TETHER FOR SPACECRAFT REACTION CONTROL SYSTEM

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.

DETAILED DESCRIPTION

FIG. 1illustrates a cut-away side-view of a forward section of a space capsule100prior to the re-entry phase, showing a tether-based RCS system comprising a control apparatus104and a reel102for holding a length of tether103, in accordance with an embodiment. Prior to re-entry, the opening at the end of the forward section of the capsule is covered by a lid101for keeping an initial length of unreeled tether105confined within the capsule. The un-reeled tether105is the portion of tether held by the reel102that is threaded through a “center hole”106of the control apparatus104and is initially coiled and stored above the control-apparatus104. As used herein, “center hole” or the like refers to the hole in the center of the control apparatus104through which a tether103is threaded. The control apparatus104is initiaily in a zero position. As used herein, zero position refers to the default position where the control apparatus' center hole is directly aligned with a spacecraft's z-axis107that passes through a spacecraft's center of mass.

FIG. 2illustrates a cut-away side-view of a forward section of a space capsule100during reentry, showing a tether-based RCS system comprising a control apparatus104and a reel102for holding a length of tether103and varying the length of a portion of “free tether”105, in accordance with an embodiment. As used herein, “free tether” or the like refers to the portion of a tether103which extends outwards from the control apparatus104and beyond a spacecraft's body.

A lid101covering the opening at the forward section of the capsule detaches from the capsule body100during re-entry and prior to the release of the tree tether105from the capsule body100, The detachment may be triggered via controls within the capsule or remotely from a mission control facility on Earth. At this point, the lid101can be considered to be a discarded expendable component. The free tether105is released from the capsule100. The tether105remains threaded through the center hole106of the control apparatus104and held in place by the reel102. The control apparatus104is initially in a zero position.

FIG. 3is a side view of a reel mechanism102for holding a length of tether103and for varying the length of the free tether105, in accordance with an embodiment. The reel102comprises two circular flanges108and a cylindrical shaft109situated horizontally between said circular flanges108, said circular flanges108having equal radii substantially larger than the radius of said cylindrical shaft109.

Each end of the cylindrical shaft109is connected to the center of a circular flange108. During flight, the tether103is stored by being wound around the cylindrical shaft109on the reel102, between the flanges108. One circular flange108is connected to a driveshaft110, said driveshaft110being further connected to a motor111. The motor111is bi-directional and turns the driveshaft110clockwise or counter-clockwise. When driven by the motor111, the driveshaft110turns the reel102accordingly and retracts or extends the tether103depending on the direction of the motor. In this embodiment, turning the driveshaft110counter-clockwise extends the tether, or causes free tether105to lengthen, and turning the driveshaft110clockwise retracts the tether103shortening the free tether105, The motor111is powered by a power source112, and can be controlled via an interface113from the spacecraft's controls. The free tether105remains threaded through the center hole106of a control apparatus104, initially in a zero position. The free tether105remains loosely coiled above the control apparatus104and remains so until the spacecraft is ready for atmospheric re-entry. On re-entry, the free tether105is released into the atmosphere and drags behind the spacecraft, serving as a hypersonic parachute. The unexposed end114of the tether103is interfaced with the spacecraft's radio communications system115, allowing the tether103to function as a radio antenna during atmospheric re-entry. Highly conductive plasma forms as a result of shock and boundary layer heating during atmospheric re-entry, blocking radio waves. The free tether105extends far behind the spacecraft, avoiding the conductive plasma and allowing the spacecraft to send and receive radio transmissions during re-entry. The tether103is made of a heat-resistant conductive material such as aluminum or steel for sending and receiving radio communications and withstanding the high temperature of the conductive plasma.

FIG. 4is a top view of a forward section of a space capsule showing a control apparatus104in the zero position, in accordance with an embodiment of the present invention. The control apparatus104is connected to four identical retracting arms116,117,118,119equidistant from each other along the inner hull120of the space capsule. Relative to the x-y axes as shown inFIG. 4, the retracting arms116,117,118,119are denoted as follows: “positive-x”116, “negative-x”117, “positive-y”118, and “negative-y”119. The control apparatus104has a center hole106through which a tether is threaded. Initially, the control apparatus104is in the zero position. The retractable arms116,117,118,119are connected to the control apparatus104by a total of eight identical tension springs121, designed to become longer under load. Each arm116,117,118,119is connected to the control apparatus104by two tension springs121. When one of the retracting arms116,117,118,119retracts into the inner hull120, a load affects all the springs121. The tension springs121have turns normally touching in the unloaded position, and the springs121have a hook, eye, or some other means of attachment at each end connecting it to the retracting arms116,117,118,119and the control apparatus104.

FIG. 5is a top view of a propellant based backup RCS system, in accordance with an embodiment. The propellant based RCS system also concurrently functions as part of a backup life support system. The propellant can comprise compressed oxygen, or a combination of compressed oxygen and other gases in a ratio suitable for sustaining human life (i.e. appropriate mixture of oxygen and nitrogen). The propellant is stored in a gas propellant tank122. There is a central hub mechanism123connecting the tank122to four gas lines denoted as: positive-x124, positive-y126, negative-x125, and negative-y127, relative to the x-y axes shown inFIG. 5. The opposite ends of the gas lines126,127,124,125are connected to translation thrusters128,129,130,131used to alter the spacecraft's velocity or attitude (pitch, yaw, roll). Each thruster128,129,130,131has a nozzle directed perpendicularly outward from the capsule's hull132. Translation thrusters128,129,130,131is that should align with the z-axis107of the capsule to avoid unwanted roll or rotation when the thruster is fired. Torque thrust is produced by the gas propellant leaving the nozzle as exhaust. A control system inside a spacecraft controls the release of the gas propellant into the gas lines126,127,124,125, said control system having the ability to selectively release the propellant into single or multiple gas lines.

While the spacecraft has a primary life-support system, the backup RCS system further functions as part of a backup life support system, supplying the breathable gas propellant to the human occupants of the spacecraft should the oxygen or carbon dioxide levels reach a predetermined danger threshold and/or the primary life-support system fails. The gas propellant tank122is further connected to a backup life-support system133by a ventilation line134. The backup life-support system comprises carbon dioxide canisters, fans, and filters. The carbon dioxide canisters remove carbon dioxide by reacting it with another chemical (i.e. lithium hydroxide, calcium hydroxide, sodium hydroxide), and the fans and filters remove dust and trace odors from within the spacecraft. The backup life-support system can be activated manually by controls within the spacecraft, or automatically when one or more sensors detect that oxygen or carbon dioxide concentrations have reached an unsafe level.FIG. 6is a side view of a propellant based backup RCS system, in accordance with an embodiment. The backup RCS system is located, relative to the tether RCS system comprising the reel102and control apparatus104. A central hub mechanism123connects a gas propellant tank122to four gas lines124,125,126, and12. The opposite ends of the gas lines are connected to translation thrusters denoted as: positive-x128, negative-x129, positive-y130and negative-y131, with respect to the x-y axes shown inFIG. 10. The translation thrusters128,129,130,131are used to alter the spacecraft's velocity or attitude (pitch, yaw, roll angles). Each thruster128,129,130,131has a nozzle directed perpendicularly outwards from the capsule's hull132. The translation thrusters128,129,130,131should align with the capsule's z-axis107. Torque thrust is produced by gas propellant leaving a nozzle as exhaust. A control system inside a spacecraft controls the release of gas propellant into the gas lines. The control system has the ability to selectively release the propellant into single or multiple gas lines.

The backup RCS also functions as part of a backup life support system133comprising fans and filters for removing dust, odors, and carbon dioxide. The gas propellant tank122is connected to the backup life support system by a ventilation line134and can be activated manually by controls within the spacecraft, or automatically when one or more sensors detect that oxygen or carbon dioxide concentrations have reached an unsafe level.

FIG. 7is a top view of a forward section of a space capsule showing the operation of the control apparatus104, in accordance with an embodiment of the present invention. The control-apparatus104is connected to four identical retracting arms116,117,118,119equidistant from each other along the inner hull120of the space capsule. Relative to the x-y axes as depicted inFIG. 7, the retracting arms are denoted as follows: “positive-x”116, “negative-x”117, “positive-y”118, and “negative-y”119. The retractable arms116,117,118,119are connected to the control apparatus104by eight identical tension springs121, designed to become longer under load. Each arm116,117,118,119is connected to the control apparatus104by two tension springs121.

InFIG. 7, the “negative-y” arm119is in a retracted position, the body of the arm having been retracted into the inner hull120of the space capsule by a retraction means. The retraction of the negative-y arm116increases the distance between said negative-y ann119and the positive-y arm118, creating a load on all the springs121. The load is caused by a movement in the negativey direction, causing the control apparatus104to also move in the negative-y direction.

The springs121attaching the positive-x and negative-x arms116,117to the control apparatus104are also pulled in the negative-y direction by the ends of the springs121attached to said control-apparatus104. The effect is that the center hole106is offset from the z-axis107in the negative-y direction by the measurement equal to the distance135from the center hole's106current position and its original zero position. A tether threaded through the center hole106would similarly be offset from the z-axis107.

FIG. 8shows a cut-away side view of the forward section of a space capsule100showing an offset135of the tether105in the negative-y direction due to a retraction of the positive-y arm, in accordance with an embodiment. The tether105is attached to and wound around a reel102, said reel102being attached to the capsule body100, said tether threaded through the center hole106of the control apparatus104. The control apparatus104is connected to four retractable arms by tension springs121.

A retraction of the negative-y arm119into the capsule's hull132creates a load affecting the tension springs121in the negative-y direction. As a result, the control apparatus104is pulled in the negative-y direction, and a tether105threaded through the center hole106is offset from the capsule's100z-axis107by a distance135equal to the difference between the center hole's106current position and its original zero position.

FIG. 9is a top view of a forward section of a space capsule showing the operation of the control apparatus104, in accordance with an embodiment. The control apparatus104is connected to four retracting arms116,117,118,119equidistant from each other along the inner hull120of the space capsule.

