CelestLabX: CelestLab s extension module

Transcription

1 ScilabTEC CelestLabX: CelestLab s extension module Alain Lamy, CNES Alain.Lamy@cnes.fr 16 May 2014

2 Space Flight Dynamics mission design at CNES Agenda What tools for mission design? -> What makes Scilab adapted to mission design? CelestLab: Our toolbox for SFD mission design CelestLabX: Extension to CelestLab Design options and choices Development aspects Contents Conclusion 2

3 The Toulouse Space Centre Prepares the French space technical policy Develops orbital systems Operates satellites Ensures compatibility with the French Operations Space Act Systems Engineering & Flight Dynamics department Mission Design and Flight Dynamics Coordination Support to project system teams (performance analyses ) Delegated responsibility on flight dynamics system, test benches, mission simulator, system tests Architects for AOCS, Command and control flight S/W Flight dynamics: Mission design Coordination (preparation of operations ) 3

4 What is flight dynamics? Flight dynamics is the field related to the orbit / attitude (orientation) of objects in space, which includes aspects such as: Defining the trajectory (around Earth, other planets, the Sun ) Determining the trajectory using measurements (from ground stations, using onboard sensors) Simulating various aspects of the mission: visibility from ground stations Controlling the trajectory, computing adequate maneuvers to keep the satellite on track. Project phases: Mission design: early stages -> prove the feasibility Preparation of the operational activities / tools / flight software for all mission phases Operations 4

5 Introduction: mission design at CNES (mission design for projects in early phases) Iterative process to: Better define a mission Prove its feasibility Exhibit the key elements Mission objectives, Hypotheses Studies Space Electrical architecture Attitude control On-board Instruments dynamics Thermics Coordination (PASO) At CNES mission analyses are carried out within a dedicated structure: PASO (*) = Concurrent Design Facility (*) Plateau d Architecture des Systèmes Orbitaux 5

6 What tools for mission design? What kind of tools do we need for mission design? (lots of studies, various tools required, there are always specific aspects...) Not so easy. Compromise between: Flexibility (adaptation of tools must be easy) Robustness (reference, reliable tools must be available) Efficiency (simple problems/questions must be answered easily) Consistency between tools Scilab appears to fullfill our needs Some time ago, we didn t use Scilab: We had unix-based solutions, with compiled program (Fortran ), shell scripts, data exchanges using files, dedicated libraries for I/O It worked but was not as flexible as we might have wished. 6

7 What makes Scilab adapted to mission design? The language is simple enough Close enough to maths Adapted to engineers: you do flight dynamics and not programming (but: writing libraries requires a bit more of «programming stuff») Can be easily used by anyone for simple calculations Scilab comes with many functions / libraries No need for external libraries for usual tasks (maths, statistics ) Graphical features included Atoms for additional features Vectorization (operations on vectors) => often well adapted for simple tasks: x = linspace(0,10,100); y = f(x); plot(x,y); Links with other langages possible We used Scilab with C, FORTRAN, and more recently Java Scilab becomes a «glue» language and a unifying platform 7

8 CelestLab = flight dynamics for Scilab Scilab flight dynamics library, pure scilab code Open source (same licence as Scilab) Available on atoms web site since end of Number of downloads > Contains ~250 functions (~20000 lines of code) Functions dealing with main flight dynamics aspects Coordinates & Frames, Trajectory and maneuvers, Orbit properties, Interplanetary, Geometry & events, Relative motion, Models, Utilities Thoroughly tested Reference data from JPL, SOFA, CNES... Lots of examples, demos (~65), tutorial pages Can be used as starting points when you have to do something close to what already exists. Provides immediate answers to common/recurrent questions => simple problems are generally easily solved. 8

9 Simple example (using CelestLab) Angle between the orbit plane and the Sun direction (beta) inc = 77.6 * %CL_deg2rad; sma = 890.e3 + %CL_eqRad; ecc = 0.001; kep0 = [sma; ecc; inc; 0; 0; 0]; cjd0 = CL_dat_cal2cjd(2020,3,10); cjd = cjd0 + (0 : 1/1440 : 10); kep = CL_ex_secularJ2(cjd0, kep0, cjd); // orbital elements // initial date // computation dates // propagate [pos, vel] = CL_oe_kep2car(kep); // position and velocity [pos_ecf, vel_ecf] = CL_fr_convert("ECI", "ECF", cjd, pos, vel); // change ref. frame sun = CL_eph_sun(cjd); sun_ecf = CL_fr_convert("ECI", "ECF", cjd, sun); // Sun position // change ref. frame beta1 = %pi/2 - CL_vectAngle(CL_cross(pos, vel), sun); beta2 = %pi/2 - CL_vectAngle(CL_cross(pos_ecf, vel_ecf), sun_ecf); scf(); plot(cjd, beta2 * %CL_rad2deg, "b"); plot(cjd, beta1 * %CL_rad2deg, "r"); xtitle("beta angle (deg)", "days"); CL_g_legend(gca(), ["Velocity / Earth", "Inertial velocity"]); CL_g_stdaxes(); 9

