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What has caused the delay of the last flight of Endeavour?
The last flight of the Space Shuttle Endeavour was delayed by 48 hours (update: in general on неопределенное the amount of time ) because of problems with the heater APU abbr> and load with the control unit. I wanted to sort out what exactly needs these components, so I did some research. There are a bunch of detailed information on the shuttles are available online, but it is very difficult to find. I gathered all here just in case someone else wants to dive into the specifics.
Shuttle bears three independent hydraulic control system of engine valves, actuators, landing gear and other devices necessary during takeoff and landing. Hydraulic pumps are powered by three auxiliary power units (APU), operating on hydrazine jet engines. Each APU weighs 40 kilograms and produces 135 horsepower (about the same power at the Honda Accord).
Hydrazine is highly toxic propellant, which upon contact with the catalyst is decomposed in the hot gas with a temperature of 925 ° C. Such fuels convenient to apply for the APU, because it does not require oxygen for the reaction, and the decay can be very easy to initiate and stop.
Apparently, the fuel heaters in the first APU is not working. Since hydrazine freezes at 2 ° C, the duplicate each APU equipped with heaters to keep the temperature subsystem above 7 ° C. Duplication of heaters allows the shuttle to work even with a malfunction in one of them, but he would not survive a second failure. If the second fuel heater fails, the fuel will freeze, and the APU will not be able to function. However, at the Space Shuttle three APU, so even non-functional one will not be a big problem. But, nevertheless, you do not want to take off with a broken heater, because there is still the risk of loss of hydraulic pressure, which is very bad.
According to статьям, problem occurs with a fuel heater of the lack of power from the load control unit, a distribution box, the feed circuit for the heater APU 1. For each APU has its own control unit.
Complex subsystem provides power supply all parts of the Space Shuttle. Three fuel cells (for 10kW) produces 28 volts DC. The fuel cell is provided with three main DC power supply bus, moreover they feed current inverter connected to the three-phase AC busbar. 117 volts, 400Hz. Because fuel cells enters the current power distribution (Distribution Assembly, DA), then tail power management unit, and then in the tail blocks of load control.
Load control units consist of semiconductor switching elements for loads up to 20 amps from the relay for loads above (but not more than 135 amps). The switching elements are covered by internal fuses.
According to reports, in the tail control unit load # 2 is shorted, or some other electrical failure which has led to a refusal to start the heater APU. Fuel blends with Endeavour to technology to gain access to all control blocks and solve the problem. If I understood everything correctly, it looks as if only one is sufficient to replace the fuse.
Difficulty Shuttle
What's cool in the shuttle, so is that the complexity increases from layer to layer. Subsystem APU is just one example. So, each APU provides lubrication system. That requires an oil pump, which is necessary for nitrogen pressurization system to start pumping in the absence of gravity. For the oil system will also need 80-pound water system evaporator ( water spray boiler i>), which is sprayed on the oil pipes chilled water, the water turns to steam discharged in kosomos. For evaporator required controllers, toggle switches and indicators for the control panel, plus one tank pressurization of nitrogen and another system of heaters to avoid frozen water.
The evaporator has nothing to do with the delay, except that it is part of APU, but it is a good example of the complexity of systems of the Space Shuttle. To sum up of only one circuit - the engine needs a hydraulic pressure, which appears only in the moment will earn APU to power hydraulic pumps that require working lubrication system, in turn, need complex system evaporator, which needs its own control system and monitoring. And that's just one small sub-loop! I omit the same complexity of the system as a system of cooling the injector (more water and nitrogen under pressure) or a fuel pump APU (which, for example, has a capacity for trapping liquid in the event of sealing of the pump, a drain hole for the case of overflow of the tank, and related with all this monitoring system).
Conclusion
Based on this level of difficulty of limiting shuttle, I do not udvlёn delays the start, and I wish good luck to NASA in the early resolution of their problems. In my opinion, until Shuttles are an engineering marvel, simpler rockets Falcon from SpaceX will be more practical to use in the long term. Pictures and most of the information from the "1988 Shuttle Reference Manual». The manual contains a very detailed and interesting description of the Space Shuttle (if you find these things interesting). I guess I should mention that this article is based on what I read, and I have nothing to do with the space program.
PS: I found details about LCA and the problems start at nasaspaceflight.com , such that Индевор I got a new LCA, and oxidized driver examined .
