The Ares I-X was not merely a rocket; it was a meticulously engineered assembly of functional parts and high-fidelity simulators, designed to provide critical data for NASA's Constellation program. This prototype, launched in 2009, was built to mimic the future Ares I launch vehicle in shape, mass, and size, despite having largely different internal hardware. Understanding its individual components and the modifications made for its test flight offers
insight into the complexities of space vehicle development and testing.
The First Stage: A Blend of Heritage and Innovation
The foundation of the Ares I-X was its first stage, which incorporated a functional four-segment solid rocket booster (SRB) motor and aft skirt directly from the Space Shuttle inventory. This motor was manufactured by ATK Launch Services. However, significant modifications and new components were integrated to adapt it for the Ares I-X's specific test objectives. New forward structures were manufactured by Major Tool & Machine, and the first-stage element was managed by Marshall Space Flight Center.
Key modifications to the aft skirt included the addition of eight booster deceleration motors, designed to pull the booster away from the upper-stage simulator, and four booster tumble motors, which caused the booster to tumble horizontally to reduce its velocity before reentry. The aft skirt also housed one of two Redundant Rate Gyro Units (RRGUs), providing crucial attitude and position data to the Fault Tolerant Inertial Navigation Unit (FTINU). To ensure proper tumbling after separation, 3,500 pounds of steel ballast were added to the aft skirt, shifting the first stage's center of gravity. An extended service tunnel along the exterior accommodated an extended linear shaped charge for the flight termination system, covering all four segments, and cabling for additional pressure and environmental instrumentation.
Simulators and Specialized Sections
Above the functional SRB, the Ares I-X featured several simulators and specialized sections. A fifth segment simulator was crucial for replicating the length and mass of the Ares I's intended five-segment motor. This simulator also housed the First Stage Avionics Module (FSAM), which contained electronics for capturing and storing flight data, providing electrical power, performing separation and parachute deployment commands, and housing video cameras to record first-stage separation. A hollow forward skirt simulated the Ares I First Stage forward skirt, while a forward skirt extension housed new, larger parachutes. These three main parachutes each had a 150-foot diameter, larger than the 136-foot Shuttle booster main parachutes. A Shuttle booster heritage nosecap covered the pilot and drogue parachutes, with jettisoning the nosecap releasing the pilot parachute, which in turn pulled out the drogue. The forward skirt extension separated from the booster to deploy the main parachutes.
Connecting the 12-foot-diameter first stage to the 18-foot-diameter upper-stage simulator was a frustum, a hollow, inverted half-cone. For the test flight, both the frustum and forward skirt extension were made of aluminum, while the forward skirt and fifth segment simulator were constructed from steel. The upper-stage simulator (USS), manufactured by NASA personnel at Glenn Research Center, was built from eleven steel segments due to transportation constraints. It simulated the shape, mass, and center of gravity of the Ares I from the interstage to the top of the Orion Crew exploration vehicle's service module, using steel ballast plates to mimic the liquid hydrogen and liquid oxygen tank masses. The USS was equipped with various sensors for temperature, vibration, thermal, and acoustic data, and housed the FTINU, which controlled the vehicle's flight and primary avionics functions. Access to the FTINU was provided through a crew hatch on the interstage segment, which also housed the roll control system. Ladders and ring-shaped platforms within each USS segment allowed access to sensors and cabling, a necessity given that Launch Complex 39B was not tall enough for direct crew access to the upper parts of Ares I-X.
Avionics and Roll Control
The avionics system of the Ares I-X was a sophisticated network designed to control its autonomous flight. It utilized hardware from the Atlas V Evolved Expendable Launch Vehicle (EELV), including the FTINU and RRGUs. The first stage's control primarily relied on heritage hardware from existing Space Shuttle systems. A new component, the Ascent Thrust Vector Controller (ATVC), served as a translation tool, enabling communication between the Atlas-based flight computer and the solid rocket booster's thrust vector control system. This ATVC was the sole new avionics box, with all other components being existing or off-the-shelf units. The vehicle also incorporated 720 thermal, acceleration, acoustic, and vibration sensors for developmental flight instrumentation, with data transmitted in real-time via telemetry or stored in the FSAM.
Crucially, an active roll control system (RoCS) was implemented to counteract the test vehicle's tendency to roll around its axis of forward motion. The RoCS consisted of two modules, positioned on opposite sides of the Upper Stage Simulator's outer skin, utilizing engines originally from Peacekeeper missiles. These modules used hypergolic monomethyl hydrazine and nitrogen tetroxide as propellants, firing tangentially to the skin and at right angles to the roll axis to generate controlling roll torque. The RoCS had two primary functions: to roll the vehicle 90 degrees after liftoff to mimic the Ares I's launch roll attitude, and to maintain a constant roll attitude during ascent until stage separation. These modules were designed and constructed by Teledyne Brown Engineering and hot-fire tested at White Sands Test Facility to ensure their pulsing duty cycle performance. The avionics system, developed by Lockheed-Martin as a subcontractor to Jacobs Engineering, was managed by Marshall Space Flight Center, highlighting the collaborative effort behind this complex prototype.
