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

[johnnymorales]

That pyramid looks just like a cinder cone or stratovolcano on Earth. Though on Ceres is could very well be a cryovolcanic cinder cone.


Here is a photo of Mt. Mayon on Earth it's close to a perfect match when you take into account the likely effects of much lower gravity on Ceres.

https://en.wikipedia.org/wiki/File:Mt.Mayon_tam3rd.jpg


It's pretty surprising they'd call it a pyramid.

It's egging on the people who live and breath conspiracies as an explanation for all that they see.

It's also pretty surprising that in place of valid scientific speculation they let loose with a nonsense comparison.

Pyramids are not cones. So why inspired them to make such a brain dead comparison.

All and all par for the course regarding the Ceres team. They apparently lack the media savvy of the New Horizons team.

You can bet anything that looks vaguely volcanic or tectonic on Pluto will be declared as such immediately with validation to come later.

The fact that the Ceres team simply refuses to engage in the type of scientific speculation that makes space exploration so exciting for the public is extremely disappointing.

Suggesting the obvious in a news release would dramatically increase the public's interest and support of this mission.

The fact that it is much larger than any Earthly cinder cone can easily be explained by Ceres having just a tiny fraction of Earth's gravity. With such low gravity a cinder cone could grow to immense heights on Ceres.

 

[OmCheeto]

Ceres in the news:

Dawn over Ceres, a mission of humankind (PBS News Hour)

I'm not sure if I missed it, or forgot it, but the first image is not familiar:

THE DWARF PLANET — This image, taken by NASA's Dawn spacecraft , shows dwarf planet Ceres from an altitude of 2,700 miles (4,400 kilometers). The image, with a resolution of 1,400 feet (410 meters) per pixel, was taken on June 6, 2015. Image by NASA/JPL-Caltech/UCLA/MPS/DLR/IDA​

Here's the video imbedded in the write-up:

Dawn mission director describes the dwarf planet Ceres
​

[edit]

By casual inspection, the northern hemisphere seems to differ markedly from the southern hemisphere. I believe Mars and Vesta share this characteristic.

From the above article, it appears you are correct:

"The southern hemisphere is less densely cratered than the northern."
​

I think that's weird.

 

[Dotini]

"The southern hemisphere is less densely cratered than the northern."
​

I think that's weird.

Weird things are fun, and mean there's more to learn.

 

[OmCheeto]

Weird things are fun, and mean there's more to learn.

I can think of no mechanism inside our solar system which would cause such a thing.
So yesterday I spent about 3 hours researching the origins of asteroids.
I found tons of conflicting information.

One person here at PF said they were formed by vacuum welding. (Sounds funny to me, and no reference was listed.) [ref] Actually, it sounded like everyone was guessing in that thread. And given the level of knowledge at PF, my guess is, that know one knows.

One website article said they were formed during the big bang. (I sense that this is totally wrong. Most references list only Hydrogen and Helium production during that period) [ref]

So I researched a bit more about novas and supernovas, wondering if anyone knew if their heavy end stage nucleosynthesized elements, nickel and iron, were distributed atomically, or in big molten blobs. I found no answer. But looking at the Crab Nebula, it looks filamentized, so I thought there might be some merit to the idea.

Anyways, my theory was, that a local star, somewhere between 1 and 4 billion years ago. in the general direction of Polaris, might have gone nova, showering us with asteroids.
I was going to do the math, on the probability, given the rate of stellar explosions, local star density, and the age of our galaxy, but I was hoping that someone knew the answers to these things, off the top of their head. I hate doing needless maths. If no one knows, I will, obligingly, do the maths.

ps. Wouldn't it be fun, if the Dawn mission, gave us the answer.

 

[marcus]

Hi Om, I've never been too good at telling when my leg was being pulled but I think if an math explanation needs to be given it would be to explain why Jupiter's gravity would interfere with all that belt of rock coalescing into a planet.

I think at one time the band of near-circular orbits at 1 AU (plus or minus) where the Earth is now probably looked like Asteroid Belt only if anything much much thicker.

