Ephemeris and hazard assessment for near-Earth asteroid (101955) Bennu based on OSIRIS-REx data

Small bodies such as the near-Earth asteroid Bennu drift in their orbit due to thermal radiation forces (the Yarkovsky effect). Ground-based observations have indicated a nonzero probability of Bennu impacting Earth, depending on how its orbit evolves. Thus, among the goals of the OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer) mission to Bennu were to precisely measure the Yarkovsky effect and refine the impact hazard assessment for this body. Here we address these objectives. Using OSIRIS-REx spacecraft tracking data, we derive meter-level constraints on the distance between Earth and Bennu from January 2019 to October 2020. While these data greatly improve the knowledge of the trajectory of Bennu, they also require an unprecedented fidelity for the modeling of an asteroid’s trajectory. In particular, special care is needed to take into account the contribution of 343 small-body perturbers and the uncertainty in their masses. Radiation effects such as the Poynting–Robertson drag, so far only considered for interplanetary dust dynamics, now become a consideration for modeling the trajectory of a 500-m asteroid such as Bennu. By employing a thermophysical model based on OSIRIS-REx’s characterization of Bennu, we estimate a semimajor axis drift of−284.6 ± 0.2m/yr (signal-to-noise ratio∼1400) at epoch 2011 January 1 caused by the Yarkovsky effect. The largest source of modeling error is solar wind drag, which may lower the magnitude of the semimajor axis drift from the Yarkovsky effect by up to 0.16 m/yr. The Yarkovsky-related semimajor axis drift varies by roughly±1m/yr as the orbit of Bennu evolves due to planetary perturbations from 1900 to 2135. The Yarkovsky thermophysical model proves to be extremely accurate by predicting a bulk density estimate within 0.1% of that estimated through gravity science analysis. Compared to the information available before the OSIRIS-REx mission, the knowledge of the circumstances of the scattering Earth encounter that will occur in 2135 improves by a factor of 20, thus allowing us to rule out many previously possible impact trajectories. However, there remain some impact trajectories compatible with the data. Prior to the spacecraft encounter, the overall impact probability through 2200 was 3.7 × 10−4 (1 in 2700). As a result of our analysis, the cumulative impact probability through 2300 becomes 5.7 × 10−4 (1 in 1750) and the most significant individual impact solution is for September 2182, with an impact probability of 3.7 × 10−4 (1 in 2700). Both Bennu and (29075) 1950 DA have a Palermo scale value of −1.42 and share the distinction as the currently most hazardous object in the asteroid catalog

System level dispersion analysis examining program benefits to a low-thrust interplanetary CubeSat from autonomous guidance and navigation

Thesis: S.M., Massachusetts Institute of Technology, Department of Aeronautics and Astronautics, 2016.Cataloged from PDF version of thesis.Includes bibliographical references (pages 162-165).Ground based measurements through the Deep Space Network (DSN) are unlikely to be available as often for CubeSats as for prior deep space programs because higher priority missions will take precedence for access to the limited and expensive DSN resource. Consequently, to make the most of CubeSats in deep space, dependence on the ground must be minimized. In this research a closed-loop Linear Covariance (LinCov) analysis was performed to quantify the effects of the guidance and navigation (GN) system on trajectory dispersions for a low-thrust CubeSat in route to entry-interface conditions at Mars. Applicable mission plan concepts, appropriate analysis settings, as well as required mission performance used in the analysis were based on input collected from industry as well as criteria from prior Mars missions and the Deep Space 1 mission. Information was gathered regarding expected ground-derived orbit determination accuracy levels as a function of decreased DSN use. Optical navigation based on line-of-sight measurements of Mars was then investigated as a means to maintain onboard navigation accuracy despite reduced DSN coverage. The ability of onboard optical navigation to reduce needed ground tracking frequency and associated costs was found practical for interplanetary cruise. The expected resulting financial benefits from decreased DSN were quantified. Recommendations for onboard GN system capabilities and mission goals are made. LinCov was also explored as the core of a basic onboard mission planner that could enable more autonomous CubeSat interplanetary trajectory management.by Dianna M. Velez.S.M

Attitude Determination and Control Subsystem Design for a CubeSat

This project continues the design and testing of the Attitude Determination and Control Subsystem (ADCS) for a nano-satellite. The primary mission objective is solar X-ray spectroscopy using the Sphinx-NG instrument, which requires that the CubeSat fly in a high-altitude, polar, sun- synchronous orbit pointing to the sun with 1-2 degrees of accuracy. The ADCS requires gyroscopes, sun sensors, and a magnetometer for attitude determination. Attitude control is executed using magnetorquers as actuators. This project focused on the analysis of attitude determination algorithms and control policies to select the most efficient and accurate methods. After method selection, simulations of the ADCS were conducted, and research was performed concerning hardware testing for the ADCS

Moon Water

Water was discovered on the Moon in October 2009 by the Chandrayaan-1 mission. The conditions on the Moon such as no atmosphere and low temperatures, made the water in the form of ice. The origins of this water were determined to be meteorites and winds. The location of the water was determined to be affected by the diurnal cycle and cold traps in craters. The goals of this report were to estimate the amount of water ice present on the Moon, the location and to detail methods to obtain this water for human use. It was calculated that approximately 3.76 X 10^12 grams of water ice is present within the cold traps of the permanently shadowed regions at the lunar poles

Successful Kinetic Impact into an Asteroid for Planetary Defense.

While no known asteroid poses a threat to Earth for at least the next century, the catalog of near-Earth asteroids is incomplete for objects whose impacts would produce regional devastation1,2. Several approaches have been proposed to potentially prevent an asteroid impact with Earth by deflecting or disrupting an asteroid1-3. A test of kinetic impact technology was identified as the highest priority space mission related to asteroid mitigation1. NASA's Double Asteroid Redirection Test (DART) mission is the first full-scale test of kinetic impact technology. The mission's target asteroid was Dimorphos, the secondary member of the S-type binary near-Earth asteroid (65803) Didymos. This binary asteroid system was chosen to enable ground-based telescopes to quantify the asteroid deflection caused by DART's impact4. While past missions have utilized impactors to investigate the properties of small bodies5,6, those earlier missions were not intended to deflect their targets and did not achieve measurable deflections. Here we report the DART spacecraft's autonomous kinetic impact into Dimorphos and reconstruct the impact event, including the timeline leading to impact, the location and nature of the DART impact site, and the size and shape of Dimorphos. The successful impact of the DART spacecraft with Dimorphos and the resulting change in Dimorphos's orbit7 demonstrates that kinetic impactor technology is a viable technique to potentially defend Earth if necessary