Here is a "back of the envelope" link budget calculation by Ron, W6RZ.
For the downlink only.
Here's a rough link budget. The Earth subtends an arc of about 2 degrees from the Moon, so a 1 foot dish on the gateway is about as large as it can get and still cover the entire Earth. So about 29 dBi of gain.
100 watts = 50 dBm
1 foot dish EIRP = 79 dBm
Worst case path loss at 10.45 GHz = 225 dB
power density on Earth = -146 dBm
Noise floor at 29K and 10 MHz bandwidth = -114 dBm
1 meter dish gain = 39 dBi
Signal at DVB-S2 receiver = -107 dBm or 7 dB above noise.
7 dB S/N could support 8PSK at 2/3 rate, which would provide 16.5 Mbps. Enough for several HDTV channels.
Or a 0.5 meter dish could work at QPSK 1/2 rate, which would provide 8.2 Mbps.