Marshall Eubanks | Massachusetts Institute of Technology (MIT) (original) (raw)

Papers by Marshall Eubanks

EGU General Assembly Conference Abstracts, Apr 1, 2016

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Objectives and requirements for Earth rotation and reference frame studies in the 1990s are discu... more Objectives and requirements for Earth rotation and reference frame studies in the 1990s are discussed. The objectives are to observe and understand interactions of air and water with the rotational dynamics of the Earth, the effects of the Earth&amp;amp;amp;#39;s crust and mantle on the dynamics and excitation of Earth rotation variations over time scales of hours to centuries, and the

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We address the problem of computing the UDP checksum on tunneling IPv6 packets when using lightwe... more We address the problem of computing the UDP checksum on tunneling IPv6 packets when using lightweight tunneling protocols.

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The Event Horizon Telescope (EHT) Collaboration recently published the first images of the superm... more The Event Horizon Telescope (EHT) Collaboration recently published the first images of the supermassive black holes in the cores of the Messier 87 and Milky Way galaxies. These observations have provided a new means to study supermassive black holes and probe physical processes occurring in the strong-field regime. We review the prospects of future observations and theoretical studies of supermassive black hole systems with the next-generation Event Horizon Telescope (ngEHT), which will greatly enhance the capabilities of the existing EHT array. These enhancements will open up several previously inaccessible avenues of investigation, thereby providing important new insights into the properties of supermassive black holes and their environments. This review describes the current state of knowledge for five key science cases, summarising the unique challenges and opportunities for fundamental physics investigations that the ngEHT will enable.

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Acta Astronautica

Nomadic worlds are objects not bound to any star(s), and are of great interest to planetary scien... more Nomadic worlds are objects not bound to any star(s), and are of great interest to planetary science and astrobiology. They have garnered attention recently on account of their detection in microlensing surveys and also from the recent discovery of interstellar planetesimals. In this paper, we evaluate the prevalence of nomadic worlds with radii of 100 km ≲ R ≲ 10 4 km, which might permit habitable conditions. The cumulative number density n > (> R) appears to follow a heuristic power law given by n > ∝ R −3. Therefore, smaller objects should be much more numerous than the largest rocky nomadic planets, and thus statistically more likely to have members relatively close to the inner Solar system. Our results suggest that tens to hundreds of planet-sized nomadic worlds may populate the spherical volume centered on Earth and circumscribed by Proxima Centauri, and thus may comprise closer interstellar targets than any stellar planetary system. For the first time, we systematically analyze the feasibility of exploring these unbounded celestial bodies via deep space missions. We investigate what near-future propulsion systems could theoretically enable us to reach nomadic worlds (of radius > R) on a 50-year timescale. Objects with R ∼ 100 km are within the purview of multiple propulsion methods such as electric sails, laser electric propulsion, and solar sails. In contrast, nomadic worlds with R ≳ 1000 km are accessible by laser sails (and perhaps nuclear fusion), thereby underscoring their vast potential for deep space exploration.

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Acta Astronautica, 2023

Nomadic worlds, i.e., objects not gravitationally bound to any star(s), are of great interest to ... more Nomadic worlds, i.e., objects not gravitationally bound to any star(s), are of great interest to planetary science and astrobiology. They have garnered attention recently due to constraints derived from microlensing surveys and the recent discovery of interstellar planetesimals. In this paper, we roughly estimate the prevalence of nomadic worlds with radii of 100 km ≲ ≲ 10 4 km. The cumulative number density > (>) appears to follow a heuristic power law given by > ∝ −3. Therefore, smaller objects are probably much more numerous than larger rocky nomadic planets, and statistically more likely to have members relatively close to the inner Solar system. Our results suggest that tens to hundreds of planet-sized nomadic worlds might populate the spherical volume centered on Earth and circumscribed by Proxima Centauri, and may thus comprise closer interstellar targets than any planets bound to stars. For the first time, we systematically analyze the feasibility of exploring these unbounded objects via deep space missions. We investigate what near-future propulsion systems could allow us to reach nomadic worlds of radius > in a 50-year flight timescale. Objects with ∼ 100 km are within the purview of multiple propulsion methods such as electric sails, laser electric propulsion, and solar sails. In contrast, nomadic worlds with ≳ 1000 km are accessible by laser sails (and perhaps nuclear fusion), thereby underscoring their vast potential for deep space exploration.

