YIR (Part II) – Lunar and Saturnian exploration captures public’s attention
Capturing and holding the attention of the general public for space exploration purposes is often a difficult thing to achieve. But 2013 saw not only NASA but also the China National Space Administration do just that through a series of new and continuing voyages to the Moon and Saturn.
YIR Part II: Lunar exploration – welcoming China to a select group:
*Click here for Part I*
When 2013 began, the United States was the only country with operating lunar probes and an active lunar exploration program.
By the end of the year, lunar operations surged with both NASA and Chinese missions expanding lunar exploration capabilities.
For NASA, 2013’s lunar exploration saw the addition of the Lunar Atmosphere and Dust Environment Explorer (LADEE) satellite to the U.S. space agency’s pantheon of operational lunar missions: ARTEMIS 1 (Acceleration, Reconnection, Turbulence and Electrodynamics of the Moon’s Interaction with the Sun 1), ARTEMIS 2, and LRO (Lunar Reconnaissance Orbiter).
(ARTEMIS 1 and 2 are repurposed THEMIS probes which were launched on their original mission in February 2007 and repurposed for lunar exploration in April-July 2011).
LADEE, the first NASA lunar exploration mission led by the Ames Research Center in collaboration with the Goddard Space Flight Center, was launched from the Wallops Flight Facility at the Mid-Atlantic Regional Spaceport in in the U.S. state of Virginia on 7 September 2013 at 0327 UTC aboard a Minotaur V rocket.
From the beginning, the general public and American news media gave considerable coverage to LADEE because of the mission’s launch location.
Since the United States first attempted to launch a probe to the moon in August 1958, which was also Humanity’s first attempt to lunch a probe to the moon, all but one of the United States’ lunar missions had attempted to or actually launched from the Cape Canaveral Air Force Station or the Kennedy Space Center in Florida.
The one previous exception had been the Clementine mission for the U.S. Air Force and NASA, which launched aboard a Titan II rocket on 25 January 1994 from the Vandenberg Air Force Base in California.
For LADEE, a new first would be a lunar launch from Wallops Flight Facility in Virginia, the first eastern seaboard lunar mission to lunch from a location other than the nation’s primary spaceport in Florida.
Due to the unique launch location, LADEE presented particular interest to the general public and American news media as its nighttime launch aboard a solid propellant vehicle would be visible to the most-densely populated corridor in the United States.
When LADEE launched, it did not disappoint – with observers witnessing the climb of the Minotaur V rocket from as far south as the state of South Carolina and throughout the populated cities of Washington D.C., Philadelphia, New York City, and Boston.
Even after the successful launch, the American news media and general public continued to maintain interest in LADEE’s launch due to a unique photo bomb event when a frog was captured on still-photography as it took a flight of it own, having been caught in the intense wind currents generated by the Minotaur V’s first stage engine at liftoff.
Scientifically, though, a unique and usually unheard of aspect to the mission was the fact that the Minotaur V rocket chosen to launch LADEE lacked the necessary thrust to place the satellite into a direct lunar transfer orbit.
Normally, though not always, NASA utilizes rockets such as the Atlas V and Delta II that have enough launch power to send lunar probes on direct insertion flight paths to the moon.
However, this time was different and required LADEE to use a unique, highly elliptical Earth orbit to make three increasingly larger orbits of Earth before it was close enough to the moon to be entered into lunar orbit.
After a month-long cruise, LADEE entered orbit of the moon on 6 October in an elliptical capture orbit of 24hour duration.
On 9 October, LADEE’s orbit was refined to a 4hour duration orbit before finally settling into a circular orbit of 250 km (160 miles) on 12 October.
LADEE then entered a commissioning and checkout period during which the first major milestone of the scientific portion of the mission was reached.
On 18 October, scientists successfully tested LADEE’s Lunar Laser Communication Demonstration (LLCD) pulsed laser system by transmitting data between the spacecraft and its ground station on Earth at a distance of 385,000 kilometers (239,000 mi).
