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Control Aspects of Aerospace Plane Docking and Undocking with Moving Ekranoplane
Copyright © IFAC Automatic Control in Aerospace. Saint-Petersburg. Russia, 2004
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CONTROL ASPECTS OF AEROSPACE PLANE DOCKING AND UNDOCKlNG WITH MOVING EKRANOPLANE A.V. Nebylov', Y. Ohkami" and N. Tomita'"
• State University ofAerospace Instrumentation, St.-Petersburg, Russia email: [email protected] "Tsukuba Space Center, JAXA , Japan e-mail: ohkami.yoshiaki(Q).jaxa.jp ••• Musashi Institute of Technology, Tokyo, Japan em ail: [email protected]
Abstract: The concept of aerospace plane (ASP) horizontal launch and landing with the assist of large-scale ekranoplane is analyzed 1• Undocking of these two winged vehicles after ASP acceleration up to the necessary initial velocity for independent flight and their docking at the final stage of ASP descent for water landing are the critical points of the concept feasibility. The requirements to appropriate systems of navigation and motion control of both wing craft are presented. The structure of the integrated system of relative motion control is suggested. Principles of docking and undocking, requirements to the main onboard systems of both vehicles are considered. Copyright © 2004 IFAC Keywords: flight control, control loops, motion parameters, digital control, control accuracy.
mass of filled up taking-off ASP must be greater by an order than a mass of landing ASP. It forces to equip taking-off ASP with a big square wing, which is excessive at landing. That is why presently ASP vertical launch with the help of rocket carrier is reputed to be cheaper than the hypothetical horizontal launch.
1. INTRODUCTION
Despite the affrrmations that expendable space vehicles are considerably cheaper than reusable ones, the repeated use of separate stages or other elements of carrier rockets is introduced step by step. As a rule, it realizes due to wings installation on detached stages of space carrier that allows implementing of their controlled landing. As for the technologies of "Shuttle" and "Buran" approach and landing on the special airdrome, they have been successfully developed already 15-20 years ago.
However, the main trends in space technologies development attests that the idea of horizontal launch should be realized over the next few years. Application of efficient air-breathing engine may change the demands to mass of fuel and oxidant in APS tanks. New constructional materials can allow reducing the mass of the great hypersonic wing of starting ASP. The technology of carrier vehicle separation into stages may be refmed to apply at horizontal launch. Lastly, inherent horizontal launch opportunity to form the orbit with arbitrary inclination and other functional abilities that are not accessible or more "expensive" at the vertical launch
Sooner or later the wings will be apparently used not only for space vehicles horizontal landing, but for their horizontal launch also, i.e. the full-scale aerospace plane (ASP) will be constructed. Certainly, at use of up-to-date technologies, an initial I The work was partly supported by the Russian Foundation for Basic Research under the project 02-01-00033.
997
in required direction that allows to lower the requirements to the ASP wing area and its engines. The using of such a heavy ekranoplane for ASP assist at launch and landing permits to create an integrated transport system with a lot of advantages. Another option consists in ekranoplane use for ASP landing only, supposing its launch by means of any other facilities. In such a case the mass of ekranoplane may be decreased several times and resulted from its required seaworthiness.
became more and more necessary for advanced space technologies and launchings market. So, it is clear, that different variants of APS composition with horizontal launch and landing must be the subject of intent attention for researchers and designers. It is also clear, that in the near future the concept of doublestage or even three-stage APS configuration will be more viable than single-stage-to-orbit vehicle. Launch, midcourse flight and landing of any space vehicle are characterized with change of flight parameters values and conditions in great range. Velocity, air density, own mass, engines thrust and many other values are varied very essentially. For providing the demandable motion trajectory at such severe conditions it is necessary to use all the accessible tools of adaptation and structure alteration of space vehicle during the flight. The main way of vehicle structure alteration consists in its construction as integrated transport system with different set of elements (stages) at different phases offlight, including descent for landing.
What are the reasons to use the ekranoplane as an additional component in space transportation system that assists at ASP landing? Three main reasons may be pointed. I. The landing point can be chosen at any area of ocean that gives wide possibilities for ASP landing trajectory selection. 2. ASP can be supplied with simplifIed and lighted landing gear or has not gear at all when landing on ekranoplane, moving with the velocity equal to ASP one. Extremely large saving of mass will be provided if all equipment for docking is an accessory of ekranoplane. The mass of gear for landing on runway may be approximately 3% of empty mass or 25-30% of payload. So, the using of ekranoplane can permit to increase the payload of ASP on 30% and to decrease accordingly the specifIc cost of launch. 3. The cosmodrome with specially prepared runway is not required. That also decreases the cost of launch. For Japan such marine technology of ASP launch and landing has a particular importance as there are no any territory for new cosmodrome construction. The advantages of taking-off in the equatorial zone are also obvious.
The idea of heavy ekranoplane use at APS horizontal launch and landing was suggested by the authors in 1995 and is advanced continuously. The main attention in this paper is paid to the principles of organization of ASP and ekranoplane relative motion control at their undocking during the APS launch and docking during APS landing.
2. CONCEPT OF ASP LAUNCH AND LANDING WITH EKRANOPLANE ASSIST The capability of heavy ekranoplane to assist ASP at take-off and landing has been proved in (T omita and Ohkami, 1995; Nebylov, A.V., Denisov V.I., TrofImov U.V, 2000; Tomita, et al, 1996). Ekranoplane is a large marine winged craft capable to fly with the application of wing-in-ground (WIG) effect at a small altitude above sea surface. This altitude has to be approximately one tenth of the wing chord. Then the lift force increases and air drag decreases due to air compaction in the space between wing and supporting surface. In Russia several heavy ekranoplanes were built and successfully experienced. Among them are experimental great machine KM (540 ton), assault vehicle Orlyonok (140 ton) and missile carrier Lun (400 ton). The projects of ekranoplanes in several thousands tons are developed (Nebylov and Wilson, 2002; Nebylov and Tomita, 2003).
Nine variants of ASP landing with ekranoplane assist were analyzed (Nebylov and Tomita, 1998; Nebylov, A.V., Denisov V.I., TrofImov U.V, 2000). The variant of ASP landing to the deck of moving ekranoplane by the use of docking and mechanical mating is the most interesting and produces the most harsh demands to motion control systems accuracy and reliability. It is clear that the absolute and relative motion control facilities will be the key factor for such landing mode actualization.
3.
PECULIARITIES OF EKRANOPLANE AS CONTROLLED OBJECT
It is known that the longitudinal stability of ekranoplane in flight requires the special structural solutions in aerodynamic scheme to create the necessary control forces and moments to be applied. A special multi-channel automatic control system for stabilization and damping of heavy ekranoplane movement has to be considered for each definite aerodynamic configuration at the initial stage of design, the problem of high accmacy and reliability measurement of parameters of flight close to the rough sea surface has to be solved, as well (Nebylov, 200 I, 2002).
It is shown (Tomita, et al., 1999) that ekranoplane with its own mass of 1500 ton is able to launch ASP with starting mass more than 500 ton and landing mass of 60-70 ton. It can solve the problems of ASP transportation from the base to the launch point which is far from human settlements and advantageous for forming the required orbit parameters, ASP fueling directly before launch and providing it with the primary speed of Mach 0.6-0.65
998
elevated for approximately !Om and, probably, the whole ASP is shifted a bit back to locate the engine muzzle in the free space.
Specific conditions of ekranoplane and ASP mutual motion at docking make it impossible to use in this transport system ekranoplane of the most known plane configuration or ekranoplane "Carrying Wing + Tail Assembly" due to its high tail which bars the way for approach.
Such initial elevation of ASP could be provided by rather powerful mechanism, which applies lifting force at the area of ASP center of gravity. It may be the extensible hydraulic column that could produce the force in 5000 kN and to be rather stable against longitudinal aerodynamical force applied to ASP connected with ekranoplane motion. Practically this column has to carry the ASP weight minus aerodynamic lifting force of ASP wing. The main part of starting ASP weight is the weight of fuel. Hence it appears that ASP has to take aboard the significant part of fuel shortly before launch, when the lifting force of ASP wing increases due to the maximum velocity of ekranoplane. This requirement is in accordance also with another demand - not to keep fuel in the tanks of ASP during the long time, as ASP could not be equipped with such perfect cryogenic facilities as accessible aboard ekranoplane.
Fig.I . Ekranoplane of "Combined Wing" configuration with docked ASP.
Another important requirement to the undocking mechanism consists in minimal disturbed forces and moments applied to ASP at its disconnection with ekranoplane. The ASP weight must be balanced by its wing lifting force. Any turning moments in the longitudinal plane must be canceled out by the right deflection angles of the elevator and flaps. That is reason for the ASP attitude stabilization system to be switched on before the launch. ASP engine thrust has to approximately balance a drag force. So, ASP engine has to be switched on also before ASP disconnection with ekranoplane.
Therefore the tail assembly of any fonn located near to a longitudinal axis of ekranoplane is inadmissible, and any consoles are possible only under their sufficient displacement from this axis in a cross direction. All central part of ekranoplane deck should be practically flat for nonnal accommodation and movement of ASP. So, the configmations of «combined wing» ekranoplane-catamaran are preferable (Nebylov, Ohkami and Tomita, 1999). The ekranoplane of with ASP displaced on its deck is shown in Fig.I. The control system of ekranoplane should ensure its given trajectory and improve dynamic properties. Nonlinear character of interrelations between separate channels of altitude, pitch, velocity, roll and yaw of this system, intensive wind and wave disturbances, the necessity of a special mode of turning away from surface obstacles and many other features give specificity to decision of the task of system synthesis, though in the task statement the ordinary for the theory of automatic control categories are used. Great inertia of heavy ekranoplane-catamaran in course maneuvering forces to put it on the given line of a linear motion in advance and actively operate only by absolute velocity at approach and docking with ASP.
Taking into account the listing above requirements, the arrangement of mechanical mating elements for connection and disconnection of ASP with ekranoplane can be drawn out as it shown in Fig.2. The central extensible column CC is the main facility at ASP launching procedure. It is buried deeply into ekranoplane body during ASP transportation to the launch area, but arises at maximal height of around IOm before ASP undocking. This column assign consists in applying the initial lifting force to ASP before the wing could carry the necessary load, and in opposing the ASP aerodynamic drag before the engine switch on. It is not necessary for CC column to manage the ASP pitch. Directly before undocking this function will belong to ASP flight control system. But for preset ASP the initial angular position and for partly help CC column in load carrying two or three another connecting elements will be used. For example, it could be a nose column NC and two tail columns TCl and TC2. NC is located on the central line in a forward part of the Ekranoplane deck. Tail columns (TC I and TC2) are located symmetrically to the right and left of the central line in a stem part of the Ekranoplane deck. The points of an arrangement of columns NC, TC 1 and TC2 from a triangle similar to the one used in
4. ARRANGEMENT AND FUNCTIONING OF MECHANICAL MATING ELEMENTS The initial position of fueled ASP on the ekranoplane deck has to be practically horizontal and close to the deck to reduce the aerodynamical drag during ekranoplane take-off and cruising flight to the area of ASP launch. At the moment of ASP engine switching on the ASP must receive around 15 0 attack angle (Nebylov and Tomita, 1998) and some space between the engine muzzle and the ekranoplane deck. That means that ASP center of gravity is 999
I. Choice of a point and time of landing in view of an opportunity of ekranoplane to arrive in the specified point in time, and the calculation of the trajectory of ASP descanting. 2. Fulfillment of standard operations of ASP entrance in atmosphere and braking up to subsonic speed. 3. Coordinated control of ASP and ekranoplane absolute motion with the purpose of maintenance of their mutual close parallel motion with a difference of altitudes about 200m and mutual mismatch in horizontal plane no more than lOOm. 4. Relative motion control system loops closure, and reduction of mutual mismatch of two vehicles in horizontal plane up to several meters and further - up to 20=101, reduction of difference in their flight altitudes up to 3-5 m at the expense of ASP descending. 5. Engaging the mechanism of docking, exact positioning of mating elements by a special quickresponse automatic system, the mating (partial or complete), attracting of ASP to ekranoplane. 6. The completion of ASP docking with ekranoplane, centering of ASP on the landing deck of ekranoplane, blocking of mating elements, ekranoplane returning to the base.