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Galaxies

The source-frequency phase-referencing (SFPR) technique has been demonstrated to have great advan... more The source-frequency phase-referencing (SFPR) technique has been demonstrated to have great advantages for mm-VLBI observations. By implementing simultaneous multi-frequency receiving systems on the next-generation Event Horizon Telescope (ngEHT) antennas, it is feasible to carry out a frequency phase transfer (FPT) which could calibrate the non-dispersive propagation errors and significantly increase the phase coherence in the visibility data. Such an increase offers an efficient approach for a weak source or structure detection. The SFPR also makes it possible for high-precision astrometry, including the core-shift measurements up to sub-mm wavelengths for Sgr A*, M 87*, etc. We also briefly discuss the technical and scheduling considerations for future SFPR observations with the ngEHT.

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P51C-1467. [23] Grün, E., Horanyi, M., Sternovsky, Z., (2011) The lunar dust environment, Planeta... more P51C-1467. [23] Grün, E., Horanyi, M., Sternovsky, Z., (2011) The lunar dust environment, Planetary and Space Science, 59, 1672-

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arXiv: Instrumentation and Methods for Astrophysics, 2019

The search for life in the universe is a major theme of astronomy and astrophysics for the next d... more The search for life in the universe is a major theme of astronomy and astrophysics for the next decade. Searches for technosignatures are complementary to searches for biosignatures, in that they offer an alternative path to discovery, and address the question of whether complex (i.e. technological) life exists elsewhere in the Galaxy. This approach has been endorsed in prior Decadal Reviews and National Academies reports, and yet the field still receives almost no federal support in the US. Because of this lack of support, searches for technosignatures, precisely the part of the search of greatest public interest, suffers from a very small pool of trained practitioners. A major source of this issue is institutional inertia at NASA, which avoids the topic as a result of decades-past political grandstanding, conflation of the effort with non-scientific topics such as UFOs, and confusion regarding the scope of the term "SETI." The Astro2020 Decadal should address this issue ...

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The accuracy of very long base interferometry earth rotation (UT1) measurements is examined by in... more The accuracy of very long base interferometry earth rotation (UT1) measurements is examined by intercomparing TEMPO and POLARIS data for 1982 and the first half of 1983. None of these data are simultaneous, and so a proper intercomparison requires accounting for the scatter introduced by the rapid, unpredictable, UT1 variations driven by exchanges of angular momentum with the atmosphere. A statistical model of these variations, based on meteorological estimates of the Atmospheric Angular Momentum is derived, and the optimal linear (Kalman) smoother for this model is constructed. The scatter between smoothed and independent raw data is consistent with the residual formal errors, which do not depend upon the actual scatter of the UT1 data. This represents the first time that an accurate prediction of the scatter between UT1 data sets were possible.

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Planetary Science Vision 2050 Workshop, Feb 1, 2017

Extra-terrestrial space elevators are technically feasible with current materials and can be part... more Extra-terrestrial space elevators are technically feasible with current materials and can be part of a transportation network to fulfill NASA's strategic exploration goals for the next three decades.

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Introduction: With the recent expansion of plans for lunar exploration there has been increased i... more Introduction: With the recent expansion of plans for lunar exploration there has been increased interest in support of operations at and near the Moon (i.e., in Cislunar Space), including robotic and crewed missions to the lunar polar regions. Real time navigation and communication will be especially difficult on the heavily shadowed lunar polar regions, given the bad lighting, the frequent lack of line of sight to the Earth, the extreme Geometrical Dilution of Precision (GDOP) for any use of terrestrial GPS and the lack, at least in the near term, of continual overhead satellite coverage. Unlike the Apollo surface Extra-Vehicular Activities (EVAs), future astronauts on polar surface EVAs will need local relays to communicate with the home base, and to perform local navigation, and communication beyond the local line of sight to a central lander.

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Introduction: 63803 Didymos is a binary nearEarth asteroid which will make a close approach to Ea... more Introduction: 63803 Didymos is a binary nearEarth asteroid which will make a close approach to Earth in early October, 2022. Observations show that the Didymos primary is roughly spherical with a diameter of ∼800 m [1, 2, 3], while the secondary, the “Didymoon”, is roughly 150 m in diameter with an orbital period of ∼11.9 hours and an orbital radius of 1.18 km. The ESA Asteroid Impact Monitoring (AIM) mission [4] was intended to rendezvous with the Didymos system as one component of the Asteroid Impact & Deflection Assessment (AIDA), mission, a planetary defense test [5]. The other AIDA component, the NASA Double Asteroid Redirection Test (DART) [6], is intended to impact the Didymoon in October, 2012, demonstrating the effectiveness of kinetic impactors for asteroid deflection. The DART impact is expected to change the Didymoon velocity by 0.3 β mm s, where β is a scale factor between the momentum of DART and the Didymoon post-impact momentum change. β is expected to be > 1 due ...

