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

[OmCheeto]

Several new things to report:

1. I was kind of bummed out, thinking that Marc Rayman was no longer doing his monthly journal, as it's now two weeks late, and I didn't remember it ever being late, so I sent him an email this morning. He kindly replied with basically the same message included in today's status report:

2016
July 13 - Extended Mission Proceeding Flawlessly

Dawn is being very productive in its extended mission. It has been taking more stereo photographs (including some in color) as well as measuring spectra of Ceres in visible, infrared, gamma rays and neutrons. The spacecraft is healthy and continuing in its orbit 240 miles (385 kilometers) above the alien surface.

For readers who follow the Dawn Journal, there has been a delay for personal reasons, but don't worry: the Dawn Journals will resume soon and will continue as long as Dawn continues its ambitious and exciting mission of exploration. There is much more to look forward to!​

2. JPL has announced that they will have a live show tomorrow:

NASA Jet Propulsion Laboratory
1 hr ago
To Boldly Go! Join us for a live-streamed public talk about the voyages of the NASA Dawn Mission to Vesta and Ceres in the Asteroid Belt. http://ustream.tv/NASAJPL2
July 14, 2016
7 p.m. PT
10 p.m. ET
0200 UTC​

3. It appears that there was more than one reason for staying in orbit around Ceres:

“The long-term monitoring of Ceres, particularly as it gets closer to perihelion — the part of its orbit with the shortest distance to the sun — has the potential to provide more significant science discoveries than a flyby of Adeona,” Mr. Green said in a statement. [ref]​

I never thought of that.

per wiki

Aphelion_: 445,410,000 km
Perihelion: 382,620,000 km​

That seems like a pretty significant difference.

per Dawn Journal, January 31, 2016

Ceres, which takes 4.6 years (one Cerean year) for each loop, attained its aphelion, or greatest distance from the sun, on Jan. 6. On that day, it was 2.98 AU (277 million miles, or 445 million kilometers) from the gravitational master of the solar system.​

So perihelion should be around April of 2018.
That would be pretty awesome if they could extend the mission that long.
Though, I think that would be a stretch.
On the other hand...

“Less than a year ago, I would have thought it was ridiculous that the spacecraft would even be operating at this point,” lead Dawn engineer Marc Rayman told the New York Times.​

And here's something I didn't know, and I find somewhat mind boggling:

One famously extendable mission has been the Mars rover Opportunity. Its primary mission was only three months long, yet it’s lasted for more than 12 years. Opportunity got another extension this time around.​

Wow.

 

[1oldman2]

Fantastic post! thanks. I particularly appreciate the heads up in item #2, got to see that, and I likely would have missed it without your post.
I hadn't thought about the possible advantages of observing Ceres and the changes as it gets in closer, might just get to study some interesting sublimation process or who knows what, but I'm glad Dawn is sticking around for the show.
I do follow what Opportunity is up to and noticed the "extension", these announcements always make me smile, I see they are considering extending the Juno science orbits if the radiation doesn't fry it first, my fingers are crossed on that one. I'm a firm believer in milking these missions for all the data we can.

 

[1oldman2]

Hi Om, A while back in this thread I mentioned reading and looking at illustrations of Ceres as a kid, thought I would show you a cover shot of the book in question.
(note the price)

 

[1oldman2]

Almost forgot !

 

[mfb]

Opportunity and all similar expensive missions get extended as long as the devices are working somewhat - would be a waste to shut them down. A rover that lasts for 50 times its design lifetime is still exceptional, of course.

 

[1oldman2]

from Chief Engineer/ Mission Director, Marc Rayman (JPL)

July 20 - Dawn Performing More Investigations of Ceres

"Since completing its last transmission of data on July 18, Dawn has been collecting
more data with all of its scientific instruments as it circles dwarf planet Ceres every 5.4
hours. It will send more data to Earth on July 21 and 22.

Dawn has been in orbit around Ceres for more than 500 days. During that time, it has
revealed complex and fascinating landscapes and provided scientists with a wealth of
information on the alien world."

 

[1oldman2]

And something new to ponder. http://www.nasa.gov/feature/jpl/the-case-of-the-missing-ceres-craters

 

[OmCheeto]

The new journal is out!

DAWN JOURNAL
July 27, 2016​

Still no hint as to a time frame for the end of the mission.
I wonder if the craft can operate just with the two remaining reaction wheels, as it sounds like the hydrazine is running low.
hmmm... If so, it could go on, for decades.

 

[1oldman2]

If so, it could go on, for decades.

Thats what mfb mentions in post #977, would be interesting.
From marc,
"the orbit will remain relatively stable for much longer than that,
perhaps even millennia. The ship will not make landfall."

