What "weed need" is a space mission!

[kladner]

Many thanks for the detailed explanation, Dubslow.

[Nick]

NASA Unveils New Public Web Portal for Research Results

Press release: https://www.nasa.gov/press-release/n...search-results

[xilman]

Earth-sized world 'around nearest star'

We already have the technology to go there and investigate in detail. Whether we have the political and economic will to embark on a project which won't give results until the early 22nd century is another matter entirely.

There are a whole bunch of technologies, perhaps the most promising are sub-1kg light sails boosted by sunlight and terrestrial (or NEO) lasers. Send off a thousand or so and some will arrive in good enough shape to report back. They only need to reach 0.05c to report back in a century or less.

[only_human]

Reddit - Press release: "SES-10 Launching to Orbit on SpaceX's Flight-Proven Falcon 9 Rocket. Leading satellite operator will be world's first company to launch a geostationary satellite on a reusable rocket in Q4 2016"

LA Times: SpaceX signs first customer for launch of a reused rocket

There also was “no material change” in the insurance rate compared to using a new Falcon 9 rocket, indicating insurers’ confidence in the launch vehicle, Halliwell said.

[diep]

Originally Posted by xilman

Earth-sized world 'around nearest star'

We already have the technology to go there and investigate in detail. Whether we have the political and economic will to embark on a project which won't give results until the early 22nd century is another matter entirely.

There are a whole bunch of technologies, perhaps the most promising are sub-1kg light sails boosted by sunlight and terrestrial (or NEO) lasers. Send off a thousand or so and some will arrive in good enough shape to report back. They only need to reach 0.05c to report back in a century or less.

Maybe my math is not so ok. Going there with current technology would be a waste of effort and time and i doubt we could produce equipment that doesn't break down for such long period of time.

However you might want to calculate a more practical goal.

How large do we need to make a telescope in space (its primary mirror) to be able to take a picture of the planet nearby proxima centauri?

Right now we only have indirect evidence by making picture of the star.

building a huge telescope in space existing out of many panels might not be such stupid idea. At earth there is gravity for example, which makes a huge telescope already soon very heavy.

With future technology delivering cargo cheaper in space we might be able to construct a massive telescope in space that can make great pictures.

Right now all telescopes are like "launch in 1 go" type telescopes that go to space.

Yet think larger. Think of autonomeous small robots in space that maintain a large structure that gets built in space. I'm not an expert in knowing at which orbit it should be.

Yet the advantages of it would be obvious. You can grow it very large over time. If something hits panels, you just need the robots to replace that panel and service it (if that's still possible). If no humans are involved you suddenly can do very cheap service flights to such project in space.

Risky Musk type rockets then might be a good solution.

So from payment viewpoint it's affordable.

[diep]

Originally Posted by xilman

Earth-sized world 'around nearest star'

We already have the technology to go there and investigate in detail. Whether we have the political and economic will to embark on a project which won't give results until the early 22nd century is another matter entirely.

There are a whole bunch of technologies, perhaps the most promising are sub-1kg light sails boosted by sunlight and terrestrial (or NEO) lasers. Send off a thousand or so and some will arrive in good enough shape to report back. They only need to reach 0.05c to report back in a century or less.

If we calculate price of such mission it's soon 5 billion dollar for the first mission. Now maybe there is reduction in price and launchcosts should go down considerable in future if you produce a lot.

However if you really want to send 1000 to Proxima Centauri, that's gonna be a very expensive mission. Even the most careful estimate i would guess in the order of 300 billion dollar.

This where most likely around Proxima Centauri there isn't any planet that has any life - as the star is big in radiation.

Paying such huge cost for a mission to a star that with high certainty can't support any life in orbit around it, is tough to find funding for.

On other hand - go do some math with a huge telescope in space existing out of many panels serviced by small (semi-)autonomeous robots. Though i would rather want to call it dedicated robots rather than autonomeous.

[xilman]

Originally Posted by diep

Maybe my math is not so ok. Going there with current technology would be a waste of effort and time and i doubt we could produce equipment that doesn't break down for such long period of time.

I don't see why your math should be a problem. What is the conceptual problem?

There are a number of space probes which are still working after twenty years. Of necessity they were built with technology now decades out of date. The Voyager probes are the best known examples but others exist.

Unsurprisingly, some terrestrial equipment has also worked perfectly for decades without maintenance. I've some computers in my loft which are over thirty years old, have never had any maintenance and still work perfectly AFAIK. Those are consumer-grade equipment which was never designed to last.

