Starship Asterisk*

Nitpicker wrote:I keep seeing references to Pluto's north pole on this illuminated side. I don't believe it is correct to call it the north pole. If Pluto were still considered a planet, the illuminated pole we see here, points comfortably below the ecliptic and invariable plane and so would be the south pole. And if considered a dwarf planet, the illuminated pole becomes the positive pole, via the right-hand rule.

(What a great image! But I'm surprised no one has complained that it is upside down. )

Huh, according to this blog from 2013, it can be considered correct to refer to the currently illuminated pole of Pluto as positive, south, or north:
http://www.planetary.org/blogs/emily-la ... raphy.html

Love it!

That's funny. I've been simply calling it "the pole" as a way to avoid figuring out whether it's the north or south.

Ok, I know this may be a stretch........but studying the north pole of Charon, the dark area seems to be actually a depression, not a plain, surrounded by shallow angled cliffs. Almost like a golf divot. Initial shape of Hydra would seem to fit in it like a piece from a jigsaw puzzle. And Hydra's apparent size would allow it to fit neatly in the gray area..........................................

montylc2001 wrote:Ok, I know this may be a stretch........but studying the north pole of Charon, the dark area seems to be actually a depression, not a plain, surrounded by shallow angled cliffs. Almost like a golf divot. Initial shape of Hydra would seem to fit in it like a piece from a jigsaw puzzle. And Hydra's apparent size would allow it to fit neatly in the gray area..........................................

Charon is ~30 times larger in diameter than Hydra, whereas the dark area at Charon's pole looks to be roughly a quarter of Charon's diameter. So, yes, a stretch of about 7.5 times.

(But look at the tantalizing feature on Charon's limb at about 2 o'clock!)

Is it really a surprise that the surfaces have relatively few craters ? Its a system whose center of gravity is outside Pluto's surface. Therefore, an incoming one will just fly through, as meteors are incredibly fast. There is a good chance that the meteor will never return back to the Pluto system. Very few that did come back formed a crater eventually.

dushyant wrote:Is it really a surprise that the surfaces have relatively few craters ? Its a system whose center of gravity is outside Pluto's surface. Therefore, an incoming one will just fly through, as meteors are incredibly fast. There is a good chance that the meteor will never return back to the Pluto system. Very few that did come back formed a crater eventually.

It doesn't really matter that the center of gravity is outside the planet. It just shifts the trajectory of bodies a little. Things that might have otherwise missed will now hit. Consider that the moons of the giant planets are often heavily cratered, despite a massively greater gravitational source very nearby.

dushyant wrote:Is it really a surprise that the surfaces have relatively few craters ? Its a system whose center of gravity is outside Pluto's surface. Therefore, an incoming one will just fly through, as meteors are incredibly fast. There is a good chance that the meteor will never return back to the Pluto system. Very few that did come back formed a crater eventually.

By that rationale, I suppose we should all have been hurtled into the Sun by now, and the Sun into the SMBH at the centre of the Milky Way. (And gravity really would suck.)

I didn't mean Hydra would be a perfect fit......if it were the result of a violent collision then of course Hydra would be smaller than the plain, which it is, and both would have ragged edges. Just a thought.

richardschumacher wrote:

Guest wrote:What is the remaining purpose of the the mission? Why didn't they put it into orbit and gather tons o' data?

It's about the best we can do with available technology and money. It takes energy to speed up and slow down a spacecraft. Moving fast enough to get to Pluto in reasonable time, New Horizons couldn't carry nearly enough rocket fuel to slow down again and enter orbit.

I know that's been the word on the street for some time. But I'm wondering about it all. When NH passed Jupiter it accelerated to 14.2mps. When it left Earth, I believe the speed worked out to about 10.1mps. When it reached Pluto, we're getting quoted around 10mps again. So some retrorockets must have fired around here someplace?... Space dust doesn't slow your speed down that much over that short a distance. If they could drop 14,000 mph as a part of this mission, I find it hard to believe that it would have been THAT expensive to drop more. The thing only is the size of a Grand Piano and weighs a lot less. I rebuild grand pianos for a living and can pick up the corner of a concert grand by myself...

Prospero wrote:

Guest wrote:What is the remaining purpose of the the mission?

