The main belt asteroid (52246) Donaldjohanson (DJ) is a likely member of the Erigone asteroid family. This implies that DJ is a fragment of a larger parent body that was destroyed in a collision about 155 million years ago. We report observations taken during a flyby of DJ by the Lucy spacecraft. We found that DJ is composed of two heavily cratered lobes, connected by a smoother neck, with overall dimensions 8.8 kilometers (km) by 4.4 km by 3.1 km. The crater density is consistent with the Erigone family's age, except for craters <0.4 km, which have been preferentially erased. DJ rotates slowly in a tumbling state, likely owing to spin-down by radiative forces. Surface spectra show iron-bearing phyllosilicates, indicating moderate aqueous evolution on the parent body.

Asteroids with diameters less than about 5 km have complex histories because they are small enough for radiative torques (that is, YORP, short for the Yarkovsky-O'Keefe-Radzievskii-Paddack effect)1 to be a notable factor in their evolution2. (152830) Dinkinesh is a small asteroid orbiting the Sun near the inner edge of the main asteroid belt with a heliocentric semimajor axis of 2.19 AU; its S-type spectrum3,4 is typical of bodies in this part of the main belt5. Here we report observations by the Lucy spacecraft6,7 as it passed within 431 km of Dinkinesh. Lucy revealed Dinkinesh, which has an effective diameter of only 720 m, to be unexpectedly complex. Of particular note is the presence of a prominent longitudinal trough overlain by a substantial equatorial ridge and the discovery of the first confirmed contact binary satellite, now named (152830) Dinkinesh I Selam. Selam consists of two near-equal-sized lobes with diameters of 210 m and 230 m. It orbits Dinkinesh at a distance of 3.1 km with an orbital period of about 52.7 h and is tidally locked. The dynamical state, angular momentum and geomorphologic observations of the system lead us to infer that the ridge and trough of Dinkinesh are probably the result of mass failure resulting from spin-up by YORP followed by the partial reaccretion of the shed material. Selam probably accreted from material shed by this event.

The Lucy mission will be the first spacecraft to study the Trojan asteroids, located on the same orbit as Jupiter at the Lagrange Points for the Jupiter-Sun orbit. Due to the large distances that the spacecraft is required to travel in order to survey the six selected asteroids, the primary mission will take over 12 years to complete. How do we design software to stand the test of time? In this paper we detail how the Lucy team implemented the lessons learned from multiple missions (Rosetta, New Horizons, CYGNSS, etc.), as well as leveraging the work of the open source software community to accelerate the development of the Trojan Planning File Generator (TPFG); the science planning and sequencing system for the Lucy mission. We explore how the convergence, and increasing stability of software practices developed around the world lead to the design decisions made on the TPFG project. TPFG is a multi-part system; a Python back-end that powers a web-based interface. We also show how utilizing popular frameworks, and following best practices have streamlined software development and enabled the Lucy team to develop an initial working version in a matter of months.

The successful operation of spacecraft requires careful planning. Each mission comes with a unique set of challenges that must be met by tools and techniques developed on a mission-specific basis. In the past, these tools have been created as Command Line Interfaces (CLIs), Remote Command Line Interfaces (Remote CLIs), or Graphical User Interfaces (GUIs). This paper presents a method for the development of these custom tools implemented for the mission planning of the CYGNSS (Cyclone Global Navigation Space System) mission: using the Django web framework to act as a remote Graphical User Interface. CYGNSS, the NASA Earth Venture Class mission which launched in late 2016, is a constellation of eight microsatellites in low Earth orbit which perform ocean wind speed measurements using reflected GPS signals to aid in weather modeling. Several tools have been developed to aid in the extensive and ongoing workload in mission planning. Now operating in the extended mission phase, the CYGNSS team is small. However, each team-member works on several projects aside from CYGNSS and performs the necessary mission planning and operations from their individual computer. Since, when using traditional tools, each operator's computer generally has a different combination of hardware, software, and operating system, developers are often required to perform custom installation and debugging for each new user of the system. This results in a system which is prone to user-specific bugs, and is not suitable for the low-cost environment in which CYGNSS operates. We present a method which alleviates these problems. We use Django, a Python-based website framework, to host a suite of mission planning tools on a local website. This framework is split into three components: the Object Relational Mapping (ORM), the Template, and the View. The Django ORM is used to access the backend database from Python. Django Templates are used to control how the tool is displayed to the end user. Django Views tie the previous two components together by taking a request from the user, retrieving data from the database, rendering a template using that data, and returning the rendered template to the user where it is displayed by a web browser. We show how each of these components is used and the benefits of using such a web based system over a traditional tool.

