Attitude and Translation Control of a Solar Sail Vehicle

A report discusses the ability to control the attitude and translation degrees-of-freedom of a solar sail vehicle by changing its center of gravity. A movement of the spacecraft s center of mass causes solar-pressure force to apply a torque to the vehicle. At the compact core of the solar-sail vehicle lies the spacecraft bus which is a large fraction of the total vehicle mass. In this concept, the bus is attached to the spacecraft by two single degree-of-freedom linear tracks. This allows relative movement of the bus in the sail plane. At the null position, the resulting solar pressure applies no torque to the vehicle. But any deviation of the bus from the null creates an offset between the spacecraft center of mass and center of solar radiation pressure, resulting in a solar-pressure torque on the vehicle which changes the vehicle attitude. Two of the three vehicle degrees of freedom can be actively controlled in this manner. The third, the roll about the sunline, requires a low-authority vane/propulsive subsystem. Translation control of the vehicle is achieved by directing the solar-pressure-induced force in the proper inertial direction. This requires attitude control. Attitude and translation degrees-of-freedom are therefore coupled. A guidance law is proposed, which allows the vehicle to stationkeep at an appropriate point on the inertially-rotating Sun-Earth line. Power requirements for moving the bus are minimal. Extensive software simulations have been performed to demonstrate the feasibility of this concept

Alternative Attitude Commanding and Control for Precise Spacecraft Landing

A report proposes an alternative method of control for precision landing on a remote planet. In the traditional method, the attitude of a spacecraft is required to track a commanded translational acceleration vector, which is generated at each time step by solving a two-point boundary value problem. No requirement of continuity is imposed on the acceleration. The translational acceleration does not necessarily vary smoothly. Tracking of a non-smooth acceleration causes the vehicle attitude to exhibit undesirable transients and poor pointing stability behavior. In the alternative method, the two-point boundary value problem is not solved at each time step. A smooth reference position profile is computed. The profile is recomputed only when the control errors get sufficiently large. The nominal attitude is still required to track the smooth reference acceleration command. A steering logic is proposed that controls the position and velocity errors about the reference profile by perturbing the attitude slightly about the nominal attitude. The overall pointing behavior is therefore smooth, greatly reducing the degree of pointing instability

Quadratic Programming for Allocating Control Effort

A computer program calculates an optimal allocation of control effort in a system that includes redundant control actuators. The program implements an iterative (but otherwise single-stage) algorithm of the quadratic-programming type. In general, in the quadratic-programming problem, one seeks the values of a set of variables that minimize a quadratic cost function, subject to a set of linear equality and inequality constraints. In this program, the cost function combines control effort (typically quantified in terms of energy or fuel consumed) and control residuals (differences between commanded and sensed values of variables to be controlled). In comparison with prior control-allocation software, this program offers approximately equal accuracy but much greater computational efficiency. In addition, this program offers flexibility, robustness to actuation failures, and a capability for selective enforcement of control requirements. The computational efficiency of this program makes it suitable for such complex, real-time applications as controlling redundant aircraft actuators or redundant spacecraft thrusters. The program is written in the C language for execution in a UNIX operating system

Planar, time-optimal, rest-to-rest slewing maneuvers of flexible spacecraft

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76605/1/AIAA-20370-687.pd

Office views and productivity-study of offices at Chandigarh, India

Abstract Major spending of organisations is on staff salaries. In order to be efficient and competitive in the profession, the staff should be productive. Staff will be productive when they are comfortable with regard to office environment. In this paper, effect of office noise on productivity of occupants is highlighted. A research to this regard was conducted in offices of capital city of Chandigarh (India). Various offices were sampled and questionnaire survey of productivity was conducted to get first hand information from office occupants

Time-optimal slewing maneuvers of flexible spacecraft.

Attitude controllers for spacecraft have been based on the assumption that the bodies being controlled are rigid. Future spacecraft, however, may be quite flexible. Many proposed applications require maneuvering such vehicles between two widely spaced quiescent states or spinning up/down these vehicles in minimum time. In this dissertation, two slewing problems have been addressed: the time-optimal, rest-to-rest slewing problem (RTRSP) and the time-optimal spinup problem (SUP). The spacecraft has been modeled as a finite-dimensional, linear, undamped, nongyroscopic system. One of the major contributions of this dissertation is the recognition and rigorous proof of symmetry of the optimal open-loop control histories about the mid-maneuver time. Necessary and sufficient conditions for optimality are transformed, exploiting the symmetry property, into a set of nonlinear algebraic equations in one half of the control switching times, the maneuver time, and the costates at the mid-maneuver time. These equations are solved using a homotopy approach. The effect of residual modes on the open-loop system performance is quantified via the residual energy, the maximum post-maneuver attitude error (for the RTRSP), and the maximum post-maneuver attitude rate error (for the SUP). Upper bounds on these performance measures are given. For the special case of a single actuator located on the rigid central body, closed form expressions for these upper bounds are obtained for an infinite dimensional evaluation model. When only one control input is used to effect the slewings, it is found that the optimal control history is independent of the control input locations. The main assumption of this work is the absence of nonlinear rotational stiffening effects. This assumption might fail to hold during slewings when 'large' rotational rates are attained. We have proposed a simple condition which, when satisfied, justifies the omission of this nonlinearity from the equations of motion. This condition is validated by numerical simulations. The results of this dissertation, therefore, can be applied to many physical situations. Moreover, the results are applicable to all linear, elastic, nongyroscopic systems possessing one rigid body mode and a finite number of undamped elastic modes.Ph.D.Aerospace engineeringUniversity of Michiganhttp://deepblue.lib.umich.edu/bitstream/2027.42/162127/1/8907144.pd