NASAs GravitationalWave Mission Concept Study Robin Stebbins Study
NASA’s Gravitational-Wave Mission Concept Study Robin Stebbins, Study Scientist Ninth LISA Symposium Paris, 22 May 2012
Outline • • Goals Elements of the study Context of the study Responses to the Request-For-Information (RFI) Science performance analysis Assessment of architectures Risk Cost This document contains no ITAR-controlled information and is suitable for public release. 2
Goals of the Study • Develop mission concepts that will accomplish some or all of the LISA science objectives at lower cost points. • Explore how mission architecture choices impact science, cost and risk. • Big Questions • Are there concepts at $300 M, $600 M or $1 B? • What is the lowest cost GW mission? • Is there a game-changing technology that hasn't been adequately considered? This document contains no ITAR-controlled information and is suitable for public release. 3
Elements of the Study • Request for Information (RFI) – due Nov. 10 th. • Core Team – ~25 GSFC, JPL & university scientists and engineers critically reviewing RFI responses • Science task force – ~15 volunteer scientists evaluating science performance of concepts • Community Science Team (CST) – 10 scientists, Rai Weiss, Ned Wright co-chairs • Public workshop – December 20 -21 st • Concurrent engineering studies by JPL’s Team-X in March and April • Final Report to NASA Headquarters – July 6 th • Presentation to the Committee on Astronomy and Astrophysics (CAA) of the National Research Council (NRC) This document contains no ITAR-controlled information and is suitable for public release. 4
Context of the Study – A Brief History of LISA • 1974 - A dinner conversation: Weiss, Bender, Misner and Pound • 1985 – LAGOS Concept (Faller, Bender, Hall, Hils and Vincent) • 1993 – LISAG - ESA M 3 study: six S/C LISA & Sagittarius • 1997 - JPL Team-X Study: 3 S/C LISA • 2001 -2015 - LISA Pathfinder and ST-7 DRS • 2001 – NASA/ESA project began • 2003 – TRIP Review • 2005 – GSFC AETD Review • 2007 – NRC BEPAC Review • 2009 – Astro 2010 Review • 2011 – NASA/ESA partnership ended • 2011 – Next Generation Gravitational-Wave Observatory (NGO) started • 2012 – ESA L 1 downselect This document contains no ITAR-controlled information and is suitable for public release. 5
Context of the Study – Activities in Europe • LISA Pathfinder • Demonstration of space-based GW technology, in late stages of I&T • 2014 launch • Technology development • • Inertial sensor electronics, charge control Optical system Laser system Pointing and point-ahead mechanisms • NGO • Highly developed concept with extensive science case and technical detail This document contains no ITAR-controlled information and is suitable for public release. 6
Context of the Study in the U. S. • Next major mission in Astrophysics starts after 2018. • The Astrophysics Division anticipates that a “probeclass” mission could be started ~2017. • The Division will not commit to a ‘large’ mission until after Astro 2020. ‘Commit’ means the Confirmation Review at the end of Phase B. • A partnership with ESA seems highly likely. That would require: • Rebuilding a partnership • Reliably coordinating two agencies’ programs 7
RFI Responses 8
RFI Responses • 17 responses total • 12 for mission concepts, several with options • 3 for instrument concepts • 2 for technologies • Four natural groups • • No-drag-free concepts (2) Geocentric orbits (4) LISA-like (5) Other (2) 9
What constitutes “LISA-like? ” • Drag-free control • Free-falling test mass • Precision stationkeeping • Continuous laser ranging • Heliocentric orbits • Constellation in stable equilateral triangle • No orbital maintenance • Million-kilometer long arms • Laser frequency noise subtraction (TDI) • Emulate Michelson’s white-light fringe condition through post-processing 10
No-Drag-Free Concepts 11
