Mercury-Redstone 4 was a Mercury program manned space mission launched on July 21, 1961 using a Redstone rocket. Its capsule was named Liberty Bell 7 and performed a suborbital flight piloted by astronaut Virgil I. "Gus" Grissom. It reached an altitude of over 118.26 mi (190 km) and traveled about 300 mi (480 km). The Redstone was MRLV-8 and the spacecraft was Mercury spacecraft # 11, the first one with a centerline window instead of two portholes.
McDonnell engineers came up with two different quick release hatches for the Mercury spacecraft. One with a latch, used on Ham's MR-2 and Shepard's MR-3 missions. The other design was an explosive release hatch. The quick release latching hatch weighed 69 lb (31 kg), too much of a weight addition to use on the orbital version of the spacecraft. The explosive hatch design used the 70 bolts of the original design; but each quarter-inch (6.35 mm) titanium bolt had a 0.06 in (1.5 mm) hole bored into it to provide a weak point. A mild detonating fuse (MDF) is installed in a channel between the inner and outer seal around the periphery of the hatch. When the MDF is ignited, the resulting gas pressure between the inner and outer seal causes the bolts to fail in tension.
There were two ways to fire the explosive hatch during recovery. On the inside of the hatch was a knobbed plunger. The pilot could remove a pin and press the plunger with a force of 5 or 6 lbf (25 N). This would detonate the explosive charge which would shear off the 70 bolts and propel the hatch 25 ft (8 m) away in 1 s. If the pin was left in place, a force of 40 lbf (180 N) was required to detonate the hatch. An outside rescuer could blow open the hatch by removing a small panel near the hatch and pulling a lanyard. The explosive hatch weighed only 23 lb (10 kg).
Before the Mercury 4 flight, Lewis Research Center and Space Task Group engineers had determined that firing the posigrade rockets into the booster-spacecraft adapter, rather than in the open, developed 78% greater thrust. This achieved a greater spacecraft-booster separation through a kind of "pop-gun" effect. By using this technique, the spacecraft separated at velocity of about 28.1 ft/s (9 m/s) rather than 15 ft/s (5 m/s) using the old procedure. Mercury 4 flight would take advantage of this new procedure.
Additional hardware changes to Mercury 4 were a redesigned fairing for the spacecraft-Redstone adapter clamp-ring and additional foam padding added to the head area of the contour couch. The fairing changes and additional foam were used to reduce vibrations the pilot experienced during the boost phase of flight. The spacecraft instrument panel was rearranged to provide a better eye scan pattern.
Redstone launch vehicle MRLV-8 arrived at Cape Canaveral on June 8, 1961. A mission review on July 15, 1961 pronounced Redstone MRLV-8 and Mercury spacecraft # 11 ready to go for the Mercury 4 mission.
Also, on July 15, 1961 Gus Grissom announced he would name Mercury 4, Liberty Bell 7. Grissom said the name was an appropriate call-sign for the bell-shaped capsule. He also said the name was synonymous with "freedom". As a tribute to the original Liberty Bell, a "crack" was painted on the side of the capsule.
The Mercury 4 mission was planned as a repeat of MR-3. It was to reach an apogee of 116 mi (187 km). The planned range was 299 mi (481 km). Grissom would experience a maximum acceleration of 6.33 g (62 m/s²) and deceleration of 10.96 g (107 m/s²).
The launch of Liberty Bell 7 was first planned for July 16. The cloud cover was too thick and the launch was postponed until July 18. On July 18, it was again postponed due to weather. Both times, the pilot had not yet boarded the spacecraft. On July 19, 1961, Grissom was aboard the Liberty Bell 7 when the flight was delayed again due to weather. At that point, it had just 10 minutes 30 seconds to go before launch.
On the morning of July 21, 1961, Gus Grissom entered the Liberty Bell 7 at 8:58 UTC and the 70 hatch bolts were put in place. At 45 minutes prior to the scheduled launch, a pad technician discovered that one of the hatch bolts was misaligned. During a 30 minute hold that was called, McDonnell and NASA Space Task Group engineers decided that the 69 remaining bolts should be sufficient to hold the hatch in place and blow it at the appropriate time. The misaligned bolt was not replaced.
