Project Orion: why the first nuclear explosion was never launched into space

Will explode - what is it?

The idea behind Project Orion was pretty simple, at least conceptually:

Use atomic bombs to create thrust that could lift a ship into space.As part of the project, General Atomics decided to develop the concept proposed in a 1955 paper by Stanislav Ulam and Cornelius Everett. 

It was they who first proposed the idea of ​​Orion.Their concept was as follows: the explosions of hydrogen bombs ejected from the ship caused the evaporation of disks ejected after the bombs. Expanding plasma and  propelled the ship. Ted Taylor, one of the leading American developers of nuclear and thermonuclear charges, developed this project further. In the winter of 1957, he was working at General Atomics. The Anglo-American physicist Freeman Dyson, who worked at Princeton, agreed to continue the development of Orion with him.

Source: US Air Force, TED / YouTube.

Of course, the explosion of one bomb is not enough tofully launch the ship into space. It would take a series of atomic explosions in rapid succession to keep the ship from falling to the ground. That is why the atomic starship was called an explosion.

Orion spacecraft engine - nuclear-pulse, inthe basis of his work is the use of the energy of a nuclear explosion. From the spacecraft in the direction opposite to the flight, a nuclear charge of a small equivalent is ejected and detonated at a relatively small distance from the spacecraft (up to 100 m). The charge is designed in such a way that most of the explosion products in the form of an expanding plasma front moving at relativistic velocities are directed to the tail of the spacecraft: where a massive reflecting plate takes on the impulse and transfers it to the ship through a system of shock absorbers (or without them - for unmanned versions). The reflective plate is protected from damage by light flash, gamma rays and high-temperature plasma by an ablative graphite lubricant coating, renewable after each blast

Source: US Air Force, TED / YouTube.

A total of Orion and Super class shipsOrion required about 800 bombs the size of a small compact car, which exploded underneath the ship at about one per second to get it into orbit.

The speed that all these atomicbombs would be two to three times faster than conventional missiles. By design, once the spacecraft reaches the vacuum of space, the speed will be stored as momentum.

Interstellar flights

Extremely high traction andspecific impulse of nuclear impulse drives allowed engineers to assume the possibility of their use not only in interplanetary, but also in interstellar flights. Thus, Freeman Dyson calculated that a ship powered by megaton thermonuclear charges with a reaction product flow rate of the order of 3000–30,000 km / s would be able to reach a maximum speed of the order of 750–15,000 km / s, that is, up to 5% of the speed of light.

In the project's boundariesOrion scientists have developed two fundamental modifications of the starship:Energy Limited andMomentum Limited.

Energy Limited Orion Starship project was a structure with a diameterreflecting plate about 20 km. These are necessary so that the plate has time to cool down between explosions without consuming ablative materials or other means of cooling. 

The total mass of the ship, according to calculations,amounted to 40 million tons, of which more than 30 million tons accounted for "fuel" - megaton charges. Of the remaining 10 million tons, five accounted for the weight of the slab, and five for the weight of the structure itself and the payload.

Exploding astern on a megaton charge every100 s (such a long period of time was calculated so that the plate had time to cool down due to radiation), the ship could accelerate to 0.33% of the speed of light (1,000 km / s) in about 100 years. The flight to Alpha Centauri, which was supposed to be the goal of the project, would have taken about 1,300 years. The huge capacity of the ship made it possible to build a real "ship of generations" on its basis, capable of supporting the reproducing human population in an artificial environment during the entire flight.

The Momentum Limited Orion Starship project was distinguished by more modest to scale.Its main difference is ablative cooling of the reflective plate by spraying graphite lubricant on it in the intervals between explosions. Although this significantly reduced the payload (due to the need to consume thousands of tons of graphite), the ship turned out to be much more compact and faster.

Obvious problems with the Orion project

As you know, in the 1960s, the authorities spared no expense in the technological race between the USA and the USSR. However, money could not fix one important problem: radiation.

Treatment of radioactive fallout from one nuclear power plantbombs is a very difficult engineering task. When it comes to eliminating the consequences of the explosion of hundreds of such bombs at an altitude of tens of kilometers, the task can be considered impossible. 

Another serious problem was the inability of the crew to work on board the starship. During operation, he would have been exposed to up to 700 rads of radiation each time the bomb exploded under Orion. 

For comparison - acute radiation sicknessdevelops as a result of relatively uniform irradiation at a dose of more than 1 Gy (100 rad) over a short period of time. Doses up to 1 Gy (100 rad) cause relatively mild changes that can be considered a pre-disease state. Doses over 1 Gy cause bone marrow or intestinal forms of acute radiation sickness of varying severity, which depend mainly on damage to the hematopoietic organs. Single exposure doses over 10 Gy are considered absolutely lethal.

In such conditions, astronauts could not even livebefore entering orbit. Of course, the Orion project team hoped that somewhere in the future a "clean" atomic bomb could be created that would not irradiate everything in its path. As you know, hopes were not justified.

We should not forget that in 1963 the USSR andThe United States signed the Nuclear Test Ban Treaty between the two countries. In fact, this led to the cessation of research in the field of ground-based nuclear pulse engines.

Project tests

It should be noted that the Orion project did not remainonly on paper. Despite the fact that the project was not implemented, scientists carried out not only calculations, but also full-scale tests. These were flight tests of models propelled by chemical explosives. The models were called put-puts, or hot rods. Several models were destroyed, but one hundred-meter flight in November 1959 was still not considered successful. Tests have shown that impulse flight is a real prospect. The test model landed intact by parachute and is now in the collection of the Smithsonian National Air and Space Museum.

Could Project Orion ever come back?

Today, the opportunity to see Saturn's rings in person or even set foot on Pluto keeps Project Orion in the imagination of many scientists and engineers.

Now, within the framework of the NASA program, Artemis planssend a crew to the moon, and Elon Musk has long been going to colonize Mars. In addition, there has been an increased interest in asteroid mining in the past few years. Ultimately, radiation exposure will ultimately have to be addressed if humans ever hope to exist outside of Earth.

Analysts are confident that if scientists can solve the radiation problem, then the Orion project could be revived.

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