From as close as Earth to beyond the reaches of our Sun’s influence, NASA’s missions have deepened our understanding of the cosmos and our place in it, capturing the imagination of people everywhere. The Dawn spacecraft, by exploring the planet-like worlds Vesta and Ceres in the main asteroid belt, has shed light on the beginnings of our solar system, some 4.6 billion years ago. How does a mission like Dawn grow from an idea to a spacecraft exploring distant worlds? In celebration of Dawn’s journey, we look at how a mission evolves from an idea into a reality.
Pre-phase A: Concept Development and Proposal
Every mission begins with a question. Sometimes these questions develop over many years, creating a community among those with a shared interest in the topic. In Dawn’s case, this topic was the evolutionary paths of Vesta and Ceres, the two largest bodies in the asteroid belt.
Before NASA puts out a call for a certain type of mission within a designated budget, scientists and engineers with shared interests assemble a team of collaborators who help develop their concept. Dawn’s team is international, with partners across the United States and in Germany and Italy. Each NASA center—in Dawn’s case, the Jet Propulsion Laboratory—selects a few concepts of high scientific merit to be presented as proposals to NASA.
During the proposal stage, the project team works almost around the clock to get their proposal into shape to win NASA’s support. The proposal undergoes rigorous review and several rounds of edits. The team works hard during this period to ensure that their proposal, while still ambitious, involves minimal risk and is within budget – two critical factors for selection. Dawn’s ambitious plan to orbit both Vesta and Ceres would be NASA’s first science-only mission to be enabled by ultra-efficient ion propulsion technology, which was previously demonstrated by the Deep Space 1 mission. And, Dawn fit within the budget of the Discovery Program.
Phase A: Concept and Technology Development
After competing against proposals from other institutions, Dawn was selected as one of NASA’s Discovery missions in late 2001, allowing it to move onto the concept and technology development phase. Here, a project’s concept is fine-tuned, and a preliminary project plan is developed. Once these are clarified, the mission proceeds to the design phase.
Phase B: Design and Technology Completion
Though a rough design is included in the proposal, it is finalized and made more precise during this phase. Early concepts for Dawn, for example, included four panels per solar array wing (compared to the five included in the final design). The team also repositioned some hardware and changed the type of antenna. Many of the changes made during this period were very technical. Each detail -- down to the number of heaters aboard the spacecraft -- was meticulously planned to ensure there were no problems down the road.
Phase C: Final Design and Fabrication
Next, the design from Phase B is submitted for reviews. Before the spacecraft is built, it’s important that the reviews catch anything that could interfere with the spacecraft’s ability to complete its mission. Once the design has passed these reviews, the spacecraft’s parts are ready to be fabricated. For Dawn, some parts were sourced from institutions both in the United States and abroad, while others were made at JPL. Dawn’s framing camera, gamma ray and neutron detector (GRaND), and visible and infrared mapping spectrometer (VIR) were from the Max Planck Institute in Germany, Los Alamos National Laboratory in New Mexico, and the Italian Space Agency, respectively.
Phase D: Assembly, Testing, and Launch
During Phase D, the spacecraft is built. Though the spacecraft should be able to withstand the harsh conditions wherever it goes, it’s crucial that the assembly process is handled carefully to ensure that the design is executed to the letter.
After each of the spacecraft’s parts have been made and tested, they are ready for assembly. The spacecraft is assembled in a climate-controlled clean room, a white, hangar-like space with filtered climate-controlled air that is designed to minimize the number of small Earthly particles, like human skin cells, that might hitch a ride. Technicians in white jumpsuits, surgical masks, and slippers carefully assemble the parts into the spacecraft. A quality assurance inspector supervises as the technicians test isolated functions, like those of a reaction wheel, for example. Dawn was assembled in Virginia by Orbital ATK.
Once the spacecraft is assembled, it undergoes a period of environmental readiness testing. Here, the spacecraft is tested under various stressors like heat, shaking, and electromagnetic fields, which mimic conditions during launch or in space. The operations team also prepares by testing their responses to simulated scenarios.
Once the spacecraft has passed all of its tests, it’s ready for launch. Dawn launched on Sept. 27, 2007, from Cape Canaveral, Florida. Though almost everything was automated in the countdown to liftoff, a large group of project team members watched attentively as final checks to the systems of the spacecraft and rocket were made. In the minutes before liftoff, the mission management team and launch director gave the final go-aheads, and the launch proceeded to its automated sequencing. There were cheers as the rocket lifted off, but the team still had to make sure that the rocket’s precious payload, the spacecraft itself, was deposited safely into space. Once the spacecraft had been released, the flight operations team ran preliminary tests to check its vitals.
At this point, or shortly after, many of the team’s hardware engineers, those who designed the spacecraft, may leave the mission and move on to other projects. The work for the flight operations team and scientists, however, is just beginning.
Phase E: Operations and Sustainment
Though years of dedication and hard work have gone into the mission thus far, Phase E is what we normally associate with a mission, since it is at this point that a spacecraft collects data. All missions send back telemetry (data about the critical operations of the spacecraft) after launch, but some have a longer wait before they can send back science data. Near-Earth missions may begin recording and sending down science data within just a few months, while others, like Dawn, may spend years flying to their target before being able to observe it. (In fact, Dawn orbited two bodies, meaning that it went through a similar process of approach and observation twice!)
During this phase, the flight operations team monitors the spacecraft and prepares for its arrival at its destination. If anything unexpected happens, the spacecraft has “safe modes” that it enters until systems operators on the ground can assess the trouble. As Dawn has experienced, safe modes can sometimes be triggered by relatively mundane interferences (like a cosmic ray strike to its electronics, for example).
The sequencing team writes code to direct the spacecraft’s observations. Sometimes the observation plans change to better explore a particular feature on the target or collect a certain type of data. For example, in order to take a better look at Ceres’ surface features, whose signs of recent geological activity may give clues to the planet’s formation, the team brought Dawn into an even lower orbit. As the spacecraft sends new data back to Earth, scientists at institutions around the globe analyze the data and share their findings in scientific journals.
This period of navigation, systems operation and data collection often lasts for several years. After meeting initial science requirements during the primary mission phase, many missions receive extensions, enabling them to continue to collect valuable data with their still-healthy spacecraft. Dawn, which accomplished its science goals in mid-2016, received two mission extensions.
Nevertheless, all missions end. In Dawn’s case, the mission will end when the spacecraft runs out of hydrazine fuel and can no longer orient its solar panels toward the Sun and point its antennas to Earth. NASA observes strict international planetary protection guidelines, which are required to prevent the contamination of specific planetary bodies by any surviving microbes aboard the spacecraft. When Dawn ends it will remain in orbit around Ceres, since Ceres’ mysteries, including its recent geological activity and the presence of both water and organics, may warrant future exploration.
Phase F: Closeout
There are few people who see a mission from its proposal phase all the way to the end. Many of the engineers involved in the design and building process leave to move on to other projects before the mission even moves into its operations phase, while some of the flight operations team members may join after launch. Though a mission can be an environment of intense focus and camaraderie, the people of a mission change just like the mission itself. Toward the end of the mission, many have already begun dividing their time among several projects. Some have even moved offices, joining the new missions that will become their homes for the next few years. When the mission ends, most of the team may be around for several weeks after, attending to administrative tasks such as writing operations reports. And for several months, a few remaining team members will continue to archive data and review project materials. Though a spacecraft’s life may end, each leaves behind a legacy of scientific and engineering insight. Dawn’s technology and data will continue to contribute to our understanding of the two bodies it explored and the history of our solar system for years to come.