to demonstrate and evaluate the capabilities of the spacecraft and launch vehicle system, and the procedures necessary for the support of future long-duration and rendezvous missions27 had been settled by the rescheduling decisions of April 1963. Gemini 3, in other words, was to show that Project Gemini was ready to meet its major goals. But just how that was to be done was not clearly defined until early 1965.
Such key questions as how long the mission was to be and how its specific objectives were to be met were much discussed. NASA Headquarters had tentatively approved the three-orbit flight suggested by the program office in April 1963. This seemed too short a mission, however, to use the rendezvous evaluation pod (REP), long planned to check out spacecraft radar and maneuvering systems. If the mission could not be lengthened, some other means must be found "to demonstrate and evaluate . . . the procedures necessary for the support of future . . . rendezvous missions." Equally unclear was how so short a flight could do much to prepare for future long-duration missions.28
MSC's Flight Operations Division did prepare a tentative mission plan in October 1963 that outlined possible use of the pod during the second orbit of a three-orbit mission. But the matter was settled when, on 4 January 1965, NASA Headquarters decided to strike the pod from Gemini 3.29 The question of mission duration surfaced again late in the summer of 1964. Word leaked to the press that Grissom and Young, backed by the Astronaut Activities Office, were pressing for an open-ended mission; that is, leaving it up to the crew to decide how many orbits to try for after Spacecraft 3 was in space. GPO was averse to the idea, since the tracking network was then geographically limited and could only fully cover three orbits. Going beyond that on the first flight might be risky. NASA Headquarters again stepped in and squelched the idea. When a reporter asked Grissom what he thought about the decision, the answer was a curt, "We can do all the testing of the spacecraft we need in three trips."30
One of the first-order objectives for Gemini 3 - one that had to be achieved for the mission to be judged a success and any threat to which was cause enough to hold or cancel the flight - was to "demonstrate and evaluate the capability to maneuver the spacecraft in orbit using the orbital attitude and maneuver system (OAMS)." Early planning thus called for several OAMS firings.31 The reason for these firings suddenly expanded in January 1965. NASA Headquarters sent Flight Operations in Houston a set of preliminary data, with orders to revise the flight plan to protect the Gemini 3 crew against the danger that Martin Caidin, in his space thriller Marooned, had posed: the failure of spacecraft retrorockets to work, stranding the crew in space. Headquarters proposed three OAMS maneuvers to place the spacecraft in a "fail safe" orbit, one from which it would reenter whether the retrorockets fired or not. Actually, Gemini orbits were too low to be permanent, so spacecraft reentry was inevitable. What the fail-safe maneuvers were designed to achieve was the spacecraft's return  promptly enough to ensure that the crew survived. Coming as it did less than three months before the planned launch, the new demand threw mission planning into turmoil. But the response was rapid. A revised tentative flight plan was ready in little more than a month, and the final plan followed on 4 March.32
The new plan called for firing the aft thrusters to free the spacecraft from the second stage of the launch vehicle, adding about 3 meters per second to its speed and putting it into an elliptical orbit with a perigee of 122 kilometers and an apogee of 182 kilometers. Just before first perigee, about an hour and a half into the flight and over Texas, a burst from the forward thrusters would cut 20 meters per second from spacecraft velocity and convert its orbit to a near circular 122 by 130 kilometers. During the second pass over the Indian Ocean, some 2 hours and 20 minutes into the mission, would come a series of out-of-plane burns totaling 4 meters per second, a part of the former flight plan to check out the OAMS, with no bearing on the fail-safe plan. Finally, over Hawaii on the third time around, there was a pre-retrofire burn to reduce speed by 28 meters per second, putting the spacecraft into an elliptic of reentry orbit with a perigee of 63 kilometers.33
Another relative latecomer to Gemini 3 was a set of experiments. Although Project Mercury had included some in-orbit experiments, no one seems to have given much thought to Gemini in that context until Mercury ended in mid-1963. That summer, the Headquarters Office of Space Sciences began looking for proposals. It joined with the Office of Manned Space Flight in setting up a Panel on In-Flight Scientific Experiments, or POISE, to pass on the merits of proposed experiments. A Manned Space Flight Experiments Board was chartered in January 1964 to decide which experiments would go on which mission, Apollo as well as Gemini.34
