Project Horus High altitude balloon project

Horus 2

Technical Information:

Launch date 8/3/2010, 11:46
Landing date 8/3/2010, 12:45
Flight duration ~ 1 hour
Launch site -35.1276, 138.8477
Landing site -34.9520, 139.5722
Flight path -
Distance traveled 68.8 km
Maximum altitude 1,479 m
Average ascent rate 1.1 m/s
Impact speed 1 m/s (3.6 km/h)
Payload weight 400g
Flight computer Arduino Duemilanove
GPS module Trimble Lassen IQ
Radio transmitter Radiometrix NTX2 25mw
Sensors Internal & external temp
Telemetry 50, 100, 150, 200, 300 baud RTTY, CRC16 checksum
Tracking Ground stations (distributed listener), 3 chase cars, web based tracker


Horus 2 was designed as a test of higher speed telemetry transmissions. The aim was the the payload would step up the baud rate as altitude thresholds were passed:

  • 0-5 km altitude: 50 baud
  • 5-7 km altitude: 100 baud
  • 7-9 km altitude: 150 baud
  • 9-11 km altitude: 200 baud
  • 11-13 km altitude: 300 baud
  • 13+ km altitude: 50 baud

The Horus 2 payload was based around the same flight computer & code as Horus 1, but a custom Arduino shield was made up to simplify assembly & launch. The shield was designed to provide a ground plane for the Lassen IQ GPS antenna, which greatly decreased the time to first fix. The payload was also modified to use lighter gauge wire (for both weight and safety) on the antenna and ground plane.

Launch results:

Unfortunately on launch day the weather was very poor, and combined with other factors, this resulted in a less than satisfactory launch. Once we'd waited for a break in the wind & rain to let the balloon go, we realized that it was underfilled & didn't have the lift we'd wanted - the balloon was only ascending at 1m/s. With the high winds, the balloon was moving faster than we could keep up.

Within 45 minutes, we realized the balloon had stopped ascending (at around 1500m) & was coming down very slowly - and still racing away from us at 80km/h. Fortunately, thanks to those listening in & some contact via the local repeaters, we still had a good idea where it was and we kept chasing it - eventually recovering it in a tree with the balloon still inflated here.

It looks as though the polystyrene payload and parachute absorbed enough water in the rain to negate the small amount of lift provided by the balloon, and the payload slowly came down, where it was dragged along the ground by the wind for some time, until it wound up in a tree.

Given the balloon didn't reach the minimum altitude for the higher baud rates to kick in (5km), the launch was not a great success - though it was certainly a learning experience for us, and we wont be making the same mistakes next time.


Horus 2 was recovered OK, and will be re-launched soon!