What "weed need" is a space mission!

[diep]

Oh boy where to start.

Nearly all cheap mirrors have an aluminium reflective coating for visible light spectra.

Gold reflects better yet doesn't cover the entire visible light spectrum. Gets used especially for infrared.

Silver on paper is reflecting very well - yet it oxidizes too fast.

In space gold gets used most for reflection. On earth aluminium most.
My own telescope has aluminium coating.

If you want that parachute behind the probe to also act as radio antenna, you'll need to give it an aluminium, silver or gold coating in short.

Why not directly make it out of aluminium then?

Much easier.

I don't see any use for graphene type materials there - asking for troubles.

Diamond reflects to all direction - no use for it as a parabolic antenna.

The reason for a parabolic antenna is to get a larger surface area to communicate. In short that shape needs to be very precisely a parabola.
You need a very stiff material. If you go toy with some plastic or carbon that bends a lot you no longer can communicate home.

The tensile strength of graphene is unrivalled - yet that's not what you need.

p.s. i don't think graphite ever will be used :)

[xilman]

Originally Posted by diep

Oh boy where to start.

Nearly all cheap mirrors have an aluminium reflective coating for visible light spectra.

Gold reflects better yet doesn't cover the entire visible light spectrum. Gets used especially for infrared.

Silver on paper is reflecting very well - yet it oxidizes too fast.

In space gold gets used most for reflection. On earth aluminium most.
My own telescope has aluminium coating.

If you want that parachute behind the probe to also act as radio antenna, you'll need to give it an aluminium, silver or gold coating in short.

Why not directly make it out of aluminium then?

Much easier.

I don't see any use for graphene type materials there - asking for troubles.

Diamond reflects to all direction - no use for it as a parabolic antenna.

The reason for a parabolic antenna is to get a larger surface area to communicate. In short that shape needs to be very precisely a parabola.
You need a very stiff material. If you go toy with some plastic or carbon that bends a lot you no longer can communicate home.

The tensile strength of graphene is unrivalled - yet that's not what you need.

p.s. i don't think graphite ever will be used :)

A pure aluminium mirror weighs far too much for use as a light sail. Metallic coated thin films are very much lighter for the same performance, as long as you don't demand high-quality imaging. The tensile strength of graphene is exactly what you need. It lets you use extremely thin films and hence extremely low mass films for a given reflecting area. Mass is of crucial importance in this project. Each probe has to have a mass under one kilogram for everything: sail, structure, detectors, comms, power supply, the lot.

For comms use, imaging isn't very important as there is only one detection element. Anything which increases the signal to noise ratio is useful for this purpose. It's nice to get more signal on the detector but if doubling the signal costs too much mass, then just use a more powerful transmitter. If the comms to the spacecraft uses a visible light laser, Al is better than Au for coating. If the laser is in the near infrared the opposite is true. Given that the sun is brightest in the optical and light from the solar system will be red-shifted by 20% or so, using near-infrared communications makes a lot of sense to me as it stands out better from sunlight.

OTOH, I don't yet know whether the launch laser would be better working in the visible or the IR, though I suspect the latter given what little I know about the achievable average power of current lasers. A 100W optical laser is quite unusual, AFAIK, whereas multi-kilowatt IR lasers are widely used in industrial cutting and machining.

Graphite (or possibly diamond, that's my suggestion not the "official" one) is suggested for the spacecraft structure, not the sail.

[diep]

Originally Posted by xilman

A pure aluminium mirror weighs far too much for use as a light sail. Metallic coated thin films are very much lighter for the same performance, as long as you don't demand high-quality imaging. The tensile strength of graphene is exactly what you need. It lets you use extremely thin films and hence extremely low mass films for a given reflecting area. Mass is of crucial importance in this project. Each probe has to have a mass under one kilogram for everything: sail, structure, detectors, comms, power supply, the lot.

For comms use, imaging isn't very important as there is only one detection element. Anything which increases the signal to noise ratio is useful for this purpose. It's nice to get more signal on the detector but if doubling the signal costs too much mass, then just use a more powerful transmitter. If the comms to the spacecraft uses a visible light laser, Al is better than Au for coating. If the laser is in the near infrared the opposite is true. Given that the sun is brightest in the optical and light from the solar system will be red-shifted by 20% or so, using near-infrared communications makes a lot of sense to me as it stands out better from sunlight.

OTOH, I don't yet know whether the launch laser would be better working in the visible or the IR, though I suspect the latter given what little I know about the achievable average power of current lasers. A 100W optical laser is quite unusual, AFAIK, whereas multi-kilowatt IR lasers are widely used in industrial cutting and machining.

Graphite (or possibly diamond, that's my suggestion not the "official" one) is suggested for the spacecraft structure, not the sail.

