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

[marcus]

Canberra antenna #45 is conversing with Dawn
EDIT that was at 10AM pacific time, when I posted earlier, now it is 3PM pacific and antenna#45 is still talking two-way with Dawn
the incoming power is 2 x 10^-17 watts (I like the danish word "atten" for eighteen, 20 attowatts)
the outgoing power is 20 kilowatts..

the incoming frequency is about 8 Ghz. so that is the frequency Dawn likes to broadcast.

It seems to me that because of the position of our two planets, Canberra should lose sight of Ceres by around noon there.
but I see that it is 8 AM in the morning in Canberra, so they have plenty of time to continue their conversation. I think they have Ceres in the sky sort of midnight to noon, maybe not the full 12 hours maybe 1AM to 11AM

Madrid would be the next one up. It is shortly past midnight there
https://eyes.nasa.gov/dsn/dsn.html
they have two antennas unassigned

 

[OmCheeto]

A new image was posted a couple of hours ago.

This animation shows the north pole of dwarf planet Ceres as seen by the Dawn spacecraft on April 10, 2015.
Dawn was at a distance of 21,000 miles (33,000 kilometers) when its framing camera took these images.
The spacecraft was maneuvering toward its first science orbit, which it will enter on April 23.​

 

[marcus]

Larger version here:
http://dawn.jpl.nasa.gov/multimedia/Ceres_north_pole.asp
showing more detail around the north pole. You can see which craters mark the north pole, they stay roughly in the same place as the planet rotates, and turn or move in tight circles.

Fullview2 http://neo.jpl.nasa.gov/orbits/fullview2.jpg shows Dawn coming around on the sunlit side!
It is slightly under 19 kkm from Ceres, has passed over the north pole, is coming around so that much of planet is now illuminated, and seems to be approximately in the right orbit plane!

If Fullview2 is at all accurate, they have done a very creditable job guiding the thing. I did not expect things to go as smoothly as the simulated view suggests they have, especially about veering the polar orbit plane so it would not align with the Sun.

Looking down on north pole, the polar orbit plane as to be rotated off of the sunline in a clockwise sense by a few degrees, like 5 degrees. then the probe will not fall in Ceres shadow during its months-long mission.
I'll try uploading the same animation Om just did in case it turns out larger:

Somehow I lost the animation feature

 

[OmCheeto]

...

Fullview2 http://neo.jpl.nasa.gov/orbits/fullview2.jpg shows Dawn coming around on the sunlit side!
It is slightly under 19 kkm from Ceres, has passed over the north pole, is coming around so that much of planet is now illuminated, and seems to be approximately in the right orbit plane!

That will teach me to capture images 5 minutes after getting up in the morning.
I didn't notice until now that JPL had replaced their picture of my log (which they shamelessly stole and gave me no credit for) with an actual representation of Ceres.

If Fullview2 is at all accurate, they have done a very creditable job guiding the thing. I did not expect things to go as smoothly as the simulated view suggests they have, especially about veering the polar orbit plane so it would not align with the Sun.

Looking down on north pole, the polar orbit plane as to be rotated off of the sunline in a clockwise sense by a few degrees, like 5 degrees. then the probe will not fall in Ceres shadow during its months-long mission.
I'll try uploading the same animation Om just did in case it turns out larger:
View attachment 82127
Somehow I lost the animation feature

Has anyone done the calculations on how out of skew Dawn will have to be at the other orbits yet?
As I recall, she'll be almost nose to nose with Ceres at LAMO.

Maybe I'll go find my baseball. I'm tired of maths*.

*I was up till 11pm last night, doing my taxes.

 

[marcus]

...
Has anyone done the calculations on how out of skew Dawn will have to be at the other orbits yet?.

