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NASA NTRSDate not supplied

Strategic Implications of Phobos as a Staging Point for Mars Surface Missions

As human exploration endeavors begin to set sights beyond low Earth orbit to the surface of the Moon, exploration of the surface of Mars continues to serve asthe “drivingdestination” to help focus development and research efforts. One Mars exploration strategy often discussed is the notion of utilizing the moons of Mars, namely Phobos,as an exploration destination prior toMars surface missions. This strategy is sometimes advocated based on the premisethat staging missions from Mars’ moons as well as exploring the moons themselves would be less costly and risky. However,understanding potential advantages of Phobos staging and exploration must be done in the context of the overall end-to-end Mars surface exploration needs, goals, objectives, campaign approach, and systems required. This paper examines the strategic implications of utilizing the moonsof Mars as a potential location for explorationof Mars. Operational concepts utilizing both Phobos and Mars orbital strategies will be examined to understand the architectural impacts of this staging strategy. The strategic implications of each operational concept are assessed to determine the overall key challenges and strategic links to other explorationdestinations. Results from this analysis indicate that,if the objective is to conduct Mars surface missions, utilizing Phobos as an exploration destination adds little benefittoward the goal of exploration of Mars.

Human↗
NASA NTRS1976

Secular acceleration of Phobos and Q of Mars

Reductions of Mariner 9 TV data of Phobos and Deimos tend to corroborate the existence of a secular acceleration of Phobos commensurate with two recently reported values based on a reprocessing of earth-based data. These values of secular acceleration have been used together with Mariner 9 data on the physical size of Phobos and earth-based photoelectric observations which infer a carbonaceous composition for Phobos to place upper and lower bounds of 50 and 150, respectively, on the tidal dissipation function of Mars. The corresponding upper and lower bounds on the tidal lag angle are 0.19 and 0.57 deg.

Smith, J. C.↗
NASA NTRS1977

The mass of Phobos

Radio tracking data associated with the February 1977 encounters between the Martian satellite Phobos and the Viking Orbiter I spacecraft have been analyzed to determine the gravitational constant of Phobos. A linear error analysis was conducted to determine the selection of data and the parameter solution set which would yield the best estimate of the gravitational constant. This error analysis indicated that the optimal data set was a data arc beginning just prior to the closest encounter and spanning three consecutive spacecraft orbits; data near periapsis were deleted. The most feasible parameter solution set consisted of the Phobos gravitational constant and the spacecraft initial conditions. The result of the data analysis was an estimate of (7.3 plus or minus 0.7) x 10 to the -4th cu km/sq sec for the gravitational constant of Phobos.

Tolson, R. H.↗
NASA NTRS1978

Phobos transit of Mars as viewed by the Viking cameras

A Viking orbiting spacecraft successfully obtained pictures of the martian satellite Phobos with Mars in the background. This is the first time that a single picture was obtained from a spacecraft which contained both a planet and a moon and had significant surface detail visible on both. The region of Mars below Phobos included volcanoes in the Tharsis Montes region. These pictures showed Phobos to be smaller than previously thought. The image of Phobos can be used as a control point to determine the map coordinates of surface features on Mars.

Duxbury, T. C.↗
NASA NTRS1979

Marsshine on Phobos

The Viking Orbiters have obtained several images of Phobos at large phase angles in which the portion of the satellite not directly illuminated by the sun is faintly visible. A photometric analysis of one such image is presented to prove that the phenomenon is real and can be explained by Marsshine (i.e., the illumination of Phobos by sunlight reflected from Mars). Such images provide cross sections of Phobos and are useful in determining the true shape and size of the satellite. The cross section observed in Picture 111A03 agrees closely with that predicted by triaxial ellipsoid model of Phobos developed by Duxbury (1974).

Goguen, J.↗
NASA NTRS1979

A possible origin for the grooves of Phobos

A hypothesis that the age and distribution of grooves on the surface of Phobos may be explained by a hybrid origin due to varying tidal stresses induced after a large impact altered the satellite's rotation rate is presented. The theory that these grooves are surface manifestations of internal fractures induced by the decay of Phobos orbit is ruled out because this mechanism would require the grooves to be extremely young features, but their implied age is greater than 10 to the 9th power yr. The location and relationship of grooves to the largest crater, Stickney, indicate that they are related to the Stickney impact, but were formed shortly after that event with orientations determined by the shape of Phobos. If the impact destroyed the condition of synchronous rotation, the changing orientation of Phobos in the gravitational field of Mars would subject its interior to stresses, producing the systems of grooves.

Weidenschilling, S. J.↗
NASA NTRS1982

Tidal rigidity of Phobos

A novel scenario is proposed in which the orbital eccentricity of Phobos results from several gravitational resonance excitations within the past one billion years, assuming that tidal friction in Phobos has had only a small effect on its orbit. Both the primordial eccentricity and inclination may have been much smaller than presently observed. Constraints imposed on tidal friction in Phobos by the apparent age of its surface, which is greater than one billion years, in addition to those of the gravitational resonance excitation scenario, can be satisfied only if the product of the rigidity and the Q factor is greater than 10 to the 12th dynes/sq cm. In view of the fact that the Q factor is only about 100, so that the rigidity must be greater than 10 to the 10th dynes/sq cm, Phobos should have substantial internal strength.

