Delta II Heavy rocket will blast GRAIL missions to the moon from Launch Pad 17B. Delta II rocket and twin GRAIL satellites are enclosed inside the Mobile Service Tower at Cape Canaveral Air Force Station. Credit: Ken Kremer
[/caption]
Another American rocket Era is about to end. The venerable Delta II rocket, steeped in history, will fly what is almost certainly its final mission from Cape Canaveral. And it will do so quite fittingly by blasting twin satellites to the moon for NASA on a unique path for a truly challenging mission to do “extraordinary science”.
On Sept. 8, the most powerful version of the Delta II, dubbed the Delta II Heavy, is slated to launch NASA’s duo of GRAIL lunar mappers on an unprecedented science mission to unlock the mysteries of the moons deep interior. There are two instantaneous launch windows at 8:37:06 a.m. and 9:16:12 a.m. EDT lasting one second each.
“GRAIL simply put, is a journey to the center of the moon,” said Ed Weiler, NASA Associate Administrator of the Science Mission Directorate in Washington,DC at a pre-launch briefing for reporters on Sept. 6.
“It will probe the interior of the moon and map its gravity field by 100 to 1000 times better than ever before. We will learn more about the interior of the moon with GRAIL than all previous lunar missions combined.”
View of Delta II rocket looking out to Atlantic Ocean from upper level of Launch Complex 17. ULA and GRAIL logos painted on side of 8 ft diameter Delta rocket. Credit: Ken Kremer
GRAIL will depart Earth from Space Launch Complex 17B (SLC-17B) at Cape Canaveral Air Force Station, Florida, which is also the last scheduled use of Pad 17B.
GRAIL logo painted on the side of Delta II Rocket 1st Stage. Photo taken from inside upper level of launch gantry. GRAIL stands for Gravity Recovery and Interior Laboratory. Credit: Ken Kremer
“Trying to understand how the moon formed, and how it evolved over its history, is one of the things we’re trying to address with the GRAIL mission,” says Maria Zuber, principal investigator for GRAIL from the Massachusetts Institute of Technology. “But also, (we’re) trying to understand how the moon is an example of how terrestrial planets in general have formed.”
“GRAIL is a mission that will study the inside of the moon from crust to core,” Zuber says.
Delta II Heavy rocket is augmented by 9 wider diameter solid rocket motors providing more thrust. Credit: Ken Kremer
So far there have been 355 launches of the Delta II family, according to NASA’s Delta II Launch Manager Tim Dunn. The Delta II is built by United Launch Alliance.
“GRAIL is the last contracted Delta II mission to be launched from Complex 17. And it will be the 356th overall Delta to be launched. Complex 17 at the Cape has a proud heritage of hosting 258 of those 355 total Delta launches to date.
Hypergolic propellants have been loaded onto the 2nd stage after assessing all the preparations for the rocket, spacecraft, the range and facilities required for launch.
“The Launch Readiness Review was successfully completed and we can proceed with the countdown,” said Dunn.
The Delta II Heavy is augmented with nine larger diameter ATK solid rocket motors.
The Mobile Service Tower will be rolled back from the Delta II rocket tonight, starting at about 10:30 p.m. EDT depending on the weather.
The weather forecast for launch remains very iffy at a 60% percent chance of “NO GO” according to NASA and Air Force officials.
A launch decision will be made tomorrow morning Sept. 8 right after the weather briefing but before fueling begins at 6:30 a.m.
The weather forecast for rollback of the Mobile Service Tower tonight remains generally favorable. There is a 40% chance of a weather issue at 10:30 p.m. which drops to 30% after midnight. Tower rollback can be pushed back about 2 hours without impacting the countdown, says NASA.
Weather remains at 60% NO GO in case of a 24 hour delay but improves over the weekend. The team has about 42 days time in the launch window.
After entering lunar orbit, the two GRAIL spacecraft will fly in a tandem formation just 55 kilometers above the lunar surface with an average separation of 200 km during the three month science phase.
