Let's take a look at solving the on-orbit challenge.
First, some terms you'll want to know.
Two-line element set, or TLE.
A data format containing information about an object's position and velocity
at a specific point in time.
It is used to calculate where a satellite will be at some point in the future,
with increasing uncertainty the further out in time.
Window of opportunity.
The period of time during which the satellite can be positioned to complete the desired goal.
Vector.
A line indicating a specific direction and magnitude.
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.
Camera boresight, camera mounting position, and camera body vector
all describe the satellite camera and where it's pointed.
Quaternion.
A number system that is handy for calculating 3D rotations.
Got it? Here we go.
The first step in solving the on-orbit challenge.
Identify the key data.
The TLE, camera mounting position, target, and window of opportunity
are all supplied in the challenge description or the on-orbit handbook.
The data is used to calculate the orbit of both the satellite and the moon
toward the window of opportunity.
And don't forget to grab the camera body vector, which will be needed later.
The second step.
Calculate the time of image by defining the relationship between these key vectors.
1. Determine the satellite to moon vector,
which points directly from the satellite towards the moon.
2. Determine the nadir vector,
which points directly from the satellite towards the center of the earth.
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.
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.
The third step.
Calculate the attitude or the position within its orbit that the satellite must
take for the camera to capture the image. This is accomplished by lots of math.
Specifically, something called a direction cosine matrix, DCM, or rotation matrix.
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 center,
which is the attitude needed to accomplish the goal.
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.
On to the final step. Apply all that information and get the image we're after.
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.
The proper order of commands would be as follows. 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.
That's it. Challenge accomplished. But what does all of this have to do with
hacking and keeping our satellites secure? The on-orbit challenge was completed with full trust.
Our satellites rely on data and sensors from multiple sources in order to complete an objective.
The TLE that was provided relied on data from the satellite and ground stations. Authenticated
communications were required to upload the proper command sequence. Trusted execution was required
to process sensor and actuator data to close control loops. Secure on-board communications
were required to carry out operations in orbit. 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, usable resource.