Abstract:
A reusable staging system comprising of a processor-based device configured to monitor one or more rocket stages of a launch vehicle having a payload, wherein the processor-based device has at least one interface communicating with the one or more rocket stages of the launch vehicle; and a memory device for storing data and executing software routines, and wherein the staging system is disposed within the payload of the launch vehicle, and wherein the staging system is configured to detect one or more detach conditions; and further configured to release the one or more rocket stages when the one or more detach conditions is met.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The invention relates generally to expendable launch vehicles, and more particularly to staging systems used in expendable launch vehicles. 
         [0002]    Multiple stage launch vehicles are generally single-use launch vehicles comprising several rocket stages. Multiple stage launch vehicles jettison one or more stages as they expend their fuel. Expendable launch vehicles are effectively multiple rockets stacked on top of each other in order to reduce the total amount of mass that needs to be accelerated to a final speed and/or height, generally to achieve orbit. While it is possible in principle to use a single stage launch vehicle, it is generally more efficient to use multiple stage launch vehicles when the detached components are not intended to be recovered intact. 
         [0003]    Each stage generally comprises of one or more motors, fuel and oxidizer tanks for a liquid fuel rocket or a casing for a solid fuel rocket. The first stage is at the bottom and is usually the largest. The second stage follows above it and is usually the next largest, etc. This is known as “linear staging.” When the first stage&#39;s motor fires, the entire spacecraft is propelled upwards. When the first stage runs out of fuel, it is detached from the rest of the spacecraft and falls away. This leaves a smaller spacecraft, with the second stage on the bottom, which then fires. This process is repeated until the final stage&#39;s motor burns out. 
         [0004]    Once a stage&#39;s fuel is expended, the space and structure which contained the fuel and the motors are useless. By detaching and discarding the stages which are no longer useful, the rocket reduces its overall weight. When a stage is discarded, the rest of the spacecraft is still traveling near to the speed that the whole assembly reached at the burn-out time of said stage. Accordingly, the thrust of subsequent stages is able to provide more acceleration than if the earlier stages or boosters were still attached. This means that the rocket needs less total fuel to reach a given velocity and/or altitude. 
         [0005]    Another advantage for using multiple stages is that each stage can use a different type of rocket motor tuned for the conditions in which it will operate. For example, the lower stage booster can use a motor suited for use at atmospheric pressure, while the upper stages can use motors suited for near vacuum conditions. Lower stages tend to require more structure than the upper stages, as they need to bear their own weight in addition to that of the stages above them. Optimizing the structure of each stage decreases the weight of the total vehicle. 
         [0006]    In between each stage, are smaller sections called interstages. Interstages generally serve as a buffer between stages to give room to house the engines. The interstage is usually detached with the stage below it so that the stage above fires. Interstages designed precisely to give just enough room for the interstage to release without touching the engines above. 
         [0007]    Usually, between the payload and the final stage is an instrument unit. The instrument unit comprises electronic systems that control the operations of the rocket from just before liftoff to when the final stage is detached, including determining when to detach each stage, and determining when to fire the next stage. The instrument unit also includes guidance and telemetry systems for the rocket. By measuring acceleration and altitude, it can calculate the position and velocity of the rocket and correct for any deviations. Essentially, the instrument unit serves as the staging system. However, like the interstages, the instrument unit is detached and discarded after the final stage burns out. This costly component must be replaced for each launch, and accordingly, there is a need for a system and method for reusing the instrument unit as a staging system in subsequent launches. 
         [0008]    The approaches described in this section are approaches that could be pursued, but not necessarily approaches that have been previously conceived or pursued. Therefore, unless otherwise indicated, it should not be assumed that any of the approaches described in this section qualify as prior art merely by virtue of their inclusion in this section. 
       BRIEF DESCRIPTION 
       [0009]    Embodiments provide a staging system instrument unit designed to be reusable for successive launches. A staging system according to certain embodiments are designed to replace traditional single-use instrument units with little or no change to existing components of the launch vehicle. Certain embodiments comprise a staging system integrated with a main control system of a payload. A payload can be a space capsule carrying passengers. 
