Hanspeter Schaub

Hanspeter Schaub
University of Colorado Boulder | CUB · Department of Aerospace Engineering Sciences (AES)

Doctor of Philosophy

About

262
Publications
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6,953
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Publications

Publications (262)
Article
Full-text available
A coupled ferrohydrodynamic interface-tracking model is introduced for the analysis of the equilibrium, linear stability, and modal response of magnetic liquid interfaces in surface tension-dominated axisymmetric multiphase flows. The incompressible viscous mass and momentum balances are solved together with the steady-state Maxwell equations by fo...
Article
Full-text available
The secondary electron method has been recently proposed to touchlessly sense the electrostatic potential of non-cooperative objects in geosynchronous equatorial orbits and deep space. This process relies on the detection of secondaries generated at the target surface, that is actively irradiated by an electron beam. Although the concept has alread...
Conference Paper
Full-text available
Ultraviolet lasers are proposed as a replacement for low-energy electron beams to induce the emission of secondary electrons in touchless spacecraft potential sensing technologies. Theoretical considerations show that the measurement process becomes significantly less sensitive to the electrostatic environment and leads to more robust, controllable...
Article
Full-text available
Electrostatic perturbations can have significant effects during terminal proximity operations in high earth orbits, with torque levels exceeding 5 mN-m during severe charging events. These torques can impart 1°/s rotational rates to uncontrolled bodies, such as debris or servicing clients, during rendezvous and proximity operations. A sub optimal,...
Conference Paper
Full-text available
The active deorbiting and passivation of launch vehicles has become key for the implementation of modern space debris mitigation guidelines. Appropriate engine restart conditions must be provided as part of this process. Ullage motors have been traditionally employed to induce active settling and ensure a gas-free propellant supply to the engines....
Conference Paper
Full-text available
This paper introduces a new guidance algorithm for discrete-event drag-modulated aerocapture, inspired by the concepts of variation-of-parameters and osculating orbits. The algorithm is implemented and tested in a high-fidelity simulation developed by NASA's Jet Propulsion Laboratory for the case of an Earth flight demonstration of aerocapture usin...
Conference Paper
Full-text available
The electrostatic tractor concept is an active debris removal method that has been proposed to remove retired satellites from Geostationary Earth Orbit without physical contact, using electrostatic forces. These forces are generated by charging the servicing satellite and the debris with an electron gun that is attached to the ser-vicer. Prior work...
Article
Full-text available
The management of fluids in space is complicated by the absence of relevant buoyancy forces. This raises significant technical issues for two-phase flow applications. Different approaches have been proposed and tested to induce phase separation in low-gravity; however, further efforts are still required to develop efficient, reliable, and safe devi...
Conference Paper
Full-text available
A method has been recently proposed to estimate the electric potential of co-orbiting spacecraft remotely using x-rays that are excited by an electron beam. Prior work focused on the theoretical foundation and experimental validation of this method using flat target plates. Although useful for the validation of this concept, flat plates do not adeq...
Article
Full-text available
Novel active sensing methods have been recently proposed to measure the electrostatic potential of non-cooperative objects in geosynchronous equatorial orbit and deep space. Such approaches make use of electron beams to excite the emission of secondary electrons and X-Rays and infer properties of the emitting surface. However, the detectability of...
Preprint
Full-text available
This paper explores expressing the relative state in the close-proximity satellite relative motion problem in terms of fundamental solution constants. The nominal uncontrolled relative state can be expressed in terms of a weighted sum of fundamental and geometrically insightful motions. These fundamental motions are obtained using Lyapunov-Floquet...
Conference Paper
[The final version of this work can be found at http://doi.org/10.2514/1.A35355] The secondary electron method has been recently proposed to touchlessly sense the electrostatic potential of non-cooperative objects in geosynchronous equatorial orbits and deep space. This process relies on the detection of secondaries generated at the target surface,...
Presentation
Full-text available
The Electrostatic Tractor (ET) has been proposed to touchlessly remove retired satellites from geostationary orbit using electrostatic forces. An electron gun is attached to the servicing satellite and aimed at the dysfunctional spacecraft. The resulting positive charge of the servicer and negative charge of the debris leads to an attractive electr...
Conference Paper
Full-text available
This paper explores the dynamics for the sensitivity of the satellite relative state to uncertainty in the initial orbit elements of the target object about which the dynamics have been linearized. These sensitivities enable rapid and highly accurate Monte Carlo analysis of the evolving uncertainty in the relative state with respect to a nearby unk...
