This program was designed with the experienced user in mind. However, we feel confident that with only a little bit of basic understanding you’ll feel comfortable using the software in no time! Here’s a very quick introduction into satellite tracking:

Basics

Satellites orbit the earth at altitudes starting around 250km (150 miles) to about 36’000km (21’800 miles). The lower the orbit, the faster the satellite: A satellite at an altitude of 800km (480 miles) will orbit the earth in roughly 90 minutes, while a satellite at 36’000km (21’800 miles) altitude will take about 24 hours to orbit the earth, if this satellite orbits the same direction as the earth is turning, these satellites seemingly stay over the same location on the earth, they are thus called “geostationary”, their orbits are called “geosynchronous”. Many weather and communication satellites are geosynchronous. The disadvantage to being so far out is the distance: For satellites taking pictures, the image resolution is lower because they are so far away and for communication, the transmitters need to be stronger to bridge the distance. The advantage is they can continuously monitor the same area, and the satellite dishes on earth can always point in the same direction. Satellites orbiting lower than about 1000km are said to be in low earth orbit (LEO), all NOAA weather satellites for instance are LEO at around 850km altitude. They deliver high resolution imagery of the weather down below, however, because they are moving so fast, the satellite dishes required to pick up their radio signals need to be able to move and track those satellites, which take about 15 minutes from rise to set on a pass that takes them overhead.

How do we know where the satellites are?

We need to know where the satellites are, both for tracking them with satellite dishes as well as to avoid collisions when a Space Shuttle or a new satellite launches, someone needs to keep track of their positions. Because outer space is not really “empty”, there’s a little bit of friction on the satellites that is hard to predict, therefore the positions of all known satellites are measured from ground based locations from all over the world by a process called laser ranging. This establishes precise positional information on a satellite, which is then published for all except military satellites in the form of what is called TLE’s (two line elements, often also called Kepler elements, due to Kepler’s equations that in part describe the orbit of a satellite). The Kepler elements basically are a sequence of numbers that, when filled into a very complex mathematical model, enable us to obtain position information for one satellite at a specific point in time. Depending on the altitude of the orbit of the satellite, Kepler elements can be up to two or more weeks old to still hold useful information. The lower the orbit however, the more unforeseen influence can affect the satellite, thus an update to the Kepler elements should be performed every 24 hours.

Very well, but what does SatWhere tell me?

SatWhere enables you to find the position and passes for your location for any of the 8000+ objects that the US Air Force Space Command keeps track of. Whether you just want to see where the International Space Station (ISS) or the Hubble Space Telescope (HST) currently are and when you can see them pass over your location, or whether you’re operating a receiving station for NOAA satellites, SatWhere tells you exactly when, where and how the object of interest is going to cross your sky. It will even see whether the object passes in front of the moon, and if it’s Iridium flares you’re after, it will predict those, too.

So much for our brief introduction, here are a few links to websites that provide more in depth coverage.

A few links

http://science.howstuffworks.com/satellite.htm

http://liftoff.msfc.nasa.gov/toc.asp?s=Tracking

Setting up for the first time

After installing the software, there are a few parameters that need to be set before the program can function properly. First, you must open the User Settings dialog: Click on the menu “Settings”, then “User…” and the following screen will come up:

Time Display

You can either display local time (as per your computer’s locale settings, note that if you live in California you’d see PST Pacific Standard Time for instance) or UTC (Universal Time Coordinated, basically the same as GMT but without any daylight savings time adjustments). This setting affects all time displays in the entire program. The time and date format display will be the same as set up in your language locale, however, the AM/PM notion is not considered very scientific (at least in my opinion) and some people may prefer the satellite pass times to be displayed in a 24h time format. If you check the “Always display satellite pass times in 24h time format” check box, this is what happens.

Location

It is imperative that your location be set as precisely as possible. If you intend to look for Iridium flares for instance, if you’re offset by only a mile or so you may entirely miss a flare! Ideally, you’d use a GPS that supports the NMEA data format (most of them do).

Updating via GPS

In order to use a GPS, you need to connect it to the computer before you start this dialog, especially when using a USB to Serial port. The program looks for available COM ports when the User Settings dialog is brought up. If your COM port is not listed in the drop down box, close the dialog, connect the GPS and try again.

After connecting the GPS, it’s as simple as clicking the “Use GPS” button and a position will be acquired. The program will let you know whether it found a position fix of sufficient accuracy or not.

Updating from the List

Alternatively, you may select your location from a list of cities around the world. Simply click on the drop down list, type the first few letters of your city’s name on the keyboard and the selection should move to where you want it. Click on the city, and you’ll be asked to confirm to replace the existing position information.

Of course it’s also possible to update the position information manually. Note that you need to use decimal degrees (i.e. N 35° 30’ = +35.5) and that North is positive, South is negative, West is negative and East is positive.