This paper explores the uniqueness of ESA Rosetta mission operations from the Alice instrument point of view, documents lessons learned, and suggests operations ideas for future missions. The Alice instrument mounted on the Rosetta orbiter is an imaging spectrograph optimized for cometary far-ultraviolet (FUV) spectroscopy with the scientific objectives of measuring properties of the escaping gas and dust, and studying the surface properties, including searching for exposed ices. We describe the operations processes during the comet encounter period, the many interfaces to contend with, the constraints that impacted Alice, and how the Alice science goals of measuring the cometary gas characteristics and their evolution were achieved. We provide details that are relevant to the use and interpretation of Alice data and published results. All these flight experiences and lessons learned will be useful for future cometary missions that include ultraviolet spectrographs in particular, and multi-instrument international payloads in general.

The flight operations of the Cyclone Global Navigation Satellite System (CYGNSS), a constellation of eight microsatellites built and operated by Southwest Research Institute (SwRI), designed to improve the intensity forecasts of Tropical Cyclones, has seen a litany of changes to its concept of operations, software, processes, and personnel. In this paper, we detail how the operations team responded to several challenges such as the reduction in personnel after the Launch and Early Orbit Operations phase, the addition of a downlink antenna in Japan, high-fidelity collection requests during the unusually active 2017 Atlantic hurricane season, and the increased demands of team members from other projects. These pressures forced the CYGNSS operations team to innovate their way to efficient operations. These innovations were enabled by embracing modern open-source tools such as Django, Bokeh, Git, the various libraries available in the Python programming language, and the capabilities that come with all of our operations engineers being competent in software development. The CYGNSS team took the approach of automating the most time-intensive tasks first, which freed up time to carefully design and test more elaborate automation solutions. We utilized the spirit of the Agile Methodology to make incremental improvements to our software suite which further enabled more sophisticated automation. Finally, we chart a path forward to fully closing the automation loop between our mission planning, and real-time Command and Control.

The Pluto system was recently explored by NASA's New Horizons spacecraft, making closest approach on 14 July 2015. Pluto's surface displays diverse landforms, terrain ages, albedos, colors, and composition gradients. Evidence is found for a water-ice crust, geologically young surface units, surface ice convection, wind streaks, volatile transport, and glacial flow. Pluto's atmosphere is highly extended, with trace hydrocarbons, a global haze layer, and a surface pressure near 10 microbars. Pluto's diverse surface geology and long-term activity raise fundamental questions about how small planets remain active many billions of years after formation. Pluto's large moon Charon displays tectonics and evidence for a heterogeneous crustal composition, its north pole displays puzzling dark terrain. Small satellites Hydra and Nix have higher albedos than expected.

Commanding the payload on a spacecraft (“uplink” sequencing and command generation) and processing the instrument data returned (“downlink” data processing) are two primary functions of Science Operations on a mission. While vitally important, it is sometimes surprisingly difficult to connect data returned from a spacecraft to the corresponding commanding and sequencing information that created the data, especially when data processing is done via an automated science data pipeline and not via a manual process with humans in the loop. For a variety of reasons it is necessary to make such a connection and close this loop. Perhaps the most important reason is to ensure that all data asked for has arrived safely on the ground. This is especially critical when the mission must erase parts of the spacecraft memory to make room for new data; mistakes here can result in permanent loss of data. Additionally, there are often key pieces of information (such as intended observation target or certain instrument modes that are not included in housekeeping, etc.) that are known only at the time of commanding and never makes it down in the telemetry. Because missions like New Horizons strive to be frugal with how much telemetry is sent back to Earth, and the telemetry may not include unambiguous identifiers (like observation ids, etc.), connecting downlinked data with uplink command information in an automated way can require creative approaches and heuristics. In this paper, we describe how these challenges were overcome on the New Horizons Mission to Pluto. The system developed involves ingesting uplink information into a database and automatically correlating it with downlinked data products. This allows for more useful data searches and the ability to attach the original intent of each observation to the processed science data. Also a new data tracking tool is now being developed to help in planning data playback from the spacecraft and to ensure data is verified on the ground before being erased from spacecraft memory. The development of these tools and techniques have also uncovered powerful lessons-learned for future missions. At the early stages of the design of a mission's dataflow, the allocation of a few more bytes of telemetry can go a long way toward making the uplink to downlink loop even easier to close on the ground, simplifying ground systems for future missions.