 

[mfb]

It won't have xenon fuel forever, at some point it will enter the shadow of Ceres unless they find some very clever orbit that precesses at the right rate - similar to sun-synchronous orbits on Earth. And that is assuming the two reaction wheels continue working - but even then, they are not sufficient for three-axis control, so some hydrazine will be spent.

 

[1oldman2]

From, http://dawnblog.jpl.nasa.gov/2014/08/31/dawn-journal-august-31/#fate

"The best place for Dawn, should it be asked to continue its work, will be in
LAMO. And when the last puffs of hydrazine are expelled, it will no longer be
able to aim its instruments at the surface, any of its ion engines in the direction
required to maneuver, its antenna at Earth, or its solar arrays at the sun. The
battery will be depleted in a matter of hours. The spacecraft will remain in orbit
as surely as the moon remains in orbit around Earth, but it will cease
operating.

Leaving the remarkable craft in orbit around the distant colossus
will be a fitting and honorable conclusion to its historic journey
of discovery.

 

[OmCheeto]

I'm totally loving one of the last questions from Marc's last talk.

1:37:00-1:39:00

Some 4 year old; "Can't we just fill up the gas tank"? [paraphrased]
Marc; "Um... no. That's a long ways away, in both time and distance." [paraphrased]

 

[Dotini]

What the heck is that!

 

[mfb]

The mountain? It has sunshine a bit longer than the surrounding terrain.

Sun is from the left, the dark areas are higher on the left than on the right, the lit areas are higher on the right than on the left.

 

[Fervent Freyja]

What the heck is that!

Looks like a worm is sticking out it.

The mountain? It has sunshine a bit longer than the surrounding terrain.

Sun is from the left, the dark areas are higher on the left than on the right, the lit areas are higher on the right than on the left.

Jeez, how much caffeine have you had today? You are like a machine!

 

[1oldman2]

What the heck is that!

You know, I thought "why not blow it up and see" which I did, with the results below. One thing caught my eye was that in the original image is a feature that looked familiar, made me wonder if there is a common geological process.
First off this one,

but then we have ahuna-mons

Which very strongly resembles (although not in scale),

 

[1oldman2]

I might as well add these latest releases also.

 

[Fervent Freyja]

Which very strongly resembles (although not in scale),

Pardon me, can you elaborate further? What do you mean not in scale? Can you provide measurements for that?

Still looks like an old electron micrograph of a parasitic worm to me!

Why can't I edit my prior post?

 

[1oldman2]

What do you mean not in scale?

The best explanation (I know this may sound a little lame) is "scale" was a bad choice of terms to use, I meant to say the objects in images #2 and #3 were vary similar in shape but very different in size.

Can you provide measurements for that?

Well, not with any accuracy, although JPL undoubtedly has a a system. The best I could do would be to enlarge the image and count pixels. both images are at a scale where each pixel equals 120 feet so a rough sense of size could be inferred. My impression is that ahuna-mons in image #2 is much larger than the feature in image #3.

Still looks like an old electron micrograph of a parasitic worm to me!

I'm assuming everyone has been talking about the enlarged image #1, kind of reminds me of an alien octopus arm complete with suckers, however I've decided that its only a common "spaceworm". (actually mfb did a great job of describing the light/shadow interplay)

Why can't I edit my prior post?

That seems to be a time sensitive thing, I've noticed after a certain amount of time I'm unable to edit or add images also
.

 

[mfb]

Unless the picture is really weird, the right side is in the shadow due to the overall curvature of Ceres, which means the feature at the terminator is a crater, not a mountain.

 

[RonL]

A time factor yes, but also edit after a response can make the respondents post completely senseless in some cases.

 

[1oldman2]

Unless the picture is really weird, the right side is in the shadow due to the overall curvature of Ceres, which means the feature at the terminator is a crater, not a mountain.

This makes sense, I sometimes feel I'm staring at a Rorschach while trying to understand the topography.

 

[1oldman2]

- from Chief Engineer/ Mission Director, Marc Rayman (JPL)

"The operations team conducted the regular assessment of Dawn's orbit and determined
that it is so good, no orbit maintenance maneuvers (OMMs) are necessary. The last time
an OMM was performed was June 17. Instead of ion thrusting during the OMM windows
on July 31-August 1 and August 8, Dawn will continue acquiring data on Ceres.

The spacecraft began collecting data with all its sensors at this low altitude of 240 miles
(385 kilometers) on Dec. 16, 2015. Tomorrow Dawn will complete its one thousandth
revolution around the dwarf planet since then."

 

[1oldman2]

http://www.nasa.gov/feature/jpl/what-s-inside-ceres-new-findings-from-gravity-data:smile :

Ceres has a special property called "hydrostatic equilibrium," which was confirmed in this study. This means that
Ceres' interior is weak enough that its shape is governed by how it rotates. Scientists reached this conclusion by
comparing Ceres' gravity field to its shape. Ceres' hydrostatic equilibrium is one reason why astronomers classified
the body as a dwarf planet in 2006.

