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17 October 2003

Aussie RocketCam Model Rocket Onboard Inflight Video Camera

by Michael Holden

View an unabridged version of this article by clicking here. We'd like to thank Ray Lahr for bringing this item to our attention. -sg

Introduction
Intrigued by the possibility of transmitting live video and audio from a model rocket to the ground? Me too.

(Note: I learnt in October 2003 that the name "RocketCam" is actually a trademark of Ecliptic Enterprises Corporation. For information regarding the Ecliptic Enterprises RocketCam(TM) systems for rockets, spacecraft and other remote platforms please see Ecliptic's website at www.eclipticenterprises.com.


The Video System
In September 2000 I purchased a microwave video transmitter / receiver system and a CCD bullet or lipstick camera. These AV (audio-visual) transmitters are generally used for domestic video extension or security applications. While the camera, which is housed in a stout cylindrical alloy case, would be more commonly employed in security monitoring application.

Various cameras were auditioned and this camera was selected for its image quality, dynamic range, high resolution and effective auto-exposure system. It is heavier, larger and less convenient to mount than the many alternative designs, but I am prepared to wear those disadvantages in order to obtain superior pictures. Examine the CCD cameras on display and compare the image quality of each, paying particular attention to noise, detail in the image and whether high contrast creates a problem for the camera.

Often inflight video downlinks are accomplished using mirror systems however it was a design requirement for my system that the camera have a direct view of the ground.

This transmitter can transmit one of four frequencies:

  • Ch1 = 2413 MHz
  • Ch2 = 2432 MHz
  • CH3 = 2451 MHz
  • CH4 = 2470 MHz.
In Australia the maximum power output is limited to 10mW. Note that these 2.4GHz microwave wireless video links use FM modulation for the vision while terrestrial analog broadcast television (ie normal TV) is AM modulated, however both systems use FM modulation for the audio.


Proof of Concept
I decided to use off-the-shelf video hardware so that I could quickly establish whether the concept of live video transmission from a model rocket was viable. At the time I didn't know a lot of radio theory and was concerned about issues such as:

  • the limited range of this very low powered system (10mW output power)
  • the effect that the rapid motion of the rocket might have on the signal ie doppler shift or other effects
  • the attenuation of the signal cased by the airframe when it was between the transmitter and receiver as the rocket rolled during flight
  • the impact of the changing orientation of the transmit antenna with respect to the receive antenna as the rocket arced over at apogee. (I was particularly keen to capture parachute ejection and was not disappointed once this was finally accomplished. I love watching the parachute unrolling and inflating in slow motion as the horizon drifts into view behind the rocket.) The deep blue of the sky suggests that the camera might have a polarising filter.

The Launch Vehicle
The mass and bulk of the components selected for the video link required the use of a larger rocket than could be safely launched with standard Estes A to D black powder motors.

Fortunately at around the same time a friend imported several Aerotech ARCAS mid-powered rocket kits from an American online hobby retailer. The diameter of the ARCAS was just sufficient to house the circuit board from the transmitter once this was removed from its case (see the construction details page), and the bullet camera could be mounted outside the rocket, parallel with the body tube, pointed directly downward and protected via a streamlined nacelle carved from a block of balsa.

The Results
The original video signals obtained during early flights were of high qualty but contained extended dropouts and are not currently available on the site. The Research Goals section further down this page discusses this problem and what appears to be its solution.

Watching the inflight model rocket video clips
I suggest the launch to apogee clip in slow motion as a starting point ie serpentine5_slo (available in either QuickTime .mov or Windows Media .wmv format) as you can enjoy the flight details including the graceful parachute deployment. If you watch carefully you can also see the engine cap flying off as the motor fires.

Extended footage of the rocket under canopy after parachute deployment is available in the long versions of each clip (ie serpentine5_slo_long.wmv) but may not be worth the extra download time for those with limited bandwidth. Under canopy the upper section of the rocket is spinning almost horizontally. However enthusiasts might enjoy stepping through the footage frame-by-frame for nice glimpses of the paddocks of country Victoria.

If you have time to download more than one clip then the normal speed clips give a realistic sense of the incredible acceleration of a rocket flight and the howl as the rocket accelerates is amazing.

Scrubbing backwards and forwards through the clip reveals interesting things about the flight of the rocket that you don't notice from the ground, and stepping frame-by-frame through the footage gives one time to linger over the details on the ground. Windows Media Player doesn't seem to allow stepping or scrubbing so I recommend QuickTime as the media playback client, so download QuickTime and then grab the QuickTime (.mov) versions of the clips because if you only ever play the footage straight through you're not getting the most out of it.

An added bonus is that the slow-motion QuickTime movies are no larger than the normal versions. To create slow motion WMV's I've had to pad the movies out with duplicate frames.