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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 307 records · Page 17
All sourcesNASA NTRSDOE OSTI
NASA NTRS2015

Multi-Objective Hybrid Optimal Control for Multiple-Flyby Low-Thrust Mission Design

Preliminary design of low-thrust interplanetary missions is a highly complex process. The mission designer must choose discrete parameters such as the number of flybys, the bodies at which those flybys are performed, and in some cases the final destination. In addition, a time-history of control variables must be chosen that defines the trajectory. There are often many thousands, if not millions, of possible trajectories to be evaluated. The customer who commissions a trajectory design is not usually interested in a point solution, but rather the exploration of the trade space of trajectories between several different objective functions. This can be a very expensive process in terms of the number of human analyst hours required. An automated approach is therefore very desirable. This work presents such an approach by posing the mission design problem as a multi-objective hybrid optimal control problem. The method is demonstrated on a hypothetical mission to the main asteroid belt.

Optimization↗
NASA NTRS1979

Flyby- and rendezvous-type comet missions from the standpoint of large-particle dust experiments

The measurement by cometary flyby and rendezvous missions of the dust particles emitted from a cometary nucleus and believed to be the major source of the interplanetary dust is considered. The impact rate per unit area of particles in a given size range on a spacecraft dust sensor is calculated in terms of the distance between comet and probe and the particle emission rate and velocity. It is concluded that large-particle (greater than 100-micron) dust analysis experiments cannot be conducted on flyby missions to short-period comets since the required miss distance is orders of magnitude smaller than the targeting error, while for a rendezvous mission much greater miss distances are possible due to the longer period of cometary contact. The problem of designing dust sensors to operate at the subkilometer per second intercept velocities of a rendezvous mission is also noted.

Sekanina, Z.↗
NASA NTRS1986

Mars mission concepts and opportunities

Trajectory and mission requirement data are presented for Earth Mars opposition and conjunction class roundtrip flyby and stopover mission opportunities available between 1997 and 2045. The opposition class flyby mission uses direct transfer trajectories to and on return from Mars. The opposition class stopover mission employs the gravitational field of Venus to accelerate the space vehicle on either the outbound or inbound leg in order to reduce the propulsion requirement associated with the opposition class mission. The conjunction class mission minimizes propulsion requirements by optimizing the stopover time at Mars.

Archie C Young↗
NASA NTRS1976

Ballistic trajectories for Mercury Orbiter missions using optimal Venus flybys, a systematic search

The considered approach, which has been previously studied by Hollenbeck et al. (1973) makes use of a Venus gravity assist. The search for ideal trajectories for Mercury Orbiter missions involves a determination of trajectories with the lowest possible Mercury approach speed. Ideal Venus-to-Mercury transfers and opportunities are discussed. The second part of the reported investigation is concerned with the determination of suitable trajectories for the trip from earth to Venus. On the basis of the obtained data it appears that the best ten trajectories can deliver spacecraft from a low of 720 kg to a high of 1230 kg to orbits with 500 km periapse and 24 hr periods. The corresponding flight times are 790 days and 1243 days.

Bender, D. F.↗
NASA NTRS2009

Importance of Model Simulations in Cassini In-Flight Mission Events

Simulation environments have been an integral part of Cassini's heritage. From the time of flight software development and testing to the beginning of the spacecraft's extended mission operations, both softsim and hardware-in-the-loop testbeds have played vital roles in verifying and validating key mission events. Satellite flybys and mission-critical events have established the need to model Titan's atmospheric torque, Enceladus' plume density, and other key parametric spacecraft environments. This paper will focus on enhancements to Cassini's Flight Software Development System (FSDS) and Integrated Test Laboratory (ITL) to model key event attributes which establish valid test environments and ensure safe spacecraft operability. Comparisons between simulated to in-flight data are presented which substantiate model validity.

FSDS↗
NASA NTRSDate not supplied

Exploring the Relationship Between Science Funding and Science Productivity on Extended Missions

