The 40th anniversary of the launch of UoSAT-1 (OSCAR-9) passed a few days ago. Among all the beacon transmitters and scientific experiments carried onboard the satellite, a monochrome Earth imaging CCD camera was included to transmit SSTV images to listeners on Earth. However, plans changed shortly before launch, and it was decided that the images would handled and sent in a digital format, instead.
The format consisted of an array of 256x256 pixels, each 4-bits wide and sent as synchronous AFSK at 1200 bits per second. Each line was preceded by a line sync code, and each frame was preceded by 32 line sync codes in a row. At 1200 bits per second, it would take 3.77 minutes to transmit one image.
In September 1987, I began monitoring UoSAT-1 and UoSAT-2 (OSCAR-11), and on September 23, 1987 I happened to capture an OSCAR-9 CCD transmission on tape.
22 years later I came across the recording, and decided to program a PIC16F88 to finally decode the picture. The PIC took clock and data signals from a homebuilt G3RUH AFSK demodulator, "got into sync" with the synchronous data stream, looked for and identified the line and frame sync codes, and then sent each detected pixel to my Linux PC as a series of asynchronous RS-232 bytes where they were finally assembled into a 256x256 Portable Grey Map image.
The results were less than impressive, but seemed typical for what OSCAR-9's camera had been capable of producing:
- uo9ccd.png (11.64 KiB) Viewed 9265 times
- uo9ccd-annotated.png (13.94 KiB) Viewed 9265 times
I had previously seen only one or two other OSCAR-9 images, both in printed materials. Based on the quality of the images, I thought they might have been rendered using a dot-matrix printer. Probably not, as this early satellite image of Sardinia and Corsica reveals similar artifacts:
- Sardinia-Corsica-UoSat-1.jpg (38.84 KiB) Viewed 9265 times
The
Navy-OSCAR 104 (NO-104) satellite launched in 2019 carried a CCD camera into orbit and transmitted images in an SSTV format on 435.350 MHz FM, but I do not believe it is still operational.
73 de John, KD2BD