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The Two‑Centimeter Chip Ran Out of Hydrazine and Left Them Waiting · Space Exploration Stories

• 0:03
  Speaker 1: A two-centimeter chip sits above an ion thruster, circling a
• 0:07
  Speaker 1: dwarf planet 400 million miles from Earth. It holds 360,000 names.
• 0:14
  Speaker 1: No one put them there by accident, and no one
• 0:17
  Speaker 1: will ever bring them back. The spacecraft carrying those names
• 0:21
  Speaker 1: was canceled. Twice. It survived four mechanical failures in deep space,
• 0:26
  Speaker 1: improvised its way through each one, and still broke records
• 0:30
  Speaker 1: that had stood for decades. The question is not whether
• 0:33
  Speaker 1: it made it, it did. The question is how anything
• 0:36
  Speaker 1: this fragile lasted this long, and what it cost to
• 0:39
  Speaker 1: keep it alive. On November 1st, 2018, NASA's Jet Propulsion
• 0:45
  Speaker 1: Laboratory received the last signal from Dawn. Hydrazine, the chemical
• 0:50
  Speaker 1: propellant that controlled the probe's orientation, was gone. The mission
• 0:55
  Speaker 1: was over. Dawn had been flying for 11 years, one month,
• 0:59
  Speaker 1: and five days. It had orbited two separate worlds, neither
• 1:04
  Speaker 1: of which any spacecraft had ever visited. It had run
• 1:07
  Speaker 1: its ion engine for 5.9 years, more than half its
• 1:11
  Speaker 1: total mission time, covering a velocity change of 25,700 miles
• 1:17
  Speaker 1: per hour. That figure was 2.7 times the previous solar
• 1:21
  Speaker 1: electric record. It would spend at least the next 20
• 1:24
  Speaker 1: years circling Ceres in a stable orbit, silent, alone, still
• 1:29
  Speaker 1: carrying those names. The record is extraordinary. The journey to
• 1:33
  Speaker 1: get there is harder to believe. The idea behind Dawn
• 1:37
  Speaker 1: did not begin with a spacecraft. It began with a tube.
• 1:42
  Speaker 1: In 1959, an engineer named Harold R. Kaufman, working at
• 1:45
  Speaker 1: NASA's Glenn Research Center in Ohio, built the first American
• 1:49
  Speaker 1: ion thruster. The device looked nothing like a rocket engine.
• 1:53
  Speaker 1: It was compact, quiet, and almost absurdly weak by the
• 1:57
  Speaker 1: standards of chemical propulsion. Its operating principle was simple. Strip
• 2:02
  Speaker 1: electrons from atoms of a propellant gas, then accelerate those
• 2:06
  Speaker 1: ions through an electric field and fire them out the back. Action, reaction,
• 2:12
  Speaker 1: motion through the void. The thrust it produced was roughly
• 2:15
  Speaker 1: 90 millinewtons. For context, that is about the weight of
• 2:19
  Speaker 1: a single sheet of paper pressing against your palm. No explosion,
• 2:23
  Speaker 1: no roar, just a pale blue glow and an almost
• 2:27
  Speaker 1: imperceptible push. What Kaufman understood, and what would take decades
• 2:32
  Speaker 1: to prove, was that an ion thruster does not need
• 2:36
  Speaker 1: to be powerful. It needs to be patient. In space,
• 2:39
  Speaker 1: with no friction and no drag, even 90 millinotons applied
• 2:43
  Speaker 1: continuously becomes something astonishing. Dawn's thrusters, derived from that original design,
• 2:49
  Speaker 1: could accelerate the spacecraft from zero to 60 miles per hour.
• 2:53
  Speaker 1: The catch, it took four days to do it. Four
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  Speaker 1: full days of continuous thrust to reach a speed a
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  Speaker 1: car achieves in under 10 seconds. That patience became a superpower.
