Dawn (spacecraft) explained

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Dawn
Mission Type:	Vesta/Ceres orbiter
Operator:	NASAJPL
Cospar Id:	2007-043A
Satcat:	32249
Website:	science.nasa.gov
Manufacturer:	Orbital Sciences^[1] JPL UCLA
Launch Mass:	2684.6order=flipNaNorder=flip^[2]
Dry Mass:	1647.1order=flipNaNorder=flip
Dimensions:	1.64xx
Power:	10 kW at 1 AU 1.3 kW at 3 AU
Launch Date:	UTC
Launch Rocket:	Delta II 7925H D-327
Launch Site:	Cape Canaveral SLC-17B
Launch Contractor:	United Launch Alliance
Disposal Type:	Decommissioned
Last Contact:	October 30, 2018
Decay Date:	~2038
Orbit Epoch:	October 30, 2018, 00:00:00 UTC^[3]
Orbit Reference:	Ceres
Orbit Regime:	Highly elliptical
Orbit Eccentricity:	0.7952
Orbit Inclination:	76.1042°
Orbit Arg Periapsis:	164.1014°
Orbit Raan:	−79.4891°
Orbit Period:	1,628.68 minutes
Interplanetary:	Type: flyby Arrival Date: February 18, 2009, 00:27:58 UTC^[4] Distance: 542km (337miles) Type: orbiter Arrival Date: July 16, 2011, 04:47 UTC^[5] Departure Date: September 5, 2012, 06:26 UTC Type: orbiter Arrival Date: March 6, 2015, 12:29 UTC
Instruments List:	Acronym1: FC Name1: Framing Camera Acronym2: VIR Name2: Visible and Infrared Spectrometer Acronym3: GRaND Name3: Gamma Ray and Neutron Detector
Programme:	Discovery program
Previous Mission:	Deep Impact
Next Mission:	Kepler
Insignia:	Dawn logo.png
Insignia Caption:	Dawn mission patch
Insignia Size:	160px

Dawn is a retired space probe that was launched by NASA in September 2007 with the mission of studying two of the three known protoplanets of the asteroid belt: Vesta and Ceres. In the fulfillment of that mission—the ninth in NASA's Discovery Program—Dawn entered orbit around Vesta on July 16, 2011, and completed a 14-month survey mission before leaving for Ceres in late 2012.^{[6] [7]} It entered orbit around Ceres on March 6, 2015.^{[8] [9]} In 2017, NASA announced that the planned nine-year mission would be extended until the probe's hydrazine fuel supply was depleted.^[10] On November 1, 2018, NASA announced that Dawn had depleted its hydrazine, and the mission was ended. The derelict probe remains in a stable orbit around Ceres.^[11]

Dawn is the first spacecraft to have orbited two extraterrestrial bodies,^[12] the first spacecraft to have visited either Vesta or Ceres, and the first to have orbited a dwarf planet.^[13]

The Dawn mission was managed by NASA's Jet Propulsion Laboratory, with spacecraft components contributed by European partners from Italy, Germany, France, and the Netherlands.^[14] It was the first NASA exploratory mission to use ion propulsion, which enabled it to enter and leave the orbit of two celestial bodies. Previous multi-target missions using rockets powered by chemical engine, such as the Voyager program, were restricted to flybys.^[15]

Project history

Technological background

The first working ion thruster in the US was built by Harold R. Kaufman in 1959 at NASA's Glenn Research Center in Ohio. The thruster was similar to the general design of a gridded electrostatic ion thruster with mercury as its propellant. Suborbital tests of the engine followed during the 1960s, and in 1964 the engine was tested on a suborbital flight aboard the Space Electric Rocket Test 1 (SERT 1). It successfully operated for the planned 31 minutes before falling back to Earth.^[16] This test was followed by an orbital test, SERT-2, in 1970.

Deep Space 1 (DS1), which NASA launched in 1998, demonstrated the long-duration use of a xenon-propelled ion thruster on a science mission,^[17] and validated a number of technologies, including the NSTAR electrostatic ion thruster, as well as performing a flyby of an asteroid and a comet.^[18] In addition to the ion thruster, among the other technologies validated by the DS1 was the Small Deep Space Transponder, which is used on Dawn for long-range communication.

Discovery Program selection

Twenty-six proposals were submitted to the Discovery Program solicitation, with budget initially targeted at US$300 million. Three semi-finalists were downselected in January 2001 for a phase-A design study: Dawn, Kepler, and INSIDE Jupiter.^[19] In December 2001 NASA selected the Kepler and the Dawn mission for the Discovery program.^[20] Both missions were initially selected for a launch in 2006.^[20]

Cancellation and reinstatement

The status of the Dawn mission changed several times. The project was cancelled in December 2003,^[21] and then reinstated in February 2004. In October 2005, work on Dawn was placed in "stand down" mode, and in January 2006, the mission was discussed in the press as "indefinitely postponed", even though NASA had made no new announcements regarding its status.^[22] On March 2, 2006, Dawn was again cancelled by NASA.^[23]

The spacecraft's manufacturer, Orbital Sciences Corporation, appealed NASA's decision, offering to build the spacecraft at cost, forgoing any profit in order to gain experience in a new market field. NASA then put the cancellation under review,^[24] and on March 27, 2006, it was announced that the mission would not be cancelled after all.^{[25] [26]} In the last week of September 2006, the Dawn mission's instrument payload integration reached full functionality. Although originally projected to cost US$373 million, cost overruns inflated the final cost of the mission to US$446 million in 2007.^[27] Christopher T. Russell was chosen to lead the Dawn mission team.

Scientific background

The Dawn mission was designed to study two large bodies in the asteroid belt in order to answer questions about the formation of the Solar System, as well as to test the performance of its ion thrusters in deep space.^[28] Ceres and Vesta were chosen as two contrasting protoplanets, the first one apparently "wet" (i.e. icy and cold) and the other "dry" (i.e. rocky), whose accretion was terminated by the formation of Jupiter. The two bodies provide a bridge in scientific understanding between the formation of rocky planets and the icy bodies of the Solar System, and under what conditions a rocky planet can hold water.^[29]

The International Astronomical Union (IAU) adopted a new definition of planet on August 24, 2006, which introduced the term "dwarf planet" for ellipsoidal worlds that were too small to qualify for planetary status by "clearing their orbital neighborhood" of other orbiting matter. Dawn is the first mission to study a dwarf planet, arriving at Ceres a few months before the arrival of the New Horizons probe at Pluto in July 2015.

Ceres comprises a third of the total mass of the asteroid belt. Its spectral characteristics suggest a composition similar to that of a water-rich carbonaceous chondrite.^[30] Vesta, a smaller, water-poor achondritic asteroid comprising a tenth of the mass of the asteroid belt, has experienced significant heating and differentiation. It shows signs of a metallic core, a Mars-like density and lunar-like basaltic flows.^[31]

Available evidence indicates that both bodies formed very early in the history of the Solar System, thereby retaining a record of events and processes from the time of the formation of the terrestrial planets. Radionuclide dating of pieces of meteorites thought to come from Vesta suggests that Vesta differentiated quickly, in three million years or less. Thermal evolution studies suggest that Ceres must have formed some time later, more than three million years after the formation of CAIs (the oldest known objects of Solar System origin).^[31]

Moreover, Vesta appears to be the source of many smaller objects in the Solar System. Most (but not all) V-type near-Earth asteroids, and some outer main-belt asteroids, have spectra similar to Vesta, and are thus known as vestoids. Five percent of the meteoritic samples found on Earth, the howardite–eucrite–diogenite (HED) meteorites, are thought to be the result of a collision or collisions with Vesta.

