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At least 343 records · Page 19
All sourcesNASA NTRSDOE OSTI
NASA NTRS2010

Fast Calculation of Abort Return Trajectories for Manned Missions to the Moon

In order to support the anytime abort requirements of a manned mission to the Moon, the vehicle abort capabilities for the translunar and circumlunar phases of the mission must be studied. Depending on the location of the abort maneuver, the maximum return time to Earth and the available propellant, two different kinds of return trajectories can be calculated: direct and fly-by. This paper presents a new method to compute these return trajectories in a deterministic and fast way without using numerical optimizers. Since no simplifications of the gravity model are required, the resulting trajectories are very accurate and can be used for both mission design and operations. This technique has been extensively used to evaluate the abort capabilities of the Orion/Altair vehicles in the Constellation program for the translunar phase of the mission.

Senent, Juan S.↗
NASA NTRS2010

Demonstration of an Aerocapture GN and C System Through Hardware-in-the-Loop Simulations

Aerocapture is an orbit insertion maneuver in which a spacecraft flies through a planetary atmosphere one time using drag force to decelerate and effect a hyperbolic to elliptical orbit change. Aerocapture employs a feedback Guidance, Navigation, and Control (GN&C) system to deliver the spacecraft into a precise postatmospheric orbit despite the uncertainties inherent in planetary atmosphere knowledge, entry targeting and aerodynamic predictions. Only small amounts of propellant are required for attitude control and orbit adjustments, thereby providing mass savings of hundreds to thousands of kilograms over conventional all-propulsive techniques. The Analytic Predictor Corrector (APC) guidance algorithm has been developed to steer the vehicle through the aerocapture maneuver using bank angle control. Through funding provided by NASA's In-Space Propulsion Technology Program, the operation of an aerocapture GN&C system has been demonstrated in high-fidelity simulations that include real-time hardware in the loop, thus increasing the Technology Readiness Level (TRL) of aerocapture GN&C. First, a non-real-time (NRT), 6-DOF trajectory simulation was developed for the aerocapture trajectory. The simulation included vehicle dynamics, gravity model, atmosphere model, aerodynamics model, inertial measurement unit (IMU) model, attitude control thruster torque models, and GN&C algorithms (including the APC aerocapture guidance). The simulation used the vehicle and mission parameters from the ST-9 mission. A 2000 case Monte Carlo simulation was performed and results show an aerocapture success rate of greater than 99.7%, greater than 95% of total delta-V required for orbit insertion is provided by aerodynamic drag, and post-aerocapture orbit plane wedge angle error is less than 0.5 deg (3-sigma). Then a real-time (RT), 6-DOF simulation for the aerocapture trajectory was developed which demonstrated the guidance software executing on a flight-like computer, interfacing with a simulated IMU and simulated thrusters, with vehicle dynamics provided by an external simulator. Five cases from the NRT simulations were run in the RT simulation environment. The results compare well to those of the NRT simulation thus verifying the RT simulation configuration. The results of the above described simulations show the aerocapture maneuver using the APC algorithm can be accomplished reliably and the algorithm is now at TRL-6. Flight validation is the next step for aerocapture technology development.

Masciarelli, James↗
NASA NTRS2012

Lunar Navigation Determination System - LaNDS

A portable comprehensive navigational system has been developed that both robotic and human explorers can use to determine their location, attitude, and heading anywhere on the lunar surface independent of external infrastructure (needs no Lunar satellite network, line of sight to the Sun or Earth, etc.). The system combines robust processing power with an extensive topographical database to create a real-time atlas (GIS Geospatial Information System) that is able to autonomously control and monitor both single unmanned rovers and fleets of rovers, as well as science payload stations. The system includes provisions for teleoperation and tele-presence. The system accepts (but does not require) inputs from a wide range of sensors. A means was needed to establish a location when the search is taken deep in a crater (looking for water ice) and out of view of Earth or any other references. A star camera can be employed to determine the user's attitude in menial space and stellar map in body space. A local nadir reference (e.g., an accelerometer that orients the nadir vector in body space) can be used in conjunction with a digital ephemeris and gravity model of the Moon to isolate the latitude, longitude, and azimuth of the user on the surface. That information can be used in conjunction with a Lunar GIS and advanced navigation planning algorithms to aid astronauts (or other assets) to navigate on the Lunar surface.

