Hybrid Rocket Propulsion for Future Space Launch by ghkgkyyt

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									                    Aero/Astro 50th Year Anniversary

                  Hybrid Rocket Propulsion for
                     Future Space Launch

                                Arif Karabeyoglu
                  President and Chief Technology Officer, SPG Inc.
Consulting Professor, Department of Aeronautics and Astronautics, Stanford University

                                   May 09, 2008
Aero/Astro 50th Year Anniversary
Hybrid Rocket Configuration
        Fuel and oxidizer are physically separated
             One of the two is in solid phase

       Most Hybrids:                  Reverse Hybrids:
        Oxidizer: Liquid                Oxidizer: Solid
          Fuel: Solid                    Fuel: Liquid

Aero/Astro 50th Year Anniversary
Hybrid Rocket System
             Solid Fuel                        Liquid Oxidizer
 •   Polymers: Thermoplastics,        •   Cryogenic: LO2
     (Polyethylene, Plexiglas),
     Rubbers (HTPB)                   •   Storable: H2O2, N2O, N2O4,
 •   Wood, Trash, Wax

Aero/Astro 50th Year Anniversary
Advantages of Hybrids
 Compared to                     Solids                    Liquids
 Simplicity            - Chemically simpler       - Mechanically simpler
                       - Tolerant to processing   - Tolerant to fabrication
                       errors                     errors
 Safety                - Reduced chemical         - Reduced fire hazard
                       explosion hazard           - Less prone to hard starts
                       - Thrust termination and
                       abort possibility
 Performance Related   - Better Isp performance   - Higher fuel density
                       - Throttling/restart       - Easy inclusion of solid
                       capability                 performance additives (Al,
 Other                 - Reduced environmental    - Reduced number and
                       impact                     mass of liquids
 Cost                  - Reduced development costs are expected
                       - Reduced recurring costs are expected

Aero/Astro 50th Year Anniversary
Hybrid Rocket History
                Early History (1932-1960)
•   1932-1933: GIRD-9 (Soviet)
    – LO2/Gellified gasoline 60 lbf thrust motor
    – Firsts
        • Hybrid rocket
        • Soviet rocket using a liquid propellant
        • First fast burning liquefying fuel
    – Tikhonravov and Korolev are designers
    – Maximum altitude: 1,500 m
•   1937: Coal/Gaseous N2O hybrid motor 2,500 lbf thrust
•   1938-1939: LOX/Graphite by H. Oberth (Germany)
•   1938-1941: Coal/GOX by California Rocket Society
•   1947: Douglas Fir/LOX by Pacific Rocket Society (US)
•   1951-1956: GE initiated the investigations in
    hybrids. H2O2/Polyethylene. (US)

Aero/Astro 50th Year Anniversary
    Hybrid Rocket History
        Era of Enlightenment (1960-1980)
•    1960's: Extensive research at various
      – Chemical Systems Division of UTC
          • Modeling (Altman, Marxman, Ordahl,
             Wooldridge, Muzzy etc…)
          • Motor testing (up to 40,000 lb thrust
      – LPC: Lockheed Propulsion Company,
        SRI: Stanford Research Institute,
        ONERA (France)
•    1964-1984: Flight System Development              CSD’s Li/LiH/PBAN-F2/O2
      – Target drone programs by Chemical                       Hybrid
        Systems Division of UTC                         Measured Isp=480 sec
          • Sandpiper, HAST, Firebolt
      – LEX Sounding Rocket (ONERA, France)
      – FLGMOTOR Sounding Rocket

                                                    Firebolt Target Drone
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    Hybrid History Recent History (1981-Present)
•     1981-1985: Starstruck company developed and sea launched the Dolphin
      sounding rocket (35 klb thrust)
•     1985-1995: AMROC continuation of Starstruck
       – Tested 10, 33, 75 klb thrust subscale motors.
       – Developed and tested the H-1800, a 250 klb LO2/HTPB motor.
•     1990’s: Hybrid Propulsion Development Program (HPDP)
       – Successfully launched a small sounding rocket.
       – Developed and tested 250 klb thrust LO2/HTPB motors.
•     2002: Lockheed developed and flight tested a 24 inch LO2/HTPB hybrid
      sounding rocket (HYSR). (60 klb thrust)
•     2003: Scaled Composites and SpaceDev have developed a N2O/HTPB         Dolphin
      hybrid for the sub-orbital vehicle SpaceShipOne. (20 klb thrust)