constructing of the three-point undercarriage for typical aircraft. These columns may be used not only at ASP launch, but at landing also. That is why these columns must have high speed of response, but are designed for rather small longitudinal and vertical loads up to 200kN.
At a stage of ASP leaving the orbit, ASP exact angular orientation with errors of not more than several angular seconds is important for correct fonnation of a brake pulse, that shows the appropriate requirements to gyro systems and astrotrackers. At a stage of aerodynamic braking the inertial system should keep the correct infonnation on angular orientation and supervise a trajectory of motion, not admitting accumulation of too large errors. After ending of this stage the trajectories of ASP and ekranoplane approach should be synthesized in view of estimations of their actual positions with GPS use. The noiseproof radio channel for data exchange between ASP and ekranoplane, uniting their control systems in an integrated complex, is necessary.
Fig. 2. Arrangement of mating elements In difference from all other columns, column NC can move in a horizontal plane, to both of lateral direction and longitudinal direction in a range of 35m. The movement is provided by a special fastacting automatic control system, using signals of ASP relative motion measuring unit.
On a stage of ASP and ekranoplane approach the high accuracy of coordinates defmition (at a level 20=50-100 m) for both flying craft in Earth frame and body frame is necessary. The main contribution to its maintenance should give GPS.
The construction of all the columns, their arrangement, the control laws for their motion and interaction of all elements of ASP and ekranoplane control complex at undocking and docking must be carefully researched and optimized. The main way of such investigation is mathematical mode ling and simulation, and this work is started now.
At a fmal stage of ASP and ekranoplane docking the high accuracy of relative motion control holding the difference of linear coordinates within the limits of shares of meter and difference of speeds - within the limits of shares of mlsec is required. Besides, in this case it is necessary a precision (within the limits of 20") stabilization of pitch, roll and yaw. On the stage of direct approach (before contact) movement of both vehicles should be close to synchronous planeparallel. At low power of the landing engine, it is possible to ensure such a mode only within the limits of a short time interval, in this connection the mating system should be rather high-speed.
5. REQUIREMENTS TO AUTOMATIC SYSTEMS AT ASP DOCKING WITH EKRANOPLANE The landing of ASP may include six stages, each of them should be supplied with the appropriate opportunities of navigation and motion control.
\000
According to the fulfilled researches, the most suitable method of reception the information on parameters of linear and angular relative motion of two wing craft at approach and docking is the use of digital television optical navigating system. It may include three or four cameras of infra-red range, placed on a deck of ekranoplane. They must control overhead hemisphere from various points of ekranoplane deck. Such a natural property of the alighting ASP as high temperature favors the functioning of infra-red cameras, which will ensure contrast ASP image irrespective of weather and daylight. The dominate of solar flare may be abated by appropriate filters . At a fmal stage of approach when ASP relative altitude become equal 5m the errors of relative motion parameters measuring will be no more than 2a= IDcm in horizontal plane, 2cr= IDcm in altitude and 2cr=20' in angles.
7. MOTION CONTROL AT DOCKING A generalized scheme of automatic control multidimension digital system for mutual motion control at docking is shown in Fig.3. As it follows from the diagram, the docking process of ASP and ekranoplane must be operated under motion control complex which involves closed control loops for ASP and ekranoplane absolute motion with controlled values matrices AASP and AEKR consequently, relative motion closed control loop with the controlled value matrices AASP - AEKR and an additional open loop channel for local shifting the docking element along and thwart landing deck with output coordinates matrix AM. The interaction of these four interconnected multidimensional loops and control algorithms optimization is a complicated problem of analysis and mode ling. The required landing trajectory of ASP is determined by synthesizer priory and described by given functional matrix A (t) . The navigation system of ASP generates an estimation of an actual motion trajectory AASP (t). The residual A (t) - AASP (t) is used in control law. Optimization allows to reduce a norm of the matrix A (t) - AASP (t) and to provide the high accuracy in holding the required landing trajectory. At the final stage of approach the errors of relative positioning may be within 2-3m, and the local positioning of matting elements (especially, nose element) could reduce the errors to 30 cm.
6. ANALYSIS OF THE POSSIBLE PROTOTYPES The landing system of ASP «Space Shuttle» for long term of operation has proved the high efficiency, however it is not completely automatic, and the large sizes of a special landing strip used at landing admit rather significant errors of control. Nevertheless, this experience is extremely important for forming the concept of landing on ekranoplane. The automatic landing system of ASP «Buran», probably, is capable to ensure higher accuracy of landing on stationary airdrome on account of more advanced means of forming the controlling radio field. However, its numerous landing beacons and other special means of radionavigation must be placed in large territory and cannot belong to one ekranoplane.
