Expected near-Miss in space

[TimothyC]

https://www.wpxi.com/news/two-satellite ... T6JMAKXIM/

By: Matt Simmons
Updated: January 28, 2020 - 10:29 AM

PITTSBURGH — A company in California that tracks low earth orbit satellites and debris is warning of a potential collision that could happen Wednesday evening at 6:39 p.m., 560 miles over Pittsburgh.

LeoLabs’ released the information Monday, which showed overlapping tracks between a decommissioned space telescope and an experimental government payload.

he older satellite, known as GGSE-4, was launched in 1967 by the U.S. military from Vandenberg Air Force Base in California. It is quite small and weighs only 10 pounds, but is reported to be attached to a larger satellite, only recently declassified, called Poppy 5. Poppy 5 has 18-meter-long booms and an additional weight of 187 pounds, according to astronomer Jonathan McDowell.



Launched in 1983 from Vandenberg Air Force Base in California, the larger satellite is much larger and called IRAS. IRAS is the first infrared telescope in orbit. IRAS is credited with leading to the discoveries of six new comets, the core of the Milky Way galaxy and a deeper understanding of the stars Vega and Fomalhaut.

After a 10-month mission, IRAS exhausted its fuel supply and has been drifting in low earth orbit ever since. IRAS is 11.8 by 10.6 by 6.7 feet and weighs nearly 2,400 pounds.

Leolabs said the satellites are projected to come with 15-30 meters of each other, but could impact given the size of IRAS and the length of GGSE-4/Poppy 5’s booms. There is a one in 100 chance of collision, which, if it happens, will happen fast as the two satellites have a relative velocity of 14.7 kilometers a second.



Space archaeologist Alice Gorman, of Flinders University, told Science Alert there was no danger to anyone on the ground in the event the collision happens and any debris would burn up in the atmosphere during re-entry.

LeoLabs said they are monitoring the situation and will provide updates as available, but also warned, "Events like this highlight the need for responsible, timely deorbiting of satellites for space sustainability moving forward.”

So, this dropped last night about 48 hours before the expected near-miss on Wednesday (~1940 Local over Pittsburgh). If they hit, we're in trouble because it's very nearly a head-on collision, and the intersection is higher by about 50km than the 2007 Chinese ASAT test, and about 150km over the Iridium 33 / Kosmos-2251 collision of 2009. That means the stuff is going to stay up for a long time, and will be on polar orbits. If there is a miss it's the second near miss in six months (Genesis II and Kosmos 1300 back in September got up to a 5% chance of a hit), and at some point we're going to run out of luck

[TimothyC]

Well, it gets better and worse.

The probability of a hit is down to 0.8%, but the approach distance is down to 13±59m.

https://twitter.com/astroEdLu/status/12 ... 54624?s=20

[TimothyC]

Updated data puts the chance of a hit a 0.1%, with an estimated miss of 13-87m

https://twitter.com/LeoLabs_Space/statu ... 1527374853

[TimothyC]

Probability is back up to 1%, with the boom placement possibly bringing it to 5%. Twelve meters is the likely pass distance.

https://twitter.com/LeoLabs_Space/statu ... 5567887361

[TimothyC]

We got lucky, again.

[SpottedKitty]

The probability of a hit is down to 0.8%, but the approach distance is down to 13±59m.

I wish I could have got away with error bars that big writing up a science experiment or statistics exercise at school...