Encyclopedia Astronautica
Mercury MR-4



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Mercury 4
Credit: NASA
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Mercury MR-4
Grissom is hoisted from the water
Credit: NASA
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Mercury MR-4
Somber Grissom aboard the carrier
Credit: NASA
Crew: Grissom. Suborbital flight; second American in space. Hatch blew after splashdown; capsule sank; astronaut barely saved before drowning. Backup crew: Glenn.

The Mercury capsule, Liberty Bell 7, manned by Astronaut Virgil I. Grissom, boosted by a Redstone rocket, reached a peak altitude of 190.3 km and a speed of 8,335 km per hour. After a flight of 15 minutes and 37 seconds, the landing was made 487 km downrange from the launch site. The hatch blew while still in water, and the capsule sank; Grissom saved, though his suit was filling up with water through open oxygen inlet lines.

This was the second and final manned suborbital Mercury Redstone flight, and the first flight with trapezoidal window. Further suborbital flights (each astronaut was to make one as a training exercise) were cancelled. An attempt to recover the capsule in very deep water in 1994 not successful. It was finally raised in the summer of 1999.

Official NASA Account of the Mission from This New Ocean: A History of Project Mercury, by Loyd S. Swenson Jr., James M. Grimwood, and Charles C. Alexander, NASA Historical Series SP-4201, 1966.

Grissom was unruffled, calm, and poised as he entered Liberty Bell 7. The count resumed and proceeded smoothly until 45 minutes before launch time, when a gantry technician discovered that one of the 70 hatch bolts was misaligned. A 30-minute hold was called, during which the McDonnell and STG supervisory engineers decided that the remaining 69 bolts were sufficient to hold and blow the hatch, so the misaligned bolt was not replaced. The countdown was resumed, but two more holds for minor reasons cost another hour's wait.

Alone in his capsule awaiting liftoff, Grissom experienced a wide range of impressions. As the gantry, or service structure, moved back from the launch vehicle, he had the illusion that he was falling. His pulse rate ranged from 64 to 162 beats per minute, depending upon his feelings. His heart beat rose during the oxygen purge, fell while the hatch bolt repair decision was being made, rose again when the go decision was made, and finally doubled at launch. His liftoff was at 7:20a.m.

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 g buildup. 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, never violent enough to impair his vision. To the watchers on the ground, the Redstone and the capsule appeared to rise slowly and to pass through a thin, broken cloud window. Then the rocket disappeared, leaving a contrail that was visible on the beach for about a minute. Grissom's cabin pressure sealed off at the proper altitude, about 27,000 feet, and he felt elated that the environmental control system was in good working order. The suit and cabin temperature, about 57.5 and 97 degrees F, respectively, were quite comfortable. Watching his instruments for the pitch rate of the Redstone, Grissom saw it follow directions as programmed, tilting over about one degree per second.

Under a 3-g load 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 6561 feet per second. Grissom had a strong sensation of tumbling during the transition from high to zero g, 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. Angular motion was perceptible to Grissom only by watching the needle move on the dial or by seeing an Earth reference by chance. Another cue to the spacecraft's movement was the Sun's rays, which gradually moved up his torso toward his face, threatening temporary blindness. Grissom fretted over the automatic turnaround that should have reversed the capsule faster.

With turnaround accomplished, the Air Force jet pilot for the first time became a space pilot, assuming manual-proportional control. A constant urge to look out the window made concentrating on his control tasks difficult. He told Shepard back in Mercury Control that the panorama of Earth's horizon, presenting an 800-mile arc at peak altitude, was fascinating. His instruments rated a poor second to the spectacle below.

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 miles.

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. He tried to report to Shepard on the high-frequency communications circuit every landmark he saw, but his transmissions were not received. These observations got Grissom behind in his work procedures, as he realized when he saw the periscope retract.

With Liberty Bell 7 at an altitude of 118.26 miles, it was now time to position the spacecraft in its reentry attitude. Grissom had initiated the retrorocket sequence and the capsule was arcing downward. His pulse reached 171 beats per minute.Retrofire gave him the distinct and peculiar feeling that he had reversed his backward flight through space and was actually moving face forward. As he plummeted downward, he saw what appeared to be two of the spent retrorockets pass across the periscope view after the retrorocket package had been jettisoned.

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 .05-g light if he had not known it was about to flash on.

Reentry presented no problem. Grissom could not feel the oscillations following the g 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, g loads, and other instrument indications. Condensation and smoke trailed off the heatshield at about 65,000 feet as Liberty Bell 7 plunged back into the atmosphere.

