Abstract: A method of weather observations by a constellation comprises at least a first cluster of three micro-satellites each orbiting around earth, and each micro-satellites comprises a spectrometer. Orbiting the three micro-satellites of the first duster around the earth in three separate orbits offset with respect to one another. Staggering the three micro-satellites with respect to one another as they orbit. Selecting the offset and the staggering, of each of the three micro-satellites with respect to one another, so that each one of the three micro-satellites have a substantially identical viewing area as each one of the three micro-satellites orbits around the earth.

Abstract: Systems and methods for calculating launch sites for a satellite constellation are provided. A carrier aircraft may be configured to launch a first satellite into the first orbit and a second satellite into the second orbit. In some embodiments, information about an accessible range of the aircraft may be received. Based on the received information, a geographical area that the aircraft can access without landing may be calculated. Using received information and the orbit parameters of the first orbit and the second orbit, a first launch site for launching the first satellite and a second launch site for launching the second satellite may be calculated. The first launch site may comprise a first geographical position and a first launch time, and the second launch site may comprise a second geographical position and a second launch time. Both launch sites may be within the calculated geographical area.

Abstract: Apparatus and methods for controlling a spacecraft for a transfer orbit. The spacecraft includes a momentum subsystem that stores angular momentum relative to a center of mass of the spacecraft, and a propulsion subsystem that includes electric thrusters. A controller identifies a target spin axis for the spacecraft, determines gimbal angles for electric thruster(s) that so that thrust forces from the electric thrusters are parallel to the target spin axis, and initiates a burn of the electric thruster(s) at the gimbal angles. The controller controls the momentum subsystem to compensate for a thruster torque produced by the burn of the electric thrusters. The momentum subsystem is able to produce a target angular momentum about the center of mass, where a coupling between the target angular momentum and an angular velocity of the spacecraft creates an offset torque to counteract the thruster torque.

Abstract: A thrust nozzle system is provided for a satellite designed to be stabilized in autorotation over a geostationary orbit, the satellite comprising three reference axes X, Y and Z, the Y axis representing the North/South axis and the Z axis corresponding to an Earth pointing direction. The thrust nozzle system comprises a first set of thrust nozzles configured for maintaining the satellite in station, the first set comprising an even number of thrust nozzles using electrical propulsion, with a pre-adjusted orientation, the even number being equal to at least 4, the thrust nozzles being oriented along three spatial components, and having, taken in pairs, different signs of X and Y components.

Abstract: A system and method are provided for determining the orientation of an inertial measurement unit (IMU). The method calculates a gyroscopic quaternion, and when the IMU accelerometer reading is about equal to gravity (1 G), a field quaternion is calculated using IMU accelerometer readings. Estimates are made of angular orientation errors due to IMU angular velocity and linear acceleration, and these angular orientation errors are used to selectively mix the gyroscopic quaternion and field quaternion to supply a current sample quaternion. Alternatively, if the accelerometer reading is not about equal to 1 G, the gyroscopic quaternion is used as the current sample quaternion. In one aspect, IMU gyroscope readings and IMU accelerometer readings are calibrated in response to determining a lack of IMU movement. Near-zero gyroscope reading jitter is removed by setting the IMU gyroscopic reading to zero, when the gyroscopic reading is near zero.

Abstract: Methods, systems, and computer readable media for topology management and geographic routing in mobile ad-hoc networks are disclosed. One method for geographic routing in mobile ad-hoc networks includes receiving a first packet requiring routing at a first mobile node configured to operate in a mobile ad-hoc network where the first mobile node and other mobile nodes move relative to each other and are connected using directional wireless communications links. The method also includes performing greedy routing for the first packet, and in response to determining that no next hop neighbor node is closer to the destination than the first mobile node, performing face routing of the first packet, wherein performing greedy routing or face routing includes storing local topology information at the mobile nodes and using the local topology information when making routing decisions.

Abstract: Described herein are systems and methods for attitude determination using infrared Earth horizon sensors (EHSs) with Gaussian response characteristics. Attitude information is acquired by detecting Earth's infrared electromagnetic radiation and, subsequently, determining the region obscured by Earth in the sensors' fields of view to compute a nadir vector estimation in the spacecraft's body frame. The method can be applied when two sensors, each with known and distinct pointing directions, detect the horizon, which is defined as having their fields of view partially obscured by Earth. The method can be implemented compactly to provide high-accuracy attitude within small spacecraft, such as CubeSat-based satellites.

Abstract: The present invention provides a method for refined attitude control based on output feedback for a flexible spacecraft.

Abstract: Methods and computer products for establishing at least one of attitude, direction and position of a moving platform. At least one skymark of known ephemeris is imaged at each of a first set of discrete instants by means of an optical sensor coupled to the platform. A measurement is also obtained of the attitude of the platform at each of a second set of discrete instants by means of an inertial navigation system. A recursive of estimation filter is then applied to successive skymark position vectors to update an estimate of platform navigation state, with the measurement of attitude of the platform tightly coupled to the estimate of platform navigation state as updated by the recursive estimation filter. Various techniques of frame stacking and multi-hypothesis tracking may be applied to improve the robustness of navigation solutions.

Abstract: A deployment algorithm that populate a group of companion satellites around a center satellite, and a control algorithm for maintaining the companion satellites in close formation around the center satellite.

Abstract: An inertial measurement system for a longitudinal projectile comprising: a first, roll gyro to be oriented substantially parallel to the longitudinal axis of the projectile; a second gyro and a third gyro with axes arranged with respect to the roll gyro such that they define a three dimensional coordinate system; a controller, arranged to: compute a current projectile attitude from the outputs of the first, second and third gyros, the computed attitude comprising a roll angle, a pitch angle and a yaw angle; compare the computed pitch and yaw angles with expected values for the pitch and yaw angles; calculate a roll angle error and a roll scale factor error based on the difference between the computed pitch and yaw angles and the expected pitch and yaw angles; and apply the calculated roll angle error and roll scale factor error to the output of the roll gyro.

Abstract: A tunable mass damper incorporates a frame and a voice coil supported in the frame. A magnet concentric with the voice coil is movable relative to the housing via the voice coil. A plurality of flexures having a first end extending from the magnet and an arm releasably coupled to the frame are adjustable to an effective length for a desired frequency of reciprocation of the magnet.

Abstract: A method for controlling an antenna of a mobile communication application system based on double quaternions in MEMS inertial navigation. The method comprises: introducing an antenna control quaternion based on a navigation attitude quaternion; in each interrupt cycle of a navigation computer, updating the two quaternions respectively using a carrier system measured by a gyroscope relative to a rotation vector of an ideal platform coordinate system; in each filter cycle, correcting the error of the navigation attitude quaternion respectively using a Kalman filter; according to the relationship between the attitudes determined by the two attitude quaternions, determining the angular speed in an antenna control instruction; and finally, driving a servo system to rotate at an antenna servo control angle converted by an antenna control quaternion attitude.

Abstract: A system and method for preventing a gimbal from exceeding a predetermined gimbal rate limit includes receiving a gimbal rate command and a gimbal rate feedback signal representative of sensed gimbal rate. The gimbal rate command and the gimbal rate feedback signal are compared, in a control circuit, to determine a gimbal rate error. A predetermined gain scaling factor is applied, in the control circuit, to the gimbal rate command to generate a scaled gimbal rate command. The gimbal is disabled when the gimbal rate error is greater than or equal to the scaled gimbal rate.

Abstract: A dual stage vehicle attitude control system includes a first attitude control module having at least two momentum wheels arranged to provide zero momentum vehicle attitude control, each momentum wheel comprises a limited travel two axis gimbal that pivots the momentum wheel along two of the three axes of the vehicle, a second attitude control module having reaction wheels arranged in a pyramid configuration to provide vehicle attitude control along at least one control axis that is common with a control axis of the at least two momentum wheels, and a controller connected to the first attitude control module and the second attitude control module, the controller being configured to coordinate actuation of the first attitude control module and the second attitude control module to rotate the vehicle in at least one of three axes of a vehicle.

Abstract: A system and method for mitigating an occurrence of a dry spot, the method may include: (1) predicting the occurrence of the dry spot by at least one of determining a location of the occurrence of the dry spot, determining a date of the occurrence of the dry spot, and determining a duration of the occurrence of the dry spot; (2) generating a visualization of the occurrence of the dry spot, and (3) modifying a star catalog to reduce an impact of the dry spot by at least one of generating a set of modification to modify the star catalog, generating a modification schedule for modifying the star catalog, and uploading the set of modifications to the star catalog.

Abstract: A method for stationing a satellite, comprises: determining a predefined trajectory for stationing of the satellite based on a model of movement of the satellite; determining parameters of the predefined control law of approximation of the trajectory and by minimizing impact on the control law of deviation from a trajectory followed by the satellite using parameters of the control law; determining a state vector of the satellite; determining a deviation between the state vector and the predefined trajectory; determining Lagrange multipliers based on a current state vector of the satellite, on a deviation between current state vector and predefined trajectory and on parameters of the predefined control law; determining parameters of the current control law of the engines based on the Lagrange multipliers and by derivation of a parameter representative of an effect of engines on the real trajectory; and controlling engines based on parameters of the current control law.

Abstract: An electronic device including a processor, at least one sensor in communication with the processor, wherein the processor is configured to determine an orientation of the device and drop event based on input from the at least one sensor. The electronic device further includes a motor in communication with the processor and a mass operably connected to the motor. The processor is configured to drive the motor when a drop event is determined and the mass is configured to rotate with respect to the motor to alter the orientation of the device.

Abstract: The present disclosure relates to the deorbiting of satellites in low orbit that have entered safe hold mode. A device makes it possible to decide in an autonomous manner and on the basis of information existing in the satellite, when and where to trigger a series of short thruster manoeuvres to modify the satellite orbit with the aim of deorbiting.

Abstract: A system and a method for commanding a spacecraft to perform a three-axis maneuver purely based on “position” (i.e., attitude) measurements. Using an “inertial gimbal concept”, a set of formulae are derived that can map a set of “inertial” motion to the spacecraft body frame based on position information so that the spacecraft can perform/follow according to the desired inertial position maneuvers commands. Also, the system and method disclosed herein employ an intrusion steering law to protect the spacecraft from acquisition failure when a long sensor intrusion occurs.

Abstract: A method of controlling the attitude of a satellite in orbit around a celestial body. The attitude of the satellite being controlled by a momentum storage device and controllable surfaces of the satellite configured to create desaturation torques in the storage device by using solar pressure. The controllable surfaces are arranged on solar panels mobile in rotation around an axis Y. At least one electric thruster configured to control the orbit of the satellite also controls the attitude of the satellite. The orientation of the electric thruster is controlled to activate the electric thruster with a thrust direction deliberately not aligned with a center of mass of the satellite to create desaturation torques in the storage device along axis Y. The controllable surfaces are controlled to create desaturation torques of the storage device in a plane orthogonal to the Y axis.

Abstract: Disclosed herein is a method for determining a trajectory for a transfer of a spacecraft from a starting space body to a target space body with respect to a given central space body, wherein the determined trajectory is optimal with respect to a given space mission requirement to be met by the transfer of the spacecraft. The method comprises providing, according to the Pontryagin maximum principle, a physical-mathematical model relating model quantities and physical quantities representing the transfer of the spacecraft with respect to the given central space body.

Abstract: A satellite inclination control method is provided. The method includes tracking optimal inclination vector control cycles for a satellite in near geosynchronous orbit, using control rates disposed to counter inclination growth of the satellite, where the control rates include continuously or quasi-continuously firings of a thruster, and where the control rates are disposed to provide convergence to the optimal inclination vector control cycles in the presence of variances in orbit determination, maneuver implementation and orbit propagation modeling errors.

Abstract: A system and method for propelling spacecraft is disclosed. An electrical propulsion system is mounted on a base stage. A plurality of spacecraft couplers are also mounted on the base stage. Each spacecraft coupler securedly attaches a spacecraft to the base stage. Each spacecraft includes an internal power source that is coupled to the electrical propulsion system via an electrical connection. The internal power source consists of solar panels and/or batteries. A power regulation circuit is coupled between the electrical propulsion system and each internal power source. The power regulation circuit is draws an equal and proportional amount of power from each spacecraft. The spacecraft are preferably satellites and the electrical propulsion system preferably propels the base stage and attached satellites from a lower-Earth orbit to a higher-Earth orbit so that the electrical propulsion system in each satellite need only be capable of providing propulsion for orbit maintenance and maneuvering.

Abstract: An improved Horizontal Situation Indicator (HSI) module for use with an aircraft, wherein the HSI module is adapted for accepting Bank Angle Commands or waypoint data from the GPS flight module and for using the same to determine a heading error. The HSI module is further adapted for outputting the heading error to the Flight Director module where it can be used to create a Roll Command for output to the Auto-Pilot, whereby the Auto-Pilot can be commanded to follow a turn using the HSI and the Flight Director without requiring an additional module be added to the aircraft to create the heading error for use by the Flight Director. The waypoint data can be of the “flyover” type or the “flyby” type.

Abstract: A system and methods are provided for combining systems of an upper stage space launch vehicle for enhancing the operation of the space vehicle. Hydrogen and oxygen already on board as propellant for the upper stage rockets is also used for other upper stage functions to include propellant tank pressurization, attitude control, vehicle settling, and electrical requirements. Specifically, gases from the propellant tanks, instead of being dumped overboard, are used as fuel and oxidizer to power an internal combustion engine that produces mechanical power for driving other elements including a starter/generator for generation of electrical current, mechanical power for fluid pumps, and other uses. The exhaust gas from the internal combustion engine is also used directly in one or more vehicle settling thrusters. Accumulators which store the waste ullage gases are pressurized and provide pressurization control for the propellant tanks.

Abstract: A system and methods are provided for combining systems of an upper stage space launch vehicle for enhancing the operation of the space vehicle. Hydrogen and oxygen already on board as propellant for the upper stage rockets is also used for other upper stage functions to include propellant tank pressurization, attitude control, vehicle settling, and electrical requirements. Specifically, gases from the propellant tanks, instead of being dumped overboard, are used as fuel and oxidizer to power an internal combustion engine that produces mechanical power for driving other elements including a starter/generator for generation of electrical current, mechanical power for fluid pumps, and other uses. The exhaust gas from the internal combustion engine is also used directly in one or more vehicle settling thrusters. Accumulators which store the waste ullage gases are pressurized and provide pressurization control for the propellant tanks.

Abstract: Various embodiments of the present invention include assemblies and methods for minimizing the amplitude of attitude jitter. In one embodiment, a split flywheel assembly includes a plurality of independent concentric flywheels axially aligned and in operable engagement with one another such that each flywheel is configured to be independently controlled in order to manipulate the phase difference therebetween.

Abstract: Methods and apparatus are presented for spacecraft operation in which a control problem is formulated using a control law or steering law as a path constraint or as a dynamic constraint, and the control problem is solved to provide a guidance command trajectory for use in operating spacecraft control momentum gyroscopes to guide the spacecraft from an initial state to a desired final state.

Abstract: A method and apparatus for deploying a group of panels. An apparatus comprises a group of panels in a folded configuration against a side of a spacecraft, a group of flexible members connected to the group of panels, and an interface system associated with the group of panels and the group of flexible members. The interface system is configured to move the group of panels from the folded configuration to a deployed configuration when the group of flexible members is extended from the spacecraft.

Abstract: An improved airship having a plurality of resilient gasbags & gas containers, a straight fuselage tubular hull with an inner air passageway & propulsion means located therein, connecting air inlet & outlet funnels fore & aft, with air deflector cones axially positioned therein, and a plurality of bifurcated winged air control surfaces axially affixed vertically & horizontally across the air inlet & outlet funnels fore & aft; further, a plurality of vectored air passageways & mechanisms, and propulsion, reverse, & directional rocket thrusters, positioned fore & aft, top, bottom, port & starboard; thereby providing improved speed, maneuverability, efficiency, adverse weather capability, reduced forward air resistance, & rearward drag; furthermore space, outer & inner atmosphere ingress & egress.

Abstract: The method for unloading the inertia wheels of a spacecraft comprising three references axes X, Y, Z, the axis Z corresponding to a pointing direction, consists in inverting the direction of accumulation of the angular momentum in the wheels by automatic rotational flipping of the spacecraft about the axis Z, the pointing direction remaining fixed. The method has application to the field of satellites or of interplanetary probes.

Abstract: A method is provided for controlling a set of at least two satellites, designed to provide a service on a geostationary orbit, rendering said service on a non-geostationary orbit, in which means involved in the performance of said service, installed on board a satellite, are deactivated when the sun can damage it, and means involved in the performance of said service installed on board another satellite of the set are activated, when this is necessary to the continuity of the service.

Abstract: Spacecraft transfer orbit operations include separating a spacecraft from a launch vehicle, while in a launch vehicle transfer orbit. The spacecraft includes a propulsion subsystem and a spacecraft controller that controls the spacecraft in a three-axis stabilized mode. With the spacecraft continuously in the three-axis stabilized mode, one or more orbit raising maneuvers are performed by firing either or both of a chemical thruster and an electric thruster firing. Any two consecutive orbit raising maneuvers are separated by a respective intervening coast period. While in the three-axis stabilized mode, the spacecraft does not rotate about any axis at a rate greater than 0.1 degree/sec and dumping of momentum stored in a reaction wheel system is avoided.

Abstract: A spacecraft reaction control system comprising: a spacecraft having a center of mass; a length of tether extending from said spacecraft and offset from said spacecraft's center of mass and means for controllably changing said extension of said offset such that a variable force is exerted upon said spacecraft by said tether, said force being offset from said center of mass.

Abstract: Technology for predicting and correcting a trajectory is described. The technology can create a model to predict a position of the reusable launch vehicle at a time in the future; observe a wind condition during ascent of the reusable launch vehicle; store the observed wind condition in a wind map; predict during ascent a position and a terminal lateral velocity of the reusable launch vehicle at a terminal altitude; and correct a flight trajectory of the reusable launch vehicle based on the wind map.

Abstract: A method of controlling inertial attitude of an artificial satellite in order to perform a navigation function and to maximize terrestrial coverage of the Earth by the satellite. The method includes deploying the artificial satellite in an orbit about the poles of the Earth; applying gyroscopic precession to the artificial satellite spin axis to precess and maintain the satellite near the ecliptic pole; deploying the artificial satellite so that the spin axis is initially perpendicular to or substantially perpendicular to sun lines; and applying gyroscopic precession to the artificial satellite spin axis to precess the spin axis away from an initial deployed attitude at a selectively-variable precession rate and to maintain the spin axis perpendicular to or substantially perpendicular to the sun lines.

Abstract: A method of and apparatus for determining and controlling the inertial attitude of a spinning artificial satellite without using a suite of inertial gyroscopes. The method and apparatus operate by tracking three astronomical objects near the Earth's ecliptic pole and the satellite's and/or star tracker's spin axis and processing the track information.

Abstract: A system, method, and apparatus are disclosed for agile dedicated spacecrafts for spinning microwave imagers and sounders. In one or more embodiments, the system, method, and apparatus involve an agile, zero net-momentum, spinning space vehicle, which includes a body and an instrument package. In one or more embodiments, the instrument package is mounted directly onto the body such that the space vehicle can point the instrument package not only along the space vehicle's orbital velocity vector, but in any direction within the space vehicle's field of regard. The space vehicle's spin axis is aligned with the instrument package's scan axis. The space vehicle experiences zero net-momentum on orbit by including a counter-rotating momentum storage device. In one or more embodiments, the instrument package is a scanning microwave imaging/sounding instrument, which is utilized as an Earth climate and weather sensor.

Abstract: An improved method for launch vehicle guidance is disclosed. A pre-computed energy-angular momentum (E-J) curve to place a launch vehicle into a target orbit is received and stored. An energy, angular momentum, radial distance, velocity magnitude, and flight path angle of the launch vehicle are computed from state vector data while the launch vehicle is traveling to the target orbit. The pre-computed E-J curve and the computed energy, angular momentum, radial distance, velocity magnitude, and flight path angle of the launch vehicle are used to determine pitch and pitch rate of the launch vehicle.

Abstract: Present novel and non-trivial systems and methods for embedding aircraft attitude data within a pixel data set and detecting inconsistent aircraft attitude information are disclosed. A pixel data set representative of the scene outside the aircraft is generated based upon the navigation data and the terrain data, attitude-exclusive data is generated based upon orientation data, and attitude-exclusive data is embedded into the pixel data set to form an embedded pixel data set. Attitude-exclusive data is comprised of attitude-exclusive pixel data having first and second pixel locations or attitude-exclusive ancillary data. Attitude-exclusive data is compared against separately-provided reference attitude data for the purpose of detecting inconsistent attitude information.