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EGU General Assembly Conference Abstracts, Apr 1, 2016

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Acta Astronautica

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Acta Astronautica, 2023

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Galaxies

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arXiv: Instrumentation and Methods for Astrophysics, 2019

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Planetary Science Vision 2050 Workshop, Feb 1, 2017

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Final Report of the Breakthrough Starshot Communications Group, 2023

• We are developing a means of interstellar travel for fast flyby missions combined with optical ... more • We are developing a means of interstellar travel for fast flyby missions combined with optical communications over interstellar range, based on swarms. of picospacecraft accelerated with laser power beaming.

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Apophis T-7 Years: Knowledge Opportunities for the Science of Planetary Defense Apophis T-7 Years: Knowledge Opportunities for the Science of Planetary Defense, 2022

In this paper, we propose using laser-driven light-sail probes to implement quick-reaction missio... more In this paper, we propose using laser-driven light-sail probes to implement quick-reaction missions to intercept PHOs approaching Earth, with an initial test of this capability using the upcoming close approach of Asteroid 99942 Apophis.

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Arxiv

To settle the question of the nature of the interstellar object 1I/'Oumuamua requires in-situ obs... more To settle the question of the nature of the interstellar object 1I/'Oumuamua requires in-situ observations via a spacecraft, as the object is already out of range of existing telescopes. Most previous proposals for reaching 1I/'Oumuamua using near-term technologies are based on the Solar Oberth Manoeuvre (SOM), as trajectories without the SOM are generally significantly inferior in terms of lower mission duration and higher total velocity requirement. While the SOM allows huge velocity gains, it is also technically challenging and thereby increases programmatic and mission-related risks. In this paper, we identify an alternative route to the interstellar object 1I/'Oumuamua, based on a launch in 2028, which does not require a SOM but has a similar performance as missions with a SOM. It instead employs a Jupiter Oberth Manoeuvre (JOM) with a total time of flight of around 26 years or so. The efficacy of this trajectory is a result of it significantly reducing the ∆V to Jupiter by exploiting the VEEGA sequence. The total ∆V of the trajectory is 15.8 km s −1 and the corresponding payload mass is 115 kg for a SLS Block 1B or 241 kg for a Block 2. A further advantage of the JOM is that the arrival speed relative to 1I/'Oumuamua is approximately 18 km s −1 , much lower than the equivalent for the SOM of around 30 km s −1 .

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1I/'Oumuamua (or 1I) and 2I/Borisov (or 2I), the first InterStellar Objects (ISOs) discovered pas... more 1I/'Oumuamua (or 1I) and 2I/Borisov (or 2I), the first InterStellar Objects (ISOs) discovered passing through the solar system, have opened up entirely new areas of exobody research. Finding additional ISOs and planning missions to intercept or rendezvous with these bodies will greatly benefit from knowledge of their likely orbits and arrival rates. Here, we use the local velocity distribution of stars from the Gaia Early Data Release 3 Catalogue of Nearby Stars and a standard gravitational focusing model to predict the velocity dependent flux of ISOs entering the solar system. With an 1I-type ISO number density of ∼0.1 AU −3 , we predict that a total of ∼6.9 such objects per year should pass within 1 AU of the Sun. There will be a fairly large high-velocity tail to this flux, with half of the incoming ISOs predicted to have a velocity at infinity, v ∞ , > 40 km s −1. Our model predicts that ∼92% of incoming ISOs will be residents of the galactic thin disk, ∼6% (∼4 per decade) will be from the thick disk, ∼1 per decade will be from the halo and at most ∼3 per century will be unbound objects, ejected from our galaxy or entering the Milky Way from another galaxy. The rate of ISOs with very low v ∞ 1.5 km s −1 is so low in our model that any incoming very low velocity ISOs are likely to be previously lost solar system objects. Finally, we estimate a cometary ISO number density of ∼7 × 10 −5 AU −3 for 2I type ISOs, leading to discovery rates for these objects possibly approaching once per decade with future telescopic surveys.