Relative to the x-y axes as depicted inFIG. 9, the retracting arms are denoted as follows: “positive-x”116, “negative-x”117, “positive-y”118, and “negative-y”119. The retractable arms116,117,118,119are connected to the control apparatus104by eight identical tension springs121, designed to become longer under load. Each arm116,117,118,119is connected to the control apparatus104by tension springs121.

InFIG. 9, the positive-x arm116is in a retracted position, the body of the arm having been retracted into the inner hull120of the space capsule by a retraction means. The retraction of the positive-x arm116increases the distance between said positive-x arm116and the negative-x arm117. The retraction of the positive-x arm116creates a load on all the springs121. The load is caused by a movement in the positive-x direction, causing the control apparatus104to also move in the positive-x direction. The springs121attaching the positive-y and negative-y arms118,119to the control apparatus104are also pulled in the positive-x direction by the ends of the springs121attached to the control apparatus104. The effect is that center hole106is offset from the z-axis107in the positive-x direction by the measurement equal to the distance135from the center hole's current position and the zero position. A tether threaded through the center hole106would similarly be offset from the z-axis107.

FIG. 10shows a cut-away side view of the forward section of a space capsule100showing an offset135of the tether105in the positive-x direction after a retraction of the positive-x arm116, in accordance with an embodiment. The tether105is attached to and wound around a reel102, said reel102being attached to the capsule body100, said tether threaded through the center hole106of the control apparatus104. The control apparatus104is connected to the four retractable arms by tension springs121. A retraction of the positive-x arm116into the capsule's hull132creates a load affecting the tension springs121in the positive-x direction. As a result, the control apparatus104is pulled in the positive-x direction, and a tether105threaded through the center hole106is offset from the capsule's z-axis107by a distance135equal to the difterence between the center hole's106current position and its original zero position.

FIG. 11shows a cut-away side view of a space capsule100with a tether RCS system and illustrates how the RCS system induces attitude control by producing a moment by offsetting a tether105from a space capsule's z-axis, in accordance with an embodiment. The tether RCS system has a reel102for holding a length of tether105. The tether105is threaded through the center hole106of a control apparatus104, said control apparatus104initially in the zero position.

A moment is a rotational effect produced by a force at some distance from an axis of rotation. The moment (M) is equal to the product of the force (F) and the distance (d) from the axis of rotation about which it is applied. InFIG. 11the control apparatus104has shifted the tether105along the capsule's x-axis136above and out of alignment with the capsule's center of mass line z-axis107, creating an offset or moment arm137. The tether's collision with molecules in the atmosphere creates a friction force138.

The line that passes through the capsule's center of gravity and is perpendicular to both the capsule's z-axis136and said moment arm137is the axis of rotation and in this case happens to be the y-axis. Moment139is the product of the friction force produced by tether138and the offset137, a distance equal to the difference between the center hole's106current position and z-axis. Here, the moment139acts about the capsule's center of mass in the clockwise direction, as viewed inFIG. 11. The effect of the moment139is that the capsule's angle of attack, relative to the atmosphere, decreases. In flight dynamics, this angle is called pitch.

FIG. 12illustrates the steps by which a space capsule100uses a tether-based RCS system to adjust pitch to decrease a space capsule's angle of attack, θA, with respect to the atmosphere140, in accordance with an embodiment. θAis the angle formed by the capsule's100z-axis107and the atmosphere140. The tether based RCS system comprises of a reel102for holding a length of tether105and a control apparatus104. The control apparatus104and the tether105are initially in the zero position. InFIG. 12, the control apparatus104offsets the tether105away from the z-axis107. As a result, the tether105is offset in a direction away from the atmosphere140by a distance135equal to the difference between the zero position and the tether's current position.

A friction force138is produced by the entire length of tether105colliding with molecules in the atmosphere140. Because the friction force138is produced at a distance135from the z-axis107, a moment139is produced, causing a rotational effect about the capsule's100center of mass141. The spacecraft107rotates in a clockwise direction, closer to the atmosphere140, by using the center of mass141as a pivot point, decreasing θA. The end result is that by offsetting the tether105, the capsule100has adjusted pitch by decreasing θAfor atmospheric reentry using the rotational effected generated by a moment139.

FIG. 13illustrates the steps by which a space capsule100uses a tether-based RCS system to adjust pitch to increase a space capsule's angle of attack, θA, with respect to the atmosphere140, in accordance with an embodiment. θAis the angle formed by the capsule's z-axis107and the atmosphere140. The tether based RCS system comprises a reel102for holding a length of tether105and a control apparatus104. The control apparatus104and the tether105are initially in the zero position. InFIG. 13, the control apparatus104offsets the tether105away from the z-axis107. As a result, the tether105is offset in a direction to'vvards the atmosphere140by a distance135equal to the difference between the zero position and the tether's current position.

A friction force138is produced by the entire length of tether105colliding with molecules in the atmosphere140. Because the friction force138is produced at a distance135from the z-axis107, a moment139is produced, causing a rotational effect about the capsule's100center of mass141. The z-axis107moves in a counterclockwise direction, further from the atmosphere140by using the center of mass141as a pivot point, increasing θA. The end result is that by offsetting the tether105, the capsule100has adjusted pitch by increasing θAfor atmospheric reentry using the rotational effect generated by a moment139.

