Reusable Rocket Stage

Abstract

The present invention relates to a rocket stage (1) for a multi-stage space launch vehicle (3), including a main engine (5) and configured for stage separation from the remainder of the space launch vehicle (3) for returning the rocket stage (1) to the Earth's surface, the rocket stage (1) comprising an inflatable hull (7) for holding lift gas from a pressure tank (9), an expansion unit (11), a propulsion and steering unit (13) for providing thrust and attitude control to the rocket stage (1), and a control unit (15) configured to initiate expansion of the hull (7) after stage separation by controlling the expansion unit (11) and to control the propulsion and steering unit (13) to steer the rocket stage (1) to a pre-determined landing point on the Earth's surface.

Description

[Technical Field]

[0001] The present invention relates to rocket stages of a multi-stage space launch vehicle, to a method for guiding rocket stages of a multi-stage space launch vehicle back to Earth for reuse, and to an airship module for attachment to the rocket stage. Summary of the Invention

[0002] Multistage space launch vehicles (or "multistage vehicles" for short) are well known for their much longer range than single-stage rockets, making them ideal for reaching remote orbits or completely escaping Earth's gravitational field. Typically, one or more lower stages provide the initial thrust during liftoff, accelerating the vehicle to a certain velocity and altitude, building up the vehicle's potential and kinetic energy before one or more upper stages are ignited. Due to economic and environmental considerations, the idea of ​​reusing at least the lowest stage of such a space launch vehicle (known as the "first stage" because it is the first stage to ignite) has gained increasing interest in the space industry. Returning the first stage of a space launch vehicle safely to Earth without significant damage and reusing it for another launch is a challenging task. This is because, at the time of stage separation—when the first stage separates from the rest of the space launch vehicle—the space launch vehicle has already reached a high altitude and speed, typically well above the altitudes used for commercial aviation, such as transatlantic and transpacific flights.

[0003] The well-known launcher systems, Falcon 9 and Falcon Heavy Launch Systems, from American aerospace manufacturer Space Exploration Technologies Corp. (SpaceX), each use a propulsive landing system, such as a side booster, to return their first stage. A propulsive landing system uses at least one thruster, such as the first stage's main engine, to provide sufficient thrust to allow the first stage to land upright, in the same direction as liftoff but in the opposite direction. However, a propulsive landing system requires additional fuel for at least the rocket stage's water landing stage, thereby impacting the launch system's payload capacity.

[0004] It is therefore an object of the present invention to improve the recovery of rocket stages, particularly the first stages of space launch vehicles, i.e., to safely return a rocket stage of a space launch vehicle to a predetermined position, preferably on the Earth's surface.

[0005] The object of the present invention is solved by further embodiments as set forth in the independent and dependent claims. DETAILED DESCRIPTION OF THE INVENTION

[0006] A first aspect of the present invention relates to a rocket stage for a multi-stage space launch vehicle, the rocket stage comprising a main engine for providing thrust for liftoff of the space launch vehicle from the Earth's surface, the rocket stage configured for stage separation from the remainder of the space launch vehicle during ascent after liftoff such that the space launch vehicle continues into space and the rocket stage returns to the Earth's surface, the rocket stage comprising: an inflatable hull for receiving and retaining lift gas from a pressure tank attached to the rocket stage; - an inflation unit that inflates the hull with lifting gas; a propulsion and steering unit that provides thrust and attitude control to the rocket stage while the vehicle hull is at least partially inflated; a control unit for controlling the expansion unit and the propulsion and steering unit; The present invention is characterized by comprising: The control unit is configured to, when a predetermined condition after stage separation is met, control the expansion unit to initiate expansion of the hull and fill the hull with lifting gas to generate aerostatic lift, thereby increasing the volume of the hull, and control the propulsion and steering unit to steer the rocket stage to descend to a predetermined landing site on the Earth's surface while the hull is at least partially filled with lifting gas during descent.

[0007] A space launch vehicle can be a vehicle used to carry a payload, such as a satellite, into Earth orbit. Reusing as many parts of a space launch vehicle as possible, especially the first rocket stage, can significantly reduce costs, especially for repeated launches, such as adding new satellites, replacing old ones, or resupplying space stations like the ISS (International Space Station).

[0008] Because a rocket stage includes a main engine to provide thrust for liftoff, the rocket stage is typically the first stage and is ignited for liftoff purposes to lift one or more upper rocket stages to a certain altitude and accelerate one or more upper rocket stages to a certain velocity, regardless of whether the rocket stage runs on liquid or solid propellant, or whether only one or more first stages are ignited in parallel to provide thrust for liftoff, or whether they are ignited some time after liftoff.