• 3:05
  Speaker 1: The first real-world tests came slowly. In 1964, CERT-1 fired
• 3:11
  Speaker 1: an ion engine in actual space for the first time.
• 3:14
  Speaker 1: In 1970, CERT-2 ran two thrusters for months at a time,
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  Speaker 1: proving they could endure. Then, in 1998, NASA flew Deep
• 3:21
  Speaker 1: Space One, a mission explicitly designed to validate the NSTA
• 3:28
  Speaker 1: ion thruster in operational conditions. It worked. The technology was ready.
• 3:35
  Speaker 1: Dawn's scientific target made the ion engine essential. The asteroid
• 3:38
  Speaker 1: belt does not hold still. Vesta and Sirius orbit the
• 3:43
  Speaker 1: sun at slightly different rates, which means their relative positions
• 3:47
  Speaker 1: shift constantly. A conventional chemical rocket could reach one of them.
• 3:51
  Speaker 1: But breaking into orbit and then escaping to travel onward
• 3:54
  Speaker 1: to the second was simply not feasible with chemical propellant.
• 3:59
  Speaker 1: The mass of fuel required would have been prohibitive. The
• 4:03
  Speaker 1: ion engine changed the arithmetic. Slow thrust, applied over years,
• 4:07
  Speaker 1: could match velocities precisely, spiral into orbit gently, and then
• 4:12
  Speaker 1: build again for the transit to the next target. The
• 4:15
  Speaker 1: mission's entire logic depended on it. Christopher T. Russell, the
• 4:19
  Speaker 1: principal investigator who would champion Dawn through every institutional crisis,
• 4:24
  Speaker 1: understood this. The science case was strong. Vesta and Ceres
• 4:29
  Speaker 1: were not random rocks. They were survivors from the solar
• 4:32
  Speaker 1: system's formation, frozen in time, geologically distinct from each other,
• 4:37
  Speaker 1: despite sitting in the same belt. Comparing them directly with
• 4:40
  Speaker 1: the same instruments from the same spacecraft would answer questions
• 4:44
  Speaker 1: about why some early planetary bodies developed metal cores and
• 4:48
  Speaker 1: others did not. In January 2001, Dawn was named a
• 4:52
  Speaker 1: semi-finalist in NASA's Discovery Program. By December of that year,
• 4:56
  Speaker 1: it was selected alongside the Kepler Space Telescope. The clock
• 5:00
  Speaker 1: had started. Then, in December 2003, NASA canceled it. The
• 5:06
  Speaker 1: reasons were institutional and budgetary. No fraud, no misconduct, no
• 5:12
  Speaker 1: single named decision maker. On record, the mission was simply cut.
• 5:16
  Speaker 1: Russell and the team pushed back. In February 2004, Dawn
• 5:22
  Speaker 1: was reinstated. In October 2005, a stand-down order halted progress again.
• 5:29
  Speaker 1: In January 2006, it was postponed. On March 2nd, 2006,
• 5:34
  Speaker 1: it was cancelled the second time. 25 days later, Orbital
• 5:39
  Speaker 1: Sciences Corporation, the contracted manufacturer, made an offer that changed
• 5:44
  Speaker 1: the outcome. They would build the spacecraft at cost, no
• 5:48
  Speaker 1: profit margin. The mission would continue if the agency allowed it.
• 5:52
  Speaker 1: On March 27th, 2006, Dawn was reinstated for the final time.
