Boeing 601HP

Boeing 601

TDRS-K, built on the 601HP platform, before launch
Manufacturer	Boeing
Production
Status	In service
Related spacecraft
Derivatives	Boeing 601HP

The Boeing 601 (sometimes referred to as the BSS-601, and previously as the HS-601) is a communications satellite bus introduced in 1987 by Hughes Space and Communications Company. The more advanced 601HP derivative (for "high power") was introduced in 1995. Hughes, and the 601 platforms, were acquired by Boeing in 2000.

The 601 bus is divided into two modules. The first module houses the propulsion system, batteries, and electronics for the bus, and bears launch vehicle loads. The second module contains shelves carrying the communications equipment, payload electronics, and heat pipes. Solar arrays, reflectors, and antenna feeds are mounted to the payload module.

The standard 601 platform supports up to 48 transponders and provides up to 4,800 watts of power. The 601HP supports up to 60 transponders and provides up to 10,000 watts.

A significant number of Boeing 601s have experienced failures in orbit, some resulting in complete failure of the satellite.

An unconfirmed number of 601s launched prior to August 1997 have a design flaw in their SCPs, where a tin-plated relay forms crystalline "whiskers" under certain specific conditions. These whiskers eventually caused an electrical short. Each satellite contains two SCPs and the backup unit will take control in the event of a failure of the primary unit. In some cases, both SCPs have failed, rendering the spacecraft unusable. A notable example was the Galaxy IV satellite. At least eight 601s have experienced SCP failures; four of which were double failures resulting in total loss of the satellite. Hughes switched to nickel plating on later 601s to resolve this problem, at the expense of payload weight.

Some 601HPs have experienced problems with their batteries, resulting in a reduction of eclipse protection. This would require some transponders to be shut down during eclipse periods.

At least four satellites with XIPS propulsion have experienced partial or total failure of the XIPS system which significantly reduced the lifespan of the satellite.