Help / Frequently Asked Questions

My Question is about:

• J-Track
• J-Track 3D
• J-Pass / J-Pass Jr.
• Live 3D Tracking Snapshots

How does it work?

J-Track uses orbit propagation.  It takes an objects location and direction (a vector) and calculates where it believes the object will be in the future if no direction changes occur. More information on how J-Track 2.5 works is on the J-Track help page.

When J-Track refreshed, all my settings such as satellites, weather map options are all reset to default.

In the past, JAVA applets have been restricted from saving information to your local machine as a security precaution.  It appears that in the future, there will be a mechanism to support this, though it may be platform dependent.  We are taking a "wait and see" position before we implement this capability.

A satellite is not where I think it should be!

See how does it work above.  If your browser has been running the applet a while, you can force a reload by clicking your browser's reload button.  This will ensure you have the latest vector.

Where are the Space Station and Shuttle?

NASA has a single place for Station and Shuttle tracking, and that is theHuman Space Flight Web site.

I get exception:java.lang.NullPointerException

Since J-Track (1.4 and 2.0) and J-Pass have JAVA class files with the same names, sometimes browsers gets confused and try to use the file loaded for one applet in the other rather than downloading a new one.  You can ensure that the new class is downloaded by dumping your cache and re-visiting the web page.

I get security exception or it doesn't load

You may be behind a firewall or proxy server which will not resolve information requested through JAVA.  Try accessing the web page using the number address rather than the name.  Here is an example:

http://science.nasa.gov/RealTime/JTrack/SpaceCraft.html

http://192.77.84.88/RealTime/JTrack/SpaceCraft.html

Another reason may be that your browser does not support JAVA.

When I resize the desktop J-Track, the world map image is missing

The applet must reload the image from the server and it takes a little time to re-establish a connection and download.  Wait a few minutes for the new image.   If no image appears, try resizing again.  Be sure you are connected to your ISP when you resize.

How do I "Download" J-Track?

J-Track is automatically downloaded every time you visit the web page which references the applet.  There is no version of J-Track which runs independent from the web page.   The applet requires access to the network to download the satellite and weather information.

How do I put J-Track on my desktop?

If you have Internet Explorer 4.0 or later for Windows, you can add J-Track to your desktop.  Internet Explorer is currently the only browser which supports the feature.

How do I get J-Track off of my desktop?

For Windows 95 - Windows 2000, right click on the desktop, select "Active Desktop", then "Customize Desktop...".  From this dialog, you can uncheck J-Track to disable it, or click the remove button to remove it entirely.

For Windows XP, right click on the desktop, select "Properties", then choose the "Desktop" tab. Click on the "Customize Desktop..." button, and choose the "Web" tab. Uncheck J-Track to disable it, or click the Delete button to remove it entirely.

When can I see a satellite pass over?

We have written J-Pass for providing satellite sighting information; it uses a much better viewing algorithm.  You can also use the "next pass" feature to estimate the next sighting (explanation). 

When using J-Track on my desktop, what will happen when I reboot?

J-Track will start automatically -- this may take a few moments. It will start in the default configuration; wait until you are connected to the internet to reconfigure.   J-Track will  synchronize from your system clock rather than our server clock. We are working on a solution to this problem.

Do I have to remain connected to the network while using J-Track?

No.

Where is my favorite satellite?

There are so many orbiting things that we had to choose a few to keep the list shorter.   If you have one that is missing, just ask and we will add it as time permits.

What are the units for altitude?

Kilometers.

Who developed J-Track?

The Mission Operations Laboratory at NASA's Marshall Space Flight Center.  This Laboratory no longer exists due to reorganization.

Is the source code available?

No.

How does it work?

J-Track 3D uses orbit propagation.  It takes an objects location and direction (a vector) and calculates where it believes the object will be in the future if no direction changes occur.  For the shuttle, many changes occur, so we update vectors frequently.

I get security exception or it doesn't load

You may be behind a firewall or proxy server which will not resolve information requested through JAVA.  Try accessing the web page using the number address rather than the name.  Here is an example:

http://science.nasa.gov/RealTime/JTrack/SpaceCraft.html

http://192.77.84.88/RealTime/JTrack/SpaceCraft.html

Another reason may be that your browser does not support JAVA.