• 5:57
  Speaker 1: The budget at selection had been $ 373 million. By launch,
• 6:02
  Speaker 1: it would reach $ 446 million. The money was real. So
• 6:07
  Speaker 1: was the gamble. Four months later, in August 2006, the
• 6:11
  Speaker 1: International Astronomical Union reclassified Pluto as a dwarf planet. Ceres,
• 6:17
  Speaker 1: one of Dawn's two targets, was simultaneously elevated to the
• 6:20
  Speaker 1: same category. The spacecraft had been cancelled and resurrected twice
• 6:24
  Speaker 1: in pursuit of a world whose classification was being rewritten
• 6:28
  Speaker 1: while the mission fought to survive. On May 17th, 2007,
• 6:33
  Speaker 1: technicians installed a microchip above Dawn's forward ion thruster. It
• 6:38
  Speaker 1: carried 360,000 names, people who had submitted them through a
• 6:43
  Speaker 1: public outreach program. The chip was the size of a thumbnail,
• 6:47
  Speaker 1: It would travel to Mars, to Vesta, to Ceres. It
• 6:51
  Speaker 1: would outlast everyone who had ever touched this spacecraft. Launch
• 6:55
  Speaker 1: was scheduled for June 2007. It did not happen in June.
• 7:00
  Speaker 1: The first delay came from a crane. A piece of
• 7:03
  Speaker 1: ground support equipment malfunctioned during preparation at Cape Canaveral's Space
• 7:07
  Speaker 1: Launch Complex 17B. Engineers stopped. They assessed. They rescheduled. Then
• 7:14
  Speaker 1: a solar array panel sustained damage during handling. The array
• 7:18
  Speaker 1: was Dawn's power source, 10 kilowatts at one astronomical unit,
• 7:23
  Speaker 1: stretched across 19 and a half meters of spacecraft. Without it,
• 7:27
  Speaker 1: the ion thrusters had nothing to run on. Repair took time.
• 7:32
  Speaker 1: Weather came next. Range tracking equipment failed after that. A
• 7:36
  Speaker 1: mandatory orbital avoidance window for the International Space Station pushed
• 7:40
  Speaker 1: the date again. Then, on the morning of a final attempt,
• 7:44
  Speaker 1: a ship entered the restricted maritime exclusion zone beneath the
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  Speaker 1: launch corridor. Six delays, ten days. On September 27, 2007,
• 7:55
  Speaker 1: at 7.34 in the morning Eastern Time, a Delta 792H
• 8:01
  Speaker 1: rocket lifted Dawn off the pad. The spacecraft that had
• 8:04
  Speaker 1: been cancelled twice, built at cost by a manufacturer willing
• 8:08
  Speaker 1: to forego profit and delayed six times in ten days,
• 8:12
  Speaker 1: was finally airborne. It carried a thumbnail-sized microchip with 360,000
• 8:18
  Speaker 1: names aboard. What it did not carry was speed. Not yet.
• 8:23
  Speaker 1: Not in any way a rocket normally measures speed. The
• 8:27
  Speaker 1: ion thrusters Dawn relied on were derived from technology. Harold
• 8:32
  Speaker 1: Kaufman had built in 1959 at NASA Glenn Research Center.
• 8:36
  Speaker 1: They worked by ionizing xenon gas and accelerating the ions electrically,
• 8:41
  Speaker 1: producing a faint blue exhaust plume. The thrust was 90
• 8:45
  Speaker 1: millinewtons per engine, roughly the weight of a piece of
• 8:48
  Speaker 1: paper resting on a surface. A chemical rocket burns hard
• 8:51
  Speaker 1: and fast. Dawn's engines whispered. At full throttle, Dawn could
• 8:56
  Speaker 1: accelerate from zero to 60 miles per hour in four days.
• 9:00
  Speaker 1: That number sounds like a joke. It was not. Applied
• 9:04
  Speaker 1: continuously across months and years, that whisper accumulated into something
• 9:08
  Speaker 1: no chemical rocket could match, without carrying an impossible fuel load.
• 9:14
  Speaker 1: By the time the mission ended, the ion engines would
• 9:17
  Speaker 1: have run for 5.9 years, 54% of total mission time,
• 9:23
  Speaker 1: and pushed the spacecraft to a velocity change of 25,700
• 9:28
  Speaker 1: miles per hour. That figure was 2.7 times the previous
• 9:32
  Speaker 1: solar electric propulsion record. But first, Dawn needed to get
• 9:36
  Speaker 1: to the asteroid belt, and the most efficient path ran
• 9:39
  Speaker 1: through Mars. On February 17th, 2009, Dawn passed Mars at
• 9:46
  Speaker 1: 549 kilometers altitude. The flyby was calculated to steal a
• 9:50
  Speaker 1: fraction of Mars' orbital momentum, a gravitational slingshot that would
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  Speaker 1: bend Dawn's trajectory toward the belt without burning extra fuel.