Longevity is not the problem, IMO. Political will is the major problem to be addressed before launching an interstellar mission.

That's not to say we shouldn't build a telescope as you describe. I whole-heartedly support the idea, not least because it would be useful for much more than looking in the close neighborhood of Proxima Centauri. Nonetheless, it is very unlikely to provide the wealth of detail that a close pass by a swarm of probes would give.

[xilman]

Originally Posted by diep

How large do we need to make a telescope in space (its primary mirror) to be able to take a picture of the planet nearby proxima centauri?

Specify the size of the planet and the working wavelength of the imager and the computation of an approximation to the telescope aperture is straightforward. What follows is a first attempt. The estimate will be wrong but should be good to within a factor of two or so.

Assumptions

• Working wavelength is 1 micron = 1e-6 m
• Distance to Proxima is 1.3 parsec = 4e16 m
• Maximum separation of planet from star is 0.05 AU or 7.5e9 m
• Diameter of planet, assumed slightly larger than Earth's = 1.5e7 m
• Desired number of pixels in diameter of planetary image = 10

To put the desired imaging capailities into familiar terms, the human eye has a resoution of 1 arcmin and the moon is 30 arcmin in diameter. Consequently, the telescope designed below will give an image showing markedly less detail than can be seen on the moon with the naked eye.

First note that much of the time the planet will not be at maximum elongation from the star but the desired image scale is such that the separation will be 10 * 7.5e9 / 1.5e7 pixels. This is 5000 pixels, so scattered starlight will be insignificant for almost all of the time.

The resolution element at the planet is (diameter / pixel size) = 1.5e6 m.

The ratio (pixel size) / (distance to planet) is thus 1.5e6/4e16 = 4e-11

Diffraction limit of an aperture diameter d working at wavelength lambda is approximately lambda / 2d. Accordingly we have 4e-11 = 1e-6 / 2d. Rearranging gives d = 1e-6 / (2 * 4e-11) = 1.3e4 m

In round numbers, a ten-kilometre optical telescope will do it.

The largest optical telescope on the earth is 0.01km across, the largest radio telescopes are 0.3-0.5km in diameter. Neither are steerable and neither need surface accuracies (much) better than 1 micron.

So you are asking for an optical telescope to be built in orbit which has a thousand times the aperture of bleeding edge ground-based instruments. In my considered opinion such a facility would be vastly more expensive to build than a thousand interstellar probes. The launch costs would be vastly more expensive. System maintenance, though possible, is also certain not to come cheap.

[diep]

Originally Posted by xilman

I don't see why your math should be a problem. What is the conceptual problem?

There are a number of space probes which are still working after twenty years. Of necessity they were built with technology now decades out of date. The Voyager probes are the best known examples but others exist.

Unsurprisingly, some terrestrial equipment has also worked perfectly for decades without maintenance. I've some computers in my loft which are over thirty years old, have never had any maintenance and still work perfectly AFAIK. Those are consumer-grade equipment which was never designed to last.

Longevity is not the problem, IMO. Political will is the major problem to be addressed before launching an interstellar mission.

That's not to say we shouldn't build a telescope as you describe. I whole-heartedly support the idea, not least because it would be useful for much more than looking in the close neighborhood of Proxima Centauri. Nonetheless, it is very unlikely to provide the wealth of detail that a close pass by a swarm of probes would give.

None of those probes will survive another century though.

For such telescope you first want to see a simple magnification calculation what size you would require to make a photo, even if it's a few pixels, of a planet orbitting another star. Such math is doable long before the concept turns into a serious plan.

What you propose is to ship unproven technology, assume the probe will survive for 2 centuries, something still unproven as well, somehow it must then be able to communicate back to us 2 centuries from now, and to ship it to a star which with near to 100% sureness according to how we use logics can't support any form of life as we know it, which then all together is gonna cost in the hundreds of billions if not more.

If something can't work in advance, companies are gonna keep that a secret. People making money are very good at getting contracts.

They also kept something quiet around hubble in that sense. They d** well knew something was wrong - and deliberately didn't investigate it as they knew something was wrong. And 'they' being the CEO's of the small tiny company grinding the mirrors.

A multibllion dollar project that for a contract of what was it 20 million dollar or so, had to spend another few billion fixing something. This where probes that travel for 2 centuries to a remote star, with the traveltime an assumption, you can't correct anything on them.

Unproven technology that's gonna travel for an unproven period of time, that's gonna pass through all sorts of belts where particles can tank the probe, and where hundreds of billions are possible to get made. The conceptual problem is that with 100% sureness some frauds will manage to get contract jobs and mess up - even if conceptual it would be possible. They are long dead and gone when their shortcuts that render every single probe useless, get unveiled.

