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In the front view, starting
from the top left, you can see the ASA Centauri board. This board was
designed 100% by ASA personnel. We chose to have the board manufactured by
a PCB board house for professional looking quality. This board contains the
interface for the sensors on the rocket to our main vehicle processor, the Rabbit Semiconductor RCM
2300. The Centauri board includes, among other things, a 12 bit A/D
converter which yields us 16 mGs of acceleration resolution with our MEMS
accelerometers. The entire Rabbit to Rocket Bus is driven by I2C components
and timing protocol. The Centauri board includes 3 pressure ports, 2-2axis
accelerometers, an 8 channel-12bit ADC, and finally chip referencing
capability all on a I2C Rabbit-compatible bus.
The silver component
just to the right of the ASA Centauri board is the GPS unit. This acquires
GPS in NMEA compatible strings and sends the information to the Rabbit via
9600 baud serial line. The rather large green board directly below the GPS
and Centauri board is the Rabbit RCM 2300 prototyping board. We chose to
use the protoboard for its ease of interfacing to the Rabbit processor and
for its own board power regulation. In future ASA flights we will replace
this protoboard and integrate it into the ASA Centauri II board, which is
coming very soon. The Rabbit RCM2300 is the flight vehicle processor. Our
good friends from Rabbit Semiconductor graciously donated 3 development
kits to our project. The Rabbit processor has performed flawlessly every
time it has flown. The co-state construct in the Dynamic C programming
language has been ideal for multitasking aboard the vehicle. We simply
could not be happier with the Rabbit. The Rabbit records all information
about the rocket, including the outgoing Telemetry, incoming GPS and soon
to be incoming ground commands to the rocket.
Traversing on down the
payload section, we come across the Terminal Node Controller (TNC). The TNC
takes in the serial telemetry formatted by the Rabbit that was sent to the
Rabbit from the I2C bus on the Centauri board. The TNC then formats the
data for packet radio and sends it to our HAM radio. The Ham radio, which
is directly below the TNC on the picture, sends the data to a transmit
antenna which is located towards the middle of the rocket. This data is
received on the ground systems at a frequency of once a second. More detail
will be giving on this during the Communications section of the ground
systems.
The Last big black box
is the battery compartment. This stores all the energy for all the
components on the rocket, except for the Recovery Avionics. The rocket is
powered by 16 AA batteries that keep all the avionics going for better than
100 mins.
The middle picture is
just showing the side profile of the avionics package. It is interesting to
note that the white piece that separates the two halves of the avionics is
two pieces of fiberglass pressed onto a grounded sheet of copper. This
helps cut down on EMI/EMC transfer for the payload.
The last picture is the
back side of the avionics. This contains mainly two items. The Power
Conditioner Control Module (PCCM) and the Video Transmitter. The PCCM takes
in raw battery voltages of 12 and 24 and converts it (using a both linear
and switching regulators) to all the voltages required by the rocket. These
happen to be 3.3V, 5V, 12V, 13.8V. Each component of the rocket was tested
with each type of regulator to evaluate how it performed and then the
decision was made as to what type of regulator to use. We of course wanted
the efficiency of a switcher but wanted the EMI friendliness of a linear.
The last item in the
avionics bay is the video transmitter. This takes video from a bore sited
camera located in the nose cone of the rocket and transmits it to the
ground. Again more detail will be given to this in the Communications
section of the Ground Systems.
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