We present results from 28 stellar occultations by the large Trans-Neptunian Object (50000) Quaoar registered between 2018 and 2025. By performing a joint analysis of this occultation data-set, along with other 9 published events, we were able to fit an oblate ellipsoid shape, with equatorial semi-axes, a and b of 566.1+2.5-2.2 km, and a polar semi-axis, c, of 511.2+3.6-3.7 km. It provides an equivalent volumetric diameter of 1094.4 +/- 4.6 km and polar oblateness of 0.097 +/- 0.011. Considering an absolute magnitude of H = 2.79 +/- 0.35, we derive a geometric albedo of pV = 0.125 +/- 0.038. We have derived new upper limits to the surface pressure of a CH4 atmosphere of 0.15 nbar (1-sigma) and 0.65 nbar (3-sigma). We also provide a table with the 36 new astrometric positions for Quaoar. Using the new system mass derived from Weywot's orbit around Quaoar, we calculated a density of 1.760 +/- 0.109 g/cm3. Moreover, from the derived size and rotation period (8.8394 +/- 0.0002 hours (Ortiz et al. 2003)), we calculate that, if Quaoar is in Maclaurin hydrostatic equilibrium state, it would have a density of 1.859 +/- 0.200 g/cm3. This result, within the error bars, is compatible with the value we found. Therefore, this work shows that Quaoar can be a Maclaurin object, being eligible as a dwarf planet.

We present observations of five stellar occultations for (11351) Leucus and reports from two efforts on (21900) Orus. Both objects are prime mission candidate targets for the Lucy Discovery mission. Combined results for Leucus indicate a very dark surface with p V = 0.037 ± 0.001, which is derived from the average of the multichord occultations. Our estimate of the triaxial ellipsoidal shape is for axial diameters of 63.8 × 36.6 × 29.6 km assuming that the spin pole is normal to the line of sight. The actual shape of the object is only roughly elliptical in profile at each epoch. Significant topography is seen with horizontal scales up to 30 km and vertical scales up to 5 km. The most significant feature is a large depression on the southern end of the object as seen from a terrestrial viewpoint. For this work we developed a method to correct for differential refraction, accounting for the difference in color between the target object and the reference stars for astrometry derived from ground-based images.

Orbits about collinear libration points are unstable, requiring stationkeeping maneuvers to maintain. Several different methods for calculating libration-point orbit stationkeeping maneuvers have been proposed. A tight control technique was used by the third International Sun-Earth Explorer (ISEE-3), the first libration-point mission. An easily-implemented “orbital energy balancing” loose control strategy was developed later and has been used successfully by the Solar Heliospheric Observatory (SOHO) and Advanced Composition Explorer (ACE). For SOHO, this loose control has resulted in station-keeping ΔV costs of just over 2 m/sec per year with maneuvers performed about four times a year, an improvement of almost a factor of four over ISEE-3’s tight control. Part of the gain probably results from better trajectory determinations from improved radiometric tracking data for SOHO. All three missions, especially SOHO, have had operational mishaps that have resulted in temporary expenditures of fuel that were much larger than expected, but in spite of these, it appears that the spacecraft can be kept in their designed halo orbits for periods longer than planned before launch.

Occultations of stars by asteroids have been observed since 1961, increasing from a very small number to now over 500 annually. We have created and regularly maintain a growing data-set of more than 5,000 observed asteroidal occultations. The data-set includes: the raw observations; astrometry at the 1 mas level based on centre of mass or figure (not illumination); where possible the asteroid's diameter to 5 km or better, and fits to shape models; the separation and diameters of asteroidal satellites; and double star discoveries with typical separations being in the tens of mas or less. The data-set is published at NASA's Planetary Data System and is regularly updated. We provide here an overview of the data-set, discuss the issues associated with determining the astrometry and diameters, and give examples of what can be derived from the data-set. We also compare the occultation diameters of asteroids with the diameters measured by the satellites NEOWISE, AKARI AcuA, and IRAS, and show that the best satellite-determined diameter is a combination of the diameters from all three satellites.

Mass transfer in an interacting binary will often strip the mass donor of its entire envelope and spin up the mass gainer to near critical rotation. The nearby B-type star Regulus represents a binary in the post-mass transfer stage: it is a rapid rotator with a very faint companion in a 40 days orbit. Here we present the results of a search for the spectral features of the stripped-down star in an extensive set of spectra with high signal-to-noise ratio and high resolution obtained with the CFHT/ESPaDOnS and TBL/NARVAL spectrographs. We first determine revised orbital elements in order to set accurate estimates of the orbital Doppler shifts at the times of observation. We then calculate cross-correlation functions of the observed and model spectra, and we search for evidence of the companion signal in the residuals after removal of the strong primary component. We detect a weak peak in the co-added residuals that has the properties expected for a faint pre-white dwarf. We use the dependence of the peak height and width on assumed secondary velocity semiamplitude to derive the semiamplitude, which yields masses ofM(1)/M = 3.7 1.4 andM(2)/M = 0.31 0.10 (assuming orbital inclination equals the spin inclination of Regulus). We estimate the temperature of the pre-white dwarfT(eff) = (20 4) kK through tests with differing temperature model spectra, and we find the radiusR(2)/R = 0.061 0.011 from the component temperatures and the flux ratio associated with the amplitude of the signal in the cross-correlation residuals.