    AMROC Motor Test

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Small Launch Vehicle Data
   Launcher       Payload*, kg    Cost#, M$    Cost/Payload, $/kg   Reliability
                                   US Launchers
   Pegasus XL         190            20.0            105,263          34/39
   Minotaur           317            19.0            59,936            7/7
   Taurus             660            36.0            54,546            6/7
                                   EU Launchers
   Vega              1,395           20.0            14,337            0/0
                                 Russian Launchers
   Dnepr              300            10.0            33,333            9/10
   Kosmos             775            12.0            15,484          422/448
   Start              167            9.0             53,892            6/6
   Strela             700            20.0            28,571            1/1
   Long March 2      1,600           23.0            14,375           22/22
   PSLV               900            15.0            16,667            4/7
                                                                              #FY02   Values
                             *Sunsynchronous Orbit: 800 km, 98.7o

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PegasusXL Launch Vehicle
                                     •       ORBITAL Sciences
                                     •       Air Launched (L1011): Dropped at 39 kft
                                     •       Propulsion System:
                                              – Stage 1: 50SXL (Solid – Alliant
                                              – Stage 2: 50XL (Solid – Alliant
                                              – Stage 3: 38 (Solid – Alliant Techsystems)
                                              – Stage 4: HAPS (Hydrazine monoprop. –

  Reasons for high recurring cost:
  – Expensive propulsion system
  – Air platform/low launch

Aero/Astro 50th Year Anniversary
PegasusXL Launch Vehicle                         Dilemma of Launch Business
                                                   – High launch costs limit the
                                                   – Low launch frequency
                                                     increase the cost
                                             •    This cycle is hard to break with
                                                  current propulsion
                                                  technologies (improvements
                                                  have been gradual since
                                             •    Disruptive technologies are
                                                  needed:        Hybrids

•   Number of launches decreased in time
•   Presently average is one launch a year

Aero/Astro 50th Year Anniversary
Hybrid Propulsion – Non-Technical Challenges
                           Non-Technical Challenges
 •   Lack of technological maturity
 •   Hard to compete against established solid and liquid technologies
 •   Established propulsion industry is fine with the status quo
 •   Smaller group of rocket professionals relative to solid and liquid rockets

 •   Keep educating young engineers on the virtues of hybrid propulsion
      – Growing number of young professionals interested in hybrid propulsion
 •   Understand that hybrids will NOT eliminate the solid and liquid technologies
      – Hybrids are complementary to other chemical rockets
      – Initially concentrate on the niche and easy applications that clearly benefit from the
        hybrid approach
 •   Suborbital Applications: Sub-orbital space tourism (SpaceShipTwo)
      – Performance is secondary to safety and cost
 •   Small launch vehicle propulsion

Aero/Astro 50th Year Anniversary
Hybrid Propulsion –Technical Challenges
                   Technical Challenges
 • Low regression rates for classical hybrid fuels
    – Results in complicated fuel grain design
 • Low frequency instabilities
    – Instabilities are common to all chemical rockets
    – They need to be eliminated
    – Expensive and long process
 • Lack of benign, high performance, cost effective
   oxidizers (common to all chemical rockets)
  • Solutions to these technical issues should be such that
    they do NOT compromise the simplicity, safety and cost
    advantages of hybrids.

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 Regression Rate Versus Fuel Port Designs
                                                  Fuel Grain
         Fuel Grain

  w                   rc                                       rc

                                           Port                     Port
            Port           Cruciform                2w

  Case                                                                     4+1 Port


Single Circular                                                                       6+1 Port Wagon

                                Decreasing Regression Rate
                                  Increasing System Size

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    Disadvantage of Multiport Designs
CSD (1967)                                                                              Martin
 13 ports                                                                               (2006)
                                                                                       43 ports

                                AMROC (1994)
                                  15 ports

                                Issues with multi-port design
•    Excessive unburned mass fraction (i.e. typically in the 5% to 10% range)
•    Complex design/fabrication, requirement for a web support structure
•    Compromised grain structural integrity, especially towards the end of the burn
•    Uneven burning of individual ports.
•    Requirement for a substantial pre-combustion chamber or individual injectors for each port

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Approaches for High Regression Rate
             Technique           Fundamental          Shortcoming

        Add oxidizing         Increase heat         • Reduced safety
        agents self -         transfer by           • Pressure
        decomposing           introducing surface     dependency
        materials             reactions
        Add metal particles   Increased radiative   • Limited
        (micron -sized)       heat transfer           improvement
                                                    • Pressure
        Add metal particles   Increased radiative   • High cost
        (nano -sized)         heat transfer         • Tricky
        Use Swirl Injection   Increased local       • Increased
                              mass flux               complexity
                                                    • Scaling?

