Heat Flow and Physical Properties Package

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Heat Flow and Physical Properties Package (HP3)
HP3 heat flow components.jpg
Components of the HP3 heat flow probe
ManufacturerGerman Aerospace Center (DLR)
Instrument typeinfrared radiometer
FunctionGeophysics of Mars
Mission duration2 years on Mars
Began operationsLanding: 26 November 2018
Mass3 kg (6.6 lb)
Power consumption2 watts
Host spacecraft
SpacecraftInSight Mars lander
Launch date5 May 2018, 11:05 (2018-05-05UTC11:05) UTC
RocketAtlas V 401[1]
Launch siteVandenberg SLC-3E[1]
COSPAR ID2018-042A

The Heat Flow and Physical Properties Package (HP3) is a science instrument onboard the InSight lander that features a probe to study the heat flow and other thermal properties of Mars. The probe is designed to penetrate 5 m below Mars' surface. In March 2019, HP3 successfully burrowed a few centimeters, but then became unable to continue. As of September 2019, work is underway to resolve the issue.

Referred to as a "self-hammering nail"[2] and nicknamed "the mole", it was designed to burrow 5 m (16 ft) below the Martian surface while trailing a tether with embedded heat sensors to measure the thermal properties of Mars' interior, and thus reveal unique information about the planet's geologic history.

HP3 was provided by the German Aerospace Center (DLR), and the tractor mole portion of the instrument was designed by the Polish company Astronika and the Space Research Centre of the Polish Academy of Sciences under contract and in close cooperation with DLR.[2][3]

The Principal Investigator is Tilman Spohn from the German Aerospace Center.[4][5]


The mission aims to understand the origin and diversity of terrestrial planets.[4] Information from the HP3 heat flow package is expected to reveal whether Mars and Earth formed from the same material, and determine how active the interior of Mars is today.[4][5][6][7][8] Additional science goals include determining the thickness of Mars' crust, the composition of its mantle, and thermal characteristics of the interior, such as the temperature gradient and heat flux.[9]

Together with the seismometer, the mission will estimate the size of Mars' core and whether the core is liquid or solid.[10] The vibrations generated by the mole will be monitored by SEIS to learn about the local subsurface.[11]

In addition to the mole, HP3 includes an infrared radiometer (HP3-RAD) mounted to the landing platform, also contributed by DLR.[12][13][14] The HP3 heat flow probe is made up of the following subsystems[15]

  • Support Structure (SS) a housing that includes:
    • Engineering tether (ET) to communicate between the support structure to the lander
    • Science tether (TEM-P) a flex PCB with 14 platinum RTDs for measuring thermal properties of the regolith.
    • Tether length monitor (TLM) optical length meter for measuring the deployed length of the science tether
  • Infrared radiometer (HP3-RAD) for measuring surface temperature.
  • Back end electronics (BEE) electronic control unit
  • Mole penetrometer for burrowing beneath the surface
    • TEM-A active thermal conductivity sensor
    • STATIL tiltmeter for determining orientation and direction of the mole.


HP3 Mars penetrator on Earth

HP3 was conceived by Gromov V. V. et al. in 1997,[2][16] and first flown as the PLUTO instrument on the failed 2003 Beagle 2 Mars lander mission.[2] HP3 evolved further and it was proposed in 2001 for a mission to Mercury,[17] in 2009 to the European Space Agency as part of the Humboldt payload onboard the ExoMars lander,[18][17] in 2010 for a mission to the Moon,[19] and in 2011 it was proposed to NASA's Discovery Program as a payload for InSight Mars lander, known at that time as GEMS (Geophysical Monitoring Station).[6] InSight was launched on 5 May 2018 and landed on 26 November 2018.

Deployment and operation[edit]

The mole penetrator unit is designed to be placed near the lander in area about 3-m long and 2-m wide.[20] The total mass of the system is approximately 3 kg (6.6 lb) and it consumes a maximum of 2 watts while the mole is active.[5]

For displacement, the mole uses a motor and a gearbox (provided by maxon motor ag) and a roller that periodically loads a spring connected to a rod that functions as a hammer. After release from the cam, the hammer accelerates downwards to hit the outer casing and cause its penetration through the regolith. Meanwhile a suppressor mass travels upwards and its kinetic energy is compensated by gravitational potential and compression of a brake spring and wire helix on the opposite side of the mole.[2]

The burrowing mole is a pointed cylinder with a smooth outer surface approximately 35 cm (14 in) in length and 3.5 cm (1.4 in) in diameter. It contains a heater to determine thermal conductivity during descent, and it trails a tether equipped with precise heat sensors placed at 10 cm (3.9 in) intervals to measure the temperature profile of the subsurface.[4][21]

In principle, every 50 cm (20 in) the probe puts out a pulse of heat and its sensors measure how the heat pulse changes with time. If the crust material is a thermal conductor, like metal, the pulse will decay quickly.[5] The mole is first allowed to cool down for two days, then it is heated to about 10 °C (50 °F) over 24 hours. Temperature sensors within the mole measure how rapidly this happens, which tells scientists the thermal conductivity of the soil.[22] Together, these measurements yield the rate of heat flowing from the interior.

