Arecibon planetaarisen tutkan Maan lähiasteroidihavainnot: 2017 joulukuu - 2019 joulukuu

We successfully observed 191 near-Earth asteroids using the Arecibo Observatory's S-band planetary radar system from 2017 December through 2019 December. We present radar cross sections for 167 asteroids; circular-polarization ratios for 112 asteroids based on Doppler-echo-power spectra measurements; and radar albedos, constraints on size and spin periods, and surface-feature and shape evaluation for 37 selected asteroids using delay-Doppler radar images with a range resolution of 75 m or finer. Out of 33 asteroids with an estimated effective diameter of at least 200 m and sufficient image quality to give clues of the shape, at least 4 (∼12%) are binary asteroids, including 1 equal-mass binary asteroid, 2017 YE5, and at least 10 (∼30%) are contact-binary asteroids. For 5 out of 112 asteroids with reliable measurements in both circular polarizations, we measured circular-polarization ratios greater than 1.0, which could indicate that they are E-type asteroids, while the mean and the 1σ standard deviation were 0.37 ± 0.23. Further, we find a mean opposite-sense circular-polarization radar albedo of 0.21 ± 0.11 for 41 asteroids (0.19 ± 0.06 for 11 S-complex asteroids). We identified two asteroids, 2011 WN15 and (505657) 2014 SR339, as possible metal-rich objects based on their unusually high radar albedos, and discuss possible evidence of water ice in 2017 YE5.Peer reviewe

More Bucks for the Bang: New Space Solutions, Impact Tourism and one Unique Science & Engineering Opportunity at T-6 Months and Counting

For now, the Planetary Defense Conference Exercise 2021's incoming fictitious(!) asteroid, 2021 PDC, seems headed for impact on October 20th, 2021, exactly 6 months after its discovery. Today (April 26th, 2021), the impact probability is 5%, in a steep rise from 1 in 2500 upon discovery six days ago. We all know how these things end. Or do we? Unless somebody kicked off another headline-grabbing media scare or wants to keep civil defense very idle very soon, chances are that it will hit (note: this is an exercise!). Taking stock, it is barely 6 months to impact, a steadily rising likelihood that it will actually happen, and a huge uncertainty of possible impact energies: First estimates range from 1.2 MtTNT to 13 GtTNT, and this is not even the worst-worst case: a 700 m diameter massive NiFe asteroid (covered by a thin veneer of Ryugu-black rubble to match size and brightness) would come in at 70 GtTNT. In down to Earth terms, this could be all between smashing fireworks over some remote area of the globe and a 7.5 km crater downtown somewhere. Considering the deliberate and sedate ways of development of interplanetary missions it seems we can only stand and stare until we know well enough where to tell people to pack up all that can be moved at all and save themselves. But then, it could just as well be a smaller bright rock. The best estimate is 120 m diameter from optical observation alone, by 13% standard albedo. NASA's upcoming DART mission to binary asteroid (65803) Didymos is designed to hit such a small target, its moonlet Dimorphos. The Deep Impact mission's impactor in 2005 successfully guided itself to the brightest spot on comet 9P/Tempel 1, a relatively small feature on the 6 km nucleus. And 'space' has changed: By the end of this decade, one satellite communication network plans to have launched over 11000 satellites at a pace of 60 per launch every other week. This level of series production is comparable in numbers to the most prolific commercial airliners. Launch vehicle production has not simply increased correspondingly - they can be reused, although in a trade for performance. Optical and radio astronomy as well as planetary radar have made great strides in the past decade, and so has the design and production capability for everyday 'high-tech' products. 60 years ago, spaceflight was invented from scratch within two years, and there are recent examples of fastpaced space projects as well as a drive towards 'responsive space'. It seems it is not quite yet time to abandon all hope. We present what could be done and what is too close to call once thinking is shoved out of the box by a clear and present danger, to show where a little more preparedness or routine would come in handy - or become decisive. And if we fail, let's stand and stare safely and well instrumented anywhere on Earth together in the greatest adventure of science

