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

[marcus]

Emily Lakdawalla commented on the 6 July status report (quoted in full two posts back)
=== http://www.planetary.org/blogs/emily-lakdawalla/2015/07091718-updates-dawn-osiris-rex-juno.html ===
The wording of this statement is a little bit ambiguous, because Dawn has already lost the use of two of its four reaction wheels, and as a result there is not one but actually two systems that work together to control its orientation: the two remaining reaction wheels and its hydrazine attitude control thrusters. So either there is a problem with one of the remaining reaction wheels (which wouldn't be too surprising at this point, nor does it jeopardize the completion of the mission, but it would be an inconvenience) or there is a problem with its thrusters (which would be much worse news). The fact that it is out of safe mode and "using the main antenna to communicate with Earth" means that they do have three-axis control of the spacecraft , which makes me inclined to think that it's another reaction wheel problem. Dawn is fully capable of completing its science mission at Ceres using only thrusters to control its orientation in space, so if this is a serious reaction wheel problem and not just a brief glitch, the mission will be just fine.
==endquote==

 

[OmCheeto]

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

July 13, 2015 - Dawn Healthy as it Orbits Ceres

Dawn remains healthy and functioning normally in its second mapping orbit at Ceres. Engineers are continuing their investigation into the anomaly that caused a discrepancy in the orientation on June 30.

When I went to check the DSN about 10 minutes , Canberra 34 & 35 were in standby mode with Dawn, just a moment later, Dawn started transmitting to #35.

hmmmm... Perhaps this is a sneaky way of JPL to get us to pay some attention to Pluto.

[edit] ps. No top secret information from the Top Ramen on the matter.

 

[marcus]

Now we know that the anomaly was with the orientation (hydrazine jets, reaction wheels, and their control) and not with propulsion.
Emily L was speculating that it could be with one or the other and trouble in the propulsion department would be more serious.
Thanks for relaying this word from the Top Ramen.

I think the long delay in restarting the attempt to spiral down to lower orbit may actually have to do with Pluto and DSN priorities. Just a guess.
Ceres and Pluto are in the same sector of the sky, so in case of emergencies the two missions would be competing for the same antennas.

It could make sense for Dawn team to have delayed until after Pluto flyby so that IF Dawn made a try to start spiraling down, and encountered another anomaly in the orientation it would be able to get an antenna assigned to it immediately and start recovery.

 

[Dotini]

The Dawn team seem to be slowly coming around to the bright spot salt explanation mentioned long ago by marcus.

http://www.washingtonpost.com/news/...te-spots-on-ceres-might-not-be-ice-after-all/
According to Christopher Russell of the University of California at Los Angeles, the Dawn mission's principal investigator, the team is "shying away from there being ice on the surface."

"The general consensus on the team right now is that water is definitely a factor on Ceres, but that the spots themselves are more likely to be just highly reflective salt, rather than water," Russell told The Post.

 

[marcus]

Judging from simview, they fixed the problem.

 

[marcus]

Turns out that announcement may have been premature! Today the Top Ramen reported that they are conducting a test to make sure the probe is ready to start the next descent. The "test" may have actually been to try a brief descent, with the thruster on, and see how things went.
http://dawn.jpl.nasa.gov/mission/status_2015.html
But I reckon it's approximately right in any case. Dawn may indeed have already started spiraling down
Simview for 4PM pacific on 15 July shows the altitude at 4.22 kkm down from 4.4 and over the past months simview has turned out to be a reasonably good approximation of reality.

 

[marcus]

Simview now shows thruster off, and DSN shows two Madrid antennas #65 and #54 devoted to Dawn, one in two way communication and the other in standby.
I think this is what constituted the TEST referred to in status report. Namely run the thruster for a day or two and then get a fix on the probe and check out how everything went.

Simview shows the altitude already diminished from 4400 to just under 4400. If that checks out and everything has behaved normally, it's good news.

 

[marcus]

Simview now shows thruster on (as of 6 am Pacific 17 July) and DSN shows no talk with Dawn.
I infer that they made the test---tried thrusting for a day or so, then shut off propulsion for something like 12 hours while they made sure everything checked out.
And I guess as a result the craft was declared OK, so they have now turned back on ion propulsion and resumed descent.

It's possible they changed which ion engine is being used. IIRC there are 3 units.

