Dawn (spacecraft)

Last updated

Dawn
Dawn spacecraft model.png
Illustration of the Dawn spacecraft
Mission typeMulti-target orbiter
Operator NASA  / JPL
COSPAR ID 2007-043A
SATCAT no. 32249
Website http://dawn.jpl.nasa.gov/
Mission durationPlanned: 9 years [1] [2]
Final: 11 years, 1 month, 5 days
Spacecraft properties
Manufacturer Orbital Sciences  · JPL  · UCLA
Launch mass1,217.7 kg (2,684.6 lb) [3]
Dry mass747.1 kg (1,647.1 lb) [3]
Dimensions1.64 × 19.7 × 1.77 m (5.4 × 65 × 5.8 ft) [3]
Power10,000 watts at 1 AU [3]
1,300 watts at 3 AU [4]
Start of mission
Launch dateSeptember 27, 2007, 11:34 (2007-09-27UTC11:34) UTC [5]
Rocket Delta II 7925H
Launch site Cape Canaveral SLC-17B
Contractor United Launch Alliance
End of mission
DisposalUncontrolled/stable orbit
Deactivated1 November 2018
Last contact31 October 2018
Flyby of Mars
Closest approachFebruary 18, 2009, 00:27:58 UTC [5]
Distance542 km (337 mi) [5]
4 Vesta orbiter
Orbital insertionJuly 16, 2011, 04:47 UTC [6]
Orbital departureSeptember 5, 2012, 06:26 UTC [5]
1 Ceres orbiter
Orbital insertionMarch 6, 2015, 12:29 UTC [5]
Dawn logo.png
Dawn mission patch
Kepler  
 

Dawn is a retired space probe launched by NASA in September 2007 with the mission of studying two of the three known protoplanets of the asteroid belt, Vesta and Ceres. [1] It was retired on 1 November 2018 and it is currently in an uncontrolled orbit around its second target, the dwarf planet Ceres. Dawn is the first spacecraft to orbit two extraterrestrial bodies, [7] the first spacecraft to visit either Vesta or Ceres, and the first to visit a dwarf planet, arriving at Ceres in March 2015, a few months before New Horizons flew by Pluto in July 2015.

Space probe unmanned robotic spacecraft that does not orbit the Earth, but, instead, explores further into outer space

A space probe is a robotic spacecraft that does not orbit Earth, but instead, explores further into outer space. A space probe may approach the Moon; travel through interplanetary space; flyby, orbit, or land on other planetary bodies; or enter interstellar space.

NASA space-related agency of the United States government

The National Aeronautics and Space Administration is an independent agency of the United States Federal Government responsible for the civilian space program, as well as aeronautics and aerospace research.

Protoplanet

A protoplanet is a large planetary embryo that originated within a protoplanetary disc and has undergone internal melting to produce a differentiated interior. Protoplanets are thought to form out of kilometer-sized planetesimals that gravitationally perturb each other's orbits and collide, gradually coalescing into the dominant planets.

Contents

Dawn entered orbit around Vesta on July 16, 2011, and completed a 14-month survey mission before leaving for Ceres in late 2012. [8] [9] It then entered orbit around Ceres on March 6, 2015. [10] [11] NASA considered, but decided against, a proposal to visit a third target. [12] On October 19, 2017, NASA announced that the mission would be extended until the probe's hydrazine fuel supply was used up. [13] On November 1, 2018, NASA announced that the Dawn spacecraft had finally exhausted all of its hydrazine fuel, thus ending its mission. The satellite is currently in an uncontrolled state about Ceres. [14]

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. [15] 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 conventional drives, such as the Voyager program, were restricted to flybys. [4]

Jet Propulsion Laboratory Research and development center and NASA field center in California, US

The Jet Propulsion Laboratory (JPL) is a federally funded research and development center and NASA field center in La Cañada Flintridge, California, United States, though it is often referred to as residing in Pasadena, California, because it has a Pasadena ZIP Code.

Ion thruster Propulsion method for spacecraft

An ion thruster or ion drive is a form of electric propulsion used for spacecraft propulsion. It creates thrust by accelerating cations by utilizing electricity. The term refers strictly to gridded electrostatic ion thrusters, and is often incorrectly loosely applied to all electric propulsion systems including electromagnetic plasma thrusters.