Mapping Orbits regarding Perturbations due to the Gravitational Field of a Cube

The orbital dynamics around irregular shaped bodies is an actual topic in astrodynamics, because celestial bodies are not perfect spheres. When it comes to small celestial bodies, like asteroids and comets, it is even more import to consider the nonspherical shape. The gravitational field around them may generate trajectories that are different from Keplerian orbits. Modeling an irregular body can be a hard task, especially because it is difficult to know the exact shape when observing it from the Earth, due to their small sizes and long distances. Some asteroids have been observed, but it is still a small amount compared to all existing asteroids in the Solar System. An approximation of their shape can be made as a sum of several known geometric shapes. Some three-dimensional figures have closed equations for the potential and, in this work, the formulation of a cube is considered. The results give the mappings showing the orbits that are less perturbed and then have a good potential to be used by spacecrafts that need to minimize station-keeping maneuvers. Points in the orbit that minimizes the perturbations are found and they can be used for constellations of nanosatellites

MASCOT Asteroid Nanolanders: From Ryugu and Didymoon towards Future Missions at ‘2021 PDC’, Apophis 2029, and Beyond

For now, the Planetary Defense Conference Exercise 2021's incoming fictitious(!) asteroid, 2021 PDC, seems headed for impact on October 20th, 2021, exactly 6 months after its discovery. Today (Monday, April 26th, 2021), the impact probability is 5%, in a steep rise from 1 in 2500 upon discovery six days ago. We all know how these things end. Or do we? Unless somebody wants to keep civil defense very busy very soon, the chance is 95% that it will not hit; instead fly by closely to Earth, swing by to a new orbit that takes it away essentially forever or back again sooner or later through a keyhole, for a re-play at different odds. This is where our story starts and the story sounds familiar: season's greetings from 2004 MN4, now better known as (99942) Apophis. One more thing is similar: the close fly-by is an easy launch opportunity to 'jump aboard' that potentially hazardous asteroid for planetary science and tracking of longterm Yarkovsky-shifted keyhole resonant return risks. Indeed, missions are currently being discussed to launch during the 2029 fly-by of Apophis to rendezvous and investigate it closely right after. Others strive for an earlier launch to rendezvous well before, to observe all of the close fly-by at Earth and what it might do to a likely delicate rubble pile asteroid. Presently, this is an unlikely if not impossible option for sudden encounters like 2021 PDC with a lead time of months. But when asteroid mining (...possibly the other ...-not-if of asteroids?) takes off in the same manner as low Earth orbit communications satellites, this option may become a reality. But for now, even if a suitable planetary mission were serendipitously ready atop a suitable launch vehicle, could you get it an asteroid lander within 6 months? Surprisingly, this option existed between late 2014 and late 2018 when the MASCOT Qualification Model turned Flight Spare was kept fully integrated and flight ready for on-ground testing to prepare for the Flight Model's brief but complete mission on Ryugu with JAXA's highly successful HAYABUSA2 probe. At the same time, the MASCOT2 detailed design study for ESA's former AIM mission within the common NASA-ESA AIDA mission to (65803) Didymos and its moonlet, Dimorphos (then affectionately known as 'Didymoon'), paved the way for long-life MASCOTs, many of which have been discussed and studied since. The thoughtful design of MASCOT’s hardware and software allowed for a very high degree of re-use and flexibility regarding scientific payloads. MASCOT2 was to investigate the interior of Didymoon by Low-Frequency Radar. Close encounters like Apophis' offer unique opportunities for Earth-based planetary radar assets to work with spacecraft near and landers on the passing asteroid. We present a range of options for radar- and composition-oriented long-life MASCOT variants - to be delivered to the surfaces of the respective asteroid bodies - for the presently most likely near miss of 2021 PDC and the most certain close fly-by of (99942) Apophis on Friday, April 13th, 2029

More Bucks for the Bang: New Space Solutions, Impact Tourism and One Unique Science & Engineering Opportunity at T-6 Months and Counting

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