Space grounds. - Page 1
Forum section: electronics / general

author: paulca
author_rank: Super Contributor
timestamp: August 11, 2019, 09:01:23 am
content: What if you are on a space ship, the ultimate floating ground and you wanted to measure your 'ground' against, say Earth. What would that voltage be? If you flew from Earth to Mars, how would you know your relative charge to the planet you approach. What is the potential between, say Earth and Mars? Does the solar system 'effect' a common reference of any kind.... does it all depend on magnetic fields? Is there an 'absolute charge'?

author: 001
author_rank: Super Contributor
timestamp: August 11, 2019, 09:56:55 am
content: Quote from: paulca on August 11, 2019, 09:01:23 amNo.

author: Electro Detective
author_rank: Super Contributor
timestamp: August 11, 2019, 11:04:06 am
content: Is a potential difference charge possible in a huge vacuum like space?At best you may drum up some annoying capacitance...?How do we know if Earth is positively or neg charged and what the other bodies are ?No wonder big money pulled out of exploration, too many variables, unanswered questions,and universe creation theories bordering on awesome BS,but great for movie scripts

author: Zero999
author_rank: Super Contributor
timestamp: August 11, 2019, 11:18:50 am
content: On a spacecraft, electrical earth or ground would simply be defined as the craft's metalwork, which should be bonded together to ensure it doesn't float at different voltages.

author: Domagoj T
author_rank: Frequent Contributor
timestamp: August 11, 2019, 11:24:01 am
content: Quote from: Electro Detective on August 11, 2019, 11:04:06 amThe Spark - a sequel to The Core and The Sunshine?A sudden solar flare hits Earth and start the ever increasing buildup of static charge. It starts with affecting mobile phones (our protagonist can reach his wife to tell the he can't pick up their child from kindergarten), then cars start to fail. TV and radio goes down and total panic ensues.Our protagonist just happens to be the lead scientist researching piezzoelectric lighters and is selected by the people in black helicopters to embark on a mission to Jupiter. Their task? Lay down a state of the art audiophile monodirectional Cat7 cable that will drain the Earth's static and save the planet.Coming to a theater near you!

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 11, 2019, 02:07:09 pm
content: Quote from: 001 on August 11, 2019, 09:56:55 amYes. Charge is the difference in the total protons and electrons in an object.There is not an absolutevoltage, however.Space is slightly conductive, due to the thin interplanetary plasma. This presumably keeps planetary bodies within, say, a billion volts or so of each other.The maximum potential (relative to infinity, i.e., the average surroundings) that can be achieved is equal to the energy of the stimulus. For example, solar x-rays can excite and kick out electrons bound to the Earth, but even if a 10keV photon gives all of its energy to an electron, it can still only leave a potential well of exactly 10kV. Corona, flares and galactic radiation have an energy spectrum dropping off in the, something like MeV range, falling in a tail through the GeV range; any higher events are so rare that the solar wind's conductive plasma overwhelms them. Hence the maximum potential of Earth relative to the Sun must be in the same voltage range.Tim

author: SiliconWizard
author_rank: Super Contributor
timestamp: August 11, 2019, 02:48:32 pm
content: Quote from: Zero999 on August 11, 2019, 11:18:50 amOf course. Now maybe one of the OP's underlying questions could be, what happens when the spacecraft gets close enough to some space body. Could there be sparks between the two?

author: paulca
author_rank: Super Contributor
timestamp: August 11, 2019, 02:48:48 pm
content: I figured NASA must have figures for Moon and Mars and that there isn't a significant charge potential between the craft and it's target body or there would be discharge shortly before landing. Then again, maybe there is, just we never seen it.I think the bits hanging off the lunar lander were the contact detection strips, but they also look like those stupid grounding strips on cars in the 1980s.

author: SiliconWizard
author_rank: Super Contributor
timestamp: August 11, 2019, 03:15:09 pm
content: Just a thought, but if it's in a complete vacuum, there would be no spark at all. I guess the potential difference would just result in a large electric field, but no current would flow until the two come into contact? The Moon has no atmosphere. But on Mars, that should be a little different.AFAIK, there is intense lightning between Jupiter and Io, so we have an example of sparking happening between two space bodies.

