Cook Inertial Propulsion?US Patent #4238968

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An Anonymous Scientist's Critique of the CIP Engine






This brief report constitutes a review of the “Cook Inertial Propulsion System”. This system is designed to replace rocket propulsion by inertial propulsion. Mr. Cook claims that he has demonstrated the principle and that a trip to Mars, for example, could be made in a few days rather than months. The new system appears to be based on unbalanced rotating parts that accelerate a spacecraft and does not require exhausting mass at high speed. If such as system does indeed function or could be made to function even inefficiently, it would revolutionize space travel by making it very inexpensive.

Unfortunately the concept of inertial propulsion seems to be negated by Newton’s Laws. Because Newton’s Laws have been enormously successful in explaining physical phenomena over the past two centuries, the likelihood that the concept of inertial propulsion is valid must be considered extremely small. Nevertheless the implications are immense if it should turn out that there should be any truth to Cook’s proposition.

Cook has presented his ideas on a web site and in a book. The book is particularly interesting as it describes the history of the man and his attempts to gain acceptance of his ideas from members of the scientific community. Cook started his career servicing complicated printing presses and showed a considerable aptitude for mechanical design. However he had no formal education in science and in this area he is essentially self-taught. The lack of training in physics has proved a serious hurdle to his promotions. However, perhaps the most fascinating part of Cook’s story concerns the role of human nature and how even the most worthwhile idea can be handled ineptly and never sees the light of day. Therefore, even though inertial propulsion is probably a pipe-dream, the story itself has merit.


The three laws of Newton describe how bodies move under the action of forces. In the world of everyday experience they appear to be self-consistent and are routinely applied to practical engineering problems as well as scientific research. Their application is not restricted to mechanical apparatus but the laws are also applied to electromagnetic devices, such as motors and generators and to aerodynamics and hydrodynamical problems. The application of the laws themselves is typically so successful that the validity of the laws is rarely questioned.

Newton’s laws can be regarded as a mathematical model for the real world. Practical experience has demonstrated that the model is extremely accurate at length scales that correspond to human experience: these can be called macro scales. However, at very small scales, at very large scales or when the relative velocity of bodies approaches the speed of light, the model fails. At small scales it is replaced by quantum mechanics, and at large scales it is replaced by general relativity. For high velocities, special relativity is a better model. This does not mean that Newton’s Laws are incorrect, as implied in Mr. Cook’s book, but only that their domain of validity is limited. In fact both the theories of quantum mechanics and relativity have been constructed so that they reduce to Newton’s laws on macro scales.

Nevertheless, Newton’s Laws are not entirely beyond criticism. This is because they embody an element of circularity. For example, if a body is found to accelerate, a force must be introduced to account for it. Sometimes it is difficult to understand how this force is generated (an example is the magnetic force). Fortunately most if not all fundamental forces appear to have been identified and the laws seem to hold in most practical circumstances.

The third law admits some differences in interpretation. It is customary to treat the two forces in this law as acting in opposite directions but along the same line (the strong form of the law). When this does not apply, the laws can be “fixed up” by associating an angular momentum with a field. This type of modification has always been successful in explaining and predicting practical phenomena.

Cook claims that Newton’s Laws do not properly take into consideration internal forces. This is simply not true. A rigid body can be regarded as a collection of particles (as in the author’s earlier report) and the third law in its strong form implies that the internal forces cancel exactly. Therefore the Laws should apply unequivocally to machinery of the type advocated by Cook for inertial propulsion.

It is important to note that according to Newton’s Laws forces internal to a rigid body will cancel exactly. If they did not, then we should observe bizarre behaviour: rigid bodies would move about seemingly of their own accord. Nevertheless, it is difficult to prove that Newton’s Laws are correct in an absolute sense and it is generally accepted by the scientific community that the model that they represent is probably imperfect. However, the level of imperfection for typical engineering problems is miniscule.



Cook claims that he has developed a system of unbalanced rotating masses that can accelerate in space as a result of internal forces and with no external force. A direct consequence of Newton’s Laws is that an isolated system that is subject to zero external force cannot accelerate but has a constant linear momentum. An alternative to this statement is that the center of mass of the system moves at constant velocity (if the mass is fixed). This seems to rule out any possibility that an inertial propulsion system can function in space.

To make a credible claim to the contrary, it is necessary either to explain how the implications of Newton’s Laws have been overcome or to demonstrate practically that the system functions as advertised and preferably both. Because of the very low a priori probability that the concept is viable, it is necessary to provide very convincing arguments for the explanation and to the test procedures in the practical demonstration.

Cook has attempted to explain his concept in his book. The force created by unbalance in a rotor is supposed to be “rectified” in much the same way as an alternating current is rectified to become a direct current. Simple attempts at rectification are doomed to failure because a proper analysis of the system (using Newton’s Laws) shows that the unbalanced forces in an isolated system are always exactly cancelled and even Cook acknowledges this fact. Moreover, the problems do not appear as arcane features of Newton’s Laws but rather in the form of clear but undesirable “reaction forces” that would be recognized by normal engineers and practical men in general. Mr. Cook has therefore concentrated on trying to remove these undesirable forces by ingenious mechanical design. These designs tend to smooth out the reaction. However, the designs have now reached the point where an oscillating mass has been introduced and even Mr. Cook cannot explain the mechanics.



The basic explanations in Cook’s book are consistent with Newton’s Laws and imply that the inertial propulsion system cannot work. In fact Mr. Cook himself has analyzed previous attempts to design and construct inertial propulsion systems and shown why they did not function. The Cook Inertial Propulsion concept (CIP) in its original form also seems not to work or at least it does not function reliably. This is probably because it suffers from the same problems as its predecessors.

