Launch video provided courtesy of United Launch Alliance
CAPE CANAVERAL, Fla – It is a mission years in the making. However, it would not be possible without the hard work of an army’s worth of engineers – and the systems that they built. How many different systems and engines are required to get the Mars Science Laboratory (MSL) rover named Curiosity to the surface of the Red Planet? The answer might surprise you.
Including the two engines that are part of the Atlas V 541 launch vehicle, it will take 50 different engines and thrusters in total to work perfectly to successfully deliver Curiosity to the dusty plains of Mars.
Starting with the launch vehicle itself, there are six separate engines that power the six-wheeled rover, safely ensconced in its fairing, out of Earth’s gravity well. For the first leg of the journey four powerful Solid Rocket Boosters (SRBs) provided by Aerojet (each of these provides 400,000 lbs of thrust) will launch the rover out of Earth’s atmosphere.
The United Launch Alliance (ULA) Atlas launch vehicle has two rocket engines that provide the remaining amount of thrust required to get MSL to orbit and send the rover on its way to Mars. The first is the Russian-built RD-180 engine (whose thrust is split between two engine bells) the second is the Centaur second stage. There are four Aerojet solid rocket motors that help the booster and Centaur upper stage to separate.
The Centaur’s trajectory is controlled by both thrust vector control of the main engine as well as a Reaction Control System or RCS comprised of liquid hydrazine propulsion systems (there are twelve roll control thrusters on the Centaur upper stage).
MSL’s cruise stage separates entirely from the Centaur upper stage and is on the long road to the Red Planet. The cruise stage has eight one-pound-thrust hydrazine thrusters that are used for trajectory maneuvers for the nine-month journey to Mars. These are used for minor corrections to keep the spacecraft on the correct course.
Curiosity’s first physical encounter with the Martian environment is referred to as Entry, Descent and Landing (EDL) – more commonly known as “six minutes of terror” – the point when mission control, back on Earth, loses contact with the spacecraft as it enters the Martian atmosphere.
Video courtesy of Lockheed Martin
Even though Mars only has roughly one percent of Earth’s atmosphere, the friction of the atmosphere caused by a spacecraft impacting it at 13,200 miles per hour (about 5,900 meters per second) – is enough to melt Curiosity if it were exposed to these extremes. The heat shield, located at the base of the cruise stage, prevents this from happening.
The heat shield, provided by Lockheed-Martin, on MSL’s cruise stage is 14.8 feet (4.5 meters) in diameter. By comparison, the heat shields that were used on the Apollo manned missions to the Moon were 13 feet (4 meters) in diameter and the ones that allowed the Mars Exploration Rovers Spirit and Opportunity to safely reach the surface of Mars were 8.7 feet (2.65 meters) in diameter.
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At this point in the mission eight engines, each providing 68 pounds of thrust come into play. These engines provide all of the trajectory control during EDL – meaning they will fire almost continuously.
Shortly thereafter – BOOM – the parachute deploy. Then the heat shield is ejected. After the parachute slow the spacecraft down to a sufficient degree, both they and the back aeroshell depart leaving just the rover and its jet pack.
During the landing phase the “SkyCrane” comes alive with eight powerful hydrazine engines, each of which give Curiosity 800 pounds of thrust. Aerojet’s Redmond Site Executive, Roger Myers, talked a bit about this segment of the landing, considered by many to be the most dramatic method of getting a vehicle to the surface of Mars.
“Because of the control requirements for the SkyCrane these engines had to be very throttleable,” Myers said. “Keeping the SkyCrane level is a must, you must have very fine control of those engines to ensure stability.”
If all has gone well up to this point, the Curiosity rover will be lowered the remaining distance to the ground via cables. Once contact with the Martian surface is detected, the cables are cut, the SkyCrane’s engines throttle up and the jet pack flies off to conduct a controlled crash (approximately a mile or so away from where Curiosity is located).
Every powered landing on Mars conducted in the U.S. unmanned space program has utilized Aerojet’s thrusters. The reliability of these small engines was recently proven – in a mission that is now almost three-and-a-half decades old.
Voyager recently conducted a course correction some 34 years after it was launched – highlighting the capability of these thrusters to perform well after launch.
“Our engines have allowed missions to fly to every planet in the solar system and we are currently on our way to Mercury and Pluto,” Myers said. “When NASA explores the solar system – Aerojet provides the propulsion components.”
The complexity of this makes me nervous, too many points of failure, I’m hoping all goes well in August. These are exciting times to be living in.
The complexity of this makes me nervous, too many points of failure, I’m hoping all goes well in August. These are exciting times to be living in.