Jump to content

Advanced satellites


Recommended Posts

16 hours ago, cubinator said:

Yes, these types of satellites provide valuable data for farmers to avoid such things as overuse of water and detect crop disease.

I have recently found new website of this new space company from South Africa. I  was supprised whet got to know that the size of some of these satellites is less than 1 m and the weight is only 45 kg.  But still, they are rather powerful.

Link to post
Share on other sites

I am quite curious what a magnetic field generator station would look like,  to shield Mars from solar wind. 

Some (citation needed)  have pointed out that any martian colony plan would have to deal with a lot of radiation from the sun because the martian magnetosphere isn't very strong.  But since we can make magnetic fields strong enough to compare with planetary fields, we could conceivably build a generator and stick it at Mars' L1. Would it be powered by solar or nuclear power,  I don't know. 

But that'd be a pretty advanced satellite. 

Link to post
Share on other sites
10 hours ago, starcaptain said:

Some (citation needed)  have pointed out that any martian colony plan would have to deal with a lot of radiation from the sun because the martian magnetosphere isn't very strong.  But since we can make magnetic fields strong enough to compare with planetary fields, we could conceivably build a generator and stick it at Mars' L1. Would it be powered by solar or nuclear power,  I don't know. 

We can make magnetic fields many orders of magnitude stronger than Earth's, but it's about range, not strength. A magnet is a dipole, so its field drops as an inverse cube once you're far enough away from magnet for it to be considered point-like. Since any satellite you can put into Space is a point object compared to planetary surface, no field we can possibly generate is going to overcome that inverse cube. Sure, you can have tens of Tesla inside the satellite itself, but a few kilometers away that magnetic field will be all but undetectable.

So the only way to shield a planet from radiation using a magnetic field is to have a source of magnetic field that's planet-sized. Does that mean we can simply run a few loops of wire around Mars and pump current through it? Actually? Yes. But it's that kind of megastructure you should be thinking of, not a satellite. And there are problems with the approach, of course. Heat generation would be off the charts from any resistive magnet - and so would your electricity bill. So you  have to go superconducting. But if you can build a superconducting ring around all of Mars, run a normal conductor rail next to it, pump about a thousand amps of current along that rail, which is harder than it sounds because of inductance, and then drop the superconducting ring bellow critical temperature and kill the current in the rail, you can make a planet-sized magnet. The energy required to energize a magnet of that size, ignoring corrections for dielectric constants, is about 1017J. That's about 3 years worth of operation from a single nuclear power plant. Given the scale of construction and that superconductor will need cooling, you'll probably want to drop a few dozen nuclear power plants along the equator to power all of that anyways. Single piece of good news, we aren't going for super high mag fields like in particle accelerators, so you can use high temperature superconductors - the sort that only need liquid nitrogen temperatures to operate, and that's way more reasonable if you need to run over 20,000km of superconducting wire and keep it all cool.

It's a huge project, but technically, all of the tech is there and we can build on such scale down here on Earth. If we absolutely had to have a magnetic field on Mars by any means necessary, we can technically start work on it right now. The hardest part is setting up industry on Mars necessary to produce building materials locally, as lifting them up from Earth isn't going to be feasible. But critical components, like reactor cores and turbine components, can be lifted from Earth, and metals you need in quantity are readily available on Mars.

Link to post
Share on other sites
20 hours ago, K^2 said:

If we absolutely had to have a magnetic field on Mars by any means necessary, we can technically start work on it right now.

*Fires up Universe Sandbox*

But seriously, the only way out would be to utilize the planet itself... This is why there were plans to somehow redirect enough asteroids to bombard Mars and make it geologically active again. Sadly it won't be done before our oceans boil I suppose so it'd be kinda futile if you already have rotating space habitat.

 

Also, idk why we went in this direction...