The drogue parachute deployed on schedule at 21,000 feet. 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 feet, which was about 1,000 feet higher than the design nominal altitude. Watching the main chute unfurl, Grissom spotted a six-inch L-shaped tear and another two-inch puncture in the canopy. Although he worried about them, the holes grew no bigger and his rate of descent soon slowed to about 28 feet per second. Dumping his peroxide control fuel, the pilot began transmitting his panel readings.

A "clunk" confirmed that the landing bag had dropped in preparation for impact. Grissom then removed his oxygen hose and opened his visor but deliberately left the suit ventilation hose attached. Impact was milder than he had expected, although the capsule heeled over in the water until Grissom was lying on his left side. He thought he was facing downward. The capsule gradually righted itself, and, as the window cleared the water, Grissom jettisoned the reserve parachute and activated the rescue aids switch. Liberty Bell 7 still appeared watertight, although it was rolling badly with the swells.

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 if 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 two miles from the impact point, which was only three miles 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.

After logging the panel data, Grissom asked the helicopters to begin the approach for pickup. He removed the pin from the hatch-cover detonator and lay back in the dry couch. "I was lying there, minding my own business," he said afterward, "when I heard a dull thud." The hatch cover blew away, and salt water swished into the capsule as it bobbed in the ocean. The third man to return from space was faced with the first serious emergency; Liberty Bell 7 was shipping water and sinking fast.

Grissom had difficulty recollecting his actions at this point, but he was certain that he had not touched the hatch-activation plunger. He doffed his helmet, grasped the instrument panel with his right hand, and scurried out 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 abandon ship.

Lieutenant John Reinhard, copilot of the nearest recovery helicopter, reported afterward that the choppers were making their final approach for pickup. 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 five feet 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, the pressure-suited spaceman swam away.

Instead of turning his attention to Grissom, Lewis completed his approach to the sinking spacecraft, as both he and Reinhard were intent on capsule recovery. This action was a conditioned reflex based on past training experience. While training off the Virginia beaches the helicopter pilots had noted that the astronauts seemed at home in and to enjoy the water. So Reinhard quickly clipped the high-frequency antenna as soon as the helicopter reached Liberty Bell 7. Throwing aside the antenna cutting device, Reinhard picked up the shepherd's hook recovery pole and carefully threaded the crook through the recovery loop on top of the capsule. By this time Lewis had lowered the helicopter to assist Reinhard in his task to a point that the chopper's three wheels were in the water. Liberty Bell 7 sank out of sight, but the pickup pole twanged as the attached cable went taut, indicating to the helicopter pilots that they had made their catch.

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 Astronaut Shepard. 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 valiantly 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 pounds, a thousand pounds 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.

On the carrier Randolph, examining physicians Strong and Laning, the same men who had gone over Shepard, found Grissom extremely tired. But the MR-4 astronaut elected to proceed with his preliminary debriefing before going on to Grand Bahama. The recovery finale, of course, continually intruded in the discussion. Grissom said he was extremely grateful to Walter Schirra for the developmental work he had done on the neck dam. He felt that this had saved his life, although later tests disclosed other difficulties. The debriefing sessions aboard the Randolph and at Grand Bahama centered on the need for more egress training (there had been none since April) and the formulation of specific emergency recovery procedures. Grissom said that he thought he should have been a little more precise in his attitude control functions. This was a moot point in view of the sluggishness he had encountered with the manual system and the apparent play in the control stick linkage. Other than this anomaly, the spacecraft had performed well; noises of the sequential events had provided good cues; vibrations had been minimal; the new window had been a delight and should prove useful on orbital flights; and the environmental control system had functioned well. But, said Grissom, there were too many couch restraint straps; the panel lights were too dim; the oxygen consumption rate was high; the urinal device needed further development; the high-frequency communication circuit was unsuccessful; and hydrogen peroxide fuel consumption proved to be high on the rate control system. The last item of that list caused little concern among the Space Task Group engineers, for they had decided that the rate command mode would be used primarily for reentry, when fuel economy was less important.

At Grand Bahama, Grissom rested and appeared to have suffered no abnormal effects from flight into space. The evaluators conceded, however, that the abnormal recovery experience would have made any such effects difficult to analyze or to attribute to flight causes. Further questioning of the astronaut followed the routine established in Shepard's debriefing.

