The major post-Cassini knowledge gap concerning Saturn's icy moon Titan is in the composition of its diverse surface, and in particular how far its rich organics may have ascended up the "ladder of life." The NASA New Frontiers 4 solicitation sought mission concepts addressing Titan's habitability and methane cycle. A team led by the Johns Hopkins University Applied Physics Laboratory (APL) proposed a revolutionary lander that uses rotors to land in Titan's thick atmosphere and low gravity and can repeatedly transit to new sites, multiplying the mission's science value from its capable instrument payload.

The MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) mission was proposed to NASA in 1998 as the next step in the robotic exploration of Mercury, following the Mariner 10 flybys in the 1970s. Six science questions framed the mission, guiding the designs of the trajectory, payload, and spacecraft. The mission design used a combination of maneuvers and planetary flybys to slow the spacecraft over a 6.6-year period in order to achieve an orbit about Mercury that would facilitate the specific measurements to be made over the course of a single Earth year. An instrument suite was chosen to provide the necessary data with measurement redundancy to guard against hardware failure during the long mission. An innovative ceramic-cloth sunshade-along with a robust fault-management system-afforded the spacecraft protection from the harsh environment as close as 0.3 AU from the Sun and allowed the use of traditional electronics, which operated at approximately room temperature. The development of a lightweight, electronically steerable phased-array antenna also proved to be enabling for the mission communications. The cadence of maneuvers and flybys during the long cruise phase proved to be demanding for the mission operations team, which remained at least as busy throughout the orbital phase of the primary mission and the two extended missions that followed. Automated science planning facilitated the collection of orders of magnitude more data than originally anticipated, all of which were delivered to the Planetary Data System on schedule.

The MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) mission used six planetary gravity assists in order to enable capture into orbit about Mercury. A key element of MESSENGER's successful trajectory was achieving the proper gravity assist from each planetary flyby. The criticality of the MESSENGER gravity assists levied tight accuracy requirements on the planetary-flyby targeting. Major errors could have precluded Mercury orbit insertion or required modifications to the trajectory that increased mission complexity, cost, and risk by requiring additional Mercury flybys and extending mission duration. Throughout the mission, MESSENGER modified its strategy for achieving accurate planetary flybys. By using solar sailing, the MESSENGER team was able to eliminate all of the flyby approach maneuvers without sacrificing flyby accuracy, thereby saving mission ΔV margin. The elimination of these approach maneuvers also markedly reduced mission risk, as these approach maneuvers were nominally planned during a time of heightened sensitivity to errors and precluded unique flyby science opportunities. The paradigm shift used by MESSENGER may be useful for other interplanetary missions, particularly if their trajectories require gravity assists in the inner solar system.

SciBox is a new technology for planning and commanding science operations for Earth-orbital and planetary space missions. It has been incrementally developed since 2001 and demonstrated on several spaceflight projects. The technology has matured to the point that it is now being used to plan and command all orbital science operations for the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) mission to Mercury. SciBox encompasses the derivation of observing sequences from science objectives, the scheduling of those sequences, the generation of spacecraft and instrument commands, and the validation of those commands prior to uploading to the spacecraft. Although the process is automated, science and observing requirements are incorporated at each step by a series of rules and parameters to optimize observing opportunities, which are tested and validated through simulation and review. Except for limited special operations and tests, there is no manual scheduling of observations or construction of command sequences. SciBox reduces the lead time for operations planning by shortening the time-consuming coordination process, reduces cost by automating the labor-intensive processes of human-in-the-loop adjudication of observing priorities, reduces operations risk by systematically checking constraints, and maximizes science return by fully evaluating the trade space of observing opportunities to meet MESSENGER science priorities within spacecraft recorder, downlink, scheduling, and orbital-geometry constraints.

The MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft, launched in August 2004 under NASA's Discovery Program, was inserted into orbit about the planet Mercury in March 2011. MESSENGER's three flybys of Mercury in 2008–2009 marked the first spacecraft visits to the innermost planet since the Mariner 10 flybys in 1974–1975. The unprecedented orbital operations are yielding new insights into the nature and evolution of Mercury. The scientific questions that frame the MESSENGER mission led to the mission measurement objectives to be achieved by the seven payload instruments and the radio science experiment. Interweaving the full set of required orbital observations in a manner that maximizes the opportunity to satisfy all mission objectives and yet meet stringent spacecraft pointing and thermal constraints was a complex optimization problem that was solved with a software tool that simulates science observations and tracks progress toward meeting each objective. The final orbital observation plan, the outcome of that optimization process, meets all mission objectives. MESSENGER's Mercury Dual Imaging System is acquiring a global monochromatic image mosaic at better than 90% coverage and at least 250m average resolution, a global color image mosaic at better than 90% coverage and at least 1km average resolution, and global stereo imaging at better than 80% coverage and at least 250m average resolution. Higher-resolution images are also being acquired of targeted areas. The elemental remote sensing instruments, including the Gamma-Ray and Neutron Spectrometer and the X-Ray Spectrometer, are being operated nearly continuously and will establish the average surface abundances of most major elements. The Visible and Infrared Spectrograph channel of MESSENGER's Mercury Atmospheric and Surface Composition Spectrometer is acquiring a global map of spectral reflectance from 300 to 1450nm wavelength at a range of incidence and emission angles. Targeted areas have been selected for spectral coverage into the ultraviolet with the Ultraviolet and Visible Spectrometer (UVVS). MESSENGER's Mercury Laser Altimeter is acquiring topographic profiles when the slant range to Mercury's surface is less than 1800km, encompassing latitudes from 20°S to the north pole. Topography over the remainder of the southern hemisphere will be derived from stereo imaging, radio occultations, and limb profiles. MESSENGER's radio science experiment is determining Mercury's gravity field from Doppler signals acquired during frequent downlinks. MESSENGER's Magnetometer is measuring the vector magnetic field both within Mercury's magnetosphere and in Mercury's solar wind environment at an instrument sampling rate of up to 20 samples/s. The UVVS is determining the three-dimensional, time-dependent distribution of Mercury's exospheric neutral and ionic species via their emission lines. During each spacecraft orbit, the Energetic Particle Spectrometer measures energetic electrons and ions, and the Fast Imaging Plasma Spectrometer measures the energies and mass per charge of thermal plasma components, both within Mercury's magnetosphere and in Mercury's solar-wind environment. The primary mission observation sequence will continue for one Earth year, until March 2012. An extended mission, currently under discussion with NASA, would add a second year of orbital observations targeting a set of focused follow-on questions that build on observations to date and take advantage of the more active Sun expected during 2012–2013. MESSENGER's total primary mission cost, projected at $446M in real-year dollars, is comparable to that of Mariner 10 after adjustment for inflation.

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After almost 5 years in development and more than 6 and a half years in cruise toward its destination, NASA's MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft finally entered orbit about Mercury on 18 March 2011, initiating a 1-year, focused investigation of the innermost planet. Operating from a highly eccentric orbit designed to keep the spacecraft safe and to facilitate the required observations, MESSENGER is using its payload of seven instruments and the spacecraft's radio-frequency telecommunications system to characterize the planet's interior, surface, atmosphere, and magnetosphere. The demands of the many measurements needed to meet the program objectives, coupled with the constraints associated with spacecraft safety and the orbital geometry, led to the adoption of an automated science-planning tool to optimize science data collection. The tool was used to design the entire year of observations prior to orbit insertion and has the capability of regenerating the plan quickly in response to anomalies in flight (e.g., spacecraft safe-mode demotions) or on the ground (e.g., missed Deep Space Network tracks). Because one Earth year spans two Mercury solar days, there are two opportunities in the course of MESSENGER's science data-collection campaign to observe any specific location on the planet with a given viewing geometry. To take advantage of this schedule, the science plan was divided into two parts. During the first solar day, priority was given to producing global map products. The second day will be used to focus on specific targets and to recover observations missed during the first half of the year. Also, complementary observations can be made in the second day that, when paired with results from the first day, form a stereo map. Although only midway through the orbital operations phase of the mission, MESSENGER had, at the end of the first Mercury solar day, already viewed the entire surface of the planet once and produced global monochrome and multispectral maps. The spacecraft's orbit has completed two local-time rotations and three rotations in longitude, allowing spatial characterization of the planet's magnetic field, development of an elevation model from northern hemisphere altimetry, and global abundance estimates for major elements. After more than 350 orbits, more than 80Gbit of compressed data have been collected, including more than 50,000 images. Calibrated data from the first 2 months in orbit have been delivered to NASA's Planetary Data System for dissemination to the science community.

MESSENGER SciBox is an automated closed-loop planning and commanding system used to optimize orbital science operations for the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) mission. The system plans all science observations for the seven science instruments on the spacecraft and also automatically generates the command sequences that drive the instruments, the guidance and control system, the solid-state recorder, the solar panels, and the radio-frequency communication system. MESSENGER SciBox interacts with the instrument scientists, mission operations team, downlink processing system, and mission design engineers to form a closed-loop system. In orbital operation, the systems employ a feedback loop, with a one-week time step, to improve the system performance. Feedback inputs are used to predict observational performance, to track all science observations, to avoid planning redundant tasks, and to recover from operational anomalies. The software tool is automated because the entire process, from ingesting the feedback inputs to creating the spacecraft and instruments commands, can function without manual interaction. I. Introduction Science operation centers for most space missions generally consist of two components: the uplink system and the downlink system. The uplink system deals with planning and scheduling of science observations, whereas the downlink system deals with the processing of observations returned from the spacecraft. Traditionally, the planning and scheduling of science observations, and the creation of associated spacecraft and instrument commands for science operation, are so time-consuming and labor-intensive that little time is left for the planning team to have close interactions with the data processing team. Any such interactions tend to be ad hoc and informal. On some missions, the two subsystems are so decoupled that they are even housed in different institutions and on separate networks. The lack of tightly coupled interaction frequently results in inefficient use of resources and a less-thanoptimum operational schedule. In this paper we describe an automated planning and commanding system that uses a closed-loop iterative process to continuously refine the science operation schedule and to generate spacecraft and instrument commands for uploading to a spacecraft. The planning system iteratively interacts with the instrument scientists, mission operations center personnel, mission design team, and downlink processing system to produce a scienceobservation-packed operational schedule and to improve the precision of planned operations. The process of ingesting feedback information from the downlink system to the generation of spacecraft and instrument commands for uplink is completely automated. This closed-loop architecture has been implemented as part of science operations for the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft now in orbit about Mercury, and it has allowed the MESSENGER team to maximize scientific return for the community with a relatively small operational staff. The closed-loop architecture and its application to MESSENGER orbital operations are the focus of this paper.

Sean C. Solomon, Ralph L. McNutt, Jr., Peter D. Bedini, Brian J. Anderson, David T. Blewett, Larry G. Evans, Robert E. Gold, Stamatios M. Krimigis, Scott L. Murchie, Larry R. Nittler, Roger J. Phillips, Louise M. Prockter, James A. Slavin, and Maria T. Zuber, Department of Terrestrial Magnetism, Carnegie Institution of Washington, 5241 Broad Branch Road, N.W., Washington, DC 20015, USA (scs@dtm.ciw.edu); Johns Hopkins University Applied Physics Laboratory, Laurel, MD 20723, USA; Computer Sciences Corporation, Lanham-Seabrook, MD 20706, USA; Academy of Athens, Athens 11527, Greece; Southwest Research Institute, Boulder, CO 80302, USA; Heliophysics Science Division, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA; Department of Earth, Atmospheric, and Planetary Sciences, MIT, Cambridge, MA 02129, USA.

When the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft enters orbit about Mercury in March 2011 it will begin a new phase in an age-old scientific study of the innermost planet. Despite being visible to the unaided eye, Mercury's proximity to the Sun makes it extremely difficult to observe from Earth. Nonetheless, over the centuries man has pursued a quest to understand the elusive planet, and has teased out information about its motions in the sky, its relation to the other planets, and its physical characteristics. A great leap was made in our understanding of Mercury when the Mariner 10 spacecraft flew past it three times in the mid-1970s, providing a rich set of close-up observations. Now, three decades later, The MESSENGER spacecraft has also visited the planet three times, and is poised to add significantly to the study with a. year-long orbital observation campaign.

NASA’s MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft is well into its voyage to initiate a new era in our understanding of the innermost planet. During 2008 MESSENGER flew by Mercury twice and completed the initial spacecraft reconnaissance of the planet begun 34 years earlier by Mariner 10. MESSENGER observations have illuminated how the 1500-km-diameter Caloris basin was a focus for magmatic and deformational activity. High-resolution images show evidence for volcanic vents, pyroclastic deposits, and volcanic flooding of its interior. Lobate scarps, discovered by Mariner 10, are the dominant tectonic landform across the planet and collectively record greater contraction of the surface than inferred from Mariner 10 images. On portions of the surface not seen by Mariner 10 are young craters with prominent ray systems that span most of a hemisphere. Variations in visible and infrared spectral reflectance correlate with geological units. The lack of an infrared absorption band near 1 μm indicates a low ferrous oxide content in surface silicates, but absorption of thermal neutrons by surface material suggests the presence of surface iron in concentrations similar to low- to intermediate-Fe lunar soils. The most unanticipated result to date is the dynamic and complex nature of Mercury’s exosphere–magnetosphere system. Magnetometer measurements point to a dynamo origin for Mercury’s main magnetic field, but that field is substantially modified by the planet’s small, dynamic magnetosphere. Emission-line measurements have revealed the distribution of neutral sodium, calcium, and magnesium in the exosphere and tail; plasma spectrometer observations indicate that these and other species become ionized to populate the planet’s magnetosphere. MESSENGER’s third Mercury flyby on 29 September 2009, the last prior to orbit insertion in 2011, largely duplicated the geometry of the second but added new observations of the planet’s surface and a new perspective on the in situ environment as solar activity continues to change. A Participating Scientist Program has brought the Science Team to its current strength of 48 scientists and their associates. The spacecraft continues to perform as designed in its challenging thermal environment. Use of solar radiation pressure for maintaining momentum balance and supplementing maneuver capability is helping to maintain propellant reserves that could enable an extended mission. The MESSENGER team is continuing its informal interaction with members of the BepiColombo project to maximize the overall scientific return from both the missions.

INSIGHTVolume 13, Issue 4 p. 11-12 Special Feature MESSENGER: An Extreme Systems Engineering Challenge Peter D. Bedini, Peter D. Bedini peter.bedini@jhuapl.edu Search for more papers by this authorEric J. Finnegan, Eric J. Finnegan eric.finnegan@jhuapl.edu Search for more papers by this author Peter D. Bedini, Peter D. Bedini peter.bedini@jhuapl.edu Search for more papers by this authorEric J. Finnegan, Eric J. Finnegan eric.finnegan@jhuapl.edu Search for more papers by this author First published: 23 June 2015 https://doi.org/10.1002/inst.201013411Citations: 1AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article.Citing Literature Volume13, Issue4December 2010Pages 11-12 RelatedInformation

MESSENGER (MErcury Surface, Space ENvironment, GEochemistry, and Ranging) is the first spacecraft to visit Mercury since the Mariner 10 flybys in 1974 and 1975 and will be the first spacecraft to orbit the innermost planet, beginning in March 2011. The science payload is designed to study all aspects of Mercury and its environment and consists of seven instruments and a radio science experiment. During the primary orbital phase of the mission, the MESSENGER team faces the challenge of scheduling science observations to meet all measurement objectives while operating in a thermally harsh environment in geometrically challenging orbits. An efficient, automated science planning and commanding system called MESSENGER SciBox has been developed to support orbital analysis and strategic planning activities prior to orbital insertion, and to schedule and command the instrument and spacecraft operation during the orbital phase. In this paper we present the architecture of MESSENGER SciBox and its application to pre-orbital simulation and inorbit operational usage.

NASA's MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft, launched on 3 August 2004, is well into its voyage to initiate a new era in our understanding of the terrestrial planets. The mission, spacecraft, and payload are designed to answer six fundamental questions regarding the innermost planet during three flybys and a one-year-long, near-polar-orbital observational campaign. The cruise phase to date has been used to commission the spacecraft and instruments and begin the transition to automated use of the instruments with on-board, time-tagged commands. An Earth flyby one year after launch, a large propulsive maneuver in December 2005, and Venus flybys in October 2006 and June 2007 began the process of changing MESSENGER's heliocentric motion. The second Venus flyby was also used to complete final rehearsals for Mercury flyby operations in January 2008 while coordinating observations with the European Space Agency's Venus Express mission. The upcoming Mercury flyby will be the first since that of Mariner 10 in 1975. Along with the second and third MESSENGER flybys in October 2008 and September 2009, that flyby will provide images of the hemisphere of Mercury never seen before by spacecraft as well as the first high-resolution information on Mercury's surface mineralogy. These three flybys, interspersed with deep space maneuvers, finish adjusting the spacecraft motion sufficiently for Mercury orbit injection to follow in March 2011. In the orbital phase, the spacecraft's nominal periapsis latitude of 60∘N will gradually drift northward as the periapsis altitude of 200km gradually drifts upward due to solar gravitational perturbations. The 12-h period and 80∘ inclination are maintained while the altitude is readjusted downward to 200km every Mercury revolution about the Sun. The profile enables mapping of the entire planet and acquiring detailed elemental and topographic data over the northern hemisphere. After conclusion of the nominal mission in March 2012, an additional year of data analysis and archiving is planned before the conclusion of the MESSENGER project. To broaden scientific participation in the mission, NASA has established a Participating Scientist Program, bringing a full complement of international scientific researchers into the mission. The MESSENGER team is also continuing its informal interaction with members of the BepiColombo project to maximize the overall scientific return from both missions.

The Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) is the powerful, technically innovative mineral-mapping camera on the Mars Reconnaissance Orbiter. The main objectives of the instrument are to map Mars' crustal composition and atmospheric processes, and to find and characterize past liquid water environments that might have provided a habitat for life. CRISM was designed, built, and tested at APL and is currently being operated from the CRISM Science Operations Center at the Laboratory. In Martian orbit, CRISM is mapping the global distribution of Mars' ices and minerals; measuring dust, ice, and trace gases in the atmosphere; and imaging several thousand key locations at high spatial and spectral resolution. First results are already changing our understanding of Martian history.