FIG. 14is a top view looking down on a space capsule100re-entering the atmosphere140, illustrating the steps by which said space capsule100uses a tether-based RCS system to adjust yaw to steer said space capsule's100approach vector142to the right of the z-axis107, relative to said capsule's100orientation in this illustration, in accordance with an embodiment. The tether-based RCS system comprises a reel102for holding a length of tether105and a control apparatus104. The control apparatus104and tether105are initially in the zero position. InFIG. 14, the control apparatus104offsets the tether105to the right of the z-axis107by a distance equal to the difference between the zero position and the tether's105current position.

A friction force138is produced by the entire length of tether105colliding with molecules in the atmosphere140. Because the friction force138is produced at a distance135from the z-axis107, a moment139is produced, causing a rotational effect about the capsule's100center of mass141. The z-axis107is shifted in a clockwise direction, relative to the capsule's100orientation in this illustration, using the center of mass141as a pivot point. The z-axis's new position143acts as the capsule's new approach vector144. The end result is that by offsetting the tether105, the capsule100has adjusted yaw and steered its direction to a new approach vector144which is to the right of the original approach vector142, relative to the capsule's100orientation in this illustration.

FIG. 15is a top view, looking down on a space capsule100re-entering the atmosphere140, illustrating the steps by which said space capsule100uses a tether-based RCS system to adjust yaw to steer said space capsule's approach vector142to the left of the z-axis107, relative to said capsule's orientation in this illustration, in accordance with an embodiment. The tether-based RCS system comprises a reel102for holding a length of tether105and a control apparatus104. The control apparatus104and the tether105are initially in the zero position. InFIG. 15, the control apparatus104offsets the tether105to the left of the z-axis107by a distance equal to the difference between the zero position and the tether's105current position.

A friction force138is produced by the entire length of tether105colliding with molecules in the atmosphere140. Because the friction force138is produced at a distance135from the z-axis107, a moment139is produced, causing a rotational effect about the capsule's center of mass141. The z-axis107is shifted in a counter-clockwise direction relative to the capsule's orientation in this illustration, using the center of mass141as a pivot point. The z-axis's new position143acts as the capsule's new approach vector144. The end result is that by offsetting the tether105, the capsule100has adjusted yaw and steered its direction to a new approach vector144which is to the left of the original approach vector142, relative to the capsule's orientation in this illustration.

An example device comprises an aerodynamic decellerator for producing a tension force from aerodynamic drag, a vehicle capable of producing lift force that changes as the angle of attack varies, and a controller connected to the decellerator and also connected to the aerodynamic vehicle, for applying the tension force produced by the decellerator to the vehicle in a controlled manner to change the vehicle's angle of attack, thus varying the lift force produced by the vehicle. An example method is to adjust the load vector applied to a reentry vehicle by an aerodynamic decelerator to accomplish controlled skip entry through the upper atmosphere thereby reducing the vehicle's forward velocity vector and minimizing dynamic and thermal loads.

An illustrative embodiment comprises an aerodynamic decellerator for producing a tension force from aerodynamic drag, a vehicle capable of producing lift force that varies with angle of attack, and a control device connecting the aerodynamic decellerator to the aerodynamic vehicle, for applying the tension force produced by the decellerator to the vehicle in a controlled manner to change the vehicle's angle of attack, thus varying the lift force produced by the vehicle. An example method comprises using the devices described herein to accomplish controlled skip entry through the upper atmosphere in order to more gradually reduce the vehicle's forward velocity vector and thereby reduce dynamic and thermal loads.

A pull point is a point where drag generated by a tether is exerted on a space craft. For inflatable structures, rigidity is the degree of pressurization sufficient to retain structural integrity despite forces encountered during atmospheric entry. Skip entry is a method of atmospheric entry comprising one or more “skips” off of the atmosphere where energy is lost.

An example atmospheric entry device comprising a controllable tether and an aerodynamic body can use a skip entry technique.

Frictional drag force applied to a tether induces tension in the tether. An example device can comprise a tether attached to an aerodynamic body and a tether controller that shifts the pull point's location.

Atmospheric re-entry, even when initiated from a circular low-Earth orbit, typically requires a thermal protection system comprising a heat shield, ablative material, or radiative dissipation techniques. Semi-analytical and numerical simulations of the atmospheric re-entry from low-Earth orbits of a capsule with a 20-km heat resistant tether attached have shown that the thermal input flux on the capsule is reduced by more than one order of magnitude with respect to a comparable re-entry without a tether.

