Hera Cubesats Trajectory Design and ConOps for Didymos Binary Asteroid Characterization

The Asteroid Impact Deflection Assessment (AIDA) mission, a collaborative effort for Planetary Defense, involves the DART and Hera spacecrafts targeting the Didymos-Dimorphos binary asteroid system. Their objectives include assessing asteroid deflection, conducting close observations, and demonstrating future mission technologies. DART, launched by NASA, impacted Dimorphos in September 2022. While Hera, an ESA spacecraft, carrying Juventas and Milani 6U-XL CubeSats, will be launch in October 2024 to reach the binary asteroid system after a two-year Cruise. Hera will arrive in December 2026 in order to characterize afterwards the result of the DART impact in terms of reshaping and deflection of Dimorphos. The French Space Agency (CNES) contributes to Hera’s mission through CubeSats preliminary trajectory design and close proximity operations for flight dynamics and payloads programming. From the mothercraft ejection to the realization of the scientific objectives of the different payloads (imager, radar, gravimeter, radio-science experiment) to landing, the proximity operations will be held in 2027 within the C-FDSOC (Cubesats Flight Dynamics and Science Operation Center, France) in support of the CMOC (Cubesat Mission Operation Center, Belgium) with direct interface with the HMOC (Hera Mission Operation Center, Germany) as all uplinks and downlinks transit through the Hera mothership. Taking into account the various constraints for each phase implies specific trajectories design with dedicated maneuver strategies and payloads acquisitions sequences through an adapted Concept of Operations shared with Hera ground segment European stakeholders and Payloads teams. This paper will therefore present the different types of trajectories and the preliminary ConOps and necessary ground segment automation elaborated to fulfill mission programming and flight dynamics objectives for the two Hera CubeSats, Milani and Juventas

Closing the transport budget of the Florida Straits

Closing the mean mass budget of the Florida Straits is fundamental to understanding the source waters of the Gulf Stream and for constraining ocean simulations and forecasts in a region of complex topography. Existing transport time series of the inflow through Yucatan Channel and the outflow at 27°N yield a 9 Sv difference in the mean, which cannot be reconciled by the two minor inflows between. Here we present a synthesis of transport estimates from throughout the Florida Straits, using velocity data collected aboard the cruise ship Explorer of the Seas. Our transports form a consistent mass budget and conform with the northern outflow from the Straits of 32.1 ± 3.3 Sv, as measured continuously by cable. In particular, we find an average of 30.0 ± 5.3 Sv for the inflow to southern Florida Straits and estimate that Old Bahama Channel contributes less than an additional 2 Sv. Key Points The mean inflow in the southern Florida Straits is estimated at 30.0 ± 5.3 Sv The mean transports are consistent from Yucatan Channel to North Florida OBC inflow is less than 2 Sv with eastward flow on top and westward flow belo

On the seasonal variability of the currents in the Straits of Florida and Yucatan Channel

Seasonal variability in the major passages of the Caribbean are investigated using 5 years of wind and current observations (Explorer of the Seas), combined with a 3 year 1/12° simulation. Seasonal fluctuations in the Florida and Yucatan passages are both characterized by semiannual cycles with transport maxima in summer and winter and minima in spring and fall. In the Straits of Florida, seasonal variability is associated with surface‐intensified fluctuations of the Florida Current and can be largely explained by along‐channel winds and wind stress curl over the Atlantic Ocean. In the Yucatan Channel, seasonal variability is more barotropic and does not covary with wind forcing but rather is associated with fluctuations of an anticyclonic recirculation to the south of the channel. Upstream, the seasonality in the Grenada Passage also covaries with seasonality in the Yucatan and Florida passages, although the Grenada Passage carries only a small fraction of the total inflow to the Caribbean. Recent in situ estimates of the mean transport in the Yucatan Channel differ by 7 Sv (30.5 Sv, Explorer of the Seas; 23.1 Sv, CANEK). An assessment of sampling errors, biases, and interannual variability seem to account for no more than 2 Sv, leaving no satisfactory explanation for the difference. In Explorer of the Seas data, flows in the Straits of Florida and Yucatan Channel display similar vertical shear structure, while CANEK data exhibit significantly lower shears in the upper 500 m, which account for all the transport difference. Key Points Transports in the Florida and Yucatan passages have similar seasonal cycles Seasonality in Florida correlates with local winds Seasonality in Yucatan correlates with an anticyclonic gyre south of the channe

Observations of the Florida and Yucatan Currents from a Caribbean Cruise Ship

Abstract The Yucatan and Florida Currents represent the majority of the warm-water return path of the global thermohaline circulation through the tropical/subtropical North Atlantic Ocean. Their transports are quantified and compared by analyzing velocity data collected aboard the cruise ship Explorer of the Seas. From 157 crossings between May 2001 and May 2006, the mean transport of the Florida Current at 26°N was estimated to be 30.8 ± 3.2 Sv (1 Sv ≡ 106 m3 s−1), with seasonal amplitude of 2.9 Sv. Upstream, the Yucatan Current was estimated from 90 crossings to be 30.3 ± 5 Sv, with seasonal amplitude of 2.7 Sv. These two currents are shown to be linked at seasonal time scales. Hence, contrary to former results, it was found that transports through the Florida Straits and the Yucatan Channel are similar, with the implication that only small inflows occur through minor channels between them

Early diagenetic processes generate iron and manganese oxide layers in the sediments of Lake Baikal, Siberia

Distinct layers of iron(III) and manganese(IV) (Fe/Mn) oxides are found buried within the reducing part of the sediments in Lake Baikal and cause considerable complexity and steep vertical gradients with respect to the redox sequence. For the on-site investigation of the responsible biogeochemical processes, we applied filter tube samplers for the extraction of sediment porewater combined with a portable capillary electrophoresis instrument for the analyses of inorganic cations and anions. On the basis of the new results, the sequence of diagenetic processes leading to the formation, transformation, and dissolution of the Fe/Mn layers was investigated. With two exemplary cores we demonstrate that the dissolution of particulate Fe and Mn is coupled to the anaerobic oxidation of CH4 (AOM) either via the reduction of sulphate (SO42-) and the subsequent generation of Fe(II) by S(-II) oxidation, or directly coupled to Fe reduction. Dissolved Fe(II) diffuses upwards to reduce particulate Mn(IV) thus forming a sharp mineral boundary. An alternative dissolution pathway is indicated by the occurrence of anaerobic nitrification of NH4+ observed at locations with Mn(IV). Furthermore, the reasons and consequences of the non-steady-state sediment pattern and the resulting redox discontinuities are discussed and a suggestion for the burial of active Fe/Mn layers is presented

Fabrication and transfer of flexible few-layers MoS2 thin film transistors to any arbitrary substrate

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