[0009] The lifting gas, preferably selected from hydrogen and helium, is released into the inflatable hull from a pressure tank. Because the density of the lifting gas is less than that of air, at least at sea level and, depending on atmospheric conditions and the choice of lifting gas, less than that of air up to a certain altitude above sea level, the inflated hull, at least partially containing the lifting gas, provides aerostatic lift through buoyancy. This concept is familiar from airships such as historic "Zeppelins," which had rigid frameworks within fabric hulls, and from so-called "blimps," which also utilize the aerostatic lift of a gas-containing hull (or gas-containing container) but lack a rigid framework and instead rely on hull tension caused by the pressure of the internal lifting gas. Preferably, the hull released from the rocket stage also does not have a rigid framework such as an aluminum truss within it, but may be constructed of semi-rigid or other flexible elements, such as polymer fibers, to withstand some tension, particularly across opposing hull segments.

[0010] With the help of the buoyancy generated by the gas-filled hull, the rocket stage can either slowly descend or, if the volume of the gas-filled hull is sufficiently large compared to the total mass of the rocket stage including the hull, enter a cruise flight stage while maintaining a constant altitude above sea level. To reach a designated location on the Earth's surface, in particular a landing site close to the launch site, the propulsion and steering unit provides thrust for translational forces acting on the rocket stage, for example to establish and / or maintain a constant velocity relative to the Earth, and also performs attitude control at the level of rotational dynamics, for example to follow commanded azimuth, bank and pitch angles. For this purpose, the propulsion and steering unit may include one of the following: - Force vector control with steerable propulsion units; -Thrust vector control by purely attitude control engines such as attitude control thrusters, or aerodynamic control surfaces, or - A combination of at least two of the above.

[0011] The control unit includes at least one hardware unit, such as a computer including a processor, memory, and appropriate input / output interfaces. Embodiments referring to a control unit may take the form of an entirely hardware embodiment, an entirely software embodiment, or an embodiment including both hardware and software elements.

[0012] In particular, the control unit is configured to perform guidance and navigation tasks to return the rocket stage having the inflated hull to a designated target location on the Earth's surface, such as a landing site, airfield, airport, truck bed, or ship bed, which may include reacting to instructions from an air traffic controller, commands from a command and control ground station, or activation of a Traffic Control Air Traffic Avoidance System (TCAS) system to orbit other air traffic in local airspace and avoid mid-air collisions with other aircraft.

[0013] The present invention provides the advantage that a rocket stage, particularly a first stage, of a space launch vehicle can be recovered after liftoff and safely guided to a predetermined landing site so that the rocket stage can be reused for another launch of the space launch vehicle. The added mass by providing a system that utilizes the buoyancy of lifting gas contained within the hull to guide the rocket stage to a predetermined landing site is generally less than the added mass required for propulsive landing systems known from the prior art, since little or no additional fuel is carried with the rocket stage for descent and landing.

[0014] According to one embodiment of the present invention, the predetermined condition after stage separation for initiating hull inflation is that the velocity of the rocket stage relative to the Earth drops below a predetermined threshold.

[0015] According to another embodiment of the invention, the expansion unit comprises an exchange unit for exchanging the lifting gas with air from the surrounding atmosphere within the volume enclosed by the hull, and the control unit is configured to control the exchange unit to initiate and carry out the exchange of the lifting gas with air such that the amount of lifting gas exchanged with air increases as the altitude of the rocket stage decreases.

[0016] The replacement of the lifting gas with ambient atmospheric air can be achieved by implementing known buoyancy compensators to compensate for the increasing ambient atmospheric density, temperature changes, and other effects that affect the buoyancy of the lifting gas as the rocket stage descends in altitude, thus compensating for the effect that the denser the ambient air, the greater the buoyancy per unit volume of lifting gas.

[0017] According to another embodiment of the invention, the control unit is configured to release lift gas from the volume enclosed by the hull and at least partially retract the hull to reduce the volume enclosed by the hull, such that the volume enclosed by the hull reduces as the altitude of the rocket stage decreases.

[0018] This embodiment is preferably applied to a hull designed as a non-rigid airship. This means that the hull does not exhibit rigid supporting structural elements such as trusses, but instead relies on the pressure of the lifting gas to apply tension and thus give the hull a dimensionally stable shape. The hull can be retracted in the same way as it was released from the storage box that houses the hull attached to or folded inside the rocket stage, but in the reverse direction. In particular, if it is assumed that the descending rocket stage is not required to be able to perform a longer ascent, loss of lifting gas into the surrounding atmosphere is acceptable.

[0019] According to another embodiment of the invention, the propulsion and steering unit comprises at least one steerable propeller or ducted fan.

[0020] The at least one steerable propeller or ducted fan is preferably steerable about a lateral horizontal axis, i.e., in the vertical plane, to control the pitch motion of the rocket stage and therefore the angle of climb and altitude on longer time scales, and / or steerable about a vertical axis to provide yaw control.

[0021] According to another embodiment of the present invention, at least one steerable propeller or ducted fan is connected to an electric motor, which is electrically powered by batteries mounted on the rocket stage or by power from solar panels disposed on the exterior surface of the hull, preferably in the form of a solar panel membrane that seamlessly contacts the exterior surface of the hull.

