Millions of Telescopes 4 Light Days From Earth Could Permanently Explore Other Solar Systems

If we send telescopes out to 4 light days we can use the gravity of the sun to amplify the power of telescopes by 100 billion times. Although we can build larger telescopes with higher resolution than exists today near to Earth, the telescopes that are sent out to gravitational lensing regions would resolve much faster. In some cases, it would take millions of years or more to resolve an image while the gravitational lens telescope could resolve in weeks.

The resolution amplification out at the gravitational lens would be mammoth compared to large telescopes near to Earth. There is a need for both. Having 100 meter or multi-kilometer telescopes on the moon or at LaGrange points would be useful for lower resolution scanning of other solar systems. The resolution could still be hundreds of times beyond the capabilities of our best existing telescopes.

For the next decade or two, the challenge will be to get a single one-meter telescope out to the right spot. The right spot is a very thin line on the opposite side of the sun to the exoplanet or target imaging object. The best lensing areas are out at 650 times further than the distance from the Earth to the Sun.

The first missions will probably be laser pushed solar sails or solar sails that slingshot around the sun. These would try to reach the gravitational lens area in about ten to twenty years. They would need to get to twenty times the speed of the Voyager spacecraft. They would travel along the optimal line for looking at another solar system.

There are about 14,000 solar systems within 100 light-years and 250,000 solar systems within 250 light-years.

The ideal situation would be to improve propulsion so that the telescopes could get to 4+ light days from Earth and then slow down and stay in the optimal observation areas. We should then mass produce telescopes dedicated for each solar system. We should even have many telescopes along the optimal sightline so that various parts of the target solar system can stay under constant observation and exploration. Each set of telescopes would like probes of the other solar system. There should be at least one telescope for each planet and some for the moons and other objects of the other solar systems.

14,000 solar systems with 100 dedicated telescopes for each solar system would be 1.4 million telescopes.
250,000 solar systems with 1000 dedicated telescopes for each solar system would be 250 million telescopes.

A mothership could carry the hundred or thousand telescopes to the specific gravitational lens line and then offload the 100 or thousands of telescopes.

The telescopes would gather megapixel images of everything in the target solar system. We would be able to watch the weather and measure the atmosphere of the exoplanets and objects.

Telescopes staying along lines in the 4 lightday to 20 light day zones would be like we had probes in other solar systems. But this would 1000 times closer and 1 million times easier in terms of energy costs and economics for each. This is space exploration that we could achieve starting around the 2040s and we could scale to the target levels by 2080.

There would be no need for starshades. The focal line for the stars would be thousands of miles away. There would only be the need for coronagraphs to blot out our own sun. The images would have to be reconstructed from the Einstein ring created by the gravity of our sun.

A large 1300 meter telescope at the gravitational lens lines would be able to image an entire exoplanet with one image. A one-meter telescope would have to piece other a full exoplanet over months or years of observations.

If tens of megawatt laser arrays beamed power to sails powering lithium-ion drives, then the spacecraft could maneuver and decelerate to hold positions on the lensing lines.

This would be about 1000 times closer than actually sending probes to the other solar systems. It would take one million times less energy.

Arxiv- Recognizing the Value of the solar Gravitational Lens for Direct Multipixel Imaging and Spectroscopy of an Exoplanet.

International Journal of Modern Physics D – Putting gravity to work: Imaging of exoplanets with the solar gravitational lens

Written By Brian Wang,

52 thoughts on “Millions of Telescopes 4 Light Days From Earth Could Permanently Explore Other Solar Systems”

  1. Thanks Roger.
    Nice research journalism.
    I’ll take a close look at the papers.

    ⋅-=≡ GoatGuy ✓ ≡=-⋅

  2. …CONTINUE 1…
    In this calculation his is not accounting for the optical properties of the SGL. This lens is not perfect and has a spherical aberration that results in a significant blur. But blur is actually very good, as at any telescope position in the image plane, the telescope see the light from the directly-imaged region on the source (the signal that this man is calculating) and also blur from the rest of the exoplanet. The blur is much stronger than the light from the directly-imaged region and allows for a significant brightness increase (compared to a blur-less case).
    As we move the telescope in the image plane, we collect the brightness at each telescope location in the image plane. Once the data is collected, we recover original image by removing the blur (using deconvolution algorithm, standard in modern astronomy).
    This is all described in our recent paper:
    and the mission is presented at
    Hope this helps.