HP3 should take about 40 days to reach 5 m (16 ft) deep.[23] As the mole burrows, it should also generate vibrations that SEIS can detect and yield information about the Martian subsurface.[11]

Animation of HP3 being deployed to the surface by the robotic arm (IDA).


Insight's HP3 components after lifting the support structure away from the mole. This image shows a region of compressed regolith around the Mole penetrometer .

In March 2019, the HP3 began burrowing into the surface sand, but became stalled after several inches/cm by what was initially suspected to be a large rock.[24] Further analysis and testing with a replica model on Earth suggested the problem may be due to insufficient friction. In June 2019, more evidence for this was revealed when the support structure was lifted off of the HP3 mole. The Martian regolith appeared to be compressed, leaving a gap around the probe. A proposal is in place to use the lander's robotic arm to press on the soil near the probe, to increase soil friction.[25][26]

HP3-RAD Infrared Radiometer[edit]

The HP3 includes a separate infrared radiometer for measuring surface temperatures, contributed by DLR and based on the MARA radiometer for the Hayabusa2 mission.[12][13][14] HP3-RAD uses thermopile detectors to measure three spectral bands: 8–14 μm, 16–19 μm and 7.8–9.6 μm.[27] HP3-RAD has a mass of 120 g (4.2 oz) (about a quarter pound).[27]

The detector is protected by a removable cover during landing.[28] The cover also serves as a calibration target for the instrument, supporting on-site calibration of the HP3-RAD.[29]

Background about infrared radiometers includes some important Mars science history.[30] They were sent to Mars in 1969 as one of four major instruments on the Mariner 6 and Mariner 7 flyby spacecraft, and the observations helped to trigger a scientific revolution in Mars knowledge.[30][31] The Mariner 6 & 7 infrared radiometer results showed that the atmosphere of Mars is composed mostly of carbon dioxide (CO2), and they were also able to detect trace amounts water on the surface of Mars.[30]

See also[edit]


