ASE Tech Elective: EAS 4412Dynamics and Control of Space Vehicles
Mrinal Kumar, Assistant Prof.Mechanical and Aerospace Engineering
SYLLABUS…
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
Relationship between 4510 and 4412
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
SENSORS ACTUATORS
An Illustrative Example*
* Taken from “Spacecraft Attitude and Control: a Practical Engineering Approach”, by Marcel J. Sidi, Cambridge University Press, 2006. Chapter 1: Introduction
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.
(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?
1. Prevent spacecraft tumble!
2. Point antennas in the right direction
3. Point payload in the right direction, e.g. cameras
4. Align solar panels perpendicular to the sun, sensitive equipment away from sun
5. Space operations, e.g. docking…
einstein.stanford.edu
Commonly used Attitude Control Methods
PASSIVE ACTIVE
Gravity Gradient Spin stabilization
Momentum wheels
Control moment gyroscopes
Magnetic Torqrods
Thrusters
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!
An Illustrative Example*: ADCS Hardware
* 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)
(~zenith)
(~east)(~north)
Reference Frames
ORF: Orbital Frame
(~velocity)
(~normal)
(~nadir)
Reference Frames
BRF: Body Frame
(~roll)
(~pitch)
(~yaw)