Author Topic: NASA - Dawn updates and discussion  (Read 409140 times)

Offline Zed_Noir

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Re: NASA - Dawn updates and discussion
« Reply #1800 on: 03/08/2017 08:44 AM »
Cryovulcanism so close to the Inner Planets? The next time a Discovery or New Frontiers-class slot comes up, I'm pretty sure there will be plenty of planetary scientists agitating for a lander for Occator Crater!
I would be surprised if there isn't at least one Discovery proposal.  A lander may be hard in a Discovery budget, though.

Somewhat in jest. Since Dawn is available as comm relay for a while. Maybe a cheap carrier spacecraft with a small airbag lander with a hypergolic crusher stage. :)

Offline Star One

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Re: NASA - Dawn updates and discussion
« Reply #1801 on: 03/22/2017 09:26 PM »
Ice in Ceres' Shadowed Craters Linked to Tilt History

Dwarf planet Ceres may be hundreds of millions of miles from Jupiter, and even farther from Saturn, but the tremendous influence of gravity from these gas giants has an appreciable effect on Ceres' orientation. In a new study, researchers from NASA's Dawn mission calculate that the axial tilt of Ceres -- the angle at which it spins as it journeys around the sun -- varies widely over the course of about 24,500 years. Astronomers consider this to be a surprisingly short period of time for such dramatic deviations.

Changes in axial tilt, or "obliquity," over the history of Ceres are related to the larger question of where frozen water can be found on Ceres' surface, scientists report in the journal Geophysical Research Letters. Given conditions on Ceres, ice would only be able to survive at extremely cold temperatures -- for example, in areas that never see the sun.

"We found a correlation between craters that stay in shadow at maximum obliquity, and bright deposits that are likely water ice," said Anton Ermakov, postdoctoral researcher at NASA's Jet Propulsion Laboratory, Pasadena, California, and lead author of the study. "Regions that never see sunlight over millions of years are more likely to have these deposits."

Cycles of Obliquity

Throughout the last 3 million years, Ceres has gone through cycles where its tilt ranges from about 2 degrees to about 20 degrees, calculations indicate.

"We cannot directly observe the changes in Ceres' orientation over time, so we used the Dawn spacecraft's measurements of shape and gravity to precisely reconstruct what turned out to be a dynamic history," said Erwan Mazarico, a co-author at NASA's Goddard Space Flight Center in Greenbelt, Maryland.

The last time the dwarf planet reached a maximum tilt, which was about 19 degrees, was 14,000 years ago, researchers said. For comparison, Earth is tilted 23.5 degrees. This significant tilt causes our planet to experience seasons: The northern hemisphere experiences summer when it is oriented toward the sun, and winter when it's pointed away from the sun. By contrast, Ceres' current tilt is about 4 degrees, so it will not have such strong seasonal effects over the course of a year there (which is about 4.6 Earth years).

How Obliquity Relates to Ice

When the axial tilt is small, relatively large regions on Ceres never receive direct sunlight, particularly at the poles. These persistently shadowed regions occupy an area of about 800 square miles (2,000 square kilometers). But when the obliquity increases, more of the craters in the polar regions receive direct exposure to the sun, and persistently shadowed areas only occupy 0.4 to 4 square miles (1 to 10 square kilometers). These areas on Ceres' surface, which stay in shadow even at high obliquity, may be cold enough to maintain surface ice, Dawn scientists said.

These craters with areas that stay in shadow over long periods of time are called "cold traps," because they are so cold and dark that volatiles -- substances easily vaporized -- that migrate into these areas can't escape, even over a billion years. A 2016 study by the Dawn team in Nature Astronomy found bright material in 10 of these craters, and data from Dawn's visible and infrared mapping spectrometer indicate that one of them contains ice.

The new study focused on polar craters and modeled how shadowing progresses as Ceres' axial tilt varies. In the northern hemisphere, only two persistently shadowed regions remain in shadow at the maximum 20-degree tilt. Both of these regions have bright deposits today. In the southern hemisphere, there are also two persistently shadowed regions at highest obliquity, and one of them clearly has a bright deposit.

