Centauri Dreams
Imagining and Planning Interstellar Exploration
Remembering the Sail Mission to Halley’s Comet
Some years back I had the pleasure of asking Lou Friedman about the solar sail he, Bruce Murray and Carl Sagan championed at the Jet Propulsion Laboratory in the 1970s. NASA had hopes of reaching Halley’s Comet with a rendezvous mission in 1986. Halley’s closest approach that year would be 0.42 AU, but the comet was on the opposite side of the Sun from the Earth, making ground viewing less than impressive. Although the JPL mission did not fly, the Soviet Vega 1 and Vega 2 conducted flybys and the European Space Agency’s Giotto probe, as well as the Japanese Suisei and Sakigake, made up an investigative ‘armada.’
But the abortive NASA concept has always stuck in my mind because it seemed so far ahead of its time. Friedman acknowledged as much in our short conversation, saying that while the ideas were sound, the solar sail technology wasn’t ready for the ambitious uses planned for it. Friedman, of course, would go on to become a founder of The Planetary Society and its long-time executive director, championing sail concepts like Cosmos 1 and the LightSail 1 and LightSail 2 spacecraft. He’s also the author of one of the earliest books on this form of propulsion, Starsailing: Solar Sails and Interstellar Travel (Wiley, 1988).
Image: This artist’s concept shows an 850-by-850-meter wide solar sail spacecraft approaching Halley’s Comet. Credit: JPL-Caltech.
Starsailing is a slim but compelling book that should be on your shelf if you’re interested in these concepts and their history. Although out of print, it’s readily available through Amazon or eBay sellers. Meanwhile, The Planetary Society’s Jason Davis has made a cache of documents from engineer Carl Berglund available that cover many details of the mission. The self-deprecating Berglund, who refers to himself as a only a ‘cog engineer’ at JPL, joined the project at about the same time that Carl Sagan displayed a model of a solar sail on The Tonight Show, and while he only spent several months working on the sail, his JPL documents remind us just how ambitious the JPL concept had become.
Not one but two designs were under consideration, the first a square sail 850 meters to the side. Bear in mind that JAXA’s IKAROS sail, the largest we’ve yet deployed in space, runs 14 meters to the side. A second design was a heliogyro, a device with long blades aptly described by Davis as looking like “two ceiling fans stacked on top of each other.” There would be 12 sail blades in all, 6 per level, and here the dimensions really are staggering. Each blade was to be 8 meters wide and 6.2 kilometers long, making for 0.6 square kilometers of sail material in a spinning blade configuration that would complete a rotation every 200 seconds.
Let’s take a closer look at that heliogyro, as it’s a design we’ve yet to see in space. In a summary document written in early 1977, Friedman describes the concept this way:
The Heliogyro presents a large reflective area to create the Solar Sail by the use of very long, thin blades, much like helicopter blades, which are used both to reflect the solar pressure and to control the vehicle. The basic concept is to spin the vehicle and to use the centrifugal force to support and stiffen the blade, and to keep it flat relative to the Sun. The spin of the vehicle also aids in the deployment of the Heliogyro blades. In addition, the blades can be pitch controlled, as with a helicopter, in order to provide attitude control and to turn the vehicle so that the reflective plane can have different orientations with respect to the Sun. Thus, the vehicle can either fly in toward the Sun or fly out into the Solar System.
Image: Halley’s Comet Heliogyro Design. Credit: JPL-Caltech, 1976).
The document depicts a deployment in which the blades unroll from their storage rollers with the help of spin thrusters that are jettisoned after the first 100 meters. After this, solar torque on the blades continues to spin up the vehicle and, over the course of a two-week period, each of the blades unfurls to its full six-kilometer length. Friedman sees the major advantage of the heliogyro as being the support provided by its centrifugal spin, which eliminates the need for a stiffening structure and provides for higher performance than a square sail. The major uncertainty: The dynamics of a 6 kilometer long spinning blade in deep space.
As to sail materials, Friedman describes blades “made out of .1 mil plastic material, with a surface density of less than 4 grams per square meter,” with surface coatings on the back to allow the sail to work at high temperatures close to the Sun. An internal newsletter from Friedman on April 13 of 1977 looks at materials requirements and notes three film candidates: Kapton, Ciba-Geigy polyimid and PBI conformal coated with parylene. These films were specified in the 1.5 to 2.5 µm range in thickness. By way of comparison, the later IKAROS sail was made of a 7.5-micrometer thick sheet of polyimide with thin-film solar cells.
