All Lego parts have two identifying numbers. An Element ID and a Design ID. Rebrickable as a great explanation, an excerpt of it is below:

The Element ID is a unique, LEGO assigned part number, for a certain color, and/or a certain print if it has one. The most common LEGO part, the "Brick 2 x 4", is known in 59 different colors, and for each color there is at least one LEGO Element ID. Note that LEGO Element ID's have 6 or 7 digits. For example, the 2 x 4 Brick is known as a "3001" (Design ID, see below). A Black 3001 has Element ID 300126, and a Brown 3001 has Element ID 4124052. Note that Element IDs can be the Design ID followed by a color code (color code 26 in case of the Black 3001), but usually Element IDs are seemingly random numbers.

Design IDs

Below is a list of each of the design ID's for the parts that make up a Lego Classic Space man. Each link will direct you to the Lego "Pick a Brick" service where you will be shown all available Lego parts with the matching design ID. But be warned Lego doesn't sell parts for every element. Many have a limited run and you will have to get your parts second hand from a site such as Bricklink.

Mini Helmet, No. 243 - Helmet Space / Town

Mini Head, No. 1 - Head Standard Grin Pattern

Mini Oxygen Bottles - Air Tanks

Mini Upper Part - Torso

Mini Lower Part - Hips and Legs Plain

Below is the modern motorcycle helmet found on many reissued Classic Space minfigs from 2000 and onwards.

Mini Crash Helmet - Helmet Motorcycle

Element IDs

To make it easier to find the correct colour torso with the space logo on it, you will find a list of links to every torso that has had an element ID assigned to it. Currently there is no element IDs for black or dark blue.

Red
White
Yellow
Blue
Black
Green
Light Bluish Gray
Pink
Orange
Purple
Brown
Dark Blue