This past week, NASA announced the approval of construction of the Interior Exploration Using Seismic Investigations, Geodesy and Heat Transport (InSight) Mars lander. Set to launch in 2016, InSight will study Mars’ interior structure and pave the way for an eventual manned mission to the Red Planet.
Following Phoenix:
InSight, to be constructed by Lockheed Martin, features a basic design derived from NASA’s Phoenix lander, which successfully touched down near Mars’ northern polar ice cap in 2008.
Phoenix studied Mars’ potential to host microbial life and assisted in confirming the presence of water ice on the Martian surface.
“We will incorporate many features from our Phoenix lander into InSight, but the differences between the missions require some modifications for the InSight spacecraft,” noted Stu Spath, InSight program manager for Lockheed Martin Space Systems.
According to the latest NASA renderings, InSight, like Phoenix, will feature a three-legged landing platform and two round solar arrays. However, InSight will carry a different assortment of scientific instruments and will land near Mars’ equator.
The equatorial landing site will provide at least two Earth years of Mars surface mission time as opposed to Phoenix’s five months and eight days of Mars surface mission time.
“The InSight mission duration is 630 days longer than Phoenix, which means that the lander will have to endure a wider range of environmental conditions on the surface,” Mr. Spath said.
Phoenix launched aboard a Delta II rocket from Cape Canaveral Air Force Station, Florida. InSight will launch on an Atlas V rocket from Vandenberg Air Force Base, California.
Deemed by a NASA as “the first ‘check-up’ of Mars in more than 4.5 billion years,” the InSight mission seeks to peer into the Mars’ internal activity to study the processes that formed the layered interior structure of Mars and other Earth-like planets.
“Our partners across the globe have made significant progress in getting to this point and are fully prepared to deliver their hardware to system integration starting this November, which is the next major milestone for the project,” added NASA InSight Project Manager Tom Hoffman.
Mission for Marsquakes:
In addition to an array of panoramic cameras, InSight will host three primary experiments that investigate the structure of Mars.
One of InSight’s experiments, the Seismic Experiment for Interior Structure (SEIS), uses a seismometer that will scout for “marsquakes.”
SEIS is being developed by the French Space Agency (CNES) and features contributions from the Institut de Physique du Globe de Paris (IPGP), the Swiss Federal Institute of Technology (ETH), the Max Planck Institute for Solar System Research (MPS), Imperial College and the Jet Propulsion Laboratory (JPL).
SEIS weighs 3 kg and consists of “a sphere including three Very Broad Band (VBB) seismic probes and their temperature sensors, three Short Period (SP) seismic probes and their temperature sensors, an acquisition electronics box… and the feedback boards for the VBB, SP probes and the MDE deployment system, a deployment system (DPL)” and “software (S/W),” according to CNES.
SEIS’ three VBBs will be oblique pendulums that are “perfectly balanced” so they move when the surface beneath them moves. They will adjust for any unevenness with gravity or with the ground.
All pendulum movement will be registered by SEIS’ displacement sensor, which consists of electrodes placed on both the mobile and fixed parts of the VBBs. The pendulums’ motion will alter the proximity of the electrodes to one another and register the pendulums’ displacement.
The three SP seismic probes aboard SEIS will measure ground acceleration, the amount that the ground shakes in a specific area during a quake. Each SP probe works by using sensors to record the motion of a mobile mass along several axes of sensibility.
SEIS, which will be supported by a frame when onboard InSight, will be lowered from the main body of the lander and will rest on three deployable feet.
The flight software accompanying SEIS will manage the instrument’s deployment, levelling and data collection and transmission. In order to maximize SEIS’ usefulness, the software will produce highly compressed reports of potential seismic activity and transmit them to Earth via InSight’s antennae.
Then, scientists will highlight particularly interesting activity from the compressed reports and trigger SEIS to transmit raw, uncompressed data of the activity.
Because seismic data must be collected constantly, SEIS’ software will erase all “useless” data to free space for further data collection.
