Atlas V launches NASA’s MSL Rover ahead of journey to Mars

by William Graham

NASA’s Mars Science Laboratory has begun its mission to the Red Planet Saturday, with a launch aboard a United Launch Alliance Atlas V rocket. Liftoff from Space Launch Complex 41 at the Cape Canaveral Air Force Station was on schedule, at the begining of the one-hour and 43 minute window, which opening at 15:02 UTC (10:02 local time).

Atlas V/MSL Mission:

The Mars Science Laboratory (MSL), or Curiosity, is an 850 kilogram rover which was launched towards Mars as part of a 3,400 kilogram spacecraft, including a protective shell, a heat shield and landing system, and a cruise stage to control its trajectory whilst en route to Mars.

Curiosity is about the size of a small car, and carries eleven instrument packages, including cameras, spectrometers, radiation, atmospheric and environmental sensors.

The main instrument suite aboard MSL is the 38-kilogram Sample Analysis at Mars (SAM) package. Using mass spectrometry and gas chromatography, SAM will measure the abundances of carbon-based compounds in samples of Martian soil, whilst a laser spectrometer will be used to determine how much hydrogen, oxygen, carbon and nitrogen are present in the atmosphere.

While SAM is MSL’s main instrument, it will not be the first to operate. Two instruments will be collecting data as Curiosity descends towards the surface of Mars. One of these is MEDLI, a technology development and atmospheric research experiment which will collect data during atmospheric entry.

The MEDLI Integrated Sensor Plugs (MISP) will record the rate at which the spacecraft’s heat shield is ablated, whilst the Mars Entry Atmospheric Data System (MEADS) will be used to record atmospheric pressure and measure changes in the spacecraft’s attitude and trajectory during entry. The data collected by MEDLI will be compared to expected design values, to evaluate the performance of the entry shell and heat shield ahead of future missions.

The other instrument designed to operate prior to landing is the Mars Descent Imager, or MARDI. Mounted on the front of the rover, pointing downwards, MARDI will capture high-resolution video of the landing site during the rover’s descent to the surface. Video will be captured from the time at which the heat shield separates from the rover’s protective shell, until the spacecraft lands, however vibrations caused by the spacecraft’s parachutes and landing thrusters may blur some of the frames of video.

After landing, the camera will be deactivated and the data it has collected will be transmitted back to Earth. The video of the landing site can then be used to plan the rover’s journey across the surface of Mars. MARDI was developed by Malin Space Science Systems, who continued work on the instrument despite it being removed from the mission in 2007, which later enabled NASA to reverse its decision and include the instrument.

MastCam, or the Mast Cameras, will be used to produce medium and high-resolution still imagery and 10 fps high-definition video of the Martian surface; with one of the cameras producing the medium resolution images, and the other the high-resolution ones. The cameras can produce true colour images, or by means of several available filters, monochromatic images.

A dedicated electronics package will process the images without interfering the Curiosity’s other systems, and the rover can store several thousand images at a time for transmission back to Earth. MastCam is so named because the cameras are located on a mast at the front of the rover.

The Chemistry and Camera experiment, or ChemCam, is mounted above MastCam. ChemCam will use a laser to vaporise rock and soil samples for spectrographic analysis, with a telescope focussed on the sample collecting light which will be fed to spectrometers within the body of the rover via fibre-optic cables. A camera will also be included in the instrument, to image rocks after the laser has been used to clear dust away from them.

ChemCam is expected to be able to differentiate between sedimentary and igneous rocks, and to study the chemical composition of rocks and soil, looking for traces of water, and for chemicals which might be harmful to humans on future manned missions to mars. The instrument will also be used to monitor the drilling of samples, and to study marks left on rocks by the effects of weathering.

The Rover Environmental Monitoring Station, REMS, is an environmental research instrument developed by Spain’s Centro de Astrobiologia. It will measure the ground and air temperatures, wind velocity, UV radiation levels, air pressure and humidity. The instrument consists of two perpendicular booms protruding from the mast, and a separate sensor to measure the air pressure. Infrared sensors to measure surface temperature are located on one boom, whilst the other houses humidity sensors. The remaining experiments are present on both booms.

Chemistry and Mineralogy, or CheMin, will be used to identify minerals present in powdered rock and soil samples collected by the rover, by means of x-ray crystallography. The instrument will fire x-ray photons at the sample, and by means of charge-coupled devices surrounding it, the angle by which they are diffracted would be measured.

The diffraction pattern can then be used to determine the structures of minerals present in the sample, and these minerals can subsequently be identified. Determining which minerals are present on Mars enables scientists to identify the conditions present on Mars when they formed, allowing the planet’s past environment to be studied.

The Radiation Assessment Detector, or RAD, will measure radiation levels on the surface of Mars, studying all types of high-energy radiation, both incident from space and emitted by the atmosphere and surface of Mars itself. RAD will use a caesium iodide crystal and silicon plates to detect alpha and gamma radiation, nucleons and ions of elements lighter than iron.