Stay tuned to Universe Today for updates overnight leading to liftoff at 8:37 a.m.
See my photo album from a recent tour of Launch Complex 17 and the Mobile Service Tower
GRAIL Flying in Formation. Using a precision formation-flying technique, the twin GRAIL spacecraft will map the moon's gravity field. The mission also will answer longstanding questions about Earth's moon, including the size of a possible inner core, and it should provide scientists with a better understanding of how Earth and other rocky planets in the solar system formed. GRAIL is a part of NASA's Discovery Program.
Low periapsis Narrow Angle Camera image of the Apollo 17 Landing Site. Image is 150 meters wide, Credit: NASA/GSFC/Arizona State University.
[/caption]
New images of the Apollo 12, 14 and 17 landing sites are the highest resolution pictures ever of human forays onto another world, as seen from a bird’s eye view — or in this case, a satellite’s eye view. The Lunar Reconnaissance Orbiter dipped to a lower altitude, just 21 kilometers (13 miles) over the lunar surface.
“We like to look at the Apollo landing site images because it’s fun,” said LRO principal investigator Mark Robinson at a media briefing today. “But LROC (Lunar Reconnaissance Orbiter Camera) is looking at the whole Moon, and we have now taken 1,500 of these very high resolution images from all around the Moon which will help scientists and engineers to plan where we want to go in the future.”
Apollo 17 landing site taken by LRO in its lower orbit, with 25 cm per pixel. Credit: NASA/Goddard/ASU
Apollo 17 landing site from the regular 50 km altitude and about 50 cm per pixel. Credit: NASA/ Goddard/ ASU Compare in the images above the Apollo 17 landing site with 25 cm per pixel (top) and 50 cm per pixel (bottom).
Most notable are the tracks where the astronauts walked show up better, and details of the landers/descent stages can be resolved better.
Robinson said he was looking at the new images of the Apollo 17 landing site in Taurus Littrow Valley with Apollo 17 astronaut Jack Schmitt and Schmitt said “You need to image the whole valley at this resolution!”
This is the third resolution of Apollo sites that the LRO team has released — the first came from LRO’s commissioning phase where the altitude was about 100 km and the resolution was about 1 meter per pixel; next came the release of images from an altitude of about 50 km, with a resolution of about 50 cm per pixel; and now from about 21-22 km altitude with a resolution of 25 cm per pixel.
“These are the sharpest images of Apollo landing sites we’ll probably ever get with LRO,” said Rich Vondrak, LRO project scientist, “as we’ll never go as low in altitude as we were in the past month.”
LRO has now returned to its circular orbit of 50 km above the surface. This altitude requires monthly reboosts and since keeping LRO in that orbit would quickly exhaust the remaining fuel, in mid-December, LRO will move to an elliptical orbit, (30 km over south pole and 200 km over north pole). LRO will be able to stay in this orbit for several more years.
“This has been a highly productive mission, releasing a total of 245 terabytes of data — which would be a stack of 52,000 DVDs,” Vondrak said. Next week the science team will put out their 7th public release of data to the Planetary Data System, making all that data available to the public.
The paths left by astronauts Alan Shepard and Edgar Mitchell on both Apollo 14 moon walks are visible in this image. (At the end of the second moon walk, Shepard famously hit two golf balls.) The descent stage of the lunar module Antares is also visible. Credit: NASA's Goddard Space Flight Center/ASU
Robinson noted that the details of what pieces of equipment are in each location are verified by images taken from the surface by the astronauts. He was asked about the flags and if they are still standing: “All we can really see is the spots where the flag was planted because the astronauts tramped down the regolith. I’m not sure if the flags still exist, given the extreme heat and cold cycle and the harsh UV environment. The flags were made of nylon, and personally I would be surprised if anything was left of them since it has been over 40 years since they were left on the Moon and the flags we have here on Earth fade after they are left outside for one summer. If the flags are still there they are probably in pretty rough shape.”
