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ascent [2008/10/15 16:07]
christra
ascent [2009/03/23 06:24] (current)
uri_ba empty links with links to wikipedia
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 === Ignition=== === Ignition===
 The ascent starts before the shuttle has even left the pad. The ascent starts before the shuttle has even left the pad.
-6.6 seconds before lift-off the three [[SSME|Space Shuttle Main Engines (SSME)]] ignite in succession, seperated by 120ms. This allows the computers to verify all three SSMEs are operational and ready to go. Because the SSMEs are off center and the SRBs are still bolted to the pad, the thrust tilts the stack about 2 ft towards the external tank (ET). It is called the "​Twang"​.+6.6 seconds before lift-off the three [[wp>​Space_shuttle_main_engines|Space Shuttle Main Engines (SSME)]] ignite in succession, seperated by 120ms. This allows the computers to verify all three SSMEs are operational and ready to go. Because the SSMEs are off center and the SRBs are still bolted to the pad, the thrust tilts the stack about 2 ft towards the external tank (ET). It is called the "​Twang"​.
  
 ===First Stage=== ===First Stage===
-When swinging back into the upright position and the SSMEs produce at least 90% thrust the [[SRB|Solid Rocket Boosters (SRBs)]] are ignited and the bolts connecting the stack to the pad are exploded and the whole package lifts off. The three SSMEs provide only about 17% of the total thrust at lift-off. The SRBs are doing most of the work. By clearing the tower at around 200ft AGL the Shuttle starts a computer controlled roll maneuver that puts the stack upside down (ET above the Shuttle) and pointing in the right direction for its planned orbit. All the launches are to an easterly trajectory among other reasons to utilize Earth rotational speed.+When swinging back into the upright position and the SSMEs produce at least 90% thrust the [[wp>​Space_Shuttle_Solid_Rocket_Booster|Solid Rocket Boosters (SRBs)]] are ignited and the bolts connecting the stack to the pad are exploded and the whole package lifts off. The three SSMEs provide only about 17% of the total thrust at lift-off. The SRBs are doing most of the work. By clearing the tower at around 200ft AGL the Shuttle starts a computer controlled roll maneuver that puts the stack upside down (ET above the Shuttle) and pointing in the right direction for its planned orbit. All the launches are to an easterly trajectory among other reasons to utilize Earth rotational speed.
  
 The first two minutes of flight are intended to move the Shuttle to the thinner atmosphere and to the highest possible speed. This is important due to the fact that two minutes is the nominal burn time for the SRBs. To prevent damage from the vehicle due to dynamic pressure that is growing with speed in the dense part of the atmosphere the thrust of the SSMEs is reduced to around 70% (launch specific) at about 30 seconds into the flight. Throttling up to maximum power occurs at about 60 seconds and maximum pressure (max Q) stresses the Shuttle shortly after it. Because air density is dropping fast with growing altitude the pressure drops in spite of growing speed after that point. 6 seconds after the computers detect that the chamber pressure of __both__ SRBs dropped below 50 PSI the SRBs are jettisoned and parachute down into the ocean where they are picked up by ships. The first two minutes of flight are intended to move the Shuttle to the thinner atmosphere and to the highest possible speed. This is important due to the fact that two minutes is the nominal burn time for the SRBs. To prevent damage from the vehicle due to dynamic pressure that is growing with speed in the dense part of the atmosphere the thrust of the SSMEs is reduced to around 70% (launch specific) at about 30 seconds into the flight. Throttling up to maximum power occurs at about 60 seconds and maximum pressure (max Q) stresses the Shuttle shortly after it. Because air density is dropping fast with growing altitude the pressure drops in spite of growing speed after that point. 6 seconds after the computers detect that the chamber pressure of __both__ SRBs dropped below 50 PSI the SRBs are jettisoned and parachute down into the ocean where they are picked up by ships.
ascent.txt ยท Last modified: 2009/03/23 06:24 by uri_ba