Chapter 7: The Apollo Add-On

About the Add-On
The X-Plane Apollo add-on is a realistic simulation of the lunar landing and docking operations of the Apollo 11 mission. In fact, it is the most complete, realistic simulation of a lunar landing available for the iPad or iPhone 4, with a wide range of missions to try.

Users can start off docked with the command module in a lunar orbit, and then separate from the command module to start the journey down to the lunar surface. After that, the lander must go through a full de-orbit burn and orbital transfer, going from lunar orbit down to the touch-down phase of the flight. All of this, of course, happens in real time with the actual weight, thrust, fuel capacity, and fuel burn of the real Apollo 11 lander.

Following the de-orbit burn and orbit transfer, users enter the most challenging phase of the flight—the powered descent. During this phase of the mission, users must keep their tail pointed in the direction of flight, running full thrust to slow the craft from orbital speed to a standstill. This phase of the flight is actually where pilots spend most of their time.

After the powered descent comes the vertical descent and landing. This is accompanied by the sounds taken from the real lander, right down to the radio call-outs made by mission control as Neil and Buzz worked their way down in 1969.

Once users have aced the landing, they can cruise around on the moon in the rover! This is a realistic simulation of the 4-wheel drive (with a separate motor for each wheel), surprisingly speedy rover that was used for the Apollo 15, 16, and 17 missions—this is a lot of fun to drive in the 1/6th gravity conditions on the moon! No wonder the astronauts drove it 17 miles in one day.

After roving around in the off-off-off-road simulator, users can launch the lander back up toward the command module (waiting in orbit) and dock with it.

Additionally, a huge number of historic pictures are included in the app, spanning from images of the control room back on Earth to the launch to the touch down on the moon and everything in between.

Purchasing the Add-On
Prior to purchasing the Apollo add-on, whenever users open the Apollo tab in the settings menu and try to launch one of the mission segments, X-Plane will display the following message:


 * [[Image: Purchasing message.gif]]

Tap the Buy Apollo as an add-on to X-Plane! button to purchase the upgrade.

Controls in Apollo
Controls in the Apollo add-on fall into one of three categories—a mission segment either has:
 * a)no control (i.e., the user watches, as in the separation, descent burn, and launch mission segments),
 * b)flight controls (as in the powered descent, vertical descent, and command module docking mission segments),
 * c)or vehicle controls (as in the lunar rover mission segment).

Flight Controls
Flight controls in Apollo are as follows.


 * [[Image: Apollo_controls.jpg]]

First, there is the throttle control (labeled 1 in the image above). For the descent phases of the mission, this goes from zero to full forward, corresponding to the bottom and top of the screen, respectively. For the command module docking, though, it goes from full backward to full forward, with zero thrust found in the center of its range.

Next is the yaw control (labeled 2 in the image above). When in the center, it does not affect the craft's motion. When dragged left, it pushes the lander's nose to the left, and when dragged right, it pushes the nose right.

The translational thrusters (whose control is labeled 3 in the previous image) serve to push the lander's entire body up, down, left, or right. Drag this control in the direction that the craft should move.

Finally, the lander's pitch and roll are controlled as in other X-Plane aircraft—tilt the iPad/iPhone forward to pitch the nose down, tilt it back to pitch the nose up, and tilt it left or right to roll the craft in the corresponding direction.

Vehicle Controls
Controlling the lunar rover is quite intuitive. Simply tilt the device forward to accelerate, tilt it back to brake, and tilt it left or right to turn in that direction.

Selecting a Mission Segment
Each mission segment can be selected by entering the Settings menu (using the same button as ever in the upper left of the screen), tapping the desired mission segment, and tapping the Go! button.

Separation
This is the segment of the mission that the application will enter when first starting up. All the user has to do is hit the SEPARATE button, and the path to touching down on the moon has begun!

Descent Burn
Following the separation from the command module is the descent burn, a 30 second firing of the engines that starts the lander toward the surface of the moon.

After beginning this portion of the mission, the rockets will automatically ignite for thirty seconds. At the end of that, the craft will be approximately 345,000 feet above the surface of the moon. Users can either choose to wait as the lander slowly makes its way down, or they can go back into the menu and select Powered Descent to skip over the wait. If users choose to wait through the unpowered portion of the descent, the sim will automatically enter the powered phase at about 45,000 feet.

Powered Descent
The objective of the powered descent phase is to slow from an orbital horizontal speed of about 3,600 miles per hour (relative to the surface of the moon) to a horizontal speed appropriate for landing—zero. This is achieved by pointing the lander's tail in the direction of the craft's motion and holding full power.

During this phase, be sure to keep the throttle slider all the way up. Use the white circle (found in the center of the screen) and the white dot to line the craft up with its direction of motion. For instance, when the white dot is above the circle, pitch the craft down so that the circle will move to meet the dot. When the dot is to the right of the circle, roll left to meet it.

Once the craft's orbital velocity has been burned off, it enters the vertical descent portion of the mission.

Vertical Descent
The vertical descent phase is where the craft descends the last 4,000 or so feet down to the surface of the moon. During this time, the lander's fore-aft and left-right velocities should be zero—that is, it should have no motion relative to the surface except its descent.

The goal here is to touch down very, very gently, with no ground speed at all and a level attitude for the lander. Use the tilt of the device to control pitch and roll, use the YAW slider to control motion left and right, and use the translational thrusters (labeled TRANS) to change left-right and fore-aft velocity. For instance, if, in the upper center of the screen, the simulator is indicating a positive fore-aft speed, drag the TRANS control down and hold it there a few seconds. If the sim is indicating a negative left-right speed, drag the TRANS control right, and so on.

In addition to all this, users must contend with the limited amount of fuel remaining. Use it wisely!

Upon touching down, the simulator will score the landing based on angular tilt, descent rate, ground speed, and the terrain hilliness.

Rove Around!
In this portion of the mission, the user is put behind the wheels of a lunar rover like the ones used for the last three Apollo missions. Tilt the iPad/iPhone forward to accelerate, back to brake, and left or right to steer.

See the Lunar Rover Wikipedia page for a video of the real rover!

Launch
For the launch stage of the mission, all the user has to do is press the Launch button. This starts the craft on its way into orbit, eventually climbing 65 miles above the moon's surface.

Command Module Dock
When docking with the command module, the goal is to be perfectly aligned with the docking hatch with very little velocity when the lander touches the command module. This is achieved by closely monitoring:
 * the throttle control, to ensure that the craft is only barely moving forward when it docks,
 * the yaw control, to ensure that the lander is aligned with the command module,
 * the pitch and roll controls, to ensure that the lander is aligned properly when it docks, and
 * the translational thrusters, to ensure that the craft's hatch meets up with the command module's hatch.

Note that the translational thruster control (labeled TRANS) adds thrust to cause movement in the direction that it is dragged (for example, if it is dragged left, it will add thrust from the right side in order to push the craft left). Note also that the throttle control likely only needs little bursts of thrust—tap somewhere in the middle of the sliders range, and it will briefly power the thruster, then stop.

After docking, the simulator will give a score based on the angular tilt, position, closure rate, and lateral speed of the craft at the time of docking.