What "weed need" is a space mission!

[xilman]

Originally Posted by diep

All images are rendered from multiple photos.

There is no other way. The previous photo taken which took quite some time from pluto by hubble, some years before that - it's just some blue pixels.

Taking photos from a large distance is very very complicated.

A kilo heavy probe is just like proposing transporting cargo between UK and China by using floating miniature containers.

You are just plain wrong. To see how wrong you are take your phone outside on a clear moonlit night and point it at the moon at full zoom. Take a picture.

You will end up with a photo of the moon at a distance of 400 thousand km with a camera which has an aperture of a few millimetres and a mass of a gram or so. Further, your camera has not been specifically optimized within those physical parameters to take especially high quality images because a phone camera has to be dirt cheap to be sold by the billion to people who really don't care that much about image quality.

All that bullshit in your other post about crashing into the star is just that: bullshit. It would take extremely precise targeting to hit the star and why would anyone want to do that? Unless a decision is made to impact something the odds are overwhelmingly likely that all the probes will just pass clean through the Proxima system.

By the time the probes get there we should know the location of the planet to within a thousand km or so. In other words, the photo could be taken from much closer than 400,000 km. Motion blur could be an issue but could be mitigated by scanning the camera field of view or by subsequent deconvolution of the blurred image. Even if the former isn't practical from mass and / or energy considerations, the latter has been standard practice for 20 years or more already.

[xilman]

Originally Posted by diep

We already know there are planets - we just want good pictures from them - the rest really is not so interesting.

That may be all you are interested in. I can assure you that there are many others who are nowhere near as blinkered in their desire for knowledge and understanding. Why did you think I posted about magnetic fields, chemical composition, thermal structure, and so forth?

[xilman]

Originally Posted by diep

p.s. graphite is something else than graphene.

I know.

Why do you think I referred to graphene only in the context of the light sail, which needs to have a large area in as small a mass as possible but doesn't need to be rigind, and graphite as a candidate for the probe's structure on which the science instruments are mounted, which needs to be rigid and as small a mass as possible?

Please pay attention to what I'm typing and please read the supplementary material to which I have given you an excellent entry point.

[xilman]

Originally Posted by J F

Indeed, we can't make single-crystal diamonds this size today, but
a while ago I did read something about diamond powder sintering,
giving polycristalline diamonds the size of some cm^3. I wonder
how big this thingies could be made if someone really tried.

But why would diamond be nicer than, for example, Al2O3 or SiC?
They have lower density, thermal and chemical stability is
quite nice, mechanical load on the structures should be low...
Radiation effects?

Single crystals have nice mechanical properties, in particular it's relatively easy to deposit microelectronic and MEMS devices on them. Graphite, being a conductor, would presumably need an insulating layer between the physical structure and the active devices. Monocrystalline diamond has wonderful mechanical, electrical, thermal and radiation hardness properties. Its density is lower than alumina (3.52 vs ~4.0) but 10% larger than SiC (3.2).

The killer is that we don't yet know how to make big enough single crystals of diamond. Sintered polycrystalline diamond (IMO, I don't know for sure) is likely to have too great a surface roughness for standard semiconductor technology to build reliably working devices on top of it. I agree SiC is a fine candidate material and easy to make in large single crystals but please remember that the diamond proposal is (AFAIK) entirely my own idea and I'm quite prepared to be convinced that it is a bad one.

[diep]

Originally Posted by xilman

I know.

Why do you think I referred to graphene only in the context of the light sail, which needs to have a large area in as small a mass as possible but doesn't need to be rigind, and graphite as a candidate for the probe's structure on which the science instruments are mounted, which needs to be rigid and as small a mass as possible?

Please pay attention to what I'm typing and please read the supplementary material to which I have given you an excellent entry point.

There is a fundamental problem of exploration:

a) communication back to the home front
b) a good description of what you saw back to the homefront

A) you keep ignoring in this. 1 meter light sail in diameter is gonna get lost in all the sounds and noises that the stars make. You need something that points to planet earth. Radio communication goes at light speed. You need a huge parabolic radio antenna to communicat to the homefront. The light sail as you pointed out you want light and very huge. Let's make it 500 meters in diameter ok and very light. No big problem.

But then we still need a huge parabolic radio antenna that points back to earth or maybe even to some point far away from the Sun as an 'in between radio station', who will say?

