Rocket Science is the Easy Part: How Government has Grounded Space Propulsion
“The Apollo moon landing was 42 years ago, and at the time many Americans thought it only a matter of time before they made their way to the next frontier. Is it simply that the problem of space travel is too difficult technologically? No–it’s that government policy has made it too difficult politically.”
Ever floated through space, 200 miles above the earth’s surface at a comfortable cruising speed of 17,500 miles per hour, while watching the earth whirl beneath you in a full revolution every 90 minutes?
Ever stood on the surface of the moon and gazed at the tiny blue-green ball where you had spent most of your life, nearly 240 thousand miles away?
Neither have I. To date, only a handful of super-wealthy individuals, paying enormous sums of money, have experienced the thrill of a trip into low earth orbit. And only a handful of stratospherically-subsidized astronauts have made it to the moon.
But if the history of capitalism tells us anything, it is that under economic freedom, yesterday’s impossibly expensive luxury can become today’s affordable commodity. Terrestrial flight was once available only to the wealthy but eventually its price came down enough that most Americans can now afford it–why not space flight? The wonderful world of space could become an affordable vacation destination. Wouldn’t you like to buy a ticket to the moon?
A New Resource Frontier
The possibilities of affordable space travel go well beyond recreation, as space is a literal and figurative gold-mine of mineral resources. For example, near earth asteroids are known to contain massive stores of platinum and other similarly valuable materials, which could potentially be mined and exploited for cheaper and more extensive application on earth (see John S. Lewis’s Mining the Sky: Untold Riches from the Asteroids, Comets, and Planets).
One company, Promethean Enterprises Inc., is already proposing to embark on the venture of space mining. As exotic and far-fetched as this sounds, space-mining could make a real difference in your life.
Consider a rare metal such as platinum, which is incredibly valuable–about $26,000 per pound (as of March 23)–not primarily for jewelry but for its vital industrial applications.
Platinum is an essential ingredient in advanced computer hard disks, cancer-treating drugs, sensors, catalytic converters, and catalysts for hydrogen fuel cells, to name just a few of its many uses. If the supply of platinum were more abundant and the price thereby reduced, the potential for further development (and cost reduction) of its many life-enhancing applications would be proportionately greater. Perhaps some new technology not currently conceived of— cost-prohibitive at platinum’s current price—would become feasible if the price were appreciably reduced due to an increase in supply.
All of this raises the question: Why have we not seen more progress toward mass-space travel? The Apollo moon landing was 42 years ago, and at the time many Americans thought it only a matter of time before they made their way to the next frontier. Is it simply that the problem of space travel is too difficult technologically? No–it’s that government policy has made it too difficult politically.
There are many aspects to this story, but here we will focus on one particularly vital aspect: rocket-propulsion technology, where spectacular innovations have been throttled by government interference.
To understand these innovations, we must first understand the basic challenge of rocket propulsion.
Rocket Propulsion: The Basics
The scientific and engineering challenges that have to be surmounted in order to produce a rocket capable of transporting a man safely from the surface of the earth into orbit, let alone to actually land on another celestial body such as the moon, are so immense that the term “rocket scientist” has become synonymous with genius in modern parlance. A major part of this challenge is generating enough force to propel a rocket, its cargo, and its fuel through the incredible resistance of the gravitational fields that exist near massive bodies such as the earth.
The need of a rocket to carry its own power source creates particularly difficult problems. To appreciate these problems, imagine you are driving your car along a steep, uphill trajectory across a distance on the order of the earth’s circumference or even greater, with no gas stations. You will, of course, need to bring along an auxiliary gas tank with reserves, which the car will have to pull. But the tank can only be so large, because every gallon of gas adds weight, and the engine can only generate so much power. At some point the weight of the fuel at the beginning of the trip will be too heavy for the car to pull, thereby rendering the trip impossible. Your car’s maximum carrying capacity will therefore determine how far it can go.
This is exactly the situation that rocket propulsion scientists must address in order to get things into space. It is why power density–power-to-weight ratio–is so crucial.