“It was amazing how quickly we were able to acquire the first signals, especially from such a distance,” said Don Cornwell, LLCD manager. “I attribute this success to the great work accomplished over the years by the Massachusetts Institute of Technology Lincoln Laboratory (MIT/LL) and their partnership with NASA.”
The test set numerous firsts for NASA including a downlink record of 622 megabits per second from spacecraft to ground and an error-free data upload rate of 20 Mbps from ground station to spacecraft.
The LLCD instrument is NASA’s first attempt at two-way space communication using an optical laser instead of traditional radio waves. The system is expected to lead to operational laser communication systems on future NASA satellites.
“LLCD is the first step on our roadmap toward building the next generation of space communication capability,” said Badri Younes, NASA’s deputy associate administrator for space communications and navigation in Washington, which sponsored LLCD. “We are encouraged by the results of the demonstration to this point, and we are confident we are on the right path to introduce this new capability into operational service soon.”
By 20 November, LADEE was successfully maneuvered into a two-hour orbit around the moon’s equator at an altitude ranging between 12-60 km (eight to 37 miles).
The orbit was specifically chosen to allow the probe to make frequent passes from lunar day to lunar night, providing scientists a full range of the changes and processes occurring within the moon’s tenuous atmosphere.
The orbit will also allow scientists to study the conditions in the lunar atmosphere during lunar sunrise and sunset, where previous crewed and robotic missions detected a mysterious glow of rays and streamers reaching high into the lunar sky.
Commissioning of the spacecraft was officially completed by 22 November with mission scientists declaring that LADEE was ready to begin the primary scientific phase of its mission.
That 100-day primary scientific phase officially began on 11 December 2013 – just 10 days after and three days before a major world power finally began and then very successfully entered the arena of lunar surface exploration.
On 1 December 2013 the China National Space Administration (CNSA) successfully began its lunar surface campaign with the launch of the Chang’e 3 mission via the Long March 3B Y-23 rocket from the Xichang Satellite Launch Center (Base 27) near Xichang, Liangshan Yi Autonomous Prefecture in Sichaun, People’s Republic of China.
Launch of the Chang’e 3 mission represented the first lunar landing and rover mission for China as part of the second phase of the Chinese Lunar Exploration Program.
Five days after launch, on 6 December, Chang’e 3 successfully achieved a lunar orbit of 15-100km after 361 seconds of variable thrust engine braking from its single main engine.
Eight days later, as the probe reached orbital periapsis, its variable thrusters fired to reduce the probe’s velocity and bring it to 100 meters above the lunar surface.
Once at this altitude, the probe hovered and moved horizontally under its own guidance to avoid surface obstacles.
The probe then descended to an altitude of 4 meters, at which point its engines were shut down and the probe free-fell to the lunar surface.
After a 12 minute landing sequence, Chang’e 3 successfully soft-landed on the surface of the moon in the Mare Imbrium at 1311 UTC on 14 December, becoming the first probe to do so since the Luna 24 mission in 1976.
With the landing, China became only the third nation behind the Soviet Union and the United States to successfully soft land a mission on the moon, and became the fourth nation to successfully send a vehicle to the surface of the moon following the Soviet Union, United States, and India’s impactor-only mission in 2009.
And as space enthusiasts around the world watched the historical event on television, NASA’s LADEE probe, 1300 km to the south of Chang’e 3’s landing site, also watched the descent and landing.
The evening before Chang’e 3’s landing, LADEE mission controllers uploaded a command sequence that scheduled the science instruments for operations during the Chang’e 3 landing period.
To gather the most accurate data possible, LADEE’s science instruments gathered data on the dust and gas species before and after the landing to provide the science team with a comparison.
As LADEE’s instruments watched, Chang’e 3 descended to the lunar surface.
After the landing observation period concluded, scientists were somewhat baffled by the evaluation of data from LADEE’s science instruments.
As reported earlier this month, the LADEE science teams’ preliminary evaluation of the data did not reveal any effects attributed to Chang’e 3. No increase in dust was observed by the LDEX instrument, no change was seen by UVS, and no propulsion products were measured by NMS.
The normal native lunar atmospheric species seen by UVS and NMS prior to Chang’e 3’s landing were also apparently unaffected.
