AD-A174 794 DEVELOPMENT OF ELECTRONIC CONTROL OF A SUPERCONDUCTIN GRAVITY GRADI0METER(U) MARYLAND UNIV COLLEGE PARK DEPT OF PHYSICS AND ASRRONOMY H J PAIK NOV 86 ETL-0447 UNCLASSIFIED DACA72-85-C-818 F/G 17/7 NL lllllllllllll ElI EEIIII~ E~hEEEh~hhhE
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AD-A174 794 DEVELOPMENT OF ELECTRONIC CONTROL OF A SUPERCONDUCTINGRAVITY GRADI0METER(U) MARYLAND UNIV COLLEGE PARK DEPTOF PHYSICS AND ASRRONOMY H J PAIK NOV 86 ETL-0447
UNCLASSIFIED DACA72-85-C-818 F/G 17/7 NL
lllllllllllllElI EEIIII~
E~hEEEh~hhhE
B111.02ILI
MICROCOPY RESOLUTION TEST CHART
NATONAL BUREAU OF STANDARDS- 1963-A
- U -- -
ETL-0447
.Development ofP% electronic control of a
superconducting gravitygradiometer - phase II
H. J. Paik
University of MarylandDepartment of Physics and AstronomyCollege Park, Maryland 20742
DTICELECTEf
November 1986 DEC 08 19W
LE(
APPROVED FOR PUBLIC RELEASE; DISTRIBUTION IS UNLIMITED
Prepared forU.S. ARMY CORP OF ENGINEERSENGINEER TOPOGRAPHIC LABORATORIESFORT BELVOIR, VIRGINIA 22060-5546
86 12 08 063" tt IRK
Destroy this report when no longer needed.Do not return it to the originator.
The findings in this report are not to be construed as an official
Department of the Army position unless so designated by otherauthorized documents.
The citation in this report of trade names of coimnercially availableproducts does not constitute official endorsement or approval of the
use of such products.
- . -.
UNCLASSIFIED jff q~SECURITY CLASSIFICATION OF THIS PAGE
Form ApprovedREPORT DOCUMENTATION PAGE OMB No 0704 0188
_ Exp Date Jun 30, 986
Ia REPORT SECURITY CLASSIFICATION lb. RESTRICTIVE MARKINGSUnclassified
2a. SECURITY CLASSIFICATION AUTHORITY 3. DISTRIBUTION/AVAILABILITY OF REPORT
2b. DECLASSIFICATION /DOWNGRADING SCHEDULE Approved for public release; distributionis unlimited.
4. PERFORMING ORGANIZATION REPORT NUMBER(S) S. MONITORING ORGANIZATION REPORT NUMBER(S)
ETL-0447
6a. NAME OF PERFORMING ORGANIZATION 6b. OFFICE SYMBOL 7a. NAME OF MONITORING ORGANIZATION(If applicable)
University of Maryland U,S, Army Engineer Topographic Laboratories
6c. ADDRESS (City, State, and ZIP Code) 7b. ADDRESS (City, State, and ZIP Code)Department of Physics and Astronomy
University of Maryland Fort Belvoir, VA 22060,5546
College Park, MD 20742
Ba. NAME OF FUNDING/SPONSORING 8b. OFFICE SYMBOL 9. PROCUREMENT INSTRUMENT IDENTIFICATION NUMBERORGANIZATION U. S. Army (If applicable)
Engineer Topographic Labs DACA72ir85-C-00108c. ADDRESS (City, State, and ZIP Code) 10. SOURCE OF FUNDING NUMBERS
PROGRAM PROJECT TASK WORK UNITFort Belvoir, VA 22060-5546 ELEMENT NO. INO. NO. ACCESSION NO
11. TITLE (Include Security Classification)
Development of Electronic Control of a Superconducting Gravity Gradiometer - Phase II
12. PERSONAL AUTHOR(S)Paik, H.J.
13a. TYPE OF REPORT 13b. TIME COVERED 114. DATE OF REPORT (Year, Month, Day) IS. PAGE COUNTFinal Technical FROM 10I4/85TO 8 61 1986, November 30
16. SUPPLEMENTARY NOTATIONThis report represents the continuation of work done under contract DACA72-84-C-0004.See reports ETL-0397, AD-A160-641, and ETL-0398, AD-A160-691.
17. COSATI CODES 18. SUBJECT TERMS (Continue on reverse if necessary and identify by block number)FIELD GROUP SUB-GROUP .7 Gravity gradiometer,
17 Gravity survey,
L Inertial navigation ,19. ABSTRACT (Continue on reverse if necessary and identify by block number)
During the contract period, we have completed the design and assembly of thebreadboard feedback circuit for the new NASA superconducting gravity gradiomete5. Thecircuit applies three kinds of feedbacks to the gradiometer instrument: (1) high fre-quency rejection, (2) cold camping, and (3) force rebalance. The primary purpose ofthese feedbacks is to increase the dynamic range of the instrument.
The circuit has been tested at room temperature and is awaiting a test in connection
with the actual gradiometer.
