Maybe it’s time to reassess the risk of space junk falling to Earth

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Chuckstar

Chuckstar

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  • #241
    qchronod said:
    A few of what I think are relevant sections from the newer paper that was linked to above:

    Potential Ozone Depletion From Satellite Demise During Atmospheric Reentry in the Era of Mega-Constellations​

    Spacecraft burn up during atmospheric reentry, loosing an average of 51%–95% of their mass in the process (Anselmo & Pardini, 2005; Pardini & Anselmo, 2019).

    In 2022, the total mass of reentering objects was estimated to be 332.5 metric tons (ESA, 2023), a 21% increase from the previous year, with 93% of that mass originated from LEO. More than one million radio-frequency spectrum allocation requests were made for planned satellites over the last 5 years (Falle et al., 2023). Forecasts point to future reentry rates of 800–3,200 metric tons per year for satellites, and up to 1,000 metric tons per year for launch vehicles (Organski et al., 2020). The engineering approach of design-for-demise (Kärräng et al., 2019; Waswa & Hoffman, 2012) and the deployment of active debris removal solutions may further exacerbate the aforementioned trend. As for natural sources, meteoroids enter the atmosphere at an average rate of over 11,750 metric tons per year (Drolshagen et al., 2017).

    The differential equation is iteratively solved for a null initial velocity at a geometric altitude of 86 km. The settling time is computed for clusters such as the ones presented in Figure 1c, with aerodynamic diameter ranging within 0.4–4.2 nm. At macro scale, the expected value for the aerodynamic diameter is estimated to be 4.1 nm (Ferreira et al., 2023b), taking up to 30 years to reach the altitude of 40 km.

    It is then possible to infer that a single reentry event of a 250-kg satellite with a 30% aluminum mass fraction yields approximately 29.8 kg worth of AlO particles and 51.0 kg of Al after thermal ablation, in the higher mesosphere.

    Studies have shown that the meteoroid flux averages at 32.2 metric tons/day considering the largest object statistically expected to hit the Earth every day has a diameter of 0.5 m (Drolshagen et al., 2017). However, objects of such size in a hypervelocity entry (Hunt et al., 2004) and excitation temperatures around 4,400 K (Jenniskens, 2004) are expected to fully demise (Guttormsen et al., 2020). Further, a comprehensive analysis of historic meteorite surveys as to chemical composition points to a mean aluminum mass fraction of 1.2% (Schulz & Glassmeier, 2021). The TOA aluminum injection from micrometeoroids is 141.1 metric tons/year, and it is taken to be time-invariant. As for anthropogenic contributions, satellite-related objects reentering from LEO totaled 121.8 metric tons in 2016 (ESA, 2017) and 308.9 metric tons in 2022 (ESA, 2023). Concerning the future mega-constellations scenario, the worst-case estimation of Organski et al. (2020) is taken, with up to 3,200 metric tons of satellites reentering each year.

    We then estimate an increase in TOA aluminum compounds (and excess ratio) originated from satellites, from 5.36 metric tons in 2016 (3.8% in excess of natural sources) to 41.7 metric tons in 2022 (excess of 29.5%). The future mega-constellations scenario of increased reentry rates would lead to 912.0 metric tons per year of TOA aluminum from satellites only (excess of 646%).
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    Right, but as pointed out above, it’s likely not the excess aluminum over baseline aluminum that probably matters, nut the excess metal oxides over baseline metal oxides that matters, which is a much smaller percent increase.
     
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    OrvGull

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  • #242
    Tom the Melaniephile said:
    They can't. The study literally said the researchers didn't do any calculations about effects on ozone.
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    The tricky bit is the effect is delayed by a decade, so by the time we have absolute proof the ozone is depleting it'll be too late.

    This thread reminds me of the people who still think the R-12 ban was a conspiracy. There is no level of proof that can satisfy everyone, especially when there's a lot of money to be made sowing doubt.
     
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    Tom the Melaniephile

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  • #243
    OrvGull said:
    The tricky bit is the effect is delayed by a decade, so by the time we have absolute proof the ozone is depleting it'll be too late.
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    Dude. Nobody is asking for "absolute proof" - and you know it. The researchers literally didn't even bother trying to make a calculation. Hell, in the prior thread we had an Arsian put together calculations.
    OrvGull said:
    This thread reminds me of the people who still think the R-12 ban was a conspiracy.
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    Why is it always some "conspiracy" to you when someone points out the flaws in your position? Making baseless personal accusations doesn't improve your position at all.

    Why are you (so far) incapable of actually having a logical discussion here? All you're doing at this point is further discrediting yourself.
     
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    Tom the Melaniephile

    Tom the Melaniephile

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  • #244
    glappkaeft said:
    This is a Dragon 2 issue so Cargo Dragon doesn't count. Cargo Dragon deorbited with its trunk, Dragon 2 doesn't. The reason Dragon 2 discards the trunk in orbit before deorbiting is that if the trunk fails to detach it is likely a complete loss of vehicle and crew.
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    You seem confused here. The current Cargo Dragon is a Dragon 2.

    en.wikipedia.org

    SpaceX Dragon 2 - Wikipedia

    en.wikipedia.org en.wikipedia.org
     
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    BrangdonJ

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  • #247
    ZenBeam said:
    I'm a day behind, so maybe this was addressed earlier, but something in your gutter being magnetic does not mean it's a meteorite.

    I guess the thought process is magnets are mysterious and meteorites are mysterious so magnets must be meteorites, but that's simply not correct.
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    The magnet helps collect them. The next step is to examine them with a microscope to determine whether they are, in fact, micrometeorites. See for example, BBC, Popular Science.

    Be aware that using magnets is now frowned upon in some circles because it destroys their magnetic history. Eg MIT News. It probably doesn't matter for microscopic ones found in your gutter which weren't going to be donated to science anyway.
     
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    Gattix

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  • #248
    BrangdonJ said:
    The magnet helps collect them. The next step is to examine them with a microscope to determine whether they are, in fact, micrometeorites. See for example, BBC, Popular Science.

    Be aware that using magnets is now frowned upon in some circles because it destroys their magnetic history. Eg MIT News. It probably doesn't matter for microscopic ones found in your gutter which weren't going to be donated to science anyway.
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    Micrometeorites are unlikely to have much magnetic memory in the first place. They are for the most part <1mm spheroids that have completely melted into a sort of rain drop shape, that's a much more effective way of getting rid of previous magnetization than hand magnets.

    And yeah, getting definitive proof that any specific bit of metal is actually a micrometeorite is going to be hard. But statistically, if you get a hold of a bunch of magnetic particles from a sufficiently old roof, probably quite a few of them in there somewhere. They're not rare at all, the haystack just has way too much hay.
     
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    mmiller7

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  • #249
    el_oscuro said:
    Perhaps they could order some of that explosive space tape from Boeing?
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    With the track record though...it probably wouldn't detonate. I mean the door wasn't supposed to explosively decompress off the plane so you would stand to reason the explosives will not explode, right?
     
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