[FRIAM] Fwd: SpaceX's Starlink constellation and space debris

[Steven A Smith]

>From a friend who likes to (over)think things like many of us here do...



-------- Forwarded Message --------
Subject: 	SpaceX's Starlink constellation and space debris
Date: 	Thu, 30 May 2019 08:23:08 -0500
From: 	Jack Horner <jhorner at cybermesa.com>
To: 	'Jack Horner' <jhorner at cybermesa.com>



 

This blurb may be of some interest to you.

 

----------------------------------- begin blurb

 

I’m not convinced by SpaceX’s story about how its Starlink constellation
(when fully populated, ~10K satellites at LEO), at least as reported in
WSJ, NYT, and SpaceX’s own press releases, is going to avoid significant
debris generation.  If we take those sources at face, SpaceX is giving
an insufficiently quantitative response to the question,

 

“Won’t Starlink eventually trash the LEO region?”.  To wit:

 

 1. Space is a big place.
 2. The satellites know how to avoid colliding with one another.
 3. If a satellite’s orbit falls outside its prescribed bounds, the
    satellite will deorbit and burn up in the atmosphere.

 

For example, a SpaceX press release says, in part:

 

-----------  begin excerpt from SpaceX press release
(https://www.spacex.com/sites/spacex/files/starlink_press_kit.pdf)

 

To adjust position on orbit, maintain intended altitude, and deorbit,
Starlink satellites feature Hall thrusters powered by krypton. Designed
and built upon the heritage of Dragon, each spacecraft is equipped with
a Startracker navigation system that allows SpaceX to point the
satellites with precision. Importantly,Starlink satellites are capable
of tracking on-orbit debris and autonomously avoiding collision (JKH:
emphasis mine). Additionally, 95 percent of all components of this
design will quickly burn in Earth’s atmosphere at the end of each
satellite’s lifecycle (JKH: emphasis mine)—exceeding all current safety
standards—with future iterative designs moving to complete disintegration.

 

------------- end excerpt from SpaceX press release

 

A fundamental modeling issue in this regime is whether an “identical and
independent distributions” (iid) probability model (which the “space is
a big place” story almost surely assumes) tells us enough.   If one
satellite collides with another, we can easily get 100 pieces whose
orbital elements are not identical. So any given collision affects can
change the probability of subsequent collisions.  (And those pieces, we
must assume, won’t have the navigational capability to avoid anything.)
 After a collision, therefore, the problem can no longer be modeled as
an iid.   As Dr. Markov would say, the probabilities chain as the
constellation evolves.

 

The Starlink debris-generation question begs for a Markov Chain Monte
Carlo (MCMC) simulation.  I wouldn’t be surprised to learn that someone
has thought about, maybe even attempted, it.  Do we have to solve
something like Gauss’s orbital equations for each piece after a
collision in order to generate a sufficiently informative ensemble for
MCMC?   What’s kind of computational resources does this require?

 

 

------------------------------- end blurb

 

Jack

 

Jack K. Horner

2130 Owens Lane

Lawrence KS 66046

Email: jhorner at cybermesa.com <mailto:jhorner at cybermesa.com>

Voice: 785-424-7579

 

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