Data on radiation levels can then be used to study the effects of radiation on the Martian surface, and to determine the extent to which humans would be exposed to radiation whilst on the surface during a future manned mission.

A neutron detector, the Detector of Albedo Neutrons or DAN, will be used to monitor neutrons emitted from the surface of Mars after stimulation by incident cosmic rays. Because the hydrogen atoms present in water molecules can act as a neutron moderator, by looking for slower-moving neutrons scientists can determine if water is present in an area.

DAN is funded by Roskosmos, the Russian Federal Space Agency, whose own Mars probe, Fobos-Grunt, remains stuck in low Earth orbit after failing to depart for the red planet earlier in the month.

MSL is equipped with a movable arm which houses two more instruments. One of these is the Alpha Particle X-ray Spectrometer, APXS, which will be placed onto an area of soil or rock, which it will bombard with alpha particles and x-rays. This will allow the elements present in the soil to be identified. Funded by the Canadian Space Agency, the APXS present of Curiosity is the third to be sent to Mars; previous-generation instruments were carried by the Spirit and Opportunity rovers.

The second instrument on the arm is the Mars Hand Lens Imager, or MAHLI, a camera capable of imaging microscopic features on rocks, with a resolution of up to 13.9 micrometres per pixel. The instrument includes a light which will allow it to be used at night, and a source of ultraviolet radiation which can be used to illuminate the soil by causing some substances to fluoresce.

The camera is expected to yield a greater understanding of the geology of Mars. The arm also carries a drill and a scoop to collect rock and soil samples respectively, and the Dust Removal Tool, a brush to clear dust from areas to be sampled.

Curiosity is the fourth rover to be sent to Mars by the United States. The first, Sojourner, was deployed by the Mars Pathfinder probe as part of NASA’s Discovery programme. Launched aboard a Delta II rocket in December 1996, Mars Pathfinder landed on Mars in July 1997 and deployed Sojourner the day after landing. The rover returned photos and analysed rocks near the landing site, using the Alpha Proton X-ray Spectrometer, a forerunner of the Alpha Particle X-ray Spectrometer carried by MSL.

The next two rover missions to Mars were the two Mars Exploration Rovers, Spirit and Opportunity. Launched by Delta II and Delta II Heavy rockets on 10 June and 8 July 2003 respectively, the two rovers landed on Mars on 4 and 25 January 2004. The rovers were intended to last for 90 sols, or Martian days, however Spirit operated for 2,210 days before contact was finally lost in March 2010. Opportunity remains operational, and is currently exploring Endeavour, a crater on Meridiani Planu.

The United States is the only country to have successfully deployed rovers on the surface of Mars, and the only country to have attempted to deploy freely moving rovers on the planet, however the Soviet Union did attempt to land two small Prop-M rovers, which would have remained tethered to the landers that deployed them, as part of the Mars-2 and Mars-3 missions. Mars-2 was lost during landing, whilst Mars-3 landed successfully, however it only operated for about 20 seconds, and never deployed its rover.

Atlas V AV-028 was used to launch the Mars Science Laboratory. It was the twenty eighth flight of an Atlas V rocket, and the maiden flight of the 541 configuration, which featured a five metre payload fairing, four solid rocket motors providing additional thrust at liftoff, and a single-engine Centaur (SEC) upper stage.

The fairing, which had an external diameter of 5.4 metres, is 20.7 metres long. This was the “short” configuration fairing, with a 23.4 metre “medium” length, or a 26.5 metre “long” fairing also available. Several four-metre diameter fairings can also be used, on launches with smaller-sized payloads, provided no more than three solid rocket motors are needed.

The Atlas V is the only member of the Atlas-Centaur family of rockets currently in service. The Atlas-Centaur was originally designed to combine the Atlas intercontinental ballistic missile with a cryogenically-propelled Centaur upper stage. It made its unsuccessful maiden flight in 1962, with its first successful launch coming the next year.

Atlas V/MSL Pre-Launch Flow Article:

The design was refined and improved over the years; by the mid 1980s the Atlas G, featuring a stretched first stage, was in service. The Atlas I, the first numerically identified member of the family, was operated between July 1990 and April 1997.

Introduced in 1991, the Atlas II incorporated uprated first stage engines, as well as a further stretch to the first stage and also a stretch to the Centaur. The Atlas IIA, with uprated second stage engines, entered service the next year. The year after that, the Atlas IIAS, with four Castor-4A solid rocket motors, began flying.

The short-lived Atlas III was operated between 2000 and 2005, and bridged the gap between the Atlas II and the Atlas V. It demonstrated the use of an RD-180 powered first stage, and a single-engine Centaur rather than the twin-engined model used for all previous launches.

The first Atlas V launch occurred in August 2002, when an Atlas V 401 deployed Eutelsat’s Hot Bird 6 satellite. The Atlas V is more modular than its predecessors; it can fly with two different fairing diameters, between zero and five boosters, and with a single of twin engine Centaur. No Dual-Engine Centaur (DEC) launches have been made to date, however it is expected that launches of Boeing’s CST-100 spacecraft will use the DEC, which offers increased performance to low Earth orbit.

