An investigation of the dynamics and control problems specifically related to the Satellite Power System (SPS), to assess performance of selected control concepts, and to identify and initiate development of advanced control technology that would enhance feasibility and performance of the SPS system was made. The initial stages of the study are reported

Juang, J. N.

Rodriquez, G.

Wang, S. J.

English

NASA Technical Reports Server

TDYNAMICS AND CONTROL OF THE SATELLITE POWER SYSTEM
S. J. Wang - J. N. Juang - G. Rodriguez
Jet Propulsion Laboratory
California Institute of Technology - Pasadena, California
R82' 22700
The SPS is the largest space system conceived to date that appears feasible
with reasonable extensions of existing control technology. It represents
a class of large platform-like structures (Fig. l) that are several orders
of magnitude larger than any of the other large space systems (multiple-
payload platforms, parabolic reflectors, etc.) currently in planning within
NASA. The SPS has in common with all large space systems many control
problems that are widely recognized within the controls community. These
problems include attitude errors due to disturbances, potential instabilities
due to truncated modes and other model errors, lack of damping, and inaccurate
preflight knowledge of the vehicle dynamics. The qualitative nature of these
problems (model errors, concentrated stresses due to large actuator size,
etc.) has emerged as a result of studies _n the general area of control of
large space structures. However, there is a need at this time, to investi-
gate the dynamics and control problems specifically related to the Satellite
Power System (SPS), to assess performance of selected control concepts, and
to identify and initiate development of advanced control technology that would
enhance feasibility and performance of the SPS system. This paper reports on
the initial stages of such a study.
One of the areas that has been under intense investigation is that of modeling
for controller design. This is widely recognized to be a major and as yet
ansolved problem in achieving precise control of large space systems (Fig. 2).
This problem arises because, to satisfy performance requirements, the control
system must have the means for predicting very accurately the vehicle dynamic
response. This is done with a dynamical model that constitutes an integral
part of the control system design. The resulting performance is critically
dependent on the accuracy of this model. Paradoxically, development and on-
board implementation of precise large structure models is difficult if not
impossible because of the many degrees-of-freedom, nonlinearities, parameter
uncertainties, difficulties in pre-flight dynamics testing_ and limitations
2 ." £ .
,.- .' "
' 2-"
: -21. "
176
https://ntrs.nasa.gov/search.jsp?R=19820014826 2020-03-21T16:25:59+00:00Z
in on-board computational capability. Hence, the model in the control
system design is at best a truncated approximation of the actual vehicle
dynamics. A systematic selection of this approximate model is required
in order to retain the significant vehicle dynamics in the controller
design, to optimize on-board computations and to ensure satisfactory control
in spite of the inevitable model errors.
Three distinct approaches have been developed in order to systematically
select the controller design model (Fig. 3). The models consist of a
hinge-connected multibody model to conduct attitude dynamics and control
studies, a continuum model to perform parametric studies of control/structure
interaction dynamics and a complete flexible multibody model for
performance prediction based on a comprehensive description of the vehicle
dynamics. Parametric analysis based on these models has revealed properties
of vehicle dynamics (such as modeshapes and frequencies) in terms of the
structural parameters (Fig. 4). This parametric model has been used to
-_demonstrate the application of system identification techniques to the
SPSdynamics and control. A quasi-inertial modeof operation (Figs. 5-7)
has been assessed parametrically and the role of damping on the attitude
dynamics investigated. Structural deformations and local slopes arising
as a result of dynamic load conditions have been obtained and related to
thepointing accuracy and transmitting efficiency of the microwave trans-
mission system (Fig. 8). Current efforts are directed toward application
of distributed control and shape determination concepts to the collector
and antenna models.
177
• -'...
l
r . _
,, ,
. £ " 2.
, L'" '
' 'C
_.__-__'_,.
.. o'. "°: -,
2
CONFIGURATION
" :'_ _' ,_._,_ _ i
[ARm: SPA_ SYSTtM
OOm
"" -" _'_470 m
FIG. 1
• NON LIMEAR
• INFINI'IIE BEGBEE$
OF FREEDOM
• EX1EIINAL
DISIURIIANCE$
• FUD(I IlUlY
• pklM_rr_ CIkMtGE$
• CONFIGUIt,ATION$
CHANI_S
• CONllmOL
INIERACIrlONS
GROUN9
EVN.UATION
MODEL
e-URm: S_S AE INFINI1E'ClMBISI_IN, SYSII$ THAT 4_
IE COMIPtJE'r_Y MOOFIJ[D
• MOOR 01101111EMJCIION IS Ik'QUlII£D 10 MINIMr n 0N,tl0kR0 I_MFI/IATIONS
IMPUEMBfIA110N COMPt_ITY
FIG. '2
CONTINUOUS MODEL
Z
%.
\ /
.FIG. 3a A
b
b
2.0
0.0
w i /5'_ _EI FREQUI_ICY
" \ p_4;
I " BEAM LENGTH
p • MASS PER UNiT LENGTH
M • END MASS
"El - BENDING MODULUS
_i " BEAM CHARACTERiSTiC
CORRESPONDING TO Ilh MODE
o'- MIp,.a
FLEXIBLE MULTI-BODY MODEL
-2.0
3.0 3.2 3.4 3.6
L I I
6.2 6,4 6.6
I I i
9.4 9.6 9.8
3,8 4,0 4,2 4.4 4.6 4.8
[ I I J I
6.8 l.O 7.2 7.4 7.6
Bz
I I I l I
_.0 10.2 ]0.4 10.6 10.8
FIG.3b 178 FIG.4 "
.%>
7)
FIG. 7 179
FIG. 8(I
FIG. 8e
,.: i _ ,
{:- o _ :
-.. , .
c" . ."
.. _.
"-L " f .. i
Y.
:/LI"
f_ . ._ : . .+
!'. '. 7..
t'q.. _,. ..
D L,.,f_ .-" .
i:;:,:i;::7.
!';"-i • '
.'-'_;,-'_'.C. "
{_ ,.', b': • .
• i _. ::,,_ i_-.-.
7: ';. :


Dynamics and control of the satellite power system

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server