No-Drag-Free Concepts • Rely on either very long arms (50 X LISA) or geometry (100 X reduction) to compensate for using the spacecraft as the test mass. • Disturbances are solar radiation pressure variability, solar wind, interplanetary magnetic field • Measure, model and correct for spurious forces (102 - 104 X) • Displacement noise from motions of the spacecraft CG, owing to, say, thermoelastic effects • Concerns about measuring solar wind and modeling/testing other disturbance (e. g. , Pioneer 12 effect)
Geocentric Concepts 13
Geocentric Concepts • Noise concerns • Thermal environment: moving sub-Sun point, eclipses • Sun in the telescope • Varying Earth albedo • Geosynchronous may have interesting modulation properties. (Mc. Williams’ talk Thursday afternoon) • LAGRANGE/Conklin described by Buchman Tuesday afternoon. • A big cost question: can you do this for a factor of 4 less by employing nanosat technology, lower reliability standards, standard bus, a different way of doing business, … a different business model? 14
LISA-like Concepts 15
LISA-like Concepts • • How far can the LISA architecture be descoped? No technical or performance issues Science performance falls off much faster than cost Found the bottom! See Jeff Livas’s talk Tuesday afternoon in LISA-NGO Technology session. 16
Other Concepts 17
Other Concepts • The superconductor idea doesn’t work. • Atom Interferometry • Atoms clouds as test masses • Atom interferometer as a phasemeter • See John Baker’s talk Thursday afternoon in Other Experiments and Alternative Design session • In. Sp. RL • Most aggressive design concept • Invoked ‘superclocks’ and resonance • Seems to require a few orders of magnitude improvement in several key performance parameters • Lacks enough definition to evaluate • Yu concept doesn’t promise to be cheaper. • Digital Interferometry is interesting. 18
Science Performance Analysis 19
Science Performance • Volume of the Universe explored • Detection numbers for source populations (Massive BHs, EMRIs, Galactic Binaries) • Discovery space • Parameter resolution All work done by Neil Cornish and the Science Task Force. See Cornish talk, Friday morning. 20
Sensitivity Curves – All 15 Concepts 21
Massive Black Hole Horizons 22
Massive Black Hole Horizons – No-Drag-Free 23
Massive Black Hole Horizons – Geocentric 24
Massive Black Hole Horizons – Geosynchronous 25
Massive Black Hole Horizons – LISA-Like 26
Detection Rates – Large Seed Models (/yr) 27
Detection Rates – Small Seed Models (/yr) 28
EMRI Horizons 29
EMRI Detections 10 M⊙ compact object, eccentricity 0. 5 at 2 yrs to plunge, spin 0. 5 central BH, SNR=15 30
WD-WD Detection Numbers 31
Parameter Estimation – LISA-like Concepts Similar detection numbers, but each descope x 3 -10 loss in resolution 32
Architecture Choices 33
Architecture Choices – Mission Design • Heliocentric – fixed, drift-away, in-line, L 2/leading/trailing, 1 AU • Geocentric – OMEGA, geosync, L 3/L 4/L 5, LEO • Compare delta-v, constellation stability, propellant, thermal, modulation of science signal, comm 34
Architecture Choices – Inertial Reference • Proof mass – cubical, parallelepiped or spherical freefalling, or torsion pendulum • Spacecraft center-of-gravity (aka no-drag-free) with modeled corrections • Atom interferometry - atoms as proof masses, atoms as secondary inertial reference • Payload as separated spacecraft 35
Architecture Choices – Measurement Strategies • Laser interferometry with laser heterodyne phase comparison – free-space or digital interferometry • Laser interferometry with atom interferometer phase comparison • Laser and clock frequency noise correction – 3 spacecraft & TDI, or very much better phase reference (AI) 36
Implementation Strategies 37
