Thomas Müller, an astronomer from the Max Planck Institute for Extraterrestrial Physics said in a press release about the water vapor finding: “Ceres could be the key to our understanding of the distribution of ice and water in the solar system. At the same time, this asteroid becomes one of the potential candidates for extraterrestrial life, along with Jupiter's moon Europa and Saturn's moon Enceladus.” What are your thoughts on that?
Dawn doesn’t have the instrumentation needed to search for life, and I think the likelihood that there’s life on Ceres is very, very, very low. What I think is more important about his comment, which I would have agreed with very strongly, is that this can tell us something about the conditions that may have led to the development of life. Whether there’s life at Ceres or not, Dawn is never going to tell us, but it will tell us about an environment in which there’s water. Perhaps there’s a source of energy. There may be other chemistry there that pertains to the chemistry that led to the development of life on earth. Dawn’s contribution to this question is not going to be about the existence of life there, but rather about the opportunities for life to form and the diversity of potential habitats in the cosmos. It’s one piece of human kind’s search for life, and that’s very exciting.
NASA’s Deep Space 1 mission successfully tested an ion propulsion system around 1999, but Dawn was the first to utilize ion propulsion throughout its mission. How is it going?
Within the [low-cost mission] Discovery Program, without ion propulsion, a mission to go to Vesta and Ceres would’ve been truly impossible without ion propulsion. Ion propulsion has 10 times the efficiency of conventional chemical propulsion. For the same amount of propellant, we can undertake much, much more ambitious missions. Dawn is actually the only spacecraft that has been planned to orbit two solar system destinations, which I think is pretty remarkable. That’s an illustration of the power of the ion propulsion. It’s like a true interplanetary spaceship… That really gives us the opportunity to learn so much more, and, of course, it’s an obvious kind of mission to undertake. Right? The idea’s been in science fiction for a long time. Go to some planet, do whatever you’re going to do there, beat somebody up and make out with them and then go to some other planet. That’s something quite remarkable, and that is part of what Flight Team is being recognized for with this great honor from the National Air and Space Museum.
What are the disadvantages of ion propulsion?
The thrust from the ion engine is very gentle. It has about 10,000 times less thrust than some planetary spacecraft. An analogy I like to give is that if you hold a single sheet of paper in your hand, the piece of paper pushes on your hand as hard as the ion engine pushes on the spacecraft. In the zero gravity, frictionless environment of space flight, gradually the effect of this thrust can build up. It would take Dawn, at maximum thrust, four days to accelerate from 0 to 60 mph, which doesn’t exactly evoke the concept of a hot rod, but because we use the propellant so parsimoniously, so efficiently, instead of thrusting for four days, we can thrust for three years. It’s what I like to call “acceleration with patience,” and if you’re a patient person - and I am; I’m a very patient guy - it’s a great way to explore the solar system. Dawn has already changed its own velocity by far, far in excess of what any other spacecraft has ever accomplished. It does take time. There are many ambitious, exciting missions that really can’t be undertaken without the tremendous capability that ion propulsion provides.
What has been your favorite moment of the Dawn mission so far?
One of the first that comes to mind is in July 2011. Twenty-five hours after Dawn got into orbit around Vesta, we established radio contact with it and determined that, indeed, it was in orbit, right on schedule, and everything worked exactly the way it was supposed to. That was a wonderful moment because for the first time humankind had a spacecraft in orbit around a main belt asteroid, and it went into orbit in a way very different from the way other spacecraft go into orbit—it’s an entirely different way of flying. Because the thrust is so gentle, it only executes smooth, gentle, gradual changes in its orbit. It spent all of the years between Earth and Vesta gradually reshaping its orbit around the sun, so that by the time it got up near Vesta, it was already in practically the same orbit around the sun that Vesta was. It just needed a gentle nudge to allow Vesta’s gravity to take hold of it. The way spacecraft normally get into orbit is they execute this big, difficult, whiplash-inducing burn to get into orbit, and yet Dawn did it with such delicacy. Realizing that that had all worked, just the way it was supposed to, to me, it was very gratifying, very exciting.
Once we started returning pictures of Vesta that were better than those from the Hubble Space Telescope, which occurred that same summer, that also was very exciting. It’s not so much being the first see it. Rather, it’s the sharing in humankind seeing them. What’s most exciting about a mission like this is that it really is a human undertaking. Everyone who’s ever gazed in wonder at the night sky is part of this. Everyone who’s curious about nature and about the reality of the universe, everyone who thirsts for knowledge and insight into the cosmos, everyone who just feels this burning passion for bold adventures and raising the human spirit, everyone who feels allure of the unknown, everyone who hungers for the rewards of aiming beyond the horizon, is part of it, and the sharing of Earth being introduced to an alien world is something I think everyone can participate in, and that, to me, is what’s most exciting about it.
You’ve been writing a journal that’s posted on the mission website since 2006, before Dawn launched, and you begin each entry with a different Dawn-related salutation. Do you have a favorite one? Have you ever repeated any?