Simview gives the altitude as 3910 km now (down from 4400) and the speed as 269 mph

 

[marcus]

in fact they did switch to another ion engine
==quote http://dawn.jpl.nasa.gov/mission/status.html ==

July 17, 2015 - Dawn Maneuvering to Third Science Orbit

NASA's Dawn spacecraft is using its ion propulsion system to descend to its third mapping orbit at Ceres, and all systems are operating well. The spiral maneuvering over the next five weeks will take the spacecraft to an altitude of ...(less than 1,500 kilometers) above the dwarf planet.

The spacecraft experienced a discrepancy in its expected orientation on June 30, triggering a safe mode. Engineers traced this anomaly to the mechanical gimbal system that swivels ion engine #3 to help control the spacecraft 's orientation during ion-thrusting. Dawn has three ion engines and uses only one at a time.

Dawn's engineering team switched to ion engine #2, which is mounted on a different gimbal, and conducted tests with it from July 14 to 16. They have confirmed that the spacecraft is ready to continue with the exploration of Ceres.

By the end of the day on July 17, Dawn will have descended to an altitude of about ... (3,900 kilometers). After arrival at its next mapping orbit -- called the High-Altitude Mapping Orbit, or HAMO -- in August, Dawn will begin taking images and other data at unprecedented resolution.
==endquote==

 

[marcus]

The simview has proven reasonably reliable and it gets regularly updated. It says Dawn's altitude is now 3200 km.
Dawn started descending from the second orbit (altitude 4400 km) on 30 June, but there was that glitch. Apparently some problem with the gimbal mounting of ion engine #3 which it was using. So they stayed in orbit at altitude 4400 km for a couple of weeks while they changed over to ion engine #2 and tested that out, and reprogrammed everything.

Then around 15 July they started descent again and already have made quite a lot of progress. Of course the probe speeds up as it goes lower. I forget what the orbital speed at the 3rd orbit (altitude 1450 km) will be. Simview gives the current speed as 0.13 km/s. This is as of 10AM pacific on 21 July.

For some reason they give the speed in higher precision in mph---currently 293 mph

 

[marcus]

Official status report:
==quote==
July 20, 2015 - Dawn's Spiral Descent Continuing Smoothly

Dawn is continuing to lower its orbital altitude. Today the spacecraft will descend from ... (3,500 kilometers) to ... (3,400 kilometers).

In its previous mapping orbit, the explorer was 2,700 miles (4,400 kilometers) above the alien world. When it completes its spiral to the third orbit, it will be about 900 miles (less than 1,500 kilometers) high.
==endquote==
Official: http://dawn.jpl.nasa.gov/mission/status.html
Unofficial: http://neo.jpl.nasa.gov/orbits/fullview2.jpg

 

[OmCheeto]

Regarding the "bright spots" crater:

Dawn at Ceres: A haze in Occator crater?
Posted by Andrew Rivkin
2015/07/21 22:54 UTC
...
Russell said that a “haze” was visible in this crater at certain times of day, and that it was seen more than once. A follow-up question, the only one there was time for, established that the haze was confined to the crater itself.
...

Apparently they've named some of the craters.

 

[marcus]

Interesting about that haze in the crater! Another status update came out today.
==quote http://dawn.jpl.nasa.gov/mission/status.html ==

July 22, 2015 - Dawn, Ceres and Earth Closest To Each Other

As Ceres (with its new permanent resident, Dawn) and Earth follow their own independent orbits around the sun, today they are at their closest since June 2014. The dwarf planet and Dawn today are 180 million miles (290 million kilometers) from our home. (For more details and a diagram, see the June Dawn Journal.)

Meanwhile, Dawn is continuing to thrust with its ion propulsion system to shrink its orbit. Today it will descend from ...3,200 kilometers to ...3,100 kilometers.
==endquote==
Simview agrees reasonably well with official update. It says as of 8pm pacific on 22 July the altitude is 3.06 kkm or about 3060 km. Fairly close to the official 3100.

Official: http://dawn.jpl.nasa.gov/mission/status.html
Unofficial: http://neo.jpl.nasa.gov/orbits/fullview2.jpg

So Ceres is on the meridian (the sky centerline) at midnight, now. that means that prime DSN antenna time is 9pm to 3am or thereabouts. Maybe anything from 7pm to 5am local time, Ceres would be in the sky and the antenna could make contact .

 

[marcus]

New update today!
==quote==
July 23, 2015 - Dawn Maneuvering to Lower Orbit

As Dawn maneuvers closer to Ceres, today it is reducing its altitude from ... 3,100 kilometers to ... 2,900 kilometers.

