Reentry Guidance for Generic RLV Using Optimal Perturbations and Error Weights AIAA20056438

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Reentry Guidance for Generic RLV Using Optimal
Perturbations and Error Weights (AIAA-2005-6438)

• Dr. Ashok Joshi K. Sivan
• Department of Aerospace Engineering,
• IIT Bombay, Mumbai, India

AIAA Guidance, Navigation Control Conference,
Hyatt Regency San Francisco, 15-18 August, 2005
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Motivation
Reentry problem is important from the following
view points Dissipation of large energy without
violating constraints Large variations in
atmospheric/vehicular characteristics Highly
uncertain operational environment
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Current Status Needs

• Current Flight Proven Methods (Space Shuttle
  HYFLEX)
• Pre-computed drag acceleration profile
  within corridor
• In-flight updating to meet range-to-go
  requirement
• Bank angle to meet terminal range requirements

• Future Reentry Guidance Requirements
• Autonomous for providing mission
  flexibility/adaptability
• Explicit satisfaction of vehicle constraints
• No ground computations and mission
  independent
• Robust against large uncertainties

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Implementation Strategies

• Predictor-Corrector as the most suitable for RLV
  applications
• Models the vehicle environment as close to
  the reality
• Autonomous adaptable to different flight
  conditions
• Ground computations not required

• Aim of present study to make predictor-corrector
  more effective
• Judicious selection of control vector for
  easy solution
• In-flight measurements for improving
  predictor model
• Correct perturbation levels for sensitivity
  computation
• Weighting option for control vector update
• Explicit inclusion of path constraints

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Guidance Problem Definition

• Given Estimate u(t) subject to
• so that at tf, terminal constraints
  is satisfied
• without violating path constraints
  

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Overall Solution Methodology
Predictor
Corrector
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Control Vectors Range
Terminal constraint through definition of
Downrange Crossrange
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Predictor Algorithm
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Corrector Algorithm
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Computation Of Jacobian
Correct Sensitivity depend on proper
perturbation levels Present Study Required
perturbation level computed on ground
stored as function of VR
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Typical Dataset for Validation

• Nominal Reentry Interface
• h 120 km, f 0o, l 0o
• V 8086 m/s, g - 3.2o, Az 100o
• Target (at 25 km)
• f - 18o, l 45.3o

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Constraints Procedure
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Perturbation Levels/Sensitivities
Range Sensitivities
Perturbation Levels
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Heat Rate Constraint Results
Heat Flux Profile
Range Profile
Control Vectors
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Heat Flux Glide Results
Heat Flux Profile
Range Profile
Control Vectors
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Results With CD Variations
Range Profile
Control Vectors
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Results With CL Variations
Range Profile
Control Vectors
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Summary
A modified Predictor-Corrector algorithm
presented Incremental angle of attack as
additional control vector Weighting matrix
for control vector correction More
appropriate perturbation parameter selection
Heat rate and equilibrium glide as explicit
constraints Strategy validated and robustness
demonstrated The proposed algorithm applicable
to wide variety of winged Vehicle configurations
RLV missions