On 2th April 2016. our test flight campaing has begun with the first launch of the year. The flight was carefully planned and the main goal was to flight-test the ReHAB v1.1 system which was bench-tested for a year.
For this flight we used the ReHAB v.1.x hardware which got an enhanced flight software since last year. In the new firmware the wathcdog and other timeout and safety features were fixed so we gained a higher reliability level. During the bench-tests no full system stop was occured, the new flight software handled all the malfunctions or risky situations as expected.
On-Board Computer (OBC)
The On-Board Computer (OBC) is based on an STM32F4 AMR cortex microcontroller. The OBC organizes the communication between the modules, collects house-keeping and GPS data and also compiles the telemetry packets. System events are logged and can be downloaded from the SD card of the OBC. The House-keeping data is also stored on the SD card.
- STM32F407VGT6 32-bit ARM Cortex-M4F microcontroller, 1 MB Flash, 192 KB RAM
- System Clock: Real Time Clock (RTC)
- UART connection for GPS modul
- CAN controller + CAN transceiver
- DCMI port for integrated camera control
- Micro SD-card slot
- Diagnostic port
- 2×20 pin stackable UPRA-BUS connector
The new On-Board Computer is produced in the UPRA form factor, in the size of 70x75mm (2.76″x2.96″). This was the second flight of this version of the OBC.
GPS coordinates, altitude and speed was provided by an NV08C-CSM module. This GPS reciever was designed for high-altitude operations and has an altitude limit of 50 kms (~32 miles), so we could track the entire flight of the balloon. The NV08C module communicates with the OBC through NMEA standard. Parsing the proper NMEA messages longitude, latitude, altitude and speed data could be processed. Each GPS NMEA word has time stamp which used for synchronize the system time. Time Sync is needed, because the Real Time Clock (RTC) unit of the OBC produce increasing slip due to the temperature decrease.
The internal temperature and the stabilized supply voltage was measured by the microcontroller of the communication unit. These data, the exchange between the COM and the OBC during the preparation of the radio communication action.
Integrated Camera System
The telemetry system has an integrated small resolution CMOS camera module that stores pictures on the SD card of the OBC. The pictures taken by the Integrated Camera System (ICS) are available for every unit of the UPRA system thus the pictures taken could be sent back via the Communication Module during flight.
The Integrated Camera System was tested before and now it is upgraded with a fish-eye lens of a 180° angle of view.
- Resolution: 320×200
- Color: yes
- Native angle of view: 65°
- Modified angle of view: 180°
- Picture format: BMP
- Connection: Integrated (DCMI)
Our self made communication unit was designed around an SI4461 FSK transreceivier integrated circuit produced by Silicon Laboratories. It could be widely configured to different solutions. The desired frequency, data rate, modulation and fequency deviation can be set. As for the test flight, the future goal is to involve the amateur radio community. Therefore, appropriet settings was choosen so they could receive data from the balloon. Our transmit frequency was in the ISM range near the 70cm band which is popular among amateur radio operators. An avarege HAM radi ohas a maximal bandwith up to 3kHz, so the data rate, frequency deviation and bandwith had to be chosen that fit into this range. So we used the 625bps data rate and 625kHz deviation. To increase the spectral efficiency, Gaussian FSK modulation was used. Since the communication is done via an additive noisy channel , it was necessary to filter out the erroneous packets , so they are supplemented with CRC error code.
The orientation of the capsule is changeing continuously, so an antenna was integrated into the system, which radiate in all directions as far as possible. Thus, a monopole antenna was connected the probe. Because, according to the ISM standard limited radiated power, the resulting SLOS was compensated by the antenna unit of ground station.
The control room of the primary ground station was installed in the radio room of HA5KFU College HAM Radio Club and we used an antenna placed on the roof of the twenty story building of Schönherz Zoltán Student Hostel. Unfortunatelly due to the type of the antenna and the large amount of environmental noise we had to relocate our groundstation. For the rest of the flight we used a handheld yagi type antenna.