Quinn, David↗
NASA NTRS2012

High Degree and Order Gravity Fields of the Moon Derived from GRAIL Data

The Gravity Recovery and Interior Laboratory (GRAIL) spacecraft conducted the mapping of the gravity field of the Moon from March 1, 2012 to May 29, 2012. The twin spacecraft acquired highly precise K Band range-rate (KBRR) intersatellite ranging data and Deep Space Network (DSN) data during this prime mission phase from altitudes of 15 to 75 km above the lunar surface over three lunar months. We have processed these data using the NASA GSFC GEODYN orbit determination and geodetic parameter estimation program, and we have determined gravity fields up to degree and order 420 in spherical harmonics. The new gravity solutions show improved correlations with LOLA-derived topography to high degree and order and resolve many lunar features in the geopotential with a resolution of less than 30 km, including for example the central peak of the crater Tycho. We discuss the methodology used for the processing of the GRAIL data, the quality of the orbit determination on the GRAIL satellites and the derivation of the solutions, and their evaluation with independent data, including Lunar Prospector. We show that with these new GRAIL gravity solutions, we can now fit the low altitude, extended mission Lunar Prospector tracking data better than with any previous gravity model that included the LP data.

Lemoine, F. G.↗
NASA NTRS2013

Gravity Recovery and Interior Laboratory (GRAIL): Extended Mission and End-Game Status

The Gravity Recovery and Interior Laboratory (GRAIL) [1], NASA s eleventh Discovery mission, successfully executed its Primary Mission (PM) in lunar orbit between March 1, 2012 and May 29, 2012. GRAIL s Extended Mission (XM) initiated on August 30, 2012 and was successfully completed on December 14, 2012. The XM provided an additional three months of gravity mapping at half the altitude (23 km) of the PM (55 km), and is providing higherresolution gravity models that are being used to map the upper crust of the Moon in unprecedented detail.

Zuber, Maria T.↗
NASA NTRS2014

Comparison of Low-Thrust Control Laws for Application in Planetocentric Space

Recent interest at NASA for the application of solar electric propulsion for the transfer of significant payloads in cislunar space has led to the development of high-fidelity simulations of such missions. With such transfers involving transfer times on the order of months, simulation time can be significant. In the past, the examination of such missions typically began with the use of lower-fidelity trajectory optimization tools such as SEPSPOT to develop and tune guidance laws which delivered optimal or near- optimal trajectories, where optimal is generally defined as minimizing propellant expenditure or time of flight. The transfer of these solutions to a high-fidelity simulation is typically an iterative process whereby the initial solution may nearly, but not precisely, meet mission objectives. Further tuning of the guidance algorithm is typically necessary when accounting for high-fidelity perturbations such as those due to more detailed gravity models, secondary-body effects, solar radiation pressure, etc. While trajectory optimization is a useful method for determining optimal performance metrics, algorithms which deliver nearly optimal performance with minimal tuning are an attractive alternative.

SOLAR ELECTRIC PROPULSION↗
NASA NTRS2015

Lunar Orbit Stability for Small Satellite Mission Design

The irregular nature of the lunar gravity field will severely affect the orbit lifetime and behavior of future lunar small satellite missions. These spacecraft need stable orbits that do not require large deltaV budgets for station-keeping maneuvers. The initial classical elements of any lunar orbit are critical to address its stability and to comply with mission requirements. This publication identifies stable regions according to different initial conditions at the time of lunar orbit insertion (LOI). High fidelity numerical simulations with two different gravity models were performed. We focus in low altitude orbits where the dominant force in orbit propagation is the existence of unevenly distributed lunar mass concentrations. These orbits follow a periodic oscillation in some of the classical elements that is particularly useful for mission design. A set of orbital maintenance strategies for various mission concepts is presented.

