In May 2000 JPL awarded four 18-month contracts to TRW, Boeing, Lockheed Martin, and
Ball Aerospace to study possible architectures for the Terrestrial Planet Finder.
The studies were undertaken with university or academic partners to look at all possible
designs for TPF during the first 6 months and then to study a small number of designs in greater detail for the remainder of the contract. Although the "strawman" design for TPF that
was discussed in the TPF Book
was an infrared formation-flying interferometer, the contractors were told not to let that
design bias or limit their investigations.
A Preliminary Architecture Review was held in December 2000,
where three out of four contractors favored optical or infrared coronagraph designs for TPF.
An interesting result of the Preliminary Review was that optical biomarkers appeared to
be very promising.
JPL then requested that two coronagraph designs and two interferometer designs
be studied in greater detail.
TRW and Ball were to study coronagraph designs and
Boeing and Lockheed Martin were to study interferometer designs.
[Boeing also independently studied a coronagraph design.]
The Final Architecture Review was held 11-13 December 2001 in San Diego
at the end of the contract.
The results of this work will provide recommendations for
technology that should be developed to support the TPF program. The following summarizes my notes from the meeting as well as my own review of the viewgraph packages.
The following appears very likely:
- Optical and infrared biomarkers appear to be very promising, and have roughly
equal interest and support amongst those involved in the contract work.
TPF sponsorted a Biomarkers Working Group study, which concluded in October 2001
with special interest in investigating optical biomarkers.
- No decision will be made concerning the final design of TPF until probably 2006.
The most promising candidate designs are variations on coronagraph and interferometer
designs, either infrared or optical. The technology for these will be studied
in the next few years.
- TPF will be technologically challenging and very expensive. Cost estimates provided
by the contractors ranged between 1.3 and 2.8 billion dollars (total life-cycle cost).
The importance of precusor missions were emphasized by the contractors and will
undoubtedly be studied further, most notably through the NASA
Extra-Solar Planets Advanced Mission Concepts Research Announcement. Winners of those
contracts should be announced sometime in the spring of 2002.
Amongst his introductory remarks at the beginning of the review, Dan Coulter, the TPF Project Manager, noted the following:
- An agreement in principle between NASA and ESA is expected to link
the TPF and Darwin missions, possibly with Japanese participation, over
the next few years.
- From 2002 to 2006 work on TPF will most likely focus on
technology development for coronagraphs and interferometers, with
a final architecture choice taking place in 2006.
- The current launch date for TPF is estimated to be 2014.
I will apologize in advance for the note-like appearance of this page. I will
make corrections and expand on the material as time permits.
There are undoubtedly errors in my notes and I would be grateful for comments or
corrections where they are due.
The viewgraph packages distributed at the Preliminary and Final Architecture Review
meetings is available on a single CDROM by request
to Chris Lindensmith at email@example.com.
Steve Kilston, Charley Noecker, David Spergel, Andreas Quirrenbach, Wes Traub, Marc Kuchner, et al.
D.N. Spergel, A new optical coronagraph for terrestrial planet detection, Appl. Opt. submitted (2001).
M.J. Kuchner and W.A. Traub, A coronagraph with a band-limited mask for finding terrestrial planets, Astrophys. J. accepted (2001).
- Coronagraph, visible wavelengths
- 10x4-m off-axis primary mirror
- Spergle & Kasdin's binary pupil with Kaiser or prolate-spheroid shaped edges
- 40-60 mas "inner working distance"
- Up to ~1000 mas field of view
- Active wavefront control: 256 x 100 actuators
- 3-130 cycles across mirror: 4.8 nm rms initially, corrected to 0.07 nm rms.
- Monolithic primary constructed from segments with AMSD technology.
- launch vehicle with 5-m fairing, eg. Ariane 5 (10-m long) or Delta IV Heavy
- Arrested-drift earth-trailing orbit, at a distance of 0.2 AU
- Cost estimates: 1.28, 1.33, or 1.9 G$
Suzi Casement, Stewart Moses, Ned Wright, John Trauger, Alan Dressler, Richard Simon, et al.
