Download PPTx

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