But the junk and rubble around 1 AU was able to start gathering and coalescing and snowballing together into one big heap called the Earth. Once one significantly bigger lump collects then it gradually pulls the rest in. But when our planet was forming it did not have the disruptive presence nearby of a planet like Jupiter to deal with.

The interesting question, for someone who wants to get into the math detail of orbital mechanics, would be to explain exactly how the proximity of Jupiter would disrupt the coalescence.

Jupiter could also have ejected asteroid matter from the belt. Pull chunks of it out of circular into eccentric orbits and then give them a gravity slingshot boost altogether out of there. That could be part of the reason there is not all that much mass in the Belt. Ceres alone represents 1/3 of the mass of the Belt. 3 x Ceres mass is really not what we expect for a usual planet.

 

[OmCheeto]

Hi Marcus,

I think I'd better slow down and start from scratch, and explain what I was looking for.
By reading Dotini and mfb's posts in sequence, I misinterpreted what Dotini had actually said.

By casual inspection, the northern hemisphere seems to differ markedly from the southern hemisphere. I believe Mars and Vesta share this characteristic.

Craters all the way down.

The illumination seems to be different for the two images, so I would be careful with comparisons.

All Dotini had said was, that they were different. I unfortunately added the two comments together and came up with; "Ceres is more heavily cratered in the north, which is true of Mars and Vesta", which is obviously not true. Unfortunately, I didn't figure that out until just now. So the original question, isn't even valid.

But I think a valid question still exists; "Why is Ceres more heavily cratered in the northern hemisphere?"

I've just spent about 6 hours trying to put the pieces together, but I think it's all just a bunch of very bad science on my part.

But all is not lost. I think I ran across the answer to your following question:

The interesting question, for someone who wants to get into the math detail of orbital mechanics, would be to explain exactly how the proximity of Jupiter would disrupt the coalescence.

Kirkwood gaps
A Kirkwood gap is a gap or dip in the distribution of the semi-major axes (or equivalently of the orbital periods) of the orbits of main-belt asteroids. They correspond to the locations of orbital resonances with Jupiter.

 

[OmCheeto]

An underexposed image of the bright spots published today:

image taken: June 15, 2015
altitude: 2,700 miles (4,400 kilometers).
resolution: 1,400 feet (410 meters) per pixel.
​

This is a heavily magnified shot from the TIFF image at JPL.

​

Well, ok. I can't see anything either. But at least they're reading my mind now.

 

[marcus]

the new Dawn Journal is out!
http://dawnblog.jpl.nasa.gov/2015/06/29/dawn-journal-june-29/

 

[marcus]

The 8th and last observation cycle in survey orbit should be completed today. So we can expect descent to the third mapping orbit (which used to be called "HAMO") to start soon.
I say that because status update http://dawn.jpl.nasa.gov/mission/status.html said the last cycle started 27 June, and a cycle lasts 3.1 days (half the time on the dayside, observing, and the rest of the time on the nightside, transmitting).

We should be seeing Dawn talking with DSN, either transmitting the data from the last cycle or getting programmed for the descent, which will take about 5 weeks if I remember right. I just checked and Canberra #45 is receiving data (it is 2AM there).
My guess is Dawn will turn on the ion thruster sometime (pacific) tomorrow, 1 July, if not earlier.

The simulated view http://neo.jpl.nasa.gov/orbits/fullview2.jpg shows the craft crossing over the N pole to the dayside. I'll bring that timetable forward, since we've turned a page. What I'm reading into it is that descent to the next orbit starts tomorrow and will take until the first week of August.

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)

EDIT: Rayman's "Mission update" for 30 June includes this:
==excerpt==
...
Tonight Dawn will power on its ion propulsion system to begin a spiral descent to the third mapping orbit. It will take about five weeks to complete the maneuvering to an altitude of about 900 miles (less than 1,500 kilometers).
==endquote==
So if that went as planned propulsion is now on. I see from DSN that Dawn is not engaged in communication so I conclude the descent is in progress.
http://dawn.jpl.nasa.gov/mission/status.html

 

[OmCheeto]

Ha ha! The "bright spots" have their own wiki page:

Bright spots on Ceres

as does the mountain:

Pyramid-shaped mountain on Ceres

I discovered these this morning, when I was trying to verify a few posts on Facebook this morning; "These bright features have an albedo of about 40% (4 times brighter than the rest of Ceres's surface).^[3]"

Reference [3] is the 90 minute lecture that Dr. Rayman gave back in April.
Having already watched it, I was listening to it, while surfing this morning. I obviously missed it.

