Starshade Rendezvous Probe MissionSara Seager (MIT), Jeremy Kasdin (Princeton), Co-PIsAndrew Gray (JPL), Study LeadAndrew Romero-Wolf (JPL), Jeff Booth (JPL) and the Starshade Probe Team

2.4 m diameter

aperture

26 m

The starshade contrast and inner working

angle are largely decoupled from the

telescope aperture size

Outer working angle only limited by the

detector

Retargeting requires starshade slews of days

to a couple of weeks

At the cost of a Probe, a starshade can be launched in time to rendezvous with WFIRST, taking advantage of the existing telescope and coronagraph instrument to reach Earth-like planet levels of contrast on ten or so nearby stars

Starshade Rendezvous Probe Mission

Probing our Nearest Sun-Like Star Neighbors

Image credit: JPL

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Starshade Concept• Originated in the 1960s by L. Spitzer• Revisited each decade since

Exo-S Probe Study (2013-2015)• The Dedicated Mission, a 30 m starshade and 1.1 m

telescope co-launches• The Rendezvous Mission, 34 m starshade launches and

meets up with WFIRST

Other Related Studies (2015-2016)• Extended Probe Study (2015), 20 m• Starshade Readiness Working Group (2016)

Starshade Rendezvous Probe Mission (2017-2019)• Selected to update the Exo-S Rendezvous Mission

concept study

Overview

Exoplanet Direct Imaging Landscape

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Adapted from plot by Vanessa Bailey

Starshade + WFIRST• Can reach down to Earth-size planets in Earth-like orbits

about sun-like stars

TESS/JWST Transiting Exoplanets• Transiting rocky planet atmospheres limited to small red

dwarf stars• Earth-sun analogs are not possible: low probability for an

Earth-orbit planet to transit and too small atmosphere superimposed on the host star

ELTs for M Dwarf Stars• Capable of direct imaging for M dwarf star rocky planets

in reflected light

Space-based direct imaging is the natural and essential next step—the next frontier for discovery in exoplanet science

Science Objectives

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1. Habitability & Planetary

Systems

Objective 1a: Habitability and Biosignature Gases.

Determine whether super-Earth size or smaller exoplanets

in the habitable zone exist around the nearest sunlike stars

and have signatures of oxygen and water vapor in their

atmospheres.

Objective 1b: The Nearest Solar System Analogs

Detect and characterize planets orbiting the nearest sun-

like stars.

2. Exozodiacal Dust

Objective 2: Brightness of Zodiacal Dust Disks. Establish if

the zodiacal cloud of our inner solar system is representative of

the population of our nearest neighbor stars.

3. Giant Exoplanet Atmospheres

Objective 3: Giant Planet Atmosphere Metallicity. Determine

the metallicity of known cool giant planets to examine trends with

planetary mass and orbital semi-major axis, and to determine if

these trends are consistent with our solar system.

Perform a “deep dive”, an intense, long integration of the 10 nearest sun-like stars with imaging and spectra for targets amenable to multiple visits to constrain orbits

1. Habitability and Planetary System Architectures

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The Deep Dive Approach

Initial ReconnaissanceFirst visit evaluates zodiacal dust brightness and detection of any exoplanets present

Orbit Determination Revisits to determine if planets are in the habitable zone of a star

Spectral CharacterizationDeep integration triggered by habitable zone exoplanet candidates. Any other planets in the field of view will also be spectroscopically characterized

JSimulation of the Solar System at 6 pc, 60 deg incl., and 1 day integration time

The sensitivity to discover and characterize Earth-like exoplanet candidates drives the observatory requirements

Credit: S. Hildebrandt

1. Habitability and Planetary System Architectures

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R=50

Starshade + WFIRST-CGI has the capability to take spectral measurements of exoplanet atmospheres

Requirements set using Earth as a model to enable the characterization of a wide class of planets

SRP BANDS

Image Credit: Aki Roberge

Planet Yield

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Discovery of a variety of exoplanets expected

All detected planets can be spectrally characterized (including for water vapor and oxygen)

Metallicity investigation yields another ~10 Jupiters

Parameter ValueAg 0.2Planet Radius 0.8–1.4 REarth

Habitable Zone (0.95–1.67) √Lsun

Solar System Zodi 1Exozodi 4.5

Earth-like planet input values

2. Exozodiacal Dust

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Main objective is to obtain 10 samples of exozodiacal dust disk brightness

Inform the HabEx deep dive and statistical distribution of warm dust disk brightness

Potentially observe the influence of planets in high dust environments

Simulated dust disk in the presence of a 5 ME exoplanet with 1 AU orbit (Stark & Kuchner 2008). r is the dust density and s is the grain size.

