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Saab Global

A submarine in space

10 min read

It's not really as crazy as it sounds to compare these two, a submarine and a spacecraft. There are many areas where parallels can be drawn between the challenges of sea depths and weightlessness outside the Earth's atmosphere. Submarines and space crafts also have one basic thing in common; they place extreme demand on design and manufacturing. Building submarines is second to space industry.

This might look like a spacecraft, but it is actually the stern of a Blekinge-class submarine that is under construction. The exterior may look simple, but the inside houses complex systems and structures for operation of the submarine beneath the waves.

Saab' shipyard in Karlskrona is one of the most modern shipyards in the world, and one of very few with the capabilities to build submarines. The shipyard has been upgraded and modified in many areas in the last few years. The working environment has been improved to eliminate heavy and monotonous work. Digital tools have been introduced and together with industrial robots and NC machines, high-precision production is assured. All this has been done with the goal of being able to build a vessel that in terms of complexity and function, is the equal of a spacecraft. Let's compare some facts and look at how advanced these two systems really are and what is similar and what is not.

There are similarities as well as differences between submarines and space ships. But they share the same need of excellent engineering and skilled craftsmen to develop and build.

There are similarities as well as differences between submarines and space ships. But they share the same need of excellent engineering and skilled craftsmen to develop and build.

More on how we build submarines here

Power and speed

The Saturn V rocket, used for the manned Moon journeys, was the most powerful rocket ever built. It was 110 meters high, weighed about 3,000 tons and carried a capsule with a crew of three. A fully equipped Blekinge-class submarine (A26) will weigh around 2,000 tons, be 62 meters long and have a crew of up to 30. 

The Saturn V rocket was used for the manned moon journeys. It carried a crew of three astronauts and their equipment for a visit to the moon.

The Saturn V rocket features first-stage engines that produce a thrust of an incredible 34 million Newtons and are powered by 1,204,000 gallons of liquid oxygen and 770,000 gallons of fuel. This was consumed in just under 3 minutes. It took the rocket to an altitude of 61 km and a speed of 8,600 km/h.

Once outside, you’re all by yourself. Up there you’ll have plenty of light to guide you, but being submerged and then venture into pitch black water is something else I imagine.
Christer Fuglesang, Swedish astronaut

The Swedish submarines have Stirling engines with associated generators for charging the batteries, which can keep the submarine operational underwater for up to several weeks. For this, the Stirling engines also use liquid oxygen. When running on the surface, the batteries can be charged with more traditional diesel generators. However, this immediately reveals the submarine's location to any enemies.

Pressure and temperature

The deepest point in the world's oceans is in the Mariana Trench, in the Pacific Ocean between Japan and the Philippines. In January 1960, Swiss deep-sea researcher Jacques Piccard led an expedition that reached the seabed at a depth of 10,916 metres.

Even in the seemingly shallow depths of the Baltic Sea, the strain on an underwater craft is extreme. The deepest point here is the Landsort Deep in Stockholm's southern archipelago. The Swedish submarine rescue vessel URF, built by Kockums, reached the bottom at a depth of 444 meters in 2015.

During a rescue mission, the URF can hold the complete crew of a submarine and in a safe way bring them to the surface. It looks like the designers were playing a lot with Transformers as kids.

A submarine 200 metres below the surface issubjected to an external pressure of 20 bar. It is comparable to taking a weight of 2 tons on the palm of your hand. A craft in the vacuum of space is subjected to an internal pressure of 1 bar. Both of these place more stringent demands on the construction of hulls and equipment, but in slightly different ways.

For a submarine, there are approximately 10,000 pipe components that, in addition to high pressures, must also handle liquids and gases that are toxic, explosive or related to life support. There are, for example, pipes for fuel, liquid oxygen, fresh water and fresh air. All pipes are fully welded, pressure-tested and x-rayed – nothing may be left to chance.

If you took out the pipes and tubes from a submarines hull and look at them separately, you will better understand the challenge to build and install them.

In terms of temperature, there are also similarities between space and the depths of the sea, albeit on a slightly different scale. A submarine must be able to operate in both Arctic and tropical waters. In extreme conditions ranging from solar radiation to icy waters, there can be a temperature range of about 60 degrees Celsius. The surface of a spacecraft orbiting Earth may in turn have a variation between the sun and shadow sides of 300 degrees. In both cases, there are requirements on material selection and joining, as well as insulation and comfort for the crew.


In space, no one can hear you scream, is a popular movie quote (Alien, directed by Ridley Scott). That's because outside the Earth's atmosphere, there is no air that can propagate sound waves. In connection with the launch of the Saturn V rocket, however, at sea level a noise level of nearly 180 dB has been measured. The pain threshold is 120 dB.

Below sea level it is just the other way around, water propagates sound very well. With sensitive microphones, you can hear a submarine from many miles away. In order to perform without detection, a submarine must be designed in such a way as to minimize all noise and vibration. Hulls and propellers are designed to counteract turbulence and vibration; engines and equipment are mounted on rubber-suspended platforms; the crew is trained to work silently. 

All in all, Swedish submarines are particularly difficult to detect – in the brackish waters of the Baltic Sea as well as in the salty depths of the Pacific Ocean. They are quieter than a whisper, which is usually specified at 20 dB.

