An analysis of the effect of aeroassist maneuvers on orbital transfer vehicle performance

This paper summarizes a Langley Research Summer Scholars (LARSS) research project (Summer 1986) dealing with the topic of the effectiveness of aeroassist maneuvers to accomplish a change in the orbital inclination of an Orbital Transfer Vehicle (OTV). This task was subject to OTV design constraints, chief of which were the axial acceleration and the aerodynamic heating rate limits of the OTV. The use of vehicle thrust to replace lost kinetic energy and, thereby, to increase the maximum possible change in orbital inclination was investigated. A relation between time in the hover orbit and payload to LEO was established. The amount of plane change possible during this type of maneuver was checked for several runs and a possible thrusting procedure to increase the plane change and still get to LEO was suggested. Finally, the sensitivity of various target parameters to controllable independent variables was established, trades between the amount of control allowed, and payload to LEO suggested

Capabilities and applications of the Program to Optimize Simulated Trajectories (POST). Program summary document

The capabilities and applications of the three-degree-of-freedom (3DOF) version and the six-degree-of-freedom (6DOF) version of the Program to Optimize Simulated Trajectories (POST) are summarized. The document supplements the detailed program manuals by providing additional information that motivates and clarifies basic capabilities, input procedures, applications and computer requirements of these programs. The information will enable prospective users to evaluate the programs, and to determine if they are applicable to their problems. Enough information is given to enable managerial personnel to evaluate the capabilities of the programs and describes the POST structure, formulation, input and output procedures, sample cases, and computer requirements. The report also provides answers to basic questions concerning planet and vehicle modeling, simulation accuracy, optimization capabilities, and general input rules. Several sample cases are presented

A study of aerocapture into Venus orbit for future exploratory missions

The potential application of aerocapture for future unmanned exploratory missions to Venus has been examined to determine if it is a viable means of capture into Venus orbit. While many probes have already been sent to Venus, none of them used an aerocapture maneuver to insert into orbit. All of them depended on bulky rocket motors to slow the craft down sufficiently to allow capture. Aerocapture uses the atmosphere to reduce the velocity of the craft until it is captured into orbit. An Apollo configuration vehicle similar in size to the Pioneer probes of the early 1980\u27s is examined over an entry velocity range of 11 km/s to 14 km/s for the entry corridor, minimizing post aerocapture delta-V, and stagnation point heating. Also included is an examination of changes in ballistic coefficient, an alternate angle of attack, and atmospheric dispersions. Because Venus is similar in size to Earth, the target orbit for all cases was an altitude of 407 km. Deceleration constraints were added in the research, after the size of the entry corridor was found to be much larger than expected. Final results showed that aerocapture would be a viable means of insertion into Venus orbit for robotic missions. The entry corridor was found to be approximately 1.65 degrees at 11 km/s decreasing to approximately 1.0 degrees at 14 km/s. Estimates of the stagnation point heating also showed that modem materials would be able to withstand the entry and protect the craft

Robust Estimation of Mahalanobis Distance in Hyperspectral Images

This dissertation develops new estimation methods that fit Johnson distributions and generalized Pareto distributions to hyperspectral Mahalanobis distances. The Johnson distribution fit is optimized using a new method which monitors the second derivative behavior of exceedance probability to mitigate potential outlier effects. This univariate distribution is then used to derive an elliptically contoured multivariate density model for the pixel data. The generalized Pareto distribution models are optimized by a new two-pass method that estimates the tail-index parameter. This method minimizes the mean squared fitting error by correcting parameter values using data distance information from an initial pass. A unique method for estimating the posterior density of the tail-index parameter for generalized Pareto models is also developed. Both the Johnson and Pareto distribution models are shown to reduce fitting error and to increase computational efficiency compared to previous models

A study of the Earth return aerocapture for a manned Mars mission

The current architecture being considered by NASA for a future manned Mars mission involves the use of an aerocapture procedure at both Mars and Earth arrival. The aerocapture will be used to decelerate and insert the vehicles into the desired orbits at the respective planets. The crew may return to Earth in a large, inflatable habitat known as the Transhab. This Transhab would be complimented with an aeroshell, which will serve the dual purposes of providing protection from the intense heat of high-speed atmospheric flight and offer some lifting ability to the vehicle as well. The aeroshell has been dubbed the Ellipsled because of the characteristic shape. This thesis represents a preliminary study of the aerocapture of the Transhab/Ellipsled vehicle upon Earth return. Undershoot and overshoot boundaries have been examined as a function of entry velocity for a variety of constraining factors such as deceleration limits and vehicle ballistic coefficient. The effects of atmospheric dispersions have also been explored. In addition, a simple 180 degree roll maneuver has been implemented in the undershoot trajectories to help target the desired 407 km circular Earth orbit. Results show that the Transhab/Ellipsled vehicle has a nominal entry corridor width of 0.5 - 0.7 degrees for entry speeds ranging from 12.5 km/s to 14.5 km/s. In addition, entry corridor comparisons have been made between the Transhab/Ellipsled and a modified Apollo capsule which is also being considered for the Earth return vehicle. Future studies should focus on refining the heating rate analyses, off-nominal vehicle aerodynamics, winds, horizontal density waves, and changes in the vehicle trim angle of attack. Furthermore, a guidance algorithm should be implemented to optimize the overall trajectory and minimize inclination changes and post-aerocapture delta V needed to circularize the orbit

