The Mercury-Atlas and Mercury-Redstone failures of the year before, as was made evident in the January 1961 report of the President-elect's Space Task Force under the leadership of Jerome B. Wiesner, had not helped build the confidence of physical and life scientists that Mercury was truly a man- rated program. An ad hoc Mercury panel was created by PSAC to delve into the scientific details and reliability of the overall Mercury system and advise the President if it appeared likely that the United States would be beset with another well-publicized but inexplicable failure. Basically, the PSAC panel sought to investigate the level of risk involved in Mercury before a man was to be committed to an actual space flight. This inquiry was penetrating. Panel members spent five days in March visiting McDonnell, Space Task Group, and Cape Canaveral, receiving a series of detailed briefings and interviews. Several medical uncertainties appeared  outstanding and worrisome, although the panel had found the NASA presentations to be frank, competent, and impressive.
The scientific objective of Mercury in determining the effects of weightlessness upon man, some felt, might have been pursued in a more clinical manner. Before the first manned flight there might have been a greater number of animal flights progressing toward absolute physiological and psychological limits. Past Mercury flight tests appeared more systematic for hardware engineering than for medical problems. As a case in point, it was noted by the panel members that the MR-2 mission had demonstrated excessive vibration and overacceleration in the launch phase, so that an additional booster test flight (MR- BD) had been inserted to precede the first manned suborbital flight. Pilots in the X-15 rocket research airplane, as well as Ham, the "space chimp" aboard MR-2, had recorded surprisingly high pulse rates concurrently with low blood pressures, yet there were no plans to include a blood-pressure measuring device in the upcoming manned flight (efforts to develop such a device were as yet unsuccessful). In addition, the panel members learned that Ham had taken his turn on the centrifuge, but that the acceleration profiles had no precise correlation with stresses and forces of those predicted for the MR-2 mission.
Despite these gnawing medical doubts, in general the PSAC panel members felt that the Mercury hardware and its reliability had been developed with great care. They were especially impressed with the redundant systems of the spacecraft, as well as the procedures and devices that had been integrated to assure pilot safety during launch. In fact, several panel members stated at STG that it seemed everything necessary to assure pilot survival had been considered.
In their final analysis, the PSAC panel assessed all risks and agreed that Mercury was ready to fly a man. The scientific purpose indeed was to determine man's suitability for the stresses and weightlessness associated with space flight.14
The orbital flight of Yuri Gagarin on April 12 seems to have removed any lingering medical qualms about manned flight. Mercury Director Gilruth had full confidence in the Space Task Group physicians and their endorsement by the space medicine community long before Vostok I. W. Randolph Lovelace II, Brigadier General Don D. Flickinger, and others familiar with the medical stresses of flight likewise had been convinced that pilot safety was fully assured. Yet if the medical profession as a whole had voiced scientific opposition to manned flight in Mercury, or if Vostok I had not flown when it did, it would have been impossible to proceed with a man in MR-3 immediately.15
Centrifuge tests of the astronaut's couch continued to raise NASA confidence in the adequacy of Mercury systems to maintain an astronaut's safety under acceleration into and deceleration from the space environment. But the abrupt negative acceleration of the final impact on Earth remained a nagging worry, particularly in case of a land landing. The aluminum honeycomb shock-attenuation material under the couch had been bought as insurance, but was it enough? Continued experiments early in 1961 at Wright-Patterson Air Force Base, Ohio,  were conducted to determine how rapidly one could stop, facing aft in the semisupine position, without exceeding human tolerance. These tests showed that forces up to 35 times a person's weight could be endured for a fraction of a second. But the volunteers so tested were momentarily stunned. In theory, this meant that a spacecraft could land without an impact bag, but the idea of having a "slightly stunned" astronaut in what should be made a routine operation was unacceptable. So STG had reassigned the development of a suitable impact bag system to Jack A. Kinzler's technical services team and to Rodney G. Rose and Peter J. Armitage. These men worked around the clock in March and April trying to perfect a seaworthy shock-absorber. All other pilot-safety systems were ready for a safe and successful flight.16
Barely a month had passed after the three chosen astronauts began training for MR-3 when the press began speculating as to which one would make the flight. On March 25, John Glenn became the favorite contender, although one report added that there was plenty of betting on Grissom, since the Air Force had been designated by the Defense Department to manage and conduct military space missions. This intimation of service competition spread quickly. Some newspapers even implied that the Army and Navy strongly suspected the Air Force had leaked Glenn's name to embarrass NASA and reduce his chances.17
