WHETHER you are on Earth or on Jupiter, NASA鈥檚 Jet Propulsion Laboratory will
help you get your bearings. The JPL鈥檚 new Internet service calculates the view
from more than 25 000 planets, moons and spacecraft.
Designers of communications systems for space probes will be able to use the
system to find out exactly when a particular celestial body rises into view. And
science-fiction writers will be able to add authenticity by accurately
describing when a moon will rise on another planet.
Three years ago, JPL put up an early version of the software, which
calculated astronomical coordinates as viewed from anywhere on Earth. Jon
Giorgini of JPL says the system includes orbital data on the Sun, all the
planets, 63 natural satellites, several spacecraft, and more than 25 000
asteroids and comets. Many amateur astronomers use it, he says, as well as NASA
mission planners. It has logged some 175 000 requests, despite the fact that
interpreting the results requires a knowledge of astronomical coordinates.
Advertisement
Now JPL has rewritten the software to calculate positions as seen from other
objects. 鈥淚t鈥檚 partly in response to the number of spacecraft-landing projects
under consideration or in planning,鈥� says Giorgini. Planners need to know where
to point a spacecraft鈥檚 antenna to communicate with Earth, and the locations of
other bodies to determine a craft鈥檚 orientation.
Users can log onto a JPL computer via the Internet, or e-mail requests
written in standard script. Instructions on using the software are available at
http://ssd.jpl.nasa.gov/horizons_doc.html.