[amsat-bb] Re: future apogee calculation

[i8cvs]

----- Original Message -----
From: "Bob- W7LRD" <w7lrd at comcast.net>
To: <amsat-bb at amsat.org>
Sent: Thursday, February 25, 2010 6:07 PM
Subject: [amsat-bb] future apogee calculation
>
> Hello
>
> Is there a "easy" way of figuring out where/when a given apogee will at a
> given lat.long?
>
> 73 Bob W7LRD
>

Hi Bob, W7LRD

Using InstantTrack it is easy but the procedure is a little bit long.

When you are in the Map Screen push F until you get a phs (phase) of 128
for AO7

At phs 128 you are at the Apogee and you can read down the map the Lat/long
of the satellite subpoint at the Apogee

If you now push E you will read the keplerian elements on the map screen and
if you push D you can read the derived velues at time.

To day Feb 26 we have:

Perigee Height : 1440.2 km
Apogee Height : 1459.0 km
Latitude of Apogee : -48.9° (South)
Rate of change of Apogee: -1.866 ° / day
Rate of change Argument of Perigee : - 1.957° / day

Now if you want to know the numbar of days that the apogee need to go
from the actual Latitude of - 48.9° South to a wanted Latitude North you
must consider that since the AO7 inclination is greater then 90° the line
of the apsides that  join the apogee with the perigee moves in the opposite
direction of the satellite.

As an example:

If you want to know how many days the Apogee needs to go from
the actual Lat of - 48.9° South to a wanted Lat of + 55.0° North the Apogee
must move by 180 + (55.0 - 48.9 ) =  186.1° in the South direction so that
the numbar of days needed are:

186.1°  /  1.957° day = 95.09 days from February 26 i.e day 1 june 2010

If you check on any tracking program you will see that AO7 on day 1 june
2010 at 10:17 UTC will be about at phs 128 at Apogee with latitude of about
+ 55° North and longitude 38.0° West with the satellite subpoint at Apogee
just in the middle of the Atlantic ocean.

InstantTrack is a great program if one know how to talk with him !

73" de

i8CVS Domenico