In lower orbits, the spacecraft circles Ceres more quickly, not only because the distance around the orbit is shorter but also because it travels faster in the dwarf planet's tighter gravitational grip. (For more on this, see this Dawn Journal explanation.) In the previous mapping orbit ... 4,400 kilometers, it took slightly more than three days to complete one revolution. Now the orbital period is a little less than two days. When Dawn is in its next mapping orbit at... less than 1,500 kilometers, each loop will take about 19 hours.
==endquote==
http://dawn.jpl.nasa.gov/mission/status.html
http://neo.jpl.nasa.gov/orbits/fullview2.jpg

Simview as of 12:20 PM pacific 23 July give the altitude as 2920 km and the speed as 0.14 km/s.

 

[marcus]

The Wikipedia on Ceres has been updated from [6] Marc Rayman's Dawn Journal of May 2015 to give latest figures on the mass, radius etc.
Mean radius
469 km
Equatorial radius
481.5 km[6]
Polar radius
445.5 km[6]
Mass
9.39×10²⁰ kg[6]
So let's calculate the orbit period at radius of 1450+470 = 1920 km
When I put in for circular orbit speed at that radius I get 180 m/s
and when I put in the circumference divided by that speed
2pi*1920 km/(G*9.39e20 kg/1920 km)^(1/2)
I get 18.55 hours.
So that agrees with what Marc Rayman says namely 19 hours for the period of the next orbit.

Just to see what the current orbit period would be, if it were circular, I put in
2pi*3470 km/(G*9.39e20 kg/3470 km)^(1/2)
and got 1.9 days
That would be for an altitude of 3000 and a radius of 470km. It agrees with today's status update (in the preceding post#540) which says "a little less than 2 days"
https://www.physicsforums.com/threa...-to-1450-km-orbit.793140/page-27#post-5177268

 

[marcus]

Marc Rayman's Dawn update says altitude 2900 km by the end of the day 23 July (see post #540 for additional info)
2900+470=3370
Because of ellipticity the descent trajectory doesn't stay radius ≤ 3370 km at first. It still has to settle down and circularize. But just for practice I'll calculate the orbit period for circular at radius 3370 km.

2pi*((3370 km)^3/(G*9.39e20 kg))^(1/2)

The googly calculator says 1.8 days.

 

[marcus]

Dawn down around altitude 2600 km now. Here's simview as of late Sunday 26 July
http://neo.jpl.nasa.gov/orbits/fullview2.jpg

It's about time for a new Dawn Journal to appear, they tend to come out around the end of the month:
http://dawn.jpl.nasa.gov/mission/journal.asp
That should give a revised schedule for when the probe will arrive at third science orbit (altitude 1450 km) and when it will start descent to the fourth and lowest orbit.

We might also get a status update soon. The last one was 23 July.
http://dawn.jpl.nasa.gov/mission/status.html

I'll bring the old schedule forward for eventual comparison. The 30 June glitch (possibly together with some other considerations) caused a two week delay.

Orbit    dates      altitude(km)  pixelsize(m) res/HST  period  soccerball at
RC3    April 23–May 9    (13,500)    (1,300)    24     15 days    (3.0 meters)
Survey    June 6-30      (4,400)      (410)     72     3.1 days    (1.0 meters)
HAMO    Aug 4–Oct 15     (1,450)      (140)     215    19 hours    (33 cm)
LAMO Dec 8–end of mission  (375)      (35)      850    5.5 hours    (8.5 cm)

 

[marcus]

There was a brief status update yesterday, noting that the spacecraft was down to 2600 km altitude. (agreeing with simview for yesterday)
==quote==
July 27, 2015 - Dawn Orbiting Closer to Ceres

Today the spacecraft is orbiting ...2,600 kilometers above the ground. As with all of Dawn's complex maneuvers from each mapping orbit to the next, the spacecraft is not taking a perfect spiral path for technical reasons. The altitude does not change as much over the course of the day today as it does some other days. Nevertheless, the probe is accurately following its carefully designed course.
==endquote==
Today, 28 July, according to simview she seems to be down to 2500 km. So as a rough estimate there is about 1000 km of descent left to go and it's progressing down at the rate of 100 km per day, roughly speaking.

It's harder to descend the closer in one gets---more momentum has to be blown off by the ion engine, with each step. So as a crude guess I'll estimate two weeks to close in the rest of the way. Dawn might be settled in at the 1450 km orbit by 14 August.

In any case I hope very much we get a Journal entry from the mission director by Friday---the journal has been coming out monthly around the end of each month.

