Mason A. Peck

Historical Review of Air-Bearing Spacecraft Simulators

An overview of air-bearing spacecraft simulators is provided. Air bearings have been used for satellite attitude determination and control hardware verie cation and software development for nearly 45 years. It is interesting to consider the history of this technology: how early systems were e rst devised and what diverse capabilities current systems provide. First a survey is given of planar systems that give a payload freedom to translate and spin. Then several classes of rotational air bearings are discussed: those which simulate three-axis satellite attitude dynamics. The subsequent section discusses perhaps the most interesting facilities: those that provide both translational and three-dimensional rotational freedom. Thediverse capabilities each styleofair-bearing testbed provides, themany settings they can be found in, and ways to improve facility performance are described.

New synchronous orbits using the geomagnetic lorentz force

The Lorentz-augmented orbits concept provides propellantless electromagnetic propulsion without a tether, using the interaction between an electrostatically charged satellite and the Earths magnetic field to provide a useful thrust. New types of Earth-synchronous orbits are found from equations governing the motion of satellites experiencing the Lorentz force in orbit. The equations of motion for such a spacecraft are derived based on a simplified magnetic field model, in which the dipole is aligned with true north. For a polar-orbiting satellite, a constant electrical charge can create arbitrary changes in the right-ascension angle. This method allows for single-orbit repeat-groundtrack low-Earth-orbit satellites. Analytical expressions for changes in orbital elements due to Lorentz forces are verified by numerical simulation for the polar and equatorial cases. In the equatorial case, manipulation of the longitude of perigee by constant electrostatic charge is possible. Perigee movement also allows for the creation of an Earth-synchronous type of orbit. The case of a dipole field, for which the north pole is not aligned with true north, is also examined. Feedback control using only the Lorentz force for actuation is shown to stabilize this general case.

Prospects and Challenges for Lorentz-Augmented Orbits

*A charged particle moving relative to a magnetic field accelerates in a direction perpendicular to its velocity and the magnetic field due to the Lorentz force. Although a negligible force for spacecraft potentials due to natural charging, this effect can be seen, for example, in the unusual celestial mechanics of dust particles in the rings of Saturn and Jupiter. This study evaluates the use of the Lorentz force as a means of orbit control for finite bodies, including small spacecraft. Although the Hamiltonian is constant in a frame that rotates with the earth, the co-rotational electrical field (associated with the rotating geomagnetic field) can do work, increasing or decreasing the orbit’s semimajor axis. A number of intriguing applications are offered, including earth escape, drag compensation, new stable satellite formations, inclination control, nodal precession control, new sunsynchronous orbits, and non-Keplerian orbits for polar satellites. A candidate spacecraft design is offered based on lessons learned from decades of research in spacecraft charging and plasma interactions. The performance of this design is demonstrated by simulation. Closed-form equations for actuator sizing are provided.

Length Scaling in Spacecraft Dynamics

Length-scaling represents a new degree offreedom for spacecraft mission design. This paper presents a method for comparing the length scales of arbitrary spacecraft and uses this approach to evaluate the relevance of 12 environmental forces and torques. Three sample spacecraft geometries are considered: a sphere, a cube, and a thin square plate, at three near-Earth altitudes: 500, 1000, and 10,000 km. This analysis offers a guide for orbit and attitude simulations of small bodies, by suggesting which effects can and cannot be neglected for a given environment and error tolerance. This approach to length scaling may enable extremely small spacecraft to exploit unfamiliar dynamic behaviors that result in solar sail maneuvers, atmospheric reentry, and Lorentz propulsion.

Reducing Base Reactions With Gyroscopic Actuation of Space-Robotic Systems

In this paper, control-moment gyroscopes (CMGs) are proposed as actuators for a spacecraft-mounted robotic arm to reduce reaction forces and torques on the spacecraft base. With the established kinematics and dynamics for a CMG robotic system, numerical simulations are performed for a general CMG system with an added payload. The analysis of an added payloads effects on otherwise reactionless CMG systems motivates the examination of possible operations concepts to reduce base reactions and power consumption. Simulation results for an example closed-loop maneuver show that base reactions can be significantly reduced, or even eliminated, with CMG actuation while using the same amount of power as a robotic system driven by conventional joint motors.

Flux-Pinned Interfaces for the Assembly, Manipulation, and Reconfiguration of Modular Space Systems

Non-contacting interactions between permanent magnets and superconductors known as “flux pinning” provide a novel way to fix many modular space systems in desired relative positions and orientations, from space stations to close-proximity formations. When cooled appropriately, these flux-pinned interfaces require no power or active control and very little mass but provide very high mechanical stiffness (>200 N/m for a few hundred grams of material) and damping (2% of critical) between modules, making the technology ideal for in-orbit assembly applications. We describe new measurements and simulations to characterize these values for spacecraft applications. Flux-pinned interfaces have so far achieved inter-module separations in the 8–10 cm range with ∼100 g of mass on each module, with the prospect of larger separations. We also discuss several means to actuate the noncontacting couplers, which is a first step toward the development of devices for the noncontacting manipulation and reconfiguration of modular space systems.

