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Abstract:

In this proceeding, we present the verification and test methods used on the Ariel Optical Ground Support Equipment (OGSE). Ariel is an ESA medium-class mission that will use the transit spectroscopy method to observe the atmospheres of ~1000 exoplanets over a nominal four-year mission. Ariel is a 1 m class cryogenic (∼ 40 K) space telescope that will be placed in a halo orbit around the Earth-Sun L2 point. To detect atmospheric molecular absorption features, the payload contains spectroscopic and photometric instruments that span 0.5–7.8 μm. To achieve Ariel’s science goals, the payload requires detailed calibration and performance verification. The payload-level engineering model calibration of the Ariel payload will take place in 2027 in a 5-m vacuum chamber at the Rutherford Appleton Laboratory’s Space Instruments Test Facility. The payload will be enclosed in a Cryogenic Test Rig (CTR) to provide a space-like (~35 K) thermal environment. During cryogenic vacuum testing, the payload will be illuminated by the OGSE. To test the payload on the ground, the OGSE needs to meet very stringent performance requirements. Notable examples include: the 214 nm RMS wavefront flatness at a 70 K operational temperature, 24 ppm detector photometric stability on hour timescales, radiometric calibration with 5% relative accuracy, and a flat fielding capability with a uniformity better than 0.5%. In addition to the performance requirements, the OGSE system features cryogenic mechanisms, a custom cryostat, and a vacuum chamber coupling system; the functionality of each must be verified. Finally, since the OGSE shares a common vacuum environment with the payload, cleanliness is therefore a key requirement on the project. In this proceeding, we will present the integration and verification plan for the OGSE system, showing how the different technical requirements will be verified.

Abstract:

Abstract We investigate the diurnal temperature variations of Europa’s surface using brightness temperatures taken by Galileo’s Photopolarimeter-Radiometer (PPR) instrument. Diurnal curves created from these data are compared to those predicted by a thermophysical model to determine what thermal inertias and Bond albedos can fit the data within a reduced chi-squared cutoff of $\chi _{\textrm {red}}^2\le 1.0$. This analysis is used to extensively quantify the uncertainty for the first time of the two thermophysical parameters derived from PPR. We map the albedo and thermal inertia for 33% and 24% of Europa’s surface area, respectively. We find a range of 0.375-0.75 for albedo and 20-110 J m−2 K−1 s−1/2 for thermal inertia. Our uncertainty analysis indicates well-constrained estimates for albedo, while upper limits for thermal inertia remain poorly constrained. When averaged across nine geological areas, albedo varies as expected: lower values are obtained for darker regions in visible wavelengths. Thermal inertia appears to vary independently from geological boundaries. The surface was also divided based on electron bombardment energy flux and non-ice composition fraction. Thermal inertia behaves opposite of what is expected: lower thermal inertias are located in regions of high-energy electron bombardment. This possibly indicates a mechanism competing with electron-induced sintering is present that is lowering the surface conductivity. No endogenic anomalies were detected that could not be explained by passive emission alone. Nevertheless, these results aid in preparing for future thermal measurements from Europa Clipper and Juice by improving the surface coverage of Europa’s passive thermal properties and providing uncertainties of their values.

Abstract:

Thermal measurements provide key constraints on the physical properties of icy satellite surfaces. On Europa, previous analyses of the Galileo Photopolarimeter-Radiometer (PPR) dataset revealed heterogeneities in thermal inertia, but the limited spatial resolution prevented a detailed thermophysical characterization. We derive high-resolution maps of the Europa surface albedo and thermal inertia and infer the microphysical properties of its icy regolith from a reanalysis of the Galileo PPR dataset by discussing the processes controlling its thermophysical evolution. We used the KRC thermal model (K refers to the conductivity ąppa, R to the density ̊ho, and C to the specific heat C) to analyze the PPR brightness temperatures and retrieve the albedo and thermal inertia. These values were then interpreted using conductivity models of porous ice to constrain the grain size and porosity. We derived a mean Bond albedo of 0.64 ± 0.06 and a mean thermal inertia of 56 ± 17 J m -2 $ K^-1 s^-1/2 (1σ). The thermal inertia shows significant spatial variations, with a low-inertia equatorial band (39 ± 7) and higher values at mid-latitudes on the leading hemisphere (56 ± 11). The trailing-hemisphere equator also exhibits higher thermal inertia (63 ± 17), likely related to compositional differences. Conductivity models indicate a porous icy regolith with grain sizes ranging from a few micrometers to a few centimeters and an average porosity of $0.61 ± 0.1 in the upper centimeters of the Europa surface. The thermal inertia distribution shows little correlation with geological units. Its agreement with modeled magnetospheric ion fluxes instead suggests that sputtering-driven sintering plays a fundamental role in shaping the thermophysical properties of Europa. The absence of a high-inertia equatorial band analogous to the PacMan anomaly on the icy moons of Saturn indicates inefficient electron-driven sintering, while temperature-gradient metamorphism might enhance grain growth at depth. The modeled surface temperatures range between ∼ 67 and 148 K at mid to low latitudes, with peak daytime values counteracting radiolytic amorphization while limiting volatile stability.

