The Terrestrial Planet Finder Coronagraph

1
The Terrestrial Planet Finder Coronagraph

• Stuart Shaklan
• TPF Coronagraph Architect
• Jet Propulsion Laboratory,
• California Institute of Technology
• July 23, 2004

2
Overview

• History
• Science Requirements
• Trade Studies
• How aggressive to make the coronagraph?
• Baseline Mission Design
• Telescope
• Thermal Control System
• Coronagraph Instrument
• Technology Development
• and into the future

3
A Brief History of the Project

• 2000-2002 Industry/University teams conducted
  feasibility study
• Concluded that with suitable technology
  investment starting now, a mission to detect
  terrestrial planets around nearby stars could be
  launched by the middle of the next decade
  (20102020).
• Summary report available at http//planetquest.jp
  l.nasa.gov/TPF/TPFrevue/FinlReps/JPL/tpfrpt1a.pdf
• In mid-2002, JPL set up Interferometer and
  Coronagraph pre-project teams
• Working toward a mission selection in 2006
• Science Working Group chartered in October 2002
• Spring 2004 NASA decided to fly a visible
  coronagraph first, followed by an IR
  interferometer.
• We are now working toward Phase A project
  status.
• JPL is the project lead.
• Goddard will build the telescope.

• Ball Aerospace 2000-2002 Pre-Phase A Final
  Architecture Review Concept
• Shaped pupil coronagraph
• Off-axis unobscured system
• 4x10m elliptical off-axis monolithic primary
  mirror
• High density deformable mirror for wave front
  correction
• l 0.5-1.7 µm
• 1 AU orbit (L2 or Earth-trailing)

4
TPF Science Requirements

• The minimum TPF must be able to detect planets
  with half the area of the Earth, and the Earths
  geometric albedo or the equivalent equilibrium
  effective temperature, searching the entire HZ of
  the 35 core-group stars with 90 completeness per
  star.
• HZ Habitable Zone 0.7 1.5 AU scaling as
  sqrt(luminosity)
• Flux ratios must be measured in 3 broad
  wavelength bands, to 10 accuracy, for at least
  50 of the detected terrestrial planets.
• The spectrum must be measured for at least 50 of
  the detected terrestrial planets to give the
  equivalent widths of O2, H2O, and O3 in the
  visible or H2O, and O3 in the infrared to an
  accuracy of 20 we desire to detect CO2 and CH4
  as well.

5
Distances, IHZ of 50 best targets
These are the 50 nearby stars that offer the best
completeness after 9 observations over 3 years.
6
Aperture Size
7
Telescope Architecture Trades
8
Baseline Mission Parameter Summary

• Aperture 6x3.5 m off-axis Cassegrain
• IWA 3 lambda/D
• DM 96 x 96 actuators
• Bandpass 500-600 nm (detection), 500-800 nm
  (spectroscopy)
• Mask 1-D linear 1-sinc2 mask (others work as
  well)
• SNR 4 per observation (photon-statistics
  limited)
• Solar Zodi V22.7 per sq. arcsec.
• Exo Zodi 2x brighter than Solar Zodi (and
  double pass for 4x total )
• Total integration time 1 year for detection
  (not including overhead)
• Total program length 3 years for detection
• 50 targets
• 9 visits per target over 3 years
• Each visit requires 3 Line-of-sight roll
  positions (two 60 degree steps)
• Photometric sensitivity delta magnitude 25

9
Sensitivity to Low Order Aberrations
Radial Cosine (s 4 l/D) Evaluated at 3 l/D

• 2nd Order Dependence
• Focus, Coma, Spherical
• 4th Order Dependence
• Tilt, Astigmatism, Trefoil
• Other occulters exhibit different dependencies
• (e.g.) Visible Nuller
• 4th order focus sensitivity

