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.
  • #421
It is 16 MB large, better don't include it here directly.
A structure in the smaller spot! Very nice.
 
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  • #422
Dawn tweeted that it is thrusting and spiraling down
https://twitter.com/NASA_Dawn/status/597880787111956480
‏@NASA_Dawn (as of 3PM pacific on 11 May)
Update: Today I am about 8,000 miles (13,000 km) above #Ceres, and using my ion engine to spiral down to my next mapping orbit

This agrees approximately with fullview2
http://neo.jpl.nasa.gov/orbits/fullview2.jpg
the simulated view also shows it on the night side of Ceres going north, with the ion beam pointed north, so as to apply braking
the simuated view is as of 2AM 12 May UT, which is I think 6pm pacific 11 May
the simulated view says 12700 km altitude. So roughly consistent
 
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  • #423
Good point!
These are simple ideas but very good to understand, if any newcomers see post #435 figure out how that works, or ask or both. Give Janus and Mfb something to do. Otherwise we have to rely on imagined hypothetical or future newcomers which we think may exist, and tailor our posts to.

If you are a spacecraft in circular orbit then braking speeds you up so if you thrust in reverse, like Dawn is now doing with its solar electric ion drive, you will spiral in slightly and speed up. And we can SEE THIS in the simulated view of Dawn
http://neo.jpl.nasa.gov/orbits/fullview2.jpg
this is a concrete example.
while in its first circular orbit, for about 15 days, Dawn was at altitude 13,500 km and going at speed right around 150 mph.
On the 10 May it began a braking thrust with its ion beam pointed in the direction it was going.
Now simulated view says it is going 153 mph. Return tomorrow to see if that speed has increased!
And it says the altitude is now (7PM pacific on 12 May) about 11.7 kkm that is almost 2000 km nearer the surface than it was to start with.
Because of a delay in refreshing, this image as it currently appears is out of date. Click on REPLY to see the current sim-view version. You don't have to reply you can just cancel or back out of replying, if you want, but when you click "reply" at the bottom of this post it will show you the current version of the sim-view graphic. It is now as of 10PM pacific 12 May and the speed is 154 mph (more than what the outdated version the system provides currently shows).
UPDATE: As of now 7AM 13 May pacific, when you press "reply" the updated version says 158 mph. So quite a lot of speeding up has happened.
http://neo.jpl.nasa.gov/orbits/fullview2.jpg
This image shows an earlier version but it will change to an updated one if you click "reply", so i am describing the situation for 7PM pacific on 12 May when I say she is flying up the night side of Ceres heading for the N pole, and thrusting to slow down. The Sun and Mars are visible so we can see the plane of the solar system currently in this sim-view.
UPDATE: Currently it says altitude 11.7 kkm and speed 154 mph, for 8PM pacific on 12 May. So we see speed continuing to climb in accordance with the reverse thrust braking by the craft.
Click on the link to get the latest sim-view figures.
UPDATE: as of 7AM 13 May, altitude 11.2 kkm and speed 158 mph.
 
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  • #424
The good[1], the bad[2], and the ugly[3]...

OmCheeto said:
...
Marc Rayman...
(YAY! My newest pen pal, and bff. :smile:)​
[1] Dr. Rayman Marc apparently saw this post, and now insists, via his last communication, that in my future email salutations, I use his first name. :bugeye: :bow:

[2] I got antsy on Saturday, waiting for the live broadcasts, and went out to mow my lawn. I have apparently lost my ability to tell time by the position of the sun, and missed his live speech, by 10 minutes. I didn't cut my throat, as, well, I'm patient enough to know that very interesting things are in our near future.

[3] Marc informed me, that I was correct, that 50,000 people usually show up for a JPL open house event. He then informed me, that only 2200 people showed up for Saturday's event. I almost had another stroke.

My latest email:

Om said:
Hi Marc,

That, is simply incomprehensible. In a metro area with over 18 million people, only 2000 showed up.

I’m glad you agree that it wouldn’t have been worth my time, as I calculated that the $500 to fly down and stay the weekend would have come out to $1000/hr for your 30 minute talk.

Though, meeting you, and all the rest, would have made it worth it.
...

And, back to the good, and another reason not to cut my throat:


Yay!
 