Spacetrack Login

SatWhere comes with a feature that automatically keeps your Kepler elements file up to date by downloading it from the SpaceTrack.org website. Ever since the September 2001 scare however, you need to be a registered user with them, which is free of charge. Note that the elements that are delivered with the program are very outdated and will certainly not produce any useful results apart from allowing you to play with the program. So the first thing you should do is click the “Click here to register” text, this will open your browser on the registration page for SpaceTrack. It’s free, but will take 24-48 hours to process. Once you have received your Username and Password, be sure to enter that into the appropriate fields.

Display Units

Last but not least, set the display units to the system you feel comfortable in. You can choose between metric (km), statute (1 mile = 1.65 km) or nautical (1 nautical mile = 1.852 km).

If you already have a SpaceTrack login, you should click the “Settings”, “Download Keplers…” menu now, so as to update to the latest version of the Kepler elements.

The next thing you will want to do is make sure your computers clock is accurate. For this, open the “Settings”, “System…” Dialog.

System Settings

Time Synchronization

If you already use time synchronization through any other service (such as the built in Windows Time Synchronization service in Windows XP) I’d strongly advise against letting them run in parallel.

Select which service you want to use to synchronize, either Internet, the GPS on your COM Port, or none.

Screenshots

While we’re here, let’s look at the screenshot options: You can have your desktop background in Windows set to either the SkyView or the EarthView window (or none), and you can enable each of the screenshot mechanisms, including running a program or a script/batch after the screenshot has been created. Make sure you enter a valid path in the filename textbox, with an extension of a well known image format, such as: .JPG, .BMP, .TGA, .TIF, .PNG. The system determines which format to save as dependent on the filename extension.

Adjusting the sliders next to the two screenshot options will determine how often the screenshot is created. The interval can be set from 1 minute to 60 minutes.

Satellite Settings

After preparing the system for the calculations that are to come, we need to select a few satellites from the “Settings”, “Satellites…” dialog:

The list to the left displays the 8000+ satellites it loads from the complete list of elements, for a computer of normal computing power (in 2005 terms), you shouldn’t select more than 200 satellites. It is possible to select all of them, but calculations will take a prohibitively long time. As a guide: On a Dual Xeon 2.8 GHz, calculating 5 passes for all satellites with lunar passes and iridium flares turned on takes on the order of 2 hours.

You can facilitate selection by filtering the list to the left: Enter “irid” into the available satellites textbox and click “Filter”. You’ll be only seeing satellites whose name contains “irid”, i.e. all Iridium satellites. Select them all and click the >>> Add >>> button. Make sure the checkboxes are checked as in the screenshot above, set the “Number of passes to look ahead” to 5 and click the “OK & Update” button.

Calculation will now take some time, check the status bar for a percentage indicator that will show you how much has been done already. If you’re on a multiprocessor machine, note that all processors are busy as the load of calculating the satellites is shared in the same number of threads as there are processors.

As soon as the calculation is done, you’ll see the results in the main window, in the pass list.

The Main Window

The main window consists of the pass list, the event log as well as the status bar. Each of those elements has something to tell you.

The Pass list

In the pass list, you’ll see the upcoming satellite passes for the satellites you selected earlier in the “Satellites” Settings dialog. The color coding on the passes that have not yet risen is simple: The higher the maximum elevation of a pass will be, the brighter the line. For a white line, you can assume the satellite will pass almost overhead, a dark gray one can pass anywhere close to the horizon.

The list is always ordered in descending AOS. What do all those terms mean? It’s really simple:

Satellite

That one is pretty clear: The name of the satellite, along with an icon signifying whether this is a daytime pass, a nighttime pass, dusk/dawn pass, lunar pass or a pass with an iridium flare. The icons are pretty self explanatory.

AOS

Stands for “Acquisition of Signal”, this is the time when the satellite rises above the horizon.

LOS

Stands for “Loss of Signal”, this is the time when the satellite sets below the horizon.

T-

Often referred to as “T minus” this is the countdown. For a satellite that has not risen yet, this is the time until AOS in hours, minutes and seconds. It can also have a +x before it, that means +x days (1 day = 24 hours) ahead.

As soon as a satellite rises above the horizon, T- refers to the time until LOS.

Rise Az

This is the Azimuth of the satellite when it rises above the horizon.

Max El

This is the azimuth and maximum elevation the satellite will reach (in azimuth @ elevation format, 270@80 means the maximum elevation is 80 degrees at precisely west, 270 degrees).

Set Az

This is the azimuth the satellite sets at.

Duration

This is the duration of the pass in minutes and seconds.

Az, El and Range

These three parameters are only visible while a satellite is above the horizon. It gives the instantaneous Azimuth, Elevation and Distance (=Range) to the satellite from the observers position.

