Research and Analysis for Planetary Defense In Situ Spacecraft Missions to Near-Earth Objects
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Brent W. Barbee↗
Engineering topics
Paul A. Abell
Publications and source records attributed to Paul A. Abell.
Technology Gaps for Rapid Response Missions to Near-Earth Objects, Interstellar Objects, and Long-Period Comets
The last several years has seen the discovery of the first two interstellar objects, the first ever planetary defense mission, recommendation for a rapid reconnaissance planetary defense demonstration, and the continued emergence of a robust commercial small satellite industry. The present and near future also consist of emerging next-generation observatories including Vera Rubin and NEO Surveyor. These seemingly disparate events converge in the context of rapid response: a cross-cutting capability that would enable NASA and the international community to quickly discover and respond to an emerging target such as a near-Earth object (NEO), interstellar object (ISO), or long-period comet (LPC) either for rapid characterization of a potential threat, or revolutionary science that would inform early solar system formation and evolution. In late October 2022, subject matter experts gathered at the California Institute of Technology in a week-long workshop sponsored by the Keck Institute for Space Studies (KISS) to address enabling mission concepts for rapid response and key technology gaps (final report in progress). These experts concurred that the ability to respond on the order of a few months is necessary for rapid in-situ characterization of a NEO, ISO, or LPC, and that while there are several technology gaps, this capability could be realized in the near future.
Technology gaps↗
PLANETARY DEFENSE: FINDINGS AND RECOMMENDATIONS FROM THE NATIONAL ACADEMIES PLANETARY SCIENCE AND ASTROBIOLOGY DECADAL SURVEY 2023 - 2032
The National Academies of Sciences, Engineering, and Medicine was chartered by the NASA Science Mission Directorate (SMD), with support from the National Science Foundation, to conduct a new decadal survey to develop a comprehensive science and mission strategy for planetary science (1). The survey was tasked to determine the current state of knowledge and to identify the most important scientific questions to be addressed in astrobiology and planetary science during the upcoming decade of 2023 - 2032. For the first time, the decadal survey also included and addressed the topic of planetary defense, now recognized as a key element of NASA’s planetary science activities under the direction of NASA’s SMD Planetary Defense Coordination Office. The topic of planetary defense was included in the decadal survey as a dedicated chapter, divided into five sections based on the framework from the U.S. National NEO Preparedness Strategy and Action Plan (2). These sections discussed: NEO Detection, Tracking, and Characterization NEO Modelling, Prediction, and Integration NEO Deflection and Disruption Missions International Cooperation on NEO Preparation NEO Impact Emergency Procedures and Action Protocols Content of these sections included identifying the activities, ground- and space-based assets, facilities, resources, technologies, and missions that should be considered to enable NEO preparedness over the next decade. Supporting inputs to this chapter involved contributions from submitted white papers authored by many members of the NEO science and planetary defense communities. In addition, a planetary defense rapid mission architecture study commissioned by the decadal survey small bodies panel and led by the Jet Propulsion Laboratory examined several different types of in-situ characterization and mitigation demonstration missions. All of this input contributed to the formulation of 42 findings and 11 recommendations that suggest a path forward for increasing our understanding of the NEO population and their associated physical characteristics, modelling the impact probabilities and hazard potential of these objects, and implementing plans to develop and test NEO impact mitigation capabilities. Including planetary defense in the decadal survey has helped sharpen the focus on this international issue and provided key inputs for stakeholders and decision makers to consider when developing future planetary defense-related activities. Such information is vital for developing a long-term integrated planetary defense capability able to protect humanity in the decades to come.
NEO Detection and Characterization↗
Hayabusa2#’s Exploration to Asteroids 2001 CC21 and 1998 KY26 Provides Key Insights Into Planetary Defense
The Hayabusa2 extended mission, nicknamed Hayabusa2# (SHARP: Small Hazardous Asteroid Reconnaissance Probe), started its mission after the Hayabusa2 spacecraft successfully returned in December 2020 to the Earth with Ryugu's samples and released the Sample Return Capsule containing it. Hayabusa2#’s key operations include flying by Near Earth Asteroid (98943) 2001 CC21 and rendezvousing with Near-Earth Asteroid 1998 KY26. The flyby is planned to be in 2026, and the rendezvous will be in 2031. Detailed investigations of these targets enable maturing key knowledge and technologies necessary for planetary defense. This paper reviews the characteristics of these targets and strategies to maximize outcomes from the mission. The spacecraft will fly by 2001 CC21 at a speed of ~5 km/s in 2026. Given constraints on the spacecraft condition, not designed to perform a flyby operation, operational plans require careful assessments to maximize the proximity observations of this asteroid. The ~700 m diameter asteroid's shape is currently unknown, though lightcurve observations suggest the asteroid is elongated. While the spin pole is not constrained well, the spin period is about 5.02 h with uncertainties of 0.01 h [1]. The taxonomic class may be L-type, which implies the presence of Calcium-aluminum-rich inclusions (CAI), one of the primitive materials in the solar system [2], although there are studies suggesting an S-type. Therefore, this must be carefully examined. Photometric and spectroscopic observations will strongly constrain this asteroid’s properties. Our rendezvous target, 1998 KY26, is a ~30 m diameter roundish object spinning at a spin period of 10.7 min, which may represent one of the common groups of Near Earth Asteroids in size and composition that give a higher likelihood of threatening the Earth. Radar and optical observations reconstructed this asteroid's shape with high uncertainties and inferred that its surface composition might be similar to that of carbonaceous asteroids [3]. No spacecraft has ever visited such small bodies. Hayabusa2# visiting 1998 KY26 will be the first mission to document its geophysical properties, offering strong insights into what most frequent invaders look like [4].