The data indicate that Ceres is "differentiated, which means that it has compositionally distinct layers at different
depths, with the densest layer at the core. Scientists also have found that, as they suspected, Ceres is much less
dense than Earth, the moon, giant asteroid Vesta (Dawn’s previous target) and other rocky bodies in our solar
system. Additionally, Ceres has long been suspected to contain low-density materials such as water ice, which the
study shows separated from the rocky material and rose to the outer layer along with other light materials.

 

[lpetrich]

Ceres's mean density is 2.161 g/cm^3 (Ceres (dwarf planet) - Wikipedia), halfway between water ice and rock.

Mountains and valleys represent departures from hydrostatic equilibrium. Their shape is preserved by the strength of their materials, and thus the maximum height of a mountain is determined by when a mountain's internal pressures are too great for its materials to hold their shape. The equation for the pressure at a mountain's base is, to a first approximation,
$$P = \rho g h$$
for pressure P, density ρ, acceleration of gravity g, and height h. So the weaker the gravity, the higher the possible mountains. Checking on List of tallest mountains in the Solar System - Wikipedia, Mauna Loa and Mauna Kea of Hawaii extend about 10.3 km above the ocean floor. They are largely made of basalt, which has a density of 2.9 g/cm^3 (Rock and Mineral Densities). That gives a pressure of 300 megapascals at its base, and that gets close to the yield strength of some metals (Yield (engineering) - Wikipedia).

One can scale the mountain heights to the Earth's gravity with this equation, and I've worked out the numbers.

• Mercury - 0.38 g - Caloris Montes - 3 km - 1.2 km
• Venus - 0.904 g - Skadi Mons - 6.4 km - 5.79 km
• Earth - 1 g - Mauna Loa, Mauna Kea - 10.3 km - 10.3 km
• Moon - 0.1654 g - Mons Huygens - 5.5 km - 0.91 km
• Mars - 0.376 g - Olympus Mons - 21.9 km - 8.23 km
• Vesta - 0.025 g - Rheasilvia central peak - 22 km - 0.55 km
• Ceres - 0.029 g - Ahuna Mons - 4 km - 0.1 km
• Io - 0.183 g - Boösaule Montes - 17.8 km - 3.26 km
• Mimas - 0.00648 g - Herschel central peak - 7 km - 0.05 km
• Dione - 0.0236 g - Janiculum Dorsa - 1.5 km - 0.035 km
• Titan - 0.138 g - Mithrim Montes - 3.3 km - 0.46 km
• Iapetus - 0.0237 g - equatorial ridge - 20 km - 0.5 km
• Oberon - 0.0353 g - unnamed limb mountain - 11 km - 0.4 km
• Pluto - 0.0632 g - Piccard Mons - 5.6 km - 0.35 km

Mars gets close to the Earth, and Venus also does respectably. But Ceres is very wimpy, even by the standards of icy dwarf planets and moons.

 

[mfb]

Yield strength at the base is not the critical point for mountains. What is the material going to do? This is not a skyscraper where the support structure is surrounded by weaker material and can buckle. Under a mountain the material simply gets more compressed. The failure modes are (a) material sliding down the hills and (b) the whole mountain side "rotating" (mountain down, surrounding terrain up). Here is a more detailed article.

The heights between different objects scale still scale with g, of course, the dimensions don't allow anything else.

 

[1oldman2]

- from Chief Engineer/ Mission Director, Marc Rayman (JPL)

August 3 - Dawn Conducting a Very Smooth Extended Mission
"Dawn is operating flawlessly as it continues its observations of Ceres. The
spacecraft is acquiring more stereo photos to improve the topographical
maps and more spectra to provide insights into the dwarf planet's
composition.

On July 30-31, Dawn aimed its five-foot (1.5-meter) main antenna at Earth
and sent its pictures and other data. The next telecommunications session
will begin shortly after 2:00 AM PDT on Aug. 4 and conclude more than 30
hours later."

 

[1oldman2]

- from Chief Engineer/ Mission Director, Marc Rayman (JPL)

August 10 - Dawn Completes Mapping at Another Stereo Angle

Dawn has completed another phase of its stereo imaging of Ceres,
providing more pictures to use in making a high resolution topographical
map. The spacecraft transmitted its latest pictures and other data to
NASA's Deep Space Network on Aug. 8-10.

For the rest of this month, the explorer will point its camera at a different
angle as it photographs the dwarf planet and uses its other sensors to
measure gamma ray, visible, infrared and neutron spectra.

