35 research outputs found
Heliocentric Effects of the DART Mission on the (65803) Didymos Binary Asteroid System
The Double Asteroid Redirect Test (DART) is NASA’s first kinetic impact–based asteroid deflection mission. The DART spacecraft will act as a projectile during a hypervelocity impact on Dimorphos, the secondary asteroid in the (65803) Didymos binary system, and alter its mutual orbital period. The initial momentum transfer between the DART spacecraft and Dimorphos is enhanced by the ejecta flung off the surface of Dimorphos. This exchange is characterized within the system by the momentum enhancement parameter, β, and on a heliocentric level by its counterpart, βe. The relationship between β and the physical characteristics of Dimorphos is discussed here. A nominal set of Dimorphos physical parameters from the design reference asteroid and impact circumstances from the design reference mission are used to initialize the ejecta particles for dynamical propagation. The results of this propagation are translated into a gradual momentum transfer onto the Didymos system barycenter. A high-quality solar system propagator is then used to produce precise estimates of the post-DART encounters between Didymos and Earth by generating updated close approach maps. Results show that even for an unexpectedly high βe, a collision between the Didymos system and Earth is practically excluded in the foreseeable future. A small but significant difference is found in modeling the overall momentum transfer when individual ejecta particles escape the Didymos system, as opposed to imparting the ejecta momentum as a single impulse at impact. This difference has implications for future asteroid deflection campaigns, especially when it is necessary to steer asteroids away from gravitational keyholes
Dynamical Characterization and Stabilization of Large Gravity-Tractor Designs
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76167/1/AIAA-32554-693.pd
Model of Double Asteroid Redirection Test Impact Ejecta Plume Observations
The Double Asteroid Redirection Test (DART) spacecraft will impact the moon Dimorphos of the [65803]
Didymos binary in order to demonstrate asteroid deflection by a kinetic impactor. DART will measure the
deflection by using ground-based telescopic observations of the orbital period change of Didymos and will carry
the Light Italian CubeSat for Imaging of Asteroids (LICIACube) cubesat, which will perform a flyby of Didymos
about 167 s after the DART impact, obtaining images of the DART impact ejecta plume. LICIACube images
showing the ejecta plume spatial structure and temporal evolution will help determine the vector momentum
transfer from the DART impact. A model is developed for the impact ejecta plume optical depth, using a pointsource scaling model of the DART impact. The model is applied to expected LICIACube plume images and shows
how plume images enable characterization of the ejecta mass versus velocity distribution. The ejecta plume
structure, as it evolves over time, is determined by the amount of ejecta that has reached a given altitude at a given
time. The evolution of the plume optical depth profiles determined from LICIACube images can distinguish
between strength-controlled and gravity-controlled impacts, by distinguishing the respective mass versus velocity
distributions. LICIACube plume images discriminate the differences in plume structure and evolution that result
from different target physical properties, mainly the strength and porosity, thereby allowing inference of these
properties to improve the determination of DART impact momentum transfer
Constraints on the perturbed mutual motion in Didymos due to impact-induced deformation of its primary after the DART impact
Binary near-Earth asteroid (65803) Didymos is the target of the proposed NASA
Double Asteroid Redirection Test (DART), part of the Asteroid Impact &
Deflection Assessment (AIDA) mission concept. In this mission, the DART
spacecraft is planned to impact the secondary body of Didymos, perturbing
mutual dynamics of the system. The primary body is currently rotating at a spin
period close to the spin barrier of asteroids, and materials ejected from the
secondary due to the DART impact are likely to reach the primary. These
conditions may cause the primary to reshape, due to landslides, or internal
deformation, changing the permanent gravity field. Here, we propose that if
shape deformation of the primary occurs, the mutual orbit of the system would
be perturbed due to a change in the gravity field. We use a numerical
simulation technique based on the full two-body problem to investigate the
shape effect on the mutual dynamics in Didymos after the DART impact. The
results show that under constant volume, shape deformation induces strong
perturbation in the mutual motion. We find that the deformation process always
causes the orbital period of the system to become shorter. If surface layers
with a thickness greater than ~0.4 m on the poles of the primary move down to
the equatorial region due to the DART impact, a change in the orbital period of
the system and in the spin period of the primary will be detected by
