Sunday 19 November 2017

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.

Friday 17 November 2017

[UPDATED] Tomorrow's SpaceX Zuma launch

click map to enlarge

If nothing interferes (the launch has been postponed twice already), SpaceX will launch the classified Zuma satellite from Cape Canaveral Pad 39A in the early hours (UT) of  November 18.

Zuma  was originally scheduled for November 16, but was delayed a day to November 17, and then yet another day to November 18.

The published Maritime Area Warnings give a window from 00:55 to 03:37 UT for the launch. From the Area Warnings, the de-orbit of the Falcon 9 Upper stage happens some 2 hours after launch over the southern Indian Ocean, during the 2nd orbital revolution.

The launch and Upper stage de-orbit hazard zones (I plotted them in red on the map above) strongly suggest a launch into a 50-degree inclined, ~400 km orbital altitude Low Earth Orbit.

The map above plots the trajectory for the first ~1.5 revolutions in such an orbit. As can be seen in the map, such an orbit lines up well with the direction of the launch hazard zones, and with the Falcon 9 upper stage de-orbit hazard zone in the Indian Ocean. The fact that the first stage will return to the Cape for a landing argues for a launch into Low Earth Orbit too.

If a ~50-degree inclined, ~400 km altitude orbit sounds familiar to you: that is because this orbit would be very similar to that of the enigmatic classified satellite USA 276 which was launched - also by SpaceX - in May 2017. This is the one that made all those peculiar close approaches to the ISS in June (see some previous posts from June and my Space Review article here). Perhaps, but this is pure speculation based on suspected potential orbital similarities only, Zuma is up for a similar mission.

It is very interesting that Zuma seems to have been contracted via a similar procedure as USA 276, and that like for USA 276, it has not been made public which Agency will operate the Zuma satellite. So there appear to be similarities from that aspect as well.

It will therefore be interesting to see how the orbit of Zuma, once launched, compares to that of USA 276 and the ISS. The orbital plane of the ISS will be overhead for Cape Canaveral near 2:38 UT on the 18th, so a launch exactly into the ISS orbital plane is possible - and will stay possible for several days to come in case the launch is postponed again (the moment of the ISS orbital plane passing over the Zuma launch site happens ~24 minutes earlier each day).

On the 18th, the orbital plane of USA 276 will be overhead for Cape Canaveral some 10 minutes before the launch window opens. With the newest delay, a launch exactly into the orbital plane of USA 276 is therefore no longer feasible.

But by launching directly at the opening of the launch window on the 18th, the orbits of Zuma and USA 276 would nevertheless still be quite close (launch at 1:00 UT would result in a difference in RAAN of 3 degrees), and differential rates of precession of the RAAN might still slowly drift the two orbits towards each other over the next weeks and months, depending on what the actual orbital altitude and inclination Zuma ends up in would be.

Therefore a launch exactly into the orbital plane of either USA 276 or the ISS, strictly speaking is not necessary to engineer close approaches (indeed, USA 276 itself was not launched exactly into the ISS orbital plane in May).

So it might be worth monitoring Zuma and its behaviour in relation to both USA 276 and the ISS in the weeks after launch. Still, it is also very well possible that Zuma has nothing to do with both spacecraft whatsoever.

UPDATE 1  17 Nov 2017, 13:00 UT:

The  maps below show a comparison of the hazard zones (from Maritime Area Warnings) for the launch of USA 276 in May 2017, and for Zuma.

click maps to enlarge

The USA 276 de-orbit area is shifted more West-wards, because the Falcon 9 upper stage de-orbit from that launch was de-orbitted one orbital revolution later than apparently planned for Zuma. The small difference in size might point to slightly different orbital altitudes for the upper stage (e.g.due to  a somewhat different collision avoidance manoeuvre after payload separation)

UPDATE 2  17 Nov 2017, 13:00 UT:

SpaceX has released a statement that, while not taking a launch tonight off the table, might indicate a further prolonged delay.


These are the Area Warnings published for the launch. They are graphically depicted in the map in the top of this post and the two maps above.

NAVAREA IV 1067/17

160055Z TO 160337Z NOV, ALTERNATE 
170055Z TO 170337Z NOV IN AREAS BOUND BY: 
A. 28-38N 080-43W, 29-12N 080-06W, 
30-04N 079-00W, 29-56N 078-52W, 
28-41N 080-10W, 28-26N 080-21W, 
28-22N 080-38W. 
B. 30-04N 079-00W, 30-52N 
078-17W, 31-32N 077-25W, 
31-54N 076-49W, 31-49N 076-45W, 
31-36N 076-57W, 30-44N 077-53W, 
29-56N 078-52W. 
2. CANCEL THIS MSG 170437Z NOV 17.// 

Authority: EASTERN RANGE 072156Z NOV 17. 

Date: 110428Z NOV 17 
Cancel: 17043700 Nov 17 

HYDROPAC 3895/17 

DNC 03, DNC 04. 
160300Z TO 160637Z NOV, ALTERNATE 
170300Z TO 170637Z NOV IN AREA BOUND BY 
30-27S 064-51E, 30-44S 067-03E, 
38-10S 082-43E, 47-22S 108-39E, 
50-30S 124-39E, 51-55S 126-03E, 
53-32S 125-05E, 54-24S 116-01E, 
53-34S 101-27E, 47-46S 082-05E, 
39-58S 069-31E, 31-56S 063-23E. 
2. CANCEL THIS MSG 170737Z NOV 17.// 

Authority: EASTERN RANGE 072155Z NOV 17. 
Date: 110407Z NOV 17 
Cancel: 17073700 Nov 17

Friday 3 November 2017

Introducing IOD Entry: software to aid observers in creating IOD formatted observational data [UPDATED]

International amateur satellite observers (well: apart from the British, who use their own format) generally use the IOD format to communicate positional measurements on satellites. The IOD format however can be cumbersome and error-prone to manually write.

In the old days, there was a neat little DOS program called ObsEntry to help you turn your data into IOD format. Unfortunately, this no longer works on newer Windows machines.

Time for something new to replace it: so I present to you IOD Entry 1.0!

IOD Entry 1.0 is software that runs under the Windows .NET framework, which is a standard component of Windows 7 and later (otherwise, the .NET framework can be downloaded here). I wrote it in Visual Basic using Microsoft Visual Studio 2017, as part of self-teaching me to code .NET windows applications in Visual Basic.

The program and how to work with it is described in detail in this mailinglist post. The program can be downloaded as a .zip file through my astronomy software page at It is (of course) freeware.

UPDATE: IOD Entry version 1.1 has now been released. It allows to choose the format of both the Right Ascencion and Declination entries. For the RA, the choice is between HH MM SS.s, or decimal degrees. For the declination, the choice is between degrees, arcminutes and arcseconds, or decimal degrees.

Version 1.1 can be downloaded at the same link above.