Should Have Skipped Jupiter Flyby?, More time at Pluto Options

[disownedsky]

There are actually three reasons for getting NH to Pluto as fast as possible, despite the higher flyby speed.  First is indeed the risk that the atmosphere may be about to freeze out, in which case every year's delay is crucial.  Second is the fact that, as Pluto moves slowly away from its equinox (which, by an interesting coincidence, is at about the same time as its perihelion), more and more of its south polar region is being shrouded in permanent shadow and thus not observable by sunlight (although you can get a dim look at it by reflected Charon light).

Third, of course, is that the longer it takes to get to Pluto, the higher the operating costs, and the higher the risk that it will fail before getting there.  The whole reason I pushed this mission with fanatical determination in "SpaceDaily" is that it's one of those extremely rare cases in space exploration when delay means a serious loss of science and increase in cost DESPITE whatever new improved technologies are discovered with time.  (Had we launched the damn thing in November 2003, as any sane NASA Administrator would have, we would have done still better in both the science and cost respects -- and we would also have been able to make a close flyby of Io, with possible great science returns from that.)

A fourth reason is that the RTG powering NH loses about 3 Watts per year. This would have started to limit what she could do at Pluto, and possibly severly limit any Kuper belt encounters. As it is, power has to be managed actively during the Pluto Encounter. NH has to maintain a certain power "floor" or she freezes her hydrazine, which is end of mission since thrusters are her only actuators for attitude control. The instruments, however, largely do not contribute to this because they are outside the thermos bottle. So, as power drops, instruments have to go off.

[mars loon]

Plus the added time at Pluto close approach is only increased by minutes. Not worth the loss in atmospheric data or KBO encounters and the rest mentioned earlier.

[Tom Tamlyn]

Plus the added time at Pluto close approach is only increased by minutes.  Not worth the loss in atmospheric data or KBO encounters and the rest mentioned earlier.

Loon,

Thanks _very_ much for that information. I suspected that that might be the case but I don't know enough physics to begin to have a useful intuition.

Is the minimal difference due to influence of Pluto's gravity well at closest approach, or because there's no such thing as an orbit that can reach Pluto which isn't PDF ("pretty darn fast") at closest approach? or both, or something completely different?

Tom Tamlyn

[tedstryk]

Loon,

Thanks _very_ much for that information.  I suspected that that might be the case but I don't know enough physics to begin to have a useful intuition.

Is the minimal difference due to influence of Pluto's gravity well at closest approach, or because there's no such thing as an orbit that can reach Pluto which isn't PDF ("pretty darn fast") at closest approach? or both, or something completely different?

Tom Tamlyn

The problem is with slowing down. A slower flyby could be made, if we were willing to use nearly the entire spacecraft mass and then some for fuel to break. Or if we were willing to take a trajectory that took forty years to get there, we would get a slower flyby. But, as it stands, in order to get to Pluto in a reasonable amount of time (and with the atmosphere possibly freezing, time is crucial), NH will be travelling so fast that it simply will not be able to slow itself down when it gets there.

[ljk4-1]

Had we put our money, time, and effort more into space probes than cars,
we could have been to Pluto and back many times by now:

"On an average day, American drivers eat up nearly 7 billion miles of
pavement - roughly the distance to Pluto and back."

[Comga]

There are actually three reasons for getting NH to Pluto as fast as possible, despite the higher flyby speed.
First is indeed the risk that the atmosphere may be about to freeze out,
Second is the fact that, as Pluto moves slowly away from its equinox more and more of its south polar region is being shrouded in permanent shadow
Third, of course, is that the longer it takes to get to Pluto, the higher the operating costs, and the higher the risk that it will fail before getting there. ..

I would like to throw some cold Hydration on this question and Nix it entirely. (Just can't reisit those awful, awful moon name puns.)

Bruce , and disownedsky, are precisely correct, as is the issue of the limit on science being the SSR capacities. There are even more risks and costs to delays. Look at Dawn and SOFIA, which nearly got cancelled for a few tens of millions of dollars, and are still fighting for their lives. As Alan Stern and others have said, New Horizons is in its native element, deep space. Where, I might add, the odds of collision with a rock are way, way less than the odds of colliding with politics here on Earth.

IIIRC, the boost at Jupiter is ~4 km/sec. Arrival speed is >11 km/sec. However, that does not mean that a flight without a Jupiter flyby would arrive at 7 km/sec. The difference would be less than 4 km/sec, because the trajectories would cross at sharger angles. So the increased time close to Pluto would be, as suggested, not significant.

In addition, Alan says that New Horizon's "dirty little secret" is that it will return more science data from Jupiter, due to the "short" range of only ~5 AU. Pluse NH flies down Jupiter's magnetotail to 1000 Rj, which will data not collected at any planet including Earth. And the Jupiter encounter is great practice, a good chance to wring out an encounter sequence.

How could it be any better than with the Jupiter flyby? (I am sure someone will have a suggestion.)

[edstrick]

Various spacecraft, including the early interplanetary Pioneers, made "accidental" or outbound encounters with Earth's magnetotail at distances of up to hundreds, if not a thousand Earth radii.

[Comga]

Various spacecraft, including the early interplanetary Pioneers, made "accidental" or outbound encounters with Earth's magnetotail at distances of up to hundreds, if not a thousand Earth radii.

Yes, but New Horizons will pass staight down Jupiter's magnetotail, not cut across it, IIRC. At least I was told the path will be unique.

[edstrick]

Sounds good!... Oh.. Voyagers also had distant encounters with the flapping magnetotail as Jupiter finally went into solar conjunction as they slowed down during the post-flyby cruise to Saturn.