# A nicer way to download the positions of the Orbcomm-2 satellites

I'm trying to watch the Orbcomm-2 satellites evolve into a constellation. They were recently placed in orbit by SpaceX (their video here) and the details are discussed in this excellent question and answer pair.

I found a way to get latitude, longitude, and altitude by clicking on each satellite listed here (Norad 41179U through 41189U). The process was awkward - I made a series of screen shots (twenty two of them - argh!) like this, two for each satellite, and interpolated to a single point in time (14:00:00 UTC 24-DEC-2015)

In Python I converted to X, Y, Z in space,

for sat in sats:

r = r_earth + sat.alt

x = r * np.cos(rads*sat.lat) * np.cos(rads*sat.lon)
y = r * np.cos(rads*sat.lat) * np.sin(rads*sat.lon)
z = r * np.sin(rads*sat.lat)

sat.r, sat.x, sat.y, sat.z = r, x, y, z


and got this:

Those are kilometers, relative to the average of the group - just to get a rough idea what is happening. The color lines are motion over 5 seconds of time.

My question: Is there an easier way to download latitude, longitude, and altitude for all of the satellites in the constellation, possibly as a text file at a single point in time?

EDIT: There are many nice programs and packages to plot astronomical and orbital data, but this question is about getting the data now and plotting it myself.

## 1 Answer

There are a few ways

1. Use a tool like Satellite Tool Kit, which will allow you to plot the spots with time.
2. Get the Two Line Elements (TLEs), and use them to find the positions directly. I believe Celestrak will have them sometime soon. I think they are updated daily. There's a nice packaged called PyEphem that helps with such things. Space Track also has the data, with a free account, although that account has to be verified. It's run by the US military, I don't know what their criteria is for accounts, but it's the best data source if you can get it.
• Great! While two-line elements are the most common way to do this, it requires some additional math. If I use those, can you point me to the lines in PyEphem that do the conversion? I don't want to import or install a whole python package. (Just grabbing the locations would be easier for me.) Could you double check those links - right now "PyEphem" is pointing to celestrak.com. Also, is Systems Took Kit free?
– uhoh
Commented Dec 25, 2015 at 0:05
• STK is free, but you have to sign up for it. There are paid versions, but they aren't required for what you want to do. If you get the TLEs from Space-Track, they have a history that will allow you to go back in time. Commented Dec 25, 2015 at 0:10
• That is tricky... Best bet is to use spacetrack, which has a frequently updating the system, with history. Then import them into STK. The names aren't listed, but there should be samples there. If there is a change in delta v, then it might be slightly out of date, but for public data, that's probably the best. Commented Dec 25, 2015 at 0:33
• Fixed the link. Commented Dec 25, 2015 at 0:52
• STK allows you to get reports, although it is a large program. I would use pyephem to get the position from tles, and get the tles from spacetrack Commented Dec 25, 2015 at 0:58