When you think about it, it's actually pretty fantastic that the spacecraft (now in its eighth year) is still functioning. Two of the four reaction wheels are worn out. Either one or two of the three alternate ion engines are no longer usable, it has been hit and temporarily stunned by high energy cosmic ray particles on several occasions, extraordinary measures are being taken to conserve hydrazine (used for attitude control) and it still has a lot of hard work ahead of it.

Om, mfb, and others please correct me here if I'm off on any of these details.

 

[marcus]

Recent (27 July) space.com article about Ceres
http://www.space.com/30054-dwarf-planet-ceres-bright-spots-atmosphere.html
new figure for equatorial radius 481 km.
haze seen over bright spots suggests they are ice, actively subliming, rather than dry salt residue.

Large areas where craters seem partially erased suggest geological activity

Color-coded topographic map (brown and red are high, up to +6 km, purple and deep blue are low, to -6km below surface average level) projected on a sphere in this animation:

The YouTube has no sound track but there is some annoying crosstalk from something else so I turn the sound off while watching. It takes only about one minute to view.

Current simview says altitude 2420 km (11:56 PM UTC = 4 PM pacific) and speed 148 m/s
(G*9.39e20kg/2900 km)^(1/2) --> 147 m/s

 

[marcus]

The new Dawn Journal
http://dawn.jpl.nasa.gov/mission/journal.asp
http://dawnblog.jpl.nasa.gov/2015/07/29/dawn-journal-july-29/
gives a revised schedule for when the probe will arrive at third science orbit (altitude 1470 km) and when it will start descent to the fourth and lowest orbit.

HAMO dates changed from Aug 4 - Oct 15 to Aug 17 – Oct 23, five fewer days will be spent in HAMO

Orbit    dates      altitude(km)  pixelsize(m) res/HST  period  soccerball at
RC3    April 23–May 9    (13,600)    (1,300)    24     15 days    (3.0 meters)
Survey    June 6-30      (4,400)      (410)     73     3.1 days    (1.0 meters)
HAMO    Aug 17–Oct 23    (1,470)      (140)     217    19 hours    (33 cm)
LAMO Dec 15–end of mission (375)      (35)      850    5.5 hours    (8.5 cm)

Here are links describing what the probe does at the different orbits. Science at LAMO was detailed in the August 2014 Journal entry
RC3
Survey
HAMO
LAMO
== http://dawnblog.jpl.nasa.gov/2014/08/31/dawn-journal-august-31/ ==
The spacecraft will use its sophisticated gamma ray and neutron detector (GRaND) to determine the atomic constituents of the material on the surface and to a depth of up to about a yard (a meter). .. it also measures the energy of each kind...
Most of the gamma rays and neutrons are byproducts of the collisions between cosmic rays (radiation from elsewhere in space) and the nuclei of atoms in the ground. ...In addition, some gamma rays are emitted by radioactive elements near the surface. Regardless of the source, the neutrons and the gamma rays that escape from Ceres and travel out into space carry a signature of the type of nucleus they came from. When GRaND intercepts the radiation, it records the energy, and scientists can translate those signatures into the identities of the atoms.
==endquote==

The way I picture it. Cosmic ray particles are typically protons. They collide with atomic nuclei on Ceres and in effect make the nuclei radioactive. The nuclei decay emitting characteristic energy gamma, from which you can tell what type nucleus it was.

Cosmic rays can penetrate down a meter or so below surface, so they can activate subsurface material. So we can be learning about the chemical elements comprising material on and slightly below Ceres surface, if all goes as planned. This does not start in earnest until 15 December.

Marc Rayman gave new figures in his journal for Ceres' radius:
equatorial 482 km
polar 447 km
average (482²447)^1/3 = 470 kmhttp://dawn.jpl.nasa.gov/mission/status.html

 

[marcus]

A new status report is out, for the 31 July.
http://dawn.jpl.nasa.gov/mission/status.html
I found a Wikipedia discussion of how gamma spectroscopy is able to detect some 20 different elements in the soil
https://en.wikipedia.org/wiki/Gamma_ray_spectrometer#Planetary_gamma-ray_spectrometers

Have to go help with supper, no time to finish, very interesting so will finish later

==quote==
How are gamma rays and neutrons produced by cosmic rays? Incoming cosmic rays—some of the highest-energy particles—collide with the nucleus of atoms in the soil. When nuclei are hit with such energy, neutrons are released, which scatter and collide with other nuclei. The nuclei get "excited" in the process, and emit gamma rays to release the extra energy so they can return to their normal rest state...
==endquote==

