Gaia First Look: Description and Status Report. The Three Dimensional Universe with GAIA Paris-Meudon, October 4-7, 2004. - PowerPoint PPT Presentation
The Three Dimensional Universe with GAIA The Three Dimensional Universe with GAIA Paris-Meudon, October 4-7, 2004 Paris-Meudon, October 4-7, 2004 Gaia First Look: Gaia First Look: Description and Status Description and Status Report Report Stefan Jordan, Uli Bastian, Helmut Lenhardt, Hans Stefan Jordan, Uli Bastian, Helmut Lenhardt, Hans Bernstein, Sonja Hirte (Astronomisches Rechen- Bernstein, Sonja Hirte (Astronomisches Rechen- Institut, Heidelberg) & Michael Institut, Heidelberg) & Michael Biermann (Landessternwarte, Heidelberg Biermann (Landessternwarte, Heidelberg ) ) Acknowledgement: Acknowledgement: - GIS routines by Lennart Lindegren (LL-37) - GIS routines by Lennart Lindegren (LL-37) - simulation data from Barcelona group (Eduard - simulation data from Barcelona group (Eduard Masana et al.) Masana et al.)
Transcript
The Three Dimensional Universe with GAIAThe Three Dimensional Universe with GAIAParis-Meudon, October 4-7, 2004Paris-Meudon, October 4-7, 2004
Gaia First Look:Gaia First Look:Description and Status ReportDescription and Status Report
Stefan Jordan, Uli Bastian, Helmut Lenhardt, Hans Bernstein, Stefan Jordan, Uli Bastian, Helmut Lenhardt, Hans Bernstein, Sonja Hirte (Astronomisches Rechen-Institut, Heidelberg) Sonja Hirte (Astronomisches Rechen-Institut, Heidelberg)
& Michael Biermann (Landessternwarte, Heidelberg& Michael Biermann (Landessternwarte, Heidelberg))
Acknowledgement:Acknowledgement:- GIS routines by Lennart Lindegren (LL-37)- GIS routines by Lennart Lindegren (LL-37)- simulation data from Barcelona group (Eduard Masana et al.)- simulation data from Barcelona group (Eduard Masana et al.)
GST13, ESTEC, 2004-09-13 2First Look, Status Report
Often heard here:Often heard here:
• GAIA is a self calibrating instrumentGAIA is a self calibrating instrument
GST13, ESTEC, 2004-09-13 3First Look, Status Report
Often heard here:Often heard here:
• GAIA is a self calibrating instrumentGAIA is a self calibrating instrument• This is true ….This is true ….
GST13, ESTEC, 2004-09-13 4First Look, Status Report
Often heard here:Often heard here:
• GAIA is a self calibrating instrumentGAIA is a self calibrating instrument• This is true ….This is true ….• However, GIS possible only after 6 months However, GIS possible only after 6 months
GST13, ESTEC, 2004-09-13 5First Look, Status Report
Often heard here:Often heard here:
• GAIA is a self calibrating instrumentGAIA is a self calibrating instrument• This is true ….This is true ….• However, GIS possible only after However, GIS possible only after 6 months6 months• Gaia can only solve for Gaia can only solve for calibrationcalibration, , attitudeattitude
and and source parameterssource parameters simultaneouslysimultaneously..
GST13, ESTEC, 2004-09-13 6First Look, Status Report
The basic problemThe basic problem
• It is difficult to immediately assess proper It is difficult to immediately assess proper functioning of all elements functioning of all elements (on the (on the μμas level)as level)
• But But very importantvery important, else risk of losing , else risk of losing many months of data and mission time.many months of data and mission time.
Some compromise must be foundSome compromise must be found
GST13, ESTEC, 2004-09-13 7First Look, Status Report
GST13, ESTEC, 2004-09-13 9First Look, Status Report
Two basic ways of attackTwo basic ways of attack
1.1. Some reduced variant of GIS, now named Some reduced variant of GIS, now named „ODIS“, One-Day Iterative Solution„ODIS“, One-Day Iterative Solution
2.2. Direct solution of the full problem of the 1-day Direct solution of the full problem of the 1-day astrometric reduction, named „astrometric reduction, named „Ring SolutionRing Solution“ “
being performed in parallelbeing performed in parallel
Note: Neither way can produce a full astrometric Note: Neither way can produce a full astrometric solution. solution.
GST13, ESTEC, 2004-09-13 10First Look, Status Report
ODIS versus Ring SolutionODIS versus Ring Solution
• Ring SolutionRing Solution::
- allows to easily and clearly detect and remove the degeneracies- allows to easily and clearly detect and remove the degeneracies- can in principle produce full covariances- can in principle produce full covariances- may be much more demanding in terms of storage and computing- may be much more demanding in terms of storage and computing
• ODISODIS::- a block-iterative scheme does not necessarily show its degeneracies- a block-iterative scheme does not necessarily show its degeneracies- a block-iterative scheme does not necessarily converge- a block-iterative scheme does not necessarily converge- the degeneracies are not easily pinned down- the degeneracies are not easily pinned down
GST13, ESTEC, 2004-09-13 11First Look, Status Report
First-Look Preprocessing using Ring First-Look Preprocessing using Ring Solution:Solution:
Direct elimination of source unknownsDirect elimination of source unknownsSources Attitude Cal.