A Feasibility Study for Using Commercial Off The Shelf (COTS) Hardware for Meeting NASA’s Need for a Commercial Orbital Transportation Services (COTS) to the International Space Station - [COTS]\u3csup\u3e2\u3c/sup\u3e

The space vehicle system concept (i.e. resupply vehicle) described is based on the new direction that President George W. Bush announced on January 14, 2004 for NASA’s Human Exploration, which has the space shuttle retiring in 2011 following the completion of the International Space Station (ISS). This leads to a problem for the ISS community regarding the capability of meeting a sixty metric-ton cargo shortfall in resupply and the ability of returning large payloads, experiment racks and any other items too large to fit into a crew only type spacecraft like the Orion or Soyuz. NASA and the ISS partners have realized these future problems and started developing various systems for resupply to ISS, but none offer the capability for large up or down mass close to that of the shuttle. Without this capability, the primary purpose behind the ISS science mission is defeated and the ability to keep the station functioning properly is at risk with limited payload delivery (i.e. replacement hardware size and mass). There is a solution to this problem and a majority of the solution has already been designed, built, and flight tested. Another portion has been studied heavily by a team at NASA for use in a slightly different mission. Following the retirement of the space shuttle fleet and the loss of heavy up and down mass capability, the only solution to the problem is to design a new spacecraft. However, the budget and new direction for NASA will not allow for a costly new payload carrying spacecraft. The solution is to use existing commercial off the shelf (COTS) hardware to minimize the costs of developing a totally new system. This paper will discuss the technical feasibility of this conceptual configuration

A COUPLED INTERPLANETARY - ENTRY, DESCENT AND LANDING TARGETING PROCEDURE

In NASA's past, targeting to a Mars landing site has required iteration between the Entry, Descent and Landing (EDL) analysts at NASA Langley Research Center and the interplanetary navigators at the Jet Propulsion Laboratory (JPL). JPL would develop thousands of arrival states at Mars based on an assumed, constant entry flight path angle and down range angle from entry to landing. Langley would perform the EDL analysis using the arrival states from JPL. Feasible trajectories developed by Langley had varying flight path and down range angles over the entire launch/arrival window forcing an iteration of the trajectory design between JPL and Langley. The iteration process was inefficient, stretching out the design phase while introducing the possibility for error. The purpose of this study is to develop a method that calculates an interplanetary trajectory from Earth to Mars and seamlessly couples the tool with Langley's EDL analysis. The method will show a novel extension to current Lambert solution methods while incorporating a multiple revolution capability

El pretérito perfecto compuesto en la enseñanza de ELE: un acercamiento didáctico

This article proposes a didactic approach to teaching the compound past tense that is known in English as “Present Perfect” (PPC for itsinitials in Spanish) in contexts of Spanish as a Foreign Language. It analysessome issues concerning the traditional view on the subject and suggests thatthe concept of generic reference proposed by Henderson (2010) provides amore coherent explanation for some occurrences to which the literature typicallyassigns a pan-Hispanic character. A didactic approach is proposed, which shiftsfrom the traditional didactic perspective of "Peninsular versus Latin American"PPC to discussing two modalities of PPC selection, which Spanish dialects adhere to a varying extent. With the aim of bolstering the dialogue between specific research in the field of PPC and applied linguistics, this approach is supported by evidence previously published in earlier works, as well as new examples from oral language. Following Long’s (1991) proposal of Focus on Form, this article suggests that explicit exposure to the parameters used by these two modalities will heighten learners’ awareness of the salience of this phenomenon, which will ultimately impact on their acquisition in the long term.En este artículo se propone un acercamiento didáctico a la enseñanza del Pretérito Perfecto Compuesto (PPC) en contextos de español como lengua extranjera. Se analizan algunos problemas de la visión tradicional sobre el tema y se plantea que el concepto de referencia genérica propuesto en Henderson (2010) da una respuesta más coherente a usos que la bibliografía suele adjudicar un carácter panhispánico. Se propone un acercamiento didáctico que cambie la tradicional perspectiva didáctica del PPC “peninsular contra americano” para pasar a hablar de dos modalidades de selección del PPC, a las cuales se adscriben en mayor o menor medida los dialectos del español. Con la intención de vigorizar el diálogo entre la investigación específica en el campo del PPC y la lingüística aplicada, la propuesta se apoya en evidencia ya publicada en obras anteriores, así como también ejemplos nuevos del registro oral. Siguiendo la propuesta de Long (1991) de Foco en la forma, se sugiere que la exposición explícita de los parámetros que utilizan estas dos modalidades aumentará la prominencia del fenómeno en la conciencia del aprendiente, lo que, en última instancia, influirá en el conocimiento a largo plazo