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68-421: All OGO satellites are built around a common parallelepiped-shaped platform (0.9 × 0.9 × 1.8 m). The satellite's orientation is maintained fixed in space ( 3-axis stabilized ) so that one of the long faces (0.9 × 1.8 m) permanently points towards Earth. On this face, as well as on the opposite face, a surface of 0.6 m² is available for scientific experiments. The attitude control system is also responsible for keeping

136-611: A field of view of 5 square degrees with the 1.5-m telescope and nearly 20 square degrees with the Catalina Schmidt. Nominal exposures are 30 seconds and the 1.5-m can reach objects fainter than 21.5 V in that time. The 1-meter follow-up telescope uses a 2000×2000-pixel CCD detector which provides a field of view of 0.3 square degrees. Starting in 2019, CSS started using the 1.54-meter (61 in) Kuiper telescope situated on Mt. Bigelow for targeted follow-up for 7–12 nights per lunation. CSS typically operates every clear night with

204-502: A 0.5-meter (20 in) f/3 Uppsala Schmidt telescope at Siding Spring Observatory in Australia. The 1.5-meter and 68-cm survey telescopes use identical, thermo-electrically cooled cameras and common software written by the CSS team. The cameras are cooled to approximately −100 °C (−148 °F) so their dark current is about 1 electron per hour. These 10,560×10,560-pixel cameras provide

272-564: A 1.5-meter (59 in) f/1.6 telescope on the peak of Mount Lemmon (MPC code G96), a 68 cm (27 in) f/1.7 Schmidt telescope near Mount Bigelow (MPC code 703), and a 1-meter (39 in) f/2.6 follow-up telescope also on Mount Lemmon (MPC code I52). The three telescopes are located in the Santa Catalina Mountains near Tucson, Arizona. The CSS southern hemisphere counterpart, the Siding Spring Survey (SSS), used

340-417: A boom deployment failure shortly after orbital injection, the spacecraft was put into a permanent spin mode of 5 rpm about the Z axis. This spin axis remained fixed with a declination of about -10 deg and right ascension of about 40 deg at launch. The initial local time of apogee was 2100 h. OGO 1 carried 20 experiments. Twelve of these were particle studies and two were magnetic field studies. In addition, there

408-633: A continuous sweeping motion that is desirable for fields and particles instruments, as well as some optical scanning instruments, but they may require complicated systems to de-spin antennas or optical instruments that must be pointed at targets for science observations or communications with Earth. Three-axis controlled craft can point optical instruments and antennas without having to de-spin them, but they may have to carry out special rotating maneuvers to best utilize their fields and particle instruments. If thrusters are used for routine stabilization, optical observations such as imaging must be designed knowing that

476-402: A ground station. The attitude control algorithms are written and implemented based on requirement for a particular attitude maneuver. Asides the implementation of passive attitude control such as the gravity-gradient stabilization , most spacecraft make use of active control which exhibits a typical attitude control loop. The design of the control algorithm depends on the actuator to be used for

544-440: A long-duration mission by producing control moments without fuel expenditure. For example, Mariner 10 adjusted its attitude using its solar cells and antennas as small solar sails. In orbit, a spacecraft with one axis much longer than the other two will spontaneously orient so that its long axis points at the planet's center of mass. This system has the virtue of needing no active control system or expenditure of fuel. The effect

612-491: A minimum of three reaction wheels must be used, with additional units providing single failure protection. See Euler angles . These are rotors spun at constant speed, mounted on gimbals to provide attitude control. Although a CMG provides control about the two axes orthogonal to the gyro spin axis, triaxial control still requires two units. A CMG is a bit more expensive in terms of cost and mass, because gimbals and their drive motors must be provided. The maximum torque (but not

680-426: A phenomenon known as Gimbal lock . A rotation matrix, on the other hand, provides a full description of the attitude at the expense of requiring nine values instead of three. The use of a rotation matrix can lead to increased computational expense and they can be more difficult to work with. Quaternions offer a decent compromise in that they do not suffer from gimbal lock and only require four values to fully describe

748-447: A role in an astrophotography exercise with the 2006 Adult Astronomy Camp ending up with a picture that was featured on Astronomy Picture of the Day. The Zooniverse project Catalina Outer Solar System Survey is a citizen science project and is listed as a NASA citizen science project. In this project, the volunteers search for trans-Neptunian objects (TNOs) in pre-processed images of

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816-511: Is a device that senses the direction to the Sun . This can be as simple as some solar cells and shades, or as complex as a steerable telescope , depending on mission requirements. An Earth sensor is a device that senses the direction to Earth . It is usually an infrared camera ; nowadays the main method to detect attitude is the star tracker , but Earth sensors are still integrated in satellites for their low cost and reliability. A star tracker

884-498: Is aerodynamic stabilization. This is achieved using a drag gradient, as demonstrated on the Get Away Special Passive Attitude Control Satellite (GASPACS) technology demonstration. In low Earth orbit, the force due to drag is many orders of magnitude more dominant than the force imparted due to gravity gradients. When a satellite is utilizing aerodynamic passive attitude control, air molecules from

952-582: Is an astronomical survey to discover comets and asteroids . It is conducted at the Steward Observatory 's Catalina Station , located near Tucson, Arizona , in the United States. CSS focuses on the search for near-Earth objects , in particular on any potentially hazardous asteroid that may pose a threat of impact . Its counterpart in the southern hemisphere was the Siding Spring Survey (SSS), closed in 2013 due to loss of funding. CSS supersedes

1020-426: Is an optical device that measures the position(s) of star (s) using photocell (s) or a camera. It uses magnitude of brightness and spectral type to identify and then calculate the relative position of stars around it. A magnetometer is a device that senses magnetic field strength and, when used in a three-axis triad, magnetic field direction. As a spacecraft navigational aid, sensed field strength and direction

1088-502: Is based on the measurement of the rate of change of body-fixed magnetometer signals. where m {\displaystyle m} is the commanded magnetic dipole moment of the magnetic torquer and K {\displaystyle K} is the proportional gain and B ˙ {\displaystyle {\dot {B}}} is the rate of change of the Earth's magnetic field. Spacecraft attitude determination

1156-485: Is called guidance, navigation and control , which also involves non-attitude concepts, such as position determination and navigation . A spacecraft's attitude must typically be stabilized and controlled for a variety of reasons. It is often needed so that the spacecraft high-gain antenna may be accurately pointed to Earth for communications, so that onboard experiments may accomplish precise pointing for accurate collection and subsequent interpretation of data, so that

1224-440: Is caused by a tidal force . The upper end of the vehicle feels less gravitational pull than the lower end. This provides a restoring torque whenever the long axis is not co-linear with the direction of gravity. Unless some means of damping is provided, the spacecraft will oscillate about the local vertical. Sometimes tethers are used to connect two parts of a satellite, to increase the stabilizing torque. A problem with such tethers

1292-401: Is compared to a map of Earth's magnetic field stored in the memory of an on-board or ground-based guidance computer. If spacecraft position is known then attitude can be inferred. Attitude cannot be measured directly by any single measurement, and so must be calculated (or estimated ) from a set of measurements (often using different sensors). This can be done either statically (calculating

1360-406: Is most common reacts to an error signal (deviation) based on attitude as follows where T c {\displaystyle T_{c}} is the control torque, e {\displaystyle e} is the attitude deviation signal, and K p , K i , K d {\displaystyle K_{\text{p}},K_{\text{i}},K_{\text{d}}} are

1428-483: Is placed in space. (For some applications such as in robotics and computer vision, it is customary to combine position and attitude together into a single description known as Pose .) Attitude can be described using a variety of methods; however, the most common are Rotation matrices , Quaternions , and Euler angles . While Euler angles are oftentimes the most straightforward representation to visualize, they can cause problems for highly-maneuverable systems because of

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1496-494: Is stored in two 28-volt nickel-cadmium batteries . The telecommunications system ensures data transfer at a rate between 1 and 64 kilobits per second . Scientific data can be transmitted in real-time or stored temporarily on one of two magnetic tape recorders with a recording speed of 1 to 4 kilobits per second and a reading speed of 64 to 128 kilobits per second. OGO 1, OGO 3, and OGO 5 were in equatorial orbits ; OGO 2, OGO 4, and OGO 6 were in lower polar orbits . The purpose of

1564-418: Is that meteoroids as small as a grain of sand can part them. Coils or (on very small satellites) permanent magnets exert a moment against the local magnetic field. This method works only where there is a magnetic field against which to react. One classic field "coil" is actually in the form of a conductive tether in a planetary magnetic field. Such a conductive tether can also generate electrical power, at

1632-617: Is the process of determining the orientation of a spacecraft (vehicle or satellite). It is a pre-requisite for spacecraft attitude control. A variety of sensors are utilized for relative and absolute attitude determination. Many sensors generate outputs that reflect the rate of change in attitude. These require a known initial attitude, or external information to use them to determine attitude. Many of this class of sensor have some noise, leading to inaccuracies if not corrected by absolute attitude sensors. Gyroscopes are devices that sense rotation in three-dimensional space without reliance on

1700-548: The University of Hawaii Institute for Astronomy (IfA), used data from the Las Cumbres Observatory (LCO) Faulkes Telescope North on Haleakala to track OGO-1. The University of Hawaii's Asteroid Terrestrial-impact Last Alert System (ATLAS), also funded by PDCO, independently observed the object. Further observations were conducted by CSS to confirm the object’s trajectory. Precision orbit calculations were conducted by

1768-695: The Center for Near-Earth Object (NEO) Studies (CNEOS) at NASA’s Jet Propulsion Laboratory , and compared to data from the European Space Agency 's NEO Coordination Center. The object was confirmed to be not an asteroid , but in fact Orbiting Geophysical Observatory-1 (OGO-1). OGO-1 reentered Earth's atmosphere and disintegrated on Saturday evening, 29 August 2020 over Southern French Polynesia . In 1970 OGO-5 used its ultraviolet photometer to observe comets Encke , Tago-Sato-Kosaka (1969 IX) and Bennett (1970 II) . This article about one or more spacecraft of

1836-437: The Earth's upper atmosphere strike the satellite in such a way that the center of pressure remains behind the center of mass, similar to how the feathers on an arrow stabilize the arrow. GASPACS utilized a 1 m inflatable 'AeroBoom', which extended behind the satellite, creating a stabilizing torque along the satellite's velocity vector. Control algorithms are computer programs that receive data from vehicle sensors and derive

1904-542: The OGO 1 spacecraft, the first of a series of six Orbiting Geophysical Observatories, was to conduct diversified geophysical experiments to obtain a better understanding of the Earth as a planet and to develop and operate a standardized observatory-type satellite. OGO 1 consisted of a main body that was parallelepipedal in form, two solar panels, each with a solar-oriented experiment package (SOEP), two orbital plane experiment packages (OPEP) and six appendages EP-1 through EP-6 supporting

1972-458: The PID controller parameters. A simple implementation of this can be the application of the proportional control for nadir pointing making use of either momentum or reaction wheels as actuators. Based on the change in momentum of the wheels, the control law can be defined in 3-axes x, y, z as This control algorithm also affects momentum dumping. Another important and common control algorithm involves

2040-472: The Sun so they can provide electrical power to the spacecraft. Cassini ' s main engine nozzles were steerable. Knowing where to point a solar panel, or scan platform, or a nozzle — that is, how to articulate it — requires knowledge of the spacecraft's attitude. Because a single subsystem keeps track of the spacecraft's attitude, the Sun's location, and Earth's location, it can compute the proper direction to point

2108-400: The Sun's direction, and 5° relative to the forward movement axis. The thermal control system uses louvers that open and close to maintain a temperature of 10 to 24°C within the satellite's body and thermal resistors for scientific experiments mounted outside. Electrical power is provided by solar panels that produce 550 watts, of which 50 watts are available for scientific experiments. The energy

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2176-433: The United States is a stub . You can help Misplaced Pages by expanding it . 3 axis stabilized spacecraft Spacecraft attitude control is the process of controlling the orientation of a spacecraft (vehicle or satellite) with respect to an inertial frame of reference or another entity such as the celestial sphere , certain fields, and nearby objects, etc. Controlling vehicle attitude requires actuators to apply

2244-634: The aeronautical field, such as: This class of sensors sense the position or orientation of fields, objects or other phenomena outside the spacecraft. A horizon sensor is an optical instrument that detects light from the 'limb' of Earth's atmosphere, i.e., at the horizon. Thermal infrared sensing is often used, which senses the comparative warmth of the atmosphere, compared to the much colder cosmic background . This sensor provides orientation with respect to Earth about two orthogonal axes. It tends to be less precise than sensors based on stellar observation. Sometimes referred to as an Earth sensor. Similar to

2312-448: The angular rate is not estimated directly, but rather the measured angular rate from the gyro is used directly to propagate the rotational dynamics forward in time. This is valid for most applications as gyros are typically far more precise than one's knowledge of disturbance torques acting on the system (which is required for precise estimation of the angular rate). For some sensors and applications (such as spacecraft using magnetometers)