[0022] According to another embodiment of the invention, the rocket stage includes a deceleration system that reduces the velocity of the rocket stage relative to the Earth, and the control unit is configured to initiate operation of the deceleration system during or after stage separation and before hull inflation.

[0023] The deceleration system is responsible for slowing the rocket stage from its initial velocity during stage separation or after the suborbital flight phase following stage separation. Deceleration is necessary to slow the rocket stage to a safe velocity for hull release and inflation.

[0024] According to another embodiment of the invention, the deceleration system is composed of a device for generating air resistance, in particular a parachute, in particular a parachute capable of withstanding hypersonic or supersonic aerodynamic speeds. Equivalents of the above and below mentioned parachutes include ballutes, etc.

[0025] According to another embodiment of the invention, the parachute is connected to the hull such that the air resistance of the parachute deploys the hull, the connection between the hull and the parachute is secured with a releasable release, and the control unit is configured to release the release when a condition is met, in particular when a predefined threshold is reached.

[0026] Preferably, the parachute is connected to the hull with a polymer cord, such as a rope or cord made of ultra-high molecular weight polyethylene fiber or aramid fiber, or a steel cable, and the air resistance of the parachute is used as a pulling force to release and deploy the hull from a storage compartment attached to or incorporated into the rocket stage, which serves to store the folded hull.

[0027] According to another embodiment of the invention, the deceleration system is realized by retro-firing the main engines of the rocket stage, preferably by the activation of at least one dedicated reverse booster, or by propulsive reverse braking, the latter by re-igniting the main engines used for lift-off.

[0028] In addition to or instead of a parachute, the deceleration system preferably comprises steerable grid fins that generate aerodynamic drag and, in particular, attitude control of the rocket stage during suborbital flight after stage separation.

[0029] According to another embodiment of the invention, the device for generating air resistance is attached to the rocket stage via a variable attachment point that is movable or repositionable (transportable) along the longitudinal axis of the rocket stage, wherein the control unit is configured to move or reposition the attachment point from its initial position at the rear of the rocket stage relative to the velocity vector toward a transverse plane of the rocket stage that constitutes the center of gravity of the rocket stage before the hull is expanded, such that before or during expansion of the hull, the body of the rocket stage is brought to a horizontal attitude from an attitude with a zero aerodynamic angle of attack relative to the longitudinal axis of the rocket stage.

[0030] The longitudinal axis of the rocket stage is approximately, and particularly exactly, aligned (i.e., parallel) with the kinematic velocity vector of the rocket stage at liftoff.

[0031] According to another embodiment of the present invention, the device for generating aerodynamic drag is attached via at least two force transmission devices, a first of which is attached to the aft end of the rocket stage and a second of which is attached to the forward end of the rocket stage relative to the velocity vector of the rocket stage before the expansion of the hull is initiated. The force transmission devices can provide only tensile force between the device for generating aerodynamic drag and the main body of the rocket stage, and at least the second of which is capable of changing its length. The control unit is configured to retract the second of the at least two force transmission devices so that the main body of the rocket stage assumes a horizontal attitude from an attitude having a zero aerodynamic angle of attack relative to the longitudinal axis of the rocket stage before the expansion of the hull. The force transmission devices are preferably cords, or ropes, strings, cables, or the like that can be considered equivalent to cords.

[0032] According to another embodiment of the invention, the fully inflated hull has the shape of a blimp, consisting of aerodynamically stabilizing tails.

[0033] According to another embodiment of the invention, the aerostatic lift force generated by the lifting gas within the volume enclosed by the at least partially inflated hull is at least as great as the force of gravity acting on the rocket stage at a given point in time, and the control unit is configured to control the propulsion and steering unit before or during descent to perform a cruise flight at a constant or increasing altitude above sea level.

[0034] According to another embodiment of the invention, the aerostatic lift force generated by the lifting gas within the volume enclosed by the at least partially inflated hull is less than the force of gravity acting on the rocket stage for at least the first 80% of the altitude descended by the rocket stage.

[0035] According to another embodiment of the present invention, the control unit is configured to induce the rocket stage into a ballistic flight after stage separation by executing a main engine cutoff, and induce it into a deceleration phase after the ballistic flight, wherein the deceleration system is inactive during the ballistic flight and active during the deceleration phase.

[0036] According to another embodiment of the present invention, the pressure tank is disposed on top of the rocket stage relative to the attitude of the rocket stage during liftoff, and the rocket stage comprises a reverse unit configured to rotate the rocket stage about its transverse axis during the ballistic phase so that, after being rotated by the reverse unit, the main engine is located at the front of the rocket stage relative to the velocity vector and the pressure tank is located at the rear of the rocket stage relative to the velocity vector.

