ACTUATOR CROSS-REFERENCE TO RELATED APPLICATIONS [0001] This application claims the benefit of, and priority to, United States Provisional Application No.63/398,453, filed on August 16, 2022, the content of which is hereby incorporated by reference herein in its entirety for all purposes. FIELD [0002] The present disclosure relates generally to the field of suspension actuators. BACKGROUND [0003] Active and passive components may be used to reduce transmission of vibrations from an unsprung mass to a sprung mass. Passive components may include springs. Active components may include actuators that are configured to apply forces between the unsprung mass and the sprung mass. As an example, using input from sensors, active suspension actuators can apply forces in opposition to vibrations from the unsprung mass. Active suspension actuators can also control a height between the sprung mass and the unsprung mass. SUMMARY [0004] One aspect of the disclosure is a suspension actuator that includes a top mount that is connectable to a sprung mass, a bottom mount that is connectable to an unsprung mass, an upper housing, and a lower housing. The suspension actuator also includes an air spring that is configured to receive a working gas in an internal chamber that is defined in part by the upper housing and the lower housing, and a ball screw actuator that is connected to the upper housing and the lower housing. The suspension actuator also includes a tube isolator that connects the top mount to the upper housing and is configured to transfer forces between the top mount and the upper housing. The tube isolator has an outer ring that is connected to the top mount, an inner ring that is connected to the upper housing, and a compliant member that is located between the outer ring and the inner ring. The tube isolator also has a first stop surface that is configured to limit axial movement of the top mount relative to the upper housing in a first direction, and a second stop surface that is configured to limit axial movement of the top mount relative to the upper housing in a second direction. [0005] In some implementations of the suspension actuator, the first stop surface and the second stop surface are formed on the inner ring. In some implementations of the suspension actuator, the tube isolator includes a compliant material layer that is formed on the first stop surface and the second stop surface. [0006] In some implementations of the suspension actuator, a first engagement surface of the top mount is positioned above the first stop surface and is engageable with the first stop surface, and a second engagement surface of the top mount is positioned below the second stop surface and is engageable with the second stop surface. In some implementations of the suspension actuator, the inner ring includes a wall portion and a projection that extends radially inward from the wall portion, the first stop surface and the second stop surface are located on the projection, and the projection is positioned between the first engagement surface and the second engagement surface of the top mount. [0007] In some implementations of the suspension actuator, the air spring defines part of a first load path between the top mount and the bottom mount, the ball screw actuator defines part of a second load path between the top mount and the bottom mount, and the tube isolator defines part of the second load path between the top mount and the bottom mount. In some implementations of the suspension actuator, the ball screw actuator includes an electric motor, a ball nut, a ball spline, and a shaft, wherein torque is selectively applied to the ball nut by the electric motor to apply force along the second load path, and the ball spline restrains rotation of the shaft relative to the upper housing. [0008] Another aspect of the disclosure is a suspension actuator that includes an upper housing, a lower housing, an air spring that is configured to receive a working gas in an internal chamber that is defined in part by the upper housing and the lower housing, and a ball screw actuator that is connected to the upper housing and the lower housing. The ball screw actuator has a stator, a tubular rotor, a ball nut that is rotated by the tubular rotor, a ball spline, and a shaft that extends through the tubular rotor, where at least part of the ball nut is located inside the tubular rotor and radially inward from the stator. [0009] In some implementations of the suspension actuator, the ball nut is supported by angular contact bearings. In some implementations, the suspension actuator includes a shoulder that is located in the tubular rotor, and a bump stop that is connected to the shaft and is engageable with the shoulder of the tubular rotor. [0010] In some implementations of the suspension actuator, the air spring defines part of a first load path between a top mount and a bottom mount, and the ball screw actuator defines part of a second load path between the top mount and the bottom mount. In some implementations of the suspension actuator, torque is selectively applied to the ball nut by electromagnetic interaction of the stator and the tubular rotor to apply force along