I Dawn dead in Ceres orbit, ran out of fuel Oct 2018

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The Dawn spacecraft successfully observed Ceres from a distance of 238,000 miles on January 13, 2015, capturing over half of its surface at a resolution of 27 pixels. The mission aimed to enter a polar orbit around Ceres, with a planned descent to an altitude of 375 km, but faced challenges due to limited hydrazine propellant for attitude control. A cosmic ray event in September 2014 had previously disrupted the propulsion system, complicating the approach trajectory. Despite these issues, the spacecraft was expected to achieve a stable orbit around Ceres, ultimately becoming a "perpetual satellite" as it ran out of fuel. The mission's success would provide valuable data on Ceres' physical characteristics and surface mapping.
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  • #1,022
The new journal is out!

DAWN JOURNAL
October 31, 2016

Some interesting things:

The relative size and angle of the 5 orbits, as they would have appeared if looking down at the north pole:
5_orbits_crop.jpg


The following paragraph had me gasp:

This fifth Ceres campaign was intricate and intensive, but it stayed right on the tight schedule. Dawn began collecting data as planned on Oct. 16 and finished transmitting its findings to Earth on Oct. 29. And it was exceedingly productive, yielding almost 3,000 photographs plus a great many infrared spectra and visible spectra containing a wealth of new information about Ceres.
[bolding mine]
​
This could mean one of two things:
1. The mission is over, or
2. Something else is about to happen​

Fortunately; "On Nov. 4, the spaceship will once again power on ion engine #2 and start another spiral to a sixth orbital observing post."

Yay! :smile:
 
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  • #1,023
That diagram indicates that shadow won't be an issue for the next months.
 
  • #1,024
mfb said:
That diagram indicates that shadow won't be an issue for the next months.
And finally, we've been given an indication where Dawn will be placed, but not the angle... :oldgrumpy:
New Ceres Views as Dawn Moves Higher
"On Nov. 4, Dawn began making its way to a sixth science orbit, which will be over 4,500 miles (7,200 kilometers) from Ceres.
...
Dawn should reach this next orbit in early December.
One goal of Dawn's sixth science orbit is to refine previously collected measurements. The spacecraft 's gamma ray and neutron spectrometer, which has been investigating the composition of Ceres' surface, will characterize the radiation from cosmic rays unrelated to Ceres. This will allow scientists to subtract "noise" from measurements of Ceres, making the information more precise.

The spacecraft is healthy..."​
ps. I've been channeling the spirit of Marcus all morning. :angel:
 
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  • #1,025
The new journal is out!

DAWN JOURNAL
November 28, 2016

It appears that Dawn is being placed in an elliptical orbit, far away from Ceres, to gather background radiation noise, in order to reduce the signal to noise ratio for their ground radiation survey.

Here's a graph I doodled to show its new relative distance. (Orbit 6)

2018.11.28.dawn.over.ceres.png
 
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  • #1,026
You cannot reduce the signal to noise ratio of previous measurements, you can only hope to understand the noise better.

Staying closer would have allowed to see the terminator region under a better angle, possibly improving the 3D mapping a bit. Measuring that background must be really important - but not so important that they would have done the measurements in earlier, higher orbits.
 
  • #1,027
You know... I used to look at Marcus's avatar and think of Mad magazine, I recently came across an old copy and immediately Marcus came to mind, all I could say was "what me worry ?"
https://www.nasa.gov/feature/jpl/where-is-the-ice-on-ceres-new-nasa-dawn-findings

At first glance, Ceres, the largest body in the main asteroid belt, may not look icy. Images from NASA's Dawn spacecraft have revealed a dark, heavily cratered world whose brightest area is made of highly reflective salts -- not ice. But newly published studies from Dawn scientists show two distinct lines of evidence for ice at or near the surface of the dwarf planet. Researchers are presenting these findings at the 2016 American Geophysical Union meeting in San Francisco.

"These studies support the idea that ice separated from rock early in Ceres’ history, forming an ice-rich crustal layer, and that ice has remained near the surface over the history of the solar system," said Carol Raymond, deputy principal investigator of the Dawn mission, based at NASA's Jet Propulsion Laboratory, Pasadena, California.
 
