Both Keldysh and Feoktistov were intrigued, and they said that although they were not free to commit their government to such a project they wanted to pursue this subject further and hear more details. Then they could advise their superiors and obtain a decision. Low agreed to send with the exchange of technical requirements scheduled for February a fuller description of the type of project he was proposing. Keldysh asked Low to refrain from mentioning this conversation publicly until there had been consultations internally. The two sides would subsequently make a public  announcement if this developed into a formal topic for negotiation. Low agreed to this arrangement.* 16
Low based his discussions with Keldysh concerning a joint rendezvous and docking mission on the "USSR US Docking Studies" prepared at MSC in late December 1970. In Houston, Clarke Covington had prepared materials on the two aspects of possible docking activities - the near and far term. For the former, he and his colleagues proposed feasibility studies of  specific docking missions and specific hardware systems that could be flown between 1972 and 1975. For the far term, the specialists suggested that the Joint Working Groups develop technical requirements and general concepts for the docking of future systems "as a continuing show of good faith."17
In effect, the MSC proposal inserted a new activity into the scheme of things as they had been agreed to earlier in Moscow. The primary focus of the October agreement had been work on compatible systems for future spacecraft. Now Caldwell Johnson, Covington, and their associates were pushing for a real mission using existing hardware. MSC specialists had listed several important guidelines. Such a joint mission should provide a public demonstration of a viable joint activity and as such should allow both countries to exhibit equal skill and effort. But above all, it should be an open, non-military enterprise that would continue NASA's philosophy of peaceful exploration in space.
To define the hardware needed for a rendezvous and docking mission, Will Taub had drawn a series of sketches showing variations on an Apollo-Soyuz mission. Covington used these in December 1970 when he briefed MSC management on five mission possibilities:
(a) proposal for a minimum-modification approach to an Apollo-Soyuz docking mission;
(b) Apollo drogue in Soyuz cone adapter, proposed to permit docking and transfer with minimum modification;
(c) proposal for an airlock adapter that would facilitate transfer between spacecraft;
(d) initial concept for an Apollo-Soyuz airlock adapter.
Two important points had to be considered for any of the docking missions - the docking gear to be used and the impact of cabin atmosphere on crew transfers. For an Apollo-Soyuz linkup, the hardware proposals ranged from a simple adaptation of the existing gear to the creation of a  special docking module with Apollo gear on one end and Soyuz gear on the other. The minimal changes to the docking equipment called for building an adapter that would permit the installation of a lunar-module-type drogue into the cone of the Soyuz. Then the Apollo could dock and latch its probe into this adapted Soyuz. This particular modification could be varied for use with either the solid face or the swing-away Soyuz docking mechanisms. A more elaborate alternative called for building an "airlock docking adapter," a mini-spacecraft that would be carried into orbit in the spacecraft lunar module adapter (SLA) behind the command and service module (CSM).** Following the CSM's docking and removal maneuver with the airlock module, the Soyuz could dock with it, employing the standard Soyuz probe. While crew transfer in the simple system would be either internal or external depending upon the type of Soyuz docking interface, the airlock module concept assumed the use of the swing-away hatch on Soyuz.
Two detailed views of the new Soyuz docking mechanism, prepared by W. K. Greasy and T. O. Ross at the Manned Spacecraft Center to give the NASA team a clearer understanding of how that system operated. One of the notes on the drawings reads, "The dimensions and scale of this drawing are based on the assumption that the spacecraft spherical diameter is 2.08 meters." As they later discovered, it was actually 2.2 meters. Otherwise their drawing was correct.
Developing an airlock module would have solved some of the problems involved in changing the pressure in either spacecraft. If the astronauts wanted to transfer to Soyuz, they would enter the airlock, close the hatch behind them, raise the pressure to 760 millimeters, and then enter the Soviet spacecraft. Going the other direction, they would enter the airlock after pre-breathing oxygen aboard Soyuz (or alternatively in the airlock itself) and when it was safe lower the pressure to 258 millimeters. Throughout this process, the pressure in each craft would remain virtually unchanged.
At this point, complexities of design seemed to abound. If the crewmen pre-breathed in the airlock module, then a full life support system would have to be included in that mini-spacecraft. If the pre-breathing occurred in Soyuz, a simpler life support system could be used in the airlock module, but the Americans would have to transfer in their suits, requiring provision for suit cooling circuits aboard Soyuz. Walter W. Guy of the Crew Systems Division urged the specialists to find a simpler way to conduct the transfers. Otherwise, life was going to be too complex for the crews.
