The European Space Agency (ESA) and Roscomos (the Russian federal space agency) had high hopes for the Schiaparelli lander, which crashed on the surface of Mars on October 19th. As part of the ExoMars program, its purpose was to test the technologies that will be used to deploy a rover to the Red Planet in 2020.
However, investigators are making progress towards determining what went wrong during the lander’s descent. Based on their most recent findings, they concluded that an anomaly took place with an on-board instrument that led to the lander detaching from its parachute and backshell prematurely. This ultimately caused it to land hard and be destroyed.
According to investigators, the data retrieved from the lander indicates that for the most part, Schiaparelli was functioning normally before it crashed. This included the parachute deploying once it had reached an altitude of 12 km and achieved a speed of 1730 km/h. When it reached an altitude of 7.8 km, the lander’s heatshield was released, and it radar altimeter provided accurate data to the lander’s on-board guidance, navigation and control system.
All of this happened according to plan and did not contribute to the fatal crash. However, an anomaly then took place with the Inertial Measurement Unit (IMU), which is there to measure the rotation rates of the vehicle. Apparently, the IMU experienced saturation shortly after the parachute was deployed, causing it to persist for one second longer than required.
This error was then fed to the navigation system, which caused it to generate an estimate altitude that was below Mars’ actual ground level. In essence, the lander thought it was closer to the ground than it actually was. As such, the the parachute and backshell of the Entry and Descent Module (EDM) were jettisoned and the braking thrusters fired prematurely – at an altitude of 3.7 km instead of 1.2 km, as planned.
This briefest of errors caused the lander to free-fall for one second longer than it was supposed to, causing it to land hard and be destroyed. The investigators have confirmed this assessment using multiple computer simulations, all of which indicate that the IMU error was responsible. However, this is still a tentative conclusion that awaits final confirmation from the agency.
As David Parker, the ESA’s Director of Human Spaceflight and Robotic Exploration, said on on Wednesday, Nov. 23rd in a ESA press release:
“This is still a very preliminary conclusion of our technical investigations. The full picture will be provided in early 2017 by the future report of an external independent inquiry board, which is now being set up, as requested by ESA’s Director General, under the chairmanship of ESA’s Inspector General. But we will have learned much from Schiaparelli that will directly contribute to the second ExoMars mission being developed with our international partners for launch in 2020.”
In other words, this accident has not deterred the ESA and Roscosmos from pursuing the next stage in the ExoMars program – which is the deployment of the ExoMars rover in 2020. When it reaches Mars in 2021, the rover will be capable of navigating autonomously across the surface, using a on-board laboratory suite to search for signs of biological life, both past and present.
In the meantime, data retrieved from Schiaparelli’s other instruments is still being analyzed, as well as information from orbiters that observed the lander’s descent. It is hoped that this will shed further light on the accident, as well as salvage something from the mission. The Trace Gas Orbiter is also starting its first series of observations since it made its arrival in orbit on Oct. 19th, and will reach its operational orbit towards the end of 2017.
Instead of a controlled descent to the surface using its thrusters, ESA’s Schiaparelli lander hit the ground hard and may very well have exploded on impact. NASA’s Mars Reconnaissance Orbiter then-and-now photos of the landing site have identified new markings on the surface of the Red Planet that are believed connected to the ill-fated lander.
Schiaparelli entered the martian atmosphere at 10:42 a.m. EDT (14:42 GMT) on October 19 and began a 6-minute descent to the surface, but contact was lost shortly before expected touchdown seconds after the parachute and back cover were discarded. One day later, the Mars Reconnaissance Orbiter took photos of the expected touchdown site as part of a planned imaging run.
One of the features is bright and can be associated with the 39-foot-wide (12-meter) diameter parachute used in the second stage of Schiaparelli’s descent. The parachute and the associated back shield were released from Schiaparelli prior to the final phase, during which its nine thrusters should have slowed it to a standstill just above the surface.
The other new feature is a fuzzy dark patch or crater roughly 50 x 130 feet (15 x 40 meters) across and about 0.6 miles (1 km) north of the parachute. It’s believed to be the impact crater created by the Schiaparelli module following a much longer free fall than planned after the thrusters were switched off prematurely.
Mission control estimates that Schiaparelli dropped from between 1.2 and 2.5 miles (2 and 4 km) altitude, striking the Martian surface at more than 186 miles an hour (300 km/h). The dark spot is either disturbed surface material or it could also be due to the lander exploding on impact, since its thruster propellant tanks were likely still full. ESA cautions that these findings are still preliminary.
Since the module’s descent trajectory was observed from three different locations, the teams are confident that they will be able to reconstruct the chain of events with great accuracy. Exactly what happened to cause the thrusters to shut down prematurely isn’t yet known.
ESA’s Philae lander, the first spacecraft to successfully soft-land on the surface of a comet and former piggyback partner to Rosetta, has not been in communication since July of 2015 and, with 67P now six months past perihelion and heading deeper out into the Solar System, it’s not likely it will ever be heard from again.
Europa’s water exists in a layer around the planet, encased in a layer of ice. Could there be life down there?
Hooray! Welcome to the 200th official episode of the Guide To Space!
First off, thank you. Thank you for watching, liking, sharing, subscribing and being a patron of our show. Yes, you. Thank you.
