(12) United States Patent
`Spencer et al.
`(10) Patent N0.2
`US 6,450,452 B1
`(45) Date of Patent:
`Sep. 17, 2002
`(75) Inventors: Robert B. Spencer, Denver, CO (US);
`Thomas D. Megna, Littleton, CO (US);
`James R. Greenwood, Littleton, CO
`4,884,770 A 12/1989 Martin ..................... .. 244/158
`5,626,310 A
`5/1997 Kelly .......................... .. 244/2
`5,716,032 A * 2/1998 Mclngvale . . . . . .
`. . . .. 244/190
`5,779,190 A * 7/1998 Rambo et al. ......... .. 244/190
`5,927,653 A
`7/1999 Mueller et al. . . . . .
`. . . .. 244/172
`(US); Daniel J. Laintz, Denver, CO
`6,036,144 A
`3/2000 Sisk . . . . . . . . . . . . . . .
`. . . .. 244/172
`(73) Assignee: Lockheed Martin Corporation,
`Bethesda, MD (US)
`( * ) Notice:
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`USC‘ 154(k)) by 0 days‘
`(21) Appl. No.: 09/578,321
`(22) Filed:
`May 24, 2000
`Related US. Application Data
`(60) Provisional application NO‘ 60/135,556’ ?led on May 24’
`(51) Int. Cl.7 ................................................ .. B64G 1/00
`(52) US' Cl' """"""""" " 244/158 R’ 244/190’
`(58) Fleld of Search """""""""""""" "
`References Cited
`6,086,020 A
`7/2000 Machiussi . . . . . . .
`. . . .. 244/158
`6,113,032 A * 9/2000 Cochran et al. .......... .. 244/172
`6,193,187 B1
`2/2001 Scott et al. .................. .. 244/2
`cued by examlner
`Primary Examiner—J. Woodrow Eldred
`(74) Attorney, Agent, or Firm—Marsh Fischmann &
`Breyfogle LLP
`Areusable ?rst stage (100) includes a booster engine system
`(102) for providing thrust during launch, a structural assem
`bly (108), canards (118), jet engines (122), Wings (124),
`elevons (126) and retractable landing gear (130). After
`separation, the jet engines (122) and aerodynamic control
`surfaces are used to return the ?rst stage to a landing strip.
`The booster system (102) includes a structurally stable outer
`skin system such as an isogrid structure. The ?rst stage (100)
`is thereby adapted for controlled descent and recovery With
`minimal structural enhancement or added mass.
`4,830,314 A
`5/1989 Hujsak ..................... .. 244/172
`19 Claims, 6 Drawing Sheets
`Space Exploration Technologies; NEW PETITION
`Exhibit 1109
`Page 1 of 12


`U.S. Patent
`Sep. 17, 2002
`Sheet 1 0f 6
`US 6,450,452 B1
`Space Exploration Technologies; NEW PETITION
`Exhibit 1109
`Page 2 of 12


`U.S. Patent
`Sep. 17, 2002
`Sheet 2 0f 6
`US 6,450,452 B1
`114 1 1
`122 g
`106101"/1'§of!$ Q1127
`Space Exploration Technologies; NEW PETITION
`Exhibit 1109
`Page 3 of 12


`Space Exploration Technologies; NEW PETITION
`Exhibit 1109
`Page 4 of 12


`Space Exploration Technologies; NEW PETITION
`Exhibit 1109
`Page 5 of 12


`U.S. Patent
`Sep. 17, 2002
`Sheet 5 0f 6
`US 6,450,452 B1
`I. I
`- /
`..:-/ ' y
`f z _ _.
`Space Exploration Technologies; NEW PETITION
`Exhibit 1109
`Page 6 of 12


`U.S. Patent
`Sep. 17, 2002
`Sheet 6 0f 6
`US 6,450,452 B1
`’L- 702
`A'L- 700
`/L- 706
`4- 707
`"L- 709
`/L_ 710
`"L- 714
`+ .
