Hacker News Reader

Comment by can16358p | Hacker News Reader

> antenna array as big as a highway billboard

I don't get it, how can something actually that small can reflect so much light? I mean, it's high up in the orbit, and an object at a height of the orbit with a size of billboard should be super small. I know it's reflecting sunlight and in darkness it shines a lot, but still I can't wrap my head around how such a small (relatively, to space) object can create some much reflection.

I know what ISS can do and I regularly observe its passes and how bright it is, but ISS is much, much bigger.

View on HN

If there's a reflection path from you to the sun hitting the panel, you're looking at a billboard-sized panel that's roughly as bright as the sun. It's far away, yes, but the stuff you're trying to look at is much much farther away, and much much less bright.

Have you ever been in an airplane during a sunny day? You can get blinded by reflections from small objects like windows, or even sparkling from water and the like. And that's sunlight that's gone through the atmosphere and back up for up to 10 kilometers, this one gets hit by direct sunlight.

I'd say that absorbent or light diffusing material should be mandatory, but absorbent material would mean the surface gets really hot.

>absorbent or light diffusing material should be mandatory

Absorbency is bad because it causes overheating and IR astronomy pollution. Diffusion is bad because it reflects light toward Earth.

Specular surfaces (mirrors) can reflect light entirely into space and away from observers on the ground.

This explains why SpaceX created their own radio-transparent, space-rated mirror. They are offering it—at cost—for use by other satellite manufacturers.

https://www.teslarati.com/spacex-shares-how-its-making-starl...

https://planet4589.org/astro/starsim/2022-05-07_SpaceX_Susta...

The effect of downward-pointing black coatings on LEO satellites is higher spacecraft temperatures, but the cost of those higher temperatures is on spacecraft design/use, not on IR astronomy. Starlink satellites run screamingly hot even without the dark coatings; if they're a problem for IR telescopes, then that should already be a problem. A few extra degrees shouldn't break the budget.

It's like someone using a mirror to reflect the sun at you - it can be quite bright if the angles line up correctly. It's called a satellite flare. Sadly, the best and most easily predictable ones, the Iridium Satellites have all been retired, so you can't easily observe one any more, but if you look on youtube, people have posted observations of them.

Interesting. I found an old page with a photo and a newer one with more recent information. I knew that Iridium as a constellation is still operating, but I wasn't aware that they introduced a different satellite design that mitigates flares. The last Iridium satellite that produced flares was deorbited in 2019. (They folks who made the second page seem disappointed about the end of that era.)

http://www.satobs.org/iridium.html

https://catchtheiridium.com/mission/

In my experience catching a surprise iridium flare was rarer than catching a non-shower meteor. I think that I had seen maybe less than dozen my whole life of looking up.

There must be some diffusion/refraction from all of the atmospheric particles as well, right? I don't think you'd be able to see it as a bright rectangular object so much as a bright fuzzy blob in the sky.

Reply on news.ycombinator.com