the second load path, and the ball spline restrains rotation of the shaft relative to the upper housing. In some implementations of the suspension actuator, the air spring includes an air spring membrane that is connected to the upper housing and the lower housing. In some implementations of the suspension actuator, the air spring membrane defines a rolling lobe configuration. [0011] Another aspect of the disclosure is a suspension actuator that includes an upper housing, a lower housing, an air spring that is configured to receive a working gas in an internal chamber that is defined in part by the upper housing and the lower housing, and a ball screw actuator that is connected to the upper housing and the lower housing. The ball screw actuator has a hollow shaft that allows transmission of the working gas between a lower portion of the internal chamber and an upper portion of the internal chamber. [0012] In some implementations of the suspension actuator, the ball screw actuator includes an electric motor, the lower portion of the internal chamber is located below the electric motor, and the upper portion of the internal chamber is located above the electric motor. In some implementations, the suspension actuator includes a pressure sensor that is located in the upper portion of the internal chamber to measure a pressure of the working gas. [0013] In some implementations of the suspension actuator, the air spring includes an air spring membrane that is connected to the upper housing and the lower housing. In some implementations of the suspension actuator, the air spring membrane defines a rolling lobe configuration. In some implementations of the suspension actuator, the air spring defines part of a first load path between a top mount and a bottom mount, and the ball screw actuator defines part of a second load path between a top mount and a bottom mount. BRIEF DESCRIPTION OF THE DRAWINGS [0014] FIG.1 is a schematic illustration of a suspension actuator in a vehicle. [0015] FIGS.2A-2C are schematic cross-section illustrations of the suspension actuator. [0016] FIG.3 is a detail view of the suspension actuator. [0017] FIG.4 is a schematic illustration of a shaft of the suspension actuator. [0018] FIG.5 is a detail view of the suspension actuator. DETAILED DESCRIPTION [0019] The disclosure herein relates to suspension actuators that are usable in an active suspension system to control the ride height of a vehicle and to reduce transmission of vibrations from an unsprung mass of the vehicle to a sprung mass of the vehicle. The suspension actuators described herein include two load paths between a top mount and a bottom mount of the suspension actuator. The first load path includes an air spring, and is configured to control the ride height of the vehicle and to dampen low frequency vibrations. The second load path includes a ball screw actuator, and is configured to dampen high frequency vibrations by applying force in opposition to vibrations experienced by the unsprung mass of the vehicle. The features described herein are directed to reducing the packaging space required for the suspension actuator, reducing mechanical complexity of the suspension actuator, and/or improving performance of the suspension actuator. [0020] FIG.1 is a schematic illustration of suspension actuator 100 in a vehicle 102. The vehicle 102 includes a body 104 (e.g., a vehicle body), a wheel assembly 106, and connecting arms 108. The vehicle 102 may be a conventional road-going vehicle that is supported by wheels and tires (e.g., four wheels and tires), as represented by the wheel assembly 106. The vehicle 102 may be a passenger vehicle or a cargo-carrying vehicle, including a passenger cabin and/or cargo space defined by the body 104. The wheel assembly 106 may include a wheel rim 110 and a tire 112 that is mounted on the wheel rim 110, with the tire 112 being configured to contact a road or other surface. The wheel rim 110 is supported for rotation, such as by connection to a wheel hub 114, a spindle, or other suitable support structure. The wheel hub 114 is connected to the body 104 so that the wheel assembly 106 is able to translate in a generally vertical direction. In the illustrated example, the wheel hub 114 is connected to the body 104 by the connecting arms 108, which extend between and are pivotally connected to the wheel hub 114 and the body 104. [0021] The suspension actuator 100 controls motion (e.g., in the generally vertical direction) of the wheel assembly 106. The suspension actuator 100 is an active suspension component that is operable to actively apply forces to the wheel assembly 106, and may be connected so that it is able to apply forces between the wheel assembly 106 and the body 104, whether connected directly or indirectly to the wheel assembly 106 and/or the body 104. For example, an upper end of the suspension actuator 100 may be connected to the body 104 and a lower end of the suspension actuator 100 may be connected to one of the connecting arms 108, as illustrated. Other configurations may be used, such as connection of the suspension actuator 100 to the wheel hub 114 or to a steering knuckle. [0022] FIGS.2A-2C are schematic