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Between 2006 and 2016, the Cassini spacecraft carried out 13 bistatic radar observations of the surface of Saturn's largest moon, Titan. Unmodulated right circularly polarized radio signals were transmitted by the spacecraft to the moon’s surface. Cassini’s high gain antenna was pointed so that specular reflections from Titan’s surface were received on Earth. Proper processing of right (RCP) and left circularly polarized (LCP) echoes from the moon can provide information about surface roughness and near-surface relative dielectric constant (ɛr) of the illuminated terrains.During Titan flybys T101, T102, T106, and T124, the track of the bistatic observations crossed the main stable liquid bodies of the north pole of Titan: Ligeia, Kraken, Punga Mare, and their estuaries. Strong and narrowband X-band (λ=3.6 cm) echoes were successfully detected from the seas at the Deep Space Network 70-meter station in Canberra.Reflected spectra feature Dirac-like shapes, with a spectral broadening around 1 Hz and lower bounded by the processing time resolution. Compared to bistatic observations of other planets, this implies unprecedentedly low RMS slope values for Titan’s seas on an effective length-scale of a few meters. Profiles of reflected LCP and RCP power are in general consistent with purely coherent reflections from the Fresnel area around the moving specular point, indicating a very flat surface.In addition, from the circular polarization power ratio, the surface dielectric constant can be derived. This can enrich our current understanding of the chemistry of Titan’s liquid hydrocarbon seas, further constraining their methane-ethane mixing ratio. From Cassini RADAR, VIMS, and ISS, Titan’s seas are expected to be ternary mixtures of methane, ethane and nitrogen (ɛr ≈ 1.6-1.9). From bistatic radar data, significant relative variations in liquid hydrocarbon composition are seen, and an unexpected correlation between the dielectric constant and incidence angle of observation seems to arise. The absolute values of permittivity are somewhat lower than expected.From the computed dielectric constant values, physical optics models are used to constrain the RMS height of the surface. This analysis provides meaningful insights into the presence of small capillary waves in the order of millimeters over the liquid surfaces of Titan, as already detected by Cassini monostatic RADAR.

In 1989 the Voyager 2 spacecraft performed a flyby of the Neptune system. In particular, a radio occultation of Triton’s ionosphere was performed on 25 August 1989. Results from this occultation experiment were published in Science by Tyler et al., and the atmospheric profiles of Triton were estimated via analysis of the real-time tracking and monitoring systems data at time resolutions of about 1 second.In recent years, thanks to an increase in the computational power of microprocessors and an expansion in their fields of application, there has been a surge in the development of optimal estimators for stochastic signals. In this context, we present a re-analysis of the radiometric data received by the Voyager 2 spacecraft during its radio occultation experiment of Triton. Using one of the latest algorithms developed in the field of signal parameters estimation, we use the radiometric measurements received during the ingress and egress phases of the mission to accurately reconstruct the sky frequency, as received by the DSS-43 antenna at the time of occultation. In particular, by performing spectral interpolation and tuning the processing parameters, we increased the frequency resolution and detection threshold around the ingress and egress epochs to maximize the scientific return from the radiometric data collected over 30 years ago.Since Voyager 2 transmitted two coherently related signals (at S and X bands), the two series of sky frequencies can be combined to isolate the Doppler frequency shift due to dispersive effects. The latter is used to compute the electron number density profiles inside the Triton ionosphere using a classical Abel transform-based method. Also, a Monte Carlo procedure is used to evaluate uncertainties in the derived profiles. The results of this analysis are consistent with those presented in the past literature, with the only difference of a slight (but important for the planning of future missions) shift in the ionosphere's peak altitude due to the use of updated Voyager and Triton ephemerides. The methods and data analysis approaches presented in this work are very relevant to the exploration of the Ice Giants, in particular for radio science observations of satellite tenuous exospheres and ionospheres.

This paper discusses the analysis of the UHF (401 MHz) plasma-induced communications blackout (and brownout) experienced by the Mars InSight spacecraft during its entry, descent, and landing (EDL) ...