Speaking of math. Please calculate the difference of the hubble primary versus the same primary that would be parabolic primary.

You'll figure out the difference is less than 0.1 nanometer. In short that's factors less than the grinding accuracy they could achieve in 1979.

In short they didn't need some complicated manner of testing that primary mirror, which you need for a hyperbolic primary mirror. A simple laser interferometer would have done - of course they took that shortcut.

Then the next question is: how the h*** could they mess that up?

Well they DID.

When one of the grinders noticed that something might be wrong - the leadership of that company took care not a single test was done that would've found the problem.

Of course they already knew that something went wrong...

The conceptual problem of a 300 billion project with zero control possible the probes actually will work for another 2 centuries during the life of those CEO's delivering junk - the conceptual problem is that someone will be carrying out the project for 150 billion dollar and mess up with 100% sureness.

[xilman]

Originally Posted by diep

If we calculate price of such mission it's soon 5 billion dollar for the first mission. Now maybe there is reduction in price and launchcosts should go down considerable in future if you produce a lot.

However if you really want to send 1000 to Proxima Centauri, that's gonna be a very expensive mission. Even the most careful estimate i would guess in the order of 300 billion dollar.

The actual probes should not cost very much each. A few grams of graphene for a square-metre sail and a wafer-sized chip. In thousand-off quantities they might cost a million USD each, for a total cost of a billion.

The launch facility will be expensive, no doubt, but again economies of scale come into play. A phased-array of numerous lasers uses relatively cheap mass-produced components. A few billion USD should cover the manufacturing and installation.

Development costs are much less easily estimated. I'd guess something in the range 1-10 billion USD.


If I'm anywhere near the right ballpark, a mission cost of, say, 20 billion USD will cover it. This is more than an order of magnitude lower than your estimate. To put things in perspective, the Apollo project cost close to 100 billion USD in 2010 dollars.

[xilman]

Originally Posted by diep

None of those probes will survive another century though.

For such telescope you first want to see a simple magnification calculation what size you would require to make a photo, even if it's a few pixels, of a planet orbitting another star. Such math is doable long before the concept turns into a serious plan.

What you propose is to ship unproven technology, assume the probe will survive for 2 centuries, something still unproven as well, somehow it must then be able to communicate back to us 2 centuries from now, and to ship it to a star which with near to 100% sureness according to how we use logics can't support any form of life as we know it, which then all together is gonna cost in the hundreds of billions if not more.

If something can't work in advance, companies are gonna keep that a secret. People making money are very good at getting contracts.

They also kept something quiet around hubble in that sense. They d** well knew something was wrong - and deliberately didn't investigate it as they knew something was wrong. And 'they' being the CEO's of the small tiny company grinding the mirrors.

A multibllion dollar project that for a contract of what was it 20 million dollar or so, had to spend another few billion fixing something. This where probes that travel for 2 centuries to a remote star, with the traveltime an assumption, you can't correct anything on them.

Unproven technology that's gonna travel for an unproven period of time, that's gonna pass through all sorts of belts where particles can tank the probe, and where hundreds of billions are possible to get made. The conceptual problem is that with 100% sureness some frauds will manage to get contract jobs and mess up - even if conceptual it would be possible. They are long dead and gone when their shortcuts that render every single probe useless, get unveiled.

Speaking of math. Please calculate the difference of the hubble primary versus the same primary that would be parabolic primary.

You'll figure out the difference is less than 0.1 nanometer. In short that's factors less than the grinding accuracy they could achieve in 1979.

In short they didn't need some complicated manner of testing that primary mirror, which you need for a hyperbolic primary mirror. A simple laser interferometer would have done - of course they took that shortcut.

Then the next question is: how the h*** could they mess that up?

Well they DID.

When one of the grinders noticed that something might be wrong - the leadership of that company took care not a single test was done that would've found the problem.

Of course they already knew that something went wrong...

If I'm in at least the right
The conceptual problem of a 300 billion project with zero control possible the probes actually will work for another 2 centuries during the life of those CEO's delivering junk - the conceptual problem is that someone will be carrying out the project for 150 billion dollar and mess up with 100% sureness.

Your duration assumptions are wildly wrong.

Current plans are for the probes to travel at 0.05 to 0.2c. Flight time is therefore 20 to 80 years. Results return at the speed of light so add another four years.

As I noted, large amounts of stuff has been shown to work perfectly for decades without any maintenance.