So to celebrate, a few weeks ago we invited the members of the Weekly Space Hangout Crew Google+ Community to suggest topics for episodes, and the winner would receive a precious iron-nickel meteorite. Congratulations Andres Munoz, this meteorite is for you.
This episode, chosen by Andres, is for everyone.
The search for life in the Solar System is about the hunt for water. Wherever we find liquid water on Earth, we find life. I’m talking everywhere. In the most briny, salty pools in Antarctica, in the hottest hot springs in Yellowstone, under glaciers, and kilometers deep underground.
So we go searching for liquid water in the Solar System.
You might be surprised to learn that Jupiter’s moon Europa has the most water in the entire Solar System. If you took all the water on Earth, collected it into a big sphere, it would measure almost 1,400 kilometers across.
Europa’s water would measure nearly 1,800 kilometers.All that water exists in a layer around Europa, encased in a layer of ice. How thick? We don’t know.
Is there life down there? We don’t know.You can say there might be, and it wouldn’t be untrue. However, if you say there isn’t, that’s way less interesting for clickbait purposes. Whenever we don’t know the answers to fundamental and intriguing questions like that, it’s time to send a mission.
Good news! An actual mission to Europa is in the works right now. In 2015, NASA approved the development of an orbiter mission to Europa. If all goes well, and nothing gets cancelled…
And nothing will get cancelled, right? Right? I heard Firefly. Which one of you said Firefly?!?
According to the plan, a spacecraft will launch in the 2020s, carrying 9 instruments to Europa. Most will be familiar cameras, mass spectrometers, and the like, to study the surface of Europa to a high level of resolution. Over the course of 45 flybys, the spacecraft will get down as close as 25 kilometers and capture it with incredible resolution.
Perhaps the most exciting, and controversial instrument on board the new Europa Orbiter mission will be its ice-penetrating radar. Mission planners battled over installing a radar this sophisticated, as it will be an enormous drain on the orbiter’s power.
This for us is incredibly exciting. It will allow the spacecraft to map out the depth and thickness of Europa’s icy exterior. Is it thick or thin? Are there pockets of water trapped just below the surface, or is it tough shell that goes on for dozens of kilometers?
The worst case scenario is that the shell goes thicker than the radar can reach, and we won’t even know how far it goes.
Whatever happens, the Europa orbiter will be a boon to science, answer outstanding questions about the moon and the chances of finding life there.
We’re just getting started. What we really want to send is a lander. Because of the intense radiation from Jupiter, the Sun, and space itself, the surface of the ice on Europa would be sterilized. But dig down a few centimeters and you might find life that’s protected from the radiation.
A future Europa lander might be equipped with a heated drill attached to a tether. The lander would be have with a heat-generated radioisotope thermoelectric generator, like most of NASA’s big, outer Solar System spacecraft.
But in addition to using it for electricity, it’ll use the raw heat to help a tethered drill to grind through the ice a few meters and sample what’s down there.
Drilling more than a few meters is probably the stuff of science fiction. Russian scientists in Antarctica drilled for almost two decades to get through 4,000 meters of ice above Lake Vostok. Imagine trying to get through 100 kilometers of the stuff, on a distant world, with a robot.
But, since I’ve talked about moving the Sun, and terraforming the Moon, maybe I shouldn’t put any bounds on my imagination. Nuclear-powered Europa submarines will get us swimming with the singing Europan space whales in no time.
Europa is the best place to search the Solar System for life, and I’m excited to see what the upcoming Europa Orbiter mission turns up. And I’m even more excited about the possibility of any future lander missions.
It was a lot of fun wrapping my brain around a topic chosen by the fans. What topic would you like us to cover next? I’ve got a whole pocket of meteorites here. Put it in the comments below.
First, I want to thank everyone. It’s been a crazy race getting up to 200 episodes, but it’s been a blast all the way through. Thanks again for all your support and here’s to 200 more!
It’s only a bright dot in a landscape of crenulated rocks, but the Rosetta team thinks it might be Philae, the little comet lander lost since November.
The Rosetta and Philae teams have worked tirelessly to search for the lander, piecing together clues of its location after a series of unfortunate events during its planned landing on the surface of Comet 67P/Churyumov-Gerasimenko last November 12.
Philae first touched down at the Agilkia landing site that day, but the harpoons that were intended to anchor it to the surface failed to work, and the ice screws alone weren’t enough to do the job. The lander bounced after touchdown and sailed above the comet’s nucleus for two hours before finally settling down at a site called Abydos a kilometer from its intended landing site.
No one yet knows exactly where Philae is, but an all-out search has finally turned up a possible candidate.
Rosetta’s navigation and high-resolution cameras identified the first landing site and also took several pictures of Philae as it traveled above the comet before coming down for a final landing. Magnetic field measurements taken by an instrument on the lander itself also helped establish its location and orientation during flight and touchdown. The lander is thought to be in rough terrain perched up against a cliff and mostly in shadow.
High resolution images of the possible landing zone were taken by Rosetta back in December when it was about 11 miles (18 km) from the comet’s surface. At this distance, the OSIRIS narrow-angle camera has a resolution of 13.4 inches (34 cm) per pixel. The body of Philae is just 39 inches (1-meter) across, while its three thin legs extend out by up to 4.6 feet (1.4-meters) from its center. In other words, Philae’s just a few pixels across — a tiny target but within reach of the camera’s eye.
