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Tiny object hits robot arm on ISS

According to the Canadian Space Agency, a very small piece of space debris hit that country’s robot arm on ISS at some point in the recent past, producing a hole about 5mm wide, or about 1/5th of an inch in diameter.

During a routine inspection on May 12 robotic operators observed the hole in the boom section of the Canadarm2. After working with NASA to take detailed images of the impact, the agencies concluded the hole is about 5mm in diameter.

The damage is limited to a small section of the arm boom and thermal blanket. CSA says despite the impact, the arm’s performance is unaffected.

While space junk is a concern, this story is not about that, even if the authorities at CSA are hyping it, and as usual the mainstream press (as indicated by the article at the link) is buying into the propaganda. Space stations like ISS and Mir are routinely hit by micrometeorites. Though most impacts are much much smaller than the object that produced this hole and do no significant harm, hits like this one have happened in the past.

However, almost all such impacts are from natural objects from space. In fact, as far as I know, tiny holes this size are always caused by natural objects (with the one exception of the hole someone in Russia accidently drilled into the hull of one Soyuz spacecraft). Yet, the officials at Canada’s space agency immediately used the discovery to lobby for action against human-made space junk, even though they also admit they have no evidence this hole was produced by space junk, and past evidence strongly suggests it was not junk.

The real story here is whether the hulls on ISS’s various modules are sufficiently robust to withstand such somewhat expected and not-so-unusual natural impacts. And based on the station’s survival without any issue now for almost a quarter century, it appears that its shielding is sufficient, and will likely work for any long term mission to Mars or beyond. In fact, that the impact did no significant harm to the robot arm, which has been operating without stop, is further proof of that good design.

This is not to say that natural objects aren’t a threat. The data just shows that the threat from really dangerous objects large enough to do real harm is very very rare, to the point that, from a cost-benefit perspective, it makes little sense to protect against them. Future interplanetary space stations can rely on the hull shielding designs now used with some confidence.

As for space junk, that certainly is a problem that must be addressed. It just isn’t what this story is really about.

Pioneer cover

From the press release: From the moment he is handed a possibility of making the first alien contact, Saunders Maxwell decides he will do it, even if doing so takes him through hell and back.

Unfortunately, that is exactly where that journey takes him.

The vision that Zimmerman paints of vibrant human colonies on the Moon, Mars, the asteroids, and beyond, indomitably fighting the harsh lifeless environment of space to build new societies, captures perfectly the emerging space race we see today.

He also captures in Pioneer the heart of the human spirit, willing to push forward no matter the odds, no matter the cost. It is that spirit that will make the exploration of the heavens possible, forever, into the never-ending future.

Available everywhere for $3.99 (before discount) at amazon, Barnes & Noble, all ebook vendors, or direct from the ebook publisher, ebookit. And if you buy it from ebookit you don't support the big tech companies and I get a bigger cut much sooner.


  • J Fincannon

    I guess I do not see how you can say “…almost all such impacts are from natural objects from space. In fact, as far as I know, tiny holes this size are always caused by natural objects”. I do not see how you could possibly determine this origin.

  • J Fincannon

    LDEF had gathered data on its surfaces which were analyzed after being brought back. This was used to build new impact models.
    FIGURE 3-1 shows the number per unit area per time for various diameters. For both debris and micrometeorites. This is a 1996 model.
    It shows roughly the same number of particles for either natural or manmade source between .001cm and .3cm diameter. The 5mm hole is .5cm in diameter, but usually the size of the impactor is much smaller than the hole diameter. Depends on the material. But based on this reference, the odds are about equal for natural vs man made in that figure.

    Another source is Figures 1 and 2 of “Overview of the Space Debris Environment”. 1995.
    It shows similar results to the other report, but it has the crater diameter in Figure 2. For .5cm diameter crater, the model shows somewhat more frequency due to man made debris than for natural causes.

    So, the ISS solar array area is 2500 m^2. How many craters the same size as on the Canada arm would be seen over 5.75 years on the array? .05 per m^2 from orbital debris and .009 per m^2 for natural sources. Or 2500*.05=125 from satellite debris and 2500*.009=22 from natural sources.

    This sounds pretty bad. Especially since the ISS solar arrays have been up there for more than 5.75 years. Of course the solar arrays have no shielding. These impacts usually go right through the solar array. They may sometimes damage it more than a minor degradation. But they have to hit the exact right spot to do so. But the array design has been made to have some excess capability to handle this kind of abuse.

    Most of the other ISS elements have shielding to absorb impacts. Robot arms and other external items might not have so much shielding.

  • J Fincannon: As always I accept your engineering wisdom in these matters. However, even though man-made objects of small size might be an equal threat as natural objects, the main point remains. The designs of the hulls for the habitable parts of ISS seems now robust, based on these impact rates.

    As for the solar arrays, it seems to me that they are functioning sufficiently despite the hit rate. Nothing lasts forever. Designs should incorporate the slow wear rate caused by these small particles.

    Moreover, if anything your good analysis shows that any interplanetary ship leaving Earth orbit and designed as ISS and Mir have been should do quite well once exposed to the natural objects in interplanetary space, since the hit rate will be at least half.

  • J Fincannon

    Mr. Zimmerman:
    Thanks for your confidence.

    You are right about the solar arrays having been designed to last. But a number of strings have been taken out of action. Oh well.

    And while it is true the orbit debris impacts will go away, I prefer them to the radiation out there. ISS and Mir did not have to worry about that.

  • Jeff Wright

    The Starlink haters will still try to exploit this.

  • wayne

    sorta realistic…..
    Gravity (2013)
    “…disconnect from Hubble, begin re-entry procedure, ISS initiate emergency evacuation…”*
    [* that, is quite a bit to do in 15 seconds]

    better realistic….
    The Expanse Se2Ep2
    “The Rocinante Attacks the Spin Station”

  • J Fincannon

    One other thing I thought of. If you take the ISS or Mir out of Low Earth Orbit into interplanetary space, then the beneficial blocking/shielding of incoming impactors by the Earth no longer exists. So, I suspect that the total number of impactors will remain relatively the same as LEO except of course they would be now 100% meteoroids.

  • Andrew_W

    If you take the ISS or Mir out of Low Earth Orbit into interplanetary space, then the beneficial blocking/shielding of incoming impactors by the Earth no longer exists. So, I suspect that the total number of impactors will remain relatively the same as LEO except of course they would be now 100% meteoroids.
    The Earth both blocks and attracts potential impactors.

  • J Fincannon

    Yes, that is true. I guess this means we have to run the analysis.

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