6 000 000
6 000
900
0
0
x x
f u l l
GST13, ESTEC, 2004-09-13 12First Look, Status Report
ODIS versus Ring SolutionODIS versus Ring Solution
• Ring SolutionRing Solution::
- allows to easily and clearly detect and remove the degeneracies- allows to easily and clearly detect and remove the degeneracies- can in principle produce full covariances- can in principle produce full covariances- may be much more demanding in terms of storage and computing- may be much more demanding in terms of storage and computing
• ODISODIS::
- a block-iterative scheme does not necessarily show its degeneracies- a block-iterative scheme does not necessarily show its degeneracies- a block-iterative scheme does not necessarily converge- a block-iterative scheme does not necessarily converge
GST13, ESTEC, 2004-09-13 13First Look, Status Report
Initial estimates for 24 hours of data, using (various) present-day Initial estimates for 24 hours of data, using (various) present-day 2 GHz Pentium III (4 GByte memory) PCs2 GHz Pentium III (4 GByte memory) PCs
•About About 5 GByte5 GByte of observed data of observed data•→→50 million parameters50 million parameters (attitude, calibration (attitude, calibration parameters, source parameters, parameters, source parameters, global parametersglobal parameters))•Computing time (extrapolated to 50 million elementary observations) without data base overhead:•Ring solution: 1600 hours•ODIS: 40 hoursAt time of GAIA: faster computersParallelization possible!
Data volume, computing timeData volume, computing time
GST13, ESTEC, 2004-09-13 14First Look, Status Report
Lessons already learnedLessons already learned
• Either FLP method (ODIS or ring solution) needs a Either FLP method (ODIS or ring solution) needs a „zeroth“ iteration„zeroth“ iteration to identify the degenerate dimensions to identify the degenerate dimensions
• Either FLP method can conveniently useEither FLP method can conveniently use quaternions quaternions in in the RGC system for the attitude representation the RGC system for the attitude representation (GAIA-SJ-002)(GAIA-SJ-002)
• Convergence behaviourConvergence behaviour of ODIS depends on block of ODIS depends on block sequence, on block size, on block composition, .....sequence, on block size, on block composition, .....We‘ll use more than 4 blocks (split AL/AC), and omit the We‘ll use more than 4 blocks (split AL/AC), and omit the ‚global‘ block (GAIA-SJ-001)‚global‘ block (GAIA-SJ-001)
• In smaller test runs: distribution of observations over time In smaller test runs: distribution of observations over time interval very important interval very important
GST13, ESTEC, 2004-09-13 15First Look, Status Report
• No across-scan instrument calibration possible within a No across-scan instrument calibration possible within a short amount of timeshort amount of time
• →→Commissioning and initial in-orbit calibration would Commissioning and initial in-orbit calibration would greatly benefit from a greatly benefit from a „zero-nu-dot“„zero-nu-dot“ scanning mode (i.e. scanning mode (i.e. scan axis remaining on the ecliptic, at 50 degrees from scan axis remaining on the ecliptic, at 50 degrees from the sun)the sun)
GST13, ESTEC, 2004-09-13 31First Look, Status Report
““Zero-nu-dot mode”Zero-nu-dot mode”Coverage of the ecliptic pole areaCoverage of the ecliptic pole area
Note: z-axis of the satellite points toward the top (on Note: z-axis of the satellite points toward the top (on day 1); sun is either 50º to the right or 50º to the left day 1); sun is either 50º to the right or 50º to the left
of it.of it.
about 8000 starsabout 8000 stars
GST13, ESTEC, 2004-09-13 32First Look, Status Report
• Commissioning and initial in-orbit calibration would greatly Commissioning and initial in-orbit calibration would greatly benefit from a benefit from a „zero-nu-dot“„zero-nu-dot“ scanning mode (i.e. scan axis scanning mode (i.e. scan axis remaining on the ecliptic, at 50 degrees from the sun)remaining on the ecliptic, at 50 degrees from the sun)
• This will provide us with a first calibration also across-scanThis will provide us with a first calibration also across-scan• Needed: Needed: Pre-GAIA astrometric observationsPre-GAIA astrometric observations of some 8000 of some 8000
stars around the ecliptic polesstars around the ecliptic poles
GST13, ESTEC, 2004-09-13 33First Look, Status Report
• Commissioning and calibration would greatly benefit from Commissioning and calibration would greatly benefit from an „an „AC calibrationAC calibration“ CCD sampling mode (i.e. strongly “ CCD sampling mode (i.e. strongly reduced across-scan binning in AF; in practical terms this reduced across-scan binning in AF; in practical terms this can be implemented by temporarily using the WY00 can be implemented by temporarily using the WY00 windows over a larger magnitude range)windows over a larger magnitude range)
GST13, ESTEC, 2004-09-13 34First Look, Status Report
First-Look Preprocessing using ODIS:First-Look Preprocessing using ODIS:Preliminary conceptPreliminary concept
• First, produce a global solution for the First, produce a global solution for the along-RGC unknownsalong-RGC unknowns only, already omitting those stars with only 1 FoV transit. only, already omitting those stars with only 1 FoV transit.• In this process, collect the In this process, collect the list of actual scan directionslist of actual scan directions for for each star each star• For those stars with sufficiently differing scan directions,For those stars with sufficiently differing scan directions, solve solve across-scan coordinatesacross-scan coordinates in subsequent solutions. in subsequent solutions. • For all across-scan attitude unknowns collect the number For all across-scan attitude unknowns collect the number of stars with across-scan solutions contributing to them. of stars with across-scan solutions contributing to them.• For those across-scan attitude unknowns with sufficiently For those across-scan attitude unknowns with sufficiently many such stars contributing, make a first solution. many such stars contributing, make a first solution.• In all further iterations, omit or „Huber away“ discordantIn all further iterations, omit or „Huber away“ discordant observations, using all unknowns selected before. observations, using all unknowns selected before.
• After first GIS: the first+last of these steps suffice (probably)After first GIS: the first+last of these steps suffice (probably)
GST13, ESTEC, 2004-09-13 35First Look, Status Report
The first look task is The first look task is not a closed not a closed
session session – – collaboration is collaboration is
