Folks around NASA don’t much care for this time of year. It was 56 years ago last week—January 27, 1967—that astronauts Gus Grissom, Ed White, and Roger Chaffee lost their lives in a launch pad fire inside their Apollo 1 spacecraft as they were running a dress rehearsal for countdown. It was 37 years ago—on January 28, 1986—that the shuttle Challenger exploded during launch due to a faulty seal that caused one of the solid rocket boosters to ignite the external fuel tank. The pair of solid boosters flew on heedlessly, leaving a gruesome, two fingered fireball in the sky as seven astronauts perished, including New Hampshire school teacher Christa McAuliffe.

Seventeen years later, on January 28, 2003, astronaut Rick Husband, commander of the shuttle Columbia, which was then in orbit, marked the anniversaries. “They made the ultimate sacrifice,” he said, “giving their lives for their country and mankind. Their dedication was an inspiration to each of us.”

America would have to find a similar kind of grim inspiration just four days later, when, on February 1—20 years ago today—Columbia met an end similar to Challenger’s, breaking apart during reentry, when hot plasma tore through the spacecraft from a breach in the leading edge of the left wing. Husband and his crew of six were killed, as the shuttle, on its way to a landing at the Kennedy Space Center in Florida, left a debris trail that stretched from eastern Texas to Louisiana.

“A poisonous rain of broken shuttle pieces fell onto backyards and roadsides and parking lots, through the roof of a dentist’s office, bits of machinery in Nacogdoches, a hand and leg in San Augustine,” wrote TIME’s Nancy Gibbs, as part of the magazine’s cover package that week.

Then-President George W. Bush scheduled a call with the family members of the lost crew for later that day and spent part of his morning studying crew biographies to see which astronauts had spouses and children.

“Tough day, tough day,” was all Bush could mutter to himself as he prepared to place the call.

It was that, indeed. NASA reacted as NASA does in such circumstances, first with a certain minimalism and stoicism. As I reported in a piece that accompanied Nancy’s: “‘A space-shuttle contingency has been declared,’ the voice of Mission Control intoned in the arid argot of the space agency. It was an echo of the understated announcement 17 years ago, when the shuttle Challenger consumed itself in an awful fireball, and the stunned NASA narrator was left to declare, ‘Obviously a major malfunction.’”

But NASA has done other things too when faced with tragedy. It has searched for the cause of the problem and fixed it. In the case of the Apollo 1 fire, that meant redesigning the spacecraft from top to bottom to avoid the kind of errant spark that set off the blaze, as well as replacing the cockpit’s pure-oxygen atmosphere—which burns like gasoline—with an oxygen-nitrogen mix when the spacecraft was at high internal pressure on the ground. (In space, where the internal pressure is much lower due to the vacuum outside, the spacecraft could safely be filled with pure oxygen.) NASA also changed all of the fabric in the spacecraft, including the astronauts’ suits, to a burn-resistant beta cloth. In the case of Challenger, fixing what went wrong meant redesigning the solid fuel boosters and changing the launch rules, to prevent a liftoff in the uncharacteristic Florida freeze that January morning that had left the engine seals brittle.

In the case of Columbia, the job meant first pinpointing the cause of the breach in the shuttle that allowed the hot plasma to infiltrate the spacecraft. It was ultimately traced via liftoff footage to a suitcase-sized piece of hard insulating foam that fell off the external tank and struck the wing in the first moments of the spacecraft’s flight. That meant doing away with the insulating foam at the spot where the tank joins the shuttle—the region from which the deadly fragment fell—and replacing it with heaters. It also meant that on future flights to the International Space Station, shuttle pilots would do a sort of pirouette of their vehicle so that station astronauts could give it a visual inspection. NASA also kept another shuttle at the ready in case a mission had to be launched to rescue a crew aboard a ship that could not reenter safely.

But both Columbia and Challenger led to another kind of change too—a sort of back to the future reversal in spacecraft design. The rocketry revolution that the shuttle program sought to herald was intended to be the end of the old model of putting humans at the top of a booster, firing them into space, and throwing away the launch vehicle after a single use. The new shuttle would be reusable, with the spacecraft itself gliding gracefully back to Earth, the spent solid boosters dropping by parachute into the ocean and being recovered, and only the external tank—little more than a huge shell of metal and plumbing—being discarded.

But there was a lifesaving advantage in the old design that NASA was eschewing with the shuttles: that business of the crew being perched atop the pyrotechnics. Ever since the days of NASA’s first crewed flights, spacecraft-and-booster stacks were designed so that sensors would detect any impending problem in the rocket and either blast the crew-carrying capsule away from it by escape engines or, in the case of the 1960s’ two-man Gemini program, signal the commander to pull a D-shaped ring that would activate parachute-equipped ejection seats.

In the newer shuttle design, the crew was placed directly next to the pyrotechnics. Challenger’s tank explosion happened with the shuttle riding atop it like a human on a horse. Columbia’s wing could never have been damaged if it hadn’t been located below the spot on the tank from which foam fell. Even before the remaining three shuttles were retired in 2011, NASA vowed that in the future it would keep fuel and humans separate, returning to the old model of crew riding at the top of the missile—a model adopted by NASA’s new moon rocket, the Space Launch System; SpaceX’s Falcon 9 and Starship rockets; and Boeing’s crew-carrying Starliner spacecraft. And in the case of SpaceX, most of the throwaway problem has been addressed, with the first stage of the Falcon 9, and both stages of the planned Starship rocket returning for upright landings, allowing them to be used again.

Now, two decades on from the most recent loss, and generations removed from the earlier ones, NASA does not let the memories of the missing men and women—or the sacrifice they made—fade. Each year, on the last Thursday of January, the space agency holds a NASA Day of Remembrance to celebrate their lives—and mourn their loss. We take space travel as a fixed fact of 20th and 21st century life. But crews take a big gamble—on physics, fate, and engineering—when they climb aboard a spacecraft. We all benefit from the fact that they do—and all are made poorer, more sorrowing, by the mercifully few times that gamble does not pay off.

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