Conference Paper
Full-text available
The Electrostatic Tractor (ET) concept utilizes attractive Coulomb forces to relocate retired satellites from Geostationary Earth Orbit (GEO) to a graveyard orbit several hundred kilometers above GEO without any physical contact. Prior research investigated the charged relative motion control performance of the ET for two spherical spacecraft, and...
Article
Full-text available
The sloshing of liquids in low-gravity entails several technical challenges for spacecraft designers and operators. Those include the generation of significant attitude disturbances, the uncontrolled displacement of the center of mass of the vehicle or the production of gas bubbles, among others. Magnetic fields can be used to induce the reorientat...
Conference Paper
Full-text available
The Electrostatic Tractor (ET) has been proposed to touchlessly remove space debris from geosynchronous orbit (GEO) by taking advantage of inter-craft Coulomb forces. A controlled spacecraft (tug) emits an electron beam onto an uncooperative or retired satellite (debris). Thus, the tug raises its own electrostatic positive potential to 10s of kilov...
Conference Paper
[The final version of this work can be found at http://doi.org/10.2514/1.A35190] Novel active sensing technologies have been recently proposed to measure the electrostatic potential and characterize non-cooperative objects in Geosynchronous Equatorial Orbit (GEO) and deep space. Such technologies make use of electron beams to excite the emission of...
Conference Paper
[The final version of this paper can be found in http://arc.aiaa.org/doi/abs/10.2514/1.A35021] The management of fluids in space is complicated by the absence of strong buoyancy forces. This raises significant technical issues for two-phase flows applications, such as water electrolysis or boiling. Different approaches have been proposed and test...
Conference Paper
Full-text available
The term sloshing refers to the movement of liquids in partially filled containers. Low-gravity sloshing plays an important role in the configuration of space vehicles, as it affects their dynamics and complicates the propellant management system design. Magnetic forces can be used to position a susceptible fluid, tune its natural frequencies, and...
Conference Paper
Full-text available
This paper develops new tools for close-proximity spacecraft relative motion guidance in slowly varying or quasi-periodic orbits in highly perturbed environments. The task of designing safe relative motion in this context is achieved using transformations of the linearized relative motion dynamics in differential orbit elements , generated from a h...
Article
This paper explores methods for approximating and analyzing the dynamics of highly perturbed spacecraft formations with an emphasis on computationally efficient approaches. This facilitates on-board computation or rapid preliminary mission design analysis. Perturbed formation dynamics are often approximated as linear time-varying (LTV) systems, for...
Conference Paper
[The final version of this paper can be found in https://doi.org/10.1016/j.actaastro.2021.06.045] The sloshing of liquids in low-gravity entails several technical challenges for spacecraft designers and operators. Those include the generation of significant attitude disturbances, the uncontrolled displacement of the center of mass of the vehicle o...
Conference Paper
Full-text available
This paper introduces new analytic approximations of the orbital state for a subset of orbits in a rotating potential with gravitational harmonics C20 = −J2 and C22. An analytic expression for the orbit radius is first obtained, then used to obtain expressions for 3 other quantities, which may be combined with equations for the right ascension of t...
Conference Paper
Full-text available
Robust rendezvous guidance is implemented in an environment with uncertain dominant gravitational harmonics C20 and C22 and poorly-known solar radiation pressure (SRP) effects. The rendezvous control design presumes the availability of a throttled low-thrust propulsion system, which can be achieved by pulsed plasma thrusters. The control minimizes...
Conference Paper
Full-text available
This paper introduces a model for spacecraft formation dynamics subject to attitude-dependent solar radiation pressure (SRP) disturbance, with the SRP model accounting for both absorption and specular/diffuse reflection. Spacecraft attitude is represented in Modified Rodriguez Parameters (MRPs), which have desirable properties over other attitude p...
Conference Paper
Full-text available
This paper explores methods for approximating and analyzing the dynamics of highly perturbed spacecraft formations, with an emphasis on computationally efficient approaches. This facilitates on-board computation or rapid preliminary mission design analysis. Perturbed formation dynamics are often approximated as linear time varying (LTV) systems, fo...
Article
Electrostatic actuation is the process of charging two spacecraft and using the resulting Coulomb interaction to exert touchless forces and torques between the two spacecraft. For all electrostatic actuation concepts, fast and accurate models for the electrostatic force and torque are needed. The Volume Multi-Sphere Method (VMSM) seeks the optimal...
