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|Above: The Spektr-R (Radioastron) observatory. Click red arrows to rotate the model.|
Previous chapter: Spektr-R mission scenario
Like all other space observatories in the Spektr series, the Spektr-R mission was built around the standard Navigator platform, which served as a service module for the spacecraft. Crowned with a large radio telescope antenna, Navigator provided all flight control and power-supply functions for Spektr-R in orbit. The telescope's scientific instruments were packaged in two containers tacked between the antenna and the Navigator service module.
The heart of the telescope would be a 10-meter antenna, sporting 27 carbon fiber petals. Petals surrounded a solid focal dish with a diameter of three meters. When open, the mirror of the telescope would have to retain its position within just two millimeters of the pre-determined curve.
Antenna opening mechanism
In a folded position, the antenna was held in place by a special spring-loaded ring, which was located just below the focal container and featuring 27 locks with spherical receptacles. At the same time, each petal was equipped with a special hook with a spherical tip fitted into the lock of the ring. Upon the activation of three pyrotechnic charges, the fixation ring would be pushed up by the springs and free the petals for opening. A single motor would be used to unfold all the petals of the antenna during a sequence, which would last from 15 minutes to two hours, according to different sources. (498, 484) The deployment sequence had two different modes, which could apply loads of 600 for nominal deployment and 1,200 kilograms in case of problems to open the petals. Near the completion of the opening process, a special sensor would confirm that petals reached the position for permanent fixation. The opening mechanism then would then deliver a final push for deployment, triggering a signal for the fixation of the petals in their operational position.
According to the official documentation of the Spektr-R project, once open, the petals would lock to each other by special pins at their edges. (484) However, according to sources involved in the project, there were no links between individual petals. Petals are grouped in three sections with nine petals in each. Three pyrotechnic devices would fix all sections in place, triggering signals from 27 contact sensors on each petal.
The petal framework was made of carbon-fiber tubes which were covered by a surface with a three-layer composition including carbon-fiber trimmings combined with aluminum honeycomb. The surface of a petal could be adjusted over a range of just seven millimeters before launch by means of 45 special screws. The solid central mirror of the dish was fixed to a pitched truss by nine connecting bolts that eliminated the influence of thermal deformation of the truss.
The pitched truss itself was a cylindrical ribbed structure made of aluminum alloy. The truss served as basic structural element for the radio telescope; it carried all the petals, the central mirror, the six supporting legs of the focal container, and all unfolding devices. In addition, the star sensors were also attached to the truss to reduce the effects of thermal deformations.
A thin aluminum coating covering the surface of the mirror was designed to give it a reflectivity of 98 percent. To reduce thermal deformations of the antenna, the tubes of the petal framework would be kept warm by special heating elements maintaining the temperature at 50C degrees. Each petal would feature 11 heaters equally distributed along its length.
On its back side, the petals were also shielded by thermal isolation with as many as 50 layers. According to mission requirements, the antenna's main surface should never be exposed to sunlight.
High above the main antenna dish, a special six-leg support container made out of carbon composite held the so-called focal container. It housed all the radio receivers of the telescope. A special sunshade attached to the focal container was expected to keep the sensitive systems of the focal container cool enough for operation.
To stay in contact with ground control from as far as 340,000 kilometers, a high-gain antenna with a 1.5 meter carbon fiber dish was mounted to the bottom side of the Navigator platform via a special retractable boom known as VIRK. The mass of the mechanism reaches around 80 kilograms. The antenna was intended for sending data in both directions and for helping synchronize frequency of the telescope with its ground counterparts. Several smaller low-gain antennas were also mounted on the Navigator.
The spacecraft was to receive electricity from a pair of solar panels which could rotate around a single axis to maximize their exposure to the Sun. The panels were developed at ISS Reshetnev (formerly NPO PM) of Zheleznogorsk, with the help from OAO Saturn of Krasnodar, which supplied photovoltaic elements. ISS Reshetnev supplied solar panels along with a newly developed fixation system, an opening hinge system and an electrical driving mechanism. (499)
To determine the telescope's position in space, it was equipped with a trio of star sensors, however just two such devices would be enough for the onboard computer to control the satellite's position in all three dimensions.
During the mission, flight controllers would have the challenging task of maintaining the spacecraft's position in space to counteract intensive pressure from the solar wind. A special reaction-wheel system was to be used to maintain the attitude control of the spacecraft.
*Roskosmos press release, May 25, 2011
International contributions into the Radioastron mission:
*After 2004 replaced by Russian payloads due to aging problems of the original instruments.
Next chapter: Spektr-R launches and works in orbit
Page author: Anatoly Zak; Last update: May 24, 2012
Page editor: Alain Chabot; Last edit: June 6, 2011
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The hexagon-shaped Navigator spacecraft bus was expected to serve as the base for the Spektr-R mission. Credit: IKI
The receiver system was largely completed by 2010. Credit: FIAN
The main antenna of the Spektr-R's radio telescope. Credit: FIAN
Spektr-R prototype mounted on top of the Fregat upper stage during its development in May 2004. Credit: NPO Lavochkin