InSight Instrument Deployment Arm

Overview

The Instrument Deployment Arm placed the InSight lander’s two primary instruments on the surface of Homestead hollow in western Elysium Planitia, then spent the rest of the mission doing work it was not built for: pressing on regolith, pinning and hammering a stuck penetrator, and throwing soil across the solar arrays to let the wind clean them. It began as the Mars Surveyor 2001 lander arm, a four-degree-of-freedom backhoe with graphite-epoxy links, a scoop-and-grapple end effector, and no force-torque sensor of any kind [2]. That grapple was designed to tolerate about 7 mm of arm positioning error when lifting the Marie Curie rover off the lander deck, deploying it in 3 cm steps until the crowfoot disengaged [2]. The version refurbished to fly on InSight replaced the links with titanium, raised the joint torques, and kept the predecessor’s blind spot: end-effector force still has to be inferred rather than measured.

The mole recovery campaign the arm carried out is described on the InSight HP3 mole page.

Specifications

Parameter	Value
Degrees of freedom	4: shoulder azimuth, shoulder elevation, elbow, wrist
Reach	1.8 m
Link material	titanium
Payload capacity	9 kg at 1.65 m extension in Mars gravity, equivalent to 33 N
Peak joint torque	35, 120, 65 and 10.5 N·m, joints 1 to 4
End effector	scoop with a 250 cm³ chamber, plus grapple
Scoop chamber	approximated as a 7.5 × 5 × 4.5 cm box plus a half box; bottom blade 7.5 cm wide
Qualified temperature range	-110 to +70 C structure and joints; -60 to +70 C motors

Source: [6].

Every row in that table is a design specification or a design capability, not a measured performance, and the same is true of the two numbers most likely to be mistaken for measurements: the 1 cm positioning accuracy and 1.5 cm instrument position knowledge are requirements the deployment system had to meet, not a demonstrated repeatability, and what was measured against them is the cross-check, an IDC stereo orthophoto and a monocular fiducial localization that agreed to 1 to 2 cm on the surface [6].

Running the motors below their qualification floor

From sol 550 the joint heaters were not run at night and the motors dropped below -90 C against a -60 C qualification floor, with no degradation and no operational impediment observed through the rest of the arm’s 1,442-sol mission, 30 C of margin below a ground qualification limit established by flying it rather than by testing it, on a single vehicle over one mission rather than as a bound on the design [6].

Force without a force sensor at the wrist

No contact force the InSight arm applied on the surface was measured directly. Every figure comes from reproducing the flight arm pose in a JPL testbed and reading a three-axis load cell in Earth gravity, and the reconstruction shows the force is strongly pose dependent: scoop pushes at the same site gave median forces that varied by a factor of three between a flat pose and a vertical-forearm pose [6]. A single contact-force figure for the arm does not exist, and the 80 N average downward force often quoted as the end effector’s capability is a nominal figure carried over unchanged from the predecessor arm’s own design description [2], not a per-activity measurement.

Cleaning the solar arrays with the scoop

Seven times the arm dumped soil from its scoop onto the lander deck so wind would carry it across the solar arrays and abrade the dust off them, and six of the seven produced a measurable power gain totaling about 15 percent of array output in that period and extending the mission by roughly 242 sols, while the seventh, dumped in low wind, produced none, since the technique depends on wind the operator does not control and the gain is not attributable dump by dump [6].

Soil properties inferred from arm contact

The arm’s contact record is the input to a soil model built by the HP3 mole team rather than a set of soil measurements in its own right. Duricrust cohesion at the landing site is 2 to 15 kPa from mole penetration resistance and cone penetration theory, corroborated by an independent estimate of about 6 kPa from the arm chopping the crust with its scoop blade [17]. Bulk density runs from about 1200 kg/m³ at the surface to 1600 kg/m³ in the deepest sand and gravel reached, a derived model of only the first 40 cm [17]. Penetration resistance in that sand and gravel layer was 5.3 MPa, seven to eighteen times higher than in the overlying duricrust [17]. Hammer strokes recorded by the seismometer gave P-wave and S-wave velocities of 114 and 60 m/s in the duricrust, and shear, bulk and Young’s moduli of 4.32, 9.84 and 11.30 MPa [17].

One deliberate mechanical experiment was run on the regolith itself: on sols 1074 to 1075 the arm pushed to four sequential commanded depths from a 1 cm standoff, with current and torque limits set for maximum downward force, and the imprint depth was read from digital elevation models built from IDC images [6].

References

Bonitz, R., Nguyen, T. and Kim, W. (2000). The Mars Surveyor 2001 Rover and Robotic Arm . IEEE Aerospace Conference. Source

BibTeX

@inproceedings{bonitz2000mars,
  title = {The Mars Surveyor 2001 Rover and Robotic Arm},
  author = {Bonitz, R. and Nguyen, T. and Kim, W.},
  booktitle = {IEEE Aerospace Conference},
  publisher = {JPL Open Repository},
  year = {2000},
  url = {https://dataverse.jpl.nasa.gov/dataset.xhtml?persistentId=hdl:2014/18730}
}

Golombek, M., Hudson, T., Bailey, P., Balabanska, N., Marteau, E., Charalambous, C., Baker, M., Lemmon, M., White, B. R., Lorenz, R. D., Spohn, T., Maki, J., Kallemeyn, P., Garvin, J. B., Newman, C., Hurst, K., Murdoch, N., Williams, N., Banerdt, W. B., Lognonné, P., Delage, P., Lapeyre, R., Gaudin, E., Yana, C., Verdier, N., Panning, M. P., Trebi-Ollennu, A., Ali, K., Mittelholz, A., Johnson, C. S., Langlais, B., Warner, N., Grant, J., Daubar, I. J., Ansan, V., Vrettos, C., Spiga, A., Banfield, D., Gomez, A. R., Mishra, P., Dotson, R., Krause, C., Sainton, G. and Gabsi, T. (2023). Results from InSight Robotic Arm Activities . Space Science Reviews. Source

