UBSEDS24 is a superpressure balloon launched by our student society. It carries a microcontroller and Raspberry Pi Zero to record telemetry and take pictures. These are then transmitted using ISM band and Amateur radio.

The superpressure balloon aims to float at a steady altitude of about 13km. Previous flights have lasted several months at this altitude.

The UBSEDS24 balloon was built from 50 micron thick PA-EVOH-PE multilayer film and was 1.9 meters in diameter. This size means the longest axis of the balloon and payload combined is more than 2 meters, and so a NOTAM was required and obtained for the launch.

View Images Here

Instructions for 300 baud RTTY

Mass Table

The mass that can be carried by the balloon is limited. For more detail about the balloon design see Richard’s talk at the UKHAS Conference 2016.

Tracker incl. Pi Zero 61.1g
Cutdown 24.5g
Streamer 3.3g
Line etc. 2.2g
Total Payload 91.1g
Free Lift 41g
Total Lift 132.1g

The flight achieved a stable altitude of 13.5 km 2.5 hours after launch. The free lift was double that used for similar previous flights, resulting in a fast and uneventful ascent. The greater upwards force will also allow the balloon to withstand faster downdrafts than previous flights.


The tracker transmits once per minute during launch and when solar power is available. Otherwise it transmits every two minutes, if power is available. At night it may be too cold even for battery operation.

UHF 434.6MHz

Telemetry is transmitted using the error-correcting Contestia 16/1000 mode on 434.635MHz USB.

300 baud RTTY is used for image downlink, except when GMSK is used (see below). Although slow, this was successfully used by Ron G8FJG to receive images. These images can be found here. Instructions for configuring dl-fldigi are here.

Some countries do not allow UHF ISM band operation. Therefore UHF is only transmitted outside the red lines on the geofence below.

This band is also used for GMSK. This performed considerably better than the previous test (UBSEDS22), although the Packet Error Rate (PER) was still high. GMSK is used to downlink images within the red area on this map. The PER was too high to recover any images.


For many countries the balloon transmits APRS packets on local frequencies. In particular this is 144.8MHz in Europe, 144.66MHz in Japan and 144.39MHz in North America.

Some countries do not allow aeronautical mobile operation, which limits the balloon from using the amateur bands. Therefore APRS is only transmitted outside the red lines on the geofence below.


If the balloon returns close to the launch site, it is possible to cut the tracker free from the balloon, so that the Raspberry Pi and SD card can be recovered. The cutdown controller cuts through the 1mm nylon cord by heating a short length of thin steel wire.

Cutdown controller

The cutdown is commanded using a 400 baud FSK signal on the 434MHz ISM band.

This was tested as it moved away from Bristol. The maximum range was 59 km at 05:58 GMT.

Testing at Brandon Hill, Bristol


The streamer is mounted between the cutdown and the tracker, and is intended to slow the decent of the tracker. It is 1m x 0.05m of bright pink ripstop nylon, and is intended to give a sea-level descent rate of 5m/s. It was designed based on results from On the Aerodynamic Drag of Streamers and Flags, A. Carruthers and A. Filippone. See Figure 11.

Habhub tracker


  • Total distance traveled: 8606.5km
  • Great circle distance: 6305.3km
  • Flight duration: 5 days, 2 hours
  • Maximum altitude: 13.6km
  • Countries passed through: gb fr it al mk gr ua ru




Thank you to all listeners who tracked this flight!

Total: 59

Callsign Telemetry Lines Received Longest Path
F80106 fr 473 420.2km
G8FJG_v gb 459 444.5km
F5APQ fr 381 376.8km
UA0SNV-1 348
F4CQA fr 320 246.0km
F1OIL fr 310 396.5km
0x17 gb 281 316.2km
ON5LT be 253 421.8km
DEV88 gb 187 236.1km
g0nzo gb 187 297.8km
JDL gb 165 250.1km
F4GUK fr 161 393.6km
G8KNN gb 131 358.4km
G6GZH gb 126 415.3km
0x17b gb 112 241.6km
RA6LFJ-10 86
M0DNY-ax gb 81 269.5km
G8DHE-1 gb 75 344.5km
F4FKB fr 74 160.9km
TK4LS fr 69 509.5km
UD6L-1 59
IQ7NK-11 50
G1BLO-2 gb 41 61.7km
F5SN 37
UB9JBL-10 36
SV2HNH-1 33
F6HTJ fr 33 402.9km
M0SBU-ax gb 19 67.0km
F5AFY 17
M0SBU gb 16 18.7km
9A0KG-10 10
IW1DTU it 9 499.7km
G8FJG_v1 gb 8 444.5km
LZ0DAP-13 7
MB7UNE-10 7
LZ1OI-4 6
M0XIN gb 5 175.6km
TA2AOB-10 4
PB0AHX nl 4 472.3km
G8FJG_rtlazel gb 3 256.5km
SV2HRT-6 3
F8KII-2 2
RA4FHE-1 2
RN6LJF-1 1
LZ0IOS-10 1
F4DBS-10 1