Article
Using thrusters for either orbital maneuvers or attitude control change the current spacecraft mass properties and results in an associated reaction force and torque. To perform orbital and attitude control using thrusters, or to obtain optimal trajectories, the impact of mass variation and depletion of the spacecraft must be thoroughly understood....
Article
Computer simulations of spacecraft dynamics are widely used in industry and academia to predict how spacecraft will behave during proposed mission concepts. Current technology and performance requirements have placed pressure on simulations to be increasingly more representative of the environment and the physics that spacecraft will encounter. Thi...
Article
The number of operational satellites and debris objects in the valuable geosynchronous ring has increased steadily over time such that active debris removal missions are necessary to ensure long-term stability. These objects are very large and tumbling, making any mission scenarios requiring physical contact very challenging. In the last 10 years,...
Article
The attitude and vibration control of a flexible spacecraft with two parallel double-gimbal variable-speed control moment gyros (DGVSCMGs) is considered. The coupled nonlinear equations of motion create a complex challenge in a pointing control development. First a Gain-Scheduled (GS) controller for a 3-axis attitude control is designed by the post...
Article
This paper derives a linear parameter-varying (LPV) model for three-axis attitude control of a spacecraft with a single double-gimbal variable-speed control moment gyroscope (DGVSCMG) and magnetic torquers (MTQs) and develops a singularity avoidance steering law. The LPV control theory provides an optimal gain-scheduled (GS) controller while consid...
Conference Paper
A spacecraft undergoing general translational and rotational motion can be affected by the sloshing of propellant. A spherical pendulum model is used for simulating this phenomenon because it can better represent the sloshing behavior for rotational dynamics in micro-gravity. This paper develops the fully coupled equations of motion of such a syste...
Article
A novel algorithm for attitude control of a spacecraft subjected to conically constrained inclusion and exclusion regions using a kinematic steering law and a rate-based attitude servo system is presented. The tracking errors are defined using switched modified Rodrigues parameters to yield, leveraging the nonuniqueness of the parametrization, a no...
Article
This Paper addresses an integrated power/attitude control system for a spacecraft with two double-gimbal variable-speed control moment gyroscopes. Double-gimbal variable-speed control moment gyroscopes are of interest because a single device is a three-degree-of-freedom attitude actuator. A double-gimbal variable-speed control moment gyroscope has...
Article
A modular scheme for generating attitude reference motions is presented. This scheme is a generic strategy to develop the guidance profile for a wide range of mission scenarios through combination of atomic guidance modules that fulfill a well-defined functionality. There are three core functionalities that conform all guidance reference motions: b...
Article
Charged space objects experience small perturbative torques and forces from their interaction with Earth’s magnetic field. These small perturbations can change the orbits of lightweight, uncontrolled debris objects dramatically even over short periods. This paper investigates the effects of the isolated Lorentz force, the effects of including or ne...
Article
Spacecraft attitude control solutions typically are torque-level algorithms that simultaneously control both the attitude and angular velocity tracking errors. In contrast, robotic control solutions are kinematic steering commands where rates are treated as the control variable, and a servo-tracking control subsystem is present to achieve the desir...
Article
Full-text available
Spacecraft can charge to negative 10's of kilo-Volts at Geosynchronous Earth Orbit (GEO) due to interactions with the space plasma. This raises spacecraft electronics or solar panel damage concerns. Spacecraft charging leads to perturbations which change the orbits of lightweight uncontrolled debris objects. A charged space object experiences a for...
Conference Paper
Computer simulations of spacecraft dynamics are widely used in industry and academia to predict how spacecraft will behave during proposed mission concepts. Current technology and performance requirements have placed pressure on simu- lations to be increasingly more representative of the environment and the physics that spacecraft will encounter. T...
Conference Paper
Stability analysis is an important tool in determining the robustness of the control system design for spacecraft missions. However, many spacecraft exhibit flexible dynamics due to solar arrays or other appended bodies. Therefore, the stability analysis needs to incorporate flexing behavior in the equations of motion. This paper outlines a method...
Chapter
Applications like the Electrostatic Tractor (ET), remote sensing of space debris objects, or planetary science investigating asteroid charging, benefit from a touchless method to assess the electrostatic potential and charge distribution of another body. In the ET, accurate predictions of the force and torque between a passive space object and tug...
Conference Paper
Recently, much attention has been paid to a double-gimbal variable-speed control moment gyro (DGVSCMG) as a new type of an attitude actuator of a spacecraft. A DGVSCMG has two gimbals attached to one variable speed wheel and can generate large three dimensional torques if the RW motor torque is sized accordingly. Implementing DGVSCMGs for attitude...
