The
New Horizons
mission performed a successful flyby of Arrokoth, a distant Kuiper-Belt Object, on January 1, 2019, representing the farthest planetary encounter to date. The navigation strategy and ...performance required to deliver the spacecraft to the desired flyby target were driven by a number of challenges including those related to Arrokoth’s viewing angle and relatively recent discovery in June 2014. These and other challenges required the
New Horizons
science and navigation teams to devise a strategy in close collaboration that would substantially reduce the flyby navigation errors. Earth-based astrometry and occultation measurements of Arrokoth were collected and used to estimate Arrokoth’s orbit and its associated uncertainties, which were in turn used to inform and reduce navigation approach and flyby uncertainties. The
New Horizons
navigation effort used these a priori orbits along with radio metric and optical navigation measurements to first predict the navigation performance in support of the flyby design, and then estimate
New Horizons
’ trajectory, maneuvers and other filter state parameters during navigation operations. An overview of the Arrokoth orbit estimation and navigation strategy and predicted performance, as well as the operational results from the initial target search campaign in 2004 through Arrokoth’s successful flyby in 2019 are presented, along with the principal challenges and most important lessons learned along the way.
New Horizons was the first mission with primary science objectives to explore the Pluto–Charon system and, in an extended mission, to observe a Kuiper Belt object (KBO). This article summarizes the ...challenges in planning and targeting the New Horizons spacecraft for the Pluto encounter and how the team addressed these challenges, reducing mission risk to ensure a successful encounter that fully met its science objectives. It also presents the navigation accuracies achieved and the lessons learned, which were later applied to planning and conducting the flyby of a newly discovered KBO, Arrokoth, during New Horizons' first extended mission.
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.
MESSENGER Mission Design and Navigation McAdams, James V; Farquhar, Robert W; Taylor, Anthony H ...
Space science reviews,
8/2007, Letnik:
131, Številka:
1-4
Journal Article
Recenzirano
Nearly three decades after the Mariner 10 spacecraft's third and final targeted Mercury flyby, the 3 August 2004 launch of the MESSENGER (MErcury Surface, Space ENvironment, GEochemistry, and ...Ranging) spacecraft began a new phase of exploration of the closest planet to our Sun. In order to ensure that the spacecraft had sufficient time for pre-launch testing, the NASA Discovery Program mission to orbit Mercury experienced launch delays that required utilization of the most complex of three possible mission profiles in 2004. During the 7.6-year mission, the spacecraft's trajectory will include six planetary flybys (including three of Mercury between January 2008 and September 2009), dozens of trajectory-correction maneuvers (TCMs), and a year in orbit around Mercury. Members of the mission design and navigation teams optimize the spacecraft's trajectory, specify TCM requirements, and predict and reconstruct the spacecraft's orbit. These primary mission design and navigation responsibilities are closely coordinated with spacecraft design limitations, operational constraints, availability of ground-based tracking stations, and science objectives. A few days after the spacecraft enters Mercury orbit in mid-March 2011, the orbit will have an 80 degree inclination relative to Mercury's equator, a 200-km minimum altitude over 60 degree N latitude, and a 12-hour period. In order to accommodate science goals that require long durations during Mercury orbit without trajectory adjustments, pairs of orbit-correction maneuvers are scheduled every 88 days (once per Mercury year).
Background.
Little is known about the incidence and etiology of healthcare-associated infections in immunosuppressed children.
Methods.
Data collected prospectively between 1983 and 2008 were used to ...analyze changes in the rate, types of infection, and infecting organisms over time in patients treated at a children's cancer hospital. Neutropenia was evaluated as a risk factor.
Results.
Over the 26-year study period, 1986 healthcare-associated infections were identified during 1653 hospitalizations. The infection rate decreased significantly from 5.6 to 2.0 infections per 100 discharges (P < .01) and from 9.0 to 3.7 infections per 1000 patient-days (P < .01). Bloodstream infections were the most common type of infection (32.7% of all infections). Staphylococci (46.4% of Gram-positive bacteria), Escherichia coli (36.7% of Gram-negative bacteria), and Candida spp. (68.7% of fungi) were the most common pathogens isolated. An absolute neutrophil count (ANC) nadir <100 per mm3 was significantly associated (P < .0001) with an increased rate of infections compared with higher ANC nadirs.
