DAWN mission to orbit 1 Ceres & 4 Vesta.

[MeteorWayne]

It only looks busy until you realize that you are looking at an area 2 or 3 AU across.

As far as the close question, how close is close for what purpose? If you mean Dawn visiting, it means a few hundred thousand km and in an orbit that would require minimal expenditure of propellant. That means a close match in orbital velocity, as well as inclination, since both require a change in velocity.

 

[EarthlingX]

It only looks busy until you realize that you are looking at an area 2 or 3 AU across.

As far as the close question, how close is close for what purpose? If you mean Dawn visiting, it means a few hundred thousand km and in an orbit that would require minimal expenditure of propellant. That means a close match in orbital velocity, as well as inclination, since both require a change in velocity.

Hm .. few hundred thousand would be 200 - 300 000 km ? .. and a similar orbit .. I will fly a couple of rounds with that range marked, see what gives, but i don't expect much, as you guys said, too close. Need to get me more orbital data for asteroid belt, this is just basic, with past and future Earth crossing asteroids (about 5 - 10 000, methinks).

I can't help noticing that Pallas orbit is very much inclined. It passes Ceres though, while Dawn is supposed to still be there, it would be rather close, if not for the inclination, with the old mission data i have in Celestia. I'm too noob to fix that, hopefully some day:

Near the mission end:

Could Dawn use Ceres for gravity assist to change inclination ? Does it have enough fuel for such a thing ?

 

[MeteorWayne]

No, Dawn can't use Ceres for that, since it will be orbiting the dwarf planet. Such shifts in orbit can only occur during flybys. And that is the real problem in reaching Pallas, the inclination, 35 degrees (Ceres is 11 degrees).

However, and visits bt Dawn to any other asteroids will be flybys anyway, since it won't have enough propellant to match an orbit and stay with the asteroid. I wonder, can you use Celstia to find when Ceres and Pallas will be closest to each other?

 

[Boris_Badenov]

As the escape velocity of Ceres is so low, is it possible to drop Dawn on the surface as was done with NEAR on Eros? Would there be any benefit of doing so if it turns out to be possible?

 

[MeteorWayne]

I suppose it would be possible, though the gravity is quite a bit higher than on Eros. But I believe the plan is to look for another asteroid (or two) two eventually fly by after the primary mission ends at Ceres. Funding permitting, of course

 

[EarthlingX]

No, Dawn can't use Ceres for that, since it will be orbiting the dwarf planet. Such shifts in orbit can only occur during flybys. And that is the real problem in reaching Pallas, the inclination, 35 degrees (Ceres is 11 degrees).

However, and visits bt Dawn to any other asteroids will be flybys anyway, since it won't have enough propellant to match an orbit and stay with the asteroid. I wonder, can you use Celestia to find when Ceres and Pallas will be closest to each other?

I can't directly ask that, sql support only for stars with add-on, but i can rewind back and forth.
One such date is on 2014 jun 16, Pallas is somewhere close to cross Ceres orbital plane, and what is interesting, it is actually between Ceres and Vesta, just inclined :
View from Ceres surface, Pallas is on it's way up:

View from a side:

Orbital data for Ceres, Vesta and Dawn is from this add-on:
http://www.celestiamotherlode.net/catal ... on_id=1220

Pallas orbital data comes with my version (1.6).

I have yet to figure out how to get data from here:
http://ssd.jpl.nasa.gov/?horizons
into the program ..

They also get close somewhere in 2016, on Pallas way down, but have to check.

 

[EarthlingX]

Not close, but Ceres crosses Pallas orbital plane somewhere around 2016 06 17, at a distance about 3AU :
View from Ceres:

From the side:


This is when i found Ceres and Pallas to be closest between 2009 and 2020:

They were rather close (1,6 AU) on 2009 11 04:
View from Ceres surface:

They will be close again around 2019 01 25 (1,7 AU) :
view from Ceres surface:

(edit, fixed links to pictures)

 

[h2ouniverse]

As the escape velocity of Ceres is so low, is it possible to drop Dawn on the surface as was done with NEAR on Eros? Would there be any benefit of doing so if it turns out to be possible?

Dear Boris,

The escape velocity is not low at all. It is about 500m/s about 50 times the one of Eros. 500 m/s represents a significant delta-V, that requires chemical propulsion and cannot be achieved by an electric propulsion for a landing. In addition, you need to be able to master the landing with adequate sensors and data processing.

Moreover, the gravity is one-fifth the one of the Moon. Hence a need for landing legs and some mastery of the shock and of the rebound.

Best regards.