While the results were surprising, the science team was quick to point out that it is actually an important and useful result for LADEE not to have detected the descent and landing as it indicates that exhaust products from a large robotic lander do not overwhelm the native lunar exosphere.
While LADEE’s observation of Chang’e 3’s landing was brief, Chang’e 3’s landing day was met not only with the historic soft landing on the moon but also with the deployment of a rover onto the lunar surface just seven hours after landing.
The Yutu rover, meaning Jade Rabbit – named after the mythological rabbit living on the surface of the moon in Chinese mythology, descended from the Chang’e 3 lander and officially made contact with the lunar surface at 2035 UTC on 14 December.
The Chang’e 3 lander is expected to survive at least one year on the lunar surface while the Yutu rover is expected to spend its three-month mission exploring a 3 square kilometer area around the lander and only travel a maximum distance of 10 kilometers away from the lander.
By 25 December, the Yutu rover and Chang’e 3 lander were placed into their first lunar night hibernation cycle as they await the return of daylight to their landing site in early January. (Night last two Earth weeks on the moon.)
Saturn – the year Earth waved at the ringed planet:
For Cassini, 2013 with another banner year in orbit of Saturn.
Orbiting what is arguably the most iconic and recognizable planet with the solar system (other than Earth) since 2004, Cassini continues to observe seasonal changes in the Saturnian system as the ringed planet continues its 29.5 Earth year-long orbit around the sun.
In April, during a close encounter with Saturn’s principal moon Titan, the Cassini orbiter’s Composite Infrared Spectrometer (CIRS) recorded seasonal ice cloud formations over Titan’s southern polar region – seasonal ice clouds that had until this year only been observed in the northern polar region of the atmosphered-moon.
“We associate this particular kind of ice cloud with winter weather on Titan, and this is the first time we have detected it anywhere but the north pole,” said the study’s lead author, Donald E. Jennings, a CIRS Co-Investigator at NASA’s Goddard Space Flight Center in Greenbelt, Maryland.
According to data returned from Cassini, the southern ice cloud is currently only detectable in the far infrared part of the light spectrum and provides evidence that an important pattern of global air circulation on Titan has reversed direction in the 9.5 years since Cassini’s arrival in the Saturnian system in July 2004.
When Cassini first observed the circulation pattern in Titan’s atmosphere, warm air from the southern hemisphere was transported to the cold north pole of the moon. Once there, the air cooled and sank down to lower layers of the atmosphere, where it formed ice clouds.
That pattern is now reversing, and with new evidence presented from Cassini, scientists have been able to trace the air current shift to within a six-month period of the Titan equinox in 2009.
The new findings stem from 2012 observations by the Cassini spacecraft and the detection in early 2012 of a high-altitude haze hood and a swirling polar vortex at Titan’s south pole, features that had long been associated with the colder north pole during Cassini’s tenure at Saturn and Titan.
By July 2012, a few months after the detection of the haze hood and vortex, this CIRS instrument aboard Cassini finally detected the southern polar ice cloud.
“This lag makes sense because first the new circulation pattern has to bring loads and loads of gases to the south pole. Then the air has to sink. The ices have to condense. And the pole has to be under enough shadow to protect the vapors that condense to form those ices,” said Carrie Anderson, a CIRS team member and Cassini participating scientist at NASA Goddard.
Interestingly enough, the identity of the ices in the polar ice clouds has yet to be determined, though scientists have ruled out simple chemicals, such as methane, ethane, and hydrogen cyanide that are typically associated with Titan.
One possibility scientists are pursing is that the ice could, interestingly enough, be a mixture of organic compounds.
Following this announcement came the release of another report from information on Titan gathered over the previous years by Cassini regarding the hydrocarbon lakes on the moon’s surface.
The longevity of the hydrocarbon lakes on Titan’s surface has long since been an area of interest for scientists as Titan is the only other body aside from Earth within the solar system that has stable liquid on its surface.
The dominant molecule on Titan is methane, which scientists are fairly sure is at the heart of a cycle on Titan that is somewhat similar to the role of water in Earth’s hydrological cycle, causing rain, carving channels, and evaporating from lakes.
