Habitable Exoplanet Observatory (HabEx)

TECHNOLOGY

The HabEx Concept telescope is optimized for direct imaging and spectroscopy of potentially habitable exoplanets and enables a wide range of general astrophysics science. All HabEx technologies are Technology Readiness Level (TRL) 4 or 5; current funding will mature all but 4 to TRL 5 by 2023. Table 1 below - one entry shown for illustration, download full table here - shows the technology readiness levels (TRL) of all HabEx enabling technologies, including elements of starshades, coronagraphs , large primary mirrors, jitter mitigation, wavefront control, and detectors.

Title	Description	Section	State of the Art	Capability Needed	TRL 2019	Expected 2023 TRL
Enabling Technologies
Starshade Petal Position Accuracy and Stability	Deploy and maintain petal position accuracy in L2 environment	11.2.1.1	Petal position deployment tolerance (≤150 µm) verified with multiple deployments of 12 m flight-like perimeter truss and no optical shield No environmental testing	Petal position deployment accuracy on 20 m perimeter truss: ±600 µm (3σ) bias Position stability in operational environment: ±400 µm (3σ) random	4	5
Starshade Petal Shape Accuracy and Stability	Starshade petal shape maintained after deployment, thermal at L2	11.2.1.2	Manufacturing tolerance (≤100 µm) verified with low fidelity 6 m long by 2.3 m prototype; No environmental tests Petal deployment tests conducted on prototype petals to demonstrate rib actuation; No post-deploy cycle and petal shape stability measurements	Petal 16 m long by 4 m wide Petal shape manufacture: ±140 µm (3σ) Post-deploy cycle and petal shape thermal stability ≤ ±160 µm (3σ)	4	5
Starshade Scattered Sunlight for Petal Edges	Limit edge-scattered sunlight and diffracted starlight with petal optical edges	11.2.2.1	Chemically etched amorphous metal edges limit solar glint flux to 25 visual magnitudes in two main lobes, verified at coupon level In-plane shape tolerance of ±20 µm met at half meter length after integration onto prototype petal In plane shape stability demonstrated post-deploy and thermal cycle Scatter performance on half meter edge verified post environment	One meter length edges assembled precisely onto petal Petal edge in-plane shape tolerance: ±66 μm (3σ) Petal edge in-lane placement tolerance: ±55 μm (3σ) Solar glint: 26.25 (TBR) visual magnitudes in two main lobes	4	5
Starshade Contrast Performance Modeling and Validation	Validate at flight-like Fresnel numbers the equations that predict the contrasts	11.2.2.2	1.5 × 10^-10contrast demonstrated at Fresnel NumberR=1 ~13 (monochromatic) Expect 1 × 10^-10 contrast demonstrated at Fresnel NumberR=1 ~13 (10% bandwidth) in March 2019	Experimentally validated models with scaled flight-like geometry and Fresnel NumberR=1 ≥12 across a broadband optical bandpass. Validated models are traceable to 1 × 10^-10 contrast system performance in space	4	5
Starshade Lateral Formation Sensing	Lateral formation flying sensing to keep telescope in starshade’s dark shadow	11.2.3.1	Simulations have shown centroid to ≤1/10th aperture with ample flux to support control loop Control algorithms demonstrated control ≤1 m radius within line of sight of the star for durations representative of typical starshade observation times	Demonstrate sensing lateral errors ≤0.40 m accuracy (≤1/10th aperture) at scaled flight separations Control algorithms demonstrated with scaled lateral control corresponding to ≤1 m of the line of sight	5	5
