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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 217 records · Page 12
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NASA NTRS1994

Navigation for Rendezvous and Orbit Missions to Small Solar-System Bodies

All previous spacecraft encounters with small solar-system bodies, such as asteroids and comets, have been flybys (e.g. Galileo's flybys of the asteroids Gaspra and Ida). Several future projects plan to build on the flyby experience and progress to the next level with rendezvous and orbit missions to small bodies. This presents several new issues and challenges for navigation which have never been considered before. This paper addresses these challenges by characterizing the different phases of a small body rendezvous and by describing the navigation requirements and goals of each phase. Prior to the encounter with the small body, improvements to its ephemeris and initial estimates of its physical parameters, e.g. size, shape, mass, rotation rate, rotation pole, and possibly outgassing, are made as accurately as ground-based measurements allow. This characterization can take place over years...

Helfrich, C. E.↗
NASA NTRS2011

Risk Balance: A Key Tool for Mission Operations Assurance

The Mission Operations Assurance (MOA) discipline actively participates as a project member to achieve their common objective of full mission success while also providing an independent risk assessment to the Project Manager and Office of Safety and Mission Success staff. The cornerstone element of MOA is the independent assessment of the risks the project faces in executing its mission. Especially as the project approaches critical mission events, it becomes imperative to clearly identify and assess the risks the project faces. Quite often there are competing options for the project to select from in deciding how to execute the event. An example includes choices between proven but aging hardware components and unused but unproven components. Timing of the event with respect to visual or telecommunications visibility can be a consideration in the case of Earth reentry or hazardous maneuver events. It is in such situations that MOA is called upon for a risk balance assessment or risk trade study to support their recommendation to the Project Manager for a specific option to select. In the following paragraphs we consider two such assessments, one for the Stardust capsule Earth return and the other for the choice of telecommunications system configuration for the EPOXI flyby of the comet Hartley 2. We discuss the development of the trade space for each project's scenario and characterize the risks of each possible option. The risk characterization we consider includes a determination of the severity or consequence of each risk if realized and the likelihood of its occurrence. We then examine the assessment process to arrive at a MOA recommendation. Finally we review each flight project's decision process and the outcome of their decisions.

operations↗
NASA NTRS1979

Solar electric propulsion system /SEPS/ program plans and system definition

The status of the NASA Solar Electric Propulsion System (SEPS) program is reviewed. The plans for SEPS definition and development include the initiation of the SEPS definition phase, the procurement for full-scale development in 1980, delivery of the SEPS for integration and tests with the comet rendezvous spacecraft in 1984, and a launch in 1985 that involves a flyby of Halley's comet in 1985 and a subsequent rendezvous with the comet Tempel 2 in 1988. In preparation for this, the acquisition process for SEPS has been initiated based on mission requirements rather than system requirements.

Austin, R. E.↗
NASA NTRS1976

Orbital error analysis for comet Encke, 1980

Before a particular comet is selected as a flyby target, the following criteria should be considered in determining its ephemeris uncertainty: (1) A target comet should have good observability during the apparition of the proposed intercept; and (2) A target comet should have a good observational history. Several well observed and consecutive apparitions allow an accurate determination of a comet's mean motion and nongravitational parameters. Using these criteria, along with statistical and empirical error analyses, it has been demonstrated that the 1980 apparition of comet Encke is an excellent opportunity for a cometary flyby space probe. For this particular apparition, a flyby to within 1,000 km of comet Encke seems possible without the use of sophisticated and expensive onboard navigation instrumentation.

Yeomans, D. K.↗
NASA NTRS1973

Mission design for a 1980 Encke slow flyby using solar electric propulsion

The comet Encke at its apparition in 1980 is investigated as the target for a solar electric slow flyby mission having a flight time of approximately two years. Mission trade off studies are performed for two modes: namely the direct earth to Encke mode and the Venus gravity assist mode. Baseline missions for each mode are selected which flyby Encke at 4 km/s 30 days before perihelion. The direct mission baseline is investigated in detail for trajectory parameters related to spacecraft and science requirements. The Venus flyby mode can deliver the same payload with a total power requirement about 20% less than the direct mode. The cost is a longer flight time and a Venus flyby at about 500 km above the surface. One asteroid can be encountered at very close range on either mission. The asteroids available and the extra propellant required are determined.