Voyager program American scientific program about the probes Voyager 1 and Voyager 2

The Voyager program is an American scientific program that employs two robotic probes, Voyager 1 and Voyager 2, to study the outer Solar System. The probes were launched in 1977 to take advantage of a favorable alignment of Jupiter, Saturn, Uranus and Neptune. Although their original mission was to study only the planetary systems of Jupiter and Saturn, Voyager 2 continued on to Uranus and Neptune. The Voyagers now explore the outer boundary of the heliosphere in interstellar space; their mission has been extended three times and they continue to transmit useful scientific data. Neither Uranus nor Neptune has been visited by a probe other than Voyager 2.

Project history

Technological background

SERT-1: first ion engine NASA spacecraft; launched on July 20, 1964. SERT-1 spacecraft.jpg
SERT-1: first ion engine NASA spacecraft; launched on July 20, 1964.

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. [18] This test was followed by an orbital test, SERT-2, in 1970.

Harold R. Kaufman is an American physicist, noted for his development of electrostatic ion thrusters for NASA during the 1950s and 1960s. Kaufman developed a compact ion source based on electron bombardment, the "Kaufman Ion Source," a variant of the duoplasmatron, for the purpose of spacecraft propulsion.

Glenn Research Center government organization in United States of America

NASA John H. Glenn Research Center at Lewis Field is a NASA center, located within the cities of Brook Park and Cleveland between Cleveland Hopkins International Airport and the Rocky River Reservation of Cleveland Metroparks, with a subsidiary facility in Sandusky, Ohio. Its director is Janet L. Kavandi. Glenn Research Center is one of ten major NASA field centers, whose primary mission is to develop science and technology for use in aeronautics and space. As of May 2012, it employed about 1,650 civil servants and 1,850 support contractors located on or near its site.

Ohio State of the United States of America

Ohio is a Midwestern state in the Great Lakes region of the United States. Of the fifty states, it is the 34th largest by area, the seventh most populous, and the tenth most densely populated. The state's capital and largest city is Columbus.

Deep Space 1 (DS1), which NASA launched in 1998, demonstrated the long-duration use of a xenon-propelled ion thruster on a science mission, [19] and validated a number of technologies, including the NSTAR electrostatic ion thruster, as well as performing a flyby of an asteroid and a comet. [20] 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. [20]

<i>Deep Space 1</i> spacecraft

Deep Space 1 (DS1) was a NASA technology demonstration spacecraft which flew by an asteroid and a comet. It was part of the New Millennium Program, dedicated to testing advanced technologies.

Xenon Chemical element with atomic number 54

Xenon is a chemical element with symbol Xe and atomic number 54. It is a colorless, dense, odorless noble gas found in the Earth's atmosphere in trace amounts. Although generally unreactive, xenon can undergo a few chemical reactions such as the formation of xenon hexafluoroplatinate, the first noble gas compound to be synthesized.

NASA Solar Technology Application Readiness

The NASA Solar Technology Application Readiness (NSTAR) is a type of spacecraft ion thruster called electrostatic ion thruster. It is a highly efficient low-thrust spacecraft propulsion running on electrical power generated by solar arrays. It uses high-voltage electrodes to accelerate ions with electrostatic forces.

Discovery Program selection

26 proposals were submitted to the Discovery Program solicitation, with budget initially targeted at 300 million USD. [21] Three semi-finalists were downselected in January 2001 for a phase-A design study: Dawn, Kepler, and INSIDE Jupiter. [22] In December 2001 NASA selected the Kepler and the Dawn mission for the Discovery program. [21] Both missions were initially selected for a launch in 2006. [21]

Discovery Program NASAs space exploration missions

NASA's Discovery Program is a series of lower-cost, highly focused American scientific space missions that are exploring the Solar System. It was founded in 1992 to implement then-NASA Administrator Daniel S. Goldin's vision of "faster, better, cheaper" planetary missions. Discovery missions differ from traditional NASA missions where targets and objectives are pre-specified. Instead, these cost-capped missions are proposed and led by a scientist called the Principal Investigator (PI). Proposing teams may include people from industry, small businesses, government laboratories, and universities. Proposals are selected through a competitive peer review process. All of the completed Discovery missions are accomplishing ground-breaking science and adding significantly to the body of knowledge about the Solar System.

Cancellation and reinstatement

The status of the Dawn mission changed several times. The project was cancelled in December 2003, [23] 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. [24] On March 2, 2006, Dawn was again cancelled by NASA. [25]

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, [26] and on March 27, 2006, it was announced that the mission would not be cancelled after all. [27] [28] 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. [29] Christopher T. Russell was chosen to lead the Dawn mission team.

