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The paper presents the first ever research and experimental results regarding the combination of a software-defined multi-Gbps modem and a broadband high power space amplifier when tested with an extended form of the industry standard DVB-S2 and LDPC rate 9/10 FEC codec. The modem supports waveforms including QPSK, 8-PSK, 16-APSK, 32-APSK, 64-APSK, and 128-QAM. The broadband high power amplifier is a space qualified traveling-wave tube (TWT), which has a passband greater than 3 GHz at 33 GHz, output power of 200 watts and efficiency greater than 60%. The modem and the TWTA together enabled an unprecedented data rate at 20 Gbps with low BER of 10-9. The presented results include a plot of the received waveform constellation, BER vs. Eb/N0 and implementation loss for each of the modulation types tested. The above results when included in an RF link budget analysis show that NASA's payload data rate can be increased by an order of magnitude (>;10X) over current state-of-practice, limited only by the spacecraft EIRP, ground receiver G/T, range, and available spectrum or bandwidth.