Bender, D. F.↗
NASA NTRS1982

Earth-return trajectory options for the 1985-86 Halley opportunity

A unique and useful family of ballistic trajectories to Halley's comet is described. The distinguishing feature of this family is that all of the trajectories return to the Earth's vicinity after the Halley intercept. It is shown that, in some cases, the original Earth-return path can be reshaped by Earth-swingby maneuvers to achieve additional small-body encounters. One mission profile includes flybys of the asteroid Geographos and comet Tempel-2 following the Halley intercept. Dual-flyby missions involving comets Encke and Borrelly and the asteroid Anteros are also discussed. Dust and gas samples are collected during the high-velocity (about 70 km/sec) flythrough of Halley, and then returned to a high-apogee Earth orbit. Aerobraking maneuvers are used to bring the sample-return spacecraft to a low-altitude circular orbit where it can be recovered by the Space Shuttle.

Farquhar, R. W.↗
NASA NTRS2005

Evidence for Liquid Water on Comets

We have reexamined the arguments for the existence of liquid water on comets, and believe that recent cometary flybys along with pre-Giotto data support its presence on short-period comets. Liquid water would affect cometary dynamics, leaving distinct signatures in precession, orbital dynamics, and potential splitting of comets. Liquid water geysers would affect cometary atmosphere, dust evolution, and non-gravitational forces that perturb the orbit. Liquid water would affect the composition of both the interior and exterior of the comet, producing geologic effects consistent with recent flyby photographs. And most importantly, liquid water suppork the growth of lifeforms, which would make a comet a biofriendly incubator for interplanetary transport. The major objection against liquid water is the necessity of a pressure vessel to prevent sublimation into space. We discuss how such a pressure vessel could naturally evolve as a pristine comet makes its first journey inside the orbit of Mars, and suggest that this type of vessel was observed by Giotto, Deep Space I, and Stardust.

Sheldon, Robert↗
NASA NTRS1979

Mission summary: Halley flyby/Tempel-2 rendezvous

A unique dual-comet flight opportunity exists in mid-1985 which includes flyby of the large and active comet Halley en route to rendezvous with second comet, Tempel-2. This mission will utilize ion propulsion at a modest performance level, based on proven technology. The Project is planned for FY81 start. Launch occurs in July 1985 via the Shuttle/IUS twin stage. Following IUS injection, the ion propulsion stage provides continuous thrust virtually throughout the 3-year flight until the Tempel-2 rendezvous in 1988. En route, a probe is deployed for encounter with Halley about 4 months after launch at a point 73 days before its perihelion. Rendezvous with Tempel-2 occurs about 60 days before the comet's perihelion during the summer of 1988 and continues for about 1 year. Earth will be in favorable relative positions for observing both the flyby and the rendezvous.

Atkins, K.↗
NASA NTRS2004

The STARDUST Discovery Mission: Data from the Encounter with Comet Wild 2 and the Expected Sample Return

On January 2,2004, the STARDUST spacecraft made the closest ever flyby (236 km) of the nucleus of a comet - Comet Wild 2. During the fly by the spacecraft collected samples of dust from the coma of the comet. These samples will be returned to Earth on January 15,2006. After a brief preliminary examination to establish the nature of the returned samples, they will be made available to the general scientific community for study. In addition to its aerogel dust collector, the STARDUST spacecraft was also equipped with instruments that made in situ measurements of the comet during the flyby. These included several dust impact monitors, a mass spectrometer, and a camera. The spacecraft's communication system was also used to place dynamical constraints on the mass of the nucleus and the number of impacts the spacecraft had with large particles. The data taken by these instruments indicate that the spacecraft successfully captured coma samples. These instruments, particularly the camera, also demonstrated that Wild 2 is unlike any other object in the Solar System previously visited by a spacecraft. During my talk I will discuss the scientific goals of the STARDUST mission and provide an overview of its design and flight to date. I will then end with a description of the exciting data returned by the spacecraft during the recent encounter with Wild 2 and discuss what these data tell us about the nature of comets. It will probably come as no surprise that the encounter data raise as many (or more) new questions as they answer old ones.

