Stardust (probe)
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| Mission history | |
|---|---|
| begin | 7.2.1999 |
| Course correction DSM-1 | January 18-22, 2000 |
| Greatest distance from the sun |
02/10/2000 |
| 1. Dust collection phase | 22.2. – 1.5.2000 |
| Standby mode after solar storm |
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| Gravity assist maneuvers | January 15, 2001 |
| Solar conjunction (no radio contact between Stardust and ground station) |
17–31.2001 |
| Course correction DSM-2 | January 18, 2002 |
| 2. Dust collection phase | 5.8. – 9.12.2002 |
| Fly by and photograph the asteroid Annefrank |
2.11.2002 |
| Solar conjunction (no radio contact between Stardust and ground station) |
April 3-18, 2003 |
| Course correction DSM-3 | June 17, 2003 |
| Flyby Wild 2 | 2.1.2004 |
| Course correction DSM-4 | 2.2.2004 |
| Decoupling return capsule | January 15, 2006 |
| Landing return capsule | January 15, 2006 |
| Reactivation for Stardust-NExT | August 13, 2007 |
| Course correction DSM 1 | September 19, 2007 |
| Gravity assist maneuver earth | 14.1.2009 |
| Course correction DSM 2 | February 18, 2010 |
| Flyby and photography 9P / temple | February 15, 2011 |
| The End | March 24, 2011 |
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The spacecraft Stardust ( English for Stardust ) was a mission of NASA , the 1999 started and finished in 2011th The aim of the mission was to capture particles from the coma of the comet Wild 2, discovered by the Swiss astronomer Paul Wild , as well as interstellar dust . The samples were brought to Earth in January 2006. $ 128.4 million was available for the development and construction of the probe as part of the Discovery program for the study of the solar system , and another $ 40 million was used for carrying out the mission. There were also costs for the launcher.
Mission objectives
Comets formed in the outer reaches of the solar system. They presumably still contain the matter from which the planets of our solar system were formed. The investigation of comet matter allows a glimpse into the time when our solar system was formed. Due to the limitations of a probe mission, a return mission with collected samples offers significant advantages over on-site investigations. Specifically, the cometary Stardust samples were expected to provide answers:
- on the mineralogical and chemical composition of comets on a submicrometer scale,
- to what extent comets resemble or differ from meteorites or interplanetary dust in their composition ,
- whether water in comets is exclusively bound in ice or also occurs in hydrated minerals,
- about anomalies of the isotopic composition ,
- on the nature of carbonaceous materials and their relationship with silicates or other minerals.
In 1993, Ulysses first demonstrated that interstellar dust flows through the solar system from the direction of Scorpio . This was confirmed by the Galileo mission in 1994, but astronomical observations only provide very imprecise information about the structure and composition of the dust particles: they are small, largely unstructured particles - one could not even exclude from the measurements, for example that they are toner particles from laser printers. For this reason, the mission's second objective is to collect interstellar dust for answers
- about the chemical composition,
- about the isotope ratios of the important elements such as C , H , Mg , Si and O ,
- about the mineral and structural properties,
- whether all particles have isotope anomalies,
- whether the silicates have a glassy or a crystalline structure and what Si: O ratio they have,
- whether graphite particles are frequent enough to explain the observed 0.22 µm extinction ,
- whether the particles are homogeneous, or z. B. consist of a silicate core with an organic shell,
- whether the particles are largely identical or whether there are different components,
- whether there are indications of change processes, such as B. by sputtering , collisions, aggregation or chemical changes.
By comparing the samples, one can draw conclusions about possible changes in the composition of today's interstellar medium compared to the time the solar system was formed and identify processes during the formation of the solar system. The previous models of the composition of interstellar dust were purely theoretical - the Stardust samples offer the first possibility of comparison with reality.
Mission history
The probe Stardust was launched on February 7, 1999 with a launch vehicle of the type Delta-II-7426 from Launch Complex 17 in Florida and placed in a solar orbit with a two-year orbit period. With a swing-by maneuver, in which the probe gained additional momentum by flying close to Earth in January 2001, the orbit was extended to a two-and-a-half year orbit. With this momentum, the probe completed two orbits of the sun before unlatching the return capsule for reentry when it met again in January 2006.
Due to this orbit characteristic, on the one hand, in addition to minor course corrections, only four orbit maneuvers had to be carried out so that the probe managed with 85 kilograms of fuel . On the other hand, there was enough time to collect sufficient amounts of interstellar dust during the first two orbits of the sun.