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The recent detection of phosphine in the atmosphere of Venus has reignited interest in the possib... more The recent detection of phosphine in the atmosphere of Venus has reignited interest in the possibility of life aloft in this environment. If the cloud decks of Venus are indeed an abode of life, it should reside in the "habitable zone" between ∼50 to ∼60 km altitude, roughly coincident with the middle cloud deck, where the temperature and pressure (but not the atmospheric composition) are similar to conditions at the Earth's surface. We outline a precursor astrobiological mission to search for such putative lifeforms in situ with instrument balloons, which could be delivered to Venus via launch opportunities in 2022-2023. This mission would collect aerosol and dust samples on small balloons floating in the Venusian cloud deck and directly scrutinize whether they include any apparent biological materials and, if so, their shapes, sizes and motility. Our balloon mission would also be equipped with a miniature mass spectrometer that ought to permit the detection of complex organic molecules. The mission is augmented by contextual cameras that will be used to search for macroscopic signs of life in the Venusian atmospheric habitable zone. Finally, mass and power constraints permitting, radio interferometric determinations of the motion of the balloons in Venusian winds, together with in situ temperature and pressure measurements, will provide valuable insight into the poorly understood meteorology of the middle cloud region.

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Science White Paper submitted to the 2023-2032 Planetary Science and Astrobiology Decadal Survey, 2020

The recent discovery of the first confirmed Interstellar Objects (ISOs) passing through the Solar... more The recent discovery of the first confirmed Interstellar Objects (ISOs) passing through the Solar System on clearly hyperbolic objects opens the potential for near term ISO missions, either to the two known objects, or to similar objects found in the future. Such ISOs are the only exobodies we have a chance of accessing directly in the near future. This White Paper focuses on the science possible from in situ spacecraft exploration of nearby ISOs. Such spacecraft missions are technically possible now and are suitable potential missions in the period covered by the 2023-2032 Decadal Survey. Spacecraft missions can determine the structure and the chemical and isotopic composition of ISO in a close flyby coupled with a small sub-probe impactor and either a mass spectrometer or a high resolution UV spectrometer; this technology will also be useful for fast missions to TransNeptune Objects (TNOs) and long period comets. ISO exploration holds the potential of providing considerable improvements in our knowledge of galactic evolution, of planetary formation, and of the cycling of astrobiologically important materials through the galaxy.

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XXXIII General Assembly and Scientific Symposium (GASS) of the International Union of Radio Science (Union Radio Scientifique Internationale-URSI), 2020

The large constellations of spacecraft planned for use in cislunar space (on the Lunar surface, i... more The large constellations of spacecraft planned for use in
cislunar space (on the Lunar surface, in Lunar orbit, and
in the vicinity of the Lunar Gateway) require new solu-
tions for positioning, navigation and timing (PNT). Here,
I describe COMPASS (Combined Observational Methods
for Positional Awareness in the Solar System), a space-
craft navigation system to provide cost-effective techniques
for the positioning of large numbers of spacecraft in cis-
lunar space. COMPASS will use beacons that emit co-
herent ultra-wideband signals designed to be interopera-
ble with existing and future Very Long Baseline Interfer-
ometry (VLBI) networks. Using differential VLBI, COM-
PASS will provide rapid determination of the interfero-
metric phase delay with picosecond level accuracy during
routine VLBI observing sessions. Multi-baseline phase-
referenced COMPASS-VLBI observations with simultane-
ous calibrator observations should thus enable sub-meter
accuracy transverse positioning and meter level lunar or-
bit determination using with small femtospacecraft beacons
and a few seconds of observation per position determina-
tion.

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XXXIII General Assembly and Scientific Symposium (GASS) of the International Union of Radio Science (Union Radio Scientifique Internationale-URSI), 2020

Both the radio International Celestial Reference Frame (ICRF) and the optical Gaia Celestial Refe... more Both the radio International Celestial Reference Frame
(ICRF) and the optical Gaia Celestial Reference Frame
(Gaia-CRF2) are derived from observations of jets pro-
duced by the Super Massive Black Holes (SMBH) power-
ing active galactic nuclei and quasars. These jets are inher-
ently subject to change and will appear different at differ-
ent observing frequencies, leading to instabilities and sys-
tematic errors in the resulting Celestial Reference Frames
(CRFs). Recently, the Event Horizon Telescope (EHT), a
mm-wave Very Long Baseline Interferometry (VLBI) array,
has observed the 40 μ as diameter shadow of the SMBH in
M87 at 1.3 mm, showing that the emitting region is smaller
than the black-hole shadow. Use of these SMBH “emis-
sion rings” (and the associated photon rings) as astrometric
references will enable the resulting CRF to be anchored di-
rectly in SMBH shadows; the ultimate reference points for
any CRF for the forseeable future. A properly equipped
space VLBI mission devoted to the observation of SMBH
event horizons could lead to a two-orders-of-magnitude im-
provement in the accuracy and stability of the ICRF in the
relatively near future.

