PASADENA, Calif. — Eight days before reaching Mars, NASA’s Mars Science Laboratory spacecraft performed a flight-path adjustment scheduled more than nine months ago.

The trajectory correction maneuver completed late Saturday may be the last one the mission needs before landing day, though two further opportunities remain on its schedule in case they are needed.

The spacecraft is on course for delivering the mission’s car-size rover, Curiosity, to a landing target beside a Martian mountain at about 10:31 p.m. PDT on Aug. 5. (1:31 a.m. on Aug. 6, EDT). After landing, the rover will spend a two-year prime mission studying whether the area has ever offered environmental conditions favorable for life.

The spacecraft used two brief thruster firings totaling about six seconds to adjust its trajectory at about 10 p.m. PDT on July 28 (1 a.m. on July 29, EDT). This maneuver had been on the mission’s schedule since before launch on Nov. 26, 2011. It altered the flight path less than any of the spacecraft’s three previous trajectory correction maneuvers on the way from Earth to Mars.

The Mars Science Laboratory spacecraft had been on a course in recent weeks that would have hit a point at the top of the Martian atmosphere about 13 miles (21 kilometers) east of the target entry point. On landing day, it can steer enough during its flight through the upper atmosphere to correct for missing the target entry point by a few miles and still land on the intended patch of Mars real estate. The mission’s engineers and managers rated the projected 13-mile miss big enough to warrant a correction maneuver.

“The purpose of this maneuver is to move the point at which Curiosity enters the atmosphere by about 13 miles,” said Tomas Martin-Mur of NASA’s Jet Propulsion Laboratory, Pasadena, Calif., chief of the mission’s navigation team. “The first look at telemetry and tracking data afterwards indicates the maneuver succeeded as planned.”

The thruster firings altered the spacecraft’s velocity by about one-fortieth of one mile per hour (one centimeter per second). Curiosity will enter Mars’ atmosphere at a speed of about 13,200 mph (5,900 meters per second).

Opportunities for two further course corrections are scheduled in the final 48 hours before landing, if needed.

“I will not be surprised if this was our last trajectory correction maneuver,” Martin Mur said of Saturday’s event. “We will be monitoring the trajectory using the antennas of the Deep Space Network to be sure Curiosity is staying on the right path for a successful entry, descent and landing.”

Descent from the top of Mars’ atmosphere to the surface will employ bold techniques enabling use of a smaller target area and heavier landed payload than were possible for any previous Mars mission. These innovations, if successful, will place a well-equipped mobile laboratory into a locale especially well-suited for its mission of discovery. The same innovations advance NASA toward capabilities needed for human missions to Mars.

As of July 30, the Mars Science Laboratory spacecraft carrying the rover Curiosity will have traveled about 343 million miles (555 million kilometers) of its 352-million-mile (567-million-kilometer) flight to Mars.


Landing a large mass on Mars is particularly challenging as the atmosphere is too thin for parachutes and aerobraking alone to be effectivewhile remaining thick enough to create stability problems when decelerating with rockets.  Although some previous missions have used airbags to cushion the shock of landing, Curiosity rover is too heavy for this to be an option. Instead, Curiosity set down on the Martian surface using a new high-precision entry, descent, and landing (EDL) system which placed it within a 20 by 7 km (12 by 4.3 mi) landing ellipse,in contrast to the 150 by 20 km (93 by 12 mi) landing ellipse of the landing systems used by the Mars Exploration Rovers.  The landing sequence alone required six vehicle configurations, 76 pyrotechnic devices, the largest supersonic parachute ever built, and more than 500,000 lines of code, in a final sequence that was dubbed “seven minutes of terror” by NASA.   The spacecraft employed several systems in a precise order, with the entry, descent and landing sequence broken down into four parts.

