Mission Information
MISSION_START_DATE 2007-09-27T12:00:00.000Z
MISSION_STOP_DATE 2017-06-30T12:00:00.000Z
Mission Overview                                                            
The Dawn spacecraft was successfully launched atop a Delta II rocket          
on September 27, 2007.  Dawn is an ion-propelled spacecraft capable           
of visiting multiple targets in the main asteroid belt.  In the baseline      
mission, Dawn flies to and orbits the main belt asteroids 1 Ceres and         
4 Vesta, orbiting Vesta for a period of not less than seven months            
and Ceres for not less than five months.  The spacecraft flies by             
Mars in a gravity assist maneuver in 2009 en route to Vesta.                  
Dawn carries three science instruments whose data is used to                  
characterize the target bodies.  The instrument suite consists of             
redundant Framing Cameras (FC1 and FC2), a Visible and Infrared mapping       
spectrometer (VIR) and a Gamma Ray and Neutron Detector (GRaND).  In          
addition to these instruments, radiometric and optical navigation data        
is used to determine the gravity field.  The Dawn mission is an               
international cooperation with instrument teams located in Germany, Italy,    
and the United States.                                                        
  Science Goals                                                               
In order to achieve the overall scientific goal of understanding              
conditions and processes acting at the solar system's earliest epoch,         
the Dawn spacecraft images the surfaces of the minor planets Vesta            
and Ceres to determine their bombardment, thermal, tectonic, and possible     
volcanic history. It determines the topography and internal structure         
of these two complementary protoplanets that have remained intact since       
their formation, by measuring their mass, shape, volume, and spin rate        
with navigation data and imagery. Dawn determines mineral and elemental       
composition from infrared, gamma ray, and neutron spectroscopy to             
constrain the thermal history and compositional evolution of Ceres and        
Vesta, and in addition provides context for meteorites (asteroid samples      
already in hand). It also uses the spectral information to search for         
water-bearing minerals.                                                       
Framing Camera (FC):                                                          
The Framing Camera is a multispectral imager that also serves as              
an optical navigation camera.  The detector is a 1024x1024 pixel              
Atmel/Thomson TH7888A CCD with 14 micron pixels.  It has eight filters        
numbered F1 through F8, including a broadband (clear) filter and              
narrow band filters ranging from 438 nm to 965 nm.  The Framing camera        
instrument includes two redundant cameras of identical design, referred       
to as FC1 and FC2.  For full information about the FC instrument, see         
Schroeder and Gutierrez-Marques (2011).                                       
Visible and Infrared Mapping Spectrometer (VIR):                              
VIR is an imaging spectrometer with an optical design derived from            
the visible channel of the Cassini Visible Infrared Mapping                   
Spectrometer (VIMS-V) and from the Rosetta Visible Infrared Thermal           
Imaging Spectrometer (VIRTIS).  It has moderate resolution and                
combines two data channels in one instrument.  The two data channels,         
Visible (spectral range 0.25-1 micron) and Infrared (spectral range           
0.95-5 micron), are committed to spectral mapping and are housed              
in the same optical subsystem.  The spectrometer has the ability to           
point and scan along the direction perpendicular to the slit.  A              
complete description of the instrument and its performance can be             
found in De Sanctis et al. (2010) and Coradini et al. (2011).                 
Gamma Ray and Neutron Detector (GRaND):                                       
GRaND is a nuclear spectrometer that will collect data needed to map          
the elemental composition of the surfaces of 4 Vesta and 1 Ceres              
(Prettyman et al. 2003B).  GRaND measures the spectrum of planetary           
gamma rays and neutrons, which originate from cosmic ray interactions         
and radioactive decay within the surface, while the spacecraft is in          
orbit around each body.  The instrument, which is mounted on the              
+Z deck of the spacecraft, consists of 21 sensors designed to                 
separately measure radiation originating from the surface of each             
asteroid and background sources, including the space energetic                
particle environment and cosmic ray interactions with the spacecraft.         
A complete description of GRaND is given in the GRaND instrument              
paper, Prettyman et al. (2011). Instrument performance during cruise          
and Mars Flyby is given by Prettyman et al. (2012).                           
  Mission Phases                                                              
(Dates in parentheses are projected at the time of writing.)                  
