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 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.
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.
In Centauri Dreams, Paul Gilster looks at peer-reviewed research on deep space exploration, with an eye toward interstellar possibilities. For many years this site coordinated its efforts with the Tau Zero Foundation. It now serves as an independent forum for deep space news and ideas. In the logo above, the leftmost star is Alpha Centauri, a triple system closer than any other star, and a primary target for early interstellar probes. To its right is Beta Centauri (not a part of the Alpha Centauri system), with Beta, Gamma, Delta and Epsilon Crucis, stars in the Southern Cross, visible at the far right (image courtesy of Marco Lorenzi).
If you'd like to submit a comment for possible publication on Centauri Dreams, I will be glad to consider it. The primary criterion is that comments contribute meaningfully to the debate. Among other criteria for selection: Comments must be on topic, directly related to the post in question, must use appropriate language, and must not be abusive to others. Civility counts. In addition, a valid email address is required for a comment to be considered. Centauri Dreams is emphatically not a soapbox for political or religious views submitted by individuals or organizations. A long form of the policy can be viewed on the Administrative page. The short form is this: If your comment is not on topic and respectful to others, I'm probably not going to run it.