ground-based measurement.Comment: 8 pages, 7 figures, 2 tables, accepted for publication in MNRA
The Scientific Measurement System of the Gravity Recovery and Interior Laboratory (GRAIL) Mission
The Gravity Recovery and Interior Laboratory (GRAIL) mission to the Moon utilized an integrated scientific measurement system comprised of flight, ground, mission, and data system elements in order to meet the end-to-end performance required to achieve its scientific objectives. Modeling and simulation efforts were carried out early in the mission that influenced and optimized the design, implementation, and testing of these elements. Because the two prime scientific observables, range between the two spacecraft and range rates between each spacecraft and ground stations, can be affected by the performance of any element of the mission, we treated every element as part of an extended science instrument, a science system. All simulations and modeling took into account the design and configuration of each element to compute the expected performance and error budgets. In the process, scientific requirements were converted to engineering specifications that became the primary drivers for development and testing. Extensive simulations demonstrated that the scientific objectives could in most cases be met with significant margin. Errors are grouped into dynamic or kinematic sources and the largest source of non-gravitational error comes from spacecraft thermal radiation. With all error models included, the baseline solution shows that estimation of the lunar gravity field is robust against both dynamic and kinematic errors and a nominal field of degree 300 or better could be achieved according to the scaled Kaula rule for the Moon. The core signature is more sensitive to modeling errors and can be recovered with a small margin
ALMA Observations of the DART Impact: Characterizing the Ejecta at Sub-Millimeter Wavelengths
We report observations of the Didymos-Dimorphos binary asteroid system using
the Atacama Large Millimeter/Submillimeter Array (ALMA) and the Atacama Compact
Array (ACA) in support of the Double Asteroid Redirection Test (DART) mission.
Our observations on UT 2022 September 15 provided a pre-impact baseline and the
first measure of Didymos-Dimorphos' spectral emissivity at mm,
which was consistent with the handful of siliceous and carbonaceous asteroids
measured at millimeter wavelengths. Our post-impact observations were conducted
using four consecutive executions each of ALMA and the ACA spanning from
T3.52 to T8.60 hours post-impact, sampling thermal emission from the
asteroids and the impact ejecta. We scaled our pre-impact baseline measurement
and subtracted it from the post-impact observations to isolate the flux density
of mm-sized grains in the ejecta. Ejecta dust masses were calculated for a
range of materials that may be representative of Dimorphos' S-type asteroid
material. The average ejecta mass over our observations is consistent with
1.3--6.4 kg, with the lower and higher values calculated for
amorphous silicates and for crystalline silicates, respectively. Owing to the
likely crystalline nature of S-type asteroid material, the higher value is
favored. These ejecta masses represent 0.3--1.5\% of Dimorphos' total mass and
are in agreement with lower limits on the ejecta mass based on measurements at
optical wavelengths. Our results provide the most sensitive measure of mm-sized
material in the ejecta and demonstrate the power of ALMA for providing
supporting observations to spaceflight missions
Pre-encounter predictions of DART impact ejecta behavior and observability
We overview various efforts within the DART Investigation Team’s Ejecta Working Group to predict the characteristics, quantity, dynamical behavior, and observability of DART impact ejecta. We discuss various methodologies for simulation of the impact/cratering process with their advantages and drawbacks in relation to initializing ejecta for subsequent dynamical propagation through and away from the Didymos system. We discuss the most relevant forces acting on ejecta once decoupled from Dimorphos’s surface and highlight various software packages we have developed and used to dynamically simulate ejecta under the action of those forces. With some additional software packages, we explore the influence of additional perturbing effects, such as interparticle collisions within true N-body codes and nonspherical and rotating particles’ interplay with solar radiation pressure. We find that early-timescale and close-proximity ejecta evolution is highly sensitive to some of these effects (e.g., collisions) while relatively insensitive to other factors. We present a methodology for turning the time-evolving size- and spatially discretized number density field output from ejecta simulations into synthetic images for multiple platforms/cameras over wide-ranging vantage points and timescales. We present such simulated images and apply preliminary analyses to them for nominal and off-nominal cases bracketing realistic total mass of ejecta and ejecta cumulative size–frequency distribution slope. Our analyses foreshadow the information content we may be able to extract from the actual images taken during and after the DART encounter by both LICIACube and Earth-vicinity telescopes.ANII: FCE_1_2019_1_15645
