# With current technology, could we build a space probe that would catch up to one of the Voyagers? **URL:** \ **Category:** In My Humble Opinion\ **Created:** [December 10, 2018, 7:22pm UTC](https://boards.straightdope.com/t/with-current-technology-could-we-build-a-space-probe-that-would-catch-up-to-one-of-the-voyagers/825905 "2018-12-10T19:22:54Z")\ **Posts on this page:** 17\ **Page:** 1
**Author:** ![hajario](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/hajario/32/171_2.png) [@hajario](https://boards.straightdope.com/u/hajario)\ **Post date:** [December 10, 2018, 7:22pm UTC](https://boards.straightdope.com/t/with-current-technology-could-we-build-a-space-probe-that-would-catch-up-to-one-of-the-voyagers/825905/1 "2018-12-10T19:22:54Z")
If so, how long would it take? ---
**Author:** ![rat\_avatar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/rat_avatar/32/255_2.png) [@rat\_avatar](https://boards.straightdope.com/u/rat_avatar)\ **Post date:** [December 10, 2018, 8:36pm UTC](https://boards.straightdope.com/t/with-current-technology-could-we-build-a-space-probe-that-would-catch-up-to-one-of-the-voyagers/825905/2 "2018-12-10T20:36:38Z")
The Voyagers are speeding away at about 17 km/s, which is much faster than the 4.4km/s high exhaust velocity max for a Liquid oxygen-liquid hydrogen rocket. You need to use the Oberth effect to speed up past that using various planetary bodies gravity well. Unfortunately the math to calculate an intercept and timing is non-trivial so I can’t help out there. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [December 10, 2018, 8:40pm UTC](https://boards.straightdope.com/t/with-current-technology-could-we-build-a-space-probe-that-would-catch-up-to-one-of-the-voyagers/825905/3 "2018-12-10T20:40:30Z")
By “catch up to”, do you mean just “reach the same distance”, or “pass close enough to it to be able to rendezvous”? If the former, then the New Horizons probe (the one that flew by Pluto) will do it in fairly short order. If the latter, well, there’s no reason we couldn’t make another probe like New Horizons, but aim it in a different direction. ---
**Author:** ![hajario](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/hajario/32/171_2.png) [@hajario](https://boards.straightdope.com/u/hajario)\ **Post date:** [December 10, 2018, 8:50pm UTC](https://boards.straightdope.com/t/with-current-technology-could-we-build-a-space-probe-that-would-catch-up-to-one-of-the-voyagers/825905/4 "2018-12-10T20:50:50Z")
> [@Chronos](#): > > By “catch up to”, do you mean just “reach the same distance”, or “pass close enough to it to be able to rendezvous”? If the former, then the New Horizons probe (the one that flew by Pluto) will do it in fairly short order. If the latter, well, there’s no reason we couldn’t make another probe like New Horizons, but aim it in a different direction. Thanks. I meant the same distance. When will New Horizons get that far? ---
**Author:** ![ftg](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ftg/32/2801_2.png) [@ftg](https://boards.straightdope.com/u/ftg)\ **Post date:** [December 10, 2018, 9:57pm UTC](https://boards.straightdope.com/t/with-current-technology-could-we-build-a-space-probe-that-would-catch-up-to-one-of-the-voyagers/825905/5 "2018-12-10T21:57:30Z")
> [@rat\_avatar](#): > > You need to use the Oberth effect to speed up past that using various planetary bodies gravity well. Unfortunately the math to calculate an intercept and timing is non-trivial so I can’t help out there. The main boost mechanism is [gravity assist](https://en.wikipedia.org/wiki/Gravity_assist). What engine firing is done at closest approach is for maximizing the change in _direction_ with the smallest amount of fuel. Probes don’t carry enough fuel to make nearly as big an impact on speed. The Voyagers took advantage of a particular alignment of planets. The particular [alignment](https://en.wikipedia.org/wiki/Grand_Tour_program) used for those occurs once every 175 years. But the New Horizon-type systems don’t need such a perfect alignment. ---
