[syhprum (OP)]

The sun grazing Parker probe must always be orientated  so that it is protected by its heat shield so there is no possibility for a transmitter dish to be directed towards the Earth if it is rigidly mounted on the body of the satellite.
Is the antenna steerable or is there sufficient power available for a low directivity antenna to be used
 

[evan_au]

Although the Parker Solar Probe comes very close to the Sun (at perihelion), it spends most of its time far from the Sun (aphelion is at the same distance as Venus).

So for the week or two when it is closest to the Sun, electromagnetic interference from the Sun will prevent radiotelescopes on Earth from receiving data from the space probe. It must be oriented so that the heat shield protects it from the Sun.

Just as Venus is often invisible from Earth because it is behind the Sun (but far from the Sun), the Parker probe will often be out of communication with the Earth, so it has to be very autonomous.

However, for most of its orbit, it will be separated far enough from the Sun in the sky that radiotelescopes on Earth can communicate with it to download the scientific data and upload new instructions. The probe has a 0.6m steerable parabolic dish. The only direction it can't point is within 14° of the Sun's center, as that direction is obstructed by the solar shield.

See: http://parkersolarprobe.jhuapl.edu/index.php#spacecraft
https://directory.eoportal.org/web/eoportal/satellite-missions/p/psp
https://en.wikipedia.org/wiki/Parker_Solar_Probe