[amsat-bb] Equatorial Crossing Data (EQX)

[Glen Gardner]

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 
North-to-South).
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).

Glen
AA8C



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.
>
> http://www.amsat.org/amsat/archive/amsat-bb/200203/msg00749.html
>
> 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).
>
> 73,
>
> Paul, N8HM
>
> On Thu, Jul 31, 2014 at 10:51 PM, EMike McCardel <mccardelm at gmail.com> wrote:
>> 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
>>
>> EMike McCardel, KC8YLD
>> VP for Educational Relations AMSAT-NA
>>
>> Sent from my iPhone
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