The OpenStep Window to Satellite Tracking
and Space Surveillance
Overview
What is Rendezvous version 4.0? Rendezvous, as used by most, is a satellite tracking program which runs under OpenStep for Mach and soon under Mac OS X Server. Its primary advantage over similar utilities on other platforms is its versatility, simplicity, and ease of use. Standard two-line element files (which are found on numerous web sites such as celestrak) can be easily loaded, and their contents listed as entries in browsers in the main window. Any object, or group of objects, can be selected from the browsers and subsequently displayed on the Ground Trace Map as small icons representing the position at the date and time selected by the user in the calendar. There is an associated ground trace line trailing from the icon which represents the path the object will travel during the next several minutes. Things Rendezvous Can Do For You First and foremost, Rendezvous will load orbital element sets from standard NORAD two-line element, or "tle", files, and display selected objects from these files in the Ground Trace Map. Besides the ground trace, the map is designed to display a wealth of information in an intuitive fashion. Through the Map Inspector, the map can be enabled to display the following information about selected objects: |
o | Current Position | |
o | Ground Trace | |
o | Solar Illumination condition | |
o | Coverage Area | |
o | Solar Terminator boundary | |
o | Lunar Shadow during Solar Eclipses |
Here is an example of the main window with several objects loaded into it: |
In this view, two objects (MIR and ZARYA) have been selected for display. The current position of the objects selected in the browsers is indicated by the little satellite and target icons. We can see that the map has been zoomed in to show details of the engagement, and we have enabled the display of the coverage area of the orbiting objects. This area, which is shown as a colored circle surrounding the icon, indicates the region of the earth which is visible by the orbiting object, but it can also be thought of as the area within which the sensor is above the horizon. Examination of the ground traces shows two things. First the sensor ground traces are colored blue, and the target traces are colored red. Second, any individual trace can have two tints which indicate the solar illumination condition of the satellite at that point in the trace. A dark, solid color denotes that the sun is shining on the satellite, while a light, nearly white tint means that the sun is not illuminating the object. The illumination condition is an important factor in determining if a satellite is visible from the ground at any given time. More detailed information about the main window and its controls are found in the section "Elements of the Main Window".
Getting the State Vector and Orbital Elements When numerical accuracy is required, you can extract the current state vector parameters in the Sensor and Target Inspectors. State vectors and orbital elements can be displayed in any of seven different commonly used coordinate systems. Read about the specifics of these in the section titled "Examining the Trajectory in Detail". That section also describes the panel which plots the azimuth, elevation, and range from the sensors to all targets. This is very useful when searching for satellites in the evening sky. Location and Display of Eclipses The dates of solar and lunar eclipses can be found using the Eclipse Prediction panel. Simply select the dates between which you want to find eclipses. Rendezvous displays all eclipses between those dates in a scrollview window. Double clicking on any entry in this scrollview automatically loads that date into the calendar of the main window and displays the eclipse. The shadow of the moon as it passes over the earth during a solar eclipse is shown. The shadow of the earth as it passes over the moon during a lunar eclipse can be shown using the Telescope Inspector. This panel shows how all the eclipses expected in 1999 were found: |
Double clicking the entry for the solar eclipse on August 11, 1999 automatically brings the main window to that date. We enabled the lunar shadow display with the map inspector and advanced the clock one hour to show the eclipse in progress:
We see the shadow of the moon covering nearly the whole Atlantic Ocean as it begins to move across eastern Europe. The shadow is composed of two regions. The large area with the same color as the solar terminator represents the penumbra, or the region of the earth that will see a partial eclipse. The small dark oval area in the middle represents umbra, or the area of the ground that will see a complete and total eclipse of the sun. Using a different panel, we can watch the moon as it passes in front of the sun as it would be seen from any location which has been loaded into the Sensors browser. Rendezvous comes with a small database of locations in the United States. This database is a simple ascii text file, and it is very easy to add entries to this file if you know the latitude and longitude of the location of interest. The view of the eclipse in the map shown above indicates that Paris, France (shown as a little yellow dot, as well as the cities of Colorado Springs and Cape Canaveral) should still be on the leading edge of the eclipse. If we display the Telescope Inspector for the sensor located at Paris, this is what we see:
