Re: Iridium, Cosmos collide

From: Brian Weeden (
Date: Thu Feb 12 2009 - 10:32:16 UTC

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    Just because the information is available does not necessarily mean
    that the correct information was provided to the correct
    decision-making authority at the correct time.  While SOCRATES does
    provide automatic CA accessible to everyone on the net, it is using
    the public TLEs which as we all know can have a significant amount of
    error.  And because the error in the TLEs is not provided you don't
    have the covariance matrix to do accurately assess probability. Basing
    a complicated and potentially expensive (in terms of fuel) maneuver
    decision on only this info is probably not recommended.
    Each satellite owner-operator needs to make their own risk assessment,
    based on not only the probability of collision but also the reduction
    of the lifetime of the satellite from expending fuel to to a collision
    avoidance maneuver.  Once the decision to maneuver is made,
    calculating the correct maneuver to minimize fuel expenditure while
    also assuring you're not maneuvering into another (possibly worse)
    close approach down the road.
    The US Air Force does do daily a conjunction assessment screening, but
    for only a limited number of objects.  NASA and ESA have looked at all
    vs all conjunction assessment scenarios (basically screening
    everything in the catalog vs everything else) and estimated that there
    would be a few thousand close approaches each day.  Sorting through
    all of those to find the ones that are the real risks, doing follow-up
    tracking and more detailed analysis to calculate hard probabilities
    and informing the right authorities requires an amount of resources
    that no one has at this point.
    That being said, I agree with your statement about conjunction
    analysis and collision avoidance being extremely important for space
    sustainability.  Getting the data, disseminating the data, and
    providing analytical tools to the right people are all important
    pieces and there are many people working on sorting this out
    (including the foundation I work for).
    Brian Weeden
    Technical Consultant
    Secure World Foundation
    On Thu, Feb 12, 2009 at 4:55 AM, B Gimle @ComHem <> wrote:
    > I was looking at data for a previous high (>1%) collision risk on
    > T.S.Kelso's SOCRATES
    > and happened to save the output for Feb.08-14
    > This collision was not on the list, but possibly this is where many
    > operators get their warnings!
    > /Björn
    > ----- Original Message ----- From: "Susan Kaltenbach" <>
    > To: <>
    > Sent: Thursday, February 12, 2009 2:04 AM
    > Subject: RE: Iridium, Cosmos collide
    >> I'm very confused.
    >> With all the tracking done by our military and our highly skilled See-Sat
    >> detectives, how could the collision have been a surprise? An important
    >> component of tracking is to predict orbital paths, is it not? The only
    >> thing
    >> that makes sense to me is some kind of sudden orbital change.
    >> I hope I'm not off topic here, but I always assumed that observing,
    >> tracking, and predicting objects in orbit were all strongly associated.
    >> And
    >> I'm pretty stunned by the whole thing.
    >> Susan Kaltenbach
    >> PS - I haven't been receiving FPSPACE messages and I'm starved for
    >> information. I hope it's just me and that their server isn't down.
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