The most effective rocket will be light, powerful, with as concentrated a form of fuel as possible. The crucial technical term here is called “specific impulse.” For a rocket system capable of generating a sufficiently high thrust relative to its structural weight, specific impulse is the critical performance-limiting factor since it is a measure of the thrust that a given engine can get out of its fuel. In other words, if one rocket has twice the specific impulse of another, then that rocket can get twice as much thrust from the same amount of fuel as its inferior counterpart.
The rockets that have been used in the past for manned space exploration have employed chemical propulsion. The essential process here is fundamentally similar to burning oil-based fuel for transportation via plane, train, or automobile, in the sense that the energy source is the same: that is the energy released during certain chemical reactions. When we burn gasoline, we are creating a reaction between the hydrocarbon-based oil fuel and the oxygen in the atmosphere, releasing large amounts of energy as the bonds of the fuel and oxygen molecules are broken and their constituent atoms are rearranged into a configuration with a lower internal energy state, which in turn releases large amounts of energy in the form of heat to power an engine.
In chemical propulsion systems, the energy is obtained through, for example, chemical reactions of hydrogen and oxygen. As with cars and other conventional forms of transportation, energy initially stored in the propellant molecules as chemical potential energy is released and converted into thermal energy through the breaking and re-forming of chemical bonds in the process of combustion. The energized propellants then produce thrust as they are accelerated to extremely high speeds while passing through a nozzle at the bottom of a rocket that serves the same purpose as the pistons in a car engine: conversion of thermal energy to useful kinetic energy.
Creating chemical propulsion systems that could put rockets into space was an epic achievement. But for many conceivable space missions, they are not good enough. For various technical reasons, there is a modest upper bound on how far into space one can travel and/or how much payload one can carry using a chemical energy source.
The Promise of Nuclear Propulsion
This is where politics comes in. For as long as there has been a space program, a better way of propelling rockets has been known and suppressed. At the time of the moon landing, scientists at NASA and Los Alamos were already in the advanced stages of development of a very compelling new propulsion technology. This new technology is capable of achieving specific impulses rated at least as high as 900 to 1000 seconds — twice that of the best chemical engine, which achieves a specific impulse of only 460 seconds. It has the potential to render obsolete chemical propulsion systems, such as those used on the Saturn rockets that carried men to the moon.
Nor is this capacity merely theoretical — its development went all the way through a series of successful, large-scale tests. These tests demonstrated that the new propulsion system would have made a manned mission to Mars possible, whereas the feasibility of such a mission using chemical systems is questionable due to safety concerns. Politicians in Washington promptly decided to kill the program.
The cancellation of the program was actually related to its success: it would have opened the door for a manned Mars mission, and would have likely replaced chemical propulsion systems due to its technical superiority, but politicians and bureaucrats in charge had reasons not to want that. The welfare state was growing and consuming a larger proportion of the federal budget, and the space program was on the chopping block; and more importantly, it was becoming apparent by 1972 (when the program was cancelled) that an attempt to launch a rocket using this new technology would be met with intense public outcry and opposition. Why? Because the new propulsion system uses not chemical but nuclear energy to heat the propellants. It is called a nuclear thermal rocket, or NTR.
The two essential functions of a rocket propulsion system, energy extraction and thrust generation, are allocated differently in an NTR, which uses nuclear reactions for its source of energy, as opposed to chemical energy. The nuclear bonds holding protons and neutrons together in an atomic nucleus are much stronger than the chemical bonds that hold atoms together in a molecule. In terms of fundamental forces, nuclei are held together using the strong nuclear force, whereas chemical bonds employ the electromagnetic force. Nuclear reactions are capable of creating a much greater amount of energy at a much higher rate than chemical reactions, and nuclear propulsion systems can get much higher specific impulses without sacrificing thrust.
After cancellation of the original NTR system, named “NERVA” (Nuclear Engine for Rocket Vehicle Applications), the government has sporadically funded and defunded additional NTR research and development projects, none of which culminated in a NTR actually being launched. For instance, in the 1980s under President Reagan’s Strategic Defense Initiative Organization (SDIO), the Department of Defense initiated “Project Timberwind,” whose purpose was to develop an advanced fission reactor system that could be used to power a solid core NTR under the Space Thermal Nuclear Propulsion (STNP) program. This NTR would propel an ICBM interceptor for defense against a nuclear attack. Technologically the project was very successful but funding was cut in 1992, as the Cold War ended.
