Engineering topics

Seal, David

Publications and source records attributed to Seal, David.

4 records

NASA NTRS2020

2020 IEEE Paper on Psyche margin management, Draft

In January 2017, the mission concept Psyche: Journey to a Metal World was one of two concepts selected by NASA for implementation as part of the 14th Discovery mission competition. Over the course of the past year, the Psyche team has actively worked to refine and mature the technical design, culminating in a successful completion of the Project Preliminary Design review and approval to proceed to Phase C in mid-2019. Psyche is a deep space mission utilizing solar electric propulsion (SEP), consisting of SPT-140 Hall thrusters which have been successfully employed on multiple commercial spacecraft. When launched, Psyche will carry over 1000 kg of Xenon, and will represent the farthest usage of electric propulsion usage from the Sun – a distance of over 3.3 AU. The use of solar electric propulsion in deep space has resulted in challenges unique to other missions. Spacecraft designs typically balance margins across two main elements – mass and power – that are independent of one another. Utilizing a low thrust trajectory through the application of electric propulsion introduces more elements - namely flight time, missed thrust percentage and thruster duty cycle. Moreover, these elements become connected, presenting additional relationships that must be considered. This paper will present an overview of the margin management process for Psyche, and how it has evolved from the early proposal stage to its current state. It will discuss the elements that are margined, their relationship with one another, and key uncertainties that must be addressed. It discusses challenges and mitigations obtained during the refinement of the Psyche project, culminating in a new margin strategy that enables optimization across many of the system elements, and will serve as a template for future deep space SEP missions.

Hart, William↗

NASA NTRS2017

NASA's Current Initiative to Improve Operations Planning

As a follow-on to the Technical Capability Assessment Team, in 2015 NASA began seven Agency-wide efforts to seek out opportunities to improve the effectiveness of NASA operations. One of these technical teams is the Mission Operations Planning team, charged with increasing interactions and efficiency for planning of mission activities. That team is chaired by the author with representatives from eight other centers across the Agency. As the strategic architects for the vision of agency-wide ops planning, the team has identified a number of new initiatives and techniques to improve planning, including: breaking down walls within centers which obstruct multi-mission planning; breaking down walls agency-wide which obstruct the sharing of ops planning lessons and capabilities; strengthening the community of practice of ops planning capability developers; establishing best practices for a variety of types of ops planning; defining standards for activity plans and timelines, and plan inputs; and recommending the presence of "multi-mission operations champions" within each center to implement these recommendations into the next decade.

Seal, David↗

NASA NTRS2017

The Epic Chronicle of Designing Cassini's Titan Flyby Altitudes

The selection and optimization of Titan flyby altitudes for NASA's Cassini mission at Saturn has traveled a long, fascinating, and often torturous sixteen-year path - starting in 2001, when pre-arrival trajectory design decisions had to be made, through April of 2017 when Cassini's last, and arguably most critical, low flyby takes place. The chronicle of designing and updating the Titan flyby altitudes have twists and turns enough to satisfy a full-length novel or feature film, including: critical design decision-making before arrival with multiple atmospheric models, high uncertainties, and limited data; early flybys that seemed to show trends that weren't there; use and misuse of statistical analysis; unexpected surprises with limited reaction time; navigation of a scientific, engineering, and management community with a wide array of inherent biases; and consideration of a variety of project risk postures in a high-scrutiny, high-impact, high-reward environment.

Bittner, Molly↗

NASA NTRS2010

Cassini's Solstice Mission

With the recent approval of NASA's flagship Cassini mission for seven more years of continued operations, dozens more Titan, Enceladus and other icy moon flybys await, as well as many occultations and multiple close passages to Saturn. Seasonal change is the principal scientific theme as Cassini extends its survey of the target-rich system over one full half-season, from just after northern winter solstice at arrival back in 2004, to northern summer solstice at the end of mission in 2017. The new seven-year mission extension requires careful propellant management as well as streamlined operations strategies with smaller spacecraft, sequencing and science teams. Cassini's never-before-envisioned end of mission scenario also includes nearly two dozen high-inclination orbits which pass between the rings and the planet allowing thrilling and unique science opportunities before entry into Saturn's atmosphere.

Seal, David↗