   All based on increasing heat transfer to fuel surface

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Entrainment Mass Transfer Mechanism

                                          •    A new transfer mechanism:
                                               – Certain fuels form a liquid
                                               – If the conditions are right,
                                                 mechanical entrainment of
                                                 liquid droplets occur
                                          •    Liquid Layer Hybrid
                                               Combustion Theory
                                               (Stanford - 1997)
                                          •    Most important scaling:
                                               – The entrainment mass
                                                 transfer increases with
                                                 decreasing viscosity of the
Regression Rate = Entrainment + Vaporization     liquid layer

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Regression Rate Law for Paraffin-Based Fuel, SP-1a

      r = 0.488 Gox.62
      &           0

                                               Three fold
                                               over HTPB
                                              is confirmed

Aero/Astro 50th Year Anniversary
Paraffin-Based Fuels Technology Progress
      Motor testing experience (SPG/Stanford/NASA Ames)
     – Small Scale(i.e. 50-100 lbf): >500 tests
     – Scale-up (i.e. 900-7000 lbf): >80 tests
     – Oxidizers: Liquid Oxygen, Gaseous Oxygen, Nitrous Oxide

                SPG work on paraffin-based fuel technology
      –   Formulation (Keep cost < 1 $/lb)
      –   Processing (24 inch OD fuel grains – 800 kg)
      –   Structural testing and modeling
      –   Internal ballistic design of single circular port hybrids
      –   Scale up motor testing (in 2009 25,000 lbf class motors)
                    Large single circular port hybrids are feasible

  Aero/Astro 50th Year Anniversary
  Low Frequency Instabilities

                                            •   Hybrids are prone to
                                                low frequency
                                                instabilities (2-100
P,                                              Hz)
                                            •   Limit cycle nature

             HPDP 250k lbf Motor 2 Test 2   8.4 inch LO2/Paraffin

                       Time, sec
      •   Many mechanisms
           – Feed system coupling
           – Intrinsic hybrid combustion
           – Chuffing at low fluxes
           – Oxidizer vaporization delay
             (common to LO2 systems)

    Aero/Astro 50th Year Anniversary
    Low Frequency Instabilities - Remedies

                                              •   Solutions used in the field
                                                   – Lockheed Martin –Michoud
                                                     and HPDP used hybrid
                                                     heaters to vaporize LO2
                                                   – AMROC injected TEA
                                                     (triethylaluminum) to
                                                     vaporize LO2
•    We believe that a LO2 motor can be
                                        •         Both solutions introduce
     made stable
                                                  complexity minimizing the
      – Without the use of heaters or TEA         simplicity advantage of hybrids
                                                   – Heaters- extra plumbing
      – By advanced injector and combustion
        chamber design                             – TEA – extra liquid,
•    Demonstrated in 7,000 lbf thrust                hazardous material
     class LO2/Paraffin motor

Aero/Astro 50th Year Anniversary
Oxidizers Overall Picture

                                                              Red: Toxic or sensitive
                                                              Blue: Low performance

      Relatively benign, low cost and readily available oxidizers: LOX, N2O

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Nitrous Oxide - Introduction               Physical
•       A saturated liquid at room temperature. Self pressurizing liquid (744 psi @ 20 C)
•       Two phase flow in the feed system (complicated injector design)
•       Highly effective green house gas (Global Warming Potential: 310 x CO2)
•       Oxidizer
•       Monopropellant. Positive heat of formation. Decomposes into N2 and O2 by
        releasing significant amount of heat
                         N 2O ! N 2 + O2 + 19.61 kcal / mole
•       Highly effective solvent for hydrocarbons
•       Mildly toxic. Anesthetic and analgesic agent still used in medicine, “Laughing gas”
                                   Nitrous Oxide Uses
    •    Oxidizer: Rocket propulsion, motor racing • Aerosol propellant: Culinary use
    •    Anesthetic Agent: Medicine, dentistry       (in whip cream dispensers)
    •    Solvent                                   • Etchant :Semiconductor industry

