The workshop began with presentations of the robotic missions that have been flown to asteroids and comets. The recently returned sample return mission Hayabusa, taking pride of place. All the presenters had war stories of the operational difficulty of flying to these objects, and some expressed surprise that their missions succeeded at all. They also talked about the high cost of these missions in terms of remote sensing equipment and the lack of good ground truth information to calibrate these instruments.
Unsurprisingly then, they all support a human mission to an asteroid or a comet near Earth to more efficiently gain scientific results. However, when asked about planetary defense, the consensus opinion wasn't just that a human mission would be nice: it is absolutely necessary.
Here's some interesting audio from the workshop.
An asteroid is heading to Earth that will kill every one of us, someday. Hopefully we will discover it and track it for long enough to have 5 or 10 years prior notice. Now what? We'd love to send a robotic probe to get some idea of what the object looks like, what it is made of, how fast it is rotating, etc. Unfortunately, a robotic mission will take at least 5 years to go from concept to launch and it has a very low chance of success at even this precursor mission. Sending a robotic mission to deflect or otherwise mitigate the threat is simply unthinkable at this time.
That means we need to send humans, and it means we need to send them to meet the threat with no robotic precursor. The astronauts will do the scientific investigation to determine the composition of the object. This will most likely include planting seismic detectors, and launching one or more kinetic impactors into the surface. Relaying this data back to Earth, the astronauts would wait for ground control, probably with the support of the national laboratories, to decide on a mitigation plan. Obviously the plan will be limited by what the astronauts have with them, so they will need to carry an array of tools for the various types of threats that may be expected.
For example, the best strategy may be to install large motors which provide constant thrust for a period of years diverting the asteroid off course just enough to miss the Earth. Such a strategy would only be possible on objects where in-situ resource utilization could produce sufficient propellant. Another strategy may just be the placement of a station keeping spacecraft with a lot of mass, possibly removed from the surface of the object, to act as a "gravity tractor", again diverting the course away from Earth. More exotic strategies may include converting rotational energy into propulsive energy using long tethers or in the drastic use of nuclear bombs.
The workshop continues today and is being webcast. Ultimately, failure to send astronauts to visit near-Earth objects within the next few decades will be fatal to humanity, so tune in and participate.