Abstract:

Abstract Unexpectedly following launch, the Lunar Trailblazer mission experienced software anomalies that led it to orient solar panels away from the sun and lose communication with Earth. This paper describes efforts to determine the spacecraft state and attempt recovery of the mission's science at the Moon. First, ground observatories at optical and radar wavelengths were engaged to maintain custody of the spacecraft and knowledge of its trajectory. Second, viability of recovery of the mission science objectives was established via testbed work to understand system behavior in fault conditions and determination of trajectories and maneuvers that would enable lunar orbit insertion. Third, optical photometry and radar doppler broadening were employed to determine Lunar Trailblazer's spin and orientation, using approaches similar to those in asteroid studies, to establish when solar panels might again receive sufficient power to boot the spacecraft and initialize its radio. Fourth, X‐band‐capable groundstations in addition to the NASA Deep Space Network were engaged to monitor for the spacecraft's radio carrier signal nearly continually, including crowd‐sourced monitoring and tip‐and‐cue style commanding. Lunar Trailblazer left the Earth‐Moon system and is in a 14‐year Earth return, heliocentric orbit. As it moved further away from Earth prospects for recovery became formidable; ultimately, the ability of the telecom system to return telemetry to Earth would have been insufficient to enable actions to recover the spacecraft, and the recovery attempt ended 6 July 2025. Lunar Trailblazer's mission recovery efforts illuminate capabilities in characterizing a 1–3.5 m 3 size non‐cooperative object in cis‐lunar space. Plain Language Summary Lunar Trailblazer is a NASA small satellite mission to study the Moon. Software errors after launch caused the spacecraft to orient solar panels away from the sun and the radio to reinitialize in a state that did not allow commanding or telemetry receipt; having depleted its batteries, it is now in a low power, “browned out” state. This paper describes the Lunar Trailblazer team recovery efforts to reestablish Earth‐spacecraft communication and return to the Moon to achieve the science objectives. The team used ground observatories at optical and radar wavelengths to keep track of the trajectory of the spacecraft, determine its orientation, and compute trajectories for Earth‐Moon system return. Along with power model and testbed data on power use during the boot/initialization sequence, this was used to determine when the spacecraft solar panels could next receive power sufficient to initialize the radio. Ultimately, while enough propellant is in the tanks that could have enabled a return to Earth through calendar year 2025, the inability to receive telemetry due to distance ended recovery attempts. The procedures employed to characterize Lunar Trailblazer's state can be used on other cis‐lunar spacecraft and near‐Earth asteroids. Key Points Over a 130‐day mission recovery attempt, Lunar Trailblazer was a non‐cooperative cis‐lunar object, characterized using Earth ground assets Radar and optical observatory data enabled reconstruction of spacecraft orientation (spin rate, spin pole) and precise long‐term trajectory An ad‐hoc global X‐band ground station network that included crowd‐sourced signal monitoring and tip‐and‐cue style commanding was created

Abstract:

Saturn’s ocean moon Enceladus is among the most compelling targets for future astrobiology-focused missions. Material erupted from the moon’s south polar “Tiger Stripe” fractures is thought to originate from a global subsurface ocean, providing a natural pathway for ocean-derived compounds to be sampled without penetrating the ice shell. Cassini observations demonstrated that Enceladus’ plume contains water vapor, ice grains, salts, organics, phosphates, and other compounds of astrobiological interest. Consequently, future landed or plume-sampling missions to Enceladus will seek to determine whether ocean-sourced organic molecules, and potentially biosignatures, can be preserved and detected in plume material.However, once plume grains are erupted and deposited onto the surface, they are exposed to multiple space weathering agents. Solar ultraviolet radiation, Saturnian magnetospheric charged particles, and galactic cosmic rays can alter or destroy organic molecules contained within surface material. The degree of processing depends not only on radiation environment and molecular susceptibility, but also on the rate at which fresh plume fallout buries previously deposited material. Identifying locations and depths where organics may remain minimally processed is therefore key for mission planning and interpretation of future measurements.Here we model the degradation and preservation of plume-deposited organics on Enceladus, using the amino acids glycine and phenylalanine as representative organic molecules and potential biosignature proxies. We combine solar UV photodestruction calculations, Geant4-based charged-particle irradiation simulations, and estimates of local plume deposition rates to produce a coupled model of irradiation and burial across the surface. Solar UV photolysis rates are calculated using experimental rate coefficients adjusted for seasonal variation in photon flux at selected locations on Enceladus, including equatorial and southern-hemisphere sites at leading and trailing longitudes. Because even small abundances of non-water-ice contaminants can strongly influence UV attenuation, we also examine the effect of trace tholin-like material mixed into the ice. Charged-particle processing is estimated using Cassini-derived magnetospheric electron spectra and a numerical transport model for the galactic cosmic ray flux at Saturn.Our results show that preservation of plume-deposited organics is highly sensitive to burial rate and season. At low to moderate surface deposition rates, less than approximately 0.002 mm yr⁻¹, newly deposited surface material is strongly processed by solar UV radiation before burial can shield it from further exposure. In such regions, there may be no practical “safe sampling depth” at which pristine or minimally processed organics can be accessed, because material has already been altered before reaching depth. By contrast, in regions receiving the highest predicted plume deposition rates, especially during local winter when solar UV exposure is reduced, burial can occur rapidly enough to protect a significant fraction of the organic inventory. Under these conditions, the near-surface stratigraphy may consist of millimeter-scale layers that alternate between relatively well-preserved and heavily photoprocessed material, reflecting seasonal variations in irradiation during emplacement.Our findings have implications for the mission design and sampling strategy of future Enceladus missions. A landed mission seeking minimally processed ocean-derived organics should prioritize regions of high plume fallout, where burial is most effective, and should consider the seasonal context of deposition and sampling. The most favorable strategy may be to collect plume grains directly before surface deposition, e.g., from a funnel on the surface or plume fly-through, thereby avoiding prolonged radiolytic and photolytic alteration. If surface sampling is required, targeting the uppermost approximately 0.1 mm of material in high-deposition regions during local winter may maximize the probability of detecting less-processed organics. More broadly, our results demonstrate that preservation potential at Enceladus is governed by the competition between surface irradiation and plume-driven burial, and that this balance should be incorporated into future landing site selection, sampling-depth requirements, and biosignature-detection strategies.