At the time the IRDM Statement of Work was issued, the docking module was still only partially defined. The initial ground rules for such a design were presented by Clarke Covington at an IRDM Study Team staff meeting on 16 August. First and foremost, the docking module should be built to accommodate (externally or internally) any additional equipment required by a joint mission so that the modifications to the basic CSM design could be kept to a minimum. There were a number of other fundamental considerations, too. Where possible, the DM should draw on the CSM for its power needs, the major exception being the DM life support system. The designers, James R. Jaax and Gerald P. Mills, agreed that normal crew transfers should not depend upon Salyut life support systems; the DM should have its own environmental control system. Covington and the Crew Systems Division engineers favored an independent system that provided the American crew with a sanctuary to withdraw to if there were difficulties during transfer.76
Since the Americans returning to the CSM would have to pre-breathe for four hours before reentering the command module, he "liked the idea of knowing that we were just minutes away from a U.S.-designed piece of equipment that you could jump back into. . . ." Even though the crew was a couple of hours away from stepping into the CSM, they would still be "in a piece of equipment that we understood . . . and which had been through our qualification program and our safety program."* 77 Further, the DM would have to be able to withstand the 760-mm-Hg pressure used in Salyut and accommodate the equipment required to communicate on the Soviet frequency. During August and September, several MSC teams worked further to define the preliminary design of the docking module, and Covington then took these materials and drew them together into a single document that could be passed nn to the contractor.78
The "Docking Module Design Study" presented by Covington to MSC and North American representatives on 29 September was a full-scale outline  of the design elements to be incorporated into the DM. In fact, the 110-page document really was quite specific on details, more so than might ordinarily have been expected. MSC was telling the contractor precisely what it wanted.79 The DM was to serve five functions:
This study also spelled out the basic dimensions for that new piece of hardware. The length of the DM from the CSM docking interface to the point at which the international docking mechanism would be attached was to be 2.54 meters,** with an additional 0.254 meter allowed for the new docking gear. The interior diameter was to be 1.42 meters with a hatch diameter at the CSM end of 0.84 meter, or the same as that used previously on the lunar module. At the Salyut end, MSC was proposing a 0.9-meter hatch.81
Hatch size was still a topic of considerable discussion in Houston. At the end of August, Glynn Lunney had written to Gilruth suggesting that a distinction be made between the hatch sizes used in an Apollo-Salyut mission and the diameters suggested for future systems. The planners looking forward to Shuttle and Space Station wanted a 1.5-meter hatch, but Lunney doubted that it was reasonable to impose that dimension on the designers preparing for Apollo-Salyut. He thought it was "fair to question whether this is the correct answer for the present and . . . foreseeable future since the schedule for the large space station will remain unclear, but it must be at least 10 or 15 years away." Since the hatches on the docking module could be made to a smaller dimension without serious design impact on future efforts, NASA would propose a 0.9-meter hatch diameter to the Soviets at the next joint talks.82
While work on defining the docking module progressed at MSC, North American at Downey, California, moved ahead with their IRDM study. The Downey engineers had made an initial presentation in Houston on 24 August, containing materials that were being generated almost daily at MSC  and North American. This process of evolving a document or presentation was called "iteration." Draft after draft was prepared, into which the latest findings or ideas were incorporated. Only after several iterations was a final report submitted.83 The second status review made by the contractor on 29 September reflected the joint effort with MSC to that date.84 Contractor ...
 personnel who came to the space center for this review also received a full presentation on the progress of MSC's Docking Module Study. They took this study home to California to use in preparing their final iteration of the IRDM study, due on 16 November.85
In five months, the combined NASA-contractor teams had drawn together a detailed outline of the multitude of considerations involved in the American half of a mission with the Soviets. Called "International Rendezvous and Docking Mission Final Briefing," this document began with a restatement of the basic objectives of such a flight. North American then reported that a "meaningful" dual mission could be performed. The modifications necessary on the CSM were reasonable, in terms of both expense and time. Looking at the docking module, the contractor reported the design to be straightforward, well within current engineering abilities, and the basic subsystems had been previously qualified in Apollo. Communications equipment that operated on the Soviet frequency was one new element that would have to be designed, manufactured, and qualified. While the DM could likely be ready to go in time for a 1974 launch, the Downey personnel responded that work on an international docking gear would have to be very carefully orchestrated to get it completed in time. The North American staff felt that a 1975 launch date would give them more flexibility and leeway but that they could have a spacecraft ready a year earlier if NASA so wished.86
The bulk of the final briefing was devoted to describing mission details, describing changes to the CSM, outlining the design and manufacture of the DM and its subsystems, and listing current Apollo hardware that could be used. Many highly technical orbital mechanics questions were addressed, not only to explain the launch time considerations for a joint docking but also to delineate such problems as the effect of lift-off schedules on the lighting available for the earth resources part of the proposed mission. The report looked into questions like the amount of reaction control system propellant that would be required, with equal attention being given to electrical power and other onboard consumables. The contractor also discussed possible areas for scientific experiments, describing some of the hardware that was available. Materials dealing with the docking module and its fabrication were equally detailed. A 249-page briefing, entitled "IRDM Programmatic Considerations Summary," and eight other sets of documents illustrated the technical feasibility of a rendezvous in earth orbit with the Soviets and testified to the ability of the NASA-industry team to work a problem in a short time.87 René Berglund's Study Task Team had done its job, and Glynn Lunney's people were getting ready for a November departure to Moscow to talk turkey with the Soviets.