Under 1 kilo you won't be able to produce something that can produce good pictures and ship them back home. Otherwise your probe could take that picture already from here and doesn't need to travel to that star.

It's all about aperture of the camera's lenzes....

Which is why i say: first calculate how large of a telescope you need to build here in orbit of earth, to take a picture of planets at other stars.
That calculation is interesting to see :)

I don't understand why you are busy with lasers at these huge distances.

At such huge distance a laser is total useless.

Typical machine that uses laser cutter is like 60 watt laser (the motors on the other hand consume kilowatts not seldom - even the steppers i have here have their own PSU each one of them :))

p.s. graphite is something else than graphene.

[diep]

Xilman, In this all the thing most underestimated seems to be how tough it is to communicate with the homefront.

The sorts of signals we analyze here from remote sources are things like quasars and big bursts of stars.

That's huge things. How to communicate back to the homefront with something under 1 kilo and no power source at all or at most some small battery?

Suppose your thing flies at 0.05c, though i know some experts are disputing all that, yet me not being an expert there will say simply: "let's continue pondering and make plans".

Or in the words here of Batalov: "Plot. Scratch your forehead. Analyze. Plan ahead. Keep it simple".

The KISS manner of communicating back to the homefront is some huge parabolic antenna. Let's say a meter or 30 diameter. Then use megawatts of electricity and try to get a signal back home and pray it gets detected.

At a speed of 0.05c you got just a few minutes to zoom in onto the planets and seconds to make a photograph of each planet you detect and then you crash into the star.

If your probe does have some sort of telescope say with diameter 1 meter, you make more of a chance to detect planets quickly and make that photo.

Then you have seconds to communicate back to earth prior to impact into the star.

In case of some star with circumstances similar to the Sun, your odds are even worse - you'd crash into the jupiter equivalent there prior to be able to take pictures.
At most your chances of making a photo of something similar like 'earth' is 25% at most in those few seconds you have prior to crashing into the 'jupiter equivalent'.

How do you communicate back?

[J F]

Originally Posted by xilman

Even nicer, in many ways, would be a diamond structure but artificial diamonds circa 10-20 cm in diameter are not currently possible.

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?

[diep]

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?

I assume because he wants to keep a souvenir as i see no other use in diamonds in a space crafts hull.

I'd build it out of a combination of metals not any sort of carbon idiocy at all.

[diep]

Xilman - seems something interesting is this link:

http://www.nasa.gov/mission_pages/hu...-20100204.html

That's one of the better pictures taken by Hubble of pluto.

If you are at 0.05c (i give you this speed for free out of appreciation) you will need to take photographs from quite a distance.

Realize Hubble is a ritchey-chretien telescope that can make very accurate pictures with a 2.4 meter diameter aperture.

So if you pass with a small probe a specific star - you've got minutes to determine what the planets are - and to take a good picture you simply need a big aperture or you will just have 1 or 2 pixels at most.

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

You need a huge aperture to make a good picture. At the distance of hubble <=> pluto, this is the maximum you can get - and taking this picture by hubble probably took quite some time.

If you'd equip the probe with a hubble sized camera the picture will be a lot worse than the hours hubble can spend taking a single picture.

[Uncwilly]

Originally Posted by diep

http://www.nasa.gov/mission_pages/hu...-20100204.html

That's one of the better pictures taken by Hubble of pluto.
.....

You need a huge aperture to make a good picture. At the distance of hubble <=> pluto, this is the maximum you can get - and taking this picture by hubble probably took quite some time.

If you'd equip the probe with a hubble sized camera the picture will be a lot worse than the hours hubble can spend taking a single picture.

You obviously did not read the caption in the link that you posted, nor the article.
Those are generated images from multiple images taken. The data were then calculated and rendered. Pluto is bright enough that Hubble does not need 'quite some time'.

Paul also (I can safely assume) has some answers to some of the imaging issues that you think that you are bringing up. There are many answers that he has up his sleeve that you have not progressed far enough in your understanding to receive. I have been watching the discussion and know that you are making some real errors in knowledge, understanding, and logic.

[diep]

Originally Posted by Uncwilly

You obviously did not read the caption in the link that you posted, nor the article.
Those are generated images from multiple images taken. The data were then calculated and rendered. Pluto is bright enough that Hubble does not need 'quite some time'.

Paul also (I can safely assume) has some answers to some of the imaging issues that you think that you are bringing up. There are many answers that he has up his sleeve that you have not progressed far enough in your understanding to receive. I have been watching the discussion and know that you are making some real errors in knowledge, understanding, and logic.

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.

[only_human]

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.

Here is a list of challenges identified so far in the Breakthrough Starshot high speed lightsail program:
https://breakthroughinitiatives.org/Challenges/3

[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.

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.

All that bullshit 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.