The candidates in the photo above are “all over the place.” To narrow down the location, the Rosetta team used radio signals sent between Philae and Rosetta as part of the COmet Nucleus Sounding Experimentor CONSERT after the final touchdown. According to Emily Baldwin’s recent posting on the Rosetta site:
“Combining data on the signal travel time between the two spacecraft with the known trajectory of Rosetta and the current best shape model for the comet, the CONSERT team have been able to establish the location of Philae to within an ellipse roughly 50 x 525 feet (16 x 160 meters) in size, just outside the rim of the Hatmehit depression.”
So what can we see there? Zooming in closer, a number of glints or bright spots appear, and they change depending on the viewing angle. But among those glints, one might be Philae. What mission scientists examined images of the area under the same lighting conditions before Philae landed and then put them side by side with those taken after November 12. That way any transient glints could be eliminated, leaving what’s left as a potential candidate.
In photos taken on December 12 and 13, a bright spot is seen that didn’t appear in the earlier photos. Might this be Philae? It’s possible and the best candidate yet. But it may also be a new physical feature that developed between November and December. Comet surfaces are forever changing as sunlight sublimates ice both on and beneath the surface
For now, we still can’t be sure if we’ve found Philae. Higher resolution pictures will be required as will patience. The comet’s too close to the Sun right now and too active. Rubble flying off the nucleus could damage Rosetta’s instruments. Mission scientists will have to wait until well after the comet’s August perihelion (closest approach to the Sun) for a closer look.
Meanwhile, mission teams remain hopeful that with increasing sunlight at the comet this summer, Philae’s solar panels will recharge its batteries and the three-legged lander will wake up and resume science studies. Three attempts have been made to contact Philae this spring and more will be made but so far, we’ve not heard a peep.
For the time being, Philae’s like that lost child in a shopping mall. The search party’s been dispatched, clues have been found and it’s only a matter of time before we see her smiling face again.
An uncontrolled, chaotic landing. Stuck in the shadow of a cliff without energy-giving sunlight. Philae and team persevered. With just 60 hours of battery power, the lander drilled, hammered and gathered science data on the surface of comet 67P/Churyumov-Gerasimenko before going into hibernation. Here’s what we know.
Despite appearances, the comet’s hard as ice. The team responsible for the MUPUS (Multi-Purpose Sensors for Surface and Sub-Surface Science) instrument hammered a probe as hard as they could into 67P’s skin but only dug in a few millimeters:
“Although the power of the hammer was gradually increased, we were not able to go deep into the surface,” said Tilman Spohn from the DLR Institute of Planetary Research, who leads the research team. “If we compare the data with laboratory measurements, we think that the probe encountered a hard surface with strength comparable to that of solid ice,” he added. This shouldn’t be surprising, since ice is the main constituent of comets, but much of 67P/C-G appears blanketed in dust, leading some to believe the surface was softer and fluffier than what Philae found.
This finding was confirmed by the SESAME experiment (Surface Electrical, Seismic and Acoustic Monitoring Experiment) where the strength of the dust-covered ice directly under the lander was “surprisingly high” according to Klaus Seidensticker from the DLR Institute. Two other SESAME instruments measured low vaporization activity and a great deal of water ice under the lander.
As far as taking the comet’s temperature, the MUPUS thermal mapper worked during the descent and on all three touchdowns. At the final site, MUPUS recorded a temperature of –243°F (–153°C) near the floor of the lander’s balcony before the instrument was deployed. The sensors cooled by a further 10°C over a period of about a half hour:
“We think this is either due to radiative transfer of heat to the cold nearby wall seen in the CIVA images or because the probe had been pushed into a cold dust pile,” says Jörg Knollenberg, instrument scientist for MUPUS at DLR. After looking at both the temperature and hammer probe data, the Philae team’s preliminary take is that the upper layers of the comet’s surface are covered in dust 4-8 inches (10-20 cm), overlaying firm ice or ice and dust mixtures.
The ROLIS camera (ROsetta Lander Imaging System) took detailed photos during the first descent to the Agilkia landing site. Later, when Philae made its final touchdown, ROLIS snapped images of the surface at close range. These photos, which have yet to be published, were taken from a different point of view than the set of panorama photos already received from the CIVA camera system.
During Philae’s active time, Rosetta used the CONSERT (COmet Nucleus Sounding Experiment by Radio wave Transmission) instrument to beam a radio signal to the lander while they were on opposite sides of the comet’s nucleus. Philae then transmitted a second signal through the comet back to Rosetta. This was to be repeated 7,500 times for each orbit of Rosetta to build up a 3D image of 67P/C-G’s interior, an otherworldly “CAT scan” as it were. These measurements were being made even as Philae lapsed into hibernation. Deeper down the ice becomes more porous as revealed by measurements made by the orbiter.
The last of the 10 instruments on board the Philae lander to be activated was the SD2 (Sampling, Drilling and Distribution subsystem), designed to provide soil samples for the COSAC and PTOLEMY instruments. Scientists are certain the drill was activated and that all the steps to move a sample to the appropriate oven for baking were performed, but the data right now show no actual delivery according to a tweet this morning from Eric Hand, reporter at Science Magazine. COSAC worked as planned however and was able to “sniff” the comet’s rarified atmosphere to detect the first organic molecules. Research is underway to determine if the compounds are simple ones like methanol and ammonia or more complex ones like the amino acids.
