Small-mass and small-volume sensors and instruments are holding
an increasing role in planetary missions, because they allow to
save resources and costs. Cubesat, microsatsats and nanosatellites based
missions are further encouraging the development of miniaturized
This session is opened, but not restricted, to the following topics:
a) presentations of small instruments flown on previous missions,
and analysis of the data they provided; b) presentations of
small instruments, sensors and cubesats on board ongoing and
planned missions; c) studies and concepts for future instrument/payload/mission
applications; d) laboratory and testing activity related to this topic.
Birgit Ritter, Özgur Karatekin, José A Carrasco, Elisa Tasev, Higinio Alavés Mañogil, Matthias Noeker, Emiel Van Ransbeek, Guillaume Noiset, and Cem Berk Senel
With the gravimeter for small solar system objects (GRASS), absolute surface accelerations in the order of nano-g can be measured. It is an innovative and extremely compact sensor that will fly as part of ESA’s Hera mission onboard the Juventas CubeSat to the binary asteroid system Didymos. In 2027, Juventas will land on the secondary body of the system, Dimorphos, and GRASS will hence measure the local gravity vector and its temporal variations at the landing site. Apart from the direct mass determination, these measurements will help in synergy with other instruments to constrain the geological substructure as well as the surface geophysical environment.
The instrument is currently under development at the Royal Observatory of Belgium, funded by the Belgian PRODEX office and in cooperation with EMXYS in Spain.
The average gravitational force expected on Dimorphos’ surface is around 4.5 x 10-5 m s-2 (or 4.5 mGal, Figure 1). Apart from the self-gravitation of the body, centrifugal forces and the acceleration due to the main body of the system contribute to the surface acceleration. The temporal variation of the signal is driven by the dynamical state of Didymoon with respect to Didymain and the related librations.
Figure1: Modeled surface gravity in the Didymos system (left) and on Dimorphos (right). Note that only a shape model for the primary body exists.
The table below lists the science objectives of the instrument for Dimorphos.
S#1 Local subsurface inhomogeneities and global mass of Dimorphos.
Determination of local gravity vector at landing location with accuracy of <1% in direction and amplitude.
S#2 Dimorphos dynamical state
Investigation of surface acceleration variations due to rotation kinematics, tides and orbital dynamics. Measurements as for S#1, but for several locations along the orbit of Dimorphos around Didymos.
S#3 Global gravity solution, interior structure and surface mass transport
Synergy of data with other instruments (radar, radio, CubeSat decent, star trackers) to obtain holistic view of gravity and interior.
The gravimeter measurement system consists of monitoring the displacement and deflection of a flat spring due to a gravitational field by a capacitive transducer. Modulation of the measured g-vector by rotation allows the rejection of the zero-g bias. In addition, no levelling is required. The gravimeter will be calibrated in-situ by using electrostatic force to compensate acceleration forces.
Two orthogonally aligned gravimeter axes, each with a rotating sensor head, enable finally the reconstruction of the full 3D gravity vector. Figure 2 shows a CAD drawing with dimensions (left) and the vibration test model of the gravimeter (right).
Figure 2: CAD drawing of the two-axes gravimeter (left) and a picture of the assembles GRASS vibration test model (right)
We will present the scientific background and application of the GRASS instrument on Dimorphos, the current instrument status, its implementation and first test results and give an outlook on future application of the instrument for other small planetary bodies.
How to cite:
Ritter, B., Karatekin, Ö., Carrasco, J. A., Tasev, E., Alavés Mañogil, H., Noeker, M., Van Ransbeek, E., Noiset, G., and Berk Senel, C.: Measuring gravity with the GRASS instrument on the Hera mission, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-1115, https://doi.org/10.5194/epsc2022-1115, 2022.
