The aperture for NASA's Space Telescope will be 2.4 meters. Although its form is conventional from an optical standpoint, it has substantial extensions of the state of the art, including provision for perfecting the optical figure of the primary mirror after it is placed in orbit, unique structural design and materials which render it immune to the severe thermal environment of space, and a pointing system which will control the direction of its line of sight to +0.007 arc-second (the head of a pin at 25 miles) for periods up to 10 hours. It will carry four or five science instruments at any one time, including cameras, spectrographs and photometers, all of which utilize electro-optical sensors, often operating in a photo-counting mode. Observational information will be transmitted to ground on a "near-real-time" basis through a data relay system which incorporates synchronous satellites and multiple ground stations. About 30 minutes of data will be available per orbit at a data rate of one megabit per second. There will be two on-board computers -- one to operate the science instruments and the other to operate the telescope. Command data is transmitted from the ground and engineering data transmitted back at a 50 kilobit per second data rate.