Shadowed Regions in Context

Ceres is the third body in the solar system found to have permanently shadowed regions. Mercury and Earth's moon are the other two, and scientists believe they received their ice from impacting bodies. However, Mercury and the moon do not have such wide variability in their tilts because of the stabilizing gravitational influence of the sun and Earth, respectively. The origin of the ice in Ceres' cold traps is more mysterious -- it may come from Ceres itself, or may be delivered by impacts from asteroids and comets. Regardless, the presence of ice in cold traps could be related to a tenuous water atmosphere, which was detected by ESA's Herschel Space Observatory in 2012-13. Water molecules that leave the surface would fall back onto Ceres, with some landing in cold traps and accumulating there.

"The idea that ice could survive on Ceres for long periods of time is important as we continue to reconstruct the dwarf planet's geological history, including whether it has been giving off water vapor," said Carol Raymond, deputy principal investigator of the Dawn mission and study co-author, based at JPL.

Dawn's mission is managed by JPL for NASA's Science Mission Directorate in Washington. Dawn is a project of the directorate's Discovery Program, managed by NASA's Marshall Space Flight Center in Huntsville, Alabama. UCLA is responsible for overall Dawn mission science. Orbital ATK Inc., in Dulles, Virginia, designed and built the spacecraft. The German Aerospace Center, Max Planck Institute for Solar System Research, Italian Space Agency and Italian National Astrophysical Institute are international partners on the mission team. For a complete list of mission participants, visit:

http://dawn.jpl.nasa.gov/mission

More information about Dawn is available at the following sites:

http://dawn.jpl.nasa.gov

http://www.nasa.gov/dawn

https://www.jpl.nasa.gov/news/news.php?feature=6787

Offline Star One

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Re: NASA - Dawn updates and discussion
« Reply #1802 on: 04/08/2017 09:23 PM »
Ceres' Temporary Atmosphere Linked to Solar Activity

Scientists have long thought that Ceres may have a very weak, transient atmosphere, but mysteries lingered about its origin and why it's not always present. Now, researchers suggest that this temporary atmosphere appears to be related to the behavior of the sun, rather than Ceres' proximity to the sun. The study was conducted by scientists from NASA's Dawn mission and others who previously identified water vapor at Ceres using other observatories.

"We think the occurrence of Ceres' transient atmosphere is the product of solar activity," said Michaela Villarreal, lead author of the new study in the Astrophysical Journal Letters and researcher at the University of California, Los Angeles.

Ceres is the largest object in the asteroid belt that lies between Mars and Jupiter. When energetic particles from the sun hit exposed ice and ice near the surface of the dwarf planet, it transfers energy to the water molecules as they collide. This frees the water molecules from the ground, allowing them to escape and create a tenuous atmosphere that may last for a week or so.

"Our results also have implications for other airless, water-rich bodies of the solar system, including the polar regions of the moon and some asteroids," said Chris Russell, principal investigator of the Dawn mission, also at UCLA. "Atmospheric releases might be expected from their surfaces, too, when solar activity erupts."

Before Dawn arrived in orbit at Ceres in 2015, evidence for an atmosphere had been detected by some observatories at certain times, but not others, suggesting that it is a transient phenomenon. In 1991, the International Ultraviolet Explorer satellite detected hydroxyl emission from Ceres, but not in 1990. Then, in 2007, the European Southern Observatory's Very Large Telescope searched for a hydroxide emission, but came up empty. The European Space Agency's Herschel Space Observatory detected water in the possible weak atmosphere, or "exosphere," of Ceres on three occasions, but did not on a fourth attempt.

As Dawn began its thorough study of Ceres in March 2015, scientists found ample evidence for water in the form of ice. The spacecraft's gamma ray and neutron detector (GRaND) has found that the uppermost surface is rich in hydrogen, which is consistent with broad expanses of water ice. This ice is nearer to the surface at higher latitudes, where temperatures are lower, a 2016 study published in the journal Science found. Ice has been detected directly at the small bright crater called Oxo and in at least one of the craters that are persistently in shadow in the northern hemisphere. Other research has suggested that persistently shadowed craters are likely to harbor ice. Additionally, the shapes of craters and other features are consistent with significant water-ice content in the crust.