Ernesto Palomba, Fabrizio Dirri, Andrea Longobardo, Chiara Gisellu, David Biondi, Marianna Angrisani, Emiliano Zampetti, Diego Scaccabarozzi, and Bortolino Saggin
Introduction: The Solar System dust is the smallest Solar System building block, and therefore its study allows understanding the early stages of the Solar System formation. The comprehension of the Solar System formation and evolution processes is also constrained by the inventory and spatial distribution of volatiles in our System. In particular, the delivery process of volatiles of astrobiological interest (water and organics) to the Earth is a key issue to understand the life formation in our planet. Asteroids and comets may have been the source of these volatiles to the terrestrial planets’ atmospheres and to the Earth’s oceans. The boundary between asteroids and comets is not well defined, and many main-belt asteroids are probably volatile-rich and would become cometary if they were moved to the inner Solar System.
Piezoelectric Crystal Microbalances (PCMs) are widely used sensors to monitor dust and particles deposition processes in space and to characterize material outgassing in vacuum. This kind of sensors converts mass changes into fundamental resonance frequency variations, according to Sauerbrey equation .
In this work we present VISTA (Volatile in-Situ Thermogravimeter Analyser), one of the two scientific payloads on board MILANI Cubesat, as part of the ESA Hera Program. The MILANI Cubesat development is led by Tyvak International, prime contractor of a consortium composed by entities and institutions from Italy, Czech Republic and Finland. The main MILANI objective is executing a scientific mission aiming at studying the binary asteroid system Didymos-Dimorphos, characterizing the asteroid with a dust sensor, i.e. VISTA, and a spectrometer, i.e. ASPECT. VISTA is developed by an Italian Consortium composed by three Research Institutes: INAF-IAPS (National Institute of Astrophysics - Institute for Space Astrophysics and Planetology), CNR-IIA (National Council of Research – Institute of Atmospheric Pollution) and Politecnico di Milano.
HERA Mission goals: Hera is a planetary defence mission under development at the European Space Agency (ESA), launching in October 2024.Hera is the European contribution to the international Asteroid Impact Deflection Assessment (AIDA) cooperation, the first planetary defence mission, in collaboration with NASA, who is responsible for DART (Double Asteroid Redirection Test) kinetic impactor spacecraft. Hera will travel to a binary asteroid system, the Didymos-Dimorphos pair of near-Earth asteroids, and will study and characterize the asteroid system after the DART impact in September 2022. In the framework of Hera mission, VISTA will accomplish the following scientific goals: 1) detect the presence of dust particles smaller than 10 µm (residual dust particles from the impact and suspended dust in the binary system or coming from dust levitation process); 2) characterization of volatiles (e.g. water) and light organics (e.g. low carbon chain compounds) by using Thermo-Gravimetric Analysis (TGA) cycles (the desorption rates ad specific temperatures are used to characterize e volatiles and organics desorbed from the sensor surface); 3) molecular contamination monitoring in support to other Cubesat instruments and ASPECT spectrometer, coming from outgassing processes on-board the spacecraft, that usually happen in the first days or weeks in orbit.
VISTA Heritage: The Consortium has a considerable heritage in the design, manufacturing and testing of PCM-based instrumentation both for laboratory and space applications coming from different ITT-Emits ESA Projects: 1) CAM (Contamination Assessment Microbalance), developed for “Evaluation of an in-situ Molecular Contamination Sensor for space use” (2014-2016) (Figure 1); 2) CAMLAB (Contamination Assessment Microbalance for LABoratory) developed for “Development of a European Quart Crystal Microbalance” (2017-2019) (Figure 2).
Figure 1. PCM Engineering Model developed during CAM-ESA Project for space applications.
Figure 2. PCM breadboard developed during CAMLAB-ESA Project for laboratory applications.
Working principle: PCMs exploit the piezoelectric properties of quartz crystals, as mass deposition on the sensing area of the instrument induces variations of the crystal resonance frequency. The core of VISTA is composed of: 1) two quartz crystals mounted in a sandwich-like configuration (one sensing crystal and the other reference crystal); 2) a Thermal Control System (TCS), composed by two integrated heaters and a Thermoelectric Cooler (TEC); 3) a Proximity Electronics (PE). The instrument is also capable of performing Thermo-Gravimetric Analysis, a technique used to monitor thermal processes involving volatile compounds, e.g absorption/desorption and deposition/sublimation, by means of the built-in heaters. The TEC is used to cool down the sensor and enhance the condensation of particles on the microbalance. VISTA is capable of monitoring particles lower than 5-10 µm and sub-µm particles.
