Hi I remember a few years ago the question arose about the launch window to the ISS. I think there was a program or algorithm that, based on the TLE of the station and lat/long of the launch site, looked at the sub-satellite points of the station orbiting over the launch site, and calculated the launch by allowing a delay so that the launch vehicle orbited behind the station prior to docking. Could anyone guide me towards the method or program, please? The reason for the request is to apply it to a review of the launch of the Shenzhou-10 spacecraft to the Tiangong-1 space station. I am interested in what the options were for the launch window of Shenzhou-10,  i.e. when other launches could have taken place, but didn't. I'm sure that there was a couple of days around the actual launch, and  a period of time before and after until the window appeared again. But I would like to nail the issue. Any help gratefully received e.g by direct email: andythomasmail AT gmail Dot com or AT yahoo Dot co Dot uk thanks in advance 73 de andy g0sfj