B) to take a good picture, regardless at which frequency you want to take it, you need to catch enough light. So the computer chip you use might be very tiny and light - yet the tube and lenses or mirrors used will be significant in diameter. For such expensive mission you definitely do not want some sort of space version of the apple iphone camera. That's not gonna cut it. You're gonna need a big diameter aperture or lenses.

For a close pass by of a planet you already will need 10 inch - yet at a speed of 0.05c you can't garantuee a close pass by - even if we do figure out somehow more details like which different planets specific stars might have or do not have and even if we might have some clue where at which moment planets are rotating based upon future telescopes (E-Elt etc).

You still are gonna need a far superior camera over other probes to generate enough data for the mission.

I'm no expert there but we're soon looking at 16 inches diameter.
That's gonna weigh something.

That 1 kilo idea is not realistic.

300 is more realistic for the total probe - and that will already require serious design and improvements over anything that was there so far.

[LaurV]

Originally Posted by xilman

Not all probes need to be identical and carry a complete set of instruments. A hundred, say could be optimised for observing magnetic fields, another hundred for optical imaging, another hundred for measuring dust properties, another hundred for measuring the thermal properties of the planetary and stellar atmospheres another hundred for measuring the chemical compostition of the same. Let's see, I'm up to five hundred probes so far. Another five hundred still to be allocated.

We here really like that idea! Warcraft in space! (or is that called starcraft, or spacecraft?) - for who didn't play warcraft, you command an army of little guys, all with different abilities, and you can send them around to gather different types of resources, or to carry on the fights with your neighbors (computer IA or other human players) which also command an army of little guys... etc. Now, every one of the little guys have different abilities and knowledge, and different weaknesses, and the practice (in all games and simulations) showed that the best army (for the same resources spent on upgrades, etc) is that one which is the most non-homogeneous, i.e. you must have a little bit of all types of the little guys in the group, as opposite to an army composed only from the "best" (fastest, most aggressive, most intelligent, most upgraded, most expensive, whatever) unit type. In different confrontation situations, the army composed only by the "best" type of little guys will doubtless find its match, i.e an enemy which exploits its weakness, and kills it. See also my argument for "diversity" which I repeatedly raised it here around. Our force stands in the fact that we are different.

Diode lasers are also dirt cheap and very low mass.

Well... not, not here. We do not agree now... Laser diodes which are bloody cheap have also a very short life time. Like 4000 hours or so. That is because they suffer a phenomenon called COD (Catastrophic Optical Damage). A powerful COD-free laser diode costs millions. We need to change the laser guns for our production laser markers from time to time (like every 20k hours or so) and it costs 40k USD each (and those are not totally COD-free). Therefore the high price of the products which are laser marked (as opposed to pad-printed), i.e. few cents more per piece, etc (the marking is very fast, few seconds, etc, depending on the logo/text/image that is marked.

[xilman]

Originally Posted by diep

There is a fundamental problem of exploration:

a) communication back to the home front
b) a good description of what you saw back to the homefront

True.

Originally Posted by diep

A) you keep ignoring in this. 1 meter light sail in diameter is gonna get lost in all the sounds and noises that the stars make. You need something that points to planet earth. Radio communication goes at light speed. You need a huge parabolic radio antenna to communicat to the homefront. The light sail as you pointed out you want light and very huge. Let's make it 500 meters in diameter ok and very light. No big problem.

But then we still need a huge parabolic radio antenna that points back to earth or maybe even to some point far away from the Sun as an 'in between radio station', who will say?

You keep ignoring what I say.
You persist in ignoring what others have to say.
You keep making bald assertions about what you believe to be necessities which you fail to justify and ignore alternatives.

Where did I say that the information sent back to earth had to be by radio? Please read this

You are correct that there is background noise, primarily from the star. Please do a little bit of reading and calculate the power per unit bandwidth to be expected from Proxima Centauri. The formulae are straightforward and the raw data on Proxima are easily available. I'll even make it easy for you by pointing you at https://en.wikipedia.org/wiki/Planck's_law and https://en.wikipedia.org/wiki/Proxima_Centauri

Then consider the power per unit bandwidth of a diode laser. Assume, say, 1W with a bandwidth of 30GHz operating at a frequency of 300THz (a wavelength of about a micron) which are fairly typical values for easily obtainable lasers. Compare that with the blackbody radiation from the star. To optimize your design, choose the diode's operating frequency (red-shifted of course) to be the same as a deep absorption line in the stellar spectrum and compare once again.

