Briefing to the Space Systems Academic Group

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Briefing to the Space Systems Academic Group

• Aerodynamic Orbital Transfer of the X-37 Orbital
  Maneuvering Vehicle
• LT John P. Pienkowski, USN
• 366 Curriculum Student
• Thesis Advisor
• Dr. Stephen Tony Whitmore
• Co-Advisor
• Dr. Michael G. Spencer

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Background
Brig Gen Anarde HQ AFSPC/XP
08/24/2001
Military Spaceplane (MSP) and Reusable Launch
Vehicle Study
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Purpose of Arnade Study

• Assess Reusable Launch Vehicles
• Operational Utility
• Science and Technology Maturity
• Assess X-33 and X-37 applicability
• Recommend position
• AF role in X-33 and X-37 programs
• Identify other options
• Establish glide slope for AF Reusable
• Launch Vehicle way ahead

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Arnade Council, Conclusions
Reusable vehicles offer potential warfighting
value Two Stage to Orbit -- the best
alternative Mix of Expendable and Reusable
Vehicles Suite of vehicles to cover the range
of ops and missions Substantial risks and
mitigations associated with continuing with the
X-33 and X-37 programs Programs fill only small
parts of flight profiles required to field
operational military space plane Do not pursue
X-33 program Approve further study of X-37 as we
develop RLV roadmap
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X-37, Concerns and Recommendations
Gaps in capability - Operations -
Technology - Performance Ops Concepts and
Requirements Definitions Immature Need to
Expand Orbital Operations Flexibility
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X-37, What is it?
Shuttle Deployment

• Prototype Re-Usable Orbital Maneuvering
• Vehicle (OMV)
• PROGRAM OBJECTIVE - Reduce cost of
• space transportation via flight demonstration
• to mature and validate advanced technology
• To and from LEO
• In-Space
• NASA/Boeing Cooperative Agreement
• X-40A flights demonstrated autonomous landing

EELV (Delta IV Launch)
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X-37 Propulsion System
Rocketdyne AR2-3A Main Engine
Propellants 90 H2O2, JP-8 Oxidizer
Tank Usable mass 2454 lbm 90 H2O2 Fuel
Tank Usable mass 327 lbm JP-8 Propellant
Mass Fraction (propellant/dry mass) Pmf
0.3900 Nominal Thrust 3,300 lbf variable
throttle multiple restart capability Vacuum
Isp 240.8 sec Total Available ?V 2544.86
ft/sec
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X-37 Propulsion System (contd)
Total Available ?V 2544.86 ft/sec
Excessive for In-Plane maneuvering Requirements
Not enough available DV for significant plane
change capability
Need to Expand Orbital Operations Flexibility
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Cost Analysis

• Costly to change a spacecrafts inclination
• DV
• fuel consumption
• Space Shuttle can change inclination only by few
  tenths of a degree
• Must launch into desired orbit
• Heavier payloads, but a single orbit
• If X-37 can be demonstrated to have potential to
  change up to 10 degrees orbital inclination
• Achieve dual use of a single spacecraft for the
  price of one launch
• Expand Orbital Operations Flexibility

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Goal

• Assess Feasibility of using aerodynamic forces to
  change the orbital inclination of a the X-37
  Spacecraft, Preserving Fuel for In-Plane
  maneuvers
• Develop Optimized Strategies for Performing these
  maneuvers

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Approach Develop real-time Piloted-Sim
that allows a wide variety of candidate maneuvers
and trajectories to be quickly assessed
Simulation serves as insight builder as to
which parameters are important to the problem
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Develop batch simulation capable ofextended
Monte-Carlo analysis Batch and real-time
simulations used for cross-validation
Piloted simulation tool can be used for
generating feasible starting trajectories
forfollow-on optimization codes (i.e. DIDO,
POST)
Approach (continued)
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Maneuver Description

• At perigee, spacecraft descends into upper
  atmosphere
• Uses aerodynamic forces to alter flight path with
  enough energy to maintain orbital velocity
• Small boost from engine allows spacecraft to
  regain altitude at new inclination

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Maneuver Description
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Maneuver Description
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Equations of Motion
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Equations of Motion (contd)
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Generalized Equations of Motion
J2 not included
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Equations of Motion (contd)
Lift/Drag Force
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Equations of Motion (contd)
X-37 Aero database
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Equations of Motion (contd)
Atmospheric Model 1976 US Standard extended to
600 km
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Equations of Motion (contd)
and of course about a zillion orbital
coordinate transformations
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Simulation Demonstrations Illustrate perigee
collapse concept Demonstrate the Need for
orbit Regulation
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Orbital Energy Regulation
Orbital Energy
Orbit decay
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Orbital Energy Regulation (contd)
Engine thrust used to return orbital energy
robbed by aerodynamic forces.
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Orbital Energy Regulation (contd)
Constrained Optimization Problem
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Orbital Energy Regulation (contd)
Constrained Optimization Problem
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Orbital Energy Regulation (contd)
Necessary Conditions for Optimization
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Orbital Energy Regulation (contd)
Necessary Conditions for Optimization
When all of the variational calculus is said
and done
Which is a dang! Simple control law
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Orbital Energy Regulation (contd)
and we can implement the control as an initial
value problem . Not! a boundary value problem!
Why?
po 0
Our final state is free .. And When t0, we are
near orbit apogee (just after de-orbit burn)
where the dissipative forces are REALLY CLOSE to
zero \the required initial throttle is zero, \
po is zero! we can integrate the co-state
equation forwards Instead of backwards! a
practical limit of many optimal control laws .
Yea, joy and clapping!
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Simulation Demonstrations Illustrate how
regulator avoids perigee collapse Show a
complete plane change cycle of greater
than 10?
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Whats Next?

• Perform complete Simulink/Labview Simulation
  cross-
• validation
• Fully evaluate Optimal Control Methods for Orbit
  stabilization/re-boost
• Implement J2 Perturbations

• Conduct parametric analysis to find optimum
  flight path
• Heating analysis during re-entry
• Assess vehicle Stability during maneuvers
• Vehicle Attitude Control Before Aero-forces
  become dominant, entry
• into aero maneuvers

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Simulink Model
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Labview Model
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Acknowledgements

• Thesis Advisor
• Dr. Stephen Tony Whitmore
• Co-Advisor
• Dr. Michael G. Spencer
• Matlab Help
• CDR Mark Couch, USN