TRMM Satellite Reentering the Atmosphere Tonight

June 15th, 2015 by Roy W. Spencer, Ph. D.
Japan's Hayabusa satellite renters the atmosphere in June, 2011.

Japan’s Hayabusa satellite renters the atmosphere in June, 2011.

NASA’s very successful Tropical Rain Measuring Mission (TRMM) satellite will mostly burn up upon reentry tonight. The latest estimated time of re-entry from right now is 4 a.m. GMT, give or take 1.5 hours.

To show you just how uncertain these predictions are, that time was moved up by 35 minutes from a prediction just 12 hours before, which is almost half a world away in terms of distance. In other words, it just about impossible to know where the satellite will reenter, except that it will be between about 35 N and 35 S latitudes.

Orbital predictions are very accurate when all you have to account for is gravity; once atmospheric drag comes into play, it’s a whole different ball game.

This news article from a couple days ago quotes NASA as saying that about 12 spacecraft components could survive re-entry and hit the surface. They also say the chance that one of these could hit someone somewhere is 1 in 4,200. I’m a little surprised it’s that high. But then there are a couple billion potential targets. đŸ˜‰

If I thought there was a decent chance it will reenter over the southeast U.S., I’d set my camera up for extended time lapse session tonight. But I’m pretty sure that would be a waste of time.

12 Responses to “TRMM Satellite Reentering the Atmosphere Tonight”

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  1. mpainter says:

    I will keep my eyes peeled and be ready to dodge lest I wind up with a cause of action against NASA.

  2. The latest prediction, taking into account how the updates have been trending, suggests reentry over extreme north or northeast Africa between 3:20 and 4:20 GMT, so I think that’s before sunrise in those areas.

    • KevinK says:

      OH NOES, think of the poor Gnu’s in it’s path…..

      Killed by a satellite fuel tank, what a way to go….

      Cheers, KevinK

  3. The portion of Earth’s surface between 35N and 35S latitudes has an area of about 2.92 E14 square meters. If all 12 large pieces are to reach the surface, then a 1 in 4,200 chance of one of them hitting a person means the total combined effective human target cross section in this latitude range is 5.8 E9 square meters. This includes areas just outside people’s bodies where the centers of fragments can pass through and these people would still be hit. I think a majority of the world’s population of about 7 E9 people lives in this latitude zone. So, 1 in 4,200 sounds plausible.

  4. Steve Case says:

    And I just ran across this:

    The True Story of Ann Hodges: History’s Only Meteorite Victim

  5. mpainter says:

    Steve: the story appeared in Life Magazine and i read it as a child. I remembered it in connection with this posting. Thanks for digging it up.

  6. Steve Case says:

    M Painter

    Glad you liked it.

  7. Alan says:

    Whoever came up with the 1 in 4,200 estimate must have been smoking crack! There would have to be a really large number of pieces to make the odds that good (or bad)…

  8. wayne says:

    Whew! Guess living at 35.5°N means an easy sleep tonight.

    Crystal Palace, confidence is high for ocean hit, I repeat, confidence is high.

    Donald L. Klipstein, you forgot to include the land/ocean fraction in your calcs where people actually do live. And how about the heavy concentration of the population living in cities, towns, homes within a small area. I fear your calcs are way, way off.

    • A person’s collision cross section area is not affected by whether land or sea is under that person. It is not affected by the presence of other persons nearby, unless a person is shielded from a satellite fragment by another person.

      The calculation of the probability that a person will be hit depends only on the number and size of surface-reaching fragments, the amount of total human target cross section area in the latitude zone where fragments can land, and the amount of earth surface (land or sea) in that latitude zone that does not have a human collision cross section area in the way of a landing fragment.

      Whoever performed the calculation apparently thinks that 12 times the average collision cross section of a person, including space outside a person’s body where a fragment’s center can pass through and that person would still probably be hit, is 1/4200 of the area of Earth’s surface in the latitude zone from 35S to 35N. Obviously, most of the people in that latitude zone are on land, and moving them to the sea without changing latitude does not change their individual probability of being hit, or the global combined probability that one of them will be hit.

      The calculation does seem to assume that falling satellite fragments won’t be stopped by roofs, etc.

      One detail that affects the calculation just occurred to me, and that is population distribution by latitude within the zone of 35S to 35N. Assuming the satellite fragments are equally likely to land anywhere under the satellite’s orbit, those 25-35 degrees from the equator are worse off than average, and those within 24 degrees of the equator have less risk than average. The satellite spent half its time ~24.75 to 35 degrees from the equator, and spent the other half less than 24.75 degrees from the equator.

  9. Beta Blocker says:

    Should the list of possible adverse impacts of climate change include a reduction in the life expectancies of our low earth orbit satellites? (Just asking.)

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