Mercury Image Directory
Liberty Bell 7 MR-4 (19)
Liberty Bell 7
Pad LC-5 ()
Virgil I "Gus" Grissom
Backup Crew: John H. Glenn, Jr.
- Spacecraft delivered to Hanger S CCAFS
Payload: Spacecraft # 11, Launch Vehicle S/N MR-8
Mercury-Redstone 4 was the fourth mission in the Mercury-Redstone series of flight tests and the second U.S. manned suborbital spaceflight. It was the next step in the progressive
research, development and training program leading to the study of man's capabilities in a
space environment during manned orbital flight.
The main objective was to corroborate the man-in-space concept. The main configuration
differences between the MR-3 spacecraft was the addition of a large viewing window and an
explosively actuated side hatch.
The addition of the large viewing window was a result of a change requested by Mercury
astronauts. This window allowed the astronauts to have a greater viewing area than the
original side port windows. The field of view was 30 degrees in the horizontal plane and 33
degrees in the vertical. The window is composed of an outer panel of 0.35-inch thick Vycor glass and a 3-layer inner panel.
The explosively actuated side hatch was used for the first time on the MR-4 flight. The
mechanically operated side hatch on the MR-3 spacecraft was in the same location and of the same size but was considerably heavier (69 pounds rather than 23 pounds). The
explosively actuated hatch utilizes an explosive charge to fracture the attaching bolts and thus separate the hatch from the spacecraft. Seventy 1/4-inch titanium bolts secure the hatch to
the doorsill. A 0.06-inch diameter hole is drilled in each bolt to provide a weak point. A mild detonating fuse
(MDF) is installed in a channel between an 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. The MDF is ignited by a manually operated igniter that requires an actuation force of around 5 pounds, after the removal of a
safety pin. The igniter can be operated externally by an attached lanyard, in which case a
force of at least 40 pounds is required in order to shear the safety pin.
Altitude: 118.3 statute miles
Duration: 0 Days, 0 hours, 15 min, 37 seconds
Distance: 302 statute miles
Max Q: 610 psf
Max G: 11.1
July 21, 1961. 7:20 a.m. EST. The launch was originally scheduled for July 18, 1961 but was rescheduled to July 19, 1961 because of unfavorable weather conditions. The launch
attempt on July 19, 1961 was canceled at T-10 minutes as a result of continued unfavorable weather. The launch was then rescheduled for July 21, 1961. The first half of the split launch
countdown was begun at 6:00am EST on July 20, 1961 at T-640 minutes. Spacecraft preparation proceeded normally thru the 12-hour planned hold period for hydrogen peroxide and pyrotechnic servicing. Evaluation of the weather at this time proved favorable and a go was given to pickup the second half of the countdown at 2:30am EST on July 20, 1961. At T-180 minutes, prior to liquid oxygen loading, a planned 1-hour hold was called
for another weather evaluation. The evaluation was favorable and the count proceeded at 3:00am EST. At T-45 minutes a 30 minute hold was called to install a
misaligned hatch bolt. At T-30 minutes, a 9-minute hold was called to turn off the pad searchlights which interfered with launch telemetry during launch. At T-15 minutes, a 41-minute hold was called to await
better cloud conditions. The count then proceeded from T-15 until liftoff. Gus Grissom was
in the spacecraft 3 hours and 22 minutes prior to launch. The spacecraft was delivered to Hanger S at Cape Canaveral, Fl on March 7, 1961. Upon
delivery, the instrumentation and selected items of the communication system were removed
from the spacecraft for bench testing. After reinstallation of the components, the systems test
proceeded as scheduled. Those tests required a total of 33 days during which the electrical, sequential, instrumentation, communication, environmental, reaction-control, and stabilization and control systems were individually tested. After system tests, the landing impact bag was
installed and then a simulated flight was run on the spacecraft. Then the parachutes and
pyrotechnics were installed and the spacecraft was weighed, balanced and then delivered to the launch complex. Twenty-one days were spent on the launch pad.
Atlantic Ocean, 302 miles East of launch site. Drogue parachute was deployed at T+9 minutes 41 seconds and main parachute at T+10 minutes 14 seconds. Landing
occurred at T+15 minutes 37 seconds.
The MR-4 flight plan was very much the same as that for MR-3. The range was 262.5
nautical miles, the maximum altitude was 102.8 nautical miles, and the period of weightlessness lasted for approximately 5 minutes.
At T-35 seconds, the spacecraft umbilical was pulled and the periscope was retracted.
During the boosted phase of flight, the flight-path angle was controlled by the launch-vehicle
control system. Launch-vehicle cutoff occurred at T+2 minutes 23 seconds, at which time
the escape tower was released by firing the escape and tower jettison rockets. Ten seconds
later, the spacecraft-to-launch-vehicle adapter clamp ring was separated, and the posigrade rockets fired to separate the spacecraft from the launch vehicle. The periscope was extended; the automatic stabilization and control system provided 5 seconds of rate
damping, followed by spacecraft turnaround. It then oriented the spacecraft to orbit attitude
of -34 degrees.
Retro sequence was initiated by timer at T+4 minutes 46 seconds, which was 30 seconds prior to the spacecraft reaching its apogee. Gus Grissom assumed control of the spacecraft attitude at T+3 minutes 5 seconds and controlled the spacecraft by the manual proportional control system to T+5 minutes 43 seconds. He initiated firing of the retrorockets at T+5 minutes 10 seconds. From T+5 minutes 43 seconds, he controlled the spacecraft by the
manual rate command system through reentry. The retrorocket package was jettisoned at T+6 minutes 7 seconds. The drogue parachute was deployed at T+9 minutes 41 seconds, and main parachute, at T+10 minutes 14 seconds.
Flight successful but the spacecraft was lost during the
post landing recovery period as a result of premature actuation of the explosively actuated side egress hatch. The capsule sank in 15,000 feet of water shortly after splashdown. The astronaut egressed from the spacecraft
immediately after hatch actuation and was retrieved after being in the water for about 3 to 4
(Reference - Results of the second U.S. manned Suborbital Space Flight July 21,