Star wreck: There's a 1 in 20 chance a NASA telescope and US military satellite will smash into each other today

Best case? They pass within metres of each other at 14.7 km per second

Updated There’s a small but distinct chance a defunct NASA infrared telescope and an old US Naval Research Laboratory satellite will crash into each other on Wednesday evening high above Pittsburgh, Pennsylvania.

LeoLabs, a Silicon Valley-based biz monitoring objects in low Earth orbits, raised the alarm over the potential collision this week. Both objects are expected to zip past one another at 14.7 kilometers per second – that’s an eye-popping 32,900 miles per hour – and early calculations suggested there was a one in ten chance of a prang.

The latest calculations show that the pair will probably just miss each other by a distance of anywhere between 15 and 30 metres (49 to 98 feet) at 1839 ET (2339 UTC). It's now thought there is about a one in 20 chance NASA’s Infrared Astronomical Satellite – a space telescope launched in 1983 – will smash into the Naval Research Laboratory's orbiting probe tonight.

The military's bird, the GGSE-4, was part of the Gravity Gradient Stabilization Experiment, and launched by the US Air Force in 1967.

The space boffins' infrared telescope has a mass of 1,090kg (2,400lb) and measures 3.6 x 3.24 x 2.05 metres (11.8 x 10.6 x 6.7 feet), whereas GGSE-4 is much smaller: it just 4.5kg (10lb), and is said to be attached to declassified NRO intelligence sat Poppy 5B, which has a mass of 86kg (190lb). An expert said if the pair cross paths, it would be like a car hitting a shopping cart.

Here’s a handy visualization charting the flight paths of each device.

If the telescope and satellite collide, 900km (560 miles) above the surface, it will spew a cloud of debris that could wreck other space hardware, and will not pose a danger to anyone below. The impact may be visible from Earth. Keeps your eyes peeled. ®

Updated to add

LeoLabs recalculated the chance of collision to one in 20, whereas previously it was one in ten then one in 100. We've revised this article to reflect this.

Finally, according to the US Space Command, the two inactive birds whizzed past each other unharmed. Boring.

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