To make it function an “oscillating mass” is required but, though the reason for this mass seems to be to remove the undesirable forces, the manner in which it does this is not clear (at least to this author). Therefore we are left with no theoretical justification for the concept.

Mr. Cook’s reply to this author’s first critique of his invention is unsatisfactory. He is unwilling to address the objections to his invention “in detail”. However, a detailed analysis is exactly what is required to provide plausibility to his assertions.

In general Cook undermines his own arguments by his use of scientific language. Words such as inertia, force and other terms from physics have specific meanings but seem to be used by him more or less interchangeably. This may be convincing to the lay-person but to a specialist this gives the impression of a general lack of competence.  Mr. Cook seems to excuse himself because of his lack of formal training. However, this explanation is unacceptable if funds are solicited.



There have been several attempts to build a working unit and a number of demonstrations of the concept have been made apparently with partial success. Unfortunately many observers have explained any success as due to non-linear frictional effects that produce the desired rectification of the forces. If this argument is true, the concept is inappropriate to propulsion in space.

Though a unit has been observed and tested by various engineers and academics, the reports are not uniformly positive. This may be partly because Mr. Cook has demonstrated his machines prematurely before they were working properly or partly because the observers did not evaluate the performance of the mechanisms appropriately. However, the result is that the demonstrations have not yet validated the concept especially in the light of the conflict with Newton’s Laws.  



Mr. Cook has expressed great surprise that his invention has not been received enthusiastically in the academic and engineering communities. This indicates a lack of understanding of the environment within these communities. New ideas of any type are not well received and the newer and more important is the idea the more scrutiny (i.e. negative comment) it receives. This is because the members of this community are very competitive and their salaries, research funds and general standing in their fields are tied strongly to their performance in publishing their own research. Therefore professional scientists as a group are not kindly disposed to newcomers to their fields, especially those who have not been through an “approved apprenticeship process”.

Though somewhat self-serving and open to outright dishonesty, the standard review process usually functions well in culling concepts that are not useful. Mr. Cook is certainly not alone in being rewarded with the treatment meted out by academics that is described in his book; many scientific practitioners have to cope with it. On the positive side, a good idea backed by persistence usually gets accepted. This typically occurs when other members of the community can see some personal advantage in adopting it.

In Mr. Cook’s case the problems are compounded by the fact that his concept is in conflict with Newton’s Laws. Academics are generally unwilling to be associated with such ideas because those academics lending support will certainly be seen as personally eccentric: any hint of eccentricity will be used by others to damage their careers. The same remark applies to Mr. Cook’s association with the proponents of UFOs.

Because venture capital is generally tied to favorable reports by so-called experts (often selected from academia), the problems with Newton’s Laws and his association with UFOs are probably sufficient to kill any prospects for funding even if his inventions were to perform well.

It is worth remarking that, if it were to function as advertised, Mr. Cook’s concept would be worth billions of dollars to him. Therefore an inventor might not wish to reveal all the details of his invention. This is the typical conundrum faced by the inventor who would like to benefit the most from his work. The fact is that a compromise is required; he has to accept that others will almost certainly make much more money out of it than he does.

On a negative note and without implying that Mr. Cook falls into this category, it is also possible that an inventor does not really believe that his concept is truly viable and seeks to make a living selling books on his ideas. 



There is no firm basis to support Mr. Cook and his inertial propulsion concept because he has not provided a plausible explanation of its workings especially in the light of its apparent conflict with Newton’s Laws. Furthermore the machinery has not unequivocally demonstrated the utility of the concept. A proper demonstration would involve several well-known, trusted experts evaluating it. Acceptance by unknown academics and/or engineers is not sufficient.

In this type of situation the obligation is definitely on Mr. Cook to provide plausible explanations and demonstrations of equipment at his own expense.


December 31, 2002.


Bob Cook's Response


I have read your report on Inertial Propulsion dated 12/31/02 as regards my invention, the CIP Engine.

From your report I can see your mind is made up and it would be futile for me to try to change it.  But I do want to point out a few facts:

1. When the book "The Death of Rocketry" was finished in June of 1980, I was still teaching myself math and physics terminology in order to better explain the CIP propulsive principle to the world of science.  But 22 years later I have greatly increased my knowledge of all aspects of spin dynamics.  I have given 3 hour lectures before scientists with doctorate degrees in various fields of physics and have been highly acclaimed.  Back in the 70's and 80's I would have been told to keep quiet after the first 3 minutes- but today is not yesterday.

2. You said in your report that "The design has now reached the point where an oscillating mass has been introduced and even Mr. Cook cannot explain the mechanics."  But if you closely read page 95 of "The Death of Rocketry", I go to great lengths to fully explain the mechanics of the oscillator feature.  Joel Dickinson was the one who said HE couldn't explain the mechanics— not Cook!

3. Scientists and engineers from United Airlines tested an early model of Cook's invention for several weeks.  Their report showed how and why (in spite of being declared in violation of the laws of motion by the U.S. patent office) the system worked!  Their dynamics analysis of 9/10/71 explains why.

4. A report prepared by Professor Ching Cao Fong (chairman of the U.C. Davis physics department) showed this system at 53% energy efficiency.  He saw a demonstration of a working model and heard a 4 hour lecture by Cook.

5. The tests conducted by Boeing Aircraft in November 1999 using the most sophisticated equipment could NOT detect the 90 to 100 pound reaction forces demanded by Newton's 3rd Law!  Where did the reaction force go?  If Newton's law was 100% correct, the force would have been detected.

There is nothing more for me to say in defense of my beliefs.

Thank you for your interest,

Bob Cook


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