* The length of time required for pre-breathing was the subject of considerable discussion between the environmental control system engineers and the medical staff at MSC. The engineers wanted to reduce the time, but the doctors called for a conservative period of three to four hours.
** This is the space required to house two average size men in space suits, allowing for the inward swing of the hatches. The diameter of the hatch was defined by the minimum size that would accommodate a suited man and his portable life support system.
76. Berglund to distribution, memo, "International Rendezvous and Docking Mission Study Team Staff Meeting of August 16, 1971," 18 Aug. 1971, together with enclosure, "Docking Module Study Plan," 14 Aug. 1971.
77. Interview, Covington-Ezell, 3 Apr. 1975.
78. "Minutes of International Rendezvous and Docking Mission, ECS Meeting," 24 Aug. 1971; and R. T. Everline to Berglund, memo, "IRDM Docking Module Meeting," 26 Aug. 1971. At this latter meeting, held on 24 Aug., Covington presented his briefing of the 16th again, this time for North American.
79. Interview, Covington-Ezell, 3 Apr. 1975; NASA, MSC, "Docking Module Design Study," 29 Sept. 1971 (revised 5 Oct. 1971).
80. NASA, MSC, "Docking Module Design Study," 29 Sept. 1971.
82. Lunney to Gilruth, memo, "Status Report," 30 Aug. 1971.
83. Berglund to distribution, memo, "Minutes of the NR International Rendezvous and Docking Mission Study Status Review," 25 Aug. 1971 ; Vu-graphs from "International Rendezvous and Docking Mission Status Review," Aug. 24, 1971; North American Rockwell, Space Division, "International Rendezvous and Docking Mission First Status Review," AP71-19, 24 Aug. 1971; NASA, MSC, "E&D Weekly Activity Report," 21-27 Aug. 1971; and Lunney to Gilruth, memo, "Status Report," 30 Aug. 1971.
84. A standard method of including new data in a contracted study was the issuance of Document Change Requests (DCRs). Between 5 Aug. and 9 Nov., 60 DCRs were made to the document, NASA, MSC, "International Rendezvous and Docking Mission Study Guidelines and Constraints Document," MSC-04750, 5 Aug. 1971, which outlined the scope of the missions and concepts to be considered in the IRDM study. For example, see letter, D. A. Nebrig to R. C. Lashbrook, "Contract NAS 9-150, Guidelines and Constraints Approved for Inclusion in MSC-04750 (International Rendezvous and Docking Mission Study)," 9 Nov. 1971, which enclosed DCRs 48-60.
85. Berglund to distribution, memo, "International Rendezvous and Docking Mission Study Team Staff Meeting of August 30, 1971," 31 Aug. 1971; Berglund to distribution, memo, "International Rendezvous and Docking Mission Staff Meeting of September 13, 1971," 15 Sept. 1971; and North American Rockwell, Space Division, "International Rendezvous and Docking Mission, Second Status Review," AP71-21, 29 Sept. 1971.
86. North American Rockwell, Space Division, "International Rendezvous and Docking Mission Final Briefing," AP71-23, 16 Nov. 1971.
87. Ibid.; also sent
with North American's briefing were the following: "IRDM Programmatic
Considerations Summary (Briefing)"; "Layouts of DM, SLA Truss"; "IRDM
Science Supplement (Briefing)," AP71-23-2, 16 Nov. 1971; "Total
Stowage Plan/List (Briefing/List)"; "Devel/Cert Test/Anal
Requirements (Write up)"; "MU/Trainer Requirements (Write Up)";
Manufacturing Engineering Producibility Study on International
Docking Module," MPA 35005, 10 Nov. 1971; and "International Docking
Systems Development Plan," SID 71-684, 5 Nov. 1971. North American
Rockwell subsequently submitted a formal report entitled
"International Rendezvous and Docking Mission," SD71-700, with
Addendum, Dec. 1971. Also see Lashbrook to A. H. Atkinson,
"Transmittal of International Rendezvous and Docking Mission (IRDM)
Report," 14 Dec. 1971; and Berglund to distribution, memo, "North
American Rockwell (NR) International Rendezvous and Docking Mission
(IRDM) Final Report," 17 Dec. 1971.