The DAWN of a new era

[spacewhale]

Such an important demonstration mission, Dawn is. Not only is it demonstrating the function of ion propulsion en route to asteroids Vesta and Ceres (if you wanna call Ceres an asteroids) - 600 plus days of firing its thrusters and counting!! - but it will also do something no other space vehicle has done yet: enter the orbit of one non-Earth body, then, leave orbit and re-enter the orbit of another non-Earth orbit.

I like the way lead mission scientist put it in an article I read on Space Geographic:

"Dawn isn't exactly a hot rod," says Rayman. "It would take 4 days to go from 0 to 60. But it ultimately achieves fantastically high velocity while consuming very little propellant. It uses only a kilogram of xenon every 4 days."

Maybe a bit hyperbolic, but I also believe it when he says this about the importance of the mission:

"Dawn is taking us all on a virtual trip through the cosmos. It's not just a mission by the JPL team, or by NASA, or by the U.S and its partner countries. It's a mission of humankind -- something that represents all of us who share a spirit of adventure and curiosity, a passion for exploration. It's an extension of ourselves into the universe."

[stealthyplains]

Dawn is amazing as is Juno!  I love the unmanned 'heavy scientific' deep space precursor missions like these.

[kevin-rf]

Does bring up a question I have had at the back of my mind, is it possible to use solar powered ion thrusters to reach solar escape or are you to far from the sun before you have gained enough velocity?

[Downix]

Does bring up a question I have had at the back of my mind, is it possible to use solar powered ion thrusters to reach solar escape or are you to far from the sun before you have gained enough velocity?

You *can* just keep going faster and faster around the sun until you have enough velocity to escape if you so chose.

[TOG]

Does bring up a question I have had at the back of my mind, is it possible to use solar powered ion thrusters to reach solar escape or are you to far from the sun before you have gained enough velocity?

You *can* just keep going faster and faster around the sun until you have enough velocity to escape if you so chose.

Or if you like, you could dip toward the sun (just a bit), picking up speed and increasing the power output due to a higher light density.  Using this technology you could get a double benefit from the path you choose.

[kevin-rf]

Does bring up a question I have had at the back of my mind, is it possible to use solar powered ion thrusters to reach solar escape or are you to far from the sun before you have gained enough velocity?

You *can* just keep going faster and faster around the sun until you have enough velocity to escape if you so chose.

The faster you go, the further from the sun your orbit gets. Less solar power. The question, which I do not know the answer for is on an ion thruster spiral out, do you have enough time as you spiral out to increase your velocity enough to leave solar system before the sun is to far to power the ion thrusters.

Dawn will take years to spiral out to Ceres and Vesta, could it get up to escape if it chose to? (Complete hypothetical since if it gets to far from the sun, the sun will set on dawn and it will go dark).

[bad_astra]

Does bring up a question I have had at the back of my mind, is it possible to use solar powered ion thrusters to reach solar escape or are you to far from the sun before you have gained enough velocity?

It would appear possible with an eliptic orbit and a few gravity assists.

[KelvinZero]

- but it will also do something no other space vehicle has done yet: enter the orbit of one non-Earth body, then, leave orbit and re-enter the orbit of another non-Earth orbit.

Another feature about ion drive asteroid missions.. I dont remember if it was this one.. was that they had not yet made up their minds on later destinations at the time of launch. Very different from a mission using chemical rockets.

I also remember a mission proposal to visit several of the moons of jupiter, stopping at each one using low energy orbital transfers

(sorry I havent been great with my references in this post )

[khallow]

Does bring up a question I have had at the back of my mind, is it possible to use solar powered ion thrusters to reach solar escape or are you to far from the sun before you have gained enough velocity?

Think of it this way. You have complete your acceleration (and achieve a certain delta v) by a certain distance from the Sun, say the orbit of Jupiter. That's a lot of distance in which to accelerate. The dry mass of Dawn is something like 825 kg. At 0.25 kg of propellant per day and 3,100 seconds impulse, I think it could rather quickly reach escape velocity, especially if coupled with a gravity assist around Venus or Jupiter.

Let's try a back of the envelop calculation. From Earth orbit, you need something like 9 km/s of delta v to escape the Sun's gravity (using that we're already moving along with Earth). Assuming we can keep the above ISP, we get that we need roughly 26% of the vehicle mass to be propellant. That's roughly 1100 kg, which is less than the actual vehicle masses. The vehicle would also need to accelerate at this rate for roughly 3 years. Assuming constant acceleration, I get that it covers a distance of roughly 3 AU in the process (I guess from the point of view of a orbiting frame of reference).

My take is that even without gravity assists, it probably could be done by using some very eccentric orbit with part of the orbit within range of the Sun. Spend the time while near enough to the Sun to boost to an even more eccentric orbit with a similar closest approach, until you eventually reach escape velocity.