Aspera-3
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ASPERA-3 ( A nalyser of S pace P LASMAS and E nergetic A toms) is a by scientists at the Swedish Institute of Space Physics ( Kiruna designed) instrument on board the Mars Express . Aspera-3 was one of the 3 main instruments of the Mars Express. It had a mission to learn more about the Martian atmosphere and its interaction with the solar wind , and to investigate the sources of the so-called ENAs (Energetic Neutral Atoms) on Mars. ASPERA-3 also had the task of analyzing and categorizing plasma and neutral gases in the vicinity of Mars. The mission started on June 2, 2003 from the Kazakh spaceport Baikonur towards Mars.
Mission objectives
The main objective of the mission was to study the interaction between the solar wind and the atmosphere of Mars and to characterize the plasma and neutral gases in the vicinity of Mars. For this purpose, Energetic Neutral Atom (ENA) imaging and in-situ measurements were used simultaneously. Further key questions of the mission were the following:
- How much is the Martian atmosphere influenced by interplanetary plasma and electromagnetic fields?
- In what form is / was there water on Mars?
- Has water been lost?
- Is there water in frozen form on Mars?
- Is it possible that life existed on Mars?
The official, specific objectives were formulated as follows:
- The determination of the current global distributions of plasma and neutral gas in the vicinity of Mars
- Studies of Plasma Induced Atmospheric Loss
- The study of atmospheric changes caused by ion bombardment
- The study of the transfer of energy between the solar wind and the ionosphere
Course of the mission
On June 2, 2003, the Mass Express took off on a Soyuz-Fregat rocket from the Baikonur spaceport in Kazakhstan . After a series of tests on the function of the sensors, this part of the mission was described as "very successful ". On June 23, the successful commissioning of the first Aspera-3 sensor was observed in the ESOC (European Space Operation Center) in Darmstadt . The last sensor was also put into operation on June 25, so that Aspera-3 was fully operational. Professor Stas Barabash of the Swedish Institute for Space Physics said that this was the moment that those in charge were most nervous about. After 6 months of flight time, Mars orbit was reached. There the Aspera-3 began the measurements. A minimum stay of 687 days in orbit was planned. From 20. to 22. On August 1st, the scientists involved in the mission met in Kiruna to discuss the progress and further planning of the mission so far.
meaning
The mission was of great importance to the ESA (European Space Association) as it was the first European Mars mission. When the Mars Express reached the orbit of Mars after a 6-month journey, the following ESA press release was accordingly euphoric. The ESA also attached great scientific importance to the mission, as it was hoped that the modern sensors would provide new knowledge about Mars, solar winds and the so-called ENAs (Energetic Neutral Atoms). Overall, the ASPERA-3 mission was another help in solving the mystery of the non-existent water on Mars.
Instruments
Main unit (MU)
- Mechanical scanner
The mechanical scanner moves the three sensors (NPI, NPD, ELS) over 180 °, so that 4π steradian can be covered when stabilized overall. The scanner has 2 stepper motors that turn a worm gear that is mounted on the moving part of the scanner. The rotation rates are 1.5 °, 3.0 ° and 6.0 ° per second and accurate to 0.2 °.
- Digital Processing Unit (DPU)
The main task of the Digital Processing Unit (DPU) is to control the sensors (NPI, NPD, ELS) and the scanner (see above). It also processes, compresses and stores the data from the sensors and forwards them along with the household data to the telemetry system of the probe . In addition, it receives and executes the commands sent to the communication system of the probe.
