Project Horus: High Altitude Ballooning

One of the hobbies I’ve taken up over the last few months has been High Altitude Ballooning with Project Horus. A group of interested people design, simulate, launch and recover a helium filled latex balloon. The flight and recovery generally last a full afternoon, and the balloon regularly reaches above 30km, with 35km being the highest achieved so far.


The ballons fly a telemetry payload which provides tracking through the reception of GPS signals and transmission of position, altitude and speed to receivers on the ground. The payload modulates the carrier of a narrow band FM transmitter in order to produce two tones, a modulation technique known as binary frequency shift keying (FSK).  Data is encapsulated in RTTY strings; 7-bit ASCII characters with coded start and stop bits, as well as parity information. The strings themselves carry a CRC16 checksum; 4 symbols of error detection for each string of approximately 50 symbols.  The transmission rate is 300 baud, at 10mW on the 70cm band using a quarter wave monopole above a ground plane.

The two FSK tones carrying RTTY as seen by fldigi

The receiver is a scanner capable of decoding Single Side Band transmissions. This decoding produces a two tone audio frequency signal that is fed into a computer, and proceed by a modified version of the fldigi program, called dl-fldigi. The modifications provide convenient presets for high altitude ballooning, as well as the facility to upload to, a web based tracking application.  The site allows the team to open up balloon tracking to anyone able to receive the telemetry signal, which can cover a large proportion of the state as the balloon reaches altitude, and provides attribution by listing the call sign of anyone who uploads a sentence.

Web based tracking software

Chase cars are able to also submit their GPS coordinates to, which helps with the chase teams knowing each other’s location, as well as for spectators watching online.

Other payloads have been flown such as APRS beacons, voice repeaters, a few experimental flight computers, and some multimedia payloads for recording the flight.

Horus 8

The first launch I attended was back in October where Horus 8 was flown in order to test my classmate’s final year project; a telemetry payload designed to operate in the Antarctic and transmit data back to a receiver in Australia.  Mark’s project was flown along with the normal Nut flight computer, as well as a HD camera intended to record 1080p video footage for the duration of the balloon flight.

Horus 8 Launch at Grahams place outside of Mt Barker

Some misshaps occured right at the start; the full balloon escaped our clutches and released an amount of it’s helium.  With limited reserve supplies, we flew with the bare minium required to obtain lift, and this meant a very slow accent rate.  Possibly due to the slow ascent rate, the balloon began to float at apogee – not gaining altitude, and therefore the normal drop in external pressure that causes the balloon to expand and busrt did not occur.

Chasing Horus 8: The front seat car computer running dl-fldigi

As it headed out over the coast towards the open ocean, it did burst, but the landing site was 50m out to sea at Carrickalinga.  As the sun went down, a strong offshore wind was pushing the payload further out of reach.  A dramatic recovery involving Terry, the project founder, employing his swimming tallents, and myself jumping on a “borrowed” canoe that we found on the beach resulted in a reocvery of all the payloads, but the electronics did not fare so well having come into contact with the sea water.

Terry on the left, myself canoeing on the right with balloon in tow
Landing path in the sea at Carrickalinga

Horus 12

Since Horus 8, I attended a second launch that was much more successful.  This launch was funded by Tony Wheeler of Lonely Planet, and the idea came from artist Chris Lansell. It flew a HD camera and a still camera, and it obtained some stunning shots at burst of the balloon fragments passing between the lens and the sun.

Horus 8 capturing balloon fragments in the sun as it tumbles

The balloon also captured some images of the recently refilled Murray River system, including Lake Alexandrina. It landed in a field of cows about 100m to the west of the river, just outside of Murray Bridge.

Coming in for landing over the river at Murray Bridge
Yorke Penisula; Gulf St Vincent; Adelaide; River Murray

I look forward to more adventures with the Horus guys as time goes by. Look out for more blog posts about experiments we fly, and the adventures we have whilst recovering them.


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