Rockets can operate in a vacuum, false posts wrongly suggest they must 'push against' something

"In a vacuum, which is space without matter, thrusters found on so-called space rockets are not usable, they cannot push the rocket because they don't have anything to push against, end of story", wrote a Facebook user in a March 10, 2025 post in Croatian. Alongside the post, he shared a TikTok video of a syringe in a large transparent chamber, which ejects white smoke before starting to move.

The English narration in the video, as well as captions in Croatian, also claims that "rockets don't work in a vacuum" because there is "nothing to propel off if it's devoid of particles".

As the video shows a syringe releasing a gas, the narrator says: "As you can see here, the rocket begins to move only when the gases physically push off the chamber".

The Croatian post was published by an account dedicated to proving the Earth is flat, an unfounded theory that often ties together other conspiracy theories (archived here).

Belief in conspiracy theories in Croatia has been on the rise (archived here). According to a 2022 poll, some 5.4 per cent of Croats believe that the world is flat, while a further six per cent are unsure about the shape of the Earth (archived here).

The post was viewed more than 2,100 times, while the TikTok video it shared was viewed more than 51,000 times.

Some users indicated they believed the video proves rockets do not work in a vacuum. "This is all clear to all who don't find it difficult to think", said one Facebook user. "I've always wondered how can engines burn if there's no air in space, and how does it move if there's no air to push off something", said a commenter on TikTok.

However, an expert told AFP the apparent delay in the launch of the mock rocket in the footage was probably caused by a slow build-up of gases.

Since the 1930s, physicists have shown that rockets can operate in space, and have proven this in numerous experiments.

Image

A screenshot of the false Facebook post.

The TikTok video with Croatian subtitles seems to be based on another video from September 2023 posted by an English-speaking TikTok user who mostly posts videos claiming to prove the Earth is flat.

Using reverse video search, AFP found that the original clip used on TikTok was taken from the video "Rocket Launch in a Giant Vacuum Chamber", uploaded to The Action Lab YouTube channel in November 2023 (archived here).

The channel, run by chemical engineer James J. Orgill films experiments to explain the underlying science behind a range of topics "from biology to physics" (archived here).

The purpose of the "Rocket Launch in a Giant Vacuum Chamber" was, as Orgill explained in the video, to test one of his favorite claims: "Can rockets really fly in space?"

He used nitrocellulose -- in the form of so-called flash paper -- stuck in a plastic syringe sealed on one end (archived here). Nitrocellulose is highly flammable and does not need oxygen to burn, so Orgill ignited it in a vacuum by heating it with a laser. As more and more nitrocellulose was shown burning up, gases increased within the syringe and exited fast, propelling the mock rocket even though there was no air in the chamber.

Rockets operate in space

The principle of rocket propulsion has been understood for nearly a century now, with rocketry pioneer Robert Goddard launching his first rocket in 1926 (archived here).

It is based on Isaac Newton's laws of motion, specifically the third law (archived here). As astrophysicist and science educator Lana Ceraj told AFP on March 19, 2025, this happens due to the conservation of momentum (archived here).

"If you eject something on one end, the rocket will move in the opposite direction", Ceraj told AFP, invoking Newton's third law, as explained here (archived here).

Physicist Slobodan Danko Bosanac, president of the Adriatic Aerospace Association, also told AFP on March 25, 2025 that "rockets work in a vacuum". Bosanac explained that it is the ejection of burned-up gases from the rocket that moves it, and it does not push against anything.

"You can see this principle everywhere. Think of firemen holding a firehose - they need two firemen to hold it so it doesn't push them away", said Bosanac, stressing that the "pushing" comes from the mass and speed of the water spewing out of the hose, not from the water "pushing off" against something. "If you compare the density of the water with air, it might as well be vacuum", said Bosanac.

Goddard -- today considered the "father of rocketry" -- initially faced scepticism for his claim that rockets can operate in a vacuum, yet he proved the concept was true in an experiment in 1916 (archived here).

The NYT published an editorial mocking him for this "absurd notion" in 1920. Some 49 and a half years later, one day after Apollo 11 was launched, the newspaper published this correction: "Further investigation and experimentation have confirmed the findings of Isaac Newton in the 17th century and it is now definitely established that a rocket can function in a vacuum as well as in an atmosphere. The Times regrets the error." 

There were 2,849 orbital launches in 2024, and 2,895 in 2023 (archived here). 

As AFP previously explained in this fact-check, the International Space Station (ISS) has been photographed from Earth, often by amateur astronomers and space enthusiasts (archived here). 

Gradual build-up of gas

The main argument in the TikTok video is that the mock rocket in the clip does not move as soon as gases start exiting the syringe, misleadingly claiming that it only begins to move "when the gases physically push off the chamber".

This is an incorrect interpretation of the video, according to Bosanac.

"It didn't move right away because the fuel starts to burn up slowly", said Bosanac, noting that the same thing can be seen in all rocket launches today. "The rocket fires up, gases start going, but the rocket is not yet moving. The amount of burning is being slowly increased, and during this time, the thrust is not strong enough to move the rocket."

"The rocket only starts moving later, when the flow of gases from the engine is enough when the force is strong enough to move the rocket. Until then, the gas can come out, we can see it, but that only means that the engine has not reached full power", said Bosanac.

"In the video, you can see the gas slowly exiting, but the rocket is not moving", said Bosanac. "By the time the gas reached the wall, the burning increased enough that the gases exit fast enough to move the rocket".

In the Action Lab video, Orgill concludes that his experiment demonstrated how rockets can operate in a vacuum, also explaining the principle of Newton's laws that govern their movement. "Rockets not only work in a vacuum but they actually work better in a vacuum than at atmospheric pressure", he said.