A 20+ year old NASA satellite is going to reenter the atmosphere tomorrow night, Wednesday 4/19 at 9:30 PM ET. That is, at 9:30 +/- 16 hours. Based on that uncertainty of +/- 16 hours, I take that to mean the point at which reentry becomes certain; that is, absolutely starts, could be any time over roughly +/- 10 full orbits. The uncertainty of where it starts reentry is the uncertainty in where it ends up. I'll approximate the 20 full orbits as 25,000 miles each or 500,000 miles.
Let me back up a minute. The satellite is called RHESSI - for the Reuven Ramaty High Energy Solar Spectroscopic Imager. The satellite was launched on February 5, 2002 to observe solar flares and coronal mass ejections from its low-Earth orbit. The goal being to help understand how such powerful bursts of energy are created by our sun. Starting in 2002 the satellite carried out its mission, but it was eventually decommissioned in August of 2018.
It weighs about 660 lbs, and while these things always burn up to some degree, NASA gives the official odds of being hit by a chunk at 1 in 2,467. I find it hard to justify that big a chance. Think of it this way: the surface area of the Earth is just under 197 million square miles. Let's be generous and say the size of the particle that doesn't burn up is a few square yards. Let's say 10 square yards. In 197 million square miles, there are 61 trillion 10 square yard patches. Around 70% of that surface area is oceans, big lakes, and followed by very lightly inhabited areas like mountains and deserts. If the satellite came down in those areas, the only way to know would be by tracking it. That brings the number of patches of land down to 30% of 61 trillion or 18 trillion.
Now, the area that the satellite can fall in is smaller than the 18 trillion patches because that's based on the entire surface area of the Earth, including the arctic ice cap, Antarctica, and the few large land masses that far north and south. The orbit never goes over those areas so the satellite couldn't come down there. The chances of being hit by debris seem to come down to a tiny object - you; maybe a square yard - getting hit by that 10 square yard debris in maybe 10 trillion possible patches. It makes the odds of winning Powerball seem certain.
RHESSI's last orbits, from the RHESSI Wiki Entry
The last time we went through one of these watches was for a Chinese upper stage re-entering.
Well, that's a Buzz Kill.
ReplyDeletesarc
Looks like I won't have to duck. The northern edge of the orbit is a bit south of me.
ReplyDeleteFrom the graph it looks like they're calling it for the south Atlantic Ocean at 1600 (UTC?) on the 23rd.
ReplyDeleteI read that date as April 17, '23, which was before this post was put up.
DeleteThe predicted time is sliding later. This page
https://www.satview.org/?sat_id=27370U
is now saying April 20 at 1359 UTC (9:59 AM).
All of these predictions have enormous uncertainties.
SiG, yes I meant the 17th. I had 23 on the brain when I typed.
DeleteSeen a rentry, was just a kid, on a BoyScout hike and camped out at the summit, was up on Mt Manadnok in NH, basicaly horizon to horizon view ip there cause Monadnock sticks up by itself, its a volcanic cone, all granite at the too so no trees to block the view, was lucky, looking right where it came over towards the west, never seen anything kije it, just my buddy and myself where awake, we where watching for meteriods, but this object lit up like magnesium burning and as it came over, it went down thru bright yellow to orange then red and faded out. Lots of smaller pieces trailed off, the most spectacular spectral event of my life. It was pretty spooky too. That was maybe 1968, so satelite rentries where rather rare I'd say. Never found out what it was. But holy cow it was like nothing i have seen before or since. It actually appeared by its siloutte even as eye spot bright it was, a large solid body right till it winked out. It was so stunning that it seemed very strange we did not hear any sound from it, like something so dramatic with this tail of fire at one point seemed half the horizon in length was eerily silent. It appeared to be pretty at a rather high altitude. And fast. Crazy fast. Fastest object by orders of magnitude my budy and I ever seen. We still never heard of anything regarding it to this day. But it was beautiful like only a thing like that can be. Left us 2 kids like just wow speechless.
ReplyDeleteNot gonna stay up and watch for it, I've got the (hopefully) starship launch at around 08:30 CDT. Since that's 06:30, I get an early start to tomorrow.
ReplyDeleteHope all goes well and no scrub.