The tracks made in 1969 by astronauts Pete Conrad and Alan Bean, the third and fourth humans to walk on the moon, can be seen in this LRO image of the Apollo 12 site. The location of the descent stage for Apollo 12's lunar module, Intrepid, also can be seen. Credit: NASA/Goddard/ASU
Since we can still see the tracks and equipment looking unchanged (at least from this vantage point) one reporter asked if these items will be on the Moon forever. “Forever is a long time, so no, they won’t be there forever,” Robinson replied. “The Moon is constantly bombarded by micrometeorites, and slowly over time the tracks will disappear, then the smaller pieces of equipment will disappear, and eventually the decent stages will probably get blasted by an a larger asteroid. The estimate is that rocks erode 1 mm per million years. In human terms it may seems like forever, but geologic terms, there will be no traces of Apollo exploration in 10 to 100 million years.”
This video shows more info and a “zoom in” of the sites:
Jane Houston Jones from JPL provides information on what’s up for September, focusing on the Moon. The next few days will be a good time to look for the Apollo landing sites — and no, you won’t be able to see any details from Earth, even with a good telescope, but it is fun to try and locate the areas humans have walked on the Moon. Jane shows you how. And of course, the GRAIL mission to the Moon is scheduled to launch on Sept. 8. Learn more about the mission here.
And as a heads up, look for new images of the Apollo landing sites from the Lunar Reconnaissance Orbiter that will be released next week. LRO recently moved closer to the Moon to take new and improved images of these historic sites. We’ll share them as soon as they are available.
Twin GRAIL Lunar Mappers being enclosed with payload fairing atop Delta II rocket. Spacecraft technicians monitor the movement of a section of the clamshell-shaped Delta payload fairing as it encloses NASA's twin Gravity Recovery and Interior Laboratory spacecraft at Space Launch Complex 17B on Cape Canaveral Air Force Station in Florida. Liftoff is slated for Sept. 8 at 8:37 a.m. EDT. Credit: NASA/Jim Grossmann
[/caption]
NASA’s powerful lunar mapping duo of GRAIL spacecraft are now poised for liftoff in just one weeks time on Thursday, Sept. 8.
Mission managers held a Flight Readiness Review on Wednesday (Aug.31) and gave a tentative approval to begin fueling the Delta II rockets second stage on Sept. 2 and 3 after evaluating all issues related to the rocket, launch pad and payloads.
Launch preparations are proceeding on schedule towards an early morning lift off from the seaside Space Launch Complex 17B (SLC-17B) at Cape Canaveral Air Force Station, Florida. There are two instantaneous launch windows at 8:37:06 a.m. and 9:16:12 a.m. EDT lasting one second each.
“Launch vehicle and spacecraft closeouts will begin on Tuesday, and the Launch Readiness Review is also scheduled for Tuesday morning,” NASA KSC spokesman George Diller told Universe Today.
“This morning’s launch countdown dress rehearsal went fine.”
“Delta II 2nd stage fueling has been rescheduled for Friday and Saturday [Sept. 2 and 3]. Last evening a software error was found in the launch processing system data base. ULA (United Launch Alliance) decided they would like to look for any additional errors before the fueling begins. There is no impact to the launch date and currently no work is scheduled on Sunday or on Labor Day,” said Diller.
The launch period extends through Oct. 19, with liftoff occurring approximately four minutes earlier each day in case of a delay. The flight plan was designed to avoid a pair of lunar eclipses occurring on December 10th, 2011 and June 4th 2012 which would interfere with the missions operations and science.
The team is keeping a close watch on the weather as the season’s next Atlantic Ocean storm heads westwards. Katia has just been upgraded to Hurricane status and follows closely on the heels of the continuing vast destruction, misery and deaths caused by Hurricane Irene earlier this week.
“The preliminary weather forecast is favorable for launch day as long as the wind remains out of the west as is currently forecast for that time of the morning,” Diller told me.