  3. Regarding the calculation from GoatGuy describing the necessity for a Starshade, here is the answer from one of the scientists from JPL working on FOCAL
    Dear Rogério,
    Thank you very much for your message.
    The article correctly says that there will be no need for starshades (to block out the light from the parent star). Two sentences down, it says that “There would only be the need for coronagraphs to blot out our own sun.”
    This is all correct and the “man with a physics background” read the article a bit too fast. AS we will only need to have an internal coronagraph to bock the light from our own sun to the level of 10^(-7), which is not not very hard. Once we block out the sun, what is left is the light from the solar corona which is a still bright, but integrating signal for 5 min with 1 m telescope, we can reach the needed sensitivity.(Larger telescope, say 2 meter, will reduce the per-pixel integration time down to 30 second only. So, no problem.)


  4. Here is his answer:
    Dear Rogério,
    Thank you very much for your message.
    The article correctly says that there will be no need for starshades (to block out the light from the parent star). Two sentences down, it says that “There would only be the need for coronagraphs to blot out our own sun.”
    This is all correct and the “man with a physics background” read the article a bit too fast. AS we will only need to have an internal coronagraph to bock the light from our own sun to the level of 10^(-7), which is not not very hard. Once we block out the sun, what is left is the light from the solar corona which is a still bright, but integrating signal for 5 min with 1 m telescope, we can reach the needed sensitivity. (Larger telescope, say 2 meter, will reduce the per-pixel integration time down to 30 second only. So, no problem.
    In this calculation his is not accounting for the optical properties of the SGL. This lens is not perfect and has a spherical aberration that results in a significant blur. But blur is actually very good, as at any telescope position in the image plane, the telescope see the light from the directly-imaged region on the source (the signal that this man is calculating) and also blur from the rest of the exoplanet. The blur is much stronger than the light from the directly-imaged region and allows for a significant brightness increase (compared to a blur-less case).
    CONTINUE (what’s up with me not being able to post the entire message?)

  5. Hello GoatGuy.

    I first contacted Dr Maccone, about the necessity of a Starshade. Dr Maccone said he was 72 and had stopped working on the FOCAL, so he kindly passed me the contacts of two Drs from JPL who headed FOCAL now.

    I contacted Dr. Slava G. Turyshev,
    Research Scientist, NIAC Phase III Fellow
    Corresponding Member, International Academy of Astronautics
    Structure of the Universe Research Group
    NASA Jet Propulsion Laboratory, MS 169-237

  6. Well, at Voyager 1 speed, it would take about 4.5 billion years to travel 250k light years. A lot of folks are pretty sure we can do six times that with current technology, cutting it down to 734 million years. A century from now I would find it difficult to believe we couldn’t top that by an order of magnitude (73.4 million years) or far more likely, two orders of magnitude, or 7.34 million years which is is moving us right into what the universe considers “realtime.”

    Given that technology increases in a holistic fashion, technologies such as endlessly repairing systems, machine-stored personalities, and printable biological bodies (if we even see a need for them at that point) all become possibilities. As does a colony ship.

    What would be the motivation for such a thing? Doesn’t matter. Experience tends to show that if someone, somewhere, can do something, it will happen. People tend to do whatever and the rationalization often follows the decision. I expect the same would be true of any other relatively advanced tool-building species.

    For similar reasons I expect that any intelligence that starts spreading in a galaxy will continue to do so, as it is unlikely to be able to stop completely, even if the majority of it wants to, unless the entire galaxy becomes entirely unable to support intelligence. Just as it will not be possible to eliminate all life on Earth unless every bit of the Earth (to a depth of several miles) becomes entirely unable to support life.