Implementation Strategies Parameter Mass Margin SGO Mid LAGRANGE OMEGA 53% 53% Payload mass (kg), power (W) CBE 216. 5 kg, 233 W 99. 7 kg, 99. 3 W Option 1: 64. 3 kg, 80 W; Option 2: 55 kg, 54 W 717 kg (3) 661 + 139 (3) ? 4553 kg 531 kg (2) 586 kg (1) 224 + 174 (2) 591 + 114 (1) 32 kg 3182 kg 147 kg (6) 374 + 465. 5 (1) 28 kg 2347 kg Atlas V 551; 6075 kg Atlas V 511; 3285 kg Falcon 9 Block 2; 2490 kg Mass rack-up Science-craft type 1 Science-craft type 2 Propulsion Module type 1 + Propulsion module type 2 + Prop LV Adapter Launch Mass Wet Launch Vehicle 38
Risk SGO-Mid/High LAGRANGE OMEGA • These are a combination of Team-X and Core Team risks. • Risk rises rapidly with modest (<10%) cost reductions. • This assessment is not complete. 39
Cost • Team-X is very conservative. • Cost estimates range from $1. 2 B to 2. 1 B. • Per science year costs • SGO-hi $450 M/yr • SGO-mid/Lagrange ~$800 -900/yr • Omega ~$1, 300 M/yr • Important cost drivers • Non-recurring costs (NRE) and recurring costs (RE) are important. • Design validation • Serial vs parallel construction of multiple units (~$150 M/yr) 40
Summary • The CST prefers SGO-Mid (3 arms, LISA-like, 1 Mkm, driftaway). • Big Questions • We found no concepts at $300 M, $600 M or $1 B. • The lowest cost GW mission is ~$1. 4 B (± 0. 2). • We found no game-changing technology that hasn't been adequately considered. • Heliocentric is a better choice than geocentric. • Three dual-string spacecraft appear to be more robust than six single-string spacecraft. • No-drag-free achieves only modest savings while incurring substantial risk. [Cost model is uncertain. ] • Three arms has lower risk and mediating cost factors relative to two arms. 41
Backup Slides 42
Feedstock • • Whitepapers (17 x~15 pages = 235) Workshop Presentations (~20 x 30 charts = 600) Core Team Work (~200 pages) Team-X input • • • Presentations (4 x ~60 charts = 240) Master Equipment Lists Functional Interface Diagrams CAD files Orbit analyses • Team-X output • Viewgraphs (~3 x 280 = 840) • Team-X reports (~3 x 10 -20 = 45) • CST Work (~50 pages) • Total: north of 2230 pages 43
Mission Design Review 1/2 Feature SGO-Mid Lagrange 1. Trajectory Phase DV [174, 153, 200] m/s Stack ~ 120 m/s to L 2 [SC 1, 3]: [460, 300] Significance: Prop module size(s), Total mass, Launch vehicle 2. Trajectory Phase Dt 17 months 27 months Omega [206, 328, 450] + 4 m/s vs. 3 210 m/s if 3 PMs 12 months (vs. ~ 7 ) Significance: Cost/complexity of trajectory phase operations (FDF & Ops) 3. Lunar Flybys Used No Yes No Significance: Cost/complexity/risk of trajectory phase operations (FDF & Ops) 4. Mission Phase Dt 2 yr / extendable 2 yr / not extendable 1 yr / extendable Significance: Cost of science operations, Amount of science, Constellation Stability ± 0. 007, ± 0. 6 , ± 1. 5 Mhz, ± 0. 12 , ± 94 Mhz, ±(0. 8, 0. 32) mrad DL/L, Da, Dn, (Dg||, Dg+) ±(0. 008, 1. 0) mrad 5. Const. Stability ± 0. 025, ± 2. 2 , ± 60 Mhz, ±(0. 17, 0. 15) mrad Significance: Cost of additional mechanisms and electronics 6. Mission Phase DV No Yes (SC 2) No Significance: Cost/sophistication of m. N-thruster system (~ 10 m/s/yr) 44
Mission Design Review 2/2 Feature 7. Distance to Earth / HGA, ISC req? SGO-Mid Lagrange Omega 24 to 55 106 km / HGA [21, 1. 5, 21] 106 km HGA/LGA, ISC/LGA 0. 6 106 km LGA Significance: Cost/complexity of communications; ISC = inter-spacecraft comm. 8. Geo. Ecliptic Orbit No No Yes Significance: (a) Sun direction variation (thermal stability) (b) Sun in telescope aperture (thermal, optical interference) (c) Earth eclipses (thermal, science interruptions) Feature 9. Launch Vehicle C 3 SGO-Mid Lagrange Omega +0. 27 (km/s)2 -0. 3 (km/s)2 -0. 05 (km/s)2 Yes (but not necessary) Significance: Launch vehicle selection 10. Single Prop Option No ( ? ) Significance: Input to possible trade for single prop module cost savings (? ) 11. “FDF” Ops Cost $ 18 M $ 27 M $ 23 M (? if 3 PMs) Cost Drivers: Trajectory and mission phase durations, trajectory complexity 45
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