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Re: TLE Availability



Here is copy of an updated message on kep's availability via 
internet.

On 30 Dec 2004 at 9:18, Dr. T.S. Kelso wrote:

> The following notice was just posted on the NASA/GSFC OIG web site today:
> 
>          Air Force Space Command has received the delegation of authority from,
>          and been assigned the responsibility of, the Secretary of Defense 
> to conduct the
>          CFE Pilot Program.  There will be dual OIG website and CFE website 
> operations
>          for 90 days during this transition period.  However, the OIG 
> website will no
>          longer be accepting new users.  The CFE Space Track website will begin
>          registering new users on 01/03/2005.  Please go to the link below 
> and logon.
>          The final transition and shutdown date of the NASA OIG web site is 
> still to be
>          determined. 12/30/2004
> 
> The Space-Track site is not yet available, but the link below (referred to 
> above) contains the following new information:
> 
>          Space-Track Web Site
> 
>          CFE Announcement #2 (30 Dec 04)
> 
>          Air Force Space Command has received the delegation of authority 
> from, and
>          been assigned the responsibility of, the Secretary of Defense to 
> conduct the
>          CFE Pilot Program The CFE Space-Track website is located at
>          http://www.space-track.org.
> 

I just read the following as i already said if i can get that anyone 
else can.


Positional Measurements

The aim of these measurements is to measure the position of the 
satellite at a certain time.

You might think that the most accurate way to estimate a satellite's 
position is when the satellite passes in front of a star. That is not 
necessarily true when the satellite and the star are not of 
comparable brightness. If a bright satellite passes 'in front of' a 
faint star, the star will dissappear in the glare of the satellite. 
It is then very difficult to make an accurate measurement. The same 
goes for a faint satellite and bright star.

The easiest way to determine the position of a satellite is when it 
passes between two not too distant stars, say at most half a degree 
apart. The stars should not be too far apart from one another since 
the accuracy of the satellite's position should be a few arcminutes 
(the moon diameter is approximately 30 arcminutes). The most accurate 
measurements are possible when the line connecting the two stars is 
perpendicular to the path of the satellite.

You start the stopwatch when you see that the satellite intersects 
the line joining the two stars. You stop the stopwatch some time 
later at e.g. a full minute (using the time signal of the radio). 
Subtracting the recorded duration from the reference time gives the 
time that the satellite passed between the two stars. You should 
always use Universal Time (UT) (also called Greenwich Mean Time - 
GMT). The time should be recorded with the highest possible accuracy. 
Since our reaction time is not better than 0.1 to 0.2 seconds, you 
should try to achieve 0.1 to 0.2 seconds precision.

Then look up the reference stars in the star atlas. You need a more 
accurate star atlas to process positional measurements (than for 
drawing predictions). You should make sure that the star atlas has 
sufficient scaling to allow for an estimating accuracy of 1 or 2 
arcminutes. Now you plot the satellite's position in the star atlas. 
E.g. if we call '1' the full distance on the segment joining the two 
stars, and if you estimated that the satellite passed at '0.4' from 
one star, you can easily plot the satellite's position in the star 
atlas (with a ruler). You can then estimate the coordinates of the 
satellite's position from the plotted position in the star atlas.

Alternatively, you can look up the position of the reference stars in 
the star catalogue and calculate the satellite's position by linearly 
interpolating between the known coordinates of the two stars.

Ted Molczan has written ObsReduce, an MS Windows program that reduces 
observations of satellites relative to the background stars into 
their precise coordinates. Observers identify their reference stars 
in a simulated binocular or telescope field of view, select them 
using the mouse, enter the observed geometric and positional data, 
and the program automatically produces a formatted observation 
report.

The accuracy of a position does not only depend on the way the 
position is measured, but on the angular velocity of the satellite. A 
low orbiting satellite (lower than 500 km) moves across the 
observer's sky with an angular velocity of 0.5 to 1 degree per 
second. During a time interval of 0.1 s (our timing precision) the 
satellite moves between 3 and 6 arcminutes, which will ultimately be 
our positional accuracy. Naturally, for higher objects the angular 
velocity will be smaller and the positional accuracy will accordingly 
be better.

One observation should contain :

    * Satellite Code. There are actually two formats for this. The 
NORAD-number (like #16619) is used by American observers. The COSPAR 
international code (like 86- 17 A) is preferred by the Royal 
Greenwich Observatory. The COSPAR code, YYNNNL, gives the year (YY) 
of launch, the number of the launch that year (NNN) and the letter 
(L) indicating the element of that launch (from A onwards), for 
example the primary payload may be A, a secondary B and the 
accompanying rocket C.

    * time in UT, up to 0.1 s accuracy.

    * position in Right Ascension and Declination.

    * estimated accuracy in time and position.

    * the magnitude (optional).

    * the observer's exact location (longitude, latitude and height)

    * the equipment used

The observer's location should be measured with a 0.1 " positional 
accuracy using geodetical maps.

Several reporting formats have been devised to faciliate the exchange 
of positional observations.

The Royal Greenwich Observatory (RGO) invites observers to send in 
positional observations of satellites on their priority list. The 
priority list contains satellites whose orbits are interesting for 
researchers. The data is used to determine orbits. The orbits are 
analyzed and the analyses are published in scientific journals.

For observing forms, the priority list and more information you can 
contact: Phil Gibbs, Satellite Laser Ranging Team (SLR), Herstmonceux 
Castle, Hailsham, East Sussex, BN27 1RP England.
----
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