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Sputnik 1 was the first artificial satellite launched by humans to orbit the Earth.

This answer begins:

Sputnik had just one single job: Prove its existence by sending a simple "beep" regularly...

and This answer begins:

Sputnik-1 was political statement. Its science value was close to zero.

Sputnik 1's designations are:

Harvard     1957 Alpha 2
COSPAR      1957-001B
SATCAT      00002

It was launched on 4 October 1957, radio signals from it were received until 26 October 1957, and it reentered the atmosphere on 4 January 1958.

It transmitted a radio beacon on 20 and 40 MHz that was heard by short wave radio enthusiasts as well as scientists around the world. Doppler shift of the beeps could allow one to estimate line-of-sight velocity as well as an epoch for local passes. Traveling in a roughly 200 x 900 km orbit with an inclination of about 65 degrees the spacecraft's orbit was constantly perturbed by atmospheric drag and Earth's oblateness as quantified by $J_2$, and the dual frequencies may have propagated differently through the ionosphere. The choice of frequencies couldn't have been an accident.

Question: In light of all of this, was all that was learned is that something that could beep, beeped? Or was a significant amount of scientific knowledge and verification of proposed models gained from careful measurements of Sputnik 1's orbit?

International Geophysical Year 1957 Source

Related:

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  • $\begingroup$ Wikipedia has some mention of ionosphere radioscience by Sputnik-1. But it has no confirming links. Also one memoir (in Russian) states that Sputnik-1 brought the first clue to upper atmosphere's higher density at day side compared with night side. The problem is the memoir is likely anecdotal and it doesn't contain references to science papers or other documents. So, in my view - it's unclear. It can be true, or it can be revisionist appropriation of discoveries made by later spacecraft to Sputnik-1. $\endgroup$ – Heopps Sep 3 at 9:01
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    $\begingroup$ I’m voting to close this question because it is inherently opinion based (my opinion: Sputnik-1 intentionally did not have much at at scientific value; the goal of the mission was to absolutely ensure being first to orbit the Earth, and that meant nixing scientific endeavors). Moreover, this is the culmination of a six year long harangue by one rather vocal user. $\endgroup$ – David Hammen Sep 3 at 10:59
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    $\begingroup$ @David Hammen: How is this opinion based? For example, surely scientists where observing Sputnik 1's trajectory and how its orbit decayed, which gave insight not available before. Other insights from just observing how Sputnik 1 behaved might have been possible, and there may be papers published about those. The question is not about what Sputnik 1 intended to do, but what we learned from it anyway. $\endgroup$ – DarkDust Sep 3 at 11:15
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    $\begingroup$ What is scientific for you? Sputnik 1 proved that the R7 worked, that spacecraft could orbit as intended etc.pp. Much of that might not seem that important today, and some people might argue that this was more like verifying engineering, but isn't that also science? The question kind of assumes that veryfying "Yep, that rocket works as we have predicted" has no scientific value, and I wonder why that is? Bleeding edge engineering is more often than not also science. $\endgroup$ – Polygnome Sep 3 at 18:18
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    $\begingroup$ @uhoh True, which is why it's a comment, or more accurately a comment on a comment, and not an answer. :) $\endgroup$ – Graham Sep 4 at 21:29
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Shot answer:

Was Sputnik-1 "only for beep" - no, it wasn't :)

It was technical test of R-7 as space launcher and test of spacecraft in orbit (athough very simple spacecraft).

Also scientists at least tried to make atmosphere research with Sputnik-1. (From my current search results I'm not sure they got much.)


Long answer:

It's current state of my dig. I'll update if I find more.

Not so much "hard evidence", but considering bunch of incomplete sources as "bona fide":

Sputnik-1 was used for 3 scientific purposes

  1. To study spacecraft functioning during spaceflight. (it sent telemetry no, looks like it didn't)

  2. To study upper atmosphere density (by trajectory tracking)

  3. To study ionosphere by radioscience.

For ionosphere study I found this (in Russian). This document cites work of 1958 by Yakov Alpert. Quotes:

2. Обзор первой научной публикации на основе анализа данных наблюдений за «Спутником-1» [Альперт и др., 1958]

... В статье описывается один из возможных методов наблюдений за радиосигналами спутника, основанный на определении моментов времени его «радиовосхода» и «радиозахода», позволяющий определять распределение электронной концентрации N(z) ионосферы выше максимума. Приводятся предварительные результаты соответствующей обработки экспериментальных данных. Анализ результатов работы приводит к некоторым важным и интересным представлениям о внешней ионосфере — получены количественные характеристики убывания электронной концентрации, а также некоторые соображения о «границе», где атмосфера соприкасается с межпланетным газом.