Quantum mechanics governs the microscopic world, where low mass and momentum reveal a natural wave–particle duality. Magnifying quantum behaviour to macroscopic scales is a major strength of the technique of cooling and trapping atomic gases, in which low momentum is engineered through extremely low temperatures. Advances in this field have achieved such precise control over atomic systems that gravity, often negligible when considering individual atoms, has emerged as a substantial obstacle. In particular, although weaker trapping fields would allow access to lower temperatures1,2, gravity empties atom traps that are too weak. Additionally, inertial sensors based on cold atoms could reach better sensitivities if the free-fall time of the atoms after release from the trap could be made longer3. Planetary orbit, specifically the condition of perpetual free-fall, offers to lift cold-atom studies beyond such terrestrial limitations. Here we report production of rubidium Bose–Einstein condensates (BECs) in an Earth-orbiting research laboratory, the Cold Atom Lab. We observe subnanokelvin BECs in weak trapping potentials with free-expansion times extending beyond one second, providing an initial demonstration of the advantages offered by a microgravity environment for cold-atom experiments and verifying the successful operation of this facility. With routine BEC production, continuing operations will support long-term investigations of trap topologies unique to microgravity4,5, atom-laser sources6, few-body physics7,8 and pathfinding techniques for atom-wave interferometry9–12. A Bose–Einstein condensate prepared in low Earth orbit shows a free-expansion time greater than one second, demonstrating the advantages of a microgravity environment for such studies.

The Goldstone Solar System Radar (GSSR) facility is the largest fully steerable ground-based radar in the world for nonclassified high-resolution ranging and imaging of planetary and small-body targets. Over the years, the use of the GSSR to detect and characterize near-Earth objects (NEOs) has become critical to keep track of potential Earth-impacting hazardous NEO. This article relates the specific modifications made to the GSSR hardware and procedures in the last few years, as well as the new capabilities derived from those upgrades: reduced complexity in remote operations, increased experimental design versatility, and increased performance on bistatic radar experiments from GSSR to other complexes. In addition, we dedicate a section to provide an update on the current GSSR power capabilities as the new klystrons are installed. The work detailed in this article is intended to reach the broader science community in order to communicate how those modifications and the derived new capabilities can make science experiments more successful.

Spacecraft-to-ground bistatic radar is an established technique that has enabled the study of the planetary surfaces and near sub-surfaces properties by using the telecommunication signals amplitude, phase, and polarization. The Planetary Radar and Radio Science group at the Jet Propulsion Laboratory (JPL) has been involved in many planetary bistatic radar experiments since the 1970's using orbiters and Deep Space Network (DSN) antennas. The recent advances in Unmanned Aerial Vehicles (UAVs) technologies are making the UAVs more popular in scientific surveying applications. One such application is the use of UAVs in bistatic radar measurements to explore surfaces on Earth. Our analyses show that UAV-based bistatic radar measurements will improve our understanding of the finer-scale characteristic variations of the surface by acquiring the higher resolution data for a specific region of interest compared to data obtained from a spacecraft. The Mars helicopter, a technology demonstration to test the first powered flight on Mars, will be the beginning of a new era of exploration with UAVs on Mars. This leap in planetary UAV technology has renewed the importance of developing a miniaturized bistatic radar instrument (under 1 kg) compatible with a UAV platform able to meet the science requirements for studying surfaces on Earth, Mars, and other planetary bodies. As part of a task at JPL, we have been working on a technology demonstration using a compact bistatic radar instrument designed to be the payload of a UAV employing signals of opportunity from Earth's orbiters, i.e. Global Positioning System (GPS). In this paper, we present our design and development of the instrument, our evaluation of different L-band antennas, the performance of compact open-loop receivers in support of Earth and planetary bistatic radar observations, and the instrument fit test on an UAV platform. As part of this publication, we also highlight the results of a field experiment dedicated to test the sensitivity of the miniaturized bistatic radar instrument to different electrical properties of the surface.

