The first, traj.pro, allows the user to specify a planet and an entry position and velocity for a spacecraft. This program then numerically integrates and displays the spacecraft trajectory until the spacecraft either impacts the planet or escapes into deep space. Type ".run traj" followed by "traj" at the IDL prompt.
The user selects a planet (Venus, Earth, Mars, Jupiter, or Titan) or can define their own. The user selects a planetary entry spacecraft (Mars Pathfinder, Galileo, Beagle 2, Huygens, or the Pioneer Venus Sounder/Large Probe) or can define their own. The user selects an entry position and velocity (Mars Pathfinder, Galileo, Beagle 2, Huygens, or the Pioneer Venus Sounder/Large Probe) or can define their own. Finally, the user selects the length and number of timesteps and a spacecraft drag coefficient.
The spacecraft trajectory is integrated until impact (for Jupiter, crossing the 1 bar level) or the end of the timesteps. Aerodynamic accelerations due to a constant scale height atmosphere and gravity control the trajectory. Assuming a constant drag coefficient is an inaccurate, but simple, assumption. Either improve this section of the code yourself or, if you can provide us with a suitable aerodynamic database, we'll happily improve the code for everyone. A plot of altitude versus time is displayed at the end of the run. Arrays containing altitude, latitude, longitude, speed, and so on can be printed, plotted, or saved at the IDL prompt. The most useful array names are listed at the end of the run, look in the code for any others you want.
The second, recon.pro, allows the user to integrate a set of measured aerodynamic accelerations to obtain their spacecraft's trajectory and profiles of atmospheric density, pressure, and temperature. Type ".run recon" followed by "recon" at the IDL prompt.
The user selects a planet (Venus, Earth, Mars, Jupiter, or Titan) or can define their own. The user selects a planetary entry spacecraft (Mars Pathfinder, Galileo, Beagle 2, Huygens, or the Pioneer Venus Sounder/Large Probe) or can define their own. The user selects an entry position and velocity (Mars Pathfinder, Galileo, Beagle 2, Huygens, or the Pioneer Venus Sounder/Large Probe) or can define their own. Finally, the user selects the length and number of timesteps in their dataset, which should be named "recon.dat", selects a spacecraft drag coefficient, and decides whether to use measured 3-axis accelerations or just those along the spacecraft symmetry axis. A version of the aerodynamic accelerations measured by Mars Pathfinder is provided.
The spacecraft trajectory is integrated until the end of the aerodynamic accelerations dataset. Assuming a constant drag coefficient is an inaccurate, but simple, assumption. Reconstructed densities and pressures will be significantly affected, reconstructed temperatures will be minimally affected. Either improve this section of the code yourself or, if you can provide us with a suitable aerodynamic database, we'll happily improve the code for everyone. A plot of temperature versus altitude is displayed at the end of the run. Arrays containing altitude, latitude, longitude, speed, and so on can be printed, plotted, or saved at the IDL prompt. The most useful array names are listed at the end of the run, look in the code for any others you want.
Some technical details ...
Download the necessary files individually ...
Or tarred together on a Sun UNIX machine ... (type "tar xvf beagle2.tar" to extract the individual files)
These programs are simplified versions of those that will process the entry accelerometer data from Beagle 2 and Huygens. We hope that they may be useful to scientists or engineers who want to (a) understand how atmospheric profiles are derived, (b) verify a published atmospheric profile, (c) see if an entry trajectory will impact the surface or skip out into space, and so on. If they are interesting as demonstrations to teachers of classical mechanics courses or as spacecraft crash testing to taxpayers, so much the better.
We welcome feedback about any aspect of these programs. If you used them and found them useful or useless, or improved and adapted them for your own uses, or have any questions, please email: withers@lpl.arizona.edu . If you used them in actual research, please consider referencing Withers, Hathi, Towner, and Zarnecki, 2002, 33rd Lunar and Planetary Science Conference, Abstract #1203. This conference abstract can be downloaded from http://www.lpl.arizona.edu/~withers/pppp/pdf/lpsc2002beagle2abs.pdf . Further details about the development of these programs can also be found at http://www.lpl.arizona.edu/~withers/pppp/pdf/oureport.pdf , a technical report to the Open University, 2001.