MSC had earlier formed its own experiments panel, which met for the last time on 16 January to pass on its advice about experiments for the first two manned Gemini missions to the NASA Headquarters group that had superseded it. Noting that Spacecraft 3 had already been built and that the shortness of the planned mission sharply limited any active participation by the crew, the panel stressed the need to find experiments that would largely conduct themselves and were nearly complete in terms of planning, design, and hardware. The panel members believed, although GPO did not, that two experiments left over from the proposed but never flown Mercury-Atlas 10 met these stringent criteria: one intended to explore the combined effects of radiation and low gravity on cells, the other to study cell growth at zero gravity. Both were approved by the Headquarters board when it met in Washington the following month.35
The first experiment had been prompted by signs of radiation  damage to cells after earlier flights, the biological effects being in some cases greater than might have been predicted from the length of exposure; this was a matter of special concern in light of plans for long-duration manned space flight. Either (or both) of two reasons might explain this anomaly: unknown biological effects produced by the "heavy primaries" component of radiation, blocked from Earth's surface by the atmosphere and hence inaccessible to terrestrial laboratories, or the interaction of radiation with some aspect of the space flight environment, such as prolonged weightlessness. Experiment S-4 was designed to furnish a basis for weighing these alternatives.
Human blood samples were to be exposed to a known quantity and quality of radiation (both in the spacecraft and on the ground) during the zero-gravity phase of the mission. The frequency of various chromosomal aberrations in both samples could then be compared. To be mounted on the right-hand hatch, the experiment was wholly self-contained in a half-kilogram (one-pound) hermetically sealed aluminum box that held the blood samples, a radiation source, and instrumentation. The copilot had only to twist the handle and push it in to start the irradiation of the blood samples. Twenty minutes later he would twist the handle in the opposite direction and pull it out to stop the experiment. Word of these actions relayed to the ground would allow them to be duplicated.* 36
The second experiment was designed to explore the possibility that cells might be directly affected by low gravity - that long-term weightlessness might produce changes with important implications for prolonged space flight. Because the effects were easier to detect in simple cell systems than in complex organisms and because theory argued that effects would appear only in cells upward of one micron across, the eggs of a sea urchin were selected as the experimental material. The eggs were to be fertilized at the start of the experiment, and the possible changes brought about by low gravity observed at several stages of the development.
The cell growth experiment was also self-contained, a sealed 2/3-kilogram (1 1/2-pound) cylinder, to be mounted on the left-hand hatch and worked by the command pilot. The handle had to be turned five times - once half an hour before flight to fertilize the eggs, then four times in flight to fix the dividing cells at specific stages of growth in successive samples. Each time the handle was turned, the fact was relayed to the laboratory, where the action would be duplicated on an identical package. Results from the simultaneous experiments would be compared later.** 37
 A third experiment found its way into Gemini 3 by a more roundabout path. Spacecraft falling back into the atmosphere are sheathed in an ionized plasma that blocks all radio communication, a source of much concern in at least two Mercury missions. In the first manned orbital flight, with John Glenn in Friendship 7, the five-minute blackout followed a signal that the capsule's heatshield was unlatched. Although the signal was wrong, Mercury control spent an agonizing five minutes until the radio link was restored. Then in the very next flight, M. Scott Carpenter's Aurora 7 overshot its planned landing point by 400 kilometers because the capsule was misaligned at retrofire. In either case, communications with the reentering spacecraft would have made many hearts beat more calmly.38
A reentry communications experiment had been proposed and accepted for Mercury-Atlas 10, but when the program ended with that mission unflown, it was suggested for Gemini. Tentatively assigned to Spacecraft 3 in March 1964, the experiment failed to win a firm place for months, largely because of its half million-dollar price tag. In July, however, the Office of Advanced Research and Technology in NASA Headquarters agreed to share the cost, and the experiment had its place in the mission confirmed.39
Research had shown that, for small objects, adding fluid to the ionized plasma during the reentry blackout could restore communications by lowering the plasma's frequency enough to allow UHF radio transmission to get through. Whether the same technique would work for an object as large as the Gemini spacecraft was now to be tested. A water expulsion system would be installed on the inside surface of one of the landing- gear doors, relics of the days when landing skids were to be used with its paraglider wing. The experiment was fully self-contained except for a starting switch inside the cabin to be thrown by the copilot when the spacecraft had fallen to about 90,000 meters. At that point, the plasma sheath would surround the spacecraft, blacking out communications. Water would be automatically injected into the plasma in timed pulses for the next two and a half minutes, while ground stations monitored and recorded UHF radio reception.***40
* Michael A. Bender, U.S. Atomic Energy Commission, was principal investigator on the radiation experiment.
