Searching for space debris elements with the Pi of the Sky system Marcin Sokołowski msok@fuw.edu.pl Soltan Institute for Nuclear Studies ( IPJ ) Warsaw, Poland 7th Integral / BART Workshop ( IBWS), 14-18 April 2010, Karlovy Vary
Outline Space Situational Awareness (SSA) project ( ESA ) Pi of the Sky prototype and new detector Algorithms for automatic identification of optical transients and moving objects Observations of satellites by Pi of the Sky prototype Marcin Sokolowski, IBWS 2010, Karlovy Vary
Is it really so bad? Marcin Sokolowski, IBWS 2010, Karlovy Vary
It becomes a problem... 12 February 2009 crash of two satellites Iridium 33 and Cosmos 2251 over northern Siberia, ~800 km above the Earth with relative speed ~ 11 km/s, producing hundreds of new small and dangerous pieces of junk! COSMOS 2251 I r id iu m I r id iu m 3 3 COSMOS 2251 3 3 Marcin Sokolowski, IBWS 2010, Karlovy Vary
Junk in space must be monitored 13,000 of artificial objects larges than 10cm can be observed in space Only ~800 are active satellites, the rest ( > 12,000 ) are rocket upper stages, dead satellites, other pieces of junk Monitoring of these objects becomes a must! Space Situational Awareness (SSA) program the European project to monitor the Earth orbital population, the space environment and possible threats The first required stage is European Space Surveillance System for : - detection and orbit determination - tracking of objects from low to geostationary orbit - estimation of maneuvers - autonomous operation! GOAL : verify weather Pi of the Sky could be a part of such a system Marcin Sokolowski, IBWS 2010, Karlovy Vary
π of the Sky prototype 2 cameras CCD 2000 2000 pixels Canon objectives f=85mm, d=f /1.2 Common Field of View 20 20 Collects 10s images ( 2s readout time ) Collects ~2000-3000 of images per night Equatorial mount Fully automatic Controlled remotly via the Internet Self diagnostics and fixing minor problems Automatic identification of short optical transients and moving objects
π of the Sky adavantages Automatic and permanent observations with on-line data analysis system Experience of Pi of the Sky team in software development and data analysis Wide field of view (accurate for survey purposes) New generation of system is currently in final preparation and testing stage. Single Detector : It will initially consist of 2 x 12 CCD cameras, covering ~1.5 70mm aperture steradians of the sky field of view of 20 x 20, CCD of 2048 x 2062 pixels Limiting magnitude ~12-13m on single 10s image THE DESIGN OF THE NEW ARRAY Marcin Sokolowski, IBWS 2010, Karlovy Vary
π of the Sky detector paramters D C C H M a t s r i zx e P i x s e i lz e C C T E C e at i dm OR C I ND C D 2 0 4 8 x 2i x 0 4 8 p 1 5 x µ 1m 25 T E 4 4 2 AS C T O T A R 2 s B p 2. 0 e n t s ~ 01 -e > S N 0 8 2 0 2 0 4 8 x 2i x 0 4 8 1 ~ 1 6 - ef o 2r M H z ~ 1 2 - ef o r M 1 H z U I N 1 5 x µ 1m 25 h u t t e r I n t e r f a c e E 3 0 C b e l oe wn v i r o n t m e e a d n o o u i st e S LT OC FD a i r c h i l d o o sl i yn sg t e m R R I P E 1 0c y M c l e s e t h e, r nu es t B 2. 0 SINGLE MOUNT FIELD OF VIEW: FOCAL LENGTH: 85 LCO: 20x20 deg mm NEXT: 20x20 deg (DEEP FOCAL RATIO: 1,2 mode) APERTURE: 70 mm 40x40 deg (WIDE mode deg) TIME OF EXPOSITION:4x20x20 10s ANGLEON/OFF RES.: MOMENT 36 /pix DETERMINATION OF SHUTTER ERROR: 20ms E W
Photmetric and astrometric precision DEVIATIONS FROM MEAN STAR POSITION PHOTOMETRIC PRECISION ASTROMETRIC ACCURACYOF THE ORDER OF 10 arcsec
Identification of optical flashes and moving objects On continuously ( 10s exposure + 2s readout time ) collected images find objects which appeared in the new image and were not present in the set of previous images FIND THE DIFFERENCE
SIMPLE EXAMPLE FLASH / SATELLITE CANDIDATES MOSTLY BACKGROUND, WHICH MUST BE EFFECTIVELY REJECTED COINCIDENCE OF EVENTS FROM 2 CAMERAS Marcin Sokolowski, IBWS 2010, Karlovy Vary
Watchout for the higheway near the Equator Single camera events
Events after coincidence Watchout for the higheway near the Equator
There are moving objects there... In order to identify ( reject them ) we retrieve Two Lines Elements ( TLE ) from the Internet resources and merge to a single large file containing ~13,000 objects OBJECT ID 1st and 2nd Derivative of Mean Motion EPOCH TLE LINE B* DRAG TERM ELEMENT NUMBER INTEGRAL 1 27540U 02048A 09107.12500000.00000129 00000-0 10000-3 0 7946 2 27540 86.7935 3.5152 8337941 265.1073 356.5884 0.33414978 4094 RIGHT ASCENSION OF ASCENDING NODE [deg] ORBIT INCLINATION [deg] ARGUMENT OF PERIGEE [deg] ECCENTRICITY MEAN MOTION [ REVOLUTION /DAY ] MEAN ANOMALY [deg]
Compare OTs with TLE database Looking for nearest satellites in radius of 1800 arcsec Recently changed to 1000 arcsec Marcin Sokolowski, IBWS 2010, Karlovy Vary
Examples of TLE satellites SL12_97028C ANIK_F3_07009A ARIANE_44L_99071B GEOSTATIONARY ( Radius ~ 35790 km ) ATLAS_CENTAUR _R_SL_B_00028B EXPRESS_AM11_04015A
Examples of TLE geostationary satellites GEOSTATIONARY ORBIT R ~ 35789 km DIRECTV_7S_04016A R ~35798 km XM_4(BLUES) R ~35786 km TELSTAR_402R_95049A R ~35802 km Marcin Sokolowski, IBWS 2010, Karlovy Vary
Satellite detection theoretical investigations for Pi of the Sky ASSUMPTION: satellite is a spherical detector structure with 100% reflectance with different radius. 8 1 0 R M A G N IT U D E 1 2 ￛ S A =T 2.0 m R S A =T 1.0 m 1 4 R S A =T 0.5 m 1 6 R S A =T 0.2 5 m R S A =T 0.1 2 5 m 1 8 0 1 A L T [ k 2m ] 3 x 1 40
Identification of tracks from events after coincidence in two cameras 160 tracks Efficiency ~99%
Track fitting details Adding new points to existing tracks only when it is close enough from the fitted line ( Dist2 < 100 ) Velocity check distance from estimated to real position must not be too large ( DistToEstimated < 20 )
Identification of tracks from events from a single camera 40 tracks
Summary Satellites can be observed with the Pi of the Sky detector, preliminary estimate is that we can observed ~1/2 of objects in TLE database It is possible to observe easy targets on geostationary orbit We have algorithms for self-identification of moving objects, track fitting is a very efficient tool ( ~99% ) Pi of the Sky can be for survey tasks and can provide orbit updates for easy targets Precision of orbit fitting is currently being tested, advices are welcome if somebody has experience... Marcin Sokolowski, IBWS 2010, Karlovy Vary
Backup
Preliminary attempts to fit orbits and obtain TLE elements