Philae: details about scientific equipment and results to date
Now that the Philae probe has been sleeping for the third day, it's time to draw a line under the scientific research.
The Philae probe is equipped with ten scientific systems with a total weight of 26.7 kg. Their main differences from the usual, terrestrial equipment - less weight, compactness, autonomy and no need for maintenance. The work on miniaturization has been really titanic: more than ten years have passed since the device was created, but so far many Philae instruments are lighter than their earthly counterparts by almost an order of magnitude, and also the situation with power consumption. In addition, stringent requirements are imposed on operating temperatures — the probe equipment functions normally in the range from –130 to +50 ° .
')
The preliminary result of the scientific work in two words - a dizzying success! Apart from problems with the landing (more precisely, fixation) of the descent vehicle, all systems worked perfectly. Despite the problems with energy, the probe managed to somehow accomplish all the priority scientific tasks.
Under the cut - a detailed description of the equipment Philae, the results, a lot of photos, a few words about the problems and even real telemetry data. (Watch out for traffic!)
All Philae research systems can be divided into four groups:
Consider them in order.
CIVA (Comet IR & Visible Analyzer) is a system of seven cameras with a resolution of 1 megapixel each and an IR spectrometer. Six cameras allow you to get a full 360 ° panoramic image, the seventh makes stereo photography possible.
An IR spectrometer is used to analyze samples taken with SD2. The working wavelength range is 1–4 µm, the spatial resolution is 40 µm.
The CIVA images have probably already been seen by everyone, but it has not yet been reported whether the IR spectra were taken. It depends on whether the sample was subjected to high-temperature pyrolysis (details in the section on SD2).
The total weight of CIVA is 4 kg.
ROLIS ( Ro setta L ander I maging S ystem) is a camera mounted on the bottom of the descent vehicle. Designed for shooting in the process of landing and after it. Allows you to put the SD2 drill in the right place. The resolution is 1 megapixel, the field of view is 75/50 ° (switches; after landing, the resolution is 0.3 mm / pixel), the camera is black and white, but equipped with red, green, blue and IR LEDs for illumination, which allows to receive color images. The minimum operating temperature is minus 150 ° C. Compression is supported, and the degree of compression may be different for different parts of the image (Region-of-Interest coding). The mass of the device is 0.4 kg.
The camera worked without any complaints. After landing, the camera photographed three more different places, although it is not entirely clear which - immediately after landing, after the first “flight” and after the second or immediately after landing, after the second “flight” and after turning the platform.
SD2 - tool for drilling, sampling and distribution of soil. The drill length is 581.6 mm, diameter is 12 mm, the maximum drilling depth is 230 mm. The drill is made of an aluminum alloy with a diamond dusting, the maximum tensile strength of the rock is 50 MPa. Operating voltage - 28 V.
The device makes a hole in the ground of a given depth, selects a portion of rock with a volume of 10–40 mm² from its bottom and places it in a heating cell (furnace). Drilling is done through a hole in the bottom of the apparatus; the location can be selected using the ROLIS camera. The probe has 26 cells for heating the samples, sixteen of them maintain the temperature up to 800 ° C (for pyrolysis of the sample), the remaining 10 - up to 180 ° C (for evaporation / mild decomposition). When heated in the latter, it is possible to conduct IR spectrometry using the CIVA device due to the presence of transparent sapphire prisms in them.
There was a risk that the apparatus would come off the comet while drilling, however, it was decided to carry it out, because without digging the depth of the ground, the scientific tasks could not be considered solved. The drilling was done on the day of 14.11 and took two hours. The drill was lowered to the maximum depth and, apparently, successfully selected a soil sample.
Since only one sample was taken, it was necessary to decide whether to send it to COSAC or Ptolemy for analysis. The mission team gave preference to COSAC - mainly because the information from it better complements the data obtained using the instruments of the orbital station (it is easier to determine inorganic compounds from orbits than organic ones). Ptolemy had to be content with dust analysis, which was also very good.
The sample was thermally treated (the temperature has not yet been clarified) and sent for analysis. Excavation, processing, transportation and analysis were carried out in a normal mode, no problems were reported. Has it been possible to obtain micrographs of the sample and IR spectra with the help of the CIVA device, has not yet been clarified.
MUPUS (MUlti-PUrpose Sensors for Surface and Sub-Surface Science) - sensors for measuring the temperature and mechanical properties of the cometary nucleus at a depth of 0–32 cm.
On the harpoons that did not work, accelerometers were installed to determine the strength and hardness of the surface of the core and thermometers to determine the temperature of the soil.
