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Comment by standardUser | Hacker News Reader

Hey smart people, if we were to launch a similar probe today using the most advanced technology available, how long would it take a probe to reach the same distance as Voyager 1?

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The Voyager probes enjoyed gravity assists from all of the outer planets [1] which won’t align again until the middle of the next century [2].

[1]: https://space.stackexchange.com/a/3522

[2]: https://space.stackexchange.com/a/5076

But...

"The beauty of the gravity assist is that you use the gravity field of a large body to change course. A common misconception is that the gravity assist increases speed, but it actually leaves speed unchanged. It's more accurate to say that the gravity assist changes direction, since velocity is both a magnitude (speed) AND a direction."

That's only thinking about it from the perspective of the planet. Relative to the planet, the magnitude of the incoming velocity vector is equal to the magnitude of the outgoing velocity vector. But in the reference frame of the sun, the planet loses an infinitesimal bit of momentum, and the spacecraft gains that momentum.

And that's assuming you don't do an extra burn at periapsis, which is far more efficient at changing speed than doing the burn in interplanetary space.

There’s an upvoted sub comment to that which has a good correction. That statement as a whole is just not true and a meaningless statement. When you pass an orbiting body you will take some of that body’s orbital momentum and add that to your current momentum. There’s really no semantic argument in my mind that could justify the above statement. You change direction because you have more in total. There’s no bending of the direction here, just addition of new vectors but that’s exactly how all acceleration works anyway so it’s a bit meaningless to make that statement and I’m really not sure what they are trying to get at. Maybe from the pov of the orbiting body there’s no change but that’s not the thing anyone cares about when doing a flyby.

I think the issue mentally is if you treat the gravity of a planet like a valley, where you accelerate into it but on the way back out you lose all that gained velocity. The difference here is that the valley moves in the opposite direction ever so slightly as you pass it, and you gain the momentum from that valley's movement. At least, I think that's how it works.

Where is the quote from? Gravity exerts a force, therefore by newton's second law there is acceleration. Nothing says the acceleration is purely angular. The closer the pass to the planet, the greater the acceleration.

Wiki explains it well. From the frame of reference of ship and planet, the relative speed is the same. But relative to the sun, the ship can be moving faster.

"A gravity assist around a planet changes a spacecraft's velocity (relative to the Sun) by entering and leaving the gravitational sphere of influence of a planet. The sum of the kinetic energies of both bodies remains constant (see elastic collision). A slingshot maneuver can therefore be used to change the spaceship's trajectory and speed relative to the Sun"

https://en.m.wikipedia.org/wiki/Gravity_assist

The lineup barely matters for gravity assist. Jupiter is the vast majority of the total you can get. Saturn has 30% of the mass and 2/3 the orbital velocity, so adding Saturn gets you only 20% more above using Jupiter alone (and the Voyagers didn't really try), and the ice giants are smaller and slower yet.

We could easily overtake Voyager via only Jupiter if we wanted to (and New Horizons eventually will), and Jupiter-to-any-target launch windows come at least every 12 years.

Solar Oberth meneuver FTW! ;-)

https://www.universetoday.com/154791/the-best-way-to-leave-t...

(I have also seen a variant with an upper stage class SRB used for the meneuver.)

New Horizons will not overtake Voyager. Nor did it use Jupiter, or any other "slingshot".

New Horizons was launched in 2006, and it will reach the same distance from the Sun as Voyager 1 is _currently_ in about 32 years.

Good lord willing and the creeks don’t rise.

It will definitely happen, the only real question is if we're still talking to New Horizon when it passes Voyager 1.

In fact I wonder if we'll stop talking to Voyager 1 before or after New Horizon.

New Horizons is slower than Voyager 1, and is also decelerating more. New Horizons will never pass the others. Voyager 1 is the fastest probe in an escape trajectory.

https://en.wikipedia.org/wiki/Voyager_1#Far_future

For some reason I thought I had read that Horizons was faster and would eventually eclipse it, odd.

Anyway I'm still curious if V1 outlasts New Horizons

I am sure that your article said that it's newer and the launch event was on the plane of the ecliptic.

I read that one too.

Anyway, the Wikipedia article says:

  After 2036, both [Voyager] probes will be out of range of the Deep Space Network.[14]

As for New Horizons:

  [The RTG] will decay too far to power the transmitters in the 2030s.

So we could lose contact with three in succession. Or, the DSN could become even deeper!

Not claiming to be smart people, but it depends on what you mean by "available." The fastest probe that we could launch soon is a sundiver solar sail. It requires no new magical technological leaps. It has been explored mostly in service of the solar gravitational lens concept. [0]

The sundiver probe could go 547 AU in 17 years. Voyager 1 is at 162 AU. So around 5 years.

[0] https://news.ycombinator.com/item?id=41865107

Really depends how much money you want to spend and if you're willing to wait a bit longer for Starship orbital refueling to be tested.

We could build a more or less arbitrarily large rocket in orbit by adding more and more fuel. More fuel means more delta-V means the probe is faster.

"Launch today" is a very undesirable constraint for this goal. All of the probes that have escaped made extensive use of gravitational slingshot effects, which are only available during favorable launch windows.

https://en.wikipedia.org/wiki/List_of_artificial_objects_lea...

Long story short: they plan these out for decades at a time, and take your best shot when the planets align, literally.

We needed the slingshotting because until recently on-orbit construction was mostly a pipe-dream.

If you can build larger ships in orbit, relatively cheaply, you can go a lot more direct, a lot faster.

Even on-orbit refueling is a huge boon for orbital assist flexibility.

It's ineffective, you need more stages.

Tsiolkovsky's equation shows how much dV you get with a given wet : dry (empty) mass of a rocket stage. Very quickly it's becoming very inefficient.

Unless you are talking about some untested rocket that dumps empty fuel tanks in pairs. (Like in the dV book by Daniel Suarez).

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