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The Space-based Gravitational-wave Observatory (SGO) Family of Mission Concepts

The Space-based Gravitational-wave Observatory (SGO) Family of Mission Concepts. Jeff Livas NASA Goddard Space Flight Center for the SGO Core Team. SGO Core Concept Team. Outline. Motivation for the study SGO Family Description SGO -High SGO-Mid SGO-Low SGO- Lowest

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The Space-based Gravitational-wave Observatory (SGO) Family of Mission Concepts

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  1. The Space-based Gravitational-wave Observatory (SGO)Family of Mission Concepts Jeff Livas NASA Goddard Space Flight Center for the SGO Core Team

  2. SGO Core Concept Team

  3. Outline • Motivation for the study • SGO Family Description • SGO-High • SGO-Mid • SGO-Low • SGO-Lowest • Science Assessment • Cost Estimate • Summary

  4. Motivation • Post March 2011 US activity question: • Why, if there wasn’t enough money for a joint mission, was there money for two separate missions at ESA and NASA? • Missions would be serial, not parallel • US activity assumed: • No funding new Astrophysics mission before JWST (2018?) • Except maybe a “Probe Class” Mission (~ $600 M) • Need to look for a “Probe Class” mission • Need to develop a flexible mission concept to match anticipated but unknown future mission cost caps • Need to prepare for a possible ~$100M role in NGO

  5. Motivation • SGO concepts designed as progressively de-scoped cost points from LISA baseline • Explore cost drivers • Arm length • Orbits • Sciencecraft configuration • Number of (identical) spacecraft (Non-recurring vs recurring cost) • Number of links • Investigate loss of science • Constraints are different for NGO so results are different • SpaceX 9 launch vehicles assumed: lower cost • Restartable second stage? • Mass constraint less severe with Falcon Heavy

  6. Previous Experience with De-Scoping Conceptually - can’t really draw this curve, but 2 features: • Threshold cost below which there is essentially no science • lose science rapidly with modest cost savings

  7. SGO Mission Concepts

  8. SGO-High vs Mid (vs LISA baseline) • SGO Mid differs from LISA by: • Detector arm length reduced from 5 Gm to 1 Gm • Science operations reduced from 5 to 2 years. • Nominal starting distance from Earth is reduced by about a factor of 2.5 to a 9-degree trailing orbit. • Telescope diameter is reduced from 40 to 25 cm, and the laser power out of the telescope is reduced from 1.2 to 0.7 W (end of life). • In-field guiding is used instead of articulating the entire optical assembly • SGO High differs from LISA by: • Preservesall LISA performance parameters • Single agency cost model (not joint mission) • Lower cost launch vehicle (shared launch on a Falcon Heavy) • Demonstratedimprovements in photoreceiver performance • More economical trajectories to the operational orbits High Mid

  9. SGO-Low • Design Goal: Reduce LISA measurement concept to minimum four-link design while retaining primary science targets. • Architecture: Four “identical” SC in 1Gm triangle, each with one payload assembly • Two “corner” SC compare laser phase via 10km free-space link very small telescopes for back link

  10. SGO - Lowest • 3 nearly identical “daughter” S/C • Single telescope handles 2 full-duplex beams?! • “corner” requires additional phasemeter and processing • S/C 2 requires periodic corrections • a milli-N thruster • Direct injection trajectory may not need a separate prop module • 2 different arm lengths allow TDI frequency noise suppression • Single string design for low cost

  11. SGO Sciencecraft Configurations • Small telescope means optical bench sets height • In-field guiding simplifies optical assembly • Launch stack fits easily into a Falcon 9 fairing • 4th S/C for SGO-Low can be accommodated • drift away orbit requires little fuel, simplifying prop module Low, Lowest High Mid

  12. SGO-Mid Science

  13. SGO-LowScience Only one polarization

  14. SGO-Lowest Science

  15. SGO Science Comparison • Covers decadal-endorsed science • Generally detects fewer sources of all types • Main science risk is shortened mission duration • Event rates uncertain; science return lower if event rates are lower

  16. Parameter Estimation (courtesy of Neil Cornish and the Science Performance Task Force)

  17. Parameter Estimation Science Loss High Mid Low Lowest

  18. Cost Estimates • Cost model includes • Non-recurring Engineering costs • “learning curve” for multiple copies • 20% additional management reserves • Scaling with mission lifetime • Scaling rates for NRE, learning curve from • Spacecraft/Vehicle-Level Cost Model • NASA/Air Force Cost Model ~ $0.5B

  19. Summary • SGO Mission concepts cover a range of costs of $480M • $1.2 to $1.66B • TeamX estimates ~ $0.5B higher • SGO Science Performance goes from full LISA to very minimal over that cost range • Most of the cost is NOT in the science instrument/payload • Full-on RFI study covered slightly larger range, but no Probe Class mission identified

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