In addition to making the transfer process somewhat easier and reducing further the possibility of oxygen enrichment to the Soviet craft, the airlock had several good features from a designer's point of view. In the first instance, all Soyuz docking aids could be secured on the exterior of the module, thus eliminating major changes to the CSM. Second, the interior surfaces of the airlock module would provide places for mounting various communication and power units that would otherwise have to be added to the CSM or to the Soyuz. But the airlock module was a new piece of hardware that would have to be designed, built, and tested. This was the major objection raised by both MSC and Headquarters.21
George Low, Wernher von Braun,**** and others at Headquarters were interested in pursuing the simpler drogue-in-cone adaptation, and it was this type of system that Low had considered in January when he had talked to Keldysh in Moscow. So in February 1971, NASA transmitted two documents to the Academy of Sciences, the first fulfilling the 1970 agreement to exchange "technical requirements for rendezvous and docking." "Preliminary Rendezvous and Docking System Requirements for United States Spacecraft" was generated to provide the Soviets with only an "overview of NASA . . . requirements and systems," not specific solutions to compatibility issues. From this general paper, the planners hoped to move on to more detailed discussions.22
 The second paper - "A Concept for a Union of Soviet Socialist Republics United States of America Rendezvous and Docking Mission" - was prepared by MSC personnel under the direction of René Berglund. Although drawn up in a relatively short time and based upon a still limited understanding of the Soyuz docking system, the document drafted by William K. Greasy and Thomas O. Ross, among others, was a rather detailed study of the docking interface for Apollo and Soyuz, presented as an illustration. Similar details were given for the necessary docking targets, communications equipment, and pre-breathing apparatus. These studies were designed to outline the way NASA would create compatibility and conduct a joint mission.23
In his letter of 17 February transmitting the two documents to Petrov, Gilruth explained why he sent the paper proposing a joint Apollo-Soyuz flight. Since this topic had been discussed by Low, Keldysh, Frutkin, and Feoktistov during January, the MSC staff had looked into the whole question of compatible systems. "In the process of our deliberation on this subject," Gilruth noted, "we have found the postulation of a specific docking mission and spacecraft configuration useful in understanding potential problem areas." He also told Petrov that analysis of such a typical mission concept - Apollo and Soyuz should "be a beneficial way of assessing compatibility during the March April Working Group Meetings."24
Gilruth then addressed the agenda for that spring gathering. "With regards to these detailed Working Group activities, I believe that a preliminary meeting . . . should be held to establish the types of spacecraft to be considered by the Working Groups." Not everyone need be present, Gilruth suggested, but he did "feel that the participation of the chairmen of our respective Working Groups would be most beneficial." For such discussions, Gilruth had appointed Glynn Lunney, Donald C. Cheatham, and Donald C. Wade to chair groups one through three respectively, and they would be joined by Arnold Frutkin, George Hardy, Caldwell Johnson, and René Berglund. "Should this suggestion meet with your approval," Gilruth continued, "I would like to invite you and your delegation . . . to the Manned Spacecraft Center, Houston, Texas, in March to conduct these discussions." Afterwards the full Working Groups could meet and begin their efforts.25
During the six months following the October meeting, MSC had begun to find some minor problems that would have to be worked out as they continued to expand the scope of their joint work- language and communications being two examples. Preliminary studies conducted at Houston, based on available Soviet data, opened as many questions as they answered. These new questions confirmed the necessity for additional information exchanges.  There was also evidence that both sides would have to come to agreement on technical translation, so that each side could be assured that the other understood precisely what had been meant by specific words, phrases, and documents.26
 Then there was the time-gap problem in coordinating these communications. For instance, when Gilruth sent a draft of his letter to Petrov to Washington for approval on 12 February , Houston was still thinking about a meeting scheduled for March/April. But these plans were to be altered several times before the meetings finally took place. Academician Petrov sent his response on 15 March to Gilruth's letter dated 17 February. Petrov's response, along with seven documents that constituted the Soviet technical requirements for compatibility, was sent via diplomatic pouch from the American Embassy in Moscow to the State Department in Washington. That agency passed the material over to NASA Headquarters, where Frutkin's office received them on the 24th. The documents were next sent out for translation, and MSC finally received them at the end of the month. Gilruth got a preliminary briefing of their contents on 1 April and dispatched his reply on the 9th. For both the February letter from Gilruth and the March letter from Petrov, the turn-around time had been almost a month. Much faster communications would be essential to any joint enterprise.27
