We have been fantasizing about an alternative to “bell-shaped” space engines for 70 years. Now we are close to having a

Since the beginning of the space age, engineers have banged their heads over and over again against the same problem: the technical impossibility of building an engine that would be both efficient in the atmosphere and in a vacuum.

So much so, that we only managed to fix it by mounting two-stage rockets: one with nozzles for the atmospheric phase and another optimized for outer space. The “middle” thing is a matter of brute force.

Is it inefficient? Yes Do we have another option? Not at the beginning.

“In principle”? Well yes, because for more than 70 years there has been no shortage of experts who thought that the solution lay in something very simple: form. As Darren Orf pointed out a few months ago, “whether it’s the German V-2 rocket, NASA’s legendary Saturn V or SpaceX’s Falcon Heavy, all rocket engines share a common attribute: their exhaust nozzles are bell-shaped. “. But what if they didn’t have it?

Essentially, the function of a nozzle is to direct the flow of gases in the direction that interests us. It seems obvious, but it’s key. Above all, because the mixture of propellants at very high temperatures generates a lot of force, but the movement of the gases is (to a large extent) random. The conventional nozzle has proven very effective in converting all that randomness into a “jet” efficient enough to put the rocket into the air. The question is, then, how do we do without it.

That’s where the ‘aerospike’ comes in: a type of engine that “would maintain its aerodynamic efficiency over a wide range of altitudes” by changing precisely the shape in question. That is, the gases are launched “along the outer face of a wedge-shaped solid volume” (the spike) and the result would also efficiently reduce this randomness.

It sounds good, very good. At the end of the day, all of this that we have explained would translate into being able to reduce the total weight of the ship and, in the process, increase the useful load. The problem? That doesn’t work.

The eternal promise of space exploration. It is true that NASA tested a prototype in the 1990s, but the result has always been the same: the different companies or agencies that have opted for the aerospike have ended up signing checks that they have not been able to pay.

And what has changed that we are talking about this? Germany has passed. In April, Berlin awarded a military contract to Polaris, a start-up dedicated to this type of technology, to investigate the possibilities of using such an engine in a space plane. The news now is that Polaris has just completed the first series of test flights of one of the key prototypes.

We are talking about 15 tests between the end of August and the beginning of September. And it is true that the MIRA-light (which is what the prototype is called) measures only two and a half meters long and is very far from what we are looking for; but the sensations are good and that has caught the attention of many people.

Does that mean we will (finally!) have an aerospike engine? At this point in the game, the most reasonable thing is to think that no, that there is a lot of work ahead and that, even in the best of all possible worlds, its effects are not going to be immediate. However, innovation in the world of engines is excellent news (and even more so if the tests go well)


Merlin and Raptor: the highly reusable rocket engines that made SpaceX a space benchmark

Size issues. But by launching reusable rockets, having smaller engines is part of success. That was Elon Musk and SpaceX’s strategy, from the already veteran Merlin engines to the newer Raptor engines, which are expected to be used in the Starship Super Heavy, the ship that aims to reach Mars.

The first test of the Merlin 1A took place in 2006. An engine made of polymers reinforced with carbon fibers which in its first test failed miserably. A year later, it was used in Falcon 1, kicking off the first private launch of liquid-fueled vehicles to orbit the Earth. Since then, these Merlin engines have accompanied SpaceX in its conquest of space.

Elon Musk believes that the launch of a modern rocket is based on use a large number of motors at the same time, controlled at the same time, which allow the thrust to be varied in real time and with a key advantage: reliability. Because if one of the engines fails, the rest stays.

From the failed “Merlin 1A” to the new Falcon 9 “empty Merlin 1D”

Merlin engines are Designed for recovery and rescue at sea. These reusable engines were designed by SpaceX for use in the Falcon 1, Falcon 9, and Falcon Heavy.

