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RØMER
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Political Boundaries
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Industrial Boundaries
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Financial Boundaries
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Ansøgt beløb detailed design fasen
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Totalt budget RØMER
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Saml. Ørsted
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AAU budget
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AAU budget 2
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AAU budget - 3
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Participants

• Science
• Institute of Physics and Astronomy, Aarhus
  University
• Danish Space Research Institute, Copenhagen
• Copenhagen University
• Technology
• Institute of Electronic Systems, Aalborg
  University
• Ørsted.DTU, Technical University of Denmark,
  Lyngby
• Industry
• TERMA A/S, Lystrup
• Alcatel Space Denmark, Ballerup
• Copenhagen Optical Company, Copenhagen
• Patria Finavitec, Tampere, Finland
• Auspace, Canberra, Australia
• Prime Optics, Eumundi, Australia

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Organization - Organization Chart
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Milestones

• April 1999 Kick-off of Feasibility Study of Rømer
• May 2000 Funding for System Definition Phase
  approved
• May 2000 Kick-off of System Definition Phase
  (SDP)
• Oct. 2000 Mid-Term Review
• Nov. 2000 Decision to eliminate the Ballerina PL
  and re-focus mission
• Nov. 2000 Decision to design Rømer as a
  single-string mission
• April 2001 System Definition Review
• May 2001 Complete Report and Documentation for
  SDP
• June 2001 Start of Detailed Design Phase
• Dec. 2001 Preliminary Design Review
• Dec. 2002 Satellite Critical Design Review
• May 2003 Satellite Integration and Test Review
• May 2004 Launch (tentatively)

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Rømer Overall Schedule
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Rømer Overall Schedule 2
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RØMER SCIENCE OBJECTIVES

• Study the structure, evolution and internal
  dynamics of a sample of stars showing
  stochastically excited, solar-like oscillations.
• This will substantially extend the very
  successful helioseismic studies of the solar
  interior.

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Corresponding Observations (SOHO)

• Note
• Extremely small amplitudes, of order parts per
  million (ppm).
• Blue amplitude much larger than red amplitude.
  Hence also signal in (blue)/(red) ratio, to be
  observed by MONS.
• Background is entirely due to solar granulation.

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Main MONS Observational Requirements

• Photometric precision. Need detection limit below
  1 ppm.
• The instrumental noise must match, but be below,
  the intrinsic stellar granulation noise.
• Requirement on precision demands strong
  defocusing.
• Temporal coverage. Each primary target must be
  observed almost continuously for at least one
  month.
• Sky coverage. Primary targets are distributed
  over the whole sky.
• Hence choose orbit giving access to entire sky
  during the mission.
• Mission duration. At least two years (baseline),
  to allow study of sufficient number of stars.
• Exclusion of variable neighbours. Include MONS
  Field Monitor to detect and correct for faint
  variable stars within telescope field of view.

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RØMER Science Payload Characteristics

• The primary science instruments include
• MONS Telescope having a 32 cm aperture, equipped
  with a high-precision photometric CCD detector
  for measuring oscillations of stellar intensity
  and color
• MONS Field Monitor for examining the field of
  view of the MONS Telescope for faint variable
  stars
• The secondary science instruments
• Forward- and aft-looking Star Trackers of the
  Attitude Control Subsystem, to be used for
  studying variable stars
• The MONS Field Monitor

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Ground Segment Architecture

• One or more Ground Stations
• A Control Center which shall have total control
  of the mission and shall provide data processing,
  storage and display
• A Science Data Center which shall prepare the
  specified user data products and disseminate them
  to the involved research institutes and
  organizations

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Orbit Requirements

• Maximize time outside the trapped proton
  radiation belts
• Allow momentum unloading using only magnetorquers
• The operational orbit shall be delivered by the
  upper stage of the launch vehicle.
• Visibility from a ground station in Denmark
• Frequent launch opportunities to the proposed
  orbit (?1 per year)

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RØMER in Molniya Orbit

• Largest separation from Earth (Apogee) 40000 km
• Smallest separation from Earth (Perigee) 600 km
• Angle between orbit and Equator (Inclination)
  63.4
• Period 11 hours 58 min. 02 sec. ( ½ siderial
  day, ideal)
• 10 hours of observations outside the radiation
  belts.
• A satellite in Molniya orbit is subjected to a
  large dose of radiation from high-energy protons
  and electrons trapped in the Earths radiation
  belts.

