Rose Tani, whose son Dan is currently in orbit as an astronaut on the International Space Station, was killed Wednesday when her car was hit by a train near her home in Lombard, Ill., outside Chicago.
Police said Ms. Tani, 90, was trying to drive around a stopped school bus at a railroad crossing when her car was hit by a commuter train. She was pronounced dead at a nearby hospital.
NASA said mission control in Houston had told Dan Tani of his mother's death.
Astronaut Tani, who left for orbit on Oct. 23, must, barring a change of plans, remain in space for now. While there is a three-seat Russian Soyuz spacecraft docked to the space station at all times in case an emergency forces the crew to return to Earth, Tani was scheduled to come home on the space shuttle Atlantis this month.
That mission was delayed by a faulty fuel sensor, and engineers are trying to figure out how to fix it. Under current plans, Atlantis will be launched no earlier than Jan. 10 -- if the sensor problem can be fixed by then.
"The entire NASA family grieves with Dan on the unexpected loss of his mother yesterday," Michael Coats, director of NASA's Johnson Space Center in Houston, said in a statement. "We will work to provide Dan and his family with any assistance that they need during this difficult time."
NASA has, in the past, contemplated what to do if there was bad news back home while an astronaut was on a long-duration space flight. Several astronauts on previous space station flights have said, before flight, that if something happened they would rather not know, since they would not be able to do anything about it.
One unavoidable exception, though it did not involve a family member, came on Sept. 11, 2001. Astronaut Frank Culbertson and two Russian crew mates were on board the space station when the terrorist attacks took place that morning.
"We're having a bad day down here on Earth," a mission manager in Houston radioed Culbertson. As it happened, the space station was going to pass over New York on its next orbit, and the astronauts were able to take pictures of the smoke plume created by the fire at the World Trade Center.
"Tears don't flow the same in space," he later said. On Sept. 12 he learned that one of the pilots of the airliner that crashed into the Pentagon, Charles Burlingame, had been a classmate of his at the U.S. Naval Academy.
Culbertson transmitted a letter from orbit a few days later. "Other than the emotional impact of our country being attacked and thousands of our citizens and maybe some friends being killed, the most overwhelming feeling being where I am is one of isolation," he wrote.
He stayed in space for three more months until the shuttle Endeavour came to get him in December 2001.
Dan Tani, barring a surprise, will probably also have to wait. He is flying with two crew mates, the American commander Peggy Whitson and Russian Flight Engineer Yuri Malenchenko. Tani and Whitson performed a spacewalk on Tuesday, the fifth of his career.
Astronaut Tani, 46, is married and has two children. He is currently on his second space flight.
Authorities in Lombard said the children on the schoolbus were being offered counseling. And people who knew Rose Tani said she was a remarkable woman.
"She was a source of good humor and inspiration," said Rob Hatfield of the First Church of Lombard, "90 years old with all of her faculties, and a work ethic that would put us all to shame."
ABC News' Gina Sunseri and Grace Huang contributed reporting for this story. Additional reporting from ABC station WLS-TV.