  7. the initial systems will clearly not stop but coast out for decades indicated by other commenters. The nearest term possibility is laser pushing and then laser powering a lithium ion drive 50,000 ISP. But getting some laser onto a target out at 600 AU to start slowing down would be very tough. The other way is to carry antimatter or some other powerful drive out to slow down. Another way would be to send some large objects that are moon sized out there and use a few of those for deceleration moves. If planet sized objects or near planet sized objects are out there (600-3000 AU). something bigger might be able to swing around and start moving back towards the solar system. If that thing had power user lasers to push against some outbound stuff. We could setup the power systems for slowing outbound things down. Robert Forward had the idea of a larger sail separating from a smaller sail and the larger donut being used to bounce deceleration to the smaller sail.

  8. It would perhaps be clear to call these sensors, and the whole thing, including the Sun, the telescope.

  9. Because Earth’s and even Jupiter’s gravity closest gravity focal points are much farther than the Sun’s (550 AU), making the problem of going there much worse. For Jupiter, its focal point starts at 5930 AU, for Earth, it starts at 15,300 AU (!).

    The Sun is a kind-of-feasible gravity lens precisely because it’s much more massive than all the planets put together and its gravity focal point is closer.

  10. Illuminate us with this tech that will come from the project that will never come about. Look at Goat’s calculations. What other pure space science experiments have spun off businesses?

  11. Any sort of rocket could probably be made with arbitrary mass ratios if you just need it to hang together in space.
    Have a huge slab of frozen water, a few layers of micron thick aluminium on the outside to stop sublimation, and the propulsion system is just mounted on one end. Small robots actively mine the ice and eventually you chew it all up and blast it out the back.
    Maybe frozen hydrogen and oxygen. In little frozen blocks with lithium coats to stop sublimation (doesn’t have to be antilithium for this application).

  12. Are you sure that’s right?
    When I try for a delta V of 2 % of C, with exhaust velocity of 5% of C, I get a fuel fraction of 33%.

  13. And at LAST we get an explanation as to why the galaxy spanning empires of SF are all the apparently “old fashioned” structure of monarchies.

    Simply put, only Monarchies, with the direct person-to-person relationships backed up by religious oaths, have any track record of being stable over time when there is a multi-year communication lag. (eg. Early Spanish, Portuguese etc. empires.)

    (And here we thought it was a simple plot device to allow young, attractive actors and actresses to play major political characters for whom their grubby romances are actually important to the story of empires.)

  14. Or… gravitational lens telescopy is so much easier and more effective than actual travel that there really may be several-to-hundreds of separate alien groups observing us, but (quantum effects aside) their observation of us does not produce effects we can observe.

    At least until we get our own interstellar observation systems working and we join the galactic community, who can of course communicate (very slowly) among themselves.

  15. See my reply below.
    TL;DR: Because the solar lens works between about 500 AU and 2000AU, any realistic speed gives you heaps of time on target. No deceleration needed.

  16. IIRC, the numbers are something like: the solar lens effect starts to work at around 500AU, is working well by 650 AU, and keeps working, though with variable focus, out to about 2000 AU.
    So, works between ~500 to ~2000 AU. Providing your telescope can vary its optics enough to adapt to the different focii.

    What this means is that if transport to 500 AU takes X years, mostly at a near constantish speed, then you are in “the zone” for 3X years. (Actually a bit better than this because you are slowing down, a bit.)

    A 20 year journey to 500 AU? then 60 years of operation.
    A 10 year journey? Then 30 years of operation.
    5 year journey? Then 15 years of operation.

    All of those are realistic mission profiles. Your power source is probably dying before you drift too far out.

    I think that works out for any realistic speeds. If you are able to get your telescope out that far in 2 years or something, THEN you have the tech to think about slowing down.

