It was an interesting year for NASA as the 2011 calendar brought about the retirement of the iconic Space Shuttle fleet, the completion of the USOS segment of the International Space Station, the launch of three new planetary missions, and the ongoing scientific endeavors of NASA’s fleet of planetary probes. In all, 2011 proved a banner year for NASA’s unmanned explorers in our solar system.

Background:

While much of the world’s attention was on NASA’s manned exploits in 2011, the US space agency was busy with its fleet of unmanned planetary explorers peppered throughout the inner and outer solar system.

In particular, NASA’s MESSENGER, Dawn, Cassini, and Voyager 1 spacecrafts increased our knowledge of Mercury, the asteroid belt, Saturn, and the outer-most boundary of our solar system, while the intrepid rover Opportunity revealed more secrets about our third closest celestial neighbor: Mars.

Calendar year 2011 for NASA also saw the launch of three new and exciting missions: the twin GRAIL probes to the moon, the Juno spacecraft to the Jupiter, and the Mars Science Laboratory rover Curiosity to Mars.

Sadly, 2011 also brought about the end of official operations for the Mars rover Spirit which survived on the red planet for over six years.

The new missions: GRAIL, Juno, and MSL:

Continuing a string of successes in planetary missions, NASA began three new planetary flights in 2011, including one designed to build the presence of the space agency around the moon.

GRAIL and the new mission to the moon:

Dubbed the GRAIL mission, the twin Gravity Recovery And Interior Laboratory spacecraft will be the first of their kind to conduct an unprecedented and detailed study of Earth’s closest celestial neighbor from the crust of its surface to its inner-most core.

Launching aboard the veteran Delta II rocket from the Cape Canaveral Air Force Station on Saturday, September 10, the twin spacecraft enjoyed an issue-free 3.5 month low energy transfer cruise to the Moon and are scheduled to arrive in lunar orbit on December 31, 2011 and January 1, 2012.

Powered by a series of solar panels on their surface, NASA hopes that the GRAIL spacecraft will answer longstanding questions about the Moon and give scientists a better understanding of how Earth and other rocky planets in the solar system formed.

Flown under NASA’s Discovery program, the principle scientific objectives of the GRAIL mission are to produce a map of the moon’s lithosphere, allow scientists to understand the moon’s thermal evolution and the evolution of breccia with in the moon’s crust, and determine more details of the moon’s interior, particularly the size of the moon’s core and the structure beneath impact basins.

Once inserted into lunar orbit, the twin GRAIL spacecraft will work in harmony with one another during the primary 82 day scientific collection phase of the mission.

While nothing beyond the 82-day primary science mission has been confirmed, it is entirely possible – based on past mission extension operations from NASA – that the GRAIL mission could enjoy a longer life in orbit of the moon.

However, this mission’s launch also signaled the apparent end of NASA’s selection of the Delta II rocket as a preferred launch vehicle. Following numerous successful flights with Delta II, NASA is now moving in the direction of selecting the Atlas V and Delta IV launch vehicles over the Delta II.

While NASA has publicly expressed optimism that a future mission could utilize the Delta II launch vehicle’s services, no such official commitment has been made and none of NASA’s currently planned missions are scheduled to use the Delta II rocket.

Therefore, the launch of the GRAIL spacecrafts marked the penultimate flight of the Delta II, with its final flight occurring in late October, and final time NASA used the veteran rocket. (GRAIL L2 Coverage).

Returning to the giant:

Nonetheless, the GRAIL mission was not the first of the new planetary missions launched by NASA in 2011. Almost exactly one month earlier in early August, NASA successfully launched the new Juno probe to the solar system’s giant: Jupiter.

Riding atop the second most powerful configuration for the Atlas V rocket, the Juno mission lifted off at 1225 EDT on 5 August 2011 – after a 51 minute delay for a technical issue and a boat in the launch restriction zone.

Since launch, Juno has traveled approximately 221 million miles and has achieved a velocity of 55,800 miles per hour relative to the sun.

Named after the Roman goddess of marriage and the wife of the god Jupiter, the Juno mission is the second mission in NASA’s New Frontiers program – the first being the New Horizons probe currently on its way to an encounter with Pluto and its moons in July 2015.

The spacecraft made its first of three Mars orbit crossings on December 13 in anticipation for its August 2016 arrival at Jupiter after a five year trek through the inner and outer solar system. During this five year trek, the spacecraft will make a flyby of Earth in October 2013 for a gravitational assist to propel itself into the outer solar system.

Once it arrives at Jupiter, Juno will enter a zenocentric orbit of the gas giant for a primary scientific mission that is scheduled to last 14 months and allow the spacecraft to study Jupiter from a polar orbit.

