2022 — DART Strikes Dimorphos
23:14:24 UTC
On September 26, 2022, a spacecraft weighing roughly 570 kilograms raced toward a small asteroid moon at approximately 6.1 kilometers per second—14,000 miles per hour.
Its destruction was not a failure.
It was the mission.
At 23:14:24 UTC, NASA's Double Asteroid Redirection Test, or DART, slammed into Dimorphos, a small moon orbiting the larger near-Earth asteroid Didymos. The collision marked humanity's first full-scale experiment designed to determine whether deliberately striking an asteroid could measurably change its motion. Neither Didymos nor Dimorphos posed a threat to Earth. That was precisely why the system was useful. Dimorphos, approximately 160 meters (525 feet) across, orbited Didymos, which is about 780 meters (2,560 feet) across. Because astronomers could measure the smaller body's orbit around its companion, they could determine whether DART's impact changed that orbit without needing to alter the asteroid system's trajectory around the Sun enough to create a hazard. DART had launched on November 24, 2021. For most of its journey, controllers on Earth guided and monitored the spacecraft. But during the final approach, the mission faced an unavoidable problem: radio signals could not travel between Earth and the spacecraft quickly enough for humans to steer DART into such a small moving target in real time. The spacecraft therefore had to finish the job itself. Its autonomous navigation system, SMART Nav, used images from DART's DRACO camera to distinguish Didymos from Dimorphos and guide the spacecraft toward the smaller body. During the final minutes, images arriving on Earth showed Dimorphos growing from a tiny point into a recognizable world. Its surface was unexpectedly covered with rocks and boulders. Then the images stopped. DART had struck its target. But the impact itself was only the beginning of the experiment. Astronomers around the world used ground-based and space-based telescopes to observe the aftermath and measure Dimorphos's orbit. Before impact, the moonlet took approximately 11 hours 55 minutes to orbit Didymos. NASA initially reported that DART shortened that period by about 32 minutes, vastly exceeding the mission's minimum-success criterion of 73 seconds. Continued measurements subsequently refined the change to roughly 33 minutes. The collision also excavated enormous amounts of material from Dimorphos. That ejecta carried momentum of its own, enhancing the effect of the impact—rather like the recoil produced when material is thrown in the opposite direction. A small Italian Space Agency spacecraft named LICIACube, which DART had released before impact, flew past the asteroid system minutes later and photographed the expanding debris. Telescopes including Hubble and James Webb also observed the event and its aftermath. DART's experiment was not designed to destroy Dimorphos or knock it dramatically out of its solar orbit. Planetary defense generally does not require such an extreme intervention. If a hazardous asteroid were discovered sufficiently far in advance, even a very small change in its velocity could accumulate over years into a large change in position. The goal would be to make the asteroid arrive at the point where it would otherwise intersect Earth's orbit a little earlier or a little later—when Earth is somewhere else.
Why It Matters: DART was the first mission to demonstrate a technique for changing the motion of a celestial body through kinetic impact. Humanity had spent centuries discovering asteroids and decades sending spacecraft to study them. On September 26, 2022, we demonstrated that—with sufficient warning—we may also be capable of changing an asteroid's trajectory to protect Earth.
Also on This Day
1960 — Pioneer 5 Becomes the Most Distant Human-Made Object in Communication with Earth
Record date; precise time not established
On September 26, 1960, NASA's Pioneer 5 reached a communications milestone as it traveled through interplanetary space. Launched on March 11, Pioneer 5 was designed primarily to investigate the environment between Earth and Venus. The small spacecraft carried instruments to measure magnetic fields, cosmic radiation, and solar particles. Unlike satellites confined to Earth orbit, Pioneer 5 entered a heliocentric orbit—an orbit around the Sun. As the spacecraft receded from Earth, engineers faced a challenge fundamental to deep-space exploration: could radio communication be maintained across increasingly enormous distances? On September 26, Pioneer 5 transmitted data from approximately 36.2 million kilometers—22.5 million miles—from Earth, establishing what was then a record for communications with a spacecraft. The accomplishment may appear modest beside the billions of kilometers across which later missions such as Voyager would communicate. But those later achievements depended upon the development of deep-space radio systems, tracking networks, sensitive antennas, and techniques first tested during missions like Pioneer. Pioneer 5 also returned valuable scientific measurements of the interplanetary magnetic field and solar energetic particles, helping scientists understand that the region between planets was not simply empty space.
Why It Matters: Pioneer 5 helped demonstrate that spacecraft could remain scientifically useful and communicate with Earth far beyond the immediate neighborhood of our planet. Its work contributed to the communications and tracking techniques upon which later planetary exploration depended.
1983 — Soyuz T-10-1 Crew Escapes a Launch-Pad Explosion
19:37:49 UTC
On September 26, 1983, cosmonauts Vladimir Titov and Gennady Strekalov sat atop a fully fueled Soyuz launch vehicle at Baikonur, preparing for a mission to the Salyut 7 space station. Then the rocket caught fire. Approximately 90 seconds before the planned launch, a valve problem caused fuel to spill near the base of the vehicle. Fire rapidly spread around the rocket. The crew was now sitting atop hundreds of tons of propellant in a launch vehicle that could explode at any moment. Ground controllers attempted to activate the spacecraft's launch escape system. The normal command path had been disrupted by the fire, requiring controllers at separate locations to send commands nearly simultaneously before the system would respond. It activated. Explosive bolts separated the Soyuz descent and orbital modules from the rest of the spacecraft, and powerful solid-fueled escape rockets pulled the crew capsule away from the burning booster. Only seconds later, the launch vehicle exploded. The escape system accelerated the capsule rapidly upward, subjecting Titov and Strekalov to forces estimated around 14 to 17 g for several seconds. The capsule climbed roughly a kilometer before separating from the escape tower and descending by parachute. Approximately five minutes after the emergency began, the cosmonauts landed a few kilometers from the launch pad. Both survived. The mission never received the normal Soyuz flight designation because it never reached orbit. It is commonly identified as Soyuz T-10-1, and in some Soviet records as Soyuz T-10A.