Lunar Science↗
NASA NTRS2016

Relative Terrain Imaging Navigation (RETINA) Tool for the Asteroid Redirect Robotic Mission (ARRM)

As a part of the NASA initiative to collect a boulder off of an asteroid and return it to Lunar orbit, the Satellite Servicing Capabilities Office (SSCO) and NASA GSFC are developing an on-board relative terrain imaging navigation algorithm for the Asteroid Redirect Robotic Mission (ARRM). After performing several flybys and dry runs to verify and refine the shape, spin, and gravity models and obtain centimeter level imagery, the spacecraft will descend to the surface of the asteroid to capture a boulder and return it to Lunar Orbit. The algorithm implements Stereophotoclinometry methods to register landmarks with images taken onboard the spacecraft, and use these measurements to estimate the position and orientation of the spacecraft with respect to the asteroid. This paper will present an overview of the ARRM GN&C system and concept of operations as well as a description of the algorithm and its implementation. These techniques will be demonstrated for the descent to the surface of the proposed asteroid of interest, 2008 EV5, and preliminary results will be shown.

Navigation↗
NASA NTRS2016

The Laser Ranging Experiment of the Lunar Reconnaissance Orbiter: Five Years of Operations and Data Analysis

We describe the results of the Laser Ranging (LR) experiment carried out from June 2009 to September 2014 in order to make one-way time-of-flight measurements of laser pulses between Earth-based laser ranging stations and the Lunar Reconnaissance Orbiter (LRO) orbiting the Moon. Over 4,000 hours of successful LR data are obtained from 10 international ground stations. The 20-30 centimeter precision of the full-rate LR data is further improved to 5-10 centimeter after conversion into normal points. The main purpose of LR is to utilize the high accuracy normal point data to improve the quality of the LRO orbits, which are nomi- nally determined by the radiometric S-band tracking data. When independently used in the LRO precision orbit determination process with the high-resolution GRAIL (Gravity Recovery and Interior Laboratory) gravity model, LR data provide good orbit solutions, with an average difference of approximately 50 meters in total position, and approximately 20 centimeters in radial direction, compared to the definitive LRO trajectory. When used in combination with the S-band tracking data, LR data help to improve the orbit accuracy in the radial direction to approximately 15 centimeters. In order to obtain highly accurate LR range measurements for precise orbit determination results, it is critical to closely model the behavior of the clocks both at the ground stations and on the spacecraft. LR provides a unique data set to calibrate the spacecraft clock. The LRO spacecraft clock is characterized by the LR data to a timing knowledge of 0.015 milliseconds over the entire 5 years of LR operation. We here present both the engineering setup of the LR experiments and the detailed analysis results of the LR data.

Mao, Dandan↗
NASA NTRS1995

Spaceborne GPS for Earth Science

With the recent completion of the Global Positioning System (GPS) constellation and lower cost spaceborne receivers GPS usage is expanding rapidly in the area of space flight projects. Several of these are discussed, such as precise orbit determination, Earth gravity model improvement, and other global geodesy enhancements; high resolution 2D/3D ionospheric imaging; and atmospheric limb sounding.

Global↗
NASA NTRS2019

Efficient computation of optimal low thrust gravity perturbed orbit transfers

We have developed a new method for solving low-thrust fuel-optimal orbit transfer problems in the vicinity of a large body (planet or asteroid), considering a high-fidelity spherical harmonic gravity model. The algorithm is formulated via the indirect optimization method, leading to a two-point boundary value problem (TPBVP). We make use of a hyperbolic tangent smoothing law for performing continuation on the thrust magnitude to reduce the sharpness of the control switches in early iterations and thus promote convergence. The TPBVP is solved using the method of particular solutions (MPS) shooting method and Picard-Chebyshev numerical integration. Application of Picard-Chebyshev integration affords an avenue for increased efficiency that is not available with step-by-step integrators. We demonstrate that computing the particular solutions with only a low-fidelity force model greatly increases the efficiency of the algorithm while ultimately achieving near machine precision accuracy. A salient feature of the MPS is that it is parallelizable, and thus further speedups are available. It is also shown that, for near Earth orbits and over a small number of en-route revolutions around the Earth, only the zonal perturbation terms are required in the costate equations to obtain a solution that is accurate to machine precision and optimal to engineering precision. The proposed framework can be used for trajectory design around small asteroids and also for orbit debris rendezvous and removal tasks.

