Poster presentations and abstracts

How to cite: Taheran, M., Duffard, R., Maier, P., Colin, A., Pahler, A., Bougueroua, S., Conti, L., Mueller, T., Lockowandt, C., Ortiz, J. L., Ångerman, M., Hanke, L., Janson, O., and Stelzer, B.: The STUDIO UV astronomy mission: a step towards a european ballon observatory, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-429, https://doi.org/10.5194/epsc2020-429, 2020.

How to cite: Phillips, C., Howell, S., Pappalardo, R., Senske, D., Korth, H., Kampmeier, J., Craft, K., Klima, R., and Leonard, E. and the Europa Clipper Science Team: Europa Clipper: Mission Status and Update, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-498, https://doi.org/10.5194/epsc2020-498, 2020.

Introduction

Planetary Radio Interferometry and Doppler Experiment (PRIDE) will exploit the signal recording and processing technology developed originally for Very Long Baseline interferometric (VLBI). The essence of PRIDE is in observing the spacecraft radio signal with a network of Earth-based radio telescopes. The PRIDE technique developed at the Joint Institute for VLBI ERIC (JIVE) together with its partners was used for several experiments with several ESA planetary science missions. It has been chosen by ESA as one of the eleven experiments of the Jupiter Icy Moons Explorer (JUICE), the first Large-class mission in the ESA’s Cosmic Vision 2015–2025 program. The mission is scheduled for launch in 2022.

Figure 1: A typical PRIDE Experiment  

1. PRIDE for JUICE Mission

PRIDE is a multidisciplinary component of the JUICE science suite. The main measured deliverables of PRIDE are lateral coordinates L(φ, θ) of spacecraft and the radial velocity of spacecraft. The former (main) measurable of PRIDE requires the phase-referencing VLBI observations (see Duev et al. [1]).  The latter employs the Doppler extraction technique described in [7,8]. Its prime deliverable will be used primarily for improvement of the Jovian system ephemerides in support to a variety of applications, ranging from gravimetry to geodynamics to fundamental physics. A typical PRIDE experiment is shown in Figure 1.

PRIDE observations are carried out by the ground segment when the spacecraft emits a radio signal for communication or radio science purposes. The methodology of PRIDE has been demonstrated with the ESA's Venus Express & Mars Express by Duev et al. 2012 [1], Molera Calvés et al. 2014 [2], Duev et al. 2016 [4], Molera Calvés et al. 2017 [8], Bocanegra et al. 2018 [7], Bocanegra et al. 2019 [8]. In addition to nominal science objectivities, the team is considering ad hoc observations around the Venus and Mars flybys during the cruise phase. A covariance analysis for a broad scope of the PRIDE measurable and Jovian system parameters have been performed to optimize the observation planning and the overall science impact of the JUICE mission (Dirkx. D et al. 2016 [4] & Dirkx. D et al. 2017 [5]).

2. Ongoing PRIDE observing projects

In 2020, we have begun a campaign to gather PRIDE tracking data of the InSight lander, with up to three tracking epochs scheduled for each of the three 2020 EVN sessions. The primary goal of these experiments is to serve as a preparatory activity for more intensive operations for ExoMars-LaRa [9].

The primary manner in which PRIDE will be able to contribute to the science objectives of LaRa is through the use of the Doppler data obtained by all receiving stations. As shown by the analysis of Bocanegra et al. 2018 [7], PRIDE Doppler data at X-band is similar, and in some cases, higher quality compared to regular closed-loop tracking data. One advantage of PRIDE lies in its diversity of receiving stations, making the data quality much less dependent on the meteorological or operational conditions at a single telescope.

Figure 2:  Frequency detections of Mars Insight (NASA) as seen from the University of Tasmania network of radio telescopes. The spacecraft signal was detected at the sky frequency of 8407.25 MHz and Doppler shift of 50 kHz along 70 minutes of tracking

Besides, we propose to merge the three-way Doppler data generated at each receiving station, to fully exploit the data encoded in all downlinks. This would allow an improved calibration of receiving station noise levels, as the noise incurred locally at the receiving ground station (including Earth tropospheric and ionospheric noise on the downlink) is independent for each station. We will use the InSight tracking data to test different practical approached to achieving this conceptual aim, and apply these ‘lessons learned’ to ExoMars-LaRa data analysis. In particular, we will apply the InSight tracking data to investigate different manners in which to weigh the data, considering the fact that the three-way Doppler noise generated at all receiving stations is highly correlated, and to investigate how inter-station biases and drifts can best be calibrated for. The results of the ongoing PRIDE observations of NASA's InSight probe will be reported elsewhere (Dirkx. D, Le Maistre. S, Dehant. V et al., in preparation).