Whichever sail design got the nod, the plan was to launch from the Space Shuttle followed by an inward spiral toward the Sun to about 0.25 AU, after which the sail would leave the ecliptic as it reached speeds in the range of 55 kilometers per second, eventually matching the trajectory of Halley’s Comet in 1986. The sail would be jettisoned at the comet, allowing the craft to use maneuvering thrusters for its operations there, which were to include a landing on the comet itself at the end of the mission.
The heliogyro option ended up winning the competition over the square sail, but sail concepts themselves lost out to solar electrical power, an ion propulsion technology like that used in the Dawn spacecraft. But funding problems and a slower than expected Space Shuttle mission schedule brought all thoughts of a Halley’s Comet mission from NASA to an untimely end.
Friedman writes in Starsailing that in the 1977 to 1978 period, the JPL team produced its design study for the mission with the help of half a dozen industrial contractors and support from the NASA Ames and Langley research centers. It was solid work that showed how viable solar sailing could be as a method of propulsion. He also describes the outcome of the Halley’s mission design:
Despite the confidence of the technical team and the completion of a valid preliminary design, however, the NASA management was conservative. They felt the design and implementation could not be accomplished in time for a 1981 launch to Halley’s Comet. NASA also thought that the technology for solar sailing was not sufficiently ‘mature’ to be implemented on a near-term space project. Indeed, the Halley mission requirements were severe — and even our willingness to incur great risk for great gain was insufficient to overcome management’s skepticism. And as it turned out, the conservatives were right, we could not have done it. It was a self-fulfilling prophecy.
But what splendid work fleshing out solar sail concepts that we continue to explore and find viable. As mentioned above, The Planetary Society’s Lightsail 2 carries the idea forward, and may become the second solar sail to demonstrate controlled flight in space. JAXA, meanwhile, has plans for an IKAROS follow-on mission to study the Jupiter Trojans.
All of that helps us keep the documents Jason Davis has collected online in perspective, a valuable look at work that has contributed to our understanding of a key propulsion concept. Looking through these documents reminds me of days I spent in 2003 going through the Robert Forward notebooks stored at the University of Alabama at Huntsville. That sense of history in the making — or in this case, history that might have been — is palpable as we consider who developed these documents and handled them at the key JPL meetings.
Image: Dig into documents like this online to see a mission design emerging. Credit: Carl Berglund / The Planetary Society / Louis Friedman.
Friedman includes in one of the newsletters a March 14, 1977 article in Science covering the JPL sail work. It reminds us how exotic sail ideas were at the time. Quoting from it:
[The sail] might also effectively open up the rest of the Solar System to manned spaceflights that cannot be considered now because of tremendous costs. JPL’s Louis Friedman thinks that a flotilla of sunjammers could embark on a manned Mars mission by the end of the century, and foresees a day when fleets of huge kites shuttle through space — as the East Indiamen plied the oceans three centuries ago — making regular stops at Mercury, Venus, Mars or the asteroids.
Exotic ideas indeed, but slowly, surely, beginning to take shape. For more background, see Davis’ Sailing to the World’s Most Famous Comet.
Starship Congress 2017
I had thought at the end of last year that 2017 would be a year of few conferences held by the various interstellar organizations. In fact, the Tennessee Valley Interstellar Workshop was the only one I was sure would occur, a meeting I knew about because it was being held in partnership with the Tau Zero Foundation as well as Starship Century. Since then, we’ve had news of the Foundations of Interstellar Studies Workshop sponsored by the Initiative for Interstellar Studies. Background on these two, including details on registration and submitting papers, can be found in Interstellar Conference News.
Now the details of a late summer meeting to be held by Icarus Interstellar have emerged. Based on the group’s online description, this is to be the third in the Starship Congress meetings, the first of which I attended in Dallas in 2013. A second was held at Drexel University in Philadelphia in 2015.
Image: The 2013 Starship Congress in Dallas was a great meeting. In front at the far right, I am easy to spot because I am one of the few in the group shot wearing a light-colored jacket. It’s hard to make out the faces here, but I think that’s Pat Galea to my right, and my son Miles next to Pat. Rachel Armstrong is in front at the left, and although it’s too tricky to identify everyone, I do see Al Jackson, Jim Benford, Eric Davis, Phil Lubin and many other friends. Credit: Icarus Interstellar.
The focus of Starship Congress 2017 is to be the Moon, an unusual choice for a deep space organization, but Icarus asks a good question: “How can we hope to gain experience living, building and working off planet without systematically capitalizing on our nearest, most accessible celestial body?”
It’s a question with both near- and far-term resonances, for we’re also talking about more or less bypassing lunar resources and going straight for Mars, an idea that pulls me up short given our lack of knowledge about human physiology beyond low Earth orbit. We can study human factors in space-based laboratories, and I know that Robert Hampson (Wake Forest School of Medicine) continues to push for a dedicated facility to study biomedical matters outside Earth’s magnetosphere. But dedicated facilities on the Moon should be a part of this.
But let me give you the Icarus Interstellar view, in the form of the call for papers for Starship Congress 2017, reproduced here verbatim.
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Call for Papers
If we want to see interstellar accomplishments in our lifetime we need a staging area in space and we need to be able to get our people and our machines up there.
We dedicate each day of our meeting to addressing actions towards making Space a Place for Everybody and welcome the community to submit papers/presentations for each of the following:
Day 1: The Moon as a Stepping Stone to the Stars (MOON):
- Living on the Moon: Lunar city planning, lunar resources, construction, power, water, radiation shielding, living and working, economy, sociology.
- Planetary, Deep Space and Interstellar exploration centered around the Moon: Spacecraft Shipyards, Lunar Space elevators, Planetary and Deep Space remote sensing Telescopes.
Day 2: Massive Space Access Project (MSAP) aka “Children in Space”:
- Earth to Moon and back: transport vehicles and systems, global logistics, tourism, legal and safety considerations, military presence.
- Children in Space: Space education, youth space education program, people with disabilities in space, when will we send the first child to space? (when children can go to the moon, everyone will want to go!)
Day 3: Massive Space Based Infrastructure (MSBI):
- Space and Lunar Industry: Space stations, mining stations, space services, telecommunications, zero gravity and lunar gravity manufacturing technology development.
- Space arts, sports, community and culture: everything not traditionally considered infrastructure, but which is necessary for humans to live, love and learn on the Moon and in space.
Submit abstracts to starshipcongress@icarusinterstellar.org by Monday, July 3rd, 2017. Papers will be approved on a rolling basis with the final agenda shared on Monday, July 10th, 2017.
Conference Registration
Register for Starship Congress 2017 here.
Hotel Registration
Starship Congress will be held at:
HYATT REGENCY MONTEREY HOTEL & SPA
One Old Golf Course Rd, Monterey, CA 93940, USA
T +1.831.657.6541 Email: megan.whetton@hyatt.com
monterey.hyatt.com
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If you’re interested in presenting at the conference, abstracts can be submitted to starshipcongress@icarusinterstellar.org by Monday, July 3rd, 2017. Papers will be approved on a rolling basis with the final agenda shared on Monday, July 10th, 2017.
Early System Evolution: The Disks around Epsilon Eridani
Nine years ago in a piece titled Asteroid Belts, Possible Planets Around Epsilon Eridani, I discussed work that Massimo Marengo was doing on the nearby star, examining rings of material around Epsilon Eridani and considering the possibilities with regard to planets. Marengo (now at Iowa State University) has recently been working with Kate Su (University of Arizona) and other colleagues, using the SOFIA telescope (Stratospheric Observatory for Infrared Astronomy) to help us refine our understanding of the evolving planetary system.
Image: Astronomers (left to right) Massimo Marengo, Andrew Helton and Kate Su study images of epsilon Eridani during their SOFIA mission. Credit: Massimo Marengo.
The researchers used the 2.5-meter telescope aboard the Boeing 747SP jetliner to collect data about the star, working at 45,000 feet in a region above most of the atmospheric water vapor that absorbs the infrared light being studied. Epsilon Eridani is a bit over 10 light years from the Sun, and about a fifth of its age, meaning we have close at hand a stellar system that can help us understand what our own Solar System was like in its youth.