Introduction: The goal of this summer internship research project was to explore the relationship between the level of funding for science team research and science productivity for planetary spaceflight missions. The productivity and funding for the prime and extended missions were compared when possible. Determining the actual rather than anecdotal relationship between the level of science team funding and their productivity will help determine the adequacy of science team funding. Additionally, determining whether productivity increases or decreases over time (within missions, or within the years between different missions) provides insights into ongoing trends. This project was conducted using data from 11 extended missions within the Planetary Science Division. The main goals of this project were to 1) quantify the level of productivity of the science team during the extended portion of each mission, 2) compare the level of productivity between different types of missions, and 3) compare the level of productivity between the prime missions and extended missions. Methodology: The central metric enters around the “publication rate” of each mission. This rate is normalized in a variety of ways, including the number of publications per year, per Co-I, and per instruments. For the most part, this data was attainable through mission websites, team rosters, and data collected from previous projects. The publication data for this project utilized the SAO/NASA Astrophysics Data System, and it consisted of a search for any papers from the extended mission that had a co-investigator as an author. The time period for these searches also included an additional two years after the end of the extended mission to account for additional time it typically takes to finish data analysis and publish papers. Data from prime missions was collected from a previous project that measured similar metrics for the same missions. When comparing the different types of missions, three factors were used: mission size, dates of the prime and extended missions, and the type of the mission (rover, flyby, orbiter, or lander). To determine mission size, missions were compared by the number of Co-I’s on the mission, the number of instruments in the payload, and the mission class. Findings: On average, prime mission publication rates were generally higher than those of extended missions. Out of the nine missions used for this comparison, six had a higher prime mission publication rate and three had a higher extended mission publication rate. This distinction was interesting to observe, but it should be noted that the methodology for determing the number of published papers differed for the prime missions and the extended missions Discovery missions were found to be the most scientifically productive. Additionally, more recent extended missions tend to possess greater productivity. When comparing missions of different types, it was found that orbiters were much more productive than other types of missions. Future Work: There are a number of opportunities to extend and improve on this project in the future. Even though the metrics used were the same, the prime mission data could be recollected from the same sources as the extended mission data (Astrophysics Data System) to insure greater consistency. The impact level of the publications could also be accounted for, and financial data could be used to compare teams with different levels of funding. Additionally, more missions could be examined to increase the sample size of these comparisons, especially the comparison of different mission types which had an incredibly small sample size for some categories.

Cameron Maxwell Thompson↗
NASA NTRS2014

The Double Flybys of the Cassini Mission: Navigation Challenges and Lessons Learned

Since 2004, the Cassini spacecraft has flown by Titan and other Saturn moons numerous times, successfully accomplishing its 100th targeted encounter of Titan in March 2014. The navigation of Cassini is challenging, even more so with "double flybys," two encounters separated by at most a few days. Because of this tight spacing, there is not enough time for a maneuver in between. Additionally, maneuvers prior to a double flyby only target one of the two encounters. This paper discusses the challenges faced by the Cassini Navigation Team with each double flyby, as well as lessons learned during operational support of each dual encounter. The strengths and weaknesses of the targeting strategies considered for each double flyby are also detailed, by comparing downstream ?V costs and changes to the non-targeted flyby conditions.

maneuver↗
NASA NTRS1990

The CRAF mission and Earth-based comet observations

The Comet Rendezvous Asteroid Flyby (CRAF) mission is now being designed and planned to perform detailed studies of a typical short period comet as it moves around its orbit, building on the data gained from the Giotto, Vega, and Suisei fast flybys of Comet Halley in 1986. CRAF will be launched in Aug. 1995 and will match orbits with short period Comet Kopff in July 2000, 850 days before perihelion at a heliocentric distance of 5.05 AU. After a series of close, slow flybys, the spacecraft will be placed in orbit around the nucleus for a better than 1 m/line-pair imaging resolution on the nucleus surface. Earth based observations of the target comet, either by ground based facilities or Earth orbiting satellites, can provide essential data for CRAF mission planning, and are needed in support of the rendezvous mission. Estimates of the nucleus size, albedo, shape, rotation period, and rotation pole orientation are needed for preliminary mission planning, resource allocation, and sequence design.

Weissman, Paul R.↗
NASA NTRS1989

Thermal design for the Comet Rendezvous Asteroid Flyby spacecraft

The mission overview of the Comet Rendezvous Asteroid Flyby (CRAF) spacecraft, which is planned to rendezvous with Comet Kopff in 1998, is presented, together with the CRAF mission trajectory. The preliminary thermal design of the CRAF spacecraft is discussed, with emphasis placed on the Low Precision Pointing Platform, Bus, Propulsion Module, and Comet Penetrator, the thermal design of which was impacted most by the comet environment. Model simulations showed the design of the bus and the propulsion module subsystems to be adequate. Configuration diagrams are included.

Tsuyuki, G. T.↗
NASA NTRS1989

Coma and tail trajectory design for the CRAF mission

The design of the trajectory for the proposed Comet Rendezvous Asteroid Flyby (CRAF) mission to study comet coma and tail development is examined. A two part trajectory is planned for the CRAF mission to study comet Kopff. It is proposed that, during the 213 day perihelion phase of the trajectory, CRAF should perform multiple petallike flybys at 50-5000 km from the comet's nucleus. Nine days after the perihelion, the spacecraft would transition into the comet tail in the antisun direction to a maximum distance of 50,000 km. The objectives of these two phases of exploration are discussed.

Ionasescu, Rodica↗
NASA NTRS1967

Galactic Jupiter probes

Galactic space probe mission involving flight through asteroid belt and Jupiter flyby

SPACE PROBE↗