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The answer to my question The first transistors in space: Germanium or Silicon? What about LEO? actually addressed both the first Germanium and Silicon transistor.

So now I've gotta ask about electron tubes (valves). It sounds like Sputnik-1 and Sputnik-2 had tubes, although 2 had a mix of both. But after that?

There are types of electron devices are used in RF amplifiers (e.g. klystrons, traveling wave tubes) and of course photomultiplier tubes are still being sent to space regularly (there - the ISS version is scheduled for 2020) and these could count as interesting answers, but what I'm primarily looking for is the small, compact devices like you'd find in an old radio, with the filament, grid(s) and plate all right next to each other.

The significance is that even then, transistors required so much less power than vacuum tubes because they didn't require heated cathodes (filaments) for thermionic emission of carriers. By doping a low band-gap semiconductor material, carriers could be generated at 0C rather than cherry-red hot. That meant that you could power a 1 watt transmitter with a few watts of electrical power, something sustainable with photovoltaics, and that was critical for making satellites long-lived.

Of course if you want to go to Venus, you just choose a higher band-gap semiconductor.

below: An assortment of electron tubes (vacuum tubes, valves); "Eine Zusammenstellung von Elektronenröhren." From here.

enter image description here

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    $\begingroup$ The efficiency of Travelling Wave Tubes is still better than that of semiconductor amplifiers. A TWT and a Klystron are different types of RF tubes. Do'nt you want to count TWTs too? $\endgroup$
    – Uwe
    Jun 14, 2017 at 19:18
  • $\begingroup$ @Uwe If I ask for a 1 Watt transmitter with the lowest required power supply (note the history tag), will you still choose a TWT over transistors? If they are indeed more efficient, it will be in a fairly narrowly defined subspace of applications. $\endgroup$
    – uhoh
    Jun 16, 2017 at 7:31
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    $\begingroup$ For New Horizons, two redundant 12 W TWTs were used. $\endgroup$
    – Uwe
    Jun 16, 2017 at 8:35
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    $\begingroup$ Once I read a statement that a radio beacon on a Soyuz descent vehicle was designed on subminiature radio tubes. Photos of soviet sub-tubes radiomuseum.org/forum/russian_subminiature_tubes.html $\endgroup$
    – A. Rumlin
    Jul 21, 2019 at 16:49
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    $\begingroup$ @A.Rumlin Those are beautiful! I'll ping here if I ask a question in Electronics SE about them. $\endgroup$
    – uhoh
    Jul 21, 2019 at 16:53

2 Answers 2

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Electron tubes were still used in the Kurs system on the Soyuz-MS and Progress-MS until March 19, 2016, when the last of the old Kurs was launched. Since then, Soyuz-MS and Progress-MS launches have used the new Kurs-NA system. I have not been able to find if the new system still uses electron tubes, but if it does then today's Progress-MS launch [June 14, 2017] would be the most recent electron tube launched.

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  • $\begingroup$ I'm going to add a little bit to the question about tubes in a few minutes. But please keep this answer - the information is interesting! $\endgroup$
    – uhoh
    Jun 15, 2017 at 2:25
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    $\begingroup$ @uhoh I believe if I'm interpreting my source correctly, the Kurs system did in fact use standard vacuum tubes in its hardware. However, I think they did not continue to use them in the Kurs-NA, so March 19, 2016 would be the last launch. $\endgroup$
    – called2voyage ♦
    Jun 15, 2017 at 13:45
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    $\begingroup$ OK In section 3.2.2 (circa page 50) there is a description of several radar-like systems for range, rate, and pointing/bearing, including a 700 RPM conical scanning antenna. I can imagine the system has been calibrated and refined over a long period and may contain electronics which while it might potentially be transistorizable, is best left the way it is because it works well and there is a huge experience base. I don't see "electron" or "tube" there but... oh, last sentence of 3.2.2 OK got it! $\endgroup$
    – uhoh
    Jun 15, 2017 at 15:27
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    $\begingroup$ My text search of that document was giving me strange results, took almost 10 minutes to load too. Now have saved to disk it's much better. $\endgroup$
    – uhoh
    Jun 15, 2017 at 15:29
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According to this paper there is currently a system which includes a traveling wave tube amplifier mounted on an exterior truss of the ISS. Not sure if that is ground-ruled out by your question or not (I am not sure what a Klystron is).

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    $\begingroup$ Klystrons are the microwave sources in microwave ovens and older radar transmitters. They have an interesting role in WWII-era technology and history. The second sentence in Wikipedia's article on traveling wave tubes says: The TWT belongs to a category of "linear beam" tubes, such as the klystron, in which the radio wave is amplified by absorbing power from a beam of electrons as it passes down the tube. so please keep your answer because I didn't know this! But I'll add something to the question also. $\endgroup$
    – uhoh
    Jun 15, 2017 at 2:23
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    $\begingroup$ No, magnetrons are used in microwave ovens, they were invented in WWII for radar. There are magnetrons and klystrons, very different types of tubes, seee wikipedia. $\endgroup$
    – Uwe
    Jun 15, 2017 at 22:19
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    $\begingroup$ @Uwe OK It seems I've put the wrong 'tron in my oven. Thanks! (btw I didn't receive notice of this comment for some reason, don't forget the 'uhoh!') $\endgroup$
    – uhoh
    Jun 16, 2017 at 7:36

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