The SpaceX "Suicide Burn"

procrastilearner (61)in #steemstem • 8 years ago

Introduction

SpaceX revolutionized the space transportation industry with the successful introduction of their booster landing technology.

In this post I am going to discuss some details of the very exciting landing strategy which is often called a 'suicide burn'.

Powered Descent

If you are going to make a powered descent onto a planet or moon the most efficient method is to do all of the deceleration right at the very end.

The reason is basically because gravity is always pulling and to simply hover or even to resist that constant pull means you are wasting fuel.

In other words, to do a more gentle deceleration for a longer period of time counteracting gravity means that you are in flight for longer and burning more fuel.

Therefore the optimal landing technique is to do all of your fuel burn for deceleration right before impact.

This obviously leaves very little margin for error hence the fairly dramatic name 'suicide burn'.

SpaceX Booster Landings

Since the margins for safety are so small, SpaceX deliberately aims the booster at the ocean at a spot a little off of the drone ship. At the very last moments the booster skews over to the ship and hits its target.

The reason for this is in case something goes wrong with the final burn, the booster will simply decide to crash into the ocean and not destroy the drone ship.

This scenario is in fact exactly what happened when they tried to land the center booster following the famous inaugural launch of the Falcon Heavy.

The re-ignition of the booster engines partially failed, the booster came in too hot and the flight computer decided to crash into the ocean. Even so, the crash still partially damaged the drone ship.

SpaceX did not invent this landing technique, it has been done in the past, most famously the Apollo moon landings which were powered landings on our nearest neighbour (the Apollo landings may be better described a staircase burns instead).

Disadvantages and Advantages

The disadvantage of landing your boosters is that you have to save fuel for the landing, fuel that could have gone into boosting the payload into orbit.

The other disadvantage is the extra weight of the required equipment such as the grid fins and the landing legs. This removes weight that could have gone into launching a heavier payload.

The advantage of landing your boosters is that you get to re-use them and save a boatload of money doing so.

This massive cost savings is what makes it all worthwhile.