看真正的X－33
资料来源 www.fas.org
X-33 VentureStar
The Reusable Launch Vehicle (RLV) Technology Program is a partnership between NASA and industry to design a new generation of launch vehicles expected to dramatically lower the costs of putting payloads in space. Today's launch systems are complex and costly to operate. The RLV program stresses a simple, fully reusable vehicle that will operate much like an airliner. NASA hopes to cut payload costs from $10,000 a pound, as it is today, to about $1,000 a pound. To accomplish this goal, NASA sought proposals from US aerospace industries for the RLV Technology Program.
On August 5, 1994, President Clinton issued the National Space Transportation Policy and designated NASA as the Lead Agency for advanced technology development and demonstration of the next generation of RLVs. Three concepts and preliminary designs were prepared independently by: (1) Lockheed Martin Skunk Works, Palmdale, California; (2) McDonnell-Douglas Aerospace, Huntington Beach, California; and (3) Rockwell International Corporation, Space Systems Division, Downey, California.
>In July 1996, NASA selected Lockheed Martin Skunk Works of Palmdale CA to design, build and test the X-33 experimental vehicle for the RLV program. The selected team consists of Lockheed-Martin (lead by the Skunk Works in Palmdale, CA), Rocketdyne (Engines), Rohr (Thermal Protection Systems), Allied Signal (Subsystems), and Sverdrup (Ground Support Equipment), and various NASA and DoD laboