[amsat-bb] Equatorial Crossing Data (EQX) (easy predictions)
bruninga at usna.edu
Fri Aug 1 19:49:48 UTC 2014
Actually, using simple pass-times, it is possible to predict with a simple
pencil, all future pass times for several weeks.
Every satelite REPEATs their daily ground track every few days or so.
AO51 repeated every 5 days, and GO32 every 9. These were sun synchronous
and so not only the ground track repeated but the time of the passes
repeated as well.
See the examples on: http://aprs.org/MobileLEOtracking.html
The ISS is not sun synchronous, but these three rules will predict future
ISS passes without any stinkin-confusor:
1) If you hear one pass, 5 out of 7 times, the next one is about 90
2) The ISS REPEATS the same ground track every other day but 51 minutes
3) For a given day, the same pass the next day is 23 minutes later.
This makes portable APRS operations in the wilderness easy. All you need
is ONE PASS time, and you can infer all the others for weeks using the
simple rules, and just keepin notes on pass TIMES when heard.
You don't need no-stinkin-computer. Satellites are in "orbit" and
Just take your favorite satellite, print out a week of passes, and then
look for the "RULE" that will predict future passes. Then all you need to
remember, is the RULE.
From: amsat-bb-bounces at amsat.org [mailto:amsat-bb-bounces at amsat.org] On
Behalf Of EMike McCardel
Sent: Friday, August 01, 2014 1:40 PM
To: Glen Gardner
Cc: amsat-bb at amsat.org
Subject: Re: [amsat-bb] Equatorial Crossing Data (EQX)
Glen, Paul and Joseph,
Thank you for your replies. I am learning a lot here. My imagination has
been captured by learning to use the Satellabe and OscarLocator prepping
for my presentation on tracking satellites at the AMSAT Training Day
during the ARRL Centennial. I also discovered a construct involving a
globe offering a 3D rendition of of a pass. This is an interesting way to
demonstrate how the earth moves independent of the orbit. I can't help but
think that some of the analogue tools of the day still have relevancy.
EMike McCardel, KC8YLD
VP for Educational Relations AMSAT-NA
Sent from my iPhone
> On Aug 1, 2014, at 11:53 AM, Glen Gardner <glen.gardner at verizon.net>
> You can easily find the times for equatorial crossing for ascending
passes from the element set.
> Consider Oscar 7
> Satellite: AO-07
> Catalog number: 07530
> Epoch time: 14211.80120610
> Element set: 27
> Inclination: 101.4754 deg
> RA of node: 192.2023 deg
> Eccentricity: 0.0011666
> Arg of perigee: 207.8798 deg
> Mean anomaly: 270.9717 deg
> Mean motion: 12.53605918 rev/day
> Decay rate: -2.2e-07 rev/day^2
> Epoch rev: 81698
> Checksum: 281
> The epoch time is the reference time for that element set. It also
happens to be the time for the ascending node (equatorial crossing
> In this case it is "14211.80120610" which comes out to the year 2014,
day 211 and the hour comes out to 19.22 hours.. or approximately 19 hours,
13 minutes, 44 seconds.
> Ignoring the decay rate, the next ascending node will be in one orbital
period. You can get this by dividing the number of minutes in a day by the
mean motion: 1440/12.53605918=114.869 minutes after the epoch time.
> Getting the descending node is more problematic if the orbit is highly
eccentric. In the case of Oscar 7, the eccentricity is small, and it is
close enough to a circular orbit that it is reasonable to assert that the
descending crossing of the equator is very close to 1/2 orbital period
after the ascending node (unless your TLE's are more than a few days old).
>> On 08/01/2014 03:07 AM, Paul Stoetzer wrote:
>> i8CVS posted the directions to calculate EQX and everything else
>> needed to use an OSCARLATOR from Keplerian elements back in 2003.
>> I haven't done any programming in forever, but maybe I'll try to
>> write a short program to automate those calculations at some point
>> (unless someone already has).
>> Paul, N8HM
>>> On Thu, Jul 31, 2014 at 10:51 PM, EMike McCardel <mccardelm at gmail.com>
>>> Does anyone know of a tracking application or program or some other
software or existing source that will still produces or publishes
equatorial crossing data for current satellites?
>>> EMike McCardel, KC8YLD
>>> VP for Educational Relations AMSAT-NA
>>> Sent from my iPhone
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