UBSEDS25 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 UBSEDS25 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. This launch was unusual as the conditions were cloudy at launch. A 2nd “tow balloon” was used to pull the main balloon through the cloud deck. This tow balloon was timed to disconnect at 05.55 BST, and this successfully occurred at an altitude of 4.6km (15,000 ft).

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.

This table does not include details of the tow balloon. See the section below.

Tracker incl. Pi Zero 63.5g
Cutdown 24.5g
Streamer 3.3g
Line etc. 2.2g
Total Payload 93.5g
Free Lift 22g
Total Lift 116g

The flight achieved a stable altitude of 12.8 km 2.5 hours after launch. The free lift was reduced to about 20g after the previous UBSEDS24 (which used a higher free lift) was lost after a relatively short flight.


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). 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. 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.

Tow Balloon

Habhub tracker


  • Total distance traveled: 3174.0km
  • Great circle distance: 1887.4km
  • Flight duration: 1 day, 15 hours
  • Maximum altitude: 13.1km
  • Countries passed through: gb fr es dz




Thank you to all listeners who tracked this flight!

Total: 54

Callsign Telemetry Lines Received Longest Path
G8FJG_v gb 137 425.8km
0x17 gb 133 271.2km
G1BLO gb 81 396.3km
G8FJG_rtl_azel gb 76 260.3km
EA1FAQ-3 67
G8KNN gb 64 387.0km
M0NRD gb 60 410.4km
EB7GYR-1 44
G8DHE-1 gb 37 349.5km
ED4ZAC-3 37
EA1WS 33
ED7ZAD-3 28
EB1TK-5 28
M0SBU-ax/p gb 27 23.5km
F6DZR-3 25
M0SBU gb 21 135.7km
G8FJG_v1 gb 19 328.2km
IW9GTD-11 19
ED2ZAE-5 18
SV3CIX 18 2455.3km
ED1ZAR-3 16
F4GUK fr 15 445.6km
F5PHW-3 14
F5OPV-10 14
G1DYQ gb 12 295.6km
F1ZGE-3 11
IS0AML-12 9
ED2ZAD-5 9
ED4ZAF-3 8
EA5AHQ-10 7
EA5URJ-10 7
EA5AHQ-15 6
EA5URV-10 5
CT1ENI-8 4
EA6VQ-15 4
M0ZOS gb 4 90.9km
IS0CAP-7 3
F5LRQ-3 3
ED1YAP-3 3
G8IMN gb 2 420.3km
F6FDN-3 1
ED4YAG-3 1
F5ZZC-4 1
ED1ZAX-3 1