FIELD OF INVENTION

The present invention relates to a technology for reusing satellites by developing a suitable re-entry module for satellites with passage for air entrapped under the module to impede extreme rise in temperature of re-entry module by reducing the adiabatic compression of entrapped air.

BACKGROUND OF THE INVENTION

Space debris is a mass of defunct artificially created objects such as old satellites and spent rocket stages and their fragments in Earth's orbit. Approximately 6% of them are operational spacecraft, 21% are old spacecraft, 17% are rocket upper stages, 13% are mission-related debris, and remaining 43% are fragments from explosions or collisions. Consequently, about 94% of the catalogued objects no longer serve any useful purpose and are collectively referred to as 'space debris' . The functional satellites represent only a small fraction of the estimated 150,000 or more objects. The problem of space debris can be solved only if the satellite that has completed the functional life is vaporised in thin air or is brought back to earth. Bringing satellite back to earth has additional advantage that it can be reused and thereby reduce the manufacturing cost of the satellites.

At present there are no re-entry module specifically designed for bringing back the satellites. The parallel technologies which are used for re-entry of cosmonauts are not suitable for bringing back satellites and do not offer economically viable solutions even after suitable arrangements to attach satellite. There are two major types re-entry vehicles to facilitate return from a space flights, the first one is "re-entry capsule" and the second one "space shuttle" with a more flexible re-entry profile. There were continuous efforts to develop space shuttle that can accomplish re-entry with improved capabilities and safety, however apart from being expensive affair it was difficult to create wings that could navigate various parts of a mission and survive the heat of re-entry. A re-entry vehicle has to withstand tremendous g-forces, pressure and heat during launch and re-entry and reentry capsule offers best solution with respect to aerodynamic stability with minimum moving parts and complexities, while traveling at supersonic speeds during re-entry and require little manoeuvring to return to Earth.

Re-entry capsule first used in 1961 is the portion of a spacecraft which returns to earth following a space flight. Since then, several changes have been done to improve different characteristics of re-entry capsule. The shape of the re-entry capsule is basically determined by its aerodynamics, which should make it stable with a little aerodynamic lift during descent to facilitate atmospheric entry. Despite its aerodynamic advantages, the re-entry capsule is exposed to extreme heat and pressure during atmospheric descent. Accordingly, heat shield is used on a capsule's blunt, slightly curved bottom to protect the crew from extremely hot temperature. The base heat shield is made of composite materials. A glass/phenolic honeycomb core is wedged between the composite layers, like an ice cream sandwich, to provide high strength while staying lightweight. The entire vehicle is covered with thermal protection, including a type of woven ceramic "blanket" similar to those used on the space shuttle, and ceramic tiles on the back shells to deflect heat.

However, no major efforts have been made to address the root cause of increase in temperature. The reason is the air, which gets trapped under the module and does not have space to move. This trapped air gets compressed to such a great extent that it gets converted into plasma. This conversion of air into plasma increases the temperature of the entire module to almost 18,000°C. High temperatures of such magnitude make it necessary to use reinforced carbon-carbon (RCC), Avcot and phenol impregnated carbon ablator to protect the module from damage. Every time the carbon gets ablated, it needs to be coated again, which increases the cost of building the modules. US5064151A describe a return vehicle for use in returning a crew to Earth from low earth orbit in a safe and relatively cost-effective manner. The return vehicle comprises a cylindrically- shaped crew compartment attached to the large diameter of a conical heat shield having a spherically rounded nose. On-board inertial navigation and cold gas control systems are used together with a de-orbit propulsion system to effect a landing near a preferred site on the surface of the Earth. US5158248A describes a re-entry vehicle that includes three detachable modular components which anticipate total re-usability. Modularization of the composite re-entry vehicle offers great flexibility in re-arranging the various modules to suit a particular mission. The three module components include a crew module, principally serving as a crew cabin, and attached thereto is a modular heat shield or re-entry module which principally provides for thermal protection of the cabin module during re-entry. Propulsion for the cabin module to achieve a particular re-entry orbit is provided by a versatile service stage which becomes detached from the other two modules upon attainment of a desired re-entry trajectory. JPH08175499A describes an atmosphere reentry capsule with reduced aerodynamic heating at the time of re-entry of an atmosphere re-entry capsule and to provide good aerodynamic motion characteristic at the time of low- level flying using a device exposed after sublimation of an ablation material by covering the ablation material with a low- level flying aerodynamic device provided on the periphery. JPH0939899A describes an atmosphere re-entry capsule with decreased aerodynamic heat generated due to acceleration or decelerating of the re-entry capsule during re-entering the atmosphere, by developing a plurality of decelerating plates housed in machine side surfaces on the circumference. The present invention addresses the problems of space debris and cost of production of satellites by developing a cost-effective re-entry module for satellite, which will assist to bring back the satellite to earth after completion of satellite's functional life and thereby enable reuse of satellite after suitable restoration work. The re-entry module of present invention also addresses the problem of extreme rise in temperature of the lower surface of re-entry capsule by reducing the amount of air trapped under the module, which impede temperature rise to extreme level and so far, there remains a need to address the said issues and develop a re-entry capsule that could achieve the better results in a cost-effective manner. SUMMARY OF THE INVENTION

