September 27

 A Journey to Two Worlds

2007 — Dawn Begins Its Journey to Vesta and Ceres

11:34 UTC

On September 27, 2007, NASA's Dawn spacecraft lifted off from Cape Canaveral aboard a Delta II Heavy rocket and began an extraordinary journey into the asteroid belt. Its destination was not one world. It was two. Dawn had been designed to investigate Vesta and Ceres, two of the largest bodies in the main asteroid belt between Mars and Jupiter. They had formed in the same general region of the early solar system, yet they evolved into remarkably different worlds. Vesta is dry, rocky, and heavily cratered—a protoplanet, or surviving planetary building block, whose interior differentiated into layers much as the terrestrial planets did. Ceres is larger, richer in water-bearing minerals and volatile materials, and massive enough for gravity to have pulled it into a nearly spherical shape. Today it is classified as a dwarf planet. By studying both with the same spacecraft and instruments, scientists hoped to understand why two bodies formed relatively close to one another could follow such different evolutionary paths. Dawn's journey depended upon a technology that had already proved itself on another remarkable spacecraft: ion propulsion. Instead of burning large quantities of chemical propellant to produce enormous thrust for a short time, Dawn electrically accelerated ions of xenon gas to extremely high speeds. The resulting thrust was extraordinarily gentle. At maximum thrust, Dawn would require about four days to accelerate from zero to 60 miles per hour. But an ion engine can continue operating for weeks or months. The result is cumulative. A tiny push maintained for a very long time can eventually change a spacecraft's velocity by an amount difficult to achieve with conventional chemical propulsion. Dawn carried three ion thrusters and approximately 425 kilograms of xenon propellant. Its enormous solar arrays—each about 8.3 meters long—generated the electrical power necessary to operate them. That propulsion system made Dawn's unprecedented itinerary possible. After launch, Dawn spent years gradually reshaping its orbit around the Sun. It flew past Mars in February 2009, using the planet's gravity to assist its journey toward Vesta. In July 2011, Dawn entered orbit around Vesta. For more than a year, it mapped and studied the protoplanet. Its observations revealed an enormous impact basin near Vesta's south pole, complex geological structures, and evidence confirming connections between Vesta and a class of meteorites found on Earth. Then Dawn did something no spacecraft had ever done. It left orbit around one extraterrestrial body and traveled to another. In September 2012, Dawn departed Vesta. Its ion engines gradually carried it farther through the asteroid belt. On March 6, 2015, Dawn entered orbit around Ceres, becoming the first spacecraft to orbit a dwarf planet. There it discovered a world far more geologically interesting than many scientists had anticipated. The famous bright deposits in Occator Crater proved to contain salts, evidence of briny material that had reached the surface. Dawn also found widespread evidence for water-related minerals and helped reveal Ceres as a chemically and geologically complex world. The spacecraft remained in orbit around Ceres until 2018, when it exhausted the hydrazine needed to control its orientation. NASA deliberately left Dawn in a stable orbit rather than allowing it to crash onto Ceres, partly because of planetary-protection considerations. The spacecraft may remain there for decades.

Why It Matters: Dawn was the first spacecraft to orbit two extraterrestrial destinations and the first to orbit a dwarf planet. Its long-duration ion propulsion system turned what would otherwise have required separate missions into a single voyage of comparative planetary exploration, revealing Vesta and Ceres as two very different survivors from the formation of the solar system.

 

Also on This Day

2003 — SMART-1 Begins Europe's First Mission to the Moon

23:14:46 UTC

On September 27, 2003, the European Space Agency's SMART-1 spacecraft lifted off aboard an Ariane 5 rocket from Europe's spaceport in Kourou, French Guiana. Its name stood for Small Missions for Advanced Research in Technology. Like NASA's Deep Space 1 before it—and Dawn after it—SMART-1 was both an explorer and a technology experiment. Its destination was the Moon, but getting there was part of the experiment. SMART-1 became ESA's first lunar mission and its first mission to use solar-electric propulsion as its primary means of traveling through space. The spacecraft carried only about 82.5 kilograms of xenon propellant for its electric propulsion system. Instead of following the relatively rapid trajectories used by Apollo spacecraft, SMART-1 began in an elongated Earth orbit and used its low-thrust electric engine to gradually enlarge that orbit. The process took months. SMART-1 fired its engine repeatedly, slowly spiraling farther from Earth while also exploiting the gravitational influence of the Moon. It was an extraordinarily fuel-efficient way to travel. The journey took more than a year, but SMART-1 was eventually captured by lunar gravity and entered orbit around the Moon. Once there, the spacecraft conducted scientific observations with a suite of miniaturized instruments. It mapped the lunar surface, investigated its mineral composition, studied the chemical elements present in lunar rocks, and searched for evidence related to water near the lunar poles. SMART-1 also tested technologies in communications, spacecraft autonomy, and compact scientific instrumentation that could be useful on future European deep-space missions. After completing its work, controllers deliberately lowered SMART-1's orbit. On September 3, 2006, the spacecraft struck the Moon in a controlled impact, allowing astronomers on Earth to observe the resulting flash and ejecta.

