 Artist's impression ofStardust collecting dust particles from Comet Wild 2 | |||||||||||||
| Names | Discovery 4 Stardust-NExT | ||||||||||||
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| Mission type | Sample return | ||||||||||||
| Operator | NASA / JPL | ||||||||||||
| COSPAR ID | 1999-003A | ||||||||||||
| SATCATno. | 25618 | ||||||||||||
| Website | solarsystem.nasa.gov | ||||||||||||
| Mission duration | Stardust: 6 years, 11 months, 8 days NExT: 4 years, 2 months, 7 days Total: 12 years, 1 month, 17 days | ||||||||||||
| Spacecraft properties | |||||||||||||
| Bus | SpaceProbe[1] | ||||||||||||
| Manufacturer | Lockheed Martin University of Washington | ||||||||||||
| Launch mass | 385 kg (849 lb)[2] | ||||||||||||
| Dry mass | 305.397 kg (673.29 lb)[3] | ||||||||||||
| Dimensions | Bus: 1.71 × 0.66 × 0.66 m[1] (5.6 × 2.16 × 2.16 ft) | ||||||||||||
| Power | 330 W (Solar array /NiH2 batteries) | ||||||||||||
| Start of mission | |||||||||||||
| Launch date | 7 February 1999, 21:04:15.238 (1999-02-07UTC21:04:15) UTC[4] | ||||||||||||
| Rocket | Delta II 7426-9.5 D-266 | ||||||||||||
| Launch site | Cape CanaveralSLC-17 | ||||||||||||
| Contractor | Lockheed Martin Space Systems | ||||||||||||
| End of mission | |||||||||||||
| Disposal | Decommissioned | ||||||||||||
| Deactivated | Spacecraft: 24 March 2011, 23:33 (2011-03-24UTC23:34) UTC[5] | ||||||||||||
| Landing date | Capsule: 15 January 2006, 10:12 UTC[6] | ||||||||||||
| Landing site | Utah Test and Training Range 40°21.9′N113°31.3′W / 40.3650°N 113.5217°W /40.3650; -113.5217 | ||||||||||||
| Flyby ofEarth | |||||||||||||
| Closest approach | 15 January 2001, 11:14:28 UTC | ||||||||||||
| Distance | 6,008 km (3,733 mi) | ||||||||||||
| Flyby of asteroid5535 Annefrank | |||||||||||||
| Closest approach | 2 November 2002, 04:50:20 UTC[7] | ||||||||||||
| Distance | 3,079 km (1,913 mi)[7] | ||||||||||||
| Flyby ofWild 2 | |||||||||||||
| Closest approach | 2 January 2004, 19:21:28 UTC[7] | ||||||||||||
| Distance | 237 km (147 mi)[7] | ||||||||||||
| Flyby ofEarth (Sample return) | |||||||||||||
| Closest approach | 15 January 2006 | ||||||||||||
| Flyby ofEarth | |||||||||||||
| Closest approach | 14 January 2009, 12:33 UTC | ||||||||||||
| Distance | 9,157 km (5,690 mi) | ||||||||||||
| Flyby of9P/Tempel | |||||||||||||
| Closest approach | 15 February 2011, 04:39:10 UTC[8] | ||||||||||||
| Distance | 181 km (112 mi)[9] | ||||||||||||
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Stardust was a 385-kilogramroboticspace probe launched byNASA on 7 February 1999. Its primary mission was to collect dust samples from thecoma ofcometWild 2, as well as samples ofcosmic dust, and return them to Earth for analysis. It was the firstsample return mission of its kind. En route to Comet Wild 2, it also flew by and studied theasteroid5535 Annefrank. The primary mission was successfully completed on 15 January 2006 when the sample return capsule returned to Earth.[10]
A mission extension, codenamedNExT, culminated in February 2011 withStardust intercepting CometTempel 1, asmall Solar System body previously visited byDeep Impact in 2005.Stardust ceased operations in March 2011.
