Re: [Starlink] Hitting an atira asteroid with a spacex starship?

[Ulrich Speidel <u.speidel@auckland.ac.nz>]

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Space is a big place indeed. Couple of points:

  * Kessler syndrome requires objects after a collision to remain (at
    least temporarily) in a sustainable orbit around Earth. That is, any
    fragments of a collision must continue to travel post collision with
    a velocity and at a trajectory that allows them to stay in an orbit
    around Earth of sorts. It's therefore almost a prerequisite for
    Kessler syndrome that the objects participating in the collision be
    in an Earth orbit before the collision. If they aren't, then most of
    the fragments will either end up down here or somewhere of no
    consequence. By definition, asteroids aren't in Earth orbits.
  * Any mission to defend against an asteroid would likely require
    intervention by impact / attachment / etc. many millions of miles
    from Earth, not in low earth orbit as some of our contributors here
    seem to assume. By the time your asteroid has reached the heights
    where most of our satellites orbit, it'd be way too late. Asteroids
    of consequence are likely to have a mass orders of magnitude higher
    than anything we can send their way, so any mission would need to
    bank on making a small difference (by crash, persistent push, or
    ...) on the object's trajectory early enough to make sure it or its
    fragments give us a wide berth.

"Don't look up" is great cinema, but you're very unlikely to get any 
naked eye visual warning of an asteroid impact that would allow you to 
see your nemesis for any great length of time. Just ask the dinosaurs: 
They didn't have any mobile devices and social media to distract their 
attention, probably did look up now and then, and for all we know didn't 
see it coming either.

On 4/11/2022 4:48 pm, Bruce Perens via Starlink wrote:
>
>
> On Thu, Nov 3, 2022 at 5:52 PM Dave Taht <dave.taht@gmail.com> wrote:
>
>     Space is a big place, and I'm pretty sure the orbit, impact, and
>     debris could be tracked.
>
>
> Actually, no. The Space Shuttle got a very concerning bulls-eye in its 
> front cockpit window a few decades ago from a tiny paint chip. The 
> speed of two objects in counter-rotating orbits when they hit imparts 
> a  truly large amount of energy. And there are now so many such things 
> that there is a significant risk to suited astronauts on EVAs.
>
> NORAD will not actually tell us how small an object it can track, nor 
> how many, this being something potentially of interest to enemies. The 
> Satellite Catalog that they publish covers objects of 10 cm diameter 
> and larger, a 1U PocketQube satellite is 5x5x5 cm plus antennas that 
> bring it to 10 cm, and the early ephemerides published by NORAD for 
> such objects can be inaccurate. We aren't allowed to launch anything 
> smaller.
>
> We also are now required to provide a position-changing ability to 
> avoid collisions, and active re-entry at the end of the life of a 
> satellite. This is mainly about the potential for Kessler Syndrome.
>
> The 60 years of thinking that orbital space is so big that we don't 
> have to concern ourselves with debris are definitely over.
>
>     What would you do with a starship that after launch, due to lost
>     tiles, or other problems is certain to burn up on re-entry? Why
>     not test getting out of orbit?
>
>
> Put it somewhere that you can use the habitable volume. Starship 
> potentially has a larger habitable volume than ISS. That is /without/ 
> converting the tanks.
>
> Otherwise, if you have the delta-V to get there, there is a junkyard 
> orbit above geosynchronous. Things will stay there for a really long 
> time. The other option is a controlled re-entry with a known 
> termination in the middle of an ocean.
>
> China drops entire stages on farmers fields and rural roads in their 
> own country quite often, but this is not thought well of by others.
>
>     That takes all the fun out of it. Impact is so much easier. Our
>     knowledge of the solar system is only skin deep.
>
>
> People are even starting to get annoyed about stuff that hits the 
> moon, although this doesn't create orbital debris unless the energy is 
> really huge.
>
>     Thanks
>
>     Bruce
>
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-- 
****************************************************************
Dr. Ulrich Speidel

School of Computer Science

Room 303S.594 (City Campus)

The University of Auckland
u.speidel@auckland.ac.nz  
http://www.cs.auckland.ac.nz/~ulrich/
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