Aero/Astro 50th Year Anniversary
Nitrous Oxide – SpaceShipTwo
        Sub-orbital Space Tourism
•   Virgin Galactic has contracted Scaled
    Composites to build SpaceShipTwo
•   SpaceShipTwo design uses a N2O
    based hybrid rocket
•   Testing of the propulsion system
    started in summer 2007

                                     Explosion at Scaled Composites facility in
                                    Mojave Airport on July 26, 2007 as they were
                                        conducting a cold flow test with N2O

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Nitrous Oxide – Explosion Hazard
            SPG Experience                                    Industrial Accidents
•   Small N2O/paraffin motor                         •    N2O used as solvent for
•   First N2O explosion in February
    2006                                             •    Welding full N2O tanks
•   Many small explosions in the feed                •    Heating source tanks with open
    system – minor damage to                              flames
                                                              Car Exploded in Garage
                Medical Accidents
•   Many medical explosions reported in
    operating theater
     – Found 10 cases (3 fatal)
•   Intestinal/colonic explosions during diathermy
     – High content of H2 and CH4 in the intestines
       and colon
     – The concentration of N2O increases
       significantly in the body cavities following its
       application as an anesthetic

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N2O Decomposition Physics
                                         •   N2O decomposition follows the
                                             elementary unimolecular reaction
    Resonant structure                                       () ( )
                                                 N 2O " N 2 1 ! + O 3 P
                                         •   This reaction is considered
                                             “abnormal” since it requires a
                                             change in multiplicity from a singlet
                                             state to a triplet state.
                                         •   This change in multiplicity is
                                             forbidden by the quantum mechanics
                                         •   The transmission can only take
                                             place through “tunneling” resulting in
                                             a reduced transmission rate
                                         •   The reaction rate for N2O is more
                                             than 12 times lower than the reaction
                                             rate predicted for a “normal”
                                             unimolecular reaction (such as the
                                             decomposition of H2O2)
    Ref.:Stearn and Eyring (1935)        •   This quantum mechanical effect is
                                             the root cause for the relative safety
                                             of N2O

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N2O Decomposition Kinetics
   •   The decomposition of N2O is believed to follow the elementary

                       N 2O + M ! 1 N 2 + O + M

                       N 2O + O ! 2 NO + NO
                         N 2O + O ! 3 N 2 + O2

   •   Steady-state assumption for [O] results in the following kinetic
       equation for the decomposition of N2O

                         d [ N 2O ]
                     !              = m k1[ N 2O][ M ]
   •   Note that m=2 and it comes from stoichiometry

 Aero/Astro 50th Year Anniversary
  N2O Decomposition Hazard
                                                      •   Largest hazard is in the
                                                          oxidizer tank during vapor
                                                          phase combustion
                                                      •   An ignition source (hot injector
                                                          plate) could start a combustion
                                                          wave which would result in
                                                          significant pressure increase

                                                      •   Deflagration in tank
          Oxidizer Tank                               •   Tank Length: 4.0 m
                                                      •   Initial pressure: 750 psi
            Risk Mitigation                           •   Max pressure: 9,100 psi
• Respect the propellant (set and                     •   Time scale is seconds
   follow strict procedures)
• Supercharge with inert gas (He)
• Incorporate a burst disk
 N2O is a widely used and fairly safe
                                        NFPA Rating
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Concluding Remarks
 •   Hybrid concept has been around since the start of the modern rocketry
 •   Hybrids lack the intense development cycle that the liquid and solid systems had since
     1940’s (primarily in the 1940-1970)
 •   The liquid and solid rocket technologies are fairly mature and the progress is slow or
     nonexistent. Hybrids could provide the disruptive propulsion technology needed to
     energize the space launch industry by
      –   Providing a safe and affordable option
      –   Breaking the present oligopoly in the rocket propulsion industry by allowing relatively small
          companies to enter the business
 •   Hybrids will not eliminate the liquid and solid systems. It is critical to find the niche
     markets for hybrids
 •   The emerging sub-orbital space tourism market is ideal since
      –   It could end up being a lucrative private market
      –   Performance is secondary to safety and cost (an easy start for the hybrid technology)
      –   The suborbital rocket ca be the basis for a much needed cost effective, reliable orbital system
 •   Solutions to the technical challenges should NOT eliminate the safety and simplicity
     advantages of hybrids.
 •   We believe that viable solutions exist for these technical problems, assuming that the
     following conditions prevail
      –   Creative and competent technical team
      –   Adequate funding for technology development