• 10:00
  Speaker 1: The maneuver worked. The spacecraft did not. During the approach,
• 10:04
  Speaker 1: a software error placed Dawn into safe mode. Instruments went offline.
• 10:09
  Speaker 1: Commands stopped executing. The team on the ground had a
• 10:12
  Speaker 1: spacecraft drifting past the one planet in the solar system
• 10:16
  Speaker 1: that could bend its course toward Vesta, and they could
• 10:18
  Speaker 1: not talk to it properly. Safe mode lasted two days.
• 10:22
  Speaker 1: Engineers restored full function on February 19th. The gravity assist
• 10:26
  Speaker 1: had already occurred. The geometry of orbital mechanics does not
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  Speaker 1: pause for software faults, and the trajectory correction had been captured.
• 10:35
  Speaker 1: But the image remained. A spacecraft going silent at the
• 10:38
  Speaker 1: exact moment it most needed to listen. Dawn's effect on
• 10:42
  Speaker 1: Mars during that pass was also recorded. The gravitational exchange
• 10:47
  Speaker 1: slightly altered Mars' orbital velocity. The calculated figure was 2.5
• 10:51
  Speaker 1: centimeters per 180 million years. The universe had noticed Dawn.
• 10:57
  Speaker 1: In its own timescale, it had responded. Dawn reached Vesta
• 11:01
  Speaker 1: on July 16th, 2011. It became the first spacecraft ever
• 11:06
  Speaker 1: to enter orbit around a body in the asteroid belt.
• 11:10
  Speaker 1: The images that came back were not what the models
• 11:13
  Speaker 1: had cleanly predicted. Vesta had a metallic core, 220 kilometers across.
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  Speaker 1: the remnant of a body, large enough to have differentiated
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  Speaker 1: separating iron from rock, the way a planet does. It
• 11:26
  Speaker 1: had gullies. Gullies suggest liquid, and liquid on an airless
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  Speaker 1: rock in the asteroid belt required explanation. Dark deposits marked
• 11:34
  Speaker 1: ancient impact sites, the chemistry pointing to carbonaceous material delivered
• 11:39
  Speaker 1: from outside. Vesta was not a simple rock. It was
• 11:43
  Speaker 1: the last surviving large planetesimal, a relic of solar system
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  Speaker 1: formation that had never been incorporated into a planet. Everything
• 11:52
  Speaker 1: larger had been swept up or destroyed. Vesta had persisted.
• 11:56
  Speaker 1: Then the reaction wheels began to fail. Dawn used reaction wheels,
• 12:01
  Speaker 1: spinning gyroscopic masses, to orient itself without burning thruster fuel.
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  Speaker 1: It carried four. In August and September of 2012, one
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  Speaker 1: wheel developed problems serious enough to delay Vesta departure. Engineers
• 12:15
  Speaker 1: managed the fault carefully and released the spacecraft. In transit
• 12:20
  Speaker 1: towards Ceres, two more wheels degraded. With three of four
• 12:24
  Speaker 1: reaction wheels compromised, the spacecraft needed a new way to
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  Speaker 1: hold its orientation. The team built one. They coupled the
• 12:31
  Speaker 1: remaining functional wheel with the ion thrusters themselves, using the
• 12:35
  Speaker 1: engine exhaust that normally pushed Dawn forward to also stabilize
• 12:39
  Speaker 1: its attitude. The spacecraft's propulsion system became its stabilization system simultaneously,
• 12:45
  Speaker 1: It was not the design. It was the only option. Then,
• 12:49
  Speaker 1: on September 11th, 2014, the ion thruster stopped. No warning.