Thus, the enduring mystery on Titan for the last nine years of Cassini’s observations has been a remarkable consistency in the size and shape of the hydrocarbon lakes – as one would expect to see the effects of methane evaporation from the lakes.
Even taking into account the occasional outburst of hydrocarbon rain on Titan, the lakes consistent appearances do not reflect what scientists would expect to see if their primary composition was methane.
This new data from Cassini has led to a new theory regarding the lakes’ composition. Since methane tends to evaporate quickly, scientists hypothesized in April that Titan’s lakes are actually dominated by methane’s sister hydrocarbon ethane, which evaporates more slowly.
Additional evidence revealed mounting evidence that indicates that the methane on Titan is constantly being lost by being broken down to form ethane and other heavier molecules and is not being replaced by fresh methane from the interior of the moon.
This could result in a depletion of Titan’s methane within tens of millions of years.
Following on the heels of the ice cloud and methane reports from Titan, Cassini also returned data on the observance of the large hurricane churning at Saturn’s north pole and of meteors breaking apart and colliding with Saturn’s rings.
Both of these observations yielded important information to scientists as well as new mysteries for Cassini to explore in the coming year that could have important impacts for Earth as we learn more about meteor impacts throughout the solar system and the process of water vapor consumption within hurricanes on Earth and Saturn.
By the end of May, scientists using data from Cassini we able to create the first global topographic map of the Titan and create what they hope is a verifiable weather forecast (including wave detection and hurricane forecasts) for Titan’s northern hemisphere in the coming years (the forecast based on nine years worth of observation by the Cassini spacecraft).
Also by the end of May came new evidence from Cassini that the Saturnian moon Dione was active in the past and could still be active now.
“A picture is emerging that suggests Dione could be a fossil of the wondrous activity Cassini discovered spraying from Saturn’s geyser moon Enceladus or perhaps a weaker copycat Enceladus,” said Bonnie Buratti of NASA’s Jet Propulsion Laboratory in Pasadena, Calif., who leads the Cassini science team that studies icy satellites.
The new evidence comes from Cassini’s magnetometer, which detected a faint particle stream coming from Dione and revealed evidence for a possible liquid or slushy layer under the moon’s rock-hard ice crust.
Examination of Hi-Res photography of the moon’s surface also revealed ancient, inactive fractures on Dione similar to the ones on Enceladus that currently spew water ice and organic particles.
Similar to Enceladus, Dione undergoes gravitational heating as the moon is stretched and squeezed during its orbit of Saturn.
While the reason why Enceladus is far more active than Dione has yet to be answered, the find of a relative liquid or slushy layer under Dione’s surface yields further evidence to the potential large-scale nature of subsurface oceans on icy worlds and moons both interior and exterior to the solar system.
With the May announcement of Dione’s potential activity revealed, attention with Saturn quickly turned to an upcoming July event that promised to unite hundreds of thousands of people across the surface of Earth.
The event, announced by NASA on 18 June, would involve the Cassini spacecraft passing into Saturn’s shadow, an event which would present the rare opportunity to collect the most detailed mosaic photograph of Saturn’s ring system while it would be backlit by the sun.
Based on the orbital parameters of the Cassini spacecraft as well as Saturn’s position relative to the sun, it was announced that the mosaic image would capture not only Saturn but also the planets Venus, Mars, as well as Earth and its moon.
Capitalizing on the ability to engage the general public’s interest with exploration at Saturn, NASA quickly created the event Wave At Saturn in which anyone who wished to participate would, between 2127-2142 UTC on 19 July, turn and wave in the direction of Saturn during the time frame in which Cassini would acquire the photograph of Earth.
The 19 July event coincided coincidently with the Mercury MESSENGER spacecraft’s campaign to search for natural satellites of the closest planet to the sun. In conjunction with the Wave At Saturn event, NASA understood that Earth would also appear in some of the images collected by MESSENGER on 20 July.
Specifically, the MESSENGER images of Earth would be taken at an angle where the illuminated side of Earth for MESSENGER would be the non-illuminated side of Earth in the Cassini image.