But to answer OP (@bearnard1244)'s question : Yes, and in fact there are two kinds of "yes" here. There are cubesat (3U) sized optical sats that can reach 3 m resolution for Earth surface - but sadly not look beneath clouds or things in the night, then there's SAR (about one to two magnitude more massive though - in the hundreds to 1000 kg mass) satellites that can reach 1m resolution, and can be used to do all sorts of clever tricks like penetrate the cloud and look at stuff at night (a given) or a thin solid surface (the video I linked here mentions one use for estimating the amount of fuel in fuel farms ! Or you can tell whether your crops is doing well or not, yeah).

Edited by YNM
Link to post
Share on other sites
On 1/3/2021 at 5:13 AM, starcaptain said:

I am quite curious what a magnetic field generator station would look like,  to shield Mars from solar wind. 

Some (citation needed)  have pointed out that any martian colony plan would have to deal with a lot of radiation from the sun because the martian magnetosphere isn't very strong.  But since we can make magnetic fields strong enough to compare with planetary fields, we could conceivably build a generator and stick it at Mars' L1. Would it be powered by solar or nuclear power,  I don't know. 

But that'd be a pretty advanced satellite. 

It would be really very advanced satellite, but I assume we are so far from it. To create such kind of satellite is not a piece of cake and we have to do a lot of steps towards it.

Link to post
Share on other sites
19 hours ago, K^2 said:

If we absolutely had to have a magnetic field on Mars by any means necessary, we can technically start work on it right now.

 

14 hours ago, YNM said:

But seriously, the only way out would be to utilize the planet itself... This is why there were plans to somehow redirect enough asteroids to bombard Mars and make it geologically active again. Sadly it'd be done before our oceans boil I suppose so it'd be kinda futile if you already have rotating space habitat.

It would probably be possible with a large magnetic field generator at Mars L1 - in fact, there was a NASA study to this effect a few years ago.

I'm not sure how much energy would be required for something like that, you might need fusion.

Link to post
Share on other sites
1 hour ago, RealKerbal3x said:

It would probably be possible with a large magnetic field generator at Mars L1 - in fact, there was a NASA study to this effect a few years ago.

I found this depiction of the Earth's magnetosphere from a website of University of Sydney :

magnetotail2.png

magnetotail.png

(unit is in Earth's Radius - about 6,400 km, so 100 RE is 640,000 km away, just about 1.5 times the distance to the Moon)

Honestly my problem is with the fact that we'd have to hide in the magnetotail rather than the main area around the generator (as it would be with an internal magnetic field). The description in the website mentions "magnetic substorms" so I'm not convinced that it'd be any safer than without any magnetic field. There's a "neutral sheet", but it is very thin, and as such very much subject to variables I suppose (suppose it's the reason the Moon doesn't count as being protected by Earth's magnetosphere even if it's within the magnetopause, say when on full moon phase). Sun-Mars L1 is about 1,100,000 km in front of Mars itself, if you want to hide inside the plasmasphere - the main protected area, like an internal magnetic field - we'd need a massive magnetic field, probably something larger than what Jupiter makes (even Io - 420,000 km away from the center of the magnetic field - is already in the Jupiter's radiation belt).

Also, while we have made stronger magnetic field (in some cases they're in common use), spatially they're not on the size of planetary magnetic fields yet.

Edited by YNM
Link to post
Share on other sites

What's wrong with proposing just a bloody large satelite?

No one seems intimidated by scribbling about Stanford Toruses or Dyson Spheres. Seeing as we're talking about manufacturing basically a Large Hadron Collider with the Diameter of Mars, what's wrong with proposing basically the same magnetic field generator thing as ever, it's just 10km tall and 1km in diameter, or something like that? And even in that, the field it makes isn't stupendously strong but it has more mass generating it?

Link to post
Share on other sites
32 minutes ago, starcaptain said:

What's wrong with proposing just a bloody large satelite?

No one seems intimidated by scribbling about Stanford Toruses or Dyson Spheres. 