  1. Guided entry: The rover is folded up within an aeroshell that protects it during the travel through space and during the atmospheric entry at Mars. Ten minutes before atmospheric entry the aeroshell separates from the cruise stage that provided power, communications and propulsion during the long flight to Mars. One minute after separation from the cruise stage thrusters on the aeroshell fire to cancel out the spacecraft’s 2-rpm rotation and achieve an orientation with the heat shield facing Mars in preparation for Atmospheric entry.  The heat shield is made of phenolic impregnated carbon ablator. The 4.5 m (15 ft) diameter heat shield, which is the largest heat shield ever flown in space, reduces the velocity of the spacecraft by ablation against the Martian atmosphere, from the atmospheric interface velocity of approximately 5.8 km/s (3.6 mi/s) down to approximately 470 m/s (1,500 ft/s), where parachute deployment is possible about four minutes later. One minute and 15 seconds after entry the heat shield will experience peak temperatures of up to 3,800 °F (2,090 °C) as atmospheric pressure converts kinetic energy into heat. Ten seconds after peak heating, that deceleration will max out at 15 g.  Much of the reduction of the landing precision error is accomplished by an entry guidance algorithm, derived from the algorithm used for guidance of the Apollo Command Modules returning to Earth in the Apollo space program.  This guidance uses the lifting force experienced by the aeroshell to “fly out” any detected error in range and thereby arrive at the targeted landing site. In order for the aeroshell to have lift, its center of mass is offset from the axial centerline that results in an off-center trim angle in atmospheric flight. This is accomplished by a series of ejectable ballast masses consisting of two 165 pound (75kg) tungsten weights that are jettisoned minutes before atmospheric entry.The lift vector is controlled by four sets of two Reaction Control System (RCS) thrusters that produce approximately 500 N (110 lbf) of thrust per pair. This ability to change the pointing of the direction of lift allows the spacecraft to react to the ambient environment, and steer toward the landing zone. Prior to parachute deployment the entry vehicle must eject more ballast mass consisting of six 55 lb (25 kg) tungsten weights such that the center of gravity offset is removed.
    MSL’s parachute is 51 ft (16 m) in diameter.
  2. Parachute descent: When the entry phase is complete and the capsule has slowed to Mach 1.7 or 578 m/s (1,900 ft/s) and at about 10 km (6.2 mi) the supersonic parachute will deploy, as was done by previous landers such as Viking, Mars Pathfinder and the Mars Exploration Rovers. The parachute has 80 suspension lines, is over 50 m (160 ft) long, and is about 16 m (52 ft) in diameter.  The parachute is capable of being deployed at Mach 2.2 and can generate up to 289 kN (65,000 lbf) of drag force in the Martian atmosphere.After the parachute has deployed, the heat shield will separate and fall away. A camera beneath the rover will acquire about 5 frames per second (with resolution of 1600×1200 pixels) below 3.7 km (2.3 mi) during a period of about 2 minutes until the rover sensors confirms successful landing.
  3. Powered descent: Following the parachute braking, at about 1.8 km (1.1 mi) altitude, still travelling at about 100 m/s (220 mph), the rover and descent stage drop out of the aeroshell.The descent stage is a platform above the rover with 8 variable thrust mono propellant hydrazine rocket thrusters on arms extending around this platform to slow the descent. Each rocket thruster, called a Mars Lander Engine (MLE),produces 400 N (90 lbf) to 3,100 N (700 lbf) of thrust and were derived from those used on the Viking landers.  Meanwhile, the rover will transform from its stowed flight configuration to a landing configuration while being lowered beneath the descent stage by the “sky crane” system.

    This artist’s concept depicts the rocket-powered descent stage’s sky crane lowering the Curiosity rover.

  4. Sky crane: For several reasons a different landing system was chosen for MSL compared to previous Mars landers and rovers. Curiosity was considered too heavy to use the airbag landing system as used on the Mars Pathfinder and Mars Exploration. A legged lander approach would have caused several design problems.  It would have needed to have engines high enough above the ground when landing to not form a dust cloud that could damage the rover’s instruments. This would have required long landing legs that would need to have significant width to keep the center of gravity low. A legged Lander would have also required ramps so the rover could drive down to the surface, which would incurred extra risk to the mission on the chance rocks or tilt would prevent Curiosity from being able to drive off the lander successfully. Faced with these challenges, the MSL engineers came up with a novel alternative solution: the sky crane.  The sky crane system will lower the rover with a 25 ft (7.6 m) tether to a soft landing—wheels down—on the surface of Mars.  This system consists of 3 bridles lowering the rover and an umbilical cable carrying electrical signals between the descent stage and rover. As the support and data cables unreel, the rover’s six motorized wheels will snap into position. At roughly 7.5 m (25 ft) below the descent stage the sky crane system slows to a halt and the rover touches down. After the rover touches down it waits 2 seconds to confirm that it is on solid ground by detecting the weight on the wheels and fires several pyros (small explosive devices) activating cable cutters on the bridle and umbilical cords to free itself from the descent stage. The descent stage flies away to a crash landing at least 500 ft (150 m) away, and possibly twice that far. The sky crane powered descent landing system had never been used in missions before.