Stephan Ulamec, Philae Lander manager, is confident that we’ll resume contact with Philae next spring when the Sun’s angle in the comet’s sky will have shifted to better illuminate the lander’s solar panels. The team managed to rotate the lander during the night of November 14-15, so that the largest solar panel is now aligned towards the Sun. One advantage of the shady site is that Philae isn’t as likely to overheat as 67P approaches the Sun en route to perihelion next year. Still, temperatures on the surface have to warm up before the battery can be recharged, and that won’t happen until next summer.
Let’s hang in there. This phoenix may rise from the cold dust again.
We may not know exactly where Philae is, but it’s doing a bang-up job sending its first photos from comet 67P/Churyumov-Gerasimenko. After bouncing three times on the surface, the lander is tilted vertically with one foot in open space in a “handstand” position. When viewing the photographs, it’s good to keep that in mind.
Although it’s difficult to say how far away the features are in the image. In an update today at a press briefing, Jean Pierre Biebring, principal investigator of CIVA/ROLIS (lander cameras), said that the features shown in the frame at lower left are about 1-meter or 3 feet away. Philae settled into its final landing spot after a harrowing first bounce that sent it flying as high as a kilometer above the comet’s surface.
After hovering for two hours, it landed a second time only to bounce back up again a short distance – this time 3 cm or about 1.5 inches. Seven minutes later it made its third and final landing. Incredibly, the little craft still functions after trampolining for hours!
Despite its awkward stance, Philae continues to do a surprising amount of good science. Scientists are still hoping to come up with a solution to better orientate the lander. Their time is probably limited. The craft landed in the shadow of a cliff, blocking sunlight to the solar panels used to charge its battery. Philae receives only 1.5 hours instead of the planned 6-7 hours of sunlight each day. That makes tomorrow a critical day. Our own Tim Reyes of Universe Today had this to say about Philae’s power requirements:
“Philae must function on a small amount of stored energy upon arrival: 1000 watt-hours (equivalent of a 100 watt bulb running for 10 hours). Once that power is drained, it will produce a maximum of 8 watts of electricity from solar panels to be stored in a 130 watt-hour battery.” You can read more about Philae’s functions in Tim’s recent article.
Ever inventive, the lander team is going to try and nudge Philae into the sunlight by operating the moving instrument called MUPUS tonight. The operation is a delicate one, since too much movement could send the probe flying off the surface once again.
Here are additional photos from the press conference showing individual segments of the panorama and other aspects of Philae’s next-to-impossible landing. As you study the crags and boulders, consider how ancient this landscape is. 67P originated in the Kuiper Belt, a large reservoir of small icy bodies located just beyond Neptune, more than 4.5 billion years ago. Either through a collision with another comet or asteroid, or through gravitational interaction with other planets, it was ejected from the Belt and fell inward toward the Sun.
Astronomers have analyzed its orbit and discovered that up until 1840, the future comet 67P never came closer than 4 times Earth’s distance from the Sun, ensuring that its ices remained as pristine as the day they formed. After that date, the comet passed near Jupiter and its orbit changed to bring it within the inner Solar System. We’re seeing a relic, a piece of dirty ice rich with history. Even a Rosetta stone of its own we can use to interpret the molecular script revealing the origin and evolution of comets.
The first Canadian mission to Mars could be blasting off towards the Red Planet in just three years time. At least, that is what Thoth Technology, a Canadian aerospace company from Pembroke, Ontario, hopes to accomplish. And two days ago, they launched an Indiegogo campaign to raise the 1.1 million dollars needed to pay for all the hardware needed to make the mission happen.
If it is successful, it would be first Canadian mission to the surface of Mars.
The project for this Canadian mission would involve sending the Northern Light lander and Beaver rover in space and land them on Mars. Once there, the Beaver rover will be deployed and begin conducting surveys of the Martian surface, alongside the many other robotic rovers and orbiters studying the Martian landscape.
“I think it’s important to do big things,” said Ben Quine, principal investigator for the mission. “Mars is the only other habitable planet in the solar system, and if we want to survive, we need to be a multi-planet species.”
Quine is the technical director and chair of the board at Thoth Technology and a professor of space engineering at York University, which is a partner on the project, houses a lot of the space testing facilities, and will analyze the data from the mission.
The main goal of the mission is to expand upon the efforts being made by NASA’s Curiosity, Spirit, and Opportunity rovers, which have only explored a half dozen sites on Mars. By exploring more areas, they hope to find other signs of life on the harsh landscape, and using knowledge gleaned from studies in the Canadian Arctic no less.
According to Quine, in Antarctica and the Canadian Arctic, photosynthetic microbes can be found in a layer a millimeter or two below the surface of the rock. Here, they are protected from the harshest of the sun’s UV rays, but can still use sunlight to produce energy.
Northern Light will look for similar life on Mars by using the lander’s robotic arm to grind away the surface of rocks. It will then use a device called a photometer to scan for different shades of green that may indicate the presence of photosynthetic organisms. Quine and his colleagues also hope to determine what future technologies will be required to sustain a future human presence.
