New Horizons is on a one-way trip, outward bound.

The planned trajectory is hyperbolic from the solar system. The flyby
speed at Pluto depends on the arrival year. For a 2006 Jan launch and a 2015 July arrival, it is about 13 km/sec.

-Alan

Are you saying that the Voyagers are *not* on hyperpolic trajectories?

Until these posts, I've always been under the impression that all four of the distant human spacecraft were travelling at above Solar escape velocity...

That 225 million years involves an orbit...around the galaxy

Doug

Doug:

That, I can accept!

And obviously, it'll be perturbed to hell and back by then, so Adios, Amigo!

Bob Shaw

Something different; I'm curious about how much fuel NH would have to take to be able to do a POI-burn. Probably a lot considering it's velocity.

Well, a low circular orbit of say, 100km around pluto would require...
umm

a=v^2/R f=MA f=gM1M2/R^2...

UMM

ahh

right

boil all that down and basically the orbital velocity of any spacecraft is....

Sqrt of G M1 / r

where G is newtons tiny number, M1 is the mass of the body ( pluto ) and r = radius from the centre of the body

I get 865 m/sec for an orbital velocity - so you'd have to have a delta V of 12.1km/sec - Consider MRO, which is 50% fuel by mass - and can manage a Delta V of about 1km/sec

Of course - if you broke into a very eliptical orbit - it would be less delta V than that - but that maths is beyond me

Doug

SO:

At roughly 400 kg's of (dry) mass, that would mean it has to descellerate roughly 20 % of MRO's mass....which will consume a fifth of 1100 kg's of fuel, being 220 kg's for each delta V of 1 km/s for NH.

Times 12,1 (or do i forget an exponent here ?) means 2660 kg's of hydrazine, which would make NH 3 tons in total.

I'll forget about it.

But then - at the beginning of that burn, you're having to decellerate 3 tons as well

It's called the rocket equation I believe, cant remember the specifics of it - but it's the equation that tells us that at launch, not only is a rocket launching it's payload, but it's launching all it's fuel as well - which gets consumed en route.
Put it this way - 12km/s is 60% MORE than the speed required to orbit the earth - and you have some very mighty rockets to start doing that

Doug

I knew i forgot about that while i was writing (you have to bring the fuel you need later on, which costs energy as well). But roughly we could say, that it would have to be an inverted delta II or something like that.

Why not brake gentle after jupiters assist with an ion thruster or something and ooze in orbit by just the right speed and angle ? Why do these OI burns always have to be so brute and violent just before passing the target ?

If you used an ion thruster it would add years to the mission. It has taken Hayabusa months to approach its target gently.

Nick

give a deceleration of 1 mN on 400kg - you've got an acceleration of 0.0000025 m/s^2

So the 12km/sec would take about 152 years

Doug

I wonder then how they'll manage to get the probe as described in the "far out" thread to 100 km/s with ion thrusters within a scientists lifetime. Stack em up probably !

Let's forget about orbitting Pluto. It's too expensive and way out of proportion. A flyby within my lifetime would be perfect for me: i am wondering about what it looks like there since i could read.

Keep in mind that for this scenario to work, NH would need to be on an elliptical orbit with a aphelion at Pluto's expected location. That would be a very slow journey.

What about a space-based launch? This'd assume a stable space station, like the ISS's descendant, and preferably one a bit higher than the ISS. Maybe a few launches of main modules, assemble in space, and send it on its way.
Even so, it'd need to be big (like, probably larger than Cassini), but at least the problem of a launch vehicle wouldn't be an issue.


That aside, I'd still love to strap an ion engine onto New Horizons and switch it on once the Pluto flyby is done. Fling the thing outta here fast.

The main problem with low-thrust orbiters for the really distant outer Solar System is that, after you thrust for a long time to get to the planet fast, you then have to thrust just as long to slow down the flyby speed enough to be able to brake into orbit around the planet when you get there. Unless, that is, you have a planet with a substantial atmosphere -- such as Uranus or Neptune -- in which case you can have the best of both worlds: use an ion drive to ram the probe into the outer Solar System rapidly, and then eject the ion-drive module just before arrival and use aerocapture to brake into orbit around the planet. Which, in fact, is exactly what JPL plans to do in its current Neptune Orbiter design.

You might, perhaps, be able to do that at Pluto, using a ballute, if you get there before the extremely thin atmosphere freezes out. (JPL is seriously considering adding a modest-sized Triton soft-lander to the Neptune Orbiter, having discovered that most of the lander's preliminary braking can be done by skimming through Triton's extremely thin air with a ballute that would be quite low-mass.) But in Pluto's case, there's a real chance that the air WILL have frozen out by the time you get there. In any case, the important thing to do with KBOs -- including Pluto -- is to examine as large an assortment of them as possible, rather than spending large amounts of money focusing on just one (even one as relatively distinctive as Pluto).