Because of this evidence for abundant ice, many scientists think that Ceres' exosphere is created in a process similar to what occurs on comets, even though they are much smaller. In that model, the closer Ceres gets to the sun, the more water vapor is released because of ice sublimating near or at the surface.

But the new study suggests comet-like behavior may not explain the mix of detections and non-detections of a weak atmosphere.

"Sublimation probably is present, but we don't think it's significant enough to produce the amount of exosphere that we're seeing," Villarreal said.

Villarreal and colleagues showed that past detections of the transient atmosphere coincided with higher concentrations of energetic protons from the sun. Non-detections coincided with lower concentrations of these particles. What's more, the best detections of Ceres' atmosphere did not occur at its closest approach to the sun. This suggests that solar activity, rather than Ceres' proximity to the sun, is a more important factor in generating an exosphere.

The research began with a 2016 Science study led by Chris Russell. The study, using GRaND data, suggested that, during a six-day period in 2015, Ceres had accelerated electrons from the solar wind to very high energies.

In its orbital path, Ceres is currently getting closer to the sun. But the sun is now in a particularly quiet period, expected to last for several more years. Since their results indicate Ceres' exosphere is related to solar activity, study authors are predicting that the dwarf planet will have little to no atmosphere for some time. However, they recommend that other observatories monitor Ceres for future emissions.

Dawn is now in its extended mission and studying Ceres in a highly elliptical orbit. Engineers are maneuvering the spacecraft to a different orbital plane so that Ceres can be viewed in a new geometry. The primary science objective is to measure cosmic rays to help determine which chemical elements lie near the surface of Ceres. As a bonus, in late April, the sun will be directly behind Dawn, when the spacecraft is at an altitude of about 12,300 miles (20,000 kilometers). Ceres will appear brighter than before in that configuration, and perhaps reveal more secrets about its composition and history.

The Dawn mission is managed by JPL for NASA's Science Mission Directorate in Washington. Dawn is a project of the directorate's Discovery Program, managed by NASA's Marshall Space Flight Center in Huntsville, Alabama. UCLA is responsible for overall Dawn mission science. Orbital ATK Inc., in Dulles, Virginia, designed and built the spacecraft. The German Aerospace Center, Max Planck Institute for Solar System Research, Italian Space Agency and Italian National Astrophysical Institute are international partners on the mission team. For a complete list of mission participants, visit:

http://dawn.jpl.nasa.gov/mission

More information about Dawn is available at the following sites:

http://www.nasa.gov/dawn

http://dawn.jpl.nasa.gov


News Media Contact

Elizabeth Landau
Jet Propulsion Laboratory, Pasadena, CA
818-354-6425
elizabeth.landau@jpl.nasa.gov

2017-097

https://www.jpl.nasa.gov/news/news.php?release=2017-098

Offline eeergo

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Re: NASA - Dawn updates and discussion
« Reply #1803 on: 04/26/2017 08:30 PM »
Third reaction wheel failure: https://solarsystem.nasa.gov/news/2017/04/26/dawn-observing-ceres-3rd-reaction-wheel-malfunctions . No important impact foreseen for now, although of course there is no redundancy left even in the custom hybrid (CMG/RCS) attitude control mode that's left.
-DaviD-

Offline vjkane

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Re: NASA - Dawn updates and discussion
« Reply #1804 on: 04/26/2017 08:49 PM »
Third reaction wheel failure: https://solarsystem.nasa.gov/news/2017/04/26/dawn-observing-ceres-3rd-reaction-wheel-malfunctions . No important impact foreseen for now, although of course there is no redundancy left even in the custom hybrid (CMG/RCS) attitude control mode that's left.
If you'll remember, the Dawn team proposed an extended mission to flyby a 3rd asteroid.  I believe that that mission was designed so it could be done only using the thrusters for attitude control.  Anyone know more?