To accomplish this, the Lockheed Martin-built spacecraft will carry nine instruments to Jupiter to study electric currents flowing along field lines in the planet’s magnetic field, ultraviolet and electromagnetic emissions of the energetic particles in Jupiter’s aurora, heat being emanated from the planet, the structure of Jupiter’s atmosphere, the magnetosphere’s structure in the planet’s polar regions, and the energy and distribution of particles and the polar regions of Jupiter’s magnetosphere.

In all, Juno will be the ninth spacecraft to visit the planet Jupiter, the first being the pioneer 10 spacecraft which flew through the Jovian system in December 1973.

Juno will be the first spacecraft to be placed into orbit around Jupiter since the Galileo mission which lasted from December 8, 1995 to September 21, 2003.

The connection between Juno to its predecessor Galileo is somewhat ironic to space fans. The Juno mission was in fact the first NASA mission to be launched after the fly out of the Space Shuttle Program. The final flight of the shuttle program flown by orbiter Atlantis landed just 15 days before Juno’s launch. The previous Jovian orbiter mission of Galileo was launched by the very same Space Shuttle – Atlantis – in 1989.

Additionally, the successful launch of the Juno mission represented the 175th flight of an Atlas rocket with a Centaur upper stage. The Atlas-Centaur duo first flew in May 1962 and has since undergone several iterations.

The most current iteration, the Atlas V rocket, is one of the most reliable U.S. domestic launch vehicles in service today. At the time of the Juno launch, the Atlas V rocket was in fact the second most reliable U.S. domestic launch vehicle behind only the Delta II rocket – given that the Shuttle had been retired just 15 days prior.

By late November, when the third of NASA’s three new planetary missions was launched, the Atlas V was the most reliable U.S. domestic launch vehicle in service following the defacto retirement of the Delta II rocket in late October due to no further customer requests for its services. (Juno L2 Coverage).

Mars Science Laboratory – Unlocking the further secrets of Mars:

NASA’s third new planetary mission of the year was perhaps the most anticipated of NASA’s unmanned missions in 2011.

Carrying the Mars Science Laboratory (MSL) rover Curiosity, the veteran Atlas V rocket flying on its 28th mission lifted off from the Cape Canaveral Air Force Station at the beginning of a 1 hour 43 minute window at 10:02 EST on 26 November 2011.

For the Atlas V rocket, the launch of Curiosity marked the 28th out of 28 successful missions for the rocket, giving the vehicle, from a payload customer standpoint, a perfect success record.

Successfully sending the MSL rover on its way to the red planet, the Atlas V rocket began what will be a nine month journey through the interplanetary medium for Curiosity.

Scheduled to arrive on 6 August 2012 at approximately 0100 EDT, the MSL will pioneer a new precision landing technology for NASA and a sky-crane touchdown to place Curiosity near the foot of a mountain inside Gale crater.

According to NASA, the new precision landing maneuvers have allowed scientists to shrink the target landing area to less than one-fourth the size of earlier Mars mission landing targets – a new innovation that without which would have made Gale crater an unacceptably hazardous area for Curiosity to land.

While the primary goal of the MSL mission is to determine whether Mars is or has ever had an environment capable of supporting life, the mission will not look for any specific type of life.

Instead, the rover will use a suite of 10 scientific instruments along with a robotic arm to analyze soil and rock samples with a complex set of laser and sensor systems.

In all, Curiosity is five times larger than its predecessors Spirit and Opportunity and has 15 times the mass of scientific experiments of Spirit and Opportunity.

Curiosity’s primary science mission phase is scheduled to last 687 Earth days or one Martian year and cover between 5-20 kilometers on Mars’s surface.

The mission was initially scheduled to launch in the 2009 Martian launch window but was delayed due to inadequate test time and technical and budgetary reasons. (MSL L2 Coverage).

NASA’s ongoing missions – from Mercury to the edge of the solar system:

While the new missions launched by NASA this year certainly offer up the potential to provide intriguing new insights into the solar system and planetary formation, the successes of ongoing NASA missions that are already collecting data on this very topic dominated much of the space community’s news in 2011.

In fact, 2011 proved to be the year in which two major historic events in the unmanned space probe arena would finally come to fruition: the successful insertion of the MESSENGER probe into orbit around the planet Mercury and a successful orbital insertion of the Dawn spacecraft around the asteroid Vesta.

MESSENGER at Mercury:

The first of these two major achievements occurred on 17 March 2011 when the MESSENGER spacecraft confirmed its successful orbital insertion of planet Mercury at 2110 EDT.

