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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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DOE OSTI2025

Dispersion Leverage Coronagraph: a nulling coronagraph for use on primary objective grating telescopes

Here, we present the Dispersion Leverage Coronagraph (DLC), a variation of the Achromatic Interfero Coronagraph (AIC) that is designed for optical systems featuring large, dispersive primary objective gratings. DLC was originally designed for the Diffractive Interfero Coronagraph Exoplanet Resolver (DICER), a notional 20 m class infrared space telescope utilizing the enhanced one-dimensional angular resolution of large diffraction gratings to discover and characterize near-Earth exoplanets. Here we develop the theoretical foundation for DLC, and apply it to DICER as an example use case. We derive important properties of the DLC system, including focal plane transmission maps, stellar leakage, residual optical path difference tolerance, and pointing error/jitter considerations. Ultimately, we found that DLC effectively nulls an on-axis target across the entire spectrum in the focal plane, allowing for 2D/λ diffraction-limited imaging. It requires asymmetrical fine-guidance tolerances on pointing error/jitter. We work through a benchmark DICER design, explaining the need for a second disperser to reduce background from Zodiacal light, and showing that it could plausibly find and characterize ∼4 nearby, habitable exoplanets around Sun-like stars in a 7-year mission; about 30% of the habitable exoplanets within 8 pc were found in our simulation. The DLC may be useful for any application requiring extremely high-resolution, close companion spectroscopy.

AIC↗
DOE OSTI2021

Probing the Capability of Future Direct-imaging Missions to Spectrally Constrain the Frequency of Earth-like Planets

A critical question in astrobiology is whether exo-Earth candidates (EECs) are Earth-like, in that they originate life that progressively oxygenates their atmospheres similarly to Earth. We propose answering this question statistically by searching for O{sub 2} and O{sub 3} on EECs with missions such as HabEx or LUVOIR. We explore the ability of these missions to constrain the fraction, f {sub E}, of EECs that are Earth-like in the event of a null detection of O{sub 2} or O{sub 3} on all observed EECs. We use the Planetary Spectrum Generator to simulate observations of EECs with O{sub 2} and O{sub 3} levels based on Earth’s history. We consider four instrument designs—LUVOIR-A (15 m), LUVOIR-B (8 m), HabEx with a starshade (4 m, “HabEx/SS”), and HabEx without a starshade (4 m, “HabEx/no-SS”)—as well as three estimates of the occurrence rate of EECs (η {sub earth}): 24%, 5%, and 0.5%. In the case of a null detection, we find that for η {sub earth} = 24%, LUVOIR-A, LUVOIR-B, and HabEx/SS would constrain f {sub E} to ≤0.094, ≤0.18, and ≤0.56, respectively. This also indicates that if f {sub E} is greater than these upper limits, we are likely to detect O{sub 3} on at least one EEC. Conversely, we find that HabEx/no-SS cannot constrain f {sub E}, due to the lack of a coronagraph ultraviolet channel. For η {sub earth} = 5%, only LUVOIR-A and LUVOIR-B would be able to constrain f {sub E}, to ≤0.45 and ≤0.85, respectively. For η {sub earth} = 0.5%, none of the missions would allow us to constrain f {sub E}, due to the low number of detectable EECs. We conclude that the ability to constrain f {sub E} is more robust to uncertainties in η {sub earth} for missions with larger aperture mirrors. However, all missions are susceptible to an inconclusive null detection if η {sub earth} is sufficiently low.

74 ATOMIC AND MOLECULAR PHYSICS↗