Long tethers have low ballistic coefficients and a large surface for heat dissipation. Moreover, a long tether is stabilized by gravity gradient and consequently tends to maintain a high angle of attack with respect to the wind velocity. The exposed surface of a 20 kilometer long1milimeter diameter tether is 20 square meters, which is larger than the typical cross section of a re-entry capsule. For example, the apollo command module's cross section is under 12 square meters. The resulting strong drag decelerates the capsule during re-entry. Where an example embodiment allows variance of the application of drag force to the re-entry vehicle, so that the force vector is offset from the vehicle's center of mass, to change the vehicle's angle of attack, allowing control of the vehicle's reentry flight path. By using this method to allow the reentry vehicle to skip in and out of the atmosphere, especially during the portion of the reentry process where the greatest thermal and mechanical loads are produced, extends the time of reentry flight in a controlled manner and reduces the peak mechanical and thermal forces acting on the reentry vehicle.

A device, and the method of its use, for controlled atmospheric entry allows for an atmospheric entry system (“system”) that may be controlled in order to produce a flight path having reduced deceleration loads over an extended period of time in order to decrease mechanical and thermal loads and stresses that occur during atmospheric entry. This will allow for a gentler more precisely controlled transit through an atmosphere.

An embodiment can be used with any spacecraft design that produces lifting force that can be varied by varing the vehicle's angle of attack. A winged shuttle, a lifting body, and a space capsule are all examples of such spacecraft. An embodiment can work with an inflateable reentry system that uses a pressurized flexible toroid to provide rigid support to a flexible conical aeroshell payload section. Synergistic benefits may be obtained by using a lightweight inflatable reentry vehicle in conjunction with an embodiment.

An inflatable aeroshell is an example of the type of aerodynamic vehicle discussed in the embodiment below. Examples of inflatable aeroshells comprise the NASA inflatable aeroshell and the Russian inflatable aeroshell. These inflatable aeroshells have the benefit of being lightweight. They also have the disadvantage of only operating in an uncontrolled ballistic reentry trajectory, which produces large thermal and mechanical loads.

An aerodynamic reentry vehicle capable of producing variable lift force when its angle of attack is varied may also be used. Examples of such vehicles include the USAF X37B robotic reuseable reentry spacecraft as shown inFIG. 18, the Soyuz and Shinzu single use reentry vehicles illustrated inFIG. 19, and the Excalibur Almaz reuseable reentry vehicle, as shown inFIG. 17.

FIG. 20shows a detail view of the tether control shown inFIGS. 17,18and19. InFIG. 20, controller501comprises a structural attachment point of the return vehicle503. Control line control means507,511and515are connected to one end of control lines505,509and515, respectively. The control line control means are adapted to be able to reel the control lines in and out so as to change their length in a controlled fashion. The end of these control lines are affixed to one end of tether105at point517. Changing the length of the control lines varies the point of action of the tension force from the tether on the vehicle so as to control the vehicle's angle of attack.

FIG. 16shows an embodiment comprising an inflateable aeroshell100and an Inflatable Aeroshell Toroid207. The toroid207of aeroshell100is made of a material such as Kevlar such that the interior of toroid207is not in fluid communication with the exterior of the toroid. For storage and transportation the toroid may be deflated. During atmospheric entry, toroid207will be inflated causing toroid207to be pressurized to a point of rigidity to retain structural integrity despite the forces acting on it during the controlled atmospheric entry process.

The inflatable aeroshell skin209is fixedly attached to the exterior surface of toroid207at one or more locations about the circumference of the exterior surface of the toroid (possibly continuously attached such that there is no fluid communication between the inflatable toroid and the skin), and extends below the center of the toroid, forming an inverted payload volume225. The skin being positioned in such a way that it forms a conical shape extending below the toroid. Skin209may be made of any material having mechanical strength sufficient to support the payload during reentry. It may be adapted to protect payload225against heating and may optionally comprise a thermal protection material211.

The aerodynamic body100comprises the toroid207and the skin209that extends from the toroid, forming a conical nose211that sits underneath the toroid. This aerodynamic body automatically orients the entry system due to the action of natural aerodynamic forces in such a way as to have the aerodynamic body sit between the payload and the source of gravity with the nose-cone211pointing toward the gravitational source. Although an embodiment can reduce the thermal and mechanical loads acting on the reentry system and payload, it does not eliminate these loads entirely. The aerodynamic body therefore also shields the payload of the system from the majority of the frictional and thermal forces generated by the device's controlled transit through the atmosphere.

The inflatable aerodynamic body acts as a lift generating body, aerodynamically orients and stabilizes the system, protects the rest of the system from friction with the atmosphere, can act as a backup life support system if it is pressurized with breathable gas, and may be provided with air bags to cushion the impact of the system when it impacts the surface of the celestial body.

The tether105is attached to the vehicle100by control system203. The tether can be deployed by any number of different tether deployment means.

The tether105is attached by any suitable mechanical means to the tether controller203. The tether extends from the tether controller203to the tether end point223. The tether105is deployed by a tether deployment means158and extends out behind the aerodynamic body100. When the tether is extended it begins colliding with the molecules that constitute the atmosphere, causing friction. The friction generated by the tether exerts a drag force which is communicated to the rest of the atmospheric entry device at the Pull Point. If the tether is 20-km-long and 1-mm diameter tether, then its surface area is 20 square meters, which is much larger than the cross section of a re-entry capsule. For example the aerodynamic surface area of the 10 foot diameter NASA inflatable reentry system is about seven square meters.

