Mainform Have you ever looked up just after sunset or before sunrise and watched a steady light moving slowly across the night sky? It may well have been a man-made satellite, many of which are visible to the naked eye - if you know when and where to look. PocketSat is an application that allows you to predict when satellites will be visible in your location, or to identify one that you happen to have seen.

PocketSat includes the following features:

bullet Customizable to compute satellite visibility from any location on Earth.
bullet Able to import orbital data for an arbitrary number of satellites from a variety of publicly available sources.
bullet Able to simultaneously compute passes for a user-selected set of satellites over a user-defined time period.
bullet Real-time sky plots with continuously updated satellite positions.
bullet Ability to set PalmOS alarms to alert you when satellites are passing over.
bullet Detailed information display for each satellite.

For those that are interested in such things, it is worth mentioning that PocketSat uses NORAD's state-of-the-art SGP4 algorithm for calculating near-Earth satellite orbits, using full double-precision arithmetic.

A word of warning, however: PocketSat is just the sort of computation-intensive application that the Palm Pilot development manuals say that the machine was not designed for. Calculating the positions of a couple of hundred satellites for a week can put a significant dent in your batteries - I'd strongly recommend rechargeables if you plan on using it a lot. I've had a lot of success with Rayovac Renewals. On the other hand, when you're standing out in a field at night, the Palm Pilot seems just right, even if the backlight is a little too bright for good night vision.

Registering PocketSat

PocketSat is a shareware application. The unregistered trial version is fully functional, but will only display positional information for 5 satellites at a time. If you are using the trial version, it might be a good idea to perform calculations for periods covering a week or more, to insure that visible passes will be found.

The registered version of PocketSat can be purchased for US$12.50 from the BigFatTail website.

Obtaining Data

The orbital data for a satellite changes with time. While a given set of data is accurate for at least a few weeks to a couple of months for low-accuracy naked-eye observation, you will eventually have to update it. Fortunately, there are quite a few sources for the web for up-to-data orbital elements. Check out the PocketSat web site for pointers to some of them.

PocketSat reads data stored in the popular TLE (Two Line Element) text format. In order to get the data into the Pilot, it can either be copied into a memo, or turned into a "PocketSat import database" by using one of several tools available at the PocketSat web site. See the section on importing data later in this manual for more details.


There are 2 files that must be installed on your Palm Pilot in order to use PocketSat:

bullet PocketSat_trial.prc (or PocketSat_reg.prc) - the PocketSat application.
bullet Mathlib.prc - Rich Heubner's invaluable double precision math library.

A third file, sampsats.pdb, is a PocketSat input database containing some (almost certainly out-of-date) sample satellite orbit data. You can either install this database to play with, or ignore it and go to the PocketSat web site to get current data


Assuming you've just installed PocketSat, but don't really feel like slogging through all of the docs, here's what you've got to do to get things running:

  • Start PocketSat. If this is the first time you've started it, you will see the Observer Location form with a default location in it. Otherwise, choose "Observer location..." from the menu.
  • Press "New" and enter your location name.
  • Enter your latitude, longitude and time zone. Don't worry too much about your altitude - if you don't know it, just enter 0 meters - it'll be close enough in most cases. Hit "OK."
  • Choose "Satellites..." from the menu.
  • Choose "Import from DB..." from the menu.
  • Select an import database (you did install one, didn't you?) and press the "Import" button. Select "OK" from the import dialog, and then "Done" from the Database Import form.
  • Back in the Satellites form, make sure all of the satellites have checkmarks next to them. If not, choose "Select All" from the menu.
  • Press the "Done" button to return to the Main Form.
  • Press the "Calc" button to begin the calculation.
  • Choose "Today" to exit the Select Start Date dialog.
  • Press "Done" to choose the current time from the Set Start Time dialog.
  • If you have the registered version, choose the next day. If you have the trial version of PocketSat, it will only calculate the first 5 selected satellites from the Satellites form, so choose an end date a week or 2 in the future to make it more likely that a satellite pass will be found.
  • Press "Done" from the Set End Time dialog to select the current time on the previously set end date.
At this point, you should be back at the Main Form, with a little "twirling" symbol at the upper right, letting you know that things are working. Note that the "Calc" button has turned into a "Stop" button. Pressing it will cancel the calculation.

Now just wait for the calculation to finish, or stop it if there are enough passes listed for you to look at. Note that you don't have to stop the calculation process in order to view pass details or to plot one, but things will seem very sluggish.

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