Abstract
We summarize a decade of effort by the Origins, Spectral Interpretation, Resource Identification, and Security–Regolith Explorer (OSIRIS-REx) mission team to build up the unique ...capabilities, processes, and procedures required to accomplish the unprecedented navigation performance required during proximity operations at asteroid (101955) Bennu. Stereophotoclinometry was a key technology used for digital terrain model (DTM) generation and landmark navigation, enabling estimation of spacecraft trajectories and Bennu’s geophysical parameters. We outline the concept of operations for OSIRIS-REx landmark navigation and the wide array of testing and verification efforts leading up to OSIRIS-REx’s arrival at Bennu. We relate the outcome of these efforts to the experiences during proximity operations. We discuss navigation and DTM performance during operations, including detailed lessons learned to carry forward for future missions.
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)
to ...be a notable factor in their evolution
. (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 spectrum
is typical of bodies in this part of the main belt
. Here we report observations by the Lucy spacecraft
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.
Topical hypochlorous acid (HOCl) has recently been proposed as a treatment of pruritus. However, it is not known whether topical HOCl decreases or promotes pruritus. This review sheds light on this ...poorly understood subject. This article describes the pathophysiology of pruritus, current treatments of pruritus, and how pH determines the properties of HOCl in solution. The article then proposes two mechanisms by which HOCl may reduce pruritus: 1) HOCl is microbicidal to cutaneous pathogens, especially Staphylococcus aureus in atopic dermatitis; 2) HOCl is anti-inflammatory and reduces the activities of histamine, leukotriene B4, and interleukin-2, all of which are implicated in the pathophysiology of itch. Lastly, this article describes conditions under which HOCl may actually cause pruritus as an adverse effect. For example, HOCl increases the activity of nerve growth factor, which promotes itch. Prolonged or high-dose HOCl exposure may also cause irritant contact dermatitis, or less commonly, allergic contact dermatitis.
The Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer (OSIRIS-REx) spacecraft was launched in September 2016 and arrived at its target, near-Earth asteroid ...(101955) Bennu in late 2018. After executing nearly two years of multi-phase proximity operations navigation and mapping campaigns, on October 20, 2020 OSIRIS-REx successfully performed the Touch-And-Go (TAG) maneuver to become the first American mission to collect a sample from an asteroid. As Bennu is one of the smallest objects ever to be visited by a planetary spacecraft, the mission presented many navigational challenges, and optical navigation (OpNav) techniques were essential to the successful execution of the mission. The specific challenges of OSIRIS-REx required nimble OpNav planning, robust data management, and quick, automated analyses and data-product delivery capabilities. In addition to the two primary image processing tools, centroid-based and landmark-based OpNav, a host of support and planning tools and procedures were developed. The multi-year operations timeline, fast maneuver cadence, and multi-phase nature of proximity operations for OSIRIS-REx motivated a streamlined and reactive image planning process. A suite of tools was developed to ensure that the mission navigation requirements were continually satisfied. On approach, the Op-N av Opportunity Analyzer (OpOpp) was used to deconflict the imaging schedule with interference from bright background stars. In-flight instrument calibration was performed using an in-house distortion calibration toolset. An Exposure Time Calculator was used to determine optimal exposure times and verify that the images would produce sufficient OpNav image data. Additionally, Fly-Point-Shoot (FPS) software was used to analyze and mitigate the effect of trajectory and pointing uncertainties on image planning and coverage. This paper describes in further detail the operational challenges of the OSIRIS-REx OpNav subsystem, as well as the tools, procedures, and strategies developed to ensure the satisfaction of navigation requirements.
During its initial orbital phase in early 2019, the Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer (OSIRIS-REx) asteroid sample return mission detected ...small particles apparently emanating from the surface of the near-Earth asteroid (101955) Bennu in optical navigation images. Identification and characterization of the physical and dynamical properties of these objects became a mission priority in terms of both spacecraft safety and scientific investigation. Traditional techniques for particle identification and tracking typically rely on manual inspection and are often time-consuming. The large number of particles associated with the Bennu events and the mission criticality rendered manual inspection techniques infeasible for long-term operational support. In this work, we present techniques for autonomously detecting potential particles in monocular images and providing initial correspondences between observations in sequential images, as implemented for the OSIRIS-REx mission.
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