NASA's Mars InSight lander is due to arrive on the Red Planet on Monday, giving scientists their first in-depth look at the martian interior.
InSight (Interior Exploration using Seismic Investigations, Geodesy and Heat Transport) is based on 2008's Phoenix Lander, which itself used components left over from the cancelled Mars Surveyor 2001 lander.
NASA prefers not to talk about Surveyor too much, seeing as the axe was wielded on the unfortunate spacecraft in the aftermath of 1999's Mars Polar Lander mishap, which blotted NASA's otherwise excellent copybook for landing on the Martian surface.
Phoenix, however, was a great success, and the stationary lander outlasted NASA's expectations, surviving nearly double the 90 Martian sols planned for the mission before succumbing to dust and cold in a way that we fervently hope the Opportunity rover has not.
Adopting an "if it ain't broke, don't fix it" approach, Jet Propulsion Lab (JPL) engineers have taken the design of the Phoenix lander and adapted it for InSight. The 360kg (once it's on the ground) lander features two solar panels, each 2.2m in diameter and will stand somewhere between 0.8 and 1.1m high, depending on how much its legs compress on landing.
Unlike Phoenix, NASA said it expects InSight to survive almost two Earth years on the surface. The solar panels should provide 600-700W on a clear Martian day and 200-300W when covered with dust.
The power, which NASA reckoned would be enough run a household blender, will drive the three main instruments carried by the lander.
The 50kg science payload comprises the Seismic Experiment for Interior Structure (SEIS), the Heat Flow and Physical Properties Probe (HP³) and the Rotation and Interior Structure Experiment (RISE).
The lander is also equipped with a robotic arm that it will use to place HP³ and RISE on the surface of the planet. By putting the equipment in direct contact with Martian dirt, scientists expect to avoid the issues experienced by the 1970s Viking landers, where seismometers on the lander picked up vibrations from the spacecraft itself rather than from the planet.
HP³ also has some burrowing to do. Tricky from the lander's deck.
SEIS, supplied by France's Centre National d'Études Spatiales (CNES), is a dome-shaped instrument containing three pendulums which will detect the seismic vibrations of Mars.
Scientists have said that data returned from the instrument will provide a glimpse into the internal activity and structure of the planet. Investigators have their fingers crossed that the device will also detect liquid water sloshing around beneath the surface as well active volcanoes underground.
The heat probe, HP³, will drill almost five metres beneath the surface of the planet after being deposited by InSight's robotic arm. The goal of the instrument is to provide a definitive measurement of the heat still flowing out from the interior of Mars.
The probe will burrow considerably deeper than the 2 metres planned for ESA's ExoMars rover (although the latter is a tad more mobile) and far more than previous NASA landers, which have mainly scratched at the surface.
According to the Principal Investigator for the instrument, Tilman Spohn, the instrument will tell scientists if Mars and Earth formed from the same "stuff", giving a clue as to the how the rocky bodies in the solar system evolved.
The final major instrument on the mission, RISE, will precisely track the location of the lander to determine how much Mars' North Pole "wobbles" as the planet orbits the Sun. Scientists will use the data to determine the size of the Mars' iron-rich core as well what other elements may be present.
The instrument, mounted on the deck of the lander, will also give an indication whether the core is liquid or solid.
Deep Space CubeSats
Along for the ride to Mars are two communication relay CubeSats, MarCO-A and B. The briefcase-sized spacecraft were intended as demonstrators, but since both have functioned admirably en-route to the Red Planet as independent flyers, they will provide a short-term communication relay for InSight as the lander heads down to the surface.
The cricket-ball sized radios in MarCO can receive in UHF and both transmit and receive in X-band, so they should be able to immediately relay data received back to Earth. The lander will be broadcasting information during entry, descent and landing in the UHF band to NASA's Mars Reconnaissance Orbiter, which cannot simultaneously receive in one band and transmit in another. Thus, without MarCO, nervous engineers on Earth could be faced with over an hour's wait for news from InSight.
Should the diminutive spacecraft prove themselves viable, NASA boffins have said the tech could have applications elsewhere in the solar system and at the very least allow for a "bring your own relay" communications option during the critical touchdown phases.
The landing timeline - striking the correct tone
The fun kicks off today at 1440 EST (1940 UTC), when the spacecraft separates from the cruise stage that has carried it to Mars. A minute later, InSight will orient itself for entry before barreling into the thin atmosphere of the red planet, starting at 1447 EST (1947 UTC) and travelling at 19,795kmph (12,300mph).
Two minutes later, engineers anticipate the heat shield of the plucky lander will hit around 1,500°C, or peak heating. 15 seconds later, the spacecraft will experience maximum deceleration which, along with the heating, could make radio contact a bit wobbly.
At 1451 EST (1951 UTC) the parachute will deploy, with the heat shield ejected seconds later. 1452 EST (1952 UTC) will see the radar turned on in order to detect the distance to the ground. Shortly after, the lander's retro-rockets will fire and InSight will slow to a constant 5 mph before touching down at 1454 EST (1954 UTC)). InSight will send a tone back to Earth at 1501 EST (2001 UTC) to indicate it is safely down.
The tone is important, and is one of a sequence that engineers on Earth will be listening for as InSight passes each landing milestone. While the tone itself doesn’t carry much in the way of information, they do give a clue as to what is happening. For example, when the parachute is deployed, InSight will slow, which in turn will change the frequency of the signal.
Two Earthbound radio telescopes, the Green Bank Observatory in West Virginia and Max Planck Institute in Efflesberg, Germany, will be trained on Mars in the hope of detecting the signals in the event of the experimental MarCOs not playing ball. MRO’s data will be transmitted to earth by around 1800 EST (2300 UTC), three hours after landing. Finally, the long-lived 2001 Mars Odyssey orbiter will send its own recording of the landing events by 2035 EST (Tuesday, 0135 UTC), including confirmation that the vital solar arrays have been deployed.
However, if everything works the way engineers hope, and the MarCOs do their stuff, buttocks will unclench at 1504 EST (2004 UTC) when the first images from the landed lander pop-up on screens on Earth.
The US investment in InSight thus far is $813.8m, including $163.4m to actually launch the thing. France and Germany have contributed about $180m for SEIS and HP³ respectively. And those CubeSats? A snip at around $18.5m. ®
Updated to add
The probe has landed in one piece.