The Juno Gravity Science Instrument is a radio science instrument onboard the Juno spacecraft, which entered orbit around Jupiter in 2016. The prime objective of the radio science investigation is to estimate the gravitational field of Jupiter from the Doppler shift on the radio link between the spacecraft and the Earth-based observing antennas of NASA's Deep Space Network (DSN). The instrument is composed of a ground component at the DSN's DSS-25 antenna, equipped with simultaneous X-band and Ka-band transmitters and receivers, and a spacecraft component, which includes X-band and Ka-band transponders to relay the transmitted signal back to Earth. The frequencies of these signals are measured using sensitive open-loop and closed-loop receivers of the DSN. Using the unique geometry of Juno's orbit around Jupiter and the exquisite precision of the radio science instrumentation (∼5-10 microns/sec one-way), the gravity field of Jupiter has been probed to unprecedented precision, allowing for discoveries of Jupiter's core size and depth of the zonal winds. This precision is thanks to detailed data processing and calibration techniques. An Advanced Water Vapor Radiometer measures the tropospheric delay and a linear combination of X-band and Ka-band links calibrates for Earth ionosphere, solar plasma, and Jovian plasma. Recent measurements probed the electron content inside Jupiter's Io Plasma Torus, a doughnut-shaped ring of charged particles caught in Jupiter's magnetosphere. Results from these measurements not only contributes to the scientific literature but also informs the performance of the instrument itself and can be used in future planning.

International audience; The Venus Express Radio Science Experiment (VeRa) was part of the scientific payload of the Venus Express (VEX) spacecraft and was targeted at the investigation of Venus’ atmosphere, surface, and gravity field as well as the interplanetary medium. This paper describes the methods and the required calibrations applied to VEX-VeRa raw radio occultation data used to retrieve vertical profiles of Venus’ ionosphere and neutral atmosphere. In this work we perform an independent analysis of a set of 25 VEX, single-frequency (X-band), occultations carried out in 2014, recorded in open-loop at the NASA Deep Space Network. Our temperature, pressure and electron density vertical profiles are in agreement with previous studies available in the literature. Furthermore, our analysis shows that Venus’ ionosphere is more influenced by the day/night condition than the latitude variations, while the neutral atmosphere experiences the opposite. Our scientific interpretation of these results is based on two major responsible effects: Venus’ high thermal inertia and the zonal winds. Their presence within Venus’ neutral atmosphere determine why in these regions a latitude dependence is predominant on the day/night condition. On the contrary, at higher altitudes the two aforementioned effects are less important or null, and Venus’ ionosphere shows higher electron density peaks in the probed day-time occultations, regardless of the latitude.

The Galileo radio tracking data were reanalysed exploiting the new knowledge of Jupiter obtained by the Juno mission, together with modern orbit determination techniques developed for the Cassini data analysis. Using Doppler data acquired during six encounters of Europa an updated gravity field of the moon was obtained, resulting in a value of C22 statistically different from the available literature. The new value suggests a thinner ice-water shell and a less dense interior.

Measuring the depth of Jupiter’s storms The atmosphere of Jupiter consists of bands of winds rotating at different rates, punctuated by giant storms. The largest storm is the Great Red Spot (GRS), which has persisted for more than a century. It has been unclear whether the storms are confined to a thin layer near the top of the atmosphere or if they extend deep into the planet. Bolton et al . used microwave observations from the Juno spacecraft to observe several storms and vortices. They found that the storms extended below the depths at which water and ammonia are expected to condense, implying a connection with the deep atmosphere. Parisi et al . analyzed gravity measurements taken while Juno flew over the GRS. They detected a perturbation in the planet’s gravitational field caused by the storm, finding that it was no more than 500 kilometers deep. In combination, these results constrain how Jupiter’s meteorology links to its deep interior. —KTS

