As the Soviets departed from Houston, Soyuz 11 was completing its 20th day in orbit docked with Salyut I. This record breaking flight had been  heralded by Keldysh as beginning a new era in space exploration. On 9 June, Blagonravov had declared in an article prepared for Krasnaya Zvezda that:
In the opinion of Soviet scientists, such stations with replacement crews constitute mankind's main highway into space. They can become unique launching pads for flights to other planets. Large scientific laboratories will spring up for research into space technology and biology, geophysics and medicine, astronomy and astrophysics. . . . In time, such stations will be linked with earth not only by radio but by a regular space mail. By periodically putting small supplies of fuel aboard, it is possible to insure the station's long-term existence by switching on the engines and reestablishing the velocity lost as a result of braking in the upper layers of the atmosphere.54
The three-man crew of Soyuz 11 (call signal "Yantar"), Georgi Timofeyevich Dobrovolskiy, Vladislav Nikolayevich Volkov, and Viktor Ivanovich Patsayev, had entered the space station on 7 June. The joined configuration of Soyuz and Salyut was 21.4 meters long with a total living space of 100 cubic meters, which gave the cosmonauts a place to conduct scientific experiments, relax, and sleep. For the next 23 days, each crewmember performed his scheduled experiments, which emphasized the study of human performance under, and reaction to, prolonged weightlessness. On the 29th, after completing their flight plan, the space dwellers transferred their scientific records, film, and log books to Soyuz in preparation for their return home.
At 9:28 in the evening, Dobrovolskiy undocked the ship and drifted free from the space station. After three additional orbits, the Soyuz 11 crew notified ground control that they were beginning their descent. Mission ...
 ...Control radioed: "Good bye, Yantar, till we see you soon on mother earth." Dobrovolskiy replied: "Thank you, be seeing you. I am starting orientation."55 At 1:35 a.m. the retrorockets were fired automatically for a seven- minute burn, and the parachutes were deployed on schedule. Mission Control tried repeatedly to contact the crew at this time, but to no avail. When the recovery crews reached the descent vehicle and opened the access hatch, Dobrovolskiy, Volkov, and Patsayev were dead in their contoured couches.56
The accident was a stunning blow to both the Soviet Union and the international aerospace community. Once again, the experimental and risky nature of man's venture into space had been made clear. While the three bodies lay in state and a Special Commission investigated the cause of the multiple deaths, wide speculation spread in the West over the significance of the tragedy for the continuation of manned space flight.
One of the prevailing theories was that man might not be able to survive long periods of weightlessness. For several years, there had been a serious debate among scientists about the effects of prolonged weightlessness. During Project Gemini, there had been "signs" that the human heart grew lazy after an extended time in zero gravity. Then in July 1969, the monkey Bonny aboard the U.S. Biosatellite 3 died of heart failure after recovery from a 9-day flight.
However, there were other theories regarding the Soviet disaster. George Low discounted the heart failure story, and Dr. Walton Jones, Deputy Director of Life Sciences in the Office of Manned Space Flight suggested that the men had died as the result of their cabin decompressing rapidly. The crew was found strapped in their seats with no apparent indication of any struggle. (The crew did not rely on space suits.) Dr. Jones said that this is how they would have appeared if a valve had leaked or the shell of the cabin had ruptured. In Houston, Dr. Charles Berry, flight surgeon to the astronauts, thought that the accident might have been caused by the release of a toxic substance. MSC Director Gilruth favored the decompression theory. Whatever the cause, both Soviet and American aerospace leaders realized the seriousness of the problem and its implications for manned flight in general and for the compatibility discussions in particular.57
As thousands of Muscovites filed by the funeral bier of the three cosmonauts on 1 July, Soviet President Nikolai V. Podgorny, Premier Kosygin, and Party General Secretary Leonid I. Brezhnev took turns standing watch as part of the honor guard. President Nixon on behalf of the United States told the Soviet leaders:
The American people join in expressing to you and the Soviet people our deepest sympathy on the tragic deaths of the three Soviet cosmonauts.  The whole world followed the exploits of these courageous explorers of the unknown and shares the anguish of their tragedy. But the achievements of cosmonauts Dobrovolsky, Volkov and Patsayev remain. It will, I am sure, prove to have contributed greatly to the further achievements of the Soviet program for the exploration of space and thus to the widening of man's horizons.58
In addition, the President sent U.S. astronaut Thomas P. Stafford to Moscow as his official representative for the funeral ceremonies held in Red Square.59
Soviet space leaders were quick to reaffirm their plans to continue manned space flight. Writing for Pravda on 4 July, Petrov spoke of the conquest of space as a "difficult path," but he repeated Brezhnev's earlier statement - "Soviet science considers the creation of orbital stations with replacement crews to be man's highway to space." The scientist argued that man could play his most important exploratory role in the study of the earth and in astronomy from platforms positioned in "near-earth space." Furthermore, such earth orbital investigation is only valuable when it is conducted for extended periods on a regular schedule. Petrov said that "the seventies will be the epoch of development and broad application of long-term manned orbital stations with replacement crews, which will make it possible to switch from episodical experiments in space to a regular watch by scientists and specialists in space laboratories."
