WEBVTT 00:01.240 --> 00:04.260 Let's take a look at solving the on-orbit challenge. 00:04.360 --> 00:06.760 First, some terms you'll want to know. 00:07.020 --> 00:09.240 Two-line element set, or TLE. 00:09.400 --> 00:15.000 A data format containing information about an object's position and velocity at a specific point in time. 00:15.000 --> 00:21.140 It is used to calculate where a satellite will be at some point in the future, with increasing uncertainty the further out in time. 00:21.140 --> 00:22.760 Window of opportunity. 00:22.940 --> 00:27.640 The period of time during which the satellite can be positioned to complete the desired goal. 00:28.120 --> 00:29.040 Vector. 00:29.040 --> 00:32.460 A line indicating a specific direction and magnitude. 00:32.500 --> 00:39.580 A satellite will have assigned X, Y, and Z vectors associated with the body of the vehicle that can be used in a coordinate system. 00:39.640 --> 00:46.780 Camera boresight, camera mounting position, and camera body vector all describe the satellite camera and where it's pointed. 00:46.940 --> 00:47.860 Quaternion. 00:47.860 --> 00:51.520 A number system that is handy for calculating 3D rotations. 00:52.060 --> 00:53.140 Got it? 00:53.140 --> 00:54.060 Here we go. 00:54.060 --> 00:56.600 The first step in solving the on-orbit challenge. 00:56.640 --> 00:58.320 Identify the key data. 00:58.320 --> 01:06.520 The TLE, camera mounting position, target, and window of opportunity are all supplied in the challenge description or the on-orbit handbook. 01:06.620 --> 01:11.740 The data is used to calculate the orbit of both the satellite and the moon toward the window of opportunity. 01:11.740 --> 01:15.740 And don't forget to grab the camera body vector, which will be needed later. 01:15.960 --> 01:17.100 The second step. 01:17.100 --> 01:21.480 Calculate the time of image by defining the relationship between these key vectors. 01:21.780 --> 01:22.480 1. 01:22.480 --> 01:27.140 Determine the satellite to moon vector, which points directly from the satellite towards the moon. 01:27.140 --> 01:27.720 2. 01:27.720 --> 01:32.540 Determine the nadir vector, which points directly from the satellite towards the center of the earth. 01:32.540 --> 01:33.100 3. 01:33.100 --> 01:34.900 Determine the angle between 1. 01:34.900 --> 01:38.280 The satellite to moon vector and the nadir vector and 2. 01:38.280 --> 01:42.560 The angle between the satellite negative z vector and the camera body vector. 01:42.720 --> 01:53.240 The instance when the difference between the two angles is minimized gives us the time of image, the moment along its orbit when the satellite will be in position to take our all-important moon shot. 01:53.920 --> 01:55.560 The third step. 01:55.560 --> 02:01.880 Calculate the attitude or the position within its orbit that the satellite must take for the camera to capture the image. 02:02.140 --> 02:05.200 This is accomplished by lots of math. 02:05.540 --> 02:11.040 Specifically, something called a direction cosine matrix, DCM, or rotation matrix. 02:11.040 --> 02:14.200 The DCM calculates a satellite attitude that points 1. 02:14.200 --> 02:16.700 The camera boresight to the moon and 2. 02:16.700 --> 02:22.780 The satellite's negative z vector to earth center, which is the attitude needed to accomplish the goal. 02:23.500 --> 02:34.840 The DCM supplies us with a specific quaternion which, when uploaded and applied to the satellite's attitude determination and control system, ADCS, moves the satellite into the desired position. 02:35.220 --> 02:36.880 On to the final step. 02:36.880 --> 02:40.640 Apply all that information and get the image we're after. 02:41.340 --> 02:50.620 We take the time of image and back out the commands around it, giving the satellite enough time to apply the quaternion and be in position when it arrives at the window of opportunity. 02:50.620 --> 02:53.260 The proper order of commands would be as follows. 02:53.260 --> 03:03.880 Turn on the ADCS, slew to the commanded quaternion, turn the camera on, set the exposure time, capture the image, and finally, turn the camera off. 03:04.080 --> 03:04.960 That's it. 03:04.960 --> 03:06.440 Challenge accomplished. 03:07.260 --> 03:11.620 But what does all of this have to do with hacking and keeping our satellites secure? 03:11.800 --> 03:15.080 The on-orbit challenge was completed with full trust. 03:15.080 --> 03:19.960 Our satellites rely on data and sensors from multiple sources in order to complete an objective. 03:19.960 --> 03:23.860 The TLE that was provided relied on data from the satellite and ground stations. 03:23.880 --> 03:28.000 Authenticated communications were required to upload the proper command sequence. 03:28.000 --> 03:33.520 Trusted execution was required to process sensor and actuator data to close control loops. 03:33.520 --> 03:37.780 Secure on-board communications were required to carry out operations in orbit. 03:37.920 --> 03:53.380 We need security-focused people to help with these problems because just as much as it takes a team of people to strap explosives to a computer to satellite into orbit, it takes a team of people from both space and security communities to ensure that space remains a viable, 03:53.380 --> 03:54.660 usable resource.