  Phase Name (Phase ID)                Start time        End time             
  -------------------------            ----------------  ----------------     
  INITIAL CHECKOUT (ICO)               2007-09-27        2008-01-19T00:00     
  EARTH-MARS CRUISE (EMC)              2008-01-19T00:00  2009-02-16T00:00     
  MARS GRAVITY ASSIST (MGA)            2009-02-16T00:00  2010-03-23T00:00     
  MARS-VESTA CRUISE (MVC)              2010-03-23T00:00  2011-05-03T10:49     
  VESTA ENCOUNTER                      2011-05-03T10:49  2012-09-10T21:50     
    VESTA SCIENCE APPROACH (VSA)       2011-05-03T10:49  2011-08-11T12:00     
    VESTA SCIENCE SURVEY (VSS)         2011-08-11T12:00  2011-08-31T20:26     
    VESTA TRANSFER TO HAMO (VTH)       2011-08-31T20:26  2011-09-29T09:59     
    VESTA SCIENCE HAMO (VSH)           2011-09-29T09:59  2011-11-02T10:40     
    VESTA TRANSFER TO LAMO (VTL)       2011-11-02T10:40  2011-12-12T22:44     
    VESTA SCIENCE LAMO (VSL)           2011-12-12T22:44  2012-05-01T11:50     
    VESTA TRANSFER TO HAMO 2 (VT2)     2012-05-01T11:50  2012-06-15T10:00     
    VESTA SCIENCE HAMO 2 (VH2)         2012-06-15T10:00  2012-07-25T15:10     
    VESTA TRANSFER TO CERES (VTC)      2012-07-25T15:10  2012-09-10T21:50     
  VESTA-CERES CRUISE (VCC)             2012-09-10T21:50  2014-12-26T02:50     
  CERES ENCOUNTER                      2014-12-26T02:50  2016-06-01           
    CERES SCIENCE APPROACH (CSA)       2014-12-26T02:50  2015-04-24T00:00     
    CERES SCIENCE RC3 (CSR)            2015-04-24T00:00  2015-05-09T10:00     
    CERES TRANSFER TO SURVEY (CTS)     2015-05-09T10:00  2015-06-04T12:00     
    CERES SCIENCE SURVEY (CSS)         2015-06-04T12:00  2015-07-01T00:00     
    CERES TRANSFER TO HAMO (CTH)       2015-07-01T00:00  2015-08-16T23:59     
    CERES SCIENCE HAMO (CSH)           2015-08-16T23:59  2015-10-23T20:30     
    CERES TRANSFER TO LAMO (CTL)       2015-10-23:20:30  2015-12-16T01:00     
    CERES SCIENCE LAMO (CSL)           2015-12-16T01:00  2016-06-19T12:00     
  END OF PRIME MISSION                 2016-06-19T12:00                       
  CERES EXTENDED MISSION               2016-06-19T12:00  2017-07-01T00:00     
   CERES EXTENDED LAMO (CXL)           2016-06-19T12:00  2016-09-02T12:00     
   CERES TRANSFER TO JULING (CTJ)      2016-09-02T12:00  2016-10-10T00:00     
   CERES EXTENDED JULING (CXJ)         2016-10-10T00:00  2016-11-03T12:00     
   CERES TRANSFER TO GRAND (CTG)       2016-11-03T12:00  2016-12-14T00:00     
   CERES EXTENDED GRAND (CXG)          2016-12-14T00:00  2017-02-23T00:00     
   CERES TRANSFER TO OPPOSITION (CTO)  2017-02-23T00:00  2017-04-28T00:00     
   CERES EXTENDED OPPOSITION (CXO)     2017-04-28T00:00  2017-07-01T00:00     
  END OF CERES EXTENDED MISSION       (2017-06-30T23:59)                      
The following mission phase activities are summarized from the Dawn           
Dawn Science Plan (Raymond 2007).                                             
Initial Checkout (ICO) - ICO covered the 60-day period following launch       
and was used to turn on and perform initial checkout of the instruments.      
Only a minimal set of instrument checkout activities were performed           
during ICO to minimize interference with critical spacecraft checkouts.       