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  • #425
This was the official word on 13 May:
"Today's altitude is between ...10,000 and 11,000 km above #Ceres"
3:00 PM pacific - 13 May 2015
Now the sim-view says for 10PM UT on 14 May, which would be 2PM pacific on 14 May
that the speed is 179 mph and the altitude in 9.44 kkm
So if official twitter and sim-view are consistent (which I suspect they are at this point) then the probe is currently descending roughly at the rate of 1000 km per day and noticeably speeding up, now 179, while in the 13,500 kkm orbit it was always going right around 150 mph

UPDATE: Official tweet for 14 May:
" Today I will spiral down from an altitude of... 10,000 km to ...8,900 km with respect to #Ceres
2:20 PM - 14 May 2015"
 
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  • #426
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  • #427
marcus said:
there is an animation that focuses specifically on one of the bright spots:
http://i.imgur.com/tsm3wN0.gif

Interesting. It's looking flatter than before.
 
  • #428
I agree. More like flat patches of ice or salt residue, level with the crater floor.

Sim-view shows the probe crossing over the N pole from dark side to light. Reverse thrusting to slow down. Thanks Mfb for updating the title!
It has already descended quite a lot.
Down from 13500 km a few days ago to (sim-view says) 7840 km, and speed has risen from 150 mph (in initial orbit) to 204 mph.
That's the current view, as of 7PM pacific on 15 May ( i.e. dated 3AM on 16th UT)

Since we turned a page, i should bring the orbit schedule forward.
Code: 
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)

There's some explanation of the table at:
https://www.physicsforums.com/threads/ceres-at-rc3-13500km-above-surface.793140/page-20#post-5089960
But it seems fairly self-explanatory. The more you descend, the faster you are going and the more work is required to descend further. At 7,800 km Dawn is more than half the way down from 13.5 to 4.4 kkm
but it is going to still take 3 weeks to come down the rest of the way.
 
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  • #429
Can we discuss Mars and space elevators in a different thread, please?Edit: The Mars/Ceres discussion got split out. There is some overlap, so some content appears twice and some references might be less clear without the other thread, but I tried my best.
 
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  • #430
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  • #431
Did you notice the bright spots in http://neo.jpl.nasa.gov/orbits/fullview2.jpg ?
Also. Ceres grows notably in size from day to day.

7110km (about one transatlantic flight), 218 mph
 
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  • #432
I'll bring forward the sketch of the descent down from RC3 (15 day orbit) to Survey (3 day orbit)
survey.jpg

It looks to me as if, in the diagram, distance to Ceres can actually increase or stay constant for a while after she goes 3/4 of the way around in the first loop.
Descent starts around 4 o'clock and goes counter clockwise, always closing in, until about 7 o'clock.

By then the probe is probably in an elliptical orbit (if she stopped thrusting) and she has excess kinetic and needs to swing out to apogee. So the thruster is fighting a tendency to swing out and it is a "draw" for a while. It does not get any closer in from, say, 7 o'clock to, say 3 or 2 o'clock. Then it starts to fall in again.

I'm probably over interpreting the diagram, which could be just a rough sketch to give the idea of a spiral, and not accurate in detail. Just a tentative interpretation.

I think sim-view has show some slowing and actual increase of the Ceres distance during the past couple of days, can't be sure, just my impression.

EDIT: Yes at least according to sim-view, I just looked and it say altitude 7.45 kkm and speed 205 mph, farther off and slower than it has been recently That was 8PM 17 May pacific time.

EDIT: noon pacific time, 18 May, 7.9 kkm and 191 mph, still farther off and still slower than yesterday.
according to sim-view.
 
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  • #433
Looks quite spirally to me, but even in the sketch the distance does increase a bit in between. The red circles are 50 pixels or about 2500km apart (with the inner one at about 5000 km).

We are bit outside the second smallest ring.

DawnCeres.png
 
  • #434
Thanks for the red circles. I think I see the outwards swing between 7 o'clock and 3 o'clock.
Simview says distance is 7.9 kkm and I think it's time for it to start approaching again.
Probe seems to have just passed over the S pole
 
  • #435
marcus said:
there is an animation that focuses specifically on one of the bright spots:
http://i.imgur.com/tsm3wN0.gif

Below are two stills from the animation. What are these artifacts in the images?
full-image-1-570x569.png
full-image-2-570x565.png
 
  • #436
Dotini, thanks for picking out those frames with the curious spots. I don't even have a guess as to what they could be. Hopefully someone else can offer a suggestion.
 
  • #437
I have a theory. The bright spot is supposedly highly reflective and it's nearly white in this image. Is it possible that the sun is directly behind the spacecraft and that is the probe's shadow?
 