References

How to cite: Pallichadath, V., Bahamon, T. B., Cimò, G., Dirkx, D., Duev, D., Gurvits, L., Calvés, G. M., and Vermeersen, B.: PRIDE: Ground-based VLBI observations for Spaceborne Probes , Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-647, https://doi.org/10.5194/epsc2020-647, 2020.

Different mass spectrometric approaches have been used to study the composition of ice and dust particles in space. Mass spectrometers onboard spacecraft such as Cassini, Rosetta and Giotto at Saturn, comet Churyumov-Gerasimenko and comet Halley respectively, have expanded our understanding of these planetary bodies by probing the composition of their dusty environments (Grün et al. 2019). The outstanding results from different space missions prove in situ mass spectrometry to be a reliable analytical tool with which to investigate the Solar System. Many of the mass spectrometers flown through the Solar System have used the impact ionisation technique, and an impact ionisation mass spectrometer, the Surface Dust Analyzer (SUDA), will be a part of NASA’s upcoming Europa-Clipper mission to Jupiter’s moon Europa. During the impact ionisation process, ice and dust grains impinging onto a detector’s solid target plate, at speeds above ≈ 1 km/s, generate a cloud of ions, neutrals and electrons (Srama et al. 2004; Auer & Sitte (1968)). The ions (cations in this work) are accelerated through a drift or reflectron region, towards a detector, from which time of flight mass spectra are generated (Friichtenicht et al. 1971).

Electrostatic accelerators are used to calibrate (Mocker et al. 2012) impact ionization mass spectrometers on Earth, accelerating micron and submicron cosmic dust analogue grains, typically metallic or with a conductive coating, to suitable velocities. As the controlled acceleration of µm-sized ice grains to these hypervelocities is not yet possible in the laboratory, an analogue experiment using Laser Induced Liquid Beam Ion Desorption (LILBID), is employed to simulate the impact ionisation process of ice grains in space (Klenner et al. 2019). In the LILBID process, a thin stream of an aqueous solution of, for example, organic compounds is exposed to laser irradiation in a vacuum. The dissolved compounds, together with the solvent matrix, are ionized and fragment when the matrix, in which charges are stochastically distributed, is dispersed (e.g. Wiederschein et al. 2015). By varying the laser power, as well the ion collection efficiency, it is possible to simulate the spectra which result from impact ionisation at varying impact speeds (Wiederschein et al. 2015, Klenner et al. 2019). The resulting cation time of flight mass spectra then contain mass spectral features corresponding to organic fragments and water cluster species. This technique has been successfully used (Postberg et al. 2009, 2018; Khawaja et al. 2019) to simulate the mass spectra produced when Cassini’s Cosmic Dust Analyzer (CDA) sampled salt- and organic-bearing ice grains emitted into space by Saturn’s moon Enceladus.

In this work we present a comparison between the mass spectral features of organic molecules generated by LILBID simulation of the impact ionisation mass spectra of organic-bearing ice grains, and the widely used standard technique of electron ionization (EI), the results of which can be found in existing databases, such as the National Institute of Standards and Technology (NIST) Chemistry WebBook.  In electron-ionisation (EI), the sample is directly exposed to a beam of high-energy electrons (≈ 70 eV) which converts neutral molecules into molecular ions (M⁺) with high internal energies. Owing to the generated energies, the structures of the molecular ions become unstable and break up, producing a characteristic population of fragment ions. We have compared the cationic fragments of isomeric carbonyl compounds measured with LILBID and with those from EI obtained from the NIST WebBook database. The tested compounds are divided into three pairs of aldehydes and ketones i.e., propanal & acetone, butanal & 2-butanone, hexanal & 2-hexanone, with 3, 4 and 6 carbon atoms, respectively. To compare the spectral features related to organic fragments, water-cluster features are excluded from the LILBID spectra. In most cases, both the LILBID and EI spectra of the compounds show typical cleavage patterns characteristic of carbonyls.

In ketones and aldehydes, for both LILBID and EI, we observe a correlation between the number of parent molecule carbon atoms and the relative intensities of particular cation fragments. We will present an in-depth comparison of the spectral features obtained from these techniques is currently, using LILBID spectra obtained for a mass spectral database applicable to the SUDA instrument on NASA’s Europa Clipper mission. The mass spectrometers (MASPEX & PEP-NIM) onboard Europa-Clipper, and ESA’s Jupiter Icy Moon Explorer (JUICE) spacecraft, respectively, will employ an EI (70 eV) technique, and the work presented here provides a valuable comparison and cross-calibration between the well-known EI and the more esoteric impact ionization techniques. Understanding the differences between the EI and impact-induced fragmentation and ionization behaviour of organics may also allow large existing libraries of EI spectra to be used to interpret the in situ impact ionization mass spectra of ice-free grains, such as those expected to be returned by JAXA’s Destiny+ mission to the unusual active asteroid 3200 Phaethon, progenitor of the Geminid meteor shower.

