Heat Flow and Physical Properties Package
HP3 on the deck of InSight on Sol 10 on Mars (Dec '18)
|Manufacturer||German Aerospace Center (DLR)|
|Instrument type||infrared radiometer|
|Function||Geophysics of Mars|
|Mission duration||2 years on Mars|
|Began operations||Landing: 26 November 2018|
|Mass||3 kg (6.6 lb)|
|Power consumption||2 watts|
|Spacecraft||InSight Mars lander|
|Launch date||5 May 2018, 11:05UTC|
|Rocket||Atlas V 401|
|Launch site||Vandenberg SLC-3E|
The Heat Flow and Physical Properties Package (HP3) is a science instrument onboard the InSight lander that features a self-penetrating probe to determine how heat flows inside Mars. InSight landed on Mars on 26 November, 2018.
Referred to as a "self-hammering nail" and nicknamed "the mole", it was designed to burrow as deep as 5 m (16 ft) below the Martian surface while trailing a tether with embedded heat sensors to measure how efficiently heat flows through Mars' core, and thus reveal unique information about the planet's interior and how it has evolved over time.
The Principal Investigator is Tilman Spohn from the German Aerospace Center (DLR).
The mission aims to understand the origin and diversity of terrestrial planets. 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. Together with the seismometer, the mission will estimate the size of Mars' core and whether the core is liquid or solid.
HP3 was conceived by Gromov V. V. et al. in 1997, and first flown as the PLUTO instrument on the failed 2003 Beagle 2 Mars lander mission. HP3 evolved further and it was proposed in 2001 for a mission to Mercury, in 2009 to the European Space Agency as part of the Humboldt payload onboard the ExoMars lander, in 2010 for a mission to the Moon, and in 2011 it was proposed to NASA's Discovery Program as a payload for InSight Mars lander, known back then as GEMS (Geophysical Monitoring Station). InSight was launched on 5 May 2018 and landed on 26 November 2018.
The version flown to Mars is nicknamed "the mole", and was designed to burrow as deep as 5 m (16 ft) below the Martian surface to measure how efficiently heat flows through Mars' core, and thus reveal unique information about the planet's interior and how it has evolved over time. HP3 was provided by the German Aerospace Center (DLR), and the tractor mole portion of the instrument was perfected by the Polish company Astronika and the Space Research Centre of the Polish Academy of Sciences under contract and in close cooperation with DLR.
For displacement, the mole uses a motor/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 eventually hitting the outer casing and causing its penetration through the regolith, whereas 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. The burrowing mole is a pointed cylinder with a smooth outer surface approximately 35 cm (13.8 in) in length and 3.5 cm (1.38 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. In principle, every 50 cm (1.5 ft) 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. Together, these measurements yield the rate of heat flowing from the interior.
HP3-RAD Infrared Radiometer
The HP3 instrument is supported by an infrared radiometer measuring surface temperatures, contributed by DLR and based on the MARA radiometer for the Hayabusa2 mission. HP3-RAD uses thermopile detectors to measure three spectral bands: 8-14 μm, 16-19 μm and 7.8-9.6 μm. HP3-RAD has a mass of 120 grams.
Background about infrared radiometers includes some important Mars science history. 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. 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.
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