The ekranoplane absolute motion control system has to ensure the required trajectory of its flight to the point of ASP landing, approach to this point from given direction at required time, and the capture of ASP by the shot-range optic navigation system. The Detaj"
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The special integrated system of navigation and motion control is necessary, the main position gauges of which should be GPS receivers at stages of approach and rapprochement and precise microwave or optic systems of local navigation at the stage of docking directly. The experience of the development of modem landing systems for deck aircraft seems to be very useful.
Syn&hesizer of required trajectories
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:
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:
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I
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The important experience of construction of an onboard control complex of ASP has been gained in Japan (Motoda, et al., 1998) during the experiment ALFLEX (Automatic Landing Flight Experiment). Completely automatic landing system, using the GPS receiver, inertial module, Air Data System, microwave system and radioaltimeter, in all flying tests has demonstrated required accuracy of control. at landing to standard airdrome.
ASP
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Il
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Fig.3 . The scheme of motion control complex 1()() 1
ekranoplane altitude at ASP landing must be strictly stabilized. Then the approaching of ASP and ekranoplane in vertical plane and lateral shift compensation will occur with a great influence of ASP and their approach in longitudinal plane can be corrected by ekranoplane speed control. At approach it is necessary to combine control on errors with control on disturbances. The ASP and ekranoplane relative motion control system becomes closed after their approach to small distance when infra-red video short-range navigation system that gives the high precision estimation of matrix elements A ASP - AEKR can operate. This allows to improve considerably the accuracy of control errors measurements and to decrease that errors with no substantial control laws structure replace. The ASP lateral deflections from ekranoplane will be suppressed generally by ASP ailerons and rudder at stable heading and minimal yaw; flaps and rudder of ASP will provide the required motion altitude and pitch angle correction at the fixed altitude of ekranoplane, but ekranoplane will be able to make up leeway in longitudinal plane by means of its speed control. Notice, that the most unfavorable external disturbance for a loop of lateral deflections depression would be a pulse rush of wind in a cross head direction. But even in this case the error will be acceptable due to the following reasons: - high landing velocity of ASP wiJI make this impulse short and its influence will be decreased; - high landing velocity of ASP wiJI increase the effectiveness of its aerodynamic control elements essentially; - a pulse of wind will influence both ASP and ekranoplane that decrease their relative shift. At the fmal stage of docking additional control loop of mating element will be switched on. It is the open loop channel for control of local shift of the mating element It must process only high-frequency components of control signals increasing operating speed of entire system to significantly decrease control errors corresponding to matrix elements A.w{t}-AEKJ!..t}-'A.J..t). The optimization of all control loops engaged at docking has to be fulfilled on criteria of minirnizatjon of maximum control errors (Nebylov, 1998).
8.
CONCLUSION
I. ASP with ekranoplane assist at horizontal takeoff could be competitive with vertical space launch system from aggregate functional, technological and life cycle cost viewpoint. 2. Ekranoplane with perfect control system can realize the idea of docking the stage that would allow ASP landing without gear. 3. The accurate and reliable control of relative motion at undocking and docking is the key problem
1002
of ASP-Ekranoplane integrated space system feasibility. 4. The analysis of the requirements to control systems and their comparison with the existing nowadays prototypes allow to predict an opportunity of all necessary onboard control systems creation in the near future. REFERENCES Motoda, T., et al. (1998). ALFLEX Flight simulation analysis and flight testing. 36'h Aerospace Sciences Meeting & Exhibit. Reno, USA, 1998. Nebylov, AV. (1998). Ensuring of control accuracy. Nauka, Moscow, in Russian with abstract in English. Nebylov AV. (2001). WIG-Flight Automatic Control Principles, Systems and Application Advantages. 15th IFAC Symposium on Automatic Control in Aerospace. Forli, Italy, pp. 542-547. Nebylov A.V. (2002). Controlled Flight Close to Rough Sea - Strategies and Means. XV IF AC World Congress. Barcelona. Nebylov, AV. and N. Tomita (1998). Control Ekranoplane designing experience revision in view of its use for aerospace plane assist at launch and landing. Proceeding of International Workshop «WISE up to ekranoplane GEMs». The Institute of Marine Engineers (Sydney Branch). Sydney, Australia, pp. 191-199. Nebylov, A.V., Denisov V.I., Trofunov U.V (2000). Commercial Approach to the problem of Russian Ekranoplanes Development.. III International Conference on Ground-Effect Machines. The Royal Society of Marine Engineers, Russian Branch, Saint-Petersburg,. pp. 99-111 . Nebylov, A.V. and P. Wilson (2002). EkranoplaneControlled Flight close to Surface. Monograph. WIT-Press, UK, 320 pp.+CD. Nebylov AV., N.Tomita. (1998). Control aspects of aerospace plane docking with ekranoplanes for water landing. 14th IFAC Symposium on Automatic Control in Aerospace. Seoul National University, Korea, pp. 389-394. Tomita, N. and Y. Ohkami (1995). A study on the application of take-off assist for a SSTO with rocket propUlsion IAF-95- V. 3.06. Tomita, N., et al. (1996). Feasibility study of a rocket-powered HITL-SSTO with ekranoplane as takeoff assist". 7th AIAA International Aerospace Planes and HypersoniC Technologies and Systems Conference. Norfolk, VA, USA, AIAA 96-4517. Tomita, N., et al. (1999). Performance and Technological Feasibility of Rocket Powered HTHL-SSTO with Take-off Assist. Acta Astronautica, 45, No.IO, pp. 629-637. Tomita, N., A.V. Nebylov, V.V. Sokolov and Y. Ohkami (1996). Performance and technological feasibility study of rocked-powered HITLSSTO with takeoff assist. 47th International Astronautical Congress. Beijing, IAF 96-V.3.05.
ELSEVIER
IFAC PUBLICATIONS www.clsevier.comllocatelifac
CONTROL ASPECTS OF AEROSPACE PLANE DOCKING AND UNDOCKlNG WITH MOVING EKRANOPLANE A.V. Nebylov', Y. Ohkami" and N. Tomita'"
• State University ofAerospace Instrumentation, St.-Petersburg, Russia email: [email protected] "Tsukuba Space Center, JAXA , Japan e-mail: ohkami.yoshiaki(Q).jaxa.jp ••• Musashi Institute of Technology, Tokyo, Japan em ail: [email protected]
Abstract: The concept of aerospace plane (ASP) horizontal launch and landing with the assist of large-scale ekranoplane is analyzed 1• Undocking of these two winged vehicles after ASP acceleration up to the necessary initial velocity for independent flight and their docking at the final stage of ASP descent for water landing are the critical points of the concept feasibility. The requirements to appropriate systems of navigation and motion control of both wing craft are presented. The structure of the integrated system of relative motion control is suggested. Principles of docking and undocking, requirements to the main onboard systems of both vehicles are considered. Copyright © 2004 IFAC Keywords: flight control, control loops, motion parameters, digital control, control accuracy.
mass of filled up taking-off ASP must be greater by an order than a mass of landing ASP. It forces to equip taking-off ASP with a big square wing, which is excessive at landing. That is why presently ASP vertical launch with the help of rocket carrier is reputed to be cheaper than the hypothetical horizontal launch.
1. INTRODUCTION
Despite the affrrmations that expendable space vehicles are considerably cheaper than reusable ones, the repeated use of separate stages or other elements of carrier rockets is introduced step by step. As a rule, it realizes due to wings installation on detached stages of space carrier that allows implementing of their controlled landing. As for the technologies of "Shuttle" and "Buran" approach and landing on the special airdrome, they have been successfully developed already 15-20 years ago.
However, the main trends in space technologies development attests that the idea of horizontal launch should be realized over the next few years. Application of efficient air-breathing engine may change the demands to mass of fuel and oxidant in APS tanks. New constructional materials can allow reducing the mass of the great hypersonic wing of starting ASP. The technology of carrier vehicle separation into stages may be refmed to apply at horizontal launch. Lastly, inherent horizontal launch opportunity to form the orbit with arbitrary inclination and other functional abilities that are not accessible or more "expensive" at the vertical launch
Sooner or later the wings will be apparently used not only for space vehicles horizontal landing, but for their horizontal launch also, i.e. the full-scale aerospace plane (ASP) will be constructed. Certainly, at use of up-to-date technologies, an initial I The work was partly supported by the Russian Foundation for Basic Research under the project 02-01-00033.
997
in required direction that allows to lower the requirements to the ASP wing area and its engines. The using of such a heavy ekranoplane for ASP assist at launch and landing permits to create an integrated transport system with a lot of advantages. Another option consists in ekranoplane use for ASP landing only, supposing its launch by means of any other facilities. In such a case the mass of ekranoplane may be decreased several times and resulted from its required seaworthiness.
became more and more necessary for advanced space technologies and launchings market. So, it is clear, that different variants of APS composition with horizontal launch and landing must be the subject of intent attention for researchers and designers. It is also clear, that in the near future the concept of doublestage or even three-stage APS configuration will be more viable than single-stage-to-orbit vehicle. Launch, midcourse flight and landing of any space vehicle are characterized with change of flight parameters values and conditions in great range. Velocity, air density, own mass, engines thrust and many other values are varied very essentially. For providing the demandable motion trajectory at such severe conditions it is necessary to use all the accessible tools of adaptation and structure alteration of space vehicle during the flight. The main way of vehicle structure alteration consists in its construction as integrated transport system with different set of elements (stages) at different phases offlight, including descent for landing.
What are the reasons to use the ekranoplane as an additional component in space transportation system that assists at ASP landing? Three main reasons may be pointed. I. The landing point can be chosen at any area of ocean that gives wide possibilities for ASP landing trajectory selection. 2. ASP can be supplied with simplifIed and lighted landing gear or has not gear at all when landing on ekranoplane, moving with the velocity equal to ASP one. Extremely large saving of mass will be provided if all equipment for docking is an accessory of ekranoplane. The mass of gear for landing on runway may be approximately 3% of empty mass or 25-30% of payload. So, the using of ekranoplane can permit to increase the payload of ASP on 30% and to decrease accordingly the specifIc cost of launch. 3. The cosmodrome with specially prepared runway is not required. That also decreases the cost of launch. For Japan such marine technology of ASP launch and landing has a particular importance as there are no any territory for new cosmodrome construction. The advantages of taking-off in the equatorial zone are also obvious.
The idea of heavy ekranoplane use at APS horizontal launch and landing was suggested by the authors in 1995 and is advanced continuously. The main attention in this paper is paid to the principles of organization of ASP and ekranoplane relative motion control at their undocking during the APS launch and docking during APS landing.
2. CONCEPT OF ASP LAUNCH AND LANDING WITH EKRANOPLANE ASSIST The capability of heavy ekranoplane to assist ASP at take-off and landing has been proved in (T omita and Ohkami, 1995; Nebylov, A.V., Denisov V.I., TrofImov U.V, 2000; Tomita, et al, 1996). Ekranoplane is a large marine winged craft capable to fly with the application of wing-in-ground (WIG) effect at a small altitude above sea surface. This altitude has to be approximately one tenth of the wing chord. Then the lift force increases and air drag decreases due to air compaction in the space between wing and supporting surface. In Russia several heavy ekranoplanes were built and successfully experienced. Among them are experimental great machine KM (540 ton), assault vehicle Orlyonok (140 ton) and missile carrier Lun (400 ton). The projects of ekranoplanes in several thousands tons are developed (Nebylov and Wilson, 2002; Nebylov and Tomita, 2003).