Introduction and Background Trident is a mission concept to investigate Neptune’s large moon Triton, an exotic candidate ocean world at 30 AU (Prockter et al., 2019, Mitchell et al. 2019). The concept is responsive to recommendations of the recent NASA Roadmap to Ocean Worlds study (Hendrix et al., 2019), and to the 2013 Planetary Decadal Survey’s habitability and workings themes (Squyres et al., 2011). The concept was chosen (Ref. 5) from proposals submitted in 2019, under NASA’s Discovery Program, and is currently in its Phase A, competing for selection with three other mission concepts. Voyager 2 showed that Triton has active resurfacing with the potential for erupting plumes and an atmosphere. Coupled with an ionosphere that can create organic snow and the potential for a subsurface ocean, Triton is an exciting exploration target to understand how habitable worlds may develop in our Solar System and beyond. Using a single flyby, Trident would map Triton, characterize active processes and determine whether the predicted subsurface ocean exists. Nominal mission By launching during 2026, Trident would take advantage of a rare, efficient gravity-assist alignment, to capitalize on a narrow – but closing – observational window that enables assessment of changes in Triton’s plume activity and surface characteristics since Voyager 2’s encounter one Neptune-Triton season ago. We have identified an optimized solution to enable a New Horizons-like fast flyby of Triton in 2038 that was proved to fit within the Discovery 2019 cost cap. The spacecraft has a robust design and uses high heritage instruments: (a) Infra-red spectrometer, (b) Narrow angle camera, (c) Wide-angle camera, (d) Triaxial magnetometer, (e) Radio science and (f) Plasma spectrometer. The mission concept builds on the New Horizons concepts of operation. Our overarching science goals are to determine: (1) if Triton has a subsurface ocean; (2) why Triton has the youngest surface of any icy world in the solar system, and which processes are responsible for this; and (3) why Triton’s ionosphere is so unusually intense. Radio Science Instrument and Objectives The Radio Science Instrument (RSI) is the assembly of the DST-R (Deep Space Transponder and Receiver) and USO (UltraStable Oscillator), see Fig. 1. Fig. 1: Trident’s Block Diagram of the Radio Science Instrument The RSI hardware involves no new technology or advanced development. The DST-Rs are provided by the Italian Space Agency (ASI). Dual USOs identical to the USO provided for the ESA/JUICE mission 3GM radio science experiment, are provided to ASI by the Israel Space Agency. ASI has a wide experience in providing RF instrumentation having led the development of several transponder units for deep space science missions in the last 30 years. The USO feeds the DST-R and generates a stable frequency reference for the uplink radio signals to be recorded on board. The DST-R works at the same time as a phase-coherent Deep Space Transponder at X-band, but also as an on-board Receiver at X- and Ka-band. The RSI contributes to two Trident science questions related to the science goals (1) and (3): “Is Triton an ocean world?” and “Why is Triton’s ionosphere so intense?”. In particular, the RSI provides three physical parameters: (a) the electron density profiles on leading and trailing hemispheres, (b) temperature via neutral atmospheric density profile, and (c) the thickness of the hydrosphere from internal mass distribution. Physical parameters (a) and (b) are estimated through simultaneous, dual frequency (X-and Ka-band) uplink radio occultations while the physical parameter (c) is inferred by gravity science observations carried out via phase-coherent Doppler tracking at X-band. Our quantitative requirements for the three above-mentioned objectives (a), (b) and (c) are as follows: - measure the electron density in the ionosphere of Triton to +/- 10% of the population detected by Voyager, i.e. to a sensitivity of 4E+9 el/m3; - measure the neutral atmosphere density and temperature to a sensitivity of +/- 0.1 Pa and +/- 5 K; - measure the gravity quadrupole coefficient C22 with ≤10% error. This paper shows how an optimal combination of on-board instrumentation, a careful trajectory design and an efficient radio science data processing strategy will lead to exceeding all quantitative radio science requirements listed above, with ample margins. Acknowledgements Authors PT, AB, LGC and MZ acknowledge financial support from Agenzia Spaziale Italiana (ASI), via contract No. 2020-13-HH.0 CUP F34I20000050005. This work was carried out in part at the California Institute of Technology, Jet Propulsion Laboratory under a contract from NASA. It describes a predecisional mission concept, for discussion and planning purposes only. The inputs of the various past and present members of the Trident team are gratefully acknowledged. References [1] L. M. Prockter, et al.: Exploring Triton with TRIDENT: a Discovery-Class Mission, 50th Lunar and Planetary Science Conference 2019 (LPI Contrib. No. 2132), Abstract 3188. [2] K. L. Mitchell, et al.: Implementation of TRIDENT: a Discovery-Class Mission to Triton, 50th Lunar and Planetary Science Conference 2019 (LPI Contrib. No. 2132), Abstract 3200. [3] Hendrix, A. R. et al. (2019) Astrobiology 19(1), doi:10.1089/ast.2018.1955. [4] Squyres, S. W. et al. (2011) Vision and Voyagers for Planetary Science in the Decade 2013-2022, National Academies Press. [5] https://www.nasa.gov/press-release/nasa-selects-four-possible-missions-to-study-the-secrets-of-the-solar-system