The tether controller203is attached to tether105and through controllable lines213,215and217to the exterior surface of the toroid. InFIG. 16these three lines are attached to the toroid every 120 degrees around the toroid in such a way as to allow the tether controller203line actuator219the ability to change the length of control lines213,215and217to change the angle of attack of the vehicle100with respect to the relative wind. The tether controller203tether length controller158can modify the aerodynamic characteristics of the tether by extending the tether, retracting the tether, altering the angle of the tether with respect to the main body of the atmospheric entry device, or altering the location at which the force being exerted on the tether is functionally communicated to the rest of the device (“Pull Point”).

The tether control lines213,215and217and the tether105itself can be extended or retracted by electric motors, by hydraulic or pneumatic actuators or even by manually pulling or winding the lines by mechanical means. This opens up the rather interesting possibility of extreme sports enthusiasts surfing the upper atmosphere from orbit.

In the lower atmosphere and at low, subsonic, speeds tether105may not generate a great deal of drag. Certain embodiments could incorporate a parachute into tether controller203. This parachute could be deployed prior to landing. Alternatively, a deployable lighter than air balloon could be incorporated into the system to inflate to let the payload float in the atmosphere. Finally, the payload, with a balloon or parachute system, could be ejected after reentry, but prior to landing. An embodiment could also incorporate inflatable air bags or foam cushions to reduce the effect of the landing impact on the payload.

In one or more embodiments, the aerodynamic body comprises toroid, a skin, a payload volume, and one or more tether attachment points (possibly comprising a controller). There could be a way of going from a compacted deflated state to a rigid inflated state). The inflation of the toroid should be completed by the transfer of some material, gas or combination of gasses by an inflation means from a volume outside of the system to the un-inflated toroid of the aerodynamic body (preferably delivered from a pressure vessel). These details are not shown as inflating a flexible toroid is within the skill of those expert in the art. If an embodiment is used for human reentry, all or part of the toroid could be pressurized with oxygen or a breathing gas mixture to serve as a source of life support breathing gas.

Skip entry is a technique for entering an atmosphere. It is beneficial for entry systems that have a relatively low lift-to-drag ratio since these sorts of entry systems have difficulty extending their landing range and deceleration period due to their aerodynamic flight characteristics. When engaging in skip entry a space object makes one or more successive “skips” off of (or through) the atmosphere. Each successive “skip” reduces the energy of the space object relative to the celestial body whose atmosphere is being entered. The skip entry provides a space object entering an atmosphere a longer period of time and course of transit through the atmosphere. The increased period of transit increases the duration of time during which the entering object can shed energy relative to the celestial body. By increasing the duration of the atmospheric transit the energy of the space object can be released more gradually. This gradual reduction of the space object's energy is advantageous because it reduces both heating and rapid deceleration due to frictional forces that result from the space object's physical interaction with the molecules of gas and other particulates that comprise the atmosphere.

Methods of achieving skip entry require precise guidance and control of the atmospheric entry system. Without precise guidance and control the atmospheric entry system attempting to achieve skip entry could fail to sustain its intended trajectory, which could result in one of a number of problems. If the atmospheric entry system takes too shallow of an entry trajectory, or achieves too much lift upon entry, the atmospheric entry system could skip entirely out of the atmosphere, and possibly out of the celestial body's gravity well. This could result in the complete loss of the atmospheric entry system and its payload. If the atmospheric entry system takes too steep of a trajectory, or has too small a velocity, the aerodynamics of the system may not generate enough lift for the atmospheric entry system to perform skip entry. This could cause the atmospheric entry system to engage in ballistic entry which could potentially destroy the atmospheric entry system and its payload due to excessive heating, high acceleration loads, or a high velocity impact with the surface of the celestial body. A third problematic possibility is that the atmospheric entry system achieves skip entry, but does so in such a way as to have the system and payload move off of its intended trajectory and land in an unintended location. The increased transit duration is effectively an increased flight path which allows for the atmosphere entry system to select a landing location from a larger potential landing area.

The method of skip entry into an atmosphere is achieved by calculating an appropriate trajectory, then initially descending into the outermost region of the atmosphere. After the initial descent, the aerodynamic profile of the atmospheric entry system (with or without help from some other forces including thrust or drag) generates lift which causes the entry system to ascend. As the object gradually ascends the gravitational force overrides the lift force and the object begins another descent into the atmosphere. This process may be repeated more than once before the atmospheric entry system loses the velocity (or other flight characteristics) required to generate sufficient lift to make another “skip.” When the object cannot, or does not wish to, make another “skip,” the atmospheric entry system travels along a ballistic trajectory through the remainder of the atmosphere. These “skips” increase the duration of the atmospheric entry system's transit in the upper, less dense, atmosphere. The increased duration of the atmospheric transit and the lower instantaneous deceleration gives this method of atmospheric entry many advantages as compared to fully ballistic atmospheric entry.

Increased duration of flight in the upper atmosphere is desirable because this is where most of the energy of reentry is dissipated. If the total energy release is made over more time, the effect is a much gentler and less stressful reentry.

