Another Reentering space debris story

These stories come up on occasion and while the chances of being affected are typically pretty low, they're always interesting. My gut feel is stories about reentering satellites are going to become more unusual because the industry is getting more concerned about potential damages to things or injuries to people. 

In this case, there are really two satellites in the forecast, a pair of US satellites designed to study the Van Allen belts, called Van Allen Probe A and Probe B. Both were launched in 2012. Both satellites were deactivated in 2019, and have been just following their orbits while they decayed over time. Probe A is the one expected to reenter soon.

As of Monday afternoon (March 9), the U.S. Space Force predicted that the satellite will reenter Earth's atmosphere on Tuesday at 7:45 p.m. EDT (2345 GMT), plus or minus 24 hours.

As always the chances of being affected by something reentering is pretty low, and NASA has given odds of "approximately 1 in 4,200," or roughly 0.025%. 

Van Allen Probes A and B in an artist's conception before the start of the mission. (Image credit: JHU/APL, NASA)

The Van Allen Probes are a project from The Johns Hopkins University Applied Physics Lab, LLC. The Van Allen Probes were originally called the Radiation Belt Storm Probes as part of NASA's Living With a Star program, and launched to a highly elliptical orbit, with an apogee (highest point of the orbits) as far away from Earth as 18,900 miles and a perigee (lowest point) as close as 384 miles. 

The mission was supposed to last just two years, but the spacecraft managed to continue operating until July 2019 (Probe B) and October 2019 (Probe A). They gathered data that scientists and mission planners analyze to this day.

"By reviewing archived data from the mission, scientists study the radiation belts surrounding Earth, which are key to predicting how solar activity impacts satellites, astronauts, and even systems on Earth such as communications, navigation and power grids," NASA officials said in the same statement. "By observing these dynamic regions, the Van Allen Probes contributed to improving forecasts of space weather events and their potential consequences." 

An interesting note here is that they were expected to stay on orbit until 2034, but the effects of some of the unusually large solar flares of this past couple of years degraded Probe A's orbit more than probe B's. Probe B isn't expected to reenter before 2030.

I'm not sure where NASA and I differ in how we figure the chances of getting hit by this kind of space junk - mainly because I've never seen how NASA (or other professionals) figure it - I just assume I'm wrong and they're right. But for comparison, the main thing to bear in mind is that things like getting hit by reentering space junk is so unlikely that it makes winning the Lotto seem like an absolute certainty. The Earth's surface is 71% water and an area of just under 197 million square miles when you take away that 71%. Both the target (you) and the satellite are a couple/few square feet out of those millions of square miles, so to convert the square miles to square feet, multiply the 197 million square miles by 27.878 million square feet per square mile to get the surface area of the Earth in square feet (5.492 x 10¹⁵). Your surface area facing the satellite's path is a few square feet, and the satellite's area (or what survives reentry) is also small.

I've touched on this topic a couple of times over the years. Like I said, I expect the number of stories about reentering satellites will be getting smaller. Gradually, over the coming years as older satellites like these come down. We'll still be seeing them.