InSight Surface Operations, 26 Nov 2018- 21 Dec 2022 Options

[nprev]

Congratulations to the InSight team on a successful landing! We'll discuss the remainder of the mission here.

[Gerald]

In case the next hammering attempt won't work in the intended way, and the mole would otherwise be given up, I'd suggest to further narrow down the root cause of the presumed bouncing.

One activity would be an attempt to verify with the scoop that there actually isn't a pebble, bedrock, or another crust layer, i.e. perform some digging. The goal is to ensure that the behaviour of the mole is unambigously caused by the property of the fine-grained soil phases. A first digging campaign would be performed in a safe distance from the mole to study the general layering structure of the soil. If this doesn't find obvious obstacles, digging next to the mole may be considered. This latter location would also be the only option to dig, if the upper duricrust turns out that it can't be penetrated by the scoop alone.

Another conceivable explanation to be ruled out is whether the density of the mole is less than the density of the soil, which would cause bouyancy.

Other experiments would repeat (cautious) hammering with different inclinations of the mole in order to get responses within a more homogenious soil environment. The bouncing might be caused by the vertical gradient of some property of the soil. If such a gradient exists, it would be smaller for a less inclined mole, with a possibly favorable change of its behaviour, but at least with additional data about inclination-dependent soil behaviour. A less inclined mole would also be able to discriminate between bouyancy (parallel to the gravity field lines) and bouncing (parallel to the hammering vector).

Since I'm not an expert in rheology, but this is a broad field of ongoing research, a student or post-doc in rheology would certainly give more advice than I could.
As usual, any experiments should be sorted by increasing risk. And I'm of course aware that things are much easier said than done.

[Brian Swift]

And I'm of course aware that things are much easier said than done.

I'll speculate the termination of further investigation is primarily a matter personnel scheduling and budget.
Implementing these ideas would require a non-trivial amount of engineering time. And if "the system" is working
well, those engineers are already scheduled to be working on and receiving their funding from other projects in 2021.
I imagine that some amount of the project's reserves budget has already been consumed by mole engineering work done in 2020.
And reducing a projects reserves budget is another form of risk.

[stevesliva]

Yeah, soil investigations would be an XM sort of thing. But it might not pencil out.

Primary mission was to be 709 sols and we're past 730? Wonder what's up there.

Different topic.
In addition to the Nature article with the "final try" comment, I notice there's a JPL release from a couple days ago, which doesn't say much about the mole:
https://www.jpl.nasa.gov/news/news.php?feature=7802

[Gerald]

Yeah, soil investigations would be an XM sort of thing. But it might not pencil out.

With an idealized tilt angle of ~53° between the pointing of the mole and the surface normal, a 5 m teather would still be long enough to reach a nominal 3 m depth required to accomplish the primary science objective (take the triangle defined by the Pythagorean triple 3³+4²=5²).
Within those constraints, this would presumably maximize the friction between the mole and the soil beneath induced by the weight of the mole.
So, this approach would probably feasible without an entirely new proposal.