Aero/Astro 50th Year Anniversary


Aero/Astro 50th Year Anniversary
Rocket Propulsion Fundamentals
                   Propulsive Force
 Mass Ejected per Unit Time x Effective Exhaust Velocity

    Mass                                            Energy

    Electric      Nuclear                Chemical      Cold Gas

                   Liquid                 Solid        Hybrid

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Hybrid Combustion Scheme
                          Velocity                                     Profiles
                                                     Te                        Yo = 1
                                                               Tb              Products
         Flame Zone
                                                          Ts                  Fuel + Products

   Fuel Grain
                      z                    x        Ta

     •    Diffusion limited combustion
           – Burning Rate Law: independent of pressure (flux dependent)
     •    Flame zone away from surface and blocking effect
           – Low regression rate

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Small Launch Vehicle Data

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Liquid Layer Hybrid Combustion Theory
 • Scaling for entrainment mass transfer
               $ #               Operational Parameters:
              Pd h               (Pressure, Oxidizer Flux)
    ment &
              % µl
               " !               Material Properties:
                                 (Viscosity, Surface Tension)
 • Modification on the classical Hybrid Combustion
    – Reduced heating requirement for the entrained
    – Reduced “Blocking Effect” due to two phase flow
    – Increased heat transfer due to the increased
      surface roughness

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Entrainment for CnH2n+2 Series
                 Methane Pentane                                                    HDPE Polymer
                  (Tested)    (Tested)   Paraffin Waxes        PE Waxes                  (Tested)

           C:          1        5          25         45       65    80                  14,000

    Mw: 16                     72         352         632      912   1262                200,000

                   Cryogenic                       Non-cryogenic

                 Gas       Liquid                   Solid                         Polymer



Aero/Astro 50th Year Anniversary
Liquefying Hybrid Fuels
• Solid cryogenic and paraffin-based hybrids: Tested by
   – Air Force (Pentane and several other hydrocarbons)
   – ORBITEC (Methane, SOX, CO etc..)
   – Stanford/SPG (Paraffin waxes)
• Very high regression rates (Factors of 3-5)

                                          • These hybrid fuels
                                            burn by forming a
                                            liquid layer on their
                                            burning surfaces
                                          • Possibility of
                                            entrainment mass
                                            transfer from the
                                            liquid layer
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Homologous Series of n-Alkanes (CnH2n+2)
• Normal Alkanes: Fully saturated, straight-chain hydrocarbons
• Examples:
Methane (CH4):
Ethane (C2H6):
 Pentane (C5H12):
“Wax” (C32H66):

    A number of practical fuels (pure form or mixtures):
   Methane, Kerosene (n~10), Paraffin Waxes (n=16-45),
   PE waxes (n=45-90), HDPE Polymer (n in thousands)

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Theory Prediction and Motor Test Data for CnH2n+2

                                              Regression rate
                                             increase over the
                                            classical value is as
                                                high as 6.1

                                             Paraffin waxes burn
                                              5-5.5 times faster
                                               than the HDPE

                                             Theory prediction is
                                               fairly accurate

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Melt Layer Temperatures for CnH2n+2 Series

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Lindemann’s Unimolecular Theory
    •   Physical steps of the first reaction are
                          N 2O + M ! a N 2O * + M
                           N 2O * + M !!" N 2O + M

                              N 2O * ! b N 2 + O
    •   Steady-state assumption for the excited complex [N2O*] results in
        the following kinetic equation
                        d [ N 2O ]   k k [ N O ][ M ]
                          !        =m a b 2
                            dt        kb + k ! a [ M ]
    •   At high pressures the reaction becomes first order
                       d [ N 2O ]    k k
                   "              = m a b [ N 2O] = m k1 [ N 2O]
                           dt         k "a
    •   At low pressures the reaction is second order
                  d [ N 2O ]
                !            = m k a [ N 2O][ M ] = m k1 [ N 2O][ M ]
    •   For N2O       k1 (T ) = 1.31011 e !30,000 T s !1

                                                39                          Karabeyoglu
Aero/Astro 50th Year Anniversary
Reaction Order Data
                                            •   Data follows the
                                                theory in general
                                            •   For pressures
                                                larger than 40
                                                atm (~600 psi) the
                                                reaction is shown
                                                to be first order
                                            •   Note that for the
                                                first order reaction
                                                the collision
                                                partner [M] does
                                                NOT play a role
                                                greatly simplifying
                                                the analysis

                        Ref.:Lewis and Hinshellwood (1938)

                       40                                      Karabeyoglu

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