How much power did the voice and data radios have on the Apollo missions? Additionally how much broadcast power is used on data transmissions from the surface of Mars?
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1$\begingroup$ It's not so much how much power you pump into the transmissions as how large antennas you can muster. Both Apollo and our current Mars missions use really large antennas Earth-side, which means that you can get away with far less power output especially from the downlink (spacecraft) transmitter. Compare What is a link budget, and how do I make one? on Amateur Radio. $\endgroup$– userCommented Dec 27, 2016 at 15:07
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3 Answers
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Apollo used about 20 watts. The total power available from the fuel cells in the service module was about 4 kW.
https://en.wikipedia.org/wiki/Unified_S-band#Emergency_key
https://en.wikipedia.org/wiki/Apollo_Command/Service_Module#Electrical_power_system
http://mars.nasa.gov/MPF/rovercom/rovfaq.html#faq6
The Sojouner rover used 100 mW for radio transmissions back to the Pathfinder lander. They tested the radio link on earth to a range of about half a mile. The maximum power from its solar array was only about 16 W. Pathfinder relayed the signal back to earth with about 12 W of power.
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MER uses a 15 W X-band solid state power amplifier, which actually delivers about 17 W RF out. The UHF relay radio has a 12 W amplifier, which delivers more like 14 W.
MSL also has a 15 W X-band SSPA for the surface (it has a 100 W X-band TWTA for cruise), and an 8.5 W UHF RF amplifier.
See Mars Exploration Rover Telecommunications and Mars Science Laboratory Telecommunications System Design for more information.
answered Dec 27, 2016 at 18:25
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$\begingroup$ The solid state power amplifier of MER provides 16.8 W of RF power and the DC power input is about 58 W. The efficiency of travelling waves tubes is much better. $\endgroup$– UweCommented Dec 28, 2016 at 10:09
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The transmitters used in the spaceships were small to save weight and power. The HF output power was small, about 20 W. For downlink to earth this was compensated by using very large antenna dishes and high gain low noise preamplifiers in the ground stations. For uplink a lot of power could be used, about 20 kW and even more. The antenna dishes used at the spaceships were much smaller than those on earth, about 2 m diameter in space and 34 to 70 m on earth. But the smaller dishes had an advantage, the beam width was larger and required less precise alignment to the ground station. The large dishes on earth and their small beam width required better alignment, but using heavy equipment this was easier on earth than in space.
