Model XP Sub-System
The XP cabin is designed for safe, enjoyable space travel. XP features room for 3 passengers and a pilot with one passenger sitting up front along side the pilot and 2 passengers in the aft seating area. Each seat features a 5-point harness system to ensure that the passengers are secure during high-G portions of the flight. Passengers also have an intercom system to hear the pilot and speak with each other, as well as monitors where they can view the external and internal cameras and view position and trajectory information as well as flight milestones.
Environmental Control and Life Support System (ECLSS):
Passengers onboard the XP are provided clean, dry air, at a comfortable pressure, and with the right mixture of gasses, especially Oxygen and Carbon Dioxide. The passengers and all the electronics in the XP also create a lot of heat that needs to be removed. XP features an Environmental Control and Life Support System that uses a chemical scrubbing agent to remove Carbon Dioxide, a condenser to remove excess water vapor, and a filter to remove any foreign items such as dirt, hair, or vomit that may be released in the cabin. The ECLSS uses cryogenic liquid nitrogen and liquid oxygen to replace the oxygen and nitrogen lost to respiration and to outflow, controlling both oxygen levels and cabin pressure. The cryogenic nature of these fluids also allows them to be used to absorb excess heat from the cabin air.
Windows and Doors:
The XP windows afford an excellent view, and they block out harmful Ultraviolet (UV) rays from the Sun, survive the heat from reentry, and withstand the pressure and temperature differentials throughout the flight. The XP windows and doors are a “plug” design with layers of high temperature glass and Lexan. Special coatings on the windows keep out harmful UV rays. They provide redundant protection from both the heat of reentry, and double-walled containment for the internal pressure.
The Rocketplane® XP is designed to operate on both turbojet and rocket power.
The turbojet propulsion plant consists of modified CJ610 jet engines that have a history of reliability and ruggedness. As a part of the J-85 engine family, these engines also have a high thrust-to-weight when compared to other turbojets. The turbojets draw jet fuel from tanks within the wings and are used by the XP for takeoff and climb to the rocket ignition point before being shutdown shortly after rocket ignition. Although not necessary for a safe and successful mission, the turbojets are reignited following reentry allowing the pilot more margin and flexibility. RGI and its contractors have done extensive research and analysis to ensure the turbojets will survive the trip into space repeatedly and reliably with little or no additional wear compared to normal atmospheric flight.
The XP is powered on its ballistic ascent by a 36,000lbf Liquid Oxygen and Kerosene (LOX/RP) rocket engine based upon the successful Atlas family of engines. This new rocket, dubbed the “AR-36” is being developed in cooperation with Polaris Propulsion and is regenerative cooled and adopts several key features from its heritage including injector design to ensure a stable, reusable, efficient, and cost effective engine. Propellant for the rocket ascent is stored in all composite LOX and RP tanks located in the aft fuselage, with helium providing ullage pressurization and purge gas. The propellant is fed via a Barber Nichols turbopump, which utilizes Hydrogen Peroxide for drive gas, resulting in long turbopump life, lower maintenance, and safe rocket abort capability.
Reaction Control System (RCS):
For exoatmospheric maneuvers, XP has a Reaction Control System (RCS) consisting of 12 cold nitrogen gas thrusters placed in opposing pairs so that they can change XPs attitude in all 3 dimensions. The RCS system, provided by Space Vector Corporation, is in three segregated zones any two of which allow full control authority, allowing system fault tolerance. The RCS will be used to orient the XP to give the passengers different views through their windows and to maintain proper orientation during reentry.
Flush Air Data System (FADS):
XP’s Mach 3.5+ flight profile makes it problematic to use the typical aircraft external probes and sensors to determine the pressure, airspeed, air density, alpha, and stall warning. Rocketplane and Utah State University teamed on an all new, patented, Flush Air Data System or FADS. This system uses an array of flush mounted sensors to calculate the values that would have been produced by a typical instrument set and is functional to hypersonic speeds.
Flight Control System (FCS):
XP features an advanced, all electric, fly-by-wire flight control system with an elevon and aileron on each wing, and all-moving tail “V-Tail”s. Pilot inputs are fed through triply redundant flight control computers which determine the rate commands for the flight controls. The electromechanical actuators operate on 270VDC power and feature internally redundant drives, and redundant cross over actuator controllers.
Electrical Power System:
The XP spends much of its time flying either exoatmospherically or in glide as it returns to base. During these portions of the flight it will have no running jet engines to run generators or other power producing devices and therefore uses stored energy systems. For this purpose the XP is equipped with a series of large Lithium Ion batteries. These batteries provide power to XPs systems at 28volts and 270volts Direct Current (DC). The electric flight control actuators use the 270VDC while the computers and other systems use the 28VDC. The Lithium Ion power system is redundant and fault tolerant and is designed to be recharged onboard the plane.
Guidance, Navigation, & Control (GN&C):
Rocketplane XP features an advanced fault tolerant GN&C system being developed by bd Systems. The Avionics system receives data from the Flush Air Data System (FADS), Global Positioning System (GPS), and an Inertial Navigation System (INS) and is tolerant to loss of GPS signal and signal reacquisition. Pilot inputs are taken from electrical stick, throttle, and pedals and are used to determine rate commands to the electromechanically actuated flight control surfaces and if necessary the RCS. The XP is a partially autonomous vehicle and from rocket ignition to atmospheric reentry, the triple redundant flight computers run both closed and open control loops to maintain the required flight.
DAS & IVHMS:
XP features a Data Acquisition System (DAS) being built by ARINC, that collects data from hundreds of sensors placed throughout the vehicle and stores it onboard the vehicle as well as transmits it to the ground. This data is used for an Integrated Vehicle Health Management System (IVHMS) in which the computers onboard XP look for anomalous behavior from the vehicles systems and structure and attempt to diagnose what maybe causing the undesirable readings. If there is any concern, the IVHMS can warn the pilot immediately. The IVHMS will also allow ground staff to determine if a system appears to need routine maintenance or repair. This system makes XP safer to fly and saves valuable time and parts cost, by servicing parts before they fail, and by knowing which areas require service, rather than undertaking exhaustive gremlin chasing between flights.
The XP will be unique amongst aircraft in that it will be the first to ever take off on its own landing gear, go into space, and then return and land on its own gear again. The wheel wells have a unique sealing system that insures that the wheels will be protected from the elements during reentry.
Thermal Protection System (TPS):
When the XP reenters Earth’s atmosphere the leading edges of the wings, tails, flight control surfaces, and nosecone will experience temperatures in excess of 600-700F. These surfaces are made of titanium which is not only very temperature resistant but light as well. The rest of the vehicle is covered in a special ceramic paint that emits over 93% of the energy it receives. In select areas such as near the rocket engine, ceramic blankets will be used to protect the fuselage from not only the heat of reentry, but also the heat produced by the rocket engine.