         [0010]    The staging system typically monitors the launch vehicle from just before take off to until the last rocket stage is detached and discarded. This is accomplished by an interface in the staging system communicating with each rocket stage. Through the interface, a staging system can monitor various parameters and determine appropriate times to detach each stage. For example, when the bottom-most stage has expended all of its fuel, or the launch vehicle has reached a pre-determined altitude and/or velocity a staging system will detach and discard the bottom-most stage from the launch vehicle. Releasing the bottom-most stage may be accomplished by various methods, such as detonating small explosive charges. A staging system may further comprise systems for guidance and telemetry. By monitoring acceleration and altitude, the staging system can correct for deviations from the launch plan. 
         [0011]    The staging system&#39;s interface is designed such that when the final stage is detached, the connection between the staging system and the last stage is severed, and the staging system ceases to monitor any stage. The staging system remains intact in the payload as it returns to the planetary surface. Afterwards, the staging system&#39;s interface may be connected to a subsequent set of rocket stages of a launch vehicle in a subsequent launch. This reusable feature is desirable in that it saves the cost of having to provide a new staging system for each launch. 
     
    
     
       DRAWINGS 
         [0012]    These and other features, aspects, and advantages of the embodiments will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein: 
           [0013]      FIG. 1  illustrates a typical multiple stage expendable launch vehicle; 
           [0014]      FIG. 2  is a diagram showing the control system of a manned space capsule payload, in accordance with an embodiment; 
           [0015]      FIG. 3  is a diagram showing how a staging system interfaces with a first set of rocket stages in accordance with an embodiment; 
           [0016]      FIG. 4  is a diagram showing how a staging system interfaces with a subsequent set of rocket stages following release of the first set of rocket stages in accordance with an embodiment; 
           [0017]      FIG. 5  diagram showing a flow chart of an exemplary technique for re-using a staging system in accordance with an embodiment; and 
           [0018]      FIG. 6  shows a schematic of a staging system in accordance with an embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0019]    Turning now to the drawings, and referring first to  FIG. 1 , a typical multiple stage expendable launch vehicle  10  is shown having an expendable staging system. The instrument unit comprising the staging system  22  monitors the launch vehicle  10  from just before take off until the last stage is detached. 
         [0020]    During a typical launch, the first stage  12  undergoes ignition and begins to burn fuel. As fuel is burned, the launch vehicle  10  is propelled by exhaust gases being ejected at high speed. Rocket stages can use either liquid or solid fuels or a combination of both as in a hybrid rocket. The type of fuel, as well as the motors for the rockets, may depend on atmospheric conditions in which a stage is intended to operate. 
         [0021]    When the staging system  22  determines that the first stage  12  has expended most or all of its fuel, the staging system  22  sends a signal to detach the first stage  12 . One method of detaching the empty stage is to detonate small explosive charges located at points where the stage is connected to the interstage  14  above it. Once the stage has separated from the launch vehicle body, it falls away back into the atmosphere. Shortly thereafter, the bottom-most interstage  14  is also detached from the launch vehicle body. The interstages are designed to be buffer zones for the engines of the subsequent stage. 
         [0022]    Once the bottom-most interstage  14  has cleared the engines of the second stage  16 , the next set of engines begins to fire, accelerating a lighter launch vehicle. Once the fuel for the second stage  16  is expended, the staging system  22  causes the second stage  16  to detach from the launch vehicle body. Shortly thereafter, the bottom-most remaining interstage  18  is released. The staging system  22  causes the third stage engines fire. In this particular illustration, the third stage  20  is also the last stage. Once the third stage  20  fuel is expended, the final stage is detached and discarded from the rocket. Having no further need to monitor rocket stages, the instrument unit  22  is subsequently detached and discarded, leaving only the payload  24 . At this point, the payload  24  will have reached its target altitude, or will have gained enough velocity to further propel it to that altitude. Target altitude is usually one sufficient to achieve lower earth orbit. The discarded instrument unit  22  is non-recoverable, and is a sunk cost of the launch. Once the final stage  20  has been detached from the launch vehicle, only the payload structure  24  is left in flight. In the example illustrated herein, the payload  24  is a manned reentry capsule. However, the payload  24  may also be an unmanned cargo vehicle or any other spacecraft. 
         [0023]      FIG. 2  shows a control system  26  for a returnable space capsule in accordance with an embodiment. System block  28  illustrates various systems for operating the capsule comprising: a flight system  30 , a navigation system  32 , a staging system  34  and life support system  36 . For purposes of illustration, only the named systems are shown, as these are generally regarded as more vital components. It should be appreciated that a system block  28  in accordance with certain embodiments could comprise various other systems and sub-systems in accordance with an embodiment. For example, the control system  26  could comprise additional systems. 
         [0024]    A user interface  38  provides means for communication with and control of systems, relaying various input and output signals to and from the systems  28 . For example, a crew member may provide reaction control system (RCS) input to the flight system  30  via user interface  38 . Similarly, a crew member may control the staging system  34  and the detachment timing of the stages via the user interface  38 , although stage detachment actions are usually monitored and configured to occur automatically at one or more carefully preset conditions, such as altitude and fuel level. 
         [0025]    Manual control of the staging system  34  risks the premature detachment of a stage. Such an occurrence may leave the launch vehicle unable to reach its intended altitude, and risks having a detached rocket stage firing its motor while flying in close proximity to the spacecraft. Manual control may be a desirable option in the event that a malfunction with the automated system causes a rocket stage or interstage to fail to detach properly. 
         [0026]    Referring now to  FIGS. 3 and 4 , a detailed view of a staging system  34  in accordance with an embodiment is illustrated. The staging system  34  comprises a processor-based control system  40 , such as a computer having one or more microprocessors. The processor-based control system  40  is powered by a power source  42 , which may be standalone, or shared from the main power source for the control system  26 . The processor-based control system  40  may interface with a memory device  44 , such as non-volatile memory (ROM) for storing software programs and variable sets for stage monitoring. Although not shown in  FIG. 3 , it should be understood that the processor-based control system may further comprise hard disk drives for storing data and programs, volatile memory (RAM), and other hardware components. 
         [0027]    The processor based control system is connected to a user interface  38 , as shown in  FIG. 3 . Data connection point  56  represents an interface connecting the processor-based control system  40  to the user interface  38 , as shown in  FIG. 4 . Manual control of the staging system  34  may be a desirable back-up feature in the event that the automated system malfunctions. The processor-based control system  40  can communicate with a guidance system  58  and a telemetry system  60  to aid the launch vehicle in correcting for any deviation from the flight plan. 
         [0028]    A data bus  48  connects the staging system  34  to the first stage  50 , second stage  52 , and final stage  54 . Data connection point  46  connects the processor-based control system  40  to the data bus  48 . Data bus  48  carries information between the processor-based control system  40  and the rocket stages. For example, the first stage  50  may send a signal to processor-based control system  40  along the data bus  48  indicating that its propellant tanks are empty. The processor-based control system  40  can determine if a target altitude has been reached by communicating with the guidance  58  and telemetry  60  systems. If the processor-based control system  40  determines that the first stage  50  should detach, it sends a signal along data bus  48 , causing the first stage  50  to detach from the launch vehicle  10 . The staging system  34  operates in a similar fashion to determine when second stage  52  and final stage  54  should detach. It should be understood that although the data bus  48  is depicted as a single line for purposes of illustration, the data bus  48  may be a plurality of data lines having one or more lines corresponding to each rocket stage, and that the data connection point  46  may be configured to receive data from each of these lines. 