Mars rover set to look for life’s  ingredients

MARS David Perlman


After the triumph of a flawless landing on Mars by the spacecraft named  Curiosity, scientists are now ready for a voyage across the surface of an  ancient Martian crater, seeking evidence that a planet other than Earth was  hospitable to life.

It will be a month or more before earthbound researchers can start Curiosity  on its first test drives and longer still for scientists to deploy the 10 key  instruments that the craft has carried from Earth.

For now, the rover is firmly settled on a pebbly patch of Martian ground near  a towering mountain whose lower slopes of water-carved rock could hold precious  carbon sediments laid down billions of years ago. Its cameras have sent back  superb high-resolution images of its landing spot – with many more to come  within days.

And what seems equally extraordinary is that a distant spacecraft called MRO,  the Mars Reconnaissance Orbiter, flying 230 miles above the Martian surface,  managed to capture a vivid image of the car-size Curiosity dangling from its  parachute barely a minute before its touchdown.

Curiosity’s engineers at NASA’s Jet  Propulsion Laboratory in Pasadena said Monday that the 1-ton rover appears  undamaged and ready for its two-year mission inside the crater named Gale and up  the layers of sedimentary rock on the lower slopes of nearby  Mount Sharp.

An engineering miracle

The spacecraft’s 7-foot-long robotic mast, carrying two crucial instruments,  is standing erect atop the rover and appears ready to do its highly complex job,  the engineers said.

“What’s amazing about it is the miracle of this engineering,” said John  P. Grotzinger, the mission’s chief scientist as he spoke in awe of the  landing that brought his team’s precious science instruments safely  to Mars.

The first images of the landing site from Curiosity’s camera show the rim of Gale  Crater and of Mount Sharp towering beyond.

“In the foreground, you can see a gravel field,” Grotzinger said. “The  question is, where does this gravel come from? It’s the first of what will be  many scientific questions to come from what’s now our new home  on Mars.”

With criticism coming from Congress over NASA’s $18 billion budget, the  agency’s leaders were tensely aware that a landing failure by Curiosity, with  $2.5 billion committed for its mission, could have meant the end of all future  high-cost space missions.

“If anybody has been harboring doubts about the status of U.S. leadership in  space, well, there’s a 1-ton automobile-sized piece of American ingenuity, and  it’s sitting on the surface of Mars right now,” said John  P. Holdren, President Obama’s science adviser, during a  news conference after the landing.

Near the top of the rover’s mast are a high-definition telescopic camera and  a powerful laser that will zap the surface of nearby rocks and pulverize them so  their powdery puffs of microscopic particles can be imaged to reveal the  elements that compose them.

After the telescopic camera, called ChemCam, for chemistry camera, surveys  the chemicals in nearby rocks, scientists will select the most promising rocks  to be sampled by still other instruments.

Only the best rocks

“If we’re lucky,” said Bethany Ehlmann, a geologist at the California  Institute of Technology who is on the ChemCam team, “we’ll be watching from  rock to rock looking for enhanced chlorates, and it would be a grand-slam home  run if we find enhanced carbonates, because carbon could tell us that Mars might  even have been inhabited long, long ago.

“But there’s a lot of ifs to that, and we’re still a long way away  from it.”

One of the most crucial instruments aboard Curiosity is called CheMin, for  chemistry and mineralogy.

Developed by David Blake, a space chemist at NASA’s Ames  Research Center in Mountain View, CheMin will analyze other samples of  Martian soil and rocks scooped from the surface by Curiosity’s robotic arm and  drilled into powder from nearby rock surfaces to seek clues to the planet’s  past chemistry.

Tori Hoehler, an oceanographer now on the CheMin team at the Ames center as a  microbiologist, said the group is awaiting a signal from Mission Control  engineers to start deploying the instrument.

“We’re trying to look … at a place where the past environment tells us that  organic carbon could have provided the conditions for life,” Hoehler said.

The essentials for life

Another instrument called SAM, for Sample Analysis at Mars, will use three  tools to seek the carbon-based compounds essential for all life, examining gases  from samples heated in Curiosity’s on-board oven to 1,800 degrees Fahrenheit and  using a mass spectrometer and a gas chromatograph to sniff out  carbon molecules.

The entire Curiosity team has been saying again and again, that their rover  is not seeking evidence of life itself, but rather the evidence of an  environment billions of years ago where life might well have existed.

But now that the Curiosity venture has begun in triumph, NASA’s future on  Mars seems assured, and the life-seeking missions to the planet are bound to  come next.