The two Voyager spacecraft use traveling wave tube amplifiers to send data back to us. These have 2 power settings: 12W and 18W. The power supply on board the Voyagers (an RTG) produces less power each year.

I'm trying to figure out what will happen when the available power drops below the level where the RTG can supply 12 W to the transmitter. Could this type of amplifier be driven at lower power levels, or is this an all-or-nothing proposition?

  • \$\begingroup\$ This probably depends on how the heater and HV are generated, do you have any design documents for the voyager radio systems you can link in? \$\endgroup\$
    – Bryan
    Jun 7, 2022 at 19:57
  • \$\begingroup\$ Nothing detailed enough, I'm afraid. All I have is block diagrams. \$\endgroup\$
    – Hobbes
    Jun 8, 2022 at 17:50

1 Answer 1


A TWTA uses a helix wound around the electron beam. The microwave signal applied to the helix interacts with with the electron beam and modulates the electron density. For good interaction the traveling wave on the helix and the electrons within the beam should have similar speed. If the acceleration voltage of the beam is too low, the electrons are too slow for the interaction with traveling wave.

So if there is too few power available to accelerate the electron beam, the amplification of the tube decreases to zero.

See https://en.wikipedia.org/wiki/Traveling-wave_tube


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