Lunar Pass Start and End

This gives the start and end time for the lunar pass (if one was found)

Flare Details

This gives the details associated with an Iridium flare: An example might read:

04:59:05 M: -1.09 Az: 150.7 El: 32.2

This means that the flare occurs at 04:59:05, will reach a magnitude of -1.09, and the maximum brightness will occur at an azimuth of 150.7° and an elevation of 32.2°.

Please note: Iridium flares have a life of their own. It’s hard to predict them reliably, both time wise as well as location wise. If the satellite is only a tiny bit offset, the mirror angles might be incorrect and no flare will be observed, or a significantly less bright one.

Color coding

The colors in the pass list have a simple meaning:

Red: The satellite is less than 10 degrees above the horizon.

Green: The satellite is more than 10 degrees above the horizon.

The EarthView Window

Select the “View”, “EarthView Window” Menu to open the EarthView and display your satellites on their way around the planet.

Left-click and drag inside the EarthView window will let you move the center longitude of the map around.

Left-click on the main dot of a satellite will show/hide that satellite’s track and will also display the location information for that particular satellite in the status bar at the bottom of the window.

Right-click will bring up the context menu, if on the satellite dot, it’s a menu just for that satellite, if anywhere else, it’s a menu for the entire window.

Cloud maps enabled

We’ll now walk through the menu options on the right click menu:

Background Options

Cloud map

Either enables or disables the cloud map in the background.

No cloud maps

Show Home Marker

This option draws a yellow cross where your position is set.

Save Screenshot as…

This option lets you save a screenshot without having any options set in the System Settings dialog.

Set Center Longitude to

You can select either a reset to 0 (Greenwich) or set it to your home longitude.

The longitude displayed while dragging the background

Satellites

This option lets you select individual satellites for display, or display all or none (look for those two at the top of the submenu, in case it is very long).

If your window is empty, you more than likely don’t have the display option for the satellites on. As soon as it’s on, you should see a swarm of satellites (depending on how many you have selected) on the map, each satellite having three dots. The main dot is the present position, the two smaller dots are the trailing positions where the satellite was 1 and 2 minutes ago.

Show Radio Horizons

This option globally turns the radio horizon display on or off. The radio horizon is the reach of a theoretical radio emission as projected onto the map. If you’re trying to pick up a radio signal from a satellite for instance, you’ll need to wait until that ring is within your position.

Show All Satellite Names

Another option that globally affects all satellites loaded: It will either display or hide the satellite name.

Recalculate Tracks Now…

It can happen that you immediately want to see updated tracks, but they haven’t been updated yet. Select this action to trigger a track recalculation.

The SkyView Window

The SkyView window displays the sky above the observers location, including the sun, the moon, the 9110 stars from the Yale Bright Star Catalogue as well as satellites and their tracks as they move across the sky. If you hover the mouse over any of the objects, including stars, a bubble help window will give you more information about it.

The SkyView window during a number of Iridium passes

Setting Orientation

Dragging the mouse while keeping the left button pressed will let you rotate the sky. You don’t have to twist your neck in case you’re not looking south, simply rotate the sky in the same direction as you’re watching. For precise reference, the heading is being displayed at the bottom of the screen while the rotation is in progress.

Other information in SkyView

There are sunrise/sunset and moonrise/moonset times displayed in the window. In breaking a certain scientific tradition, these times are strictly forward looking. In the above case for instance, the moonrise time refers to the next moonrise time, which will be tomorrow. The moonset time however is the next one as well, but that hasn’t occurred yet, so it’s happening today. The same goes for the sun, the displayed sunrise is for tomorrow, as today’s sunrise has occurred already. It’s always forward looking to the next event. Click the right mouse button in SkyView to see the context menu.

Satwhere FAQ

Q: I’m on VirtualPC on a Mac, and I don’t have a right mouse button! How do I bring up the menu?
A: The right mouse button can be emulated by holding down the <control> key on the Mac while pressing the one and only mouse button you have on the mac.

Q: I have selected a geosynchronous satellite but it doesn’t show up in the passlist. Where is it?
A: Geosynchronous satellites do not have passes, by definition. If you want to know where that satellite is, open the EarthView window and display the satellite there. If you click on the satellite, you’ll see information such as azimuth and elevation in the status bar.

Q: I have mistakenly selected all satellites and now it takes forever to calculate their passes. How can I stop that?
A: Press the <Esc> key until the calculations stop. Then go into the satellites dialog and delete the ones you don’t want to see.

Q: I managed to mess up the settings somehow. How can I reset to default settings?
A: Keep the keys <ctrl> and <shift> pressed while starting SatWhere. You’ll be asked whether you want to reset the settings, choose “Yes” and all registry settings will be reset to default.