Space Astrophysics Day Friday June

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The crew began multispectral observations, both of the optical characteristics of the atmosphere and of Soviet territory in order to provide scientists with unique data about certain locations, including lakes.

In addition, the Anna-III gamma-ray telescope was used to make the first such astronomical studies from a manned spacecraft.7 Volkov aligned the station to point the telescope at its target and then activated the automatic stabilisation system. Then Dobrovolskiy activated the apparatus to measure the energy spectrum of the gamma rays. The instrument consisted of several scintillation counters and one Cherenkov counter for measuring gamma rays, a pair of neon-filled spark chambers equipped with cameras, and a control panel. The gamma-ray telescope had a detector area of 90 cm2, drew 14 watts of power and was sensitive to radiation at energies exceeding 100 MeV (million electron volts) with an angular resolution of 1 degree, which was twice as good as instruments previously flown on unmanned satellites. Overall, the 45-kg Anna-III apparatus measured 60 x 40 x 45 cm, and included a tape cassette with a capacity of 20,000 images.

In effect, the Salyut crew were the first space astronomers. Gamma-ray astronomy had only recently become feasible, and was giving insights into the structure of the universe. Gamma rays are the most energetic form of light. They are produced by fusion reactions in the cores of stars, but are soon absorbed and so stars appear dark in this part of the electromagnetic spectrum. However, they are emitted by violent events such as a supernovas (when a massive star 'explodes') and by the much less dramatic decay of radioactive elements in space. Objects like supernova remnants, black holes, neutron stars and pulsars are all sources of celestial gamma rays. In addition, there are powerful 'flashes' known as gamma-ray bursts which can release more energy in a few seconds than the Sun will emit during its entire 10-billion-year lifetime! The exact cause of such bursts is disputed, and there may in fact be several causes. Thus far it would seem that all of the bursts originate from outside

7 Astronauts on some Gemini missions had previously conducted astronomical photography.

The Anna-Ill telescope to detect gamma rays.

our own galaxy, but it is conceivable that they might occur in our Milky Way once in every few million years, with one located within several thousand light-years of the Earth once every few hundred million years. By solving the mystery of gamma-ray bursts, scientists hope to develop further insight into the origin of the universe, the rate at which it is expanding, and its size.

The thickness of the Earth's atmosphere is approximately equivalent to 10 metres of water, so gamma rays, X-rays, ultraviolet and infrared radiations from space are absorbed. When the highly energetic atomic nuclei of cosmic rays interact with the atmosphere they generate gamma rays, but these too are absorbed. It is therefore not possible to undertake gamma-ray astronomy at ground level; it must be done at high altitude using instruments on balloons or, better still, on satellites.

The cosmonauts used the Anna-III to:

• determine the telescope's basic operational capabilities;

• investigate how the gamma-ray flux varied with directions in space; and

• correlate such observations with the flux of charged and neutral particles both directly entering the station and as secondary products in the station.

The Anna-III telescope detected gamma rays and charged particles as the station was rotated and stabilised relative to the Sun. In total, it was operated for 20 hours under the control of one cosmonaut.

The main astrophysical experiment on Salyut was the Orion telescope, which was in the transfer compartment. It had two mirrors, one 28 cm in diameter and the other 5 cm in diameter, and a focal length of 1.4 metres. The instrument was designed to make spectrograms of stars in the range 2,000-3,800 angstroms.8 At a wavelength of about 2,600 angstroms it could provide a resolution of 5 angstroms. The tracking system allowed the telescope to maintain its orientation to within one second of arc. The spectrograms were recorded in the form of photographs on 16-mm tape bearing UFSH-4 emulsion. An airlock and mechanical arm allowed a cosmonaut to replace the film cassettes. The mirrors were coated with aluminium, without protection, to enable them to be re-surfaced if they ever became tarnished by micrometeoroids. To use the instrument, one man (usually Dobrovolskiy) controlled the orientation of the station while Patsayev, who was responsible for this research, aimed the telescope. Patsayev had to operate the system quickly because there was only a 30-35-minute period on each orbit during which observations could be made - this being while in the Earth's shadow. Dobrovolskiy, sitting at the central control panel, oriented the station as specified by Patsayev in the transfer compartment with the Orion. When the target star was visible to the telescope, the station was stabilised and Patsayev started the observation. During the mission he obtained six spectrograms of the star Agena (beta Centauri) in the southern sky and nine of Vega (alpha Lyra) in the north. In fact, Vega is the 'standard star' for spectral analysis of other stars. These stars were selected because of their extremely high surface temperatures (10,000°C in the case of Vega and 24,000°C for Agena). Once an investigation was completed, Volkov used the airlock manipulator to retrieve the cassette of tape and to replace it with another one.

Salyut also had the FEK-7 photo-emulsion camera with a volume of 1.4 litres for detecting the charged particles of primary cosmic rays. The majority of cosmic rays are protons and alpha particles (helium nuclei), but there can also be much heavier nuclei. A precise knowledge of their fluxes as a function of energy was important for several reasons. Interstellar spectra can provide information about how cosmic rays are propagated and accelerated in the galaxy. In principle, this can be derived from measurements made in the upper atmosphere by demodulating the observed solar spectrum. Since protons and helium nuclei have different momenta and kinetic energies per nucleon, the comparison of their spectra provides useful constraints for modulation and acceleration theories.

The FEK-7 camera was designed to search for:

• magnetic monopoles (single magnetic charges; Dirac particles);

• trans-uranium and uranium nuclei in primordial cosmic rays, important for global astrophysics and the determination of the distribution of the sources of cosmic rays; and

• anti-nuclei and trans-nuclei to investigate the symmetry between matter and anti-matter.

Finding such particles would have important implications for theoretical physics. Similar cameras had been flown on the unmanned satellite Cosmos 213, on Zonds 5,

8 An angstrom is 1 x 10-10 metre, and is the unit in which spectra are measured. The human eye is sensitive from 4,000 to 7,000 angstroms, running from violet to red respectively. The Orion telescope was designed to observe in the ultraviolet.

The Orion astrophysical telescope.

7 and 8 flying circumlunar trajectories and on the Soyuz 5 mission, but in each case data was able to be collected only for short periods. The FEK-7 on Salyut operated for 17 hours 28 minutes. It was placed in the descent module of Soyuz 11 for return to Earth and analysis by specialists.

Another project was to determine the intensity of charged particles in the altitude range 200-300 km (where the station flew) because this radiation appeared to have been increasing since 1960. It had even been proposed that this region was occupied by clouds of electrons possessing energies as great as 300-600 MeV. When the Sun is active it can suddenly release vast numbers of charged particles, and following a major 'flare' the increased radiation can linger in the inner heliosphere (where the Earth is located) for up to a month. The Earth's magnetic field provides a degree of protection, but even in low orbit a high flux of such particles can cause damage to both electronic and biological systems. During the flight, the crew performed more than 60 operations related to the measurement of charged particles. The instrument used was able to detect protons with energies of 400 MeV and electrons exceeding 8 MeV. The observed electron flows were several hundred times less intense than those previously measured by the Cosmos 225 satellite.

At 1.06 p.m. on 11 June Salyut left the communication zone of the NIP stations, but the ship Academician Sergey Korolev in the North Atlantic was able to continue to communicate with it. The final experiment of the day was to investigate optical materials that had been exposed to the space environment. Before the crew retired, Yevpatoriya relayed through a Molniya satellite and Academician Sergey Korolev to congratulate them on their successful work so far.

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