The new paper confirms Marengo’s earlier findings that there are separate inner and outer disk structures, with the possibility that the inner disk is itself made up of more than one debris belt. Says Marengo:
“This star hosts a planetary system currently undergoing the same cataclysmic processes that happened to the solar system in its youth, at the time in which the moon gained most of its craters, Earth acquired the water in its oceans, and the conditions favorable for life on our planet were set.”
Image: This is an artist’s illustration of the Epsilon Eridani system showing Epsilon Eridani b, right foreground, a Jupiter-mass planet orbiting its parent star at the outside edge of an asteroid belt. In the background can be seen another narrow asteroid or comet belt plus an outermost belt similar in size to our Solar System’s Kuiper Belt. The similarity of the structure of the Epsilon Eridani system to our Solar System is remarkable, although Epsilon Eridani is much younger than our sun. SOFIA observations confirmed the existence of the asteroid belt adjacent to the orbit of the Jovian planet. Credit: NASA/SOFIA/Lynette Cook.
This is fine-grained work, for it requires the astronomers to separate the faint emission of Epsilon Eridani’s circumstellar disk from the bright light of the host star. But when Marengo likens the work with SOFIA to using a time machine, he has an obvious point. Debris disks result when belts of planetesimals are perturbed by newly formed planets, creating collisions that over time break the minor bodies down into dust. We know of more than 400 debris disks around other stars, but we have few systems close enough to study at high resolution. Moreover, what the paper describes as the two benchmark nearby debris disks are around A-class stars, Fomalhaut and Vega. Epsilon Eridani gives us a star much more like the Sun.
Debris disks, which can include rocky and icy bodies as well as gas and dust, can be broad, continuous disks or they can become concentrated into belts of debris. Here the analogy is to our own Solar System’s asteroid belt and Kuiper Belt, two distinct regions with one disk of debris concentrated beyond the orbit of Mars and the other beyond the orbit of Neptune. With an outer cold disk and a warm inner one assumed, the new work focuses on the inner disk. Here there are two different models for how the inner disk is formed, with implications for planets.
One model calls for an inner disk made up of two narrow rings of debris, with one ring roughly at the position of our asteroid belt around the star, and the other at a region corresponding to the orbit of Uranus. The other model sees the inner disk region being populated by dust from the outer, Kuiper Belt-like region, with material inflowing into the inner disk. The latter model assumes a single broad disk in the inner system as opposed to two belt-like rings. The new SOFIA observations favor the narrow belt model rather than a broad continuous disk.
Combining data from SOFIA with earlier Spitzer observations, the researchers found that excess emissions in the inner 25 AU region around the star are the result of a dust-producing planetesimal belt, and perhaps more than one. For it turns out that the resolution achieved by the SOFIA data was insufficient to determine whether the inner disk is itself divided into more than one narrow belts, but it did allow the team to rule out the possibility that the inner region’s warm emissions were the result of dust grains pulled in from an outer, much colder belt.
That favors the first model. The paper makes the case that in the absence of dust grains being dragged in from the cold outer belt, a planet might be necessary to explain what is seen in Epsilon Eridani’s inner disk structure. From the paper:
The observed profiles are not consistent with the case dominated by dragged-in grains (uninterrupted dust flow from the cold Kuiper-belt-analog region) as proposed by Reidemeister et al. (2011). This might suggest the need of a planet interior to the 64-au cold belt to maintain the inner dust-free zone, or a very dense cold belt where the intense collisions destroy the dust grains before they have enough time to be dragged in. In either case, some amount of dragged-in grains from the cold belt can still contribute a fraction of the emission inside 25 au; the exact amount remains to be determined by future high spatial resolution.
Image: Illustration based on Spitzer observations of the inner and outer parts of the Epsilon Eridani system compared with the corresponding components of our Solar System. Credit: NASA/JPL/Caltech/R. Hurt (SSC).
What we do have, though, is confirmation that we have at least one inner disk, and that it is near the orbit of the Jupiter-class planet that circles the star at a distance comparable to Jupiter’s from the Sun. Kate Su explains:
“The high spatial resolution of SOFIA combined with the unique wavelength coverage and impressive dynamic range of the FORCAST camera allowed us to resolve the warm emission around eps Eri, confirming the model that located the warm material near the Jovian planet’s orbit. Furthermore, a planetary mass object is needed to stop the sheet of dust from the outer zone, similar to Neptune’s role in our solar system. It really is impressive how eps Eri, a much younger version of our solar system, is put together like ours.”