[0037] Another aspect of the present invention is a method for guiding rocket stages of a multi-stage space launch vehicle back to Earth for reuse, the method comprising: providing thrust with a main engine for liftoff of the space launch vehicle from the Earth's surface; separating the rocket stages from the remainder of the space launch vehicle during ascent after liftoff so that the space launch vehicle continues into space and the rocket stages return to the Earth's surface; a control unit initiating inflation of an inflatable hull connected to the rocket stage when a predetermined condition after stage separation is met, the hull receiving and retaining lift gas from a pressure tank attached to the rocket stage to increase the volume of the hull with lift gas to generate aerostatic lift; and controlling a propulsion and steering unit to steer the rocket stage during descent to a predetermined landing site on the Earth's surface, the propulsion and steering unit providing thrust and attitude control while the hull is at least partially inflated, and during descent the hull is at least partially filled with lift gas.

[0038] The advantages and preferred embodiments of the method of the invention can be derived by applying mutatis mutandis the features of the specification given in relation to the rocket stage of the invention.

[0039] Another aspect of the invention is an airship module intended to be attached to a rocket stage, comprising: a pressure tank for containing lift gas; an expansion unit; a control unit; and a compartment for containing an inflatable hull, the inflatable hull configured to receive and hold the lift gas from the pressure tank; the expansion unit configured to perform inflation of the hull with the lift gas; the airship module further comprising a propulsion and steering unit for providing thrust and attitude control to the rocket stage while the hull is at least partially inflated; and the control unit configured to control the expansion unit and the propulsion and steering unit.

[0040] The advantages and preferred embodiments of the airship module of the invention can be derived by applying mutatis mutandis the features of the specification given in relation to the rocket stage of the invention.

[0041] The description herein, particularly the description relating to the drawings that follow, is presented for purposes of illustration and understanding and is not intended to be an exhaustive or limiting description of the invention in the form disclosed. Various modifications and variations will be apparent to those skilled in the art. In particular, the embodiments relating to the drawings have been chosen and described in order to best explain the principles and practical applications of the invention and to enable those skilled in the art to understand the invention in various embodiments with various modifications suited to particular intended uses. [Brief explanation of the drawings]

[0042] [Figure 1] Figure 1 shows the various phases of a rocket stage during and after liftoff. [Figure 2] FIG. 2 illustrates the deceleration phase and hull expansion phase of a rocket stage according to an embodiment of the present invention. [Figure 3] FIG. 3 shows a specific procedure after stage separation according to an embodiment of the present invention. [Figure 4] FIG. 4 is an exemplary connection between a parachute and an inflatable hull of a rocket stage according to an embodiment of the present invention. [Figure 5] FIG. 5 is an exemplary connection of a parachute and a rocket stage by a cord, according to an embodiment of the present invention. [Figure 6] FIG. 6 is an exemplary connection between a parachute and a rocket stage by a cord, according to an embodiment of the present invention. [Figure 7] FIG. 7 is a rocket stage with an inflated hull according to an embodiment of the present invention. [Figure 8] FIG. 8 illustrates components of a rocket stage with an airship module attached according to an embodiment of the present invention.

[0043] [Detailed description of the drawings] The figures are schematic and not to scale.

[0044] Figure 1 shows a space launch vehicle 3 from liftoff, shown as state (A), through stage separation, shown as phase (C). During liftoff (A), the lower first rocket stage 1 is rigidly coupled to the upper stage of the two-stage space launch vehicle 3. Rocket stage 1 is the first stage required to lift the space launch vehicle 3 to a certain altitude and velocity above the Earth. To this end, rocket stage 1 comprises main engines 5 (see Figure 7) that provide the thrust required for liftoff of the space launch vehicle 3 from the Earth. Approximately five minutes after liftoff (A), the space launch vehicle reaches an altitude of 70 km and tilts from its vertical liftoff position in preparation for entering an orbit around the Earth, as shown in phase (B) of Figure 1. Stage separation (C) occurs as rocket stage 1 separates from the top of the space launch vehicle 3 during its ascent after liftoff. By igniting its upper stage, the space launch vehicle 3 carrying the payload continues to fly towards a target orbit around the Earth, while the rocket stage 1 performs a re-entry maneuver in a ballistic flight and returns to the Earth's surface as described with the help of various embodiments shown in Figures 2 to 7.

[0045] FIG. 2 illustrates two exemplary stages following stage separation (C) in FIG. 1. First, there is the deceleration phase (D), which begins after the ballistic phase. Rocket stage 1 includes a deceleration system 19 equipped with a parachute to reduce the rocket stage's velocity relative to the Earth. Control unit 15 activates the deceleration system 19 during or after stage separation and before the hull 7 inflation phase (E). The parachute is jettisoned while the hull 7 is inflated with lift gas. The inflation pressure and the air resistance of the parachute prior to jettisoning help deploy the hull 7 and release it from the storage compartment located inside the rocket stage 1. The inflated hull 7 creates a drag force above the rocket stage's center of gravity, placing the rocket stage 1 in a horizontal position and generating a pitch-up moment. The hull continues to inflate after phase (E), resulting in a blimp configuration with the rocket stage 1 hanging down. For details of the blimp shape of the hull 7, see FIG. 6.

[0046] Figure 3 shows an alternative procedure to that outlined in Figure 2, following Phase (C) of Figure 1. In Figure 3, the trajectory of the center of mass of the rocket stage 1 is depicted by a dashed curve. After stage separation (Phase (C) of Figure 1), the control unit 15 induces the rocket stage 1 into a ballistic flight by performing main engine cutoff. Phase (D) of Figure 3 differs from Phase (C) of Figure 1 in that the reverse unit 23, consisting of attitude control thrusters, is activated before the rocket stage is induced into the deceleration phase after the ballistic flight. During this ballistic flight, the deceleration system 19 remains inactive and is activated only during the deceleration phase. Furthermore, during the ballistic flight, the reverse unit 23 provides thrust to the outside of the center of mass of the rocket stage 1, exerting a moment on the rocket stage 1 and causing it to rotate about its horizontal axis. During the rotation in Phase (D) of Figure 3, the rocket stage 1 rotates in the shortest possible rotation direction and reaches the reverse direction through the rotation (see Phase (E)). During liftoff, the main engines 5 face the rear of the rocket stage 1 relative to the rocket stage's velocity vector. However, after the rotation performed by the reverse unit 23 is completed, the main engines 5 face the front of the rocket stage 1 relative to the rocket stage's velocity vector. The reverse unit 23 rotates the rocket stage 1 so that its aerodynamic angle of attack is zero or close to zero relative to the longitudinal axis of the rocket stage's body. If the pressure tank 9 containing a flammable lifting gas, such as hydrogen, is located at the top of the rocket stage 1 relative to its attitude during liftoff, the pressure tank 9 is then positioned at the rear of the rocket stage 1 during Phase (F), a longer ballistic flight for re-entry into the Earth's atmosphere where it is subject to friction and the high dynamic pressure of the surrounding air relative to the rocket stage's velocity vector. In this way, the pressure tank 9 is much less exposed to the high temperatures at the front of the rocket stage 1, where the effects of dynamic pressure and heat generation are greatest.After continuing flight for re-entry into the atmosphere, a deceleration system 19 consisting of a parachute capable of withstanding supersonic airflow is deployed to slow the rocket stage 1 relative to the Earth. The parachute generates air resistance and is attached to the rocket stage 1 at a movable attachment point that is movable along the rocket stage 1's longitudinal axis. Initially, the attachment point is located at the aft end of the rocket stage 1 relative to the rocket stage 1's velocity vector until a predetermined speed is reached (see Phase (G)). Phase (H) is initiated only in the subsonic flight region to maintain predictable aerodynamic stability characteristics of the rocket stage 1's body. During this Phase (H), the attachment point moves toward the center of the rocket stage 1, thus further moving toward the rocket stage 1's center of gravity, and the rocket stage 1's body gradually rotates toward a horizontal attitude. During this maneuver, the rocket stage 1's body reaches a horizontal attitude from an aerodynamic angle of attack near zero relative to the rocket stage 1's longitudinal axis before the hull 7 expands at an altitude of 20 km above mean sea level (see Phase (I)). Thus, the hull 7 experiences little longitudinal air flow during inflation, only longitudinal flow supporting the opening of the hull from a storage compartment located within or on the surface of the body of the rocket stage 1.

[0047] Figure 4 shows an alternative configuration to that shown in phase (I) of Figure 3. In the latter, the hull 7 is deployed from the storage compartment without affecting the cord of the parachute 19, which is jettisoned at some stage during the deployment and inflation of the hull 7, whereas Figure 4 shows an alternative method in that the parachute 19 actively helps the hull 7 to deploy from the storage compartment via a pulling force generated by the air resistance of the parachute, which is greater than the air resistance of the main body of the rocket stage 1. However, even in this embodiment, the parachute 19 is jettisoned at some stage during the deployment and inflation of the hull 7.

[0048] FIG. 5 illustrates an alternative to the movable attachment point for the parachute 19 described in connection with FIG. 3. In the embodiment of FIG. 5, the parachute 19 is attached via two aramid cords attached to the aft and forward ends of the rocket stage 1. FIG. 5 shows a fixed-length aft cord and a variable-length b forward cord. During phase (G) of FIG. 3, length b is equal to or longer than the sum of length a and the length of the rocket stage 1 body, so that the parachute 19 drags behind the rocket stage 1 body, and the cord of length b does not affect the position of the parachute 19 relative to the rocket stage 1 body. Next, length b is shortened (see phase (H) of FIG. 3) until a and b are equal, the rocket stage 1 body is brought to a horizontal position, and the cords of lengths a and b bear approximately the same gravitational load on the rocket stage 1 body before the hull 7 expands.