Magnetizing a planet is something we can do now. With our current resources and our current technology.

For a satellite of the size you're proposing, we don't have technology for manufacturing materials you'd need in quantities you'd need down here on Earth. Let alone figuring out how to manufacture them in space, because you aren't lifting these quantities of material from Earth.

We can talk about Dyson Spheres, but that might as well be science fiction, because we don't have the tech necessary to even imagine how to build it practically. Is it worth discussing? Sure, but with caveat that by that point, our tech is going to be very different from anything we're imagining, so you might as well be planning a trip to the moon via canon.

A magnet wound around Mars is something we can design and possibly start building this century if there was a big enough economic and cultural drive to do so. That's why these two are very, very different discussions.

Link to post
Share on other sites
17 hours ago, starcaptain said:

Seeing as we're talking about manufacturing basically a Large Hadron Collider with the Diameter of Mars, what's wrong with proposing basically the same magnetic field generator thing as ever, it's just 10km tall and 1km in diameter, or something like that?

You'd always have to generate a larger magnetic field for the same amount of protection where the generator is off-center than when it's directly on the same spot with what you're protecting. The requirement goes from having a plasmasphere (what the surface of the Earth and most of LEO, as well as MEO up to GSO is in wrt Earth's magnetosphere) that extends up to a few tens of thousands of kilometres to something two or three times the magnetic field of Jupiter (that is to say a million kilometres in size). It'd be a waste of effort.

As for why the magnetotail (the shadow behind planetary-sized magnetic fields) is not a good place to hide in, I suggest to read up this site by the University of Sydney as for how planetary magnetic field structures are like. There are probably other sources as well where you can find more detail about the parts.

Edited by YNM
Link to post
Share on other sites
On 12/30/2020 at 6:18 PM, cubinator said:

Yes, these types of satellites provide valuable data for farmers to avoid such things as overuse of water and detect crop disease.

If I discuss with farmers, they hate those satellites. They do not give farmers anything but authorities use the data against them, because they see easily what grows, where and how much. I live in Finland, where all farming depend on subsidiaries from EU and the state, but I think situation is quite similar in other EU countries. Maybe large farming companies can buy the data and use it for their benefit it but farmers with small family business know better local conditions in their small area and buying the useful data from satellite companies is too expensive.

Link to post
Share on other sites
On 1/5/2021 at 4:13 AM, starcaptain said:

What's wrong with proposing just a bloody large satelite?

No one seems intimidated by scribbling about Stanford Toruses or Dyson Spheres. Seeing as we're talking about manufacturing basically a Large Hadron Collider with the Diameter of Mars, what's wrong with proposing basically the same magnetic field generator thing as ever, it's just 10km tall and 1km in diameter, or something like that? And even in that, the field it makes isn't stupendously strong but it has more mass generating it?

Your underestimate needed magnetic field by huge factor.

We can calculate what we could do if Earth's magnetic field disappeared. Essential parameter is not field strength at the surface of the planet but magnetic dipole moment. Earth's magnetic dipole moment p = 7.95E22 A/m^2. Let's assume that we make huge coil on equator to create respective artificial field. Magnetic moment of planar coil is p = N*I*A, where N is number of turns, I is current and A is area of the coil. N*I is

N*I = p / A = 7.95E22 A/m^2 / (pi * (6.37E6 m)^2) = 6.24E8 A.

Critical current density of common superconductor, NbTi, is about 10 kA/mm^2 at low field and temperature of liquid He. At larger current density superconductivity disappears. At 10 kA/mm^2 cross secion or 6.24 m^2 is needed around the Earth. Or about 2.5E8 m^3 or 1.58E12 kg of very rare and expensive material. In addition to that we would need liquid helium cooling system. It is clearly technomagic.

