MeteorWayne":2e7aoxim said:
Software, it's like politics, it's always Microsoft's fault. If in doubt reboot. Could be any number of reasons, but it doesn't hurt and just might help.
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Software, it's like politics, it's always Microsoft's fault. If in doubt reboot. Could be any number of reasons, but it doesn't hurt and just might help.
EarthlingX":14swmhe8 said:
A few more excerpts:
For the third time since it left Earth in September 2007, the spacecraft has received an upgrade of the software that runs in its primary computer. With a sense of grandeur and drama befitting this unique adventure, ever-poetical engineers fulfilled their dream of more than a year by denominating it OBC flight software version 9.0. Revealing their surprisingly cute and playful nature, however, most Dawn team members prefer the hypocorism “9.0” (or “nine oh”).
Engineers at JPL and Orbital Sciences Corporation began work on 9.0 almost immediately after 8.0 was installed on the spacecraft in April 2009. They continued with the careful and deliberate process of modifying the software until January, when the extensive test program commenced. It was crucial to verify not only that the new functions would work correctly but also that no unintended differences were introduced and that the existing capabilities were not compromised.
The latest software has 23 sets of changes from the previous version. Some of these are new methods of controlling the way the spacecraft will point its sensors at Vesta and Ceres in order to optimize the acquisition of data. Other modifications, based on experience gained in the ongoing operation of the spacecraft, improve its ability to handle certain potential anomalies on its own. In addition, just as 7.0 and 8.0 did, 9.0 corrects some bugs...
On June 15, the spacecraft stopped thrusting on schedule, turned to point its main antenna to Earth, and kept it there rather than returning to the thrust direction a few hours later. That allowed operators to perform the rest of these detailed checks. After confirming that both the primary and backup computers were fully healthy, they transmitted the files containing the new software.
On June 16, with all stations in mission control at JPL reporting all subsystems were healthy and stable, and all systems at the Deep Space Network performing equally well, the command to reset the computer was radioed to the distant ship. The computer dutifully rebooted for the first time since the installation of 8.0 and began running with version 9.0. Whenever the computer reboots, it puts the craft into safe mode. The team verified that the new software was running smoothly and then initiated the process of guiding the spacecraft out of safe mode and back to its normal interplanetary cruise configuration. The schedule had allowed until June 24, but by June 18, the robotic explorer was fully prepared to resume its normal duties.
Because the software upgrade went so well, the Dawn project has decided to present this exciting offer: we will install a functional copy of 9.0 on your computer or smartphone at no charge. Simply place your device in the asteroid belt, send us the coordinates, and we’ll do the rest...
Dawn resumed ion thrusting on schedule on June 24.
http://dawn.jpl.nasa.gov/mission/journal_08_30_10.asp
Dawn's journey ever-deeper into the asteroid belt continues to go well, as the spacecraft carries out its familiar routine of thrusting gently with its ion propulsion system. But the interplanetary traveler has changed some of its habits, performing certain activities a little differently now from what its many followers have been accustomed to.
Dawn is now so far from the sun, that even with its tremendous solar arrays, the most powerful ever used on an interplanetary mission, it does not receive enough sunlight to generate sufficient electrical power to operate all systems and still achieve maximum thrust.
The largest consumer of power onboard the ship, the ion propulsion system is power hungry. Indeed, the key to its remarkable effectiveness is that, in concert with the solar arrays, it converts the renewable energy from the omnipresent sunlight into thrust with a high velocity beam of xenon ions, in contrast to conventional propulsion systems, which only work with the more limited energy stored within the chemical propellants. The importance of high power to thrusting has been discussed in detail in several previous logs...
The electrical power generated by a solar cell depends on its temperature. When a cell is warmer, it is a little less efficient at transforming light into electricity, so it yields a little less power, even if the intensity of light impinging on it is unchanged.
When Dawn is not thrusting, the onboard power demand is much lower, so less power is drawn from the two huge wings of cells. That means that less of the light captured by the solar arrays is converted to electrical power. So where does the energy of that light go? When the solar panels do not need to generate as much electricity, the excess energy of the absorbed light simply turns to heat, warming the wings. Therefore, the arrays are warmer when Dawn is not thrusting; and when thrusting commences, the arrays need to cool down before they can achieve their best performance. Earlier in the mission, when Dawn was closer to the sun and could produce far more power than it needed (even when the arrays were warm), this small difference was entirely unimportant. Now it is very important...