It is thought that Ceres may have a differentiated interior;^[32] its oblateness appears too small for an undifferentiated body, which indicates that it consists of a rocky core overlain with an icy mantle.^[32] There is a large collection of potential samples from Vesta accessible to scientists, in the form of over 1,400 HED meteorites,^[33] giving insight into Vesta geologic history and structure. Vesta is thought to consist of a metallic iron–nickel core, an overlying rocky olivine mantle and crust.^{[34] [35] [36]}

Objectives

The Dawn mission's goal was to characterize the conditions and processes of the Solar System's earliest eon by investigating in detail two of the largest protoplanets remaining intact since their formation.^[37]

Although the mission has finished, the data analyses and interpretations will continue for many years. The primary question that the mission addresses is the role of size and water in determining the evolution of the planets.^[37] Ceres and Vesta are highly suitable bodies with which to address this question, as they are two of the most massive of the protoplanets. Ceres is geologically very primitive and icy, while Vesta is evolved and rocky. Their contrasting characteristics are thought to have resulted from them forming in two different regions of the early Solar System.^[37]

There are three principal scientific drivers for the mission. First, the Dawn mission can capture the earliest moments in the origin of the Solar System, granting an insight into the conditions under which these objects formed. Second, Dawn determines the nature of the building blocks from which the terrestrial planets formed, improving scientific understanding of this formation. Finally, it contrasts the formation and evolution of two small planets that followed very different evolutionary paths, allowing scientists to determine what factors control that evolution.^[37]

Instruments

NASA's Jet Propulsion Laboratory provided overall planning and management of the mission, the flight system and scientific payload development, and provided the ion propulsion system. Orbital Sciences Corporation provided the spacecraft, which constituted the company's first interplanetary mission. The Max Planck Institute for Solar System Research and the German Aerospace Center (DLR) provided the framing cameras, the Italian Space Agency provided the mapping spectrometer, and the Los Alamos National Laboratory provided the gamma ray and neutron spectrometer.

• Framing camera (FC) – Two redundant framing camera were flown. Each used a f/7.9 refractive optical system with a focal length of 150 mm.^{[38] [39]} A frame-transfer charge-coupled device (CCD), a Thomson TH7888A, at the focal plane has 1024 × 1024 sensitive 93-μrad pixels, imaging a 5.5° x 5.5° field of view. An 8-position filter wheel permits panchromatic (clear filter) and spectrally selective imaging (7 narrow band filters). The broadest filter allows imaging at wavelengths from 400 to 1050 nm. The FC computer is a custom radiation-hardened Xilinx system with a LEON2 core and 8 GiB of memory. The camera offered resolutions of 17 m/pixel for Vesta and 66 m/pixel for Ceres. Because the framing camera was vital for both science and navigation, the payload had two identical and physically separate cameras (FC1 & FC2) for redundancy, each with its own optics, electronics, and structure.^[40]
• Visible and infrared spectrometer (VIR) – This instrument is a modification of the visible and infrared thermal-imaging spectrometer used on the Rosetta and Venus Express spacecraft. It draws its heritage from the Saturn orbiter Cassinis visible and infrared mapping spectrometer. The spectrometer's VIR spectral frames are 256 (spatial) × 432 (spectral), and the slit length is 64 mrad. The mapping spectrometer incorporates two channels, both fed by a single grating. A CCD yields frames from 0.25 to 1.0 μm, while an array of HgCdTe photodiodes cooled to about 70 K spans the spectrum from 0.95 to 5.0 μm.^[41]
• Gamma Ray and Neutron Detector (GRaND)^[42]  – This instrument is based on similar instruments flown on the Lunar Prospector and Mars Odyssey space missions. It had 21 sensors with a very wide field of view. It was used to measure the abundances of the major rock-forming elements (oxygen, magnesium, aluminium, silicon, calcium, titanium, and iron) and potassium, thorium, uranium, and water (inferred from hydrogen content) in the top 1 m of the surface of Vesta and Ceres.^{[43] [44] [45] [46] [47] [48]}

A magnetometer and laser altimeter were considered for the mission, but were not ultimately flown.^[49]

Specifications

Dimensions

With its solar array in the retracted launch position, the Dawn spacecraft is 2.36m (07.74feet) wide. With its solar arrays fully extended, Dawn is 19.7m (64.6feet) wide.^[50] The solar arrays have a total area of 36.4m2.^[51] The main antenna is five feet (1.24 metres) in diameter.

Propulsion system

The Dawn spacecraft was propelled by three xenon ion thrusters derived from NSTAR technology used by the Deep Space 1 spacecraft,^[52] using one at a time. They have a specific impulse of 3,100 s and produce a thrust of 90 mN.^[53] The whole spacecraft, including the ion propulsion thrusters, was powered by a 10 kW (at 1 AU) triple-junction gallium arsenide photovoltaic solar array manufactured by Dutch Space.^{[54] [55]} Dawn was allocated 2470NaN0 of xenon for its Vesta approach, and carried another 1120NaN0 to reach Ceres,^[56] out of a total capacity of 425kg (937lb) of on-board propellant.^[57] With the propellant it carried, Dawn was able to perform a velocity change of approximately 11 km/s over the course of its mission, far more than any previous spacecraft achieved with onboard propellant after separation from its launch rocket.^[56] However, the thrust was very gentle; it took four days at full throttle to accelerate Dawn from zero to 60 mph (96 km/h). Dawn is NASA's first purely exploratory mission to use ion propulsion engines.^[58] The spacecraft also has twelve 0.9 N hydrazine thrusters for attitude control (orientation), which were also used to assist in orbital insertion.^[59]

The Dawn spacecraft was able to achieve a record-breaking level of propulsion from its ion engine.^[60] NASA noted three specific areas of excellence:^[61]

• First to orbit two different astronomical bodies (not including Earth).
• Solar-electric propulsion record, including a velocity change in space of 25,700 mph (11.49 km/s). This is 2.7 times the velocity change by solar-electric ion drive than the past record.
• Achieved 5.9 years of ion engine runtime by September 7, 2018. This amount of runtime equates to 54% of Dawn's time in outer space.

Outreach microchip

Dawn carries a memory chip bearing the names of more than 360,000 space enthusiasts.^[62] The names were submitted online as part of a public outreach effort between September 2005 and November 4, 2006.^[63] The microchip, which is two centimetres in diameter, was installed on May 17, 2007, above the spacecraft's forward ion thruster, underneath its high-gain antenna.^[64] More than one microchip was made, with a back-up copy put on display at the 2007 Open House event at the Jet Propulsion Laboratory in Pasadena, California.

Mission summary

Launch preparations

On April 10, 2007, the spacecraft arrived at the Astrotech Space Operations subsidiary of SPACEHAB, Inc. in Titusville, Florida, where it was prepared for launch.^{[65] [66]} The launch was originally scheduled for June 20, but was delayed until June 30 due to delays with part deliveries.^[67] A broken crane at the launch pad, used to raise the solid rocket boosters, further delayed the launch for a week, until July 7; prior to this, on June 15, the second stage was successfully hoisted into position.^[68] A mishap at the Astrotech Space Operations facility, involving slight damage to one of the solar arrays, did not have an effect on the launch date; however, bad weather caused the launch to slip to July 8. Range tracking problems then delayed the launch to July 9, and then July 15. Launch planning was then suspended in order to avoid conflicts with the Phoenix mission to Mars, which was successfully launched on August 4.

Launch

The launch of Dawn was rescheduled for September 26, 2007,^{[69] [70] [71]} then September 27, due to bad weather delaying fueling of the second stage, the same problem that delayed the July 7 launch attempt. The launch window extended from 07:20–07:49 EDT (11:20–11:49 GMT).^[72] During the final built-in hold at T-4 minutes, a ship entered the exclusion area offshore, the strip of ocean where the rocket boosters were likely to fall after separation. After commanding the ship to leave the area, the launch was required to wait for the end of a collision avoidance window with the International Space Station.^[73] Dawn finally launched from pad 17-B at the Cape Canaveral Air Force Station on a Delta 7925-H rocket^[74] at 07:34 EDT,^{[75] [76] [77]} reaching escape velocity with the help of a spin-stabilized solid-fueled third stage.^{[78] [79]} Thereafter, Dawn's ion thrusters took over.