  17. who worry about a lot of things ? we are all going to die one day so why bother with anything. often times lots of spinoff businesses can come from tech that had no real purpose to be sought after

  18. I still think discovering other life forms to be quite profound.. intelligent life I think will be harder yet

  19. Then we use the rocket equation, based on the high exhaust velocity of the fission fragments, to estimate the fuel fraction of various missions by the required delta-V. The delta-V of a mission was calculated using the assumption of a single stage rocket that accelerates half the distance and then deaccelerates half the distance for a total specified time duration. For example, a 10 year trip to the gravitational lens point 550AU distant from the sun, would take a delta-V of about 2% the speed of light. We assumed that the fission fragments had an exhaust velocity of 0.05 c (Isp=1.5 million), to obtain a fuel fraction 3% that of the rocket. We then added the mass of the fuel to the mass of the rocket to get the total mass, and multiplied by the acceleration implied by the mission profile to get the thrust required. This thrust had to be provided by fission fragments, which gave us the power level of the reactor, assuming some 46% of the fragments provided thrust. From these considerations we could estimate the power required by the fission fragment rocket to enable various missions.

    A 10 year mission to the 550AU gravitational lens point would require only 180kg of nuclear fuel, and a 350MW reactor power, well within the calculated thermal limit of 1GW.

  20. Other than pure science and one could argue incoming rock detection, why would we want this? Tons of money with no real payoff that I can see. We don’t get Tang or freeze-dried ice cream in the end. Let’s put those smart guys to work on water desal and fusion; making home better before we get lost in the clouds.

  21. I’ve occasionally speculated that, while solid fuel rockets typically don’t have the greatest ISP, (They top out at about 285-290, IIRC.) it might be possible to design a solid fueled rocket where the engine just chews it’s way up a rod of uncased propellant at the same rate it burns, enabling arbitrarily high mass ratios.

    A decent solid fuel rocket with a mass ratio of 2000 would have a delta V of about 21Km/s… Which gets you there in about 1200 years. OK, chemical rocketry sucks.

  22. Yep. I know. It is why I so often do the math, without being asked to. Just to check the numbers in more commonly compared units. (Not that 550 or 650 AU means anything at all to 99% of the people bandying about the pop-Sci narrative.)

    As for instance, there are 63282 AU per LY.  
    And 260,000 AU between us and Alpha Cen.
    If you are math-challenged, what is 4 light days compared to 260,000 AU?  Um… ah… hmm… who knows. 4 light days compared to 4 light years (heavy rounding) is at least ¹⁄₃₆₀ the quantity, if we remember there are 365 (or so) days per year. 

    It is a plague.
    And getting worse, year by year. 

    Insofar as I have encountered, it continues to grow, along with ‘advance math’ becoming dilute.

    ⋅-=≡ GoatGuy ✓ ≡=-⋅

  23. Yep, this is the way to establish a communication bridge between two stars, with low power and at an almost arbitrary distance.

    Of course, with the light speed roaming charge, which means latency equals to as many light years there is between you and your target plus a few days x 2 (a huge ping time indeed).

    But that won’t be a problem, if what you want is to keep the homeworld informed of the major local happenings and the other way around. Information can simply flow continually in both senses, with a few requests for special information passing from time to time.

    So good it is, that it would allow some kind of loosely unified interstellar cultures to emerge, retaining a somewhat related science, art and culture.

  24. Couldn’t the earths atmosphere be used as a large lens. You would have to compensate for turbulence but we do that now a days for land based telescope.

  25. Nice to dream but lets us get practical. SpaceX Starship would provide universities with cheap launch capabilities. The universities should get together and design a cheap large space telescope that can be mass produced for cheap. I figure anywhere from $200 million to a $billion. Doing so would keep astronomers busy for the next 100 years.

  26. Once we start using solar sails seriously we can get there fairly quickly. Weird than nobody is focusing on that. Now that private space launching is opening up, private space exploration will follow and that will probably happen.

  27. Thx for the linkie. Interesting article. Apparently by using 2 of the things, one at each end, is the quadrillions-to-quintillions of multiplier achievable.  

    This certainly solves the Drake Paradox (i.e. “where are all the aliens?”)  The most likely answer is, once alien cultures become interstellar, they set up Einstein focus stations pointing all over the place, at a well-known list of previously agreed upon targets.  Everyone is in on the gig, so the network is absolutely huge; Billions of entities could ‘talk’ to each other, limited insofar as we know it only by the length-of-time ti takes information to flow thru spacetime .  

