How They Work:“The Space Shuttle (Part III)”

As we said earlier, the engines burn mono-methyl hydrazine fuel (CH3NHNH2) and nitrogen tetroxide oxidizer (N2O4). Interestingly, when these two substances come in contact, they ignite and burn automatically (i.e., no spark required) in the absence of oxygen. Either one or both of the OMS engines can fire, depending upon the orbital manoeuvre. Each OMS engine can produce 26,400 N of thrust. The OMS engines together can accelerate the shuttle by 0.6 m/s2. This acceleration can change the shuttle’s velocity by as much as 1,000 305 m/s. To place the shuttle into orbit or to de-orbit takes about 31-153 m/s change in velocity. Orbital adjustments take about 0.61 m/s change in velocity. The engines can start and stop 1,000 times and have a total of 15 h burn time. As the shuttle rests on the pad fully fuelled, it weighs about 2 million kg (2000 tonnes). The shuttle rests on the SRBs as pre-launch and final launch preparations are going on through T minus 31 seconds; 1. T minus 31 s - the on-board computers take over the launch sequence. 2. T minus 6.6 s - the shuttle’s main engines ignites one at a time (0.12 s apart). The engines build up to more than 90 percent of their maximum thrust. 3. T minus 3 s - shuttle main engines are in lift-off position. 4. T minus 0 s -the SRBs is ignited and the shuttle lifts off the pad. 5. T plus 20 s - the shuttle rolls right (180 degree roll, 78 degree pitch). 6. T plus 60 s - shuttle engines are at maximum throttle. 7. T plus 2 min - SRBs separate from the orbiter and fuel tank at an altitude of 45 km. Main engines continue firing. Parachutes deploy from the SRBs, SRBs will land in the ocean about 225 km off the coast of Florida. Ships will recover the SRBs and tow them back to Cape Canaveral for processing and re-use. 8. T plus 7.7 min - main engines throttled down to keep acceleration below 3g’s so that the shuttle does not break apart.9. T plus 8.5 min - main engine shuts down. 10. T plus 9 min - ET separates from the orbiter. The ET will burn up upon re-entry. 11. T plus 10.5 min - OMS engines fire to place you in a low orbit. 12. T plus 45 min - OMS engines fire again to place you in a higher, circular orbit 400 km. The shuttle is now in outer space and ready to continue its mission. Once the Space Shuttle in Orbit, the shuttle orbiter is the astronauts’ home for seven to 14 days. The orbiter can be oriented so that the cargo bay doors face toward the Earth or away from the Earth depending upon the mission objectives; in fact, the orientation can be changed throughout the mission. One of the first things that the commander will do is to open the cargo bay doors to cool the orbiter. The orbiter consists of the following parts; the crew compartment - where they normally live and work, the forward fuselage (upper, lower parts) - containing support equipment (fuel cells, gas tanks) for crew compartment, the forward reaction control system (RCS) module – that contains forward rocket jets for turning the orbiter in various directions, the movable airlock - used for spacewalks and can be placed inside the crew compartment or inside the cargo bay, the mid-fuselage that contains essential parts (gas tanks, wiring, etc.) to connect the crew compartment with the aft engines, that forms the floor of the cargo bay, cargo bay doors - roof of the cargo bay and essential for cooling the orbiter, remote manipulator arm - located in the cargo bay, moves large pieces of equipment in and out of the cargo bay, platform for spacewalking astronauts, aft fuselage - contains the main engines, OMS/RCS pods (2) - contain the orbital manoeuvring engines and the aft RCS module; turn the orbiter and change orbits, airplane parts of the orbiter - fly the shuttle upon landing like the wings, tail and body flaps. (To be Cont’d) eddie@afrowebs.com