[amsat-bb] Re: Graph of eclipse/sunlight

Clive Wallis list1 at g3cwv.co.uk
Mon Jan 25 02:14:33 PST 2010

Hi Andy,

I've done quite a lot on eclipse study, although not quite what you are 
looking for.

I suggest you have a look at the SATILL package on my website 
www.g3cwv.co.uk .  It's on the general satellite and oscar-11 pages. The 
program uses James Miller's PLAN10/13 routines converted to QBASIC.
It should be possible to modify the code for your own requirements.

In the past I've produced a number of versions of the code, which have 
produced lists of data, which can be imported into a spreadsheet and 

BTW the QBASIC interpreter can be freely download from the web.

I'm currently rewriting SATILL so that it runs in BBC BASIC for Windows, 
  as this is now my preferred programming language, and allows the 
original PLAN10/13 routines to be run without modification.


73     Clive     G3CWV

        Hitchin, North Hertfordshire, UK

andy thomas wrote:
> I've been looking at some cosmonauts' historic accounts of missions
> on the Salyut series of orbital spacecraft. Characteristically they
> have drawn a graph of the eclipse and sunlight times of the long
> duration mission. The vertical axis is time after EQX of the first
> orbit of the day (the entry into and departure from eclipse is marked
> on this axis in 5 minute intervals) and the horizontal axis is the
> mission day.
> The result is a graph in which lines extend horizontally conencting
> the eclipse times (both in and out), and they have characteristically
> filled in the darkness time with dark pen. On one print the light
> time has another contour with what appears to be sun angle.
> The graph has then been added to by showing the plan and actual
> activity on that mission day.
> I would find it interesting to compute a similar graph for a long
> duration mission of the ISS. But I have some difficulty. From a TLE I
> can do the following:
> *calculate first eqx in utc
> but can't find the time of crossing into eclipse without knowing the
> position of the sun and the position of the spacecraft in relation to
> the sun (Subsatellite point?).
> Does anyone have any idea about the calculation and data involved? It
> must have been a hand calculation carried out by cosmonauts, but once
> a simple program is written I could use excel to draw the graph.
> Maybe a standard predictor program can produce a data output that
> could be rewritten into excel? I'd need the eclipse times on the
> orbit following the first eqx of the day.
> I would appreciate any input, also any thoughts of why they would
> want to draw it (have only thought of observation and power).
> many thanks
> 73 de andy G0SFJ
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