Grissom later admitted at the postflight debriefing that he was "a bit scared" at liftoff, but he added that he soon gained confidence along with the acceleration increase. Hearing the engine roar at the pedestal, he thought that his elapsed-time clock had started late. Like Shepard, he was amazed at the smooth quality of the liftoff, but then he noticed gradually more severe vibrations. These were never violent enough to impair his vision.
Grissom's cabin pressure sealed off at the proper altitude, about 27,000 ft (8.2 km), and he felt elated that the environmental control system was in good working order. The suit and cabin temperature, about 57.5 and 97 °F (14 and 36 °C), respectively, were quite comfortable. Watching his instruments for the pitch rate of the Redstone, Grissom saw it follow directions as programmed, tilting over at about 1 deg/s.
Under a 3 g (29 m/s²) acceleration on the up-leg of his flight, Grissom noticed a sudden change in the color of the horizon from light blue to jet black. His attention was distracted by the noise of the tower-jettison rocket firing on schedule. The pilot felt the separation and watched the tower through the window as it drifted off, trailing smoke, to his right. At two minutes and 22 seconds after launch, the Redstone's Rocketdyne engine cut off after building a velocity of 6,561 ft/s (1 969 m/s). Grissom had a strong sensation of tumbling during the transition from high to zero acceleration, and, while he had become familiar with this sensation in centrifuge training, for a moment he lost his bearings.
The Redstone coasted for 10 seconds after its engine cut off; then a sharp report signaled that the posigrade rockets were popping the capsule loose from the booster. Although Grissom peered out his window throughout his ship's turnaround maneuver, he never caught sight of his launch vehicle.
Turning reluctantly to his dials and control stick, Grissom made a pitch movement change but was past his desired mark. He jockeyed the handcontroller stick for position, trying to damp out all oscillations, then made a yaw movement and went too far in that direction. By the time the proper attitude was attained, the short time allocated for these maneuvers had been used, so he omitted the roll movement altogether. The manual controls impressed Grissom as very sluggish when compared to the Mercury procedures trainer. Then he switched to the new rate command control system and found perfect response, although fuel consumption was high.
After the pitch and yaw maneuvers, Grissom made a roll-over movement so he could see the ground from his window. Some land beneath the clouds (later determined to be western Florida around the Apalachicola area) appeared in the hazy distance, but the pilot was unable to identify it. Suddenly Cape Canaveral came into view so clearly that Grissom found it hard to believe that his slant-range was over 150 mi (240 km).
He saw Merritt Island, the Banana River, the Indian River, and what appeared to be a large airport runway. South of Cape Canaveral, he saw what he believed to be West Palm Beach.
Pitching the spacecraft over into a reentry attitude of 14 degrees from Earth-vertical, the pilot tried to see the stars out his observation window. Instead the glare of sunlight filled his capsule, making it difficult to read the panel dials, particularly those with blue lights. Grissom felt that he would not have noticed the 0.05 g (0.5 m/s²) light if he had not known it was about to flash on.
Reentry presented no problem. Grissom could not feel the oscillations following the acceleration buildup; he could only read them on the rate indicators. Meanwhile he continued to report to the Mercury Control Center on his electric current reading, fuel quantity, acceleration, and other instrument indications. Condensation and smoke trailed off the heatshield at about 65,000 ft (20 km) as Liberty Bell 7 plunged back into the atmosphere.
The drogue parachute deployed on schedule at 21,000 ft (6.4 km). Grissom said he saw the deployment and felt some resulting pulsating motion, but not enough to worry him. Main parachute deployment occurred at 12,300 ft (3.7 km), which was about 1,000 ft (300 m) higher than the design nominal altitude. Watching the main chute unfurl, Grissom spotted a 6 in (150 mm) L-shaped tear and another 2 in (50 mm) puncture in the canopy. Although he worried about them, the holes grew no bigger and his rate of descent soon slowed to about 28 ft/s (9 m/s). Dumping his peroxide control fuel, the pilot began transmitting his panel readings.