Offline as58

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Re: NASA - Dawn updates and discussion
« Reply #1805 on: 04/26/2017 09:52 PM »
Third reaction wheel failure: https://solarsystem.nasa.gov/news/2017/04/26/dawn-observing-ceres-3rd-reaction-wheel-malfunctions . No important impact foreseen for now, although of course there is no redundancy left even in the custom hybrid (CMG/RCS) attitude control mode that's left.
If you'll remember, the Dawn team proposed an extended mission to flyby a 3rd asteroid.  I believe that that mission was designed so it could be done only using the thrusters for attitude control.  Anyone know more?

Yes, that was said in the senior review evaluation (https://solarsystem.nasa.gov/docs/PMSR2016_Report_Final.pdf)

page 3, 2nd paragraph: "...as wheels are not needed in this Adeona EM."

Offline Hungry4info3

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Re: NASA - Dawn updates and discussion
« Reply #1806 on: 04/26/2017 10:59 PM »
If you'll remember, the Dawn team proposed an extended mission to flyby a 3rd asteroid.  I believe that that mission was designed so it could be done only using the thrusters for attitude control.  Anyone know more?
I don't know about the attitude control plan for that hypothetical scenario, but I do know the 3rd asteroid visit was not chosen as the end-of-mission architecture for Dawn.

https://www.nasa.gov/feature/new-horizons-receives-mission-extension-to-kuiper-belt-dawn-to-remain-at-ceres/

Offline Star One

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NASA - Dawn updates and discussion
« Reply #1807 on: 05/17/2017 07:36 PM »
« Last Edit: 05/17/2017 07:43 PM by Star One »

Offline Star One

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Re: NASA - Dawn updates and discussion
« Reply #1808 on: 06/18/2017 06:41 PM »
Decision is the same as last time whether to keep it at Ceres or send it elsewhere.

Dawn mission managers await NASA decision on spacecraft’s future

https://spaceflightnow.com/2017/06/17/dawn-mission-managers-await-nasa-decision-on-spacecrafts-future/

Offline Star One

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Re: NASA - Dawn updates and discussion
« Reply #1809 on: 07/06/2017 04:48 PM »
NASA reviews options for Dawn extended mission

Quote
"NASA’s Planetary Science Division has received and is now reviewing a report from an independent science review panel with regard to Dawn’s completion of Level 1 science requirements at Ceres,” Cantillo told SpaceNews.

That review is required before NASA makes a decision on Dawn’s future. The spacecraft could remain in orbit around Ceres or “use its remaining fuel to travel to another asteroid,” she said.

Cantillo said that “points of clarification” about the report are currently being discussed are part of the overall science review of the mission. “Once completed, a decision will be made, most likely in the next 30–60 days,” she said. Spacecraft operations will continue during the review process.

A project scientist said last month that the mission was considering a flyby. “It’s an option,” Carol Raymond, deputy principal investigator for Dawn at the Jet Propulsion Laboratory, said at a June 13 meeting of NASA’s Small Bodies Assessment Group (SBAG). She said then that the mission was “in the process of discussing with NASA options for a second extended mission” but declined to give additional details about those options.

http://spacenews.com/nasa-reviews-options-for-dawn-extended-mission/

Offline vjkane

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Re: NASA - Dawn updates and discussion
« Reply #1810 on: 07/06/2017 05:48 PM »
NASA reviews options for Dawn extended mission

Quote
That review is required before NASA makes a decision on Dawn’s future. The spacecraft could remain in orbit around Ceres or “use its remaining fuel to travel to another asteroid,” she said.

A project scientist said last month that the mission was considering a flyby. “It’s an option,” Carol Raymond, deputy principal investigator for Dawn at the Jet Propulsion Laboratory, said at a June 13 meeting of NASA’s Small Bodies Assessment Group (SBAG). She said then that the mission was “in the process of discussing with NASA options for a second extended mission” but declined to give additional details about those options.

http://spacenews.com/nasa-reviews-options-for-dawn-extended-mission/
I don't know if the astrodynamics work out, but my favorite choice would be 2 Pallas.  It makes an ecliptic plane crossing sometime in the next few years as I recall.  Probably just wishful thinking, though.

Offline Blackstar

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Re: NASA - Dawn updates and discussion
« Reply #1811 on: 07/06/2017 05:57 PM »
NASA reviews options for Dawn extended mission

Quote
That review is required before NASA makes a decision on Dawn’s future. The spacecraft could remain in orbit around Ceres or “use its remaining fuel to travel to another asteroid,” she said.

