carls@adaptautomation.com ("Carl H. Schmid") writes: > Am I correct in assuming that the long-term predictions should not be > considered reliable? Absolutely. 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 contributors. jim@jimking.net ("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. Cheers. Walter Nissen wnissen@tfn.net -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. ----------------------------------------------------------------- Unsubscribe from SeeSat-L by sending a message with 'unsubscribe' in the SUBJECT to SeeSat-L-request@lists.satellite.eu.org http://www2.satellite.eu.org/seesat/seesatindex.html
This archive was generated by hypermail 2b29 : Mon Feb 19 2001 - 15:23:12 PST