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1240	4260	Let's take a look at solving the on-orbit challenge.
4360	6760	First, some terms you'll want to know.
7020	9240	Two-line element set, or TLE.
9400	12900	A data format containing information about an object's position and velocity
12900	15000	at a specific point in time.
15000	18240	It is used to calculate where a satellite will be at some point in the future,
18240	21140	with increasing uncertainty the further out in time.
21140	22760	Window of opportunity.
22940	27640	The period of time during which the satellite can be positioned to complete the desired goal.
28120	29040	Vector.
29040	32460	A line indicating a specific direction and magnitude.
32500	36980	A satellite will have assigned X, Y, and Z vectors associated with the body of the vehicle
36980	39580	that can be used in a coordinate system.
39640	43300	Camera boresight, camera mounting position, and camera body vector
43300	46780	all describe the satellite camera and where it's pointed.
46940	47860	Quaternion.
47860	51520	A number system that is handy for calculating 3D rotations.
52060	54060	Got it? Here we go.
54060	56600	The first step in solving the on-orbit challenge.
56640	58320	Identify the key data.
58320	62400	The TLE, camera mounting position, target, and window of opportunity
62400	66520	are all supplied in the challenge description or the on-orbit handbook.
66620	69980	The data is used to calculate the orbit of both the satellite and the moon
69980	71740	toward the window of opportunity.
71740	75740	And don't forget to grab the camera body vector, which will be needed later.
75960	77100	The second step.
77100	81480	Calculate the time of image by defining the relationship between these key vectors.
81780	84540	1. Determine the satellite to moon vector,
84540	87140	which points directly from the satellite towards the moon.
87140	89100	2. Determine the nadir vector,
89100	92540	which points directly from the satellite towards the center of the earth.
92540	97340	3. Determine the angle between 1. The satellite to moon vector and the nadir vector
97340	102560	and 2. The angle between the satellite negative z vector and the camera body vector.
102720	105660	The instance when the difference between the two angles is minimized
105660	109120	gives us the time of image, the moment along its orbit when the
109120	113240	satellite will be in position to take our all-important moon shot.
113920	115560	The third step.
115560	119320	Calculate the attitude or the position within its orbit that the satellite must
119320	125200	take for the camera to capture the image. This is accomplished by lots of math.
125540	131040	Specifically, something called a direction cosine matrix, DCM, or rotation matrix.
131040	135700	The DCM calculates a satellite attitude that points 1. The camera boresight to the moon
135700	139780	and 2. The satellite's negative z vector to earth center,
139780	142780	which is the attitude needed to accomplish the goal.
143500	148640	The DCM supplies us with a specific quaternion which, when uploaded and applied to the satellite's
148640	154840	attitude determination and control system, ADCS, moves the satellite into the desired position.
155220	160640	On to the final step. Apply all that information and get the image we're after.
161340	165740	We take the time of image and back out the commands around it, giving the satellite enough
165740	170620	time to apply the quaternion and be in position when it arrives at the window of opportunity.
170620	177020	The proper order of commands would be as follows. Turn on the ADCS, slew to the commanded quaternion,
177020	183880	turn the camera on, set the exposure time, capture the image, and finally, turn the camera off.
184080	189240	That's it. Challenge accomplished. But what does all of this have to do with
189240	195080	hacking and keeping our satellites secure? The on-orbit challenge was completed with full trust.
195080	199960	Our satellites rely on data and sensors from multiple sources in order to complete an objective.
199960	204440	The TLE that was provided relied on data from the satellite and ground stations. Authenticated
204440	209660	communications were required to upload the proper command sequence. Trusted execution was required
209660	214900	to process sensor and actuator data to close control loops. Secure on-board communications
214900	220340	were required to carry out operations in orbit. We need security-focused people to help with these
220340	225260	problems because just as much as it takes a team of people to strap explosives to a computer to
225260	230160	satellite into orbit, it takes a team of people from both space and security communities
230160	234660	to ensure that space remains a viable, usable resource.