10 Simple example (using CelestLab) Run the script and you obtain: 10

11 CelestLab: illustrations CelestLab Demo Tool 11

12 CelestLab: illustrations Examples of CelestLab help pages 12

13 CelestLab: illustrations Reference frames in CelestLab (use of the latest standards) 13

14 Why make CelestLab open-source? No rights issues in CelestLab Make things standard => A way to share our methods, conventions Make exchanges inside the flight dynamics community easier Instead of data => we can exchange lines of code Description of methods or algorithms => answer can be: «see CelestLab» Can be used in universities for training of engineers / students in the flight dynamics domain Contributions Detections of errors is more efficient if there are many users. Users may have ideas for extensions or create useful tools based on CelestLab (that we would not have time to develop) 14

15 CelestLabX: introduction Open-source code / freeware libraries exist and we would like to use them through Scilab. -> Saves (long) coding / testing time -> Add usefull features to the libraries Sometimes efficiency implies calling native code if vectorization is not easy to achieve. Our solution: CelestLabX = CelestLab s extension: -> contains interfaces to public (or maybe specific) tools and libraries -> the additional features are made available through CelestLab (CelestLab then contains either pure Scilab code or calls to functions from CelestLabX) 15

16 Option 1: CelestLabX: Design options CelestLab (unchanged) CelestLab s extension (independent module) Drawback: Structure not clear. Not obvious from the user s perspective which library contains what. Option 2: Drawback: more complex CelestLab Extended with interfaces to various languages / native code Option 3: Advantage: - CelestLab remains simple. - User (mostly) sees CelestLab - CelestLab alone is useable CelestLab New interfaces CelestLab s extension (low level native code + interfaces) 16

17 CelestLabX: Design options Closer look at the selected option: Standard Scilab API calls C code CelestLab + new interfaces CelestLab s extension (low level native code + interfaces) What the user (mainly) sees (Standard module structure) New features now Included in Scilab for - Calling java from Scilab - Generating jar files Java code 17

18 CelestLabX: Internal structure Example with Stela interface (interface to java code): CelestLabX (STELA jar files) CelestLabX specific Java interfaces: (Java code) CelestLabX (Scilab code) CelestLab (Scilab code) <xxx>.jar Extrapolation.java Derivation.java CLx_stela_extrap() CL_stela_extrap() Included in CelestLabX STELA Interface as simple as possible (reason: simplify code, tests ) Additional features Available / CelestLabX: Change of reference Frame, coordinates... <xxx>.jar CLx_stela_register() CLx_config_set()... STELA installation directory loaded at start-up Generic functions 18

19 Development of CelestLabX Contract with Scilab Enterprises with well defined respective roles: CNES First version (prototype) C only S/E Improved version (standard module) CelestLabX Interfaces Prototypes of implementations Extended version Scilab CelestLab (new interfaces) Final version 19

20 CelestLabX: contents Initial contents STELA: CNES tool created in the context of satellite end of life regulations (limitation of the amount of debris). Used for orbit long-term propagation (prediction of satellite positions over many years, usually up to 100) Semi analytical propagation: propagation of «mean orbital elements» instead of true orbital elements => much less time consuming. Can be downloaded from Two-line elements Data representing orbital states to be used for the propagation of objects with a specific model (SGP4/SDP4) Classically used for the propagation of debris (number of objects > 10000) Open source code exists ( Probably in the future Atmospheric density models; MSIS2000 or DTM

21 For mission design at CNES : not only CelestLab! «navigator» Tools (sce, sci ) and data organized in directories (+ Descriptors) dir dir dir.sce.sci.scd tree dir dir data Low level lib. Higher level lib. (+ interfaces with C, Fortran, Java) User area Scilab «extension» Functionalities for an easier use of the tools 21

22 Stela interface in CelestLab (beta version) (Extract from CelestLab help pages) Run 22

23 A few concluding remarks Scilab has been used extensively at CNES for flight dynamics mission design for a few years now. Scilab appears to be well adapted: recurrent studies are now done much more efficiently (thanks to various tools, CelestLab in particular). CelestlabX has been created to extend CelestLab with new features written in other languages (C, Java), while keeping CelestLab simple. The alpha version of CelestLabX is beginning to be used at CNES. CelestLabX is not yet publicly available: it should (hopefully) be before next summer. Interfaces between Scilab and Java will probably be more common practice in the future at CNES as the software for the next generation of control centers will be written in Java. 23

24 For more information... For more information on CelestLab: 24