JAC Conjunction Assessment

Transcription

1 JAC Conjunction Assessment SSA Operators Workshop Denver, Colorado November 3-5, 2016 François LAPORTE Operational Flight Dynamics CNES Toulouse SUMMARY CA is not an easy task: Risk evaluation + Recommendation. Focus on the determination of the level of the risk => PoC computation + Covariance Assessment CNES developed JAC to help Owners/Operators. 2 1

2 The current situation: Since 2009 JSpOC distributes CM to O/O Space Surveillance Network JSpOC Precise and complete catalog Screening Information Messages generation C D M 3 The current situation: Since 2009 JSpOC distributes CM to O/O What is a JSpOC s CDM: The best available data to avoid collision in space: Takes benefit of the US SP catalog; Is distributed to all O/O; A description of a forecasted conjunction : TCA: Time of Closest Approach; Orbit information of the 2 objects: o Position / Velocity at TCA; o Covariance; o Orbit Determination characteristics; Information on the size of the object; Generated with geometric criteria (Miss distance & Radial separation): Emergency criteria, up to 3 days before TCA: o LEO: 1 km / 200 m; o GEO: 10 km / 5 km; Large criteria (95% capture screening): o LEO: 50 km / 2 km (maximum value), up to 7 days before TCA; o GEO: 360 km / 12 km, up to 14 days before TCA; 4 2

3 But a CDM The current situation: Since 2009 JSpOC distributes CM to O/O is NOT a conjunction ALERT: No need to maneuver for each CDM received: o Emergency criteria: ~30 CM/Year/Satellite; o Large criteria: ~3000 CM/Year/Satellite. Need to evaluate each CDM to detect a HIE according to O/O criteria; is NOT an avoidance maneuver recommendation: The real need is for an asset, on average: o LEO: ~1 maneuver per Year; o GEO: ~1 maneuver every 10 Years. 5 The current situation: Since 2009 JSpOC distributes CM to O/O An Operational Conjunction Assessment process is: I. CDM automatic acquisition and check; Acquisition / Monitoring function Covariance matrices validity Re-computation of relative geometry Closer approaches detection around TCA II. Analysis of incoming CDMs to detect HIE; III. Determination of the avoidance action. Dedicated maneuver analysis windows: to size the avoidance maneuver; to evaluate the effect on all other future conjunctions. 6 3

4 CDM Analysis: Three issues Analysis of incoming CDMs to detect HIE implies to evaluate: I. Position & Velocity of the two objects at the TCA Detect maneuverability of objects Use of JSpOC s LARGE CRITERIA to take into account O/O SKM II. Covariance of the two objects at the TCA III. Radius of the englobing sphere of each object at the TCA Automatic evaluation process of the radius from CM and user data User customization of the process 7 CDM Analysis: Covariance at the TCA: not a deterministic value PoC is very sensitive to covariance matrix C: Covariance is almost never perfectly representative of reality; Primary s and/or secondary s covariance can be: Too pessimistic; Or, too optimistic. 8 4

5 CDM Analysis: Covariance at the TCA: not a deterministic value 3 Orbit Determination Updates (with Cov. Matrix), of the position at T Expected evolution in Local Orbital Frame of OD 3 OD 1 Pos1 Vit1 Cov1 OD 2 Pos2 Vit2 Cov2 OD 3 Pos3 Vit3 Cov3 P3 P1 t1 t2 t3 T time P2 Too pessimistic covariance Too optimistic covariance P1 P2 P1 P3 P3 P2 9 CDM Analysis: Covariance at the TCA: PoC* for a PoC analysis Definition of the PoC* (expanded PoC): PoC(Kp, Ks) gives the PoC as a function of scale coefficients:» with C = Kp Cp + Ks Cs;» Kp for the Primary and Ks for the Secondary, are independent scale factors applied to covariance; PoC* is the Maximum value of PoC(Kp, Ks) with Kp and Ks in a given interval. PoC analysis: analysis of the function PoC(Kp, Ks), with Kp and Ks in a given interval; determination of the realistic values of Kp and Ks, knowing the OD parameters:» Number of observations, residuals, weighted root mean squared, energy dissipation rate,» Evolution of the OD from updated CDM. 10 5

