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50 Years of Robotic Planetary Exploration: Robert Mitchell (Cassini Program Manager at the Jet Propulsion Laboratory)
19 Dec 2011
(Source: )

What do you think are the most significant events that have occurred in the past fifty years of robotic planetary exploration? Why?

The Viking landers and orbiters would have to be high on my list for this because they were a first, and they were completely successful on the first attempt at landing on another planet. They also represented a very complex and difficult undertaking.

Another event that is high on my list for this is the Huygens entry and descent at Titan. This was also a very complex undertaking with many firsts and many involved systems that all had to work properly. It also represented a major advance in our understanding of a heretofore mysterious and not understood planetary body. Prior to the Huygens mission, Titan probably represented the body in our solar system with the most intrigue.

In your field of work, what are some examples of the great achievements and discoveries in planetary science and robotic exploration throughout the past 50 years?

The technology used to design and implement very complex trajectories using the gravitational effects of multiple bodies to achieve results that would not have been possible by any other means. Examples of this include the trajectories used by Voyager to visit all four of the gas giants by one spacecraft, the MESSENGER trajectory that was used to get a spacecraft in orbit at Mercury, the Galileo trajectory to Jupiter, the Cassini trajectory to Saturn, and the Cassini trajectory used in orbit at Saturn to visit multiple moons using relatively insignificant amounts of chemical propulsion.

The interplanetary and orbital navigation capabilities that give us the ability to safely navigate a spacecraft past the moons of Saturn at distances as low as 25 km above the surface with accuracies at the sub-kilometer level, and at distances of 1.5 billion km from Earth is a great achievement for robotic exploration.

Also, the ability to communicate with and control spacecraft >100 AU from Earth in the case of Voyager, at 10 AU from Earth in the case of Cassini, and the ability to transmit data and receive it on Earth at data rates >100 kbps are great achievements.

Is there a picture that illustrates your significant/favorite event(s)?

I was the lead of the Trajectory and Maneuver team for the Viking mission to Mars in the mid-seventies. This was the first time that NASA had attempted to land a spacecraft on another planet and it seemed to me to be a very risky endeavor. Of course, NASA had completed the Surveyor and Apollo programs on the Moon prior to this, but Mars just seemed different with its greater gravity, its atmosphere and its poorly characterized surface, at least to the resolution that mattered to a vehicle landing and staying right side up. The first Viking lander had been programmed to take an image of one of its own landing pads immediately upon touchdown, and a group of us were standing around a monitor waiting for that image to come down. The image finally began to appear on the screen, slowly and line by line in real-time as each line exposure was taken. First a grayish blur, and then a very clear beginning of the edge of the landing pad sitting on the soil, later building to show the whole pad and leg sitting on Mars. By today's standards, this is pretty routine stuff, but at the time it represented a very major accomplishment and something that had to have had a high likelihood of not working. This is more significant to me than it would be to most because I was heavily involved in making it work. That's probably the single moment in my career that I will remember the longest.

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