Reaction Engines Passed a Major Milestone, but How Does It Compare to SpaceX?

Reaction Engines completed a successful test of the pre-cooler of its SABRE engine. (Image: YouTube/Screenshot)

U.K.-based aerospace manufacturer Reaction Engines has announced the successful test of its precooler at airflow temperature conditions and confirmed that it can withstand speeds of Mach 5, which is five times the speed of sound. This is a huge milestone toward the development of the SABRE engine, which will revolutionize how we access space, as well as the future of hypersonic spaceflight. Reaction Engines will be using the SABRE engine in its proposed Skylon spaceplane.

SABRE engine

The SABRE (Synergistic Air-Breathing Rocket Engine) engine can operate in two modes — aircraft and rocket. In the aircraft mode, the engine uses oxygen from the atmosphere, while in the rocket mode, it burns an onboard oxidizer together with liquid hydrogen. Today’s jet engines are capable of speeds of up to Mach 3. The SABRE reportedly clocks in a speed of Mach 5.4 in “air-breathing” mode and Mach 25 in rocket mode.

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An air-breathing engine is propelled by hot exhaust gases formed from the air that is forced into the engine. “Reaction Engines’ Sabre design uses a system of pipes filled with helium. The air passes through these pipes and the helium helps remove any heat and the oxygen is carried to the engine. Once in space, the engine is capable of switching into rocket mode. This means the craft can travel in orbit for around 36 hours and [be] used to launch satellites,” according to the Daily Mail.

Current generation aviation engines need to carry liquid oxygen tanks when traveling at speeds in excess of 1,900 mph, as they can’t “breathe” oxygen. The SABRE engine uses atmospheric air up to an altitude of 15.5 miles, after which it switches to rocket mode. Because of this, a vehicle that uses the SABRE engine doesn’t need to carry as much oxygen, which will make it lighter and cheaper. The recent precooler test is critical since it takes the engine one step closer to demonstrating its feasibility.

“During the latest series of tests, Reaction Engines’ unique precooler successfully quenched airflow temperatures in excess of 1,000°C (~1,800°F) in less than 1/20th of a second. The tests demonstrated the pre-cooler’s ability to successfully cool airflow at speeds significantly in excess of the operational limit of any jet-engine powered aircraft in history. Mach 5 is more than twice as fast as the cruising speed of Concorde and over 50 percent faster than the SR-71 Blackbird aircraft — the world’s fastest jet-engine powered aircraft,” according to a post by Reaction Engines.

The pre-cooler successfully quenched airflow temperatures in excess of 1,000°C (~1,800°F). (Image: YouTube / Screenshot)

In addition to the precooler, two other core elements of the SABRE engine — the thrust chamber and the engine core — will be demonstrated independently over a period of four years. The core part of the engine has just completed its preliminary design review, gaining the approval of the experts at the European Space Agency (ESA). Once the engine is developed, it will allow for the manufacture of spaceplanes that are capable of horizontal take-off and landing (HOTOL).

“One of the great advantages of the Sabre propulsion concept is that it is totally modular from both design and operational perspectives… Therefore it is possible to subject each of the key components of the engine to rigorous ground testing, which fully mimics the operational conditions the engine will face up to Mach 5 flight at 25km altitude,” Richard Varvill, CTO of Reaction Engines, said to The Manufacturer. ESA has invested US$11 million into the project, with the UK Space Agency (UKSA) investing US$64 million.

Skylon is a spaceplane capable of horizontal take-off. (Image: YouTube / Screenshot)

Skylon, Falcon 9, and Falcon Heavy

Space exploration has been an expensive affair for much of history, because the launch vehicles used could only be deployed once. After these vehicles delivered the payload into space, the rockets either burned up in the atmosphere or would crash into the ocean. Two solutions have emerged to solve this problem. The first is Reaction Engines’ Skylon spaceplane, which has the ability to take off horizontally and is powered by its SABRE engine. The second option is SpaceX’s Falcon 9 and Falcon Heavy, whose rockets are capable of returning to base. While both have their own pros and cons, SpaceX does have an advantage when it comes to the financial aspects of spaceflight.


The Skylon will be 85 meters long. It is expected to have a dry mass of 52 tons and a take-off mass of 325 tons. Dry mass refers to the total mass of a spacecraft without accounting for fuel, while take-off mass refers to the final mass of the craft with everything contained in it. The spaceplane is estimated to cost a mind-numbing £1,200 million (US$1,540 million), with refuel costs to be around £820,000 (US$1.05 million). On the plus side, it can potentially be used for 200 flights. The cost per kg of the payload is calculated to be in the range of £1,050 to £1,950 (US$13,48 to US$2503).

Falcon 9

When compared to Skylon, the Falcon 9 is smaller at 68 meters in length. It has a lower dry mass of 25 tons, but a higher take-off mass of 506 tons. The Falcon 9’s payload capacity comes slightly lower at 13 tons. The cost of a Falcon 9 is just UK£40 million (US$51 million), which is almost 30 times cheaper than the Skylon. Refuel costs are pegged at UK£130,000 (US$167,000), just 16 percent of Skylon’s cost. It can be reused for 10 flights, which is far less than Skylon’s figure of 200. The cost per kg of the payload will be around UK£400 to UK£3,100 (US$513 to US$3,979) depending on whether the rockets are fully reusable or expendable.  

Falcon Heavy

The Falcon Heavy is similar to the Falcon 9 in terms of length at 68 meters. It has a higher dry mass at 66 tons and a take-off mass at 1,394 tons. The payload capacity is almost double that of Falcon 9 and Skylon at 28 tons. It is 50 percent costlier than Falcon 9 at £60 million (US$77 million), but 20 times cheaper than Skylon. Refuel costs of £350,000 (US$449,185) are more than double that of Falcon 9, but still less than 50 percent of Skylon’s numbers. It can be reused for 10 flights just like the Falcon 9. When it comes to cost per kg of payload, it offers the cheapest rates at around £200 to £1,150 (US$257 to US$1,476) based on whether the rockets are fully reusable or expendable.

Falcon Heavy is a cheaper option than Skylon and is already in use.
Falcon Heavy is a cheaper option than Skylon and is already in use. (Image:via Wikimedia Commons)

On the price front, SpaceX options come out as the winner, as their vehicle costs, refueling costs, and cost per kilogram of the payload are cheaper than what Skylon has to offer. To top it off, SpaceX is already active, using the Falcon rockets to launch satellites into space. As Skylon enters further development over the next few years, SpaceX will optimize the Falcon rockets and make them so much cheaper and more efficient than Reaction Engines might not be in a position to compete with the U.S. company.  

But no matter whoever comes out on the top of this battle between rockets and spaceplanes, it is ultimately the human race and space exploration that will be the winners. SpaceX founder Elon Musk has set a target of 2028 for setting up humanity’s first colony on Mars. NASA is targeting 2028 to 2030 as the year when it will have astronauts on the red planet. Once we set up a colony on Mars, it will become easier to set up camps on other planets and moons over the following decades. If faster-than-light travel becomes possible within this time period, we might end up exploring even planets outside the solar system before this century ends.

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