I guess it doesn't really matter what the actual albedo is, as ice/snow has a "proclaimed" variability of from 30 to 85%. [per wiki, and therefore, unreliable ]

 

[rootone]

The mountain:
"Although origin hypotheses for the mountain include volcanism, impacts, and plate tectonics, clear evidence backing any of these is currently lacking."

My bet is on it being a central 'rebound' mountain of the kind often associated with large impacts.
If this impact was very ancient, other more recent and smaller impacts could have eliminated other evidence of it - such as a discernable crater rim.

Plate tectonics and volcanism seem to me less likely on a body the size of Ceres, and if either were the case it's hard reconcile with there being just the one isolated mountain, as tectonics usually produce ranges of mountains, and volcanism usually produces several volcanos within in a well defined area..

 

[OmCheeto]

The mountain:
"Although origin hypotheses for the mountain include volcanism, impacts, and plate tectonics, clear evidence backing any of these is currently lacking."

My bet is on it being a central 'rebound' mountain of the kind often associated with large impacts.
If this impact was very ancient, other more recent and smaller impacts could have eliminated other evidence of it - such as a discernable crater rim.

Plate tectonics and volcanism seem to me less likely on a body the size of Ceres, and if either were the case it's hard reconcile with there being just the one isolated mountain, as tectonics usually produce ranges of mountains, and volcanism usually produces several volcanos within in a well defined area..

Someone, some time back, described low gravity, extra-terrestrial objects, as, "rubble piles".

It may just be a big pile of rubble.

 

[OCR]

[per wiki, and therefore, unreliable ]

Ohhhhh, my !

 

[marcus]

The 8th and last observation cycle in survey orbit should be completed today. So we can expect descent to the third mapping orbit (which used to be called "HAMO") to start soon.

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)

EDIT: Rayman's "Mission update" for 30 June includes this:
==excerpt==
...
Tonight Dawn will power on its ion propulsion system to begin a spiral descent to the third mapping orbit. It will take about five weeks to complete the maneuvering to an altitude of about 900 miles (less than 1,500 kilometers).
==endquote==
So if that went as planned propulsion is now on. I see from DSN that Dawn is not engaged in communication so I conclude the descent is in progress.
http://dawn.jpl.nasa.gov/mission/status.html

It turns out that did NOT go as planned. The craft did briefly turn on ion propulsion to start the descent, but detected something was wrong and shut down the thruster, putting itself in safe mode to allow the engineers to check things out. Rayman's status update of 6 July:
http://dawn.jpl.nasa.gov/mission/status_2015.html
==quote==

2015

July 6, 2015 - Dawn Holding in Second Mapping Orbit

NASA's Dawn spacecraft is healthy and stable, after experiencing an anomaly in the system that controls its orientation. It is still in its second mapping orbit 2,700 miles (4,400 kilometers) above dwarf planet Ceres.

On June 30, shortly after turning on its ion engine to begin the gradual spiral down to the next mapping orbit, its protective software detected the anomaly. Dawn responded as designed by stopping all activities (including thrusting), reconfiguring its systems to safe mode and transmitting a radio signal to request further instructions. On July 1 and 2, engineers made configuration changes needed to return the spacecraft to its normal operating mode. The spacecraft is out of safe mode, using the main antenna to communicate with Earth.

Dawn will remain at its current orbital altitude until the operations team has completed an analysis of what occurred and has updated the flight plan.

Because of the versatility of Dawn's ion propulsion system and the flexibility of the mission's plan for exploring Ceres, there is no special "window" for starting or completing the spiral to the third mapping orbit. The plans for the third and fourth mapping orbits can be shifted to new dates without significant changes in objectives or productivity.
==endquote==

 

[OmCheeto]

...
The plans for the third and fourth mapping orbits can be shifted to new dates without significant changes in objectives or productivity.
...

As I've suspected, all along, the project is in good hands.

 

[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