This report documents the currently-recognized most accurate values for the masses, radii, and certain mean orbital elements for the major planets, the asteroid (433) Eros, and many of the satellites of the Solar System. These values were used to produce computer-generated tables of libration-point parameters.

The Lunar Polar Hydrogen Mapper (LunaH-Map) mission will map the distribution of hydrogen around the lunar South Pole using a miniature neutron spectrometer. The mission builds upon a decade of lunar science, which has revealed both regional and more localized enrichments of water ice near the lunar poles. Localized enrichments are primarily within permanently shadowed regions (PSRs) and craters throughout the South Pole. The spatial extent of these regions is often below the resolution of previous neutron instruments that have flown on lunar missions. The neutron leakage spectrum from planetary surfaces is primarily sensitive to hydrogen abundance in the top meter of regolith, however, for neutron spectrometers with omnidirectional sensitivity, the spatial resolution is limited by the spacecraft orbital altitude above the surface. A low altitude measurement from a distance on the same scale of the PSRs could spatially isolate and constrain the hydrogen enrichments both within and around within those regions. A small spacecraft mission is ideally suited to acquire the low-altitude measurements required to localize hydrogen enrichments using neutron spectroscopy at the lunar South Pole. LunaH-Map will use a solid iodine ion propulsion system, X-Band radio communications through the NASA Deep Space Network, star tracker, Command & Data Handling System, and EPS systems from Blue Canyon Technologies, solar arrays from MMA Designs, LLC, mission design and navigation by KinetX. Spacecraft systems design, integration, qualification, test, and mission operations are performed by Arizona State University, AZ Space Technologies and Qwaltec.

DESTINY+ FLYBY. T. Arai, F. Yoshida, T. Hayamizu, H. Akitaya, T. Okamoto, H. Noda, M. Ishiguro, S. Urakawa, T. Horaguchi, M.-Y. Yamamoto, G. Hashimoto, S. Matsuura, S. Marshall, and the DESTINY+ Occultation Observation Team. Planetary Exploration Research Center, Chiba Institute of Technology, Chiba, Japan (tomoko.arai@it-chiba.ac.jp), 2 University of Occupational & Environmental Health, Fukuoka, Japan, Saga Hoshizora Astronomical Center, Japan, Japan Occultation Information Network (JOIN), Japan, National Astronomical Observatory of Japan, Japan, Seoul National University, South Korea, Japan Spaceguard Association, Japan, National Museum of Nature and Science, Tokyo, Japan, Kochi University of Technology, Kochi, Japan, Okayama University, Okayama, Japan, Kwansei Gakuin University, Hyogo, Japan, Arecibo Observatory & University of Central Florida, USA.

We present the results from four stellar occultations by (486958) Arrokoth, the flyby target of the New Horizons extended mission. Three of the four efforts led to positive detections of the body, and all constrained the presence of rings and other debris, finding none. Twenty-five mobile stations were deployed for 2017 June 3 and augmented by fixed telescopes. There were no positive detections from this effort. The event on 2017 July 10 was observed by SOFIA with one very short chord. Twenty-four deployed stations on 2017 July 17 resulted in five chords that clearly showed a complicated shape consistent with a contact binary with rough dimensions of 20 by 30 km for the overall outline. A visible albedo of 10% was derived from these data. Twenty-two systems were deployed for the fourth event on 2018 Aug 4 and resulted in two chords. The combination of the occultation data and the flyby results provides a significant refinement of the rotation period, now estimated to be 15.9380 $\pm$ 0.0005 hours. The occultation data also provided high-precision astrometric constraints on the position of the object that were crucial for supporting the navigation for the New Horizons flyby. This work demonstrates an effective method for obtaining detailed size and shape information and probing for rings and dust on distant Kuiper Belt objects as well as being an important source of positional data that can aid in spacecraft navigation that is particularly useful for small and distant bodies.

A method of long-period comets deviation from the trajectory with Earth collision is described in the paper. It is based on the use of small asteroids targeted to a comet on a trajectory with high probability of Earth impact. It is assumed that the time for completing the required operations is strongly limited. With future systems like LSST, we are likely to find threatening long-period comets with only about two years before impact. To meet this demand we propose building a “shield” from small asteroids (or builders taken from the surface of near Earth asteroids). These asteroids are selected from ones which are possible to transfer, by gravity assist maneuvers near Earth, into orbits resonant with the Earth. The most convenient but not mandatory resonance may be chosen as 1:1. The paper includes a description of the shield construction. The main constituents of appropriate operations are transfer of the spacecraft to the chosen asteroid, landing on its surface, capture of an acceptable boulder, take off from the surface of asteroid with boulder and fulfilling near Earth gravity assist maneuver. The concept is very similar to NASA’s Asteroid Redirect Mission which, although it was cancelled, produced good studies showing the feasibility of the project. But rather than transferring the asteroid boulder to a lunar orbit, it instead would be targeted on a hyperbolic trajectory to a B-plane point to put it into a heliocentric orbit resonant with Earth. These operations are repeated for several asteroids so we receive around the Earth’s orbit, a family of sky stones (with sizes of about 5-7 meters) equipped by the control systems and rocket engines with possibilities to target them into approaching hazardous sky objects, such as long period comets or asteroids. The required flexibility is achieved by possessing a fleet of small asteroids in vicinity of the Earth’s orbit having the necessary equipment to target them into dangerous celestial objects. It will be shown in the paper that it is feasible with the use of contemporary technology, including the use of a formation flying navigation method, to reach the required accuracy of dangerous object interception. **************************************

This paper investigates the continuity of several families of transfer trajectories using ballistic lunar capture. Ballistic capture trajectories are of interest for spacecraft with low-thrust propulsion or those otherwise unable to enter lunar orbit from a traditional lunar transfer orbit. A continuation model is used to map two-body problem candidate solutions into trajectories satisfying the dynamics of the Sun-Earth-Moon (SEM) restricted four-body problem. The change of each family of candidate solutions with SEM angle of the initial lunar flyby is expected to impact the ability to claim existence of a solution across a wide range of initial TLI epochs.

Near-Earth asteroid (3200) Phaethon is the primary target for the Demonstration and Experiment of Space Technology for INterplanetary voYage, Phaethon fLyby and dUst Science Phaethon fLyby with reUSable probe (DESTINY+) mission, currently being developed by the Japan Aerospace Exploration Agency (JAXA). The size of Phaethon is measured to be about 5–6 km, although numbers derived by different techniques are not in strict agreement: radar measurement suggests an sphere with a diameter of 6.2 km, or a top-shaped figure with equivalent spherical diameter of 5.5 km (Taylor et al. 2019), while two thermophysical models based on infrared data suggest a spherical diameter of 5.1 ± 0.2 km (Hanus et al. 2016) and 4.6^(+0.2)_(-0.3) km (Masiero et al. 2019), ≳2σ different from radar data.

During the Apollo era of lunar exploration, mysterious albedo patterns, called swirls, captured the imagination of the scientific community. A key aspect of this interest was due to the discovery that the swirls are associated with localized relatively strong remnant magnetic fields. Analysis of returned soil samples revealed that solar wind, galactic cosmic rays, and micrometeorite impacts change the albedo of surface soil grains, a process known as space weathering that reduces regolith reflectance over time. Thus it was natural to invoke local magnetic structures as shields that retard space weathering resulting in relatively less space weathering of the regolith in regions with the strongest localized magnetic fields. However, the origins of the magnetic anomalies and associated swirls remain enigmatic to this day. We designed the Swirl CubeSat to determine the nature of remnant lunar magnetic fields and investigate their role in moderating space weathering of the regolith and assess their suitability for radiation protection of surface assets. Swirl has one focused observational objective: characterize the magnetic field associated with the Reiner Gamma Swirl (RGS) at sub-kilometer spatial sampling, with 0.5 nTesla accuracy and 100 m spatial precision. In the Swirl mission concept, the Swirl spacecraft, a 6U CubeSat, would deploy as a secondary payload from a vehicle on a deep space trajectory. A series of maneuvers would then place the spacecraft in a low orbit that would then be modified to have a periapse of 5-10 km for thirty orbits passing over RGS. Prime Swirl observations were designed during these low-altitude passes and consist of high-resolution vector magnetic field measurements and monochrome navigation imaging.

The presented trajectory was designed for the Lunar Polar Hydrogen Mapper (LunaH-Map) 6U CubeSat, which was awarded a ride on NASA's Space Launch System (SLS) with Exploration Mission 1 (EM-1) via NASA's 2015 SIMPLEX proposal call. After deployment from EM-1's upper stage (which is planned to enter heliocentric space via a lunar flyby), the LunaH-Map CubeSat will alter its trajectory via its low-thrust ion engine to target a lunar flyby that yields a Sun-Earth-Moon weak stability boundary transfer to set up a ballistic lunar capture. Finally, the orbit energy is lowered to reach the required quasi-frozen science orbit with periselene above the lunar south pole.