Bruce Willis faces Armageddon
But over thirty years ago, a group of engineers-in-training at the Massachusetts Institute of Technology designed a far more realistic defense against a doomsday rock. Their plan would have involved a half dozen Saturn 5 rockets carrying some really big bombs.
Every nineteen years the large asteroid Icarus swings by planet Earth, often coming within four million miles of the planet - mere spitting distance in astronomical terms. Icarus last passed by Earth in 1997. Before that, its previous approach was in June 1968.
In early 1967, MIT professor Paul Sandorff gave his class of graduate students a task: suppose that instead of passing harmlessly by, Icarus was instead going to hit the Earth. The nearly mile-wide chunk of rock would hit the planet with the force of 500,000 megatons - far larger than any major earthquake or volcanic eruption. Over 33,000 times the size of the bomb that destroyed Hiroshima. At a minimum, it would kill millions, flattening buildings and trees for a radius of hundreds of miles, and/or causing huge tidal waves that would wipe out coastal cities along thousands of miles of coastline. It could even lead to a global winter that could last years. Sandorff posed a simple challenge: "You have fifteen months. How do you stop Icarus?"
MIT was then deeply involved in the Apollo program. The guidance system for the Apollo spacecraft was developed there and the country’s foremost experts in aviation and space walked the school’s halls. Sandorff’s proposal was intended to teach his students how to improvise under pressure. Intense pressure.
The class immediately split up into several working groups based upon their areas of expertise: orbits and trajectories, boosters and propulsion, spacecraft, guidance and control, communications, economics and management, and nuclear payloads. They began evaluating the different options for defeating the killer rock.
Could they launch a big bomb to the asteroid and blow it to pieces? Quick calculations showed that pulverizing a rock the size of Icarus would require a 1,000 megaton bomb. No nuclear weapon even remotely that big had ever been theorized, let alone designed or built. There was no way it could be done in the short time available. Using a bunch of smaller bombs was also not possible because they would all have to be detonated at exactly the same time. Otherwise, one bomb would vaporize the others before they detonated.
The most desirable option would be to rendezvous with Icarus when it reached aphelion - the slowest point in its orbit - in November 1967. At that point it would be easiest to rendezvous with the slow-moving asteroid and easiest to exert force to change its orbit. But such a mission would have had to be launched immediately, in spring 1967, and so it was out of the question. The group quickly determined that no rockets could conceivably be readied before 1968 and this greatly constrained their options. A slow rendezvous, or even a soft landing, was therefore totally out of the question: Icarus would be moving too fast by 1968 for a spacecraft to reach it and then reverse direction for a rendezvous.
Fast Intercept
The only option was a fast intercept - fly out to Icarus and detonate a bomb near the surface to change its course.
The best way to get the most payload to Icarus was to launch two modified Saturn 5 rockets into orbit. These would rendezvous with an Apollo 'space tug' launched atop a Titan 3 rocket. The space tug would connect up the modified S-4B third stages from the Saturns. They would then be used to push a relatively large spacecraft out to Icarus where it would detonate a large nuclear weapon.
But there were many problems with this proposal. The Saturn S-4B third stages were not designed to carry fuel in orbit for more than six hours and would require extensive modification. A spacecraft would also have to be designed from scratch and built in under a year. Most importantly, the on-orbit operations required to link up the large craft were extensive and unproven. There would be no way to practice. This plan was rejected.
What the group decided to do was to take six Saturn 5 rockets then in production, and with only minimal modifications to their payloads, use them to carry smaller bombs to Icarus. The first launch would have to take place by April 1968, only a year away, and five more launches would have to follow at two-week increments.
The actual Icarus spacecraft would have consisted of an Apollo Service Module (SM) with a five-foot cylindrical extension known as the Payload Module (PM) at the top. Instead of a Command Module, the top of the stack would be a simple aluminum cone containing a few necessary systems. Although the Apollo Command Module and its associated guidance and control systems would have been useful, its weight was prohibitive and unnecessary. Weight had to be kept to a minimum in order to enable the rocket to carry the biggest possible bomb.
The Bomb
The Payload Module would have carried a 100 megaton bomb shaped as a cylinder roughly three feet in diameter and mounted horizontally along the diameter of the spacecraft. The bomb would weigh 40,000 pounds. One side of the PM would sport a phased array radar antenna for tracking and rendezvous with the Icarus asteroid.
The plan would have used an essentially unmodified Saturn 5 rocket. At the time, the first Saturn 5 test was not scheduled until November 1967 and the planners did not know if it would work. The only real difference with the Icarus Saturn 5 was the modified adapter shroud at the top of the S-4B third stage. On a standard Apollo mission to the moon these panels normally would have enclosed the Lunar Module, with the Service Module and Command Module mounted on top. But, by modifying them and using them to enclose the Service Module and its attached Payload Module, the designers were able to improve the aerodynamics of the rocket, and more importantly, eliminate aerodynamic loads and heating on the radar antenna. In profile, the stack would have looked much like the Skylab launch vehicle lofted by the Saturn 5 in 1974, although with minor differences.