VISTA technical characteristics are shown in Table 1.
Table 1. VISTA technical characteristics.
The sublimated compounds can be characterized by calculating the enthalpy of sublimation ΔHsub, which can be retrieved with two methods: 1) by considering the deposition rates and using Van’t Hoff relation ; 2) by using Langmuir relation .
Conclusions and future works: In this work, the VISTA instrument working principle and heritage were presented. Qualification activities are currently ongoing on the VISTA Engineering Qualification Model (EQM), shown in Figure 3, in order to qualify the sensor within the expected mechanical and thermal environment and evaluate the instrument performances in a representative environment, prior integration on the MILANI Cubesat. The next phase of the research activities will be the manufacturing, integration and testing of VISTA Flight Model (FM), that will launch in 2024.
Figure 3. VISTA EQM developed for MILANI cubesat/HERA Space Mission.
References:  G. Sauerbrey 1959, Z. Phys., 155, 206-222;  Palomba E. (2016), OLEB, 46 (2-3);  S.W. Benson et al. 1968;  I. Langmuir, 1913.
How to cite:
Palomba, E., Dirri, F., Longobardo, A., Gisellu, C., Biondi, D., Angrisani, M., Zampetti, E., Scaccabarozzi, D., and Saggin, B.: Volatile in-Situ Thermogravimeter Analyser (VISTA) payload developed for MILANI cubesat for HERA Space Mission , Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-927, https://doi.org/10.5194/epsc2022-927, 2022.
Chiara Gisellu, Fabrizio Dirri, Ernesto Palomba, Andrea Longobardo, David Biondi, Marianna Angrisani, Emiliano Zampetti, Diego Scaccabarozzi, and Bortolino Saggin
Introduction: Quartz Crystals Microbalances (QCMs) are widely used sensors for monitoring and characterizing dust and particles deposition processes in different planetary environments and measuring material contamination coming from outgassing sources in space, in support to other instruments (e.g. spectrometers). Furthermore, they are capable of detecting and measuring the presence of volatile com-pounds of astrobiological interest such as water and organics. These measurements can be particularly relevant when performed on primitive asteroids or comets, or on targets of potential astrobiological interests, e.g. Mars . These sensors convert mass changes into fundamental resonance frequency variations, according to Sauerbrey equation .
The VISTA (Volatile In Situ Thermogravimetry Analyser) instrument is a QCM-based device able to perform measurements of abundance of volatiles and dust particles in planetary and asteroidal environments. The instrument can characterize the planetary regolith from 5-10 µm to sub-µm particles and monitor the contamination processes on board satellites (cubesat, etc.) caused by molecular outgassing. VISTA is one of the two scientific payloads of MILANI CubeSat, developed by Tyvak International that leads a consortium composed by entities and institutions from Italy, Czech Republic and Finland, in the framework of the Hera program of the European Space Agency (ESA). Hera, due to launch in 2024, is the ESA part of the Asteroid Impact & Deflection Assessment (AIDA) international collaboration with NASA, who is responsible for the Double Asteroid Redirection Test (DART) kinetic impactor spacecraft. The main objective of MILANI is the study of the binary asteroid system Didymos-Dimorphos, characterizing the asteroid with a dust sensor (VISTA) and a spectrometer (ASPECT).
In this work, the calibration operations and the performance tests, to assess VISTA capability of characterizing volatile compounds and simulant contaminations in vacuum chamber at low temperatures. The sensor has been developed by an Italian Consortium composed by three Research Institutes: INAF-IAPS (National Institute of Astrophysics - Institute for Space Astro-physics and Planetology), CNR-IIA (National Council of Research – Institute of Atmospheric Pollution) and Politecnico di Milano and led by INAF-IAPS.
