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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 1,333 records · Page 74
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

Entry trajectory, entry environment, and analysis of spacecraft motion for the RAM C-3 flight experiment

The RAM C-3 flight experiment was launched to study the problem of radiofrequency blackout at an entry velocity of 24,300 ft/sec. The flight is described, and data for the entry trajectory and environment, which include the effects of actual temperature measured the day of launch, are presented. An analysis of entry spacecraft motions was performed. This analysis included the determination of wind angles from measured accelerations and estimates of wind angles at high altitudes from gyro-measured rotation rates. The maximum wind angles were found to be less than 5 deg to the point of pitch-roll resonance where the total wind angle increased to 8.5 deg and the roll rate started decreasing. A plausible cause for the decrease in roll rate was shown to be a combination of trim angle and an offset center of gravity.

RAM↗
NASA NTRS2000

Trajectories to Comets Using Solar Electric Propulsion

In situ analysis of a cometary nucleus and return of a sample are high priority scientific goals. Rendezvous and sample return trajectories to comets using low-thrust ion propulsion are presented.

trajectory comet low-thrust propulsion↗
NASA NTRS2006

Motion Trajectories for Wide-area Surveying with a Rover-based Distributed Spectrometer

A mobile ground survey application that employs remote sensing as a primary means of area coverage is highlighted. It is distinguished from mobile robotic area coverage problems that employ contact or proximity-based sensing. The focus is on a specific concept for performing mobile surveys in search of biogenic gases on planetary surfaces using a distributed spectrometer -- a rover-based instrument designed for wide measurement coverage of promising search areas. Navigation algorithms for executing circular and spiral survey trajectories are presented for widearea distributed spectroscopy and evaluated based on area covered and distance traveled.

mobile robots↗
NASA NTRS2007

Planetary Moon Cycler Trajectories

Free-return cycler trajectories repeatedly shuttle a spacecraft between two bodies using little or no fuel. Here, the cycler architecture is proposed as a complementary and alternative method for designing planetary moon tours. Previously applied enumerative cycler search and optimization techniques are generalized and specifically implemented in the Jovian and Saturnian moon systems. In addition, the algorithms are tested for general use to find non-Earth heliocentric cyclers. Overall, hundreds of ideal model ballistic cycler geometries are found and several representative cases are documented and discussed. Many of the ideal model solutions are found to remain ballistic in a zero radius sphere of influence patched conic ephemeris model, and preliminary work in a high-fidelity fully integrated model demonstrates near-ballistic cycles for several example cases.

trajectory↗
NASA NTRS2011

Trajectory Design Considerations for Small Body Touch-and-Go

Outline: (1) Trajectory Description (2) Design Drivers: (2a) Dynamics (2b) Environment (2c) Spacecraft and Ground and System Capabilities (2d) Mission Objectives (3) Design Choices (4) Historical Precedents (5) Case Studies. What is Touch-and-Go (TAG)? (1) Descent to the surface (2) Brief contact (3) Ascends to a safe distance

comets↗
NASA NTRS2011

An Examination of Selected Datacom Options for the Near-Term Implementation of Trajectory Based Operations

A primary feature of the Next Generation Air Transportation System (NextGen) is trajectory based operations (TBO). Under TBO, aircraft flight plans are known to computer systems on the ground that aid in scheduling and separation. The Future Air Navigation System (FANS) was developed to support TBO, but relatively few aircraft in the US are FANSequipped. Thus, any near-term implementation must provide TBO procedures for non-FANS aircraft. Previous research has explored controller clearances, but any implementation must also provide procedures for aircraft requests. The work presented here aims to surface issues surrounding TBO communication procedures for non-FANS aircraft and for aircraft requesting deviations around weather. Three types of communication were explored: Voice, FANS, and ACARS,(Aircraft Communications Addressing and Reporting System). ACARS and FANS are datacom systems that differ in that FANS allows uplinked flight plans to be loaded into the Flight Management System (FMS), while ACARS delivers flight plans as text that must be entered manually via the Control Display Unit (CDU). Sixteen pilots (eight two-person flight decks) and four controllers participated in 32 20-minute scenarios that required the flight decks to navigate through convective weather as they approached their top of descents (TODs). Findings: The rate of non-conformance was higher than anticipated, with aircraft off path more than 20% of the time. Controllers did not differentiate between the ACARS and FANS datacom, and were mixed in their preference for Voice vs. datacom (ACARS and FANS). Pilots uniformly preferred Voice to datacom, particularly ACARS. Much of their dislike appears to result from the slow response times in the datacom conditions. As a result, participants frequently resorted to voice communication. These results imply that, before implementing TBO in environments where pilots make weather deviation requests, further research is needed to develop communication procedures that integrate voice and datacom.

