The recently concluded 65th International Astronautical Congress (IAC) in Toronto was by all appearances a successful and productive event but for the noticeable absence of senior Russian and Chinese space officials from high-profile panel discussions.

The annual gathering typically includes delegates from dozens of nations who come to exchange ideas and present status updates on space programs big and small in an open forum. Hosted by a different country each year, the conference usually offers sanctuary from geopolitical tensions, welcoming just about all comers: Representatives from Iran have regularly attended, for example, as have officials from other countries with virtually no ties to the West.

That’s how it should be, especially for a conference whose consistent underlying theme is international cooperation. It’s also appropriate given the widely held notion that cooperative space activities can survive and even help mitigate the rough patches in relations between nations.

Yet during one IAC panel that was supposed to feature the heads of the world’s major space agencies, two of the biggest and most important were conspicuous in their absence. Russian representation was similarly missing from a panel on the future of the international space station — Russia is a senior partner in that ongoing mission — while top Chinese officials were not there to update the world on their rapidly growing space program.

It certainly wasn’t for lack of trying. According to conference organizers, senior members of the Russian and Chinese delegations were denied visas needed to gain entry into Canada.

This sort of thing has happened before. Chinese delegations have been denied visas to attend space conferences in the United States, presumably due to U.S. sensitivities — and legal barriers — associated with any space-related dealings with China.

It’s not clear what happened in the latest case, although Canada does appear to be more serious than Europe and the United States about enforcing sanctions against Russia for its incursions into Ukraine over the past year. As evidence, Canada recently barred one of its government-funded satellites from being shipped to Russia for launch on a Soyuz rocket.

According to Canadian press reports, Canadian government officials acknowledged denying visas for some, but not all, members of the Russian delegation. One member, cosmonaut Sergei Krikalev, who as a veteran of several U.S.-Russian missions has become an ambassador of sorts for international collaboration, reportedly told Russian media that he simply applied too late to obtain a visa.

Either way, the conference suffered. An embarrassed Berndt Feuerbacher, a past president of the International Astronautical Federation and the moderator for the heads of agencies panel, went so far as to apologize for the lack of participation by China and Russia.

This was not the fault of the conference organizers, of course, nor can one fairly blame the Canadian Space Agency, which hosted the event and apparently did not become aware of the visa issue until just a few days before the start of proceedings. Visas are handled by Canada’s foreign ministry.

Nonetheless, the IAC organizers and hosting agencies should learn from this experience and hopefully avoid a repeat in the future. Conference attendees, particularly those from countries lacking stellar relations with the host state, should be strongly encouraged to apply for visas at the earliest possible date. Meanwhile, officials with the hosting space agency should proactively engage their counterparts in the foreign ministry — or whichever agency is responsible for granting visas — to learn whether participants from a particular country might pose an issue and, if so, to see if there’s a way to ameliorate those concerns.

The 66th IAC, scheduled to take place next fall in Jerusalem, with the Israel Space Agency acting as host, could be an interesting test of whether visa issues can be overcome. If the organizers haven’t already begun laying the groundwork to make sure the event is as widely attended as possible — Iranian attendance, for example, might be a bridge too far — now would be a great time to start.