In his letter, Petrov approached the question of an actual test flight: "As far as your new proposal . . . of an actual example of docking of the 'Soyuz' and 'Apollo' type spacecraft, it requires further study which our specialists are now engaged in." Noting that this was apparently "an intermediate solution" toward the development of compatible systems, Petrov felt that the two sides should stick to the schedule as agreed upon in the Moscow "Summary of Results." He did agree to the preliminary discussions suggested by Gilruth for planning the agenda more fully, and he proposed that they be held immediately before the Working Groups met. After asking Gilruth to select a date for the meetings, Petrov added, "From our point of view, the meeting of the Working Groups could be . . . conducted in the middle of May."28 Gilruth in turn suggested the period 17-21 May for their meeting and provided a summary of the agenda and the activities planned for the Soviets' stay in Houston.29
While his staff prepared for the Working Group meetings, Gilruth tried for an even earlier discussion with Petrov. The American Ambassador to Moscow, Jacob D. Beam, had reported to NASA via the State Department that one of Petrov's deputies had said that the installation of a compatible rendezvous and docking system on Soyuz and Apollo would be "difficult." Nevertheless, the deputy had indicated that this might be a proper topic for discussion during an upcoming visit by Petrov to the U.S. for an international symposium. Donald Morris, Frutkin's deputy, attempted to find a suitable time for Petrov and Gilruth to meet during this visit, but he was unsuccessful. Any consideration of the American proposal would have to wait until May.30
Hearing nothing to the contrary from the Soviets, MSC assumed that  the May dates were acceptable and continued planning for the meetings. Late on the afternoon of 7 May, they received word that there was going to be a change. Leonard S. Nicholson, Berglund's assistant, remembered sitting in a briefing session in which Gilruth and Frutkin were being given a report on the preparations for the visit, when Frutkin received a call from his office. The U.S.S.R. delegation would not be coming.31 The full text of the cable from Petrov, received the following morning in Houston, read: "To my regret I have to ask you to postpone meetings of our working groups [until] June due to engagements of our specialists. I shall let you know names of Soviet participants and desirable date of meeting in the near future."32 The men gathered that Saturday morning were perplexed; Gilruth asked them to study the implications of slipping the meeting date to June and then report back to him by the following Friday.
Unknown to the Americans, the Soviets were planning another significant manned launch for early June. But the Americans also had a flight in the final stages of preparation. René Berglund reported to Gilruth on 14 May that "the unanimous conclusion of the working group chairmen and myself is that a meeting in June would be very inconvenient." Glynn Lunney was particularly concerned since Apollo 15 was scheduled to be launched on 26 July. As he was deeply involved with the mission as Chief of Flight Operations, any meeting within the last 30-45 days prior to launch would pose serious scheduling difficulties. Berglund told the Director that he and the chairmen were proposing that the meeting be delayed until early September, and they had drafted a letter to that effect. He continued, "There is some question as whether we should bother to reply at all until such time as Petrov proposes a date." Clearly there was some unhappiness, but Gilruth's calm and measured approach prevailed. NASA, he decided, should await the Soviets' next move.33
* At this meeting in Moscow, Low had also presented to the cosmonauts a plaque designed by Gilruth to be placed in the Gagarin museum. As Low said to Gilruth in a 27 Jan. 1971 letter, "It was an emotional moment, and it was obvious that they were pleased at the recognition by us of their being first in space."
** The SLA, an 8.5-meter truncated cone between the service module and the launch vehicle instrument unit, enclosed the lunar module (LM) during launch and on its way to the moon.
*** The information available to NASA included materials that had appeared in the American press over the years, those obtained during the October 1970 trip, and the report sent to Houston in the first technical exchange.
**** Von Braun had been appointed Deputy Associate Administrator for Planning in Mar. 1970.
16. Low, "Notes on Trip to the Soviet Union," 15-22 Jan. 1971; and interview, Low-Ezell, 30 Apr. 1975.
17. NASA, MSC, Clarke Covington, "USSR/ US Docking Studies," 5 Jan. 1971; René A. Berglund to Gilruth, memo, "Status of USSR/ USA Docking System Activities," 17 Dec. 1970; NASA, MSC, Covington, "USSR/US Docking Study Review," 21 Dec. 1970 (draft of 5 Jan. presentation); and interview, Covington-Ezell, 3 Apr. 1975.
18. Covington, "USSR/US Docking Study Review."
19. Interview, Covington-Ezell, 3 Apr. 1975.
20. Ibid.; interview, Walter W. Guy and James R. Jaax-Ezell, 17 May 1974; and interview, Guy and Jaax-Ezell, 7 July 1974. See also NASA, MSC, NASA Technical Brief, B72-10690, "An Efficient Prebreathing Apparatus for Humans during Decompression," Dec. 1972.