2380-458: The appendages. It logically falls to the same subsystem – the Attitude and Articulation Control Subsystem (AACS), then, to manage both attitude and articulation. The name AACS may even be carried over to a spacecraft even if it has no appendages to articulate. Attitude is part of the description of how an object is placed in the space it occupies. Attitude and position fully describe how an object

2448-448: The appropriate commands to the actuators to rotate the vehicle to the desired attitude. The algorithms range from very simple, e.g. proportional control , to complex nonlinear estimators or many in-between types, depending on mission requirements. Typically, the attitude control algorithms are part of the software running on the computer hardware, which receives commands from the ground and formats vehicle data telemetry for transmission to

2516-651: The attitude using only the measurements currently available), or through the use of a statistical filter (most commonly, the Kalman filter ) that statistically combine previous attitude estimates with current sensor measurements to obtain an optimal estimate of the current attitude. Static attitude estimation methods are solutions to Wahba's problem . Many solutions have been proposed, notably Davenport's q-method, QUEST, TRIAD, and singular value decomposition . Crassidis, John L., and John L. Junkins.. Chapman and Hall/CRC, 2004. Kalman filtering can be used to sequentially estimate

2584-540: The attitude, as well as the angular rate. Because attitude dynamics (combination of rigid body dynamics and attitude kinematics) are non-linear, a linear Kalman filter is not sufficient. Because attitude dynamics is not very non-linear, the Extended Kalman filter is usually sufficient (however Crassidis and Markely demonstrated that the Unscented Kalman filter could be used, and can provide benefits in cases where

2652-413: The attitude. Attitude control can be obtained by several mechanisms, including: Vernier thrusters are the most common actuators, as they may be used for station keeping as well. Thrusters must be organized as a system to provide stabilization about all three axes, and at least two thrusters are generally used in each axis to provide torque as a couple in order to prevent imparting a translation to

2720-473: The boom experiment packages. One face of the main body was designed to point toward the Earth (+Z axis), and the line connecting the two solar panels (X axis) was intended to be perpendicular to the Earth-Sun-spacecraft plane. The solar panels were able to rotate about the X axis. The OPEPs were mounted on and could rotate about an axis which was parallel to the Z axis and attached to the main body. Due to

2788-574: The concept of detumbling, which is attenuating the angular momentum of the spacecraft. The need to detumble the spacecraft arises from the uncontrollable state after release from the launch vehicle. Most spacecraft in low Earth orbit (LEO) makes use of magnetic detumbling concept which utilizes the effect of the Earth's magnetic field . The control algorithm is called the B-Dot controller and relies on magnetic coils or torque rods as control actuators. The control law

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2856-499: The congressionally-mandated goal. In addition to identifying impact risks, the project also obtains other scientific information, including: improving the known population distribution in the main belt, finding the cometary distribution at larger perihelion distances, determining the distribution of NEOs as a product of collisional history and transport to the inner Solar System , and identifying potential targets for flight projects. The Catalina Sky Survey (CSS) uses three telescopes,

2924-480: The direction of the satellite's forward movement. Two booms, 5.7 meters long (EP-5 and EP-6) and four booms, 1.8 meters long (EP-1 to EP-4), hold scientific experiments at their ends that must be kept away from the satellite's body to meet visibility or sensitivity constraints. Additionally, the satellite is equipped with several antennas for telecommunications, the most prominent being an adjustable Yagi antenna . The scientific experiments may have their own antenna, like

2992-428: The direction opposite to that required to re-orient the vehicle. Because momentum wheels make up a small fraction of the spacecraft's mass and are computer controlled, they give precise control. Momentum wheels are generally suspended on magnetic bearings to avoid bearing friction and breakdown problems. Spacecraft Reaction wheels often use mechanical ball bearings. To maintain orientation in three dimensional space

3060-545: The discovery of 47% of the total known NEO population. For a complete listing of all minor planets discovered by the Catalina Sky Survey, see the index section in list of minor planets . The CSS team is headed by D. Carson Fuls of the Lunar and Planetary Laboratory of the University of Arizona . The full CSS team is: The CSS has helped with Astronomy Camp by showing campers how they detect NEOs. They even played

3128-402: The exception of a few nights centered on the full moon . The southern hemispheres' SSS in Australia ended in 2013 after funding was discontinued. In 2005, CSS became the most prolific NEO survey, surpassing Lincoln Near-Earth Asteroid Research (LINEAR) in total number of NEOs and potentially hazardous asteroids discovered each year since. As of 2020, the Catalina Sky Survey is responsible for