As of 2011, NASA is investigating the use of an NTR to power a manned Mars mission. The power density of a nuclear propulsion system is necessary for a manned Mars mission because it could get the crew there and back much faster than a chemical engine could. To understand this, consider again the car laden with fuel reserves, but with an engine twice as efficient. Such an engine would require half the fuel for the same trip, and would therefore cut its weight nearly in half. Lighter things can be accelerated uphill much more rapidly than heavy things when an equivalent force is applied, so you could get where you were going much faster.
In the context of a Mars mission this shorter trip time is not a matter of mere convenience, it is critical for safety reasons. When in space outside the protection of the earth’s atmosphere and magnetosphere, astronauts are exposed to dangerous cosmic radiation. The duration of this exposure must be minimized and the performance of a nuclear powered propulsion system is necessary to facilitate this.
A private firm, Ad Astra, is developing a different type of nuclear-powered propulsion system, also for the purpose of a manned Mars mission. In typical fashion the private enterprise is outdoing the government: preliminary testing indicates that Ad Astra’s amazing design — a variable specific impulse magnetoplasma rocket, or “VASIMR” — has the potential to achieve specific impulses as high as 4800 seconds — a full ten times higher than what can be achieved with the very best chemical engine!
A Mars mission would be a breeze with a propulsion system like this. Also, such a rocket might do the heavy lifting necessary to improve the feasibility and cost effectiveness of space mining, allowing men to tap into the abundant sources of wealth that exist nearby in our solar system. Imagine a 21st century “gold rush,” with finds that would make the “mother lode” look like a pittance. But don’t get too excited: “A private firm like Ad Astra can probably never muster the permissions and resources needed to make spacegoing reactors for use beyond Earth orbit.” Astra’s problem is not technological but political.
Enemies of Nuclear Propulsion
That last statement cannot be overemphasized. The public opposition to all things nuclear is such that even government agencies like NASA have to fight a steep uphill battle to send a modest nuclear reactor into space. This was the case for the small radioisotope thermoelectric generators (RTG) that were used to power the instrumentation of the unmanned Cassini deep space probe. Cassini’s 1997 launch generated vitriolic howls of protest from some segments of the public, and this reaction is illustrative of the political barriers faced by advocates of nuclear rockets.
The Cassini RTGs carry a total of about 72 pounds of plutonium. These reactors are used to power the instrumentation and control systems — the actual propulsion system is chemical, not nuclear. Despite its modest size and conventional propulsion system, one would think that the small unmanned vehicle was nothing less than an instrument of mass genocide based on the public reaction to it. On the eve of the launch, five members of Grandmothers for Peace were arrested for trespassing on the launch site while protesting the mission.
Protesters hurled pieces of debris across the barbed wire fence into the launch area. Among the swarms of protesters was Michio Kaku, a physics professor from City University of New York. Professor Kaku claimed that winds might blow plutonium onto Disney World and Universal Studios, evoking the emotionally-charged imagery of innocent children and families being showered with deadly radioactive material. The plutonium could poison the state’s orange groves, the professor warned, thereby collapsing the economy of central Florida. He predicted a possible body count as high as one million.
Johnathan Mark, author of the anti-Cassini website Stop Cassini Earth Flyby, which served as a sort of online war room for protesters seeking to stop the spacecraft’s 1999 flyby (an orbital “gravity assist” maneuver designed to minimize mission fuel requirements — which may not have been necessary if Cassini had employed a higher power density nuclear propulsion system) went even farther than professor Kaku. He maintained, even after Cassini’s safe and successful launch and flyby, that plutonium-powered space vehicles may eventually bring an end to all human life: “We’re living at a time when human beings don’t have to survive on this planet. We can go extinct like the dinosaurs.”
Were these dire warnings in proportion to the danger? Beverly Cook of the Energy Department explained that “[The RTG plutonium] cannot be exploded like a bomb.” She added that “It is an alpha emitter. Alpha radiation can be stopped by a piece of paper.”
