RETURN TO EARTH

The flight was going well, and to plan. All too soon the spacecraft’s automatic stabili­zation and control system (ASCS) initiated the turnaround maneuver, placing the blunt end of the capsule forward in preparation for assuming retro-fire attitude. Momentarily, Grissom thought he was tumbling out of control until he realized this was the automatic turnaround procedure, just as he had experienced it on the trainer. As Liberty Bell 7 swung around, a brilliant shaft of sunlight moved rapidly across his body.

The pitch and yaw axes stabilized with only a moderate amount of overshoot as pro­jected, and was off by approximately 15 degrees when he switched from autopilot to the manual proportional control system. The switchover had occurred ten seconds later than planned in order to allow more time for the ASCS to stabilize the capsule. Having taken over manual control of the spacecraft, Grissom encountered a little dif­ficulty with the attitude controls. They seemed to him to be somewhat sticky and slug­gish, and the capsule did not always respond as well as he thought it should.

“I tried to hurry the pitch-up maneuver,” was his later observation. “I controlled the roll attitude back within limits, but the view out the window had distracted me, result­ing in an overshoot in pitch. This put me behind in my schedule even more. I hit the planned yaw rate but overshot in yaw attitude again. I realized that my time for control maneuvers was up and so I decided at this point to skip the planned roll maneuver, since the roll axis had been exercised during the two previous maneuvers, and [I would] go immediately to the next task.”11

Grissom wanted to fire the retro-rockets manually whilst simultaneously using the manual controls to maintain the proper attitude. But this was not a critical operation on the suborbital flight, as he was on ballistic trajectory to begin with, and the firing of the retro-rockets was simply an exercise to test their performance. He would later stress that even though he encountered some control problems, and improvements would have to be made, he was confident that he would have been able to handle the situation if he had been in orbit. “That was the main reason I was up there, of course – to find the bugs in the system before we went all the way.”12

Although slightly behind schedule, Grissom worked hard to get the spacecraft into a good retro-fire attitude. The flight had now reached a much-anticipated point. He had been allocated a full minute for Earth observation. Not long after, the retro – sequence began automatically and Shepard, in the Mercury Control Center, began intoning the countdown to retro-fire. Grissom was still looking out of the window

when the count reached zero and, on command, he fired the retro-rockets manually. The thrust buildup was rapid and smooth, but as he continued to gaze out of the win­dow Grissom noticed a definite yaw to the right had begun. He had planned to control the capsule’s attitude during retro-fire by using the horizon as a reference, but once the right yaw began he switched his reference to the flight instruments. Once he had scanned these he turned his attention back to the panorama from his window.

“Immediately after retro-fire, Cape Canaveral came into view. It was quite easy to identify. The Banana and Indian Rivers were easy to distinguish and the white beach all along the coast was quite prominent. The colors that were the most prominent were the blue of the ocean, the brownish-green of the interior, and the white in between, which was obviously the beach and surf. I could see the building area on Cape Canaveral. I do not recall being able to distinguish individual buildings, but it was obvious that it was an area where buildings and structures had been erected.”13 After retro-fire, the retro-jettison switch was placed into the armed position and the maneuvering mode was switched to the rate command control system. Grissom made a rapid check to confirm that the system was working in all axes, and then he switched from the UHF transmitter to the HF transmitter.

“It was a strange sensation when the retros fired,” Grissom later recorded for the book, We Seven. “Just before they went, I had the distinct feeling that I was moving backwards – which I was. But when they went off, and slowed me down, I definitely felt that I was going the other way. It was an illusion, of course. I had only changed speed, not direction.

“Despite my problems with the controls, I was able to hold the spacecraft steady during the 22 seconds that it took for the three retros to finish their job. Then, right after the retro-pack jettisoned at T plus 6 minutes 7 seconds, and the dead rockets fell away, I looked through the periscope and saw something floating around outside that looked just like a retro-motor. Bits and pieces of the retro-package floated past me a couple of times. It had come loose, just as it was supposed to, and had left the heat shield clean and uncluttered for reentry.”14

Although Grissom knew the reentry could prove to be tricky, it was nevertheless uneventful. He did report observing what he described as shock waves coming off the capsule. “It looked like smoke or contrail really, but I’m pretty certain it was shocks.”15 As Liberty Bell 7 hurtled back through the atmosphere, the g-forces were rapidly building up on Grissom, making his speech and breathing a little more labored. He would report the maximum force he endured was 11.2, but as he had taken as many as 16 G in the centrifuge this was easy to take by comparison. He could also hear a roar­ing noise, which he presumed was the sound of the capsule’s blunt nose forcing its way through the atmosphere.

At T plus 9 minutes 41 seconds the drogue chute came out at the intended altitude of 21,000 feet, right on schedule. Viewing through the centerline window, Grissom saw the canister fall away and the drogue deploy. Next out was the main parachute, 23 seconds later, as planned at 12,300 feet. “I could see the complete chute when it was in the reefed condition,” he said in his later report, “and after it opened I could see, out the window, 75 percent of the chute.”16

One thing he did report at this time was seeing what appeared to be a six-inch triangular-shaped tear in one of the main chute panels. He kept a close watch on this, but it did not seem to grow any larger.

As the spacecraft was slowly swinging and rotating beneath the main parachute, Grissom was able to sense the deployment of the landing bag, intended to soften the spacecraft’s impact with the ocean and help stabilize it in the water.

Finally, at T plus 15 minutes 37 seconds, Liberty Bell 7 splashed into the Atlantic at a rate of 28 feet per second with what Grissom later described as “a good bump.” The flight part of the MR-4 mission was at an end.

In the usual competitive spirit of the Mercury astronauts, Gus Grissom would later grin broadly when he discovered his flight had reached an apogee of 102.76 nautical miles, as opposed to 101.24 nautical miles for Shepard’s MR-3 mission in May, and it had also lasted 15 seconds longer.

However, unlike the end of Shepard’s Freedom 7 mission, deep and unexpected trouble was about to befall astronaut Gus Grissom and his Liberty Bell 7 spacecraft.