Large Mirror Fabrication	Large monolith mirror that meets tight surface figure error and thermal control requirements at visible wavelengths	11.3.1.1	4.2 m diameter, 420 mm thick blanks standard Schott demonstrated computer-controlled-machine lightweighting to pocket depth of 340 mm, 4 mm rib thickness on E-ELT M5 and 240 mm deep/2 mm thick rib on Schott 700 mm diameter test unit State-of-the-practice (SOP) lightweighting has yielded large mirrors of aerial density 70 kg/m₂ Zerodur® can achieve 2.83 parts per billion/K CTE homogeneity (DKIST mirror) Wavefront stability: 25 nm rms for HST in LEO Wavefront Error of WFIRST-like primary mirror (spatial frequency cycles/beam diam. : nm RMS): 0-7 cy/D: 6.9 nm RMS 7-100 cy/D: 6.0 nm RMS >100 cy/D: 0.8 nm RMS	4.04 m diameter substrate 3–4 mm ribs, 14 mm facesheet, and pocket depth of 290 mm for 400 mm thick blank Aerial density 110 kg.m₂ < 5 ppb/K CTE homogeneity First mode ≥60 Hz Wavefront stability of 100s to a few picometers rms (depending on spatial frequency) over 100s of seconds Wavefront Error (spatial frequency cycles/beam diam. : nm RMS): 0-7 cy/D: 6.9 nm RMS 7-100 cy/D: 6.0 nm RMS >100 cy/D: 0.8 nm RMS	4	4
Large Mirror Coating Uniformity	Mirror coating with high spatial uniformity over the visible spectrum	11.3.1.2	Reflectance uniformity <0.5% of protected Ag on 2.5 m TPF Technology Demonstration Mirror IUE, HST, and GALEX used MgF₂ on Al to obtain >70% reflectivity from 0.115 µm to 2.5 µm Operational life: >28 years on HST	Reflectance uniformity <1% over 0.45–1.0 µm Reflectivity comparable to HST: 0.115–0.3 µm: ≥70 % 0.3 – 0.45 µm: ≥88% 0.45 – 1.0 µm: ≥85 % 1.0 - 1.8 µm: ≥90 % Operational life >10 years	4	4
Laser Metrology	Sensing for control of rigid body alignment of telescope front-end optics	11.3.2.1	Thermally stabilized Planar Lightwave Circuit fully tested Nd:YAG ring laser and modulator flown on LISA-Pathfinder Phase meters flown on LISA-Pathfinder and Grace Follow-On Sense at 1 kHz bandwidth Uncorrelated per gauge error of 0.1 nm Laser Met System at JPL expected TRL 6 by 9/19	Sense at 100 Hz bandwidth Uncorrelated per gauge error of 0.1 nm	5	5
Coronagraph Architecture	Suppress starlight by a factor of ≤1E-10 at visible and near-IR wavelengths	11.4.1.1	Hybrid Lyot: 6 × 10^-10 raw contrast at 10% bandwidth across angles of 3–16 λ/D demonstrated with a linear mask and an unobscured pupil in a static vacuum lab environment Vector vortex charge 4: 5 × 10^-10 raw contrast monochromatic across angles of 2–7 λ/D Lyot: 3.6 × 10^-10 raw contrast at 10% bandwidth over 3–7 λ/D in a static lab environment (DST) Vector vortex charge 6: 8.5 × 10^-9coherent contrast at 10% bandwidth across angles of 3–8 λ/D demonstrated with an unobscured pupil in a static lab environment	Vortex Charge 6 Raw contrast of ≤1 × 10^-10 Raw contrast stability of ≤2 × 10^-11 Inner working angle (IWA) ≤ 2.4 λ/D Coronagraph throughput ≥10% Bandwidth ≥20%	4	5
Zernike Wavefront Sensing and Control (ZWFS)	Sensing and control of low-order wavefront drift; monitoring of higher order Zernike modes	11.4.2	<0.36 mas rms per axis LoS residual error demonstrated in lab with a fast-steering mirror attenuating a 14 mas LOS jitter and reaction wheel inputs on Mv = 5 equivalent source; ~26 pm rms sensitivity of focus (WFIRST Coronagraph Instrument Testbed) WFE stability of 25 nm/orbit in low Earth orbit (HST). Higher low-order modes sensed to 10–100 nm WFE rms on ground-based telescopes	LoS error <0.2 mas rms per axis Wavefront stability:≤~100 pm rms over 1 second for vortex WFE <0.76 nm rms	4	5