My understanding is that Dawn can stay in the same orbit plane for duration of mission, which takes about one quarter of a Ceres year, as long as it gets the plane right for the first orbit (RC3).
If it is clockwise skew by 5 degrees for RC3 then it is OK for RC3 (at which altitude Ceres ≈ 4 degrees)
then by the time it wants to spiral down to "survey" orbit the skew will have increased naturally for the simple reason that Ceres is at a different place in its orbit . It moves counterclockwise so the sun moves counterclockwise wrt Ceres, which increases the skew angle the sun makes with a constant plane.

I think they planned the descent schedule so that they would not have to change the orbit plane. the skew angle would grow just as fast as the angular size of Ceres grows and Dawn always stays out of shadow.

I think they planned it that way, in part, because as you get closer to a planet it becomes more COSTLY in energy terms to change the orbit plane.

I could be wrong of course. I think they are going to be able to coast thru this rather smoothly because the whole mission plan has signs here and there of being well thought out. But they did have that bad cosmic ray stunning the electronics accident in September and something like that could happen again.

Thanks to Mfb for updating the header! Five times the size of the moon, and Dawn has swung over to the sunny side!

 

[OmCheeto]

My understanding is that Dawn can stay in the same orbit plane for duration of mission, which takes about one quarter of a Ceres year, as long as it gets the plane right for the first orbit (RC3).
If it is clockwise skew by 5 degrees for RC3 then it is OK for RC3 (at which altitude Ceres ≈ 4 degrees)
then by the time it wants to spiral down to "survey" orbit the skew will have increased naturally for the simple reason that Ceres is at a different place in its orbit . It moves counterclockwise so the sun moves counterclockwise wrt Ceres, which increases the skew angle the sun makes with a constant plane.

I think they planned the descent schedule so that they would not have to change the orbit plane. the skew angle would grow just as fast as the angular size of Ceres grows and Dawn always stays out of shadow.

I think they planned it that way, in part, because as you get closer to a planet it becomes more COSTLY in energy terms to change the orbit plane.

I could be wrong of course. I think they are going to be able to coast thru this rather smoothly because the whole mission plan has signs here and there of being well thought out. But they did have that bad cosmic ray stunning the electronics accident in September and something like that could happen again.

Thanks to Mfb for updating the header! Five times the size of the moon, and Dawn has swung over to the sunny side!

Oh.
5° did seem like an excessive skew for the orbit at RC3, but I hadn't even thought about the rest of the mission.
This all makes sense now.
Thanks!

 

[OmCheeto]

I suppose I can stop capturing these images now.
Things are getting a bit too dynamic.

And, just so I don't feel I wasted my time yesterday.
Here's an image of Ceres from a distance where Dawn was yesterday, which is conveniently my eye height to ground, of Dawn at LAMO orbit.

Ceres is my baseball, Dawn is some yellowish thing that fell out of my big leaf maple tree, and my toes are in the general direction that Ceres is moving in.
Dawn is not to scale.

And as Dr. Rayman says; "This is only a simulation."

 

[marcus]

Om, you realize we are almost there? The RC3 orbit radius (from planet center, not altitude) is roughly 14 kkm and fullview2 says 14.7 kkm
They give the speed as 160 mph. That is what we want to see reduced, RC3 orbit speed is something like 67 m/s which is 150 mph. So hopefully in the next 2 or 3 days they can get the speed down from 160 to around 150 mph.

About the orbit plane tilt. It looks like they have the thruster tail pointed mostly in the direction the craft is going but also just slightly Ceres-aft to push Dawn slightly Ceres-forward while it is still on the sunward side---that combined with Ceres gravity should nudge the orbit plane just enough.

 

[mfb]

The April 14 pictures are still missing, and we might get RC3 pictures within a week.

3 more days for circularizing the orbit according to the latest dawn blog entry.

"intensive observations, which will commence on April 24 as it passes over the south pole"

14500km, 730% of full moon now.

 

[OmCheeto]

Om, you realize we are almost there?

Yes, Marcus!