6 CDM Analysis: Covariance at the TCA: PoC* for a PoC analysis Covariance sensitivity analysis on PoC(Kp, Ks) Example of display: Kp in [0.5 ; 3.] and Ks in [0.5 ; 3.] If Primary s and Secondary s covariance are pessimistic the risk is over-estimated 0.5 K s 3.0 (1, 1) 3.0 K p If Primary s or Secondary s covariance is optimistic the risk is under-estimated PoC scale: from 10-0 to CDM Analysis: Covariance at the TCA: PoC analysis - Real example Example of a dangerous conjunction identified thanks to the expanded PoC analysis. CM Analysis Main Window This is the default values considered at CNES A click here, opens the dedicated PoC analysis window. Time tagged received CDMs: GNOSE = O/O for Primary; JSpOC for secondary Notice = # hours before TCA Decision to perform an avoidance maneuver because it is a risky conjunction. PoC always < CRITERIA =

7 CDM Analysis: Covariance at the TCA: PoC analysis - Real example PoC Analysis Window White when cell s PoC > As soon as Kp & Ks <1, PoC > CRITERIA; K s 4.0 If Kp and Ks < 0.6 then PoC > 10-3 Standard PoC = Kp=0.9 Ks=0.8 => PoC = Kp=0.7 Ks=0.5 => PoC = (1, 1) 4.0 The analyst must answer : Kp < 0,9 and Ks < 0,8 : realistic? K p Let s have a look at the evolution of Primary s and Secondary s covariance PoC scale: from 10-0 to CDM Analysis: Covariance at the TCA: PoC analysis - Real example Primary dispersions evolution visualization Secondary dispersions evolution visualization K s The covariance of both objects are pessimistic: the PoC can realistically be greater than the CRITERIA. K p This is a risky conjunction A classical analysis would have miss this risk 14 7

8 CDM Analysis: Covariance at the TCA: PoC forecast - Real example The high risk have been anticipated thanks to the PoC analysis window CDM #6: PoC still below blue PoC* is orange. When the orange area if bottom/left, the risk usually increases when the geometry is steady: Because dispersions reduce. Very useful to anticipate operational activities. 15 -III- CDM Analysis: Covariance Determination Covariance determination It can be an output of the Orbit Determination process: o o It must include in the Orbit Determination process very often it is an under-estimation of the reality. Post analysis of the O/O ephemeris: from historical set of ephemerides Determinated orbit Extrapolated orbit Day 1 Day 2 Day 3 Day 4 A D B F E C 1 day extrapolation: A, B, C 2 days extrapolation: D, E 3 days extrapolation: F Day 1 Day 2 Day 3 Day 4 provides statistics of dispersion in the RIN local orbital frame; from this statistics we can create a variance abacus. 16 8

9 -III- CDM Analysis: Covariance Determination Variance abacus: basic function gives the evolution of variance (in meters) in the three directions (Radial, In-track and Normal) of orbital local frame as a function of extrapolation duration (in days). Variance abacus: as a function of On Orbit Position For a given extrapolation duration, such function (the green or the red one in the above example) gives the evolution of variance (in meters) in the three directions (Radial, In-track and Normal) of orbital local frame as a function of On orbit Position (in degree). Takes into account the evolution of dispersions along the orbit due to the non-uniformity of distribution of sensors providing the measurements for the OD. This lead to a more realistic computation and reduce the uncertainties on some orbit positions. 17 Conclusion Evolution of CA Process: In the past: Miss distance & relative geometry Its minimum does not always represent the highest risk; Doesn t take into account Position uncertainties: Not a valid criteria Need to take into account position uncertainties (i.e. covariance) Now: PoC Takes into account Positions uncertainties: very good improvement; But relies on the realism of the covariance Can hide dangerous situations / Can lead to undersize avoidance action Need to take into account covariance uncertainties Next step: PoC + Covariance Assessment Takes into account covariance uncertainties 18 9

10 Conclusion CA a fully automatic process not yet: Can miss some risks / undersize avoidance action; Can lead to too many avoidance events: The final analysis must be a manual analysis. JAC can help O/O to perform this manual analysis JAC is distributed by CNES in 2 levels: Basic ( to be aware of the situation ) for free; Expert ( to take and validate a decision ) for an annual fee. jac@cnes.fr 19 10