Deformable Mirrors	Flight-qualified large-format deformable mirror	11.4.3	Micro-electromechanical DMs available up to 64 × 64 actuators, 400 µm pitch with 6 nm RMS flattened WFE; 3.3 nm RMS demonstrated on 32 × 32 DM 8.5 × 10^-9 coherent contrast at 10% bandwidth in a static test achieved with smaller 32 x 32 MEMS DMs Drive electronics in DST provide 16 bit resolution which contributes ~1 × 10^-10 to contrast floor	64 × 64 actuators Enable coronagraph raw contrasts of ≤1 × 10^-10 at ~20% bandwidth and raw contrast stability ≤2 × 10^-11 <3.3 nm RMS flattened WFE Drive electronics of at least 18 bits	4	5
Delta Doped UV and Visible Electron Multiplying CCDs	Low-noise UV and visible detectors for exoplanet characterization	11.5.1.1	1k × 1k EMCCD detectors (WFIRST) Dark current of 7 × 10^-4 e-/px/s CIC of 2.3 × 10^-3 e-/px/fram Read noise ~0 e- rms (in EM mode) Irradiated to equivalent of 6-year flux at L2 Updated design for cosmic ray tolerance under test 4k × 4k EMCCD fabricated (update with test specifics)	0.45–1.0 µm response; Dark current <10^-4 e-/px/s CIC < 3 × 10^-3 e-/px/fram Effective read noise <0.1e- rms Tolerant to a space radiation environment over mission lifetime at L2 4k × 4k format for Starshade IFS	4	5
Deep Depletion Visible Electron Multiplying CCDs	Low-noise detectors with improved QE at 940 nm for exoplanet characterization	11.5.1.1	Under investigation. e2V claims dark current is on boundary surface and not throughout volume CCD-201 is not currently made in deep depletion CCD-220 (regular CCD) dark current < 0.02 e-/px/s	QE >80% at 940 nm thicker silicon (up to 200 µm thick layer), deep depletion devices 4k × 4k format for Starshade IFS	4	4
Linear Mode Avalanche Photodiode Sensors	Near infrared wavelength (0.9 µm to 2.5 µm), extremely low noise detectors for exo-Earth IFS	11.5.1.2	HgCdTe photodiode arrays have read noise <~2 e- rms with multiple non-destructive reads; dark current <0.001 e-/s/pix; very radiation tolerant (JWST) HgCdTe APDs have dark current ~ 10–20 e-/s/pix, read noise <<1 e rms, and < 1k × 1k format LMAPD have 0.0015 e-/pix/s dark current, <1 to 0.1 e rms readout noise (SAPHIRA) for 320×256, 24 µm pixels	Read noise <<1 e- rms Dark current <0.002 e-/pix/s In a space radiation environment over mission lifetime 320 × 256 pixel array, 24 µm pixels	5	5
			LMAPD 1k × 1k formats of 15 µm pixels have << 1 e- rms read noise at gain of 25, full testing begins summer 2019	1k × 1k pixel array, 15 µm pixels	4	5
UV Microchannel Plate (MCP) Detectors	Low-noise detectors for general astrophysics as low as 0.115 µm	11.4.4	MCPs: QE 44% 0.115–0.18 µm with alkalai photocathode, 20% with GaN; dark current ≤0.1–1 counts/cm²/s with ALD activation and borosilicate plates	Dark current <0.001 e-/pix/s (173.6 counts/cm²/s), in a space radiation environment over mission lifetime, QE>50% (TBR) for 0.115–0.3 µm wavelengths	4	4
Microthrusters	Jitter is mitigated by using microthrusters instead of reaction wheels during exoplanet observations	11.6.1.1	Colloidal microthrusters 5–30 µN thrust with a resolution of ≤0.1 µN, 0.05 µN/√Hz, 100 days on orbit on LISA-Pathfinder Colloidal microthrusters with 100 µN thrust and 10 year lifetime under development Cold-gas micronewton thrusters flown on Gaia (TRL 9), 0.1 µN resolution, 1 mN max thrust, 0.1 µN/sqrt (Hz), 4 years of on-orbit operation	Thrust capability: 350 µN with 16 thruster cluster Thrust resolution 4.35 µN Thrust noise: 0.1 µN/√Hz Operating life: 5 years	5	5

