Image of the Week

Dynamical Attitude Model

 

The Dynamical Attitude Model (DAM) is a simulation software developed to achieve a detailed understanding of the Gaia attitude. Its main characteristic is that it takes into account at the same time physical effects and internal hardware components controlling the satellite. This attitude will be used as input for the Gaia data simulations by CU2.

By "attitude" we mean the orientation of the satellite and its rotation state. The attitude is characterised by a 7-component array which is recorded for time-step (1 second). This array is composed of:

  • A quaternion that defines the rotation of the Scanning Reference System (SRS, attached to the spacecraft) with respect to the ICRS. Quaternions are 4-dimensional normalised vectors, a generalisation of the complex numbers very convenient for specifying rotations.
  • A 3-dimensional vector that defines the spacecraft angular rate in the SRS.

Currently the model implements the following effects:

  • A copy of the on-board AOCS (Attitude and Orbit Control System) algorithms.
  • Thruster performance.
  • Torque due to the solar radiation pressure on the Deployable Solar Array.
  • Thermal infra-red emission from the surface of Gaia.
  • Impact of micro-meteoroids.
  • Clanks (discontinuities in the attitude).

All these effects can be modified by means of changing some input parameters, for instance thruster capabilities or micro-meteoroid characteristics. And since the code is very modular, more disturbances could be implemented in the future. The simulation considers the satellite to be a rigid body, for which the motions are described by the Euler equation. It takes about 1 week of computing time to simulate 5 years of spacecraft attitude.

These plots show 6h of spacecraft attitude. This simulation includes a micro-meteoroid impact that produces a spike in these plots at about t=15500 seconds.

  • Top left: angular distance between the actual attitude and the demanded one. Deviations from nominal values are well within the requirement limits except for when there is a hit. It must be lower than 60 arcsec during 99.73% of the time.
  • Top right: angular rate error. It is the difference between the actual rate and the demanded rate. Attitude requirements impose that it must be lower than 2 mas/s (AL) and 10 mas/s (AC) during 99.73% of the time.
  • Bottom left: scan phase (angular position of the Sun in the XY plane of the SRS), scan phase derivative, and solar aspect (angular distance to the Z(SRS) axis, always close to 45 degrees).
  • Bottom right: this plot shows how thrusters are commanded in order to counteract disturbances. The vertical axis is measured in LSB. 1 LSB (Least Significant Bit) is equivalent to 0.1 µN, and thrusters are commanded in units of 10 LSB. Thrusters are installed in opposite pairs: thrusters 1 and 3 control mainly the X(SRS) axis, thrusters 2 and 4 control mainly the Y(SRS) axis, and thrusters 5 and 6 control the Z(SRS) axis. Note that no more than three thrusters are active at the same time, opposite thruster pairs never work at the same time (because it would be inefficient), and thrusters 5 and 6 are always commanded with very little force because the torque due to the solar radiation pressure is small in the Z(SRS) axis.

For more information, please refer to:

This work is being developed by Daniel Risquez and Anthony Brown (both from Leiden Observatory), Floor van Leeuwen (IoA) and Ralf Keil (ZARM).

[Published: 13/07/2011]

 