The Cassini launch was not stopped, but the hysterical public resistance to it indicates the formidable political barriers that currently prevent the exciting and profitable advances in commercial access to space that would be made possible by the liberation of nuclear propulsion technology. The fear and antipathy that much of the public has for all things nuclear are a legacy of the anti-nuclear movement, which has repeatedly ignored the fact that in theory and in practice, generating power via nuclear fission is the safest form of practical power ever invented.
The anti-nuclear movement has been around for a long time and enjoys a great deal of success influencing pubic opinion. It has done so with apocalyptic imagery of mushroom clouds, nuclear winters and radiation poisoning, and with the help of the broader “green” movement and its anti-technology organizations such as Greenpeace who even oppose conventional energy sources such as coal and oil. The success of this smear campaign is such that the very word, “nuclear,” evokes fear in many people. Therefore when you read of a nuclear propulsion system, you may imagine a deadly monstrosity spewing radioactive materials into the atmosphere and poisoning millions of innocent, unsuspecting victims. But in fact, existing nuclear propulsion technologies do not work that way.
An NTR operates very similarly to a chemical rocket engine: propellants are heated and that thermal energy is converted into kinetic energy as the hot propellants are expanded through the mechanical nozzle. The difference is that in the case of NTRs it is a nuclear reactor that heats the propellant (usually hydrogen), rather than a chemical reaction (e.g. hydrogen/oxygen combustion). The radioactive material is not the propellant, but merely its energy source.
Ad Astra’s VASIMR uses nuclear power to ionize a noble gas propellant such as argon. The extremely high-energy plasma that results is then expanded through a magnetic nozzle. The nuclear reactor is necessitated by the power required to use such a system in a meaningful way, but again the radioactive material is not a source of propellants.
Protestations against the launch of a small plutonium reactor were way out of proportion to the risk. What about the risk from a bigger reactor? Over the years of NERVA and SNTP testing, not one nuclear-related injury occurred. The most serious accident during testing was a hydrogen explosion, in which two workers suffered foot and eardrum injuries. One of the reactors tested during the development of the NERVA system, the Phoebus, ran for 12 minutes at 4000 mega-Watts, which is approximately equal to the average power consumption of the entire country of New Zealand in 2009 according to their ministry of economic development. Phoebus was the most powerful nuclear reactor ever built. It injured no one.
The greatest danger associated with nuclear propulsion systems comes from the possibility of a catastrophic event during launch or re-entry, resulting in release of core materials into the atmosphere. It is unlikely that this material would be dispersed, however. Solid core reactor fuel elements are very robust. They are designed to withstand temperatures and high pressures up to 3500 Kelvin and 200 atmospheres, respectively, and are composed of very strong carbon composites or carbides. The fuel itself is usually a small percentage of Uranium 235 embedded inside this robust material. The robustness of these fuel elements was put to the test when a reactor designed for NERVA was purposely destroyed to simulate a fall from altitude, and no radioactive material was released. How is that for a safety record? Safe technology is the easy part; the barriers are political.
More Liberty for Space
To be clear, I am not advocating for government-funded space programs like NERVA or Cassini. I do not believe that one man’s desire to go to space should come at the expense of the man who doesn’t, and government control of the enterprise of space exploration has set it back many decades. The stunning preliminary result obtained by Ad Astra’s 4800 second VASIMR is a testament to the superiority of private ventures — even greater potential exists for nuclear powered propulsion systems. One more exotic design, the nuclear salt water rocket, is capable in theory of achieving specific impulses as high as half a million seconds while accelerating a 300 tonne spacecraft to more than 3% of the speed of light!
What we must advocate is for the liberation of private individuals and corporations to develop and use the best propulsion technologies possible. If we are going to obtain the spectacular benefits that are possible to us through accessing space, it will be through independent, commercial ventures — not government programs. And these ventures will need to be free of constraints that tether them to outdated and inefficient propulsion technologies. With all the exciting possibilities open to us, it is worth rethinking the assumptions that we may hold about the purported danger of nuclear rockets.
To reverse the damage of a longstanding smear campaign whose cultural influence has taken deep roots will be a formidable task, but a noble and worthwhile one.