SatCom System Architecture (from: Kodheli et. al., Satellite Communications in the Space Era, Mar 2020, IEEE Communication Surveys & Tutorials)
On-board processing architecture (from: A. I. Prez-Neira et. al., “Signal processing for high throughput satellites: Challenges
in new interference-limited scenarios,” IEEE Signal Processing
Magazine, vol. 36, no. 4, pp. 112–131, 2019.)

For the development of the communication components of AS-VLEOSAT1 the following institutes are responsible:

Implementation in IAP-SRWRDA Project (2014):

This realization allows only receiving.

The next step is to make a realization both suitable for receiving and sending.

One possible open-source HW is HackRF or LimeSDR instead of DVB-RTL Stick. Block diagram of HackRF:

HackRF Schematic: