James M. Longuski

• Purdue University West Lafayette

Ocean Worlds such as Europa and Enceladus are known to harbor subsurface liquid water oceans under their icy crust and are high-priority targets for in-situ exploration. Compared to the Moon and Mars, Ocean Worlds likely present a significantly more challenging environment for surface mobility systems due to the extremely cold temperature, high rad...

Mounting evidence of chemical disequilibria in the Venusian atmosphere has heightened interest in the search for life within the planet's cloud decks. Balloon systems are currently considered to be the superior class of aerial platform for extended atmospheric sampling within the clouds, providing the highest ratio of science return to risk. Balloo...

Venus is known for its extreme surface temperature and its sulfuric acid clouds. But the cloud layers on Venus have similar temperature and pressure conditions to those on the surface of Earth and are conjectured to be a possible habitat for microscopic life forms. We propose a mission concept to explore the clouds of Venus for up to 30 days to eva...

A quantitative and comparative assessment of the feasibility and mass benefit of using aerocapture at all atmosphere-bearing solar system destinations is presented, considering both lift and drag modulation control techniques. Aerocapture is shown to be feasible at Mars, Titan, and Venus with existing entry vehicles and flight-proven thermal protec...

Logistics supply chains with nodes at critical locations such as the Earth’s surface, Earth’s orbit, cis-lunar space, Mars orbit and the surface of Mars are crucial to enable sustainable human exploration of Mars. The concept of a Mars orbital logistics node is envisaged to have at least aggregation, refueling, resupply and refurbishing capabilitie...

A method for enabling large constellations of small satellites around Mars and Venus for planetary exploration.

A performance analysis for aerocapture at Uranus and Neptune is presented and considers entry corridor width, peak deceleration, peak heat rate, total heat load, and the effect of postcapture orbit on the design parameters. Aerocapture mass benefit vs chemical capture is also quantified. Design relationships are found that can be used in flight sys...

Large navigation and atmospheric uncertainties have historically driven the need for a mid-lift-to-drag L/D vehicle with L/D of 0.6--0.8 for aerocapture at Neptune. Most planetary entry vehicles flown to date are low-L/D blunt-body aeroshells with L/D less than 0.4. The lack of a heritage mid-L/D aeroshell presents a major hurdle for Neptune aeroca...

A low-thrust gravity-assist trajectory design tool is proposed that uses a recurrent neural network (RNN) to create a spacecraft steering strategy and is trained using an evolutionary algorithm. This strategy extends the concepts of genetic reinforcement learning and evolutionary neurocontrol, which both use a feedforward neural network (FNN). The...

Cycler trajectories have become an important component of Earth-to-Mars transportation systems. A salient feature of such trajectories is the necessity of achieving hyperbolic rendezvous, a requirement that if not met can result in loss of crew. The concept of hyperbolic rendezvous has been met with skepticism. In this paper, we review standard met...

An improved approximate analytical solution is developed for Yaroshevskii's classical planetary entry equation for the ballistic entry of a spacecraft into planetary atmospheres at circular speed. Poincaré's method of small parameters is used to solve for the altitude and flight path angle as a function of the spacecraft's speed. From this solution...

Artificial gravity has long been proposed to limit the harmful effects of the micro-gravity environment on human crews during mission to Mars. A tethered spacecraft spinning at 4 rpm (to avoid motion sickness) provides an attractive configuration. However, if the spacecraft is required to spin down for impulsive maneuvers and then spin up for inter...

Mars free-return trajectories are investigated both with and without the use of Venus for gravity assist. Launch dates are searched from 2015 to 2060, and focus is placed on identifying opportunities that have a short total time of flight (that is, that are fast among the available free-return opportunities) so that they may be used for a human mis...

Spacecraft employing low-thrust propulsion must be able to recover from an event in which the spacecraft stops thrusting due to an unforeseen problem. Extra propellant is carried to allow the spacecraft to reach its target in the form of propellant margin. An automated method is presented for estimating the propellant margin a spacecraft should car...

We investigate the use of nuclear-electric propulsion for human missions to Mars. Employing a patched-conic solution as our initial guess, low-thrust trajectories are designed via a continuation method. We determine the propulsion requirements for a reusable human transportation system, in which a single vehicle makes a round trip between the Earth...

Several cycler concepts have been proposed to provide safe and comfortable quarters for astronauts traveling between the Earth and Mars. However, no literature has appeared to show how these massive vehicles might be placed into their cycler trajectories. In this paper, trajectories are designed that use either leveraging or low thrust to establish...

Large-scale human exploration of Mars, and in situ exploration of Venus pose great challenges for entry, descent, and landing of spacecraft. The Adaptive Deployable Entry and Placement Technology (ADEPT), a mechanically deployable decelerator, presents an enabling alternative to the traditional rigid aeroshell technology. ADEPT helps in lowering th...

A low-thrust trajectory design study is performed for a mission to send humans to Ceres and back. The flight times are constrained to 270 days for each leg, and a grid search is performed over propulsion system power, ranging from 6 to 14 MW, and departure V∞V∞, ranging from 0 to 3 km/s. A propulsion system specific mass of 5 kg/kW is assumed. Each...

Experiments showing a variation of the nuclear decay rates of a number of different nuclei have suggested that the distance between the sample and the Sun is influencing the nuclear decay processes. In order to test this apparent correlation from Terrestrial experiments, a mission is proposed to take various isotopes on a spacecraft that has a larg...

While advantages of cycler trajectories are discussed by researchers in the literature, little attention has focused on the problem of placing cycler vehicles into well-known cycler trajectories. Previously, an analysis employing V∞ leveraging was addressed. The current paper completes the picture by considering the use of low thrust. The most sign...

Multiple-satellite-aided capture employing gravity assists of more than one Galilean moon can help capture a spacecraft into orbit about Jupiter. Each additional moon flyby reduces the propulsive ΔVΔV required for Jupiter capture. While the existence of these trajectories has been demonstrated deterministically, the challenges associated with actua...

Potential encore-mission scenarios have been considered for the Cassini mission. In this paper we discuss one of the end-of-life scenarios in which the Cassini spacecraft could perform a Saturn escape via gravity assists from Titan. It is shown that such satellite-aided escape requires a small deterministic maneuver (e.g., Δv<50 m/s), but provides...

We design a new version of a cycler orbit between Earth and Mars (known as the Aldrin cycler) in which we use low thrust to reduce the encounter velocities. We show that by reducing the encounter velocities at both planets, the propellant needed by the taxis to perform hyperbolic rendezvous can be significantly reduced. If the V-infinity reduction...

An innovative and game-changing Mars exploration mission architecture by synergizing the advantages of Inflatable Aerodynamic Decelerators, and a network of miniature space-based, aerial, surface, & subsurface exploration elements.

Experiments showing a seasonal variation of the nuclear decay rates of a number of different nuclei, and decay anomalies apparently related to solar flares and solar rotation, have suggested that the Sun may somehow be influencing nuclear decay processes. Recently, Cooper searched for such an effect in $^{238}$Pu nuclei contained in the radioisotop...

Cyclers are space trajectories that repeatedly encounter the same set of bodies indefinitely. Typically, cyclers are designed to encounter two bodies periodically, with only an occasional encounter with a third body. Because of the dynamics of the Laplace resonance in the Jupiter system, cycler trajectories that periodically return to three bodies...

We have analyzed Cs-137 decay data, obtained from a small sample onboard the MESSENGER spacecraft en route to Mercury, with the aim of setting limits on a possible correlation between nuclear decay rates and solar activity. Such a correlation has been suggested recently on the basis of data from Mn-54 decay during the solar flare of 13 December 200...

For a Europa Orbiter mission, the strategy for designing Jovian System tours that include Io flybys differs significantly from schemes developed for previous versions of the mission. Assuming that the closest approach distance of the incoming hyperbola at Jupiter is below the orbit of Io, then an Io gravity assist gives the greatest energy pump-dow...

A spacecraft capable of producing higher-than-natural electrostatic charges may achieve propellantless orbital maneuvering via the Lorentz-force interaction with a planetary magnetic field. Development of maneuver strategies for these propellantless vehicles is complicated by the fact that the perturbative Lorentz force acts along only a single lin...

Satellite-aided capture is a mission design concept used to reduce the delta-v required to capture into a planetary orbit. The technique employs close flybys of a massive moon to reduce the energy of the planet-centered orbit. A sequence of close flybys of two or more of the Galilean moons of Jupiter may further decrease the delta-v cost of Jupiter...

Spacecraft that intentionally maintain an electrostatic charge on their surface within a planetary magnetic field can manipulate the induced Lorentz force to perform propellantless maneuvers. Analytical expressions are developed that describe the process of capture with the Lorentz force and that demonstrate coupling among orbital elements (e.g., t...

A spacecraft that generates an electrostatic charge on its surface in a planetary magnetic field will be subject to a perturbative Lorentz force. Active modulation of the surface charge can take advantage of this electromagnetic perturbation to modify or to do work on the spacecraft’s orbit. Lagrange’s planetary equations are derived using the Lore...

An electrostatically charged spacecraft is subject to Lorentz force perturbations as it orbits a central body with a magnetic field. On an artificially charged spacecraft, these perturbations may be harnessed for orbital maneuvering and are particularly potent for plane-change maneuvers. The Gaussian form of the variational equations is used to dev...

Previous literature indicates that aerocapture with ballutes may provide significant mass advantages over traditional propulsive orbit capture. The possibility of using ballutes in the exploration of the atmosphere-bearing bodies in the solar system is considered, including Venus, Earth, Mars, Jupiter, Saturn. Titan, Uranus, and Neptune. The mass c...

Electrostatically charged spacecraft have been proposed for formation-flight applications in low-Earth orbit and geosynchronous Earth orbit. The inter-spacecraft Coulomb force acts internally on the formation and the induced geomagnetic Lorentz force provides an external perturbation on the satellites. The orbital altitude and local plasma conditio...

The Lorentz force may improve the effectiveness of gravity-assist flybys of celestial bodies with magnetic fields. Analytical theory is developed to assess the utility of the Lorentz force to increase both the turn angle and the orbital energy of a hyperbolic flyby without propellant cost. Lorentz-augmented gravity-assist mission applications are p...

Active modulation of the surface charge of a Lorentz spacecraft enables many capabilities - including inclination change, J2 mitigation, and planetary escape - without propellant cost. We develop Lagrange's planetary equations with the Lorentz force and use these analytical expressions to explore the dynamics. Behavior discovered empirically in ear...

Electrostatically charged spacecraft have been proposed for formation-flying applications in LEO and GEO. The inter-spacecraft Coulomb force acts internally to the formation, while the geomagnetic Lorentz force provides an external perturbation. A relative-motion dynamical model is developed that includes the effect of both Coulomb and Lorentz forc...

We compare a variety of mission scenarios to assess the strengths and weaknesses of options for Mars exploration. The mission design space is modeled along two dimensions: trajectory architectures and propulsion system technologies. We examine direct, semi-direct, stop-over, semi-cycler, and cycler architectures, and we include electric propulsion,...

An introduction to the dynamics of an electrostatically charged spacecraft in two- and three-body regimes is presented, with particular attention to a promising application at Enceladus. Equilibrium solutions to the equations of motion are found, and the stability of the orbits assessed. The perturbative Lorentz force, produced by interaction of th...

By escaping the Saturnian system, the Cassini spacecraft can reach other destinations in the solar system while satisfying planetary quarantine. The patched-conic method was used to search for trajectories that depart Saturn via gravity assist at Titan. Trajectories were found that fly by Jupiter to reach Uranus or Neptune, capture at Jupiter or Ne...

We consider the problem of a spacecraft subjected to constant body-fixed forces and moments about all three axes during a spinning-up, thrusting maneuver. In applications, undesired forces and moments can arise due to thruster imbalances and misalignments and to center-of-mass offset. In previous works, approximate analytical solutions have been fo...

Potential end-of-mission scenarios to be considered for the Cassini spacecraft must satisfy planetary quarantine requirements designed to prevent contamination of a pristine environment, which could include Titan and the other Saturnian moons. One assumed acceptable option for safe,disposal of the spacecraft includes Saturn impact trajectories. Two...

A study was conducted for limiting cases of the spinning spacecraft subject or thrusting rigid body to constant spin force by using theory of angular velocity, Eulerian angles, transverse, and axial displacements. The study used a axisymmetric spin-stabilized rigid body in an inertial frame subjected to a constant body-fixed forces and transverse m...

The problem of a spinning, axisymmetric, or nearly axisymmetric rigid body subject to constant body-fixed forces and moments about three axes is considered. Approximate closed-form analytical solutions are derived for velocity and for the transverse displacement. The analytical solutions are valid when the excursion of the spin axis with respect to...

An approximate analytical solution is, presented for the axial velocity of a spinning-up spacecraft subject to constant body-fixed forces and moments. We assume that the rigid body spins about the maximum or the minimum principal moment ofinertia. Also, it is assumed that the deviation of the spin axis from an inertially fixed direction is small. O...

A guidance algorithm was used to examine the space rendezvous process from a low-circular orbit departure, to final docking of a space vehicle taxi, with the cycler. The algorithm tracked the desired approach profile, allowing the taxi, to dock within 10 cm of the approach axis at a speed of 7 cm per second. It was observed that the docking procedu...

We present an architecture for the human exploration of Mars. This architecture is characterized by the use of parking orbits at Earth and gravity assists at Mars. An interplanetary transfer vehicle cycles from Earth orbit to Mars flyby and back, eliminating the need to launch transfer vehicles from the surfaces of Earth and Mars. Necessary develop...

Earth–Mars trajectories with low energy requirements that also limit the (transfer) time a crew spends in interplanetary space are essential to the design of cost-effective, minimal-risk missions. We compute optimal V trajectories with constraints on the transfer time of flight for launch years 2009 through 2022. We further explore the consequences...

We compute optimal low-thrust transfers (with constant thrust and constant specific impulse) between Earth and Mars over a range offlight times (from 120 to 270 days) and launch years (between 2009 and 2022). Unlike impulsive transfers, the mass-optimal trajectory depends strongly on the thrust and specific impulse of the propulsion system. A low-t...

We present cycler and semi-cycler trajectories to transport crews from Earth to a Mars base and back It is assumed that the Mars base should never be abandoned and that the cycler vehicles safely and comfortably transport twelve people at a time. Since these cycler vehicles involve a significant investment, as few as possible should be built. We ex...

A spinning, nearly-axisymmetric rigid body subject to constant body-fixed forces and moments about all three is considered. Because of constant axial torque along the spin axis, the spin rate increases linearly with time. By further assuming small deviation of spin axis (with respect to an inertially-fixed direction), an approximate closed-form ana...

We design low-thrust gravity-assist trajectories to Jupiter via gravity assists from Venus, Earth, and Mars. Trades between time of flight, mass, and hardware specifications are examined for various flyby bodies such as Mars, Earth, Venus-Earth, and Venus-Venus. We find (locally) propellant-optimal trajectories for ranges of specific impulse and sp...

In a dual-use ballute system, we use the ballute first, to aerocapture the orbiter, and second, to soft-land the payload. Using Vinh's analytic theory for aerocapture trajectories, we derive expressions for the maximum heating rates, maximum deceleration, and maximum dynamic pressure as functions of the ballistic coefficient and of the capture traj...

Low-thrust trajectories can be modeled as a series of impulsive (ΔV) maneuvers connected by conic arcs. We study new ways of parameterizing the ΔV vectors with a reduced number of variables and constraints. When optimizing low-thrust gravity-assist trajectories, the ΔV magnitudes can be parameterized with witch on/off times of the engine; the steer...

Earth-Mars cycler trajectories (cyclers) could play an important role in a future human transportation system to Mars. A particular cycler that repeats every two synodic periods and has one intermediate Earth encounter is very promising. In a circular-coplanar model it requires no propulsive maneuvers, has 153-day transfer times between Earth and M...

A spinning, nearly axisymmetric rigid body is subject to constant, body-fixed forces and transverse body-fixed torques. Because no torque is applied along the spin axis and the rigid body is nearly axisymmetric, the spin rate remains nearly constant. By further assuming small angular excursions of the spin axis (with respect to an inertially fixed...

Minimum-mass tether designs are developed for a spinning human transport that not only provides artificial gravity, but also the potential for free-return aborts. The investigation reveals that severing the tether can provide a propellant-free boost to return astronauts to Earth in the event of an aborted landing on Mars. Earth-Mars-Earth, Earth-Ma...

We construct a cycler (with acceptable transfer times and moderate encounter velocities) by patching a series of three-synodic-period semicycler trajectories together. The cycler employs high-efficiency low-thrust propulsion for trajectory maintenance and correction (thus making it a "powered" cycler). Even though the propellant usage is not insign...

Many Earth-Mars cycler trajectories are now known and their numbers continue to grow. Unfortunately, the literature on Earth-Mars cycler trajectories uses many different systems for naming the various cyclers being investigated. A nomenclature is proposed as a remedy to standardize the naming system for near-ballistic Earth-Mars cycler trajectories...

Mars human-mission scenarios can incorporate a parking orbit at either Earth or Mars. In many cases the parking orbit is not conveniently oriented with respect to the interplanetary leg (e.g., returning to Earth from a parking orbit at Mars). A method to reorient the spacecraft's orbit around a planet for a roundtrip mission is described. This meth...

The theory of general relativity can be tested by precisely measuring small changes in the trajectory of a spacecraft traveling near the sun. An important aspect of such a measurement is the potential of estimating the parameterized post-Newtonian parameters gamma and beta independently. We present a detailed covariance analysis of such a trajector...

An inflatable ballute system for aerocapture at the atmosphere-bearing planets and at Titan may provide significant performance benefits, compared to conventional propulsive capture and aerocapture technologies. Ballute simulations to date release the ballute at the appropriate instant and then ignore it to focus on the trajectory of the orbiter. T...

Human transportation systems between Earth and Mars might benefit greatly from the construction of a tether sling facility on Phobos. A tether sling has the potential to launch vehicles from Phobos to Earth with little or no propellant expended because it is solar powered. For current trajectory designs and tether materials, we show that a tether s...

The automation of a Mars aerobraking vehicle that uses reaction wheels for attitude and angular momentum control during atmospheric flythrough is investigated. In a previous study, single-axis control laws were developed for minimum onboard instrumentation to compensate for large variations in entry time and atmospheric density. Modifications of th...

Given the benefits of coupling low-thrust propulsion with gravity assists, techniques for easily identifying candi- date trajectories would be extremely useful to mission designers. The computational implementation of an analytic, shape-based method for the design of low-thrust, gravity-assist trajectories is described. Two-body motion (cen- tral b...

The Theory of General Relativity (GR) can be tested by precisely measuring the shift of a spacecraft trajectory due to GR as it flies near the Sun. We apply the PPN metric to define the governing equations of motion for the spacecraft, and carry out a covariance analysis to estimate the Eddington-Robertson-Schiff parameters, gamma and 0, by simulat...

Tracking a spacecraft near the Sun provides unique opportunities to estimate gravity param-eters and to test fundamental theories of physics. We develop a detailed covariance analysis of such trajectories, analyzing the uncertainty distribution of the first order Parameterized Post-Newtonian parameters (γ and β) and the solar quadrupole (J2) moment...

Low-thrust trajectories can be modeled by an evenly-spaced sequence of ∆V impulses connected by coasting arcs. Such a model transforms the trajectory optimization problem from an optimal control problem into a finite nonlinear programing problem. Analysis and experimental results are given to help decide which coordinate system to use for the ∆V ve...

Earth-Mars trajectories with low-energy requirements that also limit the (transfer) time a crew spends in interplanetary space are essential to the design of cost-effective, minimal-risk missions. We compute optimal ∆ ∆ ∆ ∆V trajectories with constraints on the transfer time of flight (TOF) for launch years 2009 through 2022. We further explore the...

Nuclear electric propulsion is expected to open new doors in deep space exploration. We study direct rendezvous missions to the outer planets which employ a constant-thrust, constant specific-impulse engine. We also consider how gravity assist can augment the capability of nuclear electric propulsion. We present numerical examples of gravity-assist...

Sun-orbiting spacecraft trajectories that repeatedly encounter Earth and Mars may play a central role in a future Earth-Mars transportation system. Such orbits are known as Earth-Mars cycler trajectories (cyclers). By using gravity-assist maneuvers at Earth or Mars, many cyclers can avoid using large amounts of propellant. The known cyclers were fo...

In a previous work, we proposed a new test of general relativity (GR) based on a general deflection formula which applies to all values of asymptotic speed V-infinity (0less than or equal toV(infinity)less than or equal to1). The formula simplifies to Einstein's light deflection result when V-infinity=1. At low velocity, the general deflection equa...

A Nuclear electric propulsion engine is being designed for the Jupiter Icy Moons Orbiter (JIMO) mission. In this paper, we consider other missions - to the outer planets - that could be achieved with this propulsion system. We incorporate gravity assists at Venus and Earth to deliver greater mass (to Jupiter, Saturn, Uranus, Neptune and Pluto) than...

The equations of motion for an aerobraking spacecraft are nondimensionalized. This process yields three dimensionless parameters that intrinsically describe the capability of a reaction-wheel controller to manage angular momentum during an atmospheric drag pass. These parameters, namely aeromoment, desaturation speed, and equilibrium momentum, comp...

Missions such as Mariner 10, Voyager 1, Galileo, and Stardust all used gravity-assist flybys to achieve their mission goals efficiently. Methods to design such gravity-assist missions are fairly well developed and generally assume all major maneuvers are performed impulsively by chemical rockets. The recent success of the low-thrust Deep Space 1 mi...

Conventional aerobraking requires propellant to dump the spacecraft's angular momentum and to maintain attitude control during the atmospheric flythrough. We consider how reaction wheels can be used to control the spacecraft's pitch during each atmospheric flythrough and to reduce angular momentum simultaneously. Control laws are developed for mini...

Trajectories that regularly encounter Earth and Mars but use small or no propulsive maneuvers are known as cycler trajectories, or cyclers. For cyclers that repeat after two Earth-Mars synodic periods, several variations are possible. A detailed investigation is presented of a simple two synodic period cycler, along with several promising variation...

We discuss preliminary results on constructing a powered cycler from semi-cycler trajectories. We present a powered cycler with reasonable transfer times and low encounter velocities. In addition, we develop a metric for evaluating cycler designs in comparison to other mission-to-Mars scenarios. The metric suggests that as vehicle mass (with respec...

Highly efficient low-thrust engines are providing new opportunities in mission design. Ap-plying gravity assists to low-thrust trajectories can shorten mission durations and reduce propellant costs from conventional methods. In this paper, an efficient approach is applied to the design and optimization of low-thrust gravity-assist trajectories to s...

We investigate the automation of a Mars aerobraking vehicle that uses reaction wheels for attitude and angular momentum control during atmospheric flythrough. In a previous study, single-axis control laws were developed for minimum onboard instrumentation to compensate for large variations in entry time and atmospheric density. In this paper we tes...

In this paper we seek a low-thrust version of a cycler orbit between Earth and Mars known as the Aldrin cycler. The principal goal is to design trajectories that have low flyby V at both planets while minimizing the total propellant cost. Our research is aided by several powerful software tools, including a recently developed low-thrust optimizer....

