As the crew of the final space shuttle flight prepares to return home early Thursday morning, ground teams at Mission Control in Houston is preparing to support their entry and landing at Florida's Kennedy Space Center. Among the teams at Mission Control is the National Weather Service Spaceflight Meteorology Group (SMG), which has provided landing weather support for all 135 shuttle missions. After a behind the scenes look at SMG preparations several days prior to launch, The Weather Channel's Andy Cox traveled to Kennedy Space Center for the launch.
The first of several weather-related decisions had been made before I arrived at the Kennedy Space Center. Mission managers gave the "go" to begin loading more than 500,000 gallons of liquid oxygen and hydrogen into the shuttle's external tank after receiving a forecast update from shuttle Launch Weather Officer Kathy Winters.
The combined forecast team of Winters and the USAF 45th Weather Squadron (45 WS) at Cape Canaveral, and the Spaceflight Meteorology Group in Houston had not changed their outlook and were still forecasting a 30 percent chance of good launch weather in Florida.
For an overview of the two teams forecasting shuttle weather, see this overview.
Several weather balloons released during the pre-dawn hours from nearby Cape Canaveral Air Force Station showed that the expected moisture - more than two inches of precipitable water - was still in the atmosphere.
Conditions were ripe for showers and storms to fire up once the sun came up. Occasional scattered showers had already passed over KSC before dawn, twice briefly violating the shuttle's "flight through precipitation" rule between 5:00 a.m. and 7:00 a.m. EDT.
Clouds are often a bad thing for shuttle launches and landings because they can violate several criteria if they are low enough and too widespread. Clouds with enough electric charge to cause natural or rocket-triggered lightning can also violate launch criteria and scrub a launch.
Todd McNamara with the 45 WS monitored the radar data coming from Patrick Air Force Base. McNamara used a set of software tools that allowed him to "slice and dice" the data to evaluate the launch criteria.
McNamara also used these tools to evaluate the thick cloud rule from the Lightning Launch Commit Criteria, which are designed to minimize the risk of lightning strikes to space vehicles. The thick cloud rule basically says that flight is not allowed through clouds more than 4,500 feet thick with temperatures between −20 degrees C and 0 degrees C (−4 degrees F to 32 degrees F).
The thick cloud rule was in violation on four separate occasions on launch day, with the final "go" for launch weather given at 10:18 a.m. EDT, about one hour prior to launch.
While the weather Launch Commit Criteria monitored by 45 WS were eventually observed "go" at launch time, the weather flight rules for the emergency landing site at Kennedy Space Center were a different story.
For the final launch of the thirty-year Space Shuttle Program, NASA and local authorities expected up to one million spectators in the Space Coast area of Florida.
With the enormous crowds, and the accompanying traffic around the area, NASA managers were concerned that, in the event of a late launch scrub, launch team members would not have enough time to drive home, get enough rest, and return for another attempt the following day.
As a result, NASA managers had discussed using a rough milestone - about four hours before launch - to decide whether to delay for 24 hours or 48 hours in the event of a scrub. If there was a scrub before that milestone, there would be enough time to allow for a launch the following day. Otherwise, the next attempt would be Sunday.
Leading up to that four hour mark, Launch Director Mike Leinbach and Flight Director Richard Jones asked the weather teams to evaluate the forecast for the next few days. If the weekend looked better than Friday, and Saturday's forecast was better than Sunday's, they discussed scrubbing early enough to protect a 24-hour delay.
"We were talking about whether to press on with this launch attempt or whether it was time to stop and go home before traffic would prevent everyone from getting back the next day," said Winters.
"In general, most of the collaboration between SMG and the 45 WS is done prior to launch day," said Hoeth. "In this case, Kathy and I did coordinate after the tanking briefing because of the unique situation where they were talking about scrubbing the day before we even got into it."
"We were in agreement that there wasn't a whole lot of discernible difference between the days." Saturday looked drier, but the low pressure system was expected to remain. Moisture would remain Sunday, but the system was expected to leave. "It was kind of pick your poison," according to Hoeth. "Friday was not a complete washout. If we had thought that, we would have said let's not even try today."