Thus, over the course of two days, people on every major populated continent would be able to participate in a near global image of Earth taken by two spacecraft orbiting different planets.
The Wave At Saturn event garnered more public and media attention than the MESSENGER photograph event.
At allotted time on 19 July, Cassini acquired the mosaic of Saturn and with it Earth.
Examination of the detailed photograph of the Earth revealed Cassini’s resolution power as the principal camera taking the mosaic was able to clearly capture not only Earth but also Earth’s moon (as two distinct, separate objects), helping scientist refine imaging techniques for in-solar and extra-solar moons.
While the Wave At Saturn of event garnered most of the attention, the primary purpose of the mosaic image was to study Saturn’s rings in intricate detail as the backlit nature of the ring system at that time allowed Cassini to image fine granulated particles in the rings that are normally unobservable during normal light operations.
By the end of July, scientists using data from the Cassini orbiter had finally confirmed the long-sought after and hypothesized force controlling Enceladus’ (moon) water jets and the jets’ intensities.
Since their initial discovery in 2005, the water geysers and jets of Enceladus have captivated the attention of scientists not just for their indication of a large saltwater ocean below the surface of Enceladus’ icy crust, but also for the reason for their forcefulness.
For years, scientists hypothesized that the intensity of the jets likely varied over time, but evidence could not be found to support that or to discern a recognizable pattern in the intensity of the jets.
This year, however, scientists were able to see the very changes they sought by examining infrared data of the plume as a whole (the composite ejecta from all the jets on Enceladus), obtained by Cassini’s Visual and Infrared Mapping Spectrometer (VIMS).
Analyzing data from the VIMS gathered between 2005 and 2012, scientists were able to determine that the aggregate plume from Enceladus was dimmest when the moon was at the closest point in its orbit to Saturn and would gradually brighten until Enceladus was at the most distant point in its orbit.
Comparing this new data to previous models of how Saturn squeezes and stretches Enceladus during the moon’s orbit was enough to deduce that the stronger gravitational squeeze experienced by Enceladus when it is closest to Saturn squeezes the tiger stripe formations where the jets form and prevents large amounts of material from leaving the jets.
And the discoveries kept on coming.
In August, scientists released analysis of new data points from Cassini suggesting that the moon Titan may have a rigid ice shell.
An analysis of gravity and topography data of Titan indicated that the moon’s ice shell could be rigid and that relatively small topographic features on the surface could be associated with large ice “roots” extending into the underlying ocean.
As explained by Francis Nimmo from the University of California, Santa Cruz, “Normally, if you fly over a mountain, you expect to see an increase in gravity due to the extra mass of the mountain. On Titan, when you fly over a mountain, the gravity gets lower. That’s a very odd observation.”
To explain the strange observation, scientists hypothesized that each rise in the topography on the surface of Titan is offset by a deeper “root” that is a big enough to overwhelm the gravitational effect of the rise.
In simpler terms, the rise and “root” would act like an iceberg, creating a “less gravity” pocket.
If this hypothesis is correct, it would seemingly invalidate or at the very least make it very difficult to have ice volcanoes on Titan, which some scientists have proposed to explain other features seen on the moon’s surface.
It would also suggest that plate tectonics are not recycling Titan’s ice shell.
But it wasn’t just the moons and rings of Saturn that held surprises for scientist this year; Saturn itself proved once again that it harbors deep secrets in its atmosphere.
On 3 September, scientists announced the discovery of water ice in the atmosphere of Saturn, the first such indication and detection of water ice at/in the ringed planet.
Stemming from ongoing observations of a massive atmospheric storm that first appeared in late 2010, new findings from the Cassini spacecraft revealed that the storm had dredged up water ice from more than 160 km (100 miles) below Saturn’s upper atmosphere.
Further analysis of the massive storm that has engulfed most of the northern hemisphere at 30 degrees north latitude has revealed that it functions in much the same way as a thunderstorm does on Earth, where air and water vapor are pushed high into the atmosphere.