As related by NASA, “Achieving Mercury orbit was by far the biggest milestone since MESSENGER was launched more than six and a half years ago. This accomplishment is the fruit of a tremendous amount of labor on the part of the navigation, guidance-and-control, and mission operations teams, who shepherded the spacecraft through its 4.9-billion-mile journey.”

Within days, MESSENGER had sent back its first image of Mercury from orbit and began what was thought to be a year-long Mercury science mission which was due to end on 17 March 2012.

However, on 14 November 2011, NASA announced the extension of the MESSENGER mission for an additional year of orbital operations at Mercury, ensuring the spacecraft’s operation, from a funding and ground support stance, through 17 March 2013.

This extension comes in large part due to the tremendous success of the MESSENGER mission in its first six months of operation in orbit of Mercury.

So far, MESSENGER has revealed unexpectedly high concentrations of magnesium and calcium on the night time side of Mercury and the offset to the north of the planet’s center of the magnetic field.

During the first year of its operations, MESSENGERs primary science objectives include determining accurately the surface composition of Mercury, characterizing the geological history of the planet, determing the precise strength of the magnetic field and its variations with position and altitude, investigating the presence of a liquid outer core by measuring Mercury’s liberation (oscillating motion of orbiting bodies relative to each other), determining the nature of the radar reflective materials at Mercury’s polls, and investigating the important volatile species and their sources and sinks on and near Mercury.

Following from the primary year of scientific exploration, the one year extension will be designed to explore six scientific questions regarding Mercury. Specifically these questions include: What are the sources of surface volatiles on Mercury? How late into Mercury’s history did volcanism persist? How did Mercury’s long-wavelength topography change with time? What is the origin of localized regions of enhanced exospheric density at Mercury? How does the solar cycle affect Mercury’s exosphere and volatile transport? And what is the origin of Mercury’s energetic electrons?

As related by NASA, “Advancements in science have at their core the evaluation of hypotheses in the light of new knowledge, sometimes resulting in slight changes in course, and other times resulting in paradigm shifts, opening up entirely new vistas of thought and perception.

“With the early orbital observations at Mercury we are already seeing the beginnings of such advancements. The extended mission guarantees that the best is indeed ‘yet to be’ on the MESSENGER mission, as this old-world Mercury, seen in a very new light, continues to give up its secrets.”

Farewell Spirit; New Science from Opportunity:

Few could argue the success and the legacy of the twin Mars Exploration Rovers Spirit and Opportunity. From their launch in June and July 2003, respectively, and their arrival on the red planet on 4 January 2004 and 25 January 2004, respectively, the twin rovers have beyond exceeded all expectations for their scientific mission which was only supposed to last 90 solar days.

For Opportunity, the journey on the red planet continues to this day with ongoing scientific evaluations into the past habitability of Mars and the planet’s current environmental conditions.

But for Opportunity’s twin rover Spirit, the rover which was launched first and arrived first on the red planet, the incredible journey came to a formal conclusion earlier this year when all attempts to communicate with the rover over the previous year proved unsuccessful.

After 2210 solar days on the surface of Mars, the final communication with the Spirit rover was received on 22 March 2010 at the beginning of what was expected to be a period of winter dormancy for the two rovers as they entered the Martian winter.

However, while Opportunity weathered the Martian winter, Spirit did not. After 14 months of unsuccessful attempts to communicate with the rover, NASA officially ended Spirit’s tenure on Mars on 24 May 2011.

With an original mission duration of only 90 solar days, the Spirit rover functioned above and beyond what her engineers and scientists asked her to do. Functioning 24.5 times longer than anticipated, Spirit covered 4.8 miles during her 6 year 2 month 18 day tenure on Mars, nearly 12 times the original distance goals set for the mission.

According to NASA, “Our job was to wear these rovers out exploring, to leave no unutilized capability on the surface of Mars, and for Spirit we have done that.”

Spirit was given a formal farewell on NASA television in the final week of May 2011, after which the assets that once belonged to Spirit and its mission were turned over to MSL mission team in preparation for that flight’s launch in November.

But with the demise of Spirit came a renewed focus on her twin, Opportunity. Now the longest surviving vehicle on the surface of Mars, a title the Opportunity rover has held since April 2010, Opportunity is currently exploring the rim of Endeavour crater on Mars – a crater, like the Shuttle orbiter Endeavour, named after the 18th century British sailing vessel commanded by James Cook during his first voyage of discovery to Fiji, New Zealand, and Australia.

Over the course of the Opportunity’s nearly eight year tenure on the Martian surface, the rover has driven an impressive 21 miles and has functioned more than 30 times longer than its originally planned 90 solar day mission.