For the last few months, the solar arrays have been able to meet the onboard demand when they were cool, but when they were warm, the available light was too weak to yield the power required by all systems. There were several solutions to this (some of which probably would have lent themselves to simpler and more jocose descriptions), and the one engineers chose was to initiate thrusting at a somewhat reduced throttle level, demanding less power than at full thrust. That drew enough power from the arrays to bring their temperatures down, allowing them to approach their highest efficiency. Then the sequence running in the main computer commanded the ion propulsion system to throttle up, and the arrays were able to provide the additional power. This strategy has been in use every week since April 19 and has worked flawlessly...
As Dawn moved farther from the sun, the power diminished still more. The team knew well in advance that by May, even when the array temperatures were low, there would not be enough power for all systems while at the maximum throttle level. So, beginning May 17, when the spacecraft completes its weekly communication session with its main antenna, it powers off its radio transmitter. Prior to that date, the transmitter had always been left on, even when Dawn was not in contact with Earth. The radio signal had been directed through an auxiliary antenna that broadcasts over a very wide angle in exchange for making the signal much weaker at the receiving antenna on Earth.
By July 26, that strategy was no longer sufficient to accommodate the ever-decreasing power. Since then the ion propulsion system has been throttled down during the mid-week health check. Reducing power for the ion thrust allows power to be devoted to the transmitter...
Based on extensive analyses performed in 2009, engineers had estimated that Dawn would no longer be able to sustain the highest throttle level by the last week of July 2010, even with the radio off. As it turned out, however, the craft exceeded their expectations and persisted through August 23. Finally, at a distance of 2.02 AU from the sun, it was time to reduce the power to the ion drive. From now on, Dawn will gradually decrease thrust as it travels still farther from the brilliant star. Even at lower throttle levels, however, the ion propulsion system’s efficiency is far beyond what is achievable with chemical propulsion...
In February we took a detailed look at Dawn’s daily change in velocity and recognized that it would continue to increase (thanks to the decrease in the total mass) until throttled operation would be necessary. As predicted then, the space traveler has now reached its peak acceleration of 7.6 meters per second per day (17 miles per hour for a day of thrusting). As this had been accounted for long ago in the design of the trajectory, and motivated some of the tests performed shortly after launch, the future gradual reductions in thrust have already been incorporated into the plan for keeping the ship on a steady course to Vesta and then to Ceres. ..
As the spacecraft continues its ambitious expedition through the asteroid belt, engineers have recently changed another aspect of its operation as well. On August 23, following instructions that had been stored in the main computer the previous week, Dawn powered off all four of its reaction wheels. (It’s only coincidental that that is also both the date the ion drive was throttled down to save power and the date there was a power failure in the ice cream shop at the Tribute to Coincidence.) This was the first time since the day it was launched that all the wheels were off. For most of its mission so far, Dawn has used three of these units at a time to help hold its orientation or to turn to a different orientation in the zero-gravity, frictionless environment of spaceflight by electrically changing the speed at which they spin. Wheel no. 4 developed increased friction on June 17, so it was turned off, and wheels 1 - 3 have been in use since then. Mission controllers subsequently elected to turn all the wheels off in order to help preserve them for use at Vesta and Ceres...
With the wheels being given a rest, the reaction control system takes over their function. This system fires conventional rocket propellant (perhaps even the same hydrazine formulation you use in your rocket) through small thrusters aimed in different directions to provide the required control of the craft’s orientation.
Since smoothly accomplishing the transition, Dawn has maintained its usual schedule of devoting 95% of the time to thrusting, gradually changing its orbit so that it will match Vesta’s orbit in about 11 months.
Dawn is 0.19 AU (29 million kilometers or 18 million miles) from Vesta, its next destination. It is also 2.82 AU (421 million kilometers or 262 million miles) from Earth, or 1070 times as far as the moon and 2.79 times as far as the sun. Radio signals, traveling at the universal limit of the speed of light, take 47 minutes to make the round trip....
