19 November 2018
After the cruise stage is jettisoned, the landing probe will enter the Martian atmosphere at 20:47 CET at a speed of 3600 kilometres per hour. An intervention in the landing process is not possible: Since it takes a signal from Earth to reach Mars 8 minutes and 6 seconds, the landing will have already taken place by the time the last signal from InSight before entering the atmosphere reaches Earth. The probe will reach the surface seven minutes after atmospheric entry. About half a minute after entering the atmosphere, the friction of the gas molecules of the high atmosphere will cause the heat shield to begin to glow at the tip at a temperature of about 1500 degrees Celsius and then cool again. Peak deceleration will happen about 2 minutes after atmospheric entry 15 seconds later, at up to 7.5 g. Before the parachute is deployed, friction between the atmosphere and the heat shield will remove nearly 99.5 percent of the entry vehicle’s kinetic energy.
DLR (CC-BY 3.0).
InSight's solar panels are deployed and the probe is tested in its deployment configuration during a test in the clean room. In the middle of the platform, the protective cover of the seismometer SEIS, to the right of which is the heat flux probe HP3 developed at DLR.
For the InSight mission, a landing area was sought that had to meet several scientific criteria, but above all space systems engineering criteria. For a secure energy supply from solar power and to avoid extreme diurnal and seasonal temperature variations, it could not be too far north or south of the equator, it had to be flat and, as far as possible, not covered by rocks. After a long selection process, engineers and scientists selected an area in a plain southwest of the large volcanic complex surrounding Elysium Mons. The chosen site is in Elysium Planitia, north of the Martian equator and the highland border – just a few hundred kilometres north of Gale Crater (below the ‘4’ in the latitude label), in which the NASA rover Curiosity has been driving since 2012. The image is a section of a global topographic map of Mars; blue and green are low-lying areas, yellow and red are elevated terrain. The image is about 5000 kilometres wide.
The InSight brake parachute opens at the supersonic speed of 1500 kilometres per hour. The initial load on deployment at an altitude of 12 kilometres is 55,600 Newton. Barely three minutes later, 1200 metres above the landing site, the probe will separate from the parachute and use its descent engines to decelerate until landing at around 20:53 CET. The picture shows the supersonic parachute at Lockheed-Martin in Denver, Colorado during a test.
Launched on 5 May 2018, NASA’s InSight spacecraft will land on 26 November, just north of the Martian equator, and deploy its solar panels. SEIS, an instrument for recording seismic waves (left of image), and HP3, an instrument developed by DLR to measure the thermal conductivity of the Martian regolith and the heat flow from the interior of the planet (right of image), will be placed on the surface of the planet possibly before the turn of the year.
InSight’s structural design is similar to that of NASA’s Phoenix lander from 2008. The main component is a platform two metres in diameter, on which most of the system components – the experiments in their ‘transport mode’, the antennas, the on-board computer, the thrusters, the propellant tanks and three telescopic legs are attached. A robotic arm will be deployed after landing and lift the experiments HP3 and SEIS from the platform onto the Martian surface. At the side of the platform are two solar panels, which produce a maximum of 700 watts, depending on the distance between Mars and the Sun. The RISE experiment is conducted from the platform itself.
DLR has contributed the HP3 experiment to the NASA InSight mission. HP3 stands for ‘Heat Flow and Physical Properties Package’ and the instrument was developed under the leadership of the DLR Institute of Planetary Research. The thermal conductivity of the material below the landing site and the heat flow from the interior of Mars to the surface will be measured using a penetrometer hammered five metres deep into the Martian regolith. The experiment is designed for an operational life of two Earth years. Essential components of HP3 are the ‘Mole’ and the ribbon cable with the temperature sensors, which the Mole will pull behind it into the ground to perform measurements.
The InSight mission will investigate the internal structure of Mars and the processes at play inside the planet to acquire a better understanding of the formation and evolution of earth-like planets. Similar to the other terrestrial planets – Mercury, Venus, Earth and the Moon – Mars has a metallic core surrounded by a rocky mantle, over which lies a rocky crust. According to model calculations, the core has a temperature of about 1900 degrees Celsius and could still be molten if it contains a significant amount of sulphur. This is one of the questions that the InSight mission will address. The mission will also conduct a study of seismic activity and measure the meteorite impact rate on Mars.
It will be the deepest hole ever hammered into another celestial body using manmade technology. During the NASA InSight mission, the Heat Flow and Physical Properties Package (HP3), the Mole, which was developed and built by the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) will penetrate up to five metres deep into the Martian soil to measure the temperature and thermal conductivity of the substrate materials there. This glimpse of the interior of the Red Planet will help us to better understand the formation and evolution of Earth-like bodies. The landing is scheduled to take place at 20:53 CET on 26 November 2018 on the Elysium Planitia plain, a bit north of the Martian equator. As the hour approaches, excitement is mounting over where exactly the landing probe will touch down within the 140-kilometre-long landing ellipse and where an appropriate spot for the historic Mars experiment might be found at the landing site. Until now, heat flow measurements have only been performed on the Moon, as part of the Apollo 17 mission, during which the astronauts Eugene Cernan and Jack Schmitt used a hand-powered drill to bore up to three metres into the surface.
"Our Mars mole is doing well on board InSight on its final stretch to Mars," says the Principal Investigator of the HP3 experiment, Tilman Spohn of the DLR Institute of Planetary Research in Berlin. "Checks during the cruise phase did not reveal any irregularities. Now we are eagerly yet confidently awaiting the landing just a few days from now."