Twin GRAIL Lunar Mappers are secured atop Delta II rocket and await enclose in the Delta payload fairing. The fairing will protect the spacecraft from the impact of aerodynamic pressure and heating during ascent and will be jettisoned once the spacecraft is outside the Earth's atmosphere. Credit: NASA/Jim Grossmann
The twin probes known as GRAIL-A and GRAIL-B (Gravity Recovery and Interior Laboratory) were encapsulated inside the clamshell like payload fairing on Aug. 23 The nearly identical spacecraft are mounted side by side and sit atop the Centaur upper stage.
The fairing shields the spacecraft from aerodynamic pressures, friction and extreme heating for the first few minutes of flight during ascent through the Earth atmosphere.
This Delta II Heavy booster rocket is the most powerful version of the Delta II family built by ULA. The booster’s first stage is augmented with larger diameter solid rocket motors.
GRAIL was processed for launch inside at the Astrotech payload processing facility in Titusville, Fla. See my GRAIL spacecraft photos from inside the Astrotech clean room facilities here.
“The GRAIL spacecraft inside the handling can departed Astrotech and arrived at the launch pad, SLC-17B on Aug. 18” said Tim Dunn, NASA’s Delta II Launch Director in an interview with Universe Today. “The spacecraft was then hoisted by crane onto the Delta II launch vehicle and the spacecraft mate operation was flawlessly executed by the combined ULA and NASA Delta II Team.”
An Integrated Systems Test (IST) of the mated booster and payload was completed on Aug. 22
Technicians prepare twin GRAIL spacecraft for enclosure in the Delta payload fairing. Credit: NASA/Jim Grossmann
The dynamic duo will orbit the moon in a tandam formation just 50 kilometers above the lunar surface with an average separation of 200 km. During the 90 day science phase the goal is to determine the structure of the lunar interior from crust to core and to advance understanding of the thermal evolution of the moon.
GRAIL-A & GRAIL-B will measure the lunar gravity field with unprecedented resolution up to 100 times improvement on the near side and 1000 times improvement for the far side.
NASA’s twin GRAIL Science Probes ready for Lunar Expedition
GRAIL B (left) and GRAIL A (right) spacecraft are mounted side by side on top of a payload adapter inside the clean room at Astrotech Space Operations facility. The spacecraft await lunar launch on Sept. 8, 2011. Credit: Ken Kremer
Just what will the GRAIL mission to the Moon do? Find out in just over 3 minutes with this new video about the mission. The launch of GRAIL is scheduled for Sept. 8, 2011 from Cape Canaveral Air Force Station in Florida.
NASA’s twin GRAIL Science Probes ready for Lunar Expedition. GRAIL B (left) and GRAIL A (right) spacecraft are mounted side by side on top of a payload adapter inside the clean room at Astrotech Space Operations facility. The spacecraft await lunar launch on Sept. 8, 2011. Credit: Ken Kremer
[/caption]
NASA’s GRAIL twins – dubbed GRAIL-A & GRAIL-B – are ready to embark on America’s next science expedition to the moon in less than 1 month’s time from Cape Canaveral Air Force Station, Fla.
The twin Gravity Recovery and Interior Laboratory (GRAIL) spacecraft have been exhaustively tested, fueled for flight and mounted side-by-side on a specially designed payload adapter inside the controlled environment of a clean room at the Astrotech Space Operations facility in nearby Titusville, Fla.
The next processing step is to encapsulate the lunar probes inside their protective payload fairing. The duo are set to be shipped from Astrotech to their Cape Canaveral launch pad next week on Aug. 16, where they will be mated to an already assembled Delta II booster.
Liftoff of the GRAIL twins is slated for Sept. 8 at 8:37 a.m. EDT by a Delta II Heavy rocket from Launch Complex 17 at Cape Canaveral for a nearly four month voyage to the moon.
After entering lunar orbit, the two GRAIL spacecraft will fly in a tandam formation just 50 kilometers above the lunar surface with an average separation of 200 km during the 90 day science phase.
