Webinar ProxOps

Please stay on the line:The Modeling Spacecraft Proximity Operations and Docking in STKwebinar will begin shortly: 

Please stay on the line: The Modeling Spacecraft Proximity Operations and Docking in STK webinar will begin shortly Join the internet phone session or teleconference: North America: 1.866.469.3239 International: +1.650.429.3300

Modeling Spacecraft Proximity Operations and Docking in STK: 

Modeling Spacecraft Proximity Operations and Docking in STK Tim Carrico Director, Business Development (AGI) John Carrico Senior Astrodynamics Specialist (AGI) 7 September, 2005 Mike Loucks President (SEE)

“Rendezvous,” “Prox Ops,” and “Docking” with another spacecraft: 

“Rendezvous,” “Prox Ops,” and “Docking” with another spacecraft Rendezvous: often used to describe getting a spacecraft from one orbit to a control box near but offset from another Rendezvous from 6678 km sma orbit to 6838 km sma orbit 4 maneuvers used to execute 2 Hohmann transfers Proximity Operations: Begins after rendezvous Very near another spacecraft (e.g., < 1 km) Docking: Controlling spacecraft to touch at a desired point and velocity Walter Hohmann (1880-1945)

Move closer to another spacecraft: 

Move closer to another spacecraft 2 maneuvers to move from control box at 2270 m to 214 m in about 1 orbit (139 mins) (see purple segment below) 1st maneuver starts transfer (in-track distance at end = 214 m) 2nd maneuver stops relative to station (in-track rate = 0 m/s) George Hill (1838-1914) Control Box

Display trajectory relative to another spacecraft: 

Display trajectory relative to another spacecraft Choose satellite with which to display trajectory

Relative calculation objects: 

Relative calculation objects Relative Motion: Position and velocity in local frame Formation: Relative orbital elements Special Astrogator Browser “Calculation Objects” for multiple s/c

Choosing the reference for calculation: 

Choosing the reference for calculation Relative calculation objects use reference object (set on satellite Basic Properties panel) or any other specified s/c

Move in a “straight line”: 

Move in a “straight line” Move straight along v-bar from 1,000 m to 200 m in about 5 mins Use an “automatic sequence” to trigger maneuvers when needed

Setting up an automatic sequence: 

Setting up an automatic sequence Select a sequence to be triggered when stopping condition is met “BurnDown” MCS icons brings up list of auto-sequences

Setting up an automatic sequence: 

Setting up an automatic sequence Each auto-sequence is it’s own MCS Auto-sequence can include all segments Impulsive maneuver for this example

Result of auto sequence: 

Result of auto sequence Maneuvers triggered automatically whenever radial rate exceeds 0.03 m/sec 29 maneuvers about 11 seconds apart Each maneuver 0.061 m/sec – calculated from off-line analysis Maneuver value could be targeted At the end of these maneuvers the supply spacecraft is 200 m from the station 16 Apr 2005 01:58:30.699 16 Apr 2005 01:58:41.618 16 Apr 2005 01:58:52.536 16 Apr 2005 01:59:03.454 16 Apr 2005 01:59:14.373 16 Apr 2005 01:59:25.291 16 Apr 2005 01:59:36.209 16 Apr 2005 01:59:47.127 16 Apr 2005 01:59:58.046 16 Apr 2005 02:00:08.964 16 Apr 2005 02:00:19.882 16 Apr 2005 02:00:30.800 16 Apr 2005 02:00:41.718 16 Apr 2005 02:00:52.636 16 Apr 2005 02:01:03.554 16 Apr 2005 02:01:14.471 16 Apr 2005 02:01:25.389 16 Apr 2005 02:01:36.307 16 Apr 2005 02:01:47.225 16 Apr 2005 02:01:58.143 16 Apr 2005 02:02:09.060 16 Apr 2005 02:02:19.978 16 Apr 2005 02:02:30.896 16 Apr 2005 02:02:41.813 16 Apr 2005 02:02:52.731 16 Apr 2005 02:03:03.648 16 Apr 2005 02:03:14.566 16 Apr 2005 02:03:25.483 16 Apr 2005 02:03:35.044

Docking with another spacecraft: 

Docking with another spacecraft Many maneuvers are going to be needed Maneuvers in 3 directions Start at rest, align on v-bar of target, move forward along the v-bar Used closed-loop control Custom Fuzzy Logic control law Evaluate at each integration step Set step to be 0.1 sec (10 Hz)

Mission Control Sequence flowchart: 

Mission Control Sequence flowchart

Engines add acceleration to force model: 

Engines add acceleration to force model

Custom extensibility through plug-in points: 

Custom extensibility through plug-in points

MCS for closed-loop control: 

MCS for closed-loop control

Thruster set definition: 

Thruster set definition

Thruster set definition: 

Thruster set definition

Engine definitions: 

Engine definitions

Engine definitions: 

Engine definitions

Engine definitions: 

Engine definitions

Custom function defintions: 

Custom function defintions

Custom function definitions: 

Custom function definitions

Engine Eval script: 

Engine Eval script Function docking_1_Eval_compute( stateData) ' The following allow inputs and outputs to be called via c structure syntax Dim returnValue(4) Set docking_1_Eval_Inputs = g_GetPluginArrayInterface("docking_1_Eval_Inputs") Set docking_1_Eval_Outputs = g_GetPluginArrayInterface("docking_1_Eval_Outputs") returnValue(docking_1_Eval_Outputs.status) = "Still Okay" returnValue(docking_1_Eval_Outputs.Thrust) = thrust(1) returnValue(docking_1_Eval_Outputs.ISP) = ISP(1) returnValue(docking_1_Eval_Outputs.MassFlowRate) = MassFlowRate(1) docking_1_Eval_compute = returnValue End Function