“If we are serious about living on Mars,” he said, “we need to explore it much more thoroughly. We probably need hundreds of landers to pepper the surface prior to sending people so we know exactly what it is that we’re up against, where we’d find things like minerals and where we’d want to live.”
Intrinsic to the company’s plan is the widespread exploration of Mars using low cost, off-the-shelf technology. For example, the Northern Light lander probe has a mass under 50 kg (including payload) and is made of an advanced composite material that includes thermal shielding and shock absorption. The probe includes solar arrays to generate power for the instrumentation and lander avionics.
As for the Beaver rover, its small size and low-cost mask the fact that it is like no other rover that has ever gone to Mars. For one thing, it weighs just six kilograms (13 pounds). In comparison, NASA’s Curiosity rover weighs in at a hefty 900 kilograms (1980 pounds, close to an imperial ton), forcing it to rely largely on nuclear power to lug its bulk around.
The NASA rovers, which are controlled from Earth, also move very slowly and cover only a few dozen meters per day because their commands take 15 minutes to reach Mars from Earth. By contrast, the Beaver rover is designed to be quicker, in part by being more independent.
“We’re going to embed intelligence into the rover,” Quine said, “and the rover is going to be tasked to drive around and explore the environment using autonomous algorithms built into the rover to determine things like when it should make a maneuver to avoid falling into a hole or run into a rock.”
Quine said he has already spent 12 years working on the project and his team has spent half a million dollars developing and testing prototypes of the lander and micro-rover. They’ve also performed space tests on some of the instruments by flying them on satellites in low-Earth orbit.
Thoth Technologies also recently spent $1 million leasing and repairing the Algonquin Radio Observatory from the federal government, which they plan to use as a ground station to communicate with the lander and rover when they are on Mars.
As for the tricky task of getting to Mars, Quine and his colleagues hope to barter their way aboard one of the many missions heading to Mars in 2018. These include the joint Russian-European Space Agency ExoMars rover mission and an Indian Space Research Organization mission that will likely include a lander and rover.
In exchange for hitching a ride on one of these rockets, they will collect and relay other agencies’ data from Mars via the ARO ground station, which can collect them at times of day when places like Russia and India are facing away from Mars.
Those who are interested in supporting their campaign are being incentivized with a chance to help choose the landing site for the mission, and will get rewards ranging from a Frisbee for $20 or the chance to name the lander for $1 million.
The company has also launched a social campaign – featuring Ed Robertson of the “Barenaked Ladies” – urging people to create and upload their own “Mars dance” video to marsrocks.ca.
To find out more, check out their promotional video or click on the link below:
ESA Rosetta mission planners have selected November 12th, one day later than initially planned, for the historic landing of Philae on a comet’s surface. The landing on 67P/Churyumov-Gerasimenko will be especially challenging for the washing machine-sized lander. While mission scientists consider their choice of comet for the mission to be an incredibly good one for scientific investigation and discovery, the irregular shape and rugged terrain also make for a risky landing. The whole landing is not unlike the challenge one faces in shooting a moving target in a carnival arcade game; however, this moving target is 20 kilometers below and it is also rotating.
At 8:35 GMT (3:35 AM EST), the landing sequence will begin with release of Philae by Rosetta at an altitude of 20 kilometers above the comet. The expected time of touchdown is seven hours later – 15:35 GMT (10:35 AM EST). During the descent, Philae’s ROLIS camera will take a continuous series of photos. The comet will complete more than half a rotation during the descent; comet P67’s rotation rate is 12.4 hours. The landing site will actually be on the opposite side of the comet when Philae is released and will rotate around, and if all goes as planned, meet Philae at landing site J.
Before November 12th, mission planners will maintain the option of landing at Site C. If the alternate site is chosen, the descent will begin at 13:04 GMT also on November 12 but from an altitude of 12.5 kilometers, a 4 hour descent time.
Rosetta will eject Philae with an initial velocity of approximately 2 1/2 kilometers per hour. Because the comet is so small, its gravity will add little additional speed to Philae as it falls to the surface. Philae is essentially on a ballistic trajectory and does not have any means to adjust its path.
The actions taken by Philae’s onboard computer begin only seconds from touchdown. It has a landing propulsion system but unlike conventional systems that slow down the vehicle for soft landing, Philae’s is designed to push the lander snugly onto the comet surface. There is no guarantee that Philae will land on a flat horizontal surface. A slope is probably more likely and the rocket will force the small lander’s three legs onto the slope.
Landing harpoons will be fired that are attached to cables that will be pulled in to also help Philae return upright and attach to the surface. Philae could actually bounce up or topple over if the rocket system and harpoons fail to do their job.
However, under each of the three foot pads, there are ice screws that will attempt to drill and secure Philae to the surface. This will depend on the harpoons and/or rockets functioning as planned, otherwise the action of the drills could experience resistance from hard ground and simply push the lander up rather than secure it down. Philae also has a on-board gyro to maintain its attitude during descent, and an impact dampener on the neck of the vehicle which attaches the main body to the landing struts.
Ten landing sites were picked, then down-selected to five, and then finally on September 15th, they selected Site J on the head of the smaller lobe – the head of the rubber duck, with site C as a backup. Uncertainty in the release and the trajectory of the descent to the comet’s surface means that the planners needed to find a square kilometer area for landing. But comet 67P/Churyumov-Gerasimenko simply offered no site with that much flat area clear of cliffs and boulders. Philae will be released to land at Site J which offers some smooth terrain but only about a quarter of the area needed to assure a safe landing. Philae could end up landing on the edge of a cliff or atop a large boulder and topple over.