** Principal investigator for the cell-growth investigation was Richard S. Young, Ames Research Center.
*** The experiment had originally been proposed for Mercury by William F. Cuddihy of Langley Research Center. His colleague, Lyle C. Schroeder, later took over as principal investigator for the Gemini experiment.
27 "GT-3 Mission Directive," NASA Program Gemini working paper No. 5017A, 15 Feb. 1965, p. 2-1.
28 Letter, Mathews to NASA Hq., Attn: Schneider, "Gemini Mission Assignments," GV-02183, 13 March 1964; Mathews, activity report, 28 April - 4 May 1964, p. 1; memo, Walter C. Williams to Actg. Mgr., GPO, "Third Gemini Flight," 6 June 1963; "Abstract of . . . Coordination Meeting (Electrical), May 1, 1962," 2 May 1962; "Abstract of Meeting on Trajectories and Orbits, July 3, 1963," 9 July 1963; letter, Low to Elms, 19 July 1963.
29 Memo, Christopher C. Kraft, Jr., to dist., "Proposed Mission Plan for GT-3," 25 Oct. 1963, with enclosure, "Proposed Mission Plan for the GT-3 Gemini Flight," 18 Oct. 1963; Meyer, notes on GPO staff meeting, 2 Jan. 1964; memo, Low to MSC, Attn: Mathews, "Configuration of Gemini Spacecrafts #2, 3, and 4," 4 Jan. 1964.
30 Harold R. Williams, "18 Obits [sic] Urged for Gemini Trip with Two Astronauts," The Times-Picayune, New Orleans, La., 13 Aug. 1964; "U. S. Astronauts Seeking Longer Gemini Flight," St. Louis Post-Dispatch, 27 Sept. 1964; "Gemini Astronauts Want First Flight of 18 Orbits," The Hartford (Connecticut) Courant, 27 Sept. 1964; Frank Macomber, "Grissom, Young to Orbit Thrice," The Indianapolis Star, 17 Jan. 1965; "Astronauts Ready Now."
31 "GT-3 Mission Directive," p. 2-1; memo, Mathews to Chief, Propulsion and Power Div., "GT- 3 Flight Plan dated February 3, 1965," GP-01993, 9 March 1965; memo, Mathews to Asst. Dir., Flight Ops., and Asst. Dir., Flight Crew Ops., "OAMS Insertion Maneuver for GT-3," GV-02526, 17 March 1965; TWX, Mathews to KSC, Attn: Kraft, GV-12014, 18 March 1965.
32 Eldon W. Hall and Vearl N. Huff, interview, Washington, 24 Jan.1967; memo, Edwards to Hall, "Letter from the Republican Conference to Mr. Webb," 15 May 1964; Howard W. Tindall, Jr., interview, Houston, 16 Dec. 1966; Tommy W. Holloway, "GT-3 Flight Plan," Preliminary B, 20 Sept. 1964; memo, Hall to Schneider, "Interim Status Report on Decay Safe Orbits," 11 Dec. 1964; letter, Edwards to Kraft, 5 Jan. 1965; memo, Tindall to Chief, Mission Planning and Analysis Div., "Complete revision of the GT-3 flight plan," 7 Jan. 1965; memo, Hall to Dep. Dir., Gemini, "Fail-Safe Orbits," 11 Jan. 1965; memo, Robert O. Aller to file, "Fail-safe orbit for GT-3," 15 Jan. 1965; TWX, Mathews to McDonnell, Attn: Burke, GV-52676, 15 Jan. 1965; TWX, Mathews to McDonnell, Attn: Burke, "Special Trajectory and Orbits Meeting," GP-51709, 21 Jan. 1965; "Abstract of Meeting on Trajectories and Orbits, January 27, 1965," 5 Feb.1965; memo, Aller for record, "Mission Planning for GT-3," 29 Jan. 1965; Frank J. Suler and Bobbie D. Weber, "A Proposed Mission Plan for the First Manned Gemini Flight (GT-3) Utilizing a Retrograde Maneuver Prior to Retrofire," MSC Internal Note No. 65-FM-11, 9 Feb. 1965; [Holloway], "GT-3 Flight Plan," Final, 4 March 1965; Martin Caidin, Marooned (New York, 1964).