cross-section illustrations of the suspension actuator 100. The suspension actuator 100 extends along a longitudinal axis 201 from a top mount 220 that is connectable to a sprung mass 218 to a bottom mount 222 that is connectable to an unsprung mass 219. The sprung mass 218 may be or include the body 104 of the vehicle 102. The unsprung mass 219 may be or include the wheel assembly 106 and/or connecting arms 108 of the vehicle 102. Other components may be included in the sprung mass 218 and/or in the unsprung mass 219. The suspension actuator 100 is able to extend (e.g., lengthen) and retract (e.g., shorten) to change the distance between the sprung mass 218 and the unsprung mass 219 in order to change the ride height of the vehicle 102 and/or in response to dynamic conditions experiences by the vehicle 102. The suspension actuator 100 also includes an upper housing 224, a lower housing 226, an air spring 228, a ball screw actuator 230, and a tube isolator 232. Components of the suspension actuator 100, including the top mount 220, the upper housing 224, and the lower housing 226 define an internal chamber 234 that is sealed and is configured to contain a working gas (e.g., air, nitrogen, or another suitable gas) of the air spring 228. These and other components of the suspension actuator 100 are impermeable in order to contain the working gas of the air spring. [0023] The top mount 220 is located at the top of the suspension actuator 100 and serves as a connection point for the suspension actuator 100 to the body 104 of the vehicle 102. The top mount 220 is configured so that it is connectable (e.g., by fasteners, by a clamping structure, by a pin, by a ball joint, or by another fastening structure) to the sprung mass 218 of the vehicle 102 to transfer forces between the sprung mass 218 and the suspension actuator 100. The top mount 220 is generally rigid, but may be a multi-part structure incorporating resilient elements (e.g., an elastomeric bushing) to allow for compliance between the suspension actuator 100 and the body 104 or other structure. In the illustrated implementation, the top mount 220 includes a primary portion 221a and a stop portion 221b that is rigidly connected to the primary portion and is located inside the suspension actuator 100. [0024] The tube isolator 232 is connected to the top mount 220 and to the upper housing 224. The tube isolator 232 functions to provide a compliant connection that allows relative motion of the top mount 220 with respect to the upper housing 224, primarily in a direction that is generally aligned with the longitudinal axis 201. [0025] The upper housing 224 is a rigid and impermeable housing that may be a single piece structure or a multi-piece structure. As an example, the upper housing 224 may be formed from metal. In the illustrated implementation, the upper housing 224 is a generally annular structure that includes a primary portion 225a that is rigidly connected to a connector portion 225b that defines a shoulder at which the diameter of the upper housing 224 decreases to facilitate connection to the tube isolator 232. The connector portion 225b defines an opening 225c that is oriented toward an interior space defined in part by and within the top mount 220 and the tube isolator 232. [0026] The lower housing 226 is a rigid housing that may be a single piece structure or a multi- piece structure. As an example, the lower housing 226 may be formed from metal. In the illustrated implementation, the lower housing 226 is a generally annular, approximately cylindrical structure having an open end that is oriented toward the upper housing 224, and a closed end that is opposite the open end and extends generally transverse to the longitudinal axis 201. The upper housing 224 extends telescopically into the open end of the lower housing 226, such that a radial gap 236 is defined between the upper housing 224 and the lower housing 226 in an overlapping region. The lower housing 226 is positioned radially outward from the upper housing 224 within the overlapping region. In an alternative implementation the lower housing 226 could have a smaller diameter than the upper housing 224 such that the lower housing 226 extends into the upper housing 224. [0027] On the exterior of the lower housing 226 and at the closed end thereof, the bottom mount 222 is connected to the lower housing 226. The bottom mount 222 is configured connect the suspension actuator 100 to the unsprung mass 219. The bottom mount 222 is a connector of any suitable type, configured so that it is connectable (e.g., by fasteners, by a clamping structure, by a pin, by a ball joint, or by another fastening structure) to the unsprung mass 219 of the vehicle 102. [0028] The suspension actuator 100 defines a first load path 237a between the sprung mass 218 and the unsprung mass 219 through the air spring 228. The first load path 237a is indicated by shaded areas of FIG.2B. The first load path 237a extends between the top mount 220 and the bottom mount 222, and the air spring 228 defines part of the first load path 237a. Thus, the suspension actuator 100 defines a first load path 237a between the upper end and the lower end of the