Obviously one of the major problems to be explained and resolved following the flight of Liberty Bell 7 was the malfunction of the explosive egress hatch. Before the mission, Minneapolis-Honeywell had conducted environmental tests to qualify the hatch and igniter assembly. Although the tests had been run with the pin installed, conditions had been severe. The component had been subjected to low and high temperature ranges, a 100-g shock force, and salt-spray and water-immersion tests. After MR-4, the Space Task Group established a committee that included Astronaut Schirra to study the hatch problem. Tests were conducted in an environment even more severe than that used by the manufacturer, but no premature explosions occurred. Studies were made of individuals operating the panel switches on the side nearest the actuator; the clearance margin appeared to be adequate. According to Schirra, "There was only a very remote possibility that the plunger could have been actuated inadvertently by the pilot."

The mystery of Grissom's hatch was never solved to everyone's satisfaction. Among the favorite hypotheses were that the exterior lanyard might have become entangled with the landing bag straps; that the ring seal might have been omitted on the detonation plunger, reducing the pressure necessary to actuate it; or that static electricity generated by the helicopter had fired the hatch cover. But with the spacecraft and its onboard evidence lying 15,000 feet down on the bottom of the Atlantic Ocean, it was impossible to determine the true cause. The only solution was to draft a procedure that would preclude a recurrence: henceforth the astronaut would not touch the plunger pin until the helicopter hooked on and the line was taut. As it turned out, Liberty Bell 7 was the last manned flight in Project Mercury in which helicopter retrieval of the spacecraft was planned. In addition, Grissom would be the only astronaut who used the hatch without receiving a slight hand injury. As he later reminded Glenn, Schirra, and Cooper, this helped prove he had not touched his hatch plunger.

AKA: Liberty Bell 7.
Location: In the Atlantic Ocean (5 km deep, 832 km NW of Grand Turk island, 1961-1999; Kansas Cosmosphere thereafter..
First Launch: 1961.07.21.
Last Launch: 1961.07.21.
Duration: 0.0108 days.

More... - Chronology...


Associated People
  • Glenn Glenn, John Herschel Jr (1921-) American test pilot astronaut, later a politician and US Senator. First American in orbit on his first flight, Mercury MA-6, in 1962, and oldest person in space on his second flight, STS-95, in 1998. More...
  • Grissom Grissom, Virgil Ivan 'Gus' (1926-1967) American test pilot astronaut. Flew on Mercury MR-4, Gemini 3. Second American in space and first Gemini commander. Flew 100 combat missions in Korea. Died in on-pad fire of Apollo 1. More...

See also
Associated Programs
  • Mercury Mercury was America's first man-in-space project. Setting the precedent for the later Gemini, Apollo, and Shuttle programs, any capsule configuration proposed by the contractors was acceptable as long as it was the one NASA's Langley facility, and in particular, Max Faget, had developed. McDonnell, at that time a renegade contractor of innovative Navy fighters that had a history of problems in service, received the contract. The capsule had to be as small as possible to match the payload capability of America's first ICBM, the Atlas, which would be used for orbital missions. The resulting design was less than a third of the weight of the Russian Vostok spacecraft, and more limited as a result. More...

Mercury MR-4 Chronology


1961 March 7 - . LV Family: Redstone. Launch Vehicle: Redstone MRLV.
  • Mercury spacecraft No. 11 delivered to Cape Canaveral - . Nation: USA. Program: Mercury. Flight: Mercury MR-4. Spacecraft: Mercury. Summary: Spacecraft No. 11 was delivered to Cape Canaveral for the Mercury-Redstone 4 (MR-4) ballistic manned (Grissom) flight..

1961 June 12 - . LV Family: Redstone. Launch Vehicle: Redstone MRLV.
  • Mercury Redstone launch vehicle No. 8 delivered to Cape Canaveral - . Nation: USA. Program: Mercury. Flight: Mercury MR-4. Summary: Redstone launch vehicle No. 8 was delivered to Cape Canaveral for the Mercury-Redstone 4 (MR-4) suborbital flight mission..

1961 June 22 - . LV Family: Redstone. Launch Vehicle: Redstone MRLV.
  • Redstone for Mercury MR-4 manned suborbital flight erected - . Nation: USA. Program: Mercury. Flight: Mercury MR-4. Summary: The Redstone booster for the Mercury-Redstone 4 (MR-4) manned suborbital flight mission was erected on Pad 5, at Cape Canaveral..

1961 June 22 - . LV Family: Redstone. Launch Vehicle: Redstone MRLV.
  • Mercury MR-4 recovery requirements - . Nation: USA. Program: Mercury. Flight: Mercury MR-4. Summary: Mercury-Redstone 4 (MR-4) recovery requirements were forwarded by the Space Task Group to the Navy..