Scientific background

Scale comparison of Vesta, Ceres, and Earth's moon Ceres and Vesta, Moon size comparison.jpg
Scale comparison of Vesta, Ceres, and Earth's moon

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. [1] 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. [30]

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.

Dawn image of Ceres from 13,600 km, May 4, 2015 PIA19547-Ceres-DwarfPlanet-Dawn-RC3-AnimationFrame25-20150504.jpg
Dawn image of Ceres from 13,600 km, May 4, 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. [31] 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. [32]

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). [32]

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; [33] its oblateness appears too small for an undifferentiated body, which indicates that it consists of a rocky core overlain with an icy mantle. [33] There is a large collection of potential samples from Vesta accessible to scientists, in the form of over 1,400 HED meteorites, [34] 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. [35] [36] [37]

Objectives

Animation of Dawn's trajectory from 27 September 2007 to 5 October 2018
Dawn  *   Earth *   Mars *   4 Vesta  *   1 Ceres Animation of Dawn trajectory.gif
Animation of Dawn's trajectory from 27 September 2007 to 5 October 2018
  Dawn ·   Earth  ·   Mars  ·   4 Vesta  ·   1 Ceres
Dawn's approximate flight trajectory Dawn trajectory as of September 2009.png
Dawn's approximate flight trajectory

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. [1] [38]

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. [38] 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. [38]

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. [38]

Specifications

Dawn prior to encapsulation at its launch pad on July 1, 2007 Dawn at Launch Pad.jpg
Dawn prior to encapsulation at its launch pad on July 1, 2007

Dimensions

With its solar array in the retracted launch position, the Dawn spacecraft is 2.36 meters (7.7 ft) wide. With its solar arrays fully extended, Dawn is 19.7 m (65 ft) wide. [39] The solar arrays have a total area of 36.4 m2 (392 sq ft). [40] The main antenna is five feet in diameter. [7]

Propulsion system

The Dawn spacecraft was propelled by three xenon ion thrusters derived from NSTAR technology used by the Deep Space 1 spacecraft, [41] using one at a time. They have a specific impulse of 3,100 s and produce a thrust of 90 mN. [42] 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. [43] [44] Dawn was allocated 247 kg (545 lb) of xenon for its Vesta approach, and carried another 112 kg (247 lb) to reach Ceres, [45] out of a total capacity of 425 kg (937 lb) of on-board propellant. [46] 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. [45] However, the thrust was very gentle; it took four days at full throttle to accelerate Dawn from zero to 60 mph (96 km/h). [7] Dawn is NASA's first purely exploratory mission to use ion propulsion engines. [47] The spacecraft also has twelve 0.9 N hydrazine thrusters for attitude control (orientation), which were also used to assist in orbital insertion. [48]

The Dawn spacecraft was able to achieve a record-breaking level of propulsion from its ion engine. [49] NASA noted three specific areas of excellence: [50]

Outreach microchip

Dawn carries a memory chip bearing the names of more than 360,000 space enthusiasts. [51] The names were submitted online as part of a public outreach effort between September 2005 and November 4, 2006. [52] 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. [53] 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.

Payload

Framing camera view of the Ceres bright spots PIA19559-Ceres-DwarfPlanet-Dawn-OpNav8-image1-20150516-crop.jpg
Framing camera view of the Ceres bright spots

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. [4]

A magnetometer and laser altimeter were considered for the mission, but were not ultimately flown. [65]

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. [66] [67] The launch was originally scheduled for June 20, but was delayed until June 30 due to delays with part deliveries. [68] 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. [69] 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

Dawn launching on a Delta II rocket from Cape Canaveral Air Force Station Space Launch Complex 17 on September 27, 2007 Dawn ignition.jpg
Dawn launching on a Delta II rocket from Cape Canaveral Air Force Station Space Launch Complex 17 on September 27, 2007

The launch of Dawn was rescheduled for September 26, 2007, [70] [71] [72] 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). [73] During the final built-in hold at T4 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. [74] Dawn finally launched from pad 17-B at the Cape Canaveral Air Force Station on a Delta 7925-H rocket [75] at 07:34 EDT, [76] [77] [78] reaching escape velocity with the help of a spin-stabilized solid-fueled third stage. [79] [80] Thereafter, Dawn's ion thrusters took over.