[0049] FIG. 6 illustrates an alternative to the variable attachment point of the parachute 19 described with respect to FIG. 3, which also serves as an alternative to the solution described with respect to FIG. 5. In this alternative, as depicted in FIG. 6, the location of the effective attachment point of the parachute 19 to the rocket stage 1 is variable in that a single cord is used having a first attachment point and a second attachment point. The first attachment point is located at the end of the rocket stage 1, logically separating the cord into an upper x-section and a lower y-section, but allowing it to be released from the rocket stage 1. The second attachment point of the cord is located within or near a cross section of the rocket stage 1 that includes the center of gravity of the rocket stage 1 body. Before the release of the first attachment point, only the upper x-section of the cord is under tension, while the lower y-section is loosely tucked within or on the surface of the rocket stage 1. After the release of the first attachment point, the entire length of the cord, including both the x-section and the y-section, is under tension. In FIG. 6, the parachute 19 exerts a force (primarily due to air resistance) on the rocket stage 1 body via the cord. Immediately after releasing the first attachment point, air resistance exerting a force against gravity on rocket stage 1 places the cord under tension along its entire length, and the position of the second attachment point causes the longitudinal axis of the body of rocket stage 1 to rotate over time to a horizontal position. Releasing the first attachment point can be accomplished by activating a release mechanism on rocket stage 1, for example, pyrotechnically.

[0050] Figure 7 shows the rocket stage 1 with the inflatable hull 7 fully inflated with lift gas from pressure tanks 9 attached to the rocket stage 1 (see Figure 8 for details). Two propulsion and steering units 13 are attached to the left and right sides of the rocket stage 1. These provide thrust and attitude control for the rocket stage 1 while the hull 7 is at least partially inflated. When fully inflated, the hull 7 has the shape of a blimp, consisting of aerodynamically stabilizing tail fins. Each propulsion and steering unit 13 consists of a ducted fan that can be tilted about a horizontal axis to provide pitch moment. Yaw control is achieved by rotating the upper and lower vertical stabilizers about a vertical axis. The ducted fans are driven by electric motors, which are electrically powered by batteries attached to the rocket stage 1. The hull 7 itself is rigidly connected to the main body of the rocket stage 1, particularly without loose cords, and the rocket stage 1, which functions as a blimp gondola, is connected without any degrees of freedom to allow movement between the hull 7 and the main body of the rocket stage 1. In this way, the body of the rocket stage 1 is connected to the fully inflated hull 7, preventing relative movement between the hull 7 and the body of the rocket stage 1. Furthermore, the body of the rocket stage 1 is in contact with the hull 7, i.e., there is no gap between the hull 7 and the body of the rocket stage 1.

[0051] FIG. 8 is a cross-sectional view through a rocket stage 1 carrying an airship module 21, but without showing the hull 7 in part (I) of FIG. 8 and showing only the attachable airship module 21 in part (II) of FIG. 8. The airship module 21 serves to equip an existing lower rocket stage 1 with re-entry and recovery capabilities by attaching such airship module 21 to the existing lower rocket stage 1, as shown in part (II). To this end, the attachable airship module 21 comprises a pressure tank 9 for containing lift gas, an expansion unit 11, a control unit 15, and a compartment housing an inflatable hull 7, the inflatable hull 7 configured to receive and retain the lift gas from the pressure tank 9, and the expansion unit 11 configured to perform inflation of the hull 7 with the lift gas. The airship module 21 further comprises a propulsion and steering unit 13 for providing thrust and attitude control to the rocket stage 1 while the hull 7 is at least partially inflated, and the control unit 15 is configured to control the expansion unit 11 and the propulsion and steering unit 13. The expansion unit 11, equipped with a valve, serves to inflate the hull 7 with inflation gas. The exchange unit 17, connected to the expansion unit 11, serves to exchange air from the surrounding atmosphere with the lift gas within the volume enclosed by the hull 7. The control unit 15 is configured to control the exchange unit 17 to initiate and execute the exchange of air and lift gas so that the volume of the lift gas is exchanged with air as the altitude of the rocket stage 1 decreases. The control unit 15 also serves to control the expansion unit 11 and the propulsion and steering unit 13 (see FIG. 3). The control unit 15 also controls the expansion unit 11 to initiate the expansion of the hull 7 when a predetermined condition is met after stage separation, thereby filling the hull 7 with lift gas to increase its volume in order to generate aerostatic lift, and controls the propulsion and steering unit 13 to perform a maneuver to descend the rocket stage 1 to a predetermined landing point on the Earth's surface with the hull 7 at least partially filled with lift gas during the descent, known as the ferryback flight. Further components of the rocket stage 1 are described with reference to part (I) of FIG. 8. The main engine 5 is equipped with at least one liquid propellant thruster at its lower end. [Explanation of symbols]

[0052] 1: Rocket Stage 3: Space launch vehicle 5: Main engine 7: Inflatable hull 9: Pressure tank 11: Expansion unit 13: Propulsion and steering unit 15: Control unit 17: Replacement unit 19: Deceleration system 21: Airship module 23: Reverse Unit