The deceleration can be made more gradually resulting in lower acceleration loads being put on the payload and atmospheric entry system as a whole. Slower deceleration results in less intense aeroheating of the atmospheric entry system. The lower velocities and increased transit duration also reduce heat buildup on the entry system and acceleration loading on the system, which in turn allows for less mass of the system being dedicated to shielding. The increased atmospheric transit time coupled with the smaller velocities that the entry system achieves during the atmospheric entry allows the entry system more time to and ease of maneuvering.

An example method could facilitate atmospheric entry into the Earth's atmosphere from low Earth orbit. The devices and methods described can be used to provide a controlled reentry into any planetary atmosphere from any trajectory. Of course the control rules for each entry would be unique and would have to be calculated according to means well known to those skilled in the art of trajectory planning and atmospheric reentry.

The International Space Station (“ISS”) orbits the earth in low Earth orbit (“LEO”)617. The outer bound of LEO is approximately 2,000 kilometers above the surface of the earth. In this orbit the ISS is traveling at approximately 18,000 miles per hour. In the event that some cargo needs to be safely, gently, and precisely transported from the ISS to a location on the surface of the Earth an embodiment could be used to accomplish the task.

Referring now toFIG. 21, the payload would first be attached to the deflated and compact atmospheric entry system in orbit601. Then the atmospheric entry system with the payload attached to it would be ejected from the ISS and propelled by a deorbit rocket impulse or other means into a reentry trajectory. Since the system was ejected from the ISS its orbital speed would be approximately the same as that of the ISS. As the system enters into a decaying orbit the gravitational attraction between the system and the Earth pulls the system toward the surface of the Earth with a force proportional to the square of the distance between the two objects. At some point603after the system is released from the ISS, but before the system begins to interact with the Earth's outer atmosphere, the inflation means pressurizes at least the toroid to rigidity. At some point after the toroid is inflated, the tether is extended through the use of a tether deployment means to a desired length.

As the system continues on a decaying orbit it begins to interact with the top layer of the atmosphere at an altitude of about 100 km623. As the system begins to descend into the outer limits of the Earth's atmosphere the aerodynamic drag characteristics of the aerodynamic body will cause the system to orient so that said aerodynamic body shields the payload from aeroheating. At the same time the molecules of the outer atmosphere colliding with the tether generates a frictional drag force that induces a tension in the tether. The force of this tension is exerted in the opposite direction from the system's path through atmosphere. This drag force causes the system to further decelerate. If no control is exerted on the reentry system, it will follow a pure ballistic trajectory625and experience large thermal and structural loads before impacting on the surface at point627.

As the tether decelerates the system the tether controller exerts forces onto the tether in such a way as to cause the tether drag force to impart a torque on the system. This torque force alters the system's aerodynamic flight characteristics, including angle of attack, generating a greater lift/drag ratio. As the lift force generated increases it will eventually offset the gravitational force between the system and the planetary surface at point605, causing the system to gain altitude for a period of time and extend its flight distance and time through the atmosphere before the lift force is no longer greater than the gravitational force at which point the system begins to descend again at point607. Skip entry may be used as many times as required to minimize the deceleration loads/rates on the payload, or as many times as are desired for the flight profile as is illustrated by points609,611,613. With each skip the system loses energy. The control can be as simple as measuring the deceleration force and changing the angle of attack of the reentry vehicle when the deceleration exceeds some predefined limit. In theory this could yield the result of a gentle return to the surface.

The increased period of time that skip entry allows for the system to be traversing through the atmosphere allows for an increased period of time in which the tether's drag force can gently decelerate the system. Once the system's velocity, altitude, or other flight characteristic preclude the system from engaging in any further “skips” off of the atmosphere as shown at point615the system would begin a ballistic trajectory, although the tether and tether controller could still be used for some course modification. At this point in the system's descent should be sufficiently slow as to allow parachutes, or some other deceleration means to gently lower the system to a point on the surface of the Earth, or to simply let the system fall to the surface of the celestial body at point617.

The flight path and controls exerted on the system can be optimized to provide for the slowest deceleration possible or controlled, constant, sustained deceleration rates. This allows for the atmospheric entries to be completed entirely within predetermined parameters (time of descent, acceleration load requirements, landing location).

In an embodiment the tether controller comprises one or more control cords attached to a point on the tether and a point on the toroid. The means of control would be by varying the tension on the one or more control cords so that the tether's drag force is deflected through the one or more control cords and exerted on the control cord's point(s) of attachment to the toroid. This action will cause the sum of the tensions on the tether and the one or more control cords to be functionally exerted on a point different than the device's center of gravity. This deflection would cause there to be a torque force impart to the device which would alter its aerodynamic flight characteristics. By changing the aerodynamic body's aerodynamic flight characteristics, including but not limited to its angle of attack, the lift to drag ratio of the system can be modified to correspond to a desired flight plan.

In certain embodiments, the tether controller comprises a control device that exerts a force on the tether such that there is a controllable change in the angle between the tether and the aerodynamic body. When the force exerted by the tether does not pass through the spacecraft's center of mass a torque alter's the spacecraft's angle of attack to change the lift forces acting on the system.

