# Why is the velocity vector of this rocket not aligned with the rocket's axis itself?

I am reading a book about rocket guidance. And came accross this drawing:

The missiles axis is always oriented to the moving target with this guidance system. But I was wondering, knowing the exhaust nozzles and thrusters are at the back of the missile, how is it possible to have the velocity vector (which I indicated with a red circle) to be oriented vertically like that? I was expecting this vector to be aligned with the longitudinal axis of the missile itself so that the angle alpha (angle of attack) equals 0.

Seems like, beside this one, there are other guidance methods where we try to by all means always try to keep the angle of attack equal to zero (chase guidance). What is the difference?

Entire text: http://paste.ubuntu.com/25706952

Original text: https://i.sstatic.net/3oGgL.jpg

• This is almost never true for any missile. In this particular case it's called "Proportional navigation". I know too little about it (or more accurately, forgot too much about it) to form an answer, but hopefully that key word would lead you to more helpful materials. Commented Oct 9, 2017 at 14:00

This is a schematic drawing the rockets orientation is unrelated to the velocity vector.

The drawing shows angle of the rocket at the start of its flight, which it would follow without the guidance system (left straight line) and the (theoretical) angle the rocket could have been launched at to hit the plane at the "meeting point" (lower straight line).

The angle of the rocket in this drawing is along the direct hit line most likely to symbolise it is aiming at the plane...

I don't think they would have specified that the angle alpha (angle of attack) is needed. – LandonZeKepitelOfGreytBritn

despite what the text may or may not say:

• alpha is not the angle off attack. The angle off attack is between the plane and the rocket at the moment of impact.
• alpha (as shown in the drawing) is the difference in angle between the real rocket launch angle and the angle between the launch facility and the plane in the moment of impact.

It may be that this is referred to as the angle of attack in military speech but that's wrong in the physical sense.

alpha is very much the angle of attack. it is the angle at which the body "attacks" the air, i.e. the angle between the forward axis of the vehicle and the direction of the incoming stream of air. The "moment of impact" has nothing to do with it. – Federico

You are right with your definition of angle of attack as we use it in aviation.

But the drawing has no indication of the "the direction of the incoming stream of air* (other than implicit from the rockets movement) and even if it would it would not relate the angle alpha as it is drawn since this would be unrelated to the targets movement. But in the drawing the angle alpha is related to the targets movement.

• not sure this is correct. Because the text states this: goo.gl/oahd4h , if it were for aesthetical reasons or only just for symobics I don't think they would have specified that the angle alpha (angle of attack) is needed. Entire text: paste.ubuntu.com/25706952 (can't create a short link for the translated version, you may have to translate it yourself), original text: imgur.com/a/CfWDb Commented Oct 9, 2017 at 12:06
• "the drawing has no indication of the the direction of the incoming stream of air" well, as you say "other then implicit from the rockets movement". Usually on textbooks, unless required, you neglect the wind, so in that diagram the direction of the incoming stream of air is defined. Commented Oct 9, 2017 at 12:59