Yoder, C. F.↗
NASA NTRS1986

The effect of Mars surface and Phobos propellant production on Earth launch mass

Fuel and oxidizer produced on the surface of Mars and on the Martian Moon Phobos can reduce the cumulative mass of fuel and oxidizer which must be launched to low Earth orbit for Mars exploration missions. A scenario in which ten conjunction class trajectory missions over a twenty year period land a surface base and propellant production facilities on the Martian surface and on Phobos was examined. Production of oxygen on Phobos provides the greatest benefit. If all the propellant for Mars operations and Earth return is produced at Phobos and on Mars, a 30% reduction in cumulative low Earth orbit mass can be achieved at the end of the 20 year period.

Gus R Babb↗
NASA NTRS1989

Loss of water from Phobos

A quantitative model of the migrational history of any free water in the martian satellite Phobos is presented. Results include predicted depths of retained ice and current water fluxes as a function of latitude, regolith porosity and effective pore size. It is found that, despite Phobos' small size, low albedo and proximity to the sun, ice may be present within the sounding depth of the GRUNT experiment on the Soviet Phobos Mission - at least at mid to high latitudes. Implications for other experiments on the Phobos mission are also discussed.

Fanale, Fraser P.↗
NASA NTRS1989

The gravitational field of Phobos

The external gravitational field produced by a rigid body of uniform density but irregular shape is formulated in terms of spherical harmonics. The formalism is applied to the Martian satellite Phobos. Based on a three-dimensional shape model of Phobos by Duxbury (1989), the gravitational coefficients up to degree and order 4 for a homogeneous Phobos are computed. In particular, J2 is found to be 0.105. The in-plane libration amplitude of a homogeneous Phobos is predicted to be 0.97 deg, within the rather large uncertainty of the observed value of 0.78 + or - 0.4 deg.

Chao, B. Fong↗
NASA NTRS1990

Phobos' gravity field and its influence on its orbit and physical librations

A model describing the physical libration in longitude and latitude for Phobos is derived. The major effect is the well-known longitude variation with the anomalistic orbital period and amplitude. Several additional meter-sized periodic librations in longitude exist. The latitude variation is dominated by the forced precession of Phobos' figure axis with the precession of Phobos' orbital plane. The contribution of Phobos' topography to its gravity field is estimated using the control network model of Duxbury and Callahan (1989).

Borderies, N.↗
NASA NTRS1991

Color heterogeneity of the surface of Phobos - Relationships to geologic features and comparison to meteorite analogs

Color ratio images created from multispectral observations of Phobos are analyzed in order to characterize the spectral properties of Phobos' surface, to assess their spatial distributions and relationships with geologic features, and to compare Phobos' surface materials with possible meteorite analogs. Data calibration and processing is briefly discussed, and the observed spectral properties of Phobos and their lateral variations are examined. Attention is then given to the color properties of different types of impact craters, the origin of lateral variations in surface color, the relation between the spatial distribution of color properties and independently identifiable geologic features, and the relevance of color variation spatial distribution to the origin of the grooves.

Murchie, Scott L.↗
NASA NTRS1993

The Stickney impact of Phobos - A dynamical model

The hypervelocity impact that excavated the Stickney crater on Phobos is numerically modeled in order to understand the effects this collision had on the interior and surface of Phobos. The model assumes homogeneity prior to impact based on Fujiwara's (1991) results. Constitutive relations for water ice and basalt are applied in tandem models. Fracture energetics is used to show that the impact itself is sufficient to cause the cracks observed on Phobos. It is further shown that the Stickney impact itself could not have created large voids; thus, the low density of Phobos must either be compositional in nature or else the result of porosity at a scale sufficiently small to avoid scattering the impact energy substantially.

Asphaug, E.↗
NASA NTRS1993

A simultaneous estimation of the mass of Mars and its natural satellites, Phobos and Deimos, from the orbital perturbations on the Mariner 9, Viking 1, and Viking 2 orbiters

The natural satellites of Mars, Phobos and Deimos, caused perturbations on the orbits of the Mariner 9, and the Viking spacecraft that were used to estimate the satellite masses. The Viking spacecraft were specifically targeted to make close flybys (within a few hundred kilometers) of Phobos in February 1977 and of Deimos in October 1977. These close encounters were used to estimate the moon's gravitational constant, GM (the universal constant of gravitation multiplied by the satellite mass). However, the Viking and Mariner 9 spacecraft made numerous flybys of Phobos and Deimos at distances of a few thousand kilometers. The tracking data from these more 'distant' encounters were processed to estimate the masses of Mars, Phobos, and Deimos.