References

Grün, E., Krüger, H., & Srama, R. (2019) The dawn of dust astronomy, Space Sci Rev, 2015:46.

Srama, R. et al. (2004). The Cassini cosmic dust analyzer. Space Sci Rev, 114(1– 4), 465–518.

Auer, S., & Sitte, K., (1968). Detection technique for micrometeoroids using impact ionization. Earth and Planetary Sci Lett, 4,178–183

Friichtenicht, J. F., Roy, N. L., & Moede, L. W. (1971). Cosmic Dust Analyzer. Technical Report NASA2CR2140241.

Mocker, A. et al (2012). On the applicability of laser ionization for simulating hypervelocity impacts. Journal of Applied Physics, 112(10).

Klenner, F. (2019), Analogue spectra for impact ionization mass spectra of water ice grains obtained at different impact speeds in space, Rapid Communications in Mass Spectrometry, 33(22), 1751–1760.

Wiederschein, F. et al. (2015) Charge separation and isolation in strong water droplet impacts. Physical Chemistry Chemical Physics. PCCP, 17(10), 6858–64.

Postberg, F. et al. (2009) Sodium salts in E ring ice grains from an ocean below the surface of Enceladus. Nature, 459, 1–4.

Postberg, F. et al. (2018) Macromolecular organic compounds from the depths of Enceladus, Nature, 558(7711), pp. 564–568.

Khawaja, N. et al. (2019) Low-mass nitrogen-, oxygen-bearing, and aromatic compounds in Enceladean ice grains, Monthly Notices of the Royal Astronomical Society, 489(4), pp. 5231–5243.

How to cite: Khawaja, N., Hillier, J., Klenner, F., Nölle, L., and Postberg, F.: Comparative Study of Mass Spectrometry Techniques Relevant to Current and Future Space Missions, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-827, https://doi.org/10.5194/epsc2020-827, 2020.

Abstract

The Ganymede Laser Altimeter (GALA) is one of ten instruments selected for ESA’s Jupiter Icy Moons Explorer (JUICE) mission. We will present an overview on the scientific goals as well as on the status of the instrument development and performance analysis.

ESA’s JUICE mission will explore Jupiter, its magnetosphere and satellites first in orbit around Jupiter before going finally into polar orbit around Ganymede [1]. GALA is one of ten payloads on-board the spacecraft and is developed under responsibility of the DLR Institute of Planetary Research in collaboration with industry and institutes from Germany, Japan, Switzerland and Spain. Its major objectives are to measure the surface topography and the tidal deformation of the satellite.

JUICE (Jupiter Icy Moons Explorer) will be the first orbiter around a moon (other than Earth’s moon) in solar system exploration. Its launch is planned for May/June 2022 followed by an interplanetary cruise of 7.6 years. Jupiter orbit insertion will take place by the end of 2029. An orbit maneuver will bring the spacecraft into a 500-km circular orbit in which it will be staying for at least 132 days until end of nominal mission. The latter phase will be the main period for GALA taking data. In addition data will be taken at Europa, Ganymede, and Callisto at closest approaches of flybys in the Jupiter orbiting phase.

GALA has two main objectives: (1) by range measurements it shall obtain Ganymede’s topography on global, regional and local scales. This will reveal how surface features have formed and how they are connected with the shallow interior ice shell. Global shape measurements will tell us whether the satellite is in hydrostatic state with respect to rotational and tidal forces. (2) Obtaining range measurements distributed in time along the orbital cycle, tidal variations of surface elevations will be measured. The tidal amplitudes are indicative for the presence of a subsurface ocean and would (together with complementary measurements) constrain the ice-I shell thickness [2].

GALA is a single-beam altimeter: a laser pulse (at 1064 nm wavelength) is emitted by using an actively Q-switched Nd:YAG laser firing at 30 Hz in nominal operation. A small fraction of the pulse is guided through fiber optics onto the detector characterizing the outgoing pulse and time of emission. After about 3 msec the Lambertian reflection of the pulse from the surface is received by a aperture telescope and transferred to the detector, an Avalanche Photo Diode. The signal is digitized at a sampling rate of 200 MHz and transferred to the range finder module, which determines (a) the time of flight between the emission and receiving of the pulse (b) the pulse shape, in particular the pulse-width, and (c)  the energy of the received pulse. From the time of flight of the wave-package and the spacecraft position and attitude, the distance for each shot can be converted into height above a reference surface in post-processing of the data.