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SOYUZ/FREGAT Launcher
FREGAT Upper Stage
FREGAT with Cluster II Satellites
RØMER is foreseen to be launched with a Russian
SOYUZ/FREGAT rocket in mid 2004 from Plesetsk
Cosmodrome The SOYUZ rocket has been launched
more than 1650 times and its reliability exceeds
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Launch Configuration
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Satellite Specification

• Configuration, Mass and Envelope, Orbit
• Nominal sun facing diagonal X,-Y
• Solar panels on X and -Y
• Single payload, MONS
• Main telescope, FOV in Z
• Field monitor, FOV in Z
• Radiators on -X and/or Y
• Communication antennas on the exterior of the
  satellite, X, Y
• Launch Vehicle I/F on -Z
• Mass lt120kg, Envelope 600x600x710mm
• Orbit baseline Molniya

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Structure, Mechanism and Thermal Requirements

• Accommodation of payload and platform subsystems
• Accommodation of various CCD radiators (cold
  faces)
• Accommodation of solar panels (hot faces)
  assuring optimal power input
• Accommodation of battery assembly (with easy
  access)
• Accommodation of COM antennas assuring 4p
  coverage
• Accommodation of the PAA
• Platform and payload electronics shall be
  enclosed in a common structure
• Fundamental lateral/longitudinal frequency
  requirements gt45Hz /gt90Hz

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CDH requirements

• The CDH on-board computer shall act as satellite
  brain
• Task requirements
• CDH
• ACS
• Star Tracker handling
• Parallel Star Tracker science if possible
• Packet Utilisation Standard
• SW patching and dumping
• Power safe mode
• Command loss timer
• HW/SW watchdogs

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Autonomous Control (requirements)

• MONS observation Þ three axis control
• Modes
• Fine pointing (science observation)
• Coarse pointing (target slew)
• Momentum unloading
• Safe mode (startup, sun acquisition)
• Sensors
• Primary Star Tracker (2), Rate sensors (4)
• Secondary Sun sensors (4p steradian),
  Magnetometer (3 axis)
• Actuators
• Reaction wheels (4)
• Torquer coils (3)
• Fault detection and management (SW)

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Platform network structure
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Design Philosophy

• Model philosophy
• EBB (subsystem level)
• E(Q)M (subsystem level)
• STM (subsystem and satellite level)
• RF model (satellite level)
• FM (subsystem level)
• FS (subsystem level, optional)
• Proto-flight satellite
• Satellite simulator (EM setup)
• Cleanliness TBD
• Satellite magnetic stray field lt1Am2

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Structure

• Solar panels
• Star tracker
• Radiator
• S-band antenna
• Sun sensors
• Radiator for the MONS telescope
• The MONS telescope
• Field Monitor
• Sunlight protecting lid (closed during launch)

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Key Specification

• Mass 80 kg, 100kg incl. 25 Margin.
• Size 60 x 60 x 71cm in Launch Configuration
• S/C Power 70 W avg.
• Battery 33V, 4.5Ah, Li-ion
• Mission Life Time 2 years

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Attitude Control Precision

• Attitude movements have a dramatic effect on
  photometric precision, due to small spatial
  variations in CCD sensitivity (pixel-to-pixel and
  sub-pixel).
• Need to design the instrument, telescope and
  platform carefully.
• Detailed computer simulations include
• effects of flat-field structure
• ACS jitter and shape of telescope PSF (including
  off-axis aberrations).
• readout and photon noise.
• Results photometric errors from ACS errors form
  a non-white noise source whose power spectrum has
  the same shape as the ACS errors themselves.

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Required ACS power spectrum

• Assumed flat at frequencies below 10 mHz (should
  be true if the control loop is operating
  correctly).
• Assume power spectrum falls off as frequency
  squared (i.e., as 1/f in amplitude), as seems
  likely. The spectrum can then level out at
  frequencies higher than 10 Hz.
• If ACS power spectrum shape is significantly
  different then further simulations will be needed
  to specify new requirements.
• Preliminary study by the Rømer ACS group shows
  feasibility of reaching 1.2 arcmin RMS

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Required ACS precision
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ACS Requirements What is the ACS Supposed to do?

• Stabilise Satellite from tumbling situation (2
  deg/ sec)
• Stop the tumbling and,
• Perform Sun Acquisition Maneuver
• Provide a three axis stabilised attitude for
  commanded attitudes
• Orient to desired attitude and keep it fixed
  (coarse)
• Provide a stable platform for science
  observations
• Requirements to attitude error spectrum
• Provide sufficient onboard autonomy to handle
  fault events related to ACS
• Handle one fault to prevent loss of mission
• Environment
• Molniya Orbit

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ACS Requirements
95 confidence numbers Pointing Error - P/ Y 2
arcmin - R 60 arcmin RMS Stability Error - 1.2
arcmin Slew Capacity - 180 deg in 10 minutes Sun
Exclusion - 60 degrees - max 30 seconds with Sun
lt3 deg from MONS boresight Earth/ Moon
Exclusion - 55 degrees
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Hardware Config and concept diagram
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Disturbance Environment
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Rømer Overall ACS Architecture
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Attitude Estimator Concept DesignSingle axis
analysis

• Optimal estimator update both the spacecraft
  attitude and the gyro drift rate. Kinematic gyro
  based prediction.

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Attitude Estimator Concept DesignSingle axis
analysis - 2

• Attitude and attitude rate from dynamic model of
  the spacecrafts angular motion. (uncertainty due
  to RWA etc.). Gyro data are observations.

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AD Structure
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ACS concept diagram
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AD modes
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AC modes
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ACS Workpackage breakdown
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3621
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3622
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3624
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3625
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3640
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3650
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Development Schedule
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Development Philosophy
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