Transit (Earth to Vesta)

After initial testing, during which the ion thrusters accumulated more than 11 days 14 hours of thrust, Dawn began long-term cruise propulsion on December 17, 2007. [81] 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.

Greyscale NIR image of Mars (northwest Tempe Terra), taken by Dawn during its 2009 flyby Mars image by Dawn probe.jpg
Greyscale NIR image of Mars (northwest Tempe Terra), taken by Dawn during its 2009 flyby

Dawn made its closest approach (549 km) to Mars on February 17, 2009 during a successful gravity assist. [82] [83] This flyby slowed Mars' orbital velocity by about 2.5 cm (1 in) per 180 million years. [7] 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. [84]

To cruise from Earth to its targets, Dawn traveled in an elongated outward spiral trajectory. The actual Vesta chronology and estimated[ needs update ] Ceres chronology are as follows: [2]

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. [90] 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. [91]

Vesta orbit

After being captured by Vesta's gravity and entering its orbit on July 16, 2011, [92] 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 2,750 km (1,710 mi). It assumed a 12.3-hour high-altitude mapping orbit at 680 km (420 mi) on September 27, and finally entered a 4.3-hour low-altitude mapping orbit at 210 km (130 mi) on December 8. [93] [94] [95]

Animation of Dawn's trajectory around 4 Vesta from 15 July 2011 to 10 September 2012
Dawn *   4 Vesta Animation of Dawn trajectory around 4 Vesta.gif
Animation of Dawn's trajectory around 4 Vesta from 15 July 2011 to 10 September 2012
   Dawn ·   4 Vesta

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 220 km (140 mi) 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. [92] [96] [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. [9] 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. [8] [103] [104] [105] [106]

Geologic map of Vesta based on Dawn data [107]
PIA18788-VestaAsteroid-GeologicMap-DawnMission-20141117.jpg
The most ancient and heavily cratered regions are brown; areas modified by the Veneneia and Rheasilvia impacts are purple (the Saturnalia Fossae Formation, in the north) [108] and light cyan (the Divalia Fossae Formation, equatorial), [107] respectively; the Rheasilvia impact basin interior (in the south) is dark blue, and neighboring areas of Rheasilvia ejecta (including an area within Veneneia) are light purple-blue; [109] [110] areas modified by more recent impacts or mass wasting are yellow/orange or green, respectively.

Transit (Vesta to Ceres)

Imaging dates (2014–2015) and resolution [111]
Datedistance
(km)
diameter
(px)
resolution
(km/px)
portion of disk
illuminated
December 11,200,000911294%
January 13383,000273695%
January 25237,000432296%
February 3146,000701497%
February 1283,0001227.898%
February 1946,0002224.387%
February 2540,0002553.744%
March 149,0002074.623%
April 1033,0003063.117%
April 1522,0004532.149%

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's 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[ needs update ] 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's vantage point to take pictures safely. [116]

Ceres orbit

Animation of Dawn's trajectory around Ceres from 1 February 2015 to 6 October 2018
Dawn *   Ceres Animation of Dawn trajectory around Ceres.gif
Animation of Dawn's trajectory around Ceres from 1 February 2015 to 6 October 2018
  Dawn ·   Ceres
Mapping orbits and resolution [117] Photos of Ceres by Dawn on Commons
Orbit phaseNo.Dates [118] Altitude
(km; mi) [119]
Orbital periodResolution
(km/px)
Improvement
over Hubble
Notes
RC3 1stApril 23, 2015 – May 9, 201513,500 km (8,400 mi)15 days1.324×
Survey 2ndJune 6, 2015 – June 30, 20154,400 km (2,700 mi)3.1 days0.4173×
HAMO 3rdAugust 17, 2015 – October 23, 20151,450 km (900 mi)19 hours0.14 (140 m)217×
LAMO/XMO1 4thDecember 16, 2015 – September 2, 2016375 km (233 mi)5.5 hours0.035 (35 m)850×
XMO2 5thOctober 5, 2016 – November 4, 20161,480 km (920 mi)19 hours0.14 (140 m)217× [120] [121] [122]
XMO3 6thDecember 5, 2016 – February 22, 20177,520–9,350 km
(4,670–5,810 mi)
≈8 days0.9 (est)34× (est) [121] [123]
XMO47thApril 22, 2017 – June 22, 201713,830–52,800 km
(8,590–32,810 mi)
≈29 days [124]
XMO58thJune 30, 2017 – April 16, 20184,400–39,100 km
(2,700–24,300 mi)
30 days [124] [125] [126]
XMO6 9thMay 14, 2018 – May 31, 2018440–4,700 km
(270–2,920 mi)
37 hours [127]
XMO7 (FINAL) 10thJune 6, 2018 – present35–4,000 km
(22–2,485 mi)
27.2 hours [128] [129] [130] [131]