Figure 1. VISTA EQM developed for ESA Hera space mission.
Working Principle: The instrument core is a QCM whose frequency variations directly depends on the deposited sample mass on the crystal surface during sublimation, condensation and absorption/desorption processes. The instrument consists of: 1) two quartz crystals mounted in a sandwich-like configuration; 2) a Thermal Control System (TCS), composed by two integrated heaters and a Thermoelectric Cooler (TEC); 3) a Proximity Electronics (PE). VISTA is also capable of performing Thermo-Gravimetric Analysis, which is a technique used to monitor thermal processes involving volatile compounds, e.g. deposition/sublimation and absorption/desorption. It can also monitor particles lower than 5-10 µm and sub-µm particles .
Calibration: The QCM frequency can change not only due to the mass deposition/release, but also due to the variation of environmental parameters, such as temperature and pressure. In order to disentangle frequency variations due to mass deposition and environmental parameters, the sensor is calibrated by measuring the frequency as a function of temperature. According to literature , the frequency-temperature curve follows a third-degree polynomial (Figure 2).
Figure 2. QCM frequency as a function of temperature in vacuum.
Performance tests: VISTA capability to detect contaminant depositions and to monitor the accumulation and desorption processes is verified by placing an effusion cell containing an organic compound, used as a contamination source, placed in the Field Of View (FOV) of the sensing crystal and heated up to 100°C. The experimental setup is shown in Figure 3.
Figure 3. VISTA EQM experimental setup for contamination simulation.
The QCM is connected with four screws with a copper U shape and in contact with a cold sink set to -10°C to help the molecules condensation on the crystal surface. The frequency is monitored during the tests and the deposited flux can be retrieved (Figure 4) at each temperature set point.
Figure 4. Deposition test from +50°C to +100°C.
Two methods can be used to retrieve the enthalpy of sublimation ΔHsub by using the deposition rates, i.e. the Van’t Hoff relation  or Langmuir relation . Thus, by measuring two different deposition rates, k1 and k2, at two different close temperatures T1 and T2, it is possible to obtain the compound ΔHsub by means of Van’t Hoff relation or throughout the temperature range by using Langmuir relation.
TGA cycles are then performed by heating the crystals by means of the built-in heaters. After the heating cycles, the frequency returns to its initial value, thus indicating that all the deposited mass desorbed during the test (Figure 5).
Figure 5. TGA cycles from +15°C to +50°C and from +40°C to +70°C.
The desorption rates from crystals surface can be used as well to calculate the ΔHsub and compare it with the ΔHsub results obtained during the depositions/contamination processes.
References:  E. Palomba et al (2016), OLEB, 46(2-3;  G. Sauerbrey (1959), Z. Phys., 155, 206-222;  D. Salt (1987);  S.W. Benson et al., 1968;  I. Langmuir, 1913.
How to cite:
Gisellu, C., Dirri, F., Palomba, E., Longobardo, A., Biondi, D., Angrisani, M., Zampetti, E., Scaccabarozzi, D., and Saggin, B.: Calibration and performance tests of VISTA, a microbalance for asteroid dust characterization and contamination for space mission applications, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-790, https://doi.org/10.5194/epsc2022-790, 2022.
Thermal Infrared Imager TIRI onboard Hera is now being developed for the investigation of the binary asteroid Didymos and Dimorphos in the European Space Agency Hera mission. This instrument uses a heritage from the Thermal Infrared Imager TIR on Hayabusa2, which observed the C-type asteroid 162173 Ryugu. In the Hera mission, its updated version of instrument is based on Lynred PICO 1024 Gen2 bolometer array (1024 x 768 effective pixels) with almost 4 times higher spatial resolution than TIR. The wavelength range shows 8-14 µm for the thermal average images, as well as 7.8, 8.6, 9.6, 10.6, 13.0 deg for multi-bands). Its FOV covers 13.3 x 10.0 deg with the spatial resolution of 0.013 deg/pixel.