This paper discusses recent activities at JPL that are focused on extending the Opportunistic Multiple Spacecraft Per Antenna (OMSPA) concept to include arraying multiple antennas. Specifically, we explore the ability to process multiple open loop recordings associated with multiple antennas and perform the appropriate alignment and combining. We focus on using the symbol stream combining technique and provide examples of performance measurements on actual spacecraft signals for MarCO A and B as well as the Mars Express.

Since launch, radio science has been a key component of the Juno mission to Jupiter. The prime objective of the radio science investigation is to estimate the gravitational field of Jupiter from the Doppler shift on the radio link between the spacecraft and the Earth-based observing antennas of NASA's Deep Space Network (DSN). In addition to estimation of the gravitational field, radio science has provided critical engineering support to the Juno mission. Utilizing high-sensitivity open-loop receivers and real-time signal processing, radio science is able to detect the ‘heartbeat’ of the Juno spacecraft and determine the current state of the spacecraft. The Juno spacecraft utilizes two frequencies for communication with Earth: the telecommunications system X-band link and the radio science Ka-band link. Radio science has provided communications monitoring support for the spacecraft launch in 2011, spacecraft main engine firings (including Deep Space Maneuvers in 2012 and Jupiter Orbit Insertion in 2016), the Earth gravity assist flyby in 2013, and times when the spacecraft was off-Earth point during Jupiter closest approach with a weak signal level. By measuring the signal-to-noise ratio, received carrier frequency, and subcarrier frequency of the X-band downlink signal in real-time, radio science is able to determine the state of the spacecraft in scenarios where the link margin is not sufficient to support telemetry. An off-nominal spacecraft state will change the signal-to-noise level, subcarrier frequency, and spin modulation of the carrier frequency which are detectable in the open-loop receiver of the DSN. With the addition of multiple frequency shift keying (MFSK) ‘tones’ encoding, the subcarrier frequency can be changed onboard the spacecraft for determination of selected events by the flight team. Tones were utilized during main engine firings on Juno, including Jupiter Orbit Insertion (JOI). Tones are decoded in near real-time by the Entry, Descent, and Landing (EDL) Data Analysis (EDA) system downstream of the DSN open-loop receivers. Robust implementation of hardware, software, and operations planning has ensured successful data collection and real-time status reporting of spacecraft state to the Juno mission. Lessons learned from communicating with Juno in this way while in the harsh environment of Jupiter are documented and discussed in the context of upcoming missions to Jupiter.

We describe the first demonstration of a southern hemisphere planetary radar system to detect two near-Earth asteroids (NEAs). The demonstration was conducted in a bistatic manner, with the 70 m antenna of the Canberra Deep Space Communications Complex transmitting at 2.1 GHz and reception at the Parkes Radio Telescope, outfitted with multiple receivers, and the Australia Telescope Compact Array. This initial system was used to detect the NEAs (43577) 2005 UL5 and (33342) 1998 WT24 during their close approaches in 2015 November and 2015 December, respectively. We describe the performance of the system and consider future possibilities using other antennas of the Canberra Deep Space Communications Complex as transmitters.