Dawn entered Ceres orbit on March 6, 2015, [132] 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. [133] [134] 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. [135]

From April 23 to May 9, 2015, Dawn entered an RC3 orbit (Rotation Characterization 3) at an altitude of 13,500 km (8,400 mi). The RC3 orbit lasted 15 days, during which Dawn alternated taking pictures and sensor measurements and then relayed the resulting data back to Earth. [136] 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 4,430 km (2,750 mi). In the new Survey orbit, Dawn circled Ceres every three Earth days. [137] The Survey phase lasted 22 days (7 orbits), and was designed to obtain a global view of Ceres with Dawn's 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. [138]

On August 17, 2015, Dawn entered the HAMO orbit (High-Altitude Mapping Orbit). [139] Dawn descended to an altitude of 1,480 km (920 mi), 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 375 km (233 mi). 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. [121]

Having surpassed its mapping objectives, Dawn climbed to its fifth science orbit of 1,460 km (910 mi) 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 7,200 km (4,500 mi) 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' 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. [85] NASA's Planetary Mission Senior Review Panel, however, declined the proposal in May 2016. [144] [12] 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. [85]

The one-year extension expired on June 30, 2017. [145] [146] The spacecraft was placed in an uncontrolled but relatively stable orbit around Ceres, where it ran out of hydrazine propellant on 1 November 2018, and where it will remain as a "monument" for at least 20 years. [147] [148] [149]

Ceres – some of the last views by the Dawn spacecraft (1 November 2018) [147] [148] [149]

Media

High-resolution image

High-resolution view of Ceres taken during its Low-Altitude Mapping Orbit PIA21906-Ceres-DwarfPlanet-HighResolution-Dawn-20170920.jpg
High-resolution view of Ceres taken during its Low-Altitude Mapping Orbit

Ceres atlas images

PIA20014-Ceres-SurveyAtlas-Overall-June2015.jpg
Overall
PIA20014-Ceres-SurveyAtlas-Kerwan-June2015.jpg
Kerwan section
(PDF version)
PIA20014-Ceres-SurveyAtlas-AsariZadeni-June2015.jpg
Asari-Zadeni section
(PDF version)
PIA20014-Ceres-SurveyMap-Occator-June2015.jpg
Occator section
(PDF version)

Maps of Ceres

Flyover videos

See also

Features on Ceres
Other asteroid missions

Related Research Articles

4 Vesta second largest asteroid of the main asteroid belt

Vesta is one of the largest objects in the asteroid belt, with a mean diameter of 525 kilometres (326 mi). It was discovered by the German astronomer Heinrich Wilhelm Olbers on 29 March 1807 and is named after Vesta, the virgin goddess of home and hearth from Roman mythology.

Reaction wheel

A reaction wheel (RW) is a type of flywheel used primarily by spacecraft for three axis attitude control, which doesn't require rockets or external applicators of torque. They provide a high pointing accuracy, and are particularly useful when the spacecraft must be rotated by very small amounts, such as keeping a telescope pointed at a star.

Adeona is a large asteroid from the intermediate asteroid belt, approximately 150 kilometers in diameter. Its surface is very dark, and, based upon its classification as a C-type asteroid, is probably composed of primitive carbonaceous material. The spectra of the asteroid displays evidence of aqueous alteration. The Adeona family of asteroids is named after it.

Solar electric propulsion

Solar electric propulsion (SEP) typically refers to the combination of solar cells and an ion drive to propel a spacecraft through outer space. This technology has been exploited in a variety of spacecraft by the European Space Agency, the Japanese Space Agency, Indian Space Research Organisation and NASA. SEP is valued for its potential for a high specific impulse, thus allowing less mass for propellant to be launched with a spacecraft and it has been evaluated for mission to Mars.

