The ability to safely land the Shuttle after a successful mission. The landing part of the mission, consists of three phases.
The Terminal Area Energy Management (TAEM) interface is the transition from the high AOA re-entry and Roll Reversals to controlled aerodynamic flight. It begins at 83000ft altitude, at a speed of Mach 2.5 and about 60 NM from the runway. During this phase RCS thrusters are step by step inhibited and the crew and associated automated systems perform energy and track management toward intercepting the HAC. Last used RCS thruster is for yaw control until 45000 ft or about Mach 1. In a high energy condition the guidance leads the shuttle away from the HAC to extend the flightpath and dissipate some more energy. These maneuvers are called s-turns. Below Mach 1 the commander normally takes over manual control.
The Heading Alignment Circle (HAC) represents the Shuttle's “landing pattern”. It is a large computed corkscrew-like path that puts the Shuttle in the correct position for the final approach (aligned with the runway and on energy).
The normal HAC intercept is around 50-35Kft, and the Shuttle needs to make a 90, 180 or 270 degree turn, depending on the intercept point. The Shuttle exits the HAC pattern at an altitude of around 12Kft, at which point it is already fully aligned with the runway.
The Final Approach phase in the Space Shuttle landing is somewhat similar to a normal commercial jet landing with two exceptions:
The actual approach consists of two distinct stages:
During the first stage, the Shuttle lines up with the runway at 10,000ft, 6.9 NM from the runway, flying a 17 to 19 degrees glide slope to a point 0.89 NM short of the runway. Approach speed is controlled by speed brakes (air brakes). At 3000ft the speed brake is set to a calculated position to allow touchdown at a point 2500ft down the runway.
The second stage starts at around 1750ft AGL. At this altitude the Shuttle pre-flares, changing its glide slope from the steep 17 to 19 degrees dive to a shallow 1.5 degrees glide slope all the way to touchdown. This shallower approach bleeds off the excess speed used during the initial approach and allows the Shuttle to land at a speed which is only slightly higher then that of normal jets. The nominal touch down speed depends on the Space Shuttle weight at touch down: heavy (with payload): 205 kt, normal (payload bay empty): 195 kt.
Post-SP3 HD Video Tutorial:
Landing Interface Video Tutorial (Dailymotion)
HUD collimation on SP3.6:
HUD landing video with TrackIR on SP3.6 (you-tube)