Transit to Vesta

After initial testing, during which the ion thrusters accumulated more than 11 days 14 hours of operation, Dawn began long-term cruise propulsion on December 17, 2007.^[80] On October 31, 2008, Dawn completed its first thrusting phase to send it on to Mars for a gravity assist flyby in February 2009. During this first interplanetary cruise phase, Dawn spent 270 days, or 85% of this phase, using its thrusters. It expended less than 72 kilograms of xenon propellant for a total change in velocity of 1.81 km/s. On November 20, 2008, Dawn performed its first trajectory correction maneuver (TCM1), firing its number 1 thruster for 2 hours, 11 minutes.Dawn made its closest approach (549 km) to Mars on February 17, 2009, during a successful gravity assist.^{[81] [82]} This flyby slowed Mars's orbital velocity by about 1abbr=onNaNabbr=on per 180 million years. On this day, the spacecraft placed itself in safe mode, resulting in some data acquisition loss. The spacecraft was reported to be back in full operation two days later, with no impact on the subsequent mission identified. The root cause of the event was reported to be a software programming error.^[83]

To cruise from Earth to its targets, Dawn travelled in an elongated outward spiral trajectory. The actual Vesta chronology and estimated Ceres chronology are as follows:^[84]

• September 27, 2007: launch
• February 17, 2009: Mars gravity assist
• July 16, 2011: Vesta arrival and capture
• August 11–31, 2011: Vesta survey orbit
• September 29 – November 2, 2011: Vesta first high altitude orbit
• December 12, 2011 – May 1, 2012: Vesta low altitude orbit
• June 15 – July 25, 2012: Vesta second high altitude orbit
• September 5, 2012: Vesta departure
• March 6, 2015: Ceres arrival
• June 30, 2016: End of primary Ceres operations
• July 1, 2016: Beginning of Ceres extended mission^[85]
• November 1, 2018: End of Mission

Vesta approach

As Dawn approached Vesta, the Framing Camera instrument took progressively higher-resolution images, which were published online and at news conferences by NASA and MPI.On May 3, 2011, Dawn acquired its first targeting image, 1,200,000 km from Vesta, and began its approach phase to the asteroid.^[86] On June 12, Dawn's speed relative to Vesta was slowed in preparation for its orbital insertion 34 days later.^{[87] [88]}

Dawn was scheduled to be inserted into orbit at 05:00 UTC on July 16 after a period of thrusting with its ion engines. Because its antenna was pointed away from the Earth during thrusting, scientists were not able to immediately confirm whether or not Dawn successfully made the maneuver. The spacecraft would then reorient itself, and was scheduled to check in at 06:30 UTC on July 17.^[89] NASA later confirmed that it received telemetry from Dawn indicating that the spacecraft successfully entered orbit around Vesta, making it the first spacecraft to orbit an object in the asteroid belt.^{[90] [91]} The exact time of insertion could not be confirmed, since it depended on Vesta's mass distribution, which was not precisely known and at that time had only been estimated.^[92]

Vesta orbit

After being captured by Vesta's gravity and entering its orbit on July 16, 2011,^[93] Dawn moved to a lower, closer orbit by running its xenon-ion engine using solar power. On August 2, it paused its spiralling approach to enter a 69-hour survey orbit at an altitude of 2750km (1,710miles). It assumed a 12.3-hour high-altitude mapping orbit at 680km (420miles) on September 27, and finally entered a 4.3-hour low-altitude mapping orbit at 210km (130miles) on December 8.^{[94] [95] [96]}

In May 2012, the Dawn team published preliminary results of their study of Vesta, including estimates of the size of Vesta's metal-rich core, which is theorized to be 220km (140miles) across. The scientists stated that they think that Vesta is the "last of its kind" – the only remaining example of the large planetoids that came together to form the rocky planets during the formation of the Solar System.^[97] In October 2012, further Dawn results were published, on the origin of anomalous dark spots and streaks on Vesta's surface, which were likely deposited by ancient asteroid impacts.^{[98] [99] [100]} In December 2012, it was reported that Dawn had observed gullies on the surface of Vesta that were interpreted to have been eroded by transiently flowing liquid water.^{[101] [102]} More details about the Dawn mission's scientific discoveries at Vesta are included on the Vesta page.

Dawn was originally scheduled to depart Vesta and begin its two and a half year journey to Ceres on August 26, 2012. However, a problem with one of the spacecraft's reaction wheels forced Dawn to delay its departure from Vesta's gravity until September 5, 2012.^{[103] [104] [105] [106]}

Transit to Ceres

Imaging dates (2014–2015) and resolution^[111]

Date	distance (km)	diameter (px)	resolution (km/px)	portion of disk illuminated
December 1	1,200,000	9	112	94%
January 13	383,000	27	36	95%
January 25	237,000	43	22	96%
February 3	146,000	70	14	97%
February 12	83,000	122	7.8	98%
February 19	46,000	222	4.3	87%
February 25	40,000	255	3.7	44%
March 1	49,000	207	4.6	23%
April 10	33,000	306	3.1	17%
April 15	22,000	453	2.1	49%

During its time in orbit around Vesta, the probe experienced several failures of its reaction wheels. Investigators planned to modify their activities upon arrival at Ceres for close range geographical survey mapping. The Dawn team stated that they would orient the probe using a "hybrid" mode utilizing both reaction wheels and ion thrusters. Engineers determined that this hybrid mode would conserve fuel. On November 13, 2013, during the transit, in a test preparation, Dawn engineers completed a 27-hour-long series of exercises of said hybrid mode.^[112]

On September 11, 2014, Dawn ion thruster unexpectedly ceased firing and the probe began operating in a triggered safe mode. To avoid a lapse in propulsion, the mission team hastily exchanged the active ion engine and electrical controller with another. The team stated that they had a plan in place to revive this disabled component later in 2014. The controller in the ion propulsion system may have been damaged by a high-energy particle. Upon exiting the safe mode on September 15, 2014, the probe's ion thruster resumed normal operation.^[113]

Furthermore, the Dawn investigators also found that, after the propulsion issue, Dawn could not aim its main communications antenna towards Earth. Another antenna of weaker capacity was instead temporarily retasked. To correct the problem, the probe's computer was reset and the aiming mechanism of the main antenna was restored.^[113]

Ceres approach

Dawn began photographing an extended disk of Ceres on December 1, 2014,^[114] with images of partial rotations on January 13 and 25, 2015 released as animations.Images taken from Dawn of Ceres after January 26, 2015, exceeded the resolution of comparable images from the Hubble Space Telescope.^[115]

Progression of images of Ceres taken by Dawn between January and March 2015

Because of the failure of two reaction wheels, Dawn made fewer camera observations of Ceres during its approach phase than it did during its Vesta approach. Camera observations required turning the spacecraft, which consumed precious hydrazine fuel. Seven optical navigation photo sessions (OpNav 1–7, on January 13 and 25, February 3 and 25, March 1, and April 10 and 15) and two full rotation observation sessions (RC1–2, on February 12 and 19) were planned before full observation begins with orbital capture. The gap in March and early April was due to a period when Ceres appears too close to the Sun from Dawn vantage point to take pictures safely.^[116]

Ceres orbit

Mapping orbits and resolution^[117] – Photos of Ceres by Dawn on Commons

Orbit phase	No.	Dates^[118]	Altitude (km; mi)^[119]	Orbital period	Resolution (km/px)	Improvement over Hubble	Notes
RC3	1st	April 23 – May 9, 2015	13500km (8,400miles)	15 days	1.3	24×
Survey	2nd	June 6–30, 2015	4400km (2,700miles)	3.1 days	0.41	73×
HAMO	3rd	August 17 – October 23, 2015	1450km (900miles)	19 hours	0.14 (140 m)	217×
	4th	December 16, 2015 – September 2, 2016	375km (233miles)	5.5 hours	0.035 (35 m)	850×
XMO2	5th	October 5 – November 4, 2016	1480km (920miles)	19 hours	0.14 (140 m)	217×	^[120] ^[121]
XMO3	6th	December 5, 2016 – February 22, 2017	7520-	≈8 days	0.9 (est)	34× (est)	^[122]
XMO4	7th	April 22 – June 22, 2017	13830-	≈29 days			^[123]
XMO5	8th	June 30, 2017 – April 16, 2018	4400-	30 days			^[124] ^[125]
	9th	May 14–31, 2018	440-	37 hours			^[126]
	10th	June 6, 2018 – present	35-	27.2 hours			^[127] ^[128] ^[129] ^[130]

Dawn entered Ceres orbit on March 6, 2015,^[131] four months prior to the arrival of New Horizons at Pluto. Dawn thus became the first mission to study a dwarf planet at close range.^{[132] [133]} Dawn initially entered a polar orbit around Ceres, and continued to refine its orbit. It obtained its first full topographic map of Ceres during this period.^[134]

From April 23 to May 9, 2015, Dawn entered an RC3 orbit (Rotation Characterization 3) at an altitude of 13500km (8,400miles). The RC3 orbit lasted 15 days, during which Dawn alternated taking pictures and sensor measurements and then relayed the resulting data back to Earth.^[135] On May 9, 2015, Dawn powered its ion engines and began a month-long spiral descent down to its second mapping point, a Survey orbit, three times closer to Ceres than the previous orbit. The spacecraft stopped twice to take images of Ceres during its spiral descent into the new orbit.