Why It Matters: SMART-1 was Europe's first lunar mission and demonstrated that solar-electric propulsion could be used for travel beyond Earth orbit. Its combination of technology demonstration and lunar science helped prepare ESA for more ambitious planetary exploration.

2008 — Zhai Zhigang Conducts China's First Spacewalk

Approximately 08:40–08:58 UTC

On September 27, 2008, Zhai Zhigang opened the hatch of China's Shenzhou 7 spacecraft and emerged into space. He became the first Chinese citizen to perform a spacewalk. Shenzhou 7 had launched two days earlier carrying Zhai, Liu Boming, and Jing Haipeng. China had already demonstrated that it could independently launch people into orbit. Yang Liwei had made China's first crewed orbital flight aboard Shenzhou 5 in 2003, and Shenzhou 6 had carried two crew members in 2005. Now China was attempting another essential capability: learning to work outside the spacecraft. Zhai wore the Chinese-developed Feitian spacesuit. The name, meaning roughly “flying in the heavens,” had deep roots in Chinese art and culture. Technically, however, the suit was a highly sophisticated personal spacecraft. It had to maintain pressure around Zhai's body, supply oxygen, remove carbon dioxide and heat, provide communications, and protect him from the vacuum and thermal extremes of space. Liu Boming assisted from the hatch wearing a Russian-derived Orlan spacesuit. At approximately 08:40 UTC, Zhai emerged from the orbital module. Television viewers in China and around the world watched live as he moved outside the spacecraft and waved a Chinese flag. During the excursion, he also retrieved a sample of solid lubricant that had been mounted outside Shenzhou 7 before launch. Scientists could examine the material after its exposure to the space environment. The spacewalk lasted only about 20 minutes. But its importance was much greater than its duration. Extravehicular activity is essential for many complex human-spaceflight operations. The United States and Soviet Union had used spacewalks to conduct experiments, repair spacecraft, service satellites, and ultimately construct large orbital complexes. China was developing the same capability. Years later, Chinese astronauts would perform increasingly complex spacewalks while assembling and maintaining the Tiangong space station.

Why It Matters: Zhai Zhigang's excursion made China the third nation, after the Soviet Union and United States, to independently conduct a spacewalk. It demonstrated spacesuit, airlock, life-support, and operational capabilities essential to China's later development of a permanently crewed space station.

 

The Bigger Picture

September 27 is a remarkable date because all three of its major stories concern something space exploration must eventually learn to do: move beyond the simplest way of getting somewhere.

The earliest planetary spacecraft generally used chemical rockets to receive most of the velocity they needed near the beginning of their journeys. Once released toward their destinations, they largely coasted along carefully calculated trajectories, occasionally making relatively small corrections. Ion propulsion introduced another possibility. A spacecraft could continue accelerating—not dramatically, but patiently. SMART-1 demonstrated how that approach could slowly carry a European spacecraft from Earth orbit to the Moon.

Four years later, Dawn began an even more ambitious application of the idea. Its engines allowed the spacecraft not merely to fly past Vesta and Ceres, but to enter orbit around Vesta, leave that orbit, cross the asteroid belt, and enter orbit around Ceres. That is a profound change in what a single planetary spacecraft can do. Shenzhou 7 tells the human version of a similar story. Reaching orbit is one capability. Living and working beyond the protective shell of a spacecraft is another. Zhai Zhigang's brief excursion outside Shenzhou was therefore not simply a spectacular demonstration. It was one step in China's progression: reach orbit → send multiple crew members → conduct a spacewalk → rendezvous and dock → build a space station.

September 27 consequently reminds us that exploration develops through capabilities. A new propulsion system changes the destinations a spacecraft can reach. A new spacesuit changes where an astronaut can work. A new navigation system changes what a spacecraft can attempt without constant guidance from Earth. And once a capability has been demonstrated, the next mission can build upon it. There is also a particularly satisfying historical connection between SMART-1 and Dawn. On September 27, 2003, Europe launched a spacecraft whose gentle electric engine would slowly carry it toward the Moon. Exactly four years later, on September 27, 2007, Dawn launched with ion propulsion that would eventually carry it into orbit around two separate worlds. The technology had progressed from experiment to extraordinary scientific tool.

At a Glance

2003 — 23:14:46 UTC — ESA's SMART-1 launches from French Guiana, beginning Europe's first lunar mission and a major demonstration of solar-electric propulsion.

2007 — 11:34 UTC — NASA's Dawn spacecraft launches from Cape Canaveral to explore Vesta and Ceres.

2008 — Approximately 08:40 UTC — Zhai Zhigang emerges from Shenzhou 7 and begins China's first spacewalk.

2008 — Approximately 08:58 UTC — Zhai completes the historic excursion and returns inside Shenzhou 7.

September 26

Moving a World 

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.