Preparing for recovery, he disconnected his helmet and checked himself for debarkation. The neck dam did not unroll easily; Grissom tinkered with his suit collar to ensure his buoyancy in the event that he had to get out of the spacecraft quickly. When the recovery helicopters, which had taken to the air at launch time and visually followed the contrails and parachute descent, were still about 2 mi (3 km) from the impact point, which was only 3 mi (5 km) beyond the bullseye, Lieutenant James L. Lewis, pilot of the primary recovery helicopter, radioed Grissom to ask if he was ready for pickup. He replied that he wanted them to wait five minutes while he recorded his cockpit panel data. Using a grease pencil with the pressure suit gloves was awkward, and several times the suit ventilation caused the neck dam to balloon, but the pilot simply placed his finger between neck and dam to allow the air to escape.
Grissom had difficulty recollecting his actions at this point, but he was certain that he had not touched the hatch-activation plunger. He removed his helmet, grasped the instrument panel with his right hand, and climbed out of the sloshing hatchway. Floating in the sea, he was thankful that he had unbuckled himself earlier from most of his harness, including the chest restraints, otherwise he might not have been able to exit.
Lieutenant John Reinhard, co-pilot of the nearest recovery helicopter, reported afterward that the helicopters were making their final approach for pick-up. He was preparing to cut the capsule's antenna whip (according to a new procedure) with a squib-actuated cutter at the end of a pole, when he saw the hatch cover fly off, strike the water at a distance of about 5 ft (1.5 m) from the hatch, and then go skipping over the waves. Next he saw Grissom's head appear, and the astronaut began climbing through the hatch. Once out, Grissom swam away.
Reinhard immediately prepared to pass the floating astronaut the personnel hoist. But at that moment Lewis called a warning that a detector light had flashed on the instrument panel, indicating that metal chips were in the oil sump because of engine strain. Considering the implication of impending engine failure, Lewis told Reinhard to retract the personnel hoist while he called the second chopper to retrieve the pilot.
Meanwhile Grissom, having made certain that he was not snared by any lines, noticed that the primary helicopter was having trouble raising the submerged spacecraft. He swam back to the capsule to see if he could assist but found the cable properly attached. When he looked up for the personnel line, he saw the helicopter start to move away.
Suddenly Grissom realized that he was not riding as high in the water as he had been. All the time he had been in the water he kept feeling air escape through the neck dam. The more air he lost, the less buoyancy he had. Moreover, he had forgotten to secure his suit inlet valve. Swimming was becoming difficult, and now with the second helicopter moving in he found the rotor wash between the two aircraft was making swimming more difficult. Bobbing under the waves, Grissom was scared, angry, and looking for a swimmer from one of the helicopters to help him tread water. Then he caught sight of a familiar face, that of George Cox, aboard the second helicopter. Cox was the copilot who had retrieved both the chimpanzee Ham and Shepard on the first Mercury flight. With his head barely above water, Grissom found the sight of Cox heartening.
Cox tossed the "horse-collar" lifeline straight to Grissom, who immediately wrapped himself into the sling backwards. Lack of orthodoxy mattered little to Grissom now, for he was on his way to the safety of the helicopter, even though swells dunked him twice more before he got aboard. His first thought was to get a life preserver on. Grissom had been either swimming or floating for a period of only four or five minutes, "although it seemed like an eternity to me," as he said afterward.
As the first helicopter moved away from Grissom, it struggled to raise the spacecraft high enough to drain the water from the impact bag. Once the capsule was almost clear of the water, but like an anchor it prevented the helicopter from moving forward. The flooded Liberty Bell 7 weighed over 5,000 lb (2 300 kg), 1,000 lb (450 kg) beyond the helicopter's lifting capacity. The pilot, watching his insistent red warning light, decided not to chance losing two craft in one day. He finally cast loose, allowing the spacecraft to sink swiftly. Martin Byrnes, aboard the carrier, suggested that a marker be placed at the point so that the capsule might be recovered later. Rear Admiral J. E. Clark advised Byrnes that in that area the depth was about 2,800 fathoms (5.1 km).