`Space Exploration Technologies; NEW PETITION
`Exhibit 1109
`Page 7 of 12


`US 6,450,452 B1
`This application claims priority from United States pro
`visional patent application No. 60/135,556 entitled “Fly
`Back Booster,” ?led May 24, 1999, Which is incorporated
`herein by reference.
`The present invention relates in general to reusable launch
`vehicle systems and, in particular, to a booster or launch
`vehicle stage that can be recovered after use by controlled
`aerodynamic descent to a landing area.
`The space industry is undergoing explosive groWth in
`terms of the types and numbers of missions and systems
`being deployed. Through telecommunication satellites and
`the deployment of the international space station to future
`space tours and visits the use of launch facilities is being
`greatly eXpanded. For eXample, a number of satellite con
`stellations for communication systems have been proposed
`or implemented. These constellations range from tens to
`hundreds of satellites. According to some estimates, the
`number of projected satellite launches in the neXt ten years
`alone Will double the total number of satellites launched in
`the ?rst forty years of space access. As a result of this
`activity, the capacity of eXisting launch facilities and launch
`vehicle construction facilities Will be tested. It is apparent
`that ef?cient and loWer cost operation of launch vehicles and
`launch facilities Will be demanded.
`Existing launch vehicles typically include one or more
`stages Which function to boost a payload aboard the launch
`vehicle into space. Such stages are generally disposable.
`More speci?cally, When stages of launch vehicles, such as a
`?rst stage, are no longer needed, the stages are separated
`from the upper stage, if any, and the payload interconnected
`thereto and are alloWed to fall back toWards the ground or a
`body of Water. If any portion of such a stage is reusable at
`all, substantial reconstruction is generally required. The
`disposable nature of launch vehicle stages can be an eXpen
`Reusable spacecraft and stage systems have been pro
`posed or implemented for some time. For eXample, the
`shuttles of the United States space shuttle ?eet are reusable
`after re-entry and controlled landing upon inspection and
`some refurbishment. HoWever, in order to achieve the
`velocities necessary for orbital insertion, the shuttles must
`utiliZe strap-on booster engines that are jettisoned during the
`launch process at considerable eXpense. Some eXisting or
`proposed systems are intended to permit recovery of launch
`vehicle stages such as by employing parachutes to soften
`splash doWn or landing. HoWever, such systems entail a risk
`of signi?cant damage, require substantial reconstruction of
`the stage after recovery and/or have achieved little or no
`commercial acceptance. Other proposed systems have con
`templated the use of Wings or other aerodynamic elements
`for retrieving boosters or stages. HoWever, such systems
`may require substantial structural enhancement in connec
`tion With certain stage/tank structures and, in any event, it is
`apparent that such proposed systems have generally not
`achieved commercial acceptance.
`The present invention is directed to a launch vehicle stage
`adapted for controlled aerodynamic descent back to a recov
`ery area such as a speci?ed landing area and an associated
`method of use. The invention makes use of stable stage
`structure, such as composite or aluminum isogrid
`construction, to support ?ight elements With minimal added
`mass. Through controlled descent, the stage can be recov
`ered With minimal damage, potentially alloWing for reuse
`With only routine refurbishment rather than full reconstruc
`tion. Moreover, the stage can be returned close to the launch
`site to shorten turn-around times betWeen ?ights. In this
`manner, overall launch costs may be reduced and the capac
`ity of launch facilities may be enhanced. Moreover, eXisting
`launch vehicle construction and handling resources can be
`freed for neW launch vehicle construction.
`According to one aspect of the present invention, a launch
`vehicle stage is provided With control surfaces for controlled
`aerodynamic descent. The launch vehicle stage is used to
`propel a payload system, such as a shuttle satellite and/or
`other space vehicle, toWards an upper atmosphere or space
`trajectory or orbit. The launch vehicle stage includes: a
`booster system such as a solid or liquid phase rocket booster;
`a number of control surfaces structurally interconnected to
`the booster system; and a separation system for selectively
`separating the launch vehicle stage from the payload system.
`The booster is preferably structurally stable. That is, the
`booster is preferably constructed such that its outer skin
`assembly can support longitudinal and transverse loads even
`in the absence of substantial internal pressuriZation The
`control surfaces preferably include surfaces for controlling
`roll, pitch and yaW and for providing lift. In one
`embodiment, the control surfaces include Wings, a tail,
`elevons, and canards. One or more of the control surfaces
`may be deployable betWeen a retracted position for launch
`mode operation and an eXtended position for controlled
`descent mode operation. The separation system may include
`conventional, pneumatic, hydraulic or pyrotechnic elements
`for separation of the stage from the payload system on
`command or at a predetermined time, elevation, velocity or
`the like.
`According to another aspect of the present invention, a
`launch vehicle stage is adapted for controlled ?ight based on
`command signals. The stage includes: a booster system;
`control surfaces, structurally interconnected to the booster
`system, that are moveable to control a course of descent of
`the stage; and a control system, operatively associated With
`the control surfaces, for receiving control signals concerning
`a desired maneuver of the stage and controlling the control
`surfaces based on the control signals to implement the
`desired maneuver. The stage may operate autonomously or
`by remote control. In this regard, the control system may
`receive the control signals from an onboard processor or the
`like, or may received the signals via stage-to-ground (and
`vice versa) telemetry. In either case, the control signals may
`be based at least in part on inputs from on-board or other
`instruments regarding current positional coordinates,
`attitude, altitude, velocity or other parameters.
`According to another aspect of the present invention, a
`launch vehicle stage includes controlled ?ight systems and
`landing gear for controlled descent to a landing strip at a
`selected location, preferably close to launch facilities. The
`stage includes a booster system, a controllable aerodynamic
`?ight system, and landing gear such as retractable Wheels for
`substantially horiZontal runWay landings. The controlled
`aerodynamic ?ight system preferably includes at least tWo
`Wings for providing lift suf?cient for coasting or more
`preferably, sustained ?ight from a point of separation to the
`landing area and control surfaces for guidance to the landing
`area. The landing gear preferably includes Wheel assemblies
`Space Exploration Technologies; NEW PETITION
`Exhibit 1109
`Page 8 of 12


`US 6,450,452 B1
`de?ning at least three points for landing and rolling to a stop.
`In one embodiment, a forward Wheel assembly is retracted
`into a nose structure and tWo rear Wheel assemblies are
`retracted into a fuselage structure during launch mode
`operation. The Wheel assemblies are then deployed and
`locked into a fully extended position for landing. Such
`runWay landing avoids damage and additional refurbishment
`or reconstruction that might otherWise be required in con
`nection With skid landings or splash doWns.
`According to a still further aspect of the present invention,
`a propulsion system is provided for poWered ?ight descent
`and recovery of a launch vehicle stage. The stage includes a
`booster system, a controllable ?ight aerodynamic system,
`and a propulsion system. The propulsion system may
`include one or more rocket engines or air breathing engines
`such as jet engines. Preferably, one or more jet engines are
`employed, thereby avoiding control complications associ
`ated With sloshing of substantial masses of liquid propel
`lants. Conventional jet engines, such as ?ghter jet engines,
`may be employed. It Will be appreciated that the associated
`poWer assist is useful in extending the glide path, or more
`preferably alloWing for sustained ?ight, to a desired landing
`location. Such poWered descent has particular advantages
`for retrieving stages after separation at high separation
`points (e.g., Where the ?rst stage of a multiple stage launch
`provides a signi?cant portion of the total launch velocity)
`and Where it is necessary for the stage to return at a
`substantial distance back to the launch location.
`A method for using a launch vehicle stage in accordance
`With the present invention includes the steps of: providing a
`stage including a booster system and a controlled aerody
`namic descent system, Where the booster system is struc
`turally stable so as to support aerodynamic and other loads;
`operating the booster system to provide a thrust to an
`associated payload system during launch mode operation;
`separating the stage system from the payload system after
`launch mode operation; and, after separation, operating the
`controlled aerodynamic descent system to control a course
`of descent of the stage to a landing area. The step of
`operating the controlled aerodynamic descent system may
`include monitoring the descent of the stage, receiving con
`trol signals, and deploying control surfaces of the controlled
`aerodynamic descent system to implement desired maneu
`vers. The method may further include the steps of operating
`a propulsion system to propel the stage along a trajectory
`toWards the landing area.
