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The
mechanics and the thermic
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Part 2
By Ghislain Ruy, F1HDD
Translation Fred, CU8AO
The output connectors are SMA type , except for the triggering one that is military grade.
The boxes are polished (we can use them as a mirror) to improve the thermal control. The solution retained is the double isolation: to let go in or out the less heat as possible.However, it is obvious that the most risky part is in the functioning temperature: the range should be between -20 and +70ºc, that allows the batteries to give their maximum capacity, without overstressing the electronics. Below -25º, the results are unknown.
The inside walls of the box are not polished, and consequently slightly reflecting, to preserve inside heat: It should allow rising of internal temperature in case of bad illumination. In fact, illumination is at most 50% of a "normal" satellite, because of shadows dues to the ASAP and the attaching hardware of SPOT. A "0 illumination" is possible, and some precautions have been taken for this eventuality
[photo astrium]
Missions, electronic configurations on the ASAP:
The mission fixed to the CU´s is the results of a compromise between what we intended to do , what we had available and what could be made in a reasonable delay.
It also has been determined to allow a good lifetime, giving easily readable signals from an 800km circular orbit.
Finally, some interesting/funny features were necessary, to attract the interest of ham in experimentation and bring to us knowledge for eventual similar missions.From all this, we made the following mission parameters:
CU1 (Util Load 1)
It transmit 8 channels of telemetry which represent the values:
- -Vbatt
- -2 optical sensors.
- -The temperature of an optical sensor to correct readings.
- -2 temperature readings of lower battery block.
- -1 temp. box on the bottom of X+ side.
- -1 temperature of the VCO and buffer.
The measures are done just before the transmission.
Frequencies:145.840 MHz, 120mw divided between two verticals monopoles located diametrically opposed on the ASAP.
Voice modulation: NBFM
Data Modulation: subcarrier at 1200 hz modulated at 400 bds Manchester differential.
The frames have 6 bits of data, including 1 of verification, and follow 4 bits of syncro .The duration is about 0.7 second. This value has been chosen to allow at least one good frame , with the expected fading of the signals.
The estimated lifetime is 40 days.
Sequence:
- 3 seconds of telemetry.
- 22 seconds of silence
This sequence is repeated 4 times, and followed by 7 seconds of silence, one voice message, 7 seconds (max) of silence , then strart over.
It transmits 16 channels of telemetry which are the values:
- Vbatt
- I TX
- 2 optical sensors (incidence angle and illumination)
- Temperature of 1 optical sensor to correct readings.
- 2 temperatures of lower batteries block.
- 1 temp box on the lower X+ side
- Temp TX
- RF power
- 5 V TX
- 7.5 V TX
- Temp digital recorder.
- 3 "0" channels.
The measures are done just at the end of the transmission and are sent on the next frame.
Frequency:435.270 mhz, power:1.3W divided between two monopoles fixed on the box
Voice modulation: NBFM.
Data Modulation: subcarrier at 1200 hz modulated at 400 bds Manchester differential.
The frames have 6 bits of data, including 1 of verification, and follow 4 bits of syncro .The duration is about 0.7 second. This value has been chosen to allow at least one good frame,with the expected fading of the signals
It was planned to install 3 gyrometers, but we lack of time to calibrate them, and install them as-is would have given too imprecise (and useless) indications.We had to decide not to install them and reuse the available telemetry channels for the electronics .
The antennas have been installed on the box,resulting of a proposition of Jean-François that observed that the antennas will no be sufficiently clear on the ASAP, and that we will have less losses on the top of the box. Beside, it have the advantage of shorter lenghts of coax.