Getting the Job Done: What's Mission Design All About?

"The heights by great men reached and kept
were not attained by sudden flight,
But they, while their companions slept,
were toiling upward in the night."

Henry Wadsworth Longfellow

Congratulations, you have been asked to design a mission to Saturn! Sounds like a pretty imposing task, though, huh? As is the case with any complicated problem, it is best to break things down into smaller simpler problems, and figure out what your end goals are first. Well, with a mission to Saturn, your objective is to return information about the Saturnian system; its rings, moons, magnetosphere, and last but not least, the planet itself. You want to do better than observing from the Earth or from the Hubble space telescope, so you decide to send a robotic spacecraft to Saturn. Since you wish to observe Saturn for an extended period, you decide to plan a mission where the spacecraft is captured in orbit about Saturn. This provides the opportunity for an on-site observatory to map the vast realm for many years.

Who's involved?

There are many groups of people that contribute to a planetary mission. Let's start with the Cassini scientists. There are 27 science investigations in all, each of which has an investigation representative and a Principal Investigator (kind of like a detective, as the name suggests, looking into their own case) who's usually a professor at a university.

flags These "PIs", combined with their colleagues, graduate students and research assistants are scattered around the United States, France, England, Germany, Italy, Austria, Hungary, Spain, Scandanavia, the Czech republic and the Netherlands. Many of them are involved with the European Space Agency.

They are all competing for the same resources (like space, power, mass and observation time). And we're not talking about a dozen or so scientists who will be content with "good enough." There are over two hundred world-class researchers who have spent years thinking about Saturn and whose future careers may depend on how well we do our job.

Did you know...? Including the industrial teams and the scientists at universities and research institutions there are 4,300 people currently involved in designing the Cassini mission.

Their questions about Saturn require that Cassini make very specific observations under just the right conditions. To plan these observations requires a vast amount of knowledge about Saturn, its satellites, and the spacecraft. For example, just where is the spacecraft, and in what direction must it be pointing to see the objects of interest? Will the objects fit within the camera or instrument field of view, or do we have to "back up a few paces" to get a good shot? How many other scientists want to collect information at the same time, on a totally different set of objects?

And then there's the spacecraft engineers, who actually have to build and test the real Cassini spacecraft, not the idealized super technology star trek spaceships most of us dream about. If we promise the universe to the scientists without thinking about what our current technology can realistically do, then everybody's in trouble.

The engineers have to deal with contractors, draw up blueprints, test sample components, and in general need a clear picture of what is expected of the spacecraft. Constructing a spacecraft that works demands a vast amount of knowldege about issues like how materials react in space, how heat, electric and magnetic fields affect spacecraft components, and whether the structure can support its own weight. Can the spacecraft hold itself steady enough to get clear pictures? Is there enough power to turn the instrument on? How does it know where the Sun is and not to point a sensitive camera at it? Can it find the Earth when it needs to communciate with us?

Most of the work at JPL (and that discussed here) involves designing the Cassini mission after it has launched, but there's an enormous amount of work that has to be done to ensure that the launch is a successful one. Civil servants at NASA's Lewis Research Center and launch vehicle engineers at the Lockheed-Martin corporation perform nearly all the analysis that is required to get the spacecraft launched succesfully.

compass And don't forget we have to navigate accurately to get a real spacecraft to Saturn. We'd like to get there in an hour or two, but unfortunately Saturn is about ten times as far from the Sun as the Earth is, so we can't just take a short jog through space to get there. It takes 7 years to get there, and there are a lot of things we have to do on the way to point us in the right direction (not to mention keep the spacecraft healthy on its journey).

To plan for this, navigators have to equip themselves with some pretty fancy computer programs that solve the positions of multiple bodies in the Solar System, and predict exactly where one of them is going to be lined up for us to use a "gravity assist." And the mission designers and navigators have to, for example, tell the scientists when their instrument can observe an object or describe to an engineer how long an engine has to fire to get us in orbit around Saturn.

These are just a few of the questions mission designers have to think about for a mission like Cassini to work. They have to cover all the bases and make sure everyone is on the same track together.

The mission designers are often caught in the middle of scientists who need twice as much performance yesterday, and engineers who've reached their limits of their budget or can't improve their designs fast enough to meet their schedule. It's here where the mission designers are at their best, often finding creative and unexpected solutions by looking at both sides of the picture. (Image only available electronically)

When it all comes together

In a nutshell, mission designers have to do four different things, and do them very well, for a mission to work: learn, in detail, the needs of the science community and the capabilities of the engineers and navigators; perform trade studies, often requiring radically different tools used in concert, to find problems and solutions; develop guidelines and scenarios for how things should be done; and communicate effectively the plans and procedures for the mission. You need a willingness to learn, good people, skills, a firm technical background, and a lot of persistence.

When everyone is informed about the plans for Cassini; when a scientist learns to use a template to plan many similar observations that makes operations easier; when an engineer stays late because real people need that extra five per cent of performance -- that's when the mission designers have done their job.

Prof. Manuel Grande
Last updated: 1 July 2004