The Dimorphos ejecta plume properties revealed by LICIACube
The Double Asteroid Redirection Test (DART) had an impact with Dimorphos (a satellite of the asteroid Didymos) on 26 September 20221. Ground-based observations showed that the Didymos system brightened by a factor of 8.3 after the impact because of ejecta, returning to the pre-impact brightness 23.7 days afterwards2. Hubble Space Telescope observations made from 15 minutes after impact to 18.5 days after, with a spatial resolution of 2.1 kilometres per pixel, showed a complex evolution of the ejecta3, consistent with other asteroid impact events. The momentum enhancement factor, determined using the measured binary period change4, ranges between 2.2 and 4.9, depending on the assumptions about the mass and density of Dimorphos5. Here we report observations from the LUKE and LEIA instruments on the LICIACube cube satellite, which was deployed 15 days in advance of the impact of DART. Data were taken from 71 seconds before the impact until 320 seconds afterwards. The ejecta plume was a cone with an aperture angle of 140 ± 4 degrees. The inner region of the plume was blue, becoming redder with increasing distance from Dimorphos. The ejecta plume exhibited a complex and inhomogeneous structure, characterized by filaments, dust grains and single or clustered boulders. The ejecta velocities ranged from a few tens of metres per second to about 500 metres per second.This work was supported by the Italian Space Agency (ASI) in the LICIACube project (ASI-INAF agreement AC no. 2019-31-HH.0) and by the DART mission, NASA contract 80MSFC20D0004. M.Z. acknowledges Caltech and the Jet Propulsion Laboratory for granting the University of Bologna a licence to an executable version of MONTE Project Edition software. M.Z. is grateful to D. Lubey, M. Smith, D. Mages, C. Hollenberg and S. Bhaskaran of NASA/JPL for the discussions and suggestions regarding the operational navigation of LICIACube. G.P. acknowledges financial support from the Centre national d’études spatiales (CNES, France). A.C.B. acknowledges funding by the NEO-MAPP project (grant agreement 870377, EC H2020-SPACE-2019) and by the Ministerio de Ciencia Innovación (PGC 2018) RTI2018-099464-B-I00. F.F. acknowledges funding from the Swiss National Science Foundation (SNSF) Ambizione (grant no. 193346). J.-Y.L. acknowledges the support from the NASA DART Participating Scientist Program (grant no. 80NSSC21K1131). S.D.R. and M.J. acknowledge support from the Swiss National Science Foundation (project no. 200021_207359)
Investigating the DART Impact Event with the Lucy LOng Range Reconnaissance Imager
NASA’s Lucy mission is the first to provide flyby reconnaissance of the Jovian trojan asteroids, which are thought to be primordial small bodies that formed at a variety of heliocentric distances during the early stages of the solar system’s formation and were subsequently captured into Jupiter’s L4 and L5 Lagrange stability zones. Since its successful launch on 2021-Oct-16, the Lucy spacecraft has been orbiting the sun within the inner solar system. On 2022-Oct-16, Lucy executes the first of three Earth Gravity Assists (EGAs) that put the spacecraft on the correct trajectory to achieve its encounters with the Jovian trojans. The DART kinetic impact on the secondary body of the Didymos-Dimorphos binarysystem occurs 20 days prior to EGA1, at a time when the Lucy spacecraft is well-placed to observe it. Lucy carries a sensitive panchromatic camera, the Lucy LOng Range Reconnaissance Imager (L’LORRI), which is capable of detecting the binary system with high signal-to-noise ratio (SNR) and with temporal cadences as fast as once per second.
The observing geometry from Lucy is similar to that from the Earth: the range to the Didymos system is 0.126 au from Lucy vs 0.0757 au from Earth, and the solar phase angle is 31.9 deg vs 53.2 deg. The L’LORRI investigation of the DART impact event is divided into eight separate observational phases, starting 12 hr before the impact and ending 24 hr afterwards. L’LORRI cannot resolve the binary, but instead records the total brightness, which is expected to increase after the DART impact due to reflected sunlight from the ejecta. The first two phases are designed to obtain baseline photometry of the Didymos system covering both the Didymos-Dimorphos mutual orbit period (11.92 hr) and the rotational period of Didymos (2.26 hr). Phase 3 covers the impact event itself at one second cadence, starting 3 minutes beforeimpact and ending 4 minutes afterwards. Lucy has a clear view of the predicted DART impact site, theoretically enablingL’LORRI to detect an optical flash in the unlikely event it is brighter than Didymos itself. L’LORRI observations during phases 4 through 8 are designed to monitor the temporal and spatial evolution of ejecta associated with the impact event, but ejecta don’t leave the central pixel during Lucy’s observing period unless their speed is greater than about 2 m/s