Cruise Phases - Seven days of non-thrusting periods per year were             
designated for science calibration activities.  These periods were            
used to perform functional, performance, and calibration tests of the         
instruments using stellar and planetary targets.  During cruise,              
GRaND measures the response to galactic cosmic rays and energetic             
particles in the space environment, characterizing the background             
Mars Gravity Assist (MGA) - The purpose of MGA was to add energy to the       
spacecraft trajectory to ensure adequate mass and power margins for           
the designated trajectory.   In addition, the MGA provided an                 
opportunity for instrument calibration, a readiness exercise for              
Vesta operations, an absolute calibration of GRaND, and an                    
extended source for calibrating VIR and FC.  VIR could have obtained          
scientifically valuable spectroscopy.  GRaND acquired data for direct         
comparison with data from 2001 Mars Odyssey, enabling cross calibration       
during flight.  Fortunately, none of the data gathered at Mars were critical  
to achieving the goals of the mission. The spacecraft safed shortly after     
Mars closest approach. Only a number of images and a few minutes of resolved  
GRaND data were recoverable - no VIR spectra were recovered.                  
Both Vesta are Ceres were intentionally mapped in very similar fashion. This  
both reduced planning efforts and results in similar scientific products that 
hopefully facilitates comparison of the two bodies.                           
Approach Phases - During the Vesta Approach phase the instruments             
go through complete calibration, repeating some of the activities             
that were done during the post-launch checkout calibration period,            
including annealing GRaND.  The design of the Vesta and Ceres                 
approach activities were similar, although scaled to the different            
body sizes. For both Vesta and Ceres approach phases, the FC collected        
rotation characterization (RC) maps and VIR obtained full-disc spectra        
coincident with the RCs.  The RC maps were used to accurately determine the   
pole positions of the bodies in order to get into nearly polar orbits.        
Data obtained in both approach phases provided a range of illumination angles 
to initialize the topographic model, and data to aid in finalizing            
the plans for HAMO and LAMO.  For both bodies, the final RC (RC3) was targeted
at a radius where the full disk just fit within the FC2 FOV. At Vesta, this   
occurred at a radius of ~5500 km and at Ceres it was ~14,000 km. During both  
approach phases several searches for hazards (dust, moons) were performed in  
the near-asteroid environment.  An additional activity in the Vesta Approach  
phase was to exercise the processing streams for the instruments' data, mainly
the FC and VIR, to verify that quicklook products could be produced on        
the required timelines, and to check and improve the calibration              
Survey Orbits - The goals for the Vesta and Ceres Survey orbits were          
to obtain global coverage with VIR, and to create overlapping global          
images with the FC2 in multiple filters.  The VIR Survey maps constitute the  
primary global reference set.  The VIR and FC2 global maps were used for      
defining targets to be investigated at lower altitudes, and the FC data       
contribute significantly to the topographic models.  Cross-calibration of the 
VIR and FC was facilitated by concurrent imaging during this phase.           
High Altitude Mapping Orbits (HAMO) - HAMO was used primarily to              
create global FC2 maps of the illuminated surface of the body. HAMO altitudes 
were selected to provide full global maps in a small number of orbits with    
sufficient resolution of meet our Level 1 requirements for topography in both 
horizontal and vertical dimensions. For Vesta, a full mapping (Cycle) was     
completed in 10 orbits at a radius of ~950 km. At Ceres, the Dawn resolution  
requirements were half the values for Vesta so the orbit radius was increased 
to ~1950 km and 12 orbits were required to complete a cycle. Color filter data
were acquired at or near nadir for two complete mapping cycles. This provided 
redundancy so that it was not necessary to recover individual lost images or  
orbits. Clear filter data were acquired in both nadir and off-nadir attitudes 
to meet the topography requirements. Fixed off-nadir attitudes were flown for 
complete mapping cycles. Different off-nadir angles were selected for each of 
the cycles in order to support both SPG (stereo) and SPC (clinometry)         
topographic analysis. VIR also collected as much data as could be supported by
our downlink ability during HAMO. The various off-nadir angles allowed        
different latitude bands to be efficiently mapped at both Vesta and Ceres.    