 

[MeteorWayne]

Don't know how I missed this, but a new Dawn Journal was released Dec 30:

http://dawn.jpl.nasa.gov/mission/journal_12_30_09.asp

 

[MeteorWayne]

Jan 30 Dawn Journal: (522 days to Vesta Encounter)

http://dawn.jpl.nasa.gov/mission/journal_1_30_10.asp

"Patiently and reliably continuing with its interplanetary voyage, Dawn is now flying in a new configuration and, from the perspective of those readers who may be on Earth, in a new direction.

The spacecraft still spends most of its time gradually changing its orbit around the Sun by thrusting with its ion propulsion system. The probe is outfitted with 3 ion thrusters, assigned the heartwarming names thruster #1, thruster #2, and thruster #3. (The nomenclature and locations of the units were divulged in a log shortly after launch, before such information could be distorted and used unethically by others.) The ship only uses 1 thruster at a time. All 3 were tested during the 80-day initial checkout phase of the mission, and when the interplanetary cruise phase commenced in December 2007, it was thruster #3 that was responsible for pushing the spacecraft away from the Sun......

Dawn is 0.82 AU (123 million kilometers or 76 million miles) from Earth, or 345 times as far as the moon and 0.83 times as far as the Sun. Radio signals, traveling at the universal limit of the speed of light, take 14 minutes to make the round trip.
....

 

[Philotas]

Sorry for being such a poor researcher, but does anyone know when Dawn's pictures of Vesta will surpass those of HST? I see that the spacecraft will arrive in July next year.

 

[MeteorWayne]

There's really two questions there. When could they exceed the HST view, and when will they take such an image. Those may not be at the same time

I'll try and figure out the answer to part 1...for part 2, we'll have to watch the Dawn Journal, methinks

520 days to Vesta arrival.

 

[MeteorWayne]

Latest Dawn Journal:

http://dawn.jpl.nasa.gov/mission/journal_03_28_10.asp

Excerpts:

March 28, 2010


Dear Dawnthorities,

Dawn continues patiently forging through the asteroid belt, its permanent residence, as it climbs away from Earth and the Sun. Having thrust with its ion propulsion system for more than 1.5 years, the spacecraft remains healthy and on target for its rendezvous with alien worlds.

Our interplanetary adventurer still has a great deal of ion thrusting to complete before it can begin its orbital exploration of Vesta next year...

In addition to keeping the ship sailing smoothly and on course, Dawn’s engineers (who reside and work on distant Earth) are developing the detailed instructions that will guide it into orbit around Vesta and throughout its year of operations there. This process began last month and will continue even as the probe begins executing the first of the commands in May 2011...


Most of the approach phase is dedicated to the final ion thrusting required to slip into orbit around Vesta. All of Dawn’s thrusting contributes to rendezvousing with Vesta, but the terminal thrusting will be controlled slightly differently. We will describe the process of using ion propulsion to enter orbit around another solar system body in an upcoming log. For now, however, let’s take a look at some of the other activities during the approach phase. While these are being timed in the sequences down to the second, part of the strategy for developing these sequences is to allow the team a means to update the times as the probe closes in on its target. The ion propulsion system provides flexibility in the timing that is different from most missions, and to take advantage of the benefits, the sequences must be correspondingly flexible. All the relative timing within a sequence will be fixed, but the time each sequence is activated can change. So, for example, even though we may change the date the first Vesta approach sequence begins executing by as much as a few days, once that adjustment is made, all the events within the sequence will shift by exactly the same interval. Some small changes other than timing, such as details of the probe’s orientation, may be made as well to reflect the latest information available before it is time to transmit the sequences to the spacecraft more than a year from now...


The principal activity other than thrusting during approach is the acquisition of images of Vesta with Dawn’s main science camera, primarily for navigation.

The first optical navigation images will be acquired when Dawn is about 1.2 million kilometers (750 thousand miles) from Vesta, or more than 3 times the separation between Earth and the Moon. Dawn’s camera is designed for mapping Vesta from orbit. Therefore, instead of a high-power telescope with a narrow field of view, the camera has a relatively low magnification but covers a broad area.

 

[EarthlingX]

science.nasa.gov : How Capt. Kirk Changed the World

May 4, 2010: "Standard orbit, Mr. Sulu." Captain Kirk barks out the order with such confidence. He knows the USS Enterprise can slip in and out of planetary orbits with ease. But it's only easy in the realm of science fiction. In the real world, such maneuvers have been impossible --until now.
Enter Dawn, NASA's cutting edge mission to the asteroid belt.

Powered with a futuristic sounding new technology called "ion propulsion," this spacecraft will perform space moves rivaling those of the Enterprise.

At this very moment, Dawn is slowly climbing away from the sun, beyond Mars, on its way to its first destination, asteroid Vesta. Dawn will enter "standard orbit" around this rocky world for a year, exploring its mysteries.