==quote==
These surfaces are subjected to a continual bombardment of high-energy cosmic rays, which excite nuclei in them to emit characteristic gamma-rays which can be detected from orbit. Thus an orbiting instrument can in principle map the surface distribution of the elements for an entire planet. Examples include the mapping of 20 elements observed in the exploration of Mars, the Eros asteroid and the Moon. [1] They are usually associated with neutron detectors that can look for water and ice in the soil by measuring neutrons. They are able to measure the abundance and distribution of about 20 primary elements of the periodic table, including silicon, oxygen, iron, magnesium, potassium, aluminum, calcium, sulfur, and carbon. Knowing what elements are at or near the surface will give detailed information about how planetary bodies have changed over time.
==endquote==
This is what is supposed to start in earnest around 15 December, at 375 km

 

[marcus]

The article says that neutron detection is one of the ways of detecting hydrogen in the soil---which would most likely be in the form of water.
Not sure this is relevant:
https://en.wikipedia.org/wiki/Small-angle_neutron_scattering#Technique
==quote==
The following table shows the scattering lengths for various elements (in 10⁻¹² cm).[1]

    H      D      C      N     O      P      S
-0.3742 0.6671 0.6651 0.940 0.5804 0.517 0.2847

Note that the relative scale of the scattering lengths is the same. Another important point is that the scattering from hydrogen is distinct from that of deuterium. Also, hydrogen is one of the few elements that has a negative scatter, which means that neutrons deflected from hydrogen are 180° out of phase relative to those deflected by the other elements.
==endquote==

 

[mfb]

I don't have access to the source, but 10^-12 cm are 10 femtometers, not much more than the size of a nucleus. That does not look right.

It fits to the bound coherent scattering length here, but we have unbound neutrons here.

 

[marcus]

Thanks, mfb--so that's not likely to be relevant. I'm curious about this statement in
https://en.wikipedia.org/wiki/Gamma_ray_spectrometer#Planetary_gamma-ray_spectrometers
==quote==
They are usually associated with neutron detectors that can look for water and ice in the soil by measuring neutrons.
==endquote==
Might you know or have a guess as to how detecting (and presumably measuring energies of) neutrons is a way of seeing water and ice?
I guess water is a good moderator
especially the hydrogen atom (which would most likely be occurring in water) because of its low mass is a good moderator.
And the cosmic rays probably make fast neutrons
so seeing a lot of slow ("thermal"?) neutrons might be an indicator of water.

 

[mfb]

I think so. The MESSENGER page agrees as well.

 

[marcus]

Thanks! It makes it clear---you compare the number of slow neutrons with the number of fast ones. You get an estimate of the proportion of light elements (like H) to heavier ones
==quote MESSENGER page==
The lighter the nuclei that it collides with, the more energy a neutron loses. The lightest nucleus (consisting of a single proton) is that of the element hydrogen. Since hydrogen is particularly effective at slowing the neutrons down, a large increase of slow-moving neutrons or a large decrease of neutrons of higher energy (due to this slowdown) can indicate the presence of hydrogen-rich materials such as water ice. So the numbers of fast and slow-moving neutrons detected by GRNS are clues to the relative abundance of light and heavier nuclei on the planet's surface.
==endquote==

 

[marcus]

The last time I looked, simview gave the altitude as 2150 km, probe just crossing south pole into Ceres night side. Call it 2200 km.
The target HAMO orbit altitude is 1470 km, so roughly 700 km of descent remains to be achieved.

Orbit    dates      altitude(km)  pixelsize(m) res/HST  period  soccerball at
RC3    April 23–May 9    (13,600)    (1,300)    24     15 days    (3.0 meters)
Survey    June 6-30      (4,400)      (410)     73     3.1 days    (1.0 meters)
HAMO    Aug 17–Oct 23    (1,470)      (140)     217    19 hours    (33 cm)
LAMO Dec 15–end of mission (375)      (35)      850    5.5 hours    (8.5 cm)

So we can expect Dawn to arrive at HAMO by 17 August---in a little over 2 weeks! For me the main excitement now has to do with the GRaND (gamma ray and neutron detector) instrument which only gets turned on in HAMO for purposes of calibration, to establish background levels etc. It will not get used in earnest until LAMO starts in December.

But that won't be for a while, so what can we anticipate from the time spent in HAMO (high altitude mapping orbit)? Marc Rayman discussed the activity planned for this orbit in his June 2014 Journal:
http://dawnblog.jpl.nasa.gov/2014/06/30/dawn-journal-june-30-2/

One thing will be a more precise topographical map. Better understanding of the geology probably.

