We watchers of the space program became accustomed to Space Shuttle landings, almost as much as we did their launches. On more than a hundred occasions between April 1981 and July 2011, we watched as the sleek black-and-white orbiters appeared in the Florida, California or—in the case of STS-3—in the New Mexico, plummeted like fast-moving bricks towards their runways and alighted with pinpoint grace on long expanses of concrete or dry-lakebed. Most landed without incident, although a few succumbed to burst tires, seized brakes and one almost “bounced”.
It would be foolhardy to think that shuttle landings were ever routine and their inherent dangers prompted the development of complex technologies to keep the vehicles and their crews safe. Thirty years ago this week, in January 1991, NASA awarded contracts to Rockwell International Corp.’s Space Division to implement one such technology: a technology that would take shuttle safety to new levels and become an instantly recognizable piece of its functional hardware: the “drag chute”.
But the idea of a braking parachute to assist with slowing the orbiter on the runway was by no means a new one. Right from the outset of its development in the early 1970s, it was intended that the shuttle would utilize such a system during its first four Orbital Flight Tests (OFTs). However, in 1974 the concept was deleted from consideration in the knowledge that vast expanse of dry lakebed available at Edwards Air Force Base, Calif.—the principal landing site for those early test flights—would prove more than suitable for adequate braking during touchdown and rollout.
But several landings in the pre-Challenger era generated grave cause for concern. In April 1985, shuttle Discovery landed in an eight-knot crosswind at the Kennedy Space Center (KSC) in Florida, forcing Commander Karol “Bo” Bobko to apply the right-hand brake and rudder more than the left in order to keep his ship on the runway centerline.
This “differential braking” led the inboard right-hand brake to “lock-up”, followed in short succession by its outboard counterpart. The consequence was a burst tire. From inside the orbiter, astronaut Don Williams heard the “bang, thump, thump, thump” as the crew instantly recognized that they had lost a tire. “We’d almost stopped anyway,” Williams told a NASA oral historian, years later, “so it turned out not to be a big deal, not an issue.”
Landings on the relatively narrow Shuttle Landing Facility (SLF) at KSC were called off for the remainder of the year, as improvements to the tires and brakes were implemented, with an expectation that they may resume in 1986.
The concern in Williams’ mind was that the tire loss could have led to debris problems, which could induce a puncture of another tire or even a fire. Fortunately, Discovery slowed to a smooth halt and it was only after disembarking that the astronauts saw the full extent of the damage: a trail of debris running a fair distance along the runway. So worried were ground personnel that the crew was not permitted to do their traditional “walk-around” inspection of the shuttle, lest another of the fully-pressurized tires blow.
The destruction of Challenger and the tragic loss of her STS-51L crew scuppered that brave hope and it was not until November 1990 that another shuttle crew made landfall on the Florida coast. After Challenger, efforts entered high gear to implement “arresting barriers” as additional safety mechanisms on shuttle runways and skids were considered for the landing gear to permit a “roll-on-rim” capability to achieve a predictable roll in the event of tire losses. And the drag chute was reconsidered, too.
In July 1990, NASA announced the start of drag chute tests at the Ames-Dryden Flight Research Facility at Edwards. It was noted that the new system would serve a two-fold purpose: supplementing the orbiter’s brakes to help slow its speed after touchdown, affording it the possibility to land safely in a shorter distance on the runway and reducing the likelihood of tire and brake wear. The tests were conducted using the NASA NB-52 carrier aircraft, piloted by former shuttle commander Gordon Fullerton and flown to an altitude of some 40,000 feet (12,000 meters).
Design requirementsd for the chute included an ability to bring a 248,000-pound (112,500 kg) shuttle to a complete halt within 8,000 feet (2,400 meters) with a ten-knot tail-wind and on a hot day, maximum braking at 140 knots ground-speed and with daytime temperatures of up to 39.4 degrees Celsius (103 degrees Fahrenheit). The chute was housed in a compartment pod at the base of the shuttle’s vertical stabilizer and would be manually deployed by the pilot prior to “derotation” of the nose landing gear down to the runway.
Trailing the vehicle as it barreled down to the runway, the chute would finally be jettisoned at 60 knots ground-speed to avoid damaging the bells of the three Space Shuttle Main Engines (SSMEs) just below it. Right from the start, it was intended that the chute could be employed on both lakebed and concrete runways, except in cases of crosswinds above 15 knots or repositioning problems involving the SSME bells. Deployment could occur within a range of speeds, with procedural preference for 195 knots, although not higher than around 230 knots.
Throughout the summer of 1990, air trials at Edwards saw the chute tested at landing speeds of between 160 mph (260 km/h) and 230 mph (370 km/h), with no negative effects. Although the shuttle can land at speeds as high as 260 mph (420 km/h), the NB-52 was restricted to a maximum landing speed of 230 mph (370 km/h).
Since the shuttle chute was actually a little smaller than the normal NB-52 chute, a modified orbiter drag chute compartment had to be added to the rear of the aircraft. This required its tail section to be correspondingly strengthened. Instrumentation recorded loads at various locations and aft-facing cameras monitored the deployment tests.