Why It Matters: The Soyuz T-10-1 accident provided a dramatic real-world demonstration of the value of a launch escape system. The rocket was destroyed, but its crew survived because engineers had designed for a catastrophe they hoped would never occur. Human spaceflight safety depends not only on preventing failures but also on providing a way to survive them.
1996 — Shannon Lucid Returns After a Record 188 Days in Space
12:13:20 UTC
On September 26, 1996, Space Shuttle Atlantis touched down at Kennedy Space Center, bringing astronaut Shannon Lucid home after an extraordinary 188 days in space. Lucid had launched aboard Atlantis on STS-76 on March 22 and transferred to the Russian space station Mir. She had originally expected to remain aboard for approximately four months. But delays to the Shuttle mission scheduled to retrieve her—including hurricane-related launch-pad rollbacks—extended her stay considerably. Lucid adapted. For more than six months, she lived and worked aboard Mir alongside Russian cosmonauts. She conducted life-science, materials, biotechnology, and other experiments while becoming part of the station's daily operations. Her mission was scientifically valuable, but it also represented an important human experiment in international cooperation. Only a few years had passed since the end of the Cold War. Now an American astronaut was living for months aboard a Russian space station, working within a different language, culture, engineering system, and operational environment. Atlantis arrived at Mir on STS-79 in September carrying John Blaha, who replaced Lucid as NASA's resident astronaut. After the crew exchange, Lucid boarded Atlantis for the journey home. At 12:13:20 UTC on September 26, the Shuttle landed at Kennedy Space Center. Her 188 days, 4 hours in space established a new American single-flight endurance record and a world endurance record for a woman. The American record remained hers until 2002; her women's record stood until 2007. President Bill Clinton later awarded Lucid the Congressional Space Medal of Honor.
Why It Matters: Shannon Lucid demonstrated that American astronauts could live and work productively for months aboard a foreign space station. Her mission provided valuable experience in long-duration spaceflight and international operations that helped prepare NASA and Russia for the International Space Station.
2019 — Soyuz MS-15 Completes the Final Crewed Launch from Gagarin's Start
13:57:43 UTC
On September 25 UTC—rather than September 26—2019, Soyuz MS-15 launched from Baikonur's historic Site No. 1, known as Gagarin's Start. Because some anniversary lists associate the mission with September 26 through docking or local-calendar reporting, it can appear under this date. Under our project's UTC convention, however, its launch does not belong in the September 26 chronology. Its significance remains worth noting for editorial purposes: the launch carried Jessica Meir, Oleg Skripochka, and Hazzaa AlMansoori, the first Emirati in space, and became the final crewed launch from the same launch complex used by Yuri Gagarin in 1961. We should therefore reserve that story for September 25 if we choose to include it when assembling or revising that entry.
The Bigger Picture
September 26 tells an unusually coherent story about risk. Pioneer 5 confronted the risks of distance. The farther a spacecraft traveled from Earth, the weaker its radio signal became. Engineers had to learn how to maintain contact across interplanetary space before more ambitious planetary missions could succeed. Soyuz T-10-1 confronted the immediate physical danger of human spaceflight. Engineers could not guarantee that a rocket would never explode, so they built another system whose sole purpose was to save the crew when everything else failed. Shannon Lucid confronted a different kind of challenge: duration. Living in space for more than six months demanded physical adaptation, psychological resilience, dependable life-support systems, and cooperation between people and organizations from different nations. And DART confronted a risk on an entirely different scale. Asteroid impacts are natural events. Earth's surface—and the cratered surfaces of the Moon and other worlds—preserve abundant evidence that such collisions are part of the history of the solar system. For almost all of human existence, nothing could have been done about that danger. Astronomy changed the situation. Telescopes allow us to discover near-Earth objects. Mathematics allows us to calculate their future paths. Spacecraft allow us to reach them. DART added another possibility: perhaps we can move one. That is a remarkable progression. We learned to communicate across interplanetary distances. We learned to protect people when rockets fail. We learned to live in space for months. And eventually we began testing whether knowledge of the heavens could be used to protect the planet from which all of those journeys began. September 26 therefore represents one of the deepest purposes of astronomy. For thousands of years, people watched the sky partly because the heavens affected life on Earth. DART brought that ancient relationship into the Space Age. We study the sky not only to understand what is out there, but sometimes to protect what is here.
At a Glance
1960 — Precise time not established — Pioneer 5 communicates with Earth from approximately 36.2 million kilometers away, establishing a deep-space communications record.
1983 — 19:37:49 UTC — The Soyuz T-10-1 launch escape system pulls Vladimir Titov and Gennady Strekalov away from their burning rocket seconds before it explodes.
1996 — 12:13:20 UTC — Space Shuttle Atlantis lands at Kennedy Space Center, returning Shannon Lucid after 188 days in space.
2022 — 23:14:24 UTC — NASA's DART spacecraft deliberately strikes Dimorphos at approximately 6.1 kilometers per second, conducting the first full-scale test of asteroid deflection by kinetic impact.
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