The present invention provides a solution to increasing threat of space debris and reducing the production cost of satellites by bringing back the satellite to earth after completion of their functional life and reuse them, which remained unaddressed till now and is serious concern for harmonious and economic development of space programs. The present invention also simultaneously minimizes the need of high temperature resistant materials which are exorbitantly expensive and allow use of inexpensive alternatives for thermal protection of re-entry module.

In one of the embodiment, the invention provides the re-entry module attached to the satellite comprising: i. Alpha-dome comprising a petal structures [1-5, 49] positioned on the upper surface [7] of the base for enclosing the payload, wherein petals are provided with actuators and hinge joints [8]; u Omega hexon positioned parallel to surface [9] and comprising of a base [16], a spike [24] and nozzle [15]; in Plurality of hexon positioned on the periphery of spike [24], wherein hexon is a modified scramjet engine having an outlet velocity vector positioned to be at an angle Θ to the inlet velocity vector, wherein, omega hexon is provided with a fuel base area [17], inlet vents [26] positioned with spike [24] for the inflow of free stream air, a Delta area where fuel and compressed air interact and flame holders positioned at close proximity to the delta area, wherein, the temperature at the Delta area will be high enough to allow combustion of oxygen and hydrogen at proper stoichiometric ratios, and wherein, the gases formed will expand and pass through the aerospike nozzle [15], resulting in providing retro thrust to the re-entry module. In one of the preferred embodiment, the petal structures are made of NiTinol alloy in the re-entry module.

In another embodiment, the petals are positioned to the base [7] using hinge joints [8] in the re-entry module. In still another embodiment, the petals [1-5, 49] are provided with transducers in the reentry module.

In another embodiment, the petals [1-5, 49] are provided with a silicon base with phenol impregnated carbon and other carbon-carbon composites with servos for actuation in the re-entry module. In another embodiment, the petal structures remain curled in the dormant state in the reentry module.

In still another embodiment, the petal structures get unfurled in the active state in the reentry module as shown in figures 3 and 4.

In another embodiment, the base [7] is made of carbon composites and is provided with shock absorbers in the re-entry module.

In still another embodiment, the lower surface [9] of base is provided with a coating of a temperature resistant material in the re-entry module.

In another embodiment, the spike [24] is provided with an arrangement for reducing or increasing its length according to the re-entry velocity by using a movable arm or a constant geometry before launch of re-entry module.

In another embodiment, the spike [24] is provided with six hexons in the re-entry module.

In still another embodiment, the spike [24] is made with high heat resistant materials such as phenol impregnated carbon- carbon composites or coatings of materials with high specific heat such as tantalum carbide in the re-entry module. In another embodiment, the spike [24] consists a cavity space to accommodate a hydrogen fuel tank [22] connected to a turbopump [19] through a valve [21] in the re-entry module.

In still another embodiment, the spike [24] consists a cavity space to accommodate fuel tank [22] and oxidizer tank [32], each provided with separate turbo pumps [19] and [35] for supply of fuel and oxidizer respectively in the re-entry module. In still another embodiment, the base [16] is provided with a coating of a heat resistant materials in the re-entry module. In another embodiment, the Delta area have two stream banks, first the fuel bank area [31] and the second the air bank area [29] in the re-entry module.