On November 9, 2000, Stardust was caught in the fourth strongest solar storm recorded since continuous observations began in 1976. Due to a strong solar flare , the solar wind was 100,000 times stronger than usual, whereby the twelve strongest star points of the navigation cameras, which are used to determine the course, were overlaid by misinterpretable "points" of high-energy protons. The probe then automatically switched to standby mode and waited. After the solar wind had reduced to normal strength on November 11th, the navigation systems were reset . A check of the camera systems showed no damage from the hard particle radiation, and the other on-board systems were still fully functional.
During the second orbit, on November 2, 2002, there was a close flyby of the asteroid 5535 Annefrank , only 3,300 kilometers away. The approach to Annefrank mainly served to prepare and test all systems for the actual objective of the mission Wild 2.
On January 2, 2004, Stardust finally flew at a distance of 240 km and at a relative speed of 6.1 km / s past the comet Wild 2 or through its coma. The comet's nucleus was photographed several times, using a swivel mirror in front of the camera lens to keep the nucleus in the picture. The dust collector collected coma .
Landing the capsule
After the failure of the landing parachute at Genesis in 2004, NASA began intensive research into the causes in order to avoid a similar failure at Stardust as far as possible. After the investigations that were carried out identified a simple manufacturing error as the cause, which should not be present in Stardust, NASA looked confidently towards the scheduled landing of the Stardust capsule.
On January 15, 2006 at 5:57 a.m. UTC , Stardust launched the landing capsule at an altitude of 111,000 km, which a few hours later plunged into the earth's atmosphere at a speed of 46,400 km / h (12.9 km / s), and then hanging on a parachute on the surface of the earth. This was the highest speed ever reached by an artificial object when entering the earth's atmosphere. The mother probe itself fired its engine shortly after the landing capsule was ejected and swerved to remain in a solar orbit.
The landing capsule touched down on January 15, 2006 at 10:12 a.m. UTC (11:12 a.m. CET ) on the premises of a military base in Utah . The capsule that had landed was found shortly afterwards at 10:55 UTC (3:55 a.m. local time) by helicopters using infrared sensors, direction finding and navigation devices to search for the capsule, which was still hot from the deceleration in the atmosphere, in the pitch-black night. The exact landing coordinates were 40 ° 21.9 'N, 113 ° 31.25' W ( ⊙ ).
Extended Stardust-NExT mission
On January 29, 2006, the mother probe was put into a "sleep mode" in which it was to remain indefinitely. Only a few necessary subsystems, such as the solar panels and the receiving antenna, were not switched off in order to enable the probe to be activated at a later point in time. In July 2007, NASA announced that Stardust would be directed towards Comet Temple 1 . This expanded mission was carried out under the name Stardust-NExT (New Exploration of Temple). The probe could only photograph this target and examine it with the help of its instruments.
Temple 1 was the target of the Deep Impact probe in July 2005 . At that time, the probe's impactor was brought to collision with the comet's core, leaving a crater about 20 m deep on its surface. The deep-impact mother probe, which was flying past the comet at the same time, was supposed to take pictures of the resulting crater, but could not do this because the crater was covered by a cloud of leaked material. The impact crater has now been photographed by the Stardust mother probe. To do this, it took a swing-by maneuver with a minimum altitude of 9,157 km around the earth on January 14, 2009 and ignited its engines on February 18, 2010 for 23 minutes. The Temple 1 flyby was on February 14, 2011 EST. On February 15, 04:39 UTC, the probe passed the comet's core at a distance of 181 kilometers at a speed of 10.9 km / s and sent a total of 64 images of the flyby over a distance of 5,000 kilometers. Images shortly before the closest approach show very well the area around the almost 6-year-old impact crater from the Deep Impact Impactor. The aim of the images is to try to identify possible changes on the surface and to examine the crater more closely.
Mission end
In March 2011, the last remaining fuel reserves were ignited until they were used up after 146 seconds. Since no reliable method for measuring the amount of fuel in weightlessness has been developed so far, it was hoped that the data on fuel consumption obtained in this way could be used to derive optimization options for future interplanetary missions. On March 25, 2011 at 12:33 a.m. CET (i.e. March 24, 2011 at 11:33 p.m. UTC), radio contact with the probe was finally broken. At that time she was about 312 million kilometers from Earth and had covered a distance of almost six billion kilometers in the more than twelve years of her mission. Since then, the probe has been in orbit around the sun.
Results
After a visual inspection of the airgel , it was clear that the mission was a success. A total of 45 impacts were visible to the naked eye. In total, over 150 particles were found that were larger than 10 micrometers. Researchers had only one expected such particles. After the particles were removed from the airogels, the systematic evaluation began. To do this, the airgels were cut into thin slices, photographed and evaluated with digital cameras.
