Spacecraft Navigation and Guidance

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  • Spacecraft Navigation and Guidance
  • Guidance, Navigation, and Control Systems
  • Our Mission
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  • Guidance, Navigation, and Control Systems - Advanced Solutions, Inc.

    • Direct ascent Escape velocity Expendable and reusable launch systems Launch pad Non-rocket spacelaunch Spaceport. Flight controller Ground station Pass Mission control center. Categories : Applications of control engineering Avionics Robot control Cybernetics Military electronics Unmanned vehicles Engineering stubs.

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    Views Read Edit View history. By using this site, you agree to the Terms of Use and Privacy Policy. This engineering-related article is a stub. You can help Wikipedia by expanding it. These mission segments are shown pictorially in Fig. Devices used to obtain this information are called inertial sensors and include the gyroscope and accelerometer.

    Further, for the rendezvous phase, it needs to know the relative position of the spacecraft to the targeted vehicle; rendezvous radar can be used for this purpose.

    Spacecraft Navigation and Guidance

    For the docking phase, a near-in distance-measuring sensor, such as a laser, is required. The gyroscope, or gyro as it is usually called, is a spinning wheel supported in rings called gimbals. Suppose that a gyro were mounted in a spacecraft. Suppose further that some method is used to spin the wheel and measure angular movement of the gimbals.

    A gyro used in this manner is termed a vertical gyro.

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    Rotational motion of the spacecraft about all axes except the gyro spin axis could be measured and used for guidance purposes. Some aircraft and missiles that have short flight times use gyros in this manner for attitude control during flight see, for example, the discussion in Ref. However, drift due to bearing friction and difficulties in precise readout of the gimbal positions usually make this application unsuitable for spacecraft that have precise trajectory requirements and long flight durations.

    In practical applications for modern spacecraft, the property of precession is more useful. Figure 1. Hypothetical space mission. Suppose that a gyro is mounted in a vehicle, as shown in Fig. In this drawing, the two gimbals on which the spinning wheel is mounted are clearly visible. As the vehicle rotates about the axis labeled input axis transverse to the spin axis, it exerts a torque T on the spin axis and there is precession about the axis labeled output axis.

    A measure of the rate of precession will be proportional to the vehicle rotation, as shown by Eq.

    Guidance, Navigation, and Control Systems

    A gyro used in this manner as a rate sensor is called a rate gyro. To keep the displacement of the wheel within narrow limits, a restoring torque motor must be used. Further, if the rate of precession is integrated over time, a value of vehicle angular displacement is determined. A rate gyro used in this manner is termed an integrating rate gyro. This approach to determining vehicular attitude is usually much more accurate than the vertical gyro approach. Figure 2. Gyroscopic precession. When the gyro is used as a sensor, a number of design considerations come into play.

    First, the wheel is spun using a high-efficiency electric motor. Next, in an effort to reduce volume, the wheel may be made small and the spin rate increased to retain high angular momentum, a desirable feature for measuring very small angular rates. Next, bearings inevitably cause some disturbing torques on the wheel, and in an effort to reduce this effect, the wheel may be supported on a thin film of liquid or gas in lieu of conventional bearings. An optical pickoff is preferable to inductive pickoffs to reduce reactive forces and to measure very small rates.

    Finally, restoring torque commands may be in the form of pulses that provide a compatible interface with a digital computer. Some design approaches for mechanical gyros used in spacecraft can be found in Ref. Optical Gyros.

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    Another type of sensor for measuring rotational displacement is the so-called ring laser gyro RLG. This is not a gyro in the conventional sense in that there are no moving parts. The principle of operation is the Sagnac Effect discovered in 3. The sensing element is a laser beam that is split into two beams directed clockwise and counterclockwise in a somewhat circular, closed, vacuum chamber. A conceptual design approach is shown in Fig. If the chamber is rotated in either direction about an axis perpendicular to the plane of the mirrors i. The output of the RLG can be digitized for rotational rate output and then integrated over time for a measure of angular displacement.

    The disadvantages of RLGs are the difficulty and cost of achieving and maintaining the necessary mechanical alignment 4. Figure 3. Ring laser gyro. Fiber-optic gyroscopes FOG , sometimes called interferometric fiber-optic gyroscopes IFOG , operate on the same principle as the RLG in that there are two beams of light directed in opposing loops, but in this case the medium is optical fiber. A conceptual drawing of the FOG is shown in Fig. One disadvantage is that scale factors in FOGs are usually nonlinear.

