Helios (spacecraft)

The Helios space probes were a joint project of the Federal Republic of Germany and the United States of America for the study of the sun. We have launched two space probes. The end of 1974 launched the first and the second in early 1976.


In 1966, agreed Chancellor Ludwig Erhard and U.S. President Lyndon B. Johnson signed an agreement on a common sophisticated planetary mission. What kind of mission would be, should be determined by the space agencies DFVLR and NASA. On June 10, 1969, the contract for the mission was formally ratified. It was agreed to build a probe pair, which should examine the space between the Sun and Earth more accurately and thereby come closer to the sun than any probe before.

The two probes Helios 1 and Helios 2 was a joint project of the Federal Republic of Germany (around 70 % ) and the USA (about 30%). Germany built the probes and the United States provided the launch vehicle and support with the Deep Space Network. The two probes were named after the Greek sun god Helios.


  • Helios 1 was launched under his project name Helios A on 10 December 1974, a Titan IIIE - Centaur rocket from Launch Complex 41 at Cape Canaveral. The probe reached a solar orbit with a minimum distance from the sun of 46.5 million kilometers, which is about the closest to the Sun distance of the innermost planet Mercury from the Sun. The sonnenfernste point of the orbit of Helios 1 corresponds approximately to the distance of the earth from the sun. The contact with Helios 1 was lost on 16 March 1986.
  • Helios 2 was launched under his project name Helios B on January 15, 1976 also on a Titan - Centaur rocket from the same ramp. They came up to the sun down to 43.5 million km (0.29 AU). The mission of Helios 2 already ended in December 1981.

Structure of the probes

Helios 1 and 2 (also known as Helios A and B ) were probes with the shape of an oversized spool. The maximum width was 2.77 m, the minimum 1.75 m. The height was 4.23 m for the probe body 2.12 m and with extended antenna mast. Behind the lower part of the mast is the rectangular reflector of the high-gain antenna. It is located on a low- gain antenna mast and the boom tip, a dipole antenna. The starting weight was 371 or 374 kg. The biggest challenge was to control the temperature. 50 % of the surface were covered with specular reflectors that throwing back the sunlight, in addition efficient radiators were placed on the two end faces. In addition, the shape minimized the exposure and the probes were also very well insulated. Due to the rapid rotation of one revolution per second, the surface was exposed only briefly to the sun and the heat is evenly distributed ..

After Helios 1 despite a minimum distance of 46.2 million km from the Sun had planned on board as lower temperatures, its sister probe Helios 2 was promoted to an even more sun path in which they are up to 43.4 million kilometers of the sun approached.

Of the 10 experiments with a total weight of 73.2 or 76.5 kg originated, to the financial contribution of the countries, seven from Germany and three from the United States.

The experiments related to three issues:

  • Investigation of particles ( ions, electrons, molecules) in the solar neighborhood space
  • Investigation of the interplanetary magnetic
  • Investigation of the dust and zodiacal light

Data and information

  • Helios 1 was the first spacecraft that did not come from the USSR or the USA.
  • With Helios 1, the titanium - Centaur rocket was first used successfully.
  • The two Helios probes weighed around 370 kilograms and had 10 scientific experiments on board.
  • The two probes were constructed for 18 months life, but held more than 11 years ( Helios 1 ) and 6 years ( Helios 2).
  • The probes rotated continuously about its own axis, so that the inside temperature of 20 ° C could be maintained. The outer shell heats up to up to 300 ° C.
  • The Helios program cost about 260 million U.S. dollars.
  • A reserve copy is German Museum in Munich as an exhibit.
  • The probes hold the speed record for space probes with 252,792 km / h ( 70.22 km / s) relative to the Sun.