The Rosetta ground control team will have no means of controlling and adjusting Philae during the descent. This is how it had to be because the light travel time for telecommunications from the spacecraft to Earth does not permit real-time control. The execution time and the command sequence will be delivered to Rosetta days before the November 12th landing. And ground control must maneuver Rosetta with Philae still attached to an exact point in space where the release of Philae must take place. Any inaccuracy in the initial release point will be translated all the way down to the surface and Philae would land some undesired distance away from Site J. However, ground controllers have a month and a half to practice simulations of the landing many times over with a model of the comet’s nucleus. With practice and more observational data between now and the landing, the initial conditions and model of the comet in the computer simulation will improve and raise the likelihood of a close landing to Site J.
Previous Universe Today articles on Rosetta’s Philae:
When traveling to far off lands, one packs carefully. What you carry must be comprehensive but not so much that it is a burden. And once you arrive, you must be prepared to do something extraordinary to make the long journey worthwhile.
The previous Universe Today article “How do you land on a Comet?” described Philae’s landing technique on comet 67P/Churyumov-Gerasimenko. But what will the lander do once it arrives and gets settled in its new surroundings? As Henry David Thoreau said, “It is not worthwhile to go around the world to count the cats in Zanzibar.” So it is with the Rosetta lander Philae. With the stage set – a landing site chosen and landing date of November 11th, the Philae lander is equipped with a carefully thought-out set of scientific instruments. Comprehensive and compact, Philae is a like a Swiss Army knife of tools to undertake the first on-site (in-situ) examination of a comet.
Now, consider the scientific instruments on Philae which were selected about 15 years ago. Just like any good traveler, budgets had to be set which functioned as constraints on the instrument selection that could be packed and carried along on the journey. There was a maximum weight, maximum volume, and power. The final mass of Philae is 100 kg (220 lbs). Its volume is 1 × 1 × 0.8 meters (3.3 × 3.3 × 2.6 ft) about the size of a four burner oven-range. However, Philae must function on a small amount of stored energy upon arrival: 1000 Watt-Hours (equivalent of a 100 watt bulb running for 10 hours). Once that power is drained, it will produce a maximum of 8 watts of electricity from Solar panels to be stored in a 130 Watt-Hour battery.
Without any assurance that they would land fortuitously and produce more power, the Philae designers provided a high capacity battery that is charged, one time only, by the primary spacecraft solar arrays (64 sq meters) before the descent to the comet. With an initial science command sequence on-board Philae and the battery power stored from Rosetta, Philae will not waste any time to begin analysis — not unlike a forensic analysis — to do a “dissection” of a comet. Thereafter, they utilize the smaller battery which will take at least 16 hours to recharge but will permit Philae to study 67P/Churyumov-Gerasimenko for potentially months.
There are 10 science instrument packages on the Philae lander. The instruments use absorbed, scattered, and emitted light, electrical conductivity, magnetism, heat, and even acoustics to assay the properties of the comet. Those properties include the surface structure (the morphology and chemical makeup of surface material), interior structure of P67, and the magnetic field and plasmas (ionized gases) above the surface. Additionally, Philae has an arm for one instrument and the Philae main body can be rotated 360 degrees around its Z-axis. The post which supports Philae and includes a impact dampener.
CIVA and ROLIS imaging systems. CIVA represents three cameras which share some hardware with ROLIS. CIVA-P (Panoramic) is seven identical cameras, distributed around the Philae body but with two functioning in tandem for stereo imaging. Each has a 60 degree field of view and uses as 1024×1024 CCD detector. As most people can recall, digital cameras have advanced quickly in the last 15 years. Philae’s imagers were designed in the late 1990s, near state-of-the-art, but today they are surpassed, at least in number of pixels, by most smartphones. However, besides hardware, image processing in software has advanced as well and the images may be enhanced to double their resolution.
CIVA-P will have the immediate task, as part of the initial autonomous command sequence, of surveying the complete landing site. It is critical to the deployment of other instruments. It will also utilize the Z-axis rotation of the Philae body to survey. CIVA-M/V is a microscopic 3-color imager (7 micron resolution) and CIVA-M/I is a near infra-red spectrometer (wavelength range of 1 to 4 microns) that will inspect each of the samples that is delivered to the COSAC & PTOLEMY ovens before the samples are heated.
ROLIS is a single camera, also with a 1024×1024 CCD detector, with the primary role of surveying the landing site during the descent phase. The camera is fixed and downward pointing with an f/5 (f-ratio) focus adjustable lens with a 57 degree field of view. During descent it is set to infinity and will take images every 5 seconds. Its electronics will compress the data to minimize the total data that must be stored and transmitted to Rosetta. Focus will adjust just prior to touchdown but thereafter, the camera functions in macro mode to spectroscopically survey the comet immediately underneath Philae. Rotation of the Philae body will create a “working circle” for ROLIS.
The multi-role design of ROLIS clearly shows how scientists and engineers worked together to overall reduce weight, volume, and power consumption, and make Philae possible and, together with Rosetta, fit within payload limits of the launch vehicle, power limitations of the solar cells and batteries, limitations of the command and data system and radio transmitters.
