What is the effective "range" of a Falcon Heavy rocket with a very small payload?

Question

Theoretically, If I decided to blow millions of dollars on a Falcon Heavy launch, simply to launch a 2kg cubesat as far as possible, how far could i send the payload assuming no gravity assists?

Answer 1

Perhaps the best metric for this proposition is characteristic energy (C3). Luckily NASA provides a launch vehicle performance calculator for high energy (C3 defined) launches that includes the Falcon Heavy.

I made a curve fit of the Falcon Heavy expendable launch mass values:

(Personal work, data from NASA launch vehicle performance calculator)

An extrapolation of this curve fit shows the curve intersecting the 0 kg (~2 kg) launch mass at a C3 of about 110 $km^2/s^2$:

(Personal work via Desmos)

This approximately translates to a heliocentric apoapsis near Saturn (~10 AU, calculation based on the $v_{\infty}$ of 10.5 km/s added to Earth's ~30 km/s at 1 AU).

Extending the premise of the question further with the addition of a STAR-48B kick stage brings things into ludicrous territory. Using an algorithm I previously developed to determine the added performance a STAR-48B kick stage provides, I estimate that a 2 kg mass can be thrown with a C3 of 365 $km^2/s^2$.

For reference New Horizons launched with a C3 of 158 $km^2/s^2$, which was a direct solar system escape trajectory regardless of its Jupiter and Pluto encounters. The ridiculous 365 $km^2/s^2$ enables an Earth-Jupiter direct transfer in just 255 days:

(Personal work)

And an Earth-Mars direct transfer in just 52 days:

(Personal work)

And an Earth-Pluto direct transfer in just 6.5 years:

(Personal work)

Answer 2

According to a table in the Falcon Heavy Wikipedia article, the rocket could send 3.5 tons to Pluto. This suggests that even a moderately-sized probe could achieve solar system escape velocity, ultimately achieving a distance of perhaps 60,000 light years in a few billion years as it revolves around the galaxy at a slightly different rate.

Getting beyond a few tens of thousands of light years would require velocities closer to the galactic escape velocity of 550 km/sec, not achievable using current technology.

Comments have called into question whether the Wikipedia table can be correct, and indeed it does not seem to have a citation. But the example of the New Horizons and Voyager probes, launched by smaller rockets, are supportive.

New Horizons was launched directly onto a solar escape velocity trajectory using the Atlas V 551 configuration, which seems to have a lower capacity to LEO than the Falcon Heavy.

Voyager I and II, launched on the significantly smaller Titan IIIE, were also suggestive. For instance, see this graph, indicating that Voyager II was near escape velocity when it left Earth.

In all of these example cases there was an upper stage in the Star family. Such an upper stage might be necessary in this case.