Dual Deployment

Introduction

Rockets which fly high spend more time in the air, especially with a parachute. While the parachute does prevent the rocket from being destroyed in its fall, it also gives the wind and sky more time to blow the rocket to another state or country. This is more of a problem for the high apogee rockets of course.

Single Deploy

The main way of solving this is through dual deployment. For single deploy, the parachute is triggered by an ejection charge, see Rocket Parts for what that is and how it works. However ejection charges are at the end of the day, a primitive timing method which is rather inaccurate.

What is often used instead is an *altimeter. The altimeter measures the altitude and at apogee triggers some black power to deploy the parachute. This is usually done via voltage to an igniter which is stuffed into black powder.

As a side note, apogee is the highest point traveled by the rocket, so there is no vertical motion and it is moving very slowly. This is generally a good time to deploy the parachute. Buuuuuuuuut... if you remember from the introduction, the rocket is going to be very far from you.

Dual Deployment

So we can't deploy at apogee since it is very high up. What if we deploy lower down? Unfortunately, the high speed when the parachute is deployed will tear the parachute into pieces. And the body tube (if wood) might also be shredded (called zippering) by the shock cord.

Instead you can use a smaller parachute or a streamer at apogee. This deployment is called apogee event or drogue event hence the parachute is also called a drogue parachute. For medium-size rockets, you can get away with deploying nothing at apogee and letting the nose cone portion spin around is sufficient for speed reduction.

Then at a lower altitude another parachute is deployed. This time it is the main parachute deployed at the main event. The two most common methods of doing a dual deploy are

1. Cable Cutter Dual Deploy
2. Two Parachute Dual Deploy

Either way works, but it seems like cable cutter is pretty nice because it is easily applied to any rocket.