author: tggzzz
author_rank: Super Contributor
timestamp: August 11, 2019, 03:22:35 pm
content: Quote from: paulca on August 11, 2019, 09:01:23 amYouareon such a space ship. It is rather large, ~12.7Mm in diameter.Since both the moon and the earth are conducting spheres, they have a mutual capacitance that can calculated; you can search for the standard formula. I don't think anybody has empirically validated that specific calculation, though.QuoteThat would depend on the mutual capacitance and the differential charges. The solar wind can move charges, so the potential difference is not well defined.As a thought experiments, consider the problem on a smaller scale: an aircraft and the earth. Charges can be changed via friction occurring while moving through the atmosphere.More generally, "ground" is a pretty fluid concept which has a little validity under some circumstances, and is very unhelpful under others.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 11, 2019, 03:43:02 pm
content: Planetary vacuum is good enough to do stuff like electron physics in (if not with great reliability; vacuum tubes have a much harder vacuum for this reason), so there wouldn't be much ionization, that's correct. You would have the attractive (or repulsive) force between objects, and then field emission when very close, which causes sputtering and hence a spark using the material of the objects themselves. Also bremsstrahlung (x-rays), but not really much total since we're not talking a whole lot of charge.I would expect satellites to have generally similar voltages, due to the similar materials and same physical processes.Tim

author: SiliconWizard
author_rank: Super Contributor
timestamp: August 11, 2019, 04:30:00 pm
content: Just thought about something. The ISS revolves around the Earth pretty fast. In a magnetic field. Doesn't that induce significant EMF in the ISS structures?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 11, 2019, 04:44:39 pm
content: Not really, no.If there were a beanstalk fixed to the surface, that would be different, but that's even less practical to an object in low Earth orbit.This relates to the riddle of the co-rotating homopolar generator. If the magnet spins on axis, is there induced voltage? What if the disk and magnet spin together, or just the disk?The correct result is very easy to visualize if you remember that a magnet is an array of spins. Spinning the magnet changes nothing. You might change the distribution of spins (a square magnet has, well, corners; a cylindrical magnet might be nonuniform; etc.), but those are lower order effects, not proportional to the full flux of the magnet.Indeed, spinning the disk doesn't really change anything either, butthe relative rotation between disk and contactmost definitely does.(In a planetary context, a full length (stable orbiting) beanstalk might have a "sliding" connection to the radiation belts (via field emission and impact ionization), which in turn have a path to ground via auroral currents.)Tim

author: Mr. Scram
author_rank: Super Contributor
timestamp: August 11, 2019, 05:30:36 pm
content: Quote from: SiliconWizard on August 11, 2019, 03:15:09 pmThe Io situation is quite interesting. I hadn't heard about the electric fields yet, thanks for sharing.

author: 001
author_rank: Super Contributor
timestamp: August 11, 2019, 05:34:17 pm
content: Quote from: T3sl4co1l on August 11, 2019, 02:07:09 pmAnd we know now what earths is flat

author: SiliconWizard
author_rank: Super Contributor
timestamp: August 11, 2019, 06:10:41 pm
content: Quote from: T3sl4co1l on August 11, 2019, 04:44:39 pmWe basically have a conductor (I'm assuming most of the ISS's structure is conductive, maybe a false assumption) moving in what could be considered a static magnetic field (the ISS rotates around the Earth much faster than the Earth rotates around itself, it's not geosynchronous). The ionosphere would create a return path. (If I'm not mistaken, the ISS is at ~300-400km altitude which is right in the middle of the F layer of the ionosphere...) So, we should get some motional EMF.That made me look that up a little, and it's actually been studied by the NASA. It was even considered for energy generation, but there are a couple of pitfalls. They even did experiments though.First, the geomagnetic field could be considered roughly parallel to the surface of the Earth (except near the poles), so to get any significant amount of EMF, you'd need a conductive part that is ideally perpendicular to the surface of the Earth ("vertical"). The ISS is a mostly "horizontal" structure, although there are large solar panels that are mostly vertical...Second, it would require a very long conductive structure to get anything useful. (The NASA project was I think some satellite with a flexible rod 20km long or something...) Though rotational speed relative to Earth should play a significant role?Another point is that if the structure and conditions allowed significant EMF to be induced, it would in turn slow down the moving structure. So I guess that would be hard to exploit that to generate significant amounts of energy while staying in orbit.My question was not about generating energy though (and I was surprised it had actually been considered). So, I haven't found anything specifically for the ISS, but I'd be pretty sure some EMF is induced. Probably not enough to bother, let alone try to harvest energy from that. I'd still be interested in knowing more about this.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 11, 2019, 06:49:55 pm
content: Basically any EMF generated is due to the rotation of the ISS, which isn't much because it's pointed at the sun all the time; and it would be induced in loops in the superstructure, which aren't all that big (but, being mostly solid metal, would be able to support quite a current, if they aren't intentionally insulated between).An elliptical orbit could draw power from the change in altitude <--> magnetic field intensity. But that's really just taking energy from launch.AFAIK, the tether experiments dealt with spin of the tethered pair, developing significant voltages with the length * RPM, and current through the surrounding plasma, which is not rotating with the tether.Tim

author: Electro Detective
author_rank: Super Contributor
timestamp: August 13, 2019, 11:31:33 am
content: Quote from: 001 on August 11, 2019, 05:34:17 pmIt was for many centuries, but it somehow got pumped up by a monster bellows into a rotating ball, and spun up for the last 600 yearsIt's probably copped a leak by now (golfers shoes?) and deflated again..some people have noticed