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Control object ─ small interorbital assembly (SIA) ─ is a maneuvering spacecraft provided by cruise engines, jet engines for orientation and stabilization, proper control system and computational facilities.
The main task of SIA is a payload delivery in the predetermined point of cosmic space taking into consideration the different kinds of restrictions.
According to requirements SIA should fulfill some transport operations and so it is represented in several constructive modifications [1]:
─ Transfer from orbit of 500 km height to orbit of 800 km height with payload about 150 kg. Characteristic velocity about 160 m/s is required to do this transfer and this modification is considered as a basic one. But for control system forming this modification makes it possible to apply more massive measurement unit.
─ Transfer from orbit of 500 km height to orbit of 1500 km height with payload about 110-130 kg. Characteristic velocity about 500 m/s is required to do this transfer. But for control system forming this modification requires minimal weight measurement unit.
─ Transfer from orbit of 500 km height to departure orbit with payload about 15-20 kg. Characteristic velocity no less then 3200 m/s is required to do this transfer. This modification also requires minimal weight measurement unit for control system forming.
The main tasks of SIA control system are:
• Forming of SIA orientation with required accuracy.
• Three axis orientation according to flight plan.
• Three axis orientation supporting during free flight and corrective impulse production (up to 2 minutes).
• SIA stabilization (angular rates damping) after separation.
• SIA spinning with respect to one of the axes.
• Control signal forming for corrective cruise engines.
All variety of orientation modes can be practically implemented on the single base so called kinematic principle of control law forming and quaternion algebra [2, 3].
General block diagram of SIA control system is presented to show all orientation modes and two important loops ─ kinematic and dynamic ones. Dynamic loop is a part of kinematic one [4].
Dynamic loop includes SIA as a whole physical body, measurement unit of rate gyros, executive subsystem and combined control strategy consisting of two parts ─ kinematic and dynamic control laws. Performance of dynamic loop is defined by its control law.
Kinematic loop includes dynamic loop, kinematic equations of motion and kinematic control law. Kinematic loop performance is defined by its control law under suggestion of dynamic loop negligible influence.
Particular program of flight is generated from separate control modes and a definite sequence of modes is formed. Control modes include the following ones: rotation stopping, inertial frame or orbital frame orientation, program turns, stabilization under corrective impulse production, spinning with respect to one of the body axes, solar orientation, orientation supporting in various versions.
But the main feature of all modes mentioned above is jet engines usage of small tractive force as a base elements of executive subsystem. These jet engines operate in «switch on- off» regime and their impulses are restricted by minimal duration. Besides onboard jet engine arrangement is quite important thing. Specifics noted influence greatly on control law strategy for each mode.
Conclusion:
─ It is shown the possibility to form SIA control system only with help of jet engines used for orientation, stabilization and orbit correction. Simulation and kinematic principle just proved this possibility.
─ It is suggested to apply minimal arrangement of executive subsystem based on unorthogonal configuration as opposed to orthogonal one. However, there is restriction concerning minimal impulse duration.
─ Investigation of unorthogonal configuration for main control modes under control law different parameters and initial conditions were carried out.
─ Block diagrams of control modes and math models of control system elements were developed and then the detailed simulation, were implemented according to suggested approach.
─ Performance comparison of orthogonal and unorthogonal configuration were fulfilled according to transient response time duration and total fuel consumption. The comparison showed some adventures of suggested approach.
