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Robotic Spacecraft: Far-Ranging Robots

Taken from Mars Robotics Lesson Background

Robots: Machines On the Move

The first known use of the term "robot" was by Czech playwright Karel Capek, who in 1920 wrote a play called R.U.R.: Rossum's Universal Robots. Capek used the Czech word "robot," which means "worker" or "laborer," to describe the mechanical slaves that were portrayed in his play. The first publicly-displayed robots were "Elektro" and his trusty mechanical dog, "Sparky," who were highlighted at the 1939 World's Fair Exhibition in New York City. Elektro could dance and recite a handful of words, while Sparky would happily bark alongside him. While robots were a mere curiosity in the late 1930's, they are an integral part of our daily lives today. Some robots are simple, like the automatic sprinkler system in many people's lawns. Others are more complex like the factory robots used to assemble cars or the robotic explorers NASA has sent to Mars and the rest of the solar system. Simple or complex, all robots obey the same principles and are designed using the same process.

Robots in the Real World

Unlike in science fiction, robots in the real world rarely resemble human beings. Walking, while learned naturally by every young child, is a surprisingly difficult skill. Robots, with their less-than precise sensors and motors, have a great deal more trouble mastering this task. Fortunately, robots rarely need to walk. Many robots never move from the location where they were installed!

Although research is underway to give robots artificial intelligence and "fuzzy logic" capabilities, most real robots do not have the intelligence displayed by the robots of films. In most cases, a high degree of intelligence isn't a requirement for the task the robot must perform. Once taught the steps needed to carry out the job, the robot can simply perform those steps over and over, relying on its human controllers to step in when a problem arises.

Some robots must operate in hazardous environments or in environments where humans cannot directly interact with them. In these cases, it is necessary for the robot to have much more decision-making power so that it can respond to its environment and to unforeseen circumstances. The classic examples of this case are NASA's robotic explorers to Mars and the rest of the solar system. Sending out a repair person simply isn't an option when the machine is over a 100 million km (~80 million miles) away!

Taken from Mission Possible

Robotic Exploration of the Solar System

Almost everything that we know about the Universe beyond the solar system was discovered through observations made on the Earth or in space near the Earth. However, much of what we know about the solar system has been discovered by robotic spacecraft sent to make close-up observations of the objects in our planetary system. In fact, we have learned more about the solar system in the last 50 years using robotic spacecraft than all the previous ground-based observations.

After the launch of Sputnik 1 satellite in 1957, which ushered in the Space Age, robotic spacecraft (and in the case of the Moon, human space flight) have been used to study various worlds in the solar system, with at least one spacecraft visiting each planet. In addition, robotic spacecraft have visited moons, asteroids and comets. There are spacecraft currently on their way to examine the dwarf planets Ceres and Pluto, and the spacecraft flying by Pluto may also examine at least one of the Kuiper Belt Objects, which are icy worlds beyond the orbit of Neptune discovered in the last few years. Other spacecraft missions are carrying out more detailed observations of the many different worlds in the solar system, and many more are being planned. While spacecraft are often unique in their detailed design, there are three basic types of missions: flyby, orbital or lander missions.

When planning an exploration of another world, scientists need to consider what kind of information they want to gather. They need to formulate the scientific goals of the mission, and then figure out what is the best way to meet the goals within their budget. If the study cannot be conducted with ground-based observations or telescopes located near the Earth in space, they must consider the extra cost of sending a spacecraft to explore the world by flying by, orbiting or landing on the target world. The exploration gets more complex and expensive as you progress from ground-based observations to a flyby, an orbital and a landing spacecraft mission. Most often, the final mission is a compromise between what the scientists want to find out about their target, and what real-world constraints allow.

