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FCC: SpaceX’s Starlink satellites can kill

The sky is falling! The FCC has calculated that fragments from SpaceX’s planned Starlink constellation of almost 12,000 satellites pose a risk of landing on humans on Earth.

SpaceX estimates that several kilograms of each 386-kilogram Starlink could reach the Earth’s surface with sufficient energy to harm or kill someone. NASA has fixed this figure at 15 joules—about the same wallop as a baseball traveling at 51 kilometers per hour. Depending on the satellite’s configuration, iron thruster components, stainless steel reaction wheels, or silicon carbide mirrors could survive the journey from orbit to your head.

…In March and June 2017, the FCC calculated the aggregate risk to humans from the entire constellation. Assuming the 11,927 satellites are launched on a regular basis, they will fail in the same way. Starting around six years from the first launch, an average of five satellites a day will reenter the Earth’s atmosphere, each with a tiny chance of failing to completely burn up, resulting in a part that could hit someone.

But with more than a thousand satellites falling a year, those tiny risks add up. The FCC figured out that, over their lifetime, satellites in the LEO shells posed a 1 in 5 risk of hurting or killing someone, and the VLEO satellites carried a 1 in 4 risk. IEEE Spectrum’s calculations using SpaceX’s most up-to-date information suggests that the overall risk of debris from the constellation causing an injury or death will be 45 percent.

Rather than demanding that we restrict or change what SpaceX does, I see this as an opportunity for someone designing robot satellites designed to clean up space junk. Offer your services to SpaceX. They get their problem solved easily, and you make some money.

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  • Col Beausabre

    Now wait a second, 51 kmph is roughly 34 mph. Plenty of major league baseball players get hit with baseballs moving at 3 times that speed every year, yet nobody dies. A good speed for an average pitch in the majors is about 90 mph (ya average in sliders, curves, etc with the 98 mph fast balls). According to what I remember of high school physics, kinetic energy equals one half the mass of the object times the square of its velocity. So a baseball traveling three times the 30 mph quoted in the article has roughly nine times the energy of the slower object. Yet we don’t see dead baseball plyers being carted out of the park. Yes, batters wear helmets to protect their heads, but they are much more likely to be hit elsewhere on the body (Ump and catcher protection is much more for protection from foul tips). In any case, the normal damage done is just a nasty bruise – unless the batter goes after the pitcher or catcher (see Juan Marichal vs John Roseboro). A ball player being killed by being hit by a ball, at any level, is so rare as to be national news. Bottom line, the chance of someone being killed by debris from one of SpaceX’s satellites is remote even if they are hit. You should be worrying about being killed in an auto crash (aren’t Bezos & Musk working on that too ?).

  • Andi

    That’s a good analysis; however there are two factors to consider when comparing baseballs to satellite debris.

    A baseball will deform somewhat when it hits something, meaning that the force from the collision will be lessened and spread out over a bit of time, so less of a G force and therefore less of an impact (pun intended) on the recipient. Satellite debris will most likely not deform.

    Satellite debris will most likely consist of many sharp metal edges, reducing the surface area of whatever part hits you and therefore increasing the overpressure (psi) of the collision.

  • wodun

    Rather than demanding that we restrict or change what SpaceX does, I see this as an opportunity for someone designing robot satellites designed to clean up space junk.

    Didn’t they choose the size of the satellites and the orbit precisely because they want them to have a limited life and burn up in the atmosphere? It does remove haggling over GEO slots too. With an option of collecting or refueling the satellites, what is the advantage to this orbit over others? And if collected, how difficult to change orbits to take the trash someplace else and what will be done with it?

    Since SpaceX is supposed to be just one of many companies taking this approach, it makes sense to look at the problem of debris more closely.

  • Ralph Buttigieg

    Wouldn’t SpaceX still have some control over the satellite? Surely they would dump them over the ocean to reduce risk.

  • fred k

    > overall risk of debris from the constellation causing an injury or death will be 45 percent.

    What? 45% of what? This is not a reasonable number. I call BS on this.

    First off, I believe that the sat will be operated to aim to drop into the ocean. In the case they happen to malfunction, only then, we have a very small chance of landing somewhere remotely close to humans.