... Нами рассмотрены результаты приёма радиосигналов спутника лишь за 5, 6 и 7 октября. Во всей совокупности данных (около 600 моментов начала и окончания приёма сигналов) только примерно в 60–70 случаях выполнялись условия, когда не было сложных траекторий волны на частоте 40 МГц и наблюдался «радиовосход» и «радиозаход» спутника в чистом виде, когда ωс/ω < ωс/ωэ или ωс/ω ≥ ωс/ωэ . При более детальном анализе этих данных оказалось, что иногда слышимость обрывалась по неизвестной причине на более коротких расстояниях. И, наоборот, в некоторых случаях при имевшем место отношении частот ωс/ω < ωс/ωэ дальность приёма превышала на несколько сот км максимальные теоретически возможные расстояния. Создаётся впечатление, что в некоторых сеансах это было обусловлено тем, что траектория волны была скользящей.

Translation:

2. Review of the first scientific publication based on the analysis observation data for "Sputnik-1" [Alpert et al., 1958]

... The article describes one of the possible methods for observing satellite radio signals, based on determining the points in time its "appearance" and "disappearance", which makes it possible to determine the distribution of the electron concentration N (z) of the ionosphere above the maximum. Preliminary results of the corresponding processing of experimental data are presented. Analysis of the results of the work leads to some important and interesting ideas about the external ionosphere - quantitative characteristics of decreasing electron concentration, as well as some considerations about the "boundary" where the atmosphere is in contact with the interplanetary gas.

... We have considered the results of receiving satellite radio signals only for 5th, 6th and 7th October [1957]. In the entire set of data (about 600 times of the beginning and end of signal reception), only in about 60–70 cases the conditions were satisfied e.g. there were no complex wave trajectories at the frequency 40 MHz and a "radio sunrise" and "radio entry" of the satellite was observed in a clean form when ωs / ω <ωs / ωe or ωs / ω ≥ ωs / ωe ... With a more detailed analysis these data, it turned out that sometimes audibility was cut off by an unknown reason at shorter distances. And, conversely, in some cases at the existing frequency ratio ωs / ω <ωs / ωe reception range exceeded by several hundred km the maximum theoretically possible distance. One gets the impression that in some sessions this was due to the fact that the wave trajectory was sliding.

Bold is myne.

On page 7 there is picture of ionosphere model built from Sputnik radioscience data.


About tracking of Sputnik-1 - according to Russian Wikipedia article it was tracked by several optical stations with marine chronometers. At the photos Sputnik was located in reference to known stars, that allowed to calculate current orbit parameters. Active radar or radio Doppler effect weren't used by Soviet as far as I see. Although the wiki article have no links to confirm it.

There is also claim that Sputnik-1 trajectory showed dijurnal variations of upper atmosphere densities - here is memoir (in Russian) that mentions it, but without any links to scientific publications.

Quote:

И вот запущен первый спутник. Он, конечно, тормозится в верхней атмосфере и поэтому его орбита постепенно изменяется, большая ось орбиты уменьшается. По идее, наблюдая эти изменения, можно решать обратную задачу механики - по траектории определять действующие силы, например, силы аэродинамического торможения и, как следствие, плотность атмосферы. Это только по идее. На пути осуществления ее стояло немало трудностей, блестяще преодоленных М.Л. Лидовым. Он не только разработал алгоритмы определения атмосферы и использовал эти алгоритмы для фактического определения плотности, но и открыл удивительные вариации плотности, например, суточные. На солнечной стороне Земли прогретая атмосфера "вспухает", линии равной плотности вытягиваются в сторону Солнца; поэтому на фиксированной высоте атмосфера плотнее днем, нежели ночью. Я помню, как Лидов докладывал эти результаты на совещании у М.В. Келдыша. Присутствующие геофизики были потрясены.