Why do I see Earth, but no Satellites? Or the Earth with the words "Loading Satellites"?

Some old versions of Java don't work correctly with J-Track 3D. Download the latest version. Try http://java.com for the latest.

Where is my favorite satellite?

NASA has a single place for Station and Shuttle tracking, and that is the Human Space Flight Web site.

Currently no 3D NASA tracker includes Space Station or Shuttle. In the future, J-Track 3D may be replaced or integrated with the Human Space Flight tracking tools. For other satellites, there are so many orbiting things that we had to choose a few to keep the list shorter. If you have one that is missing, just ask and we will add it as time permits.

When can I see a satellite pass over?

We have written J-Pass for providing satellite sighting information; it uses a much better viewing algorithm. 

Where are the Space Station and Shuttle?

NASA has a single place for Station and Shuttle tracking, and that is the Human Space Flight Web site. Skywatch 2.0 is very similar to J-Track, and provides tracking data for Station, Shuttle (when flying), and six other satellites. J-Track doesn't track Station or Shuttle, but offers several hundred other satellites. If funding allows, the capabilities of the two tools will eventually be combined into a single pass-prediction tool.

Where is Mir?

Mir was a Russian space station that burned up on re-entry in 2001.

What is the pop-up window about granting security?

We are just trying out digitally signing our applets.  The only thing the applet is requesting to do is to remove the extra status line on the pop-up windows that reads "Warning: Applet Window" or "Untrusted Applet Window".  In the future, we may ask to be able print as well.

This window is to ensure that applet programs don't do something like writing a pop-up window that asks for a password or something and you mistake it for your operating system and enter a password which it can then send back to its host.

We don't do that!

How does it work?

J-Pass uses orbit propagation.  It takes an objects location and direction (a vector) and calculates where it believes the object will be in the future if no direction changes occur.  For the shuttle, many changes occur, so we update vectors frequently.

Why are East and West reversed?

They are not, you are!  Most maps we see are drawn as if we are looking down from above.  However, sky charts are drawn as if we are looking up from below.  Look up with the top of your head pointing North.  Which way is East and which West?   Now try the same thing looking down.

My City is not in the list, could you add it?

In order to keep the applet's download size down, we limited the number of known cities in the list.  In the future, we hope to increase the list.

It doesn't print!

We hate this! Unfortunately, the ability for an applet to print was added to Java 1.1 and J-Pass is a 1.02 applet.  Many older browsers do not support Java 1.1 and therefore will never be able to print.  In the future, we will be adding this capability.  In the meantime, here is what you can do.

PC:

Type ALT+"PRINT SCREEN" - these are both keys on the standard PC keyboard.   This will make a picture of the window and place it in your clipboard.  Then run your favorite graphics editor (Paint which comes with Windows will do).  Select Edit -> then Paste and the image will be placed in the program.  You can then print from Paint.

MAC:

You can take a screenshot of the whole screen by using Command-Shift-3 (Apple 'clover-leaf key'-shift-3), which will save a PICT file at the top level of your hard disk, called 'Picture n'. If you're using MacOS 8.0 or higher, Command-Shift-4 lets you drag-select an area of your screen to be captured, rather than the whole screen.

I saw something on some day, what was it?

This is truly too difficult a task to expend resources to determine.  If you MUST know, you can find historical ephemeris data on the internet for the space objects and search, but most likely you will never be sure what it really was unless you preplan the viewing.

Why can't I type in a date in the future or past for passes?

Inherent to the method the program uses to calculate positions (see how it works), the accuracy of the information diminishes the farther from the vector (location and direction information) the program is using.  Most vectors are not accurate more than a week or so from the date of calculation.  If the craft has its own propulsion capability, like the shuttle, a day or hour may not be accurate depending on when it navigates.   However for most objects, we can be fairly accurate.

How does it work?

The location images use orbit propagation.  They take the crafts location and direction (a vector) and calculates where it believes it will be in the future if no direction changes occur.  For the shuttle, many changes occur, so we update vectors frequently.

Can I link to the Tracking Image from my web site?

Though you are welcome to link to our tracking images, please also link to either our home page or our tracking page and indicate that we generated the information.

Where are the Space Station and Shuttle?

NASA has a single place for Station and Shuttle tracking, and that is the Human Space Flight Web site.