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the reel and the reel motor. If a sensor is not working properly another sensor can
be used and the experiment can be executed as planned. For example by using
the altitude data from the GPS on the FISH, this can replace the reel’s speed
sensor but in lower resolution.
If the performance of the experiment, especially the motor, is as expected, the
slow reel up can be executed. During the way up, the reeling process will be
stopped to demonstrate the ability to take sensor values at different altitudes. As
soon as the FISH is back in the payload bay the data transfer performance can be
analyzed in aspect of average data rate and maximum transfer range.
If all tests went well to this point, then the first drop mode test can be executed.
3.3.1.6 First drop mode
If all sensors and actuators are working as expected, the drop can be initiated.
This drop will be a regular one for about 2 seconds. At the end of each CATCH,
the temperature of the reel motor is verified. If the motor temperature is too high,
the next drop will be delayed.
The sequence of the experiments can be chosen freely. However, since the
experiment is normally executed by an automatic sequencer, a preset sequence is
used. This sequence is most probably a drop followed by a slow reel. Then a short
break is probably necessary to transfer all sensor data from the FISH to the
payload. The drops can be repeated as often as necessary. However, the limiting
factors are the duration of the balloon in free-float, the temperature of the reel
motor, the degradation of the brake and the size of the flash memory storage.
Before the gondola is cut off from the balloon the FISH has to be reeled up and
stowed in the payload bay. As soon as the GPS and the pressure sensor detect a
high sink rate over an extended period of time, the reel.SMRT experiment is put
into power-safe mode again with only the essential sensors still being still powered
on. This time however, the high bandwidth accelerometer on the FISH that
measures acceleration in the z-direction is kept active. It is then possible to detect
the impact of the gondola. After impact detection, the experiment shuts itself down
completely in order to minimize the risk of short circuits in case the gondola lands
on a wet surface.
3.3.2 Tether break scenario
If during the experiments the tether should may break and get loose, the GPS
altitude sensor and the pressure sensor on the FISH will detect that the situation
by( considering high sink rate for more than 5 seconds and, significantly increasing
of the pressure). This triggers the deployment of the parachute which will can
decrease the sink rate so that the FISH does not pose a threat to living creatures
on the ground. If the electronics on the FISH survives after the impact, it is
possible to constantly transmit the GPS position data via the ZigBee to support the
recovery team in finding the FISH.
RXBX-09-03-15_PDR_ESA.docx