    One cannot “listen in” on this network, because the incredibly low transmission power, and the nano-arcsecond beam focussing afforded by the Einstein ring focus mechanism.  Drake Paradox solved.  

    The difficulty with ordinary space-time comm is the turn-around ‘ping time’ of one’s transmissions. If it takes 15 to 20 years turnaround for ‘packets’, one has to do a lot of “transmit and pray” com, on the hopes that outbound many-layerd error-correction doesn’t require retransmission of any part of a communications stream.  

    NOTE also, that the Nyquist business of trading off bit-rate for transmission power.  If you are happy transmitting 1 bit per second (given the slowness of the turn-around, maybe ok?), then milliwatts might be right. But want a gigabit, then 10⁹ times that power needed.  

    ⋅-⋅-⋅ Just saying, ⋅-⋅-⋅
    ⋅-=≡ GoatGuy ✓ ≡=-⋅

  28. If we are actually going to stop or get somewhat close to stopping, it will take upwards of 35 years from design to operation at the desired distance. We will need good Moon telescopes to find big ice balls close to the desired distance to shed velocity.
    There are things that could speed it up, if you want to invest a lot, and you don’t care if you are there for long.
    If you want to speed up a lot then get a dozen Starships fully fueled in lunar orbit (maybe 70 launches total?). Each takes turns pushing the rest until fuel is depleted and jettisoned. The last one launches the ion drive telescope. A lot of money spent for short data collection window. Better to take longer and stay a while. It would be nice to get data on a few thousand worlds in that direction…and launch a bunch more in other directions. 
    To be clear though, I don’t expect us to launch people to other solar systems for 100 years unless we have truly massive breakthroughs like faster than light…or we can print people when ships arrive. And I see no compelling reason to leave any time soon. We have scarcely started to populate this solar system.

  29. It’s a good mission for a fission fragment rocket; The specific impulse is high enough that the fuel fraction would be reasonably low. Achieving a decent acceleration would be tough, though.

  30. as for the use of Solar Focus to transmit data

    “Now this is interesting stuff because it demonstrates that when we do achieve the ability to create a human presence around a nearby star, we will have ways to establish regular, reliable communications. A second FOCAL mission, one established at the gravitational lens of the target star, benefits us even more. We could, for instance, create a Sun-Alpha Centauri bridge. The bit error rate becomes less and less of a factor:
    …the surprise is that… for the Sun-Alpha Cen direct radio bridge exploiting both the two gravitational lenses, this minimum transmitted power is incredibly… small! Actually it just equals less than 10-4 watts, i.e. one tenth of a milliwatt is enough to have perfect communication between the Sun and Alpha Cen through two 12-meter FOCAL spacecraft antennas.”

  31. I love how this article used “light days” to make it doesn´t seem so much distance at first read.

    It’s like those $4,99 prices… “Oh, it’s just 4 dollars!!!”

    If the article used 550 AU (minimum distance to Solar Gravitational Focus) it would hit harder at the difficulty of it.

  32. This is one of the prime reasons I want at least a century’s worth of life extension. I want to see what those 250k stars within 250 ly of us have around them.

    On a somewhat sobering note, anybody else out there could have already done it with us. Further, if they did, chances are it would have been millions of years ago, not a few centuries, unless some cosmic coincidence was involved. Yet, from what we are already seeing, a planet like ours (even without us around yet) would really leap out begging for notice. Which really helps me lean towards the “there is nobody else out there anywhere close enough to matter” viewpoint.

