Vrftjkry

How Long?

In the 1960s, unknown to most, the United States set up a secret base on the moon manned by an "extra" aboard each Apollo lander. NASA architects decided that the base must be built into the native rock, taking advantage of lava tubes to quickly conduct themselves below the surface - granting them protection from the heat, cold, and radiation behind dozens of yards of hard rock. The station was powered by a radioisotope thermo-electric generator.

Unfortunately, the base ended in tragedy. Planners had overestimated the quality of air and water scrubbers and also badly underestimated the need for spares. Changing political fortunes at home caused the base and crew to be left for dead. By accident, towards the terrible end the pressure seal on the base was ruptured exposing the crew and structure to the void.

How far forward in the future might it be possible for a future explorer, armed with a map and old government records, to find moonbase Snoopy and still be able to find any of the technology (LED lighting? Computer systems?) still operational?

Would it be possible that anything would be left after centuries? Millenia?

Space scientists strive to get samples from comets and asteroids to better understand the history of our solar system. This because anything which is kept away from the nasty solar radiation is going to take way less damage and thus bear more information.

And if this applies to some icy/rocky body formed few billions of year ago, it has to apply also to tech leftovers produced less than a century ago.

If they are buried deep enough they will get no UV or X-ray from the sun. They might get occasional high energy cosmic rays, but those events do not bring macroscopical damage. Add to this that electronic from the 60'es was much more bulky than present day, thus while a cosmic ray impact might disrupt a 7 nm track today, would just tickle a 0.05 mm track dating back to those times.
The buried artifact will just be subject to the lunar core heat flow, which is small but still sufficient to keep the temperature above the few K of deep space.

Wrapping up, I would say that:

• the exterior aspect of all the items would be preserved pretty well for geological times.


• the functionality might be affected in some cases: cold welding of dry metallic couplings, demagnetization of magnetic elements are just some of the examples that come to my mind.

First what does this base look like?

Taking earth as an analogue lava tubes are about 1-15 metres below the surface. Lets presume the base was the safest possible at 15 metres down.

Now Mars One are projecting a living space of a 1000 square metres for their habitat. So how about a roughly straight section of tube 10 metres wide and 100 metres long.

Danger list:

• Gamma Radiation


• Extreme Heat/Cold


• Space Vacuum


• Asteroids


• The Sun


• Humans

Gamma Radiation

Radiation is all around us, but Gamma Radiation is some of the most high energy. It has a nasty effect on electronics particularly computers. While it may not destroy the computers it will corrupt their running software, which might cause an automated self-destruct sequence to run, or the generators to run too high, etc...

Fortunately a few centimtres of lead or a metre of concrete will save the day. That 15 metres of rock should do the trick.

Also keep explosive things away from the habitat itself, and pipe/cable them.

Extreme Heat/Cold

Being 15metres below the ground this base won't be exposed to the extremes at the surface. Now 1 metre below the surface has a temperature of roughly -21.6 centigrade. At 15 metres we are talking somewhere between -20 and -40. Our equipment regularly survives these temperatures in the arctic/antarctic.

Given that there would be little fluctuation once the heating system failed, this would be unlikely to damage anything in the base. (Aside from initial cooling).

Space Vacuum

Worthy of note, but mostly harmless.

Space being a vacuum means that it has nothing to affect the moon base. The real problem in this scenario is in fact self-harm. The moon base being pressurised could explosively depressurise. Roughly 3000 cubic metres of air (3 metres high by the 1000 metre squared living space) would attempt to vent out one end. The air reserves and any liquid water might decide to do the same thing. Water can boil in space due to lack of air pressure.

As bad as this might sound, structurally speaking the base would be mostly fine. There would be a much larger hole in the habitat were it depressurised, and some amount of mess caused by the rapid air movement. Some things would likely have exploded due to air trapped inside them during manufacture, such as wires, batteries, and computer devices. Some of these may have survived if the government thought to manufacture space worthy versions, instead of using cheaper components presuming the habitat would protect them.

Over time the moon base will leak atmosphere, reducing the amount within. What will cause explosive depressurisation is if a hole forms.

This could be because of some external damage, it is after all in an underground tube, a disturbance could cause rock to hit the habitat and make the hole.