Claims

1. A rocket stage (1) for a multistage space launch vehicle (3), comprising: The rocket stage (1) comprises a main engine (5) for providing thrust for liftoff of the multi-stage space launch vehicle (3) from the Earth's surface, the rocket stage (1) being configured to separate from the remainder of the multi-stage space launch vehicle (3) during ascent after liftoff so that the multi-stage space launch vehicle (3) continues flying into space and the rocket stage (1) returns to the Earth's surface, the rocket stage (1) comprising: - an inflatable hull (7) for receiving and retaining lift gas from a pressure tank (9) attached to said rocket stage (1); an inflation unit (11) for inflating said inflatable hull (7) with said lifting gas; a propulsion and steering unit (13) that provides thrust and attitude control to the rocket stage (1) while the inflatable hull (7) is at least partially inflated; a control unit (15) for controlling said expansion unit (11) and said propulsion and steering unit (13); The present invention is characterized by comprising: The control unit (15) is configured to, when a predetermined condition after stage separation is satisfied, control the expansion unit (11) to start expanding the inflatable hull (7), fill the inflatable hull (7) with the lifting gas for generating aerostatic lift to increase the volume of the inflatable hull (7), and control the propulsion and steering unit (13) to steer the rocket stage (1) to descend to a predetermined landing point on the Earth's surface while the inflatable hull (7) is at least partially filled with the lifting gas during descent, wherein during the descent, a main body of the rocket stage (1) is in a horizontal position and is suspended below the inflated inflatable hull (7).

2. A rocket stage (1) for a multistage space launch vehicle (3), comprising: The rocket stage (1) comprises a main engine (5) for providing thrust for liftoff of the multi-stage space launch vehicle (3) from the Earth's surface, the rocket stage (1) being configured to separate from the remainder of the multi-stage space launch vehicle (3) during ascent after liftoff so that the multi-stage space launch vehicle (3) continues flying into space and the rocket stage (1) returns to the Earth's surface, the rocket stage (1) comprising: - an inflatable hull (7) for receiving and retaining lift gas from a pressure tank (9) attached to said rocket stage (1); an inflation unit (11) for inflating said inflatable hull (7) with said lifting gas; a propulsion and steering unit (13) that provides thrust and attitude control to the rocket stage (1) while the inflatable hull (7) is at least partially inflated; a control unit (15) for controlling said expansion unit (11) and said propulsion and steering unit (13); The present invention is characterized by comprising: the control unit (15) is configured to, when a predetermined condition after stage separation is satisfied, control the expansion unit (11) to initiate expansion of the inflatable hull (7) and fill the inflatable hull (7) with the lifting gas for generating aerostatic lift to increase the volume of the inflatable hull (7), and control the propulsion and steering unit (13) to steer the rocket stage (1) to descend to a predetermined landing site on the Earth's surface while the inflatable hull (7) is at least partially filled with the lifting gas during descent; The expansion unit (11) comprises an exchange unit (17) for exchanging the lifting gas with air from the surrounding atmosphere within the volume enclosed by the inflatable hull (7), and the control unit (15) is configured to control the exchange unit (17) to initiate and carry out the exchange of the lifting gas with air such that the amount of the lifting gas exchanged with air increases as the altitude of the rocket stage (1) decreases.

3. the control unit (15) is configured to release the lift gas from the volume enclosed by the inflatable hull (7) and at least partially retract the inflatable hull (7) to contract the volume enclosed by the inflatable hull (7), such that the volume enclosed by the inflatable hull (7) decreases as the altitude of the rocket stage (1) decreases. A rocket stage (1) according to any one of claims 1 to 2.

4. The propulsion and steering unit (13) comprises at least one steerable propeller or ducted fan. A rocket stage (1) according to any one of claims 1 to 2.

5. the rocket stage (1) includes a deceleration system (19) for reducing the velocity of the rocket stage (1) relative to the Earth, and the control unit (15) is configured to initiate operation of the deceleration system (19) during or after stage separation and before inflation of the inflatable hull (7). A rocket stage (1) according to any one of claims 1 to 2.

6. the deceleration system (19) is constituted by a device for generating air resistance, in particular a parachute; A rocket stage (1) according to claim 5.

7. the device for generating aerodynamic drag is attached to the rocket stage (1) at a variable attachment point, the attachment point being movable or repositionable along the longitudinal axis of the rocket stage (1), and the control unit (15) is configured to move or reposition the attachment point from an initial position at the rear of the rocket stage (1) relative to a velocity vector towards a transverse plane of the rocket stage (1) that constitutes the center of gravity of the rocket stage (1) before the inflatable hull (7) is inflated, so that the body of the rocket stage (1) moves from an attitude with a zero aerodynamic angle of attack relative to the longitudinal axis of the rocket stage (1) to a horizontal attitude before or during the inflation of the inflatable hull (7). A rocket stage (1) according to claim 6.