Image of the Week Archive

2017
19/10: Hertzsprung-russell diagram using Gaia DR1
05/10: Updated prediction to the Triton occultation campaign
31/08: Close stellar encounters from the first Gaia data release
16/08: Preliminary view of the Gaia sky in colour
07/07: Chariklo stellar occultation follow-up
24/04: Gaia reveals the composition of asteroids
20/04: Extra-galactic observations with Gaia
10/04: How faint are the faintest Gaia stars?
24/03: Pulsating stars to study Galactic structures
09/02: Known exoplanetary transits in Gaia data
31/01: Successful second DPAC Consortium Meeting
2016
23/12: Interactive and statistical visualisation of Gaia DR1 with vaex
16/12: Standard uncertainties for the photometric data (in GDR1)
25/11: Signature of the rotation of the galactic bar uncovered
15/11: Successful first DR1 Workshop
27/10: Microlensing Follow-Up
21/10: Asteroid Occultation
16/09: First DR1 results
14/09: Pluto Stellar Occultation
15/06: Happy Birthday, DPAC!
10/06: 1000th run of the Initial Data Treatment system
04/05: Complementing Gaia observations of the densest sky regions
22/04: A window to Gaia - the focal plane
05/04: Hipparcos interactive data access tool
24/03: Gaia spots a sunspot
29/02: Gaia sees exploding stars next door
11/02: A new heart for the Gaia Object Generator
04/02: Searching for solar siblings with Gaia
28/01: Globular cluster colour-magnitude diagrams
21/01: Gaia resolving power estimated with Pluto and Charon
12/01: 100th First-Look Weekly Report
06/01: Gaia intersects a Perseid meteoroid
2015
18/12: Tales of two clusters retold by Gaia
11/11: Lunar transit temperature plots
06/11: Gaia's sensors scan a lunar transit
03/11: Celebrity comet spotted among Gaia's stars
09/10: The SB2 stars as seen by Gaia's RVS
02/10: The colour of Gaia's eyes
24/09: Estimating distances from parallaxes
18/09: Gaia orbit reconstruction
31/07: Asteroids all around
17/07: Gaia satellite and amateur astronomers spot one in a billion star
03/07: Counting stars with Gaia
01/07: Avionics Model test bench arrives at ESOC
28/05: Short period/faint magnitude Cepheids in the Large Magellanic Cloud
19/05: Visualising Gaia Photometric Science Alerts
09/04: Gaia honours Einstein by observing his cross
02/04: 1 April - First Look Scientists play practical joke
05/03: RR Lyrae stars in the Large Magellanic Cloud as seen by Gaia
26/02: First Gaia BP/RP deblended spectra
19/02: 13 months of GBOT Gaia observations
12/02: Added Value Interface Portal for Gaia
04/02: Gaia's potential for the discovery of circumbinary planets
26/01: DIBs in three hot stars as seen by Gaia's RVS
15/01: The Tycho-Gaia Astrometric Solution
06/01: Close encounters of the stellar kind
2014
12/12: Gaia detects microlensing event
05/12: Cat's Eye Nebula as seen by Gaia
01/12: BFOSC observation of Gaia at L2
24/11: Gaia spectra of six stars
13/11: Omega Centauri as seen by Gaia
02/10: RVS Data Processing
12/09: Gaia discovers first supernova
04/08: Gaia flag arrives at ESAC
29/07: Gaia handover
15/07: Eclipsing binaries
03/07: Asteroids at the "photo finish"
19/06: Calibration image III - Messier 51
05/06: First Gaia BP/RP and RVS spectra
02/06: Sky coverage of Gaia during commissioning
03/04: Gaia source detection
21/02: Sky-background false detections in the sky mapper
14/02: Gaia calibration images II
06/02: Gaia calibration image I
28/01: Gaia telescope light path
17/01: First star shines for Gaia
14/01: Radiation Campaign #4
06/01: Asteroid detection by Gaia
2013
17/12: Gaia in the gantry
12/12: The sky in G magnitude
05/12: Pre-launch release of spectrophotometric standard stars
28/11: From one to one billion pixels
21/11: The Hipparcos all-sky map
15/10: Gaia Sunshield Deployment Test
08/10: Initial Gaia Source List
17/09: CU1 Operations Workshop
11/09: Apsis
26/08: Gaia arrival in French Guiana
20/08: Gaia cartoons
11/07: Model Soyuz Fregat video
01/07: Acoustic Testing
21/06: SOVT
03/06: CU4 meeting #15
04/04: DPCC (CNES) 
26/03: Gaia artist impression 
11/02: Gaia payload testing  
04/01: Space flyby with Gaia-like data
2012
10/12: DPAC OR#2. Testing with Planck
05/11: Galaxy detection with Gaia
09/10: Plot of part of the GUMS-10 catalogue
23/07: "Gaia" meets at Gaia
29/06: The Sky as seen by Gaia
31/05: Panorama of BAM clean room
29/03: GREAT school results
12/03: Scanning-law movie
21/02: Astrometric microlensing and Gaia
03/02: BAM with PMTS
12/01: FPA with all the CCDs and WFSs
2011
14/12: Deployable sunshield
10/11: Earth Trojan search
21/10: First Soyuz liftoff from the French Guiana
20/09: Fast 2D image reconstruction algorithm
05/09: RVS OMA
10/08: 3D distribution of the Gaia catalogue
13/07: Dynamical Attitude Model
22/06: Gaia's view of open clusters
27/05: Accuracy of the stellar transverse velocity
13/05: Vibration test of BAM mirrors
18/04: L. Lindegren, Dr. Honoris Causa of the Observatory of Paris
19/01: Detectability of stars close to Jupiter
05/01: Delivery of the WFS flight models
2010
21/12: The 100th member of CU3
17/11: Nano-JASMINE and AGIS
27/10: Eclipsing binary light curves fitted with DPAC code
13/10: Gaia broad band photometry
28/09: Measuring stellar parameters and interstellar extinction
14/09: M1 mirror
 
Please note: Entries from the period 2003-2010 are available in this PDF document.