1961 July 11 - .
  • Key Mercury personnel assignments - . Nation: USA. Program: Mercury. Flight: Mercury MR-4. The assignments were made by Walter C. Williams, Project Mercury Operations Officer, for the Mercury-Redstone 4 (MR-4) manned suborbital flight mission. These appointments included on-site liaison and consultation, public affairs, photo couriers, and technical observers. Stations covered were Mercury Control Center, Atlantic Missile Range Central Control, landing area aircraft carrier, supporting destroyers, support aircraft, and Base Operations at Patrick Air Force Base.

1961 July 13-15 - .
  • Flight readiness review for Mercury MR-4 - . Nation: USA. Program: Mercury. Flight: Mercury MR-4. Summary: A spacecraft, launch vehicle, and mission flight safety review was held in preparation for the Mercury-Redstone 4 (MR-4) manned suborbital flight mission..

1961 July 13 - . LV Family: Redstone. Launch Vehicle: Redstone MRLV.
  • Mercury-Redstone 4 (MR-4) manned suborbital flight mission rules were published. - . Nation: USA. Program: Mercury. Flight: Mercury MR-4.

1961 July 18-19 - .
  • Two attempts made to launch Mercury MR-4 - . Nation: USA. Related Persons: Grissom. Program: Mercury. Flight: Mercury MR-4. Summary: Two attempts were made to launch Mercury-Redstone 4 (MR-4) with astronaut Virgil Grissom aboard the spacecraft, but unfavorable weather forced mission postponement..

1961 July 19 - . LV Family: Redstone. Launch Vehicle: Redstone MRLV.
  • Mercury MR-4 launch scrubbed. - . Nation: USA. Program: Mercury. Class: Manned. Type: Manned spacecraft. Flight: Mercury MR-4. Spacecraft: Mercury. Summary: Mercury-Redstone (MR-4) with manned Liberty Bell 7 capsule canceled within minutes of launch because of adverse weather..

1961 July 21 - . 12:20 GMT - . Launch Site: Cape Canaveral. Launch Complex: Cape Canaveral LC5. LV Family: Redstone. Launch Vehicle: Redstone MRLV. LV Configuration: Redstone MRLV-8.
  • Mercury MR-4 - . Call Sign: Liberty Bell 7. Crew: Grissom. Backup Crew: Glenn. Nation: USA. Related Persons: Grissom; Glenn. Agency: NASA. Program: Mercury. Class: Manned. Type: Manned spacecraft. Flight: Mercury MR-4. Spacecraft: Mercury. Apogee: 189 km (117 mi). The Mercury capsule, Liberty Bell 7, manned by Astronaut Virgil I. Grissom, boosted by a Redstone rocket, reached a peak altitude of 190.3 km and a speed of 8,335 km per hour. After a flight of 15 minutes and 37 seconds, the landing was made 487 km downrange from the launch site. The hatch blew while still in water, and the capsule sank; Grissom saved, though his suit was filling up with water through open oxygen inlet lines.

    This was the second and final manned suborbital Mercury Redstone flight, and the first flight with trapezoidal window. Further suborbital flights (each astronaut was to make one as a training exercise) were cancelled. An attempt to recover the capsule in very deep water in 1994 not successful. It was finally raised in the summer of 1999.


1961 August 5 to October 12 - .
  • Tests conducted on the Mercury spacecraft explosive hatch - . Nation: USA. Program: Mercury. Flight: Mercury MR-4. Spacecraft: Mercury. Summary: A series of environmental tests was conducted on the spacecraft explosive egress hatch because of the difficulties experienced during the Mercury-Redstone 4 (MR-4) mission..

1961 August 30 - . LV Family: Redstone. Launch Vehicle: Redstone MRLV.
  • Investigation of the Mercury MR-4 explosive egress hatch. - . Nation: USA. Program: Mercury. Flight: Mercury MR-4. Spacecraft: Mercury. An investigation was conducted as a result of the premature activation of the Mercury-Redstone 4 (MR-4) explosive egress hatch. Tests were initiated in an environment more severe than had been conducted in prelaunch activities and tests, but no premature firings occurred. As a backup, McDonnell was asked to design a mechanical-type hatch. The model weighed some 60 pounds more than the explosive type, so other methods had to be sought to prevent any recurrence of the incident. A procedure was initiated which stipulated that the firing plunger safety pin would be left in place until the helicopter hook was attached to the spacecraft and tension was applied to the recovery cable.

1961 September 22 - .
  • 30-inch balloon to be installed in the Mercury spacecraft - . Nation: USA. Program: Mercury. Flight: Mercury MR-4. Spacecraft: Mercury. The Space Task Group announced that a 30-inch diameter balloon would be installed in the Mercury spacecraft to allow for ship recovery should the helicopter br forced to drop the spacecraft, as happened during the Mercury-Redstone 4 (MR-4) recovery operations.

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