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.

The south pole of the giant asteroid Vesta, as imaged by the framing camera on NASA’s Dawn spacecraft in September 2011. Image credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA |
› Full image and caption

Dear Asdawnished Readers,

Dawn is scrutinizing Vesta from its low-altitude mapping orbit (LAMO), circling the rocky world five and a half times a day. The spacecraft is healthy and continuing its intensive campaign to reveal the astonishing nature of this body in the mysterious depths of the main asteroid belt.

Since the last log, the robotic explorer has devoted most of its time to its two primary scientific objectives in this phase of the mission. With its gamma ray and neutron detector (GRaND), it has been patiently measuring Vesta’s very faint nuclear emanations. These signals reveal the atomic constituents of the material near the surface. Dawn also broadcasts a radio beacon with which navigators on distant Earth can track its orbital motion with exquisite accuracy. That allows them to measure Vesta’s gravity field and thereby infer the interior structure of this complex world. In addition to these top priorities, the spacecraft is using its camera and its visible and infrared mapping spectrometer (VIR) to obtain more detailed views than they could in the higher orbits.

As we have delved into these activities in detail in past logs, let’s consider here some more aspects of controlling this extremely remote probe as it peers down at the exotic colossus 210 kilometers (130 miles) beneath it.

Well, the first aspect that is worth noting is that it is incredibly cool! Continuing to bring this fascinating extraterrestrial orb into sharper focus is thrilling, and everyone who is moved by humankind’s bold efforts to reach into the cosmos shares in the experience. As a reminder, you can see the extraordinary sights Dawn has by going here for a new image every weekday, each revealing another intriguing aspect of the diverse landscape.

The data sent back are providing exciting and important new insights into Vesta, and those findings will continue to be announced in press releases. Therefore, we will turn our attention to a second aspect of operating in LAMO. Last month, we saw that various forces contribute to Dawn moving slightly off its planned orbital path. (That material may be worth reviewing, either to enhance appreciation of what follows or as an efficacious soporific, should the need for one ever arise.) Now let’s investigate some of the consequences. This will involve a few more technical points than most logs, but each will be explained, and together they will help illustrate one of the multitudinous complexities that must be overcome to make such a grand adventure successful.

› Continue reading Marc Rayman’s Dawn Journal

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 3-D video incorporates images from the framing camera instrument aboard NASA’s Dawn spacecraft from July to August 2011. The images were obtained as Dawn approached Vesta and circled the giant asteroid during the mission’s survey orbit phase. Survey orbit took place at an altitude of about 1,700 miles (2,700 kilometers). To view this video in 3-D use red-green, or red-blue, glasses (left eye: red; right eye: green/blue). Image credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA
› See video

Dear Dawnward Spirals,

Continuing its ambitious campaign of exploration deep in the asteroid belt, Dawn has spent most of the past month spiraling ever closer to Vesta. Fresh from the phenomenal success of mapping the alien world in detail in October, the spacecraft and its human team members are engaged in one of the most complicated parts of the mission. The reward will be the capability to scrutinize this fascinating protoplanet further.

Thanks to the extraordinary performance of its ion propulsion system, Dawn can maneuver to different orbits that are best suited for conducting each of its scientific observations. The probe is now headed for its low altitude mapping orbit (LAMO), where the focus of its investigations will be on making a census of the atomic constituents with its gamma ray and neutron sensors and on mapping the gravity field in order to determine the interior structure of this protoplanet.

As secondary objectives, Dawn will acquire more images with its camera and more spectra with its visible and infrared mapping spectrometer. As we will see in a future log, these measurements will receive a smaller share of the resources than the high priority studies. The spectacular pictures obtained already will keep scientists happy for years, and you can continue to share in the experience of marveling at the astonishing discoveries by seeing some of the best views here, including scenes captured during the spiral to LAMO.

Planning the low altitude mapping orbit around massive Vesta, with its complicated gravity field, required a great deal of sophisticated analysis. Before Dawn arrived, mission designers studied a range of possible gravitational characteristics and honed the methods they would use for plotting the actual orbit once the details of the protoplanet’s properties were ascertained. In the meantime, the team used a tentative orbit at an altitude over the equator of 180 kilometers (110 miles). As explained in a previous log, the altitude varies both because the orbit is not perfectly circular and because Vesta displays such exceptional topography. The highest elevations turn out to be at the equator, and the average altitude of that orbit would be 200 kilometers (125 miles).

Now that navigators have measured Vesta’s gravity, they have the knowledge to refine the design for LAMO, and they decided to raise it by 10 kilometers (6 miles). The target then is an average altitude of 210 kilometers (130 miles). But there is more to the specification of the orbit than simply its height. To meet all of the scientific objectives, the orientation of this orbit needs to be different from the orientation of the previous orbits, the high altitude mapping orbit (HAMO) and survey orbit.

› Continue reading Marc Rayman’s Dawn Journal

By Marc Rayman

NASA’s Dawn spacecraft has just arrived at its first target, the giant asteroid Vesta. Each month, Marc Rayman, Dawn’s chief engineer, shares an update on the mission’s progress.

NASA’s Dawn spacecraft obtained this image of the giant asteroid Vesta with its framing camera on July 24, 2011. Image credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA
› See more images | › See related video

Dear Dawncredibles,

Dawn is now beginning intensive observations of the alien world it orbits. The approach phase, which began on May 3, is complete. Today Dawn is in its survey orbit around Vesta.

Following the previous log, the spacecraft continued using its ion propulsion system to spiral around Vesta, gradually descending to its present altitude of 2700 kilometers (1700 miles). Its flight plan included more observations of Vesta, each one producing incredible views more exciting than the last. Every image revealed new and exotic landscapes. Vesta is unlike any other place humankind’s robotic ambassadors have visited. To continue to share in the thrill of discovery, remember to visit here to see a new image every day during survey orbit. Your correspondent, writing with atypical brevity, also will continue to provide progress reports here at least once a week.

As the ship sailed ever closer to the massive protoplanet during the approach phase, the gravitational attraction grew stronger. We saw in previous logs that astronomers had estimated Vesta’s mass by observing the effect of the 530-kilometer (330-mile) diameter behemoth on distant bodies, including smaller residents of the asteroid belt and even Mars. Now that navigators can detect its pull on nearby Dawn, they are improving that value. Before the explorer’s arrival, Vesta’s mass was calculated to be about 262 billion billion kilograms (289 million billion tons). Now it is measured to be about 259 billion billion kilograms (286 million billion tons), well within the previous margin of error. It is impressive how accurately astronomers had been able to determine the heft of what had appeared as little more than a point of light among the myriad stars. Nevertheless, even this small change of 1.2 percent is important for planning the rest of Dawn’s mission.

› Continue reading Marc Rayman’s August Dawn Journal