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The detection of interstellar bodies passing near the Sun offers the opportunity to observe not j... more The detection of interstellar bodies passing near the Sun offers the opportunity to observe not just objects similar to those in the solar system, but also unfamiliar objects without solar system analogues. Here I show that Asymptotic Giant Branch (AGB) stellar evolution may lead to the creation, out of stardust, of substantial numbers of nomadic Post-Main-Sequence Objects (PMSOs). ABG nucleosynthesis will produce three broad classes of PMSO chemistry, oxygen, carbon and nitrogen rich (O-rich, C-rich, N-rich, respectively), depending largely on the original stellar mass. I further show that the Interstellar Comet 2I/Borisov (2I) belongs to a kinematic dynamical stream, the Wolf 630 stream, with an age and galactic orbit consistent with its origination as a stardust comet; the apparent lack of water in the 2I coma is consistent with it being a C-rich PMSO. I also provide predictions for distinguishing stardust comets from more conventional interstellar comets and asteroids ejected during planetary formation; these can be applied to 2I in its upcoming observational phase in early 2020 as it moves away from the Sun. In particular, isotope ratios of the CNO elements could be dispositive, IR detection of the 11.3 µm SiC line, the 30 µm line, or the IR PAH lines would provide strong evidence for a C-rich PMSO and detection of Na or Li enhancement would indicate an N-rich PMSO.

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In October 2017, the first interstellar object within our solar system was discovered. Today desi... more In October 2017, the first interstellar object within our solar system was discovered. Today designated 1I/'Oumuamua, it shows characteristics that have never before been observed in a celestial body. Due to these characteristics, an in-situ investigation of 1I would be of extraordinary scientific value. Previous studies have demonstrated that a mission to 1I/'Oumuamua is feasible using current and near-term technologies however with an anticipated launch date of 2020-2021, this is too soon to be realistic. This paper aims at addressing the question of the feasibility of a mission to 1I/'Oumuamua in 2024 and beyond. Using the OITS trajectory simulation tool, various scenarios are analyzed, including a powered Jupiter flyby and Solar Oberth maneuver, a Jupiter powered flyby, and more complex flyby schemes including a Mars and Venus flyby. With a powered Jupiter flyby and Solar Oberth maneuver, we identify a trajectory to 1I/'Oumuamua with a launch date in 2033, a total velocity increment of 18.2 km/s, and arrival at 1I/'Oumuamua in 2048. With an additional deep space maneuver before the powered Jupiter flyby, a trajectory with a launch date in 2030, a total velocity increment of 15.3 km/s, and an arrival at 1I/'Oumuamua in 2052 were identified. Both launch dates would provide over a decade for spacecraft development, in contrast to the previously identified 2020-2021 launch dates. Furthermore, the distance from the Sun at the Oberth burn is at 5 Solar radii. This results in heat flux values, which are of the same order of magnitude as for the Parker Solar Probe. We conclude that a mission to 1I/'Oumuamua is feasible, using existing and near-term technologies and there is sufficient time for developing such a mission.

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Astrophysical Journal Letters, 2019

The nature of 1I/'Oumuamua (henceforth, 1I), the first interstellar object known to pass through ... more The nature of 1I/'Oumuamua (henceforth, 1I), the first interstellar object known to pass through the solar system, remains mysterious. Feng & Jones noted that the incoming 1I velocity vector "at infinity" (v ∞) is close to the motion of the Pleiades dynamical stream (or Local Association), and suggested that 1I is a young object ejected from a star in that stream. Micheli et al. subsequently detected non-gravitational acceleration in the 1I trajectory; this acceleration would not be unusual in an active comet, but 1I observations failed to reveal any signs of activity. Bialy & Loeb hypothesized that the anomalous 1I acceleration was instead due to radiation pressure, which would require an extremely low mass-to-area ratio (or area density). Here I show that a low area density can also explain the very close kinematic association of 1I and the Pleiades stream, as it renders 1I subject to drag capture by interstellar gas clouds. This supports the radiation pressure hypothesis and suggests that there is a significant population of low area density ISOs in the Galaxy, leading, through gas drag, to enhanced ISO concentrations in the galactic dynamical streams. Any interstellar object entrained in a dynamical stream will have a predictable incoming v ∞ ; targeted deep surveys using this information should be able to find dynamical stream objects months to as much as a year before their perihelion, providing the lead time needed for fast-response missions for the future in situ exploration of such objects.

