View source for RELIKT-1

{{Short description|Soviet cosmic microwave background experiment on the Prognoz 9 satellite}}
{{Infobox telescope}}
'''RELIKT-1''' from {{langx|ru|РЕЛИКТ-1}}{{efn|1=From {{langx|ru|реликтовое излучение|lit=relict radiation}} meaning 'cosmic microwave background'}} (sometimes '''RELICT-1''') was a [[Soviet Union|Soviet]] [[cosmic microwave background]] [[anisotropy]] experiment launched on board the [[Prognoz 9]] satellite on 1 July 1983. It operated until February 1984. It was the first CMB satellite (followed by the [[Cosmic Background Explorer]] in 1989) and measured the CMB dipole, the Galactic plane, and gave upper limits on the [[quadrupole moment]].

A follow-up, '''RELIKT-2''', would have been launched around 1993, and a '''RELIKT-3''' was proposed, but neither took place due to the [[dissolution of the Soviet Union]].

== Launch and observations ==
[[File:Astron orbit.gif|thumb|Prognoz 9 orbit]]
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&nbsp;km and apogee around 750,000&nbsp;km, and an orbital period of 26 days.{{r|Klypin1992}}

RELIKT-1 observed at 37&nbsp;GHz (8&nbsp;mm), with a bandwidth of 0.4&nbsp;GHz and an angular resolution of 5.8°. It used a superheterodyne, or [[Dicke-type modulation radiometer]]<ref name="lambda" /> with an automatic balancer for the two input levels with a 30-second time constant. The noise in 1 second was 31mK,{{r|Klypin1992}} with a system temperature of 300K, and a receiver temperature of 110K.{{r|Strukov1984}} The signal was sampled twice a second, and the noise was correlated between samples.{{r|Klypin1992}}

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.{{r|Klypin1992}} The experiment weight {{convert|30|kg|lb}}, and consumed 50W of power.{{r|Strukov1984}}

The radiometer was calibrated to 5% accuracy before launch, as was an internal noise source (which was used every four days during observations).{{r|Klypin1992}} Additionally the moon was used as a calibrator, as it was observed twice a month,{{r|Strukov1984}} and the in-flight system temperatures were measured to vary by 4% on a weekly basis.{{r|Klypin1992}}

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.{{r|Klypin1992}} The signal was recorded onto a tape recorder, and transmitted to Earth every four days.{{r|scienceUSSR}} 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,{{r|Klypin1992}} after collecting 15 million measurements.{{r|lambda}}

== Results ==
It measured the CMB dipole, the Galactic plane,<ref name="lambda" /> and reported constraints on the quadrupole moment.<ref name="Klypin1992" />

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.<ref name="Strukov1984" /> It also detected brighter-than-expected Galactic plane emission from compact HII regions.<ref name="Strukov1995" />

A reanalysis of the data by Strukov et al. in 1992 found a quadrupole <math>(\Delta T/T)_{quad}</math> between <math>6\times10^{-6}</math> and <math>3.3\times10^{-5}</math> at 90% confidence level, and also reported a negative anomaly at l=150°, b=-70° at a 99% confidence level,<ref name="Strukov1992" /><ref name="Strukov1992a" /><ref name="Strukov1993" />

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 <math>(\Delta T/T)_{quad} = 1.5 \times 10^{-5}</math> with a 95% confidence level, assuming a [[Matter power spectrum|Harrison-Zeldovich spectrum]], or <math><3.0\times10^{-5}</math> without assuming a model. The results were close to those measured by the [[Cosmic Background Explorer]]<ref name="Klypin1992" /> and the [[Tenerife Experiment]].<ref name="Strukov1995" />

== RELIKT-2 ==
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&nbsp;GHz (1.6mm),<ref name="Klypin1992" /> using degenerated paramps.<ref name="Strukov1995" /> 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.<ref name="Klypin1992" /> 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)|Molniya]] rocket.<ref name="scienceUSSR" /> The launch was put back to 1996, with expanded plans to observe with 1.5-3° resolution from two spacecraft in 1995,<ref name="Klypin1992" /> but ultimately never took place because of the [[Dissolution of the Soviet Union|Soviet Union's break-up]] and lack of funding.