The Io Plasma Torus (IPT) is a toroidal cloud of plasma, centered on the centrifugal equator of Jupiter at Io's orbital distance, that induces a path delay and a carrier frequency shift on radio frequency signals. Juno is currently orbiting Jupiter in a highly eccentric, 53.5-day orbit, with a perijove altitude of about 4000 km. During each perijove pass, Doppler measurements between Juno and the Earth are acquired for about eight hours centered around Jupiter's closest approach. Due to the orbital geometry, the radio frequency signal crosses the IPT, yielding a non-dynamical Doppler shift, that, if not properly calibrated, can be a potential source of bias in the Jupiter estimated gravity field coefficients. During the first perijove pass (conventionally named PJ01), a direct measurement of the downlink plasma contribution was possible by transmitting downlink signals at X and Ka-band coherent with a common X-band uplink. During the perijove passes dedicated to gravity investigations (currently PJ03, PJ06, PJ08, and PJ10) a dual-frequency link at X and Ka band allows to calibrate about 75% of the total plasma contribution on the signal, including the one due to the IPT. During non-gravity dedicated perijove passes a communication link at X band only is available, so that the signal due to the IPT can be corrected only using a model of its internal electron density distribution. Here we propose to improve the model already available in the literature using radio science Doppler data from other space missions, such as Galileo. NASA's Galileo spacecraft arrived to the Jupiter system on December 1995 and studied the Galilean satellites, Jupiter and its magnetosphere, for the following 8 years. However, the orbiter's umbrella-like High Gain Antenna (HGA) failed to correctly deploy, so that the spacecraft was able to operate using only the low-gain antenna (LGA) at S band, with its downlink data rate being much lower than originally planned. Moreover, this prevented any dual-frequency calibration of the radio link that could have corrected the dispersive signal induced by the IPT, potentially affecting the radio science experiment results. We re-analyzed Galileo Doppler measurements acquired by the Deep Space Network during the flybys of the Galilean satellites, using a local orbit determination fit, highlighting the presence of residual un-modeled signatures. The signatures were compared to the expected Doppler signal due the IPT, computed using models already available in literature, suggesting that the IPT can be effectively calibrated, removing the residual signatures, adjusting some of the model parameters.

Quantum mechanics governs the microscopic world, where low mass and momentum reveal a natural wave-particle duality. Magnifying quantum behaviour to macroscopic scales is a major strength of the technique of cooling and trapping atomic gases, in which low momentum is engineered through extremely low temperatures. Advances in this field have achieved such precise control over atomic systems that gravity, often negligible when considering individual atoms, has emerged as a substantial obstacle. In particular, although weaker trapping fields would allow access to lower temperatures

Over the last 40 years, several missions of the National Aeronautics and Space Administration (NASA) and European Space Agency (ESA) have explored the largest planet in the solar system, Jupiter. Radio Science has been a key component of each mission to the planet, where radio signals between the spacecraft and the Earth-based observing antennas have been utilized to determine the physical properties of Jupiter and its moons, their atmospheres, ionospheres, and gravity fields. As a spacecraft passes through or around the Jovian system, small changes in phase, frequency, and amplitude of the radio signal are induced by the surrounding environment. These changes are detectable and form the basis for determining gravitational fields, planetary motion, and reconstruction of atmospheric and ionospheric profiles. The era of outer-planet exploration began in 1973 and 1974 with the Pioneer 10 and 11 flybys of Jupiter. Several missions have used Jupiter's massive gravitational well to perform a gravity assist to reach farther in the solar system, starting with Pioneer 11 in 1974 and Voyager 1 and Voyager 2 in 1979 with subsequent flybys from Ulysses in 1992, Cassini-Huygens in 2000, and New Horizons in 2007. Jupiter has hosted two dedicated orbiting spacecraft thus far: Galileo from 1995-2003 and Juno from 2016 to present. Throughout this time, instrumentation advances in both spacecraft technology and technology developed for ground stations have improved the precision and accuracy of the radiometric measurements, leading to improved results from radio science investigations. The latest mission to Jupiter, Juno, includes the most advanced radio science instrumentation to date. With Juno's unique polar orbit and dual frequency radio links, it is able to probe the planet's deep interior structure and zonal wind profile with measurements of the gravitational field and probe the electron densities in the Io plasma torus, a doughnut-shaped ring around Jupiter charged with particles emitted by the volcanic activity on Io. Upcoming missions, such as the planned NASA's Europa Clipper multiple flyby mission in 2022, potential follow-on Europa Lander, and the ESA's Jupiter Icy Moons Explorer mission in 2022, may make further strides in the study of the planet and its moons utilizing radio science.