In terms of success of the mission, was the Jupiter fly-by the time when problems with the flight path was most likely to happen?

Was the odds of failure at that point ever studied? If so, what were the odds of failure to meet the mission object because something went wrong at Jupiter?

  • $\begingroup$ It's possible that a comparison of the delta-v that the flyby produced to the delta-v that New Horizons had in it's budget for post-flyby trajectory correction maneuvers would be instructive here. Was is 10:1, 100:1 1000:1? $\endgroup$
    – uhoh
    Sep 8, 2020 at 16:34
  • $\begingroup$ Is this opinion-based? There were so many points and modes of failure in play (including failure to get the mission to launch) that it is difficult to objectively identify any one of them. $\endgroup$ Sep 8, 2020 at 20:53
  • 5
    $\begingroup$ @OscarLanzi because NASA, I would be surprised if extensive risk analysis wasn't done. Actually getting hold of it is another matter... $\endgroup$ Sep 8, 2020 at 23:10
  • 3
    $\begingroup$ I would venture that launch and possible failures associated with the Pluto encounter itself were by far the two most dangerous parts of New Horizon's mission. $\endgroup$ Sep 9, 2020 at 7:37
  • $\begingroup$ I would say the biggest threat during the mission was actually the computer issue ten days before closest approach to Pluto. It actually impacted a mission objective. $\endgroup$ Sep 9, 2020 at 16:20

2 Answers 2


Definitely no.

Especially for New Horizons I would say Jupiter gravity sssist was one of "safest" stages of the mission. :) Because New Horizons' closest flyby of Jupiter was rather far - at 2.3 million kilometers.

Gravity assists require specific trajectory of flyby - with specific direction and velocity. How precize should they be, how large is error margin - it depends on how close is flyby to the "assisting" planet. If it's very close - than precision is critical, because gravity potential changes steeply there, and small error in pre-assist trajectory will result in great changes of post-assist trajectory. The changes can be so great that probably the spacecraft won't be able to correct the trajectory by propulsion. Also error in close flyby can result in the spacecraft impacting the planet and being destroyed. But if flyby is far enough - than gravitation changes slowly with distance to the planet and so error margin in spacecraft trajectory is much bigger.

Trajectory for gravity assists is usually ajusted gradually. There are planned 2-3 or more trajectory correction maneuvers (TCM) for every specific gravity assist. For example first corection several months before flyby, second couple of weeks before and third couple of days before. The last maneuvers are usually very small and sometimes even being canceled because the trajectory is already fine.

So for New Horizons - error margin for Jupiter gravity assist would be large enough. If we imagine NH would fall out of communication for several weeks during Jupiter flyby and could not perforn the final trajectory corrections - I expect trajectory error would not be so big and NH could correct it later by propulsion and reach Pluto.


Launch is usually the most dangerous time for any space mission, especially those that don't land on a celestial body. Historically there is about a 98% chance of successful launch. We've never had any issues that have resulted from a bad flyby, and had a spacecraft cruising around the Jupiter system for extended periods of time, that was never really a major risk.

In the event of New Horizons, the biggest risk was probably hitting some debris near the Pluto flyby that we didn't know about. The risk was managed by making sure to study the system before, model the gravitational regions, choosing a relatively far maximum distance, and sending a quick picture that was close up before it had made it through the entire system, to ensure that something was received.

  • $\begingroup$ I would argue that in modern times launch is rather safe. Atlas-5 rocket that launched New Horisons now have 80+ succesful launches and no one fatal mishap. For NH probably the most dangerous part was Pluto flyby - actually the spacecraft glitched just days before closest encounter, bit was succesfully restored. If not restored it would be total failure. $\endgroup$
    – Heopps
    Sep 10, 2020 at 7:35
  • $\begingroup$ That's a fair point. Hmmm. $\endgroup$
    – PearsonArtPhoto
    Sep 10, 2020 at 11:52
  • 3
    $\begingroup$ 80+ successful launches isn't incompatible with a 2% failure rate $\endgroup$
    – user20636
    Sep 11, 2020 at 2:05
  • $\begingroup$ I said historically. You are right that for certain families of rockets, the launch success rate is higher, but... $\endgroup$
    – PearsonArtPhoto
    Sep 11, 2020 at 2:20
  • $\begingroup$ 0.98^80 ≈ 1/5. Indeed nothing statistically outlandish here, especially since there's more than one rocket family and we are picking the one that didn't have any rapid unscheduled disassemblies. $\endgroup$ Sep 12, 2020 at 0:01

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.