A project scientist said last month that the mission was considering a flyby. “It’s an option,” Carol Raymond, deputy principal investigator for Dawn at the Jet Propulsion Laboratory, said at a June 13 meeting of NASA’s Small Bodies Assessment Group (SBAG). She said then that the mission was “in the process of discussing with NASA options for a second extended mission” but declined to give additional details about those options.

http://spacenews.com/nasa-reviews-options-for-dawn-extended-mission/
I don't know if the astrodynamics work out, but my favorite choice would be 2 Pallas.  It makes an ecliptic plane crossing sometime in the next few years as I recall.  Probably just wishful thinking, though.

Didn't their proposal last year require an immediate go decision in order to hit their preferred rendezvous? I bet what they can do depends upon the timing.

Offline redliox

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Re: NASA - Dawn updates and discussion
« Reply #1812 on: 07/06/2017 06:59 PM »
Didn't their proposal last year require an immediate go decision in order to hit their preferred rendezvous? I bet what they can do depends upon the timing.

Yeah I swore I heard about similar plans before.  Wasn't the ruling then that keeping Dawn in orbit was of better use than a flyby?  However, given Dawn's been at Ceres for a solid 2 years now (with Vesta just over a year for comparison) I wouldn't have any objection sending it off for a final flyby at a new target before ending the mission.

When I did a quick check via Wiki Pallas and Adeona were the previously suggested targets.  I'm curious if either remains viable although I presume a totally new target is one the menu.
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Offline Blackstar

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Re: NASA - Dawn updates and discussion
« Reply #1813 on: 07/06/2017 09:31 PM »
Yeah I swore I heard about similar plans before.  Wasn't the ruling then that keeping Dawn in orbit was of better use than a flyby?  However, given Dawn's been at Ceres for a solid 2 years now (with Vesta just over a year for comparison) I wouldn't have any objection sending it off for a final flyby at a new target before ending the mission.

Read the article, which mentions that there was concern about them achieving all their Level 1 science goals at Ceres. So they need to demonstrate that they have done that before they can argue that the spacecraft should go somewhere else. Can't have your pudding until you eat all your meat.

Offline vjkane

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Re: NASA - Dawn updates and discussion
« Reply #1814 on: 07/06/2017 10:24 PM »
Yeah I swore I heard about similar plans before.  Wasn't the ruling then that keeping Dawn in orbit was of better use than a flyby?  However, given Dawn's been at Ceres for a solid 2 years now (with Vesta just over a year for comparison) I wouldn't have any objection sending it off for a final flyby at a new target before ending the mission.

Read the article, which mentions that there was concern about them achieving all their Level 1 science goals at Ceres. So they need to demonstrate that they have done that before they can argue that the spacecraft should go somewhere else. Can't have your pudding until you eat all your meat.
I read the Senior Review report.  There top concerned seemed to be that the scientific case for visiting another asteroid instead of anally completing their mission goals at Ceres hadn't been made.  Presumably all those missions goals are done (at least those that don't burn through fuel too quickly).  Also presumably the Dawn team learned and has more time to prepare the science case for visiting another asteroid.

Offline Blackstar

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Re: NASA - Dawn updates and discussion
« Reply #1815 on: 07/07/2017 12:48 AM »
Yeah I swore I heard about similar plans before.  Wasn't the ruling then that keeping Dawn in orbit was of better use than a flyby?  However, given Dawn's been at Ceres for a solid 2 years now (with Vesta just over a year for comparison) I wouldn't have any objection sending it off for a final flyby at a new target before ending the mission.

Read the article, which mentions that there was concern about them achieving all their Level 1 science goals at Ceres. So they need to demonstrate that they have done that before they can argue that the spacecraft should go somewhere else. Can't have your pudding until you eat all your meat.
I read the Senior Review report.  There top concerned seemed to be that the scientific case for visiting another asteroid instead of anally completing their mission goals at Ceres hadn't been made.  Presumably all those missions goals are done (at least those that don't burn through fuel too quickly).  Also presumably the Dawn team learned and has more time to prepare the science case for visiting another asteroid.


