Solar array deployment

A method for solar array (28a, 28b) deployment includes deploying a first portion of solar cells of a solar array responsive to a first drag condition, charging a battery (26) with the first portion of solar cells, activating an electric thruster (24) at a first power level using the first portion of solar cells, deploying a second portion of solar cells of the solar array responsive to a second drag condition that is lower than the first drag condition, and activating the electric thruster at a second power level that is higher than the first power level using the first portion of solar cells and the second portion of solar cells.

BACKGROUND

Space vehicles, such as satellites, may include a solar array for generating power for propulsion and onboard components. A solar array is typically stowed during launch of the space vehicle and is later deployed to a relatively large surface area of solar cells for power generation.

SUMMARY

A method for solar array deployment according to an example of the present disclosure includes deploying a first portion of solar cells of a solar array responsive to a first drag condition, charging a battery with the first portion of solar cells, activating an electric thruster at a first power level using the first portion of solar cells, and deploying a second portion of solar cells of the solar array responsive to a second drag condition. The second drag condition is lower than the first drag condition. The electric thruster is then activated at a second power level using the first portion of solar cells and the second portion of solar cells. The second power level is higher than the first power level.

A further embodiment of any of the foregoing embodiments includes raising an orbit of a vehicle attached to the solar array using the electric thruster, and the deploying of the second portion of solar cells is after the raising.

In a further embodiment of any of the foregoing embodiments, the first drag condition is at a first altitude and the second drag condition is at a second, higher altitude.

In a further embodiment of any of the foregoing embodiments, the deploying of the first portion of solar cells and the deploying of the second portion of solar cells include unfolding the solar array.

In a further embodiment of any of the foregoing embodiments, the deploying of the first portion of solar cells includes unrolling the solar array.

A vehicle with a solar array according to an example of the present disclosure includes a vehicle body that has an electric thruster and a battery operable to activate the electric thruster to produce thrust. A solar array is attached to the vehicle body, and a controller is configured to deploy a first portion of solar cells of the solar array responsive to a first drag condition to charge the battery with the first portion of solar cells, activate the electric thruster at a first power level using the first portion of solar cells, deploy a second portion of solar cells of the solar array responsive to a second drag condition that is lower than the first drag condition, and activate the electric thruster at a second power level using the first portion of solar cells and the second portion of solar cells. The second power level is higher than the first power level.

In a further embodiment of any of the foregoing embodiments, the controller is configured to raise an orbit of the vehicle body using the electric thruster and then deploy the second portion of solar cells.

In a further embodiment of any of the foregoing embodiments, the first drag condition is at a first altitude and the second drag condition is at a second, higher altitude.

In a further embodiment of any of the foregoing embodiments, the solar array is moveable between stowed and deployed positions. The solar array is rolled in the stowed position.

In a further embodiment of any of the foregoing embodiments, the vehicle body is a satellite.

In a further embodiment of any of the foregoing embodiments, the controller is mounted in the vehicle body.

In a further embodiment of any of the foregoing embodiments, the first portion of solar cells deploys by unrolling.

A method for solar array deployment according to an example of the present disclosure includes deploying a first portion of solar cells of a solar array, charging a battery with the first portion of solar cells, activating an electric thruster at a first power level using the first portion of solar cells, raising an orbit of a vehicle attached to the solar array, deploying a second portion of solar cells of the solar array after raising the orbit of the vehicle, and activating the electric thruster at a second power level using the first portion of solar cells and the second portion of solar cells. The second power level is higher than the first power level.

In a further embodiment of any of the foregoing embodiments, the deploying of the first portion of solar cells is responsive to a first drag condition and the deploying of the second portion of solar cells is responsive to a second, lower drag condition.

In a further embodiment of any of the foregoing embodiments, the deploying of the first portion of solar cells and the deploying of the second portion of solar cells includes unfolding the solar array.

In a further embodiment of any of the foregoing embodiments, the deploying of the first portion of solar cells includes unrolling the solar array.

DETAILED DESCRIPTION

FIG. 1schematically illustrates an example vehicle20. In this example, the vehicle20is a satellite; however, it is to be understood that this disclosure is also applicable to other types of vehicles and space vehicles. As will be described, the vehicle20is operable to selectively deploy a solar array to reduce power requirements.

In the illustrated example the vehicle20includes a vehicle body22with one or more electric thrusters24. For example, the electric thruster or thrusters24are Hall Effect thrusters. Hall Effect thrusters may be characterized by low thrust and high efficiency compared to chemical thrusters. In practice an electric thruster can be used for a variety of purposes, including attitude control, station-keeping, and orbit raising to a final orbital position after separation from a launch vehicle.

A battery26is located in the vehicle body22and may be operable to activate the electric thruster or thrusters24to produce thrust; alternatively, the thrusters24may receive power directly from solar arrays28a/28bwithout the use of an intermediate battery. The solar arrays28a/28bare attached via arms30to the vehicle body22. Each arm30is extendable/retractable from the vehicle body22between stowed and deployed positions. Additionally or alternatively, the arms30may have telescoping features or other configurations that permit the arms30to extend and retract the solar arrays28a/28bwith respect to the vehicle body22.

