The Russian International Phobos Sample Return Mission
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Phobos Gravity Mars↗
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The second-degree gravity coefficients of Phobos from two Mars Express flybys
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X Yang↗
Sensitivity studies of Mars orbiters for Mars gravity recovery
The purpose of the study is to assess the Mars orbiters with regard to their sensitivity to the Mars gravity field. The sensitivity is evaluated and quantified in terms of the magnitude and frequency of the orbiter position and velocity perturbations. The strengths and weaknesses of each orbiter, including Mariner 9, Viking 1 and 2, Mars Observer, Phobos, and Deimos, when used as a sensor of the Mars gravity field are assessed. It is shown that Mariner 9 and Viking data supply strong information on the low degree and order coefficients, with Mariner 9 contributing to the even-ordered terms out to about degrees 10 to 12. Phobos and Deimos are shown to be able to contribute to the lowest degrees of the gravity field, while the Mars Observer, in addition to the lower-degree and -order harmonics, will be responsive to coefficients as high as degree and order 50. Emphasis is placed on the spacecraft orbit plane orientation allowing the radial velocity perturbations to be measured by the Doppler data, thus enhancing the sensitivity to the gravitational signal.
Rosborough, George W.↗
Phobos Ephemeris Improvement from Recent Spacecraft Observations
Despite 127 years of observations, there is still room for improvement in the ephemeris of the Martian satellite Phobos. Early in this history, Earth-based astrometric observations of Phobos and Deimos were used to estimate the mass and oblateness of Mars. As more data accumulated, it became clear that a secular acceleration in the longitude of Phobos was occurring, and this was attributed to tidal dissipation within Mars, yielding rough estimates of the tidal quality factor, or Q. At the epoch of the earliest spacecraft observations of Phobos, from Mariner 9 and the Viking Orbiters and Landers, the gravitational field of Mars, and resulting forces on Phobos, were still not particularly well known. Thus observations of natural and artificial satellite motions continued to contribute, each in their own way, to knowledge of the mass distribution within Mars. Improvements in tracking system accuracy, and the placement of satellites, like the 1996 Mars Global Surveyor and 2001 Mars Odyssey, in circular polar orbits has lead to dramatic improvements to knowledge of the Mars gravity field. The direct gravitational influence on Phobos is no longer expected to be a limiting factor in predicting its orbital motion. Despite that progress, a variety of observations of Phobos from recent orbiters and landers suggest that the best satellite ephemeris still has along-track orbit errors which are accumulating at a rate of 1.75 kilometers per year, with Phobos gaining on the predicted positions. These recent observations alone do not span sufficient time to separately resolve the positional error into changes in mean motion and changes in secular acceleration. However, combining them with earlier observations will allow improvements in both the mean motion and its first derivative. This latter parameter is particularly interesting, as it relates to tidal dissipation, and thus uniquely constrains the internal structure of Mars. The current best estimate of the secular acceleration rate of Mars implies a surprisingly low value for the tidal dissipation factor Q = (94 plus or minus 1). For the Earth, most tidal dissipation occurs within the oceans. The terrestrial mantle tidal Q is 280. An issue of interest is then: why, where, and how does Mars dissipate tidal energy so effectively.
Bills, B. G.↗
Mars physical parameters as determined from Mariner 9 observations of the natural satellites and Doppler tracking
Mariner 9 Doppler tracking data and television photographs of Deimos and Phobos were analyzed to determine the gravity field, mass, and spin-axis direction of Mars and the natural satellite orbits. The solutions agree with previously published results. Radio data consisted of an apoapsis state vector for each of revolutions 5-195 obtained from one-revolution fits of Doppler data. Optical data consisted of TV photographs of Phobos and Deimos taken between revolutions 25 and 221. A first-order analytical theory, extended to include dominant second-order resonance effects on the Mariner 9 orbit, was used to calculate the motion of the spacecraft, Deimos, and Phobos. The feasibility of combining radio and optical data in long-arc solutions for accurate determination of orbits and physical parameters is demonstrated. The analytical theory developed for the evolution of a highly eccentric orbit in shallow resonance is accurate to plus or minus 1 km in the apoapsis state vector of Mariner 9 over a period of 200 revolutions.
