WG2 Flight Update

ms_wg2_final_smallThe WG2 long-range balloon flight is now over as far as being able to track it is concerned; it is quite likely still in the air somewhere over Russia, however (as of 27/6/14).

The flight performed much better than we expected for a first try, covering a known distance of 1500 miles, to finally go out of ground-station range over Ukraine about 31 hours after launch.  During the flight the balloon passed through a total of 8 countries (some more than once).

The balloon’s telemetry signal was received across Europe by a network of volunteers (many of whom are amateur radio operators), and fed into the central Habitat system operated by the UK High Altitude Society (UKHAS).  This enabled the flight to be seen in real-time through the spacenear.us site.

At the time contact was lost the balloon and the tracking electronics remained in good health, with the battery expected to last perhaps a further 8 to 10 hours.  Long-range flight predictions from the last known point suggest that the balloon will, if it remains airborne, travel up into Russia and then continue East towards Siberia.

The flight did show signs of coming down as night approached on the Wednesday.  The night-time descent was much deeper than expected, and it spent much of the night bobbing precariously up and down as it travelled across the North Sea, The Netherlands and into Germany.  Luckily sunrise isn’t a long wait in June, and with the associated warming and re-pressurisation of the envelope the balloon rose back to about 8 km, where it remained.  Meteorological sounding data suggests that the loss of altitude may have been due to ice accumulation.

As a test of the new tracker the flight was extremely useful, uncovering two minor bugs which led to the speed reading being out by a factor of 10, and also the position error over Norfolk that can be seen in the picture.  Both of these bugs have been identified and will be fixed in time for the next flight.  Apart from this the system operated as designed despite reported temperatures below -30°C for a lot of the flight.

Frequency stability of the downlink could have been better, but was acceptable considering the decision not to use a temperature compensated oscillator (for cost reasons) and did not impede reception.  A future flight will test the possibility of locking the reference clock to the GPS time pulse, which should make locating the transmission much easier when at the limits of range.

The use of the Olivia data mode for the downlink instead of the more usual RTTY was a great help, with some stations reporting perfect reception despite the balloon being below their radio horizon at the time.  This mode makes use of Forward Error Correction (FEC) and interleaving in both time and frequency to dramatically improve the link performance in weak signal conditions, or in the presence of interference.

Finally I would like to extend thanks to everyone that helped with reception (a list of stations will be published once I have extracted it from the data).  PE2G in the Netherlands showed particular dedication by staying up all night on Wednesday into Thursday!

Pictures of the tracker and various screenshots can be found on the gallery.

Tracker technical details:

  • Transmitter frequency: 434.45 MHz (nominally)
  • Output power: +6 dBm (4 mW)
  • Modulation: OLIVIA 8/1000 with CW pips between bursts
  • Typical range: Horizon limited (300 km+)
  • Power supply: 0.7 V to 2.0 V (single AAA lithium cell)
  • Transmitter: SiLabs Si4060
  • CPU: Freescale Kinetis KL05Z32 (ARM Cortex M0+)
  • GPS: uBlox MAX7C (from HAB Supplies)
  • Total payload mass including battery and antennas: 12 g (with connector snap-off section removed)

Update: Here is the list of stations that participated in tracking the flight.

Callsign Lines
PE2G 1082
G6GZH 869
G8KNN 847
G8KNN-1 840
G0WXI 786
RevSpace 768
M0MKS 606
G1DYQ 571
PB0AHX 546
G8ZBJ 526
SP8CGR 499
OM1ATS 430
G8APZ 416
M0JCU 372
F1OIL 359
OM5KV-1 332
UT3BW 324
SQ6IYD 295
HA6NM 264
DutchMillbt 246
M0UPU 244
DJ3AK 237
G6SUQ 229
G7OGX 228
G8FJG 228
G3ZGZ 226
DL7AD 225
SP3MCY 215
OM5KV 210
Funsat-DW0307 178
G0CXW_2 169
SP3OSJ 156
F5APQ 152
OM1GX 149
WD8MNV 142
M0DNY_websdr 141
Leo 137
SP6IWQ 124
G4MYS 118
M0ION 113
amell 106
0x17 105
G4SGX 104
UR5BGE 102
ha2ecm 100
HA6NN 90
W7QO_websdr 89
G4MYS-2 86
jijdaar 81
m6dnu 64
M0MKS/M 54
G0TDJ 38
r00t 36
Andboga 36
G4YHE 25
OM2AMR-1 11
PB0AHX-remote 4

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