The paper is Su et al., “The Inner 25 AU Debris Distribution in the epsilon Eri System,” Astronomical Journal Vol. 153, No. 5 (25 April 2017). Abstract / preprint.
Cassini: Back into the ‘Big Empty”
Cassini’s final months are stuffed with daring science, the kind of operations you’d never venture early in a mission of this magnitude for fear you’d lose the spacecraft. With the end in sight for Cassini, though, ramping up the science return seems worth the risk. And while diving through the narrow gap between Saturn and its rings seems to be asking for trouble, the results of the first plunge on April 26 show that the region is more dust-free than expected.
“The region between the rings and Saturn is ‘the big empty,’ apparently,” says Cassini Project Manager Earl Maize of NASA’s Jet Propulsion Laboratory in Pasadena, California. “Cassini will stay the course, while the scientists work on the mystery of why the dust level is much lower than expected.”
Image: This artist’s concept shows an over-the-shoulder view of Cassini making one of its Grand Finale dives over Saturn. Credit: NASA/JPL-Caltech.
The region between Saturn and its rings was thought, based on previous models of the ring particle environment, to be free of large particles that could cripple the spacecraft. But it seemed prudent to rotate Cassini so its 4-meter antenna became a ‘bumper’ of sorts that could shield its scientific instrumentation during the dive. Such changes in orientation affect how the spacecraft takes data.
In fact, as we see in this JPL news release, Cassini’s Radio and Plasma Wave Science instrument and its magnetometer were the only two science instruments whose sensors were not in the shadow of the antenna in the first dive. It was the RPWS instrument that measured the particle count during the crossing of the ring plane and found only a few scattered hits.
“It was a bit disorienting — we weren’t hearing what we expected to hear,” says William Kurth, RPWS team lead at the University of Iowa, Iowa City. “I’ve listened to our data from the first dive several times and I can probably count on my hands the number of dust particle impacts I hear.”
Image: This video represents data collected by the Radio and Plasma Wave Science instrument on NASA’s Cassini spacecraft, as it crossed through the gap between Saturn and its rings on April 26, 2017, during the first dive of the mission’s Grand Finale. The instrument is able to record ring particles striking the spacecraft in its data. In the data from this dive, there is virtually no detectable peak in pops and cracks that represent ring particles striking the spacecraft. The lack of discernible pops and cracks indicates the region is largely free of small particles. Credits: NASA/JPL-Caltech/University of Iowa.
The particles the craft did encounter were no more than 1 micron across, about the size of particles you would find in smoke. Now we have another ring plane crossing today at 1538 EDT (1938 UTC), during which Cassini will be out of contact during closest approach to Saturn. We’ll get data return on May 3. After today, 20 ring dives will remain, with four of them passing through the innermost fringes of the rings and demanding the use of the antenna as shield. But the low dust level means that most dives will not need the shield configuration.
Image: Cassini will perform 22 orbits of Saturn during the Grand Finale. Credit: NASA/JPL-Caltech.
Each of the so-called Grand Finale orbits takes about six and a half days to complete, with the spacecraft’s speed at closest approach to Saturn in each orbit ranging from 35 to 33.6 kilometers per second. This second orbit in the series gives Cassini’s imaging cameras (its Imaging Science Subsystem) a chance to observe the rings at extremely high phase angles while the Sun is directly behind Saturn — this should allow small features like ‘ringlets’ within the rings to be observed. The spacecraft will come within 2930 kilometers of the 1-bar level in Saturn’s atmosphere while passing some 4780 kilometers from the inner edge of the D ring.
NASA Grant Award to Tau Zero Foundation
NASA has awarded a $500,000 grant to the Tau Zero Foundation for a 3-year study titled “Interstellar Propulsion Review.” Unlike prior studies, which were based on a specific mission concept, this study is an overall comparison between the different motivations, challenges, and approaches to interstellar flight. The work is split into three major 1-year phases:
1. Create an interstellar work breakdown structure (WBS) tailored to the divergent challenges and potentially disruptive prospects of interstellar flight in a manner that will allow for ‘level-playing-field’ comparisons. Prior mission and project information will be used to populate this first WBS.
