Space Rapid Transit Navigation and Control 1 Michael Paluszek, Joseph Mueller, Dr. Paul Griesemer Princeton Satellite Systems EUCASS July 4-8, 2011 St. Petersburg, Russia Outline History Vehicle Design Overview Avionics GN&C System Design Ascent Flight Boost Phase On-Orbit Maneuvering Reentry End-to-end Simulations Conclusions 2 22010 JPC History We are concerned with horizontal takeoff /horizontal landing Fully reusable vehicles Not a new idea Numerous concepts Broad classes Single stage to orbit Custom 1 st and 2 nd stages Use of a jet fighter as a first stage NASA Beta II Saenger II Skylon SSTO Rascal Venture Star X-37b Operational D-21 ASM-135a-1 B-58/ALBM MSLV Responsive Air Launch Pegasus Operational 32010 JPC Overall Concept Employs existing propulsion systems Horizontal takeoff using military turbofan At Mach 1.5 switches to hydrogen fueled ramjet At Mach 4.6 stage separation Ferry Stage glides to Mach 1.5 then starts the turbofan for a powered landing RL10B-2 powers upper stage to orbit with 2 burns On-orbit operations and reentry with HPGP thrusters Upper Stage glides to landing Two versions: SRT-M & SRT-C SRT-C sized to bring 4 crew to LEO 32010 JPC SRT-M Size Comparison X-37b 42010 JPC Selected Design Elements Ferry Stage SRT-M similar in size to F-22 Combined cycle engine Hypersonic waverider shape Fully autonomous Kneeling stage union Upper Stage Cryogenic engine powered Autonomous reentry and landing Low maintenance TPS Payload bay Rendezvous with ISS and then capture by MRMS 2010 JPC Avionics Independent avionics systems for each stage Similar to the avionics suite of a commercial airliner (Boeing 787) Same systems and levels of redundancy as modern commercial aircraft to allow for safe atmospheric flight Remotely piloted Communication system compatible with ACARS Upper Stage only: In-orbit communication similar to that of ATV Triple redundancy Inertial Reference Navigation System Upper Stage only: Optical Navigation System to replace star tracker and GPS Atmospheric and in-orbit surveillance system to monitor trajectory conflicts Include weather radar, TCAS, TAWS, mode S transponder Data processing uses INTEGRITY-178B operating system, Avionics Full-Duplex Switched Ethernet (AFDX) data network Triple redundancy processors with an independent 4th as backup BAE RAD750 3U CompactPCI single-board computers Integrated vehicle health management software 6 Upper Stage Components CMU SATCOM HF Radio/Antenna VHF Transceiver FDAMS Surveillance System Navigation Receivers (MMR, VOR, DME, ADF) Air Data INS/GPS System BAE RAD 750 Processor Ferry Stage Components CMU SATCOM HF Radio/Antenna VHF Transceiver FDAMS Surveillance System Navigation Receivers (MMR, VOR, DME, ADF) BAE RAD 750 Processor ADIRS Manual Control GN&C System Design 11 Independent control systems with identical flight software Each stage can control the other when connected First determine next launchopportunity Countdown until launch siterotates into orbital plane Launch azimuth found fromorbital inclination and launchsite latitude Launch azimuth determines reference heading during ascent: Launch Conditions 12 Ferry Stage Guidance 13 Optimal reference trajectorycomputed offline Track flight path angleat altitude waypoints,full throttle NDI Guidance Nonlinear DynamicInversion Command pitchand heading Feedback Control Designing Gain-Scheduled H point controllers Full synthesis requires detailedaero model Trajectory Optimization 14 Trajectory is parameterized Piecewise constant control Flight path angle, switch times, fuel masses are free parameters Combined cycle engine up to Mach 4.6 Rocket burn until desired transfer orbit is reached Circularization burn at apogee Boost Phase 15 Staging point: 25 km Mach 54.6 FPA = 20 ~ 30 deg Transfer Burn Burn until transfer apogeereaches ISS orbit altitude 4.5 km/s (6 min) Insertion Burn Align thrust with velocity errorvector Burn until eccentricityminimized 2.5 km/s (3 min) Upper Stage Guidance Combined attitude and orbit control system 16 Force & Torque Distribution Force and Torque Distribution RCS Pulsewidth Modulation Main Engine Gimbals Linear Program with Weighted Slack Variables solve with Simplex 17 Maneuver Planning Orbit Dynamics Relative Orbit Dynamics (LTV System) Valid for orbits: Future states are linear functions of initial state and control 18 Maneuver Planning as LP Use initial relative state to reference OR to satellite/debris Control: Full Control Vector: Relative State at Time t j : Minimize Fuel Subject to constraints 19 On-Orbit Maneuvers Relative orbit maneuvers formulated as Linear Program Discrete linear time-varying system Robust LP formulation / accounts for initial state uncertainty Offline proximity operations planning Using Prox-Ops Toolbox (MATLAB) Developed under AFRL BAA 20 Example Rendezvous Approach Relative Orbit Control Simulation Simulation in VisualCommander 21 Model Setup 22 SRT Launch Simulation Orbit Insertion Transfer Burn Circularization Burn Reaches desired semi-major axis, inclination, eccentricity, right ascension 23 SRT Reentry 24 SRT Reentry 25 Conclusions Preliminary design of a small satellite launcher is complete Fully reusable TSTO that primarily integrates existing technology Designed for responsiveness, rapid turnaround SRT-M is suitable for a large class of small satellites CubeSats, Nanosatellites, micro-satellites 425 kg to ISS orbit Size accommodates a large percentage of ISS supplies Preliminary development of unified GN&C provides foundation for ongoing design refinement and proof-of-concept 26 Future Work Modeling and System Design Detailed subsonic hypersonic aerodynamic models Integrated structure and fuel tanks for Upper Stage Improved sensor models and state estimators Glass cockpit for pilot-in-the-loop flight In-Depth Studies Dynamics and control at separation Abort scenarios ISS robotic arm capture and ISS proximity operations Ground operations 27