Alternately the most likely culprit is some chemical reaction happening within the habitat. This could be something like acid or a solvent eating through its container, and then affecting the habitat. The more likely is the oxygen in the atmosphere. It loves to react with just about everything. Fortunately your astronaut already dealt with this issue by breathing it in and leaving it as relatively inert carbon dioxide.

Asteriods

The moon gets hit by a lot of rocks, and it has no atmosphere to dissolve them before they hit.

There are a lot of different sized impact craters. Depending on how you try to count it we get around 20 million above the size of 1 km. This is pretty worrying for the moon base because even if the crater is only 2 or 3 metres deep the shockwave could collapse/damage the tunnel, and NASA is worried about that precedent too. Turns out the moons is being hit a lot and often.

If we do some rough calculations. A musketball impact roughly every 1380 years for an area of 752 square meters. That is a direct hit to this moon base, and quite likely catastrophic.

The Sun

... will swallow the earth, or come pretty close in about 7.6 Billion years.

So either the Earth (and its moon) are now parts of the Sun, or the sun is sitting so close that the moons surface starts to liquefy/erode.

Humans

Somewhere between now and the sun killing us all. Humans will want to move.

If we are tardy, the moon is a great mining opportunity for making our trans-solar space ship. I doubt the base would be preserved.

If we are enthusiastic, the Moon will be mined, settled, and used for space ship construction in the not so distant future. It is hard to determine how quickly we would find and/or destroy this base. Most human settlement occurs above the top 10 metres of ground, and it would take numerous generations to get a full population going, presuming that 1/6g is habitable by reproducing humans. Then again, presumably a 15 metre deep lava tube might make a very convenient location to setup, and be found if not immediately then shortly after.

Long answer Short

You have till the first human settlements on the moon, assuming they look for magma tubes too, because they are poorly funded/have to look for cost efficiencies.

Otherwise you probably have 1380 years, maybe a bit more if the site is luckier than expected, or the humans install an atmosphere/laser defense system.

Otherwise you have till the humans need to strip mine/convert the moon sometime later.

7.6 Billion years is the cap, excepting the serious good luck to be missed by those who fly the moon off into deep space.

How Long?

I concur with the other two answers in that everything could be potentialy functional if sufficientley shielded from hard radiation and strikes by macroscopic particles.

However we need to look at several potential problems:

Tectonic activity on the moon - until recentley it was thought that there hadn't been any since the moon's formation roughly 4.6 billion years ago.
The current best theory however is that the most recent scars formed roughly 50 million years ago, and no further activity is expected. No worries here then.

Thermo-electric generators are potentialy going to last that long, still producing energy, depending on what they're made with:

Plutonium oxide was used in the Cassini and the Galileo mission's TEGs - but:

Plutonium-238 has a half-life of 87.7 years

Which is not sufficient to provide appreciable power over a millenium. However:

Am241 (Americium) has a half-life of 432 years and could hypothetically power a
device for centuries.

The equipment was left switched on:

The usual transistor failure occurs gradually over a long period of
time and after thousands of hours of operation. The performance
degradation generally shows up as an increasing saturation current ...
the (device's) efficiency and gain suffer.

As to the monitors - I couldn't find specific figures for Cathode-Ray-Tube electron-gun life-expectancy, but the heater coils show gradual evaporation till they finaly fail - not to mention the gradual wear and tear of the phosphor - if you've ever seen an old multisync monitor you'll remember the permanent silhouette of the default screen etched there.

Electrolytic capacitors.

These are ubiquitous in electronic equipment, they rely on a water based solution inside them to work, so if they're not sealed properly it would evaporate and cause them to fail - and since any rubber seals would have degraded on this timescale... they screw things up for you.

Hot Equipment.

Any equipment that relies on fans or convection currents to keep cool is going to melt if it doesn't trip.

Conclusion.

Providing:

• It had adequate shielding.




• There are no catastrophic collisions from above.




• There's sufficient redundancy in the generators.




• The power tripped "off" when the base became abandoned.




• NASA had the foresight to use rugged tantalum-bead capacitors.

I see no barrier to securing the hatch, repressurising, brushing off the thin layer of dust that's formed and booting up, one system at a time, carefull not to overload these museum pieces. Even after 1000 years in semi-hard vacuum. Difficult to test in our lifetimes though, so even if I'm wrong I can still bet the farm with impunity.