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  • #438
A couple of tweets today, I saw about 7:40 pm pacific time, so they were shortly after noon pacific today:
https://pbs.twimg.com/profile_images/3502834940/2f750377e236127f02d96e270510d727_normal.jpeg NASA's Dawn Mission @NASA_Dawn · 7h7 hours ago
That means I'm going from altitude 7,600 to 8,200 km with respect to #Ceres today #orbitalmechanics

18 retweets32 favorites
https://pbs.twimg.com/profile_images/3502834940/2f750377e236127f02d96e270510d727_normal.jpeg NASA's Dawn Mission @NASA_Dawn · 7h7 hours ago
My planned trajectory is temporarily increasing in altitude b/c my orbit is slightly elliptical...

14 retweets40 favorites
 
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  • #439
newjerseyrunner said:
I have a theory. The bright spot is supposedly highly reflective and it's nearly white in this image. Is it possible that the sun is directly behind the spacecraft and that is the probe's shadow?

The pixel size is currently between 410 meters and 1300 meters per pixel. Those pictures were taken 4 May at altitude of 13,600 km.
http://dawn.jpl.nasa.gov/multimedia/images/image-detail.html?id=PIA19547
Code: 
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)

Very roughly the 4 May pictures were taken at 1300 meters per pixel. The dark spots would be several kilometers wide. Too wide to be the shadows of the probe.
 
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  • #440
marcus said:
Dotini, thanks for picking out those frames with the curious spots. I don't even have a guess as to what they could be. Hopefully someone else can offer a suggestion.
I'm guessing dust on the camera lens.
The donut shaped anomaly can be seen in two other frames.

frame #14
2015.05.04.Ceres.gif.frame.14.jpg


frame #17
2015.05.04.Ceres.gif.frame.17.jpg


frame #18
2015.05.04.Ceres.gif.frame.18.jpg


The only other explanation: Aliens.
 
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  • #441
Do we know the frame frequency? And does the different angular relationship to the ice fort coincide with possible rotation of the camera? I have a hard time picturing loose dust, inside the instrument. Are those the only frames that show it?
 
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  • #442
It's very unlikely that there would be dust inside the instrument, however stuck to the surface of the lens or floating above it because of static electricity I could see.
 
  • #443
Jimster41 said:
Do we know the frame frequency?
Ceres rotates once every 9 hours, if you track something on the surface (e.g. the bright spots) you can calculate it for this specific animation.

A dark spot that moves across the surface is clearly something camera- or spacecraft -related.

Dawn does not have a proper shadow, by the way. The sun has an angle of ~1/250 rad, to make a full shadow Dawn would have to be less than 500 m above the surface. Currently it is reducing illumination in a ~30 km x 30km spot by less than one part in a million.
 
  • #444
marcus said:
The pixel size is currently between 410 meters and 1300 meters per pixel. Those pictures were taken 4 May at altitude of 13,600 km.
http://dawn.jpl.nasa.gov/multimedia/images/image-detail.html?id=PIA19547
Code: 
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)

Very roughly the 4 May pictures were taken at 1300 meters per pixel. The dark spots would be several kilometers wide. Too wide to be the shadows of the probe.
Besides which, at 13,000 km, the probe would only have an angular size of 0.298 seconds of arc, while the Sun still has an angular size of ~11 minutes of arc. Thus the probe would not cast a discernible shadow of any size.
 
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  • #445
Jimster41 said:
Do we know the frame frequency? And does the different angular relationship to the ice fort coincide with possible rotation of the camera? I have a hard time picturing loose dust, inside the instrument. Are those the only frames that show it?

On the full size animated gif, I can see anomalous dark spots in every frame.

One thing I haven't been able to determine is the sensitivity of the cameras, so I don't know how long the exposures are.

The Camera System – Dawn's Eyes (MPS)
The Cameras in Numbers

Exposure times: 1 millisecond to 3.5 hours
Field of vision: 5.5 dregrees times 5.5 degrees
Memory: 8 GBit dRAM
CCD-sensor: 1024 pixel times 1024 pixel
Filter wheel: seven narrow-band filters and one clear filter

While looking for information on "dust" yesterday, I also ran across a book edited by Christopher Russell, Carol Raymond.
The Dawn Mission to Minor Planets 4 Vesta and 1 Ceres
The section on the framing cameras starts on page 263. The next chapter starts on page 328.
TMI! And lots of pages are missing.
But there are other interesting things in the book.
Electrostatic charge levitation of dust particles on the surface of dwarf planets and asteroids? (page 276)
574 pages in all. Good grief!
Fortunately for me, they hid pages 29 through 260, and 303 through 574, amongst other random page sets, or I'd still be snooping around for clues.

In the following image, "QE", stands for "Quantum Efficiency". (page 284)
Since it contains the word "Quantum", I have no idea what it means.
But I suspect it's a clue to the sensitivity of the CCD image sensors used in the cameras.

Quantum.Efficiency.page.284.MPS.framing.camera.jpg

Wiki has the following to say:

Quantum efficiency
This article deals with the term as a measurement of a device's electrical sensitivity to light. In a charge-coupled device (CCD) it is the percentage of photons hitting the device's photoreactive surface that produce charge carriers. It is measured in electrons per photon or amps per watt. Since the energy of a photon is inversely proportional to its wavelength, QE is often measured over a range of different wavelengths to characterize a device's efficiency at each photon energy level. The QE for photons with energy below the band gap is zero. Photographic film typically has a QE of much less than 10%[2], while CCDs can have a QE of well over 90% at some wavelengths.
...

[2]
Springer Handbook of Lasers and Optics
...
Speed (page 604)
The speed of photographic films can be characterized
assuming that the grain must absorb a certain number
of photons to become developable [9.64]. The referred
number of photons depends on the grain size. Thus,
there is a correlation between the speed and the grain
size. For bare silver halide emulsions (which are sen-
sitive below 500 nm), the whole volume of the grain
absorbs and the speed of the film is the grain vol-
ume times the absorption coefficient.
...

Obviously, a rabbit hole of complexity, which I should not have ventured down...

But this reminds me of trying to explain a non-functioning solar panel powered bilge pump volleyball court watering systems to an electrical laymen, who kept saying; "It all has to do with the Amps".
 
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  • #446
Dawn has reached the apoapsis (far point) of its quasi-elliptical loop and will start closing in again this evening, according to this tweet of about 2PM pacific on 19 May
https://pbs.twimg.com/profile_images/3502834940/2f750377e236127f02d96e270510d727_normal.jpeg NASA's Dawn Mission @NASA_Dawn · 4h4 hours ago
Today I am orbiting #Ceres between ... (8,200 and 8,400 km) in altitude. Tonight I will resume descending.

These tweets originate from Marc Rayman, we are told. He is providing update info and someone else relays it. The probe did swing pretty far out, it seems. From less than 7.2 to more than 8.2 kkm.
Here were some previous tweets about this, posted around noon pacific on 18 May
marcus said:
https://pbs.twimg.com/profile_images/3502834940/2f750377e236127f02d96e270510d727_normal.jpeg NASA's Dawn Mission @NASA_Dawn · 7h7 hours ago
That means I'm going from altitude 7,600 to 8,200 km with respect to #Ceres today #orbitalmechanics

https://pbs.twimg.com/profile_images/3502834940/2f750377e236127f02d96e270510d727_normal.jpeg NASA's Dawn Mission @NASA_Dawn · 7h7 hours ago
My planned trajectory is temporarily increasing in altitude b/c my orbit is slightly elliptical...
 
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  • #447
marcus said:
Dawn has reached the apoapsis (far point) of its quasi-elliptical loop and will start closing in again this evening, according to this tweet of about 2PM pacific on 19 May
https://pbs.twimg.com/profile_images/3502834940/2f750377e236127f02d96e270510d727_normal.jpeg NASA's Dawn Mission @NASA_Dawn · 4h4 hours ago
Today I am orbiting #Ceres between ... (8,200 and 8,400 km) in altitude. Tonight I will resume descending.

These tweets originate from Marc Rayman, we are told. He is providing update info and someone else relays it.
...

Do you think I"m making it up? :-p

Emails from this morning:
May 19, 2015 12:45 PM
Hi [Om],

In addition to a new image every day, I now post a mission status update one or a few times a week, as I did at Vesta. I don’t tweet, but I provide information to someone else who tweets for Dawn every day.

[The one and only] Marc [Rayman, JPL, Om's hero]
bolding and bracketed items mine.

May 19, 2015 12:42 PM
Hi [Om],

I don’t have time now to look at the forum (I have only ever visited it very briefly), but the images do have artifacts. Some are the result of dust that occasionally separates from the spacecraft and, being small and out of focus, can look larger than it really is. We have observed this throughout the mission, but the flux of dust is very low and it does not compromise the scientific value of the images. There are also electronic artifacts from the CCD. Most spacecraft experience both, and image processing removes them. We are releasing images that have not yet gone through the (time-consuming) full processing, although ultimately all the data, both uncorrected and fully corrected, calibrated, will be released. Of course, all images are scrutinized for moons and other real phenomena, but we know with 100% confidence that none of the stuff we see is anything other than an artifact.

We post a new image every (work) day.

Regards,
marc

I told him about the alien space crafts we were seeing in the images. :biggrin:
Then I got kind of bossy, and told him to post more often. :redface:

Bad Om! Bad, bad, Om!
 
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