cost guidelines: together, the seven scientific experiments cost US12.6 million dollars, about one-eighth of the total mission budget. Television photography The imaging system, the Television Photography Experiment, consisted of two Cassegrain telescopes feeding vidicon tubes. The main telescope could be bypassed to a smaller wide angle optic, but using the same tube. It had an 8-position filter wheel, with one position occupied by a mirror for the wide-angle bypass. The entire imaging system was imperiled when electric heaters attached to the cameras failed to turn on immediately after launch. To avoid the Sun's damaging heat, the cameras were deliberately placed on the spacecraft side facing away from the Sun. Consequently, the heaters were needed to prevent the cameras from losing heat and become so cold that they would become damaged. JPL engineers found that the vidicons could generate enough heat through normal operation to stay just above the critical temperature of ; therefore they advised against turning off the cameras during the flight. Test photos of the Earth and Moon showed that image quality had not been significantly affected. The mission team was pleasantly surprised when the camera heaters started working on 17 January 1974, two months after launch. Later investigation concluded that a short circuit in a different location on the probe had prevented the heater from turning on. This allowed the vidicons to be turned off as needed. Of the six main scientific instruments, the cameras were by far the most massive device. Requiring 67 watts of electricity, the cameras consumed more power than the other five instruments combined. The system returned about 7,000 photographs of Mercury and Venus during Mariner 10's flybys. Infrared radiometer The infrared radiometer detected infrared radiation given off by the surface of Mercury and the atmosphere of Venus, from which the temperature could be calculated. How quickly the surface lost heat as it rotated into the planet's dark side revealed aspects about the composition of the surface, such as whether it was made out of rocks, or out of finer particles. The infrared radiometer contained a pair of Cassegrain telescopes fixed at an angle of 120° to each other and a pair of detectors made from antimony-bismuth thermopiles. The instrument was designed to measure temperatures as cold as and as hot as . Stillman C. Chase, Jr. of the Santa Barbara Research Center headed the infrared radiometer experiment. Ultraviolet spectrometers Two ultraviolet spectrometers