6.3
Return-To-Launch-Site abort landing weather: impact upon launch availability
Tim Garner, NOAA/NWS/Spaceflight Meteorology Group, Houston, TX
Under current Launch Commit Criteria (LCC) and Flight Rules (FR) the Space Shuttle may not launch unless weather is acceptable for both launch and specified abort landings. A Space Shuttle mission abort would occur whenever orbit cannot be achieved or if there is a loss of a critical system that requires an immediate landing. If such a situation occurs very early in a flight, for example three to four minutes after launch, the Space Shuttle could perform a Return-To-Launch-Site (RTLS) abort landing at the Kennedy Space Center Shuttle Landing Facility (SLF). The Space Shuttle would literally reverse course, fly back to near where it was launched, and land approximately 25 minutes after launch at the SLF. Launch may not occur unless the forecast weather RTLS landing time is acceptable as defined in the Flight Rules. Launches that are postponed for one day or more are defined as scrubs.
RTLS weather is frequently perceived to be the primary and sometimes as the only cause of launch scrubs. As of March 2000 RTLS weather has impacted 51 (29.7%) launch attempts since the first Space Shuttle mission. Specifically, RTLS weather has been a contributing factor in 25 launch scrubs and 26 delays out of 172 launch attempt days. While these figures may seem high, only 3 launch attempts (1.7%) have been postponed by a day or more solely by RTLS weather being unacceptable. Typically there is a "weather overlap" in the LCC required for launch and the FR required for abort landings so that both launch area weather and abort landing weather is unacceptable.
The most frequent weather FR's observed to contribute to launch scrubs has been proximity of precipitation (11 times), crosswinds (8 times), proximity of thunderstorms (8 times), and low cloud ceilings (7 times). Interestingly, for weather scrubs that met LCC, but did not meet RTLS FR's the weather elements observed as unacceptable were crosswinds and cloud ceilings.
Weather-induced delays on day of launch are distributed similarly to scrubs. Most of the projected Space Shuttle missions over the next several years will be to rendezvous and construct the International Space Station. Launch windows for these missions are typically 10 minutes or less. Because of the short launch windows, statistics from previous Space Shuttle weather delays should be considered practically as scrubs for comparison. If mission managers wish to improve launch availability in the future by optimizing the RTLS weather, one should use the results of this paper to target methods for improving short-range forecasts of precipitation, thunderstorms, cloud ceilings, and crosswinds or to improve the Space Shuttle's ability to tolerate weather conditions.
Session 6, Space Vehicle Operations Support (Parallel with Session 5)
Thursday, 14 September 2000, 8:00 AM-10:00 AM
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