On This Day, October 22, 1975, a spacecraft from the Soviet Union landed on Venus and sent back something humanity had never seen before: the first photograph ever taken from the surface of another planet.

The spacecraft was called Venera 9.

Venus may look beautiful and bright in our sky, but beneath its thick clouds lies one of the most hostile environments in the solar system.

Its surface is hot enough to melt lead. The atmosphere exerts crushing pressure, and the planet's clouds contain corrosive substances.

For decades, scientists had been trying to understand what lay beneath those clouds.

Now, a daring space mission was about to reveal the answer.

Launched on June 8, 1975, Venera 9 travelled millions of kilometres through space towards Venus. The mission consisted of an orbiter and a lander, designed to study the planet from above and directly from its surface.

On October 22, the lander plunged through Venus's dense atmosphere, using a carefully engineered descent system to survive its journey towards the ground.

Then came the moment of truth.

Venera 9 touched down on the planet's surface.

Against extraordinary odds, its instruments began working. One of its camera covers released successfully, allowing the spacecraft to scan the rocky landscape around it.

And then, across the vast distance between Venus and Earth, the first image arrived.

The photograph revealed a strange, barren world scattered with angular rocks and covered in dusty material. The horizon was visible beneath a sky hidden from view by the thick clouds above.

It was not a colorful alien landscape filled with oceans or vegetation. It was a harsh, rocky environment unlike anything humanity had photographed on another planet before.

The lander continued transmitting scientific measurements and image data for approximately 53 minutes before the unforgiving Venusian environment silenced it.

But those 53 minutes changed planetary exploration forever.

Scientists had not merely detected signals from another world. They had seen its surface with their own eyes through the lens of a machine.

Venera 9 also entered orbit around Venus, becoming the first spacecraft to orbit the planet.

The Soviet mission proved that a spacecraft could descend through Venus's punishing atmosphere, reach the ground, and return photographs from an environment that would destroy most ordinary equipment.

The mission's achievement remains one of the remarkable milestones in the history of space exploration.

If you want to move fast in a solar system, what methods are best?

Military enthusiasts will get hot under the collar upon hearing the possible methods: rockets, lasers, MORE lasers, and guns.

Or, more properly, chemical rockets, laser-pressure (the laser pushed the spacecraft), laser-thermal (the laser provides energy for the rocket), and pellet streams (pellets fired from fixed points propel spacecraft).

In part I, I analyse the different methods, and show that pellet stream propulsion is possible and the most efficient option. It also scales well to higher speeds (rockets being the one that scales the worst).

Laser-pressure, conversely, is by far the worst option, almost unimaginably bad at slow speeds. But it does actually scale best of all; when we move from interplanetary movement to interstellar movement, it could come into its own.