"We had a decision point around 7:30 a.m. Eastern," Winters said. "We pushed it to 7:30 because we were going to get some more visible satellite shots and model data by that time. That was our last conversation about whether we should keep going with this weather scenario or not."
"It started looking good - or at least possible - around that time. We have enough breaks in this that we could get a launch attempt off today."
Winters said that with all of the times she's discussed weather with Leinbach - she has been the shuttle Launch Weather Officer since 2002 - that Leinbach has learned to listen to not only what she says, but how she says it. "He could tell by my tone that I was starting to feel optimistic about it."
After deciding to press on with the countdown, showers continued to form around and move through the 20 nautical mile radius around the shuttle runway used to evaluate the Return To Launch Site (RTLS) emergency landing criteria.
The cloud cover that normally causes problems for the shuttle was actually helping in this case. With the amount of moisture in the atmosphere, it wouldn't take much daytime heating for showers and storms to begin popping up all around the area.
As SMG and 45 WS were using all of the tools at their disposal to analyze the atmosphere and project that to launch time, astronaut Rick "CJ" Sturckow was flying over the KSC area in a Shuttle Training Aircraft evaluating conditions for both groups.
Sturckow helped evaluate both the thick cloud rule for 45 WS and potential areas for popup showers for both weather teams. He also performed simulated landing attempts, or "dives," into the runway to assess conditions for an emergency landing.
Despite the delay in atmospheric heating, Hoeth was still concerned about the wet atmosphere and the potential for quick shower development.
Hoeth was assisted on launch day by Mark Wiley and Doris Hood. Wiley was the Transoceanic Abort Landing (TAL) forecaster, but with benign conditions at the three overseas sites, he was able to assist Hoeth with Florida weather. Hood forecasted upper level winds and served as the Techniques Development Unit (TDU) meteorologist.
What do TDU meteorologists do? Go behind the scenes with SMG to find out.
Deciding to "go"
In the absence of an exception or waiver, shuttle flight rules state that weather at the emergency landing sites (KSC and one of three TAL sites) must be both observed and forecast "go" for launch to occur.
"I was trying to bring that point home on the loops that I didn't feel like this was a stable situation," said Hoeth. "We were observed no-go for almost the entire countdown for showers within 20 (nautical miles). I was forecast no-go for the entire time - I never did amend my forecast."
While SMG continued to evaluate RTLS weather, NASA managers began discussing a waiver for the flight rule requiring RTLS to be observed and forecast "go."
Ascent flight director Richard Jones described how that flight rules, which are written during the between-mission periods, are evaluated based on the conditions of the day.
"The flight director has to think about it not only from a meteorological perspective, but also from a mission perspective, the crew's perspective - the bigger picture," said Jones.
"When you start weighing all of those things together," Jones added, "there are certain scenarios where there might be an imperfect day from a weather perspective but good enough for a mission success and safety perspective."
Mike Moses, chair of the pre-launch Mission Management Team, praised the ascent flight control team after the successful launch.
"The team did an amazing job talking about what conditions we were truly facing," said Moses. One of the concerns that the shuttle, which lands essentially as an unpowered glider, would possibly lose energy while flying through rain and end up not being able to reach the runway at KSC.
Based on the assessment from Hoeth of a low to moderate risk of thunderstorms, flight controllers determined that the shuttle would have enough energy to make it through the expected lighter showers or have enough energy to use either end of the runway to avoid heavier showers.
As Leinbach performed the final "go"/"no go" poll about 15 minutes before launch, Jones asked to be polled again at the end. Once the waiver had been processed, the final go was given to launch Atlantis on the last space shuttle mission.
At the time an RTLS forecast would have been valid (25 minutes after launch), a small area of showers was within the 20 nautical mile radius, so RTLS conditions were observed "no go." As Hoeth noted, it is likely that those showers would have been acceptable under the rain shower exception in the flight rules.
Andy Cox covers space weather for The Weather Channel and weather.com. For the latest updates, follow @twcspacewx on Twitter.
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