By Marc Rayman

As NASA’s Dawn spacecraft investigates its first target, the giant asteroid Vesta, Marc Rayman, Dawn’s chief engineer, shares a monthly update on the mission’s progress.

This image obtained by the framing camera on NASA’s Dawn spacecraft shows the south pole of the giant asteroid Vesta. Image credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA
› Full image and caption | › Read related news release

Dear Dawnniversaries,

Dawn’s fourth anniversary of being in space is very different from its previous ones. Indeed, those days all were devoted to reaching the distant destination the ship is now exploring. Celebrating its anniversary of leaving Earth, Dawn is in orbit around a kindred terrestrial-type world, the ancient protoplanet Vesta.

The adventurer spent August on Vesta’s shores and now it’s ready to dive in. Dawn devoted most of this month to working its way down from the 2,700-kilometer (1,700-mile) survey orbit to its current altitude of about 680 kilometers (420 miles) and changing the orientation of the orbit. (For a more detailed discussion of the altitude, go here.) The sensationally successful observing campaign in survey orbit produced captivating views, revealing a complex, fascinating landscape. Now four times closer to the surface, the probe is nearly ready for an even more comprehensive exploration from the high altitude mapping orbit (HAMO). The plans for HAMO have changed very little since it was described on the third anniversary of Dawn’s launch.

Dawn’s spiral descent went extremely well. We have seen before that bodies travel at higher velocities in lower altitude orbits, where the force of gravity is greater. For example, Mercury hurtles around the sun faster than Earth in order to balance the stronger pull of gravity, and Earth’s speed is greater than that of more remote Vesta. Similarly, satellites in close orbits around Earth, such as the International Space Station, race around faster than the much more distant moon. When it began its spiral on August 31, Dawn’s orbital speed high above Vesta was 76 meters per second (170 mph), and each revolution took nearly 69 hours. Under the gentle thrust of its ion propulsion system, the spacecraft completed 18 revolutions of Vesta, the loops getting tighter and faster as the orbital altitude gradually decreased, until it arrived at its new orbit on schedule on Sept. 18. In HAMO, Dawn orbits at 135 meters per second (302 mph), circling the world beneath it every 12.3 hours.

When Dawn’s itinerary called for it to stop thrusting, it was very close to HAMO but not quite there yet. As mission planners had recognized long beforehand, small differences between the planned and the actual flight profiles were inevitable. Extensive and sophisticated analysis has been undertaken in recent years to estimate the size of such discrepancies so the intricate plans for completing all the work at Vesta could account for the time and the work needed to deliver the robotic explorer to the intended destination. In order to accomplish the intensive program of observations with its scientific instruments, the spacecraft must follow an orbital path carefully matched to the sequences of commands already developed with painstaking attention to detail. The beauty of Dawn’;s artistically choreographed pas de deux with Vesta depends on the music and the movements being well synchronized.

During its descent, Dawn paused frequently to allow controllers to update the flight profile, accounting for some of the variances in its course along the way. Following the completion of thrusting, navigators tracked the ship more extensively as it sailed around Vesta, measuring its orbit with great accuracy. This revealed not only the details of the orbital parameters (such as size, shape, and orientation) but also more about the character of Vesta’s gravity field than could be detected at higher altitudes. With the new information, the team designed two short maneuvers to adjust the orbit. The first, lasting four hours, was executed last night, and the second, half an hour shorter, will be completed tonight. After further measurements to verify the final orbit, the month of HAMO observations will begin on Sept. 29.

› Continue reading Marc Rayman’s Dawn Journal

By Julie Cooper

Each month in “Slice of History” we feature a historical photo from the JPL Archives. See more historical photos and explore the JPL Archives at https://beacon.jpl.nasa.gov/.

Cookie Cutter Missile Propellant — Photograph Number 381-490

The ORDCIT Project at NASA’s Jet Propulsion Laboratory was a research and development program about long-range jet propelled missiles. Under a contract with the Army’s Ordnance Department, a series of solid propellants were developed and tested. This photo shows a neoprene based formula referred to as ORDCIT 29, created in 1945.

Ingredients were mixed and formed into a sheet using a small roller mill. The uncured sheet was laid on a table and cut into disks, using a tool that looked like a large cookie cutter. The disks were stacked and wrapped in a neoprene liner. This cylinder was then placed in a mold and compressed. The locked mold was placed in an oven at high temperatures to vulcanize the charge and fuse the propellant and liner into one solid piece.

Twenty-one of these restricted-burning solid propellant cartridges were tested at various temperatures and various chamber pressures. The results were promising, and Progress Report No. 4-25 recommended more extensive testing.

This post was written for “Historical Photo of the Month,” a blog by Julie Cooper of JPL’s Library and Archives Group.

By Amber Jenkins

This post was written for My Big Fat Planet, a blog hosted by Amber Jenkins on NASA’s Global Climate Change site.

COLD SNAP: Petermann Glacier, Greenland. Left: June 26, 2010. Right: August 13, 2010. An iceberg more than four times the size of Manhattan broke off the Petermann Glacier (the curved, nearly vertical stripe stretching up from the bottom right of the images) along the northwestern coast of Greenland. Warmer water below the floating ice and at the sea’s surface were probably responsible for the break.
› See more images of our changing Earth from State of Flux

They say a picture says a thousand words. This week we published our 100th image in State of Flux, our gallery showing images of change around our planet. So hopefully by now you’re in awe of our home planet and the ways in which it is constantly changing, and aware of the impact us humans can have.

