Vernier nozzle

Vernier engine of the third stage of a Europa-type rocket

Vernier nozzles or Vernier thrusters are used for the thrust vector control of rockets, which means that they can be used to influence the flight direction of a rocket. They are named after the mathematician Pierre Vernier (1580–1637) who invented the Vernier scale (Nonius) , with which lengths and angles can be read very precisely.

Structure and functionality

Vernier nozzles are rocket engines themselves that can be pivoted in one or two axes. In contrast to the main engines, they are only ignited when the rocket needs to be changed. This minimizes the effort for cooling. In order to keep the ignition of the engines simple and therefore reliable, hypergol fuels are mostly used. These ignite automatically when the oxidizer and fuel are brought together in the combustion chamber. An additional ignition device, which could possibly fail, is not necessary.

use

Launch of an Atlas rocket

First and second stage engines of a Soyuz FG rocket

Most modern rockets ( Ariane , Delta , Atlas ) no longer use vernier nozzles. In the first versions of the Atlas rocket, two vernier nozzles were installed on the sides of the main tank for more precise control. In the first picture on the right, the flames of the two vernier nozzles can be clearly seen. For historical reasons, they are still used in older missile types such as the Soyuz . In the second picture on the right you can see the 20 large nozzles of the Soyuz rocket. In the outer stages there are two vernier nozzles, in the central stage the four main engines are surrounded by four vernier nozzles.

The space shuttle used vernier engines in the reaction control system for attitude control in earth orbit.

advantages and disadvantages

Vernier nozzles were mainly used in the early days of rocket technology. The reason was the immaturity of the hydraulic servo actuators, which were mainly used for thrust vector control. By using vernier nozzles, the main engine (s) could be permanently mounted. This eliminated the need for flexible lines for the fuel supply and the cardanic suspension of the main engine. Only the smaller vernier nozzles had to be swiveled, which was done with comparatively small actuators . Due to the smaller masses and forces, the control was also simpler.

In modern rockets, one or more gimbal-mounted main engines are usually used for thrust vector control. The main engines are pivoted via hydraulic (for large engines) or electrical actuators (for small engines or in higher stages) (e.g. space shuttle: 10.5 ° transverse axis , 8.5 ° yaw axis ). Due to the sophistication of modern thrust vector actuators and the omission of the vernier nozzles, their pivoting unit and fuel supply, the reliability of rockets can be increased.

Individual evidence

1. ↑ Reaction Control system. NASA, August 31, 2000, accessed on March 27, 2010 (English, from the NSTS Shuttle Reference Manual). 
2. ↑ MPS Thrust Vector Control. NASA, August 31, 2000, accessed March 27, 2010 (from the NSTS Shuttle Reference Manual).