|Spacecraft Parts: Telecommunications
The telecommunications subsystem is used for receiving and
transmitting commands and data. It is a two-way radio system,
somewhat similar to a pair of very sophisticated walkie-talkies. The
telecom subsystem on Mars Reconnaissance Orbiter is like one walkie-talkie
and the Deep Space Network
antenna back on earth is like the second.
With its large-dish antenna, powerful amplifier, and fast computer, Mars
Reconnaissance Orbiter can transmit data to earth at rates as high as 6
megabits per second, a rate ten times higher than previous Mars orbiters.
This rate is quite high considering that Mars Reconnaissance Orbiter will
achieve it while 100 million kilometers (62 million miles) from Earth.
Over its two-year primary science mission, the spacecraft is predicted
to transmit more than 34 Terabits--that's 34 million million bits. To put
it another way, that's more than all the data transmitted by all previous
JPL spacecraft put together!
The orbiter's radio operates in the X-band of the radio spectrum, at a
frequency of around 8 Gigahertz. That means that the electromagnetic
carrier wave -- onto which the data is modulated -- oscillates at 8
thousand million cycles per second. For comparison, your radio at home
is designed to receive signals from AM stations in the range of
535 - 1,700 Kilohertz, and from FM stations in the range of 88 - 108
Now, here's a question: if you could make an electromagnetic wave
that oscillates at 500 Teraherz - that's 500 million million cycles per
second - what would you have? Answer: visible light! And you produce
these amazing waves every time you flip on a light switch!
Major components of the telecom subsystem include:
||for transmitting and receiving commands
||for boosting the power of radio signals so that they are strong enough to be received at the Deep Space Network antennas
||for translating navigation and other signals from the orbiter
Also on board is Electra, a UHF
telecommunications package that is one of the engineering instruments
providing navigation and communications support to landers and rovers on
the surface of Mars. Electra allows the spacecraft to act as a relay
between the earth and landed crafts on Mars, which may not have
sufficient radio power to communicate directly with earth.