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4th WSEAS International Conference onMATHEMATICAL METHODS &
COMPUTATIONAL TECHNIQUES
IN ELECTRICAL ENGINEERING
E-mail:
Dear Sirs,
We send you a summary and report "SOME PECULIARITIES OF OPERATIVE “OKEAN-O” CONTROL".
Authors are Udaloy V.A., Ivanov N.M., Sokolov N.L., Pazdnikov V.U.
We ask you to find opportunity to include this report in conference work.
Contact telephone number: (095) 513-44-64, Sokolov N.L.
Fax: (095) 586-84-34, Sokolov N.L.
First deputy director
of Mission Control CenterV. A. Udaloy
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SOME PECULIARITIES OF OPERATIVE “OKEAN-O” CONTROL
Authors: Valeriy Alekseevich Udaloy, Nikolay Mihailovich Ivanov, Nikolay Leonidovich Sokolov, Vitaliy Valerievich Astafiev
Mission Control Center and Modeling of Central Scientific and Research Institute of machinebuilding, t. Korolev, Moscow region, Russia.
During “Okean-O” control Main Operative Group of Control (GOGU) had to support the spacecraft attitude by changing solar array position during communication session. In this paper basic peculiarities of “Okean-O” control in condition of great atmosphere parameters changes and methodic of atmosphere parameters changes calculating are submitted; process of “Okean-O” control during one of the hardest geomagnetic storms on July, 15, 2000 is described.- General information
Russian-Ukraine “Okean-O” spacecraft was launched on July 17, 1999. Russian aviation and space agency and National space agency of Ukraine financed the spacecraft. It was designed by State design office “Yuzhnoye” and built by Industrial union “Yuzhniy mashinostroitelniy zavod” (c. Dnepropetrovsk). The spacecraft was used for socio-economic and scientific purposes of Russia and Ukraine. It was controlled from Mission control and modeling center (t. Korolev, Moscow region).
Purpose of “Okean-O” spacecraft is operative receiving of information about remote probe of the Earth and World ocean in light-spectrum, infra-red and microwave ranges of spectrum; collection and transmission of information from sea, ice and ground platforms for studying and effective solving problems of environment condition and nature and man-caused processes influence on it.
“Okean-O” was created and almost ready for launch by 1986. However launch date was delayed for many reasons. That caused some technical problems including warranty period of on-board equipment. As a result one-year warranty period of spacecraft using was fixed.
“Okean-O” is the unique spacecraft. It is heavy class spacecraft; its mass is over 6 tons. Automatic “space laboratory” works by commands from the ground. It includes 11 measuring devices which supplement each other through information possibilities (laboratory length is 12 meters, diameter – 3,5 meters) – Picture 1.
Picture 1.
“Okean-O” GOGU was formed and confirmed by Joint Russian-Ukraine interstate commission. It included specialists of MCC-M, SDO “Yuzhnoye”, Space observing center (main spacecraft operator) and other Russian and Ukraine organizations.
MCC-M specialists performed functions of flight director, deputy flight director, shift flight directors, heads and shift heads of planning and analysis groups. They also performed operative interaction with organizations participating in control. Functions of deputy flight director-technique flight director were performed by SDO “Yuzhnoye” specialists.
During ''Okean-O" flight GOGU came across difficulties with spacecraft attitude support. On the third day after launch ''Ocean-O" spun out of control. Situation analysis showed that nominal work of on-board facilities control system (SUBAK) turned out to be impossible in condition of great atmosphere parameters changes. It was determined that the fly-weel which is for compensation torque moment on tangage axis ran up to its total saturation on kinetic moment on tangage axis for great atmosphere density changes. That caused SUBAK tripping and spacecraft spinning out of control.
For effective ''Okean-O" control Joint Russian-Ukraine commission suggested a new control scheme. It was based on doing periodic correction of solar array position by discrete commands during communication session.That was necessary to combine aerodynamic and gravitational moments on tangage axis, which compensate torque pro rata rate of atmosphere density change. As the solar array is used mainly for supporting positive energy balance of the spacecraft, limits on angle of solar array turn were taken into account using this scheme.
- Algorithms of fly-weel kinetic moment control using spacecraft aerodynamic moment
Research was based on using general differential equation that describes dynamic of fly-weel H kinetic moment on tangage axis [1-3].