Calculated using Fourier Plane mathematics and
small wave front perturbations in a pupil plane.
These calculations form the
Zernike C-matrix
Zernike Sensitivity coefficients appear in
worksheets Rsinc28ar, lcos4ar, rcos4ar.
Green and Shaklan, SPIE 2003
10
Shaped Pupil Aberration Sensitivity
Green and Shaklan, SPIE 2004
11
Coronagraph Forms
12
TPF Architecture Coronagraph Description
Collimator Mirror
M1
TPF-Coronagraph Payload
Polarizer, WFSC, Coronagraph, Spectrometer
M3
M2
13
Configuration Schematic

• Science Payload
• Telescope
• Coronagraph System
• Instruments

Spacecraft System
14
Sy
System Block Diagram
Telescope
6DOF Hexapod
Acquisition Camera
Coronagraph Detectors
Coronagraph Optics
Corner Cube
Secondary Mirror
P Pol
Redundant Instrument
Dispersing Prism
Spectrometer
-100C
Pupil Mask
Occulting Mask
Lyot Stop
Amplitude Phase Wavefront Correcting
Deformable Mirrors
Polarizing Beam Splitter
S Pol
-100C
Planet Detection
Primary Mirror
Insertable Pickoff Mirror
Focussing Mirror
Fast Steering Mirror
Coronagraph Thermal Radiators
Laser Metrology
Fine Guidance Camera
Fold Mirror
Coronagraph Electronics
Deformable Mirror Control
Detector Control
Power
Optical Actuator Control
Metrology
Acquisition Camera
Instrument Computer
Thermal Control
0C












Dynamic/Thermal Isolation
Spacecraft Loads
Spacecraft
Sun Shade
Thermal Control
3 Axis Gyros
Power
Launch Support Structure
Launch Vehicle
Attitude Control Sensors
LV Adapter
Visco-elastically Damped booms
Power Distribution
Pyro
Star Tracker
Spacecraft Computer
Solar Arrays
Analog Sun Sensors
Power Conditioning
Batteries
Key
Optical Path
Propulsion
Electrical Interface
Propulsion Driver Electronics
X Panel
Transponder
LGA Receive
N2H4
N2H4
RF Path
3dB Coupler
HGA
Fill
Drain
Drain
LGA Transmit
Propellant Line
Hi/Lo
Attitude Control Actuators
Pressure Transducers
Filter
Thermal Path
P
Solar Sail
Amplifier (50W)
1 axis actuator
P
P
X/-X
LGA Receive
-X Panel
Branch B
Branch A
HGA
2 axis actuator
20 lbf Thrusters
LGA Transmit
Hi/Lo
Telecom
Patch Antenna
15
Systems Summary

• Mission Overview
• 2014 Launch Date
• Earth Drift-Away orbit (ala SIRTF)
• 0.1AU/yr average earth separation rate
• No cruise phase to operating orbit
• Delta-IVH launch vehicle with 5m x 19m fairing
• 10,000 kg lift capacity to C3 of 0.4
• 5 year primary mission duration with consumables
  for 10 years
• 6 month post-launch checkout and calibration
• Planet search phase spans 3 years
• X-Band communications to 34m DSN
• Continuous link capability Hi Rate science
  downlink concurrent with data collection
• Capability to downlink 3 days of stored data
  (2Gb per day) in 1 8hr pass
• Systems Overview
• Power 3,000W solar array
• Propulsion 100kg Hydrazine in Blow-Down Mode
• No ?V required
• Provide safe sun point and some momentum
  management (solar sail is prime)
• Attitude Control 3 axis stabilized