Christopher Thomas Russell is head of the Space Physics Center at the Institute of Geophysics and Planetary Physics (IGPP) at UCLA, professor in UCLA's Department of Earth, Planetary, and Space Sciences, and Director of the UCLA Branch of the California Space Grant Consortium. He received a B.Sc. from the University of Toronto in 1964 and a Ph.D. from UCLA in 1968. In 1977 he was awarded the James B. Macelwane Medal and in 2003 the John Adam Fleming Medal by the American Geophysical Union (AGU). He is also a Fellow of the AGU. Asteroid 21459 Chrisrussell was named after him in 2008. In 2017, he was awarded the NASA Distinguished Public Service Medal. He has three grandchildren.

Sample-return mission space mission to retrieve tangible samples from an extraterrestrial location and return with them to Earth for analysis

A sample-return mission is a spacecraft mission with the goal of collecting and returning samples from an extraterrestrial location to Earth for analysis. Sample-return missions may bring back merely atoms and molecules or a deposit of complex compounds such as loose material ("soil") and rocks. These samples may be obtained in a number of ways, such as soil and rock excavation or a collector array used for capturing particles of solar wind or cometary debris.

Solar panels on spacecraft photovoltaic solar panels on spacecraft operating in the inner solar system

Spacecraft operating in the inner Solar System usually rely on the use of photovoltaic solar panels to derive electricity from sunlight. In the outer solar system, where the sunlight is too weak to produce sufficient power, radioisotope thermoelectric generators (RTGs) are used as a power source.

Ceres (dwarf planet) Dwarf planet and largest asteroid of the main asteroid belt

Ceres is the largest object in the asteroid belt that lies between the orbits of Mars and Jupiter, slightly closer to Mars's orbit. With a diameter of 945 km (587 mi), Ceres is the largest of the minor planets and the only dwarf planet inside Neptune's orbit. It is the 33rd-largest known body in the Solar System.

Electrically powered spacecraft propulsion

An electrically-powered spacecraft propulsion system uses electrical energy to change the velocity of a spacecraft. Most of these kinds of spacecraft propulsion systems work by electrically expelling propellant at high speed, but electrodynamic tethers work by interacting with a planet's magnetic field.

TAU (spacecraft) proposed unmanned space probe

TAU was a proposed unmanned space probe that would go to a distance of one thousand astronomical units from the Earth and Sun by NASA/JPL in 1987 using tested technology. One scientific purpose would be to measure the distance to other stars via stellar parallax. Studies continued into 1990, working with a launch in the 2005–2010 timeframe.

Asteroid Redirect Mission United States space mission to collect samples from an asteroid

The Asteroid Redirect Mission (ARM), also known as the Asteroid Retrieval and Utilization (ARU) mission and the Asteroid Initiative, was a space mission proposed by NASA in 2013. The Asteroid Retrieval Robotic Mission (ARRM) spacecraft would rendezvous with a large near-Earth asteroid and use robotic arms with anchoring grippers to retrieve a 4-meter boulder from the asteroid.

Near-Earth Asteroid Scout

The Near-Earth Asteroid Scout is a planned mission by NASA to develop a controllable low-cost CubeSat solar sail spacecraft capable of encountering near-Earth asteroids (NEA). The NEA Scout will be one of 13 CubeSats to be carried with the Orion EM-1 mission into a heliocentric orbit in cis-lunar space on the maiden flight of the Space Launch System (SLS) scheduled to launch in 2020. The most likely target for the mission is 1991 VG, but this may change based on launch date or other factors. After deployment in cislunar space, NEA Scout will perform a series of lunar flybys to achieve optimum departure trajectory before beginning its two-year-long cruise.

Ahuna Mons mons on Ceres

Ahuna Mons is the largest mountain on the dwarf planet and asteroid Ceres. It protrudes above otherwise smooth terrain, it is not an impact feature, and it appears to be the only mountain of its kind on Ceres. Bright streaks run top to bottom on its slopes; these streaks are thought to be salt, similar to the better known Cererian bright spots, and likely resulted from cryovolcanic activity from Ceres's interior. It is named after the traditional post-harvest festival Ahuna of the Sumi Naga people of India. In July 2018, NASA released a comparison of physical features, including Ahuna Mons, found on Ceres with similar ones present on Earth.

<i>Psyche</i> (spacecraft) Fourteenth mission in the Discovery program; orbital reconnaissance of the main belt asteroid 16 Psyche

Psyche is a planned orbiter mission that will explore the origin of planetary cores by studying the metallic asteroid,16 Psyche. Lindy Elkins-Tanton of Arizona State University is the Principal Investigator who proposed this mission for NASA's Discovery Program. NASA's Jet Propulsion Laboratory (JPL) will manage the project.

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Instruments