Telstar 1 and 2 demonstrated routing of telephone, television and other communications types between continents.

The Smithsonian Air and Space Museum pages below contain images of the satellites. They show two rows of non-very-directional antennas that completely circle the "equator" of the spherical satellite, pointing radially outwards in a complete circle.

I estimate there are about 42 of the larger antennas and 64 of the smaller ones.

Question: How were all of the over 100 antennas distributed in these two rings configured to receive and transmit signals, since at any time half to most of them wouldn't be pointing at the US or Europe?

enter image description here

This illustration from 1962 shows the major components of Bell Systems’ experimental communications satellite.

Source: Smithsonian Air and Space Museum page Satellite Components

enter image description here

Backup spacecraft for Telstar, the world’s first active communications satellite. Telstar 1 began an era of live international television. After its launch on July 10, 1962, it relayed television images between the United States and France and England.

Source: cropped from Smithsonian Air and Space Museum page Telstar


1 Answer 1


Telstar 1 carried a single transponder with 6390MHz uplink and 4170MHz downlink.

All the 72 ports in the small-aperture ring were ganged together to make a single receive antenna with a toroidal pattern that extended 30 degrees above/below the equator of the satellite, but had even gain as the satellite spun.

The 48 ports in the larger-aperture ring worked the same way for transmit.

The overall energy budget was amazingly marginal. The solar cells only provided 14W, feeding a 3W TWT. There was no power (and probably no weight budget) to do anything other than to make the antennas from passively combined ports in a time before microwave semiconductor amplifiers. The satellite had to be spin stabilized (with a passive coning damper), and there was no way to aim a higher gain antenna.

enter image description here

Source: "A General Description of the Telstar Spacecraft", R.H. Shennum and P.T. Haury, 1963, published in NASA SP-32 p.801. See particularly Figure 4 on page 806 which shows the single transponder circuit, and section VII (pp 812-816) on antennas, which includes as Figure 6 the top image in the question and the pattern described above as Figure 7 and 8.

enter image description here For more technical detail, please see "The Spacecraft Antennas", J.T. Bangert, R.S. Engelbrecht, E.T. Harkless (yes, that Harkless), R.V. Sperry and E.J. Walsh, 1963, published in NASA SP-32 p.869.

  • $\begingroup$ also, while we're on a Telstar kick, I've just asked Function of the separated, individual solar cells on Telstar 1 and 2? Why were they "special"? $\endgroup$
    – uhoh
    Commented Sep 1, 2019 at 2:17
  • 3
    $\begingroup$ Incidentally, if you want to know about Telstar, that issue of the Bell System Technical Journal (or the NASA published version of it) is a gold mine. It looks to be about 2000 pages long. $\endgroup$ Commented Sep 1, 2019 at 3:58
  • 2
    $\begingroup$ NASA-SP-32 is on ntrs. ntrs.nasa.gov/search.jsp?R=19640000959 Link is to Vol 1 but all three are there. $\endgroup$ Commented Sep 1, 2019 at 4:11
  • 2
    $\begingroup$ @OrganicMarble Thank you! $\endgroup$ Commented Sep 1, 2019 at 4:13
  • 2
    $\begingroup$ @uwe I edited "high-frequency" to "microwave" in that sentence to make it clearer. The TWT was the only microwave amplifier aboard. All the other Telstar microwave elements were passive. Transistor microwave amplifiers at these power levels started to be available with GaAs MESFETs in the early 70's, but AFAIK the first semiconductor amplifier in space was the tunnel diode amplifier in Intelsat V (1977). Microwave passive circuits have a much longer history, both on Earth and in space. $\endgroup$ Commented Sep 1, 2019 at 15:17

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.