VIR collected several times the minimum requirement of at least 5000 frames   
in the HAMO orbits where it sampled the spectral variability at smaller scales
than the global survey map. At the HAMO altitudes, the GRaND instrument begins
to see particles originating from the target body, in addition to the cosmic  
Low Altitude Mapping Orbit (LAMO) - The purpose of LAMO was to obtain         
spatially resolved neutron and gamma ray spectra of each asteroid, and get    
global tracking coverage to determine the gravity field. There were no        
Level-1 requirements to collect any images or VIR spectra at the LAMO         
altitudes at either Vesta or Ceres. However, Dawn collected as much FC2       
and VIR nadir imaging as could be fit into the data buffers. In general,      
during LAMO, the spacecraft needed to be pointed at nadir to meet the         
GRaND requirements. There were no off-nadir images, and very few color        
filter images acquired at Vesta in the LAMO orbit. At Ceres, Dawn was able    
to extend the duration of LAMO by conserving fuel. Once GRaND had met its     
Level-1 requirements and FC completed a clear filter map at nadir, Dawn began 
to acquire some targeted color images and eventually some off-nadir mapping   
cycles. The orbit of Dawn was extremely difficult to predict so most of the   
Ceres color imaging and targeted VIR cubes did not fully cover the planned    
targets in LAMO. Off-nadir coverage in LAMO was insuffient to allow high      
resolution global shape models to be produced but a few regional models       
can be created for selected targets (Occator, etc.).                          
HAMO-2 (Vesta) Dawn arrived at Vesta just before the southern summer and the  
obliquity of the orbit prevented the illumination of the northern hemisphere  
above about 30 degrees latitude. A short extended mission at Vesta was        
negotiated with NASA that allowed Dawn to delay its Ceres arrival date and    
expected end-of-mission. Dawn used this time at Vesta to extend the LAMO phase
and add a second HAMO during the spiral out to Ceres.  During the 2nd HAMO    
the subsolar latitude had moved nearly to the equator and Dawn was able to    
map nearly all of the northern hemisphere with the FC2 and greatly extend     
the VIR coverage at HAMO resolution. HAMO-2 was flown at the same radius as   
Ceres Extended Mission                                                        
Dawn was allowed to extend its mission at Ceres for roughly one year in       
order to acquire key data that were not acquired during the prime mission.    
The extended mission included three additional mapping cycles at the LAMO     
altitude in order to collect VIR spectra over high value targets Occator and  
Juling that were unsuccessfully observed in the prime mission.  In addition,  
off-nadir clear filter images were acquired to add to the high resolution     
topography and persistently shadowed region data sets. Additional GRaND and   
gravity data were also acquired. This first extended mission phase is referred
to as eXtended Mission Orbit 1 (XMO1) or Ceres eXtended LAMO (CXL).           
As soon as it was possible, the spacecraft was moved to a higher altitude     
(XMO2) as quickly as possible to conserve fuel. Dawn maintained an altitude   
that was very similar to the Prime Mission HAMO altitude for about three      
weeks. At this altitude, the VIR instrument observed Juling under a variety of
local time and illumination conditions while the camera acquired additional   
clear and color filter data and data in the persistently shadowed regions.    
This phase is also referred to as Ceres eXtended Juling or CXJ.               
After the Juling observations were complete, the spacecraft altitude was      
raised again as quickly as possible so that GRaND could acquire the long      
duration background data necessary to properly calibrate the LAMO data.       
This orbit is called XMO3 and the phase is referred to as CXG (for GRaND). At 
this radius (~8000 - 9500 km, elliptical), Dawn acquired several full         
rotation observations to look for surface changes since RC3. In the prime     
mission when the orbit altitude was lowered, it was done in a very controlled 
fashion in order to maintain a circular orbit with a desired period. During   
the extended mission ascent, the 'fast as possible' raising of the altitude   
in order to conserve fuel led to elliptical mapping orbits.                   
Finally, the orbit altitude was raised into a very elliptical orbit with      
apoapsis high enough to allow the orbit plane to be changed by 90 degrees     
(~55,000 km). This maneuver was performed so that Ceres could be observed at  
opposition (zero phase) on the inbound leg at an altitude near 20,000 km.     
This last orbit is called XMO4 and the mission phase is CXO (Opposition).     
De Sanctis, M. C., A. Coradini, E. Ammannito, G. Filacchione, M.T. Capria,    
S. Fonte, G. Magni, A. Barbis, A. Bini, M. Dami, I. Ficai-Veltroni, and       
G. Preti, VIR Team, The VIR Spectrometer, Space Sci Rev,                      
doi:10.1007/s11214-010-9668-5, 2010.                                          
A. Coradini, D. Turrini, C. Federico, G. Magni, Vesta and Ceres: crossing     
the history of the Solar system. Space Sci. Rev., 2011.                       
Prettyman, T.H. and W.C. Feldman, PDS Data Processing:  Gamma Ray and         
Neutron Detector, version 5.0, Feb. 1, 2012.  [Archived as a document         
in the Dawn GRaND Calibrated Mars Flyby data set,                             
Prettyman, T.H., W.C. Feldman, F.P. Ameduri, B.L. Barraclough, E.W.           
Cascio, K.R. Fuller, H.O. Funsten, D.J. Lawrence, G.W. McKinney,              
C.T. Russell, S.A. Soldner, S.A. Storms, C. Szeles, and R.L. Tokar,           
Gamma-ray and neutron spectrometer for the Dawn mission to 1 Ceres and        
4 Vesta, IEEE Transactions on Nuclear Science Volume: 50, Issue: 4, 1,        
August 2003B, pp. 1190-1197.                                                  
Rayman, M.D., T.C. Fraschetti, C.A. Raymond, and C.T. Russell, Dawn:          
A mission in development for exploration of main belt asteroids               
Vesta and Ceres, Acta Astronautica 58, 605-616, 2006.                         
Raymond, C.A., Dawn Science Plan, JPL D-31827, 2007. [A copy of this          
document is included in the /DOCUMENT directory of each of the Dawn           
archive volumes.]                                                             
Schroeder, S.E. and P. Gutierrez-Marques, Calibration Pipeline, MPS           
report DA-FC-MPAE-RP-272, Issue 2, Rev. a, 20 July 2011. [A copy of           
this document is included in the /DOCUMENT directory of the Dawn FC1          
and FC2 archive archive volumes.]
Mission Objectives Overview                                                 
The specific Dawn science objectives by instrument are as follows.            
Framing Camera                                                                
1. To determine the origin and evolution of Vesta and Ceres by mapping        
the extent of geologic processes on the asteroid surfaces, and by using       
the cratering record to establish a relative chronology of the crustal        
units and population of impactors in the early solar system.                  
2. To map the shape, determine the spin state, and establish the degree       
of cratering of the asteroids visited.                                        
3. To map the topography of Vesta and Ceres.                                  
4. To search for dust and satellites in the environment of the                
asteroids visited.                                                            
5. To provide a geologic, compositional and geophysical context for           
the HED meteorites.                                                           
6. To provide an opportunity to identify Ceres-derived meteorites             
in their geologic context.                                                    
Visible and Infrared Mapping Spectrometer                                     
1. To provide a geologic, compositional and geophysical context for           
the HED meteorites.                                                           
2. To provide an opportunity to identify Ceres-derived meteorites in          
their geologic context.                                                       
3. To map the thermophysical properties of Vesta and Ceres.                   
4. To determine the origin and evolution of Vesta and Ceres by                
mapping the mineralogical composition and its spatial variation               
across the asteroidal surface.                                                
Gamma Ray and Neutron Detector                                                
1. To map the major elemental composition of O, Si, Fe, Mg, Ti, Al,           
Ca, and H on Vesta and Ceres.                                                 
2. To map the trace elements U, Th, K, Gd and Sm on Vesta and Ceres.          
3. To provide a geologic, compositional and geophysical context for           
the HED meteorites.                                                           
Gravity science                                                               
1. To determine the masses of the asteroids visited.                          
2. To measure the bulk density of Vesta and Ceres, in conjunction             
with topography, and determine its heterogeneity.                             
3. To determine the gravitational fields of Vesta and Ceres.                  
The above science goals are extracted from the Dawn Science Plan              
(Raymond 2007).  Specific science measurement requirements necessary          
to meet the stated science goals are outlined in the same document,           
as well as in Rayman et al. (2006).