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Didn't they say the spacecraft will have to move around to get each pixel? That means the planet would turn between pixels and you wouldn't get a coherent image

Didn't they say the spacecraft will have to move around to get each pixel? That means the planet would turn between pixels and you wouldn't get a coherent image. It would also take a very long time to cover 10's of thousands of pixels. May need to send many imagers and combine the results...

jackmott 4y ago
These are all easily solved problems we are familiar with compared to getting spaceships there accurately. But yes usually these plans call for a swarm of these ships
WithinReason 4y ago
I wonder if you could use just 1 spacecraft and actually exploit the rotation of the planet to "scan" the planet surface in 1 dimension. The movement of your telescope would provide the other dimension, so in a slow fly-through you could get a 2D image of the planet surface. So e.g. imaging a 12000 km (Earth-size) planet at 10 km/pixel would take 1200 planet rotations, each providing a row of pixels, taking about 3 years assuming it's rotating at the speed of Earth. You would just have to know ahead of time the orientation of the planet's axis of rotation so you approach the "focal region" from the right angle.
ncmncm 4y ago
Main thing is that you don't get an image, but a single line of pixels. Such a line taken of Earth is likely to have nothing in it but ocean and clouds. If you sent a swarm, each would get its own line of pixels, as many lines as spacecraft.
- nomel 4y ago
  This is how scanners (the paper/photo kind) work, a single row of pixels, and you can make a wicked camera from one: https://www.engadget.com/2014-12-30-scanner-camera.html https://www.engadget.com/2014-12-30-scanner-camera.html
  - jjoonathan 4y ago
    The single line comes from the trajectory of the spacecraft as it flies through the focus point, reading one pixel at a time. Stopping and rastering is not possible and not close to possible with current technology. Of course, you still want a raster grid, but you have to obtain the grid by sending a swarm of different spacecraft. They each collect a line as they fly through the focus point, and then you can assemble the lines into a grid.
  - ncmncm 4y ago
    Except, it is not. The spacecraft would be taking one pixel, then awhile later another pixel, then another. It could get all kinds of dimensional details at each pixel, with full spectra, polarization, what have you, but just one at a time, unlike your scanner bed, which collects many thousands simultaneously, with as many separate optical sensor elements. After it has collected the whole series, that would be the one, thin row of pixels sent home. The next spacecraft over could collect another line and send that, watching a different bit of planet surface. Two thin line samples would not be very informative, but hundreds could be. It is actually, potentially, a bit better: the planet would be rotating while the spacecraft moves between pixel points, and the spacecraft could continue sampling the entire time, getting at a series of adjacent bits of the planet, until the planet rotates to where the first was sampled, and you can sample the next spot over, looking from an infinitesimally different angle. So, possibly, it is scanning a line across the planet's surface, and then later another line nearby. But each line would cover almost the same line as last time. Of course what it really would do is just watch the planet continuously for years, and send literally everything back, where the planet's presumed rotation could be puzzled out, and then everything could be stitched together afterward. Data from a single probe might suffice to yield an image. In effect, the spacecraft moving is sweeping across one axis very, very slowly, and the planet's rotation is sweeping on another, albeit probably not one at 90 degrees, but at some angle to the first. (It would be very unlucky for the two to align, but wholly possible.) Since all this would happen over days and years, the image would end up with an average of that many years' weather, so nothing like a snapshot. But if cloud cover ever breaks, any continents shores would anyway be sharp.
    - 4y ago
- hinkley 4y ago
  A few years ago I saw that someone had taken a photo of their back yard using a single light sensor. The idea was that at each moment of each day, the sun was in a different spot in the sky, and each day it shifted toward or away from the equator. So they stitched the samples together mathematically based on timestamp and a 3d projection of the earth. You could tell it was a backyard, but it was very gauzy, like that moment when you first wake after a nap.
  - floxy 4y ago
    Dual Photography https://graphics.stanford.edu/papers/dual_photography/ https://graphics.stanford.edu/papers/dual_photography/
marmakoide 4y ago
Having access to a single pixel of a rotating object is enough to get an image. It's more or less the 3d equivalent of an inverse Radon transform

jackmott 4y ago

These are all easily solved problems we are familiar with compared to getting spaceships there accurately. But yes usually these plans call for a swarm of these ships