Side view of twin GRAIL probes
The GRAIL spacecraft are mounted to a 3 inch high Launch Vehicle Adapter Assembly and 20 inch Payload Adapter spacer ring on top of a 30-inch high GSE stand. Credit: Ken Kremer (kenkremer.com)
GRAIL’s mission goal is to map the moon’s gravity field to high precision and thereby deduce the structure of the lunar interior from crust to core. This will also lead to a better understanding of the composition of the moon’s interior, according to Sami Asmar, GRAIL co-investigator from NASA’s Jet Propulsion Laboratory in Pasasdena, Calif., during an interview inside the Astrotech clean room at a photo opportunity for the media. A gravity experiment is also aboard the just launched Jupiter bound Juno spacecraft.
GRAIL Photo Album special taken from inside the Astrotech cleanroom facility.
Twin GRAIL lunar probes inside clean room at Astrotech. Credit: Ken KremerClose up of twin lunar probes, GRAIL- B (left) & GRAIL- A (right). Credit: Ken KremerGRAIL-B solar panels. Credit: Ken KremerGRAIL Science and Launch team inside clean room at Astrotech. Credit: Ken KremerGRAIL Co-Investigator Sami Asmar (left) from JPL and Ken Kremer discuss science objectives inside clean room at Astrotech.
Artist concept of LRO in lunar orbit. Credit: NASA
[/caption]
NASA’s Lunar Reconnaissance Orbiter (LRO) is changing our view of the Moon by literally bringing it into sharper focus with its three high resolution cameras. But now, things are about to get even sharper. Today, LRO fired its thrusters to begin dipping down from its usual orbit about 50 km above the surface and moving to an orbit that will allow the spacecraft’s cameras me to image the Apollo sites from about 20 km away.
“This will allow me to obtain images of the Apollo sites that are about 4 times sharper than my current best images,” said the LRO spacecraft on Twitter.
This is just a temporary orbit and the spacecraft will take images of and around the Apollo sites between August 14 and 19, 2011. After that, the spacecraft will return to the 50-km-orbit until December.
LRO has two narrow angle cameras (NACs) and one wide angle camera (WAC).
According to Mark Robinson, LROC Principal Investigator, who spoke at the Lunar Forum at Ames Research Center last month, as of the end of July, 2011 the amount of data returned by LRO has been about 400 gigabits of data every day, which includes 371,027 high resolution images. The WAC has taken about 160,000 images, with about 90,000 in color. In total, the spacecraft has imaged the entire Moon about 20 times with the WAC, and has imaged 20 per cent of the moon with NACs, which provides a narrower but higher resolution view.
“We want to map the whole moon at 50 cm/pixel to 200 cm/pixel, and that would be LROC’s legacy for the next 100 years of lunar exploration and science,” Robinson said.
He noted that all three cameras are performing way better than he had hoped.
“We are very excited about the quality of the data,” Robinson said.
So get ready for a little more quality views of the Apollo landing sites!
Update: as commenter MoonOrBust noted, the LRO Twitter feed had an addendum later in the day, adding that there are several technical challenges associated with getting improved resolution images at the lower altitude orbit. For example, the spacecraft will not slow from its orbital speed of about 1.6 km/s (about 3,500 mph) when it gets closer to the Moon’s surface, which might cause some image blurring, particularly for the LROC Narrow Angle Camera images. “However, it will certainly be fun to compare the images from the different orbits!” the spacecraft Tweeted.
Four snapshots from the computer simulation of a collision between the moon and a smaller companion moon show most of the companion moon is accreted as a pancake-shaped layer, forming a mountainous region on one side of the moon. Credit: M. Jutzi and E. Asphaug, Nature.
[/caption]
It’s a view science fiction fans could only hope for: twin moons in the night sky above Earth. But it might have been reality about 4 billion years ago. A new model suggests the lunar farside highlands could have been created from a collision with a smaller companion moon in what scientists from the University of California, Santa Cruz are calling “the big splat.”
Why the near and far sides of the Moon are so different has long puzzled planetary scientists. The near side is relatively low and flat, while the topography of the far side is high and mountainous, with a much thicker crust.
We actually have a somewhat lopsided Moon.