  33. This is great! I think we do well with clear goals. Getting telescopes to 650AU? That is a very clear clear goal, and seeing extrasolar planets, a sweet carrot. Voyager 1 is at about 150 AU, so 650 AU is not absurdly beyond our abilities. Though, stopping at that distance looks challenging. I hope the range that this works provides at least a few months of good functioning.
    Ion drive seems the most plausible of current or within reach technology. Don’t have much faith in laser pushing.
    Might need some very close slingshot maneuvers with the planets or the sun as well. The best strategy might be launching it at the Moon to change trajectory toward the sun and when it goes around the sun and begins to move away, put out a solar sail to pick up as much momentum as possible. The solar sail would probably be worthless beyond Jupiter. At some point it will be just that much extra mass to push with the nuclear powered ion drive, and it will have to be jettisoned.
    It is probably better to take longer getting there say, 12 years, so you are not going so fast that you have little time at the right distance. I suspect it would be best to first build a 500m telescope on the Moon so you can identify objects at or somewhat close to the distance we want the telescope. If we can find objects with sufficient mass we can take off some of the speed and extend the viewing window with reverse slingshot maneuvers. If we are lucky, maybe even stop at the distance we want to be.

  34. Yep. Any mission there would take decades to just arrive, and require astounding propulsion methods we currently don’t have. Either almost-gigawatt lasers and sails or fission fragment rockets, or something we haven’t figure out yet (electric sails?, fusion?).

    But I think a few could be launched before the 2050s, after we have confirmation of a few interesting oxygen, carbon and water bearing pixel-planets around a few hand picked nearby stars, which means arrival in the 2060s or later…

    So yeah, this isn’t for tomorrow.

  35. Is that 10s of megawatt laser what comes out of the laser or what actually is usable at the spacecraft? How much smaller is the latter than the former? I suspect it is enough smaller that a kilopower reactor would be worth putting on any such spacecraft.

  36. Now, If you filled up an entire asteroid belt with starlink satellites…you could see to the edge of the universe…

  37. As amateur astronomer, I find it fascinating, amazing. In my opinion Earth based giant telescopes are a good thing for limited period. They are easy to repair, improve. It would probably be a bad idea to start sending probes to other solar systems and much better one to observe them from the distance for some time. We don’t know if other civilisations are friendly and it is not worth risking. (Stephen Hawking said, they could be nomads, plunderers). Since there are 100 billions of solar systems with 100 of billions of planets or more and multiply that with 100 billions of galaxies(+-rough estimations) I presume there is some form of life or even many forms of it.

  38. Well, if you look at the JPL slide № 2, it says 10¹¹ light-intensity amplification. 
    If you look at the equivalent area, it is 4.37×10⁹ m². 10¹¹ is 100×10⁹ or 100 billion.
    4.37×10⁹ is 4.37 billion. 
    None of those are close to quadrillions. 
    At least, not as it is written, above.  

    In perspective, 1.3 quadrillion would be 1.3×10¹⁵ or 1300×10¹² or 1,300,000×10⁹ or 1.3 million billion times. I find that a bit far-fetched.  Perhaps you’re right though. 
    Care to share a linkie?

    With the 650 AU 10,000 m by 10,000 m ‘spot’, and doing the same calcs again

    350 W/m² • (10,000 m)² / (2π (10 LY × 365 × 24 × 60 × 60 × 299792458 )²) )
    we get 6.23×10⁻²⁵ W/m² WITHOUT amplification.  

    With 1.3×10¹⁵ amplification, we’re left with 8.1×10⁻¹⁰ W/m² at the proverbial detector sitting at 650 AU ‘orbit’.  

    I kind of rest my case… 8.1×10⁻¹⁰ W/m² from the planet, and 2.84×10⁻³ W/m² from Sol, or Sol is some 2,840,000× brighter than the 10 km by 10 km imaging spot.  You’ll definitely need a star-shade or coronagraph of some exquisite sort. 

    I definitely do make mistakes with the math.  
    I don’t generally make egregious mistakes.  
    And when I do, I am happy to admit it. 
    Thanks for the input!

    ⋅-=≡ GoatGuy ✓ ≡=-⋅

    PSL I believe the milliwatt-transmitter at the EFP for lossless transmission and reception is something of a misnomer. We can still show that the attenuation is substantially around 43,000 quadrillionth the beam homogeneous power.

    Perhaps really tight milliwatts?

  39. The amplification factor due to the lens is 1.3 quadrillion.

    Which is the reason you can get also error free communication with only milliwatts of power and a 1 meter antenna, with Alpha Centauri.