Flyby Mission
The simplest way to explore a world close-up is to have a spacecraft just fly by the body without going into orbit around it or landing on it. A flyby can get much more detailed information on the object than Earth-based observations. However, the spacecraft can only make useful observations of the world while it is nearby, and depending on the trajectory of the spacecraft, the time for observations may be limited and only a small portion of the object facing the spacecraft as it flies by may be viewable. This means that a flyby mission requires a lot of planning to optimize the way the data is gathered. Usually, the details of the planned observations -- which instrument to use at each moment, where to point the instrument, what kind of data to take, etc. -- are stored in a computer program on the spacecraft before the flyby, and the program begins executing automatically at some distance from the target. The gathered data is then sent back to the Earth for analysis after the flyby is concluded.

The costs of a robotic flyby mission vary depending on the world that is being explored. Typically the costs involve consideration for the following aspects:

  • Designing and building the instruments needed to get the desired science data;
  • The power needed to run the spacecraft and its instruments;
  • Launching the spacecraft;
  • The amount of fuel needed to fly to the world;
  • Communications needed between the Earth and the spacecraft;
  • Human labor for the scientists and engineers working on the mission;
  • The length of the mission.

Orbital Mission
While a flyby mission is the simplest (and the most likely to be successful) spacecraft mission to explore another world, it usually only offers a snapshot of one part of the world. A more complicated mission, but also one that can offer a more comprehensive science investigation, is an orbital mission, in which the spacecraft goes into an orbit around the target world. The main complication in this kind of mission compared with the flyby is the orbit insertion maneuver: firing the spacecraft's engines to change the trajectory so that the gravity of the target world can "capture" the spacecraft into an orbit around the object. An orbital mission can obtain more detailed information than a flyby since it not only will be able to see much more of (if not the entire) world, but it also can spend a longer time making repeated observations of the same area. In addition to the costs described in the context of a flyby mission, the following additional aspects must be considered for a robotic orbital mission:

  • Propellant required for the orbit insertion maneuver and for possible orbit correction maneuvers needed later;
  • Hardware and software engineering necessary to prepare the spacecraft for the orbit insertion maneuver and for orbital operations;
  • Additional instruments that may be desired for a more comprehensive science investigation;
  • More involved communications with ground control on the Earth.

Lander Mission
The landing of a spacecraft, or the landing of a probe launched from a flyby or orbiting spacecraft, to another world entails additional complexity over an orbital mission. In addition to flying to the world, the mission must plan for a safe landing of the probe. In some cases, the probe is designed to just crash on the world and provide as much information as possible before the crash, but in most cases careful planning is required to ensure a soft, safe landing on the target world's surface. Spacecraft can be slowed down during descent by firing the engines at precise moments for a predetermined duration, or by using parachutes if the target world has a substantial atmosphere. The spacecraft may also include cushioning (such as air bags) to prevent a jarring landing on the surface. Often, these options are combined to ensure a safe landing. A lander mission is riskier than a flyby or an orbital mission, since there are more chances for something to go wrong. For example, about half of all lander missions sent to Mars have failed for one reason or another. On the other hand, a lander mission can provide much more detailed information on the world than the other kinds of missions, often making the higher risk acceptable. A lander can examine the world's surface features close-up and use tools to burrow underground, drill into rocks, or take samples for analysis within the spacecraft. While most landers are stationary, some have been designed to move around the surface, providing detailed information over a larger area In addition to the costs of a flyby mission, as well as those of the orbital mission (if the mission includes an orbiting component), a lander mission involves the following additional cost considerations:

  • Fuel to slow down the spacecraft for landing;
  • Engineering and additional hardware for landing (e.g., parachute, cushioning);
  • Software engineering to prepare the spacecraft for landing;
  • Engineering necessary to make communications from the surface back to the Earth reliable;
  • Additional instruments that may be desired for a more comprehensive science investigation.