On the probe is the MUPUS TM IR camera for remote determination of the core surface temperature. (Unfortunately, I did not find any details regarding this device.)
The penetrator driven into the comet's core with a mechanical hammer is moving along the 1.5 meter mechanical arm. The maximum penetration depth is 32 cm. The penetrator is equipped with a thermometer and thermal conductivity sensor, which allows building the corresponding core profiles as the device deepens, and by the speed of clogging, you can judge the hardness of the soil. Removing the probe is not provided (only naturally in the process of erosion of the comet's nucleus).
To drive a probe into solid ground in space is not an easy task. The classic solution is a squib, but it does not allow to explore the soil in layers during the driving process. The MUPUS device uses a thirty-gram load, accelerated by a magnetic field of up to 8 m / s. After impact, the spring, on which the load is suspended, returns it to its initial position.
results
The TM infrared camera showed “a very cold sheer wall in front of the probe.” Analyzed daily fluctuations in temperature - the surface of the core quickly heats up in direct sunlight and cools quickly when they are not. Sensors in the shade of the harpoon probe also record daily temperature fluctuations.
When the device penetrated, the temperature of the penetrator decreased and some changes in the operation of other devices were noticed - apparently, while Philae moved a little and / or something stuck to the rod. Since, based on indications from the IR camera, a loose surface layer was expected (“probably small grains of minerals or organic dust like tobacco ash”), the hammer was turned on in the minimum power mode, but this did not bring success. Even after switching to the third, maximum design mode, the rod did not begin to enter the core. The team decided to activate the undocumented fourth mode, which they called "desperate." Unfortunately, after seven minutes of unsuccessful attempts the hammer failed. Thus, the ultimate strength of the core surface clearly exceeds 2 MPa (for comparison, the ultimate strength of ice is 0.7–3 MPa, concrete — 2–5 MPa, granite - 5–20 MPa). Harpoons are designed for 8–10 MPa, so it is not known if they would have entered the ground if they had fired. If entered, their sensors would give us enough valuable information.
Was the decision to “score to the last” correct? If the probe no longer wakes up, then of course. If you wake up, it will be a little insulting - suddenly the penetrator just got on some kind of solid area.
COSAC is one of the main instruments of the probe, a gas chromatography mass spectrometer (a gas chromatograph with catharometric and mass spectrometric detectors). The chromatograph carrier gas is helium. The device allows the determination of various organic substances, such as alcohols, amines, carboxylic acids, amino acids, etc. The chromatograph is equipped with eight separate columns and two detectors — a simple catharometric (non-selective device, detection of the substance by changing the thermal conductivity of the gas), because changes the sample during the study) and time-of-flight mass spectrometer with ionization by electron impact, which allows to determine the composition of the passing substance. All gas from the columns is sent to the katharometer, and then from part of the columns (on request) to the mass spectrometer.
COSAC analysis was performed immediately after drilling and processing. The processing and analysis modes have not yet been made public, but there have been no reports of problems.
Ptolemy - gas chromatograph with a mass spectrometer to determine the isotopic composition. The detector is a quadrupole ion-cyclotron (ion trap). Unlike COSAC, it is mainly intended for the determination of light elements - hydrogen, carbon, nitrogen and oxygen and the ratio of their isotopes.
Since the obtained SD2 soil sample was sent to COSAC, Ptolemy analyzed only the collected dust (“concentrated sniff”).
The mass of the device is 5 kg (for comparison, mass-produced mass spectrometers with an ion trap weigh from 60 kg to one hundred and more).
APXS (Alpha Proton X-Ray Spectrometer) is an alpha proton X-ray spectrometer designed to determine the elemental composition of the surface of the nucleus. Consists of an alpha radioactive source (curium-244) and detectors of alpha particles and x-rays. Spectroscopy of alpha particles is based on the phenomenon of Rutherford backscattering and allows you to determine carbon, nitrogen, oxygen. The X-ray detector allows you to determine the heavier elements - from sodium to zinc.
APXS is a must-have for a descent vehicle: low mass (only 640 grams!), Low power consumption (1.5 W, since in fact the experiment provides energy for radioactive decay) and universality make it almost indispensable. The only noticeable negative - the duration of the study is measured in hours.
Philae performed a surface analysis using APXS at the third, final landing site. Information about how well, yet.
SESAME (Surface Electric Sounding and Acoustic Monitoring Experiments) - 3 instruments for measuring the properties of the comet's outer layers:
Unfortunately, the CASSE devices are located at the feet of the probe, and the success of the measurement directly depends on whether all feet are on the surface, and if not, which ones.
Information about the results of SESAME has not yet been made public.