So this brings up a question that I don't know enough about to understand: is it possible for a mission to not achieve its Level 1 goals but instead conduct even more important science? Has that ever happened?

I can sort of imagine how that could happen--a rover goes looking for geology stuff and instead finds life, so the mission gives up on the geology goals and just mucks around with the goo. But I wonder where adherence to Level 1 goals might actually not be the best science approach once a mission is underway.

Offline vjkane

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Re: NASA - Dawn updates and discussion
« Reply #1816 on: 07/07/2017 01:47 AM »
Yeah I swore I heard about similar plans before.  Wasn't the ruling then that keeping Dawn in orbit was of better use than a flyby?  However, given Dawn's been at Ceres for a solid 2 years now (with Vesta just over a year for comparison) I wouldn't have any objection sending it off for a final flyby at a new target before ending the mission.

Read the article, which mentions that there was concern about them achieving all their Level 1 science goals at Ceres. So they need to demonstrate that they have done that before they can argue that the spacecraft should go somewhere else. Can't have your pudding until you eat all your meat.
I read the Senior Review report.  There top concerned seemed to be that the scientific case for visiting another asteroid instead of anally completing their mission goals at Ceres hadn't been made.  Presumably all those missions goals are done (at least those that don't burn through fuel too quickly).  Also presumably the Dawn team learned and has more time to prepare the science case for visiting another asteroid.


So this brings up a question that I don't know enough about to understand: is it possible for a mission to not achieve its Level 1 goals but instead conduct even more important science? Has that ever happened?

I can sort of imagine how that could happen--a rover goes looking for geology stuff and instead finds life, so the mission gives up on the geology goals and just mucks around with the goo. But I wonder where adherence to Level 1 goals might actually not be the best science approach once a mission is underway.
I believe that Dawn long ago achieved its level 1 goals at Ceres.  The final extension refined measurements supporting those goals.

I believe that the Senior Review panel's logic was, the asteroid flyby wasn't defined well enough to be evaluated and given that, the mission should stay at Ceres.  The current review may be evaluating whether or not Dawn can do anything more useful at Ceres given that it has to remain in a distant orbit.  If the reaction wheels had remained healthy, I could see them going for a very low orbit for targeted imaging and higher resolution GRS measurements.

Offline JH

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Re: NASA - Dawn updates and discussion
« Reply #1817 on: 07/07/2017 01:47 AM »
So this brings up a question that I don't know enough about to understand: is it possible for a mission to not achieve its Level 1 goals but instead conduct even more important science? Has that ever happened?

Something close to that happened with Cassini. After the plumes were discovered at Enceladus, a number of flybys of other moons that had been planned were cancelled in order to make room for more of Enceladus. Of course, given subsequent extensions of the mission, anything that was axed because of this has been recovered.

Offline Nomadd

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Re: NASA - Dawn updates and discussion
« Reply #1818 on: 07/07/2017 03:23 AM »


So this brings up a question that I don't know enough about to understand: is it possible for a mission to not achieve its Level 1 goals but instead conduct even more important science? Has that ever happened?

I've read so many versions of the Voyager tale that I can't keep them straight, but didn't Voyager 2 have to give up some science at Saturn and Titan to take the road to Uranus and Neptune? Or doesn't that count because Voyager 1 took up the slack?
« Last Edit: 07/07/2017 03:23 AM by Nomadd »

Offline Req

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Re: NASA - Dawn updates and discussion
« Reply #1819 on: 07/07/2017 04:45 AM »


So this brings up a question that I don't know enough about to understand: is it possible for a mission to not achieve its Level 1 goals but instead conduct even more important science? Has that ever happened?

I've read so many versions of the Voyager tale that I can't keep them straight, but didn't Voyager 2 have to give up some science at Saturn and Titan to take the road to Uranus and Neptune? Or doesn't that count because Voyager 1 took up the slack?

Titan was considered such an important science goal that Voyager 1 was sent off the plane of the solar system never to encounter anything again to get a good Titan observation campaign.  It was a major let down, but that's how it goes sometimes.

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