The new study, published in the August 4 issue of Nature, builds on the “giant impact” model for the origin of the moon, in which a Mars-sized object collided with Earth early in the history of the solar system and ejected debris that coalesced to form the moon.
According to the new computer model, the second moon around Earth would have been about 1,200 kilometers (750 miles) wide and could have formed from the same collision. Later, the smaller moon fell back onto the bigger Moon and coated one side with an extra layer of solid crust tens of kilometers thick.
“Our model works well with models of the Moon-forming giant impact, which predict there should be massive debris left in orbit about the Earth, besides the Moon itself,” said Erik Asphaug, professor of Earth and planetary sciences at UC Santa Cruz. “It agrees with what is known about the dynamical stability of such a system, the timing of the cooling of the moon, and the ages of lunar rocks.”
Other computer models have suggested a companion moon, said Asphaug, who coauthored the paper with UCSC postdoctoral researcher Martin Jutzi.
A previous collision with a smaller companion could explain why the Moon's two sides look so different. Credit: Martin Jutzi and Erik Asphaug
Asphaug and Jutzi used computer simulations to study the dynamics of the collision between the Moon and a smaller companion, which was about one-thirtieth the mass of the “main” moon. They tracked the evolution and distribution of lunar material in its aftermath.
The impact between the two bodies would have been relatively slow, at about 8,000 kph (5,000 mph) which is slow enough for rocks not to melt and no impact crater to form. Instead, the rocks and crust from the smaller moon would have spread over and around the bigger moon.
“Of course, impact modelers try to explain everything with collisions. In this case, it requires an odd collision: being slow, it does not form a crater, but splats material onto one side,” Asphaug said. “It is something new to think about.”
He and Jutzi hypothesize that the companion moon was initially trapped at one of the gravitationally stable “Trojan points” sharing the Moon’s orbit, and became destabilized after the moon’s orbit had expanded far from Earth. “The collision could have happened anywhere on the Moon,” Jutzi said. “The final body is lopsided and would reorient so that one side faces Earth.”
The model may also explain variations in the composition of the moon’s crust, which is dominated on the near side by terrain comparatively rich in potassium, rare-earth elements, and phosphorus (KREEP). These elements, as well as uranium and thorium, are believed to have been concentrated in the magma ocean that remained as molten rock solidified under the moon’s thickening crust. In the simulations, the collision squishes this KREEP-rich layer onto the opposite hemisphere, setting the stage for the geology now seen on the near side of the moon.
While the model explains many things, the jury is still out among planetary scientists as to the full history of the Moon and what really happened. Scientists say the best way to figure out the Moon’s history is to get more data from lunar orbiting spacecraft and – even better – sample return missions or human missions to study the Moon.
Oblique view of Tycho crater. Credit: NASA/GSFC/Arizona State University.
[/caption]
Here’s the Moon like you’ve never seen it before: a dramatic sunrise view of Tycho Crater on the Moon, highlighting the peaks and crags of the crater’s central uplifts. On June 10,2011 the Lunar Reconnaissance Orbiter slewed 65° to the west, allowing the Narrow Angle Camera to capture a “sideways” look at Tycho crater, resulting in a spectacular image. The central peak complex is about 15 km wide southeast to northwest (left to right in this view). Below are more images and a video which spans and zooms in to the entire image.
Tycho Crater is a very popular target with amateur astronomers since it is easily seen from Earth. The crater measures about 82 km (51 miles) in diameter, and the summit of the central peak is 2 km (6562 ft) above the crater floor, and the crater floor is about 4700 m (15,420 ft) below the rim.
Central uplifts form in larger impact craters in response to the impact event.
LROC principal investigator Mark Robinson wrote on the LRO website, “Tycho’s features are so steep and sharp because the crater is young by lunar standards, only about 110 million years old….Were these distinctive outcrops formed as a result of crushing and deformation of the target rock as the peak grew? Or do they represent preexisting rock layers that were brought intact to the surface? Imagine future geologists carefully making their way across these steep slopes, sampling a diversity of rocks brought up from depth.”
