Stone: Well, Voyager One is in interstellar space today. The date that we're using as the time when it left the solar bubble was August 25, 2012. Voyager 2 is coming along behind; and we don't know exactly when [it will enter interstellar space] because it's going through a somewhat different location from what Voyager 1 did. So it may be several more years, it really could be sooner, or it could be later. We had hopes, of course that we would reach interstellar space, but none of us knew how big the bubble is or was and none of us knew that the spacecraft could survive for so many decades that it took to get there. But we had hoped and we had planned for this day.
Samzenpus: How would you structure the space program now to support long-term goals of interstellar flights like this? Do you think this is as important as studying things closer to home?
Stone: Well, I think there are clearly a number of important frontiers still to be explored in the solar system. The ones, which are easiest to talk about, are those which involve liquid water because here on Earth wherever there is liquid water, there is microbial life. We know that there's liquid water underneath the icy crust of Europa. We know there is liquid water under the icy crust of Enceladus, a moon of Saturn. We know that the atmosphere of Titan doesn't have liquid water but it has a chemical constituency similar to what was here on Earth before life evolved. So there are really key places in the solar system. Mars, we know, had water at one time. The only question is there still water somewhere on the planet or how deep is it? And is there any evidence of past life? if we could find the liquid water then we would want to know is there any evidence of extant life.
Samzenpus: Speaking of Europa, there's been all sorts of numbers thrown about with the proposed Europa mission. Do you think that mission will actually happen in my lifetime?
Stone: I certainly hope that there will be another mission to Europa which can fly by perhaps a number of times rather than going into orbit, which is flying by and then zipping out to get out of the radiation environment and then dive back in so that one can look at Europa. As you know, the Hubble space telescope has shown evidence that there are actually plumes in the South Polar Region of Europa, which is not really a surprise. It's just that they had never been seen before.
If Dawn finds Ceres as water rich as we expect, do you think that will kick off an asteroid mining gold rush?
Stone: Yeah, I don't know that, but I think the mining aspects are probably longer off. What I think it will do is further increase interest and understanding of these bodies, which are out there. And obviously, in the long run, protecting the Earth from them. So I think that there is still a lot that still can be done about asteroids. We're just beginning to explore them.
Samzenpus: Do you think we'll see a Uranus or Neptune orbiter?
Stone: Well, I hope so, but that's certainly not in the next couple of decades because we know there's Mars and then there's Europa. Titan is a very, as I say, a very important opportunity, and Enceladus is something people are talking about. I think they will tend to take priority if one can develop a mission that looks feasible.
During each era of space exploration, going back to the mid-1970's, a manned mission to Mars has been "just 20 years away". At many points over the past 40 years, a variety of factors have converged ensure that a manned Mars mission remained just over the horizon. Even this past month, in NASA Chief Bolden's recent statements, Mars continues to be "just 20 years away", citing a need to stop at an Asteroid on the path to Mars", and budget constraints as reasons that a manned Mars mission remains an unrealized dream. Given Dr. Robert Zubrin's Mars Direct reference mission, and his more recent "transorbital railroad" concept combined with private industry, a manned Mars mission appears to be technically & economically viable — at least more so than at any point in the past 40 years. What's your assessment of Dr. Zubrin's Mars "ecosystem", as it pertains to a manned Mars mission during this 20-year time horizon?
Stone: Well, Mars, I think, is actually is being explored. It's a whole planet. You know, there's as much solid surface area on Mars as there is on Earth. And you can't imagine landing one place on the Earth and claiming to understand Earth as a planet. Once you leave Earth's orbit, it's whole different engineering problem and life is a different problem [out there] than it is in Earth orbit. The moon is in Earth orbit. When you're in Earth orbit, you can get help and you can get home. When you're in the solar orbit, you can't get any help and you can't get home. So, it's a much more challenging activity. And that's the reason it's going to take some time before that's realized. But it's taking the steps to learn how to do it that is important.
