BURAN FLIES Defying the weather

The troubleshooting was not finished until after the October Revolution holiday, celebrated on 7 November. However, as Gudilin said in one interview:

“the time has gone by when launches were hurried along to fit in with holiday dates.”

On 12 November TASS announced that the launch had been rescheduled for 15 November at 6:00 Moscow time (3:00 gmt, 8:00 local time at Baykonur). Visual observations from Mir were no longer a factor in determining the launch time, probably because orbital precession had shifted the station’s flight path such that it now passed over the cosmodrome much earlier than was acceptable for the Buran launch.

The biggest concern as launch time drew closer was the weather. While skies had been crystal clear for the launch attempt on 29 October, a low-pressure front bringing rain and strong winds was now approaching Baykonur from the Aral Sea. At 17: 00 local time (12: 00 gmt) on 14 November meteorologists reported they were seeing a tendency for the front to bypass Baykonur, although nothing could be guaranteed. Four hours later the forecast had remained unchanged and the State Commission decided to press ahead with fueling of the rocket. First to be loaded were the liquid – oxygen tanks of both the strap-on boosters and core stage, followed about two hours later by the kerosene tanks of the strap-ons and the core stage liquid-hydrogen tank. Soviet media made no secret of the iffy weather conditions. On the eve of launch, a correspondent of the Vremya evening television news program reported:

“Everything that depends on people has been done. But the weather is worsening with each passing hour. If the wind rises into a squall and the orbital vehicle… becomes covered with a crust of ice, then the launch time will be changed again.’’

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Gale warning issued at 6:15 am local time (source: wwww. buran. ru).

At midnight local time, with fueling of the liquid-oxygen tanks underway, the forecast took a turn for the worse. The low-pressure front had broken up in two parts, one of which was now headed straight for the launch site. Less than 2 hours before launch the chief weather officer handed over a gale warning to Gudilin. Conditions expected between 7:00 and 12:00 local time (2:00-7:00 gmt) both at the launch pad and the runway were strengthening southwest winds with speeds of 9 to 12m/s, gusting to 20m/s. Meanwhile, weather balloon data also showed unstable conditions up to altitudes of 25 km, with highly variable wind speeds (maximum 70m/s) and wind directions at different levels. With just 30 minutes left in the count­down, observed conditions were overcast skies with a cloud ceiling at 550 meters, drizzle, winds of 15m/s gusting to 19m/s, a temperature of +2.8°C, and visibility of 10 km. The agreed wind speed limit for launch was 15m/s, while for landing the maximum allowed wind speeds were 5 m/s for tail winds, 10 m/s for crosswinds, and 20 m/s for head winds.

The marginal weather conditions were a matter of concern for several reasons. The combination of drizzle and low temperatures posed the threat of significant ice build-up on the rocket, orbiter, and launch pad. Chunks of ice falling off the rocket during launch could cause significant damage to Buran’s fragile thermal protection system. This risk has always been well understood in the Space Shuttle program, where specialized ice inspection teams are routinely sent out to the pad in the final hours before launch. The available information suggests that the Russians considered
a 2 mm ice layer on the rocket acceptable and decided to go ahead based on the prediction prior to fueling that the thickness of the layer would not exceed 1.7 mm. All indications are that no ice inspection teams were sent to the pad and that any later estimates were based solely on close-up television shots of the launch vehicle. Apparently, those images were not always reassuring. As Gudilin later recalled:

“we could see relatively big chunks of ice falling from the rocket and the

orbiter.”

Aside from ice build-up on the vehicle, there were worries about ice formation on the runway and the general effects of cold weather on vehicle performance. Although Energiya had no solid rocket boosters, the Challenger accident, where cold tempera­tures had contributed to the failure of an О-ring seal in one of the solids, was “in the back of our minds”, as Gudilin puts it in his memoirs.

Another issue were the strong winds both at ground level and in the upper atmosphere. There were fears that ground-level winds could cause the vehicle to hit one of the launch pad structures during lift-off and that unstable upper-level winds could knock the stack off course. Weather officers at Baykonur continuously sent the latest wind data to a team of specialists at NPO Elektropribor in Kharkov, the design bureau that was responsible for Energiya’s guidance, navigation, and control systems. Computer simulations there convinced the team there was enough margin to go ahead, although the observed conditions were clearly outside the experience base for this type of launch vehicle. Winds were also near or above prescribed limits for a return-to-launch-site abort or a nominal landing. That problem was addressed by having Buran approach the runway from the northeast rather than the southwest, turning an out-of-limits tail wind into an acceptable head wind, although even that was on the limit.

The weather on 15 November 1988 violated just about every imaginable meteorological launch commit criterion for a Space Shuttle launch. Leaving aside the temperatures and the wind, two other showstoppers for a Shuttle launch that day would have been the precipitation and the low cloud cover. No NASA launch or flight director in his right mind would even consider launching or landing a Shuttle Orbiter if there is only the slightest chance of precipitation in the vicinity of the launch pad or runway. With the Orbiter moving at high speeds, precipitation has the potential of causing significant damage to the vehicle’s thermal protection system. However, for reasons that are not entirely clear, precipitation was no safety issue for the Russians, even though Buran’s thermal protection system was very similar to that of the Orbiter. Even hail was said to be an acceptable condition, although this may have been bluff more than anything else. In fact, Buran’s tiles suffered serious damage when the vehicle ran into a hail storm during a trip atop the Mriya carrier aircraft in 1989.

Cloud cover was not an issue for the Buran launch because there were no pilots on board who needed a clear view of the runway for a return to launch site or manual landing. The only clouds that meteorologists kept a close eye on were those with lightning potential. The overcast skies did prevent good ground-based optical track­ing during launch and landing, which can be a critical factor in post-flight analysis of anomalies.

Even though conditions were close to violating launch commit criteria, the team decided to fly anyway, despite another gale warning issued just 13 minutes before launch. True, the Russians’ launch weather rules in general were more relaxed than those adopted by NASA or the US Air Force, with some launches known to have taken place in near-blizzard conditions. However, the Buran mission was different from a conventional rocket launch in that the spacecraft was supposed to land like an aircraft.

All this begs the question why officials didn’t wait one or more days for the weather to clear, especially because this was the maiden flight of a vehicle vastly different from anything the Russians had flown before. Speaking shortly after the mission, former cosmonaut Gherman Titov said:

“We deliberately refused to postpone the launch and wait for ideal conditions.

The value of the flight is that its program included the maximum sum of real and

rather difficult tasks’’ [47].

Still, one can only wonder if the team didn’t suffer from what is sometimes referred to in the US as “launch fever’’. Testifying to this is an eyewitness report of one member of the meteorological support team, who claims that some of the observations that morning showed wind gusts of up to 25 m/s. However, the chief weather officer, under pressure to report good news, only presented the launch team with the weather updates that showed the lower wind speed values. The same person notes that Gudilin’s main argument in favor of launching that day was that another scrub could delay the flight until spring. It would require more testing and take them further into late autumn and possibly winter, when weather conditions can get far worse than the ones observed that morning [48].

Another concern with a lengthy delay may have been that the already frail support for the Buran program from the Soviet leadership might dwindle even further and could put the flight on indefinite hold, particularly now that the US Space Shuttle had returned to flight. Still, whatever the real motives were for launching that day, it was a decision fraught with risk [49].