14:45 〜 15:00
[PPS01-15] Shadow Chaser: a SmallSat for stellar-occultation measurements of Uranus and Neptune’s thermospheres from Earth orbit
キーワード：Uranus、Neptune、SmallSats、Ice Giants、International Cooperation
We present the Shadow Chaser mission concept to perform stellar occultation (SO) measurements of Uranus and Neptune (U&N) from Earth orbit to transform our understanding of the middle and upper atmospheres of these Ice Giants, the last class of planets yet to be explored by an orbiter. The latest Planetary Science and Astrobiology Decadal Survey recommended a Flagship orbiter mission to Uranus to be launched in the early 2030s and a subsequent New Frontiers mission to the Neptune system; the Shadow Chaser concept aims to characterize the middle and upper atmospheres of U&N to guide the design and operations of future missions to U&N.
The key progress to be enabled by Shadow Chaser over Voyager 2 (V2) and ground-based SO measurements is the vastly improved data quality to be returned by our mission concept. The mission’s main scientific objectives includes investigating the surprisingly hot thermospheres of U&N found by Voyager 2. The highly uncertain V2 results remain controversial because they could be explained only by invoking an unknown heat source. Earth-based stellar occultation measurements sense altitudes between the upper stratosphere and lower thermosphere (approximately between 0.1 and 100 microbar levels). Our effort so far has determined the performance requirements for the Shadow Chaser concept, and shown that a >20-cm telescope aperture in Earth orbit can measure SOs with less uncertainty than V2. We present potential design options that meet the performance requirements.
The Shadow Chaser concept also offers significant potential for international cooperation by observing the SO events using multiple SmallSats. Because each SmallSat measures two latitudes where the occulted star goes behind the planet (i.e. ingress) and then re-emerges (egress), multiple SmallSats placed to measure different latitudes would enable analysis of meridional structures of the middle and upper atmospheres. Characterizing the meridional structure is critical to understanding the effects of seasonal forcing; thus, measurements from an international constellation of SmallSats could transform our understanding of the middle and upper atmospheric dynamics of U&N.
Shadow Chaser will advance science, and also improve designs of future missions to U&N. In particular, measurements by Shadow Chaser will reduce the risk in an aerocapture orbit insertion maneuver, which is a technology that may enable new interplanetary trajectories, lower cost, and enhance future missions to U&N.
The key progress to be enabled by Shadow Chaser over Voyager 2 (V2) and ground-based SO measurements is the vastly improved data quality to be returned by our mission concept. The mission’s main scientific objectives includes investigating the surprisingly hot thermospheres of U&N found by Voyager 2. The highly uncertain V2 results remain controversial because they could be explained only by invoking an unknown heat source. Earth-based stellar occultation measurements sense altitudes between the upper stratosphere and lower thermosphere (approximately between 0.1 and 100 microbar levels). Our effort so far has determined the performance requirements for the Shadow Chaser concept, and shown that a >20-cm telescope aperture in Earth orbit can measure SOs with less uncertainty than V2. We present potential design options that meet the performance requirements.
The Shadow Chaser concept also offers significant potential for international cooperation by observing the SO events using multiple SmallSats. Because each SmallSat measures two latitudes where the occulted star goes behind the planet (i.e. ingress) and then re-emerges (egress), multiple SmallSats placed to measure different latitudes would enable analysis of meridional structures of the middle and upper atmospheres. Characterizing the meridional structure is critical to understanding the effects of seasonal forcing; thus, measurements from an international constellation of SmallSats could transform our understanding of the middle and upper atmospheric dynamics of U&N.
Shadow Chaser will advance science, and also improve designs of future missions to U&N. In particular, measurements by Shadow Chaser will reduce the risk in an aerocapture orbit insertion maneuver, which is a technology that may enable new interplanetary trajectories, lower cost, and enhance future missions to U&N.