## Challenge Details

Welcome to the ISS Longeron Challenge! This is an exciting new challenge that will really test your problem-solving skills. Not only will you be participating in solving a problem for NASA and the International Space Station, you also will be competing for a total prize purse of \$30,000 and NASA stickers that actually flew in space! Along with cash prizes and NASA stickers, we are also offering these limited-edition ISS Longeron Challenge t-shirts.

We wanted to give you a sneak preview of the goals and requirements, so please read below for more details. If you’re ready to compete, visit:

The goal of the challenge is to position the solar collectors on the International Space Station to generate as much power as possible during the most difficult orbital positions. The solar collectors are arranged in two groups of four Solar Array Wings (SAW). Each group is rotated by a joint called a Solar Alpha Rotary Joint (SARJ). Within each group, each of the four SAWs is rotated by a joint called a Beta Gimbal Assembly (BGA). It is your job to specify the angular position and velocity of these ten joints at each minute of the 92 minute orbit. In addition, you are allowed to adjust the orientation of the entire station by a small amount (which stays constant for the entire orbit).

For each test case you will be given the orbital parameter called the Beta Angle. You can calculate the apparent position and motion of the sun (with respect to the ISS) using the Beta Angle. The Beta Angle for each test case will be known throughout the contest, so off-line pre-calculation of answers is possible.

The amount of power generated by each SAW depends on its orientation with respect to the sun and on any shadows on the solar collectors. Code to calculate the power generated at a specific orientation will be provided for the use by contestants in the off-line tester/visualizer.

In addition to maximizing the total power output there are some constraints on the possible movements:

• Each SARJ and BGA is limited to a maximum angular velocity and to a maximum angular acceleration.
• Each SAW must produce at least some minimum average power over the orbit (which is different for each SAW).
• The sequence of positions must be cyclic, so it can be repeated on the next orbit.
• The maximum amount of BGA rotation is not limited, but exceeding a threshold will result in a score penalty.
• Some structural members of the SAW mast (called Longerons) have restrictions on how they can be shadowed.

Longerons are the four long components of the SAW’s mast. If a longeron is shadowed for a period of time it will cool and shrink. If some longerons shrink while others do not, this may stress the longerons and weaken them. This weakening would eventually lead to the failure of the mast so this must be avoided at all cost.