Optical-Mechanical Cycloramic Cameras

Selivanov and Iuri M. Gektin designed landscape cameras for Moon, Mars and Venus landers. Instead of panning a television camera, he decided to scan the scene with a pinpoint photometer. This required a much simpler apparatus with some advantages. A precise measurement of luminance was made at each pixel, and the entire landscape was returned as a single seamless image.

These cameras probably evolved from early cycloramic telephotometers by A.M. Kasatkin and others, used for low-resolution UV imaging and photometry from high altitude rockets. Luna-4 through Luna-8 contained a cycloramic optical-mechanical camera built by I.A. Rosselevich's team at the Leningrad Scientific Research Institute of Television. It was heavier and lower resolution than Selivanov's Luna-9 camera, and it operated inside a pressurized glass cylinder instead of being exposed to vacuum.

On the Luna-9 camera, seen above, the objective lens was focused at the hyperfocal distance, returning a sharp image of terrain between 1.5 meters and the horizon. Logarithmic photometry and automatic gain control (governed by a photocell) allowed the camera to operate with a wide range of luminance, from 80 to 150,000 lux. Sensitivity could also be adjusted by telecommand. The PMT and amplifer were the same as in the film scanner of the Zond-3 phototelevision camera. Remarkably, while containing vacuum tubes, a motor and the 1700 volt power supply for the PMT, the camera weighed 1.3 kilograms and consumed only 2.5 watts.

The upper assembly with oscillating mirror and motor rotated freely in the metal sleeve, making electrical contact through brushes. Scanning was vertical, with slow rotation to sweep out the horizontal image swath. The finely built mechanical action of the mirror was precise to 1/3 pixel spacing. A full 29° × 360° panorama of 6000 vertical lines could be returned in 100 minutes. On command, the camera could scan forward, in reverse, or at 4× speed for quick survey or positioning. A 250 Hz analog video signal was generated, which was frequency modulated on a 1.5 KHz subcarrier. That in term was phase modulated onto the 183.538 MHz telemetry carrier

250 cycles per line is theoretically equivalent to 500 pixels, which is how the resolution is often reported. Lunar images were sent as analog video, because a strong communication channel could be established between the Moon and the 32-meter dish at Simferopol. For later missions to Mars and Venus, the video signal was digital from camera to ground station.

The images above show part of the lunar landscape revealed by the Luna-13 camera. Pieces of the landing craft are seen in the distance on the left view. On the right, a detail at original resolution shows the extended gamma-ray densitometer and a close view of the lunar soil. These first landers relieved fears that the lunar surface might be composed of dust, into which spacecraft would sink.

It is important to remember that we can only see scans of printed images, many generations of duplication from the original electronic signal. Unless the magnetic tapes of the FM video signal are read and processed into modern digital images, we will not see the true quality of these images.

Luna-9 was the first spacecraft to land on the Moon, using an airbag landing system similar to the recent Mars Pathfinder. In 1966, it returned three panoramas. Its signals were also intercepted by the British radio telescope at Jodrell Bank, and a Manchester newspaper published the pictures before the Russian press.

Luna-13 returned five panoramas from another landing site, later that year. Taken over several days, they show the surroundings under different angles of illumination (the Moon rotates 13° per day). It had two cameras for redundancy or stereo, but one failed.

In 1971, Mars-3 was the first spacecraft to land on the red planet. Two cycloramic cameras were installed, as on Luna-13. Like the second generation lunar cameras, they had 500 × 6000 pixel resolution, and scanned at 4 lines per second.