ISS Flare?

[deanm (Dean)]

Iridium flares > (actually, that should be < !) mag. -3.5 are pretty cool.

Can the International Space Station do the same trick?!

I've never seen one, or predictions of same (eg. HA).

(Does it's lower orbit significantly reduce flare footprint & hence local occurrence?)

Dean

[doppler (Rick)]

I think iridium flares are with geostationary orbiting satellites and flash when their solar panels tilt and catch the sun from our perspective. The space station orbits the earth quite fast but if it is an over head pass it can be at -3.5 and spectacular to watch.

[Matt Wastell (Matt)]

Hi Dean
I think Iridium flares come from one type of satellites - something to do with the type of panels? I have seen the ISS pass many times and never seen an iridium type event. Not sure?

[Mick (Michael)]

The ISS and the HST can flare at times, I have seen these do this. Any Tumbling satellite can flare.

[mithrandir (Andrew)]

Iridium flares come from the Iridium communications satellites. Other satellites can flare (eg tumbling ones) but not with the predictability of these. The flares come from sunlight reflecting off the antennae, not the solar panels.

[julianh72 (Julian)]

Originally Posted by Matt Wastell

Hi Dean
I think Iridium flares come from one type of satellites - something to do with the type of panels? I have seen the ISS pass many times and never seen an iridium type event. Not sure?

Check out the Heavens Above website - enter your location details, and it will give you detailed predictions of satellite passes visible from your location, including sky charts to make finding them easy. Iridium passes with negative magnitudes are surprisingly common (every day or two for most locations), and are well worth looking out for!

[julianh72 (Julian)]

Originally Posted by doppler

I think iridium flares are with geostationary orbiting satellites and flash when their solar panels tilt and catch the sun from our perspective. The space station orbits the earth quite fast but if it is an over head pass it can be at -3.5 and spectacular to watch.

The Iridium satellites are low orbit, so pass over pretty quickly. The flash is quite short (a couple of seconds) , but can be very bright, and they are very predictable.

I've got a -6.0 at my location tomorrow morning!

[deanm (Dean)]

Thanks, all - I'm a long-time HA user: Iridium flares better than mag. -3.5 always are worth chasing (and the flare events can arise from either the solar panels or MMAs (Main Mission Antennae).

These flare events are highly predictable because the satellites are in extremely stabilised orbits (780 km) and orientations.

What I'm interested in is: is the position of the ISS' enormous, constantly-rotating solar panels similarly predictable with respect to the Earth.

This would make ISS flare predictions possible.

Dean

[MichaelSW (Michael)]

Dean,

G'day.

I recently knocked up a little Explanatory Document about Iridium Flares to stir the interest among non-astronomy friends. And yes, I got it all from Wikipedia.

Wiki says that the shape of the door-sized, reflective antenna reflects and focuses sunlight down onto the Earth's surface over an area about 10 km in diameter.

Also says that the Solar Panel arrays can produce a flare which may last a few times longer, but this will not be as bright.

Also says there are many controlled satellites in addition to Iridium satellites, which can also flare, but most flares of these satellites do not exceed magnitude −2, therefore, they are often overlooked.

However, MetOp-A and B, however, can produce predictable flares up to −5 mag. Four COSMO-SkyMed satellites can produce flares up to −4 mag., but their peculiarity is that they last much longer than the Iridium flares.

Most flares from other satellites are almost indistinguishable from dim Iridium flares.

I have only ever looked for Iridium Flares as predicted on H-A. What a great party trick though - pointing out a dim satellite to someone and getting them to watch unsuspectingly as it brightens, flares and then dims. (Then I offer to send them the Explanatory notes).

[deanm (Dean)]

Well writ, Michael!

Like you (thus your highlighting), I'm not sure that 'focus' is an appropriate
term...!

I've contacted HA's Chris Peat to see if he has any thoughts on ISS flare predictability: it certainly happens:

http://www.space.com/3942-backyard-a...on-flares.html

Cheers!

Dean

[MichaelSW (Michael)]

Dean,

G'day.

I see what you mean, but I wasn't intending to doubt the concept of 'focus' in explaining the occurrence of Iridium Flares. I can accept it as the point (albeit an area some 10km in diameter) at which the rays of sunlight meet after being reflected. Outside that area you don't see the flare.

I just sent off an e-mail to the Tech Department of Iridium Communications asking if the shape of the satellite antenna has any focusing / concentrating effect on the reflected sunlight. Hope to get an answer in 3 business days.

Will keep you posted.

Cheers.

[deanm (Dean)]

Good on ya, Michael!

It'll be interesting to see what the Iridium folk have to say - please pass on any info.

Dean