On 14 August 2014, scientists announced the identification of possibleinterstellar dust particles from theStardust capsule returned to Earth in 2006.[11][12][13][14]
Beginning in the 1980s, scientists began seeking a dedicated mission to study a comet. During the early 1990s, several missions to studyComet Halley became the first successful missions to return close-up data. However, the US cometary mission,Comet Rendezvous Asteroid Flyby, was canceled for budgetary reasons. In the mid-1990s, further support was given to a cheaper,Discovery-class mission that would study Comet Wild 2 in 2004.[1]
Stardust was competitively selected in the fall of 1995 as a NASA Discovery Program mission of low-cost with highly focused science goals.[1]: 5 Construction ofStardust began in 1996, and was subject to the maximum contamination restriction, level 5planetary protection. However, the risk of interplanetary contamination by alien life was judged low,[15] as particle impacts at over 450 metres per second (1,000 mph), even intoaerogel, were believed to be terminal for any known microorganism.[1]: 22–23
CometWild 2 was selected as the primary target of the mission for the rare chance to observe a long-period comet that has ventured close to theSun. The comet has since become a short period comet after an event in 1974, where the orbit of Wild 2 was affected by the gravitational pull ofJupiter, moving the orbit inward, closer to the Sun. In planning the mission, it was expected that most of the original material from which the comet formed would still be preserved.[1]: 5
The primary science objectives of the mission included:[7]
The spacecraft was designed, built and operated byLockheed Martin Astronautics as a Discovery-class mission in Denver, Colorado. JPL provided mission management for the NASA division for mission operations. The principal investigator of the mission was Dr. Donald Brownlee from the University of Washington.[1]: 5
The spacecraft bus measured 1.7 meters (5 ft 7 in) in length, and 0.66 meters (2 ft 2 in) in width, a design adapted from the SpaceProbe deep space bus developed byLockheed Martin Astronautics. The bus was primarily constructed withgraphite fiber panels with an aluminum honeycomb support structure underneath; the entire spacecraft was covered with polycyanate,Kapton sheeting for further protection. To maintain low costs, the spacecraft incorporated many designs and technologies used in past missions or previously developed for future missions by the Small Spacecraft Technologies Initiative (SSTI). The spacecraft featured five scientific instruments to collect data, including theStardust Sample Collection tray, which was brought back to Earth for analysis.[16]
The spacecraft wasthree-axis stabilized with eight 4.41 Nhydrazinemonopropellantthrusters, and eight 1 N thrusters to maintainattitude control (orientation); necessary minor propulsion maneuvers were performed by these thrusters as well. The spacecraft was launched with 80 kilograms of propellant. Information for spacecraft positioning was provided by astar camera using FSW to determine attitude (Stellar Compass), aninertial measurement unit, and twoSun sensors.[1]: 30–31 [16] The Stellar Compass software was provided by Intelligent Decisions, Inc.
For communicating with theDeep Space Network, the spacecraft transmitted data across theX-band using a 0.6-meter (2 ft 0 in) parabolichigh-gain antenna, medium-gain antenna (MGA) and low-gain antennas (LGA) depending on mission phase, and a 15-watttransponder design originally intended for theCassini spacecraft.[1]: 32 [16]
The probe was powered by twosolar arrays, providing an average of 330 watts of power. The arrays also includedWhipple shields to protect the delicate surfaces from the potentially damaging cometary dust while the spacecraft was in the coma of Wild 2. The solar array design was derived primarily from the Small Spacecraft Technology Initiative (SSTI) spacecraft development guidelines. The arrays provided a unique method of switching strings from series to parallel depending on the distance from the Sun. A singlenickel–hydrogen (NiH2) battery was also included to provide the spacecraft with power when the solar arrays received too little sunlight.[1]: 31 [16]
The computer on the spacecraft operated using aradiation-hardenedRAD6000 32-bit processor card. Forstoring data when the spacecraft was unable to communicate with Earth, the processor card was able to store 128 megabytes, 20% of which was occupied by the flight system software. The system software is a form ofVxWorks, anembedded operating system developed byWind River Systems.[1]: 31 [16]
| Navigation Camera (NC) | |||