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  • #1,029
Happy 2nd year anniversary of this thread!

:smile:
 
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http://news.agu.org/press-release/new-research-shows-ceres-may-have-vanishing-ice-volcanoes/
WASHINGTON, DC - A recently discovered solitary ice volcano on the dwarf planet Ceres may have some hidden older siblings, say scientists who have tested a likely way such mountains of icy rock - called cryovolcanoes - might disappear over millions of years.

"We think we have a very good case that there have been lots of cryovolcanoes on Ceres but they have deformed," said Michael Sori of the Lunar and Planetary Laboratory at the University of Arizona in Tucson, and lead author of the new paper.

Ahuna Mons is a prominent feature on Ceres, rising to about half the height of Mount Everest. Its solitary existence has puzzled scientists since they spied it.
 
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  • #1,032
From the January journal:
Dawn has already measured the light reflected over a wide range of angles, as is clear from the figure above showing the orbits. But the strongest discrimination among different textures relies on measuring the opposition surge. That is Dawn’s next objective, a bonus in the bonus extended mission.
That requires a plane change by nearly 90 degrees. Initially the fixed orbital plane was though to be a hard limit on the mission lifetime. With the high orbit Dawn now has, a plane change is possible. The high orbit also makes it easier to avoid the shadow while getting close to opposition.
 
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https://phys.org/news/2017-02-scien...e=menu&utm_medium=link&utm_campaign=item-menu
http://www.sciencedirect.com/science/article/pii/S001910351630731X
http://www.jpl.nasa.gov/spaceimages/details.php?id=PIA21419
This enhanced color composite image, made with data from the framing camera aboard NASA's Dawn spacecraft , shows the area around Ernutet crater. The bright red portions appear redder with respect to the rest of Ceres. In a 2017 study in the journal Science, researchers from the Dawn science team found that these red areas around Ernutet are associated with evidence of organic material.

:smile:
 
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mfb said:
Dawn Identifies Age of Ceres' Brightest Area

The bright material in the center of Occator Crater is about 4 million years old, 30 million years younger than the crater.

And from the Max Planck piece they referenced:

"Pictures of the crater showing haze when imaged at certain angles seem to speak for the latter. At the end of 2015 already, MPS researchers explained this phenomenon with the sublimation of water.

Recent investigations support this interpretation. The MPS researchers evaluated numerous images of Occator crater from an early phase of the mission taken from a distance of 14,000 kilometers and from low angles. They clearly show variations in brightness following a diurnal rhythm. “The nature of the light scattering at the bottom of Occator differs fundamentally from that at other parts of the Ceres surface," MPS researcher Guneshwar Singh Thangjam describes the result of his analysis. "The most likely explanation is that near the crater floor an optically thin, semi-transparent haze is formed," he adds. The researchers believe that the haze is possibly formed by sublimating water emerging from fractures in the floor of the crater when exposed to sunlight."​

I wonder if this haze has a warming effect. Occator crater is 4 km deep.
[google google google]

Ah ha!

Andrew Dessler and colleagues from Texas A&M University in College Station confirmed that the heat-amplifying effect of water vapor is potent enough to double the climate warming caused by increased levels of carbon dioxide in the atmosphere. [ref: NASA]​

I'll take that as a definite maybe.
 
  • #1,038
OmCheeto said:
Andrew Dessler and colleagues from Texas A&M University in College Station confirmed that the heat-amplifying effect of water vapor is potent enough to double the climate warming caused by increased levels of carbon dioxide in the atmosphere. [ref: NASA]
That is the atmosphere on Earth.
Ceres doesn't have a notable atmosphere.
 
  • #1,039
mfb said:
That is the atmosphere on Earth.
Ceres doesn't have a notable atmosphere.
Perhaps I should refrain from posting things so soon after waking up in the morning.
After scratching my head for a bit, a couple cups of coffee, and massive googling*, I can find no evidence that the crater is thermally different from its surroundings.

-------------
*Also, reading about the electromagnetic absorption by water, made my head hurt.
 
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  • #1,040
OmCheeto said:
I'll take that as a definite maybe.
OmCheeto said:
Perhaps I should refrain from posting things so soon after waking up in the morning.
After scratching my head for a bit, a couple cups of coffee, and massive googling*, I can find no evidence that the crater is thermally different from its surroundings.