It appears our intuition was correct - here we see the moon on its way to covering the sun as it will be seen in Paris, France on August 11, 1999. Now on to the lunar eclipses. To view the July 1999 lunar eclipse as it is seen from Albuquerque, New Mexico, we first load the USCities.gnd file into the Sensors browser. We select Albuquerque from the browser, and double click on the July 28, 1999 entry in the Eclipse Panel. We advance the time a few minutes and bring up the Telescope Inspector to see the eclipse in progress:
The moon is beginning to move into the earth's shadow and we see the "western" side of the moon darken. From the azimuth and elevation of the boresight, we see the moon is only 12 degrees above the horizon, and is located in the southwest portion of the sky at an azimuth of -124 degrees. More detailed information and a step-by-step tutorial on searching for and displaying eclipses is found in the "Finding and Displaying Eclipses" section. Making Movies Anything which is displayed in the Telescope Inspector can be made into a movie by clicking a button. Movies can be stored in .anim format or QuickTime format. Either of the solar or lunar eclipses we showed above could easily be made into a movie, and with the star database loaded and enabled for display, this would provide a movie which showed the stars moving across the sky in the background as the eclipse progressed. The section "Making Movies" provides a useful tutorial about how to make a movie using the Telescope Inspector. Viewing the Solar System During the transit of comet Hale-Bopp, I found it necessary to have a tool to show me the comet's orbit in relation to the orbits of the other planets. To this end I added the Solar System Inspector which allows one to view the heliocentric orbit of any body. When viewed with the orbits of the planets, one can get a good sense of the trajectory of a comet through the solar system. The specifics of activating this panel and using it are found in the section titled "Using the Solar System Inspector". Determining Orbits from Observations Many of us like to observe the sky and make actual measurements of the positions of satellites, planets and comets. Rendezvous has an Orbit Determination panel that allows users to take these measurements of Right Ascension and Declination and compute an orbit for the body. The orbit which is calculated for satellites can be displayed just like any other target in the Ground Trace Map, and orbits calculated for planets and comets can be displayed in the Solar System Inspector along with the orbits of the other planets. The specifics for calculating orbits from your observational data can be found in the "Orbit Determination" section. A sample measurement set for comet Hale-Bopp are included along with JPL's heliocentric element set parameters with which we can compare our results. How Rendezvous is Structured Rendezvous divides objects up into two main classes: Sensors and Targets. Sensors are objects which contain user-loadable components that enable it to "see" things. These components include the trajectory propagator, an attitude processor, a telescope, and a focal plane. The last component is included only in Rendezvous-Pro, and is not needed or intended for casual use. Each of these components is installed as a user-loadable bundle. This means that if a user has a need for a different trajectory propagator than the ones supplied, he can write and load his own propagator. Or if a user needs, for instance, a Cooley-Hat scan routine, he can implement a subclass of the attitude processor and load it in (Note: programming a new bundle requires detailed knowledge of the intrinsics of Rendezvous, and the proper header files. As of this time, these are not available to the general public. If you have a specific need, special arrangements can be made). The particular type of component which is used in a given sensor is selected using the Sensor Inspector. Any component can be "hot swapped" in or out of a sensor at any time using the Sensor Inspector. Targets are objects which contain user-loadable components that enable it to "be seen" by sensors. These components include the trajectory propagator, the attitude processor, and the radiometric generator. The last component is included only in Rendezvous-Pro, and is not needed or intended for casual use. The same orbit propagators and attitude processors which are used in sensors are also used in targets. Where to get Rendezvous? You can download Rendezvous version 3.0 and version 4.0 here:
This download contains a complete distribution of Rendezvous enabled in demo mode. When working in demo mode, all features will operate, however, the epoch time value used in the all the calculations is not the time displayed in the Calendar/Clock. A license key is required to enable this program for general use. Information for obtaining a license can be obtained directly from me here:
Or from Rob:
If You Have Trouble... As always, any problems or questions you might have using Rendezvous can be addressed to me at the address listed above. I'm always eager to hear suggestions for new features or improvements to the user interface. I hope you enjoy using Rendezvous, and would like to thank everyone for their support. |