TIRI is now in the test process to check its full functions and performances as well. The calibration for TIRI is to check its focus, to conduct radiometric and geometrical corrections, identification of materials (like terrestrial rocks and meteorites). A set of apparatus were prepared by the TIRI PI team using the collimator (Aperture: 200mm dia., temperature range of -20 to 150℃, Focal position is 60 deg or higher), the flat cavity blackbody ( 175 x 175 mm, -20 to 125 ℃ for fact change of temperature), and a cold plate plus the cryocooler for the target sample (room temperature to -123 deg). There are some rocks and meteorites to be set as the multiband test samples at the target material, With these information and the presentation, details of the TIRI preparation and development are shown. The test results for TIRI will be presented with some data set and physical properties using the sample.
How to cite:
Okada, T., Tanaka, S., Sakatani, N., Shimaki, Y., Arai, T., Senshu, H., Demura, H., Sekiguchi, T., Kouyama, T., Kanamaru, M., and Ishizaki, T.: Calibration of the Thermal Infrared Imager TIRI onboard Hera, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-1191, https://doi.org/10.5194/epsc2022-1191, 2022.
Stefano Ferretti, Vincenzo Della Corte, Alice Maria Piccirillo, Hanna Rothkaehl, Matthew Sylvest, Manish Patel, Hanno Ertel, Mark Millinger, Ivano Bertini, Stefano Fiscale, Andrea Longobardo, Laura Inno, Alessandra Rotundi, Eleonora Ammannito, and Giuseppe Sindoni
Introduction: The dust ejected by cometary nuclei encodes valuable information on the formation and evolution of the early Solar System. Several short-period comets have already been studied in situ, but their pristine condition was modified by multiple perihelion passages. Dynamically new comets (DNCs) remain pristine bodies since they never visited the inner Solar System, stationing more than 2000A.U. far away from the Sun in the Oort cloud.
Comet Interceptor (CI) is the first F-class space mission selected by the European Space Agency to study a DNC or an interstellar object entering the inner Solar System for the first time. The Dust Impact Sensor and Counter (DISC) is an instrument included in the Dust Field and Plasma (DFP) suite, part of the CI payload, dedicated to characterizing the dust encountered by the spacecraft (S/C) during its flyby in the coma of the target DNC. DISC will measure hypervelocity impacts (HVIs), in the range 10–70km/s, with cometary dust particles of 1–400μm diameter. It aims to characterize the mass distribution of dust particles in the range 10-15–10-8kg, and retrieve information on dust structural properties from impacts duration.
DISC design: DISC is a 121×115.5×46mm3 aluminum box containing both the detection system and the electronics (Fig.1). The former consists in a 100×100×0.5mm3 aluminum plate with three piezoelectric traducers (PZTs) at its corners. HVIs induce shockwaves in the sensing plate. Far from the impacted area, such waves become acoustic Lamb waves that propagate up to the PZTs, which start to vibrate at their resonant frequency. A couple of electronic boards at the bottom of the unit allows to retrieve the particles momentum and kinetic energy from PZTs vibration signal.
Fig.1: DISC sensing element and dust shield design.
DISC detection system is derived from the GIADA Impact Sensor measurement subsystem, that was designed to measure impacts of slow particles. During CI flyby, some hypervelocity dust particles might perforate DISC outer sensing diaphragm and represent a serious hazard for the instrumentation. A dedicated mechanical element preliminarily designed as made of four 1cm-thick aerogel blocks and a 1mm-thick aluminum frame was integrated into DISC design to shield the entire S/C from such dangerous impacts.
Two key aspects need to be verified to ensure that the instrument is suitable for CI aims:
DISC capability to survive the expected coma dust environment;
DISC capability to measure the momentum/energy of impacting particles in the aforementioned size and mass ranges.