Title

Description

Section

State of the Art

Capability Needed

TRL 2019

Expected 2023 TRL

Enabling Technologies

Starshade Petal Position Accuracy and Stability

Deploy and maintain petal position accuracy in L2 environment

11.2.1.1

Petal position deployment tolerance (≤150 µm) verified with multiple deployments of 12 m flight-like perimeter truss and no optical shield
No environmental testing

Petal position deployment accuracy on 20 m perimeter truss: ±600 µm (3σ) bias
Position stability in operational environment: ±400 µm (3σ) random

Starshade Petal Shape Accuracy and Stability

Starshade petal shape maintained after deployment, thermal at L2

11.2.1.2

Manufacturing tolerance (≤100 µm) verified with low fidelity 6 m long by 2.3 m prototype; No environmental tests
Petal deployment tests conducted on prototype petals to demonstrate rib actuation; No post-deploy cycle and petal shape stability measurements

Petal 16 m long by 4 m wide
Petal shape manufacture: ±140 µm (3σ)
Post-deploy cycle and petal shape thermal stability ≤ ±160 µm (3σ)

Starshade Scattered Sunlight for Petal Edges

Limit edge-scattered sunlight and diffracted starlight with petal optical edges

11.2.2.1

Chemically etched amorphous metal edges limit solar glint flux to 25 visual magnitudes in two main lobes, verified at coupon level
In-plane shape tolerance of ±20 µm met at half meter length after integration onto prototype petal
In plane shape stability demonstrated post-deploy and thermal cycle
Scatter performance on half meter edge verified post environment

One meter length edges assembled precisely onto petal
Petal edge in-plane shape tolerance: ±66 μm (3σ)
Petal edge in-lane placement tolerance: ±55 μm (3σ)
Solar glint: 26.25 (TBR) visual magnitudes in two main lobes

Starshade Contrast Performance Modeling and Validation

Validate at flight-like Fresnel numbers the equations that predict the contrasts

11.2.2.2

1.5 × 10^-10contrast demonstrated at Fresnel NumberR=1 ~13 (monochromatic)
Expect 1 × 10^-10 contrast demonstrated at Fresnel NumberR=1 ~13 (10% bandwidth) in March 2019

Experimentally validated models with scaled flight-like geometry and Fresnel NumberR=1 ≥12 across a broadband optical bandpass. Validated models are traceable to 1 × 10^-10 contrast system performance in space

Starshade Lateral Formation Sensing

Lateral formation flying sensing to keep telescope in starshade’s dark shadow

11.2.3.1

Simulations have shown centroid to ≤1/10th aperture with ample flux to support control loop
Control algorithms demonstrated control ≤1 m radius within line of sight of the star for durations representative of typical starshade observation times

Demonstrate sensing lateral errors ≤0.40 m accuracy (≤1/10th aperture) at scaled flight separations
Control algorithms demonstrated with scaled lateral control corresponding to ≤1 m of the line of sight

Large Mirror Fabrication

Large monolith mirror that meets tight surface figure error and thermal control requirements at visible wavelengths

11.3.1.1

4.2 m diameter, 420 mm thick blanks standard
Schott demonstrated computer-controlled-machine lightweighting to pocket depth of 340 mm, 4 mm rib thickness on E-ELT M5 and 240 mm deep/2 mm thick rib on Schott 700 mm diameter test unit
State-of-the-practice (SOP) lightweighting has yielded large mirrors of aerial density 70 kg/m₂
Zerodur® can achieve 2.83 parts per billion/K CTE homogeneity (DKIST mirror)
Wavefront stability: 25 nm rms for HST in LEO Wavefront Error of WFIRST-like primary mirror (spatial frequency cycles/beam diam. : nm RMS):

0-7 cy/D: 6.9 nm RMS
7-100 cy/D: 6.0 nm RMS
>100 cy/D: 0.8 nm RMS

4.04 m diameter substrate
3–4 mm ribs, 14 mm facesheet, and pocket depth of 290 mm for 400 mm thick blank
Aerial density 110 kg.m₂
< 5 ppb/K CTE homogeneity
First mode ≥60 Hz
Wavefront stability of 100s to a few picometers rms (depending on spatial frequency) over 100s of seconds
Wavefront Error (spatial frequency cycles/beam diam. : nm RMS):

0-7 cy/D: 6.9 nm RMS
7-100 cy/D: 6.0 nm RMS
>100 cy/D: 0.8 nm RMS

Large Mirror Coating Uniformity

Mirror coating with high spatial uniformity over the visible spectrum

11.3.1.2

Reflectance uniformity <0.5% of protected Ag on 2.5 m TPF Technology Demonstration Mirror
IUE, HST, and GALEX used MgF₂ on Al to obtain >70% reflectivity from 0.115 µm to 2.5 µm
Operational life: >28 years on HST