- Neutral Particle Imager (NPI)
The NPI on board the ASPERA-3 probe is a replica of the NPI-MCP sensor from ASPERA-C on board the Mars 96 mission, and it was also part of the successful Astrid satellite mission . In the NPI, the charged particles ( electrons , ions ) are removed by an electrostatic deflection system consisting of two discs with a 3 mm gap. The 5 kV potential between the earthed plate and the one with quiescent current produces a strong electromagnetic field that flings away all charged particles with an energy of up to 60 keV . Since the integral ENA flux significantly exceeds the charged particle flux for energies greater than 60 keV, this rejection energy provides a satisfactory performance. In addition, the plates also determine the elevation angle. In addition to 'on' and 'off', there are two other modes that the system can adopt, 'alternative' and 'sweeping', in order to obtain more detailed information. The space between the deflection system plates is divided into 32 sectors by plastic spokes, so that 32 azimuthal collimators with an opening of 9 × 18 ° each are created. Then the neutrals that have come through the deflection system fly towards a 32-sided, cylindrical target which, when interacting with the particles, reflects secondary and primary particles (20 °). These are then detected by an MCP stack in the chevron configuration ( the chevron configuration is explained in more detail in the English article on MCPs ) and then detected by a 32-sector anode. The MCP detects: (a) sputtered positive ions from the target material, (b) positive ions from the ionization of primary neutrals, and (c) neutrals reflected from the target surface. The aforementioned spokes are there to focus the ENAs, to focus them precisely on the cylindrical body. In one measurement, the NPI can "scan" 4π and store the data in an azimuth x increase matrix. The direction vector of 32 elements can be output every 31.25 μs . The two spokes or sectors, which are directed towards the probe itself, are blocked in order to record the number of unreported cases for the manufacture of the MCP, and the space is used to route the cables from the ELS to the DPU (see picture). The ASPERA team has overcome the problem of UV radiation and its disturbances by using a coating like the one used by Astrid and ASPERA-C: DAG 213 a Hatz based graphite solution, similar to Aquadag . In summary, one can say that the NPI is a device for the detection and localization of ENA flows.
- Neutral Particle Detector (NPD)
The Neutral Particle Detector, in turn, contributes to Energetic Neutral Atom (ENA) imaging , mainly hydrogen and oxygen, by resolving the mass and velocity of the ENAs. The NPD has 2 identical sensors. In each of these sensors, the charged particles are removed in two 90 degree sectors in order to detect the ENAs. For this purpose, an energy field is generated that removes all charged particles with an energy of at least 70 keV. In addition, incoming beams are realigned by the deflector so that when exposed to ENAs they hit the START surface, which causes another ejection of electrons. These pass the START signal on to TOF electrons. The recorded ENAs are mirrored by the START area. Since the radiation contains ionizing radiation in addition to the ENA particles, the charge must be balanced so that the measurements are not influenced. For this purpose, more rays are added to give the total amount of rays a neutral charge. The remaining ions have an energy of 80 eV after the reflection. Therefore, after being reflected, the rays hit a second surface, the STOP surface. This impact again releases additional electrons through which the STOP signal is passed on. Since the number of ejected electrons depends on the mass of the ENAs, the mass of the ENAs can be determined.
- Electron Spectrometer (ELS)
The electron spectrometer is a sensor for the energy and direction analysis of electrons and ions . This measurement can be made with an energy of up to 40 keV . The ELS is a state-of-the-art sensor with low weight and energy consumption. The electron spectrometer installed on board the Mars Express is based on the ELS of the Medusa experiments as part of the Astrid-2 mission. The ELS is the lightest sensor from Aspera-3. It consists of a collimator and an electrostatic measuring device. The particles pass through an opening and are then filtered. The electrons filtered out then hit an MCP (micro-channel plate). This small area is graded according to charge so that the charge can be measured and the ELS can create an energy spectrum. Electrons with a charge of up to 20 keV / q are measured. The ELS is mounted above the NPI sensor and has an energy resolution of 7%.