It should go without saying that the detector at earth should also be tuned to the (red-shifted) laser wavelength and have an equally narrow bandwidth.

I obliged your curiosity and calculated fthe size of an imaging telescope for you. Please do your own computations from now on. I'll give you pointers, as above, if you need the raw data but you ought to be able to use a search engine for yourself by now.

BTW, do you still think it would be cheaper to build a 10-20km diffraction-limited optical telescope in earth orbit? Cheaper than even your (IMO excessive) $300G estimate for an interstellar mission? I estimated $20G in total and $1M per probe. My estimates are 2-4 times larger than those at https://breakthroughinitiatives.org/News/4

Originally Posted by diep

B) to take a good picture, regardless at which frequency you want to take it, you need to catch enough light. So the computer chip you use might be very tiny and light - yet the tube and lenses or mirrors used will be significant in diameter. For such expensive mission you definitely do not want some sort of space version of the apple iphone camera. That's not gonna cut it. You're gonna need a big diameter aperture or lenses.

For a close pass by of a planet you already will need 10 inch - yet at a speed of 0.05c you can't garantuee a close pass by - even if we do figure out somehow more details like which different planets specific stars might have or do not have and even if we might have some clue where at which moment planets are rotating based upon future telescopes (E-Elt etc).

You still are gonna need a far superior camera over other probes to generate enough data for the mission.

I'm no expert there but we're soon looking at 16 inches diameter.
That's gonna weigh something.

That 1 kilo idea is not realistic.

300 is more realistic for the total probe - and that will already require serious design and improvements over anything that was there so far.

You state unambiguously that you are not an expert and go on to make a dogmatic claim that a 40cm-diameter camera is necessary. You are completely ignoring the views of those who are experts who believe, and can justify their beliefs, that a camera a hundred times smaller is sufficient.

Added in edit: My apologies, I was naively assuming that the camera optics needed to be localized to a small area of the spacecraft, leading to an incorrect view that the aperture would be of order one cm or less. There is no need for such a restriction and the effective aperture could be essentially the size of the spacecraft itself, or 10cm. My assumption was that a filled aperture telescope would be necessary. It quite clearly is not.


Once more: please read http://www.breakthroughinitiatives.org/Initiative/3 and links therein. Another excellent resource is http://arxiv.org/abs/1604.01356 (referenced from the Breakthrough Initiatives site) which goes into very precise detail about the light sail propulsion mechanism for spacecraft of all sizes, from sub-kilogram probes reaching 0.2c to 100-ton human-rated spacecraft for solar-system travel at 0.0026c (760 km/s). A 100kg craft (Voyager-class) would reach Mars in about a day at a speed of 0.015c. Note that we are considering only fly-by and/or long duration missions here so don't need to consider how to slow down again at the destination. (Incidentally a 100kg probe would reach Proxima in around 280 years, which is substantially longer than I believe we are currently willing to contemplate.

Figure 13 in that paper addresses communication back to earth from a sub-kg probe. The scenario considers a 1g spacecraft structure 10cm in diameter and does not use any other optical component such as the 1 metre sail for comms.

When you can back up your claims with sound and detailed physics and engineering computations I will be inclined to take them seriously. Until then you give every appearance of spouting ill-informed nonsense.

[Mark Rose]

Explosion at SpaceX launch site: http://www.bbc.com/news/world-us-canada-37247077

[kladner]

Originally Posted by Mark Rose

Explosion at SpaceX launch site: http://www.bbc.com/news/world-us-canada-37247077

Ah Shoot! Dang! etc.

[Spherical Cow]

Originally Posted by xilman

Another excellent resource is http://arxiv.org/abs/1604.01356

Thanks very much for posting that link; that's the resource I've been looking for ever since hearing about this proposal. Fascinating ideas, but on first hearing about it, I couldn't tell what was realistically doable in the future versus what was completely fantasy. Really neat.

Norm

[xilman]

Originally Posted by Spherical Cow

Thanks very much for posting that link; that's the resource I've been looking for ever since hearing about this proposal. Fascinating ideas, but on first hearing about it, I couldn't tell what was realistically doable in the future versus what was completely fantasy. Really neat.

Norm

You're welcome.

I had hoped that those interested would have found it by themselves --- it's not difficult given the heavy hints I'd already posted --- but it became clear that diep at least had failed to do so.