7 ms·

Related [1] (framed in the context of the Fermi Paradox). I love these topics. While we might be nowhere near Kesssler Syndrome, the risks of space debris impa

by cletus 2y ago

Related [1] (framed in the context of the Fermi Paradox). I love these topics. While we might be nowhere near Kesssler Syndrome, the risks of space debris impacts are very real [2]. Some of the debris we've put up there intentionally and it's quite insane, most notably Project West Ford [3]. I believe that now anything put in space has to have a plan for how it will be decommissioned. For LEO probs, that typically means burning up in the atmosphere or, if it's large enough, crashing in Point Nemo [4]. For geostationary satellites, they're typically put in a disposal or graveyard orbit [5]. That doesn't solve the problem. It just kicks the can down the road. People might think you can just accelerate a bit and leave Earth but that's not how orbital mechanics work. If you accelerate a bit you've just created a new orbit. You still need a lot of energy to leave Earth orbit. It's the same reason why dumping waste into the Sun (as some like to suggest) is completely unworkable. You can't just slow down a bit and fall slowly into the Sun. You just create a new orbit. It still takes a delta-V of ~30km/s to hit the Sun [6]. Fun fact: it requires less delta-V to reach Pluto then hit the Sun than it does to hit the Sun directly. Orbital mechanics are weird. EDIT: fixed delta-V units. [1]: https://www.youtube.com/watch?v=GCCKpI80V6M https://www.youtube.com/watch?v=GCCKpI80V6M [2]: https://www.space.com/9708-worst-space-debris-events-time.html https://www.space.com/9708-worst-space-debris-events-time.ht... [3]: https://www.wired.com/2013/08/project-west-ford/ https://www.wired.com/2013/08/project-west-ford/ [4]: https://www.atlasobscura.com/articles/strange-maps-point-nemo https://www.atlasobscura.com/articles/strange-maps-point-nem... [5]: https://en.wikipedia.org/wiki/Graveyard_orbit https://en.wikipedia.org/wiki/Graveyard_orbit [6]: https://en.wikipedia.org/wiki/Delta-v_budget https://en.wikipedia.org/wiki/Delta-v_budget

FredFS456 2y ago
> It still takes a delta-V of ~30m/s to hit the Sun. That number looks like it should be much much bigger to me.
- dabluecaboose 2y ago
  Indeed, it's off by orders of magnitude (so probably a simple typo). The Earth orbits the Sun at between 29 and 30 km/s. It would take roughly that much dV to successfully create an orbit that intersects the sun.
- tialaramex 2y ago
  The straight forward way is typically given as 30km/s so yeah, it's the wrong unit. But, you'd never actually do that, the calculations involved assume you have decided to specifically go towards the sun, maybe to get there quickly, but going to the sun is just a means to an end, so you'd actually pull shenanigans to get the same result indirectly for "only" a few km/s of delta V with carefully chosen launch windows. Which is like how it'd be easier to build a bridge from Greenland to Iceland than from Greenland to Spain. "We can't do that" versus "We can't do that either".
  - ninkendo 2y ago
    Even without gravitational slingshots, the simple solution would be to just take advantage of the oberth effect and do many, many successive burns, retrograde at aphelion and prograde at perihelion, until your perihelion is low enough to intersect the sun. It wouldn’t be crazily less delta-V but it would be appreciably lower. Another related fun fact from GP’s is that it’s way less delta-V to hit the sun from Pluto than it is from the Earth… 4.63 km/s according to wolfram: https://www.wolframalpha.com/input?i=hohmann+exit+delta+v%2C+Sun&assumption=%7B%22FS%22%7D+-%3E+%7B%7B%22HohmannExitDeltaV%22%2C+%22deltav2%22%7D%2C+%7B%22HohmannExitDeltaV%22%2C+%22r2%22%7D%2C+%7B%22HohmannExitDeltaV%22%2C+%22r1%22%7D%7D&assumption=%7B%22F%22%2C+%22HohmannExitDeltaV%22%2C+%22r2%22%7D+-%3E%2240+au%22&assumption=%7B%22F%22%2C+%22HohmannExitDeltaV%22%2C+%22r1%22%7D+-%3E%22695000000m%22 https://www.wolframalpha.com/input?i=hohmann+exit+delta+v%2C...

by cletus 2y ago

FredFS456 2y ago

> It still takes a delta-V of ~30m/s to hit the Sun. That number looks like it should be much much bigger to me.

dabluecaboose 2y ago
Indeed, it's off by orders of magnitude (so probably a simple typo). The Earth orbits the Sun at between 29 and 30 km/s. It would take roughly that much dV to successfully create an orbit that intersects the sun.
tialaramex 2y ago
The straight forward way is typically given as 30km/s so yeah, it's the wrong unit. But, you'd never actually do that, the calculations involved assume you have decided to specifically go towards the sun, maybe to get there quickly, but going to the sun is just a means to an end, so you'd actually pull shenanigans to get the same result indirectly for "only" a few km/s of delta V with carefully chosen launch windows. Which is like how it'd be easier to build a bridge from Greenland to Iceland than from Greenland to Spain. "We can't do that" versus "We can't do that either".
- ninkendo 2y ago
  Even without gravitational slingshots, the simple solution would be to just take advantage of the oberth effect and do many, many successive burns, retrograde at aphelion and prograde at perihelion, until your perihelion is low enough to intersect the sun. It wouldn’t be crazily less delta-V but it would be appreciably lower. Another related fun fact from GP’s is that it’s way less delta-V to hit the sun from Pluto than it is from the Earth… 4.63 km/s according to wolfram: https://www.wolframalpha.com/input?i=hohmann+exit+delta+v%2C+Sun&assumption=%7B%22FS%22%7D+-%3E+%7B%7B%22HohmannExitDeltaV%22%2C+%22deltav2%22%7D%2C+%7B%22HohmannExitDeltaV%22%2C+%22r2%22%7D%2C+%7B%22HohmannExitDeltaV%22%2C+%22r1%22%7D%7D&assumption=%7B%22F%22%2C+%22HohmannExitDeltaV%22%2C+%22r2%22%7D+-%3E%2240+au%22&assumption=%7B%22F%22%2C+%22HohmannExitDeltaV%22%2C+%22r1%22%7D+-%3E%22695000000m%22 https://www.wolframalpha.com/input?i=hohmann+exit+delta+v%2C...