Nine variants of ASP landing with ekranoplane assist were analyzed (Nebylov and Tomita, 1998; Nebylov, A.V., Denisov V.I., TrofImov U.V, 2000). The variant of ASP landing to the deck of moving ekranoplane by the use of docking and mechanical mating is the most interesting and produces the most harsh demands to motion control systems accuracy and reliability. It is clear that the absolute and relative motion control facilities will be the key factor for such landing mode actualization.
3.
PECULIARITIES OF EKRANOPLANE AS CONTROLLED OBJECT
It is known that the longitudinal stability of ekranoplane in flight requires the special structural solutions in aerodynamic scheme to create the necessary control forces and moments to be applied. A special multi-channel automatic control system for stabilization and damping of heavy ekranoplane movement has to be considered for each definite aerodynamic configuration at the initial stage of design, the problem of high accmacy and reliability measurement of parameters of flight close to the rough sea surface has to be solved, as well (Nebylov, 200 I, 2002).
It is shown (Tomita, et al., 1999) that ekranoplane with its own mass of 1500 ton is able to launch ASP with starting mass more than 500 ton and landing mass of 60-70 ton. It can solve the problems of ASP transportation from the base to the launch point which is far from human settlements and advantageous for forming the required orbit parameters, ASP fueling directly before launch and providing it with the primary speed of Mach 0.6-0.65
998
elevated for approximately !Om and, probably, the whole ASP is shifted a bit back to locate the engine muzzle in the free space.
Specific conditions of ekranoplane and ASP mutual motion at docking make it impossible to use in this transport system ekranoplane of the most known plane configuration or ekranoplane "Carrying Wing + Tail Assembly" due to its high tail which bars the way for approach.
Such initial elevation of ASP could be provided by rather powerful mechanism, which applies lifting force at the area of ASP center of gravity. It may be the extensible hydraulic column that could produce the force in 5000 kN and to be rather stable against longitudinal aerodynamical force applied to ASP connected with ekranoplane motion. Practically this column has to carry the ASP weight minus aerodynamic lifting force of ASP wing. The main part of starting ASP weight is the weight of fuel. Hence it appears that ASP has to take aboard the significant part of fuel shortly before launch, when the lifting force of ASP wing increases due to the maximum velocity of ekranoplane. This requirement is in accordance also with another demand - not to keep fuel in the tanks of ASP during the long time, as ASP could not be equipped with such perfect cryogenic facilities as accessible aboard ekranoplane.
Fig.I . Ekranoplane of "Combined Wing" configuration with docked ASP.
Another important requirement to the undocking mechanism consists in minimal disturbed forces and moments applied to ASP at its disconnection with ekranoplane. The ASP weight must be balanced by its wing lifting force. Any turning moments in the longitudinal plane must be canceled out by the right deflection angles of the elevator and flaps. That is reason for the ASP attitude stabilization system to be switched on before the launch. ASP engine thrust has to approximately balance a drag force. So, ASP engine has to be switched on also before ASP disconnection with ekranoplane.
Therefore the tail assembly of any fonn located near to a longitudinal axis of ekranoplane is inadmissible, and any consoles are possible only under their sufficient displacement from this axis in a cross direction. All central part of ekranoplane deck should be practically flat for nonnal accommodation and movement of ASP. So, the configmations of «combined wing» ekranoplane-catamaran are preferable (Nebylov, Ohkami and Tomita, 1999). The ekranoplane of with ASP displaced on its deck is shown in Fig.I. The control system of ekranoplane should ensure its given trajectory and improve dynamic properties. Nonlinear character of interrelations between separate channels of altitude, pitch, velocity, roll and yaw of this system, intensive wind and wave disturbances, the necessity of a special mode of turning away from surface obstacles and many other features give specificity to decision of the task of system synthesis, though in the task statement the ordinary for the theory of automatic control categories are used. Great inertia of heavy ekranoplane-catamaran in course maneuvering forces to put it on the given line of a linear motion in advance and actively operate only by absolute velocity at approach and docking with ASP.
Taking into account the listing above requirements, the arrangement of mechanical mating elements for connection and disconnection of ASP with ekranoplane can be drawn out as it shown in Fig.2. The central extensible column CC is the main facility at ASP launching procedure. It is buried deeply into ekranoplane body during ASP transportation to the launch area, but arises at maximal height of around IOm before ASP undocking. This column assign consists in applying the initial lifting force to ASP before the wing could carry the necessary load, and in opposing the ASP aerodynamic drag before the engine switch on. It is not necessary for CC column to manage the ASP pitch. Directly before undocking this function will belong to ASP flight control system. But for preset ASP the initial angular position and for partly help CC column in load carrying two or three another connecting elements will be used. For example, it could be a nose column NC and two tail columns TCl and TC2. NC is located on the central line in a forward part of the Ekranoplane deck. Tail columns (TC I and TC2) are located symmetrically to the right and left of the central line in a stem part of the Ekranoplane deck. The points of an arrangement of columns NC, TC 1 and TC2 from a triangle similar to the one used in
4. ARRANGEMENT AND FUNCTIONING OF MECHANICAL MATING ELEMENTS The initial position of fueled ASP on the ekranoplane deck has to be practically horizontal and close to the deck to reduce the aerodynamical drag during ekranoplane take-off and cruising flight to the area of ASP launch. At the moment of ASP engine switching on the ASP must receive around 15 0 attack angle (Nebylov and Tomita, 1998) and some space between the engine muzzle and the ekranoplane deck. That means that ASP center of gravity is 999
I. Choice of a point and time of landing in view of an opportunity of ekranoplane to arrive in the specified point in time, and the calculation of the trajectory of ASP descanting. 2. Fulfillment of standard operations of ASP entrance in atmosphere and braking up to subsonic speed. 3. Coordinated control of ASP and ekranoplane absolute motion with the purpose of maintenance of their mutual close parallel motion with a difference of altitudes about 200m and mutual mismatch in horizontal plane no more than lOOm. 4. Relative motion control system loops closure, and reduction of mutual mismatch of two vehicles in horizontal plane up to several meters and further - up to 20=101, reduction of difference in their flight altitudes up to 3-5 m at the expense of ASP descending. 5. Engaging the mechanism of docking, exact positioning of mating elements by a special quickresponse automatic system, the mating (partial or complete), attracting of ASP to ekranoplane. 6. The completion of ASP docking with ekranoplane, centering of ASP on the landing deck of ekranoplane, blocking of mating elements, ekranoplane returning to the base.