Each week for the past couple of years, we’ve published new images of different locations on planet Earth, showing change over time periods ranging from centuries to days. The pictures have been taken from space, by NASA’s Eyes on the Earth (its fleet of satellites whizzing above our heads), and from the ground, by real-life people. Some of the changes seen are related to, or exacerbated by, climate change, and some are not. Some document the effects of urbanization and man’s impact on the land, while others the ravage of disasters such as fires and floods.

Seeing our planet from space gives us a global view that we can’t get elsewhere. Through those eyes, we’ve witnessed damage caused by the recent tsunami in Japan, glacier melt in the Himalayas, the greening of China, the growth of Las Vegas and a century of global warming. We’ve looked at the march of deforestation in Bolivia, the rumblings of the (unpronounceable) Icelandic volcano Eyjafjallajökull, and the damming of the River Nile. Take a look below at some of our favorites. Sign up to our monthly newsletter or subscribe to our Facebook page if you want to keep up to date with our latest images. We’ll be launching a brand spanking new version of the gallery soon!

See more of some of the most stunning images from State of Flux on My Big Fat Planet.

By Marc Rayman

As NASA’s Dawn spacecraft investigates its first target, the giant asteroid Vesta, Marc Rayman, Dawn’s chief engineer, shares a monthly update on the mission’s progress.

This anaglyph image of Vesta’s equator was put together from two clear filter images, taken on July 24, 2011 by the framing camera instrument aboard NASA’s Dawn spacecraft. The anaglyph image shows hills, troughs, ridges and steep craters. Image credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA
› Full image and caption | › Read related news release

Dear Magdawnificents,

Dawn has completed the first phase of its exploration of Vesta with tremendous success, and the peripatetic adventurer is now in powered flight again, on its way to a new location from which to scrutinize its subject. Meanwhile, scientists are deeply engaged in analyzing the magnificent views the stalwart surveyor has transmitted to Earth.

Most of August was devoted to survey orbit. At an altitude of about 2,700 kilometers (1,700 miles), the ship sailed slowly around the world beneath it, completing a loop every 69 hours. Vesta rotates faster, turning once on its axis each 5 hours, 20 minutes. As we saw in the previous log, the survey orbit phase of the mission consisted of seven revolutions around Vesta, providing ample opportunities to acquire the rich bounty of data that scientists yearned for.

As Dawn follows its course, it passes over the north pole, then heads south on the day side of Vesta. On each orbit, it trained its sensors on the illuminated surface and filled its memory with the spectacular sights. On the other half of its orbit, gliding high above the dark landscape, it radioed its findings to distant Earth.

As we discussed last year, Vesta has seasons, just as your planet probably does. For readers on Earth, for example, it is summer in the northern hemisphere, and a region around the south pole is in constant darkness. On Vesta right now, the southern hemisphere is facing the sun, so everywhere between about 52 degrees north latitude and the north pole is in a long night. That ten percent of the surface is presently impossible to see. Because Dawn will stay in orbit around Vesta as together they travel around the sun, in 2012 it will be able to see some of this hidden scenery as the seasons advance.

The campaign of acquiring data in survey orbit was very complex. On the second, fourth, fifth, and sixth loops, the strategy included collecting more than Dawn’s memory could accommodate in the half of an orbit in which it was over sunlit terrain. Therefore, during those orbits, mission planners incorporated instructions to turn away from looking at Vesta to allow the spacecraft to point its main antenna to Earth for five to six hours. That provided time to transmit enough of its precious findings to make room for still more during the rest of the passage over the day side.

On the first and third revolutions, the computer in the visible and infrared mapping spectrometer (VIR) encountered an unexpected condition, so it stopped collecting data. When the spacecraft was next on the night side, controllers reconfigured the instrument so it could resume normal operation for the subsequent lap. Engineers and scientists from Italy who developed the complex device and from JPL are working closely together to establish the underlying cause. They have taken advantage of the extended periods in each orbit when the main antenna is pointing to Earth to run diagnostic tests on the unit. All indications are that it is healthy, and evidence points strongly to the glitches being related to some detail of the mode in which VIR collects and processes data. The team is confident that once they understand the behavior, they will be able to formulate plans to operate the spectrometer in ways that avoid triggering it.

Thanks to the strategy to perform more observations than needed, even with the interruptions, VIR accumulated a fantastic wealth of information. The principal scientific objective of survey orbit was to collect 5,000 sets of spectra or “frames.” A spectrum is the intensity of light at different wavelengths, and each frame consists of visible and infrared spectra at 256 locations on Vesta’s complex and mysterious surface. By the end of survey orbit, Dawn had obtained well in excess of 13,000 frames, or more than three million spectra. Acquiring more than one spectrum of the same location is valuable, as different angles of incident or reflected sunlight allow scientists to gain greater insight into the mineralogical composition and properties of the material. With an initial plan of observing 52 percent of the surface with VIR from survey orbit, the team is elated now to have spectra from about 63 percent.

The science camera has similarly overachieved. The intent was to photograph 60 percent of Vesta, but the entire 90 percent not in the darkness of northern winter has been captured at least five times. With pictures taken from multiple angles, stereo views can be constructed; and images at different times allow features to be observed under varied lighting conditions. All of the camera’s color filters were used, providing coverage in the near infrared and visible. Until recently, Vesta was known as little more than a smudge of light, but now scientists have more than 2,800 photos from Dawn’s survey.

A selection of stunning scenes of the latest world to come into the realm of humankind’s knowledge is here. As scientists pore through the treasure trove, they will continue to add their favorite views to that site.

This mission has already revealed far more about Vesta than a flyby mission could. While much more data will be obtained during the rest of Dawn’s residence there, the six gigabytes from VIR and the three gigabytes from the camera so far are enough to keep researchers busy (and extremely happy!) for a very long time as they tease out the nature of this alien world.

› Continue reading Marc Rayman’s September Dawn Journal