System Engineering a Robot. (the Space Place)
Diane Fisher · 2003
During the next decade, NASA may join with space agencies in other countries to do a very difficult Mars mission. No, we won't be ready to send people there yet. That's still quite a ways off. But we may be ready to collect Mars soil and rock samples and return them to Earth. Although no definite mission design has been selected, the mission may involve a two-part lander (since one part has to blast off from the surface carrying the samples), a rover to collect the samples on the surface, and an orbiter that can retrieve the sample canister that has been put into orbit around Mars and bring the samples back to Earth. For many reasons, returning Mars samples to Earth is still a very hard problem. Just consider for a moment the problem of the Earth-bound spacecraft in orbit around Mars. It has to find and catch the sample canister after it has blasted off the surface into Mars orbit. Mission controllers back on Earth will certainly be of no help. Mars will be so far away that a command signal would take several minutes to travel from Earth to the spacecraft. No, the sample return spacecraft will be on its own. What is needed is an autonomous rendezvous technology. This technology would enable the spacecraft to size up the situation, decide to do, and carry out its task with no help or communication with humans. NASA's New Millennium Program identifies new technologies that will be needed for future NASA missions and then tests them in space to make sure they will work. The New Millenniums Space Technology 6 mission hopes to test an Rendezvous system in Earth orbit. The rendezvous system would fly in 2004 as part of the payload onboard an Air Force satellite. The rendezvous system would include a laser radar sensor (called LIDAR) that would act as the eyes to find and detect the distance to a target spacecraft (which would be one that is no longer operating). Using the information from the LIDAR, the software would then calculate the steps necessary to reach the target and give instructions to the thrusters on the spacecraft to change its attitude (orientation in space) and velocity so that the spacecraft would move toward the target. The LIDAR would continue to give feedback to the computer, and the software would continuously check and update its calculations and instructions to the spacecraft to close in on the target. It Starts with Careful Thinking Engineers who design spacecraft systems think carefully about the problem they are trying to solve, capabilities the system must have, and how they can use all the new technologies, tools, techniques, and tricks they can think of to come up with the simplest, most effective, and foolproof design possible. The autonomous rendezvous problem is particularly difficult because there are two objects, both moving in three dimensions and oriented in different directions in space, possibly not only orbiting at different altitudes, but also in different orbital planes. No-hands Parking Let's try thinking about a much simpler problem. Let's suppose we want to design an Autonomous Parallel Parking System to help drivers park their cars in tight spaces between other cars along the street. This system would be an option (although probably not a cheap one!) that a car buyer could purchase with a new car. First, if you haven't taken driving lessons yet, see the illustrations in the next column for a short lesson on how to parallel park. Now, on the next page is an example of a proposal for an Autonomous Parallel Parking System. You may find, as we did, that the longer you think about a problem such as this, the more complex it becomes. You can keep adding what ifs and ways to deal with them. What if a car suddenly comes speeding up from behind just as the car starts backing up? What if a pedestrian steps off the curb behind the car? What if a sensor on the car detects a bird flying by and the computer thinks the car is about to hit something? …