    These particular sats will mostly burn up, with only a few pieces with a probability of surviving to the ground. This sounds roughly equivalent to the normal flux of meteorites, and way, way lower probability than failing aircraft parts or tree limbs.

    I’m open to looking for unique ideas to mitigate possible damage, but we have to use actual math to calculate probabilities, and we also have to use good judgement not to waste time and effort on very low probability “problems” with low impact.

  • Dick Eagleson


    Metal parts that have been thru a re-entry usually have any sharp edges melted into radiused curves. Those silicon carbide mirrors referred to might hold up better, but even that is doubtful.

  • Leaving the numbers aside, the studies and the article seem to assume that failed satellites randomly fall to Earth. We know that this is not true, as satellite operators generally take care to de-orbit hardware in a controlled manner, i.e. over unpopulated areas. I would think that end-of-life management would be a requirement for obtaining an operating license, and ‘We’ll just see where it lands’ isn’t an acceptable answer.

  • When I see an article like this I first like to run my own back-if-the-envelope calculation to see they are even within an order of magnitude close. So I calculated how much of there surface area of the Earth was covered by the bodies of people assuming that at least one piece was coming in at an angle. My estimate is that, for a constellation of 12,000 satellites with one object hitting the ground at the listed velocity then there would be about a 60% chance that someone would be injured. So yes, it seems as though the report isn’t crazily off. So, I would say that an ability to do a directed deorbit might be a pretty important feature for the Starlinks to have.

  • pzatchok

    I do not believe they have the fuel to change orbit enough to make sure they hit the water.

    And being so low recovery is not an option.

    The one reason for this small size is for economy. It makes is cost back inside of its lifetime and then burns up. Then is more advanced replacement takes its place.

    As for making sure they burn up all the way just change some of the materials. Granted this could make the engineering of this a bit more complex.
    Flywheels don’t have to be made of 100% metal.

  • Col Beausabre

    Doug, Without letting others see your math, your claim is impossible to critique. Please share with us how you came up with your results.

  • Edward

    pzatchok wrote: “I do not believe they have the fuel to change orbit enough to make sure they hit the water.

    They don’t have to change the orbital plane, they just have to time the reentry burn in order to make sure that the reentry is over water. The Pacific is the traditional choice for disposing of items in orbit; if you aim for it, it is hard to miss.

    From the article:

    When that fuel runs low, after around six years, the satellites will use the remainder to nudge themselves into the denser atmosphere below. Each satellite, just a little smaller in size than a Tesla Model 3, will then swiftly burn up.

    Clearly, the IEEE Spectrum is suggesting that SpaceX and Starlink will not aim for water. The article notes that there is an intention to deorbit each satellite, which implies that they will be aimed for a safe reentry, so why is there the conclusion that the SpaceX’s satellites will start killing and injuring people?

    Robert has a suggestion:

    There are a lot of competitors to SpaceX who do not want it to succeed, and it would not surprise me if they are trying to throw a wrench in the operation to stop Starlink. A bad report like yesterday’s [the article of this post] might cause big investors to back out.

    Since it is the IEEE Spectrum that is making the dire prediction that none of the satellites will be intentionally deorbited safely, one could infer that IEEE Spectrum is also one of those who do not want SpaceX to succeed.

    The lead sentence says: ‘The chance that SpaceX’s planned Starlink satellite constellation will cause an injury or death is 45 percent every six years, according to an IEEE Spectrum analysis of figures submitted by the company to the U.S. Federal Communications Commission.

    The best part of this wording is that it gets us all to believe that it is the government, not IEEE Spectrum, that has made this conclusion. Thus Robert’s headline points to the FCC, not IEEE Spectrum, as the one making the conclusion. If I hadn’t written this reply then I, too, would have been fooled by the wording, and until five minutes ago I had written that it was the FCC that did not want SpaceX to succeed. Now I know better.

    The article uses the FCC’s data, saying that “The FCC says hundreds of fragments from the Starlink constellation could reach the Earth’s surface every day,” and then implies that they will be uncontrolled in any way, randomly striking the Earth. Only later do they bury the truth that some fuel is used to intentionally deorbit the satellites, giving SpaceX the ability to save lives.

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