trajectory based operations↗
NASA NTRS2014

Tuning Monotonic Basin Hopping: Improving the Efficiency of Stochastic Search as Applied to Low-Thrust Trajectory Optimization

Trajectory optimization methods using monotonic basin hopping (MBH) have become well developed during the past decade [1, 2, 3, 4, 5, 6]. An essential component of MBH is a controlled random search through the multi-dimensional space of possible solutions. Historically, the randomness has been generated by drawing random variable (RV)s from a uniform probability distribution. Here, we investigate the generating the randomness by drawing the RVs from Cauchy and Pareto distributions, chosen because of their characteristic long tails. We demonstrate that using Cauchy distributions (as first suggested by J. Englander [3, 6]) significantly improves monotonic basin hopping (MBH) performance, and that Pareto distributions provide even greater improvements. Improved performance is defined in terms of efficiency and robustness. Efficiency is finding better solutions in less time. Robustness is efficiency that is undiminished by (a) the boundary conditions and internal constraints of the optimization problem being solved, and (b) by variations in the parameters of the probability distribution. Robustness is important for achieving performance improvements that are not problem specific. In this work we show that the performance improvements are the result of how these long-tailed distributions enable MBH to search the solution space faster and more thoroughly. In developing this explanation, we use the concepts of sub-diffusive, normally-diffusive, and super-diffusive random walks (RWs) originally developed in the field of statistical physics.

autonomous↗
NASA NTRS2014

Tuning Monotonic Basin Hopping: Improving the Efficiency of Stochastic Search as Applied to Low-Thrust Trajectory Optimization

Trajectory optimization methods using MBH have become well developed during the past decade. An essential component of MBH is a controlled random search through the multi-dimensional space of possible solutions. Historically, the randomness has been generated by drawing RVs from a uniform probability distribution. Here, we investigate the generating the randomness by drawing the RVs from Cauchy and Pareto distributions, chosen because of their characteristic long tails. We demonstrate that using Cauchy distributions (as first suggested by Englander significantly improves MBH performance, and that Pareto distributions provide even greater improvements. Improved performance is defined in terms of efficiency and robustness, where efficiency is finding better solutions in less time, and robustness is efficiency that is undiminished by (a) the boundary conditions and internal constraints of the optimization problem being solved, and (b) by variations in the parameters of the probability distribution. Robustness is important for achieving performance improvements that are not problem specific. In this work we show that the performance improvements are the result of how these long-tailed distributions enable MBH to search the solution space faster and more thoroughly. In developing this explanation, we use the concepts of sub-diffusive, normally-diffusive, and super-diffusive RWs originally developed in the field of statistical physics.

mission design↗
NASA NTRS2013

Automating Initial Guess Generation for High Fidelity Trajectory Optimization Tools

Many academic studies in spaceflight dynamics rely on simplified dynamical models, such as restricted three-body models or averaged forms of the equations of motion of an orbiter. In practice, the end result of these preliminary orbit studies needs to be transformed into more realistic models, in particular to generate good initial guesses for high-fidelity trajectory optimization tools like Mystic. This paper reviews and extends some of the approaches used in the literature to perform such a task, and explores the inherent trade-offs of such a transformation with a view toward automating it for the case of ballistic arcs. Sample test cases in the libration point regimes and small body orbiter transfers are presented.

design process↗