Then other option. Traditional copper wire. If we use hollow tubular conductor with cooling water inside we can use maybe 50 A/mm^2 (this is guess based on practical limit of 6 A/mm^2 commonly used for normal cables in houses). We would need 1248 m^2 of conductor or 4.4E11 metric tons of copper. Annual production of copper is unfortunately only about 1.7E7 metric tons. No good.

Power consumption may also be a problem. Electrical conductivity of 40000 km long copper cable is G = (58E6 S/m * 1248 m^2 / 40E6 m) = 1800 S. Dissipated power is P = I^2/G = 2.2E14 W. No good either.

It is clear that such numbers are totally insane. Mars is smaller and need less resources but not several order of magnitudes. Artificial magnetic field to protect planet is as credible as Dyson sphere or particle accelerator around the planet. May be good idea for scifi story but not in severe scientific of technical discussion.

Most numbers are from first sources Google gave and I did not have time to check calculations. I also do not have any intuitive idea are results on correct order of magnitude. If they seem to be wrong feel free to check and give a criticism.

 

Link to post
Share on other sites
3 hours ago, Hannu2 said:

We can calculate what we could do if Earth's magnetic field disappeared. Essential parameter is not field strength at the surface of the planet but magnetic dipole moment. Earth's magnetic dipole moment p = 7.95E22 A/m^2. Let's assume that we make huge coil on equator to create respective artificial field. Magnetic moment of planar coil is p = N*I*A, where N is number of turns, I is current and A is area of the coil. N*I is

N*I = p / A = 7.95E22 A/m^2 / (pi * (6.37E6 m)^2) = 6.24E8 A.

First of all, Mars being smaller would give you the same field at lower magnetic moment. p = BV/μ0, so if your goal is to maintain the same B at the surface, the current in the coil scales with radius, and so is going to be a little over half this value.

Second, like Earth, Mars has a metallic core, so relative permeability is going to be very different from 1, which gives you better magnetization at the same current in the coil. For pure iron core, it'd be around 5,000. For an iron-nickel core that's about half of the diameter of the planet it's going to be in high hundreds. All in all, between the two factors, we can easily knock three orders of magnitude off that current.

Next, the reason particle accelerators etc have to use LHe cooled magnets is primarily due to the critical field, not critical current. If you aren't trying to create fields several Tesla strong, you don't need these. We have HTSCs that provide roughly the same critical current density, on the order of 104A/mm2, at 77K. They tend to be made of cheaper materials and are much easier to manufacture in bulk. There are HTSC compositions that are viable for bulk production on Mars.

So we are looking at a wire about half a meter across, at smaller equatorial circumference, bringing us closer to 109kg of material, and kept at 77K on a planet with very thin atmosphere, making vacuum insulation very cheap, and with lower mean temperature. I mean, it's still a megastructure, but it's not a soft science-fiction megastructure. There are over 200,000km of railway in United States alone at an average of about 100kg/m. (50kg/m each rail) That's 2x1010 kg of steel just in this country. Sure, there is significant industry behind that, but this is just the railways. And they've been built over time. First railway spanning coast to coast was in the age of steam locomotives. We absolutely can build at the required scale. Doing it off world, practically in vacuum, in a trench beneath toxic soil? That's a new kind of challenge, certainly. But the key questions are whether we can bring enough power to Mars, and whether we can fabricate construction materials locally. And with nuclear power, zero regard for Martian environment, and single-minded dedication of all our Earthly resources and man power, I'm convinced we can.

I'm not saying it's a rational use of our resources right now, but this isn't, as you so wonderfully put it, technomagic.

And either way, still way more doable than a satellite.

Link to post
Share on other sites
6 minutes ago, K^2 said:

First of all, Mars being smaller would give you the same field at lower magnetic moment. p = BV/μ0, so if your goal is to maintain the same B at the surface, the current in the coil scales with radius, and so is going to be a little over half this value.

