to Iridium satellites in close proximity to each other from a
line-of-sight perspective. The most likely cause is an
non-operational satellite that died in mission orbit. The nature of
the Iridium operational orbit results in failed satellites cycling
through the slots of the other satellites within the same orbit plane,
we used to call this "The Grand Tour". Another possibility is that
you saw a satellite in a sparing orbit, where replacements are kept,
which is nominally aligned with a mission orbit plane but at a lower
altitude. These spare satellites can align along the line-of-sight
with an operational satellite and cause the appearance of "double"
flares. There are perhaps a few other possibilites, but the
aforementioned two are what I consider to be the most likely to
explain what you saw.

BRP


wrote in message ...
I had a curious experience a couple of weeks ago. The Heavens Above
website had predicted a mag -8 Iridium flare at my home. We had guests
over for the evening, so I took them out to see the show. The flare
appeared right on cue and was intensely bright. As I was explaining what
they had just seen, a second equally intense flare appeared in the exact
same spot less than a minute later. Are some of the satellites operating
in pairs? I would have expected any defunct ones to be tumbling, or at
least not nearly as bright. These two were obviously in very close orbit
and alignment.

Specifics: 40.8077N, 89.6089W, Feb 14, 19:06:45CST Iridium 43 (no idea
what the other one was, not mentioned in the prediction table)

Bryan (drop the X if you e-mail me)

brp wrote:

I used to work on the Iridium program, so I can tell you with
certainty that these satellites do not operate in pairs that are as
close together as you describe. However, they are crosslinked to
other Iridium satellites in the constellation, but this is not really
relevant to what you saw. There are several reasons that you might
see to Iridium satellites in close proximity to each other from a
line-of-sight perspective. The most likely cause is an
non-operational satellite that died in mission orbit. The nature of
the Iridium operational orbit results in failed satellites cycling
through the slots of the other satellites within the same orbit plane,
we used to call this "The Grand Tour". Another possibility is that
you saw a satellite in a sparing orbit, where replacements are kept,
which is nominally aligned with a mission orbit plane but at a lower
altitude. These spare satellites can align along the line-of-sight
with an operational satellite and cause the appearance of "double"
flares. There are perhaps a few other possibilites, but the
aforementioned two are what I consider to be the most likely to
explain what you saw.

BRP

Did the designers of the Iridium satellites realize they were going to
produce very bright flares or was this discovered after they were
launched?


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starman wrote in message ...

Did the designers of the Iridium satellites realize they were going to
produce very bright flares or was this discovered after they were
launched?

I don't recall hearing this discussed prior to the observations of
flares that were made once the satellites were in orbit. However, it
could have easily been predicted since the main mission antennas are
essentially mirrors, with a highly reflective surface canted down 40
degrees from the nadir/zenith line on all three sides of the
spacecraft.

BRP