         [0029]    When the final stage  54  is detached, the data bus  48  disconnects from the data connection point  46 . At this point, the staging system  34  has no further function until a subsequent launch. Capsule reentry operations are governed by flight, navigation, and reaction control systems. On a subsequent launch, a new set of rocket stages (first stage  50 ′, second stage  52 ′ and final stage  54 ′) can be interfaced with the staging system  34  by connecting the end  62  of a new data bus line  48 ′ to the processor-based control system  40  at data connection point  46 . For purposes of illustration, arrow A represents the direction of the connection of the new data bus  48 ′ to the staging system  34 . During launch, the operations governing the launch and detachment of the previous set of rocket stages are substantially identical. The same staging system  34  can be reused because it has not been detached and discarded at the last phase of the previous launch. 
         [0030]      FIG. 5  shows a method for re-using a staging system as illustrated in a flowchart, in accordance with an embodiment. A data bus  48  is initially interfaced with the staging system  34  by a data connection  46  on the processor-based control system  40 , as depicted in block  64 . At the start of a launch, the first stage ignites  66  and begins burning fuel, propelling the launch vehicle upwards. For purposes of illustration, a stage that is currently bottom-most is referred to as an active stage. 
         [0031]    During the launch, the staging system  34  monitors the active stage for the presence of a release condition, as depicted in block  68 . A release condition may be a combination of conditions, such as the active stage having expended all of its fuel, and the launch vehicle having reached a certain altitude. As depicted in block  70 , if a release condition is not present, the staging system  34  continues to monitor the active stage. If a release condition has been met, the staging system  34  initiates a detachment procedure for the active stage, as depicted in block  72 . As discussed previously, the detachment procedure may include sending a detach signal along a data bus  48  to the current stage, thereby triggering a release mechanism, such as detonation of small explosive charges or a mechanical mechanism, thereby detaching the current stage from the launch vehicle. The release mechanism may also trigger the detachment of the interstage between the active stage and the next stage. 
         [0032]    After the active stage is detached, the staging system  34  determines if the detached stage is the last stage, as depicted at block  74 . If the detached stage is not the last stage, the staging system  34  sends a signal on data bus  48  to activate the next stage, and the process repeats until the final stage is activated. If the detached stage is the last stage, the connection between the staging system  34  and the stages via data bus  48  may be disconnected. In one embodiment, the data bus  48  may be symbolically disconnected in the sense that it is no longer interfacing with any stages, although it may remain physically connected to the staging system  34 . In other embodiments, the data bus  48  may be physically disconnected during the release process of the final rocket stage. 
         [0033]      FIG. 6  shows a schematic of a staging system in accordance with an embodiment. The staging system comprises a processor-based control system  40 , such as a computer having one or more microprocessors. The processor-based control system  40  may interface with a memory device  44 , such as non-volatile memory (ROM) for storing software programs and variable sets for stage monitoring. The processor-based control system  40  is powered by a power source  42 , which may be standalone or shared from the main power source. The propulsion control module  80  will also be powered by a power source  42 , possibly the same power source  42  that powers the processor based control system  40 , as shown in  FIG. 6 . The propulsion control module  80  comprises an interface to the processor based control system  40  and interfaces to the launch vehicle stages  50 ,  52 ,  54 . 
         [0034]    While only certain features of the select 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 invention. 
       ELEMENT LIST 
       [0000]    
       
           10  multiple stage expendable launch vehicle (launch vehicle) 
           12  first stage 
           14  interstage 
           16  second stage 
           18  interstage 
           20  third stage 
           22  instrument unit 
           24  payload 
           26  main control system 
           28  system block 
           30  flight system 
           32  navigation system 
           34  staging system 
           36  life support 
           38  user interface 
           40  processor-based control system 
           42  power source 
           44  memory device 
           46  data connection point (staging system) 
           48  data bus 
           48 ′ next data bus 
           50  first stage 
           50 ′ next first stage 
           52  second stage 
           52 ′ next second stage 
           54  final stage 
           54 ′ next final stage 
           56  data connection point (user interface) 
           58  guidance system 
           60  telemetry system 
           62  data bus interface point 
           64  establish interface between staging system and first set of rocket stages 
           66  activate first/next stage 
           68  monitor current stage 
           70  determine if release condition met 
           72  release current stage 
           74  determine if released stage is last stage 
           76  interface with next set of rocket stages 
         A direction of interface connection