Collision Risk Assessment for Spacecraft with CASS

Transcription

1 Collision Risk Assessment for Spacecraft with CASS Ma Chaowei 2011, Oct 2011 Beijing Institute of Tracking and Telecommunications Technology

2 Ma Chaowei 2

3 Contents Introduction Basic Information of CASS Process Overview of Collision Assessment Examples of High Risk Analysis Conclusions 3

4 Introduction The risk of collision with operational satellites is higher than ever due to the increasing density of space debris. It causes an important attention on spacecraft flight-safety from all space-fairing countries. JSpOC, NASA, ESA and other organizations are performing routine analysis for the upcoming conjunction events, collision risk assessment and collision avoidance maneuvers for operational satellites. Conjunction messages between China s satellites and other space objects received from JSpOC since September BITTT has developed CASS, Conjunction Assessment tools for Spacecraft. to provide technical supports for spacecrafts flight-safety assessment. including conjunction assessment, analysis, collision probability calculation and collision avoidance maneuver simulation. based on The TLE data downloaded from space-track website (since January 2011), satellites precise ephemeris from owner/operators and other orbit parameters. Routine analysis for China s spacecrafts has been performed by CASS. 4

5 Introduction 50 kilometers miss-distance threshold has been set to monitor the conjunction events for LEO objects, 40 kilometers threshold for GEO objects. After that, most safety objects are eliminated and critical collision warning threshold are set to filter high collision risk events. For LEO objects the collision probability P is higher than 1:10,000. or the identified miss-distance ΔR is smaller than 1000m. warning results are generated in text file. For GEO objects miss-distance ΔR is smaller than 5000m. warning results are generated in text file. 5

6 Introduction For more accuracy analysis telescopes for debris detecting research and pulse radars of satellite launch centers are used to acquire tracking data and to determine the precise orbits of suspected chaser objects. Avoidance maneuver If collision probability or miss-distance are still beyond the above given threshold for LEO and GEO objects, the avoidance maneuver is planned. 6

7 Basic Info of CASS CASS is a tool package, including five independent software. CAOM, Collision Assessment Operation Management CAA, Close Approach Analysis CPC, Collision Probability Calculation OCP, Orbit Covariance Propagation AMA, Avoidance Maneuver Analysis Each software is controlled by CAOM can operate on a same workstation or different workstations can communicate with each other and exchange information by unified interface. satellite ephmeris TLE AMA high risk events maneovre orbit CAA OCP Operate Control state vector relative velocity warning report CAOM TCA, Pc,other information CPC UVW covariance coefficient The structure of the CASS 7

8 CAOM : The main control software of CASS providing an advanced user interface and graphical display functions. Operations for the collision risk analysis starts from here parameter set running control conjunction calculation results output user management database management etc Basic Info of CASS satellite ephmeris TLE AMA high risk events maneovre orbit CAA OCP Operate Control state vector relative velocity warning report CAOM TCA, Pc,other information CPC UVW covariance coefficient The structure of the CASS 8

9 CAA : The core software of CASS supports local calculation on the Windows OS in a single workstation and parallel calculation on the Linux OS in cluster servers. providing conjunction analysis between space objects in different data types. on-orbit conjunction analysis for catalogue space objects. launch window safety analysis for spacecraft which is going to fly. output the dangerous launch window and basic conjunction information for subsequent probability. miss-distance relative velocity conjunction angle UVW distance J2000 state vectors etc Basic Info of CASS AMA high risk events maneovre orbit Operate Control satellite ephmeris CAA TLE state vector relative velocity OCP warning report CAOM TCA, Pc,other information CPC UVW covariance coefficient The structure of the CASS 9

10 Basic Info of CASS OCP : The basic software for collision risk assessment providing state covariance of both the target satellite and the chaser object for probability calculation. includes two modules: SCCF (State Covariance Coefficient Fitting) and SCG (State Covariance Generating). SCCF is used to generate state covariance coefficient by polynomial fitting. SCG is used to generate UVW covariance by calculating state covariance coefficient polynomial. satellite ephmeris TLE AMA high risk events maneovre orbit CAA OCP Operate Control state vector relative velocity warning report CAOM TCA, Pc,other information CPC UVW covariance coefficient The structure of the CASS 10