Lemoine, F. G.↗
NASA NTRS1994

Radio-planetary from tie from Phobos-2 VLBI data

In an ongoing effort to improve the knowledge of the relative orientation (the 'frame tie') of the planetary ephemeris reference frame used in deep navigation and a second reference frame that is defined by the coordinates of a set of extragalactic radio sources, VLBI observations of the Soviet Phobos-2 spacecraft and nearby (in angle) radio sources were obtained at two epochs in 1989, shortly after the spacecraft entered orbit about Mars. The frame tie is an important systematic error source affecting both interplanetary navigation and the process of improving the theory of the Earth's orientation. The data from a single Phobos-2 VLBI session measure one component of the direction vector from Earth to Mars in the frame of the extragalactic radio sources (the 'radio frame'). The radio frame has been shown to be stable and internally consistent with an accuracy of 5 nrad. The planetary ephemeris reference frame has an internal consistency of approximately 15 nrad. The planetary and radio source reference frames were aligned prior to 1989 and measurements of occulations of the radio source 3C273 by the Moon. The Phobos-2 VLBI measurements provide improvement in the accuracy of two of the three angles describing a general rotation between the planetary and radio reference frames. A complete set of measurements is not available because data acquisition was terminated prematurely by loss of spacecraft. The analysis of the two Phobos-2 VLBI data sets indicates that, in the directions of the two rotation components determined by these data, the JPL planetary ephemeris DE200 is aligned with the radio frame as adopted by the International Earth Rotation Service within an accuracy of 20-40 nrad, depending on direction. The limiting errors in the solutions for these offsets are spacecraft trajectory (20 nrad), instrumental biases (19 nrad), and dependence of quasar coordinates on observing frequency (24 nrad).

Hildebrand, C. E.↗
NASA NTRS2014

Human Missions to Mars Orbit, Phobos, and Mars Surface Using 100-kWe-Class Solar Electric Propulsion

Solar electric propulsion (SEP) tugs in the 100-kWe range, may be utilized to preposition cargo in the Mars system to enable more affordable human missions to Phobos and to the surface of Mars. The SEP tug, a high heritage follow-on to the 50-kWe SEP spacecraft proposed for the Asteroid Redirect Robotic Mission (ARRM), would have the same structure, tankage, electric propulsion components, and avionics as the ARRM version, But with double the number of solar arrays, Hall thrusters, and power processor units (PPUs) and would be accommodated within the same launch envelope defined for ARRM. As a feasibility study, a 950-day human mission to Phobos using a conjunction class trajectory, such as the 2033 opportunity, was developed using two 100-kWe SEP vehicles to preposition a habitat at Phobos and propulsion stages in high Mars orbit (HMO). An architecture concept for a crewed Mars surface lander mission was also developed as a reference to build on the Phobos mission architecture, adding a lander element that could be delivered using chemical propulsion and aerocapture.

Price, Humphrey W.↗
NASA NTRS2016

Tidal Disruption of Phobos as the Cause of Surface Fractures

Phobos, the innermost satellite of Mars, displays an extensive system of grooves that are mostly symmetric about its sub-Mars point. Phobos is steadily spiraling inward due to the tides it raises on Mars lagging behind Phobos' orbital position and will suffer tidal disruption before colliding with Mars in a few tens of millions of years. We calculate the surface stress field of the deorbiting satellite and show that the first signs of tidal disruption are already present on its surface. Most of Phobos' prominent grooves have an excellent correlation with computed stress orientations. The model requires a weak interior that has very low rigidity on the tidal evolution time scale, overlain by an approximately 10-100 m exterior shell that has elastic properties similar to lunar regolith as described by Horvath et al. (1980).

Hurford, T. A.↗
NASA NTRS2020

Strategic Implications of Phobos as a Staging Point for Mars Surface Missions

As human exploration endeavors begin to set sights beyond low Earth orbit to the surface of the Moon, exploration of the surface of Mars continues to serve as the “horizon destination” to help focus development and research efforts. One Mars exploration strategy often discussed is the notion of utilizing the moons of Mars, namely Phobos, as an exploration destination prior to Mars surface missions. The premise behind this is that staging missions from Mars’ moons as well as exploring the moons themselves would be less costly and risky. However, understanding potential advantages of Phobos staging and exploration must be done in the context of the overall end-to-end Mars surface exploration needs, goals, objectives, campaign approach, and systems required. This paper examines the strategic implications of utilizing the moons of Mars as a potential location for exploration of Mars. Operational concepts utilizing both Phobos and Mars orbital strategies will be examined to understand the architectural impacts of this staging strategy. The strategic implications of each operational concept are assessed to determine the overall key challenges and strategic links to other exploration destinations. Results from this analysis indicate that, if the objective is to conduct Mars surface missions, utilizing Phobos as an exploration destination adds little benefit toward the goal of exploration of Mars.

Drake, Bret G.↗