I hope I have remembered the gist, not garbled it too much, because I cant find the page again

EDIT2
BBC Radio4 just done a piece on NH and said 2 poss. objects, flyby not till 2020.

Watching a broadcast from NASA yesterday, I heard one of their strategy experts say that their study put one interesting object so in line with their flight that rockets would have to be fired to miss it...

Pianosorplanets

Pianosorplanets wrote:I know that's been the word on the street for some time. But I'm wondering about it all. When NH passed Jupiter it accelerated to 14.2mps. When it left Earth, I believe the speed worked out to about 10.1mps. When it reached Pluto, we're getting quoted around 10mps again. So some retrorockets must have fired around here someplace?... Space dust doesn't slow your speed down that much over that short a distance. If they could drop 14,000 mph as a part of this mission, I find it hard to believe that it would have been THAT expensive to drop more. The thing only is the size of a Grand Piano and weighs a lot less. I rebuild grand pianos for a living and can pick up the corner of a concert grand by myself...

The spacecraft lost speed all the way to Jupiter, because of the pull of the Sun. The gravity assist maneuver at Jupiter boosted the speed again. From that point, it continued to lose speed (and is still losing it) because of the Sun. No rockets were involved. It is currently moving away from the Sun at 14.5 km/s, and will be slowing down for thousands of years, at least until it falls into the gravity well of some other star.

I don't think you realize just how much energy this probe has. Kinetic energy is proportional to the square of the velocity. You might be able to lift the corner of a piano, but if you encountered one that was moving at 14.5 km/s, you (and it) would be vaporized by the collision (50 billion joules, or about 12 tons of TNT equivalent). There's no practical way with a small probe to shed that much energy. An enormous amount of fuel would have been required, and of course, most of that fuel would have been used just for decelerating the unburned fuel, which would be vastly more massive than the probe alone. And an even larger rocket would have been needed at launch.

Pianosorplanets wrote:

richardschumacher wrote:

Guest wrote:What is the remaining purpose of the the mission? Why didn't they put it into orbit and gather tons o' data?

It's about the best we can do with available technology and money. It takes energy to speed up and slow down a spacecraft. Moving fast enough to get to Pluto in reasonable time, New Horizons couldn't carry nearly enough rocket fuel to slow down again and enter orbit.

I know that's been the word on the street for some time. But I'm wondering about it all. When NH passed Jupiter it accelerated to 14.2mps. When it left Earth, I believe the speed worked out to about 10.1mps. When it reached Pluto, we're getting quoted around 10mps again. So some retrorockets must have fired around here someplace?... Space dust doesn't slow your speed down that much over that short a distance. If they could drop 14,000 mph as a part of this mission, I find it hard to believe that it would have been THAT expensive to drop more. The thing only is the size of a Grand Piano and weighs a lot less. I rebuild grand pianos for a living and can pick up the corner of a concert grand by myself...

Short answer: gravity.
Detailed answer:
http://ccar.colorado.edu/asen5050/proje ... lysis.html

Pianosorplanets wrote:
When NH passed Jupiter it accelerated to 14.2mps. When it left Earth, I believe the speed worked out to about 10.1mps. When it reached Pluto, we're getting quoted around 10mps again. So some retrorockets must have fired around here someplace?... Space dust doesn't slow your speed down that much over that short a distance. If they could drop 14,000 mph as a part of this mission, I find it hard to believe that it would have been THAT expensive to drop more. The thing only is the size of a Grand Piano and weighs a lot less. I rebuild grand pianos for a living and can pick up the corner of a concert grand by myself...

Escape velocity at Jupiter's orbit is still ~11.5 mps
so no retrorockets or space dust were needed to slow down after Jupiter.

A Steinway grand piano weighs about 450 kg;
New Horizons weighs roughly the same: 395 kg plus 77 kg of hydrazine monopropellant fuel

Hydrazine monopropellant has an exhaust, v_e ~ 2.2 km/s; therefore,
in order to lose all of its 13.78 km/s velocity at Pluto NH would have required
over 200 tonnes [=395 kg x exp(13.78/2.2)] of hydrazine monopropellant fuel.

The Ares V might be able to deal with a 5 tonne NH but not a 200 tonne one.

