Abstract
The precise orbit of the Hayabusa2 spacecraft with respect to asteroid Ryugu is dynamically determined using the data sets collected by the spacecraft’s onboard laser altimeter (LIght Detection And Ranging, LIDAR) and automated image tracking (AIT). The LIDAR range data and the AIT angular data play complementary roles because LIDAR is sensitive to the line-of-sight direction from Hayabusa2 to Ryugu, while the AIT is sensitive to the directions perpendicular to it. Using LIDAR and AIT, all six components of the initial state vector can be derived stably, which is difficult to achieve using only LIDAR or AIT. The coefficient of solar radiation pressure (SRP) of the Hayabusa2 spacecraft and standard gravitational parameter (GM) of Ryugu can also be estimated in the orbit determination process, by combining multiple orbit arcs at various altitudes. In the process of orbit determination, the Ryugu-fixed coordinate of the center of the LIDAR spot is determined by fitting the range data geometrically to the topography of Ryugu using the Markov Chain Monte Carlo method. Such an approach is effective for realizing the rapid convergence of the solution. The root mean squares of the residuals of the observed minus computed values of the range and brightness-centroid direction of the image are 1.36 m and 0.0270°, respectively. The estimated values of the GM of Ryugu and a correction factor to our initial SRP model are 29.8 ± 0.3 m3/s2 and 1.13 ± 0.16, respectively.
Highlights
Hayabusa2 is an asteroid-sample return mission that is being conducted by Japan Aerospace Exploration Agency (JAXA)
Orbit determination using Light detection and ranging laser altimeter (LIDAR) and automated image tracking (AIT) data sets As mentioned in “Introduction” section the Hayabusa2 orbit can be determined by radiometric observation from the Earth
In the case of an orbiter of a body, an initial state vector of the spacecraft can be determined from the range data by using leastsquares method (LSM), if the number of range observations is sufficiently large
Summary
Hayabusa is an asteroid-sample return mission that is being conducted by Japan Aerospace Exploration Agency (JAXA). The spacecraft was launched in December 2014, performed an Earth swing-by utilizing Earth gravity in December 2015, and arrived at the target asteroid Ryugu in June 2018. Subsequent to its arrival at Ryugu, Hayabusa performed various observations and experiments, such as remote-sensing observations using onboard instruments, releases of a small rover and lander, ejection of the impactor, and sample collection from the surface and subsurface of Ryugu. Kitazato et al (2019) analyzed the spectrum absorption in the 3-μm-wavelength band obtained from the near-infrared spectrometer (NIRS3) observation and found that water was present in the form of hydrous minerals on the surface of Ryugu. The evolution process from the parent body to Ryugu was discussed based on the surface topography, spectrum, and thermal properties of Ryugu
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