In an example embodiment the tether controller comprises a means by which the pull point of the tether may be altered in at least a two dimensions to shift the tether's force vector away from the vehicle's center of gravity to impart a moment on the vehicle to adjust pitch (angle of attack) or yaw. Furthermore, the tether's length may be extended or retracted through the use of a winch to vary the magnitude of the drag force imparted by the tether. When combined this method of controlling the length of the extended tether and the location of the pull point would allow for control of the amount of drag force that the tether would generate and where that drag force is functionally imputed on the reentry vehicle. This will provide a reactive guidance means for the atmospheric entry system as it descends through an atmosphere. If the tether is electrodynamic it may also be possible to generate drag forces outside of the atmosphere.

In certain embodiments, the tether controller comprises a means of moving the tether's physical attachment point to the rest of the system (most likely to the toroid). By moving the tether's attachment point the tether controller also moves the point at which the tether's drag force is functionally imparted to the rest of the system. If the vector along which the tether's drag force is functionally imparted to the rest of the system is moved away from the system's center of mass the drag force will impart a moment on the aerodynamic body. This moment would generally result in a change in the system's angle of attack, resulting in a change in the system's aerodynamic flight characteristics.

In an example embodiment, the gas that is used to inflate the toroid to rigidity is Oxygen (O2). In this embodiment, there would be a hose equipped with a regulator allowing controllable fluid communication between the interior of the toroid and the payload volume. In this embodiment, the O2used to pressurize the toroid to rigidity could be tapped into as a life support system.

In another example embodiment, the gas that is used to inflate the toroid to rigidity is Helium (He). Helium, being an inert gas, is unlikely to react with any other chemicals that it may be exposed to, and thus is unlikely to be dangerous. Helium gas is light weight which could increase the spacecraft's buoyancy. The increased buoyancy of the system could result in a smoother, gentler deceleration and stop than a less buoyant system would allow.

In an example embodiment, the toroid has a plurality of discrete compartments in fluid communication with one another through valves. The valves could be configured so that discrete compartments could be inflated by the release of pressurization material into discrete compartments, but would not allow the decompression of one compartment to deflate any other of the discrete compartments. This configuration would help the toroid retain some structural rigidity in the event of a damage that would cause depressurization.

In certain embodiments, the skin of the aerodynamic body comprises one or more compartments in fluid communication with the toroid. These compartments inflate with the same pressurization fluid as the toroid. This would aid in the prevention of communication of heat from the outer surface of the skin of the aerodynamic body to the inner surface of the skin of the aerodynamic body.

Inflatable components are light weight and can be deflated and stored in a relatively small volume.

Certain embodiments comprise an aerodynamic body, a hypersonic decelerator, and a controller that is connected to both the hypersonic decelerator and the aerodynamic body such that the forces acting on the hypersonic decelerator are transmitted to the aerodynamic body in a controllable manner so the hypersonic decelerator and control means can be used as a RCS (reaction control system) for the aerodynamic body.

In this embodiment the aerodynamic body may comprise a capsule, a shuttle, a heat shield, or an inflatable aeroshell. The aerodynamic body will preferably have flight characteristic that can be influenced by the controlled use of the hypersonic decelerator in such a way as to result in an alteration of the aerodynamic body's flight characteristics (angle of attack, lift/drag ratio, aerodynamic profile, shape, etc.).

The aerodynamic body allows the forces generated by the hypersonic decelerator to be translated from pure decelerating drag into a means for altering the flight characteristics of the system in order for the system as a whole to be controllably maneuverable.

The hypersonic decelerator refers not to a specific decelerator system but instead could comprise one, more than one, or a combination of hypersonic decelerators that rely on drag to decelerate an object traveling through an atmosphere at hypersonic speeds. This group comprises: single line tethers, multi-line tethers, tapes, ribbons, ballutes, parachutes, wings, and sails. Different hypersonic decelerators could be used simultaneously or in sequence. The hypersonic decelerator uses the drag generated by friction between the hypersonic decelerator and the atmosphere to both decelerate the entire system and to generate forces that can be controllably transferred to the aerodynamic body in order to alter the spacecraft's flight dynamics in a controllable manner.

Multiple hypersonic decelerators may be used in conjunction with one another, either having multiple distinct hypersonic decelerators used at the same time, or with different hypersonic decelerators used at different periods during the system flight in order to correspond to different deceleration requirements. This may include but is not limited to the use of different hypersonic decelerators depending on the velocity range that the system is traveling within, or the use of different hypersonic decelerators depending on the density of the atmosphere through which the system is traveling.

The control means can be any device, system, or method of use that allows for the drag forces generated by the hypersonic decelerator to be used to alter any one or more flight characteristics of the system in such a way as to allow the flight path of the system to be controlled by alteration of the drag forces acting on the hypersonic decelerator.

In a illustrative embodiment, the aerodynamic body comprises an inflatable aeroshell, the hypersonic decelerator comprises a tether, and the controller allows the spacecraft to engage in skip (single or multiple) entry of an atmosphere.

While only certain features of the selected embodiments have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the embodiments.