At 6:23:35 p.m local time (23:39:35 UTC) two satellites will be passing directly above Pittsburgh. At least everyone hopes they will be passing, because there's a 1 in 20 chance they will be colliding.
Their relative velocity (how fast they are going compared to each other) at the time of potential impact will be 14.7 km/s. That's 33,000 mph, or 235 times faster than a head-on collision at highway speeds.
GGSE is a small sat, and weighs in at around 10lbs. IRAS is a monster at 2,300 lbs. Think Compact vs Semi and you're underestimating. This is Elephant vs Mouse. However if a mouse hit an elephant at 33,000 mph, well, that elephant probably isn't getting back up.
A direct hit could cause a huge debris cloud with hundreds if not thousands of trackable pieces, each of which will then present it's own threat of collision for years to come. The satellites are 900km up, so a lot of the debris will stick around in otherwise useful orbits. Even a glancing blow could cause significant damage and debris.
Of course there's still a 19 in 20 chance that they won't hit, and given the levels of light pollution most of Pennsylvanian-Era wont even get a decent light show even if there is a collision.
But hey, if you happen to be in Sproul State Forest or Monongahela National Forest or out in the middle of Lake Eerie with a telescope, you should probably keep an eye on the sky.
Visualisation of the satellite's paths and possible collision point:
Global light pollution map:
