Everything about Dawn Spacecraft totally explained
Dawn, launched on
September 27 2007, is a
robotic spacecraft being sent by
NASA on a
space exploration mission to the two most massive members of the
asteroid belt: the asteroid
Vesta and the
dwarf planet Ceres.
Dawn is scheduled to explore Vesta between 2011 and 2012, and Ceres in 2015. It will be the first spacecraft to visit either body.
Dawn is unusual in that it'll be the first spacecraft to enter into orbit around a celestial body, study it, and then re-embark under
powered flight to proceed to a second target. All previous multi-target study missions - such as the
Voyager program - have involved rapid
planetary flybys.
Launch
Dawn was scheduled to launch from
pad 17-B at the
Cape Canaveral Air Force Station on a
Delta 7925-H rocket. On
April 10,
2007,
Dawn arrived at the Astrotech Space Operations subsidiary of
SPACEHAB, Inc. in
Titusville, Florida, where it was prepared for launch. Launch was originally scheduled for
20 June, but was delayed until
30 June due to delays with part deliveries. A broken crane at the launch pad, used to raise the solid rocket boosters, delayed the launch for a week, until
7 July, but on
June 15 the second stage was successfully hoisted into position.
A mishap at the Astrotech Space Operations facility, involving slight damage to one of the solar arrays, didn't have an effect on the launch date, however bad weather caused the launch to slip to
8 July. Range tracking problems then delayed the launch to
9 July, and then
15 July, before the launch was delayed further to avoid knock-on delays with the
Phoenix mission to Mars, which was successfully launched on
4 August.
Launch of
Dawn was then rescheduled for
September 26,
2007. However the launch was then delayed to
27 September, due to bad weather delaying fuelling of the second stage, the same problem which had earlier delayed the
7 July launch attempt. The launch window extended from 7:20 a.m. - 7:49 a.m. EDT (11:20 - 11:49
GMT). During the final built-in hold at T-4 minutes, a ship entered the exclusion area offshore, the sea strip where the rocket boosters are likely to fall after separation. The ship was commanded to leave the area, then the launch had to wait for the end of a collision avoidance window with the
ISS. The spacecraft finally launched at 7:34 a.m. EDT from pad 17-B on a Delta II launch vehicle.
Mission
The mission's goal is to characterise the conditions and processes of the
solar system's earliest epoch by investigating in detail two of the largest
protoplanets remaining intact since their formation. Ceres and Vesta have many contrasting characteristics that are thought to have resulted from them forming in two different regions of the early solar system; Ceres is theorized to have experienced a "cool and wet" formation that may have left it with subsurface water, and Vesta is theorised to have experienced a "hot and dry" formation that resulted in a differentiated interior and surface
volcanism.
Using a framing
camera along with two redundant cameras, a visual and
infared spectrometer, and a
Gamma Ray and
Neutron Spectrometer, Dawn will take pictures and measure the chemical composition of Ceres and Vesta.
To cruise from
Earth to its targets it'll travel in a long outward
spiral. The current estimated chronology is as follows:
An extended mission in which Dawn explores other asteroids after Ceres is also possible, although unlikely.
Mission team
The Dawn mission team is led by
UCLA space scientist and Dawn Principal Investigator
Christopher T. Russell. Michael Mook is the Dawn Program Manager at
Orbital Sciences Corporation, which built the spacecraft. Armando Piloto is the Dawn Mission Manager at
Kennedy Space Center. NASA's
Jet Propulsion Laboratory provided the
Ion Propulsion System and management of the overall flight system development. The
German Aerospace Center (DLR) and the
Max Planck Institute for Solar System Research provided the framing camera, the
Italian Space Agency provided the mapping
spectrometer, and the
DOE Los Alamos National Laboratory provided the
gamma ray and
neutron spectrometer.
Motivation
Dawn is intended to study two large asteroids in order to answer questions about the formation of the
solar system.
Ceres and Vesta were chosen as two contrasting
protoplanets, one apparently "wet" (that is,
icy) and the other "dry" (or
rocky), whose accretion was terminated by the formation of
Jupiter. They provide a bridge in our understanding between the formation of rocky planets and the icy bodies of our solar system, and under what conditions a rocky planet can hold water.
The
IAU adopted a new
definition of planet on
August 24 2006, and thus, if the IAU's definition stands and the spacecraft experiences no delays,
Dawn will become the first mission to study a dwarf planet, arriving at Ceres five months prior to the arrival of
New Horizons at
Pluto.
Ceres is a dwarf planet whose mass encompasses about one-third of the total mass of the
asteroids in the
asteroid belt and whose
spectral characteristics suggest a composition similar to that of a water-rich
carbonaceous chondrite. Smaller Vesta, a water-poor
achondrite, has experienced significant heating and
differentiation. It shows signs of a metallic core, a Mars-like density and lunar-like basaltic flows.
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 only three million years. Thermal evolution studies suggest that Ceres must have formed a little later, more than three million years after the formation of
CAIs (the oldest known objects of Solar System origin).
Moreover, Vesta is 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 known as 'vestoids'. Five percent of the found
meteoritic samples on Earth, the
Howardite Eucrite Diogenite ("HED") meteorites, are thought to be the result of a collision or collisions with Vesta.
Mission cancellations and reinstatements
The status of the
Dawn mission has changed several times. In December, 2003, the project was first cancelled, and then reinstated in February, 2004. In October, 2005, work on
Dawn was placed into "stand down" mode. In January, 2006,
Dawn's "stand down" was discussed in the press as "indefinitely postponed", even though NASA had announced no new decisions regarding the mission's status. On
March 2,
2006,
Dawn was publicly, but not formally cancelled by NASA headquarters.
In an unusual step, the cancellation was placed under review, and on
27 March,
2006, it was announced that the mission wouldn't be canceled after all. In the last week of September 2006, the
Dawn mission instrument payload integration reached a full functional status.
Propulsion system
The
Dawn spacecraft is propelled by three
DS1 heritage
xenon ion thrusters (firing only one at a time). They have a
specific impulse of 3100 s and produce a
thrust of 90 mN. The whole spacecraft, including the ion propulsion thrusters, is powered by a 10 kW triple-junction solar array. To get to Vesta,
Dawn will use Xe and another to get to Ceres, out of a total of 425 kg (937 pounds) of on-board propellant. All in all, it'll perform a velocity change of over 10 km/s, far more than any other spacecraft has done.
After initial checkout, during which the ion thrusters accumulated more than 11 days of thrust,
Dawn began long-term cruise propulsion on
2007-12-17.
The Dawn microchip
Onboard
Dawn is a small computer microchip bearing the names of more than 360,000 space enthusiasts. The names were submitted online as part of a public outreach effort between September 2005 and
November 4,
2006. The microchip (about the size of a
nickel) was installed above the forward ion thruster, underneath the spacecraft's High Gain Antenna, on
May 17,
2007. More than one microchip was made, with a back-up copy on display at the
2007 Open House at the
Jet Propulsion Laboratory in
Pasadena, California.
References and notes
Further Information
Get more info on 'Dawn Spacecraft'.
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