Engine Update script excerpts: 

Engine Update script excerpts Function docking_Update_compute( stateData) … Fz = FuzzyProxOps.FuzzyZEngine(X, Z, Zdot,EngineIndex, serr) fuzzy_thrust(EngineIndex) = Fz Fy = FuzzyProxOps.FuzzyYEngine(X, Y, Ydot,EngineIndex, serr) fuzzy_thrust(EngineIndex) = Fy Fx = FuzzyProxOps.FuzzyXEngine(X,X,Xdot,EngineIndex,serr) If EngineIndex = 1 then 'Split for 2 canted X engines fuzzy_thrust(0) = Fx/2 fuzzy_thrust(1) = Fx/2 fuzzy_thrust(2) = 0 else fuzzy_thrust(EngineIndex) = Fx fuzzy_thrust(0) = 0 fuzzy_thrust(1) = 0 end if thrust(1) = fuzzy_thrust(0) ISP(1) = 310 MassFlowRate(1) = thrust(1)/(ISP(1)*9.80665) … returnValue(docking_Update_Outputs.status) = "Still Okay" docking_Update_compute = returnValue End Function

Fuzzy Logic: 

Fuzzy Logic 1965, Prof Zadeh, University of CA A scientific branch of machine logic Allows for mathematical formulation of concepts such as “slow,” “medium,” “fast” Provides for computational processing of these linguistic concepts Models how we think and make decisions Fielded in man-rated control systems True False -30 0 30 60 90 100 Slow Fast Medium Slow and Medium Lotfi A. Zadeh (1921- )

Fuzzy Logic Spacecraft Maneuvering: 

Fuzzy Logic Spacecraft Maneuvering Precision control concepts familiar to a human are hard to encode mathematically FL provides a method for encoding in spacecraft maneuvering expertise FL control systems often require less information Provides predictable and deterministic results Independent rule-based provides resiliency Slow Fast Medium Far Close Near Engine Thrust Med Engine Thrust High Engine Thrust High Engine Thrust Small Engine Thrust Small Spacecraft Speed Distance Engine Thrust Small Engine Thrust High Engine Thrust High Engine Thrust None

Fuzzy Logic Spacecraft Maneuvering: 

Fuzzy Logic Spacecraft Maneuvering In docking and prox ops, precision control concepts familiar to a human are hard to encode mathematically FL provides a method for encoding in spacecraft maneuvering expertise Provides predictable and deterministic results Slow Fast Medium Far Close Near Engine Thrust Med Engine Thrust High Engine Thrust High Engine Thrust Small Engine Thrust Small Spacecraft Speed Distance Engine Thrust Small Engine Thrust High Engine Thrust High Engine Thrust None

Engine commands: 

Engine commands Engine commands as function of distance to station and speed to alignment axis

Fuzzy sets: 

Fuzzy sets The fuzzy sets convert numerical inputs into the rule inputs

Fuzzy rules: 

Fuzzy rules Cognitive modeling of spacecraft maneuvering expertise. Maps to how experts think about precise maneuvers and acute control Provides ability for non/technical to understand mission – risk mitigation “If rate is away_fast and station is Far, then do TowardLarge”

Rule output: 

Rule output The output from the rules is used to “defuzzify” the set into a real number

“Defuzzification”: 

“Defuzzification” Two rules trigger and give Membership in two of the sets, TowardLarge and TowardSmall, which evaluate to give a real number for thrust, in Newtons

Back to Docking: 

Back to Docking

Docking results: Engine firing and distance history: 

Docking results: Engine firing and distance history

Docking results: Fuel and Mass Flow Rate: 

Docking results: Fuel and Mass Flow Rate

Custom HTML user interface: 

Custom HTML user interface

Proximity Operations: Inspection: 

Proximity Operations: Inspection

Example: Mini AERCam: 

Example: Mini AERCam

XML Controlled Maneuvers: 

XML Controlled Maneuvers An XML file is used to specify waypoints for chase spacecraft Offset to Target Hold on Station Time Standoff Range File can be read by the PrePropagate plug-in point so it’s only read once per calculation run

Prox ops inspection results: 

Prox ops inspection results

Other plug-in points in STK: 

Other plug-in points in STK Vectors Can be used for sensor pointing Constraints Custom method to determine if there is “access” between two objects Attitude Module Attitude control Communications

Summary: 

Summary Open-Loop maneuver planning works for Keplerian orbital transfers Rendezvous: relative orbital elements Simple “CW” approach: Radial, in-track, cross track Closed-loop with auto-sequences works for simple “1-D” non-Keplerian orbital transfers Moving along the “V-bar” Closed-loop with plug-in scripts works for complex 3-D non-Keplerian transfers maneuvers 3D docking Vehicle Inspection: closed loop control with way-points Many types of control laws can be used in plug-ins Fuzzy Logic works well in systems requiring complex, simultaneous (multi-axis) non-linear control Fuzzy Logic is simple way to build understandable yet powerful control laws Fuzzy Logic useful for pre-mission analysis and can be used operationally

Questions?: 

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Questions?: 

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