Additional Study Information: This study is for patients with sickle cell disease (SCD). SCD is an inherited genetic disorder in which red blood cells become abnormally shaped (sickle cells). These sickle cells may block blood vessels and result in a vaso occlusive crisis (VOC). This leads to inflammation and tissue damage and causes pain in various parts of the body. The purpose of this current research study is to compare the study drug, rivipansel, with a placebo in a larger number of subjects to find out if rivipansel is safe and effective for treating pain crisis in hospitalized subjects with SCD. Researchers use a placebo to see if the study drug works better than not taking anything and to compare the safety of the study drug with not taking anything.