No one can shoot a satellite down!

Posted By Pamela on Feb 20, 2008 | 14 comments

Was the title provocative enough for you?

For the past several days headlines all over the web have read “US to shoot down satellite.”

Ok, first off, that satellite is on its way down no matter what. That would be the problem. It doesn’t actually need shot “down.”

Second, after it gets nailed by whatever our government and military, in their wisdom, decide to fire at it, the satellite is going to hopefully smash apart into a bazillion little pieces, and some of those pieces will end up going up, while others stay in orbit, so in reality we are shooting the satellite in all directions.

An accurate, and still fantastic, headline should read, “US plans to blast satellite into little bits” or “US plans to blast satellite apart.”

The only reason this is happening is to guarantee that the satellite is in tiny enough pieces as it comes through the atmosphere that nothing makes it through intact. This is a dangerous thing to do because bad aim could knock it in unpredictable ways that lead to much badness (for instance, a glancing blow with failure to detonate could set the thing spinning and put it on a new orbital path that hits Earth sooner). Alternatively, we could blast it into a bunch of tiny pieces and a few big ones that wreck havoc either on Earth or in space. It’s not like Earth’s orbit really needs more space junk, but… More space junk is better than toxic chemicals killing a bunch of people on Earth. This is probably the best thing to do, and the best thing isn’t always a safe thing.

Bottomline: Weather willing the US will be blasting apart a satellite somewhere over the Pacific nearish Hawaii during the darkest part of the lunar eclipse tonight (so they can better see falling chunks – this has a good scientific reason). We are not shooting it down. It’s already on its way down. They’re just skeet shooting a really large metal pigeon filled with poison.

Want to learn more about the satellite (USA 193, for those wanting to know)? Check out Phil’s Bad Astronomy Blog. He’s got a video that gets into all the details.


  1. Nice point. I suspect the media is stuck on that cliche. It is still kinda catchey. Regardless, those erroneous headlines deserved to get shot down. 🙂

  2. So what should we then call the upcoming operation? “Engagement” of the satellite? That’s what the DoD folks use but I’d call that an euphemism. “Attack”? Too aggressive. “Intercept”? Too vague. So even in my – extensive – blog coverage of the events I’ve eventually used “shootdown” now andthen: because almost everyone else does, too. So in a way the MEANING of the term “shootdown” w.r.t. satellites (as opposed to airplanes) is changing as we debate this …

  3. I would guess that the “poison” story is just an excuse. More likely it has some.. er.. “confidential” components that stand a 1 in a million chance of surviving, that they don’t want certain people to know about.

  4. Well, whether or not it is their primary reason, it’s not just a “poison story.” Hydrazine is a pretty nasty chemical poison from all I have read and the satellite’s fuel tanks carry enough to be a serious danger if they land intact. The main question (and not really relevant, ultimately) is whether the first priority is hiding secret technology or destroying dangerous fuel. Either one is a good reason. Definitely go see Phil’s video (link above) – lots of good info there (as usual).

  5. When they make satellites that carry hazardous or classified substances so large that they can survive re-entry, why don’t they just equip them with self-destruct mechanisms that can be triggered on the final orbit? That would be a lot more reliable than trying to intercept it. Maybe they do have that but its’s malfunctioning. Or the Khan has changed the Prefix Code.

  6. Why do you and Phil even bring up the lunar eclipse bit? This can only be coincidental. The Moon will not rise until well after 6pm local time, after the attempt window (~17:30HST) by almost an hour. The Sun will still be well up as local sunset is 18:30 here on the big Island. And even when it does rise it will be in the last stages of partial eclipse

  7. Pam;

    I thought that you understood the physics of orbital dynamics and atmospheric drag better than this.

    I would give you a D- in physics on this subject, because you should know better!

  8. Does anyone remember when MIR space station and how large it was?

    Pam, you should know better!

  9. Hi Steve, I have no idea what you’re attacking me on.

    The satellite was on it’s way down. We hit it with a missile that shattered. This meant that the pieces (in a momentum conserving way) flew in all directions. All directions does not equal down. Some of this directions included up. Since the satellite was actually shattered by the missile, it was not shot down.

    I remember Mir well. It was deliberately deorbited in a controlled manner that: 1) maximized how much the atmosphere would destroy it, and 2) would cause the chunks to fall over the (mostly) unoccupied South Pacific.

    We had no control of US 193, this means it could enter the atmosphere on a path that limited destruction (remember the old Apollo and Gemini missions – angle of descent matters). If this happened over a populated area, then satellite parts (spy tech) and toxic fuel could both end up someplace less than desirable.

    If you are going to make attacks, please be specific and think through what you’re saying. I’m not always going to be right, but scolding me like a disobedient student for unknown reasons is just rude.

    Hey Andrew: here is a link to why Phil and I both said this shoot down eclipse were at the same time (there had been a story o S&T, but I can’t get to it due to a website error now)

  10. I would defend the ‘shoot down’ language as follows.

    If you imagine an object in a circular orbit (which this was, as are all satellites suffering from atmospheric drag eventually), and perturb it a little, then for most perturbations the new orbit will contain a component of its length that is lower than the original orbit. This lower part will be where the air is thickest so it will dominate the drag and pull the apogee down until the orbit is circular again, after which it will spiral in to ground.

    I think that means that when they broke up the satellite, the individual pieces came (or will come) down quicker than the unbroken satellite, even if you don’t count the braking effect of the increased surface area.

    While they did indeed conduct the firing at the middle of totality, I’m sceptical this was a major factor – surely they would design a system like this to operate day and night, probably using radar for the actual, um, battle damage assessment. Still, an original twist on the old “eclipse in the middle of a battle” stories – perhaps in a future war the barbarians will defeat the USA by cunningly launching their attack when no eclipses are happening

  11. “They’re just skeet shooting a really large metal pigeon filled with poison.”

    That’s so awesome, I

  12. oops, no heart symbols…. Ahem, to repeat myself, That’s so awesome, I love it! Can I have your permission to use that quote at some relevant point in the future? =)

  13. Hi Elizabeth – Feel free to use the phrase 🙂

  14. –ù—É –≤—ã –ø–æ–¥–µ—Ä–∏—Ç–µ—Å—å –µ—â–µ, —Ç–æ–∂–µ –º–Ω–µ —Å–ø–æ—Ä—â–∏–∫–∏ 🙂

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