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InSight's HP3 probe is meant to drill deep into Martian soil. And the depth of reach is determined by whether there is a rocky layer underneath or not. If it's loose soil all the way down, merrier it will be. Insight Lander probe labelled But, if the mole hits a rocky surface, can the probe retract the tether, and let the robotic arm reposition the probe to a new place?

Or in case of a uniform regolith condition, can the HP3 instrument be repositioned in multiple places to assess the homogeneity of the soil?

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    $\begingroup$ @uhoh I tried to add a picture too, but couldn't from my mobile. I'll try to add it soon too $\endgroup$ – karthikeyan Nov 26 '18 at 17:18
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    $\begingroup$ dlr.de/dlr/en/desktopdefault.aspx/tabid-11038/1865_read-27097 $\endgroup$ – uhoh Nov 26 '18 at 17:19
  • $\begingroup$ The heat flow probe does not drill, it hammers itself down into Martian soil. Drilling by rotation is not possible due to the ribbon cable to the probe $\endgroup$ – Uwe Nov 28 '18 at 10:51
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No, using information in the link provided by @uhoh.

  1. As the purpose of the HP3 probe is to take temperature measurements, it must not be in the shade of either the InSight lander or the SEIS module. It also must be within the reach of the robotic arm that places it. The two green areas below show where SEIS and HP3 can be placed. SEIS gets first priority, and HP3 gets the other side. So, even if you could re-use HP3, there isn't anywhere else to put it.

InSight instrument placement

  1. The head of the "mole" is attached by a ribbon cable, as shown in the picture below. The markings on the top and bottom of the picture are read by optical sensors, which help determine how far the mole has descended. Once in the ground, the markings are likely to get dirty, and can no longer be read. Thus, a second deployment might not be able to determine the depth into the ground.

HP3 tape

  1. In order to be reused, the ribbon cable would have to be re-wound onto its spool. I haven't found any documentation about a motor that will do that.

  2. The following quote from the article suggests that the head is designed to move only one-way:

The masses and springs are designed in such a way that the probe acts like a mechanical 'diode'. It penetrates the ground as the friction from the walls absorbs the recoil.

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  • $\begingroup$ I guess he mechanical diode reference is to indicate that the probe will move in one direction due to the internal movements of the spring and masses. And thanks for a critical analysis of the link shared by @uhoh $\endgroup$ – karthikeyan Nov 27 '18 at 6:14
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    $\begingroup$ The force necessary to pull the mole back from the soil would be too high for the ribbon cable. Pulling the ribbon cable down following the mole into the soil requires much less force. The friction between soil and cable is much smaller than between soil and mole. $\endgroup$ – Uwe Nov 28 '18 at 11:16

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