suspension actuator 100 that includes the air spring 228. [0029] The suspension actuator 100 also defines a second load path 237b between the sprung mass 218 and the unsprung mass 219 through the ball screw actuator 230. The second load path 237b is indicated by shaded areas of FIG.2C. The second load path 237b extends between the top mount 220 and the bottom mount 222, and the ball screw actuator 230 defines part of the second load path 237b. The second load path 237b may be defined through some or all of the components of the ball screw actuator 230, such as an electric motor 250, a stator 258 and a rotor 260 thereof, a shaft 252, a ball nut 254, and a ball spline 256. Thus, the suspension actuator 100 defines a second load path 237b between the upper end and the lower end of the suspension actuator 100 that includes the ball screw actuator 230. [0030] The first and second load paths 237a, 237b cooperatively function to transfer force axially between the sprung mass 218 and the unsprung mass 219. The first load path 237a is configured to carry a gravity preload of the sprung mass 218 (i.e., load due to gravity irrespective of any dynamic loading) along with a portion of a dynamic load between the sprung mass 218 and the unsprung mass 219. The second load path 237b is configured to carry another portion of the dynamic load between the sprung mass 218 and the unsprung mass 219 and provides high frequency damping functions using the ball screw actuator 230. Stated differently, the first load path 237a is intended to set a ride height for the vehicle 102 and is intended to absorb low- frequency vibrations, while the second load path 237b is intended to absorb high-frequency vibrations. [0031] The first load path 237a and the second load path 237b both apply load to the top mount 220. The air spring 228 acts directly on the top mount 220 by exposure of the top mount 220 to the pressure of the working gas in the internal chamber 234. The second load path 237b transfers load from the ball screw actuator 230 to the top mount 220 through the upper housing 224 and the tube isolator 232. [0032] As best seen in FIG.3, which is a detail view of the suspension actuator 100, the tube isolator 232 is connected to the top mount 220 and the upper housing 224 and is configured to transfer forces between the top mount 220 and the upper housing 224 so that the tube isolator 232 defines part of the second load path 237b between the top mount 220 and the bottom mount 222. The tube isolator 232 defines a compliant connection of the top mount 220 to the upper housing 224 and allows axial movement of the top mount 220 relative to the upper housing 224 in a direction that is generally aligned with the longitudinal axis 201. [0033] The tube isolator 232 has an outer ring 338 that is connected to the top mount 220 by a fixed connection, an inner ring 339 that is connected to the upper housing 224 by a fixed connection, and a compliant member 340 that is located between the outer ring 338 and the inner ring 339. The compliant member 340 is formed from an elastic and flexible material, such as an elastomeric material. The compliant member 340 allows relative motion of the outer ring 338 and the inner ring 339, for example, in response to forces along the first load path 237a and the second load path 237b. [0034] The maximum extent of motion of the top mount 220 with respect to the upper housing 224 is limited by interaction of the tube isolator 232 with the top mount 220, and more particularly, interaction of the inner ring 339 with respect to the top mount 220 since the outer ring 338 is fixed relative to the top mount 220. A first stop surface 341a is configured to limit axial movement of the top mount 220 relative to the upper housing 224 in a first direction (e.g., downward movement of the top mount 220 toward the upper housing 224), a second stop surface 341b is configured to limit axial movement of the top mount 220 relative to the upper housing 224 in a second direction (e.g., upward movement of the top mount 220 away from the upper housing 224), and a third stop surface 341c is configured to limit movement of the top mount 220 with respect to the upper housing 224 in a third direction (e.g., a radial direction relative to the longitudinal axis 201). The first stop surface 341a, the second stop surface 341b, and the third stop surface 341c are formed on the inner ring 339 of the tube isolator 232. [0035] In the illustrated implementation, a first engagement surface 342a on the primary portion 221a of the top mount 220 is positioned above the first stop surface 341a of the tube isolator 232 and is engageable with the first stop surface 341a. A second engagement surface 342b on the stop portion 221b of the top mount 220 is positioned below the second stop surface 341b of the tube isolator 232 and is engageable with the second stop surface 341b. A third engagement surface 342c on the primary portion 221a and/or on the stop portion 221b of the top mount 220 is positioned radially inward from the third stop surface 341c of the tube isolator 232 and is engageable with the third stop surface 341c. To position the first stop surface 341a, the second stop surface 