  In the event that R-Parity conserving supersymmetry (SUSY) is discovered at
the LHC, a key issue which will need to be addressed will be the consistency of
that signal with astrophysical and non-accelerator constraints on SUSY Dark
Matter. This issue is studied for the SPS1a mSUGRA benchmark model by using
measurements of end-points and thresholds in the invariant mass spectra of
various combinations of leptons and jets in ATLAS to constrain the model
parameters. These constraints are then used to assess the statistical accuracy
with which quantities such as the Dark Matter relic density and direct
detection cross-section can be measured. Systematic effects arising from the
use of different mSUGRA RGE codes are also estimated. Results indicate that for
SPS1a a statistical(systematic) precision on the relic abundance ~ 2.8% (3 %)
can be obtained given 300 fb-1 of data.