Communications with Robotic Missions

Communications with spacecraft studying other worlds are done using radio waves, which travel at the speed of light. As a result, the time between sending a signal to the spacecraft and receiving the response varies from a couple of seconds (for missions exploring the Moon) to several hours (for missions investigating the outer reaches of the solar system.) This delay makes it necessary for the spacecraft to be able to execute many commands on their own, without direct input from ground control on the Earth. Therefore, the computer programs operating robotic spacecraft must be designed carefully. For example, before firing the spacecraft's engines to make a course correction maneuver, a signal is sent from the ground control to the spacecraft to have the computer execute a series of commands to complete the necessary operations, but providing additional commands is usually not possible before the maneuver is completed. Communication with spacecraft is done using large radio antennas on Earth, such as NASA's Deep Space Network, which includes three radio antenna facilities located around the world. The time to use the network must be planned in advance. The cost for using these communication facilities can be several million dollars, depending on the frequency of communications and the amount of data transmitted.

From MarsBound! Mission to the Red Planet

The Design Process

Like the scientific process, the design process is not a simple, linear progression from one step to the next, resulting in a finished product. Although there are steps, the design process is an iterative one: designing, modifying, testing, and designing again until a finished product is made. A central tenet of engineering, however, is that there is no such thing as a "perfect" design. Each design solution has constraints, limitiations that are placed on the solution. For example, cost is a common constraint, as is the reliability or the strength of the materials being used. It will almost always turn out, however, that a design that excels in one aspect of the problem to be solved will be poor in another aspect. Making and justifying these trade-offs is a major part of the design process. Keeping in mind that the design process is not as linear as it may appear, here are the steps that are normally identified as being part of the design process:

  1. Clearly identify the problem, identifying all aspects of the issue. It's not enough to identify the problem in broad terms, for example, "There is too much traffic near our school." The specific aspects of the problem need to be identified. For example, is the traffic moving too fast, are there too many cars on the road, or is there simply poor traffic management and routing? Usually it is the "end consumer" who will specify the problem to be solved, so this is a good opportunity to explore the sociological implications of the technology that result from the design as well!
  2. dentify the functional requirements the solution must meet. If, in our previous example, the problem is poor traffic management near the school grounds, your functional requirements might include, "Traffic must enter and exit the school area within one minute," and, "It must be easy to pick up and drop off students." The functional requirements should be written so that if they are satisfied, the problem itself will also be satisfied.
  3. Identify the constraints to the solution. Again using our school traffic example, the possible constraints might be, "All traffic must remain below 15 MPH," or, "Vehicles must not pass closer than 10 m from the school building."
  4. Design a prototype. This is the step that most people think of as "design" or "engineering", but actually this is just one step in the overall process. The prototype could be a simple concept model (perhaps a drawing on a piece of paper for our school traffic example) or a complete working model (temporary lines painted on the pavement near the school). The goal is to develop something that can be tested to see if it satisfies the functional requirements and constraints. Note that the prototype does not have to satisfy all of the functional requirements. It is perfectly acceptable (and common) to test only one aspect of a complex problem at a time.
  5. Evaluate the prototype. In this step, the designer must test and evaluate his or her proposed solution. Note that this is more than simply asking, "Does it work?" In this step the designer must instead ask, "How well does it work?" Graphs and charts are a common way to display the results of this test and evaluation process. Continuing with our example, the designers in this case might collect data on how many cars pass near the school, how fast they travel, or how long it takes to load and unload passengers.
  6. Revise and retest as needed. Based on the data collected in the previous step, the designer can see where the proposed design can be improved or what new trade-offs will have to be made. The engineer then goes back to step four (and sometimes back to step one!) and repeats the process until the design satisfies, as near as possible, all of the functional requirements and constraints.
  7. Present the final product. Once the design is finished, it must be demonstrated to the "end consumer" who identified the problem in the first place. Ultimately, it is the consumer, the user of the technological solution, who decides if the problem has really been solved. If the consumer is not satisfied, usually the problem has not been well-specified or the consumer may not understand the constraints that must be placed on the solution.

For further information about NASA robots, go to

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Last Updated: 12 Sep 2014