The Spaceflight Meteorology Group

Postflight Mission Summary for STS-85

September 5, 1997

The Space Shuttle Discovery landed at Florida’s Kennedy Space Center (KSC) Shuttle Landing Facility (SLF) at 1108 UTC [7:08 AM EDT] on Tuesday, August 19, 1997 after a successful 12 days in space. The shuttle was to land on the 18th, but unfavorable weather conditions caused a wave-off and gave the 6 astronauts an extra day in space. Discovery’s 23rd flight began with an on-time launch from KSC’s Pad 39A on Thursday, August 7th. While in orbit, the crew deployed and retrieved the CRISTA-SPAS satellite which was used to study earth’s atmosphere, manipulated a small robotic arm that will be a part of the new international space station, and performed a host of other experiments.

Several days prior to launch, a southward moving cold front became the primary point of concern. Some numerical models forecast the front near KSC while others had the front becoming stationary across northern Florida. No-go weather conditions would be likely with the front near KSC. SMG forecast the front to become stationary across northern Florida. This would yield light southwesterly surface winds and a chance of fog. The front did remain across northern Florida through the launch count. The visibility dropped to 3 miles in fog at sunrise and improved to 5 miles in haze by launch time, above the 4 mile flight rule restriction, contributing to an on-time launch. Weather at the primary Trans-oceanic Abort Landing (TAL) site, Zaragoza, Spain, was “no-go” due to thunderstorms within 20 NM. However, both back-up sites, Moron, Spain and Ben Guerir, Morocco had “go” conditions, meeting the landing weather flight rule required for launch.

The landing weather would prove to be more of a challenge. For several days preceding the planned landing day, high pressure at the surface under a ridge aloft covered central Florida. At landing time each day the weather was characterized by light winds and patchy or shallow ground fog reducing visibility to 6 to 7 miles. On the day prior to landing, 8/17/97, fog developed at the SLF, reducing the visibility to 3 miles at “landing time”. The visibility then dropped to 1 mile 6 minutes later. The fog dissipated 15 minutes later.

On “landing day” the weather conditions early in the count (TD-9 Hours) were similar to that of the day before. There were two important exceptions. The wind speeds at the 500 foot level were 5 knots lighter; southerly, 5 to 7 knots. Light southwest winds are conducive to fog development at KSC. Also, an inch of rain had fallen on Meritt Island (KSC) from afternoon thunderstorms, which increased the risk of fog. Surface winds at the SLF went from light southerly early in the count to light southwest. The winds at the 500 foot level remained southerly at a steady 5 to 7 knots. The temperature - dew point spread at the surface remained at or near zero degrees. The weather recon aircraft indicated that there was a fog bank about 10 miles west of the SLF. At final de-orbit decision time, the risk of fog formation at the SLF could not be discounted. The Flight Director waved off the landing at 1000Z, 17 minutes before the burn.

Weather conditions were slightly more favorable for the landing attempt on the next day. While light rain showers had fallen around Meritt Island the previous afternoon, amounts were significantly lower than the day before. The temperature - dew point spread from the surface to 500 feet averaged 1 to 2 degrees higher. While the surface winds were light south to southwest, the winds at 500 feet were southerly 10 to 12 knots. Between TD-4 and TD-3 hours the wind speed at 500 feet increased to 12 to 14 knots, decreasing the chance of fog. By 0900Z, about TD-2 hours, the wind speed at 500 feet increased to 13 to 15 knots and the surface winds became more southerly. The chance of fog was removed from the forecast. At 1000Z the Flight Director gave a “go” for the de-orbit burn. The shuttle touched down at 1108Z. Weather conditions were nearly ideal with the surface winds from 200 degrees at 6, peaking to 9 knots, scattered clouds at 10 and 28 thousand feet, and a visibility of 9 statute miles. This was the 10th consecutive Shuttle landing at KSC.

Lead Meteorologist for STS-85 was Karl A. Silverman, working his 24th mission, fourth as Lead. Steve Sokol was Assistant Lead and Tim Oram was the Lead Techniques Development Unit (TDU) Meteorologist.

Submitted by: Karl A. Silverman