On June 6, 2015, Dawn entered the new Survey orbit at an altitude of 4430km (2,750miles). In the new Survey orbit, Dawn circled Ceres every three Earth days.^[136] The Survey phase lasted 22 days (7 orbits), and was designed to obtain a global view of Ceres with Dawn framing camera, and generate detailed global maps with the visible and infrared mapping spectrometer (VIR).

On June 30, 2015, Dawn experienced a software glitch when an anomaly in its orientation system occurred. It responded by going into safe mode and sending a signal to engineers, who fixed the error on July 2, 2015. Engineers determined the cause of the anomaly to be related to the mechanical gimbal system associated with one of Dawn's ion engines. After switching to a separate ion engine and conducting tests from July 14 through July 16, 2015, engineers certified the ability to continue the mission.^[137]

On August 17, 2015, Dawn entered the HAMO orbit (High-Altitude Mapping Orbit).^[138] Dawn descended to an altitude of 1480km (920miles), where in August 2015 it began the two-month HAMO phase. During this phase, Dawn continued to acquire near-global maps with the VIR and framing camera at higher resolution than in the Survey phase. It also imaged in stereo to resolve the surface in 3D.

On October 23, 2015, Dawn began a two-month spiral toward Ceres to achieve a LAMO orbit (Low-Altitude Mapping Orbit) at a distance of 375km (233miles). Since reaching this fourth orbit in December 2015, Dawn was scheduled to acquire data for the next three months with its gamma-ray and neutron detector (GRaND) and other instruments that identified the composition at the surface.^[139]

Having surpassed its mapping objectives, Dawn climbed to its fifth science orbit of 1460km (910miles) beginning on September 2, 2016, to complete additional observations from a different angle.^[140] Dawn began raising its altitude to its sixth science orbit of 7200km (4,500miles) on November 4, 2016, with a goal of reaching it by December 2016. The return to a higher altitude allowed for a second set of data at this altitude, which improves the overall science quality when added to the first batch. However, this time the spacecraft was placed where it was not spiraling and was orbiting in the same direction as Ceres, which reduced propellant consumption.^[141]

Mission conclusion

A flyby of the asteroid 2 Pallas after the completion of the Ceres mission was suggested but never formally considered; orbiting Pallas would not have been possible for Dawn due to the high inclination of Pallas's orbit relative to Ceres.^[142]

In April 2016, the Dawn project team submitted a proposal to NASA for an extended mission that would have seen the spacecraft break orbit from Ceres and perform a flyby of the asteroid 145 Adeona in May 2019,^[143] arguing that the science gained from visiting a third asteroid might outweigh the returns from staying at Ceres. NASA's Planetary Mission Senior Review Panel, however, declined the proposal in May 2016.^{[144] [145]} A one-year mission extension was approved, but the review panel ordered that Dawn remain at Ceres, stating that the long-term observations of the dwarf planet, particularly as it approached perihelion, would potentially yield better science.

The one-year extension expired on June 30, 2017.^{[146] [147]} The spacecraft was placed in an uncontrolled but relatively stable orbit around Ceres, where it ran out of hydrazine propellant by October 31, 2018, and where it will remain as a "monument" for at least 20 years.^{[148] [149] [150]}

Media

Flyover videos

See also

Features on Ceres

• Ahuna Mons, a mountain on Ceres
• Bright spots on Ceres
• List of geological features on Ceres

Other asteroid missions

• List of minor planets and comets visited by spacecraft
• Chang'e 2 4179 Toutatis flyby
• Galileo probe 951 Gaspra and 243 Ida flybys
• Hayabusa 25143 Itokawa rendezvous and sample return
• Hayabusa2 162173 Ryugu rendezvous and sample return
• NEAR Shoemaker 253 Mathilde flyby, orbited 433 Eros from 2000 to 2001
• OSIRIS-REx 101955 Bennu sample return mission
• Rosetta 2867 Šteins and 21 Lutetia flyby

External links

• Dawn website by Jet Propulsion Laboratory
• Dawn website by NASA
• Dawn public data archives by UCLA
• Dawn Legacy – Video (03:04) by NASA (September 7, 2018).
• Dawn Mission Archive at the NASA Planetary Data System, Small Bodies Node

Instruments

• Framing Cameras by the Max Planck Institute for Solar System Research
• Visual and Infrared Spectrometer by the Istituto Nazionale di Astrofisica
• Gamma Ray and Neutron Spectrometer by NASA (journal paper)