Here’s a close-up of the summit. The boulder in the background is 120 meters wide, and the image is about 1200 meters wide.
Oblique view of summit area of Tycho crater central peak. Credit: NASA/GSFC/Arizona State University
And here’s the entire crater:
LROC WAC mosaic of Tycho crater with lighting similar to that when the NAC oblique image was taken. Mosaic is 130 km wide, north is up. Credit: NASA/GSFC/Arizona State University.
Click on the images for larger versions on the LROC website, or see this link for more information on these images.
The view from above of the ARTEMIS orbits as they make the transition from the kidney-shaped Lissajous orbits on either side of the moon to orbiting around the moon. Credit: NASA/Goddard Space Flight Center
It took one and a half years, over 90 orbit maneuvers, and – wonderfully – many gravitational boosts and only the barest bit of fuel to move two spacecraft from their orbit around Earth to their new home around the Moon.
Along their travels, the spacecraft have been through orbits never before attempted and made lovely curlicue leaps from one orbit to the next. This summer, the two ARTEMIS spacecraft — which began their lives as part of the five-craft THEMIS mission studying Earth’s aurora – will begin to orbit the moon instead. THEMIS is an acronym for the Time History of Events and Macroscale Interaction during Substorms spacecraft.
Even with NASA’s decades of orbital mechanics experience, this journey was no easy feat. The trip required several maneuvers never before attempted, including several months when each craft moved in a kidney-shaped path on each side of the moon around, well, nothing but a gravitational point in space marked by no physical planet or object.
“No one has ever tried this orbit before, it’s an Earth-Moon libration orbit,” says David Folta a flight dynamics engineer at NASA’s Goddard Space Flight Center in Greenbelt, Md. “It’s a very unstable orbit that requires daily attention and constant adjustments.”
The journey for ARTEMIS — short for Acceleration, Reconnection, Turbulence and Electrodynamics of the Moon’s Interaction with the Sun — began in 2009, after THEMIS had completed some two years of science data collection on the magnetic environment around Earth, the aurora, and how these are affected by the sun.
The spacecraft are solar-powered, but orbits for the two outermost THEMIS spacecraft had slipped over time and were going to be subjected to regular eight-hour periods of darkness. These spacecraft could withstand up to three hours without sunlight, but this much darkness would soon leave the batteries completely discharged.
Teams at UC-Berkeley and Goddard handled the day-to-day control of the THEMIS spacecraft. The Principal Investigator for the mission, Vassilis Angelopoulos of UCLA talked to the teams about moving the two spacecraft to the moon to study the magnetic environment there. But quick models of a conventional boost technique showed that all the remaining fuel would be used simply in transit. There wouldn’t be enough left over for the fuel-hungry process of adjusting direction and speed to actually begin circling the moon.
So Angelopoulos pulled together a new, more complex multi-year-long orbit change plan. The move would rely predominantly on gravity assists from the moon and Earth to move the spacecraft into place. He brought his idea to two engineers who had been involved with launching THEMIS in the first place: David Folta and another flight engineer at Goddard, Mark Woodard. The pair used their own models to validate this new design, and the plan was on.
First step: increase the size of the orbits. The original Earth-centric orbits barely reached half way to the moon. By using small amounts of fuel to adjust speed and direction at precise moments in the orbit, the spacecraft were catapulted farther and farther out into space. It took five such adjustments for ARTEMIS P1 and 27 for ARTEMIS P2.
Next step: make the jump from Earth orbit to the tricky kidney-shaped “Lissajous” orbit, circling what’s known as a Lagrangian point on each side of the moon. These points are the places where the forces of gravity between Earth and the moon balance each other – the point does not actually offer a physical entity to circle around. ARTEMIS P1 made the leap – in a beautiful arc under and around the moon — to the Lagrangian point on the far side of the moon on August 25, 2010. The second craft made the jump to the near side of the moon on October 22. This transfer required a complex series of maneuvers including lunar gravity assists, Earth gravity assists, and deep space maneuvers. The combination of these maneuvers was needed not only to arrive at the correct spot near the moon but also at the correct time and speed.
