How spacecrafts discharge static electric charge

[Sami1999]

I was wondering how spacecraft s discharge when encountering van allen belts (for example the juno spacecraft around jupiter) since obviously there is no earthing and is it possible to remove excess charge to power something on the craft?

 

[sophiecentaur]

A spacecraft that flies through a cloud of charged particles will collect some charge. The total charge possible will depend on the Potential the craft acquires. Eventually it will start to repel similar charges and reach equilibrium.
Remember that mutual repulsion will limit the density of charged particles that can accumulate in anyone region.
The only time that the charge on a craft is cause for concern would be when it comes into contact with another but it would involve connecting what is effectively two Faraday Cages and a brief pulse of equalising current could flow.
On re- entry, any charge would soon be dissipated.

 

[Sami1999]

I was referring to charges accumulated due to high speed protons and electrons not clouds of particles, what i am trying to say is normal circuits are earthed to prevent charge from accumulating and thus preventing damage to the electronics. Even if the craft is charged it won't be enough to repel high energy particles(hope the explanation differs)

 

[anorlunda]

i am trying to say is normal circuits are earthed to prevent charge from accumulating and thus preventing damage to the electronics.

They are earthed is to prevent damage during sudden discharge. Think of the spark and zap sound you sometimes hear when you touch things in winter months.

When circuits are sitting there charged, there is no damage. Similarly, a spacecraft can carry a net charge, but that is not harmful unless it contacts something with a different charge.

But there is another problem in space. High energy cosmic rays (high energy particles, charged or neutral) can damage electronics. Therefore, the components need radiation hardening. I'm not sure how that is done. Perhaps others can help.

Here on Earth, most but not all cosmic radiation is filtered out by the atmosphere, and the magnetospere.

 

[CWatters]

Not my field but Google found...

https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2015SW001345

Spacecraft surface charging within geosynchronous orbit observed by the Van Allen Probes

Suggests some instruments can have problems.

 

[sophiecentaur]

Not my field but Google found...

https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2015SW001345

Spacecraft surface charging within geosynchronous orbit observed by the Van Allen Probes

Suggests some instruments can have problems.

That link made good reading. It's interesting that charging can affect some experimental measurements. It seems not to be a matter of safety (only up to tens of Volts involved mostly)I imagine there would be methods to dissipate the charge - such as a heated cathode to get rid of surplus electrons. Not sure about how to deal with positive ions as easily.

 

[MRBlizzard]

When there is a solar flare, 50 Mev electrons can penetrate the spacecraft skin and collect as a charge on spots in the spacecraft interior. Fast discharges can occur which burn out electronics. While the Earth's magnetic field shields most of the low orbit spacecraft , at the magnetic poles and the South Atlantic Anomaly, the magnetic field can dump electrons that the spacecraft fly through.

 

[yungman]

A spacecraft that flies through a cloud of charged particles will collect some charge. The total charge possible will depend on the Potential the craft acquires. Eventually it will start to repel similar charges and reach equilibrium.
Remember that mutual repulsion will limit the density of charged particles that can accumulate in anyone region.
The only time that the charge on a craft is cause for concern would be when it comes into contact with another but it would involve connecting what is effectively two Faraday Cages and a brief pulse of equalising current could flow.
On re- entry, any charge would soon be dissipated.

That's my question, how is the charge be dissipated? Ha ha, maybe they do this in Florida where it's humid. But what if the craft landing in a dry desert?

I should put this in perspective, I worked in designing various mass spectrometers where things are in high vacuum and with a lot of high voltage circuits. Charging of objects is a very very troubling issue. Things can be charged up to extremely high voltage very easy and when it touch the Earth ground, it can really spark depends on the amount charge. If moisture of air is the only path of discharge, it's not going to cut it. We can charge up pieces of metal on pcb to really high voltage ( where arc or corona appeared just in air). Special design precaution has to be observed where there is absolutely no floating trace or copper patch on the circuit in all the high voltage circuits even out in the air. They arc and they arc. We had fun with them.

Can rubber tires of the spacecraft able to hold the isolation? So people can discharge the spacecraft slowly after it landed?

 

[Sami1999]

That is what i was wondering about, can the charge be used to power an ion engine for example or maybe the whole spacecraft ?

 

[Sami1999]

That's my question, how is the charge be dissipated? Ha ha, maybe they do this in Florida where it's humid. But what if the craft landing in a dry desert?

I think it would be due to the plasma that forms around the ship.

 

[yungman]

That is what i was wondering about, can the charge (I know it would be somewhat minuscule) be used to power an ion engine for example or maybe the whole spacecraft .

I am not specialize in charge body, I don't think the charge of a spacecraft is minuscule. We used to find loose pieces of copper or solder spat on the pcb with arc test, we arc at about 10KV on the high voltage terminal, we turn off the light and look for arc in the unexpected place, you can find the floating piece this way. I joked and called this the sympathetic arc, where a floating piece of conductor got charge up without touching HV in air and if you give it enough dV/dt, it will jump! We had fun playing with that. A big body like a spacecraft , it can hold an enormous amount of charge. Think of charging up a capacitor. I design hifi amp, I have about 60,000uF cap on the rail, I accidentally shorted with a screw driver and it was a big arc and part of the screw driver tips and the place I short it disappeared! that's only 31V! Try the body charged to beyond 30KV, a big body with lots of surface area.

 

[Sami1999]

You already know that coronal discharge occurs when the gas is ionised at a point of concentrated electric field lines. But when a capsule for example re-enters, due to friction with the atmoshpere it get to thousands of degrees and forms plasma around it which shares the accumulated charge of the capsule with. And in the meantime the plasma keeps forming and keeps scrubbing off(since the craft is in contact with air continously) , so the capsule loses its charge to the atmosphere.