CONSERT (Comet Nucleus Sounding Experiment by Radiowave Transmission) - a radar for tomography of the comet's core. The experiment is to measure the delay and attenuation of electromagnetic waves along the path from the orbital station to Philae and back.
The study was carried out successfully, despite the battery, which was almost exhausted by that time, but it is obvious that the short measurement time did not allow the tomogram to be complete and accurate - the orbiter did not physically manage to make the required number of turns. A side effect of the experiment is to determine the location of the probe - perhaps this will help it to find it in pictures from Rosetta.
ROMAP (Rosetta Lander Magnetometer and Plasma Monitor) is a magnetometer and plasma detector for studying the magnetic field of a comet's nucleus and its interaction with the solar wind. Also allowed to monitor the process of landing.
So far, only published data on landing.
Despite the problems with fixation and nutrition, the probe brilliantly coped with the overwhelming majority of priorities. When I heard that the probe could not be fixed and he set off on an unplanned flight, I didn’t hope that everything would end so well. Ten of the most complex scientific devices flying for more than ten years, more than six billion kilometers have flown - and all ten have worked like a Swiss watch. Sincerely happy for the ESA - great job, it was a delightful fifty-seven hours.
I would like to finish the article with a poem:
The Philae probe is equipped with ten scientific systems with a total weight of 26.7 kg. Their main differences from the usual, terrestrial equipment - less weight, compactness, autonomy and no need for maintenance. The work on miniaturization has been really titanic: more than ten years have passed since the device was created, but so far many Philae instruments are lighter than their earthly counterparts by almost an order of magnitude, and also the situation with power consumption. In addition, stringent requirements are imposed on operating temperatures — the probe equipment functions normally in the range from –130 to +50 ° .
')
The preliminary result of the scientific work in two words - a dizzying success! Apart from problems with the landing (more precisely, fixation) of the descent vehicle, all systems worked perfectly. Despite the problems with energy, the probe managed to somehow accomplish all the priority scientific tasks.
Under the cut - a detailed description of the equipment Philae, the results, a lot of photos, a few words about the problems and even real telemetry data. (Watch out for traffic!)
All Philae research systems can be divided into four groups:
- Visual and infrared monitoring equipment - CIVA, ROLIS.
- Devices embedded in the core - SD2, MUPUS
- Surface analysis or sampling instruments - COSAC, Ptolemy, AXPS, SESAME
- Research equipment for the entire kernel - CONSERT, ROMAP.
Consider them in order.
Device layout
Apparatus for monitoring in the visible and infrared ranges
CIVA (Comet IR & Visible Analyzer) is a system of seven cameras with a resolution of 1 megapixel each and an IR spectrometer. Six cameras allow you to get a full 360 ° panoramic image, the seventh makes stereo photography possible.An IR spectrometer is used to analyze samples taken with SD2. The working wavelength range is 1–4 µm, the spatial resolution is 40 µm.
The CIVA images have probably already been seen by everyone, but it has not yet been reported whether the IR spectra were taken. It depends on whether the sample was subjected to high-temperature pyrolysis (details in the section on SD2).
The total weight of CIVA is 4 kg.
The layout of the cameras on the device
ROLIS ( Ro setta L ander I maging S ystem) is a camera mounted on the bottom of the descent vehicle. Designed for shooting in the process of landing and after it. Allows you to put the SD2 drill in the right place. The resolution is 1 megapixel, the field of view is 75/50 ° (switches; after landing, the resolution is 0.3 mm / pixel), the camera is black and white, but equipped with red, green, blue and IR LEDs for illumination, which allows to receive color images. The minimum operating temperature is minus 150 ° C. Compression is supported, and the degree of compression may be different for different parts of the image (Region-of-Interest coding). The mass of the device is 0.4 kg.
The camera worked without any complaints. After landing, the camera photographed three more different places, although it is not entirely clear which - immediately after landing, after the first “flight” and after the second or immediately after landing, after the second “flight” and after turning the platform.
Incoming!
Devices injected into the kernel
SD2
SD2 - tool for drilling, sampling and distribution of soil. The drill length is 581.6 mm, diameter is 12 mm, the maximum drilling depth is 230 mm. The drill is made of an aluminum alloy with a diamond dusting, the maximum tensile strength of the rock is 50 MPa. Operating voltage - 28 V.
The device makes a hole in the ground of a given depth, selects a portion of rock with a volume of 10–40 mm² from its bottom and places it in a heating cell (furnace). Drilling is done through a hole in the bottom of the apparatus; the location can be selected using the ROLIS camera. The probe has 26 cells for heating the samples, sixteen of them maintain the temperature up to 800 ° C (for pyrolysis of the sample), the remaining 10 - up to 180 ° C (for evaporation / mild decomposition). When heated in the latter, it is possible to conduct IR spectrometry using the CIVA device due to the presence of transparent sapphire prisms in them.