3196-561: The expense of orbital decay . Conversely, by inducing a counter-current, using solar cell power, the orbit may be raised. Due to massive variability in Earth's magnetic field from an ideal radial field, control laws based on torques coupling to this field will be highly non-linear. Moreover, only two-axis control is available at any given time meaning that a vehicle reorient may be necessary to null all rates. Three main types of passive attitude control exist for satellites. The first one uses gravity gradient, and it leads to four stable states with

3264-406: The heating and cooling effects of sunlight and shadow may be used intelligently for thermal control, and also for guidance: short propulsive maneuvers must be executed in the right direction. Attitude control of spacecraft is maintained using one of two principal approaches: There are advantages and disadvantages to both spin stabilization and three-axis stabilization. Spin-stabilized craft provide

3332-481: The initial estimate is poor). Multiple methods have been proposed, however the Multiplicative Extended Kalman Filter (MEKF) is by far the most common approach. This approach utilizes the multiplicative formulation of the error quaternion, which allows for the unity constraint on the quaternion to be better handled. It is also common to use a technique known as dynamic model replacement, where

3400-453: The long axis (axis with smallest moment of inertia) pointing towards Earth. As this system has four stable states, if the satellite has a preferred orientation, e.g. a camera pointed at the planet, some way to flip the satellite and its tether end-for-end is needed. The second passive system orients the satellite along Earth's magnetic field thanks to a magnet. These purely passive attitude control systems have limited pointing accuracy, because

3468-635: The maximum angular momentum change) exerted by a CMG is greater than for a momentum wheel, making it better suited to large spacecraft. A major drawback is the additional complexity, which increases the number of failure points. For this reason, the International Space Station uses a set of four CMGs to provide dual failure tolerance. Small solar sails (devices that produce thrust as a reaction force induced by reflecting incident light) may be used to make small attitude control and velocity adjustments. This application can save large amounts of fuel on

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3536-408: The observation of external objects. Classically, a gyroscope consists of a spinning mass, but there are also " ring laser gyros " utilizing coherent light reflected around a closed path. Another type of "gyro" is a hemispherical resonator gyro where a crystal cup shaped like a wine glass can be driven into oscillation just as a wine glass "sings" as a finger is rubbed around its rim. The orientation of

3604-475: The one shown in the diagram extending 9 meters from the SOEP-1 experiment on the solar panel. The satellite typically has twelve appendages deployed in orbit in two sequences to avoid any interference. The attitude control system relies on horizon sensors, cold gas thrusters , and reaction wheels . It allows the satellite to be stabilized on 3 axes with an accuracy of 2° relative to the local vertical, 5° relative to

3672-602: The opposing direction if a new orientation is to be held. Thruster systems have been used on most crewed space vehicles, including Vostok , Mercury , Gemini , Apollo , Soyuz , and the Space Shuttle . To minimize the fuel limitation on mission duration, auxiliary attitude control systems may be used to reduce vehicle rotation to lower levels, such as small ion thrusters that accelerate ionized gases electrically to extreme velocities, using power from solar cells. Momentum wheels are electric motor driven rotors made to spin in

3740-450: The oscillation is fixed in inertial space, so measuring the orientation of the oscillation relative to the spacecraft can be used to sense the motion of the spacecraft with respect to inertial space. Motion reference units are a kind of inertial measurement unit with single- or multi-axis motion sensors. They utilize MEMS gyroscopes . Some multi-axis MRUs are capable of measuring roll, pitch, yaw and heave . They have applications outside

3808-408: The other feeding into a directional antenna, were used to transmit data. A special-purpose telemetry system, feeding into either antenna, was also used to transmit wideband data in real time only. Tracking was accomplished by using radio beacons and a range and range-rate S-band transponder. Because of the boom deployment failure, the best operating mode for the data handling system was the use of one of

3876-561: The photographic Bigelow Sky Survey . The NEO Observations Program is a result of a United States 1998 congressional directive to NASA to begin a program to identify objects 1 kilometer (0.62 miles) or larger to a confidence level of 90% or better. The Catalina Sky Survey, located at the Mount Lemmon Observatory in the Catalina Mountains north of Tucson , carries out searches for near-earth objects (NEOs), contributing to

