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Comments on the page Maximum grid voltage of ion thruster got me wondering; what is the highest DC voltage ever intentionally produced by a spacecraft in space?

Photomultiplier tubes and micro-channel plates and charged particle spectrometers are common users of at least a few kV, but I suspect that there are some higher voltages out there somewhere.

10 kV? 100 kV? A megavolt?

"bonus points" for a high voltage that was intentionally produced in some way other than a conventional DC power supply rated at that voltage. They don't need a Van de Graaff generator to make their hair stand out in microgravity, but perhaps someone snuck one up for fun?

A Van de Graaff generator hair day Source

as opposed to unconventional, e.g. Van de Graaff, tether, balloon on cat, etc.

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    $\begingroup$ Long time ago when flat display screens where not available and large color display tubes were used about 20 kV DC were used for those. What about the vidicon tubes used for the Voyager cameras? $\endgroup$ – Uwe Sep 17 at 22:39
  • $\begingroup$ Might be equally interesting to find the greatest DC field strength, i.e $\frac{V}{m}$ $\endgroup$ – Carl Witthoft Sep 18 at 12:02
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    $\begingroup$ @CarlWitthoft the problem with that is that it can be quite high on microscopic scales. Put 1 volt across 20 angstroms of gate oxide in a modern CMOS transistor and what do you get? en.wikipedia.org/wiki/…. $\endgroup$ – uhoh Sep 18 at 13:33
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    $\begingroup$ A TWT microwave amplifier with about 10 W ouput typicaly used 3 kV 30 mA supplies. $\endgroup$ – Uwe Sep 18 at 23:13
  • $\begingroup$ @Uwe that's right! The traveling wave travels at the same speed as the electrons, and while they can slow the wave down compared to the speed of light, they need to have the electrons moving quite fast to keep up. I think you can add that as an answer. $\endgroup$ – uhoh Sep 19 at 0:30
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Potential answer (pun intended): 8000 volts for the Apollo television cameras.

Several voltage levels must be accounted for: as much as 8 kilovolts are required at the tube photocathode, and various voltages up to 600 volts are required at the base.

Apollo Experience Report: Television System, NASA Tech Note D-7476, p. 18

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    $\begingroup$ A lot of TWT and Klystrons tubes used for radio amplification are up around 10KV as well. Unsure how one would find a breakdown of the actual numbers. $\endgroup$ – GremlinWranger Sep 18 at 10:42
  • $\begingroup$ Best pun I've read in a long time $\endgroup$ – Pedro A Sep 20 at 16:06
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Linear accelerators have been employed in space. While "voltage" is perhaps not the right term, precisely, these do generate very high energy beams, and frequently using means (like RF, etc) other than direct acceleration by a high voltage DC supply.

There are current proposals to develop a 1MeV RF linac for experiments in space. Early experiments in the 1970s used standard DC high voltage supplies to generate beams of up to 40keV, injecting pulses into the ionosphere using sounding rockets.

Spacelab-1 also had a 7.5keV accelerator on board for a series of particle accelerator experiments.

There was also the BEAM experiment in 1989 that produced a 1MeV neutral hydrogen beam. This had a 30keV injector to the RF accelerator that used a standard DC supply at 30kV. Like the sounding rocket experiments in the '70s, this was also deployed on a sub-orbital rocket to a maximum altitude of 195km - so "in space", but not in orbit.

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  • $\begingroup$ I wouldn't say that a linac is a dc voltage, mind you. The rest are good. $\endgroup$ – Jon Custer Sep 18 at 16:28
  • $\begingroup$ @JonCuster Yes, that's why I said exactly the same thing in the answer. OP also opened the topic talking about ion thrusters, which are really just a type of accelerator. $\endgroup$ – J... Sep 18 at 16:31
  • $\begingroup$ great answer, thank you! fyi I've just asked What did three 1.2 meter spheres and a Xe+ plasma contactor look like? How did they keep the Shuttle "grounded"? $\endgroup$ – uhoh Sep 19 at 1:13
  • $\begingroup$ @JonCuster If you use a linac to charge up a capacitor (ie any object) then you do have true dc and you can arrange things not to see the macro or the micropulses. $\endgroup$ – D Duck Sep 20 at 12:05
  • $\begingroup$ @DDuck - sure, 1MV rated capacitors are easy to find. A Cockroft Walton supply is much easier to build, even at a megavolt, than a linac plus megavolt cap. $\endgroup$ – Jon Custer Sep 22 at 1:51
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The Space Tether Experiment in 1996 induced a current by dragging a conducting tether behind the Space Shuttle (and, thus, through the Earth's magnetic field). It generated 3500 volts before snapping off due to a manufacturing defect.

https://pwg.gsfc.nasa.gov/Education/wtether.html

For more about how this works in general see this answer.

For more about the tether events of STS-75 see this answer and this answer.

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Spacecraft high-voltage power supply construction, https://ntrs.nasa.gov/citations/19750015780

The following was attached to a sounding rocket?

The 100 kV, 5 uA supply shown in Figures 55 through 58 was designed as a Cockroft-Walton device contained within a vessel pressurized to 15 psig with SF6

enter image description here

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    $\begingroup$ Beautiful! I'm waxing nostalgic seeing a Cockroft-Walton. On Earth these were often immersed in transformer oil and in the good-old days those contained PCBs, but that's a different story. In this case it's possible that SF6 was chosen over transformer oil for weight reasons. Though it does say The concept of employing only ceramics, metals, and SF6 in the construction wherever possible follows the design practice developed over many years for construction of Van de Graaf generators. No encapsulants were employed. $\endgroup$ – uhoh Sep 19 at 14:53
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Travelling wave tubes frequently used as a microwave amplifier for spacecrafts need a high voltage supply. TWTs with about 10 W output power typicaly used 3 kV 30 mA supplies. 3 kV 30 mA is 90 W DC input power, about 11 % efficiency.

enter image description here

Source : http://www.r-type.org/articles/art-030.htm

L3Harris company claims to have built 3,203 TWTs in orbit, operating for over 155 million hours or 17,694 years. 5.5 years mean optime for each of the 3,203 TWTs.

This datasheet about power conditioners for TWTs contains 7; 12 and 14 kV supplies with 300 and 550 W power.

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    $\begingroup$ Excellent find, and resources, and statistics too! $\endgroup$ – uhoh Sep 19 at 13:35

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