In another embodiment, the delta region is made using heat resistant materials and will be formed as a part of the omega-hexon in the re-entry module.

In another embodiment, the air bank area [29] contains a notch [30] in the re-entry module.

In another embodiment, the notch [30] can be positioned on either of the wall and in flexible numbers as per requirements of the re-entry module.

In still another embodiment, the nozzle [15] is an aerospike nozzle, which allow the exhaust to expand according to the ambient pressure in the re-entry module.

In another embodiment, the nozzle [15] is provided with a heat resistant lining [14] in- order to restrict temperature spikes in the re-entry module.

In another embodiment, the inlet vents [26] are provided with distinct angled ramps called as wedges [25] that are positioned to direct the flow of air into the inlet vents [26] as well as compress it in the re-entry module.

In another embodiment, the fuel tank is attached directly to the strut, which constricts in its initial portion and dilate in its later portion, wherein the constricted portion will produce an oblique shock to slow down the incoming flow of air and wherein, the tip of dilated portion is provided with fuel injectors to facilitate combustion in the wake region of the reentry module. The number and geometry of struts used can be varied to increase the efficiency. The temperature at this region will be enough to initiate auto ignition of the fuel.

In another embodiment, the geometry of the entire omega hexon is made with the help of Prandtl-Meyer function

In another embodiment, the curvature of the inlet vent, which can be varied according to size and other requirements of the re-entry module is made using the Prandtl-Meyer solution.

In another embodiment, suitable ramps according to the re-entry velocity are constructed for expansion and compression fan.

In another embodiment, the geometry of re-entry module can be varied using Prandtl- Meyer solution for different re-entry velocities. In another embodiment, the re-entry module is designed using Prandtl-Meyer solution selected from different available versions or a combination of different versions.

DESCRIPTION OF THE ACCOMPANYING DRAWINGS

Figure 1: Re-entry module before launch.

Figure 2: Re-entry module.

Figure 3: Side view of the re-entry module.

Figure 4: Isometric view of re-entry module. Figure 5: Cross-section view of the omega hexon.

Figure 6: Side view of omega-hexon.

Figure 7: Delta section of the re-entry module.

Figure 8: Dual engine mode of re-entry module.

Figure 9: Flow field around re-entry module during re-entry. Figure 10: Velocity vector for two omega hexon engines.

Figure 11: Expanded view of strut fuel inlet.

Figure 12: Velocity contour for conventional model, re-entry module without fuel injection, re-entry module with strut position 1 and re-entry module with strut position 2

Figure 13: Temperature contour for conventional model, re-entry module without fuel injection, re-entry module with strut position 1 and re-entry module with strut position 2

Figure 14: Pressure contour for conventional model, re-entry module without fuel injection, re-entry module with strut position 1 and re-entry module with strut position 2

Figure 15: (a)Expanded view of strut at position one with temperature contour

(b)Expanded view of strut at position one with velocity contour. Figure 16: (a) Expanded view of strut at position two with temperature contour

(b) Expanded view of strut at position two with velocity contour. DETAILED DESCRIPTION

Space vehicles must be slowed to subsonic speeds before parachutes or air brakes are deployed while their re-entry to earth. Such vehicles have kinetic energies typically between 50 to 1800 MJ, and atmospheric dissipation is the only way of expending the kinetic energy. The amount of rocket fuel required to slow the vehicle would be nearly equal to the amount used to accelerate it initially. Therefore, it is impractical to use retro rockets for the Earth re-entry procedure. During the re-entry procedure high temperature is generated at the surface of the heat shield due to adiabatic compression and the vehicle's kinetic energy is ultimately lost to gas friction (viscosity) after the vehicle has passed-by. Other smaller energy losses include black body radiation directly from the hot gases and chemical reactions between ionized gases.