In this example, the vehicle20includes two solar arrays28a/28b;however, it is to be understood that the vehicle20may alternatively have a single solar array or may include additional solar arrays. Each solar array28a/28bincludes solar cells32(i.e., photovoltaic cells) mounted on a support structure34. For instance, the support structure34includes a cell deployment system36and a flexible cable track38, also shown inFIG. 2. The cell deployment system36may include, but is not limited to, a spring and cable system with a retarder for selectively unfolding and folding the solar arrays28a/28bbetween stowed and deployed positions. In a fully stowed position, the solar arrays28a/28bare rolled-up in a tubular configuration. In a partially or fully deployed position the solar arrays28a/28bare partially or fully unrolled for solar exposure. The flexible cable track38includes a series of links38aand pivots38bthat rotatably couple the ends of the links38atogether. Each link38ais thus rotatable relative to the immediately adjacent links38asuch that the flexible cable track38can roll over itself between cable track stowed and deployed positions. The flexible cable track38also supports one or more cables that are connected to the solar cells32.

In this example, a controller40is disposed in the vehicle body22for selectively deploying and stowing the solar arrays28a/28b.The controller40may include software, hardware, or both that may be programmed according to this disclosure. Additionally or alternatively the controller40, or portions thereof, may be ground-based and may communicate with the vehicle20via radio waves.

Generally, solar arrays on a space vehicle have a large surface area and produce considerable drag. Drag is especially challenging with use of electric thrusters at low Earth orbits up to approximately 250 to 300 miles altitude. At high levels of drag, low thrust electric thrusters have difficulty maneuvering the spacecraft and/or consume too much power to be practical. However, the vehicle20may be used with a method50of deploying a solar array as shown inFIG. 3, to selectively deploy a solar array to reduce power requirements. As an example, the controller40may be configured to control the vehicle to perform the method50.

At52, the method50includes deploying a first portion of the solar cells32responsive to a first drag condition. The term “portion” refers to one of a plurality of solar cells32disposed in one of a string, a roll, a panel, a strand or other structure. For example, a portion of the solar cells32of one or both of the solar arrays28a/28bare deployed, or unrolled, such that the deployed solar cells32can generate solar power. The first drag condition may be a drag condition associated with a low altitude, such as low Earth orbit. The solar power generated by the portion of the solar cells32is used at54to charge the battery26. As will be appreciated, the number of solar cells32deployed may be selected based on the amount of drag and the amount of desired power to be generated to achieve one or more target electrical functions, such as producing thrust. The amount of drag may be calculated or estimated based on data such as altitude, vehicle size, and solar array size. The method50may use a drag calculation or estimation directly or may use other data that is representative of drag.

At56, the first portion of solar cells32or the charged battery26activate the electric thruster24at a first power level to produce thrust. The produced electrical power may be used for onboard electronics, or to activate the electric thruster24to provide attitude control or station-keeping, but more typically will be used for orbit raising of the vehicle20. At58, a second portion of the solar cells32are additionally deployed responsive to a second, lower drag condition. The deployment of the second portion of the solar cells32may be the full deployment of the solar arrays28a/28bor may be an intermediate deployment short of full deployment. The second drag condition may be a drag condition associated with a higher altitude. Thus, the solar array or arrays28a/28bare only partially deployed at the first, higher drag condition to generate some power yet avoid drag penalty and reduce energy loss due to drag, and are more fully deployed at the second, lower drag condition where there is less drag penalty. At60, the electric thruster24is then activated at a second, higher power level using the first and second portions of the solar cells32. For example, at the second power level the thruster24may provide a higher thrust than at the first power level.

The drag conditions may alternatively be associated with factors other than altitude. For instance, the solar arrays28a/28bmay track the position of the sun. The solar arrays28a/28bmay produce less drag when oriented edge-on with respect to the direction of movement of the vehicle20than when oriented face-on. Thus, one or both of the solar arrays28a/28bmay be partially deployed at52in response to a high drag condition associated with a face-on orientation and may be more fully deployed at58in response to a low drag condition associated with an edge-on orientation.

As can be appreciated, the deployment of the solar cells32can be an incremental deployment between only a partial deployment and a full deployment. Alternatively, there may be additional increments of partial deployment associated with changing drag conditions. For instance, there may be two or more partial deployments prior to full deployment as drag diminishes with increasing altitude and/or changing solar array orientations. In another alternative, the deployment may be continuous between two partial deployments or between a partial deployment and full deployment, as a function of altitude or array orientation. Thus, altitude or orientation may serve as a surrogate for use of an actual drag calculation or estimation.

FIG. 4illustrates the vehicle20through various stages (a)-(i) of solar array deployment. The vehicle20is shown initially at (a) in a fully stowed position, such as after deployment of the vehicle20from a launch vehicle. At steps (b), (c), and (d), the arms30extend to a fully deployed arm position. At steps (e), (f), and (g) the flexible cable tracks38unfold to a fully deployed cable track position. At step (h) the cell deployment system or systems36partially deploys, or unrolls, the solar cells32of the solar arrays28a/28b(52in method50). At this stage the solar cells32may be used to generate power to charge the battery26(54of method50), followed by either using the charged battery26or the solar cells32to activate the electric thruster24to produce thrust (56of method50). At step (i) the cell deployment system or systems36fully or more fully deploy the solar cells32of the solar arrays28a/28b(58of method50). As can be appreciated, steps (a)-(g) may optionally be a part of the method50.