Hayabusa2#↗
The Payload and Operations of the Hera Mission
On 26 September 2022, NASA’s DART mission successfully impacted on Dimorphos, the secondary of the binary asteroid Didymos. DART released the Light Italian Cubesat for Imaging of Asteroids (LICIACube) two weeks before the impact, and LICIACube flew by the asteroids three minutes after the impact. On approach, DART took images of both asteroids, which, supported by additional imagery from LICIACube, characterized the pre-impact state of the Didymos system. DART changed the orbit of Dimorphos around Didymos, reducing its orbital period by 33 minutes. DART will be followed by a detailed investigation of the Didymos system and the outcome of the impact by ESA’s Hera mission. Hera will be launched in October 2024 and arrive at Didymos in early 2027. The presentation will focus on the payload of the Hera mission and the operations at the asteroid system. The main objectives of the Hera mission are to: - Measure the mass of Dimorphos to accurately measure the momentum transfer efficiency of the DART impact. - Characterise the change of the surface of Dimorphos by DART, including the properties (and existence!) of the DART crater, to improve our understanding of impact physics and to observe unweathered material, recently exposed at the surface. - Determine the physical properties of Dimorphos, including its internal structure, to allow scaling of the impact to different types of asteroids. - Measure the dynamical and physical state of the Didymos and Dimorphos system to constrain binary formation scenarios. Hera is equipped with the following payload: Two Asteroid Framing Cameras (AFCs) for both science and navigation. There resolution is ~10-4 rad/pixel, or 40 cm/pixel for close observations from 4 km. They will provide the target global properties as well as local geomorphology and will investigate the crater and impact site. They will also measure the mass of Dimorphos through the “wobble” motion of Didymos. The Planetary ALTimeter (PALT) will measure the distance to the target and shape and topography information complementary to that from AFC images. The Thermal InfraRed Imager (TIRI) will provide information about the thermal properties of the Didymos system and spectral information in the mid-infrared (6 bands from 7 – 14 µm). The Hyperscout-H hyperspectral imager will provide mineralogical information from 25 spectral bands between 665 and 975 nm. Milani, a 6 unit cubesat, will carry a visible to near-IR imaging spectrometer (ASPECT, 500 – 2500 nm) to derive mineralogical information on the composition of the asteroids, and a thermogravimeter (VISTA) to measure the abundance and constrain the composition of ambient dust particles. Juventas, a 6 unit cubesat, will carry a monostatic low-frequency radar (JuRa), and a gravimeter (GRASS) to derive interior and surface properties of the asteroids. The Radio Science experiment will measure the gravity field of the Didymos system. Measurements of the acceleration of the Hera spacecraft by the asteroid pair through the radio link between Earth and Hera will be used as well as the inter-satellite link between Hera and the two cubesats. We will describe how the goals of Hera will be achieved with the different payload elements.
Michael Küppers↗
The ESA Hera Mission: Detailed Investigation of the NASA Dart Impact Outcome and Characterization of the Binary Asteroid Didymos
The Hera mission is in development in the Space Safety Program of the European Space Agency (ESA) in collaboration with JAXA for launch in October 2024. It will rendezvous with the binary asteroid (65803) Didymos in early 2027 and over the following 6 months will investigate the properties of Didymos and its small moon Dirmorphos, including the effects of the successful impact of the NASA DART probe. DART was launched on 24 November 2021 at 06:21 UTC and successfully impacted at about 6.1 km/s on the 160 meter-size Dimorphos on 26 September 2022 at 23:14 UTC. Two weeks before impact, it deployed the Light Italian Cubesat for Imaging of Asteroids (LICIACube) that provided images during the few minutes following the impact. A campaign of observations from Earth and space provided distant images of the event, which were used to determine a reduction of 33 min in the orbital period of Dimorphos around Didymos. The Hera mission will investigate the outcome of the DART impact in detail. In particular, it will determine the effects of the impact on Dimorphos’ surface, e.g., whether it produced a crater, and if so its properties, and/or whether it led to global reshaping of Dimorphos. It will accurately measure the mass of Dimorphos, which will allow quantification of the momentum enhancement factor, which is a crucial parameter to evaluate the efficiency of the kinetic impactor technique. Hera will also determine in detail the physical, thermal and compositional properties of the asteroid, including first time measurements of the internal properties, which have a critical influence on the impact outcome. With Hera and DART together, we will have a fully documented deflection test and impact experiment that will allow us to verify our numerical impact models, to be able to extrapolate this deflection test to other asteroids and to improve our understanding of the complex geological properties and response of small asteroids. Hera consists of a mother spacecraft and two cubesats. It will perform the first rendezvous with a binary asteroid, arriving at Didymos about 4 years after DART. Hera will not only contribute significantly to the planetary defense effort by documenting entirely the outcome of the DART impact, it will also greatly advance our understanding of processes in the very low gravity regime of a small asteroidv (Dimorphos) as well as our knowledge of binary asteroids and asteroid geophysics. The mission development is progressing nominally, with the Critical Design Review having been passed in Nov. 2022. The various working groups of the Hera Science Team are working intensively to support this development and be best prepared for the surprises that Hera will offer during its visit to Didymos in 2027.
Asteroid deflection↗