It is not enough to keep B at surface constant. Magnetic field must be large enough that it can capture fast charged particles and steer them away from base. I do not know what is practical value in magnetic moment but in any case it is huge. All my numbers was several orders of magnitude larger than current production capability on Earth. And I do not believe that all other industries will be shut down to reserve all resources for mars base in next couple of thousands of years. Such a project would encounter very soon very hard resistance.

 

6 minutes ago, K^2 said:

Second, like Earth, Mars has a metallic core, so relative permeability is going to be very different from 1, which gives you better magnetization at the same current in the coil. For pure iron core, it'd be around 5,000. For an iron-nickel core that's about half of the diameter of the planet it's going to be in high hundreds. All in all, between the two factors, we can easily knock three orders of magnitude off that current.

Only some special materials have relative permeability significantly higher than vacuum. If there is iron core its temperature is well above Curie point in which ferromagnetism disappears (about 770 C). But it is not important at all. Magnetic flux density in material depends on permeability but magnetic moment of planar coil does not depend. Magnetic field must spread in any case to empty space where particles are.

Possible liquid electrically conducting layers would interact with field but I can not say how. They are very complicated interactions. But if there were such a layer on Mars it would probably have a magnetic field.

Please notice that Earth's does not have magnetic field because its iron core is permanent magnet because ferromagnetic effects but field arises in complex magnetohydrodynamic flows in in electrically conductive liquid core. Sun's dynamo works with hydrogen/helium plasma and giant planets' dynamos work with metallic hydrogen or partly ionized water and ammonia layers.

 

6 minutes ago, K^2 said:

Next, the reason particle accelerators etc have to use LHe cooled magnets is primarily due to the critical field, not critical current. If you aren't trying to create fields several Tesla strong, you don't need these. We have HTSCs that provide roughly the same critical current density, on the order of 104A/mm2, at 77K. They tend to be made of cheaper materials and are much easier to manufacture in bulk. There are HTSC compositions that are viable for bulk production on Mars.

I am not familiar with high temperature superconductors but what I found with fast browsing was quite exotic materials and technical limitations. Not anything which would not need countless "black swan" events (unexpected improbable development innovations) and decades of development to be even economical solution for energy transfer on Earth.

 

6 minutes ago, K^2 said:

and single-minded dedication of all our Earthly resources and man power, I'm convinced we can.

This kind of psychological and political magic is as unrealistic than technomagic. I do not count such thing "possible", which would take all humankind's resources during hundreds or thousands of years.

 

 

Link to post
Share on other sites
4 hours ago, Hannu2 said:

Essential parameter is not field strength at the surface of the planet but magnetic dipole moment.

Actually, I do wonder about these, but are there simulations or references that could paint off a picture of how large would the magnetosphere be for a certain strength of magnet ?

I also wonder if the further distance from the Sun would help in some way... I mean CME ejectas would get more dispersed ?

32 minutes ago, K^2 said:

kept at 77K on a planet with very thin atmosphere, making vacuum insulation very cheap, and with lower mean temperature.

I mean, ideally after making a magnetic field around Mars you'd put on Earth-like atmosphere around it... Otherwise it's not so much useful to protect the vacuum of space with magnetic fields.

6 minutes ago, Hannu2 said:

It is not enough to keep B at surface constant. Magnetic field must be large enough that it can capture fast charged particles and steer them away from base. I do not know what is practical value in magnetic moment but in any case it is huge.

[...]

Please notice that Earth's does not have magnetic field because its iron core is permanent magnet because ferromagnetic effects but field arises in complex magnetohydrodynamic flows in in electrically conductive liquid core. Sun's dynamo works with hydrogen/helium plasma and giant planets' dynamos work with metallic hydrogen or partly ionized water and ammonia layers.

Actually, wouldn't an external magnetic field influence induces more magnetism, if there's still a liquid core ? Kind of like the molten-sodium magnetic planetary core models we have right now...