Sandford, Scott A.↗
NASA NTRS1975

Trajectory design of a solar electric propulsion Encke slow flyby mission

A slow flyby of the periodic comet, Encke, prior to its perihelion passage in 1980 has been shown to be a feasible mission for a solar electric propulsion spacecraft using a moderate power level of around 15 kw. The mission is accomplished in slightly less than two years with a planned miss distance and flyby speed of 1000 km and 4 km/s respectively. The results of a performance tradeoff study are presented together with a description of the nominal trajectory. The trajectories used in these mission studies were calculated using an updated model of the 30 cm mercury bombardment thruster's performance. The trajectory simulations include optimum staging of operating thrusters as a function of input power level constraints and limits on the variation of thruster specific impulse and efficiency as a function of thruster input power.

Sauer, C. G., Jr.↗
NASA NTRS2022

Interstellar Object Encounter Trade Space Exploration

2017 and 2019 saw the discovery of the first twointerstellar objects (ISO) in the solar system, 1I ‘Oumuamuaand 2I Borisov, but left scientists with more questions thananswers as to the objects’ origins. To fully resolve these openquestions, scientists need a closer look at an interstellar objectvia a dedicated spacecraft and close approach. However, ISOspose unique engineering challenges for close encounters becauseof their extremely high relative velocity, unfavorable approachgeometry, and limited alert time; ISOs often are only discovereda few months before a spacecraft would need to launch toencounter it.Typical encounters with small bodies have occurred at relativevelocities on the order of 10 km/s with approach phase below90 deg (at least half-lit). Except for the Halley Armada in the80s, the most extreme flybys have been of comet Borrelly ata relative velocity of 16.6 km/s (but only a phase angle of 65deg) and Annefrank at a phase angle of 150 deg (but a relativevelocity of only 7.2 km/s). Furthermore, planetary missionsgenerally target bodies whose ephemerides are well constrainedbecause of many years of Earth based observations. On theother hand, ISOs typically have relative velocities of 30-90 km/s,phase angles biased towards over 90 deg, and larger positionuncertainties because of shorter ground-based observationalarcs, and thus represent much more difficult targets.Our team has been developing the flight system architecturesand technologies necessary to enable future reconnaissance ofan interstellar object by flyby, potentially including an impactor.This endeavor seeks to catalyze planetary exploration and itsintersection with exo-planet science. We establish encounterguidance, navigation, and control requirements within the tradespace of trajectories to a synthetic ISO population. Flightsystem constraints, Earth departure capabilities, and ability fora mission team to quickly respond to an inbound target limitthe accessible space for a future mission. This trade spaceanalysis reveals enabling mission architectures, and providesrecommendations for supporting investment to enable an ISOmission in the next decade.

Farnocchia, Davide↗
NASA NTRS1989

Vega-Giotto flyby missions and cometary cosmogony

The most important implication of the Vega/Giotto flyby missions to Halley's Comet for cometary cosmogony is the opportunity to absorb the results of the in-situ measurements as made onboard the spacecrafts. Unfortunately the exploration of ejecta form the nucleus was unable to provide an unambiguous definition of the chemical-mineralogical nature of the nucleus: it failed to provide information comparable to that which was expected from a sample return mission. However, the obtained results are significant enough to affect and redirect cosmogonical thinking. Accordingly, the understanding of the cometary-matter dichotomy is modified as deduced from the distiction of water-dominated volitiles and silicate-based non-volitiles. Organic carbon compounds emerge as a major constituent of cometary nuclei. Presently, it is likely that the revision of Whipple's classic concept of the icy conglomerate cannot be avoided. Affected by the Vega/Giotto flyby missions to Hally's Comet, cometary cosmogony seems to enter a new conceptual period. The results of the in-situ measurements (mass spectrometric, UV spectroscopic, and IR spectroscopic) appear to be of basic importance. A chemical explanation is employed to explain the occurrence inside the nuclei of the variety of species, as inferred from the mass spectrometric data, to predict the results of the processes possibly involved. A cosmochemical factor is postulated to operate behind the observed cometary phenomena. The chemistry of the interstellar medium, covering the circumstellar and interstellar dust, advances cometary cosmogony.