Born, G. H.↗
Modeling issues in precision orbit determination for Mars orbiter
This paper examines the accuracy of recent Mars gravity models and the importance of perturbations due to the Mars radiation pressure and the Martian moons, Phobos and Deimos, on the trajectories of Mars orbiters. A linear orbit perturbation theory is used to characterize the patterns of gravity field near resonances for the Viking and Mariner 9 spacecraft. These resonances are shown to have considerable power and their potential for contributing to Mars gravity solutions is emphasized. It is shown that some of the same resonance orders which appear in the Viking orbits, dominate the radial orbit error spectrum for Mars Observer. Results of orbit determination simulations at the Goddard Space Flight Center show that the perturbations caused by the Martian moons and the Mars radiation pressure are larger than 0.1 mm/s, the expected precision of the Mars Observer Doppler tracking data. Tests with the Viking Doppler data indicate that best analysis of these data mandates the inclusion of the Phobos gravitational perturbation in the modeling of Viking spacecraft trajectories.
Lemoine, Frank G.↗
Phobos Mobility Simulation
Phobos, the larger of Mars' moons, provides a potential staging location for human exploration of the Martian surface. Its low gravity (about 1/200th of Earth) and lack of atmosphere makes it an attractive destination before a more complex human landing on Mars is attempted. While easier to approach and depart than Mars itself, Phobos provides unique challenges to visiting crews. It is irregularly shaped, so its local gravitational field does not always point straight down with respect to the visible horizon. It is very close to Mars and tidally locked, so the Martian gravity gradient and applied acceleration greatly affect the perceived surface gravity direction and magnitude. This simulation allows the assessment of unique mobility approaches on the surface of Phobos, including hopping in particular.
Bielski, Paul↗
The JPL Mars gravity field, Mars50c, based upon Viking and Mariner 9 Doppler tracking data
This report summarizes the current JPL efforts of generating a Mars gravity field from Viking 1 and 2 and Mariner 9 Doppler tracking data. The Mars 50c solution is a complete gravity field to degree and order 50 with solutions as well for the gravitational mass of Mars, Phobos, and Deimos. The constants and models used to obtain the solution are given and the method for determining the gravity field is presented. The gravity field is compared to the best current gravity GMM1 of Goddard Space Flight Center.
Konopliv, Alexander S.↗
Phobos: Low Velocity Impacts
Mars’s inner moon, Phobos, is located deep in the planet’s gravity well and orbits far below the planet’s synchronous orbit. Images of the surface of Phobos, in particular from Viking Orbiter 1, MGS, MRO, and MEX, reveal a rich collisional history, including fresh‐looking impact craters and subdued older ones, very large impact structures (compared to the size of Phobos), such as Stickney, and much smaller ones. Sources of impactors colliding with Phobos include a priori: A) Impactors from outside the martian system (asteroids, comets, and fragments thereof); B) Impactors from Mars itself (ejecta from large impacts on Mars); and C) Impactors from Mars orbit, including impact ejecta launched from Deimos and ejecta launched from, and reintercepted by, Phobos. In addition to individual craters on Phobos, the networks of grooves on this moon have also been attributed in part or in whole to impactors from some of these sources, particularly B. We report the preliminary results of a systematic survey of the distribution, morphology, albedo, and color characteristics of fresh impact craters and associated ejecta deposits on Phobos. Considering that the different potential impactor sources listed above are expected to display distinct dominant compositions and different characteristic impact velocity regimes, we identify specific craters on Phobos that are more likely the result of low velocity impacts by impactors derived from Mars orbit than from any alternative sources. Our finding supports the hypothesis that the spectrally “Redder Unit” on Phobos may be a superficial veneer of accreted ejecta from Deimos, and that Phobos’s bulk might be distinct in composition from Deimos.