Notes and References

1. Web site: Dawn.
2. Web site: Dawn at Ceres . Press kit . NASAJet Propulsion Laboratory . March 2015.
3. Web site: Nasa Horizons Ephemeris – Target body name: Dawn (spacecraft) (-203). NASA JPL. 6 January 2022.
4. Web site: Dawn . . NASA . November 20, 2016.
5. News: NASA's Dawn Spacecraft Begins Science Orbits of Vesta . NASA . Dwayne C. . Brown . Priscilla . Vega . August 1, 2011 . August 6, 2011 . February 2, 2019 . https://web.archive.org/web/20190202164311/https://www.nasa.gov/mission_pages/dawn/news/dawn20110801.html . dead .
6. News: NASA's Dawn Spacecraft Hits Snag on Trip to 2 Asteroids . Space.com . August 15, 2012 . August 27, 2012.
7. Web site: Dawn Gets Extra Time to Explore Vesta . NASA . April 18, 2012 . April 24, 2012 . dead . https://web.archive.org/web/20120421191416/http://www.nasa.gov/mission_pages/dawn/news/dawn20120418.html . April 21, 2012 .
8. Web site: Landau . Elizabeth . Brown . Dwayne . NASA Spacecraft Becomes First to Orbit a Dwarf Planet . March 6, 2015 . NASA . March 6, 2015.
9. Web site: Dawn Journal: Ceres Orbit Insertion! . . Marc . Rayman . March 6, 2015 . March 6, 2015.
10. Web site: Dawn Mission Extended at Ceres . . Landau . Elizabeth . October 19, 2017 . October 19, 2017.
11. News: NASA's Dawn Mission to Asteroid Belt Comes to End. Northon. Karen. November 1, 2018. NASA. November 12, 2018. en.
12. Now Appearing At a Dwarf Planet Near You: NASA's Dawn Mission to the Asteroid Belt . Marc . Rayman . Silicon Valley Astronomy Lectures . Foothill College, Los Altos, CA . April 8, 2015 . July 7, 2018.
13. Book: Beyond Earth: A Chronicle of Deep Space Exploration, 1958–2016. 2. Siddiqi. Asif A.. 2017059404. 9781626830424. NASA History Program Office. second. 2018. SP2018-4041. The NASA history series. Washington, D.C..
14. News: Complexity and Challenge: Dawn Project Manager Speaks of Difficult Voyage to Vesta and Ceres . AmericaSpace . Ben . Evans . October 8, 2017 . February 28, 2018.
15. Rayman . Marc . Fraschetti, Thomas C. . Raymond, Carol A. . Russell, Christopher T. . Dawn: A mission in development for exploration of main belt asteroids Vesta and Ceres . Acta Astronautica . April 5, 2006 . 58 . 605–616 . April 14, 2011 . 10.1016/j.actaastro.2006.01.014 . 11 . 2006AcAau..58..605R.
16. Web site: Innovative Engines – Glenn Ion Propulsion Research Tames the Challenges of 21st Century Space Travel . NASA . November 19, 2007 . dead . https://web.archive.org/web/20070915023928/http://www.nasa.gov/centers/glenn/about/fs08grc.html . September 15, 2007 .
17. Mission design for deep space 1: A low-thrust technology validation mission . Rayman, M.D. and Chadbourne, P.A. and Culwell, J.S. and Williams, S.N. . Acta Astronautica . 45 . 4–9 . 381–388 . 1999 . 1999AcAau..45..381R . 10.1016/s0094-5765(99)00157-5 . dead . https://web.archive.org/web/20150509172350/http://trs-new.jpl.nasa.gov/dspace/bitstream/2014/19098/1/98-0310.pdf . May 9, 2015 .
18. Web site: Dawn Telecommunications . Jim Taylor . NASA/JPL . August 2009 . March 18, 2015.
19. Web site: NASA announces Discovery mission finalists . Spacetoday.net . January 4, 2001 . January 11, 2016.
20. Web site: Susan Reichley . 2001 News Releases - JPL Asteroid Mission Gets Thumbs Up from NASA . Jpl.nasa.gov . December 21, 2001 . January 11, 2016 . May 1, 2017 . https://web.archive.org/web/20170501104328/https://www.jpl.nasa.gov/releases/2001/release_2001_245.html . dead .
21. News: Ambrosiano . Nancy . March 28, 2006 . NASA's Dawn mission is a go . Los Alamos National Laboratory . October 1, 2007 . October 20, 2007 . https://web.archive.org/web/20071020201844/http://lanl.gov/news/index.php/fuseaction/nb.story/story_id/8140 . dead .
22. News: NASA Asteroid Mission Won't Launch This Year . 2006 . Space.com . March 4, 2006 . Alicia . Chang . February 13, 2006 . https://web.archive.org/web/20060213020557/http://www.space.com/missionlaunches/ap_060121_dawn_hold.html . dead .
23. Web site: Probe built to visit asteroids killed in budget snarl . 2006 . SpaceflightNow.com . March 4, 2006 . Stephen . Clark.
24. News: NASA reviewing canceled mission . March 16, 2006 . CNN.com . March 27, 2006 . https://web.archive.org/web/20060321081642/http://www3.cnn.com/2006/TECH/space/03/16/asteroid.mission.ap/index.html . March 21, 2006.
25. Web site: Dawn Mission Reclama . Rex . Geveden . 2006 . March 27, 2006 . June 25, 2006 . https://web.archive.org/web/20060625233756/http://www.nasa.gov/pdf/145511main_Dawn_letter.pdf . dead .
26. News: NASA Reinstates Cancelled Asteroid Mission . Tariq . Malik . March 27, 2006 . Space.com . March 27, 2006.
27. Web site: Dawn . NASA – National Space Science Data Center . July 16, 2011.
28. Web site: McCartney . Gretchen . Brown . Dwayne . Wendel . JoAnna . Legacy of NASA's Dawn, Near the End of its Mission . September 7, 2018 . . September 8, 2018.
29. Web site: DAWN Mission Objectives . NASA . February 28, 2017 . https://web.archive.org/web/20130214195648/http://dawn.jpl.nasa.gov/mission/goal_index.asp . February 14, 2013 . dead .
30. Ceres: Evolution and current state . Journal of Geophysical Research . 110 . E5 . E05009 . Thomas B. McCord . Christophe Sotin . 2005 . 10.1029/2004JE002244. 2005JGRE..110.5009M . free .
31. Web site: Vesta . Calvin J. Hamilton . January 6, 2013.
32. 10.1038/nature03938 . 2005Natur.437..224T . 16148926 . Differentiation of the asteroid Ceres as revealed by its shape . 2005 . Thomas . P. C. . Parker . J. Wm. . McFadden . L. A. . Russell . C. T. . Stern . S. A. . Sykes . M. V. . Young . E. F. . Nature . 437 . 7056 . 224–226. 17758979 .
33. Web site: Meteoritical Bulletin Database . November 27, 2014.
34. 10.1006/icar.1998.5956 . A Thermal Model for the Differentiation of Asteroid 4 Vesta, Based on Radiogenic Heating . 1998 . Ghosh . A . Icarus . 134 . 2 . 187–206 . 1998Icar..134..187G . McSween . Harry Y..
35. 10.1111/j.1945-5100.2007.tb00589.x . Sahijpal, S. . Soni, P. . Gagan, G. . Numerical simulations of the differentiation of accreting planetesimals with ²⁶Al and ⁶⁰Fe as the heat sources . Meteoritics & Planetary Science . 42 . 9 . 1529–1548 . 2007 . 2007M&PS...42.1529S. free .
36. Gupta, G. . Sahijpal, S. . Differentiation of Vesta and the parent bodies of other achondrites . . 115 . E8 . E08001 . 2010 . 10.1029/2009JE003525 . 2010JGRE..115.8001G . free .
37. News: Mission Objectives . 2006 . JPL – NASA . March 23, 2013 . https://web.archive.org/web/20130214195648/http://dawn.jpl.nasa.gov/mission/goal_index.asp . February 14, 2013 . dead .
38. Web site: Dawn Spacecraft and Instruments . August 17, 2014 . January 1, 2012 . https://web.archive.org/web/20120101212028/http://www.nasa.gov/mission_pages/dawn/spacecraft/instruments.html . dead .
39. Dawn Framing Camera: A Telescope En Route To The Asteroid Belt . 1st EIROforum School of Instrumentation. May 11–15, 2009. Geneva, Switzerland. . H. . Sierks . K.-M. . Aye . I. . Büttner . R. . Enge . W. . Goetz . P. . Gutierrez-Marques . H. . Hartwig . I. . Hejja . H. U. . Keller . W. . Kühne . T. . Maue . A. . Nathues . M. . Richards . R. . Schäfer . S. . Schröder . M. . Sperling . I. . Szemerey . S. . Mottola . T. . Behnke . U. . Carsenti . R. . Jaumann . M. . Tschentscher . B. . Fiethe . F. . Bubenhagen . H. . Michalik . K.-U. . Reiche . 5 . 2009.
40. 10.1007/s11214-011-9745-4 . The Dawn Framing Camera . 2011 . Sierks . H. . Keller . H. U. . Jaumann . R. . Michalik . H. . Behnke . T. . Bubenhagen . F. . Büttner . I. . Carsenty . U. . Christensen . U. . 8 . Space Science Reviews . 2011SSRv..163..263S . 163 . 1–4 . 263–327. 121046026 .