341b, and the third stop surface 341c for engagement with the top mount 220, the inner ring of the tube isolator 232 includes a wall portion 343a and a projection 343b that extends radially inward from the wall portion 343a. The first stop surface 341a, the second stop surface 341b, and the third stop surface 341c are located on the projection 343b, and the projection 343b is positioned between the first engagement surface 342a and the second engagement surface 342b of the top mount 220. [0036] The tube isolator 232 may include a compliant material layer 344 that is formed on the first stop surface 341a, the second stop surface 341b, and the third stop surface 341c to cushion engagement of the tube isolator 232 with the top mount 220. The compliant material layer 344 is formed from an elastic and flexible material, and may be formed from an elastomeric material. The compliant material layer 344 may be overmolded on the first stop surface 341a, the second stop surface 341b, and the third stop surface 341c of the tube isolator 232. The compliant material layer 344 may be formed integrally with the compliant member 340, or may be separate from the compliant member 340. [0037] The first load path 237a is defined between the top mount 220 and the bottom mount 222 by the air spring 228. The air spring 228 is defined by the internal chamber 234 of the suspension actuator 100, which is defined in part by the upper housing 224, the lower housing 226, the top mount 220, the tube isolator 232 and /or other components of the suspension actuator 100. The internal chamber 234 of the air spring 228 includes an upper portion 235a that is located at the upper end of the upper housing 224, adjacent to the top mount 220 and the tube isolator 232. The internal chamber 234 of the air spring 228 also includes a lower portion 235b that is located primarily in the lower housing 226. The upper portion 235a of the internal chamber 234 is in fluid communication with the lower portion 235b to define the working volume of the air spring 228, as will be described further herein. The working volume of the air spring 228 (e.g., the volume of the of the internal chamber 234) varies according to movement of the upper housing 224 with respect to the lower housing 226 and the pressure of the working gas increases and decreases accordingly. The internal chamber 234 may be configured to receive and expel the working gas through ports, valves, lines, and/or other structures. This allows, for example, changes in the ride height of the vehicle 102. [0038] To seal the working gas within the internal chamber 234 while allowing relative motion of the upper housing 224 and the lower housing 226 at the radial gap 236, the air spring 228 includes an air spring membrane 248 that is connected to the upper housing 224 and the lower housing 226. As an example, the air spring membrane 248 may be in the form of a thin sheet of resiliently flexible material that is sealingly coupled with the upper housing 224 and the lower housing 226 such that a u-shaped fold of the air spring membrane 248 is located between the upper housing 224 and the lower housing 226 in the radial gap 236. Thus, the air spring membrane 248 may define a rolling lobe configuration that allows relative movement of the upper housing 224 and the lower housing 226. Other configurations may be used. The air spring membrane 248 may also be referred to as an air spring sleeve, an air sleeve, a diaphragm, or an air spring diaphragm. [0039] The ball screw actuator 230 is a type of linear actuator that is utilized in the suspension actuator 100 to apply forces between the top mount 220 and the bottom mount 222 of the suspension actuator 100, for example, as part of active suspension control. The ball screw actuator 230 is part of the second load path 237b, and is operable to apply forces to the second load path 237b and to transmit forces along the second load path 237b. To apply forces to the second load path 237b, the ball screw actuator 230 is connected to the upper housing 224 and is connected to the lower housing 226. The ball screw actuator 230 may be backdrivable so that it can allow extension and retraction of the suspension actuator 100 in response to external forces. [0040] The ball screw actuator 230 includes the electric motor 250, the shaft 252, the ball nut 254, and the ball spline 256. The electric motor 250, the ball nut 254, and the ball spline 256 are located in the upper housing 224. The shaft 252 is connected to the lower housing 226 and extends into the upper housing 224 along the longitudinal axis 201.As will be explained herein, torque is selectively applied to the ball nut 254 by the electric motor 250, thereby applying force to the shaft 252, while the ball spline 256 restrains rotation of the shaft 252 relative to the upper housing 224. Combined operation of the ball nut 254 and the ball spline 256 in response to rotation of the electric motor 250 results in linear extension and retraction of the shaft 252 relative to the upper housing 224 and other components of the ball screw actuator 230 to apply force along the second load path 237b through the shaft 252. [0041] The electric motor 250 includes