Abstract: A method for controlling the attitude of a satellite in orbit around a celestial object, the satellite including an observation instrument, a solar panel, a radiator and a star sensor which are arranged on the satellite such that, in a reference frame associated with the satellite and defined by three orthogonal axes X, Y, and Z, the observation instrument has its observation axis parallel to the Z-axis, the solar panel is parallel to the Y-axis, the radiator is arranged on one of the sides ?X, +Y, or ?Y of the satellite, and the star sensor points to the negative X values side. The roll and pitch attitudes of the satellite are controlled during an activity period to direct the observation instrument towards areas of the celestial object to be observed, and the yaw attitude of the satellite is controlled to keep the sun on the positive X values side and ensure that a solar panel minimum insolation constraint is satisfied during observation phases of the activity period.

Abstract: The invention set forth herein describes propulsive guidance methods and apparatus for controlling and shaping an atmospheric skip reentry trajectory for a space vehicle. Embodiments of the invention may utilize a powered explicit guidance algorithm to provide a closed-loop control method for controlling a space vehicle during a skip reentry maneuver.

Abstract: Some embodiments relate to a method of controlling a flight of a flight vehicle according to a first mode of operation and changing the mode of operation to a second mode of operation having a different bandwidth than the first mode of operation. Other embodiments relate to a flight-control system for a flight vehicle configured to control a flight of a flight vehicle according to a first mode of operation and to control the flight of the flight vehicle according to a second mode of operation to use less energy than the first mode of operation. Other embodiments relate to a control actuation system configured to control positions of aerodynamic elements in a flight vehicle in response to commands from a guidance system according to a first mode of operation and to change the mode of operation to a second mode of operation having a different bandwidth than the first mode of operation.

Abstract: A method is provided for controlling a set of at least two satellites, designed to provide a service on a geostationary orbit, rendering said service on a non-geostationary orbit, in which means involved in the performance of said service, installed on board a satellite, are deactivated when the sun can damage it, and means involved in the performance of said service installed on board another satellite of the set are activated, when this is necessary to the continuity of the service.

Abstract: An exoatmospheric device comprises an inertial measurement unit comprising a spin axis gyroscope adapted to obtain data regarding angular rotation of the exoatmospheric device about a spin axis, and at least one off-spin axis gyroscope adapted to obtain data regarding angular oscillation of the spin axis. The exoatmospheric device further comprises a processing unit coupled to the inertial measurement unit and adapted to detect attitude error by analyzing correlations between the measured rotation about the spin axis and the measured angular oscillation of the spin axis.

Abstract: Provided is a method and system for maneuvering a first spacecraft relative to a nearby second spacecraft that occupies a finite volume of space including obstacles in the vicinity of the second from a measured present relative position to a desired ending relative position. A trajectory is computed for the first spacecraft from the present relative position to the ending relative position using the A* algorithm. One or more thrusters of the first spacecraft are then fired. The first spacecraft's relative position and velocity are then measured and compared to the computed trajectory.

Abstract: The aim of the method of controlling at least one mechanical system exhibiting at least one flexible structure element and at least one actuator or group of actuators is to reduce the level of vibrations of said element while controlling the actuator or group of actuators in such a way as to achieve at least one objective assigned to the mechanical system. The control consists of increments having to be carried out at a sampling period T, each of the increments being constant in amplitude in a sampling time interval extending between two successive sampling instants and each of the increments being applied during a duration which is less than or equal to the sampling period T. In each sampling interval, at least one of the initial and final instants of application of the increment is modified by adding a variable, random or pseudo-random, temporal deviation dT.

Abstract: A system and a method for commanding a spacecraft to perform a three-axis maneuver purely based on “position” (i.e., attitude) measurements. Using an “inertial gimbal concept”, a set of formulae are derived that can map a set of “inertial” motion to the spacecraft body frame based on position information so that the spacecraft can perform/follow according to the desired inertial position maneuvers commands. Also, the system and method disclosed herein employ an intrusion steering law to protect the spacecraft from acquisition failure when a long sensor intrusion occurs.

Abstract: Vehicle attitude is estimated relative to a ground surface over which the vehicle is traveling. An actual image of the ground surface over which the vehicle is traveling is compared with stored or predicted model images of the ground surface. The model images have corresponding known vehicle attitudes associated therewith. For one of the model images that most closely matches the actual image, the known vehicle attitude associated therewith is an estimate of an actual vehicle attitude relative to the ground surface over which the vehicle is traveling.