As a result of those trials, engineers predicted that it would reduce shuttle landing rollout distances between 1,000 feet (300 meters) and 2,000 feet (600 meters). And on 4 January 1991—30 years ago, this week—NASA modified its production contract with prime contractor Rockwell International Corp. by $33.3 million for the in-development shuttle Endeavour to incorporate the chute.
The work was conducted at Rockwell’s facilities in Downey, Calif., and Palmdale, Calif. It would be utilized for the first time on Endeavour’s maiden voyage, STS-49 in May 1992. The other three shuttles would then receive the chute modification: in order, Columbia was the second to receive it, followed by Discovery, and finally Atlantis.
Launched on 7 May 1992, the first drag chute saw service nine days later as Endeavour rolled out on Runway 22 at Edwards, to close out STS-49. Commander Dan Brandenstein achieved a perfect landing, with all six wheels—main landing gear and nose landing gear—firmly on the runway, before Pilot Kevin Chilton punched out the chute.
As intended, the chute compartment door blew away and a mortar fired to deploy the 9-foot-wide (2.7-meter) pilot chute. This then extracted the 40-foot-diameter (12-meter) main chute, which “reefed” to 40 percent of its total size for 3.5 seconds to lessen the initial structural loads on Endeavour herself. It trailed the orbiter by 89.5 feet (27.2 meters) on a 41.5-foot (12.6-meter) riser.
Finally, the reefing line cutter allowed the main chute to blossom open to its fully inflated configuration. Photographic analysis of the STS-49 landing showed that the reefed chute rode at a slightly higher angle than anticipated and the departure trajectory of the chute compartment door differed from the NB-52 tests. Additionally, its behavior and closeness to the shuttle’s centerline were attributed to the effect of aerodynamic flow for the fully-open speed brake.
“We really didn’t feel any of the opening shock,” Brandenstein said of the reefing. “But when it opened the full way, there was a significant tug on our shoulder harnesses and we were getting about an eight-foot-squared-per-second deceleration rate.” He allowed the chute to slow them down to about 100 knots, before gradually applying Endeavour’s brakes. At 60 knots, the chute was jettisoned.
Subsequent missions typically deployed the chute between main landing gear and nose gear touchdown. But on STS-47 in September 1992, it was found that the canopy noticeably “dragged” the orbiter sideways on the runway. This was also detected by the STS-52 crew a few weeks later, who observed a sideways shift to their left of about 15 feet (4.5 meters) on the 300-foot-wide (90-meter) runway.
Commander Jim Wetherbee detected a perceptible “tug” into the wind as the canopy entered its fully-reefed configuration. He felt that it did not pose significant concerns on such a wide runway, although Wetherbee did stress that Transoceanic Abort Landing (TAL) sites with narrower runways might pose greater issues pertaining to controllability.
From STS-49 in May 1992 through STS-135 in July 2011, the chute rode with dozens of returning shuttles, playing a key role in bringing their crews to a smooth halt on the runway with minimal impact upon brakes and tires. On the whole, its performance throughout the remainder of the program was admirable.
One off-nominal instance occurred in October 1998 on STS-95—the “John Glenn Flight”—when the drag chute compartment door panel detached and fell away during liftoff. The aluminum door, measuring 18 inches (46 cm) by 22 inches (56 cm) and weighing about 11 pounds (5 kg), was seen to hit the shuttle’s uppermost main engine, then disappearing from view.
Shuttle Discovery’s nine-day mission proceeded without incident, but with no certainty over the health of the drag chute in its now-doorless compartment, NASA erred on the side of caution and opted not to deploy it on touchdown. In fact, no one knew if it was even still intact and, if it was, whether or not it might inadvertently deploy during flight.
Commander Curt Brown and Pilot Steve Lindsey were given instructions for how to respond in the event of a problem. Should the chute accidentally deploy at an altitude of below 9 miles (15 km), they were told to expect the shuttle’s nose to pitch upwards slightly.
In such an eventuality, Brown was to remove his hands from the control column and Lindsey would hit the ARM, DEPLOY and JETTISON switches to rid themselves of the pesky chute. Should it deploy at lower altitudes of, say, less than 170 feet (50 meters) above the runway, the pilots would have to respond quickly, or the chute would pull Discovery’s nose upwards, increasing her sink-rate and causing her to hit the runway hard.
In the morning mail on landing day, 7 November 1998, Lindsey was told to keep his hands on the instrument panel, with the covers of the ARM, DEPLOY and JETTISON switches up, allowing him to flip all three before the chute could even unreef and inflate.
As circumstances transpired, Discovery landed without incident. The Shuttle Training Aircraft (STA), flown by Chief Astronaut Charlie Precourt, had earlier conducted weather observations and now was put to work visually monitoring the drag chute. Nothing untoward occurred and the shuttle touched down on concrete Runway 33 at the Kennedy Space Center (KSC) in Florida, with Brown and Lindsey facing no controllability problems.
By the end of its career in 2011, drag chutes had guided 86 shuttles to a smooth halt on runways at Edwards or KSC, playing a significant role in reducing wear on brakes and tires and improving the overall flight safety of this experimental and inherently dangerous flying machine.