`For a more complete understanding of the present inven
`tion and further advantages thereof, reference is noW made
`to the folloWing detailed description taken in conjunction
`With the draWings, in Which:
`FIG. 1 is a perspective vieW of a reusable ?rst stage in
`accordance With the present invention;
`FIG. 2 is an exploded, top plan vieW of the reusable ?rst
`stage of the FIG. 1;
`FIG. 3 is an exploded, side vieW of the reusable ?rst stage
`of FIG. 1;
`FIG. 4 illustrates a number of different con?gurations of
`one or more reusable stages interconnected to a launch
`vehicle and payload system in accordance With the present
`FIG. 5 is a chart illustrating the performance of various
`launch vehicles utiliZing one or more stages in accordance
`With the present invention;
`FIG. 6 illustrates a launch and ?ight path of a launch
`vehicle and stage in accordance With the present invention;
`FIG. 7 is a ?oWchart illustrating a process of reusing
`reusable stage in accordance With the present invention.
`In the folloWing description, the invention is set forth in
`the context of a reusable ?rst stage including propulsion and
`controlled descent systems. Although the folloWing descrip
`tion therefore sets forth a particularly advantageous imple
`mentation of the present invention, it Will be appreciated that
`various aspects of the reusable stage may vary from appli
`cation to application in accordance With the present inven
`tion. For example, in the folloWing description, an embodi
`ment of the reusable stage is described Which utiliZes jet
`engines during controlled descent. This is particularly
`advantageous for ?rst stage implementations or other imple
`mentations Where an extended glide path or sustained ?ight
`may be desired. HoWever, it Will be appreciated that certain
`implementations, such as upper stage or other high separa
`tion point implementations, may alloW for controlled aero
`dynamic descent of the reusable stage runWay landings
`Without propulsion. Similarly, although a number of possible
`con?gurations are set forth beloW for various types of
`conventional launch vehicles, it Will be appreciated that
`other con?gurations may be utiliZed depending, for
`example, on the siZe and con?guration of the launch vehicle,
`the mass of the payload, the desired orbit (high atmosphere,
`loW earth orbit, geosynchronous orbit, or interplanetary
`trajectory), the number of boosters employed, and other
`Referring to FIGS. 1—3, a reusable ?rst stage is generally
`identi?ed by the reference numeral 100. The stage 100
`includes a booster engine system 102 for providing a thrust
`to the associated launch vehicle for propelling the launch
`vehicle toWards a desired orbit. The illustrated thruster
`system 102 includes a number of propellant tanks 104 and
`an engine including noZZle 106 for expelling the propellants
`to generate thrust. For example, one of the tanks may include
`liquid oxygen and another tank may include any of various
`liquid rocket fuels. When the liquid rocket fuel contacts the
`liquid oxygen in the rocket engine combustion chamber,
`combustion occurs such that the propellants are discharged
`at high velocity through noZZle 106 to generate thrust. As
`Will be understood from the description beloW, the illustrated
`booster system 102 may be any of various existing booster
`systems or other booster systems as may be developed. The
`illustrated system 102 may be, for example, an RD-180
`engine marketed by Pratt & Whitney.
`The illustrated booster system 102 has a structurally
`stable construction. That is, the outer layer or skin structure
`can support longitudinal and transverse loads even When the
`internal tank pressure is relieved. Such longitudinal loads
`may be experienced due to forWard acceleration during
`launch and other longitudinal components of acceleration
`associated With vibrations and maneuvering. Transverse
`loads may be experienced in connection With controlled
`descent and associated lift and maneuvering forces. In this
`regard, each of the propellant tanks and other skin structures
`may include stringers or other reinforcing structure for
`strengthening the outer skin later. The illustrated skin struc
`ture is preferably an isogrid or othogrid structure formed
`from aluminum or other metal or a lightWeight composite
`material. Such grid structures include ribs that extend both
`along the longitudinal axis of the booster system and cir
`cumferentially. Such ribs may be disposed at an angle to the
`longitudinal axis or a cross-sectional circumference rather
`than being aligned thereWith.