In the very next Mercury flight, Astronaut Wally Schirra manually blew Sigma 7's hatch after splashdown, in a deliberate attempt to dispel the rumor that Grissom might have blown Liberty Bell 7's hatch deliberately. As anticipated, the kickback from the manual trigger left Schirra with a visible injury to his right hand. Grissom was uninjured when he exited the capsule.
Several years later, during an interview on April 12, 1965, Grissom said he thought the hatch may have been triggered because the external release lanyard came loose. On Liberty Bell 7, the external release lanyard was only held in place by a single screw. It was better secured on later flights. This theory is accepted by Guenter Wendt, "Pad Fuhrer" for most early American manned spaceflights.
Ironically, the inability to open a hatch swiftly contributed to Grissom's death, as well as Ed White and Roger B. Chaffee, in the Apollo 1 launch-pad fire. Use of an explosive hatch had been rejected following the discovery by engineers that, in fact, an explosive egress system on a spacecraft could inadvertently fire without being triggered. Following the Apollo fire, Block II Apollo spacecraft were equipped with rapid-opening systems.
|T+00:00:00||Liftoff||Mercury-Redstone lifts off, onboard clock starts.|
|T+00:00:16||Pitch Program||Redstone pitches over 2 deg/s from 90 deg to 45 deg.|
|T+00:00:40||End Pitch Program||Redstone reaches 45 deg pitch.|
|T+00:01:24||Max Q||Maximum dynamic pressure ~575 lbf/ft² (28 kPa).|
|T+00:02:20||BECO||Redstone engine shutdown - Booster Engine Cutoff. Velocity 5,200 mph (2.3 km/s)|
|T+00:02:22||Tower Jettison||Escape Tower Jettison, no longer needed.|
|T+00:02:24||Capsule Separation||Posigrade rockets fire for 1 s giving 15 ft/s (4.6 m/s) separation.|
|T+00:02:35||Turnaround Maneuver||Capsule (ASCS) system rotates capsule 180 deg, to heat shield forward attitude. Nose is pitched down 34 deg to retro fire position.|
|T+00:05:00||Apogee||Apogee of about 115 mi (185 km) reached at 150 mi (240 km) downrange from launch site.|
|T+00:05:15||Retrofire||Three retro rockets fire for 10 s each. They are started at 5 s intervals, firing overlaps. Delta-V of 550 ft/s (168 m/s) is taken off forward velocity.|
|T+00:05:45||Retract Periscope||Periscope is automatically retracted in preparation for reentry.|
|T+00:06:15||Retro Pack Jettison||One minute after retrofire retro pack is jettisoned, leaving heatshield clear.|
|T+00:06:20||Retro Attitude Maneuver||(ASCS) orients capsule in 34 deg nose down pitch, 0 deg roll, 0 deg yaw.|
|T+00:07:15||.05 g Maneuver||(ASCS) detects beginning of reentry and rolls capsule at 10 deg/s to stabilize capsule during reentry.|
|T+00:09:38||Drogue Parachute Deploy||Drogue parachute deployed at 22,000 ft (6.7 km) slowing descent to 365 ft/s (111 m/s) and stabilizing capsule.|
|T+00:09:45||Snorkel Deploy||Fresh air snorkel deploys at 20,000 ft (6 km). (ECS) switches to emergency oxygen rate to cool cabin.|
|T+00:10:15||Main Parachute Deploy||Main parachute deploys at 10,000 ft (3 km). Descent rate slows to 30 ft/s (9 m/s)|
|T+00:10:20||Landing Bag Deploy||Landing Bag Deploys, dropping heat shield down 4 ft (1.2 m).|
|T+00:10:20||Fuel Dump||Remaining hydrogen peroxide fuel automatically dumped.|
|T+00:15:30||Splashdown||Capsule lands in water about 300 mi (500 km) downrange from launch site.|
|T+00:15:30||Rescue Aids Deploy||Rescue aid package deployed. The package includes green dye marker, recovery radio beacon and whip antenna.|