From my understanding, both voyager 1 and voyager 2 used a gravity assisted slingshot method to leave the solar system.


  • Since the planetary alignment used won't happen again for a while, how long would it take modern rockets(ie. falcon 9, SLS, or Starship) to reach interstellar space? That is, past the Oort cloud.
  • What engine would be suitable for such a trip(ie. ion propulsion, normal vacuum engine, solar sail)?
  • Is it feasible or would it be best to wait until the planets are once again enough aligned(I believe that won't occur until the 22nd century)?
  • Are there any current plans in place for such a mission by the likes of NASA or the European space Agency?

Note: Suitable answers would incorporate the different questions when applicable. Ie, if there are not plans in place for such a mission available to the public, just make note of it and move on.

  • $\begingroup$ For the record, the 1999 Interstellar probe was intended to travel out 200 AU in 15 years. $\endgroup$ May 21, 2021 at 3:08
  • 2
    $\begingroup$ I think you mean past the heliopause, not the Oort cloud. When astronomers talk about interstellar space, they mean outside the Sun's magnetosphere. But the Oort cloud may extend as far as a light year and its boundary won't be reached by Voyager for many thousands of years. $\endgroup$ May 21, 2021 at 4:29
  • $\begingroup$ Sadly, a sling-shot maneuver around Sol does not produce time-travel unless you're already in warp drive (ST-TOS) $\endgroup$ May 21, 2021 at 14:34
  • $\begingroup$ I was going to look at a system of refueling points with tankers in place, but I doubt that would do any good unless the tankers were accelerated to match planned speeds. $\endgroup$ May 21, 2021 at 14:40

1 Answer 1


This is a great question and it can have several answers depending on propulsion technology. I will address only a solar sail.

171 days! (+30 years of development & approaching the Sun1)

Wikipedia's Heliosphere; heliopause says:

In September 2013, NASA announced that Voyager 1 had crossed the heliopause as of 25 August 2012. This was at a distance of 121 AU (18 billion km) from the Sun.

If we used a solar sail based on extreme but with expense and effort achievable techology with almost no payload besides the sail, and start at 0.5 0.1 AU (!!!) from the Sun, a terminal velocity of 1225 km/sec which is absurdly fast! (0.4% the speed of light)

From this answer to Maximum velocity achieved by solar sail

enter image description here

That gets you to the heliopause in 171 days, but you need to add that to the 30 years it took you to fund and develop the project!

So I think you can get there sooner using conventional or nuclear thermal propulsion, and probably in conjunction with a flyby of at least one or two planets.

1hat tip to @CarlWitthoft

  • 2
    $\begingroup$ To be fair, you should include the time required to get from Earth to 0.X AU $\endgroup$ May 21, 2021 at 14:36
  • $\begingroup$ @CarlWitthoft good point! The 30 years is a ballpark so I've just added "...& approaching the Sun" $\endgroup$
    – uhoh
    May 22, 2021 at 0:51
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    $\begingroup$ The problem with this Table is that the accelerations are LUDICROUSLY too large. To achieve even the least acceleration of the list, 0.3m/s2 at 1 AU, require the sail to have a mass of less than 10 MICROgram per square meter. That means 10 grams per square kilometer!!!!! $\endgroup$ May 22, 2021 at 11:48
  • $\begingroup$ A 2.5nm thick aluminum foil without any support is an "achievable techology"? $\endgroup$
    – asdfex
    May 22, 2021 at 12:29
  • $\begingroup$ @asdfex "with expense and effort" and "30 years of development"... Anyway, as I mentioned I recommend that other forms of propulsion be used, and invite others to write those answers. Go for it! $\endgroup$
    – uhoh
    May 22, 2021 at 13:25

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