Problems for a flyby mission of the Sun

Abstract

HELIOS A/B, the first missions inside the orbit of Mercury towards the Sun were launched from Cape Kennedy in Dec. 1974 and Jan. 1976. The interplanetary cruise in the ecliptic plane carried the HELIOS solar probe in elliptic orbits around the Sun to a perihelion as close as 0.3 Astronomical Units from the Sun (approx. 45 million km). Twelve scientific experiments (ten active and two passive) investigated physical phenomena in interplanetary space originating from the Sun and from solar activity in general. The design and development of the HELIOS solar probe presented a number of engineering highlights, the most outstanding of which was the design of the thermal control system. The need for a highly reliable spacecraft with considerable operational constraints as determined by orbit and mission characteristics, e.g. communication distance up to 300 million km, black-out periods without telecommunication link for up to 65 days, extended mission period of 15–18 months, etc. has made the solution of many technical problems very intricate. Problems resulting from a realistic simulation of the environment in which the spacecraft was expected to operate, performance requirements which were not “state of the art” at the beginning of the development and problems resulting from quality defects in the hardware discovered during testing as well as the problems on design and operation capabilities gave reasons for severe concerns about the ability to meet the primary mission objectives within the schedule and financial constraints. The paper describes the processing of the major technical problems experienced from analysis to the course of action taken to eliminate a negative impact on the mission leading to launch readyness for the originally planned date. It is shown that the basic HELIOS design is essentially valid for a solar mission into a distance closer than 0.3 AU to the Sun.