(1)
where M – summary external moment on tangage axis, ω – rate of the spacecraft spinning on tangage axis.
In general case summary external moment includes gravitational, aerodynamic, magnetic moments and moments caused by solar pressure, slackness of spacecraft construction and so on.
Only using special methods of numerical integration the differential equation could be solved.
Some simplifications that fit to nominal spacecraft work were made:
- rates of spacecraft movement in relation to its center of mass are near to zero;
- summary external moment M is constant at limited time periods and flight periods with constant position of solar array inclination angle;
- aerodynamic moment changes value abruptly during solar array turn.
Notice, the assumption about period constancy of summary external moment helps to increase accuracy of calculations in condition of atmosphere density difference by phased re-calculation of value M.
So, fly-weel kinetic moment dependence on time:
(2)
Values H0 and H′0 could be determined by telemetry of fly-weel kinetic moment on tangage axis. Let - time moments of kinetic moment measurement on tangage axis, n – appropriate values of kinetic moment.
To determine optimal value H0 and H′0 we use least-squares method [4]. Residual vector:
Criterion of optimality Ф(H):
(3)
It is necessary to fulfill the following condition to criterion of optimality gets minimum:
(4)
Putting criterion of optimality (3) in the equation (4) we get the following system of linear equations:
(5)
Solving the system of equations (5) we get the following values H0 and H′0:
After finding values H0 and H′0, we can use them in formula (2) to forecast value of kinetic moment.
Aerodynamic moment dependence on solar array turn angle during nominal spacecraft flight would look:
Ма() = МКА + МСБcos,
where - MKA – aerodynamic momentproduced by spacecraft body, MСБ – aerodynamic moment produced by solar array if it is transversely to oncoming air stream.
Such position of solar array appropriate to α=0. Taking into account this the equation (2) is changed to:
Н(t) = Н1 + (М* + МСБcos1) (t-t1),
Where M* - summary external moment on tangage axis mines aerodynamic moment produced by solar array.
Spacecraft control strategy is striving for getting some necessary value H2 at the moment t=t2 or for getting near-zero value forecasting change gradient H(t).
In the first case condition H(t)=H2 is fulfilled if solar array turn angle α=α2 which is calculated by formula:
2 = arccos[ (- М*)]. (6)
In the second case the formula is:
0 при - 1
2 = arccos(-) при 0 -1(7)
при - 0
So calculated by formulas (6), (7) values of solar array inclination angle refer to oncoming air stream allow to support necessary combinations of summary external moment constituents at which turning speed of fly-weel on tangage axis doesn’t get limiting values.
- Control by changing solar array position during communication sessions
After analysis of control system work in condition of great atmosphere density difference it was fixed that supporting of spacecraft attitude is possible only by holding 5-6 (equally spased from each other if it’s possible) communication sessions per day when operative decisions about turn of solar array should be made.
Such control scheme demanded around-the-clock work of GOGU personal. During communication session lasting 10-12 minutes the specialists had to estimate control and energy supply systems work taking into consideration angle α influence on changing of fly-weel spinning dynamic (6,7); to determine program of solar array turn (direction and time); to issue order of discrete commands to spacecraft board and to get sure in their right fulfillment and influence on on-board systems. As such scheme wasn’t provided in advance GOGU specialists learnt new functions within short period.
This scheme turned out to be effective both in condition of season-latitudinal atmosphere parameters change and during great atmosphere density difference caused by extreme magnetic storms (they often took place in 2000-2001 and were very hard). It is worth to describe order of GOGU operations during one of the hardest magnetic storm (July 14, 2000) which influenced on ''Okean-O" control on July 15-16, 2000. According to HTML files [5] at that time Japanese satellite (ASCA) spun out of control (it had functioned on-orbit since 1993 and included big X-Ray telescope for studying black holes, dark matter and evolution of the universe.
It’s important to note that GOGU received warning about forecasting extreme magnetic storm from Center of geophysics forecast IZMIRAN. That allowed GOGU specialists to work out a number of control strategies.
The solar array was placed on angle α=53º refer to the plane of spacecraft movement. That caused producing negative kinetic moment on tangage axis and range extension of change VZ at forecasting atmosphere density increasing. Change dynamic of kinetic moment on tangage axis and value of solar array inclination angle refer to flight time is on picture 2.
