Question: **Dateline**: 2067

**Setting**: A research base at the bottom of the [Marianas Trench](https://en.wikipedia.org/wiki/Mariana_Trench)

**Depth**: 10,000 meters.

**Mission Duration**: Thirty days

A research base lies at the bottom of the Marianas Trench, housing 10-12 scientists of both sexes and a cat.

The mission starts well, the team have trained together for months, and they're tight knit. At least they thought they were...

One by one, they start to die, and it becomes obvious that their deaths are not accidental.

**Question**:

What would be a reasonable prime purpose of this research mission? For what reason would a dozen scientists be sent to the bottom of the ocean for a month where a robot/scans would not be appropriate?

Answer: 
**Mars practice.**

I hope someone remembers Pauly Shore and Biodome, and thinks about that movie often. In any case, a reasonable premise for this deep sea mission could be practice for a prolonged space mission on the moon, Mars or elsewhere. This was the original goal behind [Biosphere 2](https://en.wikipedia.org/wiki/Biosphere_2): a contained environment where teams could practice for long extraterrestrial assignments. 

 One could make a case that the ISS could better serve in this role but there are any number of reasons why a practice run like this might not be doable in the ISS. Maybe ISS is reserved for months in advance, or the microgravity means it is a poor simulation, or it does not allow cats.
We would like to build underwater buildings with internal pressures of 100 atmospheres or more, which reduces the strength needed by the outer hull to keep the water out. A hydrogen-oxygen-helium mixture works, but hydrogen is a narcotic at those pressures. A special narcotics-blocking agent will supposedly allow people to function normally, but must pass Phase II trials to assess its effectiveness and side effects.

The scientists will use an abandoned military facility at the bottom of the Marianas Trench to save on costs, and because it happens to have built-in mechanisms capable of supporting 100 atmospheres of pressure.

Bummer - it turns out that long term side-effects of the drug include paranoid delusions. Bonus: the scientists would like to discontinue its use, but they have found cracks in the facility's hull and must keep the air pressure high to avoid collapse. It's going to be a long month.

<https://www.divecompare.com/blog/different-gases-used-for-diving/>