 

[1oldman2]

- from Chief Engineer/ Mission Director, Marc Rayman (JPL)

August 10 - Dawn Completes Mapping at Another Stereo Angle

Dawn has completed another phase of its stereo imaging of Ceres,
providing more pictures to use in making a high resolution topographical
map. The spacecraft transmitted its latest pictures and other data to
NASA's Deep Space Network on Aug. 8-10.

For the rest of this month, the explorer will point its camera at a different
angle as it photographs the dwarf planet and uses its other sensors to
measure gamma ray, visible, infrared and neutron spectra.

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[1oldman2]

- from Chief Engineer/ Mission Director, Marc Rayman (JPL)

August 17 - Dawn Healthy and Performing Well

Dawn is collecting new Ceres data as it orbits the dwarf planet every 5.4 hours
at an altitude of 240 miles (385 kilometers).

On Aug. 13-14, the spacecraft sent a large volume of findings to Dawn mission
control at JPL. Later today it will again turn to point its main antenna at Earth to
begin another communications session that will last for more than 30 hours. On
Aug. 19, it will resume its measurements.

https://www.physicsforums.com/attachments/104865

https://www.physicsforums.com/attachments/104866

 

[1oldman2]

- from Chief Engineer/ Mission Director, Marc Rayman (JPL)

August 24 - Dawn Very Productive in Extended Mission

As Dawn continues its extended mission, it is using all of its scientific
instruments to study Ceres. The probe is scheduled to radio its most recent
pictures and other data to Earth from about 11:00 p.m. PDT on Aug. 26 until
shortly after 5:00 a.m. PDT on Aug. 28. It will then turn its sights back to Ceres.

The spacecraft has been carrying out all of its activities perfectly. Scientists have
received an extraordinary wealth of information about the dwarf planet, far
exceeding what they anticipated when Dawn descended to this fourth science
orbit more than eight months ago.

 

[OmCheeto]

Grand news, IMHO:

NEWS | AUGUST 31, 2016
Dawn Sets Course for Higher Orbit
...
On Sept. 2, Dawn will begin spiraling upward to about 910 miles (1,460 kilometers) from Ceres.
...

 

[OmCheeto]

And the new journal is out.

DAWN[/PLAIN] JOURNAL
August 31, 2016

Dear Sedawntary Readers,
...​

 

[1oldman2]

http://www.space.com/33934-dwarf-planet-ceres-ice-volcano-discoveries.html

Observations by NASA's Ceres-orbiting Dawn spacecraft indicate that "ice
volcanos" have erupted on the dwarf planet in the recent past and that Ceres'
crust is an odd ice-rock mixture that has never been observed before,
scientists reported in a series of six new studies published online today (Sept.
1) in the journal Science.

http://www.sciencemag.org/news/2016/09/ice-volcano-spotted-ceres-asteroid-belt-s-dwarf-planet

 

[1oldman2]

- from Chief Engineer/ Mission Director, Marc Rayman (JPL)

September 6 - Dawn Climbing to Higher Altitude

On schedule on Sept. 2, Dawn began firing its ion engine to raise its orbital
altitude. Its average height above the alien world today is 290 miles (465
kilometers). As the spacecraft moves higher, it orbits more slowly because
Ceres' gravitational hold weakens. In Dawn's low orbit at 240 miles (385
kilometers), each revolution took less than 5.5 hours. Today, Dawn takes more
than six hours to circle the dwarf planet.September 2 - Dawn Begins Maneuvering to Higher Altitude

Dawn radioed the last of its low altitude data to JPL this morning, marking the
conclusion of an outstandingly productive phase of its exploration at Ceres from
240 miles (385 kilometers) above the alien world. Then the spacecraft turned its
main antenna away from Earth on schedule to begin five weeks of maneuvering
to a higher orbit. (For details, see the August Dawn Journal.)

Dawn's ultraefficient ion engine will consume very little xenon propellant during
the upward spiral. The thrust is very gentle so progress will be gradual. By the
end of the day today, the probe will have moved to an orbit about 6 miles (10
kilometers) higher.

Also see, http://dawn.jpl.nasa.gov/news/news-detail.html?id=6611

A lonely 3-mile-high (5-kilometer-high) mountain on Ceres is likely volcanic in
origin, and the dwarf planet may have a weak, temporary atmosphere. These
are just two of many new insights about Ceres from NASA's Dawn mission
published this week in six papers in the journal Science.

A surprising finding emerged in the paper led by Russell: Dawn may have
detected a weak, temporary atmosphere. Dawn's gamma ray and neutron
(GRaND) detector observed evidence that Ceres had accelerated electrons from
the solar wind to very high energies over a period of about six days. In theory,
the interaction between the solar wind's energetic particles and atmospheric
molecules could explain the GRaND observations.