A RELIKT-3 was also planned, which would have observed at 34–90&nbsp;GHz with a resolution around 1°.<ref name="Klypin1992" />
==Notes==
{{Notelist}}

== References ==
{{Reflist | refs=
<ref name="Klypin1992">{{Cite Q|Q68552080}}</ref>
<ref name="Strukov1992">{{cite journal|last1=Strukov |first1=I. A. |last2=Brukhanov |first2=A. A. |last3=Skulachev |first3=D. P. |last4=Sazhin |first4=M. V. |title=Anisotropy of the microwave background radiation |journal= Soviet Astronomy Letters |year=1992 |volume=18 |issue=5 |pages= 153–156 |bibcode=1992SvAL...18..153S}}</ref>
<ref name="scienceUSSR">{{cite web |title=Взгляд в прошлое Вселенной ("A glimpse into the past of the universe", "Science in the USSR" 1992 #4) |url=http://epizodsspace.airbase.ru/bibl/nauka-v-ussr/1992/vzglad.html |website=epizodsspace.airbase.ru |access-date=26 April 2021|language=ru}}</ref>
<ref name="lambda">{{cite web |title=LAMBDA - Relikt Overview |url=https://lambda.gsfc.nasa.gov/product/relikt/ |website=lambda.gsfc.nasa.gov |access-date=26 April 2021}}</ref>
<ref name="Strukov1984">{{cite journal |last1=Strukov |first1=I. A. |last2=Skulachev |first2=D. P. |title=Deep-Space Measurements of the Microwave Background Anisotropy - First Results of the Relikt Experiment |journal=Soviet Astronomy Letters |date=1984 |volume=10 |pages=1–4 |bibcode=1984SvAL...10....1S |url=https://ui.adsabs.harvard.edu/abs/1984SvAL...10....1S/abstract}}</ref>
<ref name="Strukov1993">{{cite journal |last1=Strukov |first1=I. A. |last2=Brukhanov |first2=A. A. |last3=Skulachev |first3=D. P. |last4=Sazhin |first4=M. V. |title=Anisotropy of relic radiation in the RELICT-1 experiment and parameters of grand unification |journal=Physics Letters B |date=1 September 1993 |volume=315 |issue=1–2 |pages=198–202 |doi=10.1016/0370-2693(93)90180-P |bibcode=1993PhLB..315..198S |url=https://ui.adsabs.harvard.edu/abs/1993PhLB..315..198S/abstract |issn=0370-2693}}</ref>
<ref name="Strukov1992a">{{cite journal |last1=Strukov |first1=I. A. |last2=Brukhanov |first2=A. A. |last3=Skulachev |first3=D. P. |last4=Sazhin |first4=M. V. |title=The Relikt-1 experiment - New results |journal=Monthly Notices of the Royal Astronomical Society |date=1 September 1992 |volume=258 |issue=2 |pages=37P–40P |doi=10.1093/mnras/258.1.37P |bibcode=1992MNRAS.258P..37S |issn=0035-8711|doi-access=free }}</ref>
<ref name="Strukov1995">{{cite report |last1=Strukov |first1=I. |last2=Skulachev |first2=D. |last3=Brjukhanov |first3=A. |title=The results of RELICT-1 spaceborne experiment |date=1995 |pages=139 |url=https://ui.adsabs.harvard.edu/abs/1995foap.conf..139S/abstract |bibcode=1995foap.conf..139S}}</ref>
}}

{{CMB experiments}}
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[[Category:1983 in spaceflight]]
[[Category:1983 in the Soviet Union]]
[[Category:Cosmic microwave background experiments]]
[[Category:Space telescopes]]
[[Category:Soviet space observatories]]
[[Category:Spacecraft launched in 1983]]