Conclusions.
Despite a steady expansion in hospital capacity and patient encounters over the last 3 decades, rates of healthcare-associated infections decreased significantly at our hospital. These data suggest that sustained decreases in the rate of healthcare-associated infections in immunosuppressed children are possible. An ANC <100 per mm3 is a risk factor for healthcare-associated infections in this population.
To determine the influence of needle gauge in Mantoux skin testing for tuberculosis.
Randomized selection of either a 27- or 30-gauge needle for Mantoux skin test placement; observer-blinded.
Annual ...hospital employee screening.
Six hundred twenty-five employees working in clinical and laboratory research environments.
Blinded observers found that the use of 27-gauge needles caused increased bleeding and bruising compared with 30-gauge needles (p≤0.007 for each). However, the 27-gauge needle produced larger blebs and less leakage of tuberculin solution (p≤0.0003). Conclusion: Smaller gauge needles could potentially cause false-negative screening results because of decreased antigen delivery. Use of needle gauges smaller than 27 gauge should be avoided until their reliability is validated.
Recovery of near's mission to eros Dunham, David W.; Farquhar, Robert W.; McAdams, James V. ...
Acta astronautica,
07/2000, Letnik:
47, Številka:
2-9
Journal Article
Recenzirano
On December 20, 1998, the main bipropellant thruster on the Near Earth Asteroid Rendezvous (NEAR) spacecraft was commanded to start a 15-minute burn. It was the first and largest of four planned ...maneuvers that would cancel NEAR's velocity relative to (433) Eros to allow capture into orbit about the asteroid in January 1999. But the burn aborted and the spacecraft tumbled, causing loss of communication. The spacecraft corrected the problem, but used 29 kg of fuel in the process. A day later, NEAR was reacquired with just enough time to upload a sequence of commands to image Eros extensively as the spacecraft hurtled past the asteroid on December 23. The NEAR team designed a large bipropellant maneuver that successfully cancelled most of NEAR's velocity relative to Eros on January 3, 1999. But then NEAR was almost 1 million kilometers from Eros, so a long `U-turn' journey was begun to return to the asteroid on February 14, 2000. The spacecraft remains healthy and enough fuel remains to enter orbit about Eros to complete all of the mission goals. This will be the first time that an interplanetary spacecraft has failed an orbital capture burn and returned to accomplish its objectives. This is possible because NEAR had a generous fuel supply and a robust contingency plan.
A Mercury orbiter mission is challenging from thermal and mass perspectives. The Mercury Surface, Space Environment, Geochemistry, and Ranging (MESSENGER) mission overcomes these challenges while ...avoiding esoteric technologies by using an innovative approach with commonly available materials, minimal moving parts, and maximum heritage. This approach yields a spacecraft with good margins in all categories and low technical risk. The key concepts are a ceramic-cloth sunshade, an integrated lightweight structure and high- performance propulsion system, and a solar array incorporating optical solar reflectors (OSRs). The sunshade maintains the spacecraft at room temperature. The integrated structure and propulsion system provides ample mass margin. The solar array with OSRs, which has already undergone significant testing, provides thermal margin even if the panels are inadvertently pointed directly at the Sun at 0.3 AU.
0.3
AU
.
MESSENGER Mission Design and Navigation MCADAMS, James V; FARQUHAR, Robert W; TAYLOR, Anthony H ...
Space science reviews,
2007, Letnik:
131, Številka:
1-4
Journal Article
When the NEAR Shoemaker spacecraft began its orbit about the asteroid 433 Eros on 14 February 2000, it marked the beginning of many firsts for deep space navigation. Among these were the design and ...estimation techniques that were necessary to plan and execute navigation of the first spacecraft to orbit and land on an irregularly shaped small body. This article describes the navigation strategy and results for the rendezvous, orbit, and landing phases of the NEAR mission. Included are descriptions of the new techniques developed to deal with navigation challenges encountered during rendezvous and the year-long orbit phase. The orbit phase included circular orbits down to a 35-km radius and elliptical orbits that targeted overflights to within 2.7 km above the surface. The orbit phase ended on 12 February 2001, when NEAR Shoemaker was guided to a soft landing on the surface of Eros.
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