Gravity-Assist Maneuvers Augmented by the Lorentz Force

of Lorentz Augmented Orbits (LAOs) on gravity-assist maneuvers are examined. In this study, we consider a spacecraft carrying a net electrostatic charge that performs a hyperbolic flyby of a planet with a non-negligible magnetosphere. It the charge on the satellite is modulated, the usefulness and eectiveness of the flyby can be extended in several ways with no expenditure of propellant. Both analytical and simulation results are presented for satellites in equatorial orbits within dipole magnetic fields. The spacecraft’s exit asymptote from the flyby target’s sphere of influence can be changed to an arbitrary direction. The spacecraft can also be captured at the target planet, or the assist maneuver can be timed with more flexibility than a gravity-only flyby.

Energetics of Control Moment Gyroscopes as Joint Actuators

acts only along the joint axis, eliminating undesirable gyroscopic reaction torques. Both analysis and simulation of a single-link robotdemonstrate thatthecontrol momentgyroscopepower isequal totheequivalentjointmotorpower for a large range of gimbal inertias and maximum gimbal angles. The transverse rate of the link does not affect this result.Atwo-link robot withorthogonal joint axes givesresultssimilar tothe single-link systemunless momentumis not conserved about the joint. For a two-link robot with parallel joint axes, control moment gyroscopes outperform joint motors in power required when the joints rotate with opposite sign; the reverse is true when the joints act in unison. These surprising differences arise because control moment gyroscopes produce body torques with a zerotorque boundary condition at the joint, whereas joint motors produce torques that are reacted onto two adjacent links. The analysis concludes with pros and cons of control moment gyroscopes as robotic joint actuators.

Lorentz-Augmented Jovian Orbit Insertion

The Lorentz force acting on a statically charged body moving with respect to a rotating magnetic field is evaluated as a means of capture into a Jovian orbit. This study offers insight into the classes of captures available as a function of the spacecrafts charge-to-mass ratio and approach conditions. A range of these parameters is simulated using low-order magnetosphere and gravity models and a bang-off controller. The results suggest that charge-to-mass ratios on the order of 0.1 C/kg are required to capture a spacecraft with a hyperbolic equatorial approach to an orbit similar to that of Jupiters moon Europa. The Lorentz-augmented-orbit architecture is related to a similar technology: electrodynamic tethers. Using a high-order magnetic field and gravity model, we recreate a sample electrodynamic-tether Jovian capture mission using Lorentz-augmented orbits with a charge-to-mass ratio of 0.0975 C/kg over 2.5 years. We conclude that Lorentz-augmented-orbit maneuvers are capable of reducing a spacecrafts energy and eccentricity into a bounded circular Jovian orbit for typical mission requirements. A simple feasibility study suggests that Lorentz-augmented-orbit spacecraft designs capable of Jovian orbit insertion are challenging, but likely possible.

Scissored-Pair Control-Moment Gyros : A Mechanical Constraint Saves Power

Constraint Saves Power Daniel Brown and Mason A. Peck 2 Cornell University, Ithaca, New York, 14853 Introduction CISSORED-pair control-moment gyros have been around for over a century. Brennan’s monorail used two counter-rotating flywheels with gearing between the ir gimbals to provide symmetric stabilization aroun d left or right turns [1, 2]. Also referred to as twin gyros, sciss ored pairs maintain equal-magnitude and opposite-si gn gimbal angles for two control-moment gyros (CMGs) with par allel gimbal axes [3, 4]. A scissored pair, like an y array of CMGs, provides attitude-control torque via momentum exchange with the body on which it is mounted. The Skylabera Astronaut Maneuvering Research Vehicle used sci ssored pairs for attitude control [5, 6]. These dev ic s have also been studied as gyrodampers of large space structur es [7, 8]. A robot with single revolute joints requ ires output torque along a single axis. The enforced symmetry o f a scissored pair provides such a torque without i ntroducing large reaction torques in the robot. Such a system could be used to rapidly maneuver a payload with le ss power than rapidly maneuvering the entire spacecraft [9]. We consider a scissored pair that uses a mechanical constraint, such as gears or a mechanical linkage, to nforce the gimbal symmetry. We compare it to a scissored p air of independent CMGs. Each CMG in a scissored pa ir of independently driven CMGs has its own gimbal motor, which needlessly uses power to react what should b e a workless constraint torque. As explained in this no te, the gear cancels certain torques that would oth erwise act on the independent CMGs. The gear also replaces the tw o independent gimbal motors with a single motor, wh ich may represent improved mass and volume efficiency in th e electromechanical design. An early double-gimbal CMG concept with mechanical synchronization is describe d y Liska [10]. This note discusses the reduction in power use and the effect on motor size that a geared scissore d pair provides as compared to an independent sciss ored pair. Scissored pairs attempt to mitigate some of the dif ficulties associated with traditional CMGs that ari se from the changing direction of the CMG output torque. Accomm odating the changing output-torque direction is amo ng the greatest challenges of CMG-based attitude-control s ystem design because this effect can lead to intern al si gularities