SPACE SHUTTLE 45 Some facts are stranger than science fiction : once when the computer called a halt to the shuttle launch procedure, NASA tried to bypass the computer command. Fortunately, they were unsuccessful. The ship's oil had become contaminated and the oil filters, in two out of three auxiliary power units, had become clogged. This would have caused the jamming of the shut-de's hydraulic system that controls the landing gear. Malfunctioning of the landing gear would have led to a crash landing at a speed where nothing would be left to be salvaged. What is indeed surprising is the haste with which the programme was made to proceed, although the first four flights, which were test flights^ revealed that the shutde performance, design and system components were far from satisfactory. Usually, manned launches are undertaken only after the system is perfected to the maximum possible extent and after sufficient test flights are carried out to evaluate performance The widely known facts of the test flights show that the shutde's insulating tiles fell off with unfailing regularity during launches, and communication channels with ground stations repeatedly failed. TV cameras malfunctioned too often, even the life support system was badly flawed and many wondered whether the shutde was, a 'bankable' proposition. More serious, however, were the scores of problems with its rockets (the boosters in particular) and the fuel lines. The potential for a major mishap was not an unlikely event, but near certainty. The principle hypothesis for the event relates to the defects in the booster. The Solid Rocket Boosters (SRB) consists of a pair of identically designed, 46 m tall and 4 meters wide rockets weighing 590,000 kg. They are made up of four main segments attached to each other by 177 steel pins. On the fatal flight one of the segments was new; the others had flown previously. At the top of the boosters there is a nose containing the avionics and ignitor for the fuel, and at the other end, the rocket exhaust. On every shutde mission, the two boosters supply about 3 million pounds of thrust, providing the power to propel the orbiter out of Earth's atmosphere. On this ill fated 25th mission, the boosters and the Challenger's own liquid fuel engines were propelling into orbit the heaviest ever space cargo of all the shutde missions. The Challenger, its fuel rockets and other equipment weighed 2 million kg. (405 m pounds) at launching. NASA was reluctant to disclose what the net weight of pay load is. Shutde's cryogenic liquid fuel rockets burn the highly volatile mix of liquid hydrogen and oxygen. The external fuel tank which holds this fuel is a kind of thermos flask containing 383,000 million gallons of liquid hydrogen at minus 217°C and 143,000 million gallons of liquid oxygen at minus 147°C. They are stored in separate compartments and is fed to the five shuttle rockets through 17 inch diameter aluminimum and steel piping. At launch, orbiter's main engines are ignited to yield more than a million pounds of thrust. The shutde with its external liquid fuel tank and SRBs begin the lift off, rocking into a tight arc. Then as it steadies itself,