  1. ^ a b Clark, Stephen (19 December 2013). "Mars lander to launch from California on Atlas 5 in 2016". Spaceflight Now. Retrieved 20 December 2013.
  2. ^ a b c d e Hammering Mechanism for HP3 Experiment (InSight). (PDF) Jerzy Grygorczuk1, Łukasz Wiśniewski1, Bartosz Kędziora1, Maciej Borys, Rafał Przybyła1, Tomasz Kuciński1, Maciej Ossowski, Wojciech Konior,Olaf Krömer, Tilman Spohn, Marta Tokarz and Mateusz Białek. European Space Mechanisms and Tribology Symposium; 2016.
  3. ^ "Polish Kret will fly to Mars". Science in Poland. Retrieved 5 May 2018.
  4. ^ a b c d Banerdt, W. Bruce (2012). InSight – Geophysical Mission to Mars (PDF). 26th Mars Exploration Program Analysis Group Meeting. 4 October 2012. Monrovia, California.
  5. ^ a b c d HP3 Overview. NASA. Accessed: 15 July 2018.
  6. ^ a b Grott, M.; Spohn, T.; Banerdt, W. B.; Smrekar, S.; Hudson, T. L.; et al. (October 2011). Measuring Heat Flow on Mars: The Heat Flow and Physical Properties Package on GEMS (PDF). EPSC-DPS Joint Meeting 2011. 2–7 October 2011. Nantes, France. Bibcode:2011epsc.conf..379G. EPSC-DPS2011-379-1.
  7. ^ Cite error: The named reference mtm was invoked but never defined (see the help page).
  8. ^ Agle, D. C. (20 August 2012). "New Insight on Mars Expected From new NASA Mission". NASA.
  9. ^ mars.nasa.gov. "Goals | Science". NASA's InSight Mars Lander. Retrieved 3 September 2019.
  10. ^ Kremer, Ken (2 March 2012). "NASAs Proposed 'InSight' Lander would Peer to the Center of Mars in 2016". Universe Today. Retrieved 27 March 2012.
  11. ^ a b mars.nasa.gov. "Surface Operations | Timeline". NASA's InSight Mars Lander. Retrieved 24 December 2018.
  12. ^ a b Banerdt, W. Bruce (7 March 2013). InSight: A Geophysical Mission to a Terrestrial Planet Interior (PDF). Committee on Astrobiology and Planetary Science. 6–8 March 2013. Washington, D.C.
  13. ^ a b "InSight: In Depth". Solar System Exploration. NASA. Retrieved 2 February 2018.
  14. ^ a b Grott, M.; et al. (July 2017). "The MASCOT Radiometer MARA for the Hayabusa 2 Mission". Space Science Reviews. 208 (1–4): 413–431. Bibcode:2017SSRv..208..413G. doi:10.1007/s11214-016-0272-1.
  15. ^ "HP3 heat flow probe". DLR Portal. Retrieved 2 September 2019.
  16. ^ Gromov V.V. et al.: The mobile penetrometer, a "mole" for sub-surface soil investigation. In Proc. of 7th European Space Mechanisms and Tribology Symposium. 1997.
  17. ^ a b A heat flow and physical properties package for the surface of Mercury. Tilman Spohn, Karsten Seiferlin. Planetary and Space Science 49(14-15):1571-1577 December 2001. doi:10.1016/S0032-0633(01)00094-0
  18. ^ HP3 on ExoMars. Krause, C.; Izzo, M.; Re, E.; Mehls, C.; Richter, L.; Coste, P. EGU General Assembly 2009, held 19–24 April 2009 in Vienna, Austria.
  19. ^ Measuring heat flow on the Moon — The Heat Flow and Physical Properties Package HP3. (PDF) T. Spohn, M. Grott L. Richter, J. Knollenberg, S.E. Smrekar, and the HP3 instrument team. Ground-based Geophysics on the Moon (2010). Lunar and Planetary Institute, conference 2010.
  20. ^ "Instruments Deployment - SEIS / Mars InSight". www.seis-insight.eu. Retrieved 26 December 2018.
  21. ^ "HP3 (Heat Flow and Physical Properties Probe)". NASA. Retrieved 24 August 2015.
  22. ^ NASA's InSight Prepares to Take Mars' Temperature. Jet Propulsion Laboratory. NASA. 13 February 2018.
  23. ^ InSight- Surface Operations. NASA. Accessed on 18 December 2018.
  24. ^ Dickinson, David (11 March 2019). "Mars Insight's "Mole" Hits a Snag". Sky & Telescope. AAS Sky Publishing, LLC. Retrieved 1 September 2019.
  25. ^ Dickinson, David (3 July 2019). "A Strategy to Get the Mars Insight Lander Back in the Drilling Business". Sky & Telescope. AAS Sky Publishing, LLC. Retrieved 31 August 2019.
  26. ^ "NASA's InSight Uncovers the 'Mole'". NASA/JPL. Retrieved 31 August 2019.
  27. ^ a b Kopp, et all - HP3-RAD: A compact radiometer design with on-site calibration for in-situ exploration
  28. ^ Kopp, Emanuel; Mueller, Nils; Grott, Matthias; Walter, Ingo; Knollenberg, Jörg; Hanschke, Frank; Kessler, Ernst; Meyer, Hans-Georg (1 September 2016). "HP3-RAD: a compact radiometer design with on-site calibration for in-situ exploration". Infrared Remote Sensing and Instrumentation Xxiv. 9973: 99730T. Bibcode:2016SPIE.9973E..0TK. doi:10.1117/12.2236190.
  29. ^ Kopp, Emanuel; Mueller, Nils; Grott, Matthias; Walter, Ingo; Knollenberg, Jörg; Hanschke, Frank; Kessler, Ernst; Meyer, Hans-Georg (2016). "HP3-RAD: A compact radiometer design with on-site calibration for in-situ exploration" (PDF). Infrared Remote Sensing and Instrumentation Xxiv. 9973: 99730T. Bibcode:2016SPIE.9973E..0TK. doi:10.1117/12.2236190.
  30. ^ a b c "Infrared Spectrometer and the Exploration of Mars". American Chemical Society. Retrieved 26 December 2018.
  31. ^ Chdse, S. C. (1 March 1969). "Infrared radiometer for the 1969 mariner mission to Mars". Applied Optics. 8 (3): 639. doi:10.1364/AO.8.000639. ISSN 1559-128X. PMID 20072273.

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