Publications of results first concerned the particles that can be assigned to the comet's tail of Wild 2 . The large molecules of polymers that were found , especially the amino acid glycine, deserve special mention . There was also new evidence of the presence of liquid water, not just ice, from this space far from the sun. Liquid water and amino acids are building blocks for the creation of living things .
The search for interstellar dust particles also began. These do not come from comet Wild 2, but from the depths of space. It is hoped to find around 45 such particles, but initial results are only 4 particles. In 2014, evidence for the interstellar origin of 7 particles was presented in a Science article. In order to find these from the abundance of cometary particles, the approx. 1.5 million images have been exhibited since the beginning of August 2006 on a website of the University of Berkeley , where every Internet user can help with the search through the Stardust @ home program. Using a virtual microscope (English Virtual Microscope ) can be analyzed recordings. The project has been in phase 6 since June 2013.
A comet particle (diameter: approx. 2 micrometers)
Close-up of the impact point of a dust particle
Image of a particle trace in the airgel
technology
The probe was built by Lockheed Martin Astronautics and is based on the design of the SpaceProbe deep space bus . A single engine is available for course corrections , which, due to the orbit characteristics of the probe, only requires 85 kilograms of hydrazine (N 2 H 4 ) as fuel. The position of the probe is stabilized in all three axes during the entire flight. The location is determined primarily by determining the position of stars using the navigation camera, additionally during course corrections and the flyby of Wild 2 with acceleration sensors, and as a backup option using sun sensors.
| Crowds | |
|---|---|
| probe | 254 kg |
| Return capsule | 46 kg |
| fuel | 85 kg |
| Total mass | 385 kg |
The central processing unit RAD6000 , which is based on a 32-bit POWER processor, is responsible for the complete control and data processing. 128 megabytes of memory are available on the processor card, 20% of which is used for the operating system and control programs. The rest serves as a buffer for 600 Mbit (75 MB) image data from the navigation camera, 100 Mbit (12.5 MB) data from the dust analyzer and 16 Mbit (2 MB) data from the dust flow analyzer before they are sent to earth. Radio contact is guaranteed via the X-band of the Deep Space Network . Stardust has a 60 centimeter parabolic antenna with 15 watt transmission power, which was developed for the Cassini probe. Two solar panels with a total area of 6.6 m² are used for power supply . A nickel-hydrogen accumulator with 16 Ah is also available for periods of shadowing and phases of high power consumption . The power supply was developed for the Small Spacecraft Technology Initiative (SSTI) . For safety reasons, all components are designed redundantly to compensate for failures.
To protect the probe when it approaches the comet, which takes place at 6.1 km / s, there is a protective shield, the Whipple shield , on the front of the probe . The shield consists of two layers of ceramic material in the area of the solar panels and three layers of ceramic material in the main area of the probe to slow down impacting particles, behind each of these layers a Nextel fabric is attached to absorb the debris from the bumper layers. The structure is able to keep particles up to a size of one centimeter away from the instruments.
The navigation camera is primarily used for optical navigation of the probe while approaching game 2. The distance to the comet's nucleus is precisely determined from the data so that sufficient dust samples can be collected, while the probe also maintains the greatest possible safety distance to minimize the risk. The data of the CCD detector are digitized to 12 bits, read out at 300 kPixels per second and subjected to 12 to 8 bit data compression (dynamic compression).
The camera should also deliver high-resolution images of the comet as it flies by, from which three-dimensional maps of the nucleus are to be calculated. Several filters are available to obtain information about the composition of the coma , the dynamics of gas and dust as well as the jets through recordings at different wavelengths . The camera design is a further development or uses parts and technologies from the Voyager , Pathfinder , MISR , Milstar and Cassini missions.
The optical system has a focal length f of 202 millimeters, an aperture of f / 3.5 and a CCD sensor with 1024 × 1024 pixels. It is designed for the spectral range from 380 to 1,000 nanometers. The resolution is 60 microradians / pixel in a field of view of 3.5 × 3.5 degrees. A scanning mirror is attached in front of the camera optics so that the comet's nucleus can be kept in the camera's field of view during the flyby of Wild 2. For the duration of the direct encounter, the core is observed via a periscope, so that the sensitive camera optics behind the Whipple shield are protected from damage.
Dust flow monitor
The dust flow monitoring system ( D ust F lux M onitor , DFM) consists of the actual dust flow monitor and two additional acoustic impact sensors for the rarer but dangerous impacts of larger particles. The tasks of the system consist of
- the observation of the dust in the vicinity of the probe, in order to be able to better interpret abnormal behavior of the probe.
