Rosetta's High Gain Antenna passes critical review
7 February 2001
Even as the Rosetta Electrical Qualification Model (EQM) continues to be put through its paces in Italy, the Rosetta team is looking forward to the next stage in the spacecraft's development programme.Earlier this week, the Swiss company HTS (High Technology Systems) was given the go-ahead to complete construction of the Orbiter's high gain antenna (HGA) after a three-day Critical Design Review in Wallisellen, near Zurich.
"We have already built two similar antennas for the Rosetta Structural Thermal Model and the EQM, so we were not surprised that everything went well," said HTS Technical Director, Thomas Schilliger. "In fact, we have already started on the manufacturing, since we have such a tight launch schedule to meet."
"The antenna actually comprises four main components: the antenna itself, the pointing mechanism, the hold down and release mechanism, and the pointing mechanism electronics," he explained. "We have three main subcontractors. Saab Ericsson Space in Gothenburg, Sweden, make the antenna substructure; ETEL of Switzerland build the electronics; and BAE Systems Advanced Technology Centres from the United Kingdom are responsible for the rotary joints."
The high gain antenna will be a vital component in the communications link between the Earth and the Rosetta spacecraft as it travels far beyond the asteroid belt in search of Comet Wirtanen. The 2.4 m diameter dish will be used to relay large amounts of information to Earth at high data rates over a distance of more than 500 million km.
"In order to achieve this, the HGA has to point very accurately in azimuth (to each side) and elevation," explained Mr. Schilliger. "When we launch, the antenna will be held in place against the side of the spacecraft at three points. To deploy it, we release the clamps, then move it out to about 90 degrees before starting to rotate it in azimuth. In its operational mode, it will eventually move through half a circle (180 degrees of elevation) in order to face towards the Earth."
It is also vital to save every kilogram of weight when launching a heavy spacecraft to the depths of the Solar System. For this reason, the HGA is largely made of carbon fibre and tips the scales at just 45 kg, (including the electronics).
Now that HTS has the green light for completion of the antenna, the company will be striving to meet its completion date of May 2001. The complex components will then be shipped to Italy for assembly on the Rosetta flight model.