The New Horizons spacecraft was launched in January of 2006, and is now more than half way to its encounter with the Pluto System. Planning of the encounter has been underway, and the command loads for the period around close approach have been built in preparation for rehearsals in the summers of 2012 and 2013, followed by the actual encounter in July 2015. The Science Operations team at SwRI has been working closely with the Mission Operations team in building and testing the command loads, using a variety of tools. Similar to other fast flyby missions, the highest priority science takes place in the few days around Pluto closest approach. The encounter command load is optimized for maximum data collection during the short time period when the spacecraft is close to the Pluto system, and tested to be robust to any problems that may occur. The great distances and light times to the spacecraft at the time of encounter have also presented a unique set of issues to solve in the encounter planning. The Science Operations team has developed a process and a set of tools to facilitate the planning, scheduling, and sequencing the science command loads for the New Horizons mission. These tools will be discussed in this paper.

The NASA Alice ultraviolet (UV) imaging spectrograph on board the ESA Rosetta comet orbiter successfully conducted a series of flyby observations of the large asteroid (21) Lutetia in the days surrounding Rosetta's closest approach on 2010 July 10. Observations included a search for emission lines from gas, and spectral observations of the Lutetia's surface reflectance. No emissions from gas around Lutetia were observed. Regarding the surface reflectance, we found that Lutetia has a distinctly different albedo and slope than both the asteroid (2867) Steins and Earth's moon, the two most analogous objects studied in the far ultraviolet (FUV). Further, Lutetia's similar to 10% geometric albedo near 1800 angstrom is significantly lower than its 16%-19% albedo near 5500 angstrom. Moreover, the FUV albedo shows a precipitous drop (to similar to 4%) between 1800 angstrom and 1600 angstrom, representing the strongest spectral absorption feature observed in Lutetia's spectrum at any observed wavelength. Our surface reflectance fits are not unique but are consistent with a surface dominated by an EH5 chondrite, combined with multiple other possible surface constituents, including anorthite, water frost, and SO2 frost or a similar mid-UV absorber. The water frost identification is consistent with some data sets but inconsistent with others. The anorthite (feldspar) identification suggests that Lutetia is a differentiated body.

We describe in-flight calibration of the Cassini Imaging Science Sub-system narrow- and wide-angle cameras using data from 2004 to 2009. We report on the photometric performance of the cameras including the use of polarization filters, point spread functions over a dynamic range greater than 107, gain and loss of hot pixels, changes in flat fields, and an analysis of charge transfer efficiency. Hot pixel behavior is more complicated than can be understood by a process of activation by cosmic ray damage and deactivation by annealing. Point spread function (PSF) analysis revealed a ghost feature associated with the narrow-angle camera Green filter. More generally, the observed PSFs do not fall off with distance as rapidly as expected if diffraction were the primary contributor. Stray light produces significant signal far from the center of the PSF. Our photometric analysis made use of calibrated spectra from eighteen stars and the spectral shape of the satellite Enceladus. The analysis revealed a shutter offset that differed from pre-launch calibration. It affects the shortest exposures. Star photometry results are reproducible to a few percent in most filters. No degradation in charge transfer efficiency has been detected although uncertainties are large. The results of this work have been digitally archived and incorporated into our calibration software CISSCAL available online.

The dusty jovian ring system must be replenished continuously from embedded source bodies. The New Horizons spacecraft has performed a comprehensive search for kilometer-sized moons within the system, which might have revealed the larger members of this population. No new moons were found, however, indicating a sharp cutoff in the population of jovian bodies smaller than 8-kilometer-radius Adrastea. However, the search revealed two families of clumps in the main ring: one close pair and one cluster of three to five. All orbit within a brighter ringlet just interior to Adrastea. Their properties are very different from those of the few other clumpy rings known; the origin and nonrandom distribution of these features remain unexplained, but resonant confinement by Metis may play a role.