Juno probe's speed is in relation to what frame of reference? When describing the velocity of space probes in general (the Juno probe in particular) what frame of reference is the velocity quoted in? 
This is in relation to the news of the Juno Satellite approaching Jupiter. Excerpt from one of the news outlets: 

As Juno approaches its destination on July 4, Jupiter’s tremendous gravitational pull will accelerate the spacecraft to blazing speeds of more than 150,000 mph (241,000 km/h), making Juno one of the fastest human-made objects ever built.

Now is this frame the reference frame of Jupiter? Yet how is the reference frame usually decided with other space craft? This is mostly in regards to understanding news from NASA and similar sources. I didn't know if there was a standard.
 A: Without seeing the particular example you have in mind it's impossible to be definitive, but without any context, for a probe in the Solar System, I'd assume heliocentric coordinates. Unless it's an orbital velocity around some other body, or an escape velocity from some other body, or of course if it's specifically stated to be in some other frame.
A: 
Juno probe's speed is in relation to what frame of reference?

The escape speed of Jupiter is ~59.5 km/s and 150,000 kph ~ 67.1 km/s, so this speed must be in reference to the sun otherwise the spacecraft would not stay in orbit.
Jupiter's orbital speed about the sun is ~13.1 km/s, which subtracted from the 67.1 km/s would result in ~54 km/s, thus more consistent with an orbital velocity (which must be less than the escape velocity).
For circular orbits, the stable orbital speeds go as:
$$
V = \sqrt{ \frac{ 2 \ G \ M }{ r } }
$$
where $G$ is the gravitational constant, $M$ is the mass of the body about which the spacecraft orbits, and $r$ is the radius from the center of the body of the circular orbit.  Thus, as $r$ increases, $V$ must decrease, which is why the orbital speed must be less than the escape velocity.

"...blazing speeds of more than 150,000 mph (241,000 km/h), making Juno one of the fastest human-made objects ever built..."

The speed quoted in this statement must be in relation to heliocentric coordinates, otherwise the spacecraft could not be in orbit about Jupiter.