Atlas V launches from Cape Canaveral occur from Space Launch Complex 41, the northernmost active complex on the Cape. SLC-41 was originally built as part of the Integrate-Transfer-Launch complex, along with nearby SLC-40, to support Titan IIIC launches during the 1960s. The first launch from the pad occurred in December 1965.

In the early 1970s, the complex was modified to accommodate the Titan IIIE, which replaced the Transtage third stage used on the Titan IIIC with the much more powerful Centaur-D1T. The Titan IIIE, which launched exclusively from SLC-41, deployed the Viking, Voyager and Helios probes to study Mars, the outer planets, and the Sun.

SLC-41 later became a Titan IV launch complex, supporting the Titan IV’s maiden flight in June 1989. Ten Titan IVs were launched from the pad, the last being Titan B-27, which failed to place a Defense Support Program satellite into the correct orbit in April 1999. Six months later SLC-41 was demolished ahead of its conversion for use by Atlas V rockets, which culminated in the maiden flight of the Atlas V in June 2002.

During the Titan era, rockets to be launched from SLC-41 were assembled in the Vertical Integration Building (VIB), before being transported to the pad atop a mobile platform on rails for payload installation and launch. Atlas rockets are instead assembled, and have their payloads installed, in the Vertical Integration Facility (VIF), which is only 550 metres away from the pad. In 2006, the disused VIB was demolished.

Following assembly, payload integration and final testing, AV-028 was transported from the VIF to the pad atop its mobile launch platform on Friday. The rocket departed the VIF at 13:02 UTC (08:02 local), and arrived at the pad 41 minutes later. The launch was originally scheduled to have occurred on Friday, following a rollout on Thursday, however a 24 hour delay was called to replace a faulty battery in the rocket’s range safety systems.

When the countdown reached T-2.7 seconds, the first stage’s RD-180 engine ignited. The Common Core Booster (CCB), which is the first stage of the Atlas V, is fuelled by RP-1 and liquid oxygen, and powered by a single engine. Four solid rocket motors, manufactured by Aerojet, provide additional thrust at liftoff, and ignited when the countdown reached zero. At tha point the rocket was ready to lift off, however liftoff itself did not occur until T+1.1 seconds, when the vehicle’s thrust exceeded its weight.

About a second after liftoff, the engines reached full thrust, with the rocket executing a manoeuvre to attain the correct attitude for its ascent at T+5.2 seconds.

AV-028 reached supersonic speed at around 34.6 seconds mission elapsed time, as it passed through the sound barrier. Just under twelve seconds later the vehicle experienced the area of maximum dynamic pressure, or Max-Q.

Burnout of the four solid rocket motors came between 85 and 90 seconds into the flight, with separation occurring 112.5 seconds after launch. Separation of the payload fairing, used to protect MSL during its ascent through Earth’s atmosphere, came three minutes and 24.9 seconds into the mission, followed shortly afterwards by the forward load reactor, an aluminium structure used to dampen vibrations within the fairing

About 22 seconds after the fairing separated, the first stage engine was throttled down to maintain a force due to acceleration of 4.6G. First stage flight ended with Booster Engine Cutoff, or BECO, which occurred around four minutes and 21.5 seconds after launch.

Stage separation happened six seconds later, with the Centaur igniting just less than ten seconds after that. The Centaur is a cryogenically-fuelled upper stage, which uses liquid hydrogen propellant and liquid oxygen oxidiser. It is powered by a single RL10A-4-2 engine.

To deploy MSL into a heliocentric orbit, AV-028’s Centaur made two burns. The first lasted six minutes, 52.4 seconds, reaching an initial parking orbit. This was followed by a coast phase lasting approximately 19 and a half minutes.

Following the coast phase, a second burn was made, lasting around 480 seconds, sending MSL on its way to Mars. About three and three quarter minutes after the end of the second burn, MSL separated from the Centaur to begin its mission. The timing of the second burn was dependent on the time and date of launch, and consequently was subject to change.

MSL is the third and last spacecraft launched on a mission to Mars this year. The previous two, Fobos-Grunt and Yinghuo-1, were placed into low Earth orbit by a Zenit-2SB rocket earlier this month.

Following a successful launch, the Fobos-Grunt spacecraft failed to execute its first two engine burns to depart Earth orbit, and engineers have been having difficulty communicating with it since. It looks unlikely that the spacecraft can be saved, however efforts to recover it are still ongoing. Yinghuo-1 remains attached to Fobos-Grunt, and will also be lost if Fobos-Grunt cannot be made to depart Earth orbit.

This is the final Atlas V launch of the year, and the last of eleven launches conducted by United Launch Alliance in 2011. ULA’s next scheduled launch is of a Delta IV carrying a Wideband Global Satcom communications satellite in late January next year. The next scheduled Atlas V launch will be of the first Mobile User Objective System (MUOS) communications satellite in February.

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