Dust shield assessment: We verified DISC dust shield performance using a two-stage Light-Gas Gun (LGG) (Open University, Milton Keynes) to shoot mm-sized particles of various materials at speeds around 5km/s[5,6]. This facility allowed to test the instrument resistance to momenta in the range 10-2–10-1kg·m/s and to energies of the order of 102J. The dust shield showed good resistance up to energies of about 200J, released by a 3mm nylon bead at 5.5km/s. DISC resistance to higher-energy particles can be improved by increasing the aerogel thickness, without any further modifications to the general design.
These experiments proved that DISC is compatible with the foreseen coma dust environment. Integrating a thicker aerogel layer in the design will reduce the risk of failure due to higher-energy particles to low enough values even for the S/C more exposed to the dust flux. The S/C beneath DISC unit is further protected by DISC lower layers.
DISC performance: DISC will measure momenta in the range 10-11–10-3kg·m/s. The LGG facility allows to reach high momentum values by shooting heavy particles, but their collision dynamics is very different from what expected for cometary dust. A different strategy to simulate the foreseen impact momentum range is needed.
A Van der Graaf (VdG) gun can shoot μm-sized dust particles up to 20km/s, reproducing momenta of 10-9–10-7kg·m/s.
The tested impact parameters range can be extended by simulating HVIs effects with a high-power pulsed laser beam. Laser intensity, beam dimension, and pulse duration can be regulated to respectively match impact pressure, section, and shock duration of the corresponding particle. Laser intensities of 109–1010W/cm2 can generate surface pressures from kbar to Mbar, typical of cometary dust particles colliding at 3–6km/s. Using our Nd:YAG laser (λ=1064nm), which emits τ=6ns pulses with pulse energy of Epulse=1.2J, we can cover a momentum range of 10-10–10-5kg·m/s. Since laser simulated and VdG real impacts share part of the released momentum range, laser shots can be calibrated and their representativity verified with real collisions.
The energy range expected for dust impacts measured during CI flyby is 10-7–102J. Laser simulated impacts cannot reach the higher energy values. However, the energy/pulse duration range is pretty vast and with some attenuators and pulse reducers the central/left part of the parameters space (around mJ energy and ns pulse time) could be reasonably covered.
Fig.2. shows the optical setup: a polarizer attenuator splits the beam and allows to regulate its power; a couple of mirrors prevents backwards reflections to get to the laser output aperture; a beam expander enlarges the beam, which enters a vacuum chamber and is focused by a plano-convex lens on the DISC breadboard mounted on a 3-axis translational stage. The vacuum chamber is fundamental to prevent plasma generation in air around the focus.
Fig.2: Optical setup for high-power pulsed laser simulated HVIs.
By properly tuning the laser parameters, this strategy allows to achieve representative simulations of cometary dust HVIs. In addition to assess DISC performances, simulating the same impact many times provides large statistics to calibrate DISC detection system and momentum/kinetic energy retrieval methodology with great accuracy.
References:  Keller H. U. and Kührt E. (2020) Space Sci. Rev., 216(1), 1–26.  Snodgrass C. and Jones G. H. (2019) Nat. Commun., 10(1), 1–4.  Della Corte V. et al. (2021) LPSC LII, Abstract #2332.  Esposito F. et al. (2002) Adv. Space Res., 29(8), 1159–1163.  McDonnell J. A. M. (2006) Int. J. Impact Eng., 33(1–12), 410–418.  Hibbert R. et al. (2017) Procedia Eng., 204, 208–214.  Di Paolo F. et al. (2021) LPSC LII, Abstract #1238.  Friichtenicht J. F. (1962) Rev. Sci. Instrum., 33(2), 209–212.  Pirri A. N. (1977) Phys. Fluids, 20(2), 221–228.
How to cite:
Ferretti, S., Della Corte, V., Piccirillo, A. M., Rothkaehl, H., Sylvest, M., Patel, M., Ertel, H., Millinger, M., Bertini, I., Fiscale, S., Longobardo, A., Inno, L., Rotundi, A., Ammannito, E., and Sindoni, G.: Analysis of dust shield and detection system response to hypervelocity impacts for Comet Interceptor Dust Impact Sensor and Counter, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-1163, https://doi.org/10.5194/epsc2022-1163, 2022.
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