Reflectance uniformity <1% over 0.45–1.0 µm
Reflectivity comparable to HST:

0.115–0.3 µm: ≥70 %
0.3 – 0.45 µm: ≥88%
0.45 – 1.0 µm: ≥85 %
1.0 - 1.8 µm: ≥90 %

Operational life >10 years

Laser Metrology

Sensing for control of rigid body alignment of telescope front-end optics

11.3.2.1

Thermally stabilized Planar Lightwave Circuit fully tested
Nd:YAG ring laser and modulator flown on LISA-Pathfinder
Phase meters flown on LISA-Pathfinder and Grace Follow-On
Sense at 1 kHz bandwidth
Uncorrelated per gauge error of 0.1 nm
Laser Met System at JPL expected TRL 6 by 9/19

Sense at 100 Hz bandwidth
Uncorrelated per gauge error of 0.1 nm

Coronagraph Architecture

Suppress starlight by a factor of ≤1E-10 at visible and near-IR wavelengths

11.4.1.1

Hybrid Lyot: 6 × 10^-10 raw contrast at 10% bandwidth across angles of 3–16 λ/D demonstrated with a linear mask and an unobscured pupil in a static vacuum lab environment
Vector vortex charge 4: 5 × 10^-10 raw contrast monochromatic across angles of 2–7 λ/D
Lyot: 3.6 × 10^-10 raw contrast at 10% bandwidth over 3–7 λ/D in a static lab environment (DST)
Vector vortex charge 6: 8.5 × 10^-9coherent contrast at 10% bandwidth across angles of 3–8 λ/D demonstrated with an unobscured pupil in a static lab environment

Vortex Charge 6
Raw contrast of ≤1 × 10^-10
Raw contrast stability of ≤2 × 10^-11
Inner working angle (IWA) ≤ 2.4 λ/D
Coronagraph throughput ≥10%
Bandwidth ≥20%

Zernike Wavefront Sensing and Control (ZWFS)

Sensing and control of low-order wavefront drift; monitoring of higher order Zernike modes

11.4.2

<0.36 mas rms per axis LoS residual error demonstrated in lab with a fast-steering mirror attenuating a 14 mas LOS jitter and reaction wheel inputs on Mv = 5 equivalent source; ~26 pm rms sensitivity of focus (WFIRST Coronagraph Instrument Testbed)
WFE stability of 25 nm/orbit in low Earth orbit (HST). Higher low-order modes sensed to 10–100 nm WFE rms on ground-based telescopes

LoS error <0.2 mas rms per axis
Wavefront stability:≤~100 pm rms over 1 second for vortex
WFE <0.76 nm rms

Deformable Mirrors

Flight-qualified large-format deformable mirror

11.4.3

Micro-electromechanical DMs available up to 64 × 64 actuators, 400 µm pitch with 6 nm RMS flattened WFE; 3.3 nm RMS demonstrated on 32 × 32 DM
8.5 × 10^-9 coherent contrast at 10% bandwidth in a static test achieved with smaller 32 x 32 MEMS DMs
Drive electronics in DST provide 16 bit resolution which contributes ~1 × 10^-10 to contrast floor

64 × 64 actuators
Enable coronagraph raw contrasts of ≤1 × 10^-10 at ~20% bandwidth and raw contrast stability ≤2 × 10^-11
<3.3 nm RMS flattened WFE
Drive electronics of at least 18 bits

Delta Doped UV and Visible Electron Multiplying CCDs

Low-noise UV and visible detectors for exoplanet characterization

11.5.1.1

1k × 1k EMCCD detectors (WFIRST)
Dark current of 7 × 10^-4 e-/px/s
CIC of 2.3 × 10^-3 e-/px/fram
Read noise ~0 e- rms (in EM mode)
Irradiated to equivalent of 6-year flux at L2
Updated design for cosmic ray tolerance under test
4k × 4k EMCCD fabricated (update with test specifics)

0.45–1.0 µm response;
Dark current <10^-4 e-/px/s
CIC < 3 × 10^-3 e-/px/fram
Effective read noise <0.1e- rms
Tolerant to a space radiation environment over mission lifetime at L2
4k × 4k format for Starshade IFS

