Janus and Lunar Trailblazer: Lockheed Martin Deep Space SmallSats for NASA SIMPLEx Missions

NASA’s Small Innovative Missions for Planetary Exploration (SIMPLEx) program is a principal investigator-led planetary science program focusing on small spacecraft. In the SIMPLEx-2 opportunity, the cost cap for SIMPLEx missions is approximately 1/10th the cost of the next larger class of planetary exploration missions, the Discovery Program. Unlike Discovery missions, SIMPLEx missions launch as rideshare payloads with other NASA primary missions. Lockheed Martin has developed a science-capable deep space small spacecraft architecture to support two missions selected for the SIMPLEx-2 opportunity: Janus and Lunar Trailblazer. Janus is a two-spacecraft mission to fly by two different binary Near Earth Asteroids, partnered with Dr. Dan Scheeres at the University of Colorado Boulder. Lunar Trailblazer is a lunar orbiter led by Dr. Bethany Ehlmann at Caltech which will map water on the Moon; both have passed PDR and are confirmed for flight. Janus will launch first, in August 2022. A scalable suite of hardware subsystems enables the same low-cost spacecraft architecture to support both missions with a high degree of commonality, despite their disparate mission designs, environments, physical configuration, and science operations. As both missions move through project implementation, the management and engineering teams have learned valuable lessons for developing deep space-capable small spacecraft, adapting from both Earth-orbiting SmallSats and traditional larger planetary exploration missions in the Discovery and New Frontiers program classes. Key lessons learned include the value of early and close coordination between interested science teams and spacecraft providers, the need to tailor the complexity of science investigations to SmallSat spacecraft capabilities, the importance of evaluating component lifetimes against the deep space mission environment, and the challenge of planetary mission design to a rideshare launch. Rideshare missions on planetary launches must meet schedules determined by primary spacecraft with inexorable planetary launch windows and must provide enough propulsion to reach their own destinations which may include planetary orbit insertion or targeting a completely different solar system destination than the primary spacecraft

The Role of Ejecta in the Small Crater Populations on the Mid-Sized Saturnian Satellites

We find evidence that crater ejecta play an important role in the small crater populations on the Saturnian satellites, and more broadly, on cratered surfaces throughout the Solar System. We measure crater populations in Cassini images of Enceladus, Rhea, and Mimas, focusing on image data with scales less than 500 m/pixel. We use recent updates to crater scaling laws and their constants to estimate the amount of mass ejected in three different velocity ranges: (i) greater than escape velocity, (ii) less than escape velocity and faster than the minimum velocity required to make a secondary crater (v_min), and (iii) velocities less than v_min. Although the vast majority of mass on each satellite is ejected at speeds less than v_min, our calculations demonstrate that the differences in mass available in the other two categories should lead to observable differences in the small crater populations; the predictions are borne out by the measurements we have made to date. Rhea, Tethys, and Dione have sufficient surface gravities to retain ejecta moving fast enough to make secondary crater populations. The smaller satellites, such as Enceladus but especially Mimas, are expected to have little or no traditional secondary populations because their escape velocities are near the threshold velocity necessary to make a secondary crater. Our work clarifies why the Galilean satellites have extensive secondary crater populations relative to the Saturnian satellites. The presence, extent, and sizes of sesquinary craters (craters formed by ejecta that escape into temporary orbits around Saturn before re-impacting the surface) is not yet well understood. Finally, our work provides further evidence for a "shallow" size-frequency distribution (slope index of ~2 for a differential power-law) for comets a few km diameter and smaller. [slightly abbreviated]Comment: Submitted to Icarus. 77 double-spaced pages, including 25 figures and 5 table

The global surface roughness of 25143 Itokawa

Surface roughness is an important metric in understanding how the geologic history of an asteroid affects its small-scale topography and it provides an additional means to quantitatively compare one asteroid with another. In this study, we report the first detailed global surface roughness maps of 25143 Itokawa at horizontal scales from 8--32~m. Comparison of the spatial distribution of the surface roughness of Itokawa with 433 Eros, the other asteroid for which this kind of analysis has been possible, indicates that the two asteroids are dominated by different geologic processes. On Itokawa, the surface roughness reflects the results of down-slope activity that moves fine grained material into geopotential lows and leaves large blocks in geopotential highs. On 433 Eros, the surface roughness is controlled by geologically-recent large impact craters. In addition, large longitudinal spatial variations of surface roughness could impact the role of YORP on Itokawa

