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900	5580	Yesterday, our teams collectively worked their way through Challenges 0 through 2,
5580	8660	leaving with half of the challenges solved by at least one team,
8660	11380	and three challenges remaining to be solved today.
11920	15160	PFS grew their lead throughout the day yesterday,
15160	18060	but the biggest drama occurred after hours.
18060	22000	When the 4 p.m. Pacific deadline for the On Orbit Challenge passed,
22000	25780	only four teams had submitted solutions deemed acceptable.
25780	27620	What's an acceptable solution?
28860	31760	Let's take a look at solving the On Orbit Challenge.
31940	34380	First, some terms you'll want to know.
34640	36860	Two-line element set, or TLE.
37000	42620	A data format containing information about an object's position and velocity at a specific point in time.
42620	45880	It is used to calculate where a satellite will be at some point in the future,
45880	48740	with increasing uncertainty the further out in time.
48740	50400	Window of opportunity.
50560	55260	The period of time during which the satellite can be positioned to complete the desired goal.
55260	60000	Vector. A line indicating a specific direction in magnitude.
60160	67260	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.
67260	74420	Camera boresight, camera mounting position, and camera body vector all describe the satellite camera and where it's pointed.
74520	79180	Quaternion. A number system that is handy for calculating 3D rotations.
79640	81660	Got it? Here we go.
81660	86040	The first step in solving the on-orbit challenge. Identify the key data.
86080	94100	The TLE, camera mounting position, target, and window of opportunity are all supplied in the challenge description or the on-orbit handbook.
94260	99380	The data is used to calculate the orbit of both the satellite and the moon toward the window of opportunity.
99380	103340	And don't forget to grab the camera body vector, which will be needed later.
103580	109020	The second step. Calculate the time of image by defining the relationship between these key vectors.
109020	114800	1. Determine the satellite-to-moon vector, which points directly from the satellite towards the moon.
114800	120060	2. Determine the nadir vector, which points directly from the satellite towards the center of the Earth.
120060	130200	3. Determine the angle between 1. the satellite-to-moon vector and the nadir vector and 2. the angle between the satellite negative Z vector and the camera body vector.
130200	135220	The instance when the difference between the two angles is minimized gives us the time of image,
135220	140900	the moment along its orbit when the satellite will be in position to take our all-important moonshot.
141840	149440	The third step. Calculate the attitude or the position within its orbit that the satellite must take for the camera to capture the image.
149540	152760	This is accomplished by lots of math.
153140	158600	Specifically, something called a direction cosine matrix, DCM, or rotation matrix.
158600	167300	The DCM calculates a satellite attitude that points 1. the camera boresight to the moon and 2. the satellite's negative Z vector to Earth's center,
167300	170440	which is the attitude needed to accomplish the goal.
170940	179600	The DCM supplies us with a specific quaternion which, when uploaded and applied to the satellite's attitude determination and control system, ADCS,
179600	182540	moves the satellite into the desired position.
182540	188240	On to the final step. Apply all that information and get the image we're after.
188780	198320	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.
198340	200840	The proper order of commands would be as follows.
200840	211460	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.
211460	214160	That's it. Challenge accomplished.
214700	219320	But what does all of this have to do with hacking and keeping our satellites secure?
219400	222740	The on-orbit challenge was completed with full trust.
222740	227480	Our satellites rely on data and sensors from multiple sources in order to complete an objective.
227480	231480	The TLE that was provided relied on data from the satellite and ground stations.
231480	235620	Authenticated communications were required to upload the proper command sequence.
235620	241040	Trusted execution was required to process sensor and actuator data to close control loops.
241040	245360	Secure onboard communications were required to carry out operations in orbit.
245560	254460	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 get a satellite into orbit,
254460	262500	it takes a team of people from both space and security communities to ensure that space remains a viable, usable resource.
264640	269360	The four teams with successful on-orbit solutions during the time period were
269900	274620	Poland Cannon to Space. In fact, theirs came well over an hour before anyone else's.
274700	286280	ADD Vulcan, Flux Rocket Repeat, and Samurai all came in within about 10 minutes of each other within the last 15 minutes of that window.
286600	292480	Remember, the on-orbit portion involves a team computing a mission plan for an actual satellite to take a picture of a moon.
292480	302460	All acceptable solutions were evaluated and the most accurate solution submitted before the 4 p.m. deadline will be chosen to be sent into space into our orbiting satellite.
302520	306730	We'll learn whose solution that was amongst those four later on today.
307060	314980	As we entered into our overtime period after the 4 p.m. deadline yesterday, the alternate acceptance criteria kicked into play.
314980	325100	While the four teams submitting before 4 p.m. were automatically eligible for their solution to be sent and automatically into prize eligibility, we had to get more teams available.
325100	332620	The limit was six. This meant that two teams of the remaining four would be out of contention for the final prize pool.
332880	341280	The four teams fighting for those two spots included PFS, 1553, 1064 Seabred, and Solarwine.
341280	348480	1553 managed to submit a solution that was valid only three minutes after the deadline, quickly grabbing that fifth spot.
348560	354680	That left PFS, 1064 Seabred, and Solarwine on the ropes for that last spot.
354760	364540	PFS and 1064 Seabred were number one and number four on the scoreboard at that point, so no matter what happened, someone in contention for the podium would not be eligible.
364540	370080	All of the contest organizers were on a shared video chat, waiting to see the results as they came in.
370080	378400	1064 Seabred had what looked to be an extremely close solution that was just outside the acceptance criteria, and PFS didn't seem to be close.
378400	391020	Then, at 7.48 p.m. Eastern, or 4.48 p.m. Pacific, PFS came in with a valid solution, just edging out 1064 Seabred and Solarwine on the list of on-orbit acceptance.
393400	399280	Unfortunately, that means that 1064 Seabred and Solarwine are both ineligible for a spot on the podium.
399280	402380	That said, they can still have an impact on the game.
402440	409760	Either team scoring first blood will potentially change the number of available points left on the board for their competitors and impact the final result.
409800	418720	It's sad to see two great teams out of contention for the prize pool, but they can still end up on the leaderboard from a points perspective and attain the associated bragging rights.
418720	423400	In fact, let's go ahead and take a look at the scoreboard now in our live octagon feed.
424340	426300	And they definitely haven't slowed down.
426300	430600	You'll notice that Solarwine actually scored first blood on Challenge 3.
430620	433560	Congratulations to them for the great work overnight.
433700	440620	The pressure is now on the remaining teams to show that they made good use of the downtime as well to land Challenge 3.
440620	447480	You can also see Flux Repeat Rocket scoring just before this broadcast with only a 5% reduction in total points.
447480	449440	So that's a good amount of points for them.
449760	454580	That means Solarwine and Flux Repeat Rocket are both moving on to Challenge 4.
480330	485010	This is the first time we've seen Flux Repeat Rocket make a big move on the scoreboard.
485010	486570	Let's check out their team bio.
516200	523560	Like many of the combined CTF teams that we've seen here today, I have good memories of playing Hack Lou CTF.
523560	528660	In fact, it's often the case that the competition participants are also organizers in other times.
528660	537960	So one of those teams that makes up the composition of Flux Repeat Rocket, Flux Fingers, runs Hack Lou, which is another great CTF competition you should check out.
538060	539720	What an exciting first day.
539720	544420	I'm looking forward to seeing what happens today as our teams battle through these last few challenges.
544420	550600	Come back and join us at our 10.50am Pacific, 1.50pm Eastern for our next competition update.