Spohn and a number of other DLR scientists will be at the Jet Propulsion Laboratory (JPL) on 26 November, which runs the mission for NASA. Also present will be scientists from the DLR Microgravity User Support Center in Cologne (MUSC), which is directly involved with the mission operations team that is controlling the mole. "From the landing and the choice of a definitive site on the surface all the way through to the successful penetration of the Martian soil, we will be working directly with our US colleagues at the control centre in Pasadena, California," says HP3 Operations Manager Christian Krause.
The deployment of the HP3 experiment is now planned for early January 2019. At this point, the penetrometer will gradually hammer down to a depth of five metres in 50-centimetre progressions over three phases that will be repeatedly interrupted by measurements and checks. It will use a fully automatic electrically powered hammer mechanism and pull a tether fitted with measuring sensors behind it along into the Martian soil. "As we do not know what surprises – hard rocks, for instance – may await us underground, we will proceed with great caution and are planning to reach our target depth within several weeks, in March 2019," adds Spohn. Another part of the HP3 experiment involves an infrared radiometer, which will be activated shortly after the landing and will measure the surface thermal radiation yielding the temperature of Mars from the lander platform. Together, these datasets will make it possible to draw conclusions about the planet's heat flow.
Landing in a 'car park'
In order to mitigate the risks to the mission, the engineers and scientists have chosen a landing area southwest of the large Elysium volcanic complex, on the Elysium Planitia plain, which is largely flat and free of large stones and rocks. The deliberate monotony of this landing site, essential for conducting measurements beneath the surface of Mars, has led NASA researchers to describe the landing, in tongue-in-cheek fashion, as taking place on a large 'parking lot'. Yet even here, precise analysis of landing site will be necessary from the very start. Once this has been done, a robotic arm will set the seismometer SEIS (Seismic Experiment for Interior Structure), built under the lead of CNES by an international consortium to which DLR has also contributed, down on the surface. The seismometer will record waves that originate from marsquakes and meteorite impacts and propagate through the planet. As a next step, the HP3'Mole' experiment, which was developed and built at DLR, will be placed on the surface. The InSight landing platform also carries the US experiment RISE (Rotation and Interior Structure Experiment), which will record fluctuations in the Mars' rotation axis.
Braking manoeuvre at 1500 degrees Celsius
Before the measurements can begin, InSight must first endure the roughly seven-minute critical Entry, Descent and Landing phase (EDL). On 26 November 2018 at 20:47 CET, the probe will enter the Martian atmosphere at a shallow angle. In the process, the protective shield will heat up to around 1500 degrees Celsius within three minutes. The friction with the Martian atmosphere will slow down the probe until a parachute opens 12 kilometres above the ground, allowing the lander to slowly float down to the planet's surface. Upon separation from the parachute at an altitude of 1200 metres, InSight will be decelerated by its descent engines. Contact will be maintained with the space probe during its flight to Mars and over the course of the mission via the 70-metre antennas of NASA's Deep Space Network in California, Australia and Spain. The NASA Mars Reconnaissance Orbiter and Mars Odyssey 2001 probes will fly over the InSight landing site twice per Martian day and will serve as relay stations for communications with Earth.
Looking at Mars to discover how Earth was formed
InSight is a stationary geophysical observatory, and the only one of its kind in the history of Solar System research. Its main scientific task is to investigate the interior and composition of our neighbouring planet, examining the evolution, structure and physical properties of the crust, mantle and core, thus enabling us to draw conclusions about the formation and evolution of terrestrial bodies. Mars is the perfect destination, as it is relatively easy to reach and makes an ideal comparison object to Earth.
The processes that took place after the formation of a metal core inside Mars and in the overlying rock mantle and crust likely slowed down faster than they did on Earth. As such, the fingerprints of the processes that once formed the core, mantle and crust of Earth-like planets may have been better preserved on Mars to this day. Researchers are thus hoping to gain a deeper understanding of what occurred from the formation of Earth up to the evolution of life, also comparing these processes with those that occurred on its closest neighbours, Mercury, Venus and Mars, as well as looking at rocky planets orbiting other stars. The researchers are curious as to whether there is still a hot, molten core at the centre of Mars – as there is on Earth – and whether this is completely molten, unlike on Earth, as some theories suggest. Tilman Spohn, who developed this theory together with fellow scientists from the US in the 1990s, maintains that "This model would easily explain the lack of a magnetic field on Mars today".
The HP3 experiment on the NASA InSight mission
The InSight mission is being conducted by the Jet Propulsion Laboratory (JPL) in Pasadena, California, on behalf of NASA's Science Mission Directorate. The InSight mission is part of the NASA Discovery Program. DLR is contributing to the mission with its HP3 (Heat Flow and Physical Properties Package) experiment. The DLR Institute of Planetary Research, which was responsible for developing the experiment in collaboration with the DLR institutes of Space Systems, Optical Sensor Systems, Space Operations and Astronaut Training, Composite Structures and Adaptive Systems, System Dynamics and Control, and Robotics and Mechatronics, is leading the experiment. The industry partners Astronika, CBK Space Research Centre, Magson and Sonaca are also involved. The Space Research Institute at the Austrian Academy of Science and the University of Kaiserslautern are scientific partners for the project. HP3 is operated by the DLR Microgravity User Support Centre (MUSC) in Cologne.
Detailed information on InSight and the HP3 experiment are available on DLR's dedicated mission site: www.dlr.de/en/insight. For mission updates follow @NASAInSight on Twitter.
Last modified:26/11/2018 16:31:55