TORONTO — Multiple Russian and Chinese space engineers failed to obtain visas to attend the 65th International Astronautical Congress (IAC) here this year, an absence that undermined space agency arguments that space cooperation should not be subject to short-term political issues.

The absence of many in the planned Russian and Chinese delegations left gaps in sessions related to the future of the international space station, the development of new Chinese rockets and other topics.

At a panel featuring the heads of the world’s major space agencies, the Mexican Space Agency stood in for the missing Chinese and Russian participants. Almost all of those making speeches — the heads of the U.S., European, Indian, Canadian and Japanese space agencies, in addition to Mexico — stressed the need for international collaboration at a time when no nation can go it alone.

NASA Administrator Charles Bolden said that if one looked only at the way the international space station is being managed — both in orbit and in terms of astronaut launches and returns aboard Soyuz capsules — one would have no idea of the tensions now stressing relations between Russia and the West.

China has always been a special case in the United States, where NASA by law is prohibited from doing much with China’s quickly expanding space program.

The U.S. government has specifically exempted the space station, where Russia is the biggest of NASA’s partners, from any embargoes or sanctions following Russia’s incursion into Ukraine.

Berndt Feuerbacher, a past president of the International Astronautical Federation and the moderator of the panel with the heads of space agencies, publicly apologized for the visa issues that have put so many holes in this year’s IAC program, and stretched the credibility of the idea that space is a protected domain.

“This was not our intention,” Feuerbacher said when questioned about how a panel discussing global space cooperation could do without China and Russia. “It is very unfortunate that problems in the visa area meant those delegations could not be here today. I apologize.”

Walter Natynczyk, president of the Canadian Space Agency, said it is Canada’s foreign ministry that handles visa issues and that the Canadian Space Agency — host of this year’s IAC — was not made aware of the visa issue until only a couple of days before the congress started Sept. 29.

To date, Canada is the only Western government to have extended Russian sanctions to barring a satellite from being exported to Russia for launch aboard a Soyuz rocket. A Canadian maritime monitoring satellite, which was financed by the government but was to be used as part of Canada’s exactEarth commercial venture, was denied an export license at the last minute, apparently because of pressure from Canada’s large Ukrainian expatriate community.

The United States, Europe and Asian nations have continued to send commercial and scientific satellites to Russia for launch.

The annual IAC has always prided itself on being an island of nearly pure engineering and future-think in a world of political upheaval. Iranian delegates have been regular attendees, as have representatives from other nations whose space programs have zero contact with the West.

Peter B. de Selding was the Paris bureau chief for SpaceNews.