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The first definitely interstellar object 1I/'Oumuamua (previously A/2017 U1) observed in our sola... more The first definitely interstellar object 1I/'Oumuamua (previously A/2017 U1) observed in our solar system provides the opportunity to directly study material from other star systems. Can such objects be intercepted? The challenge of reaching the object within a reasonable timeframe is formidable due to its high heliocentric hyperbolic excess velocity of about 26 km/s; much faster than any vehicle yet launched. This paper presents a high-level analysis of potential near-term options for such a mission. Launching a spacecraft in a reasonable timeframe of 5-10 years requires a hyperbolic solar system excess velocity between 33 to 76 km/s for mission durations between 30 to 5 years. Different mission durations and their velocity requirements are explored with respect to the launch date, assuming direct impulsive transfer to the intercept trajectory. Several technology options are outlined, ranging from a close solar Oberth Maneuver using chemical propulsion, and the more advanced options of solar and laser sails. To maximize science return decelerating the spacecraft at 'Oumuamua is highly desirable, due to the minimal science return from a hyper-velocity encounter. It is concluded that although reaching the object is challenging, there seem to be viable options based on current and near-term technology.

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Compact Composite Objects (CCOs), nuggets of dense Color-Flavor-Locked Superconducting quark matt... more Compact Composite Objects (CCOs), nuggets of dense Color-Flavor-Locked Superconducting quark matter created before or during the Quantum Chromo- Dynamics phase transition in the early universe, could provide a natural explanation for both Dark Matter (DM) and the observed cosmological baryon asymmetry, without requiring modifications to fundamental physics. This hypothesis implies a relic CCO population in the Solar System, captured during its formation, which would lead to a population of “strange asteroids,” bodies with mm-radii quark matter cores and ordinary matter (rock or ice) mantles. This hypothesis is supported by the observed population of small Very Fast Rotating (VFR) asteroids (bodies with rotation periods as short as 25 sec); the VFR data are consistent with a population of strange asteroids with core masses of order 10^10 - 10^11 kg. If the VFR asteroids are indeed strange asteroids their CCO cores could be mined using the techniques being developed for asteroid mining. Besides being intrinsically of great scientific interest, CCO cores could also serve as very powerful sources of energy, releasing a substantial fraction of the mass energy of incident particles as their quarks are absorbed into the QCD superfluid. Through a process analogous to Andreev reflection in superconductors[7], even normal matter CCOs could be used as antimatter factories, potentially providing as much as 10^9 kg of antimatter per CCO. While of course speculative, this energy source, if realized, would be suitable for propelling starships to a substantial fraction of the speed of light, and could be found, extracted and exploited in our Solar System with existing and near-term developments in technology.

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Chameleon fields are a way to "hide" a scale gravitational field, avoiding the stringent constant... more Chameleon fields are a way to "hide" a scale gravitational field, avoiding the stringent constant on static Brans Dicke scalar fields. Because chameleon fields are hidden in ordinary matter by an increase in the mass of the chameleon, the group velocity of the field is lowered, which means that non-relativistic vibrating or moving masses could potentially be much more efficient at generating propagating scalar fields than they are at generating gravitational waves (i.e., tensor fields propagating at the speed of light). As propagating scalar fields will carry momentum, this could lead to novel means of generating thrust for propulsion in space.

