How much longer would New Horizons take to reach Pluto without the Jupiter slingshot?

Question

A recent answer by PearsonArtPhoto claims:

New Horizons was launched at Solar System Escape Velocity, meaning it could have visited anywhere beyond Earth without stopping. It did visit Jupiter, however, that was to allow it to leave even faster, the Jupiter stop was purely optional.

In one hand, this operation shortened the wait time, reduced risk associated with deterioration of the probe over time, and reduced cost of upkeep of the mission (through making it shorter).

On the other hand, it made the flyby of Pluto awfully fast and short, resulting in only so much data from the brief closest approach. A slower flyby would give the probe more time to collect and send data. Slow enough, it might even allow for a capture into Pluto orbit.

Weighing costs and benefits - how much longer would skipping the Jupiter assist make the period to reach Pluto? And how much slower would the flyby be?

Answer 1

It was said in here that the time to reach Pluto was shortened by 3 years. It's also said that after the Jupiter flyby the probe gained ~ 4 km/s accelerating to the speed of 23 km/s relative to the Sun. We can use simple Keplerian estimate (ignoring all complexities of the actual orbital mechanics) to obtain the speed when the probe approaches Pluto, \begin{equation} \frac{v_1^2}{2}-\frac{\mu}{R_1}=\frac{v_2^2}{2}-\frac{\mu}{R_2} \end{equation} That gives ~8 km/s without flyby and ~15 km/s with flyby. This simple estimate doesn't tell you what the relative velocity to the Pluto would be without the Jupiter flyby but considering it's current orbital velocity of ~5.5 km/s and escape velocity ~1.2 km/s one may safely assume that even in the best case scenario it would still be ~4 km/s instead of ~13.8 km/s, so we talk about 3 times longer Pluto flyby at best.

To orbit the Pluto without the Jupiter flyby the probe would still have to perform an insertion maneveur losing even in the best case ~3 km/s whereas it had only 290 m/s delta-v budget. Of course the probe could be launched in such a way that it would approach Pluto at very low relative speed but then it's orbital period would be about half of the orbital period of Pluto, so we talk about ~50 year journey to Pluto. The orbiter should have been a specially designed for that mission, much heavier because of the booster required for insertion and therefore would require a different launch rocket.

Another point is that the Pluto orbit has rather significant inclination. Much of the delta-v at the launch would be spent to put the probe on sufficiently inclined orbit resulting in much lower speed than that naive estimate gives. The Jupiter flyby inclined its orbit for free.

The higher speed also means that the New Horizons will be able to reach other Kuiper belt objects in much shorter time. For example it's expected to pass by just 3500 km from (486958) 2014 MU$_{69}$ already in 2019.

And of course Jupiter is interesting by itself. Its flyby allowed to obtain some extra scientific data.

Answer 2

Depending on the time of launch, there were 4 different major plans for the NH mission profile. The first 3 involved Jupiter flybys, and would have an arrival date of 2015, 2016, or 2017. The last was a direct flyby, which I believe would have been 2019-2020, per this article (.

As for the scientific value, going slower through the system would have allowed for a few more photographs, at more risk to the spacecraft and missing the Jupiter flyby. But the biggest thing is something that actually proved to not be a worry, but only after the mission launched. The thought when NH launched was that Pluto's atmosphere would freeze. Pluto is actually near its closest approach to the Sun, which was in 1999, and it was thought when it launched that the atmosphere would freeze as it got further from the sun. The earlier timeline had more of a chance of seeing that atmosphere, along with a clearer landscape (Not covered in frozen nitrogen). Further modeling determined this wasn't likely, but only in 2014.

Bottom line is, the Jupiter flyby approach path was the best path. The benefit from a slower approach would have been negligible, and the scientific bounty was much higher to do the Jupiter flyby.