NASA’s Gravitational-Wave Mission Concept Study

Robin Stebbins, Study ScientistNinth LISA Symposium

Paris, 22 May 2012

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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

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This document contains no ITAR-controlled information and is suitable for public release.

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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 $300M, $600M or $1B?• What is the lowest cost GW mission?• Is there a game-changing technology that hasn't been

adequately considered?

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Elements of the Study• Request for Information (RFI) – due Nov. 10th.• 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 20-21st • Concurrent engineering studies by JPL’s Team-X in March and

April• Final Report to NASA Headquarters – July 6th

• Presentation to the Committee on Astronomy and Astrophysics (CAA) of the National Research Council (NRC)

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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 M3 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 – Astro2010 Review• 2011 – NASA/ESA partnership ended• 2011 – Next Generation Gravitational-Wave

Observatory (NGO) started• 2012 – ESA L1 downselect

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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

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Context of the Study in the U.S.• Next major mission in Astrophysics starts after 2018.• The Astrophysics Division anticipates that a “probe-

class” mission could be started ~2017.• The Division will not commit to a ‘large’ mission until

after Astro2020. ‘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

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RFI Responses

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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)

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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

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No-Drag-Free Concepts

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No-Drag-Free Concepts• Rely on either very long arms (50X LISA) or geometry

(100X 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 effect)

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Geocentric Concepts

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Geocentric Concepts• Noise concerns

• Thermal environment: moving sub-Sun point, eclipses• Sun in the telescope• Varying Earth albedo

• Geosynchronous may have interesting modulation properties. (McWilliams’ 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?

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LISA-like Concepts

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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.

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Other Concepts

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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

• InSpRL• 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.

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Science Performance Analysis

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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.

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Sensitivity Curves – All 15 Concepts

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Massive Black Hole Horizons

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Massive Black Hole Horizons – No-Drag-Free

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Massive Black Hole Horizons – Geocentric

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Massive Black Hole Horizons – Geosynchronous

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Massive Black Hole Horizons – LISA-Like

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Detection Rates – Large Seed Models (/yr)

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Detection Rates – Small Seed Models (/yr)

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EMRI Horizons

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EMRI Detections

10 M⊙ compact object, eccentricity 0.5 at 2 yrs to plunge, spin 0.5 central BH, SNR=15

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WD-WD Detection Numbers

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Parameter Estimation – LISA-like Concepts

Similar detection numbers, but each descope x 3-10 loss in resolution

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Architecture Choices

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Architecture Choices – Mission Design• Heliocentric – fixed, drift-away, in-line,

L2/leading/trailing, 1 AU• Geocentric – OMEGA, geosync, L3/L4/L5, LEO• Compare delta-v, constellation stability, propellant,

thermal, modulation of science signal, comm

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Architecture Choices – Inertial Reference• Proof mass – cubical, parallelepiped or spherical free-

falling, 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

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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)

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Implementation Strategies

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Implementation Strategies

Parameter SGO Mid LAGRANGE OMEGAMass Margin 53% 53% 53%

Payload mass (kg), power (W) CBE 216.5 kg, 233 W 99.7 kg, 99.3 W Option 1: 64.3 kg, 80W; Option 2: 55 kg, 54W

Mass rack-up Science-craft type 1Science-craft type 2

Propulsion Module type 1 + PropPropulsion module type 2 + Prop

LV AdapterLaunch Mass Wet

717 kg (3) 661 + 139 (3) ?4553 kg

531 kg (2)586 kg (1)224 + 174 (2)591 + 114 (1) 32 kg3182 kg

147 kg (6) 374 + 465.5 (1) 28 kg2347 kg

Launch Vehicle Atlas V 551; 6075 kg

Atlas V 511; 3285 kg

Falcon 9 Block 2;2490 kg

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RiskSGO-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.

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Cost

• Team-X is very conservative.• Cost estimates range from $1.2B to 2.1B.• Per science year costs

• SGO-hi $450M/yr • SGO-mid/Lagrange ~$800-900/yr• Omega ~$1,300M/yr

• Important cost drivers• Non-recurring costs (NRE) and recurring costs (RE) are

important.• Design validation• Serial vs parallel construction of multiple units (~$150M/yr)

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Summary• The CST prefers SGO-Mid (3 arms, LISA-like, 1 Mkm, drift-away).• Big Questions

• We found no concepts at $300M, $600M or $1B.• The lowest cost GW mission is ~$1.4B (±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.

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Backup Slides

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Feedstock• Whitepapers (17x~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

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Mission Design Review 1/2 Feature SGO-Mid Lagrange Omega

1. Trajectory Phase DV [174, 153, 200] m/s Stack ~ 120 m/s to L2[SC1, 3]: [460, 300]

[206, 328, 450] + 4 m/svs. 3210 m/s if 3 PMs

Significance: Prop module size(s), Total mass, Launch vehicle

2. Trajectory Phase Dt 17 months 27 months 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

5. Const. Stability DL/L, Da, Dn, (Dg||,

Dg+)

±0.007, ±0.6, ±1.5 Mhz, ±(0.008, 1.0) mrad

±0.1, ±0.12, ±94 Mhz, ±(0.8, 0.32) mrad

±0.025, ±2.2, ±60 Mhz, ±(0.17, 0.15) mrad

Significance: Cost of additional mechanisms and electronics

6. Mission Phase DV No Yes (SC2) No

Significance: Cost/sophistication of mN-thruster system (~ 10 m/s/yr)

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Mission Design Review 2/2 Feature SGO-Mid Lagrange Omega

7. Distance to Earth / HGA, ISC req?

24 to 55 106 km /HGA

[21, 1.5, 21]106 kmHGA/LGA, ISC/LGA

0.6106 km LGA

Significance: Cost/complexity of communications; ISC = inter-spacecraft comm.

8. GeoEcliptic 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 SGO-Mid Lagrange Omega

9. Launch Vehicle C3 +0.27 (km/s)2 -0.3 (km/s)2 -0.05 (km/s)2

Significance: Launch vehicle selection

10. Single Prop Option No (?) Yes (but not necessary) Yes (but not necessary)

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