JPL veterans and relative newcomers to the Lab joined to make Dawn a success well beyond expectations. Over its 11-year mission powered by ion propulsion, the spacecraft was the first to orbit an object in the main asteroid belt between Mars and Jupiter and the only spacecraft to orbit two extraterrestrial targets—the planet-like world Vesta and dwarf planet Ceres. The pair serve as time capsules back to the dawn of the Solar System.
Each of Dawn’s three 12-inch-diameter ion thrust units is movable in two axes to allow for migration of the spacecraft's center of mass, allowing the attitude-control system to use the ion thrusters to help control spacecraft attitude. The thrusters use an electrical charge to accelerate ions from xenon fuel to a speed seven to 10 times that of chemical engines. At maximum thrust, each of Dawn’s three ion propulsion engines produces about the same amount of force involved in holding a single piece of notebook paper in your hand.
The mission overcame significant engineering challenges, most notably the loss of the reaction wheels that control the spacecraft’s orientation in space. But ingenuity, creativity and teamwork allowed Dawn to proceed and achieve its science goals and beyond.
Dawn reached Vesta in 2011 and investigated it from surface to core during 14 months in orbit. Vesta was shown to be a dry, rocky, differentiated body with a basaltic crust on the surface, and an iron core, similar to terrestrial planets and Earth's moon. Dawn confirmed that many meteorites here on Earth came from Vesta.
In 2012, Dawn left Vesta and traveled for more than two years before entering orbit around Ceres, where it has been collecting data since 2015. Ceres surprised scientists with its heavily cratered surface, a mixture of clays, salt and ice. Young deposits on Ceres indicated there is a process still active inside of the body that’s mobilizing salty materials and bringing them to the surface.
As Dawn runs out of hydrazine and the mission comes to a close sometime between late September and mid-October, team members shared their experiences and best memories with Universe.
Q: The way Dawn has turned out is a lot different from when it was first conceived and also from when it was launched. How did the team respond, particularly to the loss of reaction wheels?
Carol Raymond, principal investigator
We used all the capability of the mission to achieve science beyond expectations. Even though we launched with defective reaction wheels, the team responded in their usual extraordinary way to rise up and overcome this challenge by programming a new hybrid attitude control system using the remaining two wheels and hydrazine jets. If the team and the spacecraft had not been so capable, the loss of the reaction wheels could have been devastating.
Marc Rayman, chief engineer and mission manager
The spacecraft we’re flying now and the mission we’re doing were not envisioned in the proposal; for that matter, even when we arrived at Vesta. Having lost all reaction-wheel control, we were flying a different spacecraft. In addition, over the course of the mission, we uploaded new software that gave us new functionality and capability. The mission we’re doing right now at Ceres has an elliptical orbit that dips down so low, every 27 hours the spacecraft gets down to only about three times the height above the ground than you are when you fly across country on a commercial aircraft. That’s pretty amazing. We never thought about doing that. Yet we’re doing it successfully and this team is doing it flawlessly.
Q: Please describe what attracted you to the Dawn mission. What are your personal highlights?
Paul Fieseler, spacecraft team chief, systems engineer
I have been with this mission since the spacecraft was being built and will follow it through to its last day. I liked the fact that the mission was going someplace completely unexplored, and doing it with the futuristic sounding “ion propulsion.” My job is to allow Dawn to be operated in a way to acquire as much scientific data as possible, while staying within the limits of what the spacecraft is capable of.
Kristina Larson, lead systems engineer
I joined as a summer intern in 2008 and have been part of the spacecraft team ever since. When Dawn launched in 2007, we really did not know what to expect from Vesta and Ceres. I have witnessed approaching both bodies, watching them grow from a pixel into a blurry blob and then into magnificent, cratered, fascinating bodies. It reminds me of how it feels to be backpacking, days into the wilderness, and crest a pass to find a hidden alpine lake. To be able to do that same sort of exploration but in space is beyond my wildest childhood dreams!
Carol Polanskey, science operations system engineer
Once the hardware was delivered for testing I became deeply involved in the instrument functional and operations scenario testing. It was incredible to be sending commands to these instruments as if they were in space but they were really only several meters away bolted to the spacecraft within plain sight. This was the most exhausting and stressful time of the mission but a period I now look back on with much fondness.
