Introducing a new web resource: Launchtower

Before new launches, I frequently publish orbital element (TLE) estimates that can help satellite observers plan observations of the payload and/or associated rocket stage directly after launch.

Untill now, I published these pre-launch estimated TLE's on the SeeSat-L Mailing List and occasionally also on this blog. And I will keep doing that: but I realized that it would perhaps be good to have a central website for these pre-flight TLE's.

So I introduce to you: Launchtower (http://launchtower.langbroek.org).

The TLE estimates in question are based on public information about the launch site, launch date and launch time, and (if made public) the orbital altitude and orbital inclination aimed for.

For classified launches (where this information usually is not available), educated guesses are made based on amongst others information gleaned from NOTAM's and Navigational Warnings. These provide information on launch time windows, and the orbital inclination aimed for, which can often be deduced from the launch azimuth, which in turn can be deduced from the locations of the launch hazard areas and upper stage deorbit areas found in Navigational Warnings.

The website will provide TLE estimates for launches that are "of interest". The criteria for what comprises "of interest" are basically:  those launches that are of interest to me.

Generally speaking, these will be: classified launches; human spaceflight; and launches that overfly Europe on the initial revolution.

TLE's can be used to plot a sky track for your location, using predictive software like for example HeavenSat.

 
UPDATE:

On request, I have added a plain-text file URL as well, to which you can point software that can (stupidly) only load TLE's from plain text files on a web-adres. Link is on the main Launchtower page.

Introducing TLE from Proxy

A simple way to estimate orbital elements for an upcoming launch, is to use elements from a previous, similar launch as a proxy.

For example, for a newly to be launched SpaceX DRAGON cargo spacecraft to the ISS launching from Cape Canaveral pad 39A, you can use a previous DRAGON launch from Cape Canaveral and then modify the elements to the new launch date and launch time. The method is described here by Ted Molczan in a Seesat-L mailinglist post from June 2002.

Basically, the method takes the elset from the previous launch and adjusts the epoch and RAAN values (all else being kept equal) based on the time difference between the original launch and the new launch.

To aid in this and make it as simple as a few buttonclicks, I have written TLE from Proxy. The program runs under the Windows .NET framework, and can be downloaded on my website.

Using the program is very simple, involving these five simple steps:

1.  Obtain a TLE for a previous similar launch from Space-Track;
2.  Paste line 1 and line 2 of this elset into the input box;
3.  Fill in the date and time (in UT) of that launch;
4.  Fill in the date and time (UT) of the new launch;
5.  Press the button.

A new TLE will now be generated.

Note that in order for this to work, the launch must be from the same launch site, towards the same launch azimuth, and with a same launch-to-destination scenario.