Then Dawn will do something unprecedented in real-world spaceflight: exit the orbit of one distant body, and fly to and orbit another. The second destination is asteroid Ceres.

An artist's concept of Dawn in "standard orbit" around asteroid Vesta.

[youtube]http://www.youtube.com/watch?v=IjR36EAR_B4[/youtube]

 

[3488]

Thank You very much for the updates Wayne & EarthlingX.

DAWN update with KECK telescope Adaptive Optics of rotating 4 Vesta. Monday 5th & Tuesday 6th April 2010.

Observations are to support the arrival of the DAWN spacecraft in July 2011.

Asteroid 4 Vesta. Green filter used in the KECK telescope rotating movie to bring out Olivine.

Andrew Brown.

 

[MeteorWayne]

Excellent Andrew, Thanx!!

 

[3488]

You are very welcome Wayne. It is fantastic stuff.

Nice update, I was tipped off on TWITTER. Shows how well DAWN's Ion Thruster is working.

Dawn Spacecraft Fires Past Record for Speed Change.

Andrew Brown.

 

[MeteorWayne]

Excerpts:

Zooming deep toward the heart of the asteroid belt, NASA's Dawn spacecraft has accelerated itself into the record books for the biggest single speed boost ever by a spacecraft engine.

The ion-propelled spacecraft set the new record while on its way to visit the asteroid belt's two biggest space rocks, Ceres and Vesta.

"We are using this amazing ion-engine technology as a stepping-stone to orbit and explore two of the asteroid belt's most mysterious objects, Vesta and Ceres," said Robert Mase, Dawn project manager from NASA's Jet Propulsion Laboratory (JPL), located in Pasadena, Calif.

...

The all-time velocity change record was previously held by NASA's Deep Space 1 probe, which was the first interplanetary spacecraft to use ion propulsion technology. Ion propulsion creates thrust by consistently accelerating ions through a nozzle using electrostatic force.

Deep Space 1's record fell on June 5, when the Dawn spacecraft's accumulated acceleration over the course of the mission sailed past the 9,600 mph (15,449 kph) mark.

 

[Fomalhautian]

Deep Space 1's record fell on June 5, when the Dawn spacecraft's accumulated acceleration over the course of the mission sailed past the 9,600 mph (15,449 kph) mark.

Absolutely amazing. Another small step for man.......

 

[EarthlingX]

http://www.jpl.nasa.gov : Engineers Assess Dawn's Reaction Wheel

June 29, 2010

Dawn Mission Status Update

Engineers are studying the reaction wheels on NASA's Dawn spacecraft after automatic sensors detected excess friction building up in one of them and powered it off early on the morning of June 17, 2010. Reaction wheels spin to help a spacecraft maintain attitude control, and Dawn, which is exploring the asteroid belt, uses three wheels in normal operations.

The three other reaction wheels are functioning normally. Mission managers said plans for Dawn to visit the asteroid Vesta in 2011 and 2012 and dwarf planet Ceres in 2015 will not be not affected.

 

[EarthlingX]

http://www.planetary.org : Dawn Journal: Dawn 9.0

Jun. 30, 2010 | 06:24 PDT | 13:24 UTC

By Marc Rayman

Dear Daw9.0s,
A new version of the Dawn spacecraft is continuing the ambitious journey through the asteroid belt to uncharted distant worlds. Now holding a new solar system record, the probe is thrusting with its ion propulsion system, patiently and gently changing its orbit around the sun to match that of the immense protoplanet Vesta (and subsequently dwarf planet Ceres).

 

[3488]

Thanks for the updates EarthlingX.

The gyroscope problem does not worry me, this kind of issue is expected & the gyroscope is still working. Even if that one fails, DAWN wil lstill go on just fine. It is something to keep an eye on though.

Andrew Brown.

 

[MeteorWayne]

From the description, it's not a gyroscope, but rather a reaction wheel, which is used to align the spacecraft without the use of propellant. In the long run, the loss of one can probably be absorbed with judicious planning, but if it's a systemic problem, it could shorten the effective mission time should another fail.

 

[scottb50]

From the description, it's not a gyroscope, but rather a reaction wheel, which is used to align the spacecraft without the use of propellant. In the long run, the loss of one can probably be absorbed with judicious planning, but if it's a systemic problem, it could shorten the effective mission time should another fail.

Or it might be software or sensors. A little too early to reducing the odds I'd say.

 

[MeteorWayne]

I'd say the diagnosis of increased friction is supported by multiple sensors including heat and power consumption, so is unlikely to be an instrumental problem, though anything is possible.