The two "Helios" probes look very similar. "Helios-A" has a mass of , and "Helios-B" has a mass of . Their scientific payloads have a mass of on "Helios-A" and on "Helios-B". The central bodies are sixteen-sided prisms in diameter and high. Most of the equipment and instrumentation is mounted in this central body. The exceptions are the masts and antennae used during experiments and small telescopes that measure the zodiacal light and which emerge from the central body. Two conical solar panels extend above and below the central body, giving the assembly the appearance of a diabolo or spool of thread.