To make Space Shuttle launches as economical as possible, the reuse of flight hardware is crucial. Unlike rocket boosters previously used in the space program, the Space Shuttle's solid rocket booster (SRB) casings and associated flight hardware are recovered at sea. The expended boosters are disassembled, refurbished and reloaded with solid propellant for reuse.
The two retrieval ships which perform the SRB recovery, the Liberty Star and Freedom Star, are unique vessels specifically designed and constructed for this task. Recovery Vessel (R/V) Freedom Star and R/V Liberty Star are owned by NASA. They were built at Atlantic Marine Shipyard, Fort George Island, near Jacksonville, Fla., in 1980 and 1981. The ships are 176 feet (53.6 meters) in length, 37 feet (11.2 meters) in width, and draw about 12 feet (3.6 meters) of water. Each ship displaces 1,052 tons (957 metric tons).
Each ship is propelled by two main engines providing a total of 2,900 horsepower. The main engines turn two seven-foot (2.1-meter) propellers with controllable pitch, which provides greater response time and maneuverability. The ships also are equipped with two thrusters. The stern thruster is a water jet system that allows the ship to move in any direction without the use of propellers. This system was installed to protect the endangered manatee population that inhabits regions of the Banana River where the ships are based. The system also allows divers to work near the ship during operations at a greatly reduced risk.
Improvements have been made to the ships since they first began service. In addition to controllable pitch propellers, both vessels are now outfitted with highly precise Global Positioning System (GPS) navigation equipment.
The ship's complement includes a crew of ten; a nine-person SRB retrieval team, a retrieval supervisor, a NASA representative, and observers. The maximum complement is 24 persons.
The typical Shuttle flight trajectory takes the vehicle away from the continental United States and over the Atlantic Ocean. Power is provided by the combination of the orbiter's three main engines and the twin SRBs.
A pair of SRBs, fully loaded with propellant, weigh about 1.4 million pounds (635,040 kilograms) apiece. They stand 149.2 feet (45.5 meters) tall, and have a diameter of 12 feet (3.6 meters). The boosters in use today are the largest solid propellant motors ever developed for space flight and the first to be used on a manned space vehicle. These boosters will propel the orbiter to a speed of 3,512 miles per hour (5,652 kilometers per hour).
At approximately two minutes after the Space Shuttle lifts off from the launch pad, the twin SRBs have expended their fuel. The boosters separate from the orbiter and its external tank at an altitude of approximately 30.3 statute miles (26.3 nautical miles/48.7 kilometers) above the Earth's surface. After separation, momentum will propel the SRBs for another 70 seconds to an altitude of 44.5 statute miles (38.6 nautical miles/71.6 kilometers) before they begin their long tumble back to Earth.
The nose cap of each booster is jettisoned at an altitude of 2.9 statute miles (2.5 nautical miles/4.6 kilometers) and deploys the pilot parachute. The pilot parachute immediately deploys the drogue parachute which is attached to the top of the frustum, the cone-shaped structure at the forward end of the booster.
At an altitude of 1.3 statute miles (1.1 nautical miles/2.1 kilometers), the frustums separate from the boosters. This releases three main parachutes housed within the frustums. It is these chutes that will quickly slow the booster's speed from 230 miles per hour (370.1 kilometers an hour) to a speed of 51 miles per hour (82.1 kilometers per hour). At approximately seven minutes after liftoff, the boosters will impact the Atlantic Ocean. The splashdown area is a box of about 6.9 by 10.4 statute miles (six by nine nautical miles/11.1 by 16.7 kilometers) located about 140 nautical miles (160 statute miles/257.6 kilometers) downrange from the launch pad.
The retrieval ships are on station at the time of splashdown, at about 9.2-11.5 statute miles (8-10 nautical miles/14.8-18.5 kilometers) from the impact area. As soon as the boosters enter the water, the ships accelerate to a speed of 15 knots (17.3 miles/27.8 kilometers an hour) and quickly close on the boosters.
Each ship retrieves one booster. Upon arrival, the team first conducts a visual assessment of the flight hardware. The main parachutes are the first items to be brought on board. Their shroud lines are wound onto each of three of the four reels on the ship's deck. The drogue parachute, attached to the frustum, is reeled onto the fourth reel until the frustum is approximately 50 feet astern of the ship. The 5,000-pound (2,268-kilogram) frustum is then lifted from the water using the ship's power block and deck crane.
With the chutes and frustum recovered, attention turns to the SRB. The dive team prepares for booster recovery. Two small inflatable boats, with eight retrieval divers aboard, are deployed. The job of the first dive team is to install a Diver-Operated Plug (DOP) in the nozzle of the booster. The DOP is launched from the ship and towed to the booster by one of the small boats. An air hose is then deployed from the ship. Once dive preparations are complete, the dive team enters the water for DOP insertion. The DOP is 22 feet (6.7 meters) in length and weighs 1,100 pounds (498 kilograms). It is neutrally buoyant in water, meaning it neither floats nor sinks, and is easily guided to the aft skirt at a depth of about 110 feet (33.5 meters) by the divers. A quick inspection of the nozzle is conducted. The DOP is then inserted into the booster nozzle. Once the DOP legs are locked in place and the nozzle sealed, an air hose is attached.
The second team double-checks the aft skirt and DOP installation to ensure there are no problems. After the second dive is completed, dewatering operations begin. Air is pumped from the ship through the DOP and into the booster, displacing water within the casing. As the process continues, the booster rises in the water until it becomes top-heavy. It falls horizontally, like a log in the water. Air pumping continues until all water is expelled from the empty casing.
The final step in the ocean retrieval procedure is to connect the ship's tow line. Once the tow connection is made, the divers return to the ship and the trip to NASA's Hangar AF on Cape Canaveral Air Station begins.
The ships enter Port Canaveral, where the booster is changed from the stern tow position to a position alongside the ship, the hip tow position, to allow greater control. The ships then pass through a drawbridge, Canaveral Locks, and transit the Banana River to Hangar AF. They are lifted from the water with Straddle-Lift cranes and placed on rail cars to begin the disassembly and refurbishment process.
Well suited for their role supporting Space Shuttle operations, the Liberty Star and Freedom Star also have proven themselves in other operations. Over the years, both vessels have seen service in side-scan sonar operations, cable-laying, underwater search and salvage, drone aircraft recovery, as platforms for robotic submarine operations and numerous support roles for other government agencies. They have a proven record of reliability and performance.