“We think this huge thunderstorm is driving these cloud particles upward, sort of like a volcano bringing up material from the depths and making it visible from outside the atmosphere,” said Lawrence Sromovsky of the University of Wisconsin.
“The upper haze is so optically thick that it is only in the stormy regions where the haze is penetrated by powerful updrafts that you can see evidence for the ammonia ice and the water ice. Those storm particles have an infrared color signature that is very different from the haze particles in the surrounding atmosphere.”
By the end of September, it was announced that Cassini had detected propylene on Titan.
Propylene is a chemical used to make food storage containers, car bumpers, and other plastic consumer products.
The detection of propylene on Titan represents the first such detection of the plastic ingredient on any celestial body other than Earth.
Meanwhile, as 2013 drew to a close, scientists were busy analyzing data from Cassini’s three mid-year flybys of Titan, two of which were performed in July and one in September.
The flybys presented rare perfect viewing conditions for Cassini’s instruments of the northern polar region of Titan that had previously been shrouded from the spacecraft’s view during Titan’s northern hemisphere winter.
The flybys have presented the most detailed map of the northern hydrocarbon lake/sea region on Titan and given scientists new information about the 900 x 1800 kilometer region where 97 percent of the moon’s surface liquid congregates.
“Scientists have been wondering why Titan’s lakes are where they are. These images show us that the bedrock and geology must be creating a particularly inviting environment for lakes in this [region],” said Randolph Kirk, a Cassini radar team member at the U.S. Geological Survey in Flagstaff, Arizona.
“We think it may be something like the formation of the prehistoric lake called Lake Lahontan near Lake Tahoe in Nevada and California, where deformation of the crust created fissures that could be filled up with liquid.”
The flybys also confirmed that Ligeia Mare, one of the two largest seas on Titan, is primarily methane (something that seemingly contradicts early-in-the-year hypotheses that the lakes and seas were primarily ethane) in composition and is approximately 170m deep.
“Ligeia Mare turned out to be just the right depth for radar to detect a signal back from the sea floor, which is a signal we didn’t think we’d be able to get,” said Marco Mastrogiuseppe, a Cassini radar team associate at Sapienza University of Rome.
“The measurement we made shows Ligeia to be deeper in at least one place than the average depth of Lake Michigan.”
These unexpected measurements gave scientists the ability to estimate the total volume of liquids on Titan.
Based on observations so far, scientists believe there is approximately 2,000 cubic miles of liquid hydrocarbons on the surface of Titan, about 40 times more than all the proven oil reserves of the Earth.
Looking ahead for Cassini, as has been the case since 2010, the projected end of mission plan is for a controlled fall into Saturn’s atmosphere in 2017.
However, there are several other options NASA could pursue instead of crashing Cassini into Saturn.
For end of mission consideration, NASA could also choose to impact Cassini into one of the icy satellites of Saturn or into the ring system, specifically the planet’s main rings.
However, if funding was to become available, NASA could look at a series of other options that would both see the end of the Cassini mission or its continuation in an extended and altered form.
For end of mission consideration, NASA could boost Cassini’s orbit to one that is stable to prevent possible contamination on possible life bearing moons. Another option would be to swing Cassini out of Saturn orbit and place it into a heliocentric orbit prior to the cessation of spacecraft operations.
Additionally, NASA could look at extending Cassini’s mission and placing the spacecraft into an escape trajectory to one of the other gas or ice giants of the solar system or a Centaur asteroid of Saturn.
While escape to a gas giant, ice giant, or centaur asteroid is deemed as one of the lowest return possibilities for science, NASA has noted that it would take up to 12 years after Saturn departure for Cassini to reach Jupiter, 20 years to reach Uranus, and 40 years to reach Neptune.
By that point, given the spacecraft’s age, NASA has deemed science “unlikely.”
Nonetheless, as long as no catastrophic event occurs to the spacecraft, Cassini will continue returning scientific data on the Saturnian system until at least 2017.
Part III of NASASpaceflight.com’s Year In Review series will be published in the coming two days and focus on Martian and extra-solar exploration and discoveries.
*Click here for Part I*
(Images via NASA, JPL and L2).
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