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SEIS will be the first seismometer on Mars since NASA’s Viking 2 seismometer in 1976. Viking 2’s seismometer found only one potential marsquake, and its data was marred by false readings from wind interference, according to NASA technical reports.
A Planetary Hammer
The Heat Flow and Physical Properties Package (HP³) is another of Insight’s experiments.
Designed by The German Aerospace Institute (DLR), HP³ will hammer 5 meters into the Martian surface, further than any probe has ever peered into Mars’ interior, and take subterranean temperature readings. 
“HP3 consists of a so called ‘Mole’, which will hammer itself into the subsurface. The mole pulls an instrumented tether behind it, which is equipped with temperature sensors to determine the thermal gradient in the ground,” noted DLR information.
“The mole is targeted for a depth of 5 m below the surface. In addition to the temperature sensors, the mole is equipped with heating foils, which will be used to determine the thermal conductivity of the regolith by operating the mole as a modified line heat source.”
A lander-mounted radiometer, which will measure surface temperatures at the landing site, will complement HP³. Surface temperature readings will allow scientists to better interpret temperature variations HP³ encounters as it probes below the Martian surface.
For instance, a shadowed area of surface may cause cooler temperature readings in the soil below it. In addition, the radiometer will detect the dust coverage and soil compaction of the surface.
HP³ is derived from the designs of both the Multi-Purpose Sensor (MUPUS) aboard ESA’s Rosetta spacecraft and the Planetary Underground Tool (PLUTO), which would have peered beneath the Martian surface from the Beagle 2 lander.
Tracking Wobble:
The Rotation and Interior Structure Experiment (RISE), another InSight experiment, will calculate the precession, or wobble, of Mars’ axis and provide clues to Mars’ internal structure.
RISE is being developed by NASA’s JPL and will build on previous studies of Mars’ wobble, including studies by the Viking, Mars Pathfinder and Mars Odyssey missions.
According to RISE documentation from the 2012 Lunar and Planetary Science Conference, RISE, like the studies before it, will use the Doppler shift, or change in frequency over time, of radio signals sent between Earth and Mars to calculate the degree of wobble in Mars’ axis.
Improved estimates of the amount of wobble in Mars’ axis will lead to more precise estimates of the size and consistency of the planet’s core, which is thought to be fluid. 
Data from RISE will improve estimates of Mars’ rotation-rate variation, which is the irregularity in the rate of Mars’ rotation.
Mars’ rotation-rate variation is an effect of “seasonal exchange of CO2 between the atmosphere and the ice caps,” according to the conference documentation.
The RISE equipment, which includes “multiple antennas, a transponder for detection of signals from Earth and generation of signals coherent with the received signals, and a solid-state power amplifier for generating the signals transmitted back to Earth,” will double as a backup for InSight’s primary data relay system, the conference materials say.
Normally, InSight will use an ultra-high frequency (UHF) radio to transmit data to the Mars Reconnaissance Orbiter (MRO) and the Mars Odyssey spacecraft.
The orbiters then will relay the data to Earth, providing a more energy-efficient data transmission pathway than direct lander-to-Earth transmissions. However, should orbiter relay become inhibited, RISE’s antennae will provide direct transmission of a “moderate” amount of data to Earth.
InSight for Humans:
InSight’s mission is part of NASA’s broader push to better understand Mars and send humans to the Red Planet.
Once it lands on Mars, InSight will join a growing fleet of active NASA and ESA robotic vehicles on and around Mars, including the Mars Express orbiter, the 2001 Mars Odyssey orbiter, the Opportunity rover, MRO and, most recently, the Mars Science Laboratory (MSL) rover.
Under current proposals, InSight may be followed by Mars 2020, an MSL-derived rover that would continue NASA’s investigation into Mars’ past habitability.
NASA’s ultimate goal, as conceptualized in the latest NASA concept of operations (ConOps) documentation, is to use the under-development Space Launch System (SLS) and Orion crew vehicle, along with habitation and landing modules, to send humans on a long-duration mission to Mars sometime in the 2030s.
(Images via NASA, NASA JPL, DLR and CNES).