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What is the fastest vehicle currently in space? With our current technology, at what point does physics start to restrict our speed in space?

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    $\begingroup$ Is there any kind of meta policy on questions whose answers will change over relatively short timescales? space.stackexchange.com/a/10193/11262 is relevant to all-time records, but the "currently" seems to make this not-a-duplicate. $\endgroup$
    – Erin Anne
    Jul 14, 2018 at 5:09
  • $\begingroup$ Your main question is still somewhat confusing $\endgroup$
    – Cornelis
    Jul 14, 2018 at 17:11
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    $\begingroup$ @Conelisinspace the title contains bot past and future tense although the grammar my not be perfect. $\endgroup$
    – Muze
    Jul 14, 2018 at 18:51
  • $\begingroup$ There is a chance that this describes the fastest ever velocity of a spacecraft (in a sense) close to the Earth and measured relative to the Earth: en.wikipedia.org/wiki/… $\endgroup$ Jul 15, 2018 at 17:32

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If you want speed, look for mass. Things closest to the Sun will tend to be moving the fastest.

For example the Messenger spacecraft reached almost 63 km/s when in an elliptical orbit who's perihelion matched Mercury's position.

In the 2nd plot you can see the red line (speed wrt Mercury) drops to a very low value in 2011, that's when it entered into orbit around Mercury.

I'm now looking for data for Mariner-10.

I have estimated that In the future the Parker Solar Probe will reach about 195 km/s as it passes within a few million km of the Sun!

Data below from JPL's Horizions.

enter image description here

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The only absolute limit imposed by physics is the speed of light, but with our current technology -- reaction engines based on Newton's laws of motion -- we're limited by practical engineering issues and Tsiolkovsky's rocket equation to speeds on the order of 1/10000 of the speed of light.

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    $\begingroup$ "Do I contradict myself? Very well, then I contradict myself, I am large, I contain multitudes." - Walt Whitman $\endgroup$ Jul 14, 2018 at 4:33
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    $\begingroup$ The 17 km/s is the fastest radial velocity with respect to the Sun? Anything in a heliocentric orbit near Earth's is moving like ~30 km/s, just not away from the Sun. $\endgroup$
    – uhoh
    Jul 14, 2018 at 5:00
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    $\begingroup$ I think a much better measure of this sort of records would be the specific orbital energy; if we could turn Voyager 2 around (say, by a flyby of some interstellar planet) and get it near Earth, it would blow all the 30km/s vessels out of the vacuum. And crashing it into the Sun would beat all the records. Current 17km/s is so unimpressive only because most of its orbital energy is in the potential energy. IIRC New Horizons is currently faster - but by the time it reaches where Voyager 2 is now, it will be much slower. $\endgroup$
    – SF.
    Jul 14, 2018 at 8:45
  • $\begingroup$ @SF. agreed. The Voyagers and New Horizons have very high $C_3$. $\endgroup$
    – uhoh
    Jul 14, 2018 at 9:00
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    $\begingroup$ Good points, I’ll delete the first part of my answer. $\endgroup$ Jul 14, 2018 at 10:07
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I think it's useful to note that the whole concept of fastest velocity in space is some confusing.

For example - altough Parker Solar Probe will be the fastest spacecraft even made, it will not have enough velocity to ever reach Mars from it's trajectory. Paradox?

Spacecraft are not like race cars on track where the fastest wins.

The better analogy are cars at a road in mountain region. The vehicle in a valley can have big velocity 120 km/h, but it's not enough to drive at the top of 1-km-high mountain by inertia only. Opposite, another car at the mountain's top can drive slowly 20 km/h, but it's total energy (kinetic + potential) is higher that the energy of the first car in the valley. If we drive the second car down from 1-km mountain without breaking, its final velocity will be insane.

It's the same for spacecraft. The total energy (kinetic + potential) of a spacecraft tells us where it can fly and where can not, and how much time we need to reach our target.

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    $\begingroup$ Thus the concept of C3 , or "excess v^2 above escape velocity". (1, 2) Anything bound to the Sun has a negative $C_3$ , anything with escape velocity has positive $C_3$ . Once you know a spacecraft's heliocentric $C_3$, you can get the current velocity $v$ from the current distance from the Sun $r$ from $v^2 = C_3 + 2mμ/r$. $\endgroup$
    – uhoh
    Jul 14, 2018 at 8:55
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    $\begingroup$ ...oops, that's $v^2 = C_3 + 2 \mu / r$ the $m \mu$ is a typo $\endgroup$
    – uhoh
    Jul 15, 2018 at 5:41
  • $\begingroup$ let me know when it does $\endgroup$
    – Muze
    Dec 29, 2018 at 1:53
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As far as I know the New Horizons spacecraft was the fastest ever space probe launched into space with a speed of 16.26km/s and there are other type of speed records held by Helios an Juno spacecrafts.

The below link is worth checking

http://www.guinnessworldrecords.com/news/2016/7/nasa%E2%80%99s-juno-probe-recognised-by-guinness-world-records-as-fastest-ever-spacecraft

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