BibTeX

@article{golombek2023results,
  title = {Results from InSight Robotic Arm Activities},
  author = {Golombek, M. and Hudson, T. and Bailey, Philip and Balabanska, Nadya and Marteau, E. and Charalambous, C. and Baker, Michael and Lemmon, M. and White, Bruce R. and Lorenz, Ralph D. and Spohn, Tilman and Maki, J. and Kallemeyn, P. and Garvin, James B. and Newman, C. and Hurst, Kenneth and Murdoch, Naomi and Williams, N. and Banerdt, W. Bruce and Lognonné, P. and Delage, P. and Lapeyre, R. and Gaudin, E. and Yana, Charles and Verdier, N. and Panning, Mark P. and Trebi-Ollennu, Ashitey and Ali, K. and Mittelholz, A. and Johnson, Christopher S. and Langlais, B. and Warner, N. and Grant, J. and Daubar, Ingrid J. and Ansan, Veronique and Vrettos, Christos and Spiga, Aymeric and Banfield, Don and Gomez, Annabel R. and Mishra, Pranay and Dotson, Ryan and Krause, Christian and Sainton, G. and Gabsi, T.},
  journal = {Space Science Reviews},
  publisher = {JPL Open Repository},
  year = {2023},
  doi = {10.48577/jpl.87kgn1}
}

Spohn, T., Hudson, T. L., Marteau, E., Golombek, M., Grott, M., Wippermann, T., Ali, K. S., Schmelzbach, C., Kedar, S., Hurst, K., Trebi-Ollennu, A., Krause, C. and Kroemer, O. (2022). The InSight HP3 Penetrator (Mole) on Mars: Soil Properties Derived From the Penetration Attempts and Related Activities . Space Science Reviews. Source

BibTeX

@article{spohn2022insightb,
  title = {The InSight HP3 Penetrator (Mole) on Mars: Soil Properties Derived From the Penetration Attempts and Related Activities},
  author = {Spohn, Tilman and Hudson, Troy L. and Marteau, Elodie and Golombek, Matthew and Grott, Matthias and Wippermann, Torben and Ali, Khaled S. and Schmelzbach, Cedric and Kedar, Sharon and Hurst, Kenneth and Trebi-Ollennu, Ashitey and Krause, Christian and Kroemer, Olaf},
  journal = {Space Science Reviews},
  volume = {218},
  pages = {72},
  year = {2022},
  doi = {10.1007/s11214-022-00941-z},
  abstract = {Abstract The NASA InSight Lander on Mars includes the Heat Flow and Physical Properties Package HP 3 to measure the surface heat flow of the planet. The package uses temperature sensors that would have been brought to the target depth of 3–5 m by a small penetrator, nicknamed the mole. The mole requiring friction on its hull to balance remaining recoil from its hammer mechanism did not penetrate to the targeted depth. Instead, by precessing about a point midway along its hull, it carved a 7 cm deep and 5–6 cm wide pit and reached a depth of initially 31 cm. The root cause of the failure – as was determined through an extensive, almost two years long campaign – was a lack of friction in an unexpectedly thick cohesive duricrust. During the campaign – described in detail in this paper – the mole penetrated further aided by friction applied using the scoop at the end of the robotic Instrument Deployment Arm and by direct support by the latter. The mole tip finally reached a depth of about 37 cm, bringing the mole back-end 1–2 cm below the surface. It reversed its downward motion twice during attempts to provide friction through pressure on the regolith instead of directly with the scoop to the mole hull. The penetration record of the mole was used to infer mechanical soil parameters such as the penetration resistance of the duricrust of 0.3–0.7 MPa and a penetration resistance of a deeper layer ( $&gt;30~\text{cm}$ &gt; 30 cm depth) of $4.9\pm0.4~\text{MPa}$ 4.9 ± 0.4 MPa . Using the mole’s thermal sensors, thermal conductivity and diffusivity were measured. Applying cone penetration theory, the resistance of the duricrust was used to estimate a cohesion of the latter of 2–15 kPa depending on the internal friction angle of the duricrust. Pushing the scoop with its blade into the surface and chopping off a piece of duricrust provided another estimate of the cohesion of 5.8 kPa. The hammerings of the mole were recorded by the seismometer SEIS and the signals were used to derive P-wave and S-wave velocities representative of the topmost tens of cm of the regolith. Together with the density provided by a thermal conductivity and diffusivity measurement using the mole’s thermal sensors, the elastic moduli were calculated from the seismic velocities. Using empirical correlations from terrestrial soil studies between the shear modulus and cohesion, the previous cohesion estimates were found to be consistent with the elastic moduli. The combined data were used to derive a model of the regolith that has an about 20 cm thick duricrust underneath a 1 cm thick unconsolidated layer of sand mixed with dust and above another 10 cm of unconsolidated sand. Underneath the latter, a layer more resistant to penetration and possibly containing debris from a small impact crater is inferred. The thermal conductivity increases from 14 mW/m K to 34 mW/m K through the 1 cm sand/dust layer, keeps the latter value in the duricrust and the sand layer underneath and then increases to 64 mW/m K in the sand/gravel layer below.}
}

InSight Instrument Deployment Arm

Overview

Specifications

Running the motors below their qualification floor

Force without a force sensor at the wrist

Cleaning the solar arrays with the scoop

Soil properties inferred from arm contact

References

Further reading