16
Minimum Mission Configuration
Secondary Mirror
X
Z
10m
Primary Mirror
6m
Back end coronagraph optics
10m
Y
Optical Bench
Tertiary mirror surface
Z
3.5m
17
Telescope and Secondary Mirror Assemblies
Secondary Bracket
Thermal Enclosure
Actuated hexapod
Acquisition Camera
Secondary Mirror
Deployed secondary tower
Primary mirror (6m x 3.5m)
Cross section of deployed V-groove layers
Deployed HGA
Dynamic isolation (3 pl)
Reaction wheels (6)
V-groove deployment boom
Spacecraft bus
Spacecraft equipment support panel
Spacecraft equipment support panel
Deployed solar array
Thruster cluster (2 pl)
Primary mirror thermal enclosure (coronagraph
sensor and spectrograph inside)
Deployed v-groove platform
Propulsion tank (2 pl)
18
Laser Truss for TPF Coronagraph
Beam Launcher
Fiber Optics (2)
Power, signal
Corner cube
Six metrology beams form an optical truss with
0.3 nm resolution. In addition to the identified
components, a stabilized NPRO laser
(wavelength1.3 um), a heterodyne frequency
modulation system, and fiber distribution system
are used. The laser and modulation system feed
the beam launchers from a remote location on the
s/c. Corner cubes must be attached around the
perimeter of the optics so as not to obscure the
beam. They are required to maintain sub-nm
piston (normal to optical surfaces) stability
during observations. For short design, we get
factor of 2 more precision with 1.6x more precise
metrology.
19
Metrology System Configuration
Corner Cube with vertex removed
Beam Launchers
Isothermal Cavity
20
Stowed Mechanical Configuration

• Stowed Configuration in Delta IV-H (19.8m govt
  standard)

1.448m dia
Top View
5.08m (OD)
16.484m
19.814m
12.192m
4.57m (ID)
Launch support cylinder closed on both ends to
control contamination on primary mirror
21
Deployment
22
Thermal Control Concept - Cocoon

• V-Groove Radiator Cocoon
• Sunshine heats one side of radiator outer
  v-groove shield heats emits IR light
• Shiny surfaces reflect IR light outward into space

• Cocoon Advantages
• Fully blocks sun light, earth or moon shine from
  telescope baffle at near 90º angle
• Isolates baffle by keeping heat from sun in outer
  layers
• Deploys in same direction as telescope baffle

23
Minimum Mission Thermal Modeling
Telescope Steady-State Temperature for Two 20 deg
Dither Cases (80 to 100 170 to 190)
Temperature (C) Distribution for all Sun Angles
(variationsltmC)
Delta Temperature (C) for Dither from 80 to 100
deg
Delta Temperature (C) for Dither from 170 to 190
deg
19.0C
0.041C
0.0014C
-0.0032C
-142C
-0.035C
24
Thermal Modeling Continued
25
Dynamic Results 2 stage passive isolation
Rigid Optics Wavefront Error Design meets
requirements passively
Flexible Primary Wavefront ErrorMode 8
exceedance can be avoided by running wheels above
4hz
26
Top 14 Contrast Contibutors
Major contrast contributor in the Error Budget.
The numbers shown do not include reserve factors.
0.09 mas 1-sigma per axis
0.8 mas 1-sigma per axis
dL 217 pm 1-sigma
Z4 Z8 Z12
df/f 2.95e-11 1 sigma
Z42.28 pm 3-sigma
Z120.3 pm 3-sigma
Z41.4 pm 3-sigma
Z80.57 pm 3-sigma
27
Integral Field Unit
Spectrograph
Collimator Optics
Lenslet Array
Cold Pupil
AO Focus
Grating
Filters
Pupil Plane
R.I. Camera Singlet
Camera Optics
R. I. Collimating Singlet
Focal Plane
Lenslet
Detector
Reimaging Optics
Slide from J. Larkin, presented at TPF-C
Technical Interchange Meeting, June 9, 2004
28
Additional Instrument accomodations
Telescope
Coronagraph
Telescope Field Stop
400nm to 950nm
Dichroic Splitter
0.95um to 1.7um
29
Ecltel170 2.5arcmin FFOV, 4 mirror Best Fit
30
Conclusion

• Working toward a 2014 launch date.
• Phase A start hoped for in January 2007
• Current Trades
• Telescope size 6 8 m
• Sun-shade form and deployment
• Active or passive vibration isolation
• Cassegrain or Gregorian Telescope
• Technology issues
• Polarization coating design and uniformity to
  eliminate cross-polarization
• Mask leakage mask design with acceptable phase
  and amplitude errors
• Modeling do our models have the right physics to
  characterize stability at picometer levels?
• Active Wave Front Sensing can we actively
  stabilize speckles while we observe?