21. Interview, Covington-Ezell, 3 Apr. 1975; and Covington, "USSR/US Docking Study Review."
22. NASA, MSC, "Preliminary Rendezvous and Docking Requirements for United States Spacecraft," 2 Feb. 1971. This document was compiled with the help of many people at MSC under the editorial supervision of Leonard S. Nicholson.
23. NASA, MSC, "A Concept for a Union of Soviet Socialists Republics/United States of America Rendezvous and Docking Mission," 2 Feb. 1971.
24. Gilruth to Petrov, 17 Feb. 1971.
25. Ibid.; and Gilruth to Myers, 12 Feb. 1971.
26. NASA, MSC, "A Synopsis of the Russian/American Docking Systems Activities," 8 Feb. 1971.
27. Briefing Vu-graphs from "Planning for USA/USSR Preliminary Mating" [n.d.]; Eldon W. Hall to Philip Culbertson, memo, "Weekly Activities Report," 25 Mar. 1971; NASA, MSC, "E&D Weekly Activity Report," 6-12 Mar. 1971, 20-26 Max. 1971, and 3-9 Apr. 1971; and James L. Roberts to Glynn S. Lunney, memo, "International Rendezvous and Docking Activity," 20 Aug. 1971.
28. Petrov to Gilruth, 15 Mar. 1971. The seven papers that constituted the Soviet technical requirements were as follows: "Tekhnicheskiye trebovaniya k sistemam i oborudovaniyu kosmicheskikh korabley i stantsiy obespechivayushchim ikh sblizheniye i stykovku" [Specifications for rendezvous and docking systems and equipment for spacecraft and space stations], "Predlozheniya po sistemam doordinat dlya razrobotki metodov i sredstv sblizheniya i stykovki kosmicheskikh korabley i stantsiy" [Proposed coordinate systems for developing methods and equipment for use in the rendezvous and docking of spacecraft and space stations], "Tekhnicheskiye trebovaniya na razrabotku stykovochnogo ustroystva dlya kosmicheskikh korabley i stantsiy, obespechivayushchego ikh stykovku" [Specifications for the development of a docking mechanism for docking spacecraft and space stations], "Tekhnicheskiye trebovaniya k atmosfere obitayemykh otsekov, sposobam otkrytiya vkhodnykh lyukov, pnevmogidroelcktrorazyeman mezhdu skafandrami kosmonavtov i bortom kosmicheskikh korabley ili stantsiy" [Technical requirements for cabin atmospheres, means of opening entry hatches, pneumo-hydro-electrical connections between cosmonauts suits and equipment aboard space vehicles and stations], "Technicheskiye trebovaniya k radio-apparatus dlya svyazi mezhdu ekipazhami kosmicheskikh korabley i stantsiy" [Technical requirements for radio equipment for communications between crews of space vehicles and stations], "Ogranicheniya po raspolozheniyu elementov konstruktsii i oborudovaniya pri sblizhenii i stykovke kosmicheskikh korabley i stantsiy" [Restrictions on the placement of structural elements and equipment in rendezvous and docking of space vehicles and stations], and "Technicheskiye po dinamike stykovki kosmicheskikh korabley i stantsiy" [Technical requirements in regard to the docking of space vehicles and stations] .
29. Gilruth to Petrov, 9 Apr. 1971; and Lunney to Caldwell C. Johnson, memo, "Preparations for Mid-May Soviet Talks," 9 Apr. 1971.
30. TWX, Jacob D. Beam, Ambassador, to Secretary of State, "Space Cooperation: Local Expenses for Exchanges," 19 Mar. 1971.
31. Vu-graph briefing charts from "Dr. Gilruth/Mr. Frutkin Meeting, May 7, 1971, USSR Visit" [n.d.]; and TWX, Beam to Secretary of State, "Space Docking Meeting," 7 May 1971: "Vereshchetin informed science officer that delegation must postpone until sometime in mid-June. Letter from Keldysh on whole range of cooperation to Low to be delivered to science officer Monday."
32. TWX, Petrov to Gilruth, 8 May 1971; interview, Nicholson-Ezell, 16 July 1974; and interview, Nicholson-Ezell, 6 June 1975.
33. Berglund to Gilruth, note, 14 May 1971; Gilruth to Petrov [not sent] ; "Soviet-U.S. Parley on Space Cancelled," New York Times, 23 May 1971; and Jack Hartsfield, "Apollo-Soyuz Link-up Proposal Gets Nowhere," Huntsville Times, 4 May 1971.