33 "Abstract of Trajectories and Orbits Meeting;, January 27, 1965"; Suler and Weber, "A Proposed Mission Plan," p. 1; "GT-3 Mission Directive," p. 3-1; "GT-3 Mission Report," p. 4-1.
34 Letter, Homer E. Newell to "Dear Colleague," 20 Aug. 1963, with enclosures; memo, Willis B. Foster to Dir., Program Review and Resources Management, "Submission for 1964 Presidents Annual Report," 30 Oct. 1964, with enclosures; memo, Foster to Chief, Lunar and Planetary Br., "Establishment of Manned Space Flight Experiments Board," 5 Jan. 1963 [sic-1964J; memo, Verne C. Fryklund, Jr., to Dir., Space Sciences, "Manned Space Flight Experiments Board," 28 Oct. 1963; letter, Schneider to Mathews, 24 Jan.1964, with enclosures, letter, D. Brainerd Holmes to Robert R. Gilruth, 23 Aug. 1963, and Assoc. Adm., Manned Space Flight, to dist., "Establishment of a Manned Space Flight Experiments Board," NASA Management Instruction M 9000.002, 14 Jan. 1964; memo, Mueller to dist., "Manned Space Flight Experiments Board," 17 March 1964.
35 MSC Management Instruction No. 37-1-1, "In-Flight Experimental Programs," 18 July 1963; MSC Management Instruction No. 2-3-1, "Manned Spacecraft Center In-Flight Scientific Experiments Coordination Panel," 15 Oct. 1962; letter, Mathews to Schneider, GP-61010, 15 March 1965; memo, Newell to Assoc. Adm., Manned Space Flight, "Proposed scientific experiments for the Gemini 3 flight," 14 Nov. 1963; memo, Jocelyn R. Gill to Schneider; "Gemini Scientific Proposals," 14 Nov. 1963; Warren Gillespie, Jr., acting secretary, "Minutes of In-Flight Scientific Experiments Coordination Panel, January 16, 1964"; letter, Mathews to NASA Hq., Attn: Low, "Scientific investigations during the GT-3 missions [sic]," GPO-01101-M, 10 Jan. 1964; letter, Mathews to NASA Hq., Attn: Low, "Scientific Experiments for Early Gemini Missions," GP-03439, 5 Feb. 1964; memo, Foster to Assoc. Adm., "Recommended scientific investigations during the GT-3 Mission," 11 Feb.1964; memo, Mathews to Gemini Procurement, Attn: Larry G. Damewood, "Integration of two NASA experiments on GT-3," GP-03511, 12 March 1964.
36 Gillespie, "In-Flight Experiments Panel Meeting"; Gordon C. Hrabal, "Experiments for GT-3 Mission," NASA Program Gemini working paper No. 5014, 22 Sept. 1964, pp. 5-1 through -11; "GT-3 Mission Report," p. 8-3.
37 Hrabal, "Experiments for GT-5," pp. 4-1 through -10; "GT-3 Mission Report," pp. 8-1, -2.
38 Hrabal, "Experiments for GT-3," pp. 6-1 through -17; Loyd S. Swenson, Jr., James M. Grimwood, and Charles C. Alexander, This New Ocean: A History of Project Mercury, NASA SP-4201 (Washington, 1966), pp. 431-32, 453-56, 597.