The RC3 orbit radius (from planet center, not altitude) is roughly 14 kkm and fullview2 says 14.7 kkm
They give the speed as 160 mph. That is what we want to see reduced, RC3 orbit speed is something like 67 m/s which is 150 mph. So hopefully in the next 2 or 3 days they can get the speed down from 160 to around 150 mph.

About the orbit plane tilt. It looks like they have the thruster tail pointed mostly in the direction the craft is going but also just slightly Ceres-aft to push Dawn slightly Ceres-forward while it is still on the sunward side---that combined with Ceres gravity should nudge the orbit plane just enough.

I haven't had time to figure out what stars we are looking at. The sun view shows the sun in Gemini, so Dawn should be looking at the southern region of Sagittarius.
And has anyone noticed that they are updating the simulation images much more frequently?
Here are the last three image time stamps:

4.20.2015 13:31:09 UTC
4.20.2015 14:07:07 UTC
4.20.2015 15:27:05 UTC

The April 14 pictures are still missing

They're here!

There's also an animated gif.

 

[marcus]

...3 more days for circularizing the orbit according to the latest dawn blog entry.

"intensive observations, which will commence on April 24 as it passes over the south pole"

Since we've turned a page, I'll bring forward some possibly useful references. Om's timeline trajectory has been remarkably useful and even though made on 2 Feb, over 2 months ago has proven accurate within a day or two! Imagine the day-spot labels in the upper figure advanced by one or two on the last leg (say 24 March to 24 April) so that 24 April falls directly below the planet. It's easy to make that mental adjustment to what is still a useful map and record of the approach.

The RC3 orbit speed needed is 67 m/s or 150 mph and the simulated view says speed is currently 72 m/s or 161 mph. So slowing down the last little bit is clearly the main order of business. Fullview2 shows the ion tail pointed almost exactly in the direction the craft is going. Here are simulated view links:
http://neo.jpl.nasa.gov/orbits/fullview2.jpg
http://neo.jpl.nasa.gov/orbits/fullview1.jpg
Dawn is roughly between Ceres and the Sun so in the view of Ceres, looking from sunwards, we see Dawn's main antenna dish.
In the view of the Sun (including Earth and Mars, with recognizable constellations such as Gemini and the upper part of Orion), Dawn's dish is on the other side from us, hence not visible.
The probe has its thruster beam pointed slightly Ceres-aft so that (besides slowing down) it will drift slightly Ceres-forward (in the direction of Ceres orbital motion) while it is on the sunlit side of the planet. this is part of adjusting the plane of Dawn's polar orbit around Ceres to keep it out of the planet's shadow when it rounds the S pole and comes up on the dark side.

Mfb mentioned the Dawn Journal, a blog kept by mission director Marc Rayman. It's been remarkably informative and fun to read over the past few months. Here's the link to the mission journal's index:
http://dawn.jpl.nasa.gov/mission/journal.asp
Here's the Ceres part of the Dawn photo/image gallery:
http://dawn.jpl.nasa.gov/multimedia/Ceres_science_gallery.asp
If anyone is curious, Om's original posting of that timeline trajectory is post#47 on page 3 of this thread:
https://www.physicsforums.com/threa...-size-of-full-moon.793140/page-3#post-4996800
Quite simply, it was adapted from a couple of figures in Rayman's November journal which did not have the day-circles labeled. Tagging the days with dates made the whole thing easier to read and use.

 

[marcus]

Speed went down for the first time! since the probe started spiraling into circular orbit. At least on the simulated view. This morning it had crept up to 161 mph, but a new fullview2 update as of 19:30 UTC shows it eased back to 160 mph.

I guess this means we can proceed with our plans to colonize the planet, Om. We need to figure out how to best to excavate air-tight bubbles deep in the ice for the colonists to live in. And how to provide cheerful lighting and amusement facilities.

 

[OmCheeto]

Speed went down for the first time! since the probe started spiraling into circular orbit. At least on the simulated view. This morning it had crept up to 161 mph, but a new fullview2 update as of 19:30 UTC shows it eased back to 160 mph.

hmmm... I'm not sure how to interpret the following:

NASA's Dawn Mission ‏@NASA_Dawn 1 hour ago
Today's orbit speed: 155 mph with respect to #Ceres, accelerating as I get closer

Should they have said decelerating? Or do rocket scientists only speak of positive and negative acceleration?
On the other hand, a change in speed is always an acceleration.
Ha! I don't think I've ever thought about that before.
Never mind.

I guess this means we can proceed with our plans to colonize the planet, Om. We need to figure out how to best to excavate air-tight bubbles deep in the ice for the colonists to live in. And how to provide cheerful lighting and amusement facilities.

Grand idea, Marcus! And perhaps the Cereans have already done it for us. Those headlights might be domes of ice, covering grand cities. I think I spotted another one in todays image. Though it is more of a splat than a headlight, and quite a bit dimmer.

 

[marcus]

I think it is just a discrepancy between the simulated view, which said 160 today, and the tweet which says 155.
I'm inclined to trust the tweet.
if I'd realized there was such a large discrepancy I would have held off posting about the speed, or used the Twitter information.

Thanks for pointing that out.

BTW they seem to agree better about the distance "less than 9000 miles" and a bit under 14.4 kkm.

 

[OmCheeto]

Ceres will be completing its first RC3 orbit right around my birthday.
Thank you, Marcus, for inviting me along for this ride.

I think it is just a discrepancy between the simulated view, which said 160 today, and the tweet which says 155.
I'm inclined to trust the tweet.
if I'd realized there was such a large discrepancy I would have held off posting about the speed, or used the Twitter information.

Thanks for pointing that out.

BTW they seem to agree better about the distance "less than 9000 miles" and a bit under 14.4 kkm.

I don't recall seeing a reason behind why the statistics in the images don't match what is really going on.
And I don't think I noticed until just now, that RC3 is just one orbit. It will start its descent down to the "survey" orbit, right around my birthday.
I don't think I could have asked for a better birthday present.

Thank you, Marcus, for inviting me along for this ride.

ps. Today is the first time in 6 days that a question has passed moderation on Dr. Rayman's blog. I can only imagine, that he is quite busy. I wonder when his birthday is. I'd like to send him something. Though, Tim Berners-Lee turned down my offer of chocolates, in appreciation for the WWW, many years ago. Probably a good thing. Can you imagine getting 3+ billion boxes of chocolate on your birthday every year?

 

[OmCheeto]

Has anyone noticed that the simulated images are already showing shadowing on the southern edge of Ceres?
This would mean that Dawn has already passed the equator.
Though the speed is still listed as 158 mph, and the tweet said 155 mph, 17 hours ago.

I wish I knew how to make a moving gif. The simulation images are being updated almost every hour. It's quite a bit of fun to scroll through them.

4.21.2015.140707
4.21.2015.152313
4.21.2015.163913

Here's a funny tweet from the other day:

NASA's Dawn Mission retweeted

Angela Gibson @AgilistaAG · Apr 19
Dr Green "Here is our best wrong model for Ceres" probably within a year thru @NASA_Dawn mission will know #NEAF

I think I missed the word "wrong" in there yesterday.

I'm still not fluent in twitter speak, so it took me a few minutes figure out that they weren't talking to someone/something called "NEAF".
NEAF = Northeast Astronomy Forum
They held a conference at SUNY Rockland Community College in Suffern, New York, April 18 & 19, 2015
2015 Speakers: Jim Green, Dir. of Planetary Science, at NASA Headquarters

 

[Dotini]

Some nice lights and shadows on this processed image,

A processed still image of Ceres from the above animated sequence of images.
Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA
Full Image
- See more at: http://dawn.jpl.nasa.gov/news/Ceres...k_into_view.asp#sthash.S27bW4aj.QmWqgwXm.dpuf

 

[OmCheeto]

NASA's Dawn Mission ‏@NASA_Dawn 31 minutes ago
...and 8,500 miles is about 14,000 kilometers #metricsystem​

Teasers!

8710 miles & 14020 km
157 mph & 0.07 km/sec
(from http://neo.jpl.nasa.gov/orbits/fullview2.jpg : 4/21/2015 21:22:49 UTC)

 

[Dotini]

What are the bright spots?

I've heard some ideas:
1. ice
2. salt flats
3. cryovolcanoes
4. water vapor
5. a combination of the above
6. it's better to remain baffled for a little while longer

We may well be on the edge of discovery. Is Marcus still plumping for salt flats?

 

[marcus]

At this point the ambiguity of altitude vs radius begins to make minor trouble. Rayman and/or the Dawn tweeter may like to talk to public in terms of altitude (RC3 = 13,500 km) distance from the closest point on the surface.
While the guy who does fullview2 and the other simulated views may like to use orbit radius (more conventional physicsish , RC3 = 13,975 km)

 

[marcus]

Dotini, depending on the time of day I'll be plumping either for salt flats or "some combination of the the above". I've read that the rest of the surface is very low albedo (10%, didn't Emily Lakdawala say something like that?) So the bright spots might not actually need to be very bright by ordinary standards--I expect they could still show up very bright by contrast.

 

[marcus]

I now think fullview2 speeds have been more reliable after all. Just a hunch. The tweeter seems to me to have been calculating the speed gain as the radius shrank, and reporting that without counting the effect of thrust.
fullview2 seems to me to have embodied consistent physics and it now says 153 mph as the probe is beginning to pass over the S pole.

We will know it's passing over S pole when we see a "half-Ceres" phase.

And then the probe should not be crossing the terminator at 90 degrees, from light into dark. It should be crossing into the leftthand dark quadrant. Like at an angle of 95 degrees, instead of 90. That way when it comes back over the N pole, from dark into light, it will be heading into the righthand light quadrant, say at an angle of 85 degrees. (usual counterclockwise angle convention taking terminator as x axis)

By that time it may be going only 150 mph, which would be 67 m/s or RC3 orbit speed assuming the Ceres mass of 943 billion billion kg. Just guessing.
Of course fullview2 could be using the wrong mass and be wrong many ways, but so far it is telling a consistent story and I haven't seen a good reason to doubt it.

 

[OmCheeto]

Fun trivia tweet from the Dawn team:

https://pbs.twimg.com/profile_images/3502834940/2f750377e236127f02d96e270510d727_normal.jpeg NASA's Dawn Mission @NASA_Dawn · 1 hour ago
Fact: My total delta-V -- the total sum of velocity changes that this spacecraft has done since launch -- is now more than 24,000 mph
​

Ahh... the power of solar motivated ion drive.

 

[mfb]

= 10.7 km/s

Distance to Ceres seems to be very stable at 13.990 km. Once it switches off the ion drives we can see the final velocity, cover the "distance to surface or distance to center" issue, and make guesses what Marc Rayman will announce as mass in May.

 

[OmCheeto]

What are the bright spots?

I've heard some ideas:
1. ice
2. salt flats
3. cryovolcanoes
4. water vapor
5. a combination of the above
6. it's better to remain baffled for a little while longer

We may well be on the edge of discovery. Is Marcus still plumping for salt flats?

7. Ice Tardises

​

 

[marcus]

= 10.7 km/s

Distance to Ceres seems to be very stable at 13.990 km. Once it switches off the ion drives we can see the final velocity, cover the "distance to surface or distance to center" issue, and make guesses what Marc Rayman will announce as mass in May.

Quite true. That said, it's still exciting to watch the simulated view (which has been fairly close to reality so far.) View shows half-Ceres phase. speed 151mph (nominally we expect 150 so very close) and as you say distance steady at about 14 kkm. The dateline is 2AM, 23 April. UT.

I would say that if you trust fullview2, give or take a few hours and time zones, it IS now in circular polar orbit. With the orbit plane angled off the sun direction by a few degrees. And it is passing over the Cerean south pole region. Yahoo!

I don't expect them to stop and take pictures any time soon. They might. But it seems more likely that they will be be extremely busy doing all kinds of checks and making all sorts of preparations. Might even see them in radio (doppler) navigation contact. Does anybody know when a photoshoot is scheduled?

 

[marcus]

fullview2 now indicates Dawn is in the planned circular orbit at radius 14 kkm (steady for a couple of days) and speed 150 mph (67 m/s)
passing over S pole
and crossing the terminator at a sufficient angle to keep the craft out of Ceres' shadow as it comes up north on the dark side.
We see the solar panels edge-on because they are facing the sun, which is at right angles to our line of sight.

The dateline on fullview2 is currently 23 April, 8 AM UT
http://neo.jpl.nasa.gov/orbits/fullview2.jpg
This image is the the first one I've seen showing 150 mph for speed relative Ceres,
which is what it has to be for circular orbit at this radius, assuming Ceres mass 943 billion billion kg.
(G*943e18 kg/14000 km)^(1/2) = 67.05 m/s
or 149.98 mph

https://eyes.nasa.gov/dsn/dsn.html Deep Space Network currently shows Dawn in 2-way radio communication with Goldstone antenna #24 (as of 4:35 AM pacific, around 12 hours UT)
the power received is shown varying around 18 attowatt.
125 kilobit per second at 8 GHz.
to me this suggests that the craft has turned off thruster and aimed its main antenna at Earth

 

[OmCheeto]

...
to me this suggests that the craft has turned off thruster and aimed its main antenna at Earth

Does this mean someone should say shout; "We're here"!
Within the last few minutes, Goldstone stopped communicating, and Canberra dish #35 is receiving data.
Currently: 4/23/2015 14:23 UTC (7:23 am PST)

 

[marcus]

It's official in a sense
fullview2 shows thrust off and the probe re-oriented to point antenna at Earth, confirming the Deep Space Network activity we saw earlier this morning.
Also fullview2 changed its range reporting format from "distance to Ceres" which had been 14 kkm
to "altitude above Ceres" which is 13.52 kkm, close to the expected 13500 km.

It's significant and it resolves for us the minor ambiguity about distance (from center) and altitude (above surface).
And it makes sense to change over: altitude above surface is going to be the optically pertinent range as time goes on and the probe gets closer.
People may want to check the DSN site to get an idea of the information flow
https://eyes.nasa.gov/dsn/dsn.html now that Dawn is apparently in its planned initial destination orbit ("RC3" for "rotation characterization")
Here are the tentative plans, orbitwise, from the mission director's journal of 31 March
http://dawn.jpl.nasa.gov/mission/journal.asp

orbit     dates     altitude(km)    pixel(m) XHubble  period   analogy
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)

Columns:
Orbit code name
Tentative dates
Altitude in (kilometers)
Resolution in (meters) per pixel
Resolution compared to Hubble
Orbit period
Equivalent distance of a soccer ball

 

[marcus]

Even though we are looking at the beginning of the most interesting part of the mission the first-time study of one of the solar system's ice-ball orbs, I'm inclined to reflect on what I think are already significant innovative achievements in several directions:
solar powered ion propulsion (10-fold more efficient than chemical rocket)
a different kind of trajectory (smooth steady-thrust curves)
precision remote navigation in and out of orbits at several AU distance
the extent to which the craft seems robotic, to have intelligent control delegated to it

I don't know enough to judge the level of innovation on the last point but was impressed by the extent of independent operation, the probe was thrusting much of the time unsupervised (70% of the time it has been abroad, most of that time un-monitored and under its own guidance)