- the provision of real-time flow measurements of larger coma particles in order to detect possible dangers early on when the probe approaches the comet's comet.
- the measurement of the spatial and temporal changes in the flow of dust particles and their mass distribution during the fly-by of the comet Wild 2.
- the provision of the environmental conditions for the collected dust samples. The dust flow monitor contains a special polarized plastic polyvinylidene fluoride (PVDF) that provides electrical pulse signals when it is hit by small particles at high speed.
The dust flow monitor is a further development of sensors that were used on previous missions. This includes
- the dust counter and mass analyzer of the Vega missions to Comet Halley
- the ERIS Observer instrument which provided excellent data but which is still considered secret (i.e. not yet released)
- the SPADUS instrument ( SPA ce DUS t ) of the ARGOS satellite ( Advanced Research and Global Observation Satellite ) , which was launched in February 1999
- the high flow detector ( H igh R ate D etector , HRD) of the Cassini mission to Saturn, which was started in October 1997th
The dust flow monitor consists of the sensor unit ( S ensor U nit ), the electronics box ( E lectronics B ox ) and the two acoustic sensors. The SU consists of two independent PVDF dust sensors mounted in a frame in front of the Whipple shield. Each sensor is connected to the EB inside the probe with a 1.4 meter cable. The SU provides cumulative and differential flows in a mass range from 10 −11 to 10 −4 grams, as well as cumulative flows for masses over 10 −4 grams.
An acoustic sensor is attached to the first Whipple shield, the second on a rigid carbon fiber-epoxy resin plate on the first Nextel ceiling, which, according to laboratory measurements, is triggered by particles that are at least 1 millimeter in size through the bumper. These sensors are made of a piezoelectric quartz - acoustic transducers , each of the shield converts vibration into electrical signals, which are forwarded to the EB.
Scientific instruments
Dust analyzer
The dust analyzer ( C ometary and I nterstellar D ust A nalyzer , CIDA) examines the dust that falls on the instrument in real time in order to send the data back to earth. The same instrument design was also used for the Giotto probe and the two Vega probes. It is a mass spectrometer that determines the ion masses based on their transit time in the instrument, whereby the functionality is kept very simple. When the dust falls on the target, an electrically charged grid separates ions that move through the instrument, reflect back at the reflector and are caught again by the detector. Here, heavier ions need a longer time from the grid to the detector than lighter ones.
CIDA consists of an inlet opening, a corrugated aluminum foil as the target, the ion extractor, the time-of-flight mass spectrometer and the detector. In contrast to the Giotto mission, the target film does not have to be moved due to the lower dust flow from Wild 2 compared to Halley . In addition, the target area has been increased from 5 cm² to 50 cm².
At 6.1 km / s, the relative speed of the probe when it flies past Wild 2, both ionized atoms and molecular ions can be important for the observation , so extensive analyzes can be carried out with a sensitivity range of 1 to at least 150 amu . The data can also be recorded so that they can possibly only be sent back to Earth weeks after the comet encounter, since the data connection will already be busy with the image data during the approach to the comet.
CIDA was built under the leadership of DARA in close cooperation with the Max Planck Institute for Aeronomy in Lindau by the company von Hoerner & Sulger in Schwetzingen , the software was developed by the Finnish Meteorological Institute in Helsinki .
Dust collector
The dust collector consists of one and three centimeter thick silicate airgel blocks that are fastened in modular aluminum cells. One side of the approximately 1,000 square centimeter collector is used to collect interstellar dust, the other side to collect cometary material. This was possible because the dust particles punch conical holes in the gel, at the ends of which they come to a standstill. In this way, the origin or direction can be determined in any case
The main problem with the collection of interstellar dust and coma material is the deceleration of the particles without changing their structure and composition - they had a relative speed of 6.1 km / s when they encountered Wild 2. The airgel used is ideally suited for this purpose due to its highly porous structure, which consists of 99.8 percent cavities, as the particles are slowed down comparatively gently - the gel has roughly the same density as air under normal conditions - and due to the transparency of the material are easy to find again. Nevertheless, the evaluation is not easy - due to the relationship between the number of particles and the impact area, the search, according to scientists, is like trying to "find four ants on a soccer field".
Return capsule
The return capsule ( S ample R eturn C apsule , SRC) is a compact system that essentially consists of the sample canister, the heat shield and the top cover, as well as navigation aids and a small parachute system. While the sample is being taken, the top cover is folded back and the dust collector, which has the shape of a tennis racket, unfolds. When the sampling is complete, the dust collector is folded up again and the return capsule is hermetically sealed.