-------------
*Also, reading about the electromagnetic absorption by water, made my head hurt.
More coffee is the answer. (unless the answer is 42)
I believe the process of sublimation will lower the temperature, (citation needed) https://en.wikipedia.org/wiki/Enthalpy_of_sublimation
 
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1oldman2 said:
More coffee is the answer. (unless the answer is 42)
I believe the process of sublimation will lower the temperature, (citation needed) https://en.wikipedia.org/wiki/Enthalpy_of_sublimation
I believe you. No citation required from me.

ps. Peculiar thing though, in my googlings this morning, I couldn't find any recent data on Ceres surface temperatures.
Wiki's latest entry on the highest temperature is from 1993. [ref]
I'm not saying the data hasn't been published, but I can't seem to find it.
Pondering now if I should send Marc Rayman another email. It has been 8 months.
 
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  • #1,042
1oldman2 said:
I believe the process of sublimation will lower the temperature, (citation needed) https://en.wikipedia.org/wiki/Enthalpy_of_sublimation
Completely negligible. Using all the sunlight to sublimate ice, it would go through the surface at a rate of 2.5 meters per year - or 10,000 km in 4 million years. The actual change seems to be lower than 1 km in 4 million years.
 
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  • #1,043
OmCheeto said:
I believe you. No citation required from me.

ps. Peculiar thing though, in my googlings this morning, I couldn't find any recent data on Ceres surface temperatures.
Wiki's latest entry on the highest temperature is from 1993. [ref]
I'm not saying the data hasn't been published, but I can't seem to find it.
Pondering now if I should send Marc Rayman another email. It has been 8 months.
I did some looking around and came up with this info, nothing newer than 2015 but it's probably in the 'ol ballpark. :smile:
(Sort of almost relative) http://www.nature.com/nature/journal/v528/n7581/full/nature15754.html

An excerpt from http://www.hou.usra.edu/meetings/lpsc2015/pdf/1745.pdf
(this is rather early in the Ceres phase of Dawns mission so I imagine there is better data to be had at this time.)
"In the 4.5-5.1 μm range,
NESR is dominated by fluctuations of the thermal
emission from the spectrometer, which result in a lowest
measurable temperature of ~170 K, i.e. no temperature
below this threshold can be accurately retrieved by
VIR. This means that VIR cannot measure temperatures
on the nightside of Ceres, as well as in the northern
polar region that will undergo permanent shadowing
conditions throughout Dawn's nominal orbital mission phases."

Ahh... Here we go, not sure of this sites reputation but it appears believable.
https://www.reference.com/science/temperature-ceres-d1b17887e9678a2d#
The quick answer says,
The surface temperature of Ceres averages 130 to 200 degrees Kelvin.

Then there's this, https://www.princeton.edu/~willman/planetary_systems/Sol/Ceres/
It lists a surface temperature of roughly -100 degrees C.
 
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  • #1,047
May Journal is out. :thumbup:
https://dawn.jpl.nasa.gov/mission/journal_05_24_17.html
"On the other side of the solar system, invisible by virtue both of the blinding glare of the sun and by the vastness of the distance, Dawn is continuing its remarkable cosmic adventure. Orbiting high above dwarf planet Ceres, the spacecraft is healthy and performing all of its assignments successfully even when confronted with what appears to be adversity."
 
  • #1,049
Dawn's extended mission will end June 30. The future is currently discussed.

One of the options discussed: Send it to another asteroid. It was discussed earlier already, but then scientists decided to study Ceres more. Now the idea comes up again. Dawn is in a high orbit already, it wouldn't take too much delta_v to escape and to change the orbit a bit. Firing the ion thrusters also saves hydrazine.
 
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  • #1,050
mfb said:
The future is currently discussed.
A very interesting article, thanks. I can't imagine not squeezing every bit of usefulness from Dawn, shutting it down would be a loss of resources that would be hard to justify. I'm betting they choose a flyby mission to another Asteroid rather than burn the remaining fuel at Ceres, although there seems to be a fair supply remaining the rate of consumption is far lower when not maintaining its current orbit compared to interplanetary travel. Curious to see what NASA decides to do with the program.
 
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