**Author:** ![bump](https://avatars.discourse-cdn.com/v4/letter/b/7c8e57/32.png) [@bump](https://boards.straightdope.com/u/bump)\ **Post date:** [December 10, 2018, 10:13pm UTC](https://boards.straightdope.com/t/with-current-technology-could-we-build-a-space-probe-that-would-catch-up-to-one-of-the-voyagers/825905/6 "2018-12-10T22:13:04Z")
What about ion thrusters like HiPEP, VASIMR or NSTAR? Seems like if we wanted to, they could use those to eventually catch up to the Voyager probes, given enough reaction mass and gravity assists. ---
**Author:** ![MEBuckner](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mebuckner/32/2896_2.png) [@MEBuckner](https://boards.straightdope.com/u/MEBuckner)\ **Post date:** [December 10, 2018, 10:21pm UTC](https://boards.straightdope.com/t/with-current-technology-could-we-build-a-space-probe-that-would-catch-up-to-one-of-the-voyagers/825905/7 "2018-12-10T22:21:17Z")
Depends on what you mean by “current technology”, and just how badly we really needed or wanted to intercept the space probe in question. My understanding is that with something like [Project Orion](https://en.wikipedia.org/wiki/Project_Orion_(nuclear_propulsion)), it would be quite do-able, and, assuming we could overcome the _engineering_ challenges involved in such a thing, might not even take all that long to intercept the _Voyager_ in question once it was launched. (We’re talking about a spacecraft with a maximum velocity of maybe 3% of light speed, which may not sound like much, but is hundreds of times faster than the _Voyager_ probes or even _New Horizons_.) Project Orion is pretty out there, but it isn’t like a [warp drive](https://en.wikipedia.org/wiki/Alcubierre_drive) or anything like that; there don’t seem to be any “First, discover a substance with negative mass…” steps involved. Overcoming the _political_ challenges involved in such a project would–I hope!–be even more formidable than the engineering issues. We’re talking about launching a large spaceship from the surface of Earth by _blasting it into space with multiple thermonuclear explosions_; unless we had incontrovertible evidence that anthropophagous aliens were about to intercept _Voyager 2_ and take the famous Golden Record as an invitation to set up a new Rigellian Fried Human franchise on Sol III (“Rigellian Fried Human! It’s tentacle-lickin’ good!”) launching such a mission would be a fairly batshit crazy thing for our civilization to do. ---
**Author:** ![rat\_avatar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/rat_avatar/32/255_2.png) [@rat\_avatar](https://boards.straightdope.com/u/rat_avatar)\ **Post date:** [December 10, 2018, 10:38pm UTC](https://boards.straightdope.com/t/with-current-technology-could-we-build-a-space-probe-that-would-catch-up-to-one-of-the-voyagers/825905/8 "2018-12-10T22:38:34Z")
> [@ftg](#): > > The main boost mechanism is [gravity assist](https://en.wikipedia.org/wiki/Gravity_assist). What engine firing is done at closest approach is for maximizing the change in _direction_ with the smallest amount of fuel. Probes don’t carry enough fuel to make nearly as big an impact on speed. > > The Voyagers took advantage of a particular alignment of planets. The particular [alignment](https://en.wikipedia.org/wiki/Grand_Tour_program) used for those occurs once every 175 years. But the New Horizon-type systems don’t need such a perfect alignment. The fact that Voyager used Jupiter, Saturn, Uranus, and Neptune for those gravity assists and that window won’t open up again until ~2151 as you mentioned, is why I mentioned the Oberth effect. You would have to figure out how to carry enough fuel to use the Oberth effect, just as New Horizon did but at a larger scale. I suppose you could use lots and lots of inner planet accelerations like the Parker Solar Probe used, but in the other direction but it would be hard and you would probably have to extend the Ephemeris past the current used PPN terms. ---
**Author:** ![Exapno\_Mapcase](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/exapno_mapcase/32/1051_2.png) [@Exapno\_Mapcase](https://boards.straightdope.com/u/Exapno_Mapcase)\ **Post date:** [December 11, 2018, 3:01am UTC](https://boards.straightdope.com/t/with-current-technology-could-we-build-a-space-probe-that-would-catch-up-to-one-of-the-voyagers/825905/9 "2018-12-11T03:01:44Z")
> [@MEBuckner](#): > > My understanding is that with something like [Project Orion](https://en.wikipedia.org/wiki/Project_Orion_(nuclear_propulsion)), it would be quite do-able, and, **assuming we could overcome the _engineering_ challenges involved i** n such a thing, Isn’t this the exact definition of _not_ current technology? ---
**Author:** ![Isamu](https://avatars.discourse-cdn.com/v4/letter/i/7c8e57/32.png) [@Isamu](https://boards.straightdope.com/u/Isamu)\ **Post date:** [December 11, 2018, 3:23am UTC](https://boards.straightdope.com/t/with-current-technology-could-we-build-a-space-probe-that-would-catch-up-to-one-of-the-voyagers/825905/10 "2018-12-11T03:23:48Z")
Well, havent’t the voyagers come to a stop after bumping into the edge of the heliosphere and whatever is pushing back against that? Oh, OK I see recent news. ---
**Author:** ![bump](https://avatars.discourse-cdn.com/v4/letter/b/7c8e57/32.png) [@bump](https://boards.straightdope.com/u/bump)\ **Post date:** [December 11, 2018, 7:52pm UTC](https://boards.straightdope.com/t/with-current-technology-could-we-build-a-space-probe-that-would-catch-up-to-one-of-the-voyagers/825905/11 "2018-12-11T19:52:50Z")
> [@bump](#): > > What about ion thrusters like HiPEP, VASIMR or NSTAR? Seems like if we wanted to, they could use those to eventually catch up to the Voyager probes, given enough reaction mass and gravity assists. FWIW, the Dawn probe, which was powered by NSTAR derived ion thrusters, achieved a 41,360 kph total velocity change. > **[Solar System Exploration Stories - NASA Science](https://science.nasa.gov/solar-system/stories/?order=publish_date%2Bdesc&per_page=50&page=0&search=&fs=&fc=&ft=dawn&category=)** ---
**Author:** ![K364](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/k364/32/5_2.png) [@K364](https://boards.straightdope.com/u/K364)\ **Post date:** [December 11, 2018, 10:21pm UTC](https://boards.straightdope.com/t/with-current-technology-could-we-build-a-space-probe-that-would-catch-up-to-one-of-the-voyagers/825905/12 "2018-12-11T22:21:19Z")
[Starshot could do it.](https://www.space.com/32551-breakthrough-starshot-interstellar-spacecraft-infographic.html) “The probes would be accelerated to 20 percent of the speed of light in about two minutes… This velocity would get the probe past the orbit Pluto in three days and to the nearest star in 20 years.” ---
**Author:** ![Gorsnak](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/gorsnak/32/7587_2.png) [@Gorsnak](https://boards.straightdope.com/u/Gorsnak)\ **Post date:** [December 11, 2018, 11:47pm UTC](https://boards.straightdope.com/t/with-current-technology-could-we-build-a-space-probe-that-would-catch-up-to-one-of-the-voyagers/825905/13 "2018-12-11T23:47:44Z")
> [@rat\_avatar](#): > > The Voyagers are speeding away at about 17 km/s, which is much faster than the 4.4km/s high exhaust velocity max for a Liquid oxygen-liquid hydrogen rocket. > > You need to use the Oberth effect to speed up past that using various planetary bodies gravity well. Unfortunately the math to calculate an intercept and timing is non-trivial so I can’t help out there. Are you saying that if I’m traveling away from Earth at 4.5km/s and chuck stuff out the back at 4.4km/s that I won’t accelerate? Because I don’t think that’s how Newton’s 3rd Law works. The Tsiolkovsky Rocket Equation is going to put a practical limit on how much delta-V you can get out of a rocket with 4.4km/s exhaust velocity, but that limit should be significantly higher than 4.4km/s or orbital rockets wouldn’t work. ---
**Author:** ![rat\_avatar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/rat_avatar/32/255_2.png) [@rat\_avatar](https://boards.straightdope.com/u/rat_avatar)\ **Post date:** [December 12, 2018, 12:30am UTC](https://boards.straightdope.com/t/with-current-technology-could-we-build-a-space-probe-that-would-catch-up-to-one-of-the-voyagers/825905/14 "2018-12-12T00:30:35Z")
> [@Gorsnak](#): > > Are you saying that if I’m traveling away from Earth at 4.5km/s and chuck stuff out the back at 4.4km/s that I won’t accelerate? Because I don’t think that’s how Newton’s 3rd Law works. The Tsiolkovsky Rocket Equation is going to put a practical limit on how much delta-V you can get out of a rocket with 4.4km/s exhaust velocity, but that limit should be significantly higher than 4.4km/s or orbital rockets wouldn’t work. No, I am saying the faster you can toss mass out of the back of the rocket the more efficient it is. The Tsiolkovsky rocket equation, or “delta vee” will be cruel if you do the actual math though. Δv = v[sub]exhaust[/sub] \* ln(mass[sub]0[/sub]/mass[sub]1[/sub]) If your rocket weighs 1,000,000 kg, with an only unrealistic dead weight of 10 kg and you have exaust that is 4.4km/s you could get up to 50.65 km/s. If you can get it to where your non-fuel total rocket mass is 1% of the total mass with fuel you would only get to 20.26 km/s. If you have 50% fuel you can only get to 3.0 km/s. The natural log will ruin your day even with the ideal rocket law. ---
**Author:** ![Exapno\_Mapcase](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/exapno_mapcase/32/1051_2.png) [@Exapno\_Mapcase](https://boards.straightdope.com/u/Exapno_Mapcase)\ **Post date:** [December 12, 2018, 1:23am UTC](https://boards.straightdope.com/t/with-current-technology-could-we-build-a-space-probe-that-would-catch-up-to-one-of-the-voyagers/825905/15 "2018-12-12T01:23:37Z")
> [@K364](#): > > [Starshot could do it.](https://www.space.com/32551-breakthrough-starshot-interstellar-spacecraft-infographic.html) > > “The probes would be accelerated to 20 percent of the speed of light in about two minutes… This velocity would get the probe past the orbit Pluto in three days and to the nearest star in 20 years.” Isn’t this also the exact definition of _not_ current technology? ---
**Author:** ![Asuka](https://avatars.discourse-cdn.com/v4/letter/a/dec6dc/32.png) [@Asuka](https://boards.straightdope.com/u/Asuka)\ **Post date:** [December 12, 2018, 2:13am UTC](https://boards.straightdope.com/t/with-current-technology-could-we-build-a-space-probe-that-would-catch-up-to-one-of-the-voyagers/825905/16 "2018-12-12T02:13:36Z")
> [@Exapno\_Mapcase](#): > > Isn’t this the exact definition of _not_ current technology? From what I understand it wasn’t the engineering challenges that stopped Orion, but the results of the engineering challenges that stopped it. Basically to perfect it they would have to detonate a lot of nukes in mid-air and obviously that won’t have very good ecological consequences. If we absolutely did not give a shit about fallout Orion could be built today pretty easily. ---
**Author:** ![Gatopescado](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/gatopescado/32/5711_2.png) [@Gatopescado](https://boards.straightdope.com/u/Gatopescado)\ **Post date:** [December 12, 2018, 11:02pm UTC](https://boards.straightdope.com/t/with-current-technology-could-we-build-a-space-probe-that-would-catch-up-to-one-of-the-voyagers/825905/17 "2018-12-12T23:02:38Z")
Sure, why not? How hard could it be? It’s not Rocket Sci… Oh, wait a minute…