The gorund station used the same radio hardware as the COM module on the balloon with a GND firmware. We used an Arduino UNO board to control the radio module and transmitted the telemetry packets to a PC. This prototype version of our ground station hardware is not suitable for picture download, so we couldn’t test this function in this flight.
The ReHAB-150 capsule prototype was used during the testflight. It has a reinforced aluminium frame which not only provides the antenna fastening, but also allows to connect outer sensors and experiments easily. The probe has a multilayer insulation which built up from a polystyrol box covered with space-blanket.
The parachute is a self made octogonal desing made of lightweight, bright color fabric. In the design and manufacturing, the Pulcsi és Foltmékör fabric processing team helped us.
The designated liftoff time was 9:00(UTC).
The launch site was assembled one hour before the launch behind building Q of the Budapest University of Technology and Economics. Meanwhile on the ground station the configuration of control room and the secondary GPS tracker was executed. We used PAWAN 1200gr balloons for the flight as usual. Until the gas has arrived the last pre-flight communication tests were performed and the parachute was prepared. Everything went as planned yet we still managed to gain a 30 minute delay.
10:30 – Helium Gas arrives. Inflation tools are prepared
10:50 – Beginning of inflation
11:10 – Balloon is filled. PayLoad Train is connected to the balloon
11:20 – GO from the ground station. Every system GO, GO for launch
11:30 – Launch
11:35 – Proper telemetry messages arrived, balloon is trackable. Disassembly of the launch site
11:50 – Ground station relocation
13:31 – Telemetry packet with the highest altitude value: 32888 m (~107900 ft)
15:20 – Last telemetry packet arrives: 1426 m (4678 ft)
16:00 – Recovery team liftoff
Recovery of the probe
The last position of the balloon was 4 km (2.5 miles) from the Kecskemét Airforce Base in east-north-east direction at the altitude of 1426 m (4678 ft). During the search we used a mobile ground station to catch any radio messages from the balloon. The search was started from the last known position to the direction we predicted from the last few trackpoints of the balloon. Unfortunatelly we didn’t count the wind direction and speed and we went to the opposite direction az the balloon. The wind direction changed at 1500 m (5000 ft) of altitude from WNW to ENE which changed the path of our balloon.
During recovery we searched the area East from Kecskemét, but this just let us further and further from the real position of the balloon..
The search was countinued until dark, but with no results so we returned to Budapest without the probe.
After the flight we spent the time with processing of the radio telemetry data, simulation data and meteorological data of the launch day. After the processing it was clear that the balloon changed its direction at 1500 m (5000 ft) of altitude and headed to west-south-west. With the processed data we determined different landing zones.
The MH 59. Szentgyörgyi Dezső Military Airforce Base was in one of the landing zones, so we contacted with the flight control crew of the base, but until today no foreign objects were reported on the base. Unfortunatelly the balloon is too small for the modern flight radars to identify so the flight control crew couldn’t help us with flight data either.
After determine the most possible landing zone (red area on the picture) we tried a second recovery mission. After we arrived at the location it was clear to us that it would be an impossible mission. Most of the landing zone is covered with thick woodland area. We checked the most possible landing spots in the forest, but we would need another full-day mission with 4-6 recovery personnel to cover the whole woodland area.
We asked the residents of the nearby farms if they seen our balloon, but they couldn’t help us with usable information. Because the batteries are dead since the landing, only visual search could lead us to the balloon.
It was a succesful fligth since we proved that the fligt computer was operated as expected. We had stable radio telemetry from 32888 m (107 900 ft) altitude and it was stable the whole flight.
Although we didn’t find the balloon we don’t give up hope. We will organize another recovery mission. We also hope that someone find the balloon, and contact us, because there is valuble information and pictures on the SD-Card.
We had a lot of help during the preparation and the flight. The ground station was installed in the HA5KFU College HAM Radio Club operator room. The team of BME-GND University Satellite Ground Station helped us in the preparation of the live radio tracking as in previous flights.
We would like to thank all of you, who helped this balloon launch carried out!
Many thanks for the pictures to Csaba Pálos!