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  Speaker 1: No gradual decline. The engine simply ceased firing. Dawn entered
• 13:00
  Speaker 1: safe mode again. The same silence that had fallen over
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  Speaker 1: Mars five years earlier, now 360 million kilometers from Earth,
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  Speaker 1: with Ceres still ahead, and no chemical backup engine to
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  Speaker 1: reach it. The signal delay between Earth and Dawn was significant.
• 13:18
  Speaker 1: Commands took minutes to arrive. Responses took minutes to return.
• 13:22
  Speaker 1: Every diagnostic exchange consumed time the mission could not easily spare.
• 13:27
  Speaker 1: Engineers swapped to the backup engine and backup controller. They
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  Speaker 1: ran diagnostics across four days. The leading assessment was a
• 13:35
  Speaker 1: possible high energy particle strike, a single cosmic ray or
• 13:39
  Speaker 1: energetic proton hitting the electronics at the wrong moment. The
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  Speaker 1: cause was never confirmed. On September 15th, 2014, Dawn resumed thrust.
• 13:50
  Speaker 1: The probe that had been cancelled twice, delayed six times,
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  Speaker 1: gone silent at Mars, lost reaction wheels in transit, and
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  Speaker 1: now survived an unexplained engine stop in deep space, pointed
• 14:02
  Speaker 1: itself at Ceres, and kept going. 360,000 names, still aboard.
• 14:09
  Speaker 1: Still moving, on March 6th, 2015, Dawn slipped into orbit
• 14:15
  Speaker 1: around Ceres. The approach had taken months of careful thrust
• 14:19
  Speaker 1: the ion engine pushing at 90 millinotons. Less force than
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  Speaker 1: the weight of a few sheets of paper, but doing
• 14:26
  Speaker 1: it continuously, hour after hour, week after week. The spacecraft
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  Speaker 1: that had lost three reaction wheels survived an unexplained engine
• 14:35
  Speaker 1: shutdown in deep space. and been canceled twice before leaving
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  Speaker 1: the ground, was now the first human-made object ever to
• 14:42
  Speaker 1: orbit a dwarf planet. No mission before it had done this.
• 14:46
  Speaker 1: Not one. The team began pulling Dawn inward through a
• 14:50
  Speaker 1: sequence of orbital shells, from 13,500 kilometers down to 4,430,
• 14:53
  Speaker 1: then to 1,480, then, finally, to 375 kilometers above the surface,
• 15:05
  Speaker 1: close enough for the gamma ray and neutron detector built
• 15:08
  Speaker 1: by Los Alamos to read the elemental chemistry of the
• 15:12
  Speaker 1: ground itself. The cameras capable of resolving detail down to
• 15:15
  Speaker 1: 66 meters per pixel at that distance began returning images
• 15:19
  Speaker 1: of a world no human eye had ever seen clearly.
• 15:23
  Speaker 1: What they found on Ceres was not what anyone expected.
• 15:27
  Speaker 1: There were bright spots, extraordinarily bright. They sat inside a
• 15:31
  Speaker 1: crater called a cater, white against the gray terrain, blazing
• 15:35
  Speaker 1: in images that looked almost like a processing error. They
• 15:38
  Speaker 1: were not. They were deposits of sodium carbonate, salt left
• 15:42
  Speaker 1: by briny water that had migrated upward through the crust
• 15:46
  Speaker 1: and evaporated. Ceres was not a dead rock. It was
• 15:50
  Speaker 1: geologically active, at least in its recent past, and possibly
• 15:54
  Speaker 1: in its present. That discovery alone would have justified the mission.
