AO-40 YACE Pictures

Orbit number 337, July 24, 2001

The YACE (Yet Another Camera Experiment) aboard the AMSAT OSCAR 40 spacecraft was used to take images of Earth to verify the spacecraft's attitude.

Eight pictures were taken at 7 minute intervals. The JPEG quality was Q=25 in order to keep the file size small, and the same Q as was used for Earth images pre-incident. The JPEGs are 256-level (8 bit) greyscale.

Click on the small image to see the full-size image.

Original Despun UTC time MA
11:39:41 9.10
11:46:41 10.66
11:53:44 12.24
12:00:44 13.80
12:07:44 15.36
12:14:44 16.93
12:21:44 18.49
12:28:44 20.05

The MA values shown above are based on Keplerian elements derived by AMSAT ranging measurements. The IHU-2 clock was checked and was correct within a few seconds. Spin rate was 2.225 rpm. The camera field of view is 20.74 x 20.74.

Comments

1. The spacecraft spins 16 during the exposure so there is some minor distortion in the raw images.

2. Despun images are also supplied. The larger cross indicates the spin axis, the smaller cross is the camera image center; the camera boresight is misaligned by 1.35.

3. The first image is always grey because the AGC has not fully settled.

4. The Earth's edge is in most of these images, and the angular distance from the bore-sight indicates an attitude of alon/alat = 309.8/7.3 ; accuracy approx +/- 0.2.

5. Some cloud detail is visible in these images. This image shows the viewing conditions at MA 13.80:

(click for a bigger version)

Check out this graph showing how the measurements are interpreted to fix the spacecraft attitude:

(click for a bigger version)


Article and analysis by James Miller, G3RUH, July 24, 2001, for the AO-40 command team.