# Re: navstar

From: Bjoern Gimle (b_gimle@algonet.se)
Date: Thu Jul 27 2000 - 01:03:55 PDT

• Next message: bruce_musson@dofasco.ca: "RE: Where was ISS ?"

```> NAVSTAR 48 (USA 151)
> 1 26407U 00040A   00203.00016569  .00000064  00000-0  10000-3 0   158
> 2 26407  55.0641 228.3909 0045522 273.8447  85.7199  1.99170076   175
...
> NAVSTAR 48 (USA 151)
> 1 26407U 00040A   00201.47067160  .00040912 -37353-6  44785-3 0   128
> 2 26407  39.1123 221.1967 6078237 196.7985 127.6911  4.02681484   123

> So between July 19 and July 20, this satellite quickly had a change in
orbit.
> This is the fatest I have ever seen a gps satellite change orbit.
> I thought it takes a few days to change a satellite's orbit.
> So what's going on here.

ALLCOLA (or COLA) can be used to find the time of a short-impulse orbit
change.
Then, a prediction program like TRAKSTAR, TRACK16 or HANDE can be used to
find the speed in the two orbits, and the position.
ALLCOLA gives the date of manouvre 2000-07-19. With the earliest elset (11)
:

UTC Time    Range Elset Orbit separation
12:14:25.83 423.5 13 12
12:23:24.36 6.3   15 6.2
12:23:27.18 9.4   14 5.2

With elset 12:

12:14:26.99 426.9 13 12.8
12:23:25.69 7.5   15 6.2
12:23:28.51 12.5  14 5.1

If the later elsets had larger distances than the first, secondary or
low-power manoeuvres could be suspected.
Now, the likely reason is that elset 13 is inaccurate.

Using the elsets 12/15 at time 12:23:25.69, Track16 XYZ xdot Ydot Zdot are:
(-13861.32  -22020   6052.5) (1.95583 -0.52096 1.36465) before, and
(-13866.013 -22013.6 6033.5) (2.28915 -0.62697 3.04609) after.

Since the predictions differ, I ought to have picked two predictions closer
in location, instead of the same time.

The absolute speed difference is 1.42 km/s, but since there is a large
change in inclination (39 to 55 degrees), and the apogee of the initial
orbit was higher than the target,
the speed difference vector (0.33332,-0.10601,1.68144) is larger, and not in
the direction of flight.

The components of the velocity change, in the direction of original motion,
are
1.23 km/s forward, 1.12 km/s left, and 0.44 km/s up.

Since the inclination increase (dogleg to the left) occurred at 13 deg N, an
increase of the RA of Ascending Node also occurred ( 221 to 228 )

-- b_gimle@algonet.se (home)  http://www.algonet.se/~b_gimle --
-- COSPAR 5919, MALMA,    59.2576 N, 18.6172 E, 23 m         --
> So between July 19 and July 20, this satellite quickly had a change in
orbit. This is the fatest I
> have ever seen a gps satellite change orbit. I thought it takes a few days
to change a satellite's
>
> orbit. So what's going on here.
>
> Thanks
>
> Kevin Fetter
>
> __________________________________________________
> Do You Yahoo!?
> Get Yahoo! Mail - Free email you can access from anywhere!
> http://mail.yahoo.com/
>
> -----------------------------------------------------------------
> 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
>
>

-----------------------------------------------------------------
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 : Thu Jul 27 2000 - 01:06:15 PDT