A design concept for the High Resolution Imager on the Habitable Worlds Observatory

Introduction to the show: ident: Astrophysics. The day in astrophysics: observations, models and what the data forces.

Vera: I'm Vera.

Jocelyn: And I'm Jocelyn, here with Subrahmanyan.

Vera: We're looking at the paper: "A design concept for the High Resolution Imager on the Habitable Worlds Observatory".

Jocelyn: Here's the gist of the paper. The Habitable Worlds Observatory (HWO) High Resolution Imager (HRI) design concept explores an architecture that integrates imaging, grism spectroscopy, and astrometry to meet NASA's demanding science requirements for searching for life on exoplanets and conducting transformational astrophysics The single most informative sentence about the paper's subject and finding is: A design concept for HRI, developed during concurrent design sessions by flowing down science requirements within the envelope of NASA’s EAC-1 telescope architecture Instrument Requirements and Science Drivers The instrument's design is driven by a broad range of science cases spanning exoplanetary science, solar system science, and extragalactic astrophysics The astrometric channel is critical for exoplanetary science because it supplies the planet’s mass, which is required to interpret atmospheric spectra HRI's wide wavelength range and grisms support transmission and emission spectroscopy of transiting planets from ultraviolet to infrared Solar system science goals include observations of ocean worlds like Europa, Enceladus, and Ceres Extragalactic astrophysics aims to test whether dark matter is cold and particulate or something else through substructure counting in dark matter haloes Optical Design and Beam Splitting The optical design minimizes the number of reflective surfaces upstream of the dichroic to maximize throughput and stability The instrument splits light into an ultraviolet–visible (UVIS) arm covering 200–900 nm and a near-infrared (NIR) arm covering 0.9–2.2 µm using a dichroic The split is placed at 900 nm to suit the short-wavelength limit of the infrared detector material and keep the silicon channel within its useful range The UVIS arm requires diffraction-limited performance at 420 nm, while the NIR arm needs only diffraction limited at 850 nm The forward interchange mechanism (FIM) allows for reconfiguration between simultaneous two-arm operation and single-arm operation for higher throughput Thermal and Mechanical Architecture The thermal design employs a three-nested temperature zone architecture, holding six subsystems at temperatures from 75 K to 293 K within a 4.28 m2 radiator requirement The astrometric channel alone accounts for 140 W of dissipation, while the entire NIR focal plane dissipates less than a watt The mass budget shows that the imager mass is 415 kg including the astrometric channel, which comfortably meets the 450 kg requirement excluding astrometry Data Handling and Observing Modes The detector and readout electronics offer a family of operating points along a single curve that exchanges illuminated area for cadence across roughly three orders of magnitude The imager supports five observing modes, including full frame survey mode, planetary defence mode, fast framerate imaging mode, super-fast framerate monitoring mode, and a dedicated guiding mode Mode 5 provides fine guidance and runs alongside whatever else the instrument is doing Science data move over SpaceFibre rather than SpaceWire to allow for high data rates and virtual channels for time-critical guidance data Coupled Design Dependencies The study revealed two dominant dependency chains where a choice made in one place is paid for in another, specifically the detector requirements chain and the optical requirements chain The detector requirements chain shows that meeting read noise goals can reduce ASIC dissipation by roughly a factor of ten but still requires slightly more radiator area due to lower operating temperatures The optical requirements chain demonstrates that splitting the beam into separate ultraviolet–visible and near-infrared trains allows for simultaneous multiband coverage at the cost of reduced throughput Both chains compete for the same volume, mass, and radiator budget The design leaves its optimization to a phase in which the telescope model, and therefore the input beam, are stable The study concluded that a wide-band, near diffractionlimited imager meeting HWO’s expectations is feasible within requirements for mass, volume, and power Four choices define the architecture, each coupled to science goals rather than being an engineering convenience The next phase will retain the concurrent design approach to combine the best features of this study with a previously separate UK feasibility study The UK Space Agency has funded a continuation of this study for the next phase The next phase will retain the concurrent design approach to combine the best features of this and a previously separate UK feasibility study into a single instrument concept, while adding international partners Acknowledgements The study described here was funded by the UK Space Agency through grants UKRI3163 and UKRI5725 The astrometric channel is developed by a separately-funded French team We thank colleagues at NASA’s HWO Technology Maturation Project Office for their engagement throughout, including every day of our Concurrent Design studies, and the staff of the Concurrent Design Facility at the University of Portsmouth Data Availability No new observational data were generated by this study The instrument design parameters quoted in this paper are given in full in the tables and figures References Acton D.