• 15:59
  Speaker 1: But Dawn was also measuring something harder to see. Beneath
• 16:03
  Speaker 1: the surface, Neutron flux data pointed to substantial water ice
• 16:08
  Speaker 1: mixed into the upper crust. Ceres, the largest body in
• 16:11
  Speaker 1: the asteroid belt, the object astronomers had debated classifying for
• 16:16
  Speaker 1: two centuries, was wet. It held more fresh water than
• 16:20
  Speaker 1: all of Earth's surface combined. The spacecraft that had been
• 16:24
  Speaker 1: built at cost, launched on the seventh attempt and repaired
• 16:27
  Speaker 1: in deep space with improvised engineering, was now rewriting the
• 16:31
  Speaker 1: map of where water exists in the solar system. Christopher
• 16:35
  Speaker 1: Russell's team extended the mission. There was still hydrazine left
• 16:39
  Speaker 1: in the attitude control tanks. Not much, but enough to
• 16:42
  Speaker 1: keep the wheels and thrusters oriented, to keep the antenna pointed,
• 16:46
  Speaker 1: to keep the data flowing. In 2017, NASA approved continuation
• 16:52
  Speaker 1: until the propellant ran out. A proposal arrived in 2016
• 16:56
  Speaker 1: to redirect Dawn toward asteroid 145 Adona. After finishing, At Ceres,
• 17:04
  Speaker 1: the team declined. There was not enough hydrazine to reach
• 17:07
  Speaker 1: it and still maintain control. Dawn would stay. It would
• 17:11
  Speaker 1: keep mapping, keep measuring, keep transmitting until the lost drop
• 17:15
  Speaker 1: of propellant was gone. The final tally of engine runtime
• 17:19
  Speaker 1: reached 5.9 years of continuous ion thrust by September 7th, 2018.
• 17:25
  Speaker 1: That was 54% of the entire mission elapsed time. The
• 17:30
  Speaker 1: Delta V, the total change in velocity, accumulated across the
• 17:33
  Speaker 1: mission reached 25,700 miles per hour. That was 2.7 times
• 17:40
  Speaker 1: the previous solar electric propulsion record. Harold Kaufman had fired
• 17:45
  Speaker 1: his first ion thruster in a vacuum chamber at NASA
• 17:48
  Speaker 1: Glenn in 1959, six decades later. His principal had carried
• 17:53
  Speaker 1: a spacecraft across 1.7 billion miles of space and broken
• 17:58
  Speaker 1: every record the technology had ever set then. On November 1st, 2018,
• 18:03
  Speaker 1: the hydrazine was gone. Dawn could no longer point its
• 18:08
  Speaker 1: antenna toward Earth. It could no longer adjust its orbit.
• 18:11
  Speaker 1: It could no longer do anything but drift in the precise,
• 18:15
  Speaker 1: gravitationally locked drift of a spacecraft in stable orbit. NASA confirmed.
• 18:21
  Speaker 1: The orbit would persist for a minimum of 20 years,
• 18:25
  Speaker 1: possibly much longer. The probe was not falling. It was
• 18:29
  Speaker 1: not escaping. It was staying. 360,000 names still aboard, still circling.
• 18:36
  Speaker 1: The records were read into the official account without ceremony.
• 18:40
  Speaker 1: First spacecraft to orbit two separate extraterrestrial bodies. First to
• 18:45
  Speaker 1: visit the asteroid Vesta. First to orbit a body in
• 18:48
  Speaker 1: the asteroid belt. First to orbit a dwarf planet. Each
• 18:53
  Speaker 1: one a category that had never existed in a mission
• 18:56
  Speaker 1: log before Dawn filled it. But the record that carries
• 19:00
  Speaker 1: the most weight is quieter than any of those. On
• 19:03
  Speaker 1: May 17th, 2007, a two-centimeter microchip was installed above Dawn's
• 19:09
  Speaker 1: forward ion thruster. It held 360,000 names, people who had
• 19:14
  Speaker 1: submitted them through a public outreach program who had asked,
• 19:18
  Speaker 1: in whatever small way a name can ask, to go somewhere.
