The Spaceflight Meteorology Group

Postflight Mission Summary for STS-89

February 5, 1998

The Space Shuttle Endeavour touched down at the Kennedy Space Center (KSC) Shuttle Landing Facility at 4:35 PM CST January 31, 1998 marking the completion of STS-89. Liftoff occurred as scheduled at 8:48 PM CST January 22, 1998.

The primary weather concern on the evening of the launch was the proximity of thunderstorm anvils to the launch site. Although showers and thunderstorms were well west of east central Florida, the anvils were encroaching upon the region. Current launch commit criteria and flight rules state that the shuttle must avoid the non-transparent parts of thunderstorm anvils by 10 to 20 miles depending upon the launch or landing phase. The consensus among atmospheric electricity experts is that the thunderstorm anvil (especially the non-transparent part) can still contain enough charge for the shuttle to trigger lightning and so should be avoided. Radar, the National Lightning Detection Network, Lightning Detection and Ranging (LDAR), digital satellite imagery, and aircraft reconnaissance reports were critical tools in determining the presence, location, motion, and transparency of thunderstorm anvils moving into the Florida peninsula on launch evening. After thorough analysis by forecasters at the Spaceflight Meteorology Group (SMG) and USAF 45th Weather Squadron, the thunderstorm anvil issue was agreed to be safe for launch and for any possible abort landing.

Very few clouds and light winds greeted the return of Endevour on the afternoon of January 31. Although the weather appeared ideal for landing, jet stream winds aloft prompted concerns over turbulence and which landing profile to use. The crosswind component of the wind at the altitude where the shuttle intercepts the Heading Alignment Cone (HAC) were the greatest ever observed during a shuttle landing. Observations from frequent KSC rawinsondes, pilot reports (PIREPS), dedicated weather reconnaissance aircraft reports, and the KSC 50MHz doppler radar wind profiler were of paramount importance in the upper wind and turbulence forecasts issued by SMG for landing. A comparison of wind direction and speed from the 16:47 UTC profiler (with significantly higher shears) versus the landing balloon released at 22:38 UTC is shown in Figure 1.

Figure 1. Direction vs. Height and Velocity vs. Height for 22:38 UTC KSC Rawinsonde (green) and 16:47 UTC KSC Wind Profiler (light blue).

SMG forecasters also contacted the Senior Duty Meteorologist Bill Kneas at NCEP to request a special rawinsonde release from Tampa with short notice (Figure 2). This was extremely useful in determining the strength, depth, and character of the jet stream over central Florida. No reports of turbulence were received from the crew.

Figure 2. Tampa Bay SkewT-log p diagram for 20Z release.

SMG weather team lead for ascent and entry of STS-89 was Tim Garner. The TAL site forecaster for launch day and assistant lead was Dan Bellue. Preparation of briefing graphics, weather systems troubleshooting, and other meteorological assistance was the job of Tim Oram as Techniques Development Meteorologist. Other SMG staff meteorologists supported the flight. Systems analysts from the United Space Alliance monitored and managed the Meteorological Interactive Data Display System for STS-89. The next mission, STS-90, is currently scheduled for liftoff in April, 1998.

Submitted by:
Tim Garner
STS-89 Lead Forecaster