Dynamics and Control of Space Vehicles ASE Tech Elective: EAS 4412 Dynamics and Control of Space Vehicles Mrinal Kumar, Assistant Prof. Mechanical and Aerospace Engineering

SYLLABUS…

Relationship between 4510 and 4412 EAS 4510: Keplerian Mechanics --- Considers motion of two particles moving under the influence of gravity... EAS 4412: Zoom into orbit… study the rotational motion of the spacecraft as a rigid three dimensional object

ADCS: Attitude DETERMINATION and CONTROL System What is Spacecraft Attitude? “Orientation of the spacecraft with respect to some suitable inertial reference frame” For rigid spacecraft, orientation of spacecraft orientation of its body-frame ADCS: Attitude DETERMINATION and CONTROL System ACTUATORS SENSORS

An Illustrative Example* Spacecraft: Geostationary communications satellite, e.g. U.S. Intelsat V, European Kopernikus Main structural parts: Central body: ~ cube-like structure with cross-section 1.5 × 2.0 m Solar arrays in N-S direction, with panel dimensions 1.5 × 7.0 m Antenna tower directed toward Earth, carrying various communication payloads, e.g. global and beacon horns, communication feed systems, hemi/zone and spot reflectors, TM/TC antenna. Sensors, e.g. sun sensors and Controllers, e.g. reaction thrusters; placed over the central body and panels. * Taken from “Spacecraft Attitude and Control: a Practical Engineering Approach”, by Marcel J. Sidi, Cambridge University Press, 2006. Chapter 1: Introduction

(Broad) Types of (Geocentric) Spacecraft The earliest ones Explorer I: USA, 1958 Sputnik I: Russia, 1957 Artemis (ESA): GEO Orbcomm: LEO Communication (commsats) Remote Sensing HST: Space observing Landsat: Earth observing

Why do we need ADCS? Prevent spacecraft tumble! Point antennas in the right direction Point payload in the right direction, e.g. cameras Align solar panels perpendicular to the sun, sensitive equipment away from sun Space operations, e.g. docking… einstein.stanford.edu

Commonly used Attitude Control Methods PASSIVE ACTIVE Gravity Gradient Spin stabilization Momentum wheels Thrusters Control moment gyroscopes Magnetic Torqrods

An Illustrative Example*: ADCS Hardware Spacecraft: Geostationary communications satellite, e.g. U.S. Intelsat V, European Kopernikus Typical Attitude and Orbit and Control System Hardware (AOCS)**: Reaction bipropellant thrust system, consisting of one 420-N thruster for orbit transfer and two independent (one redundant) low-thrust systems consisting of eight 10-N thrusters each Two momentum wheels (one redundant) of 35 N-m-sec each Two infrared horizon sensors (one redundant) Four fine sun sensors (two redundant) Twelve coarse sun sensors for safety reasons (six redundant) Two three-axis coarse rate gyros; and, Two three-axis integrating gyros Redundancy ensures system reliability! * Taken from “Spacecraft Attitude and Control: a Practical Engineering Approach”, by Marcel J. Sidi, Cambridge University Press, 2006. Chapter 1: Introduction ** Notice the difference between ADCS and AOCS

Reference Frames ECI: (Earth Centered Inertial)

Reference Frames ECEF: (Earth Centered Earth Fixed)

Reference Frames TRF: (Topological) (~north) (~east) (~zenith)

Reference Frames ORF: Orbital Frame (~velocity) (~nadir) (~normal)

Reference Frames BRF: Body Frame (~roll) (~yaw) (~pitch)