Aeronautics and astronautics – Spacecraft – With fuel system details
Reexamination Certificate
2002-10-07
2003-12-23
Swiatek, Robert P. (Department: 3644)
Aeronautics and astronautics
Spacecraft
With fuel system details
C244S003200, C701S013000
Reexamination Certificate
active
06666410
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to a load relief system for a launch vehicle and more particularly to a load relief system for a launch vehicle which measures the winds in near real time and provides control commands that compensate for wind load on the launch vehicle by reducing the total angle of attack.
BACKGROUND OF THE INVENTION
The decision whether to proceed with the launch of vehicles such as rockets, missiles, the Space Shuttle, and the like, is determined in part by the prevailing wind conditions at altitudes up to approximately thirty kilometers above the Earth. Strong winds at altitudes up to approximately 30 kilometers an impart significant bending loads on the launch vehicle during ascent and hence often result in a decision to scrub the launch. Scrubbed launches are expensive and can increase the cost of the launch by as much as five hundred thousand dollars per day.
Conventional systems for reducing the load on a launch vehicle during ascent rely on balloon wind measurement systems, such as jimsphere or rawindsonde balloons, to determine the wind speed and direction at high altitudes. These balloon systems are generally released every hour up to six hours before the scheduled liftoff, and drift with the prevailing wind. The movement or drift of the balloon is generally measured with a ground based radar tracking system. However, because of the associated wind drift of the balloons, these wind measurement systems do not measure the wind speed and direction along the actual expected flight path of the vehicle. The balloon based systems are also unreliable because of loss of radar tracking and mechanical balloon failure. Moreover, the prior art balloon systems generally require approximately sixty to ninety minutes to reach their peak altitude (e.g., 30 kilometers). These systems also require additional time to post process the radar tracking data to estimate and determine the wind profile for launch. Once the wind profile has been determined, it is typically stored and used during the flight of the launch vehicle by an on-board flight processor to reduce the effects of those measured winds during ascent. However, because wind speed and direction are constantly changing, the actual winds experienced by the launch vehicle during flight can be significantly different from those measured prior to flight.
Present systems for reducing the load on a launch vehicle use the previously determined wind profile (e.g., 60 to 90 minutes old at the time of launch of the vehicle) in a largely reactive traditional feedback guidance and control system. Typical guidance and control systems modulate the attitude of the vehicle to provide load relief during the launch vehicle ascent. These guidance and control systems generally employ polynomial curve fits of the measured wind profile and utilize traditional control loops with additional load relief compensation to reduce the loads on the launch vehicle. However, polynomial curve fits of the wind profile tend to average or filter out the effects of rapidly changing winds such as wind shears. Moreover, the prior art load relief systems tend to be reactive in nature. In this regard, during vehicle ascent, an on-board inertial measurement unit (IMU) requires time to detect any actual and/or uncompensated wind shear. Due to this time delay, the majority of the load due to the wind shear has already been transferred to the launch vehicle.
SUMMARY OF THE INVENTION
It is therefore an object of this invention to provide an improved load relief system for a launch vehicle.
It is a further object of this invention to provide such a load relief system in which the wind sensor senses the wind speed and direction approximately every three minutes at altitudes up to approximately thirty kilometers above the Earth.
It is a further object of this invention to provide such a load relief system in which the wind sensor senses the wind speed and direction in the range of about every one minute to about every fifteen minutes at altitudes up to approximately thirty kilometers above the Earth.
It is a further object of this invention to provide such a load relief system in which the wind speed and direction provided reflect the actual prevailing wind conditions experienced during the flight of the launch vehicle.
It is a further object of this invention to provide such a load relief system which efficiently reduces aerodynamic loads on the launch vehicle during flight.
It is a further object of this invention to provide such a load relief system which accurately predicts a trajectory path of the launch vehicle which reduces the load experienced by the launch vehicle by comparing the predicted trajectory to a desired trajectory.
It is a further object of this invention to provide such a load relief system which efficiently provides load relief to the launch vehicle when the vehicle is subjected to wind shear.
It is a further object of this invention to provide such a load relief system which efficiently provides control commands which compensate for wind induced loads on the launch vehicle by reducing the total angle of attack of the launch vehicle.
It is a further object of this invention to provide such a load relief system which reduces the number of scrubbed launches.
The invention results from the realization that a truly effective and robust load relief system for a launch vehicle can be achieved by a unique combination of a wind sensing system responsive to atmospheric winds for providing an output of sensed wind speed and direction at selected locations; a plant model responsive to the sensed wind speed and direction within a finite time horizon, the current state of the launch vehicle, and control commands of the launch vehicle to predict the trajectory of the launch vehicle; an error circuit responsive to the predicted trajectory and a reference trajectory to produce a trajectory error, and an optimizer responsive to the trajectory error and configured to provide control commands that compensate for wind loads over the finite horizon of the launch vehicle by reducing the total angle of attack.
This invention features a load relief system for a launch vehicle including a wind sensing system responsive to wind speed and direction at selected locations for providing an output of sensed wind speed and wind direction at the selected locations, a plant model responsive to the sensed wind speed and direction within a finite horizon, a current state of the launch vehicle, and control commands of the launch vehicle to predict the trajectory of the launch vehicle, an error circuit responsive to the predicted trajectory and a reference trajectory to produce a trajectory error, and an optimizer responsive to the trajectory error and configured to provide control commands to compensate for wind load over the finite horizon of the launch vehicle by reducing the total angle of attack.
In a preferred embodiment, the wind sensing system may sense the wind speed and wind direction at altitudes up to approximately 30 kilometers. The wind sensing system may be mounted on the launch vehicle. The wind sensing system may sense the wind speed and wind direction approximately in real-time. The wind sensing system may be located proximate a launch platform of the launch vehicle and may sense wind speed and direction at least approximately every three minutes or in the range of about every one minute to every fifteen minutes. The wind sensing system may be located on an aircraft and may sense wind speed and direction at least approximately every three minutes or in the range of about every one minute to every fifteen minutes. The launch vehicle may be chosen from the group consisting of Delta, Atlas, Arian, Titan, and Space Shuttle. The wind sensing system may include a Doppler Light Detection and Ranging (LIDAR) sensor. The wind sensing system may include a radar system. The LIDAR sensor may emit an eye safe energy beam pulse. The load relief system of this invention may further include a wind correlator, responsive to the wind sensing system and
Boelitz Frederick Wall
Gibson Christopher Michael
Martin Andrew Allen
Miotto Piero
Singh Leena
Iandiorio & Teska
Swiatek Robert P.
The Charles Stark Draper Laboratory Inc.
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