Article
Past and current magnetosphere missions employ conventional spacecraft formations for in situ observations of the geomagnetic tail. Conventional spacecraft flying in inertially fixed Keplerian orbits are only aligned with the geomagnetic tail once per year, since the geomagnetic tail is always aligned with the Earth-Sun line, and therefore, rotates...
Conference Paper
Control moment gyroscopes (CMGs) and variable-speed control moment gyroscopes (VSCMGs) are a popular method for spacecraft attitude control and fine pointing. However, since these devices typically operate at high wheel speeds, mass imbalances within the wheels act as a primary source of angular jitter. Although these effects are often characterize...
Article
To study the spatial and temporal variations of plasma in the highly dynamic environment of the magnetosphere, multiple spacecraft must fly in a formation. The objective for this study is to investigate the feasibility of solar sail formation flying in the Earth-centered, Sun-synchronous orbit regime. The focus of this effort is to enable formation...
Article
The geosynchronous (GEO) orbital regime is becoming cluttered with derelict space debris, which raises the collision risk for satellites in a very valuable orbit. Touchless reorbiting options have been proposed for moving this debris to a graveyard orbit to avoid the risk of physically docking with large, multiton defunct satellites that can be tum...
Conference Paper
Using thrusters for either orbital maneuvers or attitude control change the current spacecraft mass properties and results in an associated reaction force and torque. To perform orbital and attitude control using thrusters, or to obtain optimal trajectories, the impact of mass variation and depletion of the spacecraft must be thoroughly understood....
Article
Autonomous, low-thrust guidance for active disposal of geosynchronous debris, subject to collision avoidance with the local debris population, is studied. A bisection method is employed to determine trajectory modifications to avoid a conjuncting debris object by a range of distances, assuming a range of collision lead times. A parametric study is...
Conference Paper
A large portion of spacecraft missions have stringent pointing, attitude knowledge, and control requirements. This results in the necessity of high fidelity dynamics modeled in the numerical simulation of the spacecraft. A crucial aspect of this high fidelity is modeling the components susceptible to flexing and vibration. For most spacecraft, the...
Conference Paper
A key source of pointing jitter is due to reaction wheels (RWs) mass imbalance about the wheel spin axis. Although these effects are often characterized through experimentation in order to validate requirements, it is of interest to include jitter in a computer simulation of the spacecraft in the early stages of spacecraft development. An estimate...
Article
The success of previous lunar science missions can be expanded upon by using a constellation of satellites to increase the lunar surface coverage. A constellation could also serve as a communications or GPS network for a lunar human base. Small-sats, deployed from a single mothercraft, are proposed to achieve a lunar constellation. The establishmen...
Article
The motion of abandoned satellites near the geostationary (GEO) region has been extensively studied, modeled, and compared to the motion of station-kept, operational satellites, providing insights into the evolution of uncontrolled orbits at GEO. Analytic developments produced a family of curves represented in the ascending node versus inclination...
Article
The conjunction challenges of low-thrust engines for continuous thrust re-orbiting of geosynchronous (GEO) objects to super-synchronous disposal orbits are investigated, with applications to end-of-life mitigation and active debris removal (ADR) technologies. In particular, the low maneuverability of low-thrust systems renders collision avoidance a...
Conference Paper
Charged spacecraft experience electrostatic forces and torques from both charged neighboring spacecraft and the local space environment itself. The Multi Sphere Method (MSM) is a recent methodology to numerically approximate electrostatic forces significantly faster than realtime. This allows the simulation of the complex charged astrodynamics that...
Article
Circumnavigation relative motion is considered for application such as inspecting a space object for damage, or characterizing space debris before engaging a remediation operation. Faster-than-natural circumnavigation is a guidance method in which the deputy spacecraft is advanced ahead of the natural Keplerian relative motion. A state transition m...
Conference Paper
For many spacecraft with deployable structural components, such as solar panels or deployable antennas, the rigid-body assumption does not accurately model the full system dynamics. Spacecraft with large deployed solar panels exhibit flexible dynamics that can impact the final pointing and jitter performance of an attitude control system, or the si...
Article
The relative motion about 4179 Toutatis is studied in order to investigate the feasibility of formation flying as an alternative concept for future asteroid exploration missions. In particular, the existence of quasi-frozen orbits about slowly rotating bodies allows us to compute families of periodic orbits in the body-fixed frame of the asteroid....