And so the first satellite was launched. It is, of course, decelerated in the upper atmosphere and therefore its orbit gradually changes, the major axis of the orbit decreases. In theory, observing these changes, it is possible to solve the inverse problem of mechanics - by the trajectory to determine the acting forces, for example, the forces of aerodynamic braking and, as a consequence, the density of the atmosphere. This is just an idea. Many difficulties stood in the way of its implementation, brilliantly overcome by M.L. Lidov. He not only developed algorithms for determining the atmosphere and used those algorithms to actually determine density, but he also discovered amazing variations in density, such as diurnal. On the sunny side of the Earth, the heated atmosphere "swells", lines of equal density are stretched towards the Sun; therefore, at a fixed altitude, the atmosphere is denser during the day than at night. I remember how Lidov reported these results at a meeting with M.V. Keldysh. The geophysicists present were shocked.

Hyperlinks in quote are myne.


WARNING!

I suggest to take the information without "hard sources" with grain of salt. It can be prone to some historical revisionism or at least errors. For example Wikipedia page cites memoir by Svedish scientist Bengt Hultqvist, but looking at the linked book it's clear he worked with the data of Sputnik-3, not Sputnik-1. (http://www.iki.rssi.ru/books/2007pervaya_r.pdf - 7 Mb, in Russian)

Quote:

Мы, как и миллионы других людей по всему миру, наблюдали за маленькой яркой точкой, пересекающей небо в часы заката и восхода, и ловили сигналы «бип-бип-бип» Спутника по радио. Мы с большим интересом следили за тем, какой громкий резонанс вызвало это событие во всех средствах массовой информации, и скоро начали думать над тем, как можно было бы использовать радиоизлучение Спутника для научных исследований. Мы начали измерения суммарного электронного состава ионосферы, используя эффект Фарадея, и одна из первых докторских диссертаций, написанных в обсерватории, основывалась на подобных измерениях по радиопередачам Спутника-3.

Translation:

We, like millions of other people around the world, watched a small bright dot crossing the sky at sunset and sunrise, and caught the signals "beep-beep-beep" of the Satellite on the radio. We followed with great interest what a loud resonance this event caused in all the media, and soon began to think about how it could be to use the satellite radio emission for scientific research. We have begun measuring the total electronic composition of the ionosphere using Faraday's effect, and one of the first doctoral dissertations written at the observatory was based on similar measurements from Sputnik-3 radio transmissions.

... If I had access to Russian scientific publications of late 1950es I could say something more precise, but I haven't.

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    $\begingroup$ "радиозаход" would be "radio sunset", as a counterpart for "radio sunrise": the exact moment when radio transmissions from the satellite cease because it's too far below the horizon. $\endgroup$ – svavil Sep 3 at 18:22
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    $\begingroup$ @svavil - I've changed translation to "appearance" and "disappearance". "Radio sunset" can be confusing. If anybody knows the correct term - feel free to edit. $\endgroup$ – Heopps Sep 3 at 19:44
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    $\begingroup$ Suggest "radio appearance" and "radio disappearance", since the radio part is there in the Russian. Also, it's in both paragraphs so the translation should probably use the same terms in both places. $\endgroup$ – luser droog Sep 4 at 3:08
  • $\begingroup$ радиозаход - An event when the source of the radio signal ceases to be radiovisible due to the fact that it is hidden behind a celestial body. $\endgroup$ – A. Rumlin Sep 6 at 13:06
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    $\begingroup$ "Shot answer: Was Sputnik-1 "only for beep" - no, it wasn't :)" Note that my question is only "What science was improved..." and did not ask what it was "for". Even if Sputnik "only" beeped once in orbit, the beeping in orbit told us much more than "beep"! $\endgroup$ – uhoh Sep 7 at 0:08
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I don't know what the USSR was trying to do with it, but I know what the US Navy did with it. Researchers at the Johns Hopkins University's Applied Physics Lab used the Doppler shift on the 20 MHz tone to determine Sputnik-1's orbit, plus ionospheric electron density and a couple of other things (like a transmitter frequency offset of ~1 kHz from the nominal 20 MHz), and then designed the first satellite navigation system, Transit, based on that principle, which is still used today in DORIS to produce centimeter-scale accuracy for earth science radar altimetry missions.