Low velocity impact↗
Refueling with In-Situ Produced Propellants
In-situ produced propellants have been identified in many architecture studies as key to implementing feasible chemical propulsion missions to destinations beyond lunar orbit. Some of the more noteworthy ones include: launching from Mars to return to Earth (either direct from the surface, or via an orbital rendezvous); using the Earth-Moon Lagrange point as a place to refuel Mars transfer stages with Lunar surface produced propellants; and using Mars Moon Phobos as a place to produce propellants for descent and ascent stages bound for the Mars surface. However successful implementation of these strategies require an ability to successfully transfer propellants from the in-situ production equipment into the propellant tankage of the rocket stage used to move to the desired location. In many circumstances the most desirable location for this transfer to occur is in the low-gravity environment of space. In support of low earth orbit propellant depot concepts, extensive studies have been conducted on transferring propellants in-space. Most of these propellant transfer techniques will be applicable to low gravity operations in other locations. Even ground-based transfer operations on the Moon, Mars, and especially Phobos could benefit from the propellant conserving techniques used for depot refueling. This paper will review the literature of in-situ propellants and refueling to: assess the performance benefits of the use in-situ propellants for mission concepts; review the parallels with propellant depot efforts; assess the progress of the techniques required; and provide recommendations for future research.
In-Situ Propellants↗
Satellite orbit determination
The determination of the Mars-centered ephemerides of the Viking Orbiters and positions of the Landers from two way Doppler and range data is described. An overview of mission satellite orbit determination functions and methods is given. Topics covered include: postmaneuver orbit convergence, local orbit knowledge accuracies, the effects of interplanetary media, use of constrained solutions, and solving through trim burns. Procedure and results relevant to the determination of the planet gravity field are included. Results relative to sensing Mars' gravity field during the extended mission are presented along with a discussion of the Phobos Flyby Experiment conducted during February 1977.
Hildebrand, C. E.↗
Exploration EVA System Concept of Operations
The Exploration Extravehicular Activity (xEVA) System concept of operations (con ops) captures the National Aeronautics and Space Administration’s (NASA’s) current aims future missions to all potential Exploration destinations. This document captures the mission architectures, stakeholder expectations, and high level definitions of the capabilities and interfaces associated with the xEVA System. This includes missions to Gateway in cislunar space, the lunar surface, a redirected asteroid in cislunar space, Near Earth Asteroids (NEA), Mars’ orbit, the moons of Mars (Phobos and Deimos), and the surface of Mars. These missions, which include microgravity, milli-gravity, and partial-gravity surface EVAs, will involve a variety of engineering (maintenance, contingency, pioneering, construction) and science tasks. This document also captures information concerning vehicles and habitats with which the xEVA System will interface. The concepts of operations (con ops) detailed in this document are informed by the Artemis Program and a multitude of Exploration studies, and are also influenced by various integrated operational analog testing.
David Coan↗
Mars physical parameters as determined from Mariner 9 observations of the natural satellites
Derivation of values for the Mars gravity field, as well as the mass and spin axis direction, by processing combined radio and optical data taken with the Mariner 9 spacecraft. The optical data consists of 62 TV photographs of Phobos and Deimos taken during the Mars orbiting phase of Mariner 9. The radio data consists of apoapsis state vectors obtained from 195 one-revolution fits of the Doppler data. A first-order analytic theory is used to model both the satellites and the spacecraft's motion. However, the shallow resonance condition of Mariner 9's orbit necessitated development of a partial second-order theory to model the long-period perturbations which derive from Mars even-order tesseral harmonics. Use of an analytic theory allows rapid and inexpensive processing of both data types simultaneously. The results are in good agreement with those previously published from Mariner 9 Doppler and landmark data.
Born, G. H.↗
Alternative Strategies for Exploring Mars and the Moons of Mars
The possible human exploration of Mars represents one of civilization s next major challenges and is an enterprise that would confirm the potential of humans to leave our home planet system and make our way outward into the cosmos. As exploration endeavors begin to set sights beyond low Earth orbit, potential exploration of the surface of Mars continues to serve as the horizon destination to help focus technology development and research efforts. Recent thoughts on exploration follow a flexible path approach beginning with missions that do not extend down into planetary gravity wells including surface exploration. Consistent with that flexible path strategy is the notion of exploring the moons of Mars, namely Phobos and Deimos, prior to exploring the surface. The premise behind this thought is that exploring Mars moons would be less costly and risky since these missions would avoid the difficulties associated with landing on the surface and subsequent ascent back to orbit. A complete assessment of this strategy has not been performed in the context of the flexible path approach and is needed to clearly understand all of the advantages and disadvantages. This paper examines the strategic implications of possible human exploration of the moons of Mars as a potential prelude to surface exploration. Various operational concepts for Phobos and Deimos exploration that include the infusion of different propulsion technologies are assessed in terms of mission duration, technologies required, overall risk and difficulty, and operational construct. Finally, the strategic implications of each concept are assessed to determine the overall key challenges and strategic links to other key flexible path destinations.
