With an explanation but no public apology for the flip-flop, NASA told Chinese astrophysics researchers they could re-book their already canceled flights to California to attend a space telescope conference in November.

"The US space agency has lifted its earlier ban on Chinese scientists attending the conference, and it could set a good precedent to protect Chinese scientists from experiencing similar unfairness in the future," Wu Yanqin, astronomy professor at the University of Toronto, told China Daily on Tuesday.

Wu said she could understand if NASA banned foreign nationals from the country's application research in astrophysics, but this was a conference on basic research, which demands international cooperation.

"There are no boundaries on basic research," she said, "which is why so many scientists argued against it."

Wu is the tutor of Xie Jiwei, who was among the six Chinese researchers whose applications to attend an international conference on NASA's Kepler space telescope at Ames Research Center in California next month were turned down.

NASA spokesman Allard Beutel told BBC that the ban on Chinese scientists, announced earlier this month, was prompted by new counter-espionage legislation restricting foreign nationals' access to NASA facilities.

"The initial decision was based on a misinterpretation of the agency's policy regarding foreign nationals," Beutel was quoted as saying.

NASA officials have earlier said the restriction policy was based on legislation signed by President Barack Obama in 2011 that prohibits government funds from being used to host Chinese nationals at NASA facilities.

"We were able to clarify that interpretation and correct the decision, but it didn't happen until the federal government reopened last Thursday," the NASA spokesman said.

In recent weeks, some prominent US scientists took issue with the ban and threatened to boycott the meeting in protest, including Yale astronomy professor Debra Fischer and Berkeley professor Geoff Marcy.

"Every United States astronomer with whom I have spoken agrees that our colleaguesfrom China and other restricted nations should be allowed to attend sciencemeetings," said Fischer, whose Chinese teammate was also denied attendance.

She said several people worked very hard to "find a solution" and "change the policy" and most of the legislation seems to have been sponsored by one person - Congressman Frank Wolf, whochairsthe subcommitteethat oversees NASA's funding.

"My hope is that the Chinese people understand that scientists in the US are united and acting to make sure this discriminatory policy ends," she said.