Design the Deep Impact Mission

You have been asked to look at the science objectives for the Deep Impact mission and to design the spacecraft necessary to meet those objectives. The science objectives are to travel to a comet nucleus and make a deep crater in it. You are trying to determine the structure and composition of a comet nucleus and to find for the first time what lies beneath its surface:

1. Observe how the crater forms
2. Measure the crater's depth and diameter
3. Measure the composition of the interior of the crater and its ejecta
4. Determine the changes in natural outgassing produced by the impact

Here are things for you to consider:

1. You will have only one opportunity to make this crater
2. The comet chosen is close enough to Earth to be observed from there as well during impact.
3. The comet is moving fast and you will be considered a flyby mission. You will not have the budget or resources to land on or fly with the comet.
4. Your goals are to make a crater but also to be able to see the results in space.
5. It will take you time to get there and you must plan for a way to power the spacecraft.
6. You must have communication among everything in space and the team on Earth.

Answer:

Carl Buck, Flight Systems Engineer, summarizes things you must consider when designing a mission.

A spacecraft is the culmination of a few very general, and many very detailed requirements. These range from "it has to go to a comet" to "it has to take pictures of the comet nucleus at 3.5 meters resolution." A spacecraft designed to impact and image a comet has different requirements than one that will softly land a rover on the surface of Mars. For example, the requirements for a fast and agile sports car would be much different than those for an SUV for off-road use. These very general requirements outlining the use of the vehicle would result in a lot of other requirements dictating everything from its size and style, to the stiffness of the suspension and type of tires to use.

So, in the case of Deep Impact, we were required to design two spacecrafts with very different requirements to travel as one vehicle. We had to design the impactor to track the comet nucleus for the last twenty-four hours prior to impact. This resulted in the requirements for a spacecraft with a small camera, a propulsion system, a small battery to last one day, and a computer to control all of it. The flyby spacecraft, on the other hand, has to operate for the six months it takes to get from the Earth to the comet, drop off the impactor into the path of the approaching comet nucleus, and then take pictures from far away of the impactor hitting the comet. The long trip means the flyby spacecraft has to have solar arrays to keep charging the battery, and it has to have a really big telescope to see the comet and crater from a distance (in our case a high and a medium resolution camera). The flyby also has to hold onto the impactor while they are both launched on a single rocket, and then be able to let go of it when the time comes to let it hit the comet.

So, we took what started with a few general requirements from the scientists about what they wanted to know about comets, and these turned into thousands of requirements for all the components that make up the two spacecrafts. When we were done designing these vehicles, assembling them, and testing them to prove we meet all these requirements, we had what you now see built today.

So, let's see where we stand now. How many of the following requirements did you find as you thought about the Deep Impact mission to Tempel 1?

Requirements for Deep Impact:

1. A spacecraft (the flyby spacecraft) that is able to carry the impacting spacecraft, release it at the proper time, move away to a safe distance and watch what happens on impact.
2. There must be observing instruments (the high and the medium resolution instruments) on the flyby spacecraft so that it can record images.
3. The imaging instruments will help us see the structure but if we want to know the composition, we need an instrument that can read the chemical elements of a comet (in our case - a spectrometer).
4. The flyby spacecraft has to travel for 6 months and can't carry enough propulsion to space so it will need a source to gather power and a place to store it (in our case - a solar panel and a battery).
5. The flyby will need to be able to return its data and that of the impacting spacecraft so there will need to be a resource for that (our antenna).
6. The impactor spacecraft will need an imaging instrument which it will use to aim and also to send data back to the flyby spacecraft.
7. The impactor will need to have enough mass to be smaller in size but make a large crater (our impactor is 370kg/820lbs and mostly copper).

There are many other factors that exist that become requirements for the design of a mission but the lists above are a good start. If you want to read more about the spacecraft and their instruments, click here.

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