Space Rapid Transit (SRT)
Two of the major challenges facing the United States space program today are to bring time-critical payloads into low-earth orbit and to bring astronauts into orbit safely and economically. Princeton Satellite Systems is designing two vehicles to solve this problem, the SRT-M and SRT-C.
SRT is a horizontally-launched, horizontally landing fully reusable two-stage to orbit vehicle. This concept is not new and was the basis for the German Saenger and NASA Beta concepts. SRT-M is designed to bring 200 kg payloads to the International Space Station. This would fully test the SRT concept and provide the U.S. with a responsive launch vehicle. The SRT-C is a larger vehicle designed to bring 6 astronauts and 1000 kg to the ISS.
The SRT-C would bring astronauts into orbit where they could transfer to the ISS or to an Orion-based space transportation system that does not need reentry capability. The Orion could then be optimized for in-space operation. The Augustine Commission is reported to state that all rocket based manned launchers are equivalent in risk to the flight crew. This system has the potential to greatly reduce the risk, possibly to the airline level.
A benefit of the development of this system is that the ferry stage would provide technology for future high Mach number airliners. This would jumpstart the next generation of civilian and military passenger aircraft.
The SRT ferry stage uses conventional military turbofan engines using jet fuel to reach Mach 1.5. At that point a hydrogen fueled ramjet propels to vehicle to Mach 5.5 at an altitude of 25 km. Dual fuel permits the ferry stage to easily move the SRT between airfields. Stage separation occurs and a liquid oxygen/liquid hydrogen rocket engine (based on the Pratt & Whitney RL-60 for the SRT-M and the SSME for the SRT-C) takes the orbiter into earth orbit. The SRT-M ferry stage is roughly F-22 sized and the SRT-M orbiter is similar to the NASA/DARPA/Air Force X-37B. The SRT-C ferry stage is similar in size to the TU-160, the largest supersonic aircraft built to date. A hydrogen fueled ramjet was tested by MBB as part of the German Saenger program. The reaction control system on the second stage would use the Swedish Space Corporation's HPGP Thruster which use a green propellant. This would simplify ground operations. The orbiter attaches below the ferry stage for ease of ground integration. Both have undercarriages so integration on the ground is simply a matter of rolling the orbiter under the ferry stage.
The figure below shows the SRT system.
The figure below shows the trajectory.
The figures below show the two SRT stages.
A simulation of an SRT-M attitude maneuver in VisualCommander. SRT uses 16 pulsewidth modulated thrusters for attitude and orbit control. The main engine is used for larger maneuvers.
SRT-M approaches the International Space Station in a simulation test of the rendezvous and formation flying software.
The following movie shows an x-axis attitude maneuver using the reaction control system. The RCS system is monopropellant. The maneuver is initiated from a command sent from the attitude control page. The attitude control system uses a PID controller which generates angular acceleration commands from a delta-quaternion input. The acceleration commands are multiplied by the current value of the inertia matrix to compute a three axis torque. Simplex is used to convert the torque into pulsewidths for the 16 reaction control thrusters.
A reorientation maneuver of the Space Rapid Transit upper stage.
The following movie shows an SRT rendezvous with the ISS. The guidance system uses the 16 thrusters for simultaneous orbit and attitude control.
A VisualCommander page shows the maneuver.
Download a flyer with more information about the Space Rapid Transit system.
For further information, please contact Dr. Paul Griesemer.
Email: pgreisemer at psatellite.com.
Phone: 609-482-3042.