Role of human spaceflight
As a national leader in robotic exploration of the solar system, what do you think is the role of human spaceflight in the future? Should NASA be developing a human mission to the Moon, Mars, Europa, and beyond? How should the NASA balance the needs of good science and cost/safety issues versus the romance of human exploration?
Stone: Well, I think the two programs really drive themselves and of course, they drive each other. I think the robotic program clearly has momentum and partly, that's because in the case of Mars, it's there as a precursor to future human space flight. But, it's obviously not an immediate issue. Human space flight is still some decades off before there is a Mars mission. And exactly what the nature of leaving Earth orbit is, is something which will evolve as we learn more about the challenges of building systems to operate for long durations in space and support life, and also the effects of space on humans. I mean, there are really five frontiers of space. There is the physical frontier that's going somewhere, sending something somewhere where nothing has been before. There's the knowledge frontier that's understanding what's out there. There is the technology frontier that is developing the systems you need to do things in space. There's the applications frontier that is using space to better life here on Earth. And then there's the human frontier, which is effective and efficient functioning of humans in the space environment. And that's another huge frontier, which we are just really still beginning to explore. I think there is more we need to learn. We are learning things and there is more that we need to learn in terms of the engineering aspects, that is the technology frontier. It's challenging to leave Earth orbit.
Samzenpus: In your time at JPL, what would you say was the program you're most proud of?
Stone: I think the thing during the 90's was launching Cassini, another large flagship mission, which is doing a great job of exploring Saturn, Saturn's rings, and Titan. But at the same time, we developed the program, which allowed us to get back to Mars every two years rather than every 20 years. And that really has opened up not only Mars, but it's opened up asteroid missions and other missions, which can be done on a smaller scale and done more often.
Samzenpus: What project turned out to be the most difficult for you?
Stone: From a project point of view?
Stone: Well, it's clear that Voyager has been the most important project and also in many ways, the most challenging because it was the first automated spacecraft that could fly itself and integrate the whole set of instruments we had. It was a challenge to do that in five years. Fortunately, I was just part of a big team that did it and we've been lucky to have both spacecrafts still operational almost 37 years since launch now.
Samzenpus: What do you see as the most promising tech on the horizon and how do you prioritize which breakthroughs are the most promising?
Stone: These frontiers I mentioned are immense. There's not just one thing in each of those frontiers. There are many things. The challenge we have is deciding which ones to do because we can't do everything. We can't even do a little bit of everything. We can just do some things. And the challenge is designing a set of things to do, which step by step we learn how we expand those frontiers and we learn how to do things in space. There are decadal surveys done by the scientific community, which are informed by the state of technology development or the possibility of technology development. They develop a set of recommendations for what to do in planetary science, what to do in astronomy, what to do in Earth sciences, and what to do in heliospheric sciences. Those are four decadal surveys that the community does every 10 years to try to update for the new technology, update for the new knowledge and lay out a plan for the coming decade. And that's the way it's done in the science area.
If you could choose one robotic exploration mission that is not currently in the works, what would it be and why?
Stone: Well, there are many missions, which NASA's trying to do but in the Planetary program, I think the next major mission will be a rover on Mars which will start caching, that is collecting samples and securing them for eventual return. Because ultimately, one does want to return samples from Mars to be able to apply the full technology of Earth-based laboratories to analyzing them.
Samzenpus: Lastly, there's been a lot of political issues with the international space station recently. Do you think we should plan to have our own space station eventually or do you think the politics will work themselves out?
Stone: Well, I'm not really that close to it, but I think we already have a space station; it's a major investment that the world has made. The human frontier really is an important frontier as I have mentioned, and the space station can do a lot with helping understand the effects of space on the human system, if there are any sorts of protocols, which can compensate or counteract those effects. Obviously, there are certain fundamental physics things that can be done in space that you can't easily do when you're on the surface of the Earth. There may well be some observations, which can benefit from being on the station having to do with Astronomy for instance, or high-energy particles.