 | The camera is intended for targeting comet Wild 2 during the flyby of the nucleus. It captures black and white images through a filter wheel making it possible to assemble color images and detect certain gas and dust emissions in the coma. It also captures images at variousphase angles, making it possible to create a three-dimensional model of a target to better understand the origin, morphology, and mineralogical inhomogeneities on the surface of the nucleus. The camera utilizes the optical assembly from theVoyager Wide Angle Camera. It is additionally fitted with a scanning mirror to vary the viewing angle and avoid potentially damaging particles. For environmental testing and verification of the NAVCAM the only remaining Voyager spare camera assembly was used as a collimator for testing of the primary imaging optics. A target at the focal point of the spare was imaged through the optical path of the NAVCAM for verification.[17][18]
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| Cometary and Interstellar Dust Analyzer (CIDA) | |||
 | The dust analyzer is amass spectrometer able to provide real-time detection and analysis of certain compounds and elements. Particles enter the instrument after colliding with asilverimpact plate and traveling down a tube to the detector. The detector is then able to detect the mass of separate ions by measuring the time taken for each ion to enter and travel through the instrument. Identical instruments were also included onGiotto andVega 1 and 2.[19][20]
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| Dust Flux Monitor Instrument (DFMI) | |||
 | Located on theWhipple shield at the front of the spacecraft, the sensor unit provides data regarding the flux and size distribution of particles in the environment around Wild 2. It records data by generating electric pulses as a special polarized plastic (PVDF) sensor is struck by high energy particles as small as a few micrometers.[21][22]
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| Stardust Sample Collection (SSC) | |||
 | The particle collector usesaerogel, a low-density, inert, microporous, silica-based substance, to capture dust grains as the spacecraft passes through the coma of Wild 2. After sample collection was complete, the collector receded into the Sample Return Capsule for entering the Earth's atmosphere. The capsule with encased samples would be retrieved from Earth's surface and studied.[23][24]
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| Dynamic Science Experiment (DSE) | |||
The experiment will primarily utilize theX band telecommunications system to conduct radio science on Wild 2, to determine the mass of the comet; secondarily the inertial measurement unit is utilized to estimate the impact of large particle collisions on the spacecraft.[25][26]
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Comet and interstellar particles are collected in ultra low densityaerogel. Thetennis racket-sized collector tray contained ninety blocks of aerogel, providing more than 1,000 square centimeters of surface area to capturecometary andinterstellar dust grains.
To collect the particles without damaging them, asilicon-based solid with a porous,sponge-like structure is used in which 99.8 percent of the volume is empty space. Aerogel has1⁄1000 the density ofglass, another silicon-based solid to which it may be compared. When a particle hits the aerogel, it becomes buried in the material, creating a long track, up to 200 times the length of the grain. The aerogel was packed in an aluminium grid and fitted into a Sample Return Capsule (SRC), which was to be released from the spacecraft as it passed Earth in 2006.
To analyze the aerogel for interstellar dust, one million photographs will be needed to image the entirety of the sampled grains. The images will bedistributed to home computer users to aid in the study of the data using a program titled,Stardust@home. In April 2014, NASA reported they had recovered seven particles of interstellar dust from the aerogel.[27]
Stardust was launched carrying two sets of identical pairs of square 10.16-centimeter (4 in) siliconwafers. Each pair featured engravings of well over one million names of people who participated in the public outreach program by filling out internet forms available in late 1997 and mid-1998. One pair of the microchips was positioned on the spacecraft and the other was attached to the sample return capsule.[1]: 24
Stardust was launched at 21:04:15 UTC on 7 February 1999, by theNational Aeronautics and Space Administration fromSpace Launch Complex 17A at theCape Canaveral Air Force Station in Florida, aboard aDelta II 7426 launch vehicle. The complete burn sequence lasted for 27 minutes bringing the spacecraft into a heliocentric orbit that would bring the spacecraft around theSun and pastEarth for agravity assist maneuver in 2001, to reach asteroid5535 Annefrank in 2002 andComet Wild 2 in 2004 at a low flyby velocity of 6.1 km/s. In 2004, the spacecraft performed a course correction that would allow it to pass by Earth a second time in 2006, to release the Sample Return Capsule for a landing in Utah in theBonneville Salt Flats.[1]: 14–22 [7]