Drake, Bret G.↗
Alternative Strategies for Exploring Mars and the Moons of Mars
The human exploration of Mars represents one of civilizations next major challenges and is an enterprise that would confirm the potential of humans to leave our home planet system and make our way outward into the cosmos. As exploration endeavors begin to set sights beyond low-Earth orbit, exploration of the surface of Mars continues to serve as the horizon destination to help focus technology development and research efforts. Recent thoughts on exploration follow a flexible path approach beginning with missions which do not extend down into planetary gravity wells including surface exploration. Consistent with that flexible path strategy is the notion of exploring the moons of Mars, namely Phobos and Deimos, prior to exploring the surface. The premise behind this thought is that exploring Mars moons would be less costly and risky since these missions would avoid the difficulties associated with landing on the surface and subsequent ascent back to orbit. A complete assessment of this strategy has not been performed in the context of the flexible path approach and is needed to clearly understand all of the advantages and disadvantages. This paper examines the strategic implications of human exploration of the moons of Mars as a potential prelude to surface exploration. Various operational concepts for Phobos and Deimos exploration that include the infusion of different propulsion technologies are assessed in terms of mission duration, technologies required, overall risk and difficulty, and operational construct. Finally, the strategic implications of each concept are assessed to determine the overall key challenges and strategic links to other key flexible path destinations.
Drake, Bret G.↗
The mass of Mars, Phobos, and Deimos, from the analysis of the Mariner 9 and Viking Orbiter tracking data
We have estimated the mass of Phobos, Deimos, and Mars using the Viking Orbiter and Mariner 9 tracking data. We divided the data into 282 arcs and sorted the data by periapse height, by inclination, and by satellite. The data were processed with the GEODYN/SOLVE orbit determination programs, which have previously been used to analyze planetary tracking data. The a priori Mars gravity field applied in this study was the 50th degree and order GMM-1 (Goddard Mars Model-1) model. The subsets of data were carefully edited to remove any arcs with close encounters of less than 500 km with either Phobos or Deimos. Whereas previous investigators have used close flybys (less than 500 km) to estimate the satellite masses, we have attempted to estimate the masses of Phobos and Deimos from multiday arcs which only included more distant encounters. The subsets of data were further edited to eliminate spurious data near solar conjunction (Nov.-Dec. 1976 and January 1979). In addition, the Viking-1 data from Oct. through Dec. 1978 were also excluded because of the low periapse altitude (as low as 232 km) and thus high sensitivity to atmospheric drag.
Smith, D. E.↗
Mariner 9 - An instrument of dynamical science
We review and evaluate the contributions of Mariner 9 in improving our knowledge of the dynamical characteristics of Mars and its two satellites, Phobos and Deimos. Primary results include the discovery of the large gravitational and topographical bulge in the Tharsis region, the development of a detailed gravity model representable as coefficients in a spherical harmonic expansion, the development of a topographic model exhibiting a three kilometer displacement of the center of figure from the center of mass, and the determination of the size, shape and motion of Phobos and Deimos.
Jordan, J. F.↗
The dynamics of submicron-sized dust particles lost from Phobos
The dynamics of submicron-sized dielectric particles lost from the Martian moon Phobos are studied in connection with the possible detection of dust by the Phobos 2 spacecraft. The motion of these small dust grains is influenced not only by gravity but also by solar radiation pressure and electromagnetic forces. The plasma environment of Mars is described by applying a hybrid gasdynamic-cometary model. Some of the submicron-sized grains ejected at speeds on the order of a few tens meters per second can stay in orbit around Mars for several months forming a nonuniform and time-dependent dust halo.
Horanyi, M.↗