Fiasco with Gyro. Hope with magnetic sensor. Power Plant.
Testing gyro was calibrated for range of temperatures, calibrating values 64K of 3x16-bit words was stored in memory. Gyro has fixed in stable position with X axe oriented to a North Star, Y to the West and Z orthogonal to X-Y forward to the Earth’s rotation axe. Drift of a zero was in a range of 5 degree per 256sec (4 minutes). Sensor was forced to max possible sensitivity (undocumented future in ITG-3200, but it gives 1/115=0.009 degree per sec – it still require 10 better sensitivity to detect earth rotation). Sensor set to 296 samples per sec (microprocessor is slow – needs to be at least 32MHz). Zero drift was random (range from 0.01 – 5.0 degree per 4 minutes) and not depend of a derivative of a temperature. Drift was related to an orientation of a gyro, and on a previous gyro’s readings (possible that factory calibration gives drift).
Such drift is totally not acceptable for navigation, needs to eliminate error first. On the Earth or on the Moon it is possible to do this by reading accelerometer and magnetic sensor orientation. Field of gravity is stable on the Earth and the Moon, and magneto sensor readings on the Earth are stable too (for sure to some extend). Reading from accelerometer gives absolute reading. Flying average from accelerometer can give good indication of an absence or existence of rotation and can allow to exterminate gyro’s zero drift.
Normally this is done by Kalman filter, it assuming that absolute direction is for a gravity field and based on that assumption correction to gyro’s readings (speed of a rotation) can be done. Kalman filter works good when noisy measurements done for predictable object. It is nice and well known approach, source code available for such filters including combination of 3-x accelerometer and 3-x magneto sensor. But such approach is not working on the low Earth orbit. Hope is for a magnetic sensors – first needs to calculate flying average of a 3D magnetic field orientation. If flying average during 2 sec (500 samples) is not in moving than current drift of a gyro assumed as a zero.
Then time measured for a slowest changes (derivative of a orientation) gives point on a orbit when satellite crossed equator. Two times btw crossing the equator can give Keplers elements of a orbit. Checking point will be apogee and perigee – direction of a magnetic field at those two points must achieve maximum of a derivative of a direction of a magnetic field. Current position of a magnetic poles will give offset for a final ... see more on ... http://www.adobri.com/ProjectComm.aspx
Solar panels combined in 4 groups. 4 high capacitance capacitors can be charged by any solar panel’s groups . To control such process require 16 pins for a control. Then 4 charged capacitors can give power to 4 main users of a power – (a) backup microprocessor, main electronic including main computer; (b) backup communication; (c) main communication amplifiers; (d) orientation stepper motors/ 2.4GHz antenna deployment. This power distribution require another 16 pins. Power source for main communication amplifier controls by pins on a STM_BT microprocessor. Power source for stepper motors controls by STM_SM microprocessor. Power source for a main electronics controls by STM_MEM microprocessor.
Assumed 3 different mode of power operation.
- Initially first capacitor gives power to STM_MEM module. When it powered up it can monitor state of any 4 capacitors and switch itself power source to any of it. At this point all onboard electronics and users are switched off.
- Then at a time when it is enough power accumulated by power plant STM_MEM can go to second mode - powered backup communication module, gyro module, camera module, stepper motors/orientation module, main communication module. Each of the modules on a request from command stream from STM_MEM can initiate ... See more on ... http://www.adobri.com/ProjectCr.aspx and http://www.adobri.com/ProjectComm.aspx