• 19:22
  Speaker 1: That chip traveled to Mars. It traveled to Vesta, to
• 19:26
  Speaker 1: the deepest orbit at 210 kilometers above a world with
• 19:30
  Speaker 1: a metallic core 220 kilometers wide. It traveled to Ceres,
• 19:35
  Speaker 1: down to 375 kilometers above the salt-bright floor of a
• 19:40
  Speaker 1: Cater crater. It is there now. It will not be retrieved.
• 19:45
  Speaker 1: No mission is planned. No retrieval is possible in any
• 19:49
  Speaker 1: operational sense the names are not coming back every cancellation
• 19:53
  Speaker 1: memo every stand down every six launch delays in 10
• 19:57
  Speaker 1: days every reaction wheel that seized every engine that went
• 20:01
  Speaker 1: silent in deep space was survived and the consequence of
• 20:05
  Speaker 1: surviving is that those names are now a permanent feature
• 20:08
  Speaker 1: of the Serrarian system, not as loss. The mission succeeded
• 20:12
  Speaker 1: beyond what the people who fought to save it had
• 20:15
  Speaker 1: reason to expect. But as permanence, they are in orbit
• 20:20
  Speaker 1: the way a moon is in orbit, by physics, for decades,
• 20:24
  Speaker 1: possibly longer. Dawn entered the planning process as a question
• 20:28
  Speaker 1: about how the early solar system formed. Why Vesta and Ceres,
• 20:34
  Speaker 1: neighbors in the belt, look so different from each other.
• 20:37
  Speaker 1: Vesta is dry, differentiated, rocky, its surface scarred by a
• 20:42
  Speaker 1: collision that nearly destroyed it. Ceres is wet, chemically complex.
• 20:47
  Speaker 1: Its bright spots evidence of a process still not fully understood.
• 20:51
  Speaker 1: The question the mission posed was answered. These two bodies
• 20:55
  Speaker 1: evolved along radically different paths, shaped by where and when
• 20:59
  Speaker 1: they formed in the disk of material that became the planets.
• 21:03
  Speaker 1: The solar system's early history is written in the difference
• 21:07
  Speaker 1: between them. And Don read it. The ion engine that
• 21:10
  Speaker 1: made all of it possible. The engine that could only
• 21:13
  Speaker 1: push with the force of a piece of paper that
• 21:15
  Speaker 1: needed four days to accelerate from zero to 60 miles
• 21:18
  Speaker 1: per hour. That ran for 5.9 years without a chemical
• 21:22
  Speaker 1: rocket to fall back on validated a technology that NASA
• 21:25
  Speaker 1: had tested in a vacuum chamber in 1959 and waited
• 21:29
  Speaker 1: four decades to trust at scale. Every future mission that
• 21:33
  Speaker 1: uses solar electric propulsion carries something of that proof forward.
• 21:37
  Speaker 1: The spacecraft is silent now. It does not transmit. It
• 21:41
  Speaker 1: does not receive. It orbits in the same darkness it
• 21:45
  Speaker 1: has always moved through above a world that turns slowly
• 21:48
  Speaker 1: beneath it, bright salt catching whatever sunlight reaches that far
• 21:52
  Speaker 1: from the sun, 375 kilometers below the probe. A cater
• 21:57
  Speaker 1: crater reflects light the way it always has, the way
• 22:00
  Speaker 1: it did before any instrument ever saw it. The way
• 22:03
  Speaker 1: it will long after the last person who worked on
• 22:05
  Speaker 1: the mission is gone. Dawn did not go nowhere. A
• 22:09
  Speaker 1: Cater Crater reflects light the way it always has. The
• 22:12
  Speaker 1: way it did before any instrument ever saw it. The
• 22:15
  Speaker 1: way it will long after the last person who worked
• 22:18
  Speaker 1: on the mission is gone. Bright salt, catching whatever sunlight
• 22:21
  Speaker 1: reaches that far from the sun. This show is made
• 22:24
  Speaker 1: by Obo Media.