Deep Depletion Visible Electron Multiplying CCDs

Low-noise detectors with improved QE at 940 nm for exoplanet characterization

11.5.1.1

Under investigation. e2V claims dark current is on boundary surface and not throughout volume
CCD-201 is not currently made in deep depletion
CCD-220 (regular CCD) dark current < 0.02 e-/px/s

QE >80% at 940 nm
thicker silicon (up to 200 µm thick layer), deep depletion devices
4k × 4k format for Starshade IFS

Linear Mode Avalanche Photodiode Sensors

Near infrared wavelength (0.9 µm to 2.5 µm), extremely low noise detectors for exo-Earth IFS

11.5.1.2

HgCdTe photodiode arrays have read noise <~2 e- rms with multiple non-destructive reads; dark current <0.001 e-/s/pix; very radiation tolerant (JWST)
HgCdTe APDs have dark current ~ 10–20 e-/s/pix, read noise <<1 e rms, and < 1k × 1k format
LMAPD have 0.0015 e-/pix/s dark current, <1 to 0.1 e rms readout noise (SAPHIRA) for 320×256, 24 µm pixels

Read noise <<1 e- rms
Dark current <0.002 e-/pix/s
In a space radiation environment over mission lifetime
320 × 256 pixel array, 24 µm pixels

LMAPD 1k × 1k formats of 15 µm pixels have << 1 e- rms read noise at gain of 25, full testing begins summer 2019

1k × 1k pixel array, 15 µm pixels

UV Microchannel Plate (MCP) Detectors

Low-noise detectors for general astrophysics as low as 0.115 µm

11.4.4

MCPs: QE 44% 0.115–0.18 µm with alkalai photocathode, 20% with GaN; dark current ≤0.1–1 counts/cm²/s with ALD activation and borosilicate plates

Dark current <0.001 e-/pix/s (173.6 counts/cm²/s), in a space radiation environment over mission lifetime,
QE>50% (TBR) for 0.115–0.3 µm wavelengths

Microthrusters

Jitter is mitigated by using microthrusters instead of reaction wheels during exoplanet observations

11.6.1.1

Colloidal microthrusters 5–30 µN thrust with a resolution of ≤0.1 µN, 0.05 µN/√Hz, 100 days on orbit on LISA-Pathfinder
Colloidal microthrusters with 100 µN thrust and 10 year lifetime under development
Cold-gas micronewton thrusters flown on Gaia (TRL 9), 0.1 µN resolution, 1 mN max thrust, 0.1 µN/sqrt (Hz), 4 years of on-orbit operation

Thrust capability: 350 µN with 16 thruster cluster
Thrust resolution 4.35 µN
Thrust noise: 0.1 µN/√Hz
Operating life: 5 years

The technology roadmaps (Figure 1 to Figure 6 below) show the steps of development of current technology readiness level (TRL) to TRL 6 for each of the HabEx enabling technologies listed in Table 1.

Figure E-1. Roadmap to TRL 6 for large mirror fabrication of a 4 m monolithic mirror and for large mirror coating uniformity.

Figure E-2. The Roadmaps to TRL 6 for coronagraph architecture, Zernike wavefront sensor (WFS), and deformable mirrors (DMs) feed into a single coronagraph architecture testbed. For DMs, flight-like units including cables and connectors are put through environmental testing and post-testing verification separate from the engineering unit DMs in the coronagraph testbed.

Figure E-3. Roadmap to TRL 6 for detectors including linear mode avalanche photodiode (LMPAD), delta doped electron multiplying charge coupled devices (EMCCDs), deep depleted EMCCDs, and microchannel plate (MCP) detectors.

Figure E-4. The Roadmap to TRL 6 for starshade lateral formation sensing (SLATE) includes a high-fidelity upgrade to the previous low-fidelity SLATE testbed.

Figure E-5. Top-level summary of key activities that mature the starshade mechanical technologies to TRL 5. Credit: S5 Technology Development Plan

Figure E-6. Items marked ‘full-scale’ are full-scale for a 26 m S5 reference mission and half scale for the HabEx 52 m starshade. Half-scale, high-fidelity test articles are sufficient for TRL 6. Credit: S. Case Bradford

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