During the second encounter with Earth, the Sample Return Capsule was released on Jan 15, 2006.[7] Immediately afterwards,Stardust was put into a "divert maneuver" to avoid entering the atmosphere alongside the capsule. Under twenty kilograms of propellant remained onboard after the maneuver.[7] On 29 January 2006, the spacecraft was put in hibernation mode with only the solar panels and receiver active, in a 3-yearheliocentric orbit that would return it to Earth vicinity on 14 January 2009.[7][28]
A subsequent mission extension was approved on 3 July 2007, to bring the spacecraft back to full operation for a flyby ofComet Tempel 1 in 2011. The mission extension was the first to revisit asmall Solar System body and used the remaining propellant, signaling the end of the useful life for the spacecraft.[29]
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At 04:50:20 UTC on 2 November 2002,Stardust encountered asteroid 5535 Annefrank from a distance of 3,079 km (1,913 mi).[7] The solar phase angle ranged from 130 degrees to 47 degrees during the period of observations. This encounter was used primarily as an engineering test of the spacecraft and ground operations in preparation for the encounter with Comet Wild 2 in 2003.[7]
At 19:21:28 UTC, on 2 January 2004,Stardust encounteredComet Wild 2[34] on the sunward side with a relative velocity of 6.1 km/s at a distance of 237 km (147 mi).[7] The original encounter distance was planned to be 150 km (93 mi), but this was changed after a safety review board increased the closest approach distance to minimize the potential for catastrophic dust collisions.[7]
The relative velocity between the comet and the spacecraft was such that the comet actually overtook the spacecraft from behind as they traveled around the Sun. During the encounter, the spacecraft was on the Sunlit side of the nucleus, approaching at a solar phase angle of 70 degrees, reaching a minimum angle of 3 degrees near closest approach and departing at a phase angle of 110 degrees.[7] TheAutoNav software was used during the flyby.[35]: 11
During the flyby the spacecraft deployed the Sample Collection plate to collectdust grain samples from thecoma, and took detailed pictures of the icynucleus.[36]
On 19 March 2006,Stardust scientists announced that they were considering the possibility of redirecting the spacecraft on a secondary mission to imageComet Tempel 1. The comet was previously the target of theDeep Impact mission in 2005, sending an impactor into the surface. The possibility of this extension could be vital for gathering images of the impact crater whichDeep Impact was unsuccessful in capturing due to dust from the impact obscuring the surface.
On 3 July 2007 the mission extension was approved and renamedNew Exploration of Tempel 1 (NExT). This investigation would provide the first look at the changes to a comet nucleus produced after a close approach to the Sun. NExT also would extend the mapping of Tempel 1, making it the most mapped comet nucleus to date. This mapping would help address the major questions of comet nucleus geology. The flyby mission was expected to consume almost all of the remaining fuel, signaling the end of the operability of the spacecraft.[29] TheAutoNav software (for autonomous navigation) would control the spacecraft for the 30 minutes prior to encounter.[37]
The mission objectives included the following:[37]
At 04:39:10 UTC on 15 February 2011,Stardust-NExT encountered Tempel 1 from a distance of 181 km (112 mi).[8][9] An estimated 72 images were acquired during the encounter. These showed changes in the terrain and revealed portions of the comet never seen byDeep Impact.[38] The impact site fromDeep Impact was also observed, though it was barely visible due to material settling back into the crater.[39]
On 24 March 2011 at approximately 23:00 UTC,Stardust conducted a burn to consume its remaining fuel.[33] The spacecraft had little fuel left and scientists hoped the data collected would help in the development of a more accurate system for estimating fuel levels on spacecraft. After the data had been collected, no further antenna aiming was possible and the transmitter was switched off. The spacecraft sent an acknowledgement from approximately 312 million km (194 million mi) away in space.[5]