2. Identify and work with subject matter experts to populate the WBS with their most recent reliable data.
3. Analyze uploaded data to identify (1) the most consequential knowledge gaps and (2) recommend research. Once all these phases are completed, the tools and methods are available to repeat the assessments as needed.
Your Inputs Sought
Tau Zero invites the participation of the broader interstellar community to affect this grant, with this call for papers for the next Tennessee Valley Interstellar Workshop (TVIW). This call is in addition to the more general call for abstracts issued from the TVIW hosts, whose topics and conditions can be found here.
Seeding Infrastructure
Many interstellar mission concepts rely on substantial infrastructure in our solar system to build, power, and launch their vehicles. What is seldom addressed, however, is how to begin to build that infrastructure, incrementally and affordably. Abstracts are invited that address that gap, with an emphasis on defining the first infrastructure missions that (a) can be launched with existing spacecraft, (b) provide an immediate utility in space, and (c) are part of a larger plan to extend that capability. This encompasses power production and distribution, mining, construction material processing, in-space construction, and propellant harvesting and delivery.
Exoplanet Science Instruments
What scientific instruments should an interstellar probe carry to collect meaningful information about an exoplanet – information that cannot be obtained from Earth-based astronomy alone? How close would such a probe need to get to an exoplanet to collect this information and how much time will it take within that distance to collect enough data to reach meaningful conclusions? What volume of data would need to be communicated back to Earth? What are projected mass and power requirements for such instrumentation? Abstracts are sought that discuss these instrumentation requirements, characteristics, and the trade-offs between minimizing instrumentation and maximizing information. Papers can be as basic as compiling a list of existing, relevant instrumentation for baseline comparisons, all the way to projections of the minimal mass, power, and computational ability for basic observations. Abstracts are also welcome that discus trends in the abilities of Earth-based exoplanet science and how this affects the instrumentation requirements of interstellar probes.
Foundationally Consistent Baselines
Different mission/vehicle concepts often use different projected performances for common functions such as: (a) heat rejection, (b) energy storage, (c) power management and distribution (PMAD), (d) magnetic nozzles, (e) communication with Earth, (f) equipment longevity, (g) structural mass {if built in space}, and (h) guidance, navigation and control (GNC). Fair comparisons of mission-vehicle concepts are difficult when different values are used for such baseline technologies. Presentations are invited that can credibly delineate reasonable performance estimates for such common functionalities so that future mission-vehicle studies can use common baselines for comparison (e.g. efficiencies, specific masses, readiness levels, etc).
Consistent Comparison Measures
It is difficult to objectively compare different interstellar propulsion and power concepts that use different fundamental methods with method-specific performance measures (e.g. rocket specific impulse, laser pointing accuracy, etc). Abstracts are sought for suggested alternatives to compare both the abilities and resource requirements of diverse interstellar mission concepts – measures that are consistent across all modalities (perhaps in terms of energy, power, mass, mission time, etc.).
Humanities – Interstellar Prerequisite of a Mature Humanity
The energy levels required for interstellar flight are large enough to have the potential to become weapons of mass destruction. Hence, a key prerequisite for achieving interstellar flight is not technical, but societal. Human civilization must mature to where it can wield these energy levels for the greater good instead of on each other. Abstracts are invited that explore these issues in rigorous, academic depth, or suggest how to begin such studies.
Humanities – World Ships as a Crucible of Cultural Study
In addition to the physical life support that has to function reliably for centuries aboard world ships, the culture of the on-board colony will also require a sustainably peaceful governance system along with a culture where the individual citizens live meaningful lives. Abstracts are invited that explore these issues in rigorous, academic depth, or suggest how to begin such studies.
Breakthrough Propulsion Physics
In addition to propulsion and power concepts based on known physics, it is prudent to also consider the possibility that new physics discoveries will lead to breakthrough propulsion, such as faster-than-light transport or propellant-less space drives. Abstracts are sought that identify relevant open questions in physics and then how to further investigate those unknowns. The connection between the open question in physics and its propulsion or power relevance must be explicit. Note, this is not an invitation for new theories or speculations about propulsion devices. Instead, this is a call to identify credible lines of inquiry that might lead to testable, relevant hypotheses. This invitation includes seeking experimental proposals for testing critical relevant questions in physics.