3944-728: The precise location must also be known. While pose estimation can be employed, for spacecraft it is usually sufficient to estimate the position (via Orbit determination ) separate from the attitude estimation. For terrestrial vehicles and spacecraft operating near the Earth, the advent of Satellite navigation systems allows for precise position knowledge to be obtained easily. This problem becomes more complicated for deep space vehicles, or terrestrial vehicles operating in Global Navigation Satellite System (GNSS) denied environments (see Navigation ). Catalina Sky Survey Catalina Sky Survey ( CSS ; obs. code : 703 )

4012-419: The solar panels continuously oriented perpendicularly to the solar rays. The cubic SOEP (Solar Oriented Experiment Package) receptacles, attached to the ends of the solar panels on both faces, can accommodate experiments on a surface of 0.1 m². At one end of the satellite's body, two OPEP-1 (Orbital Plane Experiment Package) and OPEP-2 experiment sets are mounted on an adjustable support that keeps them oriented in

4080-719: The spacecraft is always slowly rocking back and forth, and not always exactly predictably. Reaction wheels provide a much steadier spacecraft from which to make observations, but they add mass to the spacecraft, they have a limited mechanical lifetime, and they require frequent momentum desaturation maneuvers, which can perturb navigation solutions because of accelerations imparted by the use of thrusters. Many spacecraft have components that require articulation. Voyager and Galileo , for example, were designed with scan platforms for pointing optical instruments at their targets largely independently of spacecraft orientation. Many spacecraft, such as Mars orbiters, have solar panels that must track

4148-545: The spacecraft perigee had increased to 46,000 km and the inclination had increased to 58.8 deg. The University of Arizona's Catalina Sky Survey (CSS), funded by NASA’s Planetary Defense Coordination Office (PDCO), detected an object late in the evening of 25 August 2020 which appeared to be on an impact trajectory with Earth. Two Maui middle school students also observed the 250-pound (110 kg) object. Maui Waena Intermediate School eighth-graders Holden Suzuki and Wilson Chau, with mentor outreach astronomer J.D. Armstrong of

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4216-450: The spacecraft will oscillate around energy minima. This drawback is overcome by adding damper, which can be hysteretic materials or a viscous damper. The viscous damper is a small can or tank of fluid mounted in the spacecraft, possibly with internal baffles to increase internal friction. Friction within the damper will gradually convert oscillation energy into heat dissipated within the viscous damper. A third form of passive attitude control

4284-508: The specific attitude maneuver although using a simple proportional–integral–derivative controller ( PID controller ) satisfies most control needs. The appropriate commands to the actuators are obtained based on error signals described as the difference between the measured and desired attitude. The error signals are commonly measured as euler angles (Φ, θ, Ψ), however an alternative to this could be described in terms of direction cosine matrix or error quaternions . The PID controller which

4352-447: The torques needed to orient the vehicle to a desired attitude, and algorithms to command the actuators based on the current attitude and specification of a desired attitude. Before and during attitude control can be performed, spacecraft attitude determination must be performed, which requires sensors for absolute or relative measurement. The broader integrated field that studies the combination of sensors, actuators and algorithms

4420-419: The vehicle. Their limitations are fuel usage, engine wear, and cycles of the control valves. The fuel efficiency of an attitude control system is determined by its specific impulse (proportional to exhaust velocity) and the smallest torque impulse it can provide (which determines how often the thrusters must fire to provide precise control). Thrusters must be fired in one direction to start rotation, and again in

4488-460: The way that a terrestrial gyrocompass uses a pendulum to sense local gravity and force its gyro into alignment with Earth's spin vector, and therefore point north, an orbital gyrocompass uses a horizon sensor to sense the direction to Earth's center, and a gyro to sense rotation about an axis normal to the orbit plane. Thus, the horizon sensor provides pitch and roll measurements, and the gyro provides yaw. See Tait-Bryan angles . A Sun sensor

4556-399: The wideband transmitters and the directional antenna. All data received from the omnidirectional antenna were noisy. During September 1964, acceptable data were received over 70% of the orbital path. By June 1969, data acquisition was limited to 10% of the orbital path. The spacecraft was placed in a standby status November 25, 1969, and all support was terminated November 1, 1971. By April 1970

4624-408: Was one experiment for each of the following types of studies: interplanetary dust, VLF, Lyman-alpha, gegenschein, atmospheric mass, and radio astronomy. Real-time data were transmitted at 1, 8, or 64 kbs depending on the distance of the spacecraft from the Earth. Playback data were tape recorded at 1 kbs and transmitted at 64 kbs. Two wideband transmitters, one feeding into an omnidirectional antenna and

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