The astronauts themselves watched all these conjectures with amusement, keeping tight the secret knowledge of their order of succession. According to Voas, their psychologist and training officer, there was only one thing that terrified all seven: the fear that something might prevent one of them from flying his own mission when the time came.18
Speculation on the designated pilot abated shortly after Robert C. Seamans, Jr., third in command at NASA Headquarters, appeared before the House Science and Astronautics Committee and testified that each astronaut would have his flight training opportunity aboard a Mercury-Redstone at six-week intervals. Gilruth had, of course, long since decided on an order of preference among the three astronauts designated, and had informed them of it, but everyone kept the secret well because of the ever present likelihood of unforeseen changes.19
Toward the end of April there was so much publicity that some Senators, among them Republican John J. Williams of Delaware and Democrat J. W. Fulbright of Arkansas, thought the flight should be postponed and then conducted in secret lest it become a well-publicized failure. This was not the general view in Congress, however. Most members, while aware of the danger of too much publicity, felt tradition required the press to have free access to events of such magnitude as the first American manned space flight. Besides, the Russians had received international criticism for conducting an ultra- secret space program.
While many highly placed officials, several close to President Kennedy, were apprehensive about the possibility of an overly publicized fiasco, others pressed to get the manned space flight program moving. On March 22, at a White House meeting, Hugh L. Dryden had explained to the President that no  unwarranted risks would be involved in the first manned Mercury flight, and that the decision to "go" was that of the project management best qualified to assess the operational hazards. When the notion was raised in late April that MR-3 should be postponed until all possible hazards had been removed, Edward C. Welsh, Executive Secretary of the National Aeronautics and Space Council, observed to the President, "Why postpone a success?"
President Kennedy wanted to be assured of a much better than average chance for success and asked for these assurances almost until launch. On the day preceding the flight, the President's personal secretary, Evelyn Lincoln, called NASA Headquarters Public Information Officer Paul P. Haney at the MR-3 News Center in Cocoa Beach, Florida. She said the President wanted to review television coverage plans. Live coverage was to begin two minutes before launch. After some delay, Mrs. Lincoln said the President had asked Press Secretary Pierre Salinger to handle the call. Salinger said the President was concerned over the reliability of the escape system in the event of a Redstone malfunction. Haney reviewed the history of the launch escape system for the President's office and Salinger said the information should satisfy the President's inquiry.20
Cancellation of the flight on Tuesday, May 2, because of inclement weather, forced a recycle of the systems countdown for a 48- hour period. On Thursday unfavorable weather again prevented the launch. Countdown did begin, however, for a Friday launch.21
As it happened, the press and public learned the MR-3 astronaut's identity only after the countdown had been canceled, 2 hours and 20 minutes before launch, on May 2. Shepard had been waiting in Hangar S in his pressure suit ready to go for more than 3 hours. Gilruth reaffirmed his prime pilot decision a day before the scheduled launch, basing Shepard's selection on advice from his medical, training, and technical assistants.22 But he had withheld his announcement because of the chance for a last-minute change.
The American public participated vicariously in the experiment. For the first time, the maiden flight of a revolutionary manned vehicle, climaxing years of research and development, was open wide to public view. Only a handful of spectators saw the Wright Brothers accomplish man's first powered flight in 1903. In many parts of the country and the world, people accepted that event only years afterward. But for the American taxpayers' first manned space flight, NASA arranged procedures well in advance to enable all domestic news media and foreign news services to view and report the events surrounding MR-3. By April 24, some 350 correspondents were registered. As a result of their activities, the dateline "Cape Canaveral" soon became familiar to all the world. Radio and television coverage was equally energetic; telecasts originating at the Cape, particularly on May 5, were enthralling.23
Starting at 8:30 p.m. on May 4, the countdown proceeded without a hitch. Around midnight a built-in hold was called for the purpose of installing the pyrotechnics, servicing the hydrogen peroxide system, and allowing the operations  team some rest. The countdown was resumed in the early morning hours of May 5, and another intended hold occurred some two and a half hours before the 7 a.m. anticipated launch to assure that spacecraft checkout was complete before transporting the astronaut to the pad area.