Something is broken in me, the translator (most likely it is when I accidentally pressed down, then freewheeling autosave), and not as a topic Litters translation. Therefore, write the link here - Ken Shirriff i> < br />
Source: geektimes.ru/post/249768/
Shuttle bears three independent hydraulic control system of engine valves, actuators, landing gear and other devices necessary during takeoff and landing. Hydraulic pumps are powered by three auxiliary power units (APU), operating on hydrazine jet engines. Each APU weighs 40 kilograms and produces 135 horsepower (about the same power at the Honda Accord).
Hydrazine is highly toxic propellant, which upon contact with the catalyst is decomposed in the hot gas with a temperature of 925 ° C. Such fuels convenient to apply for the APU, because it does not require oxygen for the reaction, and the decay can be very easy to initiate and stop.
Apparently, the fuel heaters in the first APU is not working. Since hydrazine freezes at 2 ° C, the duplicate each APU equipped with heaters to keep the temperature subsystem above 7 ° C. Duplication of heaters allows the shuttle to work even with a malfunction in one of them, but he would not survive a second failure. If the second fuel heater fails, the fuel will freeze, and the APU will not be able to function. However, at the Space Shuttle three APU, so even non-functional one will not be a big problem. But, nevertheless, you do not want to take off with a broken heater, because there is still the risk of loss of hydraulic pressure, which is very bad.
According to статьям, problem occurs with a fuel heater of the lack of power from the load control unit, a distribution box, the feed circuit for the heater APU 1. For each APU has its own control unit.
Complex subsystem provides power supply all parts of the Space Shuttle. Three fuel cells (for 10kW) produces 28 volts DC. The fuel cell is provided with three main DC power supply bus, moreover they feed current inverter connected to the three-phase AC busbar. 117 volts, 400Hz. Because fuel cells enters the current power distribution (Distribution Assembly, DA), then tail power management unit, and then in the tail blocks of load control.
Load control units consist of semiconductor switching elements for loads up to 20 amps from the relay for loads above (but not more than 135 amps). The switching elements are covered by internal fuses.
According to reports, in the tail control unit load # 2 is shorted, or some other electrical failure which has led to a refusal to start the heater APU. Fuel blends with Endeavour to technology to gain access to all control blocks and solve the problem. If I understood everything correctly, it looks as if only one is sufficient to replace the fuse.
Difficulty Shuttle
What's cool in the shuttle, so is that the complexity increases from layer to layer. Subsystem APU is just one example. So, each APU provides lubrication system. That requires an oil pump, which is necessary for nitrogen pressurization system to start pumping in the absence of gravity. For the oil system will also need 80-pound water system evaporator ( water spray boiler i>), which is sprayed on the oil pipes chilled water, the water turns to steam discharged in kosomos. For evaporator required controllers, toggle switches and indicators for the control panel, plus one tank pressurization of nitrogen and another system of heaters to avoid frozen water.
The evaporator has nothing to do with the delay, except that it is part of APU, but it is a good example of the complexity of systems of the Space Shuttle. To sum up of only one circuit - the engine needs a hydraulic pressure, which appears only in the moment will earn APU to power hydraulic pumps that require working lubrication system, in turn, need complex system evaporator, which needs its own control system and monitoring. And that's just one small sub-loop! I omit the same complexity of the system as a system of cooling the injector (more water and nitrogen under pressure) or a fuel pump APU (which, for example, has a capacity for trapping liquid in the event of sealing of the pump, a drain hole for the case of overflow of the tank, and related with all this monitoring system).
Conclusion
Based on this level of difficulty of limiting shuttle, I do not udvlёn delays the start, and I wish good luck to NASA in the early resolution of their problems. In my opinion, until Shuttles are an engineering marvel, simpler rockets Falcon from SpaceX will be more practical to use in the long term. Pictures and most of the information from the "1988 Shuttle Reference Manual». The manual contains a very detailed and interesting description of the Space Shuttle (if you find these things interesting). I guess I should mention that this article is based on what I read, and I have nothing to do with the space program.
PS: I found details about LCA and the problems start at nasaspaceflight.com , such that Индевор I got a new LCA, and oxidized driver examined .
Something is broken in me, the translator (most likely it is when I accidentally pressed down, then freewheeling autosave), and not as a topic Litters translation. Therefore, write the link here - Ken Shirriff i> < br />
Source: geektimes.ru/post/249768/