3. Metallicity of Known Giant Exoplanet Atmospheres

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Objective is to test the correlation of metallicity in giant exoplanet atmospheres with planet properties: mass and semi-major axis

Adapted from Wakeford+, 2017

Credit N. Lewis and B. MacIntosh

Observation Model

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WFIRST and StarshadeWFIRST Starshade Accommodations

• Starshade Acquisition Camera

– Used to acquire the starshade beacon after retargeting

• Formation Control Sensing and Commanding

– CGI LOWFS used for sensing offsets by capturing pupil plane images of out-of-science band starlight S-band radio

• S-band radio link

• Coronagraph filters

– Five custom filters in CGI

– 3 26% imaging bands

– 2 20% bands in IFS, R50 spectroscopy• WFIRST participates in rendezvous, formation control, and

science

• The starshade team has flowed requirements to WFIRST through an Interface Requirements Document (IRD)

The Starshade• Petal subsystem• Inner disk subsystem• Petal Launch Restraint Unfurl System (PLUS)

Requirement DescriptionThreshold

Value

Starlight SuppressionInstrument contrast 1×10-10

Solar Scatter Lobe brightness visual magnitude

V ≥ 25 mags

Lateral Formation Sensing & Control

Later position sensor accuracy that supports ±1 m control

≤ ±30 cm

Petal Shape Pre-launch accuracy ≤ ±70 µm

On-orbit thermal stability

≤ ±80 µm

Petal Position Pre-launch accuracy ≤ ±300 µm

On-orbit thermal stability

≤ ±200 µm

Driving RequirementsInner Working Angle ≤ 103 mas

Contrast (at IWA) ≤ 10-10

Flux Sensitivity: scattered light from starshade < background

Mission Duration: starshade must maintain thermal and mechanical stability for 3 years

Science Payload: Starshade

Starshade Technology Gaps

(1) Starlight Suppression

Suppressing diffracted light from on-axis

starlight and optical modeling (S-2)

Suppressing scatted light off petal

edges from off-axis Sunlight (S-1)

Positioning the petals to high accuracy, blocking on-axis starlight,

maintaining overall shape on a highly stable structure (S-5)

Fabricating the

petals to high

accuracy (S-4)

(2) Formation Sensing

(3) Deployment Accuracy

and Shape Stability

Sensing the lateral offset

between the spacecraft (S-3)

S-# corresponds to ExEP

Starshade Technology Gap

(http://exoplanets.nasa.gov/e

xep/technology/gap-lists)16

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J F M A M J J A S O N D

J F M A M J J A S O N D

Epsilon Indi A

Altair

Delta Pavonis

Procyon A

Sirius A

Omicron 2 Eridani

Epsilon Eridani

82 Eridani

Tau Ceti

J F M A M J J A S O N D J F M A M J J A S O N D

J F M A M J J A S O N D J F M A M J J A S O N D

Spacecraft

Events and Maneuvers

Contact with DSN 34 meter antenna 2 hours/day, 3 days/week; 4 days/week during maneuversDSN

Science

Laun

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Rend

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TCM

1 L

+3

2029 2030

Cumulative Science Delta-v

TCM

2 L

+30

Science Maneuvers

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Summary

Starshade Rendezvous Probe opens a new frontier: the possibility of detecting Earth-like exoplanets orbiting nearby sun-like stars in the next decade

Starshade Probe will provide the first direct imaging examination of planetary systems in our nearest sun-like stars, including their habitable zones, giant exoplanets, and warm dust disks, opening a new frontier

Starshade Probe will determine whether the metallicity and mass of known gas giant exoplanets follows the correlation observed in our own solar system, fueling planetary formation studies

Beyond its science objectives, Starshade Probe will be an invaluable demonstration of technology and operations for future missions

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Probing our Nearest Sun-Like Star Neighbors

Image credit: JPL