About ORCAS
The ORCAS mission, a first-of-its-kind hybrid space and ground observatory, will enable new science, otherwise only accessible to flagship class missions over a decade from now, at a SmallSat budget, providing unprecedented angular resolution, exquisite sensitivity and a unique flux calibrator. By enabling adaptive optics and flux calibration observations, ORCAS will deliver highly detailed images, unlocking the ability to detect a population of supermassive black hole binaries for the first time, as well as constraining the number densities of the faintest star forming clumps and understanding dark energy by measuring the distances of 10 billion year old supernovae. It will also deliver calibrated light that will vastly improve cosmology measurements, among many other advances. The low-cost ORCAS mission operating in collaboration with the W. M. Keck observatory will provide Great Observatory quality capabilities open to all US observers via a community driven observation plan. These observations will result in unique science for the mission, while also complementing and extending the science of HST, JWST, and Roman, as well as other potential future missions.
The ORCAS AS3 Report puts forward in detail the scientific reasoning for the ORCAS mission, and demonstrates that ORCAS could answer fundamental scientific questions of the 2020's, addressing our community goals. We do so by establishing the mission science traceability matrix and deriving the engineering requirements for each mission subsystem. We show that there is a viable and robust path for the ORCAS mission to achieve its scientific goals within a reasonable time frame and budget. Finally, the report presents technical details and major subsystems, including the spacecraft, payload, ground elements, mission operation concept, etc., and show that they could meet the science case requirements.
The ORCAS mission explicitly addresses two of the top three priorities of the 2010 Decadal Survey: "Cosmic Dawn: Searching for the First Stars, Galaxies, and Black Holes," and "Physics of the Universe: Understanding Scientific Principles." One of the great mysteries is the existence and growth of super-massive black holes through the merger of protogalaxies and the accretion of gas and stars; our ability to solve this mystery is limited by current angular resolution and sensitivity. The cosmic dark energy is likewise a mystery that has only grown deeper as measurements improve and disagreements appear. Photometric calibration is currently one of the largest error terms in dark energy measurements. ORCAS explores a new parameter regime in angular resolution and sensitivity, allowing for huge potential advances for these questions. Additionally, the flux calibrator would go far beyond our current capabilities, leading to quantitative advances in dark energy.
ORCAS is designed to both: 1) identify and characterize the velocity structures of the physical environments of Active Galactic Nuclei (AGN), especially M87* and those containing two or more nuclei, and 2) resolve discrepancies in measurements of the cosmic dark energy, both with spectroscopic observations of high redshift Supernovae (SNe) and with improvements in flux calibration for all SNe. These objectives drive the design requirements, and the design then enables investigations of high redshift galaxy structures, circumstellar disks, exoplanet formation, and Solar System objects.
These objectives are met by a new combination of space and ground hardware which will enable high performance Adaptive Optics (AO) at visible and NIR wavelengths on the Keck 10~m telescopes. We deploy low-risk flight hardware, which includes a commercial ESPA-Grande class satellite bus with solar electric propulsion (SEP) carrying a modified commercial laser module as an AO beacon and a photometric calibrator. The spacecraft is positioned in a 5-day Highly Elliptical Orbit (HEO), enabling 3 AO observation opportunities per orbit, such that the spacecraft remains within the isoplanatic patch (region of good AO performance) for periods of up to a few hours (target declination and wavelength dependent). The available mission sky coverage is the Keck observable sky. The bus is augmented with a high-altitude GPS system demonstrated by GSFC on the MMS (Magnetospheric Multiscale) mission, enabling high precision orbit management to place the ORCAS predicted trajectory within (± 3 milliarcsec, 3σ). ORCAS will enable ~ 300 AO observations and 1,500 photometric observations throughout its 3-year mission lifetime.