On 15 January 2006, at 05:57 UTC, the Sample Return Capsule successfully separated fromStardust. The SRC re-entered the Earth's atmosphere at 09:57 UTC,[40] with a velocity of 12.9 km/s, the fastest reentry speed into Earth's atmosphere ever achieved by a human-made object.[41] The capsule followed a drastic reentry profile, going from a velocity of Mach 36 to subsonic speed within 110 seconds.[42][failed verification] Peakdeceleration was 34 g,[43] encountered 40 seconds into the reentry at an altitude of 55 km overSpring Creek, Nevada.[42] Thephenolic-impregnated carbon ablator (PICA)heat shield, produced by Fiber Materials Inc., reached a temperature of more than 2,900 °C during this steep reentry.[44] The capsule then parachuted to the ground, finally landing at 10:12 UTC at theUtah Test and Training Range, near the U.S. ArmyDugway Proving Ground.[6][45] The capsule was then transported by military aircraft from Utah toEllington Air Force Base inHouston,Texas, then transferred by road in an unannounced convoy to the Planetary Materials Curatorial facility atJohnson Space Center in Houston to begin analysis.[7][46]
The sample container was taken to aclean room with a cleanliness factor 100 times that of a hospital operating room to ensure the interstellar and comet dust was not contaminated.[47] Preliminary estimations suggested at least a million microscopic specks of dust were embedded in theaerogel collector. Ten particles were found to be at least 100 micrometers (0.1 mm) and the largest approximately 1,000 micrometers (1 mm). An estimated 45 interstellar dust impacts were also found on the sample collector, which resided on the back side of the cometary dust collector. Dust grains are being observed and analyzed by a volunteer team through thecitizen science project,Stardust@Home.
The combined mass of the harvested sample was approximately 1 mg.[48]
In December 2006, seven papers were published in the scientific journalScience, discussing initial details of the sample analysis. Among the findings are: a wide range oforganic compounds, including two that contain biologically usablenitrogen; indigenousaliphatic hydrocarbons with longer chain lengths than those observed in the diffuseinterstellar medium; abundant amorphoussilicates in addition to crystalline silicates such asolivine andpyroxene, proving consistency with the mixing ofSolar System and interstellar matter, previously deducedspectroscopically from ground observations;[49] hydrous silicates and carbonate minerals were found to be absent, suggesting a lack of aqueous processing of the cometary dust; limited pure carbon (CHON)[clarification needed] was also found in the samples returned;methylamine andethylamine was found in the aerogel but was not associated with specific particles.
In 2010, Dr. Andrew Westphal announced thatStardust@home volunteer Bruce Hudson found a track (labeled "I1043,1,30") among the many images of the aerogel that may contain an interstellar dust grain.[50] The program allows for any volunteer discoveries to be recognized and named by the volunteer. Hudson named his discovery "Orion".[51]
In April 2011, scientists from theUniversity of Arizona discovered evidence for the presence of liquid water in CometWild 2. They have found iron andcopper sulfide minerals that must have formed in the presence of water. The discovery shatters the existing paradigm that comets never get warm enough to melt their icy bulk.[52] In the spring of 2014, the recovery of particles of interstellar dust from the Discovery program's Stardust mission was announced.[53]
The Stardust samples are currently available for everyone to identify after completing the training at Berkeley webpage.[54]
The return capsule is currently located at theNational Air and Space Museum inWashington, D.C. It began exhibition there on 1 October 2008, the 50th anniversary of the establishment of NASA. The return capsule is displayed in sample collection mode, alongside a sample of the aerogel used to collect samples.[55]
The comet samples show that the outer regions of the earlySolar System were not isolated and were not a refuge where interstellar materials could commonly survive.[56] The data suggest that high-temperature inner Solar System material formed and was subsequently transferred to theKuiper belt.[57]
In 2009 it was announced byNASA that scientists had identified one of the fundamental chemical building blocks of life in a comet for the first time:glycine, an amino acid, was detected in the material ejected from Comet Wild 2 in 2004 and captured by theStardust probe. Glycine has been detected in meteorites before and there are also observations in interstellar gas clouds, but theStardust find is described as a first in cometary material. Isotope analysis indicates that theLate Heavy Bombardment included cometary impacts after the Earth coalesced but before life evolved.[58] Carl Pilcher, who leads NASA's Astrobiology Institute commented that "The discovery of glycine in a comet supports the idea that the fundamental building blocks of life are prevalent in space, and strengthens the argument that life in the universe may be common rather than rare."[59]
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