It cannot be said that the first versions of Merlin engines are successful. The Merlin 1A was only used once on the Falcon 1. While the Merlin 1B, an improved version with a 1,860 kW turbine was to be used on the Falcon 9 Heavy, but its use was discontinued at profit of the Merlin 1C.

At the end of 2007, SpaceX continued its engine development with the Merlin 1C version. At this point it had a regeneratively cooled nozzle and combustion chamber. But it was not until 2011 that the version of the engine that served as the basis was finally obtained of the main versions of Space X.

1D Merlin engine.

The Merlin 1D was first used in 2013 and in 2017 the company celebrated having produced the 400th in this series. Then, these Merlin engines had been started more than 440 times on orbital missions and more than 5,600 times in tests and launches, thus reaffirming its value as a reusable engine. Together, these engines have been running for over 400,000 seconds, enough power to launch 3,600 tonnes into space, which equates to the weight of 7 ISS.

Use of Merlin engines RP-1, a petroleum derivative similar to kerosene and liquid oxygen as materials to produce rocket propulsion.

The Falcon 9 takes its name from the nine Merlin engines used.

According to the technical data of the Falcon 9, which takes its name from the nine Merlin engines used, these engines have a thrust of 650 kN, a Specific vacuum pulse 311s and a 63.5 ton rise in sea level. Design details for the Merlin 1D engine were not openly shared by SpaceX, but the company said the Falcon 9 was « the world’s most powerful operational rocket. , by a factor of two ”.

In November 2013, Elon Musk explained that the engine was running at 85% of its potential and that these numbers could be improved. The result came with the Falcon 9 v1.1, which in addition to changing the placement of the nine engines, has evolved into the Merlin 1D empty.

Falcon 9 v1.0 (left) vs Falcon 9 v1.1 with Merlin 1D Vacuum engines (right).

The latest Merlin 1D vacuum motors have a pushing capacity 80 tons, with a specific impulse of 348 seconds. After several years of use, according to daily astronaut data, these Merlin engines are 99.9% reliable and can be reused for about 10 flights. However, last March, one of the Merlin 1D engines had problems. The first since 2012. For this reason, SpaceX and NASA have decided to launch an investigation.

The cost of these 1D Merlin is less than a million dollars. A very economical quantity which corresponds to the objective of putting many rockets into orbit. However, Elon Musk’s plans go further (literally) and for his larger rockets they have a different set of engines.

Raptor, the new generation of SpaceX engines

With a height of 68 meters and up to 3,300 tons of fuel, the Super Heavy is billed as a rocket quite far from the Falcon 9. And for this reason, it also has another series of engines, the Raptors. While the Starship plans to integrate seven, the Super Heavy will add 37 Raptor engines, powered by methane and oxygen, in an attempt to achieve its ambitious goal of reaching Mars.

At 90%, the Raptor engines are already able to deliver twice the horsepower of the Merlin 1D, although the cost is also double. As described by EveryDay Astronaut, the raptor engine has a boost higher than any other rocket except the space shuttle, with the additional cost of 70 times less in power.

The Raptor engine is intended for « the next generation of SpaceX launchers, designed for the exploration and colonization of Mars, » said Elon Musk in 2013 when development of this new series of engines began. Slightly larger, but also more powerful and reusable.

The design requires at least 170 metric tons of force. The engine reached a chamber pressure of 172 mT and 257 bar with a hot propellant, which means 10% to 20% more with deep cryonics.

– Elon Musk (@elonmusk) 7 février 2019

During testing at the Texas site, the Raptor engine achieved a 172 ton boost, although still under 200 tons, which Elon Musk says is enough to energize the Starship or Super Heavy.

Size comparison. Via Reddit

“There is no other rocket engine capable of producing as much energy from methane and liquid oxygen as the Raptor engine,” said Tim Dodd, expert behind the chain for Everyday Astronaut. “And the idea is to make it more reusable. Something that will definitely help their business strategy if they can make it fly over and over again. According to SpaceX, these Raptor engines are designed to be reused up to 1000 times.

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Source: Engadget