1. 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

2. SYLLABUS…

3. 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

4. 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

5. 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, Chapter 1: Introduction

6. (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

7. 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

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

9. 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, Chapter 1: Introduction
** Notice the difference between ADCS and AOCS

10. Reference Frames
ECI:
(Earth Centered Inertial)

11. Reference Frames
ECEF:
(Earth Centered
Earth Fixed)

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

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

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