constructing of the three-point undercarriage for typical aircraft. These columns may be used not only at ASP launch, but at landing also. That is why these columns must have high speed of response, but are designed for rather small longitudinal and vertical loads up to 200kN.
At a stage of ASP leaving the orbit, ASP exact angular orientation with errors of not more than several angular seconds is important for correct fonnation of a brake pulse, that shows the appropriate requirements to gyro systems and astrotrackers. At a stage of aerodynamic braking the inertial system should keep the correct infonnation on angular orientation and supervise a trajectory of motion, not admitting accumulation of too large errors. After ending of this stage the trajectories of ASP and ekranoplane approach should be synthesized in view of estimations of their actual positions with GPS use. The noiseproof radio channel for data exchange between ASP and ekranoplane, uniting their control systems in an integrated complex, is necessary.
Fig. 2. Arrangement of mating elements In difference from all other columns, column NC can move in a horizontal plane, to both of lateral direction and longitudinal direction in a range of 35m. The movement is provided by a special fastacting automatic control system, using signals of ASP relative motion measuring unit.
On a stage of ASP and ekranoplane approach the high accuracy of coordinates defmition (at a level 20=50-100 m) for both flying craft in Earth frame and body frame is necessary. The main contribution to its maintenance should give GPS.
The construction of all the columns, their arrangement, the control laws for their motion and interaction of all elements of ASP and ekranoplane control complex at undocking and docking must be carefully researched and optimized. The main way of such investigation is mathematical mode ling and simulation, and this work is started now.
At a fmal stage of ASP and ekranoplane docking the high accuracy of relative motion control holding the difference of linear coordinates within the limits of shares of meter and difference of speeds - within the limits of shares of mlsec is required. Besides, in this case it is necessary a precision (within the limits of 20") stabilization of pitch, roll and yaw. On the stage of direct approach (before contact) movement of both vehicles should be close to synchronous planeparallel. At low power of the landing engine, it is possible to ensure such a mode only within the limits of a short time interval, in this connection the mating system should be rather high-speed.
5. REQUIREMENTS TO AUTOMATIC SYSTEMS AT ASP DOCKING WITH EKRANOPLANE The landing of ASP may include six stages, each of them should be supplied with the appropriate opportunities of navigation and motion control.
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According to the fulfilled researches, the most suitable method of reception the information on parameters of linear and angular relative motion of two wing craft at approach and docking is the use of digital television optical navigating system. It may include three or four cameras of infra-red range, placed on a deck of ekranoplane. They must control overhead hemisphere from various points of ekranoplane deck. Such a natural property of the alighting ASP as high temperature favors the functioning of infra-red cameras, which will ensure contrast ASP image irrespective of weather and daylight. The dominate of solar flare may be abated by appropriate filters . At a fmal stage of approach when ASP relative altitude become equal 5m the errors of relative motion parameters measuring will be no more than 2a= IDcm in horizontal plane, 2cr= IDcm in altitude and 2cr=20' in angles.
7. MOTION CONTROL AT DOCKING A generalized scheme of automatic control multidimension digital system for mutual motion control at docking is shown in Fig.3. As it follows from the diagram, the docking process of ASP and ekranoplane must be operated under motion control complex which involves closed control loops for ASP and ekranoplane absolute motion with controlled values matrices AASP and AEKR consequently, relative motion closed control loop with the controlled value matrices AASP - AEKR and an additional open loop channel for local shifting the docking element along and thwart landing deck with output coordinates matrix AM. The interaction of these four interconnected multidimensional loops and control algorithms optimization is a complicated problem of analysis and mode ling. The required landing trajectory of ASP is determined by synthesizer priory and described by given functional matrix A (t) . The navigation system of ASP generates an estimation of an actual motion trajectory AASP (t). The residual A (t) - AASP (t) is used in control law. Optimization allows to reduce a norm of the matrix A (t) - AASP (t) and to provide the high accuracy in holding the required landing trajectory. At the final stage of approach the errors of relative positioning may be within 2-3m, and the local positioning of matting elements (especially, nose element) could reduce the errors to 30 cm.
6. ANALYSIS OF THE POSSIBLE PROTOTYPES The landing system of ASP «Space Shuttle» for long term of operation has proved the high efficiency, however it is not completely automatic, and the large sizes of a special landing strip used at landing admit rather significant errors of control. Nevertheless, this experience is extremely important for forming the concept of landing on ekranoplane. The automatic landing system of ASP «Buran», probably, is capable to ensure higher accuracy of landing on stationary airdrome on account of more advanced means of forming the controlling radio field. However, its numerous landing beacons and other special means of radionavigation must be placed in large territory and cannot belong to one ekranoplane.