The present invention relates to developing a re-entry module with distinct petal structures for payload protection and specific constructional arrangement of hexon engines to provide retro-thrust, which when enabled, reduces the rise in temperature of re-entry module upon entry in to earth's atmosphere. Therefore, the present invention makes the reentry module safer by addressing temperature related problems, which is one of the major threat and cause of accidents. The present invention also simultaneously minimizes the need of high temperature resistant materials which are exorbitantly expensive and allow use of inexpensive alternatives for thermal protection. The re-entry module of present invention comprises of distinct petal structures [1,2,3,4,5,49] positioned on the upper portion of the re-entry module known as alpha- dome. The number of petals can be varied according to size and other requirements of the re-entry module. The petals [1-5,49] without any restriction on selection from other suitable materials are made of NiTinol alloy, which has a melting point of 1300° C. The selection of material of petals is variable according to the requirements of re-entry module. The shape memory characteristic of NiTinol is the property useful in particular for the present invention. The petal structures will be curled, which is dormant state after the satellite/payload is jettisoned from the upper rocket stage [50]. Thereafter, the petals [1-5, 49] will remain in dormant state until actuated using actuators [8], which in turn can be modified as hinges, which are positioned at the lower end of the respective petal and fixed to the upper surface of the base [7] of the module. Upon actuation, the petal structure [1-5, 49] unfurls to its original shape. The petal structure now encloses the entire satellite/payload [6]. A passive temperature control system on both sides of NiTinol petal structure is provided. The inner layer of the petal structure contains transducers to measure the temperature and internal pressure of the system. The petal structure is alternatively actuated with a silicon base with phenol impregnated carbon and other carbon-carbon composites with servos or other actuators instead of heat actuation. During the re-entry, when the petals structure encloses the satellite/payload [6] completely, the alpha dome becomes a closed system in which the external state variables cannot influence the internal state variables and vice-e-versa. An inert gas is thereafter pumped into the alpha dome to prevent any fire accident due to short circuits. The petal structure is attached to the upper surface of the base [7], which is made of carbon composites and holds the satellite to the re-entry module and is provided with shock absorbers [48] which in turn along with said base acts as vibration dampers caused due to exposure to high g-forces during lift-off and re-entry.

The petal structure is positioned to the base [7] using hinge joints [8]. The hinge joints [8] will allow the angular displacement of the Nitinol petal structures during actuation. The lower surface [9] of base [7] is coated with temperature resistant material so that the heat from the stagnation point due to radiation and conduction will have a minimum impact to the satellite.

The solar panel [10] of satellite/payload [6] are retracted before the actuation of petal structures [1-5, 49]. The solar panels [10] are positioned such that they can be retracted inwards upon completion of the satellite's life time. Alternatively, the solar panels can also be positioned to be detachable and the petal structure encloses only the payload. The petal structure [1-5, 49] is provided with temperature sensors, which convey feedback to the thermal control system of re-entry module for maintaining the temperature inside the alpha dome.

The bottom part of re-entry module is provided with structure "omega hexon", which has cuboidal extrusions called as hexons emerging from the inlet spike [24]. The number of hexons can be varied according to size and other requirements of the re-entry module. Hexon is a modified scramjet engine, wherein the outlet velocity vector is positioned to be at an angle Θ to the inlet velocity vector in contrast to conventional scramjet engine where the inlet velocity vector is parallel to the outlet velocity vector. Positioning outlet velocity vector at an angle Θ to the inlet velocity vector is carried out to achieve deceleration. The design of the hexon is made according to Prandtl-Meyer solution and can be varied by using appropriate expansion and compression fans at suitable places. The thrust produced by hexon can be calculated as shown in figure 10 using the following equation:

Θ1=Θ2 and T1=T2, that is if the thrust by both the hexon is equal then the resultant thrust produced by the hexons will be equal to Tnet = 2Tcos(0/2).

The equation can be suitably modified for using higher number of hexon engines. The angle of attack of the re-entry module can be changed by changing the corresponding angles between the thrust vectors, which alter the thrust of corresponding hexon engines. Accordingly, in order to have zero angle of attack for the re-entry module during re-entry the angle between the thrust vectors should be equal.

The spike [24] is positioned to act as the inlet of the hexon engine and will be the first to have contact with the free stream air. The length of the spike can be modified according to the re-entry velocity by using movable arm or by constant geometry according to the reentry velocity. Spike can be made with appropriate number of deviations to facilitate efficient combustion. The spike is made with high heat resistant materials such as phenol impregnated carbon- carbon composites or coatings of materials with high specific heat such as tantalum carbide. The spike can be built in three different alternatives:

1) In one of the alternatives the spike [24] is made hollow, with a hydrogen fuel tank

[22] attached to a turbo pump [19] through a valve [21], which regulates the flow of liquid hydrogen to the delta area.