There was a risk that the apparatus would come off the comet while drilling, however, it was decided to carry it out, because without digging the depth of the ground, the scientific tasks could not be considered solved. The drilling was done on the day of 14.11 and took two hours. The drill was lowered to the maximum depth and, apparently, successfully selected a soil sample.
Since only one sample was taken, it was necessary to decide whether to send it to COSAC or Ptolemy for analysis. The mission team gave preference to COSAC - mainly because the information from it better complements the data obtained using the instruments of the orbital station (it is easier to determine inorganic compounds from orbits than organic ones). Ptolemy had to be content with dust analysis, which was also very good.
The sample was thermally treated (the temperature has not yet been clarified) and sent for analysis. Excavation, processing, transportation and analysis were carried out in a normal mode, no problems were reported. Has it been possible to obtain micrographs of the sample and IR spectra with the help of the CIVA device, has not yet been clarified.
Scheme and photos of the device
Pickup pipe pulled out:
Arrows indicate cells for stoves:
Sapphire prism furnace:
Tests are underway:
Pickup pipe pulled out:
Arrows indicate cells for stoves:
Sapphire prism furnace:
Tests are underway:
Telemetry of the first comet core drilling history! Enters ... and leaves ... great comes out!
On the scale of ordinates - departure of the drill in mm (red graph). It is a pity that there is no data from the ammeter, one could see when the drill entered the ground. 
MUPUS
MUPUS (MUlti-PUrpose Sensors for Surface and Sub-Surface Science) - sensors for measuring the temperature and mechanical properties of the cometary nucleus at a depth of 0–32 cm.
On the harpoons that did not work, accelerometers were installed to determine the strength and hardness of the surface of the core and thermometers to determine the temperature of the soil.
On the probe is the MUPUS TM IR camera for remote determination of the core surface temperature. (Unfortunately, I did not find any details regarding this device.)
The penetrator driven into the comet's core with a mechanical hammer is moving along the 1.5 meter mechanical arm. The maximum penetration depth is 32 cm. The penetrator is equipped with a thermometer and thermal conductivity sensor, which allows building the corresponding core profiles as the device deepens, and by the speed of clogging, you can judge the hardness of the soil. Removing the probe is not provided (only naturally in the process of erosion of the comet's nucleus).
To drive a probe into solid ground in space is not an easy task. The classic solution is a squib, but it does not allow to explore the soil in layers during the driving process. The MUPUS device uses a thirty-gram load, accelerated by a magnetic field of up to 8 m / s. After impact, the spring, on which the load is suspended, returns it to its initial position.
Scheme and photos of the device
results
The TM infrared camera showed “a very cold sheer wall in front of the probe.” Analyzed daily fluctuations in temperature - the surface of the core quickly heats up in direct sunlight and cools quickly when they are not. Sensors in the shade of the harpoon probe also record daily temperature fluctuations.
When the device penetrated, the temperature of the penetrator decreased and some changes in the operation of other devices were noticed - apparently, while Philae moved a little and / or something stuck to the rod. Since, based on indications from the IR camera, a loose surface layer was expected (“probably small grains of minerals or organic dust like tobacco ash”), the hammer was turned on in the minimum power mode, but this did not bring success. Even after switching to the third, maximum design mode, the rod did not begin to enter the core. The team decided to activate the undocumented fourth mode, which they called "desperate." Unfortunately, after seven minutes of unsuccessful attempts the hammer failed. Thus, the ultimate strength of the core surface clearly exceeds 2 MPa (for comparison, the ultimate strength of ice is 0.7–3 MPa, concrete — 2–5 MPa, granite - 5–20 MPa). Harpoons are designed for 8–10 MPa, so it is not known if they would have entered the ground if they had fired. If entered, their sensors would give us enough valuable information.
Was the decision to “score to the last” correct? If the probe no longer wakes up, then of course. If you wake up, it will be a little insulting - suddenly the penetrator just got on some kind of solid area.
Instruments for surface analysis or sampling
COSAC is one of the main instruments of the probe, a gas chromatography mass spectrometer (a gas chromatograph with catharometric and mass spectrometric detectors). The chromatograph carrier gas is helium. The device allows the determination of various organic substances, such as alcohols, amines, carboxylic acids, amino acids, etc. The chromatograph is equipped with eight separate columns and two detectors — a simple catharometric (non-selective device, detection of the substance by changing the thermal conductivity of the gas), because changes the sample during the study) and time-of-flight mass spectrometer with ionization by electron impact, which allows to determine the composition of the passing substance. All gas from the columns is sent to the katharometer, and then from part of the columns (on request) to the mass spectrometer.