Article
Touchless detumbling of space debris is investigated to enable orbital servicing or active debris removal. Using active charge transfer between a tug and debris object, control torques are created to reduce the debris spin rate prior to making any physical contact. In this work, the tug shape is spherical and the debris is assumed to be cylindrical...
Article
In order to ameliorate the ever increasing space situational awareness risks at Geosynchronous (GEO) orbits, spacecraft rendezvous is desirable for servicing or repositioning operations. When large GEO spacecraft loose station keeping control, they can acquire sizable rotational momenta that imperil proximity operations and docking. Remote electros...
Article
Forecasting of localized debris congestion in the geostationary (GEO) ring is performed to formulate and investigate methodology for identifying the debris objects that pose the highest risk to operational satellites in this ring. Proximity and speed relative to GEO during near-miss events detected under a torus intersection metric are translated i...
Article
Space debris is a topic of concern among many in the space community. Most forecasting analyses look centuries into the future to attempt to predict how severe debris densities and fluxes will become in orbit regimes of interest. Conversely, space operators currently do not treat space debris as a major mission hazard. This survey paper outlines th...
Article
A comparison of different methods to estimate the sun-direction vector using a partially underdetermined set of cosine-type coarse sun sensors (CSS), while simultaneously controlling the attitude towards a power-positive orientation, is presented. CSS are commonly used in performing power-positive sun-pointing and are attractive due to their relati...
Article
A recent proposed technique for geostationary debris mitigation is the electrostatic tractor. The tug vehicle approaches a debris object to within 20 m and emits a focused electron beam onto it. This results in a negative charge on the debris and a positive charge on the tug vehicle. Used in conjunction with low thrust, the electrostatic force is u...
Article
The relative attitude is studied between two charge controlled spacecraft being held at a fixed separation distance. While one body has a spherical shape, the 2nd body is assumed to be non-spherical and tumbling. The attitude control goal is to arrest the rotation of the 2nd body. While prior work has identified the existence of torques between cha...
Conference Paper
Full-text available
The relative motion about 4179 Toutatis is studied in order to investigate the feasibility of formation flying as an alternative concept for future asteroid exploration missions. In particular, the existence of quasi-frozen orbits about slowly rotating bodies 1 allows to compute families of periodic orbits in the body-fixed frame of the asteroid. S...
Article
A description of an attitude control system for a 3-axis stabilized spacecraft is presented. Using modified Rodrigues parameters, a globally stabilizing nonlinear feedback control law is derived that enables tracking of an arbitrary, time-varying reference attitude. This new control incorporates integral feedback while avoiding any quadratic rate f...
Article
The prospects of touchlessly detumbling a small, multiple meters in size, space object using electrostatic forces are intriguing. Physically capturing an object with a large rotation rate poses significant momentum transfer and collision risks. If the spin rate is reduced to less than 1 degree per second, relative motion sensing and control associa...
Article
Exploration of the Earth׳s magnetosphere using solar sails has advantages over the use of traditional spacecraft in inertially fixed orbits because of the solar sails׳ capability to stay in the geomagnetic tail for longer periods. In this paper, solar sail formation flying in Earth-centered slightly inclined orbits is investigated, with each solar...
Article
Propulsion, path planning and control of satellite formations in Geostationary Earth Orbits (GEO) and other high Earth Orbits is a challenging problem. This paper presents the results of the analysis of two types of controllers for satellite formation flying; the first one linear, using classical Proportional-Derivative (PD) control, and the second...
Article
In high Earth orbits, spacecraft surface charging due to ambient plasma and the photoelectric effect can produce disruptive electrostatic forces to the order of 10-1000 micro-Newtons between close-flying spacecraft flying with separation distances up to 100 meters. Rather than fighting them, these forces could be utilized to propel spacecraft to fo...
Article
The use of an electrostatic force to perform general orbit corrections on a passive geosynchronous space object is investigated. Using inertial thrusters, a space tug approaches and settles into a piecewise fixed relative location with respect to a deputy object that needs to be towed to a new orbital location. Once in place, an electrostatic force...
Article
The effects of on-orbit fragmentation events on localized debris congestion in each of the longitude slots of the geosynchronous orbit (GEO) regime are evaluated by simulating explosions and collisions of uncontrolled rocket bodies in multiple orbit configurations, including libration about one or both of the gravitational wells located at 75°E and...
Article
Asteroid retrieval, satellite servicing, and debris removal concepts often rely on a thrusting vehicle to redirect and steer a passive object. One effective way to tow the object is through a tether. This study employs a discretized tether model attached to six degree-of-freedom end bodies. To reduce the risk of a post-burn collision between the en...