`The illustrated stage 100 also includes a structural assem
`bly 108 for use in structurally interconnecting the booster
`Space Exploration Technologies; NEW PETITION
`Exhibit 1109
`Page 9 of 12


`US 6,450,452 B1
`system to the launch vehicle (until separation) and to the
`?ight systems as Will be described below. The structural
`assembly 108 includes a nose portion 110, a fairing portion
`112 and a fuselage shell 114. The nose portion 110 is shaped
`to provide for improved aerodynamic performance, e.g.,
`reduce drag, during both launch mode and controlled
`descent mode operation. In addition, the nose portion 110
`houses retractable landing gear prior to landing as Will be
`described beloW. The nose portion may also provide heat
`shielding and house various instruments.
`The fairing portion 112 and fuselage shell 114 house the
`booster system 102 and provide additional support for
`aerodynamic structure used in controlled descent. It Will be
`appreciated that the structural assembly 108 should be
`lightWeight While providing sufficient structural support to
`sustain substantial acceleration associated With launch, sepa
`ration and controlled descent and landing. In this regard, the
`structural assembly 108 may be constructed from aluminum
`or lightWeight alloys or composite materials, and is prefer
`ably constructed using knoWn aerospace techniques for
`minimiZing mass. In this regard, the structural assembly 108
`may be fabricated from a grid material as discussed above or
`otherWise include strengthening ribs or stringers. The fuse
`lage shell 114 also houses additional landing gear prior to
`deployment for landing.
`The reusable ?rst stage 100 preferably includes aerody
`namic structure for controlled descent to a desired landing
`area. In this regard, the aerodynamic structure preferably
`includes elements for providing lift sufficient to support the
`stage on a desired ?ight or glide path and control surfaces for
`controlling the roll, pitch and yaW of the stage so as to guide
`the stage to the desired landing area. In the illustrated
`embodiment, the reusable ?rst stage includes a vertical tail
`116. The illustrated tail 116 is suf?cient in siZe to provide the
`desired yaW control and prevent or alloW recovery from any
`?at spin of the stage. In this regard, the illustrated tail 116
`includes a rudder surface 117 that is rotatable about a
`vertical axis for yaW control.
`The illustrated reusable ?rst stage 100 also includes
`canards 118 and nacelles 120 extending from the fairing
`section 112. The nacelles 120 house jet engines 122 used for
`poWered ?ight during descent. It Will be appreciated that
`such poWered ?ight can extend the ?ight path as is particu
`larly useful in returning the ?rst stage to a landing area
`proximate to the launch facility so as to reduce turn-around
`times betWeen ?ights. It Will be appreciated that various
`types of propulsion systems including rocket propulsion
`systems may be utiliZed in accordance With the present
`invention. HoWever, rocket propulsion systems may intro
`duce certain control complications due to substantial masses
`of sloshing propellants. Accordingly, in the illustrated
`embodiment, jet engines 122 are utiliZed. Speci?cally, a pair
`of jet engines are located on opposite sides of the fairing
`portion 112. The pair of engines provides the desired pro
`pulsion poWer and also provides a degree of redundancy in
`the event of engine failure. The illustrated engines, 122 are
`Pratt and Whitney 229 jet engines Which may be upgraded
`for optimal thrust and performance. Advantageously, a com
`mon liquid fuel, such as RP or JP and may be utiliZed to
`operate both the rocket engines of the thruster system 102
`and the jet engines 122.
`The canards 118 provide lift and also serve to move the
`center of lift forWard relative to the overall structure of the
`reusable ?rst stage 100. The canards 118 may be deployable,
`e.g., rotatable about a horiZontal axis, for supplemental pitch
`control. In addition, the illustrated canards 118 are pivotable
`relative to an axis Where the canards 118 are attached to the
`nacelles 120 such that the canards 118 can be pivoted
`upWard or doWnWard relative to the structural assembly 108.
