Dinosaurs, penguins and Baby Yoda: What are zero-g indicators?

If you watched the launch of the Crew-3 mission to the International Space Station at the end of October, you might have noticed an additional occupant inside the spacecraft alongside the four astronauts.

It was a sequined toy turtle, chosen in recognition of two of the astronauts being the first members of their astronaut class (nicknamed ‘the Turtles’) to fly in space. It is a zero-g indicator.

Crew-3’s zero-g indicator floats inside their spacecraft | Credit: NASA/SpaceX

Zero-g indicators serve no real technical purpose. Usually toys, they instead can act as ‘mascots’, good luck charms of sorts, and are a fun way for astronauts and cosmonauts to get their families involved in their missions.

As their name suggests, however, their primary purpose is to provide a visual indication to the crew that they have reached weightlessness. Tethered to a part of the spacecraft’s cabin by a piece of chord, they start to float when the rocket’s main engine cuts off.

The history of zero-g indicators can be traced back to the very first crewed spaceflight. When Yuri Gagarin became the first human in space in 1961, he had with him in his Vostok spacecraft a small doll.

In the US, they were first adopted during the Space Shuttle programme, which began in 1981.

The most recognisable zero-g indicator is arguably one of the most recent. In May 2020 SpaceX and NASA launched the Demo-2 mission to the International Space Station with Bob Behnken and Doug Hurley onboard. It was the first launch of American astronauts from American soil since the last Space Shuttle mission in 2011, and it understandably garnered a lot of attention.

Tremor first appeared during a live broadcast not long after Demo-2’s launch

Alongside Behnken and Hurley, there was one more occupant of the Crew Dragon spacecraft – a sequined dinosaur named Tremor.

Both Behnken and Hurley have sons who are interested in dinosaurs. Prior to the mission, every toy dinosaur in both of their households was rounded up, and Tremor (who belongs to Hurley’s son) wound up being the one they chose to go into space with their fathers.

In recent times, zero-g indicators have prompted surges in sales of the same toy on Earth.

For instance, on 2 March 2019 SpaceX and NASA launched Demo-1, an uncrewed test flight to the International Space Station. Onboard was a test dummy called Ripley, and also a zero-g indicator named ‘Little Earth’.

Zero-g indicators ‘Tremor’ and ‘Little Earth’ float in front of a spacesuit being prepared for an EVA | Credit: NASA

The makers of Little Earth, a company called Celestial Buddies, actually had to put out a statement in response to the subsequent increase in demand.

We at Celestial Buddies had no advance information about Earth’s participation in the launch, although a sudden flurry of orders for Earth in the 48 hours prior to lift off had us wonder if something was afoot.

By the time the rocket left Cape [Canaveral], however, our entire inventory of Earth had been completely sold out, with scores of orders still unfilled.

We apologise for our current lack of Earths… but we have never had one of our products launched into space before, and we were taken totally by surprise.

Celestial Buddies

Other recent zero-g indicators include a Baby Yoda from the TV show The Mandalorian chosen by the Crew-1 astronauts in November 2020, and a penguin called Guin Guin chosen by the Crew-2 astronauts in April 2021.

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