Janus: Launch of a NASA SmallSat Mission to Near-Earth Binary Asteroids

Janus is a two-spacecraft SmallSat mission to fly by two different pairs of binary near Earth asteroids, (175706) 1996 FG3 and (35107) 1991 VH. The two identical Janus spacecraft are scheduled to launch during a launch period opening 1 August 2022 as secondary payloads with the NASA Psyche mission, on a SpaceX Falcon Heavy launch vehicle. Janus is led by principal investigator Dr. Dan Scheeres at the University of Colorado Boulder and managed, built, and operated by Lockheed Martin. These planetary SmallSats share many deep space challenges similar to larger missions: Janus must execute deep space maneuvers to achieve hundreds of meters per second ΔV to reach its destinations, close a telecommunication link at ranges up to 2.4 AU, autonomously manage a several-month-long telecommunications blackout during solar conjunction, operate at a maximum Sun range of 1.62 AU, and survive for approximately four years in interplanetary space before encountering their target asteroids. During the encounters, the spacecraft will return high resolution visible and infra-red images of the asteroids. In getting Janus to the pad, the implementation team successfully managed an aggressive mission schedule despite COVID-19 related supply chain impacts and work environments, all while remaining on target for the SIMPLEx-2 cost cap. Janus is a pathfinder for achievable and affordable SmallSat science missions and demonstrates the valuable partnership between an experienced deep space mission engineering team, the SmallSat commercial component industry, and a forward- looking NASA model for Class-D science missions

Lucy Mission to the Trojan Asteroids: Science Goals

The Lucy Mission is a NASA Discovery-class mission to send a highly capable and robust spacecraft to investigate seven primitive bodies near both the L4 and L5 Lagrange points with Jupiter: the Jupiter Trojan asteroids. These planetesimals from the outer planetary system have been preserved since early in solar system history. The Lucy mission will fly by and extensively study a diverse selection of Trojan asteroids, including all the recognized taxonomic classes, a collisional family member, and a near equal-mass binary. It will visit objects with diameters ranging from roughly 1 km to 100 km. The payload suite consists of a color camera and infrared imaging spectrometer, a high-resolution panchromatic imager, and a thermal infrared spectrometer. Additionally, two spacecraft subsystems will also contribute to the science investigations: the terminal tracking cameras will supplement imaging during closest approach and the telecommunication subsystem will be used to measure the mass of the Trojans. The science goals are derived from the 2013 Planetary Decadal Survey and include determining the surface composition, assessing the geology, determining the bulk properties, and searching for satellites and rings

Geotechnical Properties Of Asteroids Affecting Surface Operations, Mining, And In Situ Resource Utilization Activities

Geotechnical properties of a granular material affect all surface operations from mobility to landing and excavation. As such, significant efforts to study and model these properties are necessary before sending a spacecraft. Lack of knowledge of regolith material properties adversely affected Apollo, Lunokhod, and Mars Exploration Rover missions; hence additional measures need to be undertaken to prevent potential failures or delays of future missions, in particular missions to explore low-gravity asteroidal surfaces. Geotechnical properties of regolith include cohesion and friction angle, which affect material strength. Friction angle is gravity-dependent, whereas cohesion is not. It is therefore much easier to study and model surface regolith on planetary bodies with significant gravity such as the Moon or Mars. If gravity becomes extremely low, for example, on asteroids, cohesive forces start to dominate. This chapter addresses geotechnical properties of asteroid regolith and their implications for safe mission surface operations. The chapter starts with a high-level overview of soil mechanics followed by an overview of asteroid’s regolith from past and current missions. Models related to regolith are presented with specific emphasis on sources of cohesion. Several examples of surface operations are given (landing, boulder retrieval, excavation) to illustrate the effect of various properties on the hardware

Assessing the Sampleability of Bennu’s Surface for the OSIRIS-REx Asteroid Sample Return Mission

Abstract NASA’s first asteroid sample return mission, OSIRIS-REx, collected a sample from the surface of near-Earth asteroid Bennu in October 2020 and will deliver it to Earth in September 2023. Selecting a sample collection site on Bennu’s surface was challenging due to the surprising lack of large ponded deposits of regolith particles exclusively fine enough ( ≤ 2 cm $\leq2~\text{cm}$ diameter) to be ingested by the spacecraft’s Touch-and-Go Sample Acquisition Mechanism (TAGSAM). Here we describe the Sampleability Map of Bennu, which was constructed to aid in the selection of candidate sampling sites and to estimate the probability of collecting sufficient sample. “Sampleability” is a numeric score that expresses the compatibility of a given area’s surface properties with the sampling mechanism. The algorithm that determines sampleability is a best fit functional form to an extensive suite of laboratory testing outcomes tracking the TAGSAM performance as a function of four observable properties of the target asteroid. The algorithm and testing were designed to measure and subsequently predict TAGSAM collection amounts as a function of the minimum particle size, maximum particle size, particle size frequency distribution, and the tilt of the TAGSAM head off the surface. The sampleability algorithm operated at two general scales, consistent with the resolution and coverage of data collected during the mission. The first scale was global and evaluated nearly the full surface. Due to Bennu’s unexpected boulder coverage and lack of ponded regolith deposits, the global sampleability efforts relied heavily on additional strategies to find and characterize regions of interest based on quantifying and avoiding areas heavily covered by material too large to be collected. The second scale was site-specific and used higher-resolution data to predict collected mass at a given contact location. The rigorous sampleability assessments gave the mission confidence to select the best possible sample collection site and directly enabled successful collection of hundreds of grams of material