Summarizing the work conducted on board Salyut by the crew of Soyuz 11, Petrov restated the value of their contributions to science. In addition to the medical and biological experiments, they had carried out a number of studies related to weather and earth resources. According to the Soviet spokesman, the data returned in Soyuz would be used by students of agriculture, land reclamation, geodesy, and cartography, as well as by meteorologists to improve their forecasts. With words apparently aimed at domestic critics of the Soviet manned space program, Petrov reported:
The experience of the cosmonauts' work has shown that the Salyut manned station is a space laboratory well adapted for experiments in orbital flight conditions. Such stations are opening broad prospects for the continuation and development of the research carried out by the first Salyut crew. . . . Ahead lie new flights into space and the creation of new inhabited orbital stations of the Salyut type. Undoubtedly, even larger and more complex manned multipurpose and specialized space stations will be built. But the significance of the work carried out by the first crew of the first manned orbital station . . . will never fade.60
The Special State Commission investigating the Soyuz 11 deaths released a public statement on 12 July. After reporting that the flight had  proceeded normally up to the beginning of reentry, the Commission stated:
On the ship's descent trajectory, 30 minutes before landing, there occurred a rapid drop of pressure within the descent vehicle which led to the sudden deaths of the cosmonauts. . . . The drop in pressure resulted from a loss of the ship's sealing. An inspection of the descent vehicle . . .showed that there are no failures in its structure.61
The reasons for the "seal" failure were still under investigation, this terse statement continued.
While the official report apparently eliminated weightlessness and physical deconditioning as causes for the accident, the seal failure statement raised a new question. Americans preparing for Apollo 15 wondered if the Soyuz problem was of the type that might be experienced with an Apollo spacecraft. MSC Director Gilruth wrote Petrov shortly after the accident and asked him that question. Petrov reassured the Americans that "the drop in pressure resulted from a concrete failure of one of the elements of the descent vehicle system. Since it is a matter of specific and particular defect we are sure that it cannot be related to 'Apollo' spacecraft."62 Soyuz 11's misfortune did not affect NASA's plans for the launch of Apollo 15, but it did lead to some discussions outside the space agency on the safety of Soviet hardware.63
54. Library of Congress, Federal Research Division, "Soyuz-11 Triumph and Tragedy," S & T News Feature, Item No. 454 [n.d.].
55. V. Golobachev and T. Borisov, "Duty Carried Out to the End," Trud, 2 July 1971.
56. "Cause Sought in Soyuz Tragedy," Aviation Week and Space Technology, 5 July 1971, pp. 12- 15; and Peter Smolders, Soviets in Space (Guildford and London, 1973), pp. 246-247.
57. "3 Cosmonauts in Space Lab Found Dead after Recovery," Washington Post, 30 June 1971; Arthur J. Snider, "Has Man Reached His Space Limit," Washington Evening Star, 30 June 1971; Don Kirkman, "Soyuz Air Leak Blamed," Washington Daily News, 1 July 1971; Robert C. Cowen, "Soviet Loss Underscores Space Dangers," Christian Science Monitor, 1 July 1971; Thomas O'Toole, "Soyuz 11 Deaths Assessed," Washington Post, 1 July 1971; Jonathan Spivak, "Deaths of Cosmonauts Are Unlikely To Delay U.S. Space Program," Wall Street Journal, 1 July 1971; Charlotte Saikowski, "Space Tragedy Probed," Christian Science Monitor, 1 July 1971; and interview, Charles A. Berry-W. David Compton, 10 Apr. 1975. See also NASA Press Conference, MSC, "Statement on the Soyuz 11 Flight," 30 June 1971.
58. TWX, George G. Coletto to all Station Directors, MSFN, 30 June 1971.
59. Stuart Auerbach, "Cosmonaut Deaths Laid to Faulty Hatch," Washington Post, 3 July 1971. Low offered the following statement on 30 June: "The death of the three Soviet Cosmonauts is a terrible tragedy. They were pioneers in their achievements in space - in establishing the first manned space station. Our hearts go out to their families and to their colleagues."
60. Petrov, "On the Threshold of New Achievements," Pravda, 4 July 1971; "Salute Missions to Go On," Washington Post, 5 July 1971; Walter Sullivan, "Tragedy: When the Hatch Was Opened the Men Were Dead," New York Times, 4 July 1971; and Bernard Gwertzman, "Soviet Space Scientist States Salyut Program Will Continue," New York Times, 5 July 1971.
61. TWX, Goddard Network Operations Control Center to all Station Directors, 13 July 1971; Bernard Gwertzman, "Cause Confirmed in 3 Soyuz Deaths," New York Times, 12 July 1971; and Dean Mills, "Russia Blames the Soyuz Deaths on Failure of Seal," Baltimore Sun, 12 July 1971.
62. Petrov to Gilruth [n.d.; with enclosure, letter, Yu. P. Khomenko to Gilruth, 17 July 1971]; and "Russia, U.S. Exchange Space-Tragedy Notes," Baltimore Sun, 20 July 1971.
63. "Apollo's Safeguards
Are Emphasized by U.S. Space Experts," Chicago Tribune, 20 July
1971; and Thomas O'Toole, "Apollo 15 Crewmen To Suit Up To Avert
Soyuz 11 Disaster," Washington
Post, 20 July 1971.