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The Space-based Gravitational-wave Observatory (SGO) Family of Mission Concepts Jeff Livas NASA Goddard Space Flight Center for the SGO Core Team LISA Symposium Paris, France 21-25 May 2012 1 SGO Core Concept Team LISA Symposium Paris, France 21-25 May 2012 2 Outline • Motivation for the study • SGO Family Description – – – – SGO-High SGO-Mid SGO-Low SGO-Lowest • Science Assessment • Cost Estimate • Summary LISA Symposium Paris, France 21-25 May 2012 3 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 1 1 2 • US activity assumed: – No funding new Astrophysics mission before JWST (2018?) o 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 LISA Symposium Paris, France 21-25 May 2012 4 Motivation • SGO concepts designed as progressively de-scoped cost points from LISA baseline – Explore cost drivers o Arm length o Orbits o Sciencecraft configuration o Number of (identical) spacecraft (Non-recurring vs recurring cost) o 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 LISA Symposium Paris, France 21-25 May 2012 5 Previous Experience with De-Scoping Conceptually - can’t really draw this curve, but 2 features: 1) Threshold cost below which there is essentially no science 2) lose science rapidly with modest cost savings LISA Symposium Paris, France 21-25 May 2012 6 SGO Mission Concepts LISA Symposium Paris, France 21-25 May 2012 7 SGO-High vs Mid (vs LISA baseline) • SGO High differs from LISA by: • Preserves all LISA performance parameters • Single agency cost model (not joint mission) • Lower cost launch vehicle (shared launch on a Falcon Heavy) • Demonstrated improvements in photoreceiver performance • More economical trajectories to the operational orbits High LISA Symposium Paris, France 21-25 May 2012 • 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 Mid 8 SGO-Low • Design Goal: Reduce LISA measurement concept to minimum fourlink 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 LISA Symposium Paris, France 21-25 May 2012 9 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 LISA Symposium Paris, France 21-25 May 2012 10 SGO Sciencecraft Configurations High • • • Low, Lowest Small telescope means optical bench sets height In-field guiding simplifies optical assembly Launch stack fits easily into a Falcon 9 fairing – • Mid 4th S/C for SGO-Low can be accommodated drift away orbit requires little fuel, simplifying prop module LISA Symposium Paris, France 21-25 May 2012 11 SGO-Mid Science LISA Symposium Paris, France 21-25 May 2012 12 SGO-Low Science Only one polarization LISA Symposium Paris, France 21-25 May 2012 13 SGO-Lowest Science LISA Symposium Paris, France 21-25 May 2012 14 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 LISA Symposium Paris, France 21-25 May 2012 15 Parameter Estimation LISA Symposium Paris, France 21-25 May 2012 (courtesy of Neil Cornish and the Science Performance Task Force) 16 Parameter Estimation Science Loss High Mid Low Lowest LISA Symposium Paris, France 21-25 May 2012 17 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 LISA Symposium Paris, France 21-25 May 2012 ~ $0.5B 18 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 LISA Symposium Paris, France 21-25 May 2012 19