Submarines built in Sweden are renowned for their silent operation. During exercises, several navies around the world have failed in their search for the Gotland-class submarines.

Missions and external threats

Most submarines have military missions in the form of, among other things, reconnaissance and weapons operations. As a result, they are also exposed to external threats from enemies in the form of mines, torpedoes and depth charges, for example. Submarines manufactured by Kockums are designed to withstand underwater detonations. Crew compartments and systems are placed on rubber-suspended platforms that absorb and dampen the shockwaves from powerful explosions. Before delivery, all Swedish submarines are tested by being subjected to realistic and controlled detonations. With crew on board.

Apart from in sci-fi movies, there are no hostile threats to manned spacecraft. However, they can be exposed to space debris. Small particles traveling at supersonic speeds can cause major damage to a spacecraft's shell and crew members on spacewalks. (Outside the Earth's atmosphere there is no sound, but we still use the speed comparison as an illustration.)

The new Blekinge-class submarines will make it possible to carry out tasks similar to those on spacewalks. While underwater, divers and equipment can be sent out and brought in via a lock, called Multi Mission Portal™. Something that is completely new and thus far unique. This lock is functionally not much different from what is on the ISS space station. But it will be exposed to far greater pressure differences than that what exist in space.

Christer Fuglesang, Swedish astronaut and “spacewalker” compares the two systems and their challenges:

A26 divers
The Multi Mission Portal™ is a feature unique to the new Blekinge-class submarines.

"To me as an astronaut this is the most exciting moment! Prior to getting out for a spacewalk you get into the suit, checking it piece by piece, and everything, I mean everything, must run perfectly. And once outside, you’re all by yourself. Up there you’ll have plenty of light to guide you, but being submerged and then venture into pitch black water is something else I imagine. Fun fact, as we’re also talking about submarines here, is that we did practical training for space walks here on Earth in water prior to our space missions, to give an as space-like feeling as possible. Though we didn’t have a multi mission portal in the same sense the new A26 submarine will have. Again, all of this really craves the most out of the engineers involved and I’m really impressed with the concept", says Christer Fuglesang.

I see many similarities – and differences – to space tech in terms of challenges. And the size of a submarine really struck me. Those things are huge!
Christer Fuglesang
Astronaut Christer Fuglesang during one of his spacewalks. Photo: NASA / Public domain

Life support systems

Common to spacecraft and submarines is that advanced systems are required to keep the crew alive. The breathing air must maintain an even level of oxygen, carbon dioxide and nitrogen. The type of systems on both craft for reducing the carbon dioxide content from the exhaled air are basically the same.

"They’re both crafted with a priority of bring life-sustaining systems into a challenging, not to say deadly,  atmosphere which of course poses a lot of challenges for the people engineering. When visiting the Saab shipyard in Karlskrona I see many similarities – and differences – to space tech in terms of challenges. And the size of a submarine really struck me. Those things are huge! And of course so is the international space station", Fuglesang comments.

When it comes to water for drink, food and hygiene, you can use desalination on board the submarine and have virtually unlimited access to fresh water. For spacecraft, however, the amount of water is limited, and up to 80% of the water is recycled from, among other things, exhaled air, sewage and laundry.

Before a submarine leaves port, it bunkers food and supplies for its entire mission. Good and nutritious food is an important factor that affects how well a crew can perform their mission. Swedish submarines are known for their talented chefs and good food, which is appreciated during weeks at sea.

On board a submarine, the galley is a very tight compartment, where the chef is supposed to prepare the most delicious meals for the crew.

On board, for example, the international space station ISS, food is only served that is pre-packaged and can be eaten without the risk of airborne crumbs. Although there is variation, it may be a bit monotonous for the crew that can spend up to 6 months on board. The record in space is held by cosmonaut Valery Polyakov, who from 1994 to 1995 spent 438 days aboard the Russian Mir space station. We don't know what he thought of the food.

Design and manufacture

Development and manufacture of a new submarine class, such as the Blekinge-class, can take over 10 years. Fully comparable to spacecraft. Developers have to contend with challenges such as packing many complex systems into a confined space. Systems that production personnel will then have to build and assemble.

Production of both spacecraft and submarines relies on computer support and industrial robots. This means that every detail and subsystem is designed, described and defined in a 3D model. In conjunction with production, this information can then be used as input for welding robots, machining tools and as installation instructions.

The protective equipment used during sand blasting of submarine components makes you look like a creature from a sci-fi movie. But the purpose is to protect against abrasive particles.

Spacecraft are largely assembled in a cleanroom environment. A strand of hair can be devastating for strength and function. Submarine production is not quite so demanding, although for some system components, there are similar requirements. An unsealed valve or leaking cable bushing can quickly result in serious incidents at higher pressures below the surface.

Those who now visit Saab's submarine shipyard in Karlskrona will see a facility that is safe and efficient for both employees and the environment.

Major investments have been made here in recent years in the working environment, machinery and expertise. The shipyard area may be over 300 years old, and World Heritage listed, but it is presently the site of the world's most modern production facility for a whole new generation of submarines. Staffed by a new generation of talented and dedicated shipbuilders, building something second to spacecrafts: submarines.

A26 divers

Want to learn more?

Saab’s submarines are based on generations of evolutionary design. Building on more than 100 years’ experience, 7 submarine classes have been delivered across 3 continents.