Using a series of Earth and moon gravity assists – and only the barest bit of fuel – the ARTEMIS spacecraft entered into orbit around the moon’s Lagrangian points in the winter of 2010. Credit: NASA Goddard Space Flight Center/Scientific Visualization Studio
History was made. Numerous satellites orbit Lagrangian points between Earth and the Sun but, while this orbit had been studied extensively, it had never before been attempted.
Not only was this an engineering feat in and of itself, but the spacecraft were now in an ideal spot to study magnetism some distance from the moon. In this position, they could spot how the solar wind – made up of ionized gas known as plasma — flows past the Moon and tries to fill in the vacuum on the other side. A task made complicated since the plasma is forced by the magnetic fields to travel along certain paths.
“It’s a veritable zoo of plasma phenomena,” says David Sibeck, the project manager for THEMIS and ARTEMIS at Goddard. “The Moon carves out a cavity in the solar wind, and then we get to watch how that fills in. It’s anything but boring. There’s microphysics and particle physics and wave particle interaction and boundaries and layers. All things we haven’t had a chance to study before in the plasma.”
Life for the flight engineers was anything but boring too. Keeping something in orbit around a spot that has little to mark it except for the balance of gravity is no simple task. The spacecraft required regular corrections to keep it on track and Folta and Woodard watched it daily.
“We would get updated orbit information around 9 a.m. every day,” says Woodard. “We’d run that through our software and get an estimate of what our next maneuver should be. We’d go back and forth with Berkeley and together we’d validate a maneuver until we knew it was going to work and keep us flying for another week.”
The team learned from experience. Slight adjustments often had bigger consequences than expected. They eventually found the optimal places where corrections seemed to require less subsequent fine-tuning. These sweet spots came whenever the spacecraft crossed an imaginary line joining Earth and the Moon, though nothing in theories had predicted such a thing.
The daily vigilance turned out to be crucial. On October 14, the P1 spacecraft orbit and attitude changed unexpectedly. The first thought was that the tracking system might have failed, but that didn’t seem to be the problem. However, the ARTEMIS team also noticed that the whole craft had begun to spin about 0.001 revolutions per minute faster. One of the instruments that measures electric fields also stopped working. Best guess? The sphere at the end of that instrument’s 82-foot boom had broken off – perhaps because it was struck by something. That sphere was just three ounces on a spacecraft that weighed nearly 190 pounds — but it adjusted ARTEMIS P1’s speed enough that had they caught the anomaly even a few days later they would have had to waste a prohibitive amount of fuel to get back on course.
An artist's concept of the ARTEMIS spacecraft in orbit around the Moon. Credit: NASA
As it is, ARTEMIS will make it to the moon with even more fuel than originally estimated. There will be enough fuel for orbit corrections for seven to 10 years and then enough left over to bring the two craft down to the moon.
“We are thrilled with the work of the mission planners,” says Sibeck. “They are going to get us much closer to the moon than we could have hoped. That’s crucial for providing high quality data about the moon’s interior, its surface composition, and whether there are pockets of magnetism there.”
On January 9, 2011, ARTEMIS P1 jumped over the moon and joined ARTEMIS P2 on the side of the Moon closest to Earth. Now the last steps are about to begin.
On June 27, P1 will spiral in toward the moon and enter lunar orbit. On July 17, P2 will follow. P2 will travel in the same direction with the Moon, or in prograde; P1 will travel in the opposite direction, in retrograde.
“We’ve been monitoring ARTEMIS every day and developing maneuvers every week. It’s been a challenge, but we’ve uncovered some great things,” says Folta, who will now focus his attention on other NASA flights such as the MAVEN mission to Mars that is scheduled to launch in 2013. “But soon we’ll be done with this final maneuvering and, well, we’ll be back to just being ARTEMIS consultants.”
See additional ARTEMIS imagery and video at this link.