Lang, Bruno↗
NASA NTRS1975

Limited variance control in statistical low thrust guidance analysis

Difficulties arise in guiding a solar electric propulsion spacecraft due to nongravitational accelerations caused by random fluctuations in the magnitude and direction of the thrust vector. These difficulties may be handled by using a low thrust guidance law based on the linear-quadratic-Gaussian problem of stochastic control theory with a minimum terminal miss performance criterion. Explicit constraints are imposed on the variances of the control parameters, and an algorithm based on the Hilbert space extension of a parameter optimization method is presented for calculation of gains in the guidance law. The terminal navigation of a 1980 flyby mission to the comet Encke is used as an example.

Jacobson, R. A.↗
NASA NTRS1975

On the calculation of low-thrust fail-safe trajectories

A guidance algorithm is developed for a low-thrust spacecraft such that target intercept is possible in spite of premature thrust termination along the trajectory. Such a trajectory is called a 'fail-safe' trajectory and the spacecraft thrust is utilized to minimize the relative target-spacecraft approach speed. The fail-safe guidance algorithm is solved using the concept of a critical thrust plane and a non-critical thrust direction. Several examples of fail-safe guidance are presented for a solar-electric propulsion flyby mission to the comet Encke.

Sauer, C. G., Jr.↗
NASA NTRS1978

Cometary exploration in the shuttle era

A comprehensive program plan for cometary exploration in the 1980-2000 time frame is proposed. Plans for ground-based observations, a Spacelab cometary observatory, and the Space Telescope are included in the observational program. The cometary mission sequence begins with a dual-spacecraft flyby of Halley's comet. The nominal mission strategy calls for a simultaneous launch of two spacecraft towards an intercept with Halley in March 1986. After the Halley encounter, the spacecraft are retargeted: one to intercept comet Borrelly in January 1988 and the other to intercept comet Tempel-2 in September 1988. The additional cometary intercepts are accomplished by utilizing a novel Earth-swingby technique. The next mission in the cometary program plan, a rendezvous with Encke's comet, is scheduled for launch in early 1990. It is planned to rendezvous with Encke in September 1992 at a heliocentric distance of 4 AU. Following this near-aphelion rendezvous, the spacecraft will remain with with Encke through the next two perihelion passages in February 1994 and May 1997. The rendezvous mission will be terminated about seven months after the second perihelion passage.

Farquhar, R. W.↗
NASA NTRS1984

The Mariner Mark II progream

The concept used in the design of the Mariner Mark II (MMII) spacecraft is consistent with the solar system exploration strategies which were developed by the Space Science Board of the National Academy of Sciences. The missions to comets, main belt asteroids, and outer planets are sufficiently similar to make possible a use of almost all of the design, hardware, and software in most engineering subsystems, without significant modification, for subsequent missions. Mariner Mark II missions are discussed, taking into account a comet rendezvous with asteroid flyby, the Saturn Flyby/Titan Probe, the Cassini or Saturn Orbiter/Titan Probe, the Main Belt Asteroid Rendezvous mission, the Uranus Flyby/Uranus Probe mission, and the Neptune Flyby/Neptune Probe mission.

Draper, R. F.↗
NASA NTRS1986

Future planetary exploration

The past, present, and future of planetary exploration are reviewed. A histogram of U.S. space launches between 1957 and 1983 shows that the peak activity came in 1966. Launchings of vehicles for planetary exploration also peaked in 1966, but the decreasing rate since that time has been partially offset by increased payload sophistication. Missions discussed include: the Galileo mission to Jupiter, several missions to Halley's comet, and missions to Venus. Missions in the early stages of planning include a Venus Radar Mapper, a Mars Geoscience/Climatology Orbiter, an ESA mission (Kepler) to orbit Mars, and a NASA Comet Rendezvous and Asteroid Flyby mission.

Kivelson, M. G.↗