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The discovery of pulsars with masses of ∼ 2 solar masses (2 M ⊙) provides strong support for the ... more The discovery of pulsars with masses of ∼ 2 solar masses (2 M ⊙) provides strong support for the existence of strange quark matter in nature [1]. The discovery of ultra-dense pulsar planets [2] indicates that strange quark matter objects need not be gravitationally confined and supports the hypothesis that strange quark matter is a stable state of matter [3]. Stable quark matter nuggets have been proposed as an explanation for dark matter [4], being consistent with astronomical constraints if they have masses, M, in the range 10 5 kg M 10 16 kg. Quark matter objects in this mass range would have diameters of order 1 mm, extremely high densities (10 15 kg m −3), and the mass of a small asteroid. Quark nuggets would not be " dark, " but would interact with ordinary matter and with photons, satisfying astronomical constraints on dark matter through their relative rarity instead of through a lack of interactions with photons or baryons [5]. Under very general assumptions primordial quark nuggets would attract nearby normal matter and thus should be expected to possess ordinary matter mantles, appearing superficially to be ordinary planetesimals or asteroids. For reasonable models of galactic dark matter velocity distributions the total amount of captured dark matter in a solar-type protoplanetary nebula might be as large as ∼ 10 −8 to 10 −6 M ⊙ ; these quark nuggets would reside today in the cores of the Sun, planets and asteroids. The quark nugget theory is likely to be confirmed or denied as a consequence of the exploration and mining of 100-meter sized Near Earth Objects (NEO), as the existence of a quark core should be evident to in situ spacecraft examination of such small bodies. Such " strange asteroids " would be dominated by the mass of their strange matter core, having a high density and possibly also a strong magnetic field [6]. Strange asteroids would, however, possess relatively small moments of inertia, and thus could be spun up to unusually fast rotation rates under Yarkovsky-O'Keefe-Radzievskii-Paddack (YORP) radiative torquing [7]. Small NEO do indeed contain a population apparently consistent with these predictions, suggesting that some 200-meter diameter or smaller asteroids may contain cores of strange quark matter, and that these objects should be sought among the extremely rapidly rotating small NEO [8]. If some small asteroids are indeed strange asteroids their quark matter cores could be extracted using the techniques being developed for asteroid mining. The discovery of even a single quark nugget in the Solar System would of course be of immense scientific value, but would also likely be important in the economic development of the solar system. At low temperatures and high densities the lowest energy quark matterstate appears to be the so-called Color-Flavor-Locked (CFL) superconducting state [9, 10, 11, 12, 13, 14]. CFL quark matter may be stable at zero temperature, and if it made up the dark matter it would be the fundamental state of matter, both more stable than 56 Fe and more prevalent than normal hadronic matter. It is not possible to model strange quark matter properly with lattice QCD [15], and so it is likely that quark nuggets will reveal new QCD physics, but it appears likely that quark matter in the solar system could be used as an energy source, enabling nuclear fusion either through the creation of antimatter through color Andreev reflection [16, 17], or by using small quark matter fragments as a catalysis for pynconuclear fusion [18]. While of course speculative, this energy source could be suitable for propelling starships to a substantial fraction of the speed of light, and, assuming the existance of strange quark matter, could be realized in our Solar System with existing and near-term developments in technology. References [1] T. Klähn, R. Łastowiecki, and D. Blaschke. Implications of the measurement of pulsars with two solar masses for quark matter in compact stars and heavy-ion collisions: A Nambu-Jona-Lasinio model case study. Phys. Rev. D,

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The Deep Space Gateway (DSG) proposed for cis-lunar space offers an opportunity to both improve t... more The Deep Space Gateway (DSG) proposed for cis-lunar space offers an opportunity to both improve tests of fundamental physics and to develop chronometric navigation techniques for the hu- man exploration of Mars and beyond. Here we outline how the DSG, equipped with highly accurate optical atomic clocks and optical phase coherent links with the Earth and other spacecraft, can used to develop and apply the science of chronometric geodesy and navigation, where the clock-spacecraft system is used to both position the spacecraft and measure adjacent gravitational fields.

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A human presence on Mars will, with current technology, require 6 to 9 month journeys in deep spa... more A human presence on Mars will, with current technology, require 6 to 9 month journeys in deep space to go between between the Earth and Mars, and also to return. There have been proposals both to bring asteroidal resources to cislunar space for use by astronauts in these journeys, and to conduct them using Mars cyclers, spacecraft on repeating orbits, to provide re-usable crew habitation. We combine these ideas, proposing to use asteroids that happen to be in or nearly in Mars cycler orbits as locations for deep space habitats and a source for resources to be used during the voyage. Even small asteroids, for example, should be able to provide tons of water for radiation shielding and agricultural hydroponics. These asteroids, once outfitted, would protect and sustain Mars-bound travelers, providing a cost-effective means of extending human presence into the solar system. Mars cycler orbits can be either powered, requiring propulsion to maintain a repeat orbit, or ballistic, repeating purely through orbital dynamics [1, 2]; useful ballistic Mars cycler orbits are generally commensurate with both the Earth-Mars synodic period (the time required for two orbiting bodies to repeat the same relative orbital orientation) and the orbital periods of the Earth and Mars. Asteroids in ballistic cycler orbits could provide lodging and logistical support in deep space without any orbital adjustments; other bodies approxmately in cycler orbits could have their orbits adjusted appropriately through the use of solar radiation pressure or other techniques developed to change asteroid orbits for planetary protection.

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The closest exoplanet is likely not to be Proxima Centauri b, but an as yet unknown nomadic exopl... more The closest exoplanet is likely not to be Proxima Centauri b, but an as yet unknown nomadic exoplanet. I describe how densely populated near-interstellar space is likely to be, and what steps should be taken to find our nearest neighbors.

