Dr. Cleave had a stroke, said her sister, Bobbie Cleave.

Dr. Cleave’s nearly four decades at NASA — including flights aboard the space shuttle Atlantis in 1985 and 1989 — covered the program’s early successes and its most crushing tragedy. She was in astronaut training in 1981 when the Columbia made the first shuttle launch, and she was part of mission control in 1983 when Challenger astronaut Sally Ride became the first U.S. woman in space.

Then in January 1986, with one space shuttle mission under her belt, Dr. Cleave was in a NASA conference room in Houston watching the broadcast of the Challenger as it exploded 73 seconds into its flight, killing all seven crew members including teacher Christa McAuliffe. Dr. Cleave was part of the post-disaster teams that assessed potential design flaws, such as the O-rings that failed in the Challenger’s right solid rocket booster.

“Before my first flight … I basically told my family, ‘Hey, I might not be coming back,’ because I think a lot of us understood that the system was really getting pushed,” she said in a NASA oral history, “but that’s what we’d signed up to do.”

When the chance came up for another flight, Dr. Cleave had no hesitation. She was selected as a mission specialist for the Atlantis in May 1989 that successfully deployed the Magellan probe to Venus. Magellan went on to map more than 95 percent of the planet’s surface and take measurements of its superheated atmosphere.

During the Atlantis’s orbits, Dr. Cleave often looked down at patches of farmland and other deforested gaps in the vast Amazon rainforest. She made the decision during the mission that she would return to environmental research, the heart of her studies before entering NASA in 1980.

“The amount of deforestation I could see, just in the five years between my two space flights down there, scared the hell out of me,” she told the Orlando Sentinel earlier this year.

Dr. Cleave shifted to NASA’s projects on climate and environment, leading studies that used satellites to track ocean ecology such as levels of phytoplankton and other plant life. The data offered more clues of the effects of a warming planet on the food chain and general ocean health.

In lectures, Dr. Cleave gave audiences a taste of her self-deprecating wit and a heavy dose of blunt urgency.

“I get to study green slime on a global scale,” she told the Association for Women Geoscientists at a meeting at the Snowbird resort in Utah in 1997.

She added that the pace and scale of disruptions in ocean patterns and ecology caused by human-driven climate change were irrefutable. “Boom! You get fish kills — no food and less oxygen,” she said, describing the Pacific warming cycles known as El Nino and its effect on ocean life and monsoon-like storms. “And you guys get to kayak down Main Street in Salt Lake City.”

Dr. Cleave said she saw the space shuttle missions as part of critical science to assess the effects of climate change and other human-caused environmental crises such as those involving pesticides and farm fertilizers spilling into waterways.

“Space-based data collection is the only way we’re going to figure it all out,” she once said.

‘Too short’ for airlines

Mary Louise Cleave was born in Southampton, N.Y., on Feb. 5, 1947, and raised in another Long Island community, Great Neck. Her father was a music teacher, and her mother taught special education. They also ran a summer camp on Lake Champlain for 20 years.

She started taking flying lessons on Long Island at age 14, using money she earned babysitting. She thought about becoming a flight attendant. “But I was too short,” she told the New York Times. “In those days, you had to be 5 foot 4 inches and I’m only 5-2.”

Then she applied to veterinarian school at Cornell University. At the time, women were not accepted. “They used to discriminate based on gender at all the professional schools,” she said.

She received an undergraduate degree in biology from Colorado State University in 1969 and received a master’s degree in microbial ecology in 1975 from Utah State University, where she also completed a doctorate in civil and environmental engineering in 1979.

One day, a fellow student told her to check out a NASA notice at the post office seeking engineers for astronaut training.

“He said, ‘You’re the one engineering student I know who is crazy enough to do this,’” she recounted to Newsday.

“I said, ‘You’re right.’”

On her first space shuttle mission, in late-1985, Dr. Cleave was flight engineer and operated a robotic arm used during spacewalks by other crew members to test construction methods for building a space station.

She also was handed the emergency task of fixing a malfunction in Atlantis’s toilet, she told NASA oral history interviewer Rebecca Wright.

“Sir, I’m used to working on the other end of the pipe,” she recounted her comments to mission control, noting her past work in water and environment.

“It must be how you got that title of ‘first space plumber,’” Wright said.

“Yes,” chuckled Dr. Cleave, “or ‘sanitary fairy.’”

Dr. Cleave retired from NASA in 2007 as associate administrator of NASA’s science mission directorate based in Washington. She later mentored students through the Astronaut Scholarship Foundation, which offers scholarships to students in science, technology, engineering and mathematics.

Survivors include two sisters.

Before Dr. Cleave’s second Atlantis mission, she asked mission specialist Mark C. Lee about where he wanted to sit for the launch. It was his first time on a space shuttle crew, and Dr. Cleave wanted to give him the option: one of the four places on the flight deck or the lone spot assigned to the lower level. Dr. Cleave was initially disappointed when Lee picked the flight deck.

“I thought it was a really lousy deal. I’m going to be all by myself down there and I can’t see a thing,” she said in the NASA interview.

To her surprise, she loved it. “I could hoot. I could holler,” she said, “I could have a marvelous time, and, man, that’s a ride.”