41. 10.1007/s11214-010-9668-5 . The VIR Spectrometer . 2011 . de Sanctis . M. C. . Coradini . A. . Ammannito . E. . Filacchione . G. . Capria . M. T. . Fonte . S. . Magni . G. . Barbis . A. . Bini . A. . 8 . Space Science Reviews . 2011SSRv..163..329D . 163 . 1–4 . 329–369. 121295356 .
42. T.H. Prettyman Gamma Ray and Neutron Spectrometer for Dawn, Lunar and Planetary Science XXXVII (2006), abstract 2231
43. Web site: Science Payload . March 21, 2010 . NASA . dead . https://web.archive.org/web/20100527113905/http://dawn.jpl.nasa.gov/technology/index.asp . May 27, 2010 .
44. Web site: GRaND science instrument moves closer to launch from Cape . March 21, 2010 . NASA . dead . https://web.archive.org/web/20110521184228/http://dawn.jpl.nasa.gov/technology/GRaND.asp . May 21, 2011 .
45. 10.1111/j.1945-5100.1997.tb01582.x . 1997M&PS...32..929R . A magma ocean on Vesta: Core formation and petrogenesis of eucrites and diogenites . 1997 . Righter . Kevin . 929–944 . Drake . Michael J. . Meteoritics & Planetary Science . 32 . 6. 128684062 . free .
46. 10.1111/j.1945-5100.2001.tb01892.x . 2001M&PS...36..501D . 2001 . Drake . 501–513 . Michael J. . Meteoritics & Planetary Science . 36 . 4 . The eucrite/Vesta story. free .
47. 10.1117/12.578551 . Proceedings of SPIEMapping the elemental composition of Ceres and Vesta: Dawn's gamma ray and neutron detector . 2004 . Prettyman . Thomas H. . 5660 . 107 . Instruments, Science, and Methods for Geospace and Planetary Remote Sensing. 119514228 .
48. 10.1109/TNS.2003.815156 . 2003ITNS...50.1190P . Gamma-ray and neutron spectrometer for the Dawn mission to 1 Ceres and 4 Vesta . IEEE Transactions on Nuclear Science. August 2003 . 50 . 4 . 1190–1197 . T.H. . Prettyman. 122574914 .
49. News: James . Oberg . September 27, 2007 . Spacecraft's ion drive gets its day in the sun . NBC News . November 25, 2018.
50. Web site: Dawn Mission Overview . NASA . August 17, 2014 . December 4, 2011 . https://web.archive.org/web/20111204160818/http://www.nasa.gov/mission_pages/dawn/spacecraft/ . dead .
51. Web site: Solar Power for Outer Planets Study . NASA . Scott W. Benson . November 8, 2007 . November 27, 2014.
52. Web site: Dawn Mission . NASA – JPL . July 18, 2011.
53. Web site: Dawn, Ion Propulsion . NASA . September 28, 2007.
54. Web site: Dawn, Spacecraft . NASA . September 28, 2007.
55. Web site: Dawn Solar Arrays . July 18, 2011 . 2007 . Dutch Space.
56. Ion propulsion: An enabling technology for the Dawn Mission . Garner . Charles E. . Rayman . Mark M. . Whiffen . Greg J. . Brophy . John R. . Mikes . Steven C. . February 10, 2013 . Jet Propulsion Laboratory, National Aeronautics and Space Administration . Kauai, Hawaii . 23rd AAS/AIAA Spaceflight Mechanics Meeting . 2014/44151 .
57. Web site: Watanabe . Susan . July 5, 2007 . Dawn: Spacecraft & Instruments . NASA . August 10, 2006 . December 4, 2011 . https://web.archive.org/web/20111204160818/http://www.nasa.gov/mission_pages/dawn/spacecraft/ . dead .
58. Web site: Dawn Lifts Off . National Geographic Society . https://web.archive.org/web/20071021041049/http://news.nationalgeographic.com/news/2007/09/photogalleries/wip-week48/ . dead . October 21, 2007 . September 28, 2007.
59. Web site: NSSDC – Spacecraft – Details . 2007 . NASA . January 22, 2015.
60. Web site: Dawn Mission Mission. dawn.jpl.nasa.gov. en. November 24, 2018.
61. Web site: Overview | Dawn.
62. Web site: All Aboard the Dawn Spacecraft . May 20, 2007 . JPL – NASA . May 21, 2007.
63. Web site: Send Your Name to the Asteroid Belt . November 4, 2006 . JPL.NASA.gov . June 21, 2007 . https://web.archive.org/web/20070411054822/http://dawn.jpl.nasa.gov/DawnCommunity/Sendname2asteroid/index_asteroid_blt.aspx . April 11, 2007.
64. Web site: Kennedy Media Gallery . May 17, 2007 . NASA . June 21, 2007 . dead . https://web.archive.org/web/20071021000520/http://mediaarchive.ksc.nasa.gov/detail.cfm?mediaid=32165 . October 21, 2007 .
65. Web site: Dawn arrives in Florida . Spaceflight Now . April 2007 . June 28, 2013.
66. Web site: Dawn at Astrotech's Payload Processing Facility . Space and Astronautics News . April 11, 2007 . June 28, 2013 . dead . https://web.archive.org/web/20070927205639/http://www.space.gs/11-apr-2007-dawn.html . September 27, 2007 .
67. Web site: Launch of Dawn asteroid mission postponed again . New Scientist . 2007 . June 28, 2013.
68. Web site: Expendable Launch Vehicle Status Report . June 18, 2007 . June 28, 2013 . NASA . June 23, 2017 . https://web.archive.org/web/20170623162250/https://www.nasa.gov/centers/kennedy/launchingrockets/status/2007/elvstatus-20070618.html . dead .
69. Web site: NASA Mission to Asteroid Belt Rescheduled for September Launch . July 7, 2007 . NASA . November 9, 2013 . May 1, 2017 . https://web.archive.org/web/20170501120258/https://www.nasa.gov/mission_pages/dawn/news/HQ_07150_Dawn_postpone_Sep.html . dead .
70. Web site: Dawn Launch Date . NASA launch schedule . September 1, 2007.
71. Book: The Dawn Mission to Minor Planets 4 Vesta and 1 Ceres . Christopher . Russell . Carol . Raymond . Springer Science+Business Media . New York . 978-1-4614-4903-4 . 10.1007/978-1-4614-4903-4 . 2012. 2012dmmp.book.....R . 132296936 .
72. Web site: Expendable Launch Vehicle Status Report . September 7, 2007 . NASA . November 9, 2013 . June 23, 2017 . https://web.archive.org/web/20170623162100/https://www.nasa.gov/centers/kennedy/launchingrockets/status/2007/elvstatus-20070907.html . dead .
73. Web site: NASA's Launch Blog . September 27, 2007 . NASA . November 9, 2013 . June 30, 2017 . https://web.archive.org/web/20170630183958/http://www.nasa.gov/mission_pages/dawn/launch/launch-blog.html . dead .
74. Web site: Expendable Launch Vehicle Status Report . May 11, 2007 . NASA . November 9, 2013 . June 23, 2017 . https://web.archive.org/web/20170623162426/http://www.nasa.gov/centers/kennedy/launchingrockets/status/2007/elvstatus-20070511.html . dead .
75. Web site: ULA—One Team for Assured Access to Space . ulalaunch.com . November 9, 2013 . https://web.archive.org/web/20070928093124/http://www.ulalaunch.com/images/product_sheet/Delta_Product_Sheet_FINAL.pdf . September 28, 2007.
76. Web site: NASA's Launch Coverage . September 27, 2007 . NASA . November 9, 2013 . June 24, 2017 . https://web.archive.org/web/20170624120420/https://www.nasa.gov/mission_pages/dawn/launch/index.html . dead .
77. Web site: Dawn Spacecraft Successfully Launched . NASA . September 27, 2007 . November 9, 2013 . May 15, 2017 . https://web.archive.org/web/20170515230530/http://www.nasa.gov/mission_pages/dawn/news/dawn-20070927.html . dead .
78. Web site: Dawn Journal . September 12, 2007 . July 21, 2014 . Jet Propulsion Laboratory .
79. Web site: Dear Dawnivores . August 24, 2008 . November 9, 2013 . Marc D. . Rayman . May 30, 2012 . https://archive.today/20120530164742/http://www-ssc.igpp.ucla.edu/dawn/DawnJournal_24August08.html . dead .
80. Web site: Dawn Journal: December 17, 2007 . Rayman . Marc D. . JPL . November 9, 2013.
81. Web site: Dawn Journal: Aiming away from a bull's eye at Mars . November 9, 2013 . Marc D. . Rayman . The Planetary Society . https://web.archive.org/web/20110716023248/http://www-ssc.igpp.ucla.edu/dawn/DawnJournal_24August08.html . July 16, 2011.
82. News: Asteroid-Bound Probe Zooms Past Mars . Space.com . Tariq . Malik . February 18, 2009 . November 9, 2013.
83. Web site: Dawn Receives Gravity Assist from Mars . February 28, 2009 . January 9, 2018 . NASA/JPL.