Greg Whiffen, lead mission designer and maneuver designer
Before launch, I contributed an algorithm to steer the spacecraft that was needed as a proof of concept in 2001, because at that time there were no methods available to reliably and optimally maneuver a spacecraft like Dawn into and out of orbits around bodies like Vesta and Ceres. To have designed and guided Dawn throughout its mission is a trajectory and maneuver designer's dream come true.
Chuck Garner, ion propulsion system operations
I was hired into JPL’s Electric Propulsion Group in 1981. In those days, electric propulsion was viewed as a technology of the future and always would be. It was always my dream to work on a mission that uses electric propulsion, and when the opportunity to support Dawn materialized I jumped on it. I began working on Dawn around 2002 and have been supporting the mission ever since.
Dan Grebow, mission designer and maneuver designer
I started at JPL in 2010, three years after Dawn launched. I began working on Dawn when the spacecraft left Vesta in 2012. Because of its unique ion propulsion system, the mission seemed more challenging than conventional space missions, which is what I was looking for. I worked on early stages of development of Dawn’s mission at Ceres, designing the spacecraft’s trajectory even before it arrived there. And when the project decided to fly over Occator Crater for the second extended mission, I helped design the orbit that flew directly over the crater and verified it was stable.
Q: Career wise, has Dawn allowed you to grow, to be better than you were before you started on it?
How many people can say they helped operate an ion propulsion system on a deep-space mission for 11 years? That’s been very cool.
Dawn is the mission on which I’ve learned how to operate a spacecraft. Starting as an intern during undergrad, I came in with a bunch of knowledge of how to build a plane but near none on how to operate something in space, let alone something going as far away from Earth as Dawn. My mentors on the project answered my millions of daily questions, and continued to expand my responsibilities over the years, providing me with a really invaluable education.
Dawn has certainly given me the opportunity to learn on the go. The toughest parts, and the parts where you learn the most, are the same. That is, when the mission is attempting to do something new, be it the first time lighting the thrusters, entering orbit about an asteroid, or diving the spacecraft down to altitudes lower than it was ever supposed to go.
Dawn has defined my career. As soon as I showed up on Lab in 2001, I had a little involvement in the proposal. Given my specialty in low-thrust trajectory design and Dawn's status as the greatest low-thrust mission to date, it has undeniably been fantastic for my career. My goals of development of methods to best design missions for and operate electric propulsion/low-thrust spacecraft could not have been better served than by being a part of the Dawn team.
Absolutely. Dawn gave me the opportunity to work with an amazing group of people. We encountered problems, like when the spacecraft lost its second reaction wheel, or when the spacecraft safed on approach to Ceres, but the team worked as a unit to come up with a solution, and in the end the mission was a success. The knowledge and experiences I gained from Dawn have made me better equipped to work on future JPL missions.
Dawn introduced me to the development process of a mission, starting midway through the design and build cycle. I feel a strong sense of ownership for architecting the science observation concepts for this unique orbital mapping mission. My experience working with the science instrument on the ground allowed me to understand them so deeply that now it almost feels like I am there with them. Sometimes I catch myself saying things like, “we are in orbit around Ceres,” which causes people to ask if Dawn is a manned spacecraft.
I’ve learned a tremendous amount from the team of scientists and engineers during the 17 years I’ve been on the project. That has led me to work towards future missions by playing a role in the mission formulation process, especially in the small bodies area, to become principal investigator of the magnetometer instrument on Europa Clipper, to join the Psyche team as a science co-investigator and to lead several competitive mission proposals. But the best part is that I got to join in the thrill of exploring new worlds, and they turned out to be super interesting and important to understanding the early solar system. I used to explore the ocean floor in remote areas of our planet, then I worked in the beautiful, hostile environment of Antarctica. Exploring the asteroid belt and seeing alien landscapes for the first time has been an absolute thrill that rivals anything in my professional life.
For more information on Dawn, visit https://dawn.jpl.nasa.gov/mission/toolkit.