 

[mfb]

We also get a factor 3 better resolution for all images.
And hopefully spectroscopic data from the bright spots and other areas.

 

[marcus]

Good point, better resolution and hopefully spectroscopic data.
As of 6PM pacific on 3 August, simview says the altitude is 2020 km, which leaves about 550 km left to descend (to reach the target 1470 km).

Simview also gives the speed as 158 m/s.

Remember Rayman's new figure for average radius is 470 km, so 2020 translates to 2490 km
(G*9.39e20kg/2490 km)^(1/2) ---> 158.6 m/s

So according to Simview the speed IS what it would have to be for circular orbit at that altitude. It wouldn't be surprising, though, for Simview to be slightly off. We may get another status update from Rayman to compare.
http://dawn.jpl.nasa.gov/mission/status.html
http://neo.jpl.nasa.gov/orbits/fullview2.jpg

 

[mfb]

The ion engine becomes weaker and weaker relative to the orbital parameters, so the descent orbit becomes more circular - acceleration within a single orbit becomes a small effect.

 

[marcus]

That makes sense! The spiral should be more circular this time even though (for navigation) they have shut off the ion engine for part of a day on a couple of occasions.
Mission director posted a status update for 3 August which confirmed what Simview indicated---that by the end of the day the probe was down to altitude 2000 km

 

[marcus]

A reminder of one of the reasons Ceres is an especially interesting solar system body. Its shape is only slightly oblate, indicating that it has differentiated into layers, by density. Its low density suggests it contains a huge amount of water (with various other chemical compounds dissolved in it). This would be primarily as ice--although I suppose there could be subsurface patches of liquid. Here's a projected cutaway diagram:

I suspect humanity may eventually want to set up chemical manufacturing industry in Ceres ice mantle.
Subsurface liquid water, circulated, could provide cooling for power generation.
Bulk chemicals already in orbit, in low gravity so easy to move, are potentially of high economic value.

Simview as of 10PM pacific on 4 August gave the altitude as 1930 km and speed just over 160 m/s---the target altitude for the next orbit is 1470 km, which means an orbit radius of 1940 km.
(G*9.39e20 kg/1940 km)^(1/2) ⇒ 180 m/s

 

[mfb]

You don't need the very deep natural water (if it exists at all) for cooling. A massive amount of ice is sufficient for cooling - dumping low power into it will melt some water which is a better conductor and allows to dump even more power into it.
Nuclear power (fusion or fission) is the only relevant application that could generate more heat than required. Some heating is needed for a station (even unmanned), and solar panels don't provide that.

 

[marcus]

... A massive amount of ice is sufficient for cooling - dumping low power into it will melt some water which is a better conductor and allows to dump even more power into it.
Nuclear power (fusion or fission) is the only relevant application that could generate more heat than required. Some heating is needed for a station (even unmanned), and solar panels don't provide that.

I agree. I wasn't thinking of naturally occurring liquid water but of this application. Waste heat could melt a limited volume of ice and make a subsurface cooling pond. If the water volume then dispersed heat widely enough into the ice, it could be conducted away by the ice without further melting. An application for nuclear power.

I suspect humanity may eventually want to set up chemical manufacturing industry in Ceres ice mantle.
Subsurface liquid water, circulated, could provide cooling for power generation.
Bulk chemicals already in orbit, in low gravity so easy to move, are potentially of high economic value.

Simview as of 10PM pacific on 4 August gave the altitude as 1930 km and speed just over 160 m/s---the target altitude for the next orbit is 1470 km, which means an orbit radius of 1940 km.
(G*9.39e20 kg/1940 km)^(1/2) ⇒ 180 m/s

As of 5 PM pacific 6 August, simview gave the altitude 1820 km and speed 164 m/s

 

[marcus]

New animation. 2 minutes. Vertical relief is 5x exaggerated.

Mountain's height is given as 4 miles which would be over 6 km. Interesting dark streaks down one side and light streaks down the other, like a volcano with two colors of lava

The probe is now spiraling down to its next-to-final orbit, altitude 1470 km. Should be there is about 10 days and start mapping and spectroscopy on 17 August.

DSN shows it is in radio contact with Goldstone antenna #24---a regular navigation break. Simview shows the ion engine temporarily turned off.

The craft is at altitude 1810 km, so it has about 340 km left to descend. Simview shows the current speed as about 165 m/s.