Getting NASA’s InSight Heat Probe The Rest Of The Way

InSight HP3 instrument
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A perfect deployment of InSight’s Heat Flow and Physical Properties Package (HP3) would place a heat probe up to 16 feet below Mars’ surface to record its interior temperature. But the self-hammering spike stalled at about 12 inches.

The Gist: NASA’s InSight heat probe is stuck, and the team thinks (and hopes) it’s because of the soil not causing enough friction for the self-hammering spike to hit its target depth. A meticulous plan to use the lander’s robotic arm to help get the probe moving again will get started in late June.

What happened? There are a couple of possibilities. Worst case it’s a rock, and the team can’t do much about it. InSight is a lander, not a rover. The team can only work with what’s right under them, and pulling the instrument out isn’t an option. But the team believes a different problem could be the cause. The soil is providing less friction than they expected.

The self-driving spike needs loose soil to flow around it to create enough friction to work against the recoil. Here’s a GIF showing how the probe burrows into the ground.

If the soil is holding together better than expected, than the probe hammers away in place. At least with this problem, there is a potential solution. After testing for several months, the team believes they can use the lander’s robotic arm to press against the ground near the probe to increase the friction of the surrounding soil. A replica in a test bed at a JPL lab shows how this would work.

To try this fix, the robotic arm must first carefully remove the support structure that deployed HP3 in the first place. And carefully is an understatement. It’ll slowly lift the support structure in three phases over a week. Engineers will be analyzing images of this process closely to make sure the probe isn’t coming out of the ground. If it comes out, this part of the InSight mission is over.

If HP3 ends up not working, the InSight mission can still go on. The lander also came to Mars with a seismometer to measure potential Marsquakes. This part of the mission is already seeing results.

But HP3 Instrument Systems Engineer Troy Lee Hudson sums it up best today. “As an engineer, I want to see the instrument we’ve worked on for a decade do the thing it was designed to do.”

It’ll be a while before we know if the HP3 part of the mission can be saved. Right now, the plan is to start lifting the support structure by the end of June. By mid-July, the team should know how they want to proceed from there. After that, more testing before they try the fix.

Hudson also touched why it takes so long to do this in a Q&A:

“We don’t want to take an action that makes the situation worse, so we’ve been moving very carefully. InSight is also a Discovery class mission, meaning it was meant to be more affordable — and to accept more risk — than a flagship NASA mission. So the team is very small; we don’t command the lander every day, and commands that are sent up need to be rigorously tested to make sure they’ll work the way we want them to. We want every action to be safe for HP3, the robotic arm and InSight’s seismometer, which is very close by.”

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