Shepard, awakened at 1:10 a.m., began an unhurried but precise routine involving a shower and a shave. With his physician, William K. Douglas, his understudy, John Glenn, and a few other members of the operational team, he sat down to a breakfast consisting of orange juice, a filet mignon wrapped in bacon, and some scrambled eggs. Shepard had begun a low- residue diet three days before the anticipated launch. At 2:40 a.m. he received a physical examination. This was followed by the placement of biosensors at points indicated by tattoo marks on his body. He was now ready for Joe W. Schmitt, an STG suit technician, to assist him in donning the pressure suit.24
Shepard entered the transfer van at 3:55 a.m. In the van, on the way to the pad, he lay on a couch while technicians purged his suit with oxygen. When the van arrived at the pad, Schmitt began to attach the astronaut's gloves while Gordon Cooper briefed him on the launch status.
At 5:15 a.m. Shepard, carrying his portable air conditioner, ascended the gantry, and five minutes later he entered the spacecraft. If everything went well, he had two hours and five minutes to wait before liftoff. While Shepard was preparing to lower himself into the couch, his right foot slipped off the right elbow support. But he eased himself into position without further difficulty.
Schmitt fastened the harness and helped with the hose connections. Then he solemnly shook the spaceman's gloved hand. "Happy landings, Commander!" chorused the gantry crew.
For Alan Shepard, this was the most dramatic moment of his 37 years, a moment he would recall with the most acute poignancy for the rest of his life. Afterward he told how his heart quickened as the hatch was closed.
The sensation was brief; his heartbeat soon returned to normal. At 6:25 a.m. he began a denitrogenation procedure by breathing pure oxygen. This was to prevent aeroembolism, or decompression sickness, the airman's equivalent of the deep- sea diver's bends.25
Now the countdown resumed.
At 15 minutes before launch the sky became slightly overcast, so photographic conditions were below par. Weathermen said the conditions would clear in 35 to 40 minutes, and a hold was called. Shepard became resigned to this hold and relaxed by peering through the periscope. He was not uncomfortable, because he was able to shift his body in the couch. Telemetered biomedical data confirmed that his condition was good. While waiting for the clouds to clear away, a hold was called to replace a 115-volt, 400-cycle inverter in the electrical system of the launch vehicle. This hold lasted for 52 minutes, after which the count was recycled to 35 minutes before launch.  At the 15-minute point, one of the Goddard IBM 7090 computers in Maryland was found to be in error. Making this correction required a complete computer recheck-run. After a total hold time of two hours and 34 minutes, the count continued and progressed without more trouble. Shepard had been in the capsule four hours and 14 minutes when the final seconds ticked off to liftoff.26
Two minutes before the launch, voice communications between the astronaut and the operations team switched from Cooper in the blockhouse to Donald K. Slayton in the Mercury Control Center. From that point until launch, the "talk" was continuous as each panel monitor advised Slayton of his system's status for relay to Shepard. To the astronaut the monitors seemed slow in reporting the go condition, and this he attributed to his own eagerness to be off. Schirra was now circling above in his F- 106 chase plane, waiting to follow the Redstone and Shepard as high as he could. Because of his excitement, Shepard said he failed to hear much of the closing countdown, with the exception of the firing command. During this period his pulse rate rose from 80 per minute to 126 at the liftoff signal. This rise caused no medical concern, for it was about the same as that of an automobile driver moving out from a service road to a freeway crowded with heavy traffic. Shepard was not alone in his excitement; he was joined by the operations team, the press corps at the Cape, and millions of people viewing the liftoff on television.27
14 Based on a series of interviews. Also see Mae M. Link, Space Medicine in Project Mercury, NASA SP-4003 (Washington, 1965), 112-125. See also p. 331 of this work.
15 A. Duane Catterson, interview, Houston, April 10, 1964.
16 Stanley C. White, Richard S. Johnston, and Gerard J. Pesman, "Review of Biomedical Systems Prior to the MR-3 Ballistic Flight," undated. Another criticism leveled by members of the PSAC panel in March 1961 was that the fire hazard in a pure oxygen atmosphere had not been sufficiently dealt with through tests. The subject had been considered by STG; the conclusion was that depressurization would serve as an excellent fire extinguisher. Robert B. Voas, interview, Houston, April 15, 1964. See also p. 287.