2) In the second alternative the spike [24] is provided with both fuel tank [22] and oxidizer tank [32]. Separate turbo pump [19] for fuel and [35] for oxidizer are provided to facilitate supply of fuel and oxidizer respectively.

3) In third alternative the fuel tank is attached directly to the strut, through which fuel is sprayed. The geometry of strut can be varied according to size and other requirements of the re-entry module.

The spike [24] upon contacting free stream air produces the initial shock as shown in figure 9. This initial shock will slow down the velocity of re-entry module and at the same time increases the pressure and temperature of the free stream air across the shock. The shock produced by the spike [24] is oblique shock [36] and will further interact with the bow shock [37] produced by the base [16] of omega hexon. The distance between the base of omega hexon and the bow shock is called as the standoff distance. Re-circulation region [38] is present between the spike [24] and the base. Another re -circulation region [41] is present across the side walls of the module and is followed by the wake region [43] behind the module. Expansion fan [39-40] is created due to convex region at the two corners, as well as the nozzels. The air flow continues to move to a neck region [45] leading to a recompression shock [44]. The base [16] will experience the peak temperature, and hence is provided with a coating of a heat resistant materials. The free stream air subsequent to the initial shock will be compressed and forced to pass through the inlet [26]. The air further passes through the vent [51] where it encounters a notch [30], which will create a vortex and pressure variations. This will help in efficient combustion of fuel in the hexon. The fuel is stored inside the spike [24] which is partially made hollow. The fuel will be stored in a cryogenic fuel tank [22] and will be pumped through a turbo pump [19], through the channel [20]. The flow of hydrogen is controlled by a valve [21]. The fuel then passes to the Delta area. Alternatively, a strut is positioned in-between the flow path to compress the supersonic flow to a decreased velocity, which facilitate combustion of fuel sprayed in the wake region. The area where fuel and compressed air interact is called as Delta area, as shown in figure 7, which has two stream banks, one the fuel bank area [31] and the air bank area [29]. The material used for the delta region and combustion area will be heat resistant and will be formed as a part of the hexon. The air bank area [29] contains a notch [30]. The notch can be placed on either of the wall depending on efficiency requirements. The notch will create a strong vortex and an oblique shock wave to slow down the incoming air for ensuring uniform mixing of fuel and air. The edges of notch [30] will experience temperature spikes and will require special coating of temperature resistant materials. The geometry of notch can be varied according to the requirements of the re-entry module. The fuel base area [17] takes the hydrogen from the turbo pump [19] and supply it to the Delta area. Flame holders are positioned near the delta area. The temperature at the Delta area will be high enough to initiate auto-combustion of fuel. A temperature sensor is placed on the upper lining [31] of fuel base to record the temperatures during combustion. Combustion will take place ahead of the notch [29] and the gases formed will tend to expand and pass through the diverging nozzle [15]. This will increase the mass outflow than the inflow, resulting in deceleration of the re-entry module.

The nozzle [15] is an aerospike nozzle. As the re-entry module will descend down through the atmosphere, the pressure will vary drastically. The aerospike nozzle will allow the exhaust to expand or contract according to the ambient pressure. The nozzle [15] has a heat resistant lining [14] in-order to restrict temperature spikes reaching the main systems. The inlet will be having closed areas when the number of hexon used is such that the inlet vents are not sufficient to cover the circumference of the conical spike. The wedges [25] are positioned to direct the flow into the inlet vents [26] in order to make sure that there are no stagnation points near the inlets [26] .

In another modification of the re-entry module of present invention called as dual engine mode, both the fuel tank [22] and oxidizer tank [32] are positioned inside the partially hollow spike [24]. Separate turbo pump [19] for fuel and [35] for oxidizer are provided to facilitate supply of fuel and oxidizer respectively.

The flow of fuel and oxidizer from fuel tank [22] and oxidizer tank [32] is controlled using the valves [21] and [33] respectively and the fuel and oxidizer will be mixed in the delta area. The expanded gases will accelerate through the diverging aerospike nozzle [15] producing retro thrust.