Vorg and Shirna arrive on Inter Minor with their Miniscope, a futuristic peepshow containing alien species trapped in tiny moments of time. Unbeknownst to everybody, including himself, the 3rd Doctor lands the TARDIS inside the machine and it’s his attempts to discover his true whereabouts that really set the plot rolling along.
This is just about my favourite Jon Pertwee story, written by the late great Robert Holmes, the master of classic Who story telling.
The space suits seen in it are dispensed with in the first few minutes of the first episode once the travellers disembark from the cargo hold of the ship that brings them to the alien world. Story wise, I would assume that there must have been helmets worn with them although they’re never seen on screen. The suits are of a similar style to those worn by the Thals a few stories later in The Planet of the Daleks.