Published : Monday, November 19, 2018 | 6:28 AM
When NASA’s robotic probe InSight approaches Mars next Monday, November 26, after a more than 300 million mile cruise from Earth, scientists and engineers at the Jet Propulsion Laboratory in Pasadena will be keeping their fingers crossed nothing goes wrong during the anticipated “seven minutes of terror” – the time it takes for the rover to travel from the top of Mars’ atmosphere to the Red Planet’s surface.
The JPL team said it is confident InSight will land safely, with its cargo of critical science instruments intact, at about 11:47 a.m. Pacific the Monday after Thanksgiving.
But the team will have to go through anguish waiting to find out whether the landing was successful after about 14 minutes, which is the time it takes for the signal from the spacecraft to make it to Earth.
The team will not be doing any backseat driving nor manual joysticking for InSight. Instead, the flight computer on board will be doing the driving on its own, says Rob Grover, JPL systems lead for the EDL (entry, descent and landing) phase of the mission.
“There’s a classic term for it,” Grover says. “The seven minutes of terror.”
JPL actually started using the “seven minutes of terror” phrase as NASA’s rover Curiosity approached Mars in 2012.
“Sometimes when we look at it, it looks crazy,” JPL engineer Adam Steltzner said in a NASA educational video about Curiosity, days before the earlier lander actually touched down that year. “It is the result of reasoned, engineering thought, but it still looks crazy. From the top of the atmosphere, down to the surface, it takes us seven minutes. It takes 14 minutes or so for the signal from the spacecraft to make it to Earth – that’s how far Mars is away from us. So, when we first get word that we’ve touched the top of the atmosphere, the vehicle has been alive – or dead – on the surface, for at least seven minutes.”
Although InSight is the result of many important improvements from the Curiosity system, its design was based mainly on the Phoenix spacecraft that landed at Mars’ North Pole in 2008. Both Phoenix and InSight were built by Lockheed Martin Space in Denver.
Other than some tweaks to its heat shield and parachute, the overall landing design is still very much the same: after separating from a cruise stage, an aeroshell descends through the atmosphere. The parachute and retro-rockets slow the spacecraft down, and suspended legs absorb some shock from the touchdown.
Next Monday, the same entry-descent-landing sequence is expected to happen – and while some people are looking for Cyber Monday deals, scientists and engineers at JPL will be monitoring their screens for something else: signals from the spacecraft that it successfully touched down on the Red Planet.
“Our hearts will be pounding,” Grover says in the Forbes interview.
From about 70 miles up in Mars’ atmosphere, the capsule containing the InSight lander detaches from the cruise stage of the rocket that launched from Vandenberg Air Force Base in California on May 5.
Then the capsule, just before reaching the edge of the planet’s atmosphere, points itself at just the right angle, “plus or minus a quarter of a degree,” Grover says. Too shallow an angle, and the spacecraft skips off the atmosphere. Too steep, and it burns up.
InSight then descends at 12,300 miles per hour – almost three-and-a-half miles per second – and heats up because of the friction.
The friction also slows down the spacecraft by more than 90 percent within two minutes – but that’s still 1,000 miles per hour!
At about seven miles up in the atmosphere, InSight deploys its large parachute, as large as 39 feet in diameter. Within 15 seconds, the lander jettisons its heat shield, and makes use of Mars’ thinner air – just one percent of Earth’s – to control its descent.
After another 10 seconds, the lander’s three legs deploy, ready to absorb the shock when it touches down. At the same time, its 12 descent engines turn on, about a mile above the Martian surface. The engines, controlled by onboard guidance software, further reduce velocity to about five miles per hour right before landing.
One other factor the scientists and engineers at JPL are worried about is the landing spot’s condition at that time. NASA said InSight will land during northern hemisphere autumn on Mars, when dust storms are known to have grown to global proportions in some prior years.
“We’ve been rehearsing for that,” Grover says in the Forbes magazine report. “We’ll land successfully in just about any conditions thought possible during the season.”
As soon as it in on the ground, InSight will start working on its science mission dedicated to studying the deep interior of the planet – the first mission ever to do so.
A pair of miniature spacecraft – CubeSats – called MarCO, for Mars Cube One, have been trailing InSight as a separate NASA technology experiment since May. If the MarCOs make it to Mars, they will attempt to relay data from InSight as it enters the Martian atmosphere and lands. If successful, this could represent a new kind of communication capability to Earth.
NASA TV will broadcast live updates on the landing starting at 11 a.m. Pacific, and follow up with a post-landing news briefing not earlier than 2 p.m.
For the latest on InSight, visit www.jpl.nasa.gov.