39 Memo, Clifford H. Nelson to Eugene C. Draley, "Proposed Reentry Experiment on the Mercury Capsule for Studying Radio Frequency Transmission Blackout," 12 June 1962; memo, Nelson to Draley, subject as above, 18 June 1962; memo, Nelson to Assoc. Dir., "Proposed Mercury Capsule Blackout Elimination Experiment," 27 June 1962, with enclosure, memo, William F. Cuddihy to Kleinknecht, "Proposed Reentry Experiment on the Mercury Capsule for Studying Radio Frequency Transmission Blackout," 27 June 1962; memo, Kleinknecht to Langley, Attn: Axel T. Mattson, "Proposed reentry experiment on the Mercury spacecraft for studying radio frequency transmission blackout," 27 July 1962; memo, Cuddihy to Mattson, "Blackout Info," 8 Oct. 1962, with enclosure, letter, Cuddihy to Lewis R. Fisher, n.d., with enclosure, "Reentry Communication Methods," 2 Oct. 1962; memo, [Cuddihy] to Norman G. Foster, "Information requested for Reentry Communication Experiment," 29 Jan. 1963; memo, Fisher to Kleinknecht, "Summary of February 25, 1963 Meeting of In-Flight Scientific Experiments Coordination Panel," 26 Feb. 1963, with enclosure; memo, John H. Kimzey to Chief, Systems Evaluation and Development Div., "In-Flight Scientific Experiments for MA-10," 27 Feb. 1963; memo, Mattson to MSC, Attn: William O. Armstrong, "Proposal for Reentry Communications Experiment to Be Flown on Gemini Spacecraft," 1 Oct. 1963, with enclosure; memo, Lyle C. Schroeder to Clinton E. Brown, "Status of Proposed Gemini Reentry Communication Experiment," 21 Jan. 1964; memo, Mathews to Actg. Chief, Gemini Procurement, "Reentry Communications Experiment for GT-3," GP-03518, 16 March 1964; memo, Schroeder to Brown, "Status, Reentry Communications Experiment on Gemini," 17 March 1964; memo, Boyd C. Myers II to Dir., MSF Program Control, "Request for Additional Information on Costs for Incorporating Reentry Communications Experiment on Gemini," 1 May 1964; TWX, Mathews to NASA Hq., Attn: Schneider, "NASA Gemini Experiment POISE 3, Reentry Communications," GP-54726, 13 May 1964; memo, Cuddihy to Assoc. Dir., "Reentry Communications Experiment for GT-3 Flight," 13 May 1964; Mathews, activity report, 17 May - 20 June 1964, p. 1; memo, William E. Lilly to Dep. Assoc. Adm., Adv. Research and Technology, "Reentry Communications Experiment (T-1) on Gemini," 15 May 1964; memo, Myers to Dir., MSF Program Control, "Reentry Communications Experiment on Gemini," 25 May 1964; William Armstrong, "Notes on Reentry Communications Experiment," 10 June 1964; TWX, W. G. Robinson to MSC, Attn: Stephen Armstrong, "Contract NAS 9-170, Experiment Order 63-05, NASA Re-Entry Communications," MAC 306-16-6880, 26 June 1964; memo, Myers to Dir., MSF Program Control, "Reentry Communications Experiment on Gemini," 29 June 1964; memo, Mathews to Chief, Gemini Spacecraft Br., "Statement of Work, GP-44, dated April 3, 1964, for the integration of the Reentry Communications Experiment into Spacecraft 3," GP-03760, 10 July 1964; memo, Schroeder to MRB files, "Status, Gemini Reentry Communication Experiment," 17 July 1964; memo, Mathews to Langley, Attn: Floyd L. Thompson, "Langley Research Center Reentry Communications Experiment, T-1, Gemini Mission GT-3," GP-61140, 23 April 1965.
40 Hrabal, "Experiments for GT-3," pp. 6-1 through -13; memo, Schroeder to Assoc. Dir., "Flight Crew Support Requested during the Gemini Reentry Communications Experiment," 9 April 1964; Cuddihy memo, 27 June 1962; Schroeder memo, 21 Jan. 1964.