News of Titov’s death was slow to reach the United States, where two Russian cosmonauts just returned from a U.S. shuttle mission to the International Space Station.

Yuri Malenchenko and Boris Morukov, who landed at NASA’s Kennedy Space Center in Florida Wednesday, were clearly shocked when told about Titov’s death at a post-landing press conference Thursday.

"That’s really bad news," said Yuri Malenchenko, a Mir veteran who flew aboard a NASA space shuttle for his first time during the Atlantis mission.

Morukov, meanwhile, noted that Titov’s flight was a groundbreaking record-setter.

"His flight was very important because he worked in space for one whole day. He got 17 orbits, which was a long time for that period," he said.

Only Yuri Gagarin had flown in orbit before Titov, and his single-orbit flight lasted only 89 minutes.

Morukov, a medical doctor, also credited Titov with jump-starting the field of space medicine -- a field in which he is considered one of the world’s leading experts.

"We got maybe the first interesting medical data after this flight because [Titov] explained that microgravity may cause trouble with the vesicular system," he said. "And so it was very important for the next missions because we had to create countermeasures" to ward off the potentially debilitating effects of long stays in weightlessness.

Titov’s death, meanwhile, was more than the loss of an icon from the early days of the Soviet Union’s once-vaunted space program. It also was a loss of one of the most ardent advocates of Russia’s continuing quest to explore space.

"He was a very interesting man. In the last several years of his life he was our congressman, and he supported the Russian space program very well," Morukov said. "It’s very bad news for us."