About the Workshop
The TVIW is a scientific and educational association that promotes interstellar exploration, travel, and communications. The TVIW provides an opportunity for relaxed sharing of ideas in directions that will stimulate and encourage interstellar exploration including propulsion, communications, and research. The ‘Workshop’ theme suggests that the direction should go beyond that of a ‘conference’. Attendees are encouraged not only to present intellectual concepts but to develop these concepts to suggest projects, collaboration, active research and mission planning. It should be a time for engaging discussions, thought provoking ideas, and boundless optimism contemplating a future that may one day be within the reach of humanity. Though the TVIW concept was intended to be regional (viz., the American Southeast), it is now, in fact, an internationally recognized event.
Presentation and Publication Requirements
Abstracts should describe content that can be introduced in a 20 minute presentation, followed by 5 minutes for Q&A. Though not a firm requirement, it is desirable that the author prepare a manuscript suitable for submission to a peer-reviewed journal (such as the Journal of the British Interplanetary Society for general papers). The workshop organizers plan to video and stream the presentations, and share the presentation charts with participants.
Submission Requirements
Submit 1-2 page PDF including the following information (file size cannot exceed 3 MB):
– Title
– Presenting author & affiliation.
– Coauthors and respective affiliations.
– Abstract text between 300 to 500 words in length
– Outline for the body of the report
– Cite at least 3 references upon which the work is based
– Cite the most recent publication by the presenting author that relates to the invited topics.
Where to Submit
The Tau Zero specific interests are in addition to a more general call for papers from TVIW. If you are submitting an abstract for the more general coverage of the TVIW, then visit this page. For the Tau Zero specific topics of interest, email your PDF to: Info@TauZero.aero for submissions.
Due Dates
10-May-2017 Submission deadline for TZF Paper Abstracts
31-May-2017 Accepted TZF papers announced
30-Jun-2017 Last day for early registration
30-Sep-2017 Deadline for electronic submittal of all final presentation materials
4-Oct-2017 TVIW 2017 begins
Selections Process
Tau Zero reserves the right to reject any abstract it deems as out of scope or not satisfactorily substantive. It is expected, as a minimum, that abstracts:
– Address the requested topics
– Adhere to the submission requirements
– Reflect that the presentation will be based on sound, credible information instead of speculative or subjective assertions.
Questions can be directed to: Info@TauZero.aero
About Tau Zero
Tau Zero is a 501(c) non-profit organization dedicated to accelerating progress toward the scientific breakthroughs required to support interstellar flight. The Foundation’s efforts, driven by the experts most capable of addressing the formidable challenges of interstellar flight, include fundamental scientific research, encouraging and supporting academic involvement in sciences related to its goals, empowering youth in this quest, forging collaborations for cross-fertilization, and engaging governmental and industry support on a global scale.
Tau Zero’s motto is “Ad Astra Incrementis” – to the stars in ever-expanding steps.
PG Note: To prevent redundancy, I’ve closed comments on this post so that comments can flow to Tau Zero at the address above.
Planetary Discovery around Ultracool Star
I have a special enthusiasm for microlensing as a means of exoplanet discovery. With microlensing, you never know what you’re going to come up with. Transits are easier to detect when the planet is close to its star, and hence transits more frequently. Radial velocity likewise sends its loudest signal when a planet is large and close. Microlensing, detecting the ‘bending’ of light from a background object as it is affected by a nearer star’s gravitational field, can turn up a planet whether near to its star or far, and in a wide range of masses. It can also be used to study planetary populations as distant as the galactic bulge and beyond.
Now we have news of a cold planet about the size of the Earth orbiting what may turn out to be a brown dwarf, and is in any case no more than 7.8 percent the mass of our Sun. Is this an object like TRAPPIST-1, the ultra-cool dwarf star we’ve had so much to say about in recent days as investigations of its 7 planets continue? If so, the planet OGLE-2016-BLG-1195Lb is in no way as interesting from an astrobiological point of view. It’s probably colder than Pluto. It is also the lowest-mass planet ever found using the microlensing technique.
Image: This artist’s concept shows OGLE-2016-BLG-1195Lb, reported in a 2017 study in the Astrophysical Journal Letters. Study authors used the Korea Microlensing Telescope Network (KMTNet), operated by the Korea Astronomy and Space Science Institute, and NASA’s Spitzer Space Telescope, to track the microlensing event and find the planet. Credit: NASA/JPL-Caltech.
But don’t think this frigid world, about 13000 light years away, doesn’t have its uses. It is part of an ongoing investigation into the distribution of planets in the galaxy. The OGLE designation signifies the ground-based Optical Gravitational Lensing Experiment survey, run by the University of Warsaw, which alerted astronomers to the initial microlensing event. The authors of the study on OGLE-2016-BLG-1195Lb then used the Korea Microlensing Telescope Network (KMTNet) as well as the Spitzer space telescope to study the outcome.
With this planet, we are at the lowest end of what microlensing can detect with current methods. We’ll need to get to NASA’s upcoming Wide Field Infrared Survey Telescope (WFIRST) to begin finding smaller bodies than this. Tuning up the method will be useful as we work on understanding how planets are distributed in the Milky Way, since microlensing can find planets at distances far beyond the capabilities of other detection methods. Specifically, will we find a difference in the planet populations of the Milky Way’s central bulge as compared to its disk? OGLE-2016-BLG-1195Lb is a member of the disk population.
“Although we only have a handful of planetary systems with well-determined distances that are this far outside our solar system, the lack of Spitzer detections in the bulge suggests that planets may be less common toward the center of our galaxy than in the disk,” says Geoff Bryden, astronomer at JPL and co-author of the study.
Let’s dig a little deeper, though, into planet formation around ultracool stars. A 2007 paper by Matthew Payne and Giuseppe Lodato looked at the core accretion method of planet formation in the context of very low mass stars and brown dwarfs, arguing that if such objects have protoplanetary disks in the range of several Jupiter masses, then Earth-mass planets should be frequent around them, typically at about 1 AU from the star. But if brown dwarf disks contain less than a Jupiter mass of material, then they probably cannot form a planet.
The OGLE-2016-BLG-1195Lb paper runs through the scholarship, including a 2013 study from Daniel Apai showing that disks occur as frequently around ultracool dwarfs as around Sun-like stars. And a 2016 paper from Leonardo Testi and colleagues found evidence for dusty disks around 11 of 17 young brown dwarfs studied. A Herschel study from Sebastian Daemgen and team, likewise in 2016, found that half of the ultracool dwarf disks it examined were of at least one Jupiter mass.
So we’re making progress at learning about planet formation in ultracool environments, and here again microlensing comes to the fore. Stars this faint, and their even fainter planets, are a tough challenge for most planetary detection methods, though four have been found with direct imaging. Microlensing does not rely on light from the system being studied, but it can give us information about the planetary and stellar masses involved. And indeed, we have four previous microlensing events that have found planets around ultracool dwarfs.
Two of these previous microlensing detections show planets as small as a few Earth masses, and OGLE-2016-BLG-1195Lb lowers the detected mass still further. From the paper:
These [previous discoveries] suggest that the protoplanetary disks of ultracool dwarfs have sufficient mass to form terrestrial planets, as also hinted at by direct imaging of such disks. The location of these planets, at about 1 AU, support planet formation predictions. However, since the sensitivity of current microlensing surveys for systems with such small mass ratios is very narrow, around projected separations of ?1AU, they cannot set strong constraints on the presence of planets elsewhere around ultracool dwarfs, such as the much closer separations seen in the TRAPPIST-1 system.
Small planets may be common around ultracool dwarfs, an idea that previous microlensing discoveries reinforce, along with the work on protoplanetary disks and the seven planets orbiting TRAPPIST-1. As to our expectations regarding planets in the galactic bulge as opposed to the disk, the jury is still out. The planets Spitzer has thus far found in its microlensing campaign for the galactic distribution of planets are all located in the disk. We have two upcoming Spitzer microlensing campaigns, one this year and one next, which should offer additional insights. The key question: Is the galactic bulge deficient in planets?
The paper is Shvartzvald et al., “An Earth-mass Planet in a 1-AU Orbit around an Ultracool Dwarf,” accepted at Astrophysical Journal Letters (preprint).
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