Dr. Marc D. Rayman
9:30 p.m. PDT August 30, 2010
Dawn's journey ever-deeper into the asteroid belt continues to go well, as the spacecraft carries out its familiar routine of thrusting gently with its ion propulsion system. But the interplanetary traveler has changed some of its habits, performing certain activities a little differently now from what its many followers have been accustomed to.
Dawn is now so far from the sun, that even with its tremendous solar arrays, the most powerful ever used on an interplanetary mission, it does not receive enough sunlight to generate sufficient electrical power to operate all systems and still achieve maximum thrust.
The largest consumer of power onboard the ship, the ion propulsion system is power hungry. Indeed, the key to its remarkable effectiveness is that, in concert with the solar arrays, it converts the renewable energy from the omnipresent sunlight into thrust with a high velocity beam of xenon ions, in contrast to conventional propulsion systems, which only work with the more limited energy stored within the chemical propellants. The importance of high power to thrusting has been discussed in detail in several previous logs...
The electrical power generated by a solar cell depends on its temperature. When a cell is warmer, it is a little less efficient at transforming light into electricity, so it yields a little less power, even if the intensity of light impinging on it is unchanged.
When Dawn is not thrusting, the onboard power demand is much lower, so less power is drawn from the two huge wings of cells. That means that less of the light captured by the solar arrays is converted to electrical power. So where does the energy of that light go? When the solar panels do not need to generate as much electricity, the excess energy of the absorbed light simply turns to heat, warming the wings. Therefore, the arrays are warmer when Dawn is not thrusting; and when thrusting commences, the arrays need to cool down before they can achieve their best performance. Earlier in the mission, when Dawn was closer to the sun and could produce far more power than it needed (even when the arrays were warm), this small difference was entirely unimportant. Now it is very important...
For the last few months, the solar arrays have been able to meet the onboard demand when they were cool, but when they were warm, the available light was too weak to yield the power required by all systems. There were several solutions to this (some of which probably would have lent themselves to simpler and more jocose descriptions), and the one engineers chose was to initiate thrusting at a somewhat reduced throttle level, demanding less power than at full thrust. That drew enough power from the arrays to bring their temperatures down, allowing them to approach their highest efficiency. Then the sequence running in the main computer commanded the ion propulsion system to throttle up, and the arrays were able to provide the additional power. This strategy has been in use every week since April 19 and has worked flawlessly...
As Dawn moved farther from the sun, the power diminished still more. The team knew well in advance that by May, even when the array temperatures were low, there would not be enough power for all systems while at the maximum throttle level. So, beginning May 17, when the spacecraft completes its weekly communication session with its main antenna, it powers off its radio transmitter. Prior to that date, the transmitter had always been left on, even when Dawn was not in contact with Earth. The radio signal had been directed through an auxiliary antenna that broadcasts over a very wide angle in exchange for making the signal much weaker at the receiving antenna on Earth.
By July 26, that strategy was no longer sufficient to accommodate the ever-decreasing power. Since then the ion propulsion system has been throttled down during the mid-week health check. Reducing power for the ion thrust allows power to be devoted to the transmitter...
Based on extensive analyses performed in 2009, engineers had estimated that Dawn would no longer be able to sustain the highest throttle level by the last week of July 2010, even with the radio off. As it turned out, however, the craft exceeded their expectations and persisted through August 23. Finally, at a distance of 2.02 AU from the sun, it was time to reduce the power to the ion drive. From now on, Dawn will gradually decrease thrust as it travels still farther from the brilliant star. Even at lower throttle levels, however, the ion propulsion system’s efficiency is far beyond what is achievable with chemical propulsion...
In February we took a detailed look at Dawn’s daily change in velocity and recognized that it would continue to increase (thanks to the decrease in the total mass) until throttled operation would be necessary. As predicted then, the space traveler has now reached its peak acceleration of 7.6 meters per second per day (17 miles per hour for a day of thrusting). As this had been accounted for long ago in the design of the trajectory, and motivated some of the tests performed shortly after launch, the future gradual reductions in thrust have already been incorporated into the plan for keeping the ship on a steady course to Vesta and then to Ceres. ..