The ekranoplane absolute motion control system has to ensure the required trajectory of its flight to the point of ASP landing, approach to this point from given direction at required time, and the capture of ASP by the shot-range optic navigation system. The Detaj"
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The special integrated system of navigation and motion control is necessary, the main position gauges of which should be GPS receivers at stages of approach and rapprochement and precise microwave or optic systems of local navigation at the stage of docking directly. The experience of the development of modem landing systems for deck aircraft seems to be very useful.
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The important experience of construction of an onboard control complex of ASP has been gained in Japan (Motoda, et al., 1998) during the experiment ALFLEX (Automatic Landing Flight Experiment). Completely automatic landing system, using the GPS receiver, inertial module, Air Data System, microwave system and radioaltimeter, in all flying tests has demonstrated required accuracy of control. at landing to standard airdrome.
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ekranoplane altitude at ASP landing must be strictly stabilized. Then the approaching of ASP and ekranoplane in vertical plane and lateral shift compensation will occur with a great influence of ASP and their approach in longitudinal plane can be corrected by ekranoplane speed control. At approach it is necessary to combine control on errors with control on disturbances. The ASP and ekranoplane relative motion control system becomes closed after their approach to small distance when infra-red video short-range navigation system that gives the high precision estimation of matrix elements A ASP - AEKR can operate. This allows to improve considerably the accuracy of control errors measurements and to decrease that errors with no substantial control laws structure replace. The ASP lateral deflections from ekranoplane will be suppressed generally by ASP ailerons and rudder at stable heading and minimal yaw; flaps and rudder of ASP will provide the required motion altitude and pitch angle correction at the fixed altitude of ekranoplane, but ekranoplane will be able to make up leeway in longitudinal plane by means of its speed control. Notice, that the most unfavorable external disturbance for a loop of lateral deflections depression would be a pulse rush of wind in a cross head direction. But even in this case the error will be acceptable due to the following reasons: - high landing velocity of ASP wiJI make this impulse short and its influence will be decreased; - high landing velocity of ASP wiJI increase the effectiveness of its aerodynamic control elements essentially; - a pulse of wind will influence both ASP and ekranoplane that decrease their relative shift. At the fmal stage of docking additional control loop of mating element will be switched on. It is the open loop channel for control of local shift of the mating element It must process only high-frequency components of control signals increasing operating speed of entire system to significantly decrease control errors corresponding to matrix elements A.w{t}-AEKJ!..t}-'A.J..t). The optimization of all control loops engaged at docking has to be fulfilled on criteria of minirnizatjon of maximum control errors (Nebylov, 1998).
8.
CONCLUSION
I. ASP with ekranoplane assist at horizontal takeoff could be competitive with vertical space launch system from aggregate functional, technological and life cycle cost viewpoint. 2. Ekranoplane with perfect control system can realize the idea of docking the stage that would allow ASP landing without gear. 3. The accurate and reliable control of relative motion at undocking and docking is the key problem
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of ASP-Ekranoplane integrated space system feasibility. 4. The analysis of the requirements to control systems and their comparison with the existing nowadays prototypes allow to predict an opportunity of all necessary onboard control systems creation in the near future. REFERENCES Motoda, T., et al. (1998). ALFLEX Flight simulation analysis and flight testing. 36'h Aerospace Sciences Meeting & Exhibit. Reno, USA, 1998. Nebylov, AV. (1998). Ensuring of control accuracy. Nauka, Moscow, in Russian with abstract in English. Nebylov AV. (2001). WIG-Flight Automatic Control Principles, Systems and Application Advantages. 15th IFAC Symposium on Automatic Control in Aerospace. Forli, Italy, pp. 542-547. Nebylov A.V. (2002). Controlled Flight Close to Rough Sea - Strategies and Means. XV IF AC World Congress. Barcelona. Nebylov, AV. and N. Tomita (1998). Control Ekranoplane designing experience revision in view of its use for aerospace plane assist at launch and landing. Proceeding of International Workshop «WISE up to ekranoplane GEMs». The Institute of Marine Engineers (Sydney Branch). Sydney, Australia, pp. 191-199. Nebylov, A.V., Denisov V.I., Trofunov U.V (2000). Commercial Approach to the problem of Russian Ekranoplanes Development.. III International Conference on Ground-Effect Machines. The Royal Society of Marine Engineers, Russian Branch, Saint-Petersburg,. pp. 99-111 . Nebylov, A.V. and P. Wilson (2002). EkranoplaneControlled Flight close to Surface. Monograph. WIT-Press, UK, 320 pp.+CD. Nebylov AV., N.Tomita. (1998). Control aspects of aerospace plane docking with ekranoplanes for water landing. 14th IFAC Symposium on Automatic Control in Aerospace. Seoul National University, Korea, pp. 389-394. Tomita, N. and Y. Ohkami (1995). A study on the application of take-off assist for a SSTO with rocket propUlsion IAF-95- V. 3.06. Tomita, N., et al. (1996). Feasibility study of a rocket-powered HITL-SSTO with ekranoplane as takeoff assist". 7th AIAA International Aerospace Planes and HypersoniC Technologies and Systems Conference. Norfolk, VA, USA, AIAA 96-4517. Tomita, N., et al. (1999). Performance and Technological Feasibility of Rocket Powered HTHL-SSTO with Take-off Assist. Acta Astronautica, 45, No.IO, pp. 629-637. Tomita, N., A.V. Nebylov, V.V. Sokolov and Y. Ohkami (1996). Performance and technological feasibility study of rocked-powered HITLSSTO with takeoff assist. 47th International Astronautical Congress. Beijing, IAF 96-V.3.05.