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Secondary unit
- Ion Mass Analyzer (IMA)
IMA (or ICA) is an improved version of the previous ion mass spectographers TICS (Freja), IMIS (ASPERA-C) and IMI ( Planet-B ). It is a copy of the ICA instrument launched on board Rosetta in 2003 for Comet Wirtanen. Particles come through a grid into the IMA and then fly through a deflection system that throws particles between 45 ° and 135 ° out of orbit in order to direct the rest into the 'electrostatic analyzer' (ESA) (article only available here in English) (2mm column, in comparison: IMA diameter 45mm), which only lets through ions of a certain energy and focuses them. The focused ions are deflected into a cylindrical magnetic field generated by permanent magnets. The lighter ions are deflected more strongly than the heavier ones from the center of the field. Finally they land on the MCP and are detected by an anode system. The ions can be analyzed for their direction and the mass per charge at the same time . The magnetic component can be pre-magnetized in order to accelerate ions and to obtain a selection according to the order of magnitude and resolution of the mass. The electrons of the MCP are recorded by an imaging anode system. It consists of 32 concentric rings that show the radial position of the impact (represents ion mass), and 16 sector anodes that measure the azimuthal impact position (represents the ion entry angle). The readout system is based on discrete preamplifiers . 6 MOCAD chips ("Monolithic Octal Charge Amplifier / Pulse Discriminator") offer 48 independent channels for the 32 rings and 16 sectors of the anode. This information can then be sent to your own DPU and analyzed there. In conclusion, the IMA is an instrument that can measure the mass and energy of ions in the Martian atmosphere.
- IMA DPU
IMA also has a separate DPU which, like the main unit, collects data and controls the other systems.
Technical specifications
| parameter | NPI | NPD | ELS | IMA |
|---|---|---|---|---|
| Measured particles | ENA | ENA | Electrons | Ions |
| Energy pallet , KeV per charge | 0.1 - 60 | 0.1 - 10 | 0.01 - 20 | 0.01 - 30 |
| Energy dissolution | - | 80% | 7% | 10% |
| Mass dissolution | - | 0.1 - 10 keV H,
0.3 - <100 keV O |
- |
m / q = 1, 2,
4, 8, 16> 20 |
| Angular resolution ( FWHM ) | 4.6 × 11.5 ° | 5 × 30 ° | 10 × 22.5 ° | 4.5 × 22.5 ° |
| Field of view | 9 ° × 344 ° | 9 ° × 180 ° | 10 ° × 360 ° | 4.6 ° × 360 ° |
| Efficiency,% | 1 | 1-25 | not specified | not specified |
| Time resolution (completely 3D), s | 32 | 32 | 32 | 32 |
| Mass, kg | 0.7 | 1.3 | 0.3 | 2.2 |
| Power, W | 0.8 | 1.5 | 0.6 | 3.5 |
Holdings
The Mars-Express mission was a project of the ESA (European Space Association). After the start, the Mars Express mission was observed from the ESOC (European Space Operation Center) in Darmstadt. The ASPERA-3 instrument was developed by the Swedish Institute for Space Physics in Kiruna. In Kiruna, 15 research groups from 10 European countries as well as from the USA and Japan worked on the development of the complex sensors.
Results of the mission
It is difficult to differentiate between results of the Mars-Express mission in general and those that can be attributed to the Aspera-3. The following findings are attributable to the Mars-Express mission in general, but were in part obtained by the Aspera-3 instrument:
- Evidence of frozen water on the southern polar cap of Mars
- Detection of methane in the atmosphere
- Evidence for the existence of liquid water on the surface of Mars in the past
- Findings about winds on the surface
Individual evidence
- ^ Aspera-3. Retrieved April 7, 2017 .
- ↑ ASPERA-3. Retrieved April 7, 2017 .
- ^ Swedish Institute of Space Physics. (No longer available online.) Archived from the original on April 3, 2016 ; Retrieved April 5, 2017 . Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
- ↑ Electron Spectrometer - Meaning - Encyclo. Retrieved April 4, 2017 (American English).
- ↑ Christopher Russell: The Mars Plasma Environment . Ed .: Springer Science & Business Media. 2010, ISBN 978-0-387-70943-7 , pp. 501 .
- ^ S. Barabash: ASPERA-3: Analyzer of Space Plasmas and Energetic Ions for Mars Express . Ed .: ESA.
- ^ Instrument design. Retrieved April 7, 2017 (UK English).
- ^ S. Barabash and many others: ASPERA-3: Analyzer of Space Plasmas and Energetic Ions for Mars Express .
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↑ esa: Buried craters and underground ice -
Mars Express uncovers depths of Mars . In: European Space Agency . ( esa.int [accessed April 6, 2017]).