On the return to earth, shortly before Stardust crossed the earth's orbit , the return capsule was released, whereby it was given a rotary movement (twist) to stabilize its position. Then it flew in free fall through the earth's atmosphere, stabilized by the position of the center of gravity, the rotational movement and the aerodynamic shape. At a height of about three kilometers, a parachute opened to reduce the speed of fall. The landing was on schedule within the 84 × 30 kilometer area of the Utah Test and Training Range (UTTR). To make it easier to find the capsule, it had a UHF direction finder . In addition, the landing was followed with ground-based radar systems and could be filmed with infrared cameras. Once recovered, the capsule was taken to the Johnson Space Center , where it was opened and the collected dust extracted and analyzed.
See also
literature
- Thorsten Dambeck: The new picture of comets . Bild der Wissenschaft , December 2007, pages 38-43, ISSN 0006-2375
- AJ Westphal, et al .: Constraints on the Interstellar Dust Flux Based on Stardust @ Home Search Results. , 42nd Lunar and Planetary Science Conference, March 2011, abstract @NASA ads, online (PDF), accessed August 1, 2011
- Stardust. In: Bernd Leitenberger: With space probes to the planetary spaces: New beginning until today 1993 to 2018 , Edition Raumfahrt Kompakt, Norderstedt 2018, ISBN 978-3-7460-6544-1 , pp. 101-108
Web links
- Stardust site of NASA (English)
- Stardust-Next site of NASA (English)
- Stardust - explanations by Bernd Leitenberger
- extrasolar-planets.com - Stardust Mission
- Stardust @ Home - online search for "stardust"
Individual evidence
- ^ NASA Gives Two Successful Spacecraft New Assignments
- ^ NASA report: Blasting a Hole in a Comet: Take 2 , September 26, 2007
- ↑ FlugRevue April 2010, p. 76: Boost for Stardust-NExT
- ↑ NASA JPL NASA's Stardust Spacecraft Completes Comet Flyby
- ↑ STARDUST: Mission end after twelve years astronews.de (March 25, 2011)
- ↑ Jamie E. Elsila, et al .: Cometary glycine detected in samples returned by Stardust. Meteoritics & Planetary Science 44, No. 9, pages 1323-1330 (2009), online (PDF) gsfc.nasa.gov, accessed on August 23, 2014
- ↑ Cecile LeBlanc: Evidence for liquid water on the surface of comet wild-2 , Eartsky, April 7, 2011, accessed on August 23, 2014
- ↑ Projects: Stardust @ home stardustathome.ssl.berkeley.edu, accessed on November 16, 2012
- ↑ Evidence for interstellar origin of seven dust particles collected by the Stardust spacecraft , accessed on August 23, 2014
- ^ Helga Rietz: Seven grains of stardust . Neue Zürcher Zeitung, August 20, 2014, p. 52
- ^ About Stardust @ Home ; Stardust Timeline stardustathome.ssl.berkeley.edu, accessed August 1, 2011
- ↑ a b c d Ray L. Newburn Jr., Shyam Bhaskaran, Thomas C. Duxbury, George Fraschetti, Tom Radey, Mark Schwochert: Stardust Imaging Camera , in Journal of Geophysical Research, Vol. 108, NO. E10, 8116, doi: 10.1029 / 2003JE002081 , 2003.
- ↑ vH & S - CIDA Instrument. Retrieved February 7, 2019 .
- ↑ a b Catching Comet Dust With Airgel - NASA text on the JPL's dust collector principle , accessed on February 7, 2019.
Launched Missions: ISEE-3 / ICE (1978) | Vega (1984) | Sakigake (1985) | Giotto (1985) | Suisei (1985) | Galileo (1989) | Clementine (1994) | NEAR (1996) | Deep Space 1 (1998) | Stardust (1999) | Contour (2002) | Hayabusa (2003) | Rosetta (2004) | Deep Impact (2005) | New Horizons (2006) | Dawn (2007) | Chang'e-2 (2010) | Hayabusa 2 (2014) | Osiris-Rex (2016)
Planned missions: DART (2021) | Lucy (2021) | Near-Earth Asteroid Scout (2021) | Psyche (2022) | Janus (2022) | Destiny Plus (2022) | Hera (2023) | Comet Interceptor (2028)
Canceled missions: NEAP | Don Quixote | New asteroid initiative
Overview: Chronology of the space probes for comets and asteroids
