Scientists and curious people all over the planet have dreamt of interplanetary travel. Is this sci-fi trope finally within our grasp? NASA saw great success with its DAWN mission, which explored the giant asteroid Vesta and the dwarf planet Ceres. The DAWN mission successfully hopped from one extraterrestrial destination to another, potentially laying the groundwork for exploring multiple planets in future missions.
Success of DAWN
NASA’s robotic DAWN spacecraft, developed by Northrop Grumman, achieved several major milestones in its 11 years of spaceflight. According to NASA, DAWN was the first spacecraft to:
- Orbit two planetary bodies
- Orbit an object in the main asteroid belt
- Visit a dwarf planet
It collected data and images about Vesta and Ceres, two bodies that scientists barely understood before the mission.
“There was some expectation based on observations done by earth telescopes or Hubble, but we really didn’t know what we would find at either of these places until we got there,” says Joe Makowski, DAWN Operations Program Manager.
The spacecraft launched in 2007 and made the slow but steady trek to the asteroid belt. It orbited Vesta from mid-2011 until 2012, then spent the next three years traveling to Ceres. It studied Ceres from 2015 through 2018, and though the mission has been completed, scientists are still making new discoveries from the 100,000 images that DAWN collected.
By getting a closer look at bodies in the asteroid belt, scientists confirmed that asteroids, protoplanets and dwarf planets are much more than a bunch of giant space rocks. They are diverse astronomical bodies that hold evidence of how the early solar system was organized and evolved. The mission revealed that Vesta’s surface contains a historical record of the many thousands of impacts it has seen since it formed, and that it has trace amounts of water, which was unexpected.
In August 2020, NBC News reported that the latest scientific analysis revealed that Ceres is more geologically active than scientists previously thought. DAWN revealed that it has surface features such as huge salt-domes, muddy ‘ice-volcanos,’ and potentially some liquid saltwater beneath the surface. This reinforced the idea that dwarf planets like Ceres could have previously hosted sub-surface oceans — and possibly still do — according to NASA.
The key to visiting multiple places in the solar system in one mission is having an efficient propulsion system for the spacecraft. While many other spacecraft are powered by chemical propulsion, DAWN used solar electric propulsion — using solar power to drive its ion engines — provided by NASA’s Jet Propulsion Laboratory. Dawn’s solar electric propulsion was about ten times more efficient than chemical propulsion, requiring only a tenth of the propellant to go the same distance.
So, does that mean that ion propulsion is the technical key to interplanetary travel? Perhaps.
Ion propulsion worked especially well for a mission like DAWN that required orbiting two different bodies, because the bodies were close enough to the sun. It could have limitations in other scenarios. “Solar electric propulsion works well until you get somewhere around Jupiter and Saturn,” Makowski explains. He adds, “Those planets are so far from the sun, where solar energy is so limited, that you need another electrical power source.”
Lessons for the Future of Space Travel
Ion propulsion with new power sources may be the silver bullet for interplanetary space travel, with lessons from DAWN providing the foundation for future missions.
“Another big challenge with planetary missions is fault management,” says Makowski. This means making sure that if something goes wrong with the spacecraft’s hardware, the software can detect the problem and make adjustments to correct these failures. This is critical for interplanetary travel where the spacecraft are too far from Earth for constant communication.
As Makowski says, “If you’re supposed to be thrusting and you’re not, and you don’t talk to Earth for five days, the spacecraft won’t be in the place in the sky where you expect it to be.” He explains that over the course of the 11-year mission, the fault management system helped the spacecraft safely recover from any issues that arose. During the handful of issues that happened during the mission, ground crews could adjust trajectories and get DAWN back on track with plenty of propellant to spare, aided by the ion propulsion system’s efficiency.
According to Makowski, the team that designed and built DAWN have already used variants of the electric propulsion and fault management systems for:
- Communication satellites
- A proposed mission to fly to a comet
- The Cygnus cargo spacecraft that resupplies the International Space Station
- The mission extension vehicle (MEV), a new vehicle that flies to orbiting satellites to refuel them.
Space exploration is a time-consuming and expensive endeavor. Each mission builds on the last, allowing us to become more efficient in our exploration. As we learned from Dawn, harnessing lessons from today’s missions, allows us to develop a greater understanding of our place in the history of the solar system.
“An achievement like DAWN just opens us up to a universe of possibilities,” says Makowski. “You can look back and say – we learned something from that project — more than we ever expected.”