NASA’s Mars InSight probe will land on the Red Planet tomorrow, November 26, about 3:00 pm ET. It carries instruments that will give scientists their first data on the interior of Mars — its core, crust and mantle. The probe is accompanied by two tiny spacecraft called cubesats that will relay data back to Earth during InSight’s entry, descent and landing (EDL) sequence. This is the first time cubesats have been sent into deep space. NASA is optimistic they will work properly and spacecraft controllers at the Jet Propulsion Laboratory (JPL) will quickly know if InSight landed safety. If not, it could take several hours to confirm InSight’s status using signals relayed through other spacecraft.

InSight is a stationary lander, not a rover like Curiosity or Opportunity. Once it settles down on the plains of Elysium Planitia, it will stay there and deploy instruments that will “take the planet’s vital signs, its pulse, and temperature” according to NASA.

The landing site was chosen because it is flat and has few large rocks that could endanger the landing since the purpose of the spacecraft is not to explore surface features, but what lies below. InSight project manager Tom Hoffman said at a press briefing today that Elysium Planitia means Heavenly Plain and it is just that, plain. “Not the most exciting place to be,” but safe.

EDL is the most challenging part of the mission at this point. It does not use the Skycrane system that got Curiosity to the surface, but is based on technologies used for NASA’s Phoenix spacecraft that landed on Mars in 2008. Over the course of about 6.5 minutes, InSight will descend through the atmosphere, deploy a large parachute, extend three shock-absorbing legs, and then fire 12 descent engines to slow the spacecraft to a soft landing at 5 miles (8 kilometers) per hour.

It takes 8 minutes for signals to travel from Mars to Earth, so InSight will have landed safely, or not, by the time the signals arrive here.

NASA has several methods for knowing whether the landing is successful: radio telescopes on Earth, signals directly from InSight to NASA’s Deep Space Network (DSN), signals relayed through the MarCO cubesats, or signals relayed through two NASA spacecraft already in orbit around Mars — Mars Reconnaissance Orbiter (MRO) and Mars Odyssey. How quickly it will know depends on which of those works first.

Radio telescopes at Green Bank, West Virginia and Efflesberg, Germany will listen for signals that will confirm that certain events like parachute deployment have occurred, but provide little data other than that. NASA is hoping that the MarCO cubesats will relay more detailed data from InSight as they fly past the planet. The tiny spacecraft were launched with InSight and separated from it enroute to Mars. They have been trailing behind and will continue on past Mars as InSight lands, serving the communications relay function only during EDL.

InSight also will be transmitting to MRO and Odyssey, but they cannot relay the data to Earth until they are in the correct orbital position, which will take several hours.

Hoffman said what he will be listening for is an X-band “beep” that InSight should transmit 7 minutes after landing when its X-band antenna is pointed directly at Earth and the DSN. If nothing is heard, however, he reassuringly said that “not all is lost” because it may mean only that InSight landed in safe mode. Its solar arrays will deploy autonomously and communications will be routed through the two orbiting spacecraft instead. Data from MRO is expected at Earth by 6:00 pm ET and from Odyssey by 8:30 pm ET on Monday.

InSight carries a seismometer, SEIS (Seismic Experiment for Interior Structure), and a Heat Flow and Physics Properties Probe (HP3). SEIS was provided by the French space agency, CNES, with the participation of other European institutes and JPL. HP3 was provided by the German space agency, DLR. JPL supplied a Rotation and Interior Structure Experiment (RISE) that will use the spacecraft communication system to provide precise measurements of the planet’s rotation. The spacecraft was built by Lockheed Martin.

InSight was originally supposed to launch in March 2016, but a problem with the French-built SEIS instrument delayed it at the last minute. In September 2016, NASA decided to proceed with the mission even though it meant an additional $153.8 million on top of the original $650 million budget. NASA said at the time that it would not have to delay or cancel other ongoing science missions to absorb the overrun, but there might be fewer opportunities in the future.

Bruce Banerdt, the principal investigator for InSight, called the mission a dream come true during today’s press conference. He has wanted to get a seismometer on Mars since he was a graduate student in geology at JPL in the 1970s when the Viking 1 and Viking 2 probes landed on Mars — the first spacecraft to successfully land there.

Those seismometers did not function correctly and none of the other Mars landers have carried them since.

The Viking seismometers were mounted on the landers and were susceptible to wind noise. InSight’s SEIS will be placed onto the surface using a robotic arm.

He described this as a “slow motion” mission because it will take 2-3 months to deploy the scientific instruments and another month to calibrate them to get the “cleanest” data. It will be 6 months before scientists have a “glimmer” of what they are looking for and the full two-year prime mission (in Earth years) before even the basic questions are answered.

The result will be a three dimensional map of the interior of Mars and a look back through 4.5 billion years to the formation of the solar system, which will lead to a better understanding of Earth’s own evolution.

Hoffman said one final trajectory correction maneuver (TCM) will be made today to ensure InSight lands just where NASA wants it to. After that, it is up to the spacecraft to perform its tasks correctly.

Thomas Zurbuchen, NASA’s Associate Administrator for the Science Mission Directorate, stressed how difficult it is to land on Mars. “Never take Mars for granted,” he warned. “Mars is hard.”

NASA will broadcast landing events and commentary beginning at 2:00 pm ET tomorrow. A post-landing press conference will take place no earlier than 5:00 pm ET. The mission has significant international participation and more than 80 organizations around the globe are planning landing events.