Glossary - Autonomous and Autonomic Systems - page 248

Orbit propagation Extrapolation of spacecraft position and velocity
vectors from actual measurements at an earlier time.
Period An orbital period is the time it takes a spacecraft (or celestial object)
to complete an orbit.
Predicted orbit Extrapolated spacecraft position and velocity (as a func-
tion of time) determined by applying mathematical models of physical
processes (e.g., the Earth's gravitational potential) to actual measure-
ments of the spacecraft orbit at an earlier time.
Propagation For orbits, extrapolation of a spacecraft position and velocity
from a known starting value. For attitudes, use of relative attitude in-
formation (from gyros) to extrapolate spacecraft absolute pointing from a
starting, measured absolute attitude (for example, from star tracker data).
Propellant Thruster fuel.
Pulse-beat monitor Extension of heart-beat monitor with health urgency
tones.
Quaternion A mathematical representational system involving parameter-
ization of the three pieces of information supplied by Euler angles in
terms of a four-dimensional unit vector, which facilitates descriptions of
spacecraft attitudes. The quaternion lacks the singularity issues present
in Euler angle formulations and is more compact than the nine elements
of the direction cosine matrix. Quaternions also are easily manipulated
to determine (or incorporate) changes in attitude, a useful feature when
supporting attitude slews.
Reaction wheel A flywheel rotated with an electric motor, used on a space-
craft to transfer angular momentum to or from the spacecraft body,
thereby effecting a change in the spacecraft's attitude without firing a
thruster.
Reference data Inertial frame information from a model, catalog, etc. that
can be combined with attitude observations in order to determine the
spacecraft orientation.
Self-* Self-managing properties.
Self-anticipating The ability to predict likely outcomes or to simulate self-*
actions.
Self-awareness The ability to perceive and compute with its own internal
state in relation to its own knowledge and capabilities. Relates to the
concept of “Know thy self.”
Self-chop The initial four (and generic) self properties (configuration, heal-
ing, optimization, and protection).
Self-configuring A system's ability to configure and re-configure itself to
meet policies/goals.
Self-critical The ability to consider whether policies are being met or goals
are being achieved (see self-reflecting).
Self-defining The ability to reference (and operate in a manner determined
by) internal data and the internal definitions of that data (i.e., metadata).