Space Rapid Transit (SRT)
Introduction
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 class of horizontally-launched, horizontally landing fully reusable two-stage to orbit vehicles. This concept is not new and was the basis for the German Saenger and NASA Beta concepts. SRT-M is designed to bring 425 kg payloads to the International Space Station. The SRT-C is a larger vehicle designed to bring 6 astronauts and 1000 kg to the ISS.
The SRT Ferry Stage is a waverider design that uses conventional military turbofan engines to reach Mach 1.5. At that point a coaxial ramjet propels to vehicle to Mach 4.6 at an altitude of 25 km. The Ferry Stage flies well within the flight envelope of the X-15 and its maximum speed is not much higher than the cruise speed of the SR-71.
Dual fuel permits the Ferry Stage to easily move the SRT between airfields. Stage separation occurs and a liquid oxygen/liquid hydrogen rocket engine, the Pratt & Whitney RL 10B-2 for the SRT-M and the SSME for the SRT-C, takes the Upper Stage into earth orbit. The reaction control system on the Upper Stage would use the Swedish Space Corporation's HPGP Thruster which use a green propellant. This would simplify ground operations.
The Upper Stage rolls onto the Ferry Stage unfueled. The Ferry Stage has kneeling landing gear. Both stages are then fueled and launch proceeds.
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.
Both stages have the same core avionics suite which is based on the Boeing 787 avionics. The Upper Stage has additional avionics for on-orbit and ISS operation.
The figure below shows overall system concept.
The optimal trajectory shows the transition points during the flight. The coaxial ramjet burn completes at 12 minutes after launch. The Ferry Stage then glides until it reaches Mach 1.5 than flies under turbofan power back to the airfield. The RL 10B-2 fires twice and is not used again during the mission. Reentry is done using the RCS system. In this way the main engine can be reused for up to 7 flights. The short duration of the powered parts of the flight simplify the design of the cryogenic tanks since long time storage of hydrogen is not required.
Screen Shots from VisualCommander SRT Simulations
The figures below show the two SRT stages.
SRT takeoff is shown in the images below. The Ferry Stage is under turbojet power.
The following figures show SRT in the vicinity of the ISS. SRT-M is large enough to carry the recently failed ISS pump to the ISS.
The Upper Stage reentry trajectory is based on methods developed for the Space Shuttle Orbiter. The RCS system initiates the reentry maneuvers. RCS control and aerodynamic control is blended during reentry using a linear programming algorithm.
The following figures show departure from the ISS and the pitch-over prior to reentry into the atmosphere.
Movies
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 SRT launch through ISS rendezvous.
SRT launch through ISS rendezvous
Documentation
Download a white paper with more information about the Space Rapid Transit system.
Using the SRT-M as an ISS lifeboat.
Papers
"Space Rapid Transit Navigation and Control", Paul Griesemer, Joseph Mueller, Michael Paluszek and Pooja Raghavan at EUCASS 2011, 4 - 8 July 2011 in St. Petersburg Russia.
"System Design of a Reusable, Horizontal Take-Off/Horizontal Landing Two Stage to Orbit Vehicle", Paul R. Griesemer, Joseph B. Mueller, Michael A. Paluszek and Jingwen Du at the 2010 Joint Propulsion Conference, 5 - 28 July 2010 in Nashville, TN, USA.
"Unified GN&C System for the Space Rapid Transit Launch Vehicle", Joseph B. Mueller, Paul R. Griesemer, Michael A. Paluszek and Jingwen Du at the 2010 AIAA GN&C Conference, 2 - 5 August 2010 in Toronto Ontario, Canada.
"Space Rapid Transit for Rapid Spacecraft Deployment", Paul R. Griesemer, Michael A. Paluszek, Joseph B. Mueller and Eloisa de Castro, at the 2011 Reinventing Space Conference, 3 - 5 May 2011 in Los Angeles, California.
For More Information
For further information, please contact Michael Paluszek.
Email: map at psatellite.com.
Phone: (609) 275-9606.