# [amsat-bb] Equatorial Crossing Data (EQX)

EMike McCardel mccardelm at gmail.com
Fri Aug 1 17:39:37 UTC 2014

```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

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> wrote:
>
>
>
> 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
>>
>> 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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>> _______________________________________________
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```