8. the aerodynamic drag generating device is attached via at least two force transmission devices, a first of the at least two force transmission devices being attached to the aft end of the rocket stage (1) and a second of the at least two force transmission devices being attached to the forward end of the rocket stage (1) relative to a velocity vector of the rocket stage (1) when inflation of the inflatable hull (7) is initiated, the force transmission devices being capable of providing a tensile force between the aerodynamic drag generating device and the rocket stage (1) body, at least the second of the at least two force transmission devices being capable of changing a length, and the control unit (15) being configured to retract the second of the at least two force transmission devices so that the rocket stage (1) body assumes a horizontal attitude from an attitude with a zero aerodynamic angle of attack relative to a longitudinal axis of the rocket stage (1) before inflation of the inflatable hull (7). A rocket stage (1) according to claim 6.

9. The inflatable hull (7), when fully inflated, has the shape of a blimp consisting of an aerodynamically stabilising tail. A rocket stage (1) according to any one of claims 1 to 2.

10. the aerostatic lift force generated by the lifting gas within the volume enclosed by the at least partially inflated inflatable hull (7) is at least as strong as the force of gravity acting on the rocket stage (1) at any given time, and the control unit (15) is configured to control the propulsion and steering unit (13) before or during descent to perform a cruise flight at a constant or increasing altitude above sea level. A rocket stage (1) according to any one of claims 1 to 2.

11. the aerostatic lift force generated by the lifting gas within the volume enclosed by the at least partially inflated inflatable hull (7) is less than the force of gravity acting on the rocket stage (1) for at least the first 80% of the altitude of the rocket stage (1) as it descends; A rocket stage (1) according to any one of claims 1 to 2.

12. The rocket stage (1) is equipped with a deceleration system (19) for reducing the velocity of the rocket stage (1) relative to the Earth, and the control unit (15) is configured to guide the rocket stage (1) into a ballistic flight after stage separation by performing main engine cutoff, and to guide the rocket stage (1) into a deceleration phase after the ballistic flight, and the deceleration system (19) is inactive during the ballistic flight and active during the deceleration phase. A rocket stage (1) according to any one of claims 1 to 2.

13. the pressure tank (9) is disposed on top of the rocket stage (1) with respect to the attitude of the rocket stage (1) during lift-off, the rocket stage (1) is equipped with a reverse unit (23), the reverse unit (23) rotates the rocket stage (1) around its transverse axis during a ballistic phase, and after being rotated by the reverse unit (23), the main engine (5) is located at the front of the rocket stage (1) with respect to a velocity vector, and the pressure tank (9) is located at the rear of the rocket stage (1) with respect to the velocity vector. A rocket stage (1) according to claim 12.

14. 1. A method for guiding a rocket stage (1) of a multistage space launch vehicle (3) to Earth for reuse, the rocket stage (1) providing thrust with a main engine (5) for liftoff of the multistage space launch vehicle (3) from the Earth's surface, the rocket stage (1) separating from the remainder of the multistage space launch vehicle (3) during ascent after liftoff such that the multistage space launch vehicle (3) continues into space and the rocket stage (1) returns to the Earth's surface, a control unit (15) initiating inflation of an inflatable hull (7) connected to the rocket stage (1) when a predetermined condition after stage separation is met, the inflatable hull (7) returning to the rocket stage (1), receiving and retaining lift gas from a pressure tank (9) attached to a stage (1) for increasing the volume of the inflatable hull (7) with the lift gas to generate aerostatic lift; and controlling a propulsion and steering unit (13) to steer the rocket stage (1) during descent to a predetermined landing point on the Earth's surface, the propulsion and steering unit (13) providing thrust and attitude control while the inflatable hull (7) is at least partially inflated, the inflatable hull (7) at least partially filling with the lift gas during descent, and the main body of the rocket stage (1) being in a horizontal position and suspended below the inflated inflatable hull (7) during the descent.

15. An airship module (21) mounted on a rocket stage (1) comprises a pressure tank (9) containing lifting gas, an expansion unit (11), a control unit (15), and a compartment containing an inflatable hull (7), the inflatable hull (7) configured to receive and retain the lifting gas from the pressure tank (9), the expansion unit (11) configured to perform inflation of the inflatable hull (7) with the lifting gas, and the airship module (21) provides thrust to the rocket stage (1) while the inflatable hull (7) is at least partially inflated. and a propulsion and steering unit (13) for providing attitude control, wherein the control unit (15) is configured to control the expansion unit (11) and the propulsion and steering unit (13), and the control unit (15) is configured to keep the main body of the rocket stage (1) in a horizontal attitude while the rocket stage (1) descends to a predetermined landing point on the Earth's surface, and the main body of the rocket stage (1) is configured to be suspended below the inflated inflatable hull (7) during the descent of the rocket stage (1).

Images