# I Dawn moving to low Ceres orbit, mission extended until hydrazine runs out

1. Jul 29, 2016

### RonL

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

2. Jul 29, 2016

### 1oldman2

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

3. Aug 1, 2016

### 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."

4. Aug 3, 2016

### 1oldman2

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

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.

Last edited by a moderator: May 8, 2017
5. Aug 6, 2016

### 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.

6. Aug 6, 2016

### Staff: Mentor

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.

7. Aug 8, 2016

### 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."

8. Aug 16, 2016

### 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.

9. Aug 16, 2016

### 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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10. Aug 19, 2016

### 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.

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11. Aug 27, 2016

### 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
exceeding what they anticipated when Dawn descended to this fourth science
orbit more than eight months ago.

12. Aug 31, 2016

### OmCheeto

Grand news, IMHO:

13. Sep 1, 2016

### OmCheeto

Last edited by a moderator: May 8, 2017
14. Sep 1, 2016

### 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

15. Sep 8, 2016

### 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.

16. Sep 27, 2016

### OmCheeto

Happy 9th anniversary!
An indication as to how near we are to the end of the journey; "The spacecraft has used 68 of the 71 gallons (256 of the 270 liters) of xenon it carried when it rode its rocket from Earth into space".

No word on hydrazine reserves.

Another statistic; "Since launch, ... Dawn has traveled ... 3.6 billion miles, or 5.8 billion kilometers".

Which means that Dawn gets about 53,000,000 mpg. (22,700,000 km/liter)

17. Oct 16, 2016

### 1oldman2

Three gallons left, wonder what that will be worth in mission time ?

- from Chief Engineer/ Mission Director, Marc Rayman (JPL)
October 12 - Dawn Team Preparing for New Ceres Observations

Orbiting Ceres at an altitude of about 920 miles (1,480 kilometers), Dawn is traveling over the alien landscapes at about 400 mph (645 kilometers per hour). After ion thrusting concluded last week, navigators measured the parameters of the orbit very accurately. The actual orbit is so close to the planned orbit that the expected refinements in the timing of observations are unnecessary. To optimize the quality of the data to be collected, engineers are making small adjustments to the direction the spacecraft will point its sensors for some of the measurements. Science observations will begin on Oct. 16

October 6 - Dawn Completes Ascent Spiral

Dawn concluded its ascent on schedule last night by stopping its ion engine at 11:02:48 p.m. PDT. When it began the spiral climb on Sept. 2, the spacecraft was in a 5.4-hour orbit at an altitude of 240 miles (385 kilometers). Now it is in an 18.9-hour orbit about 920 miles (1,480 kilometers) above Ceres. Navigators will measure its orbital parameters carefully to pin down the details. Mission controllers will use the results to refine the timing of Dawn's new observations of the dwarf planet, which are scheduled to begin on Oct. 16.

Nine years ago today, Dawn thrust with its remarkable ion propulsion in space for the first time. As explained in the latest Dawn Journal, the explorer has used its ion engines extensively in the intervening nine years to accomplish extraordinary feats in its interplanetary expedition.

18. Oct 16, 2016

### OmCheeto

Well, they claim that when the mission ends, Dawn will be in a permanent stable orbit around Ceres. Which I think implies that they don't really need it anymore. Which I think implies, that they can continue the mission until another reaction wheel fails, and the hydrazine runs out. Of course there's also the problem of Dawn entering Ceres shadow, which, without knowing it's current orbital inclination relative to the sun, I can't even make a guess as to when that will occur. Perhaps I'll go back through the last log and see if I missed that bit of information.

19. Oct 16, 2016

### OmCheeto

Marc only mentions; "...The angle to the sun will be smaller...", in the Aug 31 journal entry.

One day, I will kill him.
But then again, he has slipped us some very top secret information about the mission in the past.
Perhaps not.

20. Oct 16, 2016

### 1oldman2

It would be like sacrificing the queen in a close chess game.

21. Oct 23, 2016

### OmCheeto

22. Oct 31, 2016

### OmCheeto

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:

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!

23. Nov 1, 2016

### Staff: Mentor

That diagram indicates that shadow won't be an issue for the next months.

24. Nov 18, 2016

### OmCheeto

And finally, we've been given an indication where Dawn will be placed, but not the angle......
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.

Last edited: Nov 18, 2016
25. Nov 28, 2016

### OmCheeto

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)