 

[Sami1999]

So in theory can two plates bombarded around the clock accumulate enough charge that if they where connected through a piece of wire supply an almost constant current.

I am not specialize in charge body, I don't think the charge of a spacecraft is minuscule. We used to find loose pieces of copper or solder spat on the pcb with arc test, we arc at about 10KV on the high voltage terminal, we turn off the light and look for arc in the unexpected place, you can find the floating piece this way. I joked and called this the sympathetic arc, where a floating piece of conductor got charge up without touching HV in air and if you give it enough dV/dt, it will jump! We had fun playing with that. A big body like a spacecraft , it can hold an enormous amount of charge. Think of charging up a capacitor. I design hifi amp, I have about 60,000uF cap on the rail, I accidentally shorted with a screw driver and it was a big arc and part of the screw driver tips and the place I short it disappeared! that's only 31V! Try the body charged to beyond 30KV, a big body with lots of surface area.

 

[yungman]

That I have no idea anymore.

 

[darth boozer]

Always ask the people with experience.

https://www.nasa.gov/offices/nesc/a...he-potential-dangers-of- spacecraft -charging

 

[sophiecentaur]

I don't think the charge of a spacecraft is minuscule.

A 2m spherical satellite will have a capacitance of a few hundred pF. The typical values of Potential of a charged object in space seem to be up to hundreds of volts . That doesn't represent much charge (say a μC). Even with the suggested few kV that's found in a few instances (?), the charge will only be say about a mC.
I could understand that a potential of a few kV could greatly affect equipment that's actually measuring charged particles up there. That is a very relevant effect, of course, but is can hardly be a safety issue (any worse than every for every plane that lands in very dry air) and I wonder what mechanism could damage on board equipment.

 

[yungman]

A 2m spherical satellite will have a capacitance of a few hundred pF. The typical values of Potential of a charged object in space seem to be up to hundreds of volts . That doesn't represent much charge (say a μC). Even with the suggested few kV that's found in a few instances (?), the charge will only be say about a mC.
I could understand that a potential of a few kV could greatly affect equipment that's actually measuring charged particles up there. That is a very relevant effect, of course, but is can hardly be a safety issue (any worse than every for every plane that lands in very dry air) and I wonder what mechanism could damage on board equipment.

I have seen body in free space or air charge up to beyond 10KV, What I was talking about the corona and sympathetic arc don't happen until it's beyond 8 or 9KV. I have no idea how high the potential can go, from my limited understanding, unless you have a path to discharge, it will keep charging higher and higher until it's high enough to arc over. Also, a charge body might not be the same as a capacitor except it holds charge. Don't think it's a few thousand pF, it can produce quite an arc. Remember Q=CV, V extremely high even small C can charge up.

I don't know how charge body and how much charge can it hold ( how high the voltage can go) and how high voltage can be charge up. By looking at static discharge in winter with cloths, it's way above 1KV for sure.

As I said, I am just talking, more like join in the conversation, not that I have the knowledge. More like guessing.

 

[sophiecentaur]

, it will keep charging higher and higher until it's high enough to arc over.

Arc over to where? I am trying to imagine an actual Potential Difference between two objects, rather than the absolute Potential that's being discussed. Am I missing something obvious? The only sort of discharge I could imagine would be corona on sharp points. That would imply the need for the same sort of devices you get on church spires and you can bet they would be there if they were needed / useful.
Maybe there could be high PDs within the craft, between isolated parts but, again, couldn't this be detected and discharged actively or passively (spark gaps)?

 

[yungman]

I think I better stop, I don't know space craft.

 

[Sami1999]

Maybe there could be high PDs within the craft, between isolated parts but, again, couldn't this be detected and discharged actively or passively (spark gaps)?

How would a charged spacecraft discharge in vacuum?
(obviously coronal discharge can happen in vacuum)
But it has nothing to discharge onto.

 

[sophiecentaur]

How would a charged spacecraft discharge in vacuum?
(obviously coronal discharge can happen in vacuum)
But it has nothing to discharge onto.

A charged body has a repulsive field around it which can repel the excess charges, once they are free of the local attraction of the metal surface. You could use the thermionic effect to produce an electron 'gas' around the craft and that could cause a discharging current. Alternatively, if the charge is net positive, an ion generator could do the same job, I reckon.

 

[trurle]

How would a charged spacecraft discharge in vacuum?
(obviously coronal discharge can happen in vacuum)
But it has nothing to discharge onto.

1) Usually spacecraft do not discharge into vacuum. It is quite routine to have moderate voltages between parts of spacecraft to accumulate though (200V is typical on ISS), sometimes producing arcing along surface of extended appendages, especially solar panels. It looks frightening during test, but damage is small because the currents are also very small (nano-amperes range).
2) If the charging/arcing is undesirable, for example for spacecraft s with plasma sensors, the specialized device (so called plasma contactor) is deployed. It is usually a length of non-insulated wire with stabilization head at end. All arcing is concentrated on the tip of stabilization head. Another charge-control device is neutralizer (electron gun) used on spacecraft with ion engines.

 

[sophiecentaur]

moderate voltages between parts of spacecraft to accumulate

It clearly can't be bothering anyone or they'd do something about it. I can't think how it occurs if everything is bonded electrically. Perhaps there are plastic parts involved??

 

[trurle]

It clearly can't be bothering anyone or they'd do something about it. I can't think how it occurs if everything is bonded electrically. Perhaps there are plastic parts involved??

Most common location for space corona discharge is across cover glass of solar panels.