[Rugoz]

As I said before, a perfect telescope as big as the Earth would not be enough. Those are hard physical limitations, not technological ones.

I don't know where you got that from. The baseline must be big, obviously, that doesn't mean you have to fill it with mirrors. See the picture below. 1060m2 (150*1.5^2*pi) of mirrors with 100km baseline. How are there no physical limitations for 1g probes? The satellites that make high-res pictures of Earth have all big optics.

[Harmattan]

This is exactly what I said: only coarse images even of a very close planet.

More precisely I said before that a lens the size of the Earth (or an interferometer cohort the size of the Earth) would give a 1km resolution for Alpha Centauri. Here you have something 260 times smaller giving a 400 times worse resolution for something three times farther: imaging simulations have shown that a 150km hypertelescope having 150 apertures of 3m can produce resolved images of an Earth-like planet at 3pc containing 30x30 resolved elements (resels) within a 3 hour exposure

Now imagine that you wanted a 1m resolution: you would need to spread your elements over a 400k times bigger distance. But then you would need an exposure time of 3 * 400k hours. I hope you are patient.

Probes are the only realistic solution for accurate imaging of exo-planets. Accurate as in "able to detect and observe a civilization".

[Rich]

Processors hit a similar wall more than 10 years ago, when logic gates stopped getting smaller and speed essentially stopped increasing. We have developed workarounds like multiple cores, and software -- in some fields -- has improved, but silicon wafer data processing technology can be considered mature.

Logic gates have continued getting smaller. Up until Haswell at the same pace. Even since Haswell the slow down in process node generations has only been 15 to 25%. The problem is processors generate too much heat. Heat rises above linear for clock speed. After 28 nm to 22 nm they have also stopped getting cheaper.

[Rugoz]

Now imagine that you wanted a 1m resolution: you would need to spread your elemnts over a 400k times bigger distance. But then you would need an exposure time of 3 * 400k hours. I hope you are patient.

The size is irrelevant in space, but you'd need more mirrors to collect more light, probably millions of them. But I find it silly to even speculate about 1m resolution. The problem is you vastly underestimate the difficulty of sending a spacecraft to 0.2c or similar speeds, let alone braking at arrival. The technology simply doesn't exist.

Or lets put it this way:

The Starshot guys think they can build an interstellar probe that:

- Has a 4m sail (mirror) that reflects 99,9999% of the light, because otherwise it would be vaporized by 100GW of lasers.
- Withstands 60'000g of acceleration.
- Can be shot on a trajectory that intersects precisely with an exoplanet light years later (even New Horizons had to constantly adjust its course on the way to Pluto).
- Hopefully doesn't collide with any Interstellar dust.
- Does communication over several light years.
- Has cameras, energy source etc.

And all of it is only allowed to weight 1 gram!!

Sorry, but the chances that we can build 1 gram mirrors for a large telescope in the future are much higher.

[Harmattan]

The problem is you vastly underestimate the difficulty of sending a spacecraft to 0.2c or similar speeds, let alone braking at arrival. The technology simply doesn't exist.

It is challenging without any doubt. That being said, I do not think we are that far from this level.

* An extremely thin sail that repels 99.9999% of a single wavelength does not seem to be a big deal. I am sure we already know crystalline structures that fit the role with just a few atoms thick.

* Regarding the slowdown and course corrections, I think they are manageable provided enough time is afforded (a few decades if necessary). Also keep in mind that the required force is proportional to the weight.

* Some smartwatches are already below 50g and this includes a tactile screen, buttons and wristband. Two decades ago it would have taken a few kilograms at least.


On the other end for a large cohort you need a propulsion system that can keep all elements synchronized for hours with a precision of a few nanometers, despite the fact that the gravitational forces will vastly differ between one point of this very large cohort to another. This may be impossible before a very long time and will likely require a heavy enough system.

[Rugoz]

It is challenging without any doubt. That being said, I do not think we are that far from this level.

* An extremely thin sail that repels 99.9999% of a single wavelength does not seem to be a big deal. I am sure we already know crystalline structures that fit the role with just a few atoms thick.

* Regarding the slowdown and course corrections, I think they are manageable provided enough time is afforded (a few decades if necessary). Also keep in mind that the required force is proportional to the weight.

* Some smartwatches are already below 50g and this includes a tactile screen, buttons and wristband. Two decades ago it would have taken a few kilograms at least.


On the other end for a large cohort you need a propulsion system that can keep all elements synchronized for hours with a precision of a few nanometers, despite the fact that the gravitational forces will vastly differ between one point of this very large cohort to another. This may be impossible before a very long time and will likely require a heavy enough system.

Slowdown is only possible if you have another 100GW laser on the other side.

Anyway, we are extremely far from this level and none of it will happen in my lifetime, of that I'm certain.

[Harmattan]

Slowdown is only possible if you have another 100GW laser on the other side.

Fortunately not!

For the start understand that energy can be either produced quickly over a small time span, or slowly over a long one. The 100GW laser would be used for 2 minutes, so you could counter it with just 1kW over 10 years. This looks too much for a tiny reactor or battery with current technology but it does not matter.

Indeed, we have solutions that let nature steal the energy we initially gave to the probe, and also solutions that exploit the high speed to produce a lot of energy. A solar sail would do the former by exploiting the long distance: an average 5 micronewtons force for half of the distance would be enough. This would passively slow down the probe by letting the stellar wind steal the energy. This is also lightweight, robust and simple.

Another example of alternative would be a magnetic tether, which would use the high speed of the probe in the star's magnetic field to act like a dynamo. Not only this would passively slow down the probe, but also it would convert this kinetic energy into electrical energy received by the probe! This energy could be used to further slow down, change the course and charge the systems. Actually it could be the primary energy source of the probe.

[Rugoz]

Fortunately not!

And here you come again with scifi fantasies. Of course if you just ignore mass or think it can all be done at masses several orders of magnitude lower than today then this debate is pointless. Everything becomes possible.

[Igor Antunov]

Anyway, we are extremely far from this level and none of it will happen in my lifetime, of that I'm certain.

I was at the barber today, he has been cutting hair for over 60 years. I wonder what he would have deemed possible in 1945 when he opened his shop.

[Harmattan]

Of course if you just ignore mass or think it can all be done at masses several orders of magnitude lower than today then this debate is pointless. Everything becomes possible.

The weight does not matter: those devices are a constant fraction of the total weight regardless of that one. And you do not have some of the problems you would have with a 5km sail for a shuttle.

Also I fail to see what is "sci-fi" about a little mirror or a stick wrapped in a coil. This is difficult because of the other constrains but you speculate about the real difficulty and exaggerate it without considering the true problem.

Stephen Hawking cautions the project and a notorious investor financially backs it. Both are physicists and have a far better idea of the difficulties than you do. Maybe it will never exist but at least give the project some credit.

[Rugoz]

Stephen Hawking cautions the project and a notorious investor financially backs it. Both are physicists and have a far better idea of the difficulties than you do. Maybe it will never exist but at least give the project some credit.

Hawking gets wheeled in on every occasion nowadays.

The $100m won't get them anywhere.

For the record, this is what an interplanetary probe looks like (New Horizons):