There’s so much about spaceflight history that you won’t easily realize until you dig deeper.

That’s especially true when it comes to experiments that accompanied a failed space probe.

My recent posts have lamented the few lunar rovers around, and how work on rovers that could visit very inhospitable worlds is continuing.

But I want to talk a bit, in this brief article, about PROP-M.

It’s a name we rarely hear. I certainly didn’t know about it until I started to research the BepiColombo Mercury probe and a cancelled lander/rover element originally planned.

PROP-M was part of the first successful successful touchdown on the Martian surface. No, that officially wasn’t Viking 1. It was a Soviet probe–Mars 3.

Mars 3
A Soviet Academy of Sciences photo of what Mars 3 looked like.

Mars 3 was launched in May, 1971, and made a landing later that December–5 years before the American lander arrived in 1976.

But “successful” and “operational” are two separate matters. While Mars 3 made a landing, something failed on it about 15 seconds after touchdown.

The probe transmitted some garbage image data and then fell silent, never to be heard from again.

If Mars 3 had become the first fully operational lander on Mars, as Viking 1 became, we may have seen PROP-M in action.

As rovers go, PROP-M was the most diminutive one ever made.

It was barely ten pounds (4.4 kg). It had only a couple of instruments, one to measure soil density and another to assess the soil strength.

The rover had no independent means of communication or power. It was connected to the lander by a long power and data umbilical.

How the little thing would’ve moved about was gold.


With no wheels, PROP-M used a rotating set of skis, ambling ahead, incapable of a left or right motion.

Here’s an old Soviet film depicting Mars 3 in its initial operation, including the rover deployment and locomotion.

Mars 3 might have been found by a Russian space enthusiast back in 2013, thanks to images from the Mars Reconnaissance Orbiter’s HIRISE camera. He shared his findings with NASA, which supported his findings.

So, props to PROP-M, the rover that never was.