WithinReason 4y ago

I wonder if you could use just 1 spacecraft and actually exploit the rotation of the planet to "scan" the planet surface in 1 dimension. The movement of your telescope would provide the other dimension, so in a slow fly-through you could get a 2D image of the planet surface. So e.g. imaging a 12000 km (Earth-size) planet at 10 km/pixel would take 1200 planet rotations, each providing a row of pixels, taking about 3 years assuming it's rotating at the speed of Earth. You would just have to know ahead of time the orientation of the planet's axis of rotation so you approach the "focal region" from the right angle.

ncmncm 4y ago

Main thing is that you don't get an image, but a single line of pixels. Such a line taken of Earth is likely to have nothing in it but ocean and clouds. If you sent a swarm, each would get its own line of pixels, as many lines as spacecraft.

nomel 4y ago
This is how scanners (the paper/photo kind) work, a single row of pixels, and you can make a wicked camera from one: https://www.engadget.com/2014-12-30-scanner-camera.html https://www.engadget.com/2014-12-30-scanner-camera.html
- jjoonathan 4y ago
  The single line comes from the trajectory of the spacecraft as it flies through the focus point, reading one pixel at a time. Stopping and rastering is not possible and not close to possible with current technology. Of course, you still want a raster grid, but you have to obtain the grid by sending a swarm of different spacecraft. They each collect a line as they fly through the focus point, and then you can assemble the lines into a grid.
- ncmncm 4y ago
  Except, it is not. The spacecraft would be taking one pixel, then awhile later another pixel, then another. It could get all kinds of dimensional details at each pixel, with full spectra, polarization, what have you, but just one at a time, unlike your scanner bed, which collects many thousands simultaneously, with as many separate optical sensor elements. After it has collected the whole series, that would be the one, thin row of pixels sent home. The next spacecraft over could collect another line and send that, watching a different bit of planet surface. Two thin line samples would not be very informative, but hundreds could be. It is actually, potentially, a bit better: the planet would be rotating while the spacecraft moves between pixel points, and the spacecraft could continue sampling the entire time, getting at a series of adjacent bits of the planet, until the planet rotates to where the first was sampled, and you can sample the next spot over, looking from an infinitesimally different angle. So, possibly, it is scanning a line across the planet's surface, and then later another line nearby. But each line would cover almost the same line as last time. Of course what it really would do is just watch the planet continuously for years, and send literally everything back, where the planet's presumed rotation could be puzzled out, and then everything could be stitched together afterward. Data from a single probe might suffice to yield an image. In effect, the spacecraft moving is sweeping across one axis very, very slowly, and the planet's rotation is sweeping on another, albeit probably not one at 90 degrees, but at some angle to the first. (It would be very unlucky for the two to align, but wholly possible.) Since all this would happen over days and years, the image would end up with an average of that many years' weather, so nothing like a snapshot. But if cloud cover ever breaks, any continents shores would anyway be sharp.
  - 4y ago
hinkley 4y ago
A few years ago I saw that someone had taken a photo of their back yard using a single light sensor. The idea was that at each moment of each day, the sun was in a different spot in the sky, and each day it shifted toward or away from the equator. So they stitched the samples together mathematically based on timestamp and a 3d projection of the earth. You could tell it was a backyard, but it was very gauzy, like that moment when you first wake after a nap.
- floxy 4y ago
  Dual Photography https://graphics.stanford.edu/papers/dual_photography/ https://graphics.stanford.edu/papers/dual_photography/

marmakoide 4y ago

Having access to a single pixel of a rotating object is enough to get an image. It's more or less the 3d equivalent of an inverse Radon transform