COSAC analysis was performed immediately after drilling and processing. The processing and analysis modes have not yet been made public, but there have been no reports of problems.
Ptolemy - gas chromatograph with a mass spectrometer to determine the isotopic composition. The detector is a quadrupole ion-cyclotron (ion trap). Unlike COSAC, it is mainly intended for the determination of light elements - hydrogen, carbon, nitrogen and oxygen and the ratio of their isotopes.
Since the obtained SD2 soil sample was sent to COSAC, Ptolemy analyzed only the collected dust (“concentrated sniff”).
The mass of the device is 5 kg (for comparison, mass-produced mass spectrometers with an ion trap weigh from 60 kg to one hundred and more).
APXS (Alpha Proton X-Ray Spectrometer) is an alpha proton X-ray spectrometer designed to determine the elemental composition of the surface of the nucleus. Consists of an alpha radioactive source (curium-244) and detectors of alpha particles and x-rays. Spectroscopy of alpha particles is based on the phenomenon of Rutherford backscattering and allows you to determine carbon, nitrogen, oxygen. The X-ray detector allows you to determine the heavier elements - from sodium to zinc.
APXS is a must-have for a descent vehicle: low mass (only 640 grams!), Low power consumption (1.5 W, since in fact the experiment provides energy for radioactive decay) and universality make it almost indispensable. The only noticeable negative - the duration of the study is measured in hours.
Philae performed a surface analysis using APXS at the third, final landing site. Information about how well, yet.
Device layout
SESAME (Surface Electric Sounding and Acoustic Monitoring Experiments) - 3 instruments for measuring the properties of the comet's outer layers:
- CASSE (Cometary Acoustic Sounding Surface Experiment) - an experiment in acoustic research of the comet's surface,
- PP (Permittivity Probe) - the study of its electrical characteristics, which allows to determine the amount of ice at a depth of up to 2 m,
- DIM (Dust Impact Monitor) detects dust and ice particles deposited on the surface of the core.
Unfortunately, the CASSE devices are located at the feet of the probe, and the success of the measurement directly depends on whether all feet are on the surface, and if not, which ones.
Information about the results of SESAME has not yet been made public.
Nuclear-wide research equipment
CONSERT (Comet Nucleus Sounding Experiment by Radiowave Transmission) - a radar for tomography of the comet's core. The experiment is to measure the delay and attenuation of electromagnetic waves along the path from the orbital station to Philae and back.
The study was carried out successfully, despite the battery, which was almost exhausted by that time, but it is obvious that the short measurement time did not allow the tomogram to be complete and accurate - the orbiter did not physically manage to make the required number of turns. A side effect of the experiment is to determine the location of the probe - perhaps this will help it to find it in pictures from Rosetta.
ROMAP (Rosetta Lander Magnetometer and Plasma Monitor) is a magnetometer and plasma detector for studying the magnetic field of a comet's nucleus and its interaction with the solar wind. Also allowed to monitor the process of landing.So far, only published data on landing.
Use ROMAP to accurately determine the bounce time of the machine.
What (so far) failed to do
- Shoot the harpoons. The only really serious mission problem. The reason seems to be the use of nitrocellulose in the pyro cartridges, which, according to recent studies, are unreliable in vacuum. The problem is offensive, because it was possible to replace the composition with something else without problems. The remaining shortcomings are consequences of the lack of energy caused by the flights.
- It was not possible to analyze the material of the core with the help of Ptolemy - there was neither time nor desire to drill the second time (the loose probe could easily have flown off somewhere).
- Do not have time to properly enlighten the core of the radar.
- Unable to enter PEN into the core - the surface was much harder than expected. In general, there is no one's fault here, MUPUS has worked according to the specifications.
- Starting clamping engines also failed, but it is hardly a problem, since the harpoons did not work.
Preliminary result
Despite the problems with fixation and nutrition, the probe brilliantly coped with the overwhelming majority of priorities. When I heard that the probe could not be fixed and he set off on an unplanned flight, I didn’t hope that everything would end so well. Ten of the most complex scientific devices flying for more than ten years, more than six billion kilometers have flown - and all ten have worked like a Swiss watch. Sincerely happy for the ESA - great job, it was a delightful fifty-seven hours.
I would like to finish the article with a poem:
Source: https://habr.com/ru/post/363061/
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