APXS. This is a Alpha Proton X-ray Spectrometer. This is a near must-have instrument of the space scientist’s Swiss Army Knife. APXS spectrometers have become a common fixture on all Mars Rover missions and Philae’s is an upgraded version of Mars Pathfinder’s. The legacy of the APXS design is the early experiments by Ernest Rutherford and others that led to discovering the structure of the atom and the quantum nature of light and matter.
This instrument has a small source of Alpha particle emission (Curium 244) essential to its operation. The principles of Rutherford Back-scattering of Alpha particles is used to detect the presence of lighter elements such as Hydrogen or Beryllium (those close to an Alpha particle in mass, a Helium nucleus). The mass of such lighter elemental particles will absorb a measurable amount of energy from the Alpha particle during an elastic collision; as happens in Rutherford back-scattering near 180 degrees. However, some Alpha particles are absorbed rather than reflected by the nuclei of the material. Absorption of an Alpha particle causes emission of a proton with a measurable kinetic energy that is also unique to the elemental particle from which it came (in the cometary material); this is used to detect heavier elements such as magnesium or sulfur. Lastly, inner shell electrons in the material of interest can be expelled by Alpha particles. When electrons from outer shells replace these lost electrons, they emit an X-Ray of specific energy (quantum) that is unique to that elementary particle; thus, heavier elements such as Iron or Nickel are detectable. APXS is the embodiment of early 20th Century Particles Physics.
CONSERT.COmet Nucleus Sounding Experiment by Radio wave Transmission, as the name suggests, will transmit radio waves into the comet’s nucleus. The Rosetta orbiter transmits 90 MHz radio waves and simultaneously Philae stands on the surface to receive with the comet residing between them. Consequently, the time of travel through the comet and the remaining energy of the radio waves is a signature of the material through which it propagated. Many radio transmissions and receptions by CONSERT through a multitude of angles will be required to determine the interior structure of the comet. It is similar to how one might sense the shape of a shadowy object standing in front of you by panning one’s head left and right to watch how the silhouette changes; altogether your brain perceives the shape of the object. With CONSERT data, a complex deconvolution process using computers is necessary. The precision to which the comet’s interior is known improves with more measurements.
MUPUS.Multi-Purpose Sensor for Surface and Subsurface Science is a suite of detectors for measuring the energy balance, thermal and mechanical properties of the comet’s surface and subsurface down to a depth of 30 cm (1 foot). There are three major parts to MUPUS. There is the PEN which is the penetrator tube. PEN is attached to a hammering arm that extends up to 1.2 meters from the body. It deploys with sufficient downward force to penetrate and bury PEN below the surface; multiple hammer strokes are possible. At the tip, or anchor, of PEN (the penetrator tube) is an accelerometer and standard PT100 (Platinum Resistance Thermometer). Together, the anchor sensors will determine the hardness profile at the landing site and the thermal diffusivity at the final depth [ref]. As it penetrates the surfaces, more or less deceleration indicates harder or softer material. The PEN includes an array of 16 thermal detectors along its length to measure subsurface temperatures and thermal conductivity. The PEN also has a heat source to transmit heat to the cometary material and measure its thermal dynamics. With the heat source off, detectors in PEN will monitor the temperature and energy balance of the comet as it approaches the Sun and heats up. The second part is the MUPUS TM, a radiometer atop the PEN which will measure thermal dynamics of the surface. TM consists of four thermopile sensors with optical filters to cover a wavelength range from 6-25 µm.
SD2 Sample Drill and Distribution device will penetrate the surface and subsurface to a depth of 20 cm. Each retrieved sample will be a few cubic millimeters in volume and distributed to 26 ovens mounted on a carousel. The ovens heat the sample which creates a gas that is delivered to the gas chromatographs and mass spectrometers that are COSAC and PTOLEMY. Observations and analysis of APXS and ROLIS data will be used to determine the sampling locations all of which will be on a “working circle” from the rotation of Philae’s body about its Z-axis.
COSACCometary Sampling and Composition experiment. The first gas chromatograph (GC) I saw was in a college lab and was being used by the lab manager for forensic tests supporting the local police department. The intent of Philae is nothing less than to perform forensic tests on a comet hundred of million of miles from Earth. Philae is effectively Sherlock Holmes’ spy glass and Sherlock is all the researchers back on Earth. The COSAC gas chromatograph includes a mass spectrometer and will measure the quantities of elements and molecules, particularly complex organic molecules, making up comet material. While that first lab GC I saw was closer to the size of Philae, the two GCs in Philae are about the size of shoe boxes.
PTOLEMY. An Evolved Gas Analyzer [ref], a different type of gas chromatograph. The purpose of Ptolemy is to measure the quantities of specific isotopes to derive the isotopic ratios, for example, 2 parts isotope C12 to one part C13. By definition, isotopes of an element have the same number of protons but different numbers of neutrons in their nuclei. One example is the 3 isotopes of Carbon, C12, C13 and C14; the numbers being the number of neutrons. Some isotopes are stable while others can be unstable – radioactive and decay into stable forms of the same element or into other elements. What is of interest to Ptolemy investigators is the ratio of stable isotopes (natural and not those affected by, or that result from, radioactive decay) for the elements H, C, N, O and S, but particularly Carbon. The ratios will be telltale indicators of where and how comets are created. Until now, spectroscopic measurements of comets to determine isotopic ratios have been from a distance and the accuracy has been inadequate for drawing firm conclusions about the origin of comets and how comets are linked to the creation of planets and the evolution of the Solar Nebula, the birthplace of our planetary system surrounding the Sun, our star. An evolved gas analyzer will heat up a sample (~1000 C) to transform the materials into a gaseous state which a spectrometer can very accurately measure quantities. A similar instrument, TEGA (Thermal Evolved Gas Analyzer) was an instrument on Mars Phoenix lander.