84. Web site: GSpace Topics: Dawn . Planetary Society . November 9, 2013.
85. News: Pluto probe's extended mission approved, but new Dawn destination denied . Spaceflight Now . Stephen . Clark . July 2, 2016 . June 21, 2017.
86. http://www.nasa.gov/mission_pages/dawn/news/dawn20110511.html "NASA's Dawn Captures First Image of Nearing Asteroid"
87. Web site: NASA'S Dawn Spacecraft Begins Science Orbits Of Vesta . NASA . August 1, 2011 . August 7, 2014 . November 22, 2013 . https://web.archive.org/web/20131122164137/http://www.nasa.gov/home/hqnews/2011/aug/HQ_11-254_Dawn_Image.html . dead .
88. https://web.archive.org/web/20090322131458/http://neo.jpl.nasa.gov/orbits/fullview4.jpg "View of Vesta from Dawn"
89. News: Wall . Mike . NASA Spacecraft Now Orbiting Huge Asteroid Vesta ... Hopefully . . July 16, 2011 . July 17, 2011.
90. News: Dawn probe orbits asteroid Vesta . July 17, 2011 . Jonathan . Amos . BBC . January 22, 2015.
91. Book: Beyond Earth: A Chronicle of Deep Space Exploration, 1958–2016. 2. Siddiqi. Asif A.. 2017059404. 9781626830424. NASA History Program Office. second. 2018. SP2018-4041. The NASA history series. Washington, D.C..
92. News: Vega . Priscilla . Brown . Dwayne . NASA's Dawn Spacecraft Enters Orbit Around Asteroid Vesta . NASA . July 16, 2011 . July 17, 2011 . June 19, 2012 . https://web.archive.org/web/20120619102718/http://www.nasa.gov/mission_pages/dawn/news/dawn20110716.html . dead .
93. Dawn at Vesta: Testing the Protoplanetary Paradigm . . C. T. . Russell . Raymond . C. A. . Coradini . A. . McSween . H. Y. . Zuber . M. T. . Nathues . A. . De Sanctis . M. C. . Jaumann . R. . Konopliv . A. S. . Preusker . F. . Asmar . S. W. . Park . R. S. . Gaskell . R. . Keller . H. U. . Mottola . S. . Roatsch . T. . Scully . J. E. C. . Smith . D. E. . Tricarico . P. . Toplis . M. J. . Christensen . U. R. . Feldman . W. C. . Lawrence . D. J. . McCoy . T. J. . Prettyman . T. H. . Reedy . R. C. . Sykes . M. E. . Titus . T. N. . 5 . 336 . 6082 . 684–686 . May 11, 2012 . 10.1126/science.1219381 . 2012Sci...336..684R . 22582253. 206540168 .
94. Web site: Mission Status Updates . NASAJet Propulsion Laboratory . Marc . Rayman . 2011.
95. The Dawn Mission to Vesta and Ceres . . C. T. . Russell . C. A. . Raymond . 163 . 1–4 . 3–23 . December 2011 . 10.1007/s11214-011-9836-2 . 2011SSRv..163....3R. 121717060 .
96. The Dawn of Vesta Science . 32nd International Electric Propulsion Conference. September 11–15, 2011. Wiesbaden, Germany. . Charles E. . Garner . Marc D. . Rayman . John R. . Brophy . Steven C. . Mikes . 2011 . IEPC-2011-326 . May 6, 2012 . November 9, 2013 . https://web.archive.org/web/20131109124425/http://erps.spacegrant.org/uploads/images/images/iepc_articledownload_1988-2007/2011index/IEPC-2011-326.pdf . dead .
97. News: Asteroid Vesta is 'last of a kind' rock . BBC News . Jonathan . Amos . May 11, 2012 . January 20, 2015.
98. Delivery of dark material to Vesta via carbonaceous chondritic impacts . . Reddy . Vishnu . Le Corre . Lucille . O'Brien . David P. . Nathues . Andreas . Cloutis . Edward A. . Durda . Daniel D. . Bottke . William F. . Bhatt . Megha U. . Nesvorny . David . Buczkowski . Debra . Scully . Jennifer E.C. . Palmer . Elizabeth M. . Sierks . Holger . Mann . Paul J. . Becker . Kris J. . Beck . Andrew W. . Mittlefehldt . David . Li . Jian-Yang . Gaskell . Robert . Russell . Christopher T. . Gaffey . Michael J. . McSween . Harry Y. . McCord . Thomas B. . Combe . Jean-Philippe . Blewett . David . 5 . 221 . 2 . 544–559 . November–December 2012 . 10.1016/j.icarus.2012.08.011 . 2012Icar..221..544R . 1208.2833. 37947646 .
99. Dark material on Vesta from the infall of carbonaceous volatile-rich material . . T. B. . McCord . Li . J.-Y. . Combe . J.-P. . McSween . H. Y. . Jaumann . R. . Reddy . V. . Tosi . F. . Williams . D. A. . Blewett . D. T. . Turrini . D. . Palomba . E. . Pieters . C. M. . De Sanctis . M. C. . Ammannito . E. . Capria . M. T. . Le Corre . L. . Longobardo . A. . Nathues . A. . Mittlefehldt . D. W. . Schröder . S. E. . Hiesinger . H. . Beck . A. W. . Capaccioni . F. . Carsenty . U. . Keller . H. U. . Denevi . B. W. . Sunshine . J. M. . Raymond . C. A. . Russell . C. T. . 5 . 491 . 7422 . 83–86 . November 2012 . 10.1038/nature11561 . 2012Natur.491...83M . 23128228. 2058249 .
100. News: NASA's Dawn Spacecraft Probes Proto-Planet Vesta, Discovers Deposits that Give Scientists Insight into the Origins of the Solar System . Latinos Post . James . Paladino . October 31, 2012 . November 28, 2012.
101. Sub-Curvilinear Gullies Interpreted as Evidence for Transient Water Flow on Vesta . 45th Lunar and Planetary Science Conference. March 17–21, 2014. The Woodlands, Texas. . J. E. C. . Scully . C. T. . Russell . A. . Yin . R. . Jaumann . E. . Carey . H. Y. . McSween . J. . Castillo-Rogez . C. A. . Raymond . V. . Reddy . L. . Le Corre . 5 . 2014 . 2014LPI....45.1796S.
102. News: Dawn probe spies possible water-cut gullies on Vesta . BBC News . Jonathan . Amos . December 6, 2012 . December 8, 2012.
103. News: Dawn departs Vesta to become first asteroid hopper . New Scientist . Short sharp Science . Jacob . Aron . September 6, 2012 . November 9, 2013 . September 7, 2012 . https://web.archive.org/web/20120907134311/http://www.newscientist.com/blogs/shortsharpscience/2012/09/asteroid-hopping-spacecraft-ma.html . dead .
104. Web site: Dawn Engineers Assess Reaction Wheel . NASAJet Propulsion Laboratory . Jia-Rui C. . Cook . August 18, 2012 . January 22, 2015 . https://web.archive.org/web/20150315131809/http://dawn.jpl.nasa.gov/feature_stories/engineers_assess_reaction_wheel.asp . March 15, 2015.
105. Web site: Dawn has departed the giant asteroid Vesta . NASAJet Propulsion Laboratory . Jia-Rui C. . Cook . September 5, 2012 . https://web.archive.org/web/20150414203658/http://dawn.jpl.nasa.gov/feature_stories/dawn_departs_vesta.asp . April 14, 2015.
106. News: NASA's Dawn Spacecraft Says Goodbye to Giant Asteroid Vesta . Space.com via Yahoo! News . September 5, 2012 . September 6, 2012.
107. Introduction: The geologic mapping of Vesta . . David A. . Williams . R. Aileen . Yingst . W. Brent . Garry . 244 . 1–12 . December 2014 . 10.1016/j.icarus.2014.03.001 . 2014Icar..244....1W . 2286/R.I.28071 . free . September 24, 2019 . August 31, 2021 . https://web.archive.org/web/20210831111836/https://repository.asu.edu/attachments/144882/content/ND_I_Williams_etal_2014_preprint.pdf . dead .
108. Geomorphology and structural geology of Saturnalia Fossae and adjacent structures in the northern hemisphere of Vesta . Icarus . Scully . J. E. C. . Yin . A. . Russell . C. T. . Buczkowski . D. L. . Williams . D. A. . Blewett . D. T. . Ruesch . O. . Hiesinger . H. . Le Corre . L. . Mercer . C. . Yingst . R. A. . Garry . W. B. . Jaumann . R. . Roatsch . T. . Preusker . F. . Gaskell . R. W. . Schröder . S. E. . Ammannito . E. . Pieters . C. M. . Raymond . C. A. . 5 . 244 . 23–40 . December 2014 . 10.1016/j.icarus.2014.01.013 . 2014Icar..244...23S. 2286/R.I.28070 . free .
109. Imprint of the Rheasilvia impact on Vesta – Geologic mapping of quadrangles Gegania and Lucaria . Icarus . Schäfer . M. . Nathues . A. . Williams . D. A. . Mittlefehldt . D. W. . Le Corre . L. . Buczkowski . D. L. . Kneissl . T. . Thangjam . G. S. . Hoffmann . M. . Schmedemann . N. . Schäfer . T. . Scully . J. E. C. . Li . J. Y. . Reddy . V. . Garry . W. B. . Krohn . K. . Yingst . R. A. . Gaskell . R. W. . Russell . C. T. . 5 . 244 . 60–73 . December 2014 . 10.1016/j.icarus.2014.06.026 . 2014Icar..244...60S. 2286/R.I.28060 . free .
