Goofs

In the opening sequence of the jet flying, it is obviously different from the one that is taxiing after landing. The jet on the ground is painted brown and black under the nose, while the one previously flying was entirely white.

When Haydon's airplane flies over the base, he gives his altitude as 9,000 feet, but is obviously much lower than that.

"Lefty" Blake is right handed. (Though to be fair, this might be a deliberate joke, like calling a very tall man "Shorty.")

The Rocket/Plane could not be powered by jets. Jets breathe air. That's why rockets are used in "real" space travel.

Repeatedly, the characters state "there is no gravity in space" or "in space where we are beyond gravity..." Gravity is everywhere. There is no place in the Universe where gravity's effects are not felt.

Weightlessness exists outside of the spaceship. Earth's gravity exists inside the ship.

During the ship's ascent, the string pulling the model can clearly be seen in some shots, and the model bobbles up and down several times. Later, the strings holding up the model of the bomb are also plainly visible in some shots.

During the launch sequence, the exhaust smoke casts a shadow on the blue sky.

The people on the spaceship would not be able to just walk around in the low gravity environment. The would float freely about the cabin.

Fluids cannot be poured into a cup sitting on a flat surface below the bottle it is being poured from in space. It would just disperse in the air. And fluids can't be drunk from open cups in space. The fluid would simply float out of the cup.

When the bomb is first pushed away from the Rocket ship and is floating in space an obvious wire can be seen that the prop is suspended from.

At the briefing near the start of the film, both Commander Haydon and Professor Blandford use the word "schedule", pronouncing it the American way, with an "sk" sound. Since both men are British and the film is set in Britain, they should naturally have used the British "sh" pronunciation of the word.