`Such pivoting provides for enhance subsonic and supersonic
`The illustrated stage 100 also includes a pair of Wings 124
`Which are the primary lifting surfaces of the stage 100. It Will
`be appreciated that the siZe and con?guration of the Wings
`may be selected based on a variety of lift related factors such
`as anticipated maximum speed and elevation, required land
`ing speed, the anticipated mass of the stage 100, and other
`factors. The illustrated Wings 124 have a sWept pro?le for
`reduced drag and enhanced high speed performance. The
`Wings 124 also include elevons 126 at the trailing edges
`thereof for pitch and roll control. In this regard, the elevons
`126 are separately or collectively pivotable about a substan
`tially horiZontal axis. In this regard, the elevons can be
`operated in unison for pitch control like conventional
`elevators/stabiliZers and can be operated separately for roll
`control like conventional Wing ?aps.
`In order to alloW for runWay landings, the stage 100
`includes landing gear 130. As illustrated, the landing gear
`130 is retractable, e.g., using conventional hydraulics or
`other actuators, betWeen a stoWed position and a deployed
`position. In this regard, the landing gear 130 may be stoWed
`Within the nose section 110 and the fuselage shell 114 during
`launch mode and during an initial portion of the descent
`mode for reduced drag. The landing gear 130 can then be
`deployed to a fully extended position for landing. Also
`shoWn in FIG. 3 are separation assemblies 127 that alloW for
`structural interconnection of the stage 100 to a launch
`vehicle during launch and then alloW for selective separation
`When the ?rst stage is fully used. Any conventional separa
`tion assemblies may be used in this regard such as, for
`example, pyrotechnic separation units employing explosive
`bolts. The stage 100 also includes attitude control systems
`101 for controlling the attitude of the stage 100 at high
`altitudes Where aerodynamic control surfaces have limited,
`if any, effectiveness. The attitude control systems 101 may
`include small rockets aligned on various axes that can be
`pulsed to achieve a desired attitude for deceleration and
`thermal control.
`FIG. 4 illustrates various con?gurations for using the
`reusable ?rst stage in connection With conventional launch
`vehicles. As shoWn, the reusable ?rst stage may be used as
`a single ?rst stage booster or in pairs or in larger groupings
`as may be desired for particular applications. Also, as can be
`observed from FIG. 4, one or more reusable ?rst stage
`boosters may be used in combination With conventional
`disposable boosters Where the launch vehicle con?guration
`or other considerations so Warrant. Finally, it Will also be
`observed that the reusable ?rst stage can be used in a variety
`of applications involving different payload vehicles and can
`be used With or Without additional stages to reach orbit.
`FIG. 5 illustrates the expected performance of the various
`launch vehicle con?gurations using the reusable ?rst stage in
`accordance With the present invention. It Will be observed
`that the con?gurations shoWn in FIG. 5 generally correspond
`to the con?gurations identi?ed in FIG. 4. The performance
`is shoWn in this case in relation to a conventional Delta III
`rocket for delivering a payload to loW earth orbit. It Will thus
`be observed that the reusable ?rst stage of the present
`invention can be used in a variety of applications by recon
`?guring the launch vehicles. Also, it Will be observed that
`the reusable ?rst stage of the present invention can be readily
`implemented in a variety of conventional launch vehicle
`applications thereby substantially reducing development
`costs and enabling the bene?ts of the present invention to be
`immediately realiZed.
`Space Exploration Technologies; NEW PETITION
`Exhibit 1109
`Page 10 of 12


`US 6,450,452 B1
`FIG. 6 illustrates an overall ?ight path of a launch vehicle
`utilizing multiple reusable ?rst stage boosters in accordance
`With the present invention. In the illustrated example, the
`reusable ?rst stage boosters are used in launching a space
`shuttle Which also utiliZes a disposable propellant tank. As
`shoWn, the launch vehicle is launched from a launch facility
`600. The launch vehicle then ascends toWards orbit under
`thrust from the tWo reusable ?rst stage boosters as Well as
`the common core booster. A separation of the reusable ?rst
`stage boosters from the launch vehicles happens approxi
`mately at the separation point 602. That is, at separation
`point 602, the separation system is activated to detach each
`of the reusable ?rst stage boosters from the launch vehicle.