    Also, the fiber must be carefully chosen to avoid the potential of becoming unserviceable due to aging or radiation in space. An extensive discussion of the FOG may be found in 5. Vibratory Gyros. The vibratory gyro is another type of gyro different from the classical mechanical gyro. The ancestry of this type can be traced to the experiments of G. Bryan, a British physicist, who studied vibrating wine glasses 6.

    He discovered that the induced vibrational pattern on a glass would move precess if the wine glass were rotated about its stem and that the displacement was proportional to the rotational rate. This is shown in Fig. An example of this type of gyro is the hemispherical resonator gyroscope HRG discussed in Ref.

    In this example, the resonating element that is analogous to the wine glass is a mm diameter bell made of fused silica. A surrounding housing induces vibration and also senses the nodal pattern shift through the use of capacitive pick-offs.

    Our Mission

    The analysis and computational techniques associated with the navigation and guidance of spacecraft are now in a mature state of development. However the. Guidance, navigation and control is a branch of engineering dealing with the design of systems to control the movement of vehicles, especially, automobiles, ships, aircraft, and spacecraft.

    The main advantage of the HRG is that there are no moving parts other than the resonator bell. A disadvantage is that the case must be evacuated and vacuum-sealed to prevent air damping. Figure 4. Fiber-optic gyro. Figure 5. Vibrating bell gyro. The tuning fork gyro shown in Fig. In this case, the tines are excited in the plane of the tines. As the tuning fork is rotated about an axis parallel to the tines, they tend to continue oscillating in the original plane, as shown in the vector diagram in the figure.

    The vector component perpendicular to the plane of the tines is proportional to the rotational rate and may be measured by capacitive or optical sensing. Materials used for the tuning fork include crystalline quartz and silicon. Crystalline quartz is a highly stable piezoelectric material suitable for micromachining 8. In the case of silicon, the fork may be part of an integrated circuit chip where the controlling and sensing electronics are designed into the chip 9.

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    You previously purchased this article through ReadCube. Materials used for the tuning fork include crystalline quartz and silicon. This is a minimum energy maneuver where the thrusting is done at the apogee and perigee of the orbit. Springer Professional. Let m1 represent the mass of Earth; Earth is of uniform density and is spherically symmetrical, that is, the oblateness of Earth is ignored. A discussion of the historical background of this development can be found in Ref. Figure 6.

    Accelerometers are devices used to sense changes in velocity. This sensing mass, sometimes called the proof mass, may be suspended in a number of ways and held in the neutral position by a magnetic field. As the acceleration is sensed by the mass and it begins to move, a pickoff detects the movement and sends a restoring signal through an amplifier to the restoring coil. Rather than hold the mass in a neutral position, some designs force the mass to swing back and forth on a pendulum using a series of back and forth pulses.

    This restoring circuit also sends the restoring pulses to a counter that adds the positive and negative pulses algebraically; the sum represents the sensed acceleration.

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    If the counter is coupled with a digital computer and integrated over time, it can keep an ongoing status of vehicle velocity. Figure 6. Tuning fork gyro. Advancements in the past decade in microelectromechanical systems MEMS , also known as microsystems technology MST , have produced accel-erometers of continually decreasing size, mass, and power usage Nanotechnology, generally defined as the next order of size reduction, will no doubt reduce the size of accelerometers further.

    Guidance, Navigation, and Control Systems - Advanced Solutions, Inc.

    Inertial Measurement Units. The stable platform, variously referred to as the inertial platform, guidance platform,or inertial measurement unit IMU is a common application of gyros and accelerometers. In a typical approach, a group of three single-axis gyros or two dual-axis gyros is mounted on a rigid platform, and their input axes are aligned orthogonally. Three single-axis accelerometers, or two dual-axis accelerometers, are also mounted orthogonally on the platform.

    The platform is then mounted on two or three gimbals, and the restoring torque signals from the gyros are used to command the gimbal drive motors. The result is that, after initial erection and alignment, the platform is maintained inertially fixed in space. A platform designed in this manner provides an inertial attitude reference and measures accelerations along the inertially fixed axes of the platform.

    This information can be used by a flight computer to calculate and maintain the status of attitude, acceleration, velocity, and position of the platform. For a further discussion of IMUs, see Ref.