Volume 9, Number 3 • May/June 2001

X-37 Program Gets Boost

In the early morning of March 14, 2001, the X-40A glided to the runway at Edwards Air Force Base in California, its nose wheel set down smoothly and the test vehicle rolled to a gentle stop. However, no pilot exited the craft, for there was no pilot. The X-40A flew itself, guided by its onboard systems.

“It was truly a beautiful sight, and cause for celebration,” said Susan Turner, NASA’s X-37 program manager at NASA Marshall Space Flight Center in Huntsville, Alabama.

The X-40A’s free flight and landing were conducted as part of the X-37 program, intended to reduce the risk of flight testing the X-37, not from 15,000 feet like the X-40A, but from low-Earth orbit. The X-37 is an experimental re-entry vehicle that will enable NASA to test advanced technologies in the harsh environment of space and in returning through Earth’s atmosphere.

This first successful test of the X-40A by NASA was a big step forward for the X-37 program. Its primary objective was to validate the vehicle’s Computed Air Data Systems (CADS), which also will be used in the flight control system of the X-37.

“Our initial review of the test shows the vehicle’s performance matched our predictions nearly perfectly,” said Turner.

This flight also demonstrated the kind of teamwork that will be needed for NASA to develop a second-generation reusable launch vehicle capable of replacing today’s Space Shuttle. The Boeing Company, NASA’s partner in X-37, made major modifications to the X-40A, on loan from the U.S. Air Force, which also participates in the X-37 program. NASA Dryden Flight Research Center, with the cooperation of Edwards Air Force Base, conducted the test. The X-40A was lifted into the sky and released by a U.S. Army Chinook helicopter provided by Fort Rucker, Alabama.

The X-37 program consists of three phases of flight testing: the X-40A free flight series is phase one; phase two will be atmospheric testing, with the X-37 being dropped from a B-52; phase three will be the orbital test flights.

“Incremental testing is a cost-effective approach to designing an experimental spacecraft,” said Turner. “By leveraging an existing asset—the X-40A—we obtain valuable information which enhances the likelihood of mission success for the X-37.

“Upcoming free flights will push the envelope further. Each time, we’ll change some of the test variables of the X-40A to check the vehicle’s controllability and maneuverability in a different flight situation. The results will help us determine our safety parameters when we fly the X-37,” said Turner.

A second free flight test of the X-40A took place in early April. The objectives were the same as the first flight; however, engineers modified control variables to see the vehicle’s response.

The X-40A test vehicle was built in 1998 for the Air Force by The Boeing Company at its Seal Beach, California, facility. It has a fuselage length of 22 feet, a wingspan of 12 feet and weighs about 2,600 pounds. It is an 85 percent scale version of the X-37.

The X-37 government team, led by the Marshall Center, includes NASA Ames Research Center, Moffett Field, California; Johnson Space Flight Center, Houston, Texas; Kennedy Space Center, Cape Canaveral, Florida; Goddard Space Flight Center, Greenbelt, Maryland; Langley Research Center, Hampton, Virginia; Dryden Flight Research Center and the Air Force Flight Test Center, both at Edwards Air Force Base in Edwards, California; and the Space and Missile Systems Center and the Air Force Research Laboratory in Albuquerque, New Mexico. Boeing’s facility at Seal Beach, California, leads the X-37 industry team.

For more information about the X-37 or the X-40A, contact Mark Skoog at NASA Dryden Flight Research Center, 661/276-5774, mark.skoog@dfrc.nasa.gov. Please mention you read about it in Innovation.

Oxygen Sensors Qualified for Flight NASA Dryden Flight Research Center has conducted rigorous testing and qualified an inexpensive commercial off-the-shelf (COTS) oxygen sensor that, during flight tests, accurately and reliably aids assessment of the hazards associated with propulsion systems supplemented by oxidizers. Future flight test vehicles continue to rely on such energetic propellants as liquid and/or gaseous oxygen and hydrogen for purposes of demonstration because these propellants deliver high, specific impulses. A commercially available oxygen sensor and its temperature controller have been qualified for flight and will be used aboard the Hyper-X airplane. Photo provided by NASA Dryden Flight Research Center. In preparation for flight testing in the Linear Aerospike SR-71 Experiment (LASRE) program, commercial sensors intended originally for medical and automotive application were qualified for flight. After a rigorous process of qualification and calibration, the sensors have now been added to the Hyper-X program, a proposed experimental hydrogen-fueled hypersonic aircraft, and are scheduled for use in future flight test projects. The sensor in question is a commercial-grade miniature fuel cell, a small transducer that converts chemical energy into electrical energy. The vendor has estimated the sensor life expectancy to be approximately 2.4 years. However, because of the criticality of these sensors, it was decided that in the LASRE project, each such sensor would be replaced when its response deteriorates or it reaches a calendar life of 1.5 years. Twelve of the sensors and their respective thermal controllers were integrated into the LASRE flight test fixture and were flight tested to a speed of Mach 1.6 and an altitude of 52,000 feet. Eight of the original twelve sensors remained onboard after removal of the LASRE for some follow-on flight tests at speeds up to Mach 3.03, altitudes to 73,000 feet and exposure to internal temperatures greater than 130 degrees Fahrenheit. Even though the temperatures rose above the temperature-controller limits and the manufacturer’s specifications for operation, the oxygen sensors exhibited no significant drift. Four sensor suites are to be incorporated into the Hyper-X airplane for safety during the flight test in which the Hyper-X will be carried by a B-52 airplane. These sensors will be used to verify the desired and expected chemical inertness—specifically, the lack of oxidizing gas—in the interior of the vehicle. They are being calibrated in much the same manner as in the LASRE program, but dynamic-response and sensor-recovery tests will be performed in addition, for comparison with results of tests in the boost and free phases of the flight of the Hyper-X. For more information, please contact Neal Hass at NASA Dryden Flight Research Center 661/276-2641, neal.hass@mail.dfrc.nasa.gov. Please mention you read about it in Innovation.