Hearing Galileo's Whisper Across the Solar System
The larger the collecting area of an antenna, the weaker the radio signal it can collect
and focus, and the faster the spacecraft can send down its data without getting
"garbled". Very large Earth receiving satellite dishes are needed because Galileo
is very far away and the amount of electromagnetic energy decreases with the
square of the distance from the source.
- How many Galileos does it take to turn on a light bulb??
- With the existing Earth receiving stations , it would take
energy collected from 10 BILLION GALILEOS OVER THE
LIFE OF THE SOLAR SYSTEM TO LIGHT ONE 100-WATT
LIGHT BULB FOR 1 SECOND!!!!
And yet, we can detect this very weak signal and send back
pictures and other information with it.
The antenna "hears" both signal (data) and noise (static) and uses hardware and software to maximize signal
and minimize noise. The data rate or number of data bits per second (bps) a spacecraft can transfer to an Earth
station depends on the communications capabilities of both systems.
Galileo will record and later transmit all of its data through its low gain antenna (see spacecraft diagram on
page 7). The Deep Space Network, with its 70-meter antennae, can receive data from Galileo at Jupiter at the
rate of 10 bps (equal to about 1 letter per second). Several new capabilities will be ready by 1996 to increase
the rate to 160 bps (about two sentences per second). These include connecting the ground antennas together in
arrays (increases received signal), use of an Ultracone (decreases communications noise) and improved
receivers (makes more effective use of available received signal).
Compare the "fast" rate of 2 sentences per second to the "slow" rate of 1 letter per second . Use the first 2 lines of a favorite story or poem. It would take one second to recite using the faster rate.... how long using the slower rate?
Q: The Deep Space Network has 70-meter
antennae at stations located in Spain,
Australia and the U.S. (California). Why do
you think these places were chosen?
H: Stars on this map show where they're
Bibliography & Other Sources of Information
Basics of Space Flight Learners' Workbook, 1993, JPL publication D-9774.
Beatty, K. and A. Chaikin, The New Solar System, 1990, Sky Publishing Corporation & Cambridge University Press.
Glass, B.P. Introduction to Planetary Geology, 1982, Cambridge University Press.
Hunt, G. and P. Moore, Jupiter, 1981, Rand McNally Library of Astronomical Atlases for Amateur and Professional Observers.
The Galileo Mission, 1992, Space Science Reviews, Volume 60, Numbers 1/4, Kluwer Academic Publishers.
Yeates, C. et al, Galileo: Exploration of Jupiter's System, 1985, NASA publication SP-479.
We Want Your Opinion!
Suggestions and ideas to improve the Galileo Curriculum Module are always welcome. Please let us know how we're doing by contacting us through electronic mail or written mail. The e-mail address to use is: email@example.com. The
mailing address is given on the first page.
Along with this Module (and others to follow), the Galileo Outreach Team has a new poster available and maintains a World Wide
Web homepage (http://www/jpl.nasa.gov:80/galileo/). The Project's newsletter, the Galileo Messenger, is available through the
address shown on the first page.
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Last modified prior to September, 2000 by the Windows Team
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