re: Mir

From: Walter Nissen (
Date: Mon Feb 19 2001 - 15:50:17 PST

  • Next message: Walter Nissen: "Re: FEB14-15.OBS" ("Carl H. Schmid") writes:
    > Am I correct in assuming that the long-term predictions should not be
    > considered reliable?
    No long-term predictions are reliable.
    heavens-above uses elsets, typically from OIG.  Typical elsets, from any
    typical source, are bloated with useless trash, filler bits, ASCII bits,
    insignificant bits; but, even with these, typical OIG elsets contain
    fairly accurate information with only 1 exception.  Unfortunately, this
    exception is the drag factors, 1 of the most critical data.  Thus,
    predictions made from them typically become grossly inaccurate after
    only days, or even hours.
    Even if the drag factors were accurate, long-term propagation from them
    would fail because the atmosphere is constantly expanding and
    contracting.  Thus, the path followed is "wavy".  An elset is merely
    tangential, or technically, osculating.  Even if perfectly accurate,
    even if a perfect model were used, even if totally unpowered, reality
    would diverge.  A drag factor appropriate for the next few hours might
    well be different than one appropriate for the next few days.
    If you take elsets from the last month or so, and use them to predict a
    current pass, you can assume the latest elset generates an accurate
    prediction.  The others differ typically overwhelmingly for 1 reason,
    because the drag factors are bad.  If you pick a really old elset that
    generates a good current prediction and copy its drag factors into all
    the other elsets, typically, those elsets will become quite good.
    Typically, I find that recent empirical drag (computing differentials
    from the MMs in recent elsets) is better than typical drag factors in
    the most recent elset.
    When I think, based on a trend in the MMs, that the atmosphere is
    expanding, i.e., that the drag is increasing, I usually increment the
    drag factors to a moderately higher value.  Or at least choose to use
    the elset with the largest drag factors.  That way, at least people are
    looking a bit early.  And not late.
    People who know more about this subject than I do, Mike McCants, Ted
    Molczan, Russell Eberst, Rainer Kracht, Bj"orn Gimle, Bart De Pontieu,
    Alan Pickup, Harro Zimmer, etc., are urgently requested to correct any
    errors and provide any amplifications with which they might choose to
    grace us.  I offer to edit any such contributions at the request of
     ("Jim King") writes:
    > Wristwatches:  My wife bought a handful of $10 Casio wristwatches at a
    > discount store, set them all, put them on a shelf, and then let them
    > run for a couple weeks.  Then she picked the one that had the least
    > error, and returned all the others to the store.
    I think this works for thermometers (with due consideration for
    shioplifting observation, you needn't leave the store with more than
    one), but I'm not so sure about watches.  The quartz crystal can change
    its frequency.  Worse, the rate varies with battery voltage so either
    drift or frequent battery changes must occur.
    I don't have data to support this, but I think they tend to run faster
    and faster, so buying one that runs slightly slow might be optimal.
    Generally, I think, though a bit more trouble, calibrating the slew is
    more successful than trying to eliminate it.
    Walter Nissen         
    -81.8637, 41.3735, 256m elevation
    It is a myth that Al Gore "won the popular vote".  One distinguishes
    between winning a race and receiving more votes.  There was no race for
    the popular vote.  Thus, there was no winner.  In actuality, the parties
    allocated weeks of time and $100,000,000's in the race for electors.
    Had the allocations been made for a race for the popular vote, Gore
    might also have lost that race by 154 votes.  Separately, we will
    probably never know the true impact of various improper means of
    influencing the result, such as the series of Gore-favorable calls and
    non-calls made by VNS while the polls were still open on election
    afternoon and evening, 2000-11-07, attempts to discourage certain
    voters, party control of the various election canvassing boards, various
    classical means of election fraud, etc.  Further, one distinguishes
    between winning "a popular vote" and "the popular vote".  Gore won more
    popular votes; he did not win the popular vote.
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