======================================================================== Visual Satellite Observing F A Q Chapter-02 How Can I Predict When A Satellite Is Visible? ======================================================================== ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ + This FAQ chapter is "under construction". Some of the + + sections may be unwritten as yet. Other sections may + + contain out-of-date, unreviewed, or "starter" material. + + Yet other sections may be works in progress, partially + + written and reviewed. + ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ + In this chapter, the following sections are considered + + to be completed (written and reviewed): + + None + ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ ---- 2.0 How Can I Predict When a Satellite is Visible? ---- 2.1 Prediction Software If you want to set about generating your own predictions for observing then naturally you'll need some software. What follows is a selection of software for various platforms with a short description of each. ---- 2.1.1 Software for DOS PC's ---- 2.1.1.1 QuickSat 2.10d Mike McCants' program uses two-line elements to generate predictions which include an estimate of magnitude. Text based, reading the input parameters from a formatted file. A comprehensive magnitudes file is packaged with it. ---- 2.1.1.2 STS Plus Dave Ransom's program uses the SGP4 model to produce tabulated predictions, orthographic views and ground tracks from two line or AMSAT elements. $10 shareware. ---- 2.1.1.3 SkyMap Version 5.10 Rob Matson's program uses SGP, SGP4 and HANDE models for prediction. Plots star maps with and without satellite tracks. Able to search collections of elements with specified conditions. Useful for identifying satellites. Produces output for HP printers. Also able to plot rocket trajectories. Shareware. $25 suggested. ---- 2.1.1.4 Traksat Version 3.10 Paul Traufler's excellent shareware program ($25) genrates predictions from two line elements. It also produces a graphical display of the ground track in various projections and a plot of the pass against the local (star-filled) sky. Uses GUI interface under MSDOS. Propagation models used are SGP4 and SDP4. ---- 2.1.1.5 PC-Track ---- 2.1.1.6 SatPro ---- 2.1.2 Software for MS Windows ---- 2.1.2.1 SatSpy A commercial package for tracking satellites under Windows. ---- 2.1.2.2 Micro Orbiter 3.0 A commercial package for tracking up to 20 satellites in 9 different map projections under DOS. Uses NORAD/USSPACECOM SPG4. ---- 2.1.3 Software for the Apple ---- 2.1.3.1 Orbitrack Version 2.15 This shareware package ($10) authored by Bill Bard, will furnish you with predictions, a ground track plot and a view of the pass against a star background. Requires System version 4.1 or later. ---- 2.1.4 Software for Unix machines ---- 2.1.4.1 Sattrack Version 3.1 Manfred Bester's excellent sattrack is free for personal use and is distributed as C source ready to build on Linux, BSD, HP, IBM and Sun workstations. Using the USSPACECOM (NORAD) SGP4 model it can provide a live tabulated display for one or many satellites. It can be used to generate prediction tables or you can just watch the live X11 display of the groundtrack. Suitable for amateur radio or visual observing. It reads NASA/ USSPACECOM two line elements and can generate AMSAT format lement sets. Future versions will include the SDP4 deep space propagation model, a live sky plot indicating satellite positions in the observers local sky, red night-vision display, fast forward mode, ability to input changing weather conditions and modeling of the apparent brightness of the satellite. Manfred maintains a web page for sattrack. ---- 2.1.4.2 Xsat Version 1.2 Dave Curry's public domain satellite tracker produces an X11 display of ground tracks. Can generate a visibility list for a given location and produce postscript outputs of the display. Uses N3EMO's source code for the predictions. Actually this is C source code suitable for the core of a prediction program. Available from any comp.sources.misc archive, volume 11. ---- 2.2 Orbital Element Data ---- 2.2.1 What are "two-line elements" (TLE's)? ---- 2.2.2 Where can I get TLE's? There are several locations of recent orbital data to be found about the net. Most often they are in the form of two-line, or Keplerian elements. These data sets detail the orbital parameters for a given satellite at a given time and can be used in a prediction model (such as SPG4) to locate the