An ion propulsion system (such as that on the Dawn spacecraft) would be feasible
but that would require continuous deceleration from Jupiter flyby and a ~20 year voyage.

neufer wrote:Escape velocity at Jupiter's orbit is still ~11.5 mps

Meters per second?

Solar escape velocity at Jupiter's orbit (5.2 AU) is 18.5 kilometers per second.

Chris Peterson wrote:

neufer wrote:
Escape velocity at Jupiter's orbit is still ~11.5 mps

Meters per second?

Solar escape velocity at Jupiter's orbit (5.2 AU) is 18.5 kilometers per second.

"Pianosorplanets" was clearly using mps (= MPS = miles per second) so I was responding in kind.

Sorry for the confusion.

neufer wrote:

Chris Peterson wrote:

neufer wrote:
Escape velocity at Jupiter's orbit is still ~11.5 mps

Meters per second?

Solar escape velocity at Jupiter's orbit (5.2 AU) is 18.5 kilometers per second.

"Pianosorplanets" was clearly using mps (= MPS = miles per second) so I was responding in kind.

Sorry for the confusion.

Ah. I just assumed his numbers were wrong, and didn't pay any attention to them, but rather to the question itself. Silly units, miles per second.

The success of the mission is a great achievement.

In the information brought up through the 'survived its close encounter with Pluto' link I was surprised to read "New Horizons is collecting so much data it will take 16 months to send it all back to Earth"

Unfortunately the power supply only generates 200 watts so information transmissions are very limited in bandwidth

Just sayin' ... this sure looks like a PLANET to me. In fact, back in 1953 Clyde Tombaugh himself told me that it was.

DavidLeodis wrote:The success of the mission is a great achievement.

In the information brought up through the 'survived its close encounter with Pluto' link I was surprised to read "New Horizons is collecting so much data it will take 16 months to send it all back to Earth"

Yes, I found this impressive. It seems that the mission planners, knowing they would have to be content with one short pass, found a way to pack everything into the experience that they could.

As to that question of slowing down on arrival, I know there's one way to do it, and that's to smash into the planet. More seriously, though, NASA long ago became adept at making great use of gravity assists. Is there a corresponding way to obtain a "gravity hindrance"? Not that it would initially seem a useful thing, but surely the NH probe could have left Jupiter travelling slower, rather than faster, correct? Of course that's not what we wanted. But suppose we wanted to fly a probe into the Saturn system very fast and to decelerate more than our fuel alone could accomplish. Could careful targeting and selective burns have it swing around several moons and use them as a sequence of brakes? At first guess, though, it seems that if you can't use a given body's gravity to capture the probe in the first place, it is probably very limited how much you can steer around it and get any slow down.

MarkBour wrote:
As to that question of slowing down on arrival, I know there's one way to do it, and that's to smash into the planet. More seriously, though, NASA long ago became adept at making great use of gravity assists. Is there a corresponding way to obtain a "gravity hindrance"? Not that it would initially seem a useful thing, but surely the NH probe could have left Jupiter travelling slower, rather than faster, correct? Of course that's not what we wanted. But suppose we wanted to fly a probe into the Saturn system very fast and to decelerate more than our fuel alone could accomplish. Could careful targeting and selective burns have it swing around several moons and use them as a sequence of brakes? At first guess, though, it seems that if you can't use a given body's gravity to capture the probe in the first place, it is probably very limited how much you can steer around it and get any slow down.

• If one throws a ball in the air at 32 ft/s
  it will come to a stop 16 ft up (after one second)
  for an average speed of 16 ft/s ( = 32/2).

If NH had done what it already did by getting a boost at Jupiter but then using ion rockets (in conjunction with the Sun's gravity) to decelerate at a constant rate after the Jupiter encounter it could have arrived at Pluto in ~ 20 years with a final radial velocity close to zero.

By also using these ion rockets to impart a constant angular acceleration the NH could end up matching Pluto's angular velocity of ~ 4 km/s.

The ion rockets could then finally be used to put NH into orbit (as they have done twice with the Dawn spacecraft).

It is important to have the "initial" velocity as high as possible such that with constant deceleration (i.e., mostly by the Sun at first and ion propulsion at the end) the average velocity (~ 0.5 * "initial" velocity) is still relatively impressive.

While this would work and should likely be tried with NH2, if it were tried with NH, we would still be waiting for another 10.5 years just to learn what we now know