20. DISTRIBUTION/AVAILABILITY OF ABSTRACT 21 ABSTRACT SECURITY CLASSIFICATION33 UNCLASSIFIED/UNLIMITED 0-) SAME AS RPT. 0 DTIC USERS Unclassified
22a. NAME OF RESPONSIBLE INDIVIDUAL 22b TELEPHONE (Include Area Code) 22c OFFICE SYMBOL
Dr. H. Baussus von Luetzow (202) 355-2662 ETL,-IR-G
DO FORM 1473,84 MAR 83 APR edition may be used until exhausted SECURITY CLASSIFICATION OF THIS PAGEAll other editions are obsolete UNCLASSIFIED
- - , o , . , - - - • -,* -
PREFACE
This document was generated under contract DACA72-85-C-0010 for the U.S. ArmyEngineer Topographic Laboratories, Fort Belvoir, Virginia, by the Departmentof Physics and Astronomy, University of Maryland, College Park, Maryland. Itdescribes a continuation of the work done under contract DACA72-84-C-0004.(See reports ETL-0397, AD-A160-641, and ETL-0398, AD-A160-691.) The Contract-ing Officer's Technical Representative was Dr. Hans G. Baussus Von Luetzow.
The work described in this report is documented in three quarterly progressreports and a final report.
Accession For
NTIS ORA&IDTIC TAB
Unannounced (JJustification
By
* Distribution/Availability Codes
)Avail and/orDist Special
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BACKGROUND
A prototype superconducting gravity gradlometer has been
demonstrated during the five-year period from 1980 to 1985
primarily with NASA support [1]. The instrument measured one
diagonal component of the gravity gradient tensor. Without any
feedback control, the passive superconducting gradiometer has
yielded noise performance of 0.3 - 0.7 E Hz'i/3(l E _ 1 Ebtvos u
We are now developing an advanced three-axis superconducting
gravity gradiometer and a six-axis superconducting accelerometer
under a joint sponsorship of NASA, Air Force Geophysical
Laboratory and Army Engineers Topographic Laboratory. The primary
objective of the new NASA contract is to develop a three-axis
(three diagonal components) gravity gradiometer with 3 X 104 E
Hz - /2 for spaceborne geodesy. The Air Force is funding
specifically the development of the six-axis accelerometer [2],
which measures three linear and three angular acceleration
components. This instrument will be integrated with the
gradlometer to provide dynamic signals for platform control and
error compensation.
The Army Contract is to develop electronic control of the
superconducting gravity gradiometer. The support came from the
Army Corps of Engineers Topographic Laboratory (with Dr. H.G.
Baussus von Luetzow as Contracting Officer's Representative ) in
two segments: $44,000 to cover Phase I effort (June 20, 1984 -
April 19, 1985) and $51,000 for Phase II (October 4, 1985 - August
4, 1986). In Phase I, we studied the general problem of feedback-1-
control of the gravity gradiometer and demonstrated the technique
using room temperature accelerometers. In Phase II, we developed
a breadboard circuit that applies three kinds of feedbacks to the
cryogenic gradiometer. This report concerns the work performed
under the Phase II Contract with the Army.
TECHNICAL REPORT
During the contract period: October 4, 1985 - August 4,
1986, we have completed the design and assembly of the breadboard
feedback circuit for the new NASA superconducting gravity
gradiometer. The circuit applies three kinds of feedbacks to the
gradiometer instrument: (1) high frequency rejection, (2) cold
damping, and (3) force rebalance. The primary purpose of these
feedbacks is to increase the dynamic range of the instrument.
The test of the prototype gradiometer has shown that the
dynamic range of the gradiometer can be exceeded due to resonant
modes of the instrument and the cryostat insert driven by seismic
noise. In the early work, this problem has been overcome by
applying passive vibration isolation that attenuates the seismic
noise above 1 Hz. In order to extend the sensitivity of the
instrument by three orders of magnitude for space application,
and/or to realize the demonstrated sensitivity (-1 E Hz- "') in a
moving base environment where background seismic noise can be four
orders of magnitude higher than in the laboratory, it is essential
that the dynamic range of the instrument is increased by at least
four orders of magnitude by means of feedback. In Phase II of the
Army Contract, we assembled the feedback circuit which can
-2-
accomplish this task.
(1) The high frequency spectrum of the gradiometer output
(which Is mainly seismic) above the signal bandwidth Is fed back
to the SQUID to reject the Interfering seismic signals. (2) The
signals around the two resonant modes of the coupled oscillator
system in each axis of the gradiometer are narrowbanded, 900
phase-shifted, and fed back to the gradiometer proof masses to
actively damp the resonances. (3) Finally, the signals in the
signal bandwidth (0 - 1 Hz) are fed back to the proof masses with
1800 phase shift to force-rebalance the gradiometer. The circuit
has been tested at room temperature and is awaiting a test in
connection with the actual gradiometer.
Six almost-identical circuit boards are needed to cover all
the modes in the three-axis gradlometer. With the available funds
in the Army Contract, we have completed only one of these boards.
After tests and adjustments, five additional copies of this
circuit will have to be assembled. We hope to receive Phase III
funds to carry out this task.
Another type of electronic control needs to be applied to the
gradiometer-accelerometer system. With twelve signal channels and
hundreds of parameters to adjust in the combined system, it is
essential that the instrument is computer-controlled. Software
will have to be developed for automatic initialization,
calibration, and platform control. As a first step in this
direction, computer interface electronics for the two instruments
have been constructed with funds from NASA and the Air Force.
Much more work remains to be done In this area.
We attach here three quarterly progress reports that cover-3-
9k-1-
the period of this contract. The detailed theoretical and
experimental work on the superconducting gravity gradiometer has
been reported to NASA (Reference 1).
REFERENCES
[1] Final Report on NASA Contract NAS8-33822, University of