Design of attitude control system for a sounding rocket is established by using a control loop which incorporates a lead network to convert position output into a feedback signal that is approximately proportional to position, plus a constant times rate

Keltz, W. L.

English

NASA Technical Reports Server

1972	 1	 B72-10052 
NASA TECH BRIEF 
Ames Research Center 	
_4V 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage 
commercial application. Tech Briefs are available on a subscription basis from the National Technical Information 
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Adaptive Position Control Loop 
The problem: 
Design an attitude control system for a sounding 
rocket which minimizes the time required to achieve 
coarse pointing over a wide range of initial error 
angles up to 900 and consumes a minimum amount
The solution: 
Establish a control loop which incorporates a lead 
network to convert the position output into a feed-
back signal that is approximately proportional to 
position, plus a constant times rate. Either of two 
Polarity	 Torque to	 Vehicle 
Sensor	 Inertia Ratio	 Dynamics 
Odeg/sec2	 i/s2	 9 deg Attitude oc = 0 + 
. QHJh
C2 SI
 
_V 
Of b
F"". ^ ^ - 
OP.
Lead Network 
I  
ki 
[14S/11 H	 L 1+s/2c
k1 sin 9 
Angular 
Position 
Sensor 
of cold gas for the maneuver. Thrusters will operate 
in the bang-bang mode and push-pull configuration 
to supply a control torque that is plus or minus a 
saturation value and never zero. Gas pressure is un-
regulated, hence thrust will decay exponentially dur-
ing acquisition. The only sensor on board produces a 
signal proportional to the sine of the angle of error.
different values of ratio of position to rate feedback 
is selected depending on the magnitude of the posi-
tion error signal. The direction of thrust is determined 
by the sign of the feedback signal, with sense selected 
to cause vehicle response to trend toward the desired 
position to rate ratio. 
The optimum ratio in any given case is a function 
AdIlk	 (continued overleaf) 
This document was prepared under the sponsorship of the National 	 . Government assumes any liability resulting from the use of the 
Aeronautics and Space Administration. Neither the United States	 information contained in this document, or warrants that such use 
Government nor any person acting on behalf of the United States 	 will be free from privately owned-rights.
https://ntrs.nasa.gov/search.jsp?R=19720000052 2020-03-17T03:24:36+00:00Z
of the initial error. A ratio that will minimize over-
shoot at large angles will cause the system to "creep" 
in the vicinity of small errors. This difficulty is re-
solved by switching to a faster rate when the error 
draws within a preset value. 
The result is a simple adaptive control system that 
conserves gas by minimizing the overall time of 
function. 
How it's done: 
The essential elements of the control loop are as 
shown in the diagram. One practical design for a lead 
network with two alternate position to rate values is 
illustrated. 
The feedback signal, Ofb, is compared with the 
desired signal, e, of zero angle at zero rate. The sign 
of the difference is detected by the polarity sensor, 
which then determines the direction of the torque. 
The resulting angular acceleration of the vehicle 
is proportional to o', the ratio of torque to inertia, and 
acts in the direction that will reduce efb. 
The feedback loop starts with the attitude sensor 
whose output is proportional to the sine of the angle 
E). The lead network develops a rate signal through 
the action of resistor R1 and capacitors Cj and C2. 
This is added to the position signal at resistor R2. 
Electronic switch Si is opened at smaller angles of 
error, removing C2 from the circuit, and reducing the 
rate component. Operation of Si is not dependent on 
angular velocity Ô, but is governed by e only, as the 
vehicle response is constrained by e. 
This is expressed in the transfer characteristic 
shown, wherein the ratio of position to rate feedback 
is governed by the lead-break frequency w i,. The lag 
corner frequencyW2e is kept sufficiently larger than 
W 1 ,, to insure that the network output is approximately 
proportional to position plus a constant times rate.
A tpical ratio of w 2,/w ic is 100. A typical ratio of 
W 1, at small angles to wit, at large angles is 4 or 5 to 1. . 
Notes: 
1. This approach avoids the difficulty of establishing 
a fixed slew rate, where it is difficult to compute e 
electronically from sin e, especially in the vicinity 
of 90°. 
2. Digital computer simulations strongly supported 
the use of two lead-break frequencies over a single 
one as a technique for achieving substantial reduc-
tion in time required for coarse acquisition. 
3. The following documentation may be obtained 
from: 
National Technical Information Service 
Springfield, Virginia 22151 
Single document price $3.00 
(or microfiche $0.95) 
Reference: NASA CR-73304 (N69-29306), 
Fluidic Proportional Thruster System. 
4. Requests for additional information may be di-
rected to: 
Technology Utilization Officer 
Ames Research Center 
Moffett Field, California 94035 
Reference: TSP72-10052 
Patent status: 
No patent action is contemplated by NASA. 
Source: W. L. Keltz of
General Electric Company,
Specialty Fluids Operation 
under contract to
Ames Research Center 
(ARC-10255) 
Category 02


Adaptive position control loop

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