RELIKT-1

RELIKT-1 was launched on board the Prognoz-9 satellite on 1 January 1983. The satellite was in a highly eccentric orbit, with perigee around 1,000 km and apogee around 750,000 km, and an orbital period of 26 days.[1]

RELIKT-1 observed at 37 GHz (8 mm), with a bandwidth of 0.4 GHz and an angular resolution of 5.8°. It used a superheterodyne, or Dicke-type modulation radiometer[2] with an automatic balancer for the two input levels with a 30-second time constant. The noise in 1 second was 31mK,[1] with a system temperature of 300K, and a receiver temperature of 110K.[3] The signal was sampled twice a second, and the noise was correlated between samples.[1]

The receiver used two corrugated horn antennas, one pointing parallel to the spacecraft spin axis, the other pointing at a parabolic antenna to point at 90° from the spin axis. The satellite rotated every 120 seconds.[1] The experiment weight 30 kilograms (66 lb), and consumed 50W of power.[3]

The radiometer was calibrated to 5% accuracy before launch, as was an internal noise source (which was used every four days during observations).[1] Additionally the moon was used as a calibrator, as it was observed twice a month,[3] and the in-flight system temperatures were measured to vary by 4% on a weekly basis.[1]

The satellite rotation axis was kept constant for a week, giving 5040 scans of a great circle, after which it was changed to a new axis.[1] The signal was recorded onto a tape recorder, and transmitted to Earth every four days.[4] It observed for 6 months, giving 31 different scans that covered the whole sky, all of which intersected at the ecliptic poles. The experiment ceased observations in February 1984,[1] after collecting 15 million measurements.[2]

It measured the CMB dipole, the Galactic plane,[2] and reported constraints on the quadrupole moment.[1]

The first dipole measurement was reported in 1984, while the telescope was still observing, at 2.1±0.5mK, and upper limits on the quadrupole of 0.2mK.[3] It also detected brighter-than-expected Galactic plane emission from compact HII regions.[5]

A reanalysis of the data by Strukov et al. in 1992 found a quadrupole ${\displaystyle (\Delta T/T)_{quad}}$ between ${\displaystyle 6\times 10^{-6}}$ and ${\displaystyle 3.3\times 10^{-5}}$ at 90% confidence level, and also reported a negative anomaly at l=150°, b=-70° at a 99% confidence level,[6][7][8]

Another reanalysis of the data by Klypin, Stukov and Skulachev in 1992 found a dipole of 3.15±0.12mK, with a direction of 11h17m±10m and -7.5°±2.5°. It placed a limit on the CMB quadrupole of ${\displaystyle (\Delta T/T)_{quad}=1.5\times 10^{-5}}$ with a 95% confidence level, assuming a Harrison-Zeldovich spectrum, or ${\displaystyle <3.0\times 10^{-5}}$ without assuming a model. The results were close to those measured by the Cosmic Background Explorer[1] and the Tenerife Experiment.[5]

The second RELIKT satellite would have been launched in mid-1993. It would have had five channels to observe at 21.7 (13.8), 24.5 (8.7), 59.0 (5.1), 83.0 (3.6) and 193 GHz (1.6mm),[1] using degenerated paramps.[5] It would have had corrugated horns to give a resolution of 7°, and a more distant orbit to avoid contamination from the Moon and Sun, with a mission duration around 2 years, to give a better sensitivity than COBE.[1] It would have been cooled to 100K. It was constructed, and was undergoing tests in 1992. It would have been launched as the Libris satellite on a Molniya rocket.[4] The launch was put back to 1996, with expanded plans to observe with 1.5-3° resolution from two spacecraft in 1995,[1] but ultimately never took place because of the Soviet Union's break-up and lack of funding.

A RELIKT-3 was also planned, which would have observed at 34–90 GHz with a resolution around 1°.[1]