While going through the topic called "Combinations of Ducted Jet Engines and Rocket Engines" in Chapter 1 of Sutton & Biblarz's Rocket Propulsion Elements, 9th Ed I found the section below.

Line 2 tells that air-augmented rocket propulsion combines the principles while line 1 of 2nd paragraph tells that integral rocket-ramjet propulsion combines the actions of rocket and ramjet!

Is the architecture of the above types of propulsion techniques same?

Sutton, Figure 1-7; Combinations of Ducted Jet Engines and Rocket Engines

FIGURE 1–7. Simplified diagram of an air-launched missile with integral rocket–ramjet propulsion. After the solid propellant has been consumed in boosting the vehicle to flight speed, the rocket combustion chamber becomes the ramjet combustion chamber with air burning the ramjet liquid fuel. Igniter and steering mechanisms are not shown.

Ducted rocket propulsion systems, sometimes called air-augmented rocket propulsion systems, combine the principles of rocket and ramjet engines; they give higher performance (specific impulse) than chemical rocket engines but can only operate within the earth’s atmosphere. Usually, the term air-augmented rocket denotes mix- ing of air with the rocket exhaust (made fuel rich for afterburning) in proportions that enable the propulsion device to retain those characteristics that typify rocket engines, for example, high static thrust and high thrust-to-weight ratio. In contrast, the ducted rocket is often like a ramjet in that it must be boosted to operating speed and uses the rocket components more as a fuel-rich gas generator (liquid or solid).

The action of rocket propulsion systems and ramjets can be combined. An example of these two are propulsion systems operating in sequence and then in tandem and yet utilizing a common combustion chamber volume, as shown in Fig. 1–7. Such a low-volume configuration, known as an integral rocket–ramjet, has been attractive


1 Answer 1


There are three different devices being described here. The second two are closely related, while the first is different.

The picture you have included is a device that functions first as a rocket until its solid rocket propellant is exhausted, and then reconfigures to use the rocket chamber as a ramjet chamber. It cannot operate as a ramjet before the solid rocket propellant is exhausted, and it cannot do the reverse either. This is ultimately a mass-saving trick as opposed to, say, jettisoning the solid rocket stage and having a separate ramjet engine.

Air-augmented rocket systems are a completely different device. They work by using an air intake and duct to entrain air into the rocket exhaust stream, thereby significantly improving specific impulse as long as atmosphere intake is available.

The "ducted rocket" in turn sounds like what the author of Ignition calls a "ramrocket", in which a rocket engine is used which either burns extremely fuel-rich or otherwise produces a flammable exhaust, which can then provide either rocket thrust or in turn serve as the fuel for a ramjet. In Ignition the idea that this could serve as a self-boosting ramjet was mentioned.


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.