the stator 258 and the rotor 260. The stator 258 and the rotor 260 are annular structures that may be arranged along the longitudinal axis 201 of the suspension actuator 100. The rotor 260 may extend along the longitudinal axis 201, and may extend around the shaft 252, which passes through the rotor 260. The stator 258 is arranged around the rotor 260 and is positioned radially outward from the rotor 260. The stator 258 is disposed in the upper housing 224. The stator 258 may be mounted directly to an interior wall of the upper housing 224 or may be disposed in a separate housing that is located in the upper housing 224. [0042] The stator 258 may be of conventional design, for example, including a laminated body that supports stator coils 262, where the stator coils 262 are electromagnetic components of any suitable type that are configured to be selectively energized. The stator coils 262 may be of the wire wound type or of the bar wound type. The rotor 260 is a rotatable component that extends along the longitudinal axis 201 of the suspension actuator 100. The rotor 260 includes magnetic components 264 that are located in a circular array around a tubular output shaft 266 that defines a passageway therethrough in the direction of the longitudinal axis 201. Thus, the rotor 260 may be referred to as a tubular rotor. Although a specific implementation is described herein, including the stator coils 262 and the magnetic components 264, the rotor 260 and the stator 258 may be configured according to any suitable motor-generator such that electromagnetic interaction of the rotor 260 and the stator 258 results in rotation of the rotor 260 when the electric motor 250 is energized (e.g., by selective energization of the stator coils 262). Thus, the rotor 260 is configured to rotate as a result of electromagnetic interaction between the stator 258 and the rotor 260. [0043] The shaft 252 extends through the tubular output shaft 266 of the rotor 260, for example, along the longitudinal axis 201, and is configured to interact with the ball nut 254 and the ball spline 256. As shown in FIG.4, which is a schematic illustration of the shaft 252, a helical groove 470 may be defined on the shaft 252 (e.g., extending around the shaft 252 in a helical configuration) for interaction with the ball nut 254, and axial grooves 472 may extend along the shaft 252 in the direction of the longitudinal axis 201 for interaction with the ball spline 256. [0044] The shaft 252 is a hollow shaft, having a passage 268 that extends therethrough between upper and lower ends in the direction of the longitudinal axis 201. The passage 268 of the shaft 252 allows transmission of the working gas of the air spring 228 between the lower portion 235b of the internal chamber 234, which is located above the electric motor 250 of the ball screw actuator 230, and the upper portion 235a of the internal chamber 234, which is located below the electric motor 250 of the ball screw actuator 230. In the lower portion 235b of the internal chamber 234, the working gas may enter and exit the passage 268 at the lower end of the shaft 252 through a coupler 274 that connects to the shaft 252 to the lower housing 226, or another configuration may be used, such as a port that extends radially through the shaft 252. The working gas may enter and exit the passage 268 at the upper portion 235a of the internal chamber 234 through the open end of the shaft 252. [0045] The shaft 252 may be connected to the lower housing 226, either indirectly using the coupler 274 or directly, in a suitable manner such as by use of fasteners or by welding to define a fixed connection between the shaft 252 and the lower housing 226. Thus, the shaft 252 and the lower housing 226 move in unison in response to operation of the electric motor 250 or in response to external forces that are applied to the suspension actuator 100 and reacted through the ball screw actuator 230. At a bottom end of the shaft 242, such as adjacent to the coupler 274, a bumper 275 made of a resilient and flexible material may be provided to limit downward movement of the upper housing 224 with respect to the lower housing 226 and to cushion engagement of the upper housing 224 relative to the lower housing 226. [0046] As seen in FIG.5, which is a detail view showing part of the suspension actuator 100 including the ball screw actuator 230, the tubular output shaft 266 of the rotor 260 defines an interior space having a generally cylindrical configuration, so that the shaft 252 may pass through the tubular output shaft 266. Between an upper end of the shaft 252 and the ball nut 254, a shoulder 567 is located in the interior space of the tubular output shaft 266, and extends generally transverse to the longitudinal axis 201 in the illustrated implementation. The shoulder 567 extends radially inward from the inner surface of the tubular output shaft 266 but is spaced from the outer surface of the shaft 252 and is not in engagement with the shaft 252. A bump stop 553 may be located at the upper end of the shaft 252, and is engageable with the shoulder 567 of the tubular output shaft 266 of the rotor 260 in order to define an end limit of travel for the