Junkins, John L.↗
NASA NTRSDate not supplied

Lunar Relay Onboard Navigation Performance and Effects on Lander Descent to Surface

A system of Lunar relay satellites has been proposed to address communication and navigation needs and ensure robustness for the variety of upcoming robotic and human exploration missions to the Moon. The relays are envisioned to estimate self position and time knowledge onboard, allowing the system to provide in-situ navigation services to missions in the Lunar and cis-Lunar environment. The quality and accuracy of those services are highly dependent on the navigation performance of the relay itself. To assess the Lunar relay navigation performance, a series of orbit determination (OD) Monte Carlo (MC) simulations are run using Lunar gravity modeling up to a degree and order of 250 and a variety of onboard clocks and measurement types including weak-signal GNSS, Ground Network (GN) pseudorange (PR) and Doppler, and optical navigation (OpNav) center-finding (CF). The estimated trajectories produced by these Lunar relay MC simulations, along with the associated errors, and transmitted navigation reference signal parameters, are used to evaluate the expected navigation performance of a user on a descent trajectory to the Lunar surface. The scenario features a lander system performing onboard navigation relying on one-way range and Doppler measurements from reference signals emitted by the Lunar relay. This paper can be used as a reference in determining the onboard clock and measurement types necessary to obtain acceptable navigation performance for the Lunar relay, and as a baseline for Lunar lander navigation performance using accurate measurements from a relay reference signal.

Jeffrey L. Small↗
NASA NTRSDate not supplied

Lunar Relay Onboard Navigation Performance and Effects on Lander Descent to Surface

A system of Lunar relay satellites has been proposed to address communication and navigation needs and ensure robustness for the variety of upcoming robotic and human exploration missions to the Moon. The relays are envisioned to estimate self-position and time knowledge onboard, allowing the system to provide in-situ navigation services to missions in the Lunar and cis-Lunar environment. The quality and accuracy of those services are highly dependent on the navigation performance of the relay itself. To assess the Lunar relay navigation performance, a series of orbit determination (OD) Monte Carlo (MC) simulations are run using Lunar gravity modeling up to a degree and order of 250 and a variety of onboard clocks and measurement types including weak-signal GNSS, Ground Network (GN) pseudorange (PR) and Doppler, and optical navigation (OpNav) center-finding (CF). The estimated trajectories produced by these Lunar relay MC simulations, along with the associated errors, and transmitted navigation reference signal parameters, are used to evaluate the expected navigation performance of a user on a descent trajectory to the Lunar surface. The scenario features a lander system performing onboard navigation relying on one-way range and Doppler measurements from reference signals emitted by the Lunar relay. This paper can be used as a reference in determining the onboard clock and measurement types necessary to obtain acceptable navigation performance for the Lunar relay, and as a baseline for Lunar lander navigation performance using accurate measurements from a relay reference signal.

