The Wikipedia subsection Moonquake says:

Information about moonquakes comes from seismometers placed on the Moon by Apollo astronauts from 1969 through 1972. The instruments placed by the Apollo 12, 14, 15 and 16 functioned perfectly until they were switched off in 1977.

According to NASA, there are at least four different kinds of moonquakes:

  • Deep moonquakes (~700 km below the surface, probably tidal in origin)
  • Meteorite impact vibrations
  • Thermal moonquakes (the frigid lunar crust expands when sunlight returns after the two-week lunar night)
  • Shallow moonquakes (20 or 30 kilometers below the surface) The first three kinds of moonquakes mentioned above tend to be mild; however, shallow moonquakes can register up to 5.5 on the Richter scale. Between 1972 and 1977, 28 shallow moonquakes were observed. On Earth, quakes of magnitude 4.5 and above can cause damage to buildings and other rigid structures.

Question: Why were the "perfectly functioning" seismometers placed by Apollo 12, 14, 15 and 16 astronauts all shut off in 1977?

See the question Any potential downside to throwing personal life support out the door on the Moon? for more about the Apollo lunar seismometers.

below: images from ALSEP, Apollo Lunar Surface Experiments Package, 20 November 1969 – 30 September 1977, by Hamish Lindsay, Click for full size.

NASA scientists Lunar data NASA Lunar seismogram


From Wikipedia:

The ALSEP system and instruments were controlled by commands from Earth. The stations ran from deployment until they were turned off on 30 September 1977 due primarily to budgetary considerations. Additionally, by 1977 the power packs could not run both the transmitter and any other instrument, and the ALSEP control room was needed for the attempt to reactivate Skylab. ALSEP systems are visible in several images taken by the Lunar Reconnaissance Orbiter during its orbits over Apollo landing sites.

From a NASA page about ALSEP:

ALSEP was a collection of geophysical instruments designed to continue to monitor the environment of each Apollo landing site for a period of at least a year after the astronauts had departed. Designed for a life of one year (Apollo 17 was designed for two), they ended up working for up to 8 years, the experiments permanently shut down by Mission Control on 30 September 1977.

From a NASA paper about shutdown of ALSEP:


On September 30, against the backdrop of a waning moon, science instruments on the lunar surface will be turned off and the ALSEP (Apollo Lunar Surface Experiments Package) control center at NASA's Johnson Space Center, Houston, will be dismantled.
The Apollo lunar science stations will be shut down because of dwindling power reserves at the stations and budgetary limitations here on Earth.

The timing is perhaps appropriate, for every day the small radioactive thermoelectric generators which power the stations decay a little more. When the next year rolls around there are good odds that at least one of the stations will have so little power only the transmitters could function anyway.

The "perfectly functioning" seismometers have worked for eight years, but they would have stoped working in a short time anyway without the necessary electric power from the RTGs.

  • 5
    $\begingroup$ I expect Sept. 30 was the cutoff because it is the last day of the US government fiscal year; if you don't have a legally enacted appropriation and apportionment for the new year, continuing to spend (or obligate) money will likely get you fired and it is not impossible to go to prison for this. $\endgroup$ – dave_thompson_085 Apr 7 '18 at 11:46
  • 4
    $\begingroup$ @uhoh When you no longer use a device, do you not shut it off? It's good practice, plus human nature. Practical reasons - eliminate extraneous broadcasts from the surface that might interfere with other observations. Less practical - it makes less sense to leave something on when you're done than it does to turn it off. $\endgroup$ – Saiboogu Apr 7 '18 at 13:52
  • 2
    $\begingroup$ @dave_thompson_085: A cite from VF5.pdf: "At the end of the fiscal year the ALSEP stations will be left on their own, all but their transmitters muted. Funding for the technical and scientific support needed to maintain the stations will cease on September 30." $\endgroup$ – Uwe Apr 8 '18 at 9:12
  • 1
    $\begingroup$ @Saiboogu Aha, it seems they may in fact NOT have turned off the transmitters after all! I've just asked Were the Apollo lunar transmitter signals ever analyzed or used after the experiments were shut down? $\endgroup$ – uhoh Apr 8 '18 at 13:11
  • 1
    $\begingroup$ @Uwe "ditto" to you as well. So now I understand what you mean by "muted", there could be an unmodulated carrier, but no data. Perhaps the answer should be adjusted; the seismometers and other experiments were shut down so that there would be enough power to let the transmitters continue to operate! $\endgroup$ – uhoh Apr 8 '18 at 13:27

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