shaft 252 relative to the ball screw actuator 230. [0047] The ball nut 254 is a rotatable component of the ball screw actuator 230. The ball nut 254 is connected to the rotor 260 of the electric motor 250 and is rotated in unison with the rotor 260. As the ball nut 254 is rotated by the rotor 260, the ball nut 254 engages the shaft 252 through engagement of recirculating ball bearings that are disposed in the ball nut 254 with the helical groove 470, which results in axial translation of the shaft 252 relative to the upper housing 224 in response to rotation of the ball nut 254. Thus, the shaft 252 is a translatable shaft, since it is able to translate linearly relative to portions of the suspension actuator 100, including the upper housing 224. [0048] As best seen in FIG.5, the ball nut 254 is coupled to the rotor 260 of the electric motor 250, and at least part of the ball nut 254 is located inside the tubular output shaft 266 of the rotor 260 (e.g., inside the tubular rotor) and located radially inward from the stator 258. An upper end of the ball nut 254 is located adjacent to and downward from the shoulder 567 that is formed inside the tubular output shaft 266. The upper end of the ball nut 254 is located above the lower end of the stator 258 and/or the stator coils 262 in the direction of the longitudinal axis 201 between the bottom mount 222 and the top mount 220. This configuration provides for compact packaging of the ball nut 254 relative to the ball screw actuator 230. In order to react the axial loads that are applied to the ball nut 254 by the shaft 252 and to allow rotation of the ball nut 254 relative to the upper housing 224 and the shaft 252, the ball nut 254 is supported with respect to the upper housing 224 by angular contact bearings 576 that are connected to the ball nut 254 and to the upper housing 224. As an example, the angular contact bearings 576 may have inner and outer raceways that are displaced relative to each other in order to allow the angular contact bearings 576 to react loads in the axial direction (e.g., in the direction of the longitudinal axis 201) and in the radial direction (e.g., radially outward from the longitudinal axis 201). [0049] The ball spline 256 is fixed relative to the upper housing 224 and is configured to restrain rotation of the shaft 252 so that the shaft 252 translates in response to rotation of the ball nut 254. The ball spline 256 includes recirculating ball bearings that engage the axial grooves 472 of the shaft 252 so that the shaft 252 is restrained from rotating with respect to the ball spline 256. Since the ball spline 256 is fixed to the upper housing 224, the shaft 252 is therefore restrained from rotating with respect to the upper housing 224. [0050] The suspension actuator 100 may include cooling features to absorb heat generated by operation of the electric motor 250 of the ball screw actuator 230. In the illustrated implementation, a cooling jacket 578 (e.g., a rigid sleeve made of metal of other suitable material) is located on the exterior of the suspension actuator 100, and extends around the upper housing 224. A cooling channel 580 is defined between the cooling jacket 578 and the upper housing 224 and the cooling jacket 578 is sealed to the upper housing 224 to prevent leakage from the cooling channel 580. A fluid cooling medium (e.g., liquid coolant) may be supplied to the cooling channel 580 to absorb heat from the upper housing 224. [0051] With further reference to FIG.1, the suspension actuator 100 may include a control system 282 that includes electrical, pneumatic, and/or hydraulic control components. Sealed ports may be formed through a portion of the suspension actuator 100, such as the upper housing 224, to allow electrical, pneumatic, and hydraulic supply lines to pass into the suspension actuator 100. The control system 282 may include control circuits that control operation of the ball screw actuator 230, pneumatic valves that control flow of the working gas into and out of the suspension actuator 100, and/or hydraulic valves that control flow of the fluid cooling medium into and out of the suspension actuator 100. [0052] To control operations of the suspension actuator 100, sensors may be located in the suspension actuator 100, such as on a sensor circuit board 284. The sensor circuit board 284 may include sensors or may be connected to sensors that are associated with other components of the suspension actuator 100. The sensor circuit board 284 may be located in the upper portion 235a of the internal chamber 234. As one example, the sensor circuit board 284 may include a pressure sensor 286 that is located in the upper portion 235a of the internal chamber 234 to measure a pressure of the working gas of the air spring 228. Other sensors that may be included in the sensor circuit board 284 or connected to the sensor circuit board 284 include a force sensor associated with the first load path 237a, a force sensor associated with the second load path 237b, a displacement sensor associated with the tube isolator 232, a displacement sensor associated with the shaft 242, a rotary encoder associated with the electric motor 250, and/or accelerometers.