Vera: S., et al., 2012, in Space Telescopes and Instrumentation 2012: Optical, Infrared, and Millimeter Wave.

Jocelyn: p.

Vera: 844 Adhikari S., Banerjee A., Boddy K.

Title and authors: Vera: Now we're going to talk about what the paper actually says about the design concept for this High Resolution Imager on the Habitable Worlds Observatory. It sets out exactly how they structured their instrument to handle all those demanding science cases.

Jocelyn: They describe how they split the light into two main arms, an ultraviolet-visible arm and a near-infrared arm, using a dichroic placed at nine hundred nm. That specific choice of splitting wavelength is important for their detector material limitations.

Subrahmanyan: From a theoretical side, that spectral coverage from ultraviolet to infrared is what allows them to probe different chemical species in the atmospheres of transiting planets, which is essential for habitability studies.

Vera: And they detail the optical design by minimizing reflective surfaces before the dichroic to keep throughput high and stability up. They also mention a forward interchange mechanism that lets them reconfigure between two-arm and single-arm operation.

Jocelyn: That reconfiguration ability suggests flexibility, which is important for different observing modes, like when you need to switch between survey mode and something faster.

Subrahmanyan: Flexibility in the optical train affects the achievable angular resolution across that wide wavelength range, so those design choices have direct consequences on what we can resolve.

The paper's summary: Vera: The summary of this paper boils down to a few major points. They show how they managed to meet the requirements for mass, volume, and power while still achieving a wide-band, near diffraction-limited imager.

Jocelyn: They highlight that the astrometric channel is critical because it supplies the planet's mass needed to interpret spectra, and they detail how this channel shares volume allocation with other parts of the design.

Subrahmanyan: The paper points out two dominant dependency chains: one involving detector requirements and another involving optical requirements. These chains compete for the same budget, meaning a choice in one area directly impacts the other.

Vera: Specifically, they show how meeting read noise goals on the detectors can reduce ASIC dissipation by roughly a factor of ten, but that still needs more radiator area because of lower operating temperatures.

Jocelyn: And the optical chain shows that splitting the beam into UVIS and NIR trains lets them get multiband coverage simultaneously, but it comes at a cost to throughput.

Subrahmanyan: The paper concludes that meeting these requirements for mass, volume, and power for a wide-band imager is feasible within those constraints. It’s a confirmation of the concept study's viability under NASA’s EAC-one baseline <ref:2610.29957#pg1>.

The paper's improvements: Vera: This section focuses on how the paper suggests they can improve the initial design concept. They focus on addressing those two dependency chains we just talked about—detector and optical requirements.

Jocelyn: The paper shows that meeting read noise goals can reduce ASIC dissipation by a factor of ten, which is a positive for power constraints, but it also requires slightly more radiator area because of lower operating temperatures.

Subrahmanyan: And on the optical side, splitting the beam into separate ultraviolet-visible and near-infrared trains allows for simultaneous multiband coverage at the cost of reduced throughput. They are balancing those trade-offs carefully here.

Vera: The paper notes that these two chains compete for the same volume, mass, and radiator budget, so they have to optimize where they spend their limited resources.

Jocelyn: They also mention that the design leaves its optimization to a phase where the telescope model and input beam become stable before final tuning. That means there's still room for refinement later on.

Subrahmanyan: The main improvement suggested is that these coupled designs are driven by science goals rather than just engineering convenience, which they emphasize as a key guiding principle moving forward.

Conclusion: Vera: So, to wrap up the paper "A design concept for the High Resolution Imager on the Habitable Worlds Observatory", they confirm that a wide-band, near diffraction-limited imager meeting HWO’s expectations is feasible within mass, volume, and power requirements.

Jocelyn: They emphasize that four choices define the architecture, and each choice is coupled to science goals rather than just an engineering convenience. It’s not about picking the best hardware for hardware's sake here.

Subrahmanyan: From a theoretical perspective, this design concept provides a path forward by showing how the necessary astrometric channel connects to structure formation studies and tests on dark matter substructure.

Vera: It confirms that they can get that planet mass measurement needed for exoplanet science while maintaining the infrared capabilities for studying things like Europa or Enceladus.

Jocelyn: They’re moving into the next phase, combining this concurrent design approach with a separate UK feasibility study, and they have continued funding from the UK Space Agency to do that.

Subrahmanyan: It sounds like the next step is taking these combined concepts—this paper and that earlier study—and integrating them with international partners for the final instrument concept.

Vera: That’s where things get really interesting, seeing how all those different science drivers actually merge into one functional instrument.

Jocelyn: It gives us a concrete picture of what the next set of tests will look like when they start building out this HRI design.