One area o interest for me is to develop electronic modules for rockets: data loggers, transmitters etc. In 2016 I was asked to develop a telemetry system for an experimental rocket developed by UPB.
Because of the space limitation in my country this rocket cannot be recovered. It had to be launched from “Capul Midia” army facility, towards the sea and to to fell in the Black Sea.
All information about flight parameters had to be transmitted during flight through telemetry. Initial plan was for this rocket to fly up to 50km or even 100km in altitude so an proper ground station was created. The main plan was to have an downlink on 70cm band an uplink on 2m band.
Fig1: Ground Station Antennas
As project progressed the expectation for rocket performance decreased but we keep the initial parameters as guiding values for the development of the telemetry system.
One imposed requirement was to have same ground system an all launches, at least the antenna and rotator system
2016 launch:
For the first flight expectations were high. I asked for permission to have a clear protocol to other radio amateurs to receive the data. It was granted, so I decided to use radio packet AX.25 9600baud G3RUH protocol.
All signal processing was done on a PIC32MX microcontroller and the data was provided through a SPI DAC as audio signal. To minimize side lobes the digital signal was filtered with a raised cosine filter:
Fig2: Raised cosine filtered digital signal
Fig3: Ground Station setup
We decided to use two receiving setups, one using Yaesu 897d plus SCS tracker, and the second setup was using FunCube SDR stick , SDR# and MixW.
Fig4: MixW decoding data
In parallel with MixW a secondary decoding software was developed in LabView:
Fig5: LabView FSK decoder
For some strange reason we had a requirement to fit our telemetry module in the stack of other experiments, so we had to make round PCB’s , not our first option but we accepted for the sake of the experiment.
To keep the situation as interesting the planned “flight computer” that had to be created by another contractor it was not ready so we had to add some sensors next to our telemetry work .. not big deal we can do this. The result was a funny looking contraption that worked:
Fig6: 3D model of the telemtry system + sensors
Flight: during flight we realized how lite control we have over the nonexistent schedule. While other radio amateurs were expecting launch to happen at known hour, the flight was moved earlier without much warning. So a couple of peoples were pretty disappointing for missing this experiment. Fortunately our ground station received data and we were able to provide curves from accelerometer and gyroscope on board of our telemetry module.
2017: For the following year launch we planned a complete redesign of the telemetry system. This time we focused to implement a double layer FEC (or concatenated FEC) Convolutional + Reed Solomon… The new setup looked a lot different:
Fig7: Double layer FEC telemetry system + sensors
The system is based on TI transceivers, and as receiving system we actually used an TI evaluation board with custom firmware to perform the FEC decoding. This design proved very reliable and was used on all three flights that followed.
The rocket was a 2 stage Katyusha (NATO designation GRAD, or the “reactive propelled projectile of 122mm caliber” ) . This rocket had a plastic cone to allow the RF signal to get out since mot of the rocket it’s iron. The receiving station was behind the rocket in the most unfortunate position because it’s not in the radiation lobe of the monopole. For this reason the TX had a significant power and RX station big antennas and good LNA made by Kuhne. Placing the antenna outside of the rocket was not an option.
Fig8. Two stage rocket with RF transparent cone
Andrei Hapenciuc 