The 100 megaton bomb would have been a challenge. At the time, the largest weapon ever developed for the American nuclear arsenal was a 25 megaton bomb. The Soviets had detonated a 58 megaton bomb earlier in the decade which could have easily been developed into a 100 megaton weapon. However, although the Soviets have not (and still have not) released the weight of this bomb - they were never as good at miniaturizing their bombs as the United States. It is likely that their 100 megaton bomb would have weighed far more than the 40,000 pound weight limit for Icarus. The United States would have had to build its own bomb to save the planet.
The Rockets
The Icarus plan required a total of nine Saturn 5 rockets. Three were test flights and the remaining six were interceptors. At the time, NASA planned on having only six Saturn V’s available by April 1968, so the production schedule would have to be dramatically increased. In addition, another launch pad would have to be built at Cape Kennedy. Launch Complex 39-C would have to be built, north of the two existing pads, in order to enable the high flight rate needed for the Saturn launches, all of which had to get off the ground in six weeks.
In addition to the nine Saturn 5s, the Icarus plan called for five Atlas Agena rockets carrying modified versions of the Mariner II deep space probe. Known as the Intercept Monitoring Satellite (IMS), these probes would be used to observe the actual detonation of the nuclear bombs when they reached the asteroid. Very little was known about how nuclear weapons would actually behave in space, let alone how the blast would affect an asteroid, and so the IMS was considered vital to the mission.
Interceptor One
In late February 1968, the first IMS spacecraft would lift off atop its Atlas Agena booster. It would linger in Earth orbit only a short time before being sent on its way to rendezvous with Icarus. A little over a month later, Interceptor One would thunder aloft on seven and a half million pounds of thrust. After a coast of one orbit or less, the S-4B stage would fire, boosting the Icarus spacecraft out of earth orbit and toward the asteroid. Soon after, the adapter shroud panels would peel back like the petals of a flower and the Icarus spacecraft with its 100 megaton bomb would separate. Its Service Propulsion System engine would fire, adding more velocity to the spacecraft.
After a coast of approximately 60 days, with several course corrections along the way, an optical sensor aboard the spacecraft would acquire Icarus only three hours before rendezvous. The spacecraft then entered the 'terminal phase.' Four minutes before rendezvous the radar system would begin to supply range information for making final correction maneuvers. At five seconds before impact, a fuzing radar would acquire the asteroid and arm the bomb. If all went as planned, detonation would occur within 100 feet of the surface of Icarus along the sunlit edge. The resulting explosion would either fragment or deflect the killer rock off its collision course.
The IMS spacecraft would monitor the detonation with its sensors, relaying the data back to earth so that the mission planners could refine their calculations. At the time that Interceptor One would reach Icarus, Interceptor Two would be right behind it by only a couple of weeks. And several more would be following right on Interceptor Two’s heels. Most of these would be accompanied by an IMS flight. But there was only time enough to launch five IMS flights.
The planners proposed six bombs for the mission. But they faced huge unknowns. The biggest problem was that nobody knew exactly what asteroids in general, and Icarus in particular, were made of. Was Icarus dense or light? Exactly how big was it? How was it shaped?
Furthermore, nobody was sure how a nuclear bomb would act in space or how it would affect Icarus. There was no way to get everything right on the first try and so several bombs would have to be detonated before planners even began to understand what they were doing. And if one or more of the bombs was a dud, or detonated too far from the asteroid, the mission controllers would have to improvise quickly as their thin stream of Interceptor spacecraft streaked heavenward to save the planet.
All this time, Icarus would be heading toward earth.
Conclusion
Project Icarus was only a study proposal. It was never formally adopted or even evaluated by the United States government. There was no independent evaluation of whether or not the proposal was even feasible. There might be some hidden flaw to the plan that was never identified. The MIT group did brief a number of people in the NASA on the proposal, however, and several of the MIT grads later went to work for the space agency.
There have been several unofficial asteroid defense proposals made by various aerospace experts in the ensuing 33 years, including some utilizing the now-defunct Soviet Energia booster. None of them were as carefully planned as the Icarus project. Today the issue of asteroid defense still has a high “giggle factor” associated with it — nobody in power in the American government takes the threat seriously.
But the Project Icarus model is probably worth dusting off and trying again either as an exercise for aerospace engineering students or for a government science and engineering advisory board. Although it would not be a valid contingency plan, at least it would help to identify our options in the event that something like this happened. If humanity suddenly realized that an asteroid was heading our way and we had only two years to respond, could we do something? Or would we simply be condemned to sit back and stare at the clock, waiting for the brief flash in the upper atmosphere signifying impending doom?
Dwayne A. Day is an independent space policy analyst living in Vienna, Virginia. He holds a Ph.D. from The George Washington University and has written numerous articles on civilian and military space policy and history. He was the primary editor for "Eye in the Sky: The Story of the CORONA Spy Satellites". He is a frequent contributor to SPACE ONLINE.
