When you must send the machine
Sometimes a robot is the better choice. Sometimes it is the only one. Two disasters, one year apart, drew that line in public.
In April 2010 the Deepwater Horizon rig exploded and sank, leaving a well gushing oil 1,500 metres down in the Gulf of Mexico. For 87 days, every attempt to cap it — every valve turned, every saw cut, every cap lowered — was carried out by work-class ROVs, a dozen or more at a time, their pilots crowded into control vans on ships above. At that depth there was no plan B involving people. The robots were not assisting the response; at the seafloor, they were the response.
A year later, robots of the opposite kind closed another wound. Air France 447 had gone down in the mid-Atlantic in 2009, and two years of searching had found nothing. In 2011 a team deployed REMUS 6000s — autonomous, untethered torpedo-shaped robots that fly sonar surveys on their own for a day at a time. Within a week of the campaign's start, they had mapped the debris field at about 3,900 metres, leading to the recovery of the flight recorders and, finally, answers.
An ROV with a human's hands on the sticks; an AUV trusted to search alone in the dark. Neither is "better". They sit on different rungs of the same ladder.
The intervention ladder
When something must happen underwater, engineers climb four rungs. Replace: send the machine instead of a person wherever the job is deep, long, or lethal — the Deepwater ROVs, the AF447 survey. Nobody dives a blowout.
Extend: when people do go, machines stretch their reach — a diver's sonar, a submersible's manipulator arm, Alvin carrying scientists' eyes to the vents.
Reach: some places no human craft visits at all — under polar ice shelves, inside flooded tunnels and wreck interiors, in the hadal trenches. There the choice is a robot or nothing.
Restrain: and sometimes the mission is to not touch — survey a war grave without disturbing it, watch a reef without landing on it. Standoff sensing is intervention too. The Observatory's own protection tiers are this rung written into a database: some wrecks you may approach, some you may only know exist.
Five real-world missions, one at a time. Choose which rung of the ladder fits — replace, extend, reach, or restrain — and see the reasoning after each call.
Fly to the stretch of mid-Atlantic where the REMUS fleet found AF447 in 2011 — a needle recovered from 3,900 metres by robots searching alone.