Link to post
Share on other sites
7 minutes ago, YNM said:

Actually, wouldn't an external magnetic field influence induces more magnetism, if there's still a liquid core ? Kind of like the molten-sodium magnetic planetary core models we have right now...

Probably yes. As far as I know planetary dynamos (sources of magnetic fields) are not very well understood. But it is believed that weak cosmic magnetic fields act as seed fields which start magnetic processes in rotating electrically connected liquids. When process is started field amplifies itself and increases many orders of magnitude and rotation of body gives energy. But it is complicated, field may be asymmetric, it changes during time, even change polarity etc.

But it there probably is not such layer on Mars because otherwise it would generate magnetic field. Mars has cooled and most of its small metal core (Mars has much smaller iron core than Earth, even relatively on planet's size) is solidified.

Link to post
Share on other sites
13 minutes ago, Hannu2 said:

But it there probably is not such layer on Mars because otherwise it would generate magnetic field. Mars has cooled and most of its small metal core (Mars has much smaller iron core than Earth, even relatively on planet's size) is solidified.

idk, NASA says that there's some degree of molten core still left (articles here, here and here, and one paper about magnetic field variability and strength which sadly I can't access [article off the paper here] - haven't tried the preprints though), so maybe there're some amount of hope.

Though I'd still champion that, if we really want to do it, we have got to warm up the planet first by bombarding it with asteroids. Sadly it'd take longer than for the Sun (or ourselves) to boil the sea and atmosphere here off first...

Edited by YNM
Link to post
Share on other sites
6 hours ago, Hannu2 said:

It is not enough to keep B at surface constant.

It would be, if we had no other sources of current. ∇.B = 0, and ∇xB is proportional to current density. Fixing magnetic field at any 3D surface fixes it for the entire space if we don't have other significant sources of current. But yes. Strictly speaking, we aren't talking about the same surface. Mars is smaller, and at any rate, the configuration of the field is going to be different. However, for space weather, if we get the same B field at poles, we should be in a good place. Yes, it's a ballpark estimate. If you need something more precise, you'll have to do simulations of the entire magnetosphere, including solar wind currents, as magnetic fields generated by these greatly contribute to the overall dynamics of the magnetosphere. So strength of the field at the poles is your best proxy.

6 hours ago, Hannu2 said:

Curie point in which ferromagnetism disappears (about 770 C).

That is a very good point and completely slipped my mind. Yes, you are right. We are basically dealing with μ0 everywhere.

So with that in mind, I tried replacing a single loop with a Helmholtz coil arrangement, and that brings down current to 3x108A per loop to match Earth's B at poles. Even with reduced circumference of each coil compared to equatorial, the net savings on are about 20% over single loop. Without a ferromagnetic core, I don't have any ideas of how to bring it lower.

Yeah, I concede the point. My estimates were a few orders of magnitude off, so that's enough to push it definitively into science fiction territory.

 

Strictly as an academic note at this point:

7 hours ago, Hannu2 said:

I am not familiar with high temperature superconductors but what I found with fast browsing was quite exotic materials and technical limitations. Not anything which would not need countless "black swan" events (unexpected improbable development innovations) and decades of development to be even economical solution for energy transfer on Earth.

HTSCs aren't any more exotic than high field SCs you have been quoting. Don't confuse them with room temperature SCs, which is what we need for power transfer on Earth. The only significant limitation of good HTSCs we have right now are that they still require roughly LN2 temperatures, which is why 77K is a common temperature to quote the properties at, and they have comparatively low critical fields. So you can't use HTSCs for medical imaging and particle accelerators. Since it's too expensive to cool them for power transfer and they can't produce large magnetic fields, applications of HTSCs are very narrow on Earth. But in environments that are naturally very cold or allow for easy insulation, HTSCs can be quite practical. I suspect we'll see a lot more use out of them as we expand our outer Sol exploration.

Link to post
Share on other sites
This thread is quite old. Please consider starting a new thread rather than reviving this one.

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...