The Syrian airfield prepare for reception of military aircraft of China
The latest news about fast emergence in borders of Syria of navy of China encouraged Syrians and res[...]
Go for PDI
When FIDO, the flight dynamics officer, had planned the DOI manoeuvre, he arranged for the resultant descent orbit to have a perilune of about 15,000 metres altitude over a point on the Moon 500 kilometres uprange of the landing site, this being where the descent to the surface would begin. As the LM coasted towards this point, with all the required checks completed, the flight director spoke over his communication loop to all the flight controllers in the MOCR. briefly interrogating each relevant controller as to whether, as far as his area of responsibility was concerned, he was happy for the mission to proceed to the next stage – powered descent initiation (PDI).
Ten minutes prior to PDI, the commander started P63 running in the LM’s computer, which would handle the start of the burn and most of the subsequent descent.
“Okay. Master arm’s on,” said David Scott with less than a minute to go to PDI in Apollo 15’s LM Falcon. “1 have two lights.” Lxplosivcly operated valves were ready to fire and let supercritical helium enter the propellant tanks.
“Average g,” said Scott as the DSKY blanked, showing that the guidance system, the PGNS, had begun to measure the acceleration acting on the spacecraft and that it would average out the short-term transients that might be associated with engine startup. “Armed the deseent [engine]. We have guidance.”
“Standing by for ullage,” said Irwin.
“Standing by for ullage,” repeated Scott, in the conventional challenge-and – response manner of those steeped in aviation. The thrusters that pointed in the same direction as the main engine (against the direction of travel) were burned for a short period to settle the heavy propellants to the bottom of their tanks so that, on ignition, the light helium gas would be at the opposite end of the tank from the plumbing that led to the engine.
“Go for the Pro,” said Scott. Then, “Pro,” as he pressed the ’Proceed’ button on the computer to give P63 permission to proceed with ignition and the commencement of the braking phase of the deseent.