`The separation point 602 may be selected at a particular
`elevation, at a particular velocity, or to occur at a certain
`time after liftoff. Generally, the separation point 602 Will
`generally coincide With near depletion of the propellant
`tanks of the reusable ?rst stage boosters.
`Due to momentum and any continuing rocket burn, the
`reusable ?rst stage boosters Will ascend for some time after
`separation. This ascending portion of the ?ight path is
`generally indicated at 604. During this ascending portion
`604 of the ?ight path, the attitude control system of the
`reusable ?rst stage may be activated to control the attitude
`of the reusable ?rst stage and to guide the reusable ?rst stage
`along a path selected to facilitate return of the reusable ?rst
`stage to a landing strip 606 proximate to the launch facility
`600. It Will be understood that returning the reusable ?rst
`stage to a landing strip 606 close to the launch facility may
`be reduce turn-around times betWeen missions. During the
`ascending portion 604 of the ?ight path, the attitude of the
`reusable ?rst stage may be selected to help sloW the reusable
`?rst stage to subsonic speeds as may be desired for over
`?ying populated areas. Also, the various control surfaces
`may be utiliZed (if effective) to manage elevation and stage
`positioning so as to minimiZe the amount of fuel that is
`required to guide the stage back to the landing strip 606.
`In the illustrated ?ight path, the reusable ?rst stages turn
`back toWards the launch facility 600 close to the top of the
`ascending portion 604 of the ?ight path. At this time, it may
`be desirable to minimiZe the load carried by the reusable ?rst
`stage in order to reduce the required landing speed and
`otherWise facilitate landing. For example, any excess pro
`pellants or other expendable elements may be discharged at
`this time for splashdoWn or landing in a secured area.
`Depending on the particular application, a jet engine ignition
`may occur at some time during the ensuing descending
`portion 608 of the ?ight path. The timing of jet engine
`ignition (if necessary) Will depend on a variety of factors
`including the elevation of the separation point 602, the
`length of the ?ight path back to the landing strip 606, the rate
`of descent, atmospheric conditions, etc. In this regard, it Will
`be appreciated that various ?ight parameters may be moni
`tored to control the ?ight path, the operation of the jet
`engines and the operation of the control surfaces. On-board
`instruments may measure effective travel speed, elevation,
`the location coordinates of the stage, the attitude of the stage,
`and the positions of the deployable control surfaces. Read
`ings from these instruments may be reported to an on-board
`processor for autonomous control of the landing approach.
`Alternatively, readings from these instruments may be
`reported to a ground based control station Which in turn
`controls operation of the jet engine and control surfaces via
`control commands transmitted to the stage.
`Upon approaching the landing strip 606, for example, and
`upon reaching a de?ned elevation, the landing gear may be
`deployed from its stoWed position to a fully extended
`position for landing. Finally, upon touchdoWn, the reusable
`stage may be alloWed to roll to a stop or may be actively
`sloWed by reversing the jet engines, deploying parachutes,
`or employing other braking systems.
`FIG. 7 is a ?oW chart providing a summary of a process
`for using the reusable ?rst stage. The process 700 is initiated
`by igniting (702) the reusable stages and any other booster
`systems to launch the launch vehicle and payload. After
`launch, the launch trajectory is monitored (704) to identify
`the ?rst stage separation point. For example, the separation
`point may be identi?ed based on elapsed time, elevation,
`velocity or other parameters. Upon identi?cation of the
`separation point, booster main engine cut-off (705) is actu
`ated and the reusable stage is separated (706) from the
`launch vehicle, for example, by activating a pyrotechnic
`separation system. After separation, the reaction control
`system phase of ?ight is initiated (707), and the reaction
`control system is utiliZed to execute (708) an aerodynamic
`tWin. Initiation of the reaction control system transfers
`control of the stage from the gimbal structure of the main
`thruster engine, Which executes maneuvers by thrust
`vectoring, to the reaction control orbital maneuvering sys
`tem that controls attitude by pulsing attitude control rockets.
`As noted above, this system provides attitude control Where
`the atm

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