Missions to Mars: We've had many successes, but lots of failures too
Landing on Mars is nail-biting experience
The latest mission to Mars, NASA's InSight lander, is the 56th attempt to reach the red planet since the former Soviet Union first tried in 1960. During that time, about half of those missions have failed.
I've had the privilege of witnessing more than one Mars mission at the Jet Propulsion Laboratory in Pasadena, Calif., where the American robot missions are controlled. Tension is always high, especially during what they call "eight minutes of terror," when attempting to land softly on the surface, and for good reason. A lot can go wrong along the way.
Blasting a robot off the Earth by our most powerful rockets, travelling for six or seven months through the cold vacuum of deep space, then screaming in through the Martian atmosphere at hypersonic speeds for a pinpoint soft landing involves thousands of steps, and every one of them has to go exactly right. Many missions have been lost due to simple glitches that have doomed them to failure.
Rocket boosters can blow up, or fail to fire to push the spacecraft out of Earth orbit. Radios fail, or faulty commands cause missions to miss the planet completely. Fuel tanks leak, stranding spacecraft. Faulty sensors lead to disastrous navigation errors. Touching down safely on another world is not easy.
Reason for celebration
When everything goes right, it is a highly emotional experience to be among international journalists and scientists as our little robotic ambassador from Earth pays a visit to an alien planet. One memorable one for me was the landing of the Spirit rover in 2004.
As we listened to the controller give reports on its altitude and speed, there came a strange moment when we knew that, in real time, the lander had already reached the surface of Mars but we didn't yet know if it was alive or dead. We were caught in a time delay. The signal from the spacecraft takes up to 20 minutes to cross the huge distance between Mars and Earth. We only got to watching the landing after it had already happened. This time delay also means these robots are entirely on their own, performing all the sequences of the landing without human help. All we can do back on Earth is watch and hope.
As the data starts streaming in, the controller calls out the events as they happen during the eight tension-filled minutes it takes to go from the top of the atmosphere travelling around 20,000 km/hr to zero at the ground.
"Contact with the atmosphere...maximum G load...parachute deploy...heat shield jettison...retro-fire...touchdown!" At every stage, louder and louder cheers erupt in the room, with the final one as ecstatic as New Year's Eve in Times Square. We made it alive.
Then, the first pictures arrive and we gaze across an alien landscape never seen by human eyes. It is truly an out-of-this-world experience. But amid the joy is a solemn feeling that were were fortunate to have arrived in one piece because so many little things could have gone wrong along the way.
Gut-wrenching experience when missions go wrong
At an earlier mission in 1999, the Mars Polar Lander was on a similar approach to the northern regions of the planet to search for ice in the permafrost. Everything was proceeding normally as the spacecraft plowed into the Martian atmosphere until the dreaded call no one wanted to hear came across the intercom: "We have loss of signal."
Suddenly, the stream of data coming down from space came to an end. The spacecraft had not reached the surface yet, so maybe it was interference from the atmosphere and the signal would return. We waited. The press room was as silent as space itself. Anxious moments later, the time for touchdown came and went without a sound. We waited longer for any sign the lander was safe, but word never arrived. A dark cloud came over the entire complex as the realization that a multi-million-dollar mission had been lost at the very last minute.
It turned out that in an effort to reduce the cost of planetary space missions, a radar system that normally tells a spacecraft its altitude and speed during descent was replaced with a simple motion sensor that would feel the "thump" as the spacecraft hit the ground and immediately shut off the engines. Unfortunately, when the landing legs were unfolded before touchdown, they went "thump," and the sensor shut the engines down while it was still several kilometres up, so it fell to the ground like a meteorite.
That loss was the second in a row after the previous year when the Mars Climate Orbiter entered the atmosphere too steeply and burned up because of a measurement mix-up. One team was using imperial units and another metric to calculate the thrust of the engine and the resulting confusion doomed the spacecraft. It was a simple human error with a costly result.
For the scientists, these failures represent the loss of years of work designing, building and flying the complex machines, as well as scientific careers that were based on doing experiments on another planet. Sometimes they do get a second chance, as in the case of the Phoenix mission, which rose from the ashes by using the backup spacecraft from the Polar Lander, and reached Mars successfully.
No one likes to see the failure of a robotic space mission. But it is better to sort out the mistakes and learn lessons now, because when humans travel to Mars, the stakes will be far, far higher.