The safety of the crew is the top priority for human exploration of Mars. If an unexpected emergency occurs, a free-return trajectory can bring the spacecraft back to the Earth without a large trajectory correction maneuver. Such mission-abort scenarios are analyzed by searching for various Mars free-return trajectories, including gravity assist fr...

Aerogravity-assist trajectories are optimized in the sense of maximizing DeltaV obtained by the flyby, maximizing aphelion, minimizing perihelion, and minimizing the time of flight for a particular destination planet. A graphical method based on Tisserand's criterion is introduced to identify potential aerogravity-assist trajectories. To demonstrat...

A new analytical technique directly related to Tisserand's criterion that permits the quick identification of all viable ballistic gravity-assist sequences to a given destination is introduced. The method is best presented by a simple graphical technique. The graphical technique readily demonstrates that gravity assists via Venus, Earth, and Jupite...

We derive a simple formula which gives the general relativistic deflection of a spacecraft, idealized as a point mass, for all values of the asymptotic speed V(infinity) (0< or =V(infinity)< or =1). Using this formula we suggest a new test of general relativity (GR) which can be carried out during a proposed interstellar mission that involves a clo...

Gravity-assist trajectories have been a key to outer Solar System exploration. In particular, the gravity-assist tour of the Jovian satellites has contributed significantly to the success of the Galileo mission. A comparison of the Jovian system to the Uranian system reveals that the two possess similar satellite/planet mass ratios. Tisserand graph...

Aerogravity assist enhances the technique of gravity assist through the use of a lifting vehicle that flies through the atmosphere of the swingby planet. An algorithm is developed that automatically searches for such trajectories to destination planets including Pluto, Neptune, Saturn, Mars, and Venus. Trajectories for lift-to drag (L/D) ratios ran...

Gravity-assist trajectories to Jupiter, launching between 1999 and 2031, are identified using patched-conic techniques. The classical trajectories, such as the Venus-Earth-Earth gravity assist, and many less conventional paths, such as Venus-Mars-Venus-Earth, are examined. Flight times of up to about seven years are considered. The DeltaV-optimized...

We analyze the motion of a spinning asymmetric rigid body subject to constant torque along one of the principal axes. Periodic solutions for the angular velocity vector and the corresponding kinematic parameters are given in terms of Fourier series expansions. Three semi-analytic solution methods are presented: one-period integration, Newton's meth...

Because of the imperfection of spacecraft assembly, there always exist misalignment and offset torques during thrust maneuvers. In the case of an axially thrusting spin-stabilized spacecraft, these torques disturb the angular momentum vector in inertial space causing a velocity pointing error. Much insight can be gained by analytically solving the...

In this paper we investigate tours of the Jovian satellites Europa Ganymede, and Callisto for the Europa Orbiter Mission. The principal goal of the tour design is to lower arrival V_ for the final Europa encounter while meeting all of the design constraints. Key constraints arise from considering the total time of the tour and the radiation dosage...

Automated trajectory design software is used to thoroughly search the near-future trajectory space for missions with low launch energies to the outer planets using aerogravity assists at Venus and Mars and at Mars alone. Aerogravity assist is shown to reduce the required hyperbolic excess launch velocities and total flight times by more than half f...

We use Floquet theory to solve the problem of large angular excursions of the spin axis of a rigid body, A semi-analytic solution is presented for the attitude motion of a spinning nearly axisymmetric spacecraft subject to constant transverse torques. Based on the assumption that the spin rate remains nearly constant, we employ a Cayley-Klein repre...

A study is performed to find the minimum-order model that can achieve an accuracy of 1 km in the dynamic propagation of the Saturnian satellites over a period of four years. The need for such an investigation has risen out of recent advances in the accuracy of orbit determination techniques that are to be used in the Cassini mission. Effects such a...

In the aerobraking tether concept, a probe, connected to an orbiter by a long, thin tether, passes through the atmosphere of a target planet to provide a desired velocity change, while keeping the orbiter above the sensible atmosphere. In earlier work, simple analytic models have been developed which accurately describe the characteristics of the m...