110. Morphology and formation ages of mid-sized post-Rheasilvia craters – Geology of quadrangle Tuccia, Vesta . Icarus . Kneissl . T. . Schmedemann . N. . Reddy . V. . Williams . D. A. . Walter . S. H. G. . Neesemann . A. . Michael . G. G. . Jaumann . R. . Krohn . K. . Preusker . F. . Roatsch . T. . Le Corre . L. . Nathues . A. . Hoffmann . M. . Schäfer . M. . Buczkowski . D. . Garry . W. B. . Yingst . R. A. . Mest . S. C. . Russell . C. T. . Raymond . C. A. . 5 . 244 . 133–157 . December 2014 . 10.1016/j.icarus.2014.02.012 . 2014Icar..244..133K. 2286/R.I.28058 . free .
111. Web site: Dawn Journal February 25 . https://web.archive.org/web/20150227143103/http://dawnblog.jpl.nasa.gov/2015/02/25/dawn-journal-february-25/#table . dead . February 27, 2015 . NASA . February 25, 2015 . March 1, 2015.
112. Web site: Dawn Fills out its Ceres Dance Card . NASA/JPL . December 3, 2013 . March 18, 2015 . dead . https://web.archive.org/web/20150415025503/http://dawn.jpl.nasa.gov/feature_stories/Dawn_Fills_Out_Ceres_Dance_Card.asp . April 15, 2015 .
113. Web site: Dawn Operating Normally After Safe Mode Triggered . NASA/JPL . September 16, 2014 . March 18, 2015 . dead . https://web.archive.org/web/20141225012242/http://dawn.jpl.nasa.gov/feature_stories/Dawn_operated_normally.asp . December 25, 2014.
114. Web site: Dawn Journal . https://web.archive.org/web/20150101091612/http://dawnblog.jpl.nasa.gov/2014/12/29/dawn-journal-december-29/ . dead . January 1, 2015 . NASA/JPL . December 29, 2014 . January 21, 2015.
115. Web site: Dawn Journal October 31 . NASA . October 31, 2014 . January 18, 2015 . dead . https://web.archive.org/web/20150120120112/http://dawnblog.jpl.nasa.gov/2014/10/31/dawn-journal-october-31/#sthash.OPRlufJs.dpuf . January 20, 2015 .
116. Web site: Dawn Journal January 29 . https://web.archive.org/web/20150202001407/http://dawnblog.jpl.nasa.gov/2015/01/29/dawn-journal-january-29/ . dead . February 2, 2015 . NASA . January 29, 2015 . February 13, 2015.
117. Web site: Dawn Journal March 31 [2015] ]. NASAJet Propulsion Laboratory . Marc . Rayman . March 31, 2015 . September 9, 2015 . dead . https://web.archive.org/web/20150905091717/http://dawnblog.jpl.nasa.gov/2015/03/31/dawn-journal-march-31-2/#table . September 5, 2015 .
118. Web site: Dawn Journal: Descent to HAMO . . Marc . Rayman . July 30, 2015 . September 9, 2015.
119. Distance from surface, not radius of the orbit
120. Web site: PIA21221: Dawn XMO2 Image 1 . NASAJet Propulsion Laboratory . November 7, 2016 . November 20, 2016.
121. Web site: Dawn Journal: November 28, 2016 . NASAJet Propulsion Laboratory . Marc . Rayman . November 28, 2016 . December 30, 2016.
122. Web site: Dawn Journal: December 29, 2016 . NASAJet Propulsion Laboratory . Marc . Rayman . December 29, 2016 . December 30, 2016.
123. Web site: 2017 Mission Status Updates . NASAJet Propulsion Laboratory . Marc . Rayman . 2017.
124. Web site: Dawn Journal: Getting Elliptical . The Planetary Society . Marc . Rayman . May 25, 2018 . June 5, 2018.
125. Web site: Dear Vernal Dawnquinoxes . NASA . Marc . Rayman . March 20, 2018 . June 5, 2018.
126. Web site: 2018 Mission Status Archive . NASAJet Propulsion Laboratory . Marc . Rayman . 2018.
127. Web site: Rayman . Marc . Dawn – Mission Status . August 9, 2018 . . September 12, 2018 .
128. Web site: Clark . Stephen . Dawn spacecraft flying low over Ceres . June 15, 2018 . SpaceFlightNow.com . June 16, 2018 .
129. News: Dawn will enter lowest ever orbit around Ceres . Spaceflight Insider . Laurel . Kornfeld . June 2, 2018 . June 5, 2018 . June 5, 2018 . https://web.archive.org/web/20180605042452/http://www.spaceflightinsider.com/missions/solar-system/dawn-will-enter-lowest-ever-orbit-around-ceres/ . dead .
130. Web site: Dear Isaac Newdawn, Charles Dawnwin, Albert Einsdawn and all other science enthusiasts . NASA . Marc . Rayman . April 29, 2018 . June 5, 2018.
131. News: Dawn Spacecraft Slips Quietly Into Orbit Around Dwarf Planet Ceres . NBC News . Alan . Boyle . March 6, 2015 . March 11, 2015.
132. Web site: NASA's Dawn Fills out its Ceres Dance Card . NASAJet Propulsion Laboratory . Jia-Rui . Cook . December 3, 2013 . December 8, 2013.
133. Book: Ceres: Its Origin, Evolution and Structure and Dawn's Potential Contribution . The Dawn Mission to Minor Planets 4 Vesta and 1 Ceres . Springer New York . Thomas B. . McCord . Julie . Castillo-Rogez . Andy . Rivkin . 63–76 . 2012 . 10.1007/978-1-4614-4903-4_5 . 978-1-4614-4902-7.
134. Web site: LPSC 2015: First results from Dawn at Ceres: provisional place names and possible plumes . The Planetary Society . Emily . Lakdawalla . March 19, 2015 . March 21, 2015.
135. Web site: Dawn Journal February 28 . https://web.archive.org/web/20140311065323/http://dawnblog.jpl.nasa.gov/2014/02/28/dawn-journal-february-28-2014/ . dead . March 11, 2014 . NASAJet Propulsion Laboratory . Marc . Rayman . February 28, 2014 . February 13, 2015.
136. Web site: Ceres Animation Showcases Bright Spots . NASAJet Propulsion Laboratory . Landau . Elizabeth . May 11, 2015 . May 13, 2015.
137. Web site: Dawn Maneuvering to Third Science Orbit . NASAJet Propulsion Laboratory . Elizabeth . Landau . July 17, 2015 . July 20, 2015.
138. Web site: Dawn Mission Enters High Altitude Mapping Orbit Over Ceres . The Catholic Astronomer . . Bob . Trembley . August 21, 2015 . August 28, 2015.
139. Web site: Dawn Mission Status Updates . NASAJet Propulsion Laboratory . October 16, 2015 . October 17, 2015.
140. Web site: Dawn Sets Course for Higher Orbit . NASAJet Propulsion Laboratory . Elizabeth . Landau . August 31, 2016 . November 20, 2016.
141. Web site: New Ceres Views as Dawn Moves Higher . NASAJet Propulsion Laboratory . Elizabeth . Landau . November 18, 2016 . November 20, 2016.
142. Web site: Dawn Journal December 29 . https://web.archive.org/web/20150101091612/http://dawnblog.jpl.nasa.gov/2014/12/29/dawn-journal-december-29/#comment-7392 . dead . January 1, 2015 . NASA/JPL . January 11, 2015 . March 10, 2015.
143. News: NASA's Dawn probe may visit third asteroid after Ceres and Vesta . New Scientist . Govert . Schilling . April 20, 2016 . April 24, 2016.
144. Web site: Report for Planetary Mission Senior Review 2016 . NASA . J. Douglas . McCuistion . June 17, 2016 . June 22, 2017 . https://web.archive.org/web/20161222114712/https://solarsystem.nasa.gov/docs/PMSR2016_Report_Final.pdf . December 22, 2016 . dead .
145. News: NASA's Dawn spacecraft won't be leaving dwarf planet Ceres . The Verge . Loren . Grush . July 1, 2016 . June 19, 2017.
146. News: Dawn mission managers await NASA decision on spacecraft's future . Spaceflight Now . Clark . Stephen . June 17, 2017 . June 19, 2017.
147. Web site: Dawn Journal . NASAJet Propulsion Laboratory . Marc D. . Rayman . September 27, 2017.
148. Web site: Brown . Dwayne . Wendel . JoAnna . McCartney . Gretchen . The Legacy of NASA's Dawn, Near End of Mission . September 6, 2018 . . November 2, 2018 . September 13, 2018 . https://web.archive.org/web/20180913152025/https://www.nasa.gov/feature/jpl/the-legacy-of-nasa-s-dawn-near-end-of-mission/ . dead .
149. News: Brown . Dwayne . Wendel . JoAnna . McCartney . Gretchen . NASA's Dawn Mission to Asteroid Belt Comes to End . November 1, 2018 . . November 2, 2018 .
150. News: Chang . Kenneth . NASA's Dawn Mission to the Asteroid Belt Says Good Night – Launched in 2007, the spacecraft discovered bright spots on Ceres and forbidding terrain on Vesta. . November 1, 2018 . . November 2, 2018 .