17 Newport News Times-Herald, March 25, 1961; Shreveport Times, April 2, 1961. Howard I. Gibbons, then associated with the Newport News Daily Press, later of the Public Affairs Office, MSC, interviewed the seven astronauts on July 7, 1959, at a NASA Press Day event. The following Sunday, Gibbons predicted in the Daily Press that Alan Shepard would be the first astronaut in space. As far as can be determined, this was the first speculation in the matter. "It was just a good guess," said Gibbons.
18 Voas interview.
19 Shepard interview; Gilruth, interview, Houston, March 18, 1964.
20 Memo, Public Affairs Officer, MSC, to Chief, Hist. and Library Services Br., March 11, 1964. There was some resistance to the publicity buildup. The painful experience of Dec. 6, 1957, when the public witnessed the spectacular launchpad failure of the Vanguard booster, America's first attempt to launch an artificial satellite, had not been forgotten. Wall Street Journal, May 2, 1961.
21 Washington Post, May 3, 1961; New York Times, May 5, 1961; memos, John H. Disher, Head, Advanced Manned Systems, NASA, to Administrator, "Mercury-Redstone Launching," May 1, 1961, and May 4, 1961.
22 Chicago Tribune, April 29 and 30, 1961; Washington Daily News, April 29, 1961; Washington Evening Star, April 29, 1961; Washington Post, May 1, 1961; Baltimore Sun, April 30, 1961; New York Times, May 2 and 3, 1961; Newport News Times-Herald, May 2, 1961; "Mercury Astronauts Work as a Team on MR-3," undated. A statement by Gilruth on the mode of pilot selection for MR-3 is contained in NASA Fifth Semiannual Report to Congress, Oct. 1, 1960, through June 30, 1961 (Washington, 1962), 15, 17, 18.
23 "NASA Note to Editors," April 24, 1961; New York Times, May 2, 1961.
24 Conference on Medical Results of the First U.S. Manned Sub-orbital Space Flight, 7, 8; "Pilot Preparation for MR-3 Mission," anon., undated. Safety measures, including appropriate actions, covering each time segment of the second half of the split countdown were published just before the MR-3 mission in "Emergency Handbook for Pad Area Rescue, Mercury-Redstone, Capsule 7," May 2, 1961. This document later was revised and reissued on June 29, 1961, to cover Capsule 11 and the MR-4 flight.
25 Ibid.; Sjoberg, April 4 memo; "Postlaunch Report for MR-3," 43-45. During the early part of the countdown on May 5, John Glenn,the backup pilot, spent considerable time in the spacecraft assisting in systems checkouts. To help relieve any tension Shepard might have built up, Glenn pasted a little sign on the spacecraft panel, reading "No handball playing here." This bit of levity hearkened back to their training days. Later he went to Mercury Control Center and stood behind Donald K. Slayton, spacecraft communicator, helping to gather data to feed to Shepard during the flight.
26 "Postlaunch Report for MR-3," 45-46; Conference on Medical Results, 8; memo, Henry E. Clements to Christopher C. Kraft, Jr., "Test 108, 4-5 May, 1961, Network Status Monitor Report," May 8, 1961; "Mercury Redstone 3 Press Conference"; memo, Disher to Administrator, "Mercury-Redstone Mission," undated. After four hours without relief and with only a primitive urine collection system, his underwear got wet, but the suit air regenerating system worked very well. Sjoberg, Aug. 22 memo; Lee McMillion, interview, Houston, Oct. 30, 1963; memo, Carl R. Huss to Flight Dir., "Record and Comments on Activities and Observations Made at Retrofire Controller's Position During Test 108 (MR-3)," May 5, 1961.
27 "Postlaunch Report for MR-3"; Conference on Medical Results of the First U.S. Manned Suborbital Space Flight, 74; Shepard, speech, Society of Experimental Test Pilots, Los Angeles, Sept. 30, 1961; letter, John A. Powers to W. J. Phillippi, Aug. 4, 1961. As for the other astronauts, Carpenter and Grissom observed from the Mercury Control Center.