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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.

uhoh
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    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? – Uwe Sep 17 '20 at 22:39
  • Might be equally interesting to find the greatest DC field strength, i.e $\frac{V}{m}$ – Carl Witthoft Sep 18 '20 at 12:02
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    @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? https://en.wikipedia.org/wiki/Gate_oxide#:~:text=A%20conductive%20gate%20material%20is,the%20conductance%20of%20the%20channel. – uhoh Sep 18 '20 at 13:33
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    A TWT microwave amplifier with about 10 W ouput typicaly used 3 kV 30 mA supplies. – Uwe Sep 18 '20 at 23:13
  • @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. – uhoh Sep 19 '20 at 00:30
  • "a DC power supply rated at that voltage" is not exactly a way to create voltage, that's kinda circular, like saying "bonus points for going to space without just using a spacecraft". – user253751 Sep 20 '20 at 11:54
  • @user253751 a tether and Van de Graaff generator are two examples of things that might employ DC power supplies but not contain"a DC power supply rated at that voltage" that those devices achieve. There may be other examples as well; what is the more precise wording that you propose? – uhoh Sep 20 '20 at 12:02
  • @uhoh I mean the VdG generator itself is a DC power supply. So is the tether. They supply DC power, no? – user253751 Sep 20 '20 at 12:32
  • @user253751 in that sense anything is a DC power supply, and by extension again, everything is anything. For me I'll stick with conventions, and once again I'll invite; what is the more precise wording that you propose? – uhoh Sep 20 '20 at 12:40
  • @user253751 I've made an edit and added a footnote, how does that look? – uhoh Sep 20 '20 at 12:55

5 Answers5

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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

DrSheldon
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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.

J...
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  • I wouldn't say that a linac is a dc voltage, mind you. The rest are good. – Jon Custer Sep 18 '20 at 16:28
  • @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. – J... Sep 18 '20 at 16:31
  • 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"? – uhoh Sep 19 '20 at 01:13
  • @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. – D Duck Sep 20 '20 at 12:05
  • @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. – Jon Custer Sep 22 '20 at 01:51
  • @JonCuster My "in orbit" capacitor is just another object orbiting with me. The dielectric is space (a vacuum) and I can use my linac to fire high energy electrons at the "plate". It's an expensive capacitor (not COTS) but is do-able. A 25 MeV linac isn't so large that it couldn't be placed into orbit - my available voltage could be 25 MV. The limit would be the breakdown voltage of space - but you could solve that by putting everything in a bag (the co-orbiting "plate" and bag) and filling the bag with pressurised SF6. The limit then would be the size of linac you could launch into orbit. – D Duck Sep 22 '20 at 11:38
  • @DDuck It doesn't work that way. High energy interactions will take place when the beam impacts an object. It won't "stick" as a charge on your capacitor - it will smash and ablate material, produce xrays, secondary electrons, etc. – J... Sep 22 '20 at 11:51
  • @DDuck - many accelerators down here on earth are in "bags" of SF6 - things don't work magically better up in space. All the same physics limitations prevail. Yes, you could charge something (temporarily) to a MV or more, and it would have the power of a static shock. – Jon Custer Sep 22 '20 at 12:07
  • I'm working on the claiming the world record as in the OP's question "Highest DC voltage ever intentionally produced in space?" No mention there about the charge required - just a voltage. – D Duck Sep 22 '20 at 15:34
  • @J... My linac looks like a current source (a few mA) and a compliance of 25 MV. The "plate" could be thick enough so no secondary electrons or photons escape. My plate will charge up, the voltage increases and in the limit putting the last few electrons on it are the voltage potential of the source. The linac gives me a 25 MV source and then my "plate" will be at 25 MV. This all assumes that there is no alternate path for the electrons to return to the body of the linac. – D Duck Sep 22 '20 at 15:43
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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.

uhoh
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JohnHunt
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    The tether actually melted in two due to an electric discharge. Some sources give 4.4 kV. https://ntrs.nasa.gov/api/citations/19970011947/downloads/19970011947.pdf – Organic Marble Sep 18 '20 at 13:22
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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

0xDBFB7
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    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. – uhoh Sep 19 '20 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.

Uwe
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