To this day, Opportunity continues to perform extensive geological analysis of Martian rocks and planetary surface features, including the very recent discovery of a mineral vein deposited by water on the surface of Mars.

In October of this year, Opportunity and her twin, Spirit, were selected for lifetime achievement award honors as part of the Breakthrough Awards presented by Popular Mechanics magazine.

Dawn in the asteroid belt – Achieving orbit of Vesta:

Launched aboard a Delta II rocket on 27 September 2007, the Dawn spacecraft completed its near four year journey to the asteroid belt on 16 July 2011 when it entered orbit of the Vesta asteroid.

After being captured by Vesta’s gravity, the Dawn spacecraft maneuvered itself into a lower and closer orbit by firing its xenon ion rocket engines to enter a 4.3-hour low altitude mapping orbit.

For the Dawn mission, the goal of the overall flight is to characterize the conditions and processes of the solar system’s earliest eon by investigating the two largest protoplanets, Ceres and Vesta.

Vesta, the second most massive asteroid in the asteroid belt after the dwarf planet Ceres, is estimated to contain approximately 9% of the total mass of the asteroid belt.

Comparatively, though, little is known about Vesta except that it is one of the largest protoplanetary objects remaining intact since the formation of the solar system. Currently, it is believed that both Ceres and Vesta formed in two different regions of the early solar system before migrating to their current location within the asteroid belt.

Since its arrival in July, the Dawn spacecraft has helped shed new light on Vesta, including the fact that it appears to be one of the most rugged – in terms of surface topography – bodies in the asteroid belt.

While information on how the surface features of Vesta were formed is still forthcoming, Dawn has revealed that some of the surface features of the asteroid in its southern hemisphere are only 1-2 billion years old, considerably younger than regions on the asteroid’s northern hemisphere.

Dawn has also helped reveal an interesting diversity in the composition of the craters on Vesta as well as the asteroid’s overall surface composition.

In all, Dawn has roughly seven more months of observations at Vesta before its ion engines will be fired again to take it out of orbit of Vesta and put the spacecraft on course for rendezvous with the dwarf planet Ceres in February 2015.

Cassini at Saturn – The storm on Saturn and the year of Saturnian moons:

Perhaps one of the most interesting scientific missions to take place in 2011 was the ongoing mission of Cassini at Saturn.

From discovering new heat sources on Saturn’s intriguing moon Enceladus, to finding that seasonal rains transform the surface of Titan, to observing a raging storm on Saturn itself, and finally to a flyby of Enceladus, the Cassini mission has given us invaluable insight into the Saturnian system.

Beginning the year with the incredible discovery that heat output from the south polar region of Saturn’s moon Enceladus was much greater than originally thought possible, NASA’s Cassini spacecraft showed that heat-generated power was approximately 15.8 gigawatts in Enceladus’ southern polar region.

While Enceladus’ geologically active southern polar region was discovered in 2005, a 2007 study, according to NASA, “predicted the internal heat of Enceladus, if principally generated by tidal forces arising from the orbital resonance between Enceladus and another moon, Dione, could be no greater than 1.1 gigawatts averaged over the long term” – a hypothesis proved incorrect about Cassini earlier this year.

A possible explanation for the high heat flow observed in Enceladus could have a great deal to do with the amount of liquid water present under Enceladus’ surface.

This potential explanation for the higher-than-expected power output on Enceladus comes from the direct measure of ice crystals released from underneath the surface of Enceladus by surface geysers.

These ice crystals, as sampled by Cassini during a flyby of Enceladus, contained salt-rich particles that could potentially be frozen droplets of a saltwater ocean in contact with Enceladus’ mineral-rich rocky core.

This potential discovery of a massive underground saltwater ocean on Enceladus, a liquid ocean made possible by tidal energy from Enceladus’ interaction with other moons of Saturn and Saturn itself, has garnered a new astrobiological interest in Saturn’s moon as yet another place in the solar system where life could potentially exist.

Following on the heels of this discovery, the Cassini spacecraft observed methane rain showers around Titan’s equatorial regions. Following observations of large rain cloud systems in 2010, a predominantly dark surface near Titan’s equatorial region indicates that Titan’s surface is directly affected by seasonal changes within the Saturnian system as well as weather systems on Titan itself.

According to a NASA news release on 17 March 2011, an arrow-shaped storm appeared in the equatorial regions on Sept. 27, 2010 and a broad band of clouds appeared the next month. Over the next few months, Cassini monitored short-lived surface changes of Titan’s surface.

These observations suggest that recent weather on Titan is similar to that over Earth’s tropics.

