  Both Phase 1 of the Square Kilometre Array (SKA1) and the full SKA have the
potential to dramatically increase the science return from future astrophysics,
heliophysics, and especially planetary missions, primarily due to the greater
sensitivity (AEFF / TSYS) compared with existing or planned spacecraft tracking
facilities. While this is not traditional radio astronomy, it is an opportunity
for productive synergy between the large investment in the SKA and the even
larger investments in space missions to maximize the total scientific value
returned to society. Specific applications include short-term increases in
downlink data rate during critical mission phases or spacecraft emergencies,
enabling new mission concepts based on small probes with low power and small
antennas, high precision angular tracking via VLBI phase referencing using
in-beam calibrators, and greater range and signal/noise ratio for bi-static
planetary radar observations. Future use of higher frequencies (e.g., 32 GHz
and optical) for spacecraft communications will not eliminate the need for high
sensitivities at lower frequencies. Many atmospheric probes and any spacecraft
using low gain antennas require frequencies below a few GHz. The SKA1 baseline
design covers VHF/UHF frequencies appropriate for some planetary atmospheric
probes (band 1) as well as the standard 2.3 GHz deep space downlink frequency
allocation (band 3). SKA1-MID also covers the most widely used deep space
downlink allocation at 8.4 GHz (band 5). Even a 50% deployment of SKA1-MID will
still result in a factor of several increase in sensitivity compared to the
current 70-m Deep Space Network tracking antennas, along with an advantageous
geographic location. The assumptions of a 10X increase in sensitivity and 20X
increase in angular resolution for SKA result in a truly unique and spectacular
future spacecraft tracking capability.
