Shuttle Booster Rocket Recovery

by Jim Bates

The U.S.'s National Aeronautics and Space Administration (best known by its acronym, NASA) recently announced that American astronaut Dr. Shannon Lucid would have to remain aboard the Russian space station "Mir" until mid-September (extending six weeks beyond the original return time). That unexpected extension, which will force later scheduled missions, was because replacements would be needed for the two solid-fuel booster rockets scheduled to be used for the launch of the shuttle "Atlantis" on a retrieval mission to return the woman astronaut to earth at the completion of her assigned mission.

On July 12, NASA managers decided to replace the reusable solid rocket motors on the Space Shuttle "Atlantis" because of concerns about reliability of certain components. Technicians disassembling the motors of the "Columbia" shuttle (STS-78) used on the previous space mission noted that hot gas had seeped into J-joints of the motor's "field joints." An investigation concluded that risk of a field joint failure was improbable on the scheduled STS-79 Atlantis mission because a new field joint cleaning process and adhesive were used in motor assembly. However, the decision to replace the STS-79 solid rocket motors was made to improve the safety margin of critical J-joints. NASA continues to be haunted by the horrific "Challenger" accident in 1986 when both primary and backup O-rings failed during a fiery liftoff.

Mrs. Shannon, a 53-year old biochemist, and mother of three grown children (her youngest daughter is a computer scientist), had been launched from Earth into space on March 22. It was her fifth space flight, a world record for women. Two days later, on March 24, she transferred from the American shuttle to the Russian space vehicle, to be the second American astronaut to live aboard the 10-year-old Mir station, sharing the close quarters with two male Russian astronauts. She has surpassed the July 1995 record of a male American astronaut and physician who spent 112 days on Mir. (The world endurance record for space travel is 15 months, held by a Russian.)

Dr. Lucid is the second of eight Americans who will, in keeping with a U.S.-Russian space agreement, be aboard Mir in rotating shifts until the end of 1997, when construction is scheduled to begin on an international space station.

American space shuttles are launched high into space while secured to a primary rocket engine from which the shuttle later separates when ready to enter into a predetermined orbit about planet Earth.

During the initial lift-off phase of the launch, two 15-story shuttle booster rockets (SRBs) -- each containing rubbery, highly explosive fuel -- located on left and right sides of the main rocket engine, are also ignited to provide an additional powerful kick to send the shuttle up and away from the launch site.

More than two minutes later, nearly 30 miles up, the two expended SRB bodies are separated from the primary rocket that continues to burn and carries the shuttle still higher. Though their job is done, the emptied reusable propellant casings continue to rise for another 70-plus seconds, impelled onward by momentum, but steadily slowing, finally reaching the apogee of their travel, then arcing into a downward path toward the surface far below.

NASA scientists, to increase the margin of safety for the crew of the shuttle launched to retrieve Dr. Lucid from Mir, opted to substitute critical parts of the booster rockets, thereby delaying the Atlantis mission until mid-September.

* * *

What goes on when shuttle rocket boosters separate from a space-bound shuttle's primary rocket and then are returned to earth?

You might know -- from television and media photographs -- that the reusable boosters land in the ocean by parachute; that everything is picked up by ships patrolling the preplanned landing areas, returned to a land-based refurbishment area, fixed up, and used for another shuttle flight. Sounds simple enough, doesn't it?

But it really is not a simple and brief process. Equipment is complex; multiple processes are labor-intensive and time-consuming. Here is what is actually involved:

Two 150-foot long, 12.5-foot-diameter rocket "boosters" are part of a shuttle launch system. Attached to the main rocket -- firing in conjunction with it for liftoff -- both SRBs separate from the rocket at a predetermined time in the flight path and start return to the surface, with landing planned for 100 miles at sea.

Booster Separation

Booster separation takes place 124 seconds after launch, at an altitude of 156,000 feet (over 29 miles high). The SRB continues upward ascent, but slowing, toward an apogee of 238,000 feet (45-plus miles), reached at T196.0 (T = seconds after launch). Then return to earth begins, moving in a tilted, nose-high, high-angle-of-attack flight path.

At T325.0 (48,500 feet), the fast-descending SRB is in a high-angle-of-attack reentry mode. In another 24.4 seconds (T349.4; 16,000 feet), the SRB nosecap (measuring 6.2 feet high) is ejected and the 11.5-foot-diameter pilot chute is deployed at 360 mile per hour. That action releases restraints and the stabilizing 54-foot-diameter drogue parachute is freed. It is designed to deploy at any SRB angle above the horizon and orients the SRB to a vertical attitude for later proper deployment of a cluster of three main 136-foot-diameter parachutes still stowed within the frustum lowered by the drogue chute.

The drogue chute goes through three distinct inflation stages in just 12 seconds. Each stage is accomplished by pyrotechnically actuated cutters that sever a "reefing line" that keeps the skirt of the drogue gathered until the line is cut. At deployment (T351.4; 14,820 feet) the first reefed condition is 60% of canopy inflation; second reefing stage is 80%-inflation (T358.3; 11,590 feet). At T362.8 and 9,640 feet, the drogue chute disreefs and fully inflates, slowing SRB steady descent to 250 mph.

Some 10 seconds later (T371.0; 6,000 feet), "main parachute cluster" deployment occurs. The cluster is mounted in a 10.5-foot-high "frustum" (a geometrical term describing a form) attached to the SRB's "forward skirt." At that 10-second mark, the frustum is pyrotechnically separated from the SRB and the drogue chute rapidly decelerates the frustum as the SRB continues falling.