As the spacecraft continues its ambitious expedition through the asteroid belt, engineers have recently changed another aspect of its operation as well. On August 23, following instructions that had been stored in the main computer the previous week, Dawn powered off all four of its reaction wheels. (It’s only coincidental that that is also both the date the ion drive was throttled down to save power and the date there was a power failure in the ice cream shop at the Tribute to Coincidence.) This was the first time since the day it was launched that all the wheels were off. For most of its mission so far, Dawn has used three of these units at a time to help hold its orientation or to turn to a different orientation in the zero-gravity, frictionless environment of spaceflight by electrically changing the speed at which they spin. Wheel no. 4 developed increased friction on June 17, so it was turned off, and wheels 1 - 3 have been in use since then. Mission controllers subsequently elected to turn all the wheels off in order to help preserve them for use at Vesta and Ceres...
With the wheels being given a rest, the reaction control system takes over their function. This system fires conventional rocket propellant (perhaps even the same hydrazine formulation you use in your rocket) through small thrusters aimed in different directions to provide the required control of the craft’s orientation.
Since smoothly accomplishing the transition, Dawn has maintained its usual schedule of devoting 95% of the time to thrusting, gradually changing its orbit so that it will match Vesta’s orbit in about 11 months.
Dawn is 0.19 AU (29 million kilometers or 18 million miles) from Vesta, its next destination. It is also 2.82 AU (421 million kilometers or 262 million miles) from Earth, or 1070 times as far as the moon and 2.79 times as far as the sun. Radio signals, traveling at the universal limit of the speed of light, take 47 minutes to make the round trip....
Dr. Marc D. Rayman
9:30 p.m. PDT August 30, 2010
Q: When do we expect to get the first interesting images of 4 Vesta from Dawn? It's now only 23 million km away, and here's what 21 Lutetia looked like to Rosetta at 900000 km, so 25 times closer than 4 Vesta is now:
http://3.bp.blogspot.com/__e2VLp6gwyk/T ... +image.jpg
A comparison of them to scale (except the probe of course):
http://1.bp.blogspot.com/__e2VLp6gwyk/T ... ion+km.PNG
http://3.bp.blogspot.com/__e2VLp6gwyk/T ... +image.jpg
A comparison of them to scale (except the probe of course):
http://1.bp.blogspot.com/__e2VLp6gwyk/T ... ion+km.PNG
http://www.planetary.org : New Hubble images and rotation movie of Vesta
www.nasa.gov : New Spin on Vesta (NASA video)
[youtube]http://www.youtube.com/watch?v=ENOoB3086wg[/youtube]
..
...
Vesta from Hubble
Credit: NASA / ESA / STScI / UMd
...
Rotating Vesta
This animation is composed of 20 images of Vesta captured on May 14 and 16, 2007 by the Wide Field Planetary Camera 2. Vesta has a mean diameter of approximately 530 kilometers (330 miles), but is slightly shorter pole-to-pole (464 km / 288 mi) than it is at the equator (570 km / 354 mi) and rotates in 5.34 hours. The colors are not true colors but do show color variations across the surface. Credit: NASA, ESA, and Lucy McFadden (U. Maryland)
www.nasa.gov : New Spin on Vesta (NASA video)
Hi EarthlingX,
Fascinating update.
The fact that the 4 Vesta Vernal Equinox will be later means that we'll get more time to examine that south polar crater & 13 KM tall central mountain, one of tallest mountains in the solar system not on Mars, Io or Iapetus.
4 Vesta really apprars to be very spherical overall, the northern hemisphere particularly so. Will be interesting to see the varying crater densities, lava pains if they exist & or volcanic features, if they still exist, assuming impacts have not obliterated them. Mind you DAWN should still see most of 4 Vesta well before having to leave for 1 Ceres.
Andrew Brown.
Fascinating update.
The fact that the 4 Vesta Vernal Equinox will be later means that we'll get more time to examine that south polar crater & 13 KM tall central mountain, one of tallest mountains in the solar system not on Mars, Io or Iapetus.
4 Vesta really apprars to be very spherical overall, the northern hemisphere particularly so. Will be interesting to see the varying crater densities, lava pains if they exist & or volcanic features, if they still exist, assuming impacts have not obliterated them. Mind you DAWN should still see most of 4 Vesta well before having to leave for 1 Ceres.
Andrew Brown.
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