  40. See calculation below. Even by incredibly extraordinary thrusting means, just “getting there” appears to be a multi-decadal or century-plus reality. I coudl be wrong of course. Have been in the past. People are pretty good finding unicorn horn thrusters in grandpa’s dilapidated shed.

  41. 650 AU? 

    I think the problem devolves to “how heavy is the telescope being chucked to the Einstein focal point?”

    Clearly, nothing as massive as the Hubble or Webb.  
    Given that it only need be a few dozen m² in aperture, AND it only delivers a few dozen pixels, nothing more complex than an unfurling piece of space-hardened plastic, patterned as a Fresnel plate, focussing in a few meters onto a nice sensitive 6-some of color specific photodiodes. Maybe just a big handful of kilograms! (Need a power supply, that lasts decades, probably radioactive decay). 

    Less than a ton. More than a loaf of bread.

    Still, getting less-than-a-ton of telescope to the exact right spot to be useful, then slowing it down … to be useful, in a finite amount of time, mostly drift … might require some massive laser thrusting (or neutral beam) tech on the inner-solar-system side. 100 km/s is 21 AU/year. That’d take over 30 years to get there. Almost 40. Maybe OK. But how to stop the 100 km/s outbound drift? Eek! The same numbers as below, to anti-chuck it!

    (100,000 m/s)² × 0.5 = 5000 MJ/kg of kinetic energy.  
    Also, 100,000 N-sec per kg of thrust. 
    Good photon sails deliver 6×10⁻⁹ N-s per reflected joule of photons.  
    100,000 ÷ 6×10⁻⁹ = 15,000 gigajoules/kg. 4,200 megawatt-hours per kg. 
    Well, there’s that. Got to take into account the mass of sail, too.  

    Anyway, fun with math.
    ⋅-=≡ GoatGuy ✓ ≡=-⋅

  42. Hmmm…

    4 light-days

    ( 4 day ) • ( 24 hr/day ) • ( 60 min/hr ) • ( 60 sec/min ) • ( 299,792,458 m/s ) = 104×10¹² m

    1 AU = 149.5×10⁹ m

    104×10¹² m ÷ 149.5×10⁹ m/AU = 693 AU

    Well, there is that. The brightness of Sol would be

    1363 W/m² at 1 AU • (¹⁄₆₉₃)² = 2.84 mW/m²

    How does that compare to the brightness multiplier, said to be 10¹¹×?

    If it is an earth-y planet we’re peering at, then ‘it’ emits roughly 350 W/m² in all directions from every m² of its surface. The calculations call for a 10,000 by 10,000 m ‘pixel’ resolution. That’d be 

    10,000 × 10,000 × 350 W/m² = 35,000,000,000 W.  

    However, in a hemispherical isotropic radiation, one has to divide by 2π, and distance-squared.  

    Brightness, here is natively 6.23×10⁻²⁵ W/m² without amplification.
    6×10⁻¹⁴ W/m² with 10¹¹ amplification.  

    That is still QUITE A BIT DIMMER than Sol. 

    A starshade for Sol would definitely be necessary. No doubt about it. 

    ⋅-⋅-⋅ Just saying, ⋅-⋅-⋅
    ⋅-=≡ GoatGuy ✓ ≡=-⋅

  43. Agreed. This is something I don’t see anyone trying to do before the 2040s.
    At least, not on the government side.
    There will be several projects trying to take pixel sized pictures of Earth like planets in the meantime, which is I guess good enough.

  44. For the next decade or two, the challenge will be to get a single one-meter telescope out to the right spot.

    Err… I hope so, but I think the actual timeline is going to be a lot slower than that.

  45. Yep. And what a magnificent end result of our automated exploration (and eventual exploitation) of the Solar System.

    Because this can only reasonably be accomplished with production in series of the telescopes, and most likely in space.

    The same kind of industrial self-replication capabilities that could give us O’Neill habitats, will also give us a clear look at the closest stellar neighbors.

    When humanity finally goes to the stars, it won’t be blindly.

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