Image stabilization and pixel shifting for a nanosatellite imaging system
A satellite imaging system includes a camera with a pixel shifting mechanism, thermally stable imaging payload, and high-stability attitude determination and control system (ADCS) to improve image resolution. To address the overall stabilization requirement, the satellite incorporates a number of design elements that, in combination, provide the stable result required for good imaging.
1. A satellite imaging system, mounted on or within a satellite adapted for use in orbit, for capturing images to be taken from the orbit, the satellite imaging system comprising:
a telescope section arranged to receive incoming light;
a lens system, comprising at least one lens positioned in an optical path;
a camera having a sensor array that shifts in a perpendicular shift relative to an optical axis of the optical path while capturing an image to be captured to improve the resolution thereof; and
an attitude determination and control system, whereby the the attitude determination and control system stabilizes the satellite while capturing the image to be captured, in part by counteracting movement of the satellite that is caused by, or is predicted to be caused by, the perpendicular shift of the sensor array.
2. The satellite imaging system of claim 1 , further comprising:
an active disturbance cancellation system, whereby a combination of mechanisms, sensors, and computer algorithms reduce the effect of disturbances while capturing the image to be captured; and
a high-rate data readout and recording system, whereby multiple images can be collected within a shortened time period to limit the effect of vibration upon image quality.
3. The satellite imaging system of claim 1 , further comprising:
a pixel shifting mechanism capable of shifting the sensor array relative to the optical path; and
an image capture system coupled to the sensor array to read sensor readings and record pixel light readings, wherein the pixel light readings correspond to the image being captured,
wherein the sensor array comprises pixel sensors that can sense light energy impinging on pixels of the sensor array, and wherein the sensor array is positioned to receive the light energy from the optical path after the light energy has passed, at least in part, through the lens system.
4. The satellite imaging system of claim 3 , further comprising:
an attitude determination and control system that counteracts movement of the satellite that is caused by, or is predicted to be caused by, movement of the sensor array and/or operation of the pixel shifting mechanism.
5. The satellite imaging system of claim 4 , wherein the attitude determination and control stabilizes the satellite for a duration of an exposure time of the image being captured.
6. The satellite imaging system of claim 3 , wherein the pixel shifting mechanism comprises a motor mechanism that can move the sensor array one half of a pixel width left/right and/or one half of a pixel width up/down.
7. The satellite imaging system of claim 3 , wherein the pixel shifting mechanism comprises a motor mechanism that can move the sensor array one third of a pixel width up, one third of a pixel width down, one third of a pixel width to the left, one third of a pixel width to the right, and combinations of those movements.
8. The satellite imaging system of claim 3 , wherein the pixel shifting mechanism comprises semiconductor elements that expand/contract upon application of an electrical potential.
9. The satellite imaging system of claim 8 , wherein the pixel shifting mechanism comprises piezoelectric elements that provide movement of around a few microns.
10. The satellite imaging system of claim 1 , wherein the image being captured has a resolution higher than that of the sensor array as a result of a combination of sensor readings read from a plurality of positions of the sensor array in the optical path, wherein the plurality of positions comprise subpixel shifting.
11. The satellite imaging system of claim 1 , wherein the sensor array comprises individual pixel sensors formed of a charge coupled device (CCD) or of a complementary metal-oxide semiconductor (CMOS) sensor, in a square two-dimensional array.
12. The satellite imaging system of claim 11 , wherein the square two-dimensional array comprises a pattern of pixels sensitive to different colors.
13. The satellite imaging system of claim 12 , wherein the different colors are a red color range, a green color range, and a blue color range, with a ratio of approximately half green, one quarter red, and one quarter blue.
14. The satellite imaging system of claim 1 , further comprising a pixel shifting mechanism capable of shifting the sensor array relative to the optical path, wherein the pixel shifting mechanism comprises a plurality of plates configured to move such that a center of mass of the plurality of plates is substantially stationary while the plurality of plates moves relative to the optical path.
15. The satellite imaging system of claim 14 , wherein the plurality of plates comprises two plates, each having mounted thereon a portion of the sensor array.
16. The satellite imaging system of claim 14 , wherein one plate of the plurality of plates has mounted thereon all sensors of the sensor array.
17. The satellite imaging system of claim 1 wherein the attitude determination and control system comprises a plurality of reaction wheels and/or a plurality of torque rods to provide for rotational control of the satellite, thereby imparting a torque about a center of mass of the satellite and/or causing the satellite to start rotating, rotate to a position and stop at that position to allow for the optical path to remain pointed at a fixed point on Earth even as the satellite moves along its orbit.