Furthermore, around the same time as these previous observations, Cassini also monitored the birth of a violent storm in Saturn’s northern hemisphere that eventually grew to stretch around the entire planet.

Initially witnessing the formation of the storm in December 2010, Cassini witnessed the rapid expansion of the storm that eventually produced a 3,000-mile-wide dark vortex.

The storm became the first major storm on Saturn to be observed by an orbiting spacecraft and studied at thermal and infrared wave lengths.

Since the storm’s creation, Cassini monitored the changing composition of Saturn’s atmosphere, including the appearance of ammonia from deep in the atmosphere, from a mixing of air from different levels.

Finally, in early November 2011, Cassini made a close flyby of Saturn’s moon Enceladus, acquiring the first detailed radar images of the moon on November 6. The images were the first high resolution radar observations made of any icy moon other than Titan.

The flyby also provided scientists the opportunity to obtain detailed measurements of Enceladus’ icy jets in order to make new measurements of hot spots underneath Enceladus’ surface.

To the edge of the solar system – Voyager 1 and the great unknown:

For NASA’s unmanned interplanetary missions, 2011 ended with the exciting discovery that the Voyager 1 space probe is closer than thought to exiting the solar system and entering the interstellar medium.

Described by NASA has a cosmic purgatory, new information from the Voyager 1’s scientific instruments over the previous year indicate that the spacecraft has entered a new region between our solar system and interstellar space.

In this new region, the wind of charged particles streaming out from our sun, particles which compose the magnetic field of our solar system, begin to “pile up” while higher energy particles from inside our solar system appear to be leaking out into the interstellar medium.

According to NASA, “Voyager tells us now that we’re in a stagnation region in the outermost layer of the bubble around our solar system. Voyager is showing that what is outside is pushing back. We shouldn’t have long to wait to find out what the space between stars is really like.”

But while Voyager 1 is close to passing into the interstellar medium, indications from the spacecraft show that the magnetic field lines from the sun have not changed direction. This is a direct indication that Voyager 1 is still within the heliosphere, the area in which the charged particles from the sun are still the dominant force.

While this new information is exciting and gives us a better understanding of the outer-most reaches of our solar system, it does not change the previous statement from NASA that Voyager 1 could enter the interstellar medium at any time now.

While the exact date on which Voyager 1 will exit the solar system, becoming the first manmade object to do so in recorded history, cannot be precisely calculated, all indications are that Voyager 1 will enter the interstellar medium sometime in the next few years.

Click here for our two previous Voyager Feature Articles:

http://www.nasaspaceflight.com/2011/08/voyagers-unprecedented-on-going-mission-exploration/

http://www.nasaspaceflight.com/2011/08/thirty-four-years-voyager-2-continues-explore/

Into 2012 – A year to capitalize on what’s come before:

While 2011 was a banner year for NASA in terms of interplanetary science, 2012 should be an even more exciting year.

In the next year, the MESSENGER spacecraft will continue its observations of planet Mercury while observing the planet at close range during the solar maximum cycle of our sun. It is hoped the MESSENGER will be able to monitor the solar maximum’s effect on the inner-most planet in our solar system.

Meanwhile, much closer to home, he twin GRAIL spacecraft will begin to unlock further secrets of our closest celestial neighbor in terms of its composition and formation in the early years of the solar system.

Furthermore, NASA will have the privilege of being the only space agency in the world to attempt a landing of a rover on Mars. This distinction comes after the failed Martian launch attempt from Russia of the Fobos-Grunt probe in November 2011.

And while Cassini will continue to observe the Saturnian system and Voyager 1 continues to get ever-closer to the interstellar boundary between our solar system and interstellar space, NASA will conduct of the launch of the NuSTAR, the Nuclear Spectroscopic Telescope Array to allow astronomers to study the universe in high energy X-rays.

That mission is currently scheduled to launch on March 14, 2012 aboard the Pegasus XL rocket from the Reagan Test Site in Kwajalein Atoll.

This will be followed by the launch of the Radiation Belts Storm Probes atop an Atlas V rocket from the Cape Canaveral Air Force Station.

This mission, dubbed RBSP, will help our understanding of the sun’s influence on Earth and near-Earth space by studying the Earth’s radiation belts on various scales of space and time.

That mission is currently scheduled to launch on August 23, 2012.

Following the launch of that mission, NASA will align itself for the launch of the Interface Region Imaging Spectrograph, or IRIS. This mission, which is progressing toward a target launch date of December 1, 2012 will be flown aboard the Pegasus XL rocket from Vandenberg Air Force Base in California.

The mission itself is designed to provide information on energy transport into the corona and solar wind and provide an archetype for all stellar atmospheres.

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