  We propose an atom interferometer gravitational wave detector in low Earth
orbit (AGIS-LEO). Gravitational waves can be observed by comparing a pair of
atom interferometers separated over a ~30 km baseline. In the proposed
configuration, one or three of these interferometer pairs are simultaneously
operated through the use of two or three satellites in formation flight. The
three satellite configuration allows for the increased suppression of multiple
noise sources and for the detection of stochastic gravitational wave signals.
The mission will offer a strain sensitivity of < 10^(-18) / Hz^(1/2) in the 50
mHz - 10 Hz frequency range, providing access to a rich scientific region with
substantial discovery potential. This band is not currently addressed with the
LIGO or LISA instruments. We analyze systematic backgrounds that are relevant
to the mission and discuss how they can be mitigated at the required levels.
Some of these effects do not appear to have been considered previously in the
context of atom interferometry, and we therefore expect that our analysis will
be broadly relevant to atom interferometric precision measurements. Finally, we
present a brief conceptual overview of shorter-baseline (< 100 m) atom
interferometer configurations that could be deployed as proof-of-principle
instruments on the International Space Station (AGIS-ISS) or an independent
satellite.
