Titan III Mars Explorer Transfer Orbital Stage Delivery to the PHSFThis NASA Kennedy Space Center video presents live footage of the delivery of the Titan III Mars Explorer Transfer Orbital Stage (TOS) to the Payload Hazardous Servicing Facility (PHSF). The TOS is a single-stage, solid propellant upper stage vehicle used to propel a spacecraft from low Earth orbit toward it's ultimate destination. The TOS is delivered to the PHSF where it is designed to accommodate a variety of NASA and NASA customer payloads and can be used as a payload processing facility (PPF) or a hazardous processing facility (HPF).