11 Basic Info of CASS CPC : The most important software for collision risk assessment used to calculate the collision probability and the maximum probability of a given conjunction events while conjunction information comes from CAA and state covariance of target and chaser object comes from OCP. some important information, including TCA, miss-distance, relative velocity, conjunction angle, UVW covariance and J2000 state vectors, are picked out to calculate the collision probability at TCA. satellite ephmeris TLE AMA high risk events maneovre orbit CAA OCP Operate Control state vector relative velocity warning report CAOM TCA, Pc,other information CPC UVW covariance coefficient The structure of the CASS 11

12 AMA : Is still underway. Basic Info of CASS designed to simulate the possible maneuver orbit to avoid high collision risk events. if miss-distance or collision probability are beyond the given thresholds, AMA receives the close conjunction information, generates maneuver orbit and return it to CAA. additional running to ensure that the maneuver orbit does not introduce other conjunction events. The results from AMA only provide the reference for O/O. The finial maneuver orbit generation and decision should be made by O/O themselves. satellite ephmeris TLE AMA high risk events maneovre orbit CAA OCP Operate Control state vector relative velocity warning report CAOM TCA, Pc,other information CPC UVW covariance coefficient The structure of the CASS 12

13 Process Overviews of CA Main process includes five steps conjunction analysis orbit error analysis collision probability calculation high risk events reconfirm warning report generation. TLEs satellite ephemeris and covariance TLE propagation error Conjunction analysis Orbit error analysis other orbit parameters and covariance satellite precise orbit error other orbit parameters propagation error Collision probability no less than distance threshold or larger than probability threshold yes High risk events reconfirm chaser objects precise orbit and covariance no less than distance threshold or larger than probability threshold yes safety objects Warning report generation Routine process flow for CA 13

14 Process Overviews of CA Conjunction analysis When detecting new TLE data, satellite ephemeris or other orbit parameters located at the default place, CASS starts to run and check the parameters set by CAOM, including start time, end time, warning threshold, running workstation or server. Afterwards, CAA starts and analyzes upcoming conjunction events for the next seven days between China s on-orbit satellites and other space objects. Orbit error analysis and Pc calculation For those conjunction events and chaser objects, OCP starts to calculate the state covariance of target objects and chaser objects at TCA, and output UVW error to CPC for collision probability calculation. High risk events reconfirm If the collision probability and miss-distance are beyond than given thresholds, the acquisition of additional tracking data of the chaser object is put forward, and another high risk events reconfirm will be made with the some process as long as precise chaser objects received. Warning report generation If the assessment of the collision risk is still higher than given threshold, warning report is generated and sent to project manager to make decision for avoidance maneuver. 14

15 Examples of High Risk Analysis YAOGAN 7 with SL-14 Rocket YAOGAN 7(SSN 36110, COSPAR 09069A), launched on 9 Dec 2009 by China, is a satellite operated in low Earth orbit( km 97.9 ). SL-14 R/B(SSN 23659, COSPAR 95046C), launched on 31 Aug 1995 by Russia, is a rocket body remained in low Earth orbit( km 82.5 ). When received message from JSpOC on 12 Jul 2010, YAOGAN 7 ephemeris, tracking data and the precise orbit data of SL-14 R/B was required. The conjunction event was reconfirmed on 11 Jan 2011 by historical TLE data. 15

16 Examples of High Risk Analysis YAOGAN 7 with SL-14 Rocket Based on the historical TLE data There was indeed a high risk conjunction between the two objects at 2010-Jul-12 at 18:31:43(UTC) and an overall miss-distance of 356 meters, a radial of 60 meters and a collision probability of 3.6e-4 at longitude 32,latitude 82. launched on 9 Dec 2009 by China. Both the miss-distance and collision probability were beyond the thresholds. Based on satellite ephemeris and the acquired precise orbit of SL-14 R/B The result changed with the collision probability of 2.9e-6 and of 534m. The miss-distance was still less than 1000m, otherwise, the collision probability was less than threshold of 1:10,000. We pay attention to the conjunction event, but did not plan avoidance maneuver. the historical results of the event calculated by using historical TLE data from 2010-Jul-6 to 2010-Jul-12 16

17 Conclusions Main content of this paper Presents the composition, structure, functions of CASS Introduces the process for the identification and assessment of operational spacecraft high-risk conjunction events. The examples of YAOGAN 7 was used to illustrate process effect with CASS. Further work upgrade the CASS package add collision probability calculation for overtake conjunction add collision confidence assessment finish the test of AMA. 17

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