Magnetic storm influence on ''Okean-O" got noticeable during communication session at orbit 5352 (14:33:41 – 14:47:03, July 15, 2000). At that time sudden increasing of fly-weel spinning speed was locked in on tangage axis: kinetic moment increased from –5 to –1,2 N·m·s in period between orbits 5349 and 5352. On the next communication session (orbit 5355 (19:32:33 – 19:44:50)) activity of kinetic moment increasing increased, value VZ got 5,5 N·m·s. GOGU personal made a decision to turn solar array to angle α=59º to decrease aerodynamic torque on tangage axis. Operative analysis of control system during communication session at orbit 5356 (21:08:28 – 21:22:01) showed that such operation caused only delay of kinetic moment increasing. That was evidence of extremely great increasing of atmosphere density. At the same orbit the solar array was placed on angle α=65º. That allowed to delay increasing VZ. Between orbits 5358 and 5359 the spacecraft was out of radio visibility areas of ground control complexes. Following analysis of the reproduced telemetry showed that during this period atmosphere density had increased maximum. As a result at orbit 5360 (04:02:02 – 04:15:31, July 16, 2000) the fly-weel was on the verge of total charging on tangage axis: VZ was coming up to limited value and there was danger of loosing the spacecraft attitude. At this orbit the solar array was turned to angle α=90º. That helped to decrease aerodynamic torque and kinetic moment VZ on tangage axis. By the next orbit 5361 (05:39:58 – 05:49:49) kinetic moment had been decreased in 1,5 times.
Conducted by analysis group research showed that the top atmosphere density had decreased by that time. GOGU personal had to determine efficient scheme of the solar array turn to prevent from abrupt decreasing of kinetic moment and getting the fly-weel negative charged. To do that the solar array was turned to the angle α=77º during communication session at orbit 5362 (07:14:14 – 07:27:46). However this operation only delayed VZ increasing and at orbit 5364 value VZ was –0,6 N·m·s. Then the angle of the solar array inclination was decreased gradually. At orbit 5369 (18:29:56 – 18:36:22) kinetic moment VZ continued decreasing and got value –9,2 N·m·s, angle α=61º. At orbit 5370 (20:01:29 – 20:14:29) kinetic moment VZ got value –11,4 N·m·s. GOGU specialists decided to turn the solar array to the angle α=31º to stop such abrupt fly-weel approach to the verge of total charging. At orbit 5371 (21:38:17 – 21:51:31) kinetic moment VZ increased to value –3,6 N·m·s. Later on atmosphere density change became damped wavy. That didn’t caused any complications in ''Okean-O" control.
On the pictures 3,4 there are data which describe fly-weel kinetic moment VZ change and programs of the solar array turn during magnetic storms on March 31 – April 1, 2001 and on November 24-25, 2001.
- Conclusion
Using of the such ''Okean-O" control scheme showed its high effectiveness in condition of magnetic storms and their consequence which took place in 2000-2001. The scheme helped to support nominal ''Okean-O" work for two years. Within this time many requests of Russian, Ukraine and other users of science information were fulfilled: high quality space photos were received. They were used in search of gas and oil fields, in research of natural Earth resources, in farming, in solution of administrative tasks, in observation of ecological processes in the environment, in meteorology, in navigation, in fishery and other fields of socio-economic and science activity.
Along with this during ''Okean-O" control much information was received which could be used for atmosphere density change analysis and for analysis of magnetic storms influence on atmosphere density change. Originality of this information lies in that existing models of atmosphere density forecasting are rather inaccurate and need significant revision.
LITERATURE
- Rasygraev A.P. Base of spacecraft flight control. – Moscow, “Mashinostroenie”, 1990.
- Beletskiy V.V., Yanshin A.M. Aerodynamic power influence on artificial satellite spinning. – Kiev, “Naukova dumka”, 1984.
- Bazhinov I.K., Pochukaev V.N. Optimal planning of navigation measurements at space flight. – Moscow, “Mashinostroenie”, 1976.
- Korn G., Korn T. Mathematics reference book for workers and engineers. – Moscow, “Nauka”, 1978.
- ASCA in Safe Mode. ASCA Project Scientist: Dr. Nicholas E. White, , 301-286-8443, Web Representative: Eunice Eng.