Jeffrey L. Small↗
NASA NTRS2022

The International DORIS Service contribution to ITRF2020

For the realization of the 2020 International Terrestrial Reference Frame (ITRF2020), the International DORIS Service delivered to the International Earth Rotation and Reference Systems Service (IERS) a set of 1456 weekly solution files from 1993.0 to 2021.0 including station coordinates and Earth orientation parameters (EOPs). The data come from fourteen DORIS satellites: TOPEX/Poseidon, SPOT-2, SPOT-3, SPOT-4, SPOT-5, Envisat, Jason-1, Jason-2, Cryosat-2, Saral, HY-2A, Jason-3, Sentinel-3A and Sentinel-3B. In their processing, the four analysis centers which contributed to the DORIS combined solution used the latest time variable gravity models, the new mean pole and diurnal-subdiurnal tidal EOP models recommended by IERS. In addition, all the analysis centers included in their processing precise SPOT-5 solar panel angle values and quaternions for, at least, the Jason satellites. Furthermore, a new Alcatel phase center variation model was implemented for the ITRF2020 processing. The main objective of this study is to present the combination process and to analyze the impact of the new modeling on the performance of the new combined solution. Comparisons with the IDS contribution to ITRF2014 show that i) the application of the new phase center variations for the Alcatel DORIS ground antennas in the data processing combined with the gradual replacement over time of the Alcatel by Starec antennas implies a scale drift from 1993.0 to 2002.5 and ii) thanks to a better modeling of the surface forces on the satellites, the new combined solution shows smaller annual and 118-day signals in the geocenter. A new DORIS terrestrial reference frame was computed to evaluate the intrinsic quality of the new combined solution. That evaluation shows that over almost the full time span the intrinsic IDS scale values lie in a range of ±5 mm. After mid-2008, the new DORIS reference frame has an internal position consistency in North-East-Up better than 7.5 mm.

DORIS↗
NASA NTRSDate not supplied

Relative Motion for Short-Term Loitering in the Gateway NRHO

Numerous vehicles will visit Gateway throughout the expected mission lifetime, and much like Gateway, these vehicles will operate in a Near Rectilinear Halo Orbit (NRHO). Short-term loitering strategies are explored for these vehicles. The objective of this analysis is to illuminate concepts that enable safe loitering, while considering the operational limitations to the design process. To highlight relative motion, a linear sensitivity analysis is applied. The linear approach offers an initial guess strategy for generating loiter architectures in the high-fidelity gravity model. Methods of constructing transfers between loitering regimes are explored.

Stephen T Scheuerle↗
NASA NTRS1987

Geophysical parameters from the analysis of laser ranging to starlette

Starlette Satellite Laser Ranging (SLR) data were used, along with several other satellite data sets, for the solution of a preliminary gravity field model for TOPEX, PTGF1. A further improvement in the earth gravity model was accomplished using data collected by 12 satellites to solve another preliminary gravity model for TOPEX, designated PTGF2. The solution for the Earth Rotation Parameter (ERP) was derived from the analysis of SLR data to Starlette during the MERIT Campaign. Starlette orbits in 1976 and 1983 were analyzed for the mapping of the tidal response of the earth. Publications and conference presentations pertinent to research are listed.

Schutz, B. E.↗
NASA NTRS1984

Modeling of zero gravity venting

The venting of cylindrical containers partially filled with initially saturated liquids was conducted under zero gravity conditions and compared with an analytical model which determined the effect of interfacial mass transfer on the ullage pressure response during venting. A model is proposed to improve the estimation of the interfacial mass transfer. Duhammel's superposition integral is incorporated in this analysis to approximate the transient temperature response of the interface, treating the liquid as a semiinfinite solid with conduction heat transfer. This approach to estimating interfacial mass transfer gives improved response when compared to previous models. The model still predicts a pressure decrease greater than those in the experiments reported.

Merte, H., Jr.↗
NASA NTRS1986

Modeling of zero gravity venting: Studies of two-phase heat transfer under reduced gravity

The objective is to predict the pressure response of a saturated liquid-vapor system when undergoing a venting or depressurization process in zero gravity at low vent rates. An experimental investigation of the venting of cylindrical containers partially filled with initially saturated liquids was previously conducted under zero-gravity conditions and compared with an analytical model which incorporated the effect of interfacial mass transfer on the ullage pressure response during venting. A new model is presented to improve the estimation of the interfacial mass transfer. Duhammel's superposition integral is incorporated to approximate the transient temperature response of the interface, treating the liquid as a semi-infinite solid with conduction heat transfer. Account is also taken of the condensation taking place within the bulk of a saturated vapor as isentropic expansion takes place. Computational results are presented for the venting of R-11 from a given vessel and initial state for five different venting rates over a period of three seconds, and compared to prior NASA experiments. An improvement in the prediction of the final pressure takes place, but is still considerably below the measurements.

Merte, H., Jr.↗