Three main parachutes, connected to fittings on the SRB forward skirt, deploy from the bottom of the frustum. Simultaneously, each main canopy goes through three inflation stages in 17 seconds -- in the same manner as the drogue parachute -- sequentially slowing the SRB from 250 mph to 50 mph (75 feet per second). With the three main canopies deployed, the already-separated drogue chute/frustum assembly descends to the ocean, splashing down at 40 mph, 45 seconds after the SRB.

Main Canopy Disreefing

Main canopy first-reefed-condition is 15% of full inflation (T375, 4,873 feet); second stage of disreefing is 37%-inflation (T383.6; 2,840 feet); full inflation occurs at T388.9 and 2,050 feet. The elapsed deployment/inflation time of pilot, drogue, and main parachutes after nose cap separation is 39.5 seconds. The SRB splashes into the ocean at T414.3, traveling at 50 mph, 65 seconds after the SRB nose cap separated.

Canopy Retrieval and Recovery

A shipboard retrieval crew recovers all items from the ocean and delivers them to a Parachute Refurbishment Facility (PRF) at Kennedy Space Center in Florida. The parachute is constantly kept wet while aboard the ship to prevent ocean salt from crystallizing on fabric.

At the PRF, the wet parachutes are untangled, washed, dried, inspected, repaired, and packed. Untangling takes place in an outside, covered "defoul" area.

A crew typically takes four hours to untangle and hang a parachute on a wash/dry rack mounted on a monorail system. The parachute is then taken along the monorail into an above- ground, 30,000-gallon washer. The concrete structure is filled to a six-foot depth with fresh water, immersing the parachute. Water is circulated for one hour at 1,300 gallons per minute.

When the washer is drained, the parachute is transferred along the monorail into a dryer and dried with 140-degree hot air at 13,000 cubic feet per minute. Drying takes three hours in winter, five hours in summer because of greater humidity in that season

From the dryer, the parachute is moved into one of four aisles of the air-conditioned indoor area where the remainder of processing takes place. Three aisles are dual-purpose, where refurbishment and packing can be done. The fourth is for refurbishment only and is used for badly damaged parachutes.

Canopy Assembly Refurbishment

Refurbishment starts with detailed inspection under high intensity lighting. After inspection, the Engineering Department identifies damage as "acceptable," "standard repair," or "nonstandard repair."

Repair work begins, using various state-of-the-art sewing machines. Nonstandard repairs require that samples be manufactured and tested for satisfactory strength. Standard repairs previously had this same validation.

One main canopy typically needs more than 400 repairs, generally requiring over a week to make.

Packing Main Canopies

Packing each main canopy begins with installing two reefing lines that intentionally keep a canopy skirt together, preventing full expansion until the line is severed, thus controlling staged parachute opening (pyrotechnic cutters are installed later).

Suspension lines are placed in a tensioning fixture, then tacked together with thread, to aid later packing. Under 2,400-pound tension, the bulky, heavy canopy is pleated manually

The canopy is then sequentially stowed, apex first, into an upside-down (open end up) deployment bag positioned in a shipping container. The canopy is periodically compressed with a 10,000-pound press to make it fit bag volume. Pyrotechnic reefing line cutters are installed (each line has redundant cutters). The bag's canopy compartment flaps are closed with chain lacing. Next, the 200 feet of suspension line elements are tied to the bag at two-foot intervals with 35- pound breakcord. With all lines stowed, line compartment flaps are closed with chain lacing.

High-Speed System Deployment

Here is an interesting note: The total packing operation takes a crew about one week to complete, but the deployment sequence, covering the length of a football field, takes only little more than one second!

Readying for Shipment

When three main 136-foot-diameter canopies are packed they are put into a metal support structure to form a parachute cluster. The cluster, mounted on a transportation pallet, is shipped to the Assembly and Refurbishment Facility (ARF). A drogue parachute is shipped separately, along with a new pilot chute. The parachutes are then integrated with an SRB frustum at the ARF.

To understand the magnitude of the work of the Parachute Refurbishment Facility, study the "numbers" for each parachute component of an SRB recovery system (many other parts greatly add to complexity of the entire system):

Pilot Parachute

Nominal diameter: 11.5 feet

Canopy: Conical ribbon; 16 gores; 16% porosity (See Note 1)

Weight: 35 pounds

Suspension lines: 18 feet long

Design load: 14,500 pounds

Drogue Parachute

Nominal diameter: 54 feet

Canopy: Conical ribbon; 60 gores; 16% porosity

Weight: 1,100 pounds

Suspension lines: 105 feet long; 60 lines in 12 groups

Design load: 270,000 pounds

Main Parachute (3 per SRB)

Nominal diameter: 136.0 feet

Canopy: Conical ribbon; 160 gores; 16% porosity

Weight: 2,150 pounds

Suspension lines: 204 feet long; 160 in eight dispersion bridles

Design load: 175,000 pounds

Note 1 -- "Porosity" in a parachute canopy refers to the ratio of space (or "void" or "interstitial area") to the total area of the canopy, expressed in percentage. An example would be a round solid-fabric canopy (such as in a pilot's emergency rig or the auxiliary ("reserve") parachute used by a sport parachutist/skydiver), where the canopy is altered (modified) for steerability by having portions removed to create large thrust "windows" and smaller combined drive/steering slots (openings). The percentage would refer to the material removed to create the openings desired. Porosity is often incorrectly used synonymously used with "permeability."

Permeability is a measurement rate that defines the "mass rate of flow" (or the "volume rate of flow") for an area of cloth. In the U.S., permeability is measured by determining the amount of air passed through one square foot of fabric per minute using one half inch of water pressure. Porosity is often incorrectly used in place of permeability.

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