Falcon Heavy Model Rocket

This is a 1/48 scale model of the SpaceX Falcon Heavy rocket

An early CAD render of the vehicle

Each of the three cores carries a flight computer, parachute deployment system, and thrust vector control assembly. The upper stage flies with thrust vector control as well, and it carries a 3d printed sports car – no Falcon Heavy model would be complete without one.

Avionics

The Falcon Heavy flight computers are upgraded versions of Signal, a computer designed and built specifically for thrust vector control in model rockets. Each computer has a set of MEMS gyroscopes and accelerometers for sensing movement and orientation on the rocket, the same kind of sensors found in most smartphones. A barometric pressure sensor is used to determine the rocket’s altitude above ground level.

The inertial measurement unit (IMU) houses 3 gyroscopes and accelerometers. It is unbelievably small.

The flight software is written in C++, . Flight guidance is computed using quaternions, which are more computationally efficient, and are used for guidance in some space launch vehicles. 

On each flight computer, a 48mhz Cortex M0 processor reads the flight sensors at 400hz and logs 31 channels of data to a flash chip, 40 times per second. Every second that Falcon Heavy is in the air, 4,960 points of data are recorded onboard – never too much data.

Each Signal flight computer weighs just 15 grams

Mechanics

Stage separation at 1/4th speed

The attachment points at the top of each side core slide down a ramp on the center core, giving them a bit of clearance during stage separation. This passive setup keeps things very simple during flight, but the cores are usually bolted together while the vehicle is on the ground. All three cores are also connected at the base of the vehicle using a slightly simpler thrust plate.

Stage separation during flight 1 of the Falcon Heavy model

The side cores remain attached to vehicle by maintaining a slightly higher net thrust force than the center core/upper stage. As soon as the CC/US produces more net thrust than the side cores, the stages will separate. For flexibility, each side core also has a slot for a small separation motor. When used, the sep motor fires at a slight angle through the side core to ensure a clean separation away from the center core. This setup has not been needed on flights so far, but may be helpful later down the road.

The center core of the Falcon Heavy model goes through two boost phases during flight. During the first phase, the side cores are attached. Right around side core burnout, the center core lights a second motor, and the second boost phase begins. These two rocket motors are mounted on top of each other in the center core’s thrust vectoring mount. When the second motor ignites, the lower, spent motor, is ejected. This same technique used to control ascent and propulsive landing motors in other BPS.space rockets.

Roll control on the Falcon Heavy model

The rocket motors in each stage of the Falcon Heavy model can be gimbaled ±5 degrees in any direction. Because the side cores are not firing directly through the vehicle’s center of mass, they can be used not just for pitch and yaw, but roll control as well. Each multi-core flight runs a roll program which usually targets 20 degrees of positive roll, executed at 30-40 degrees per second.

Organized chaos

The center core of the Falcon Heavy model goes through two boost phases during flight. During the first phase, the side cores are attached. Right around side core burnout, the center core lights a second motor, and the second boost phase begins. These two rocket motors are mounted on top of each other in the center core’s thrust vectoring mount. When the second motor ignites, the lower, spent motor, is ejected. This same technique used to control ascent and propulsive landing motors in other BPS.space rockets.

Testing

Static Fire

In February of 2018, the full Falcon Heavy rocket was held down on the launch pad for a static fire test. Some space launch vehicles will fire their engines for a few seconds on the launch pad to make sure everything is working properly before launch day. The purpose of this static fire was instead to make sure the new launch pad was working correctly, and frankly, to get some cool footage for project promotion.

Center Core Test Flight

Each individual stage of the rocket was tested on its own before the first full FH launch. Many of these early tests also served as testbeds for the Signal R2 thrust vectoring kit, which was still in development at the time. First, the centre core was tested by itself. The flight was a success; the core was recovered and flight-tested several more times.

Booster Test Flight

After several more flights of the center core, the side cores were attached for a full booster test flight. The center core had a software bug which caused instability after stage separation. However, the most complex parts of the flight were successfully tested, including proper ignition timing, a roll program, and a mostly clean stage separation(right booster was damaged by the center core at stage sep).

Upper Stage Test Flight

Before attaching it to the center core, the upper stage was tested on its own as well. The first test flight was unsuccessful, which is why it’s important to test! The flight failed for several reasons, mostly having to do with the stability and tuning of the vehicle.

Booster Test Flight

After several more flights of the center core, the side cores were attached for a full booster test flight. The center core had a software bug which caused instability after stage separation. However, the most complex parts of the flight were successfully tested, including proper ignition timing, a roll program, and a mostly clean stage separation(right booster was damaged by the center core at stage sep).

Flight 1

Aerial view of flight 1

Flight 1 of the Falcon Heavy model was a partial success. The more complex ignition sequence worked as intended, letting the center core burn a bit on the pad. The first boost phase of flight was picture perfect. Both side cores hit the roll program target dead on, rolling to +20 degrees at 40 degrees per second beginning at T+0.9 seconds. The vehicle remained stable during boost phase one. After a clean separation of both side cores, the center core lost control.

The Falcon Heavy model right before booster separation

A heat induced structural failure in the center core’s motor mount resulted in a loss of thrust vector control. After sensing a loss of control, the upper stage’s flight computer called an in-flight abort, blowing the fairing apart to deploy its parachute. As the rocket began falling, the center core deployed the upper stage, and its own chutes, bringing both stages safely to the ground. Both side cores had reached the ground softly under their own parachutes by that point. The rocket remains in excellent condition, thanks to the in-flight abort system.

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