SESAMESurface Electrical Sounding and Acoustic Monitoring Experiment This instrument involves three unique detectors. The first is the SESAME/CASSE, the acoustic detector. Each landing foot of Philae has acoustic emitters and receivers. Each of the legs will take turns transmitting acoustic waves (100 Hertz to KiloHertz range) into the comet which the sensors of the other legs will measure. How that wave is attenuated, that is, weakened and transformed, by the cometary material it passes through, can be used along with other cometary properties gained from Philae instruments, to determine daily and seasonal variations in the comet’s structure to a depth of about 2 meters. Also, in a passive (listening) mode, CASSE will monitor sound waves from creaks, groans inside the comet caused potentially by stresses from Solar heating and venting gases.
Next is the SESAME/PP detector – the Permittivity Probe. Permittivity is the measure of the resistance a material has to electric fields. SESAME/PP will deliver an oscillating (sine wave) electric field into the comet. Philae’s feet carry the receivers – electrodes and AC sine generators to emit the electric field. The resistance of the cometary material to about a 2 meter depth is thus measured providing another essential property of the comet – the permittivity.
The third detector is called SESAME/DIM. This is the comet dust counter. There were several references used to compile these instrument descriptions. For this instrument, there is, what I would call, a beautiful description which I will simply quote here with reference. “The Dust Impact Monitor (DIM) cube on top of the Lander balcony is a dust sensor with three active orthogonal (50 × 16) mm piezo sensors. From the measurement of the transient peak voltage and half contact duration, velocities and radii of impacting dust particles can be calculated. Particles with radii from about 0.5 µm to 3 mm and velocities from 0.025–0.25 m/s can be measured. If the background noise is very high, or the rate and/or the amplitudes of the burst signal are too high, the system automatically switches to the so called Average Continuous mode; i.e., only the average signal will be obtained, giving a measure of the dust flux.” [ref]
ROMAPRosetta Lander Magnetometer and Plasma detector also includes a third detector, a pressure sensor. Several spacecraft have flown by comets and an intrinsic magnetic field, one created by the comet’s nucleus (the main body) has never been detected. If an intrinsic magnetic field exists, it is likely to be very weak and landing on the surface would be necessary. Finding one would be extraordinary and would turn theories regarding comets on their heads. Low and behold Philae has a fluxgate magnetometer.
The Earth’s magnetic (B) field surrounding us is measured in the 10s of thousands of nano-Teslas (SI unit, billionth of a Tesla). Beyond Earth’s field, the planets, asteroids, and comets are all immersed in the Sun’s magnetic field which, near the Earth, is measured in single digits, 5 to 10 nano-Tesla. Philae’s detector has a range of +/- 2000 nanoTesla; a just in case range but one readily offered by fluxgates. It has a sensitivity of 1/100th of a nanoTesla. So, ESA and Rosetta came prepared. The magnetometer can detect a very minute field if it’s there. Now let’s consider the Plasma detector.
Much of the dynamics of the Universe involves the interaction of plasma – ionized gases (generally missing one or more electrons thus carrying a positive electric charge) with magnetic fields. Comets also involve such interactions and Philae carries a plasma detector to measure the energy, density and direction of electrons and of positively charged ions. Active comets are releasing essentially a neutral gas into space plus small solid (dust) particles. The Sun’s ultraviolet radiation partially ionizes the cometary gas of the comet’s tail, that is, creates a plasma. At some distance from the comet nucleus depending on how hot and dense that plasma is, there is a standoff between the Sun’s magnetic field and the plasma of the tail. The Sun’s B field drapes around the comet’s tail kind of like a white sheet draped over a Halloween trick-or-treater but without eye holes.
So at P67’s surface, Philae’s ROMAP/SPM detector, electrostatic analyzers and a Faraday Cup sensor will measure free electrons and ions in the not so empty space. A “cold” plasma surrounds the comet; SPM will detect ion kinetic energy in the range of 40 to 8000 electron-volts (eV) and electrons from 0.35 eV to 4200 eV. Last but not least, ROMAP includes a pressure sensor which can measure very low pressure – a millionth or a billionth or less than the air pressure we enjoy on Earth. A Penning Vacuum gauge is utilized which ionizes the primarily neutral gas near the surface and measures the current that is generated.
Philae will carry 10 instrument suites to the surface of 67P/Churyumov-Gerasimenko but altogether the ten represent 15 different types of detectors. Some are interdependent, that is, in order to derive certain properties, one needs multiple data sets. Landing Philae on the comet surface will provide the means to measure many properties of a comet for the fist time and others with significantly higher accuracy. Altogether, scientists will come closer to understanding the origins of comets and their contribution to the evolution of the Solar System.