Part: CubeSense V3
Doc: User Manual
Ver:
1.11
Page: 18
4.3
SRAM over-current protection
When high energy radiation causes a latch-up inside the SRAM, it will result in a high current
draw that may permanently damage the SRAM. CubeSense is fitted with a current sensor to
monitor the SRAM. In the case that the SRAM experiences an over-current, power to the SRAM
is turned off and an internal status flag is set in the CubeSense. Subsequent usage of the sensor
will result in an error response indicating an SRAM over-current. The
“Power”
-telemetry frame
(ID = 26) can be used to read the SRAM current or to check for SRAM over-current. After an
over-current has occurred, the user can clear the over-current flag, to re-enable the use of the
SRAM by using the “
Clear SRAM overcurrent flag
” Telecomman
d (ID = 11). In the case of
permanent SRAM failure, CubeSense will no longer be able to provide detections or image
downloads.
4.4
Nadir Detection Adjustment
Using a false Nadir detection in the satellite EKF can cause instability. The Nadir algorithm of
CubeSense utilizes simple logic to reject such false detections and displaying a Bad Fit error.
There are four adjustable parameters that can be used to reject false nadir detections
–
the
Max Deviation Percentage, Max Bad Edges, Max Radius
and
Min Radius
parameters.
The Nadir sensor algorithm attempts to fit a circle to a number of detected edge points. The
Min-
and
Max Radius
parameters (telecommand 15) can be used to specify the valid range of
the circle radius. This will depend on the height of the satellite in its orbit. The
Max Deviation
Percentage
(telecommand 14) is the tolerance that is allowed for all detected points to lie on
or close to the fitted circle. If there are more than
Max Bad Edges
such points, a detection error
is reported. Do not adjust any of these parameters without first consulting CubeSpace.
4.5
Sensor masking
The Nadir sensor may in some configurations have antennas or other deployable structures in
its field of view. For these cases, a mask on these images is required to avoid false detections.
The sun sensor’s detection algorithm does not require any masking
to function, but in cases
where the object in its FOV is reflective, it may provide false detections. A mask should then
be placed over the reflective area to avoid this.
To mask an object, the coordinates of a square can be sent to CubeSense via telecommand
52. Every pixel that falls within this square will be ignored by the detection algorithms. To mask
more complex objects in the FOV, multiple squares (up to 5) can be defined. To find the
coordinates that should be entered, a full resolution bitmap image should be downloaded
from CubeSense via the GSP program. Open the image with
Microsoft Paint
and hold the
mouse over the top-left corner of the object to mask and note the minimum X and Y pixel
values as shown in Figure 7. Then hold the mouse over the bottom-right corner and note the