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    $\begingroup$ Oh that's cool! This is because of dispersion (different refractive index at different wavelengths) which lead to different paths for the two frequencies. This allowed listeners to learn information on electron density distribution. Cool! Like I mentioned in the question, 20 and 40 MHz were not likely chosen by accident. $\endgroup$ – uhoh Sep 3 at 19:14
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Sputnik 1 was pressurized with nitrogen at 1.3atm. The period of the beeping was tied to a pressure sensor. The logic was being that if anything (such as a micrometeoroid) penetrated the satellite, the change in pressure would detect this and inform the scientists on the ground. This simple test had scientific value for the later programs with living samples (including manned spacecraft). Sources:

A Brief History of Sputnik 1

Sputnik 1 (Wikipedia)

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    $\begingroup$ There was also a temperature sensor, but it's not clear to me from Wikipedia if it gave continuous temperature data or only indicated if it went out of a specific temperature range. $\endgroup$ – Russell Borogove Sep 3 at 16:59
  • $\begingroup$ Cool! I learned something. $\endgroup$ – Organic Marble Sep 3 at 18:53
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    $\begingroup$ @RussellBorogove, the "temperature sensor" was a simple bimetallic strip: it could tell if the temperature was over or under a set point. $\endgroup$ – Mark Sep 3 at 20:10
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After the fact, yes, Sputnik 1 had some scientific value. But all it did was beep. That is a fact. It had no scientific payloads.

No matter how much one sugarcoats the after the fact scientific discoveries inferred from Sputnik-1's orbit, the fact is that the Soviet Union intentionally stripped Sputnik-1 of all of the scientific instruments that the USSR Academy of Sciences wanted to install on that first spacecraft to orbit the Earth, replacing them with a radio transmitter than had negligible scientific value. Many of those scientific instruments were built and were installed on Sputnik-3. Sputnik-3 was however launched after the US launched Vanguard-1, which also had scientific payloads.

The sole purpose of Sputnik-1 was to be the first object sent by mankind into orbit and to be able to prove to the world that it was in space (by sending beeps). Being the first in space was in and of itself a spectacular feat, and the leadership of the Soviet Union knew this very well. Despite the fact that all it did was beep, Sputnik-1 places much, much higher in importance historically than did Vanguard-1 or Sputnik-3, both of which place much, much higher in importance scientifically than did Sputnik-1.

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    $\begingroup$ Comments are not for extended discussion; this conversation has been moved to chat. $\endgroup$ – called2voyage Sep 3 at 12:19
  • $\begingroup$ @called2voyage -- Thank you. $\endgroup$ – David Hammen Sep 3 at 12:38
  • $\begingroup$ Wasn't the German V2 rocket the first to reach space? (even though it was a suborbital flight) So the Sputnik was not the first in space, just the first achieving any kind of orbit. $\endgroup$ – vsz Sep 4 at 9:45
  • $\begingroup$ @vsz I specifically wrote that Sputnik-1 was "the first object sent by mankind into orbit" so as to distinguish Sputnik-1 from its suborbital predecessors. $\endgroup$ – David Hammen Sep 4 at 9:53
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Both internal pressure and temperature of Sputnik 1 were encoded in the radio signal.

Analysis of the radio signals was used to gather information about the electron density of the ionosphere. If the temperature exceeded 50 °C (122 °F) or fell below 0 °C (32 °F), another control thermal switch was activated, changing the duration of the radio signal pulses.[57] Sputnik 1 was filled with dry nitrogen, pressurized to 1.3 atm.[40] The satellite had a barometric switch, activated if the pressure inside the satellite fell below 130 kPa, which would have indicated failure of the pressure vessel or puncture by a meteor, and would have changed the duration of radio signal impulse.

Source Wikipedia.

But it was no analog encoding and no digital encoding using a small number of bits. Only the states:

  • temperature above 50 °C
  • temperature lower than 50 °C and above 0 °C
  • temperature lower than 0 °C
  • pressure above 130 kPa
  • pressure below 130 kPa

were transmitted as the duration of the radio pulses and not more.

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