satellite. AMSAT, the Radio Amateur Satellite Corporation, have an excellent explanation of the format. Such element sets can be obtained from sources listed in the following section. ---- 2.2.2.1 Internet resources FTP Dr T S Kelso's data at the Air Force Inst. of Technology. The astro directories at Nic.funet.fi. The SEDS archive at the University of Arizona. Elements at NASA's JPL. A large number of these element sets are mirrored locally. Dr. Kelso's AFIT site provides elements for weather, amateur, GPS, comsat and visual objects, to name but a few groups. The SEDS and JPL sites archive Ted Molczan's element file and Allen Thomson's 'mother of all element files' which both include elements for the classified satellites which aren't published by NASA/USSPACECOM. The FUNET archives mirror the JPL and AFIT sites. HTTP AMSAT's WWW server. NASA's SPACELINK carries shuttle elements, both during a flight and prior to it. They also have a file of elements for the more visual satellites. We keep an up-todate shuttle pre-launch element set at VSOHP. But you can also take a look at the Web-page of the shuttle and Mir elements maintained by Gary Morris. LISTSERV AMSAT run a listserver which distributes elements. Send a message to listserv@amsat.org asking to be added to the KEPS list. The shuttle elements mailing list provides you with exactly that. Send a message with the word 'help' in the body to listserv@ucsd.edu. USENET Dr Kelso posts elements to sci.space.news and sci.space.shuttle whilst AMSAT post elements to rec.radio.amateur.space Note that AMSAT also provide elements in a multi-line format which details the nature of each element parameter. This is for software requiring manual input of the elements. Some packages come with tools to carry out the conversion of this AMSAT format to NASA/USSPACECOM two line elements. Data in the form of state vectors, are also posted to sci.space.shuttle and rec.radio.amateur.space. These can be converted to two line elements suitable for SGP4 propagation models using Ken Ernandes' vec2tle program. TELNET Similar vectors can be obtained from the NASA Orbital Information Group (OIG) BBS. They also provide shuttle elements and data for most other objects in the USSPACECOM(NORAD) catalogue. Telnet to oig1.gsfc.nasa.gov and login as oig with password goddard1. After going through a simple registration process you can download the data you desire. ---- 2.2.2.2 Uncompressed TLE files ---- 2.2.2.3 Compressed TLE files ---- 2.2.2.4 BBS's ---- 2.2.2.5 FidoNet ---- 2.2.3 Why are there so many different types of TLE files? ---- 2.2.4 What are "keplerian elements"? ---- 2.2.5 What are "state vectors?" ---- 2.2.5.1 What is VEC2TLE? Ken Ernandes computer program, Vec2tle, converts a state vector (position, velocity data) to a two line element set. Can also re-epoch elements or accomodate on-orbit maneuvers. Free for amateur use. ---- 2.2.6 How often should TLE's be updated? ---- 2.3 Helpful Utilities for maintaining TLE files ---- 2.4 Troubleshooting -- I Didn't See Anything. Why? ---- 2.4.1 Is your latitude and longitude entered correctly? ---- 2.4.2 Is the offset to Universal Time set correctly? ---- 2.4.3 Were you looking in the right place? ---- 2.4.4 Did the satellite maneuver or decay? ---- 2.4.5 Was the satellite bright enough to be seen? ---- 2.4.5.1 Phase Angle ---- 2.4.5.2 Could the satellite have already gone into the Earth's shadow? ---- 2.4.6 Is your time accurate? ---- 2.4.6.1 Radio time services ---- 2.4.6.2 Telephone time services ======================================================================== This FAQ was written by members of the SeeSat-L mailing list, which is devoted to visual satellite observation. Members of this group also maintain a World Wide Web site. The home page can be found at the URL: http://www.satobs.org/ The information on the VSOHP web site is much more dynamic than that found in this FAQ. For example, the VSOHP site contains current satellite visibility and decay predictions, as well as information about current and upcoming Space Shuttle missions and Mir dockings. The VSOHP site also contains many images, equations, and data/program files that could not be included in this FAQ while maintaining its plain text form. This FAQ and the VSOHP web site are maintained asynchronously, but an effort is made to synchronize information contents as much as possible. The material in this FAQ chapter was last updated in February 1998. ========================================================================