R. Simon and Vogt AAS 197 #49.05 7,058 stars withing 50 pc
- Coronagraph, infrared wavelengths, 7-17 microns
- 28-m longest diagonal, 36 mirror segments - adequate for dimmest stars on target list
- 80 mas occulting spot diameter
- Diffraction limited at 7 microns
- Coronagraph field of view, 10 x 10 arcseconds
- Primary and secondary mirror passively cooled to 70 K
- Instrument passively cooled to ~30 K
- Surface roughness < 10 nm rms
- Mid spatial frequencies < 4 nm rms
- launch vehicle with 5-m fairing, eg. Delta IV Heavy
- L2 orbit
- Cost estimate: 1.896 G$
Boeing - SVS
Mike Kaplan, Steve Ridgeway, Dan Gezari, Olivier Guyon,
Pete Nisenson, ,Jean Schneider,
Bruno Lopez, Remi Soummer, et al.
Non-redundant Linear Array (Hyper-telescope)
- A. Labeyrie, Resolved imaging of extra-solar planets with future 10-100km
optical interferometric arrays, Astron. Astrophys. Supp. Ser. 118, 517 (1996).
- A. Boccaletti et al, Icarus 145, 628.
- The nulling stellar coronagraph: O. Guyon et al., PASP 111, 1321-1330 (1999).
Phase mask references:
- Roddier and Roddier PASP 109, 815-820 (1997).
- P. Riaud et al., The Four-Quadrant Phase Mask Coronagraph. II. Simulations.
Pub. Astron. Soc. Pac. 113, 1145 (2001)
The hypertelescope is a hybrid interferometer/coronagraph with image-plane beam
combination. The interferometer is used to obtain high angular resolution and
the coronagraphic stop/mask is used to reject the starlight.
At a first image plane, a coronagraphic stop (phase mask) scatters the star-light
out of the field of a secondary image plane where planets are detected. Pupil
densification is required for the coronagraph to be efficient. For the linear
array, outlined here, the input apertures are re-arranged in a densified circular
pupil, and are then de-densified afterwards.
Apodized Square Apertures
- Interferometer, infrared wavelengths, 7-17 microns.
- 100-m structure
- Seven 3-m diameter telescopes in a non-redundant linear array
- Hypertelescope beam combiner, with sub-pupils arranged along the circumference
of a circle, about 20 reflections per arm in total beam-train.
- Passively cooled to 70 K
- Three launches required: 2 shuttle and 1 Delta IV
- Human assisted assembly in Low Earth Orbit during the two shuttle missions.
- Boosted from LEO to L2 orbit
- Cost estimate: 2.83 G$
P. Nisenson and C. Papaliolios Astrophys. J. 548
, L201 (2001).
Sonine function apodization: Oliver (1975).
P. Jacquinot and B. Roizen-Dossier, Prog. Opt. 3
- Coronagraph-type design, visible wavelengths
- 8-m square aperture
- 62 mas minimum detectable planet-star separation
- Jacquinot apodization (30% more throughput than Sonine) in re-imaged pupil
- Rms surface error < lambda/1800; Figure control WFE < lambda/200
- 3 or 4 mirror segmented design
- Cooled by not cryo - Possibly temperature controlled at 220 K
- Delta IV or shuttle launch
- L2 orbit
- Simulated for 3-30 cycles/mirror and lambda/1000 waves.
- No cost estimate provided.
Domenick Tenerelli, Nick Wolf, Roger Angel, Phil Hinz, D. Miller, et al.
Although a brief bibliography of nulling interferometery exists, the array design that was described by Nick Woolf et al. has yet to be published. However, the design of the nulling combiner is two-staged design
based on the combiners described by Serabyn and Colavita:
E. Serabyn, M.M. Colavita, Fully symmetric nulling beam combiners,
Appl. Opt. 40, 1668 (2001).
Four-element Double-Bracewell Nulling Arrays
9-m, 21-m, 40-m fixed-structure linear arrays and a Free Flyer design discussed.
Only the 40-m array and Free Flyer designs would meet the mission requirements
of > 150 stars surveyed for planets, and the
40-m structure will be outlined here.
Biomarkers Study Reference
- Interferometer, infrared wavelengths, 7-17 microns.
- Passively cooled to 40-45 K.
- 40-m double-Bracewell, fixed-structure, linear array
- 4 telescopes, 3.5-m diameter
- Theta-squared null
- Serabyn-Colavita two-stage nuller design with added phase plate.
- Launch vehicle, Atlas 5
- Orbit: L2 or Earth trailing (not specified)
- Cost estimate: 1.741 G$
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