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Abstract for the 2012 Lunar and Planetary Science Conference

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Abstract Submitted to the 65th International Astronautical Congress Session A3.4 Small Bodies Mis... more Abstract Submitted to the 65th International Astronautical Congress Session A3.4 Small Bodies Missions and Technologies

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Dark Matter (DM) is rarely considered to be important in the formation and his- tory of the Solar... more Dark Matter (DM) is rarely considered to be important in the formation and his- tory of the Solar system. However, under very general assumptions there would be significant “primordial capture” of DM due to gravitational potential changes during the collapse of proto-planetary nebulae.

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2024 NASA NIAC Symposium, 2024

Our target is the planet Proxima b orbiting in the habitable zone of Proxima Centauri, the neares... more Our target is the planet Proxima b orbiting in the habitable zone of Proxima Centauri, the nearest star to the Sun. Laser power beaming will enable the sending of gram-mass picospacecraft on interstellar missions at ~20% of the speed of light, or 0.2 c. At this velocity, the journey would take 21 years, while spending < 3 seconds within 100,000 km of Proxima b. As the cost of these missions is likely to be dominated by the cost of the launch infrastructure; once this is built, large expeditions of thousands of probes could be sent to a nearby star systems for a relatively modest incremental cost. Our “Coracle” probe concept has a mass of ~4 grams and a diameter of 4 meters. A swarm of 1000 such probes should be able to send 1 kilobit per second of data back to Earth, or 4 gigabytes over the one year after the Proxima encounter.

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Recent research has revealed the existence of a large population of ``nomadic planets,'' planets ... more Recent research has revealed the existence of a large population of ``nomadic planets,'' planets not in orbit around any star, and these nomadic planets have been shown to be potentially capable of supporting biospheres. The density of Interstellar nomadic planets is large enough that some such planets should be considerably closer to the Sun than even the closest stars. If such close nomadic planets can be found, they would offer compelling destinations for initial interstellar missions.

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51st Lunar Planetary Science Conference , 2020

With the recent expansion of plans for lunar exploration there has been increased interest in sup... more With the recent expansion of plans for lunar exploration there has been increased interest in support of operations at and near the Moon (i.e., in Cislunar Space), including robotic and crewed missions to the lunar polar regions. Real time navigation and communication will be especially difficult on the heavily shadowed lunar polar regions, given the bad lighting, the frequent lack of line of sight to the Earth, the extreme Geometrical Dilution of Precision (GDOP) for any use of terrestrial GPS and the lack, at least in the near term, of continual overhead satellite coverage. Unlike the Apollo surface Extra-Vehicular Activities (EVAs), future astronauts on polar surface EVAs will need local relays to communicate with the home base, and to perform local navigation, and communication beyond the local line of sight to a central lander.

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Lunar and Planetary Science Conference, 2019

The volume rate σ v ∞ sampled by surveys as a function of the velocity at infinity, v ∞ , after a... more The volume rate σ v ∞ sampled by surveys as a function of the velocity at infinity, v ∞ , after accounting for gravitational focusing (which changes the cross section, σ). This function provides a proxy for the relative interstellar asteroid detection probability as a function of v ∞. The detection probability for the Pleiades stream is poor compared to slower moving ISOs; the detection of 1I suggests an enhanced ISO density in that stream. Note that present surveys have a streak limit (an upper limit on the angular motions of detectable objects); shown here is the PanSTARRS streak limit of 10• day −1 (which applied at the time of the discovery of 1I). ISOs from the fast moving Hercules stream will be hard to detect without software improvements, such as synthetic tracking.

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A Schumann Resonance is an electromagnetic oscillation excited in a closed waveguide formed by mu... more A Schumann Resonance is an electromagnetic oscillation excited in a closed waveguide formed by multiple reflecting layers at or near the surface of a planetary body. The waveguide, for spherical bodies with uniform reflecting layers, is a resonant cavity with a fundamental wavelength ∼ the circumference of the body. A Schumann Resonance was detected on Titan at ∼36 Hz by the Huygens probe, with the resonant cavity being formed by Titan’s and subsurface ocean and the excitation thought to result from currents in the ionosphere induced by the advected Saturnian magnetic field. The same mechanisms should apply to Europa, leading to a prediction of a Schumann resonance between near-surface charged particles and the subsurface ocean which can be used to explore the subsurface of that ocean world. Similar considerations lead to the possibility of full-body Schumann-type resonances on small bodies (asteroids and comets), with the reflecting layer being provided by photo-disassociated electrons at the surface.

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