Calculating the Angular Momentum of a planet I want to calculate the Angular Momentum of any planet at any point on the orbit around the Sun.
Example: I want to calculate the Angular Momentum of Pluto today, on Jan 27, 2021 00:00:00 Hrs
Where can I get the actual data to calculate this?
I will need Mass, Velocity and Radius to calculate. Do I need the θ too?
Is it readily calculated by NASA?
http://hyperphysics.phy-astr.gsu.edu/hbase/amom.html
The big essential fact about momentum is that it is conserved (in the presence of a central force, as is the case here). So the Angular momentum of Pluto today is the same as it was yesterday, and the same as last year and (excepting perturbations) the same as it has ever been.
It is easiest to calculate for a body that is moving perpendicular to its position vector. This is always true for circular motion, about the centre of the circle.  It is not true for elliptical motion, except at apoapsis and periapsis.
At these times $L = mvr$.  For Pluto the periapsis speed is $v = 6.10\, km/s$ the distance is 4.44 billion km and the mass is $1.31 × 10^{22}$ kg.  To get the angular momentum you've got to multiply them together. If you want SI units, convert those km to m first.
The angular momentum today is the same.
Alternately you can use the relationship
$L= \sqrt{\mu \ell}$ where $\mu = GM =1.33×10^{20}$ and $\ell$ is the semi latus rectum or $\ell=a(1+e^2)$, and you have to plug in the semimajor axis for Pluto and eccentricity of its orbit.
Or you can look it up, since it is constant $L=3.6\times 10^{38}$