RTLS Overview

If an engine fails during the first 4 minutes of ascent, the shuttle cannot achieve orbit. For the first 3 minutes or so of ascent, it cannot even reach a TAL. The only runway near enough to be reached is one near the launch site. In order to reach this runway, the shuttle must literally reverse course and fly back the way it came.

The turn to reverse course is called powered pitcharound (PPA), and the timing of PPA is critically important. Since the orbiter is powerless once the main engines are shut down, these engines must be shut down when the orbiter has enough speed and altitude to glide to the runway. Also, in order to safely separate the orbiter from the ET, the ET should have no more than 2 percent propellant remaining. More propellant might slosh around and cause the tank to lurch and collide with the orbiter. Therefore, the shuttle must turn back toward the launch site at the exact instant that will allow it to arrive at MECO with the right amounts of speed, altitude, and propellant.

If the RTLS is declared before the time of PPA, the shuttle has to perform what is called fuel wasting. This means pointing the shuttle more vertical (called lofting) to minimize loss of altitude while still flying away from the launch site and runway. This continues until the shuttle must execute PPA and turn back toward the launch site. From this point on, the shuttle thrusts back toward the runway until it reaches MECO conditions. These conditions are specified as 2 percent propellant remaining with the right speed, direction, and altitude to glide to a landing.

Then the orbiter separates from the ET and begins to glide back to the runway. During this gliding flight (called glide return to launch site (GRTLS)), the orbiter may perform certain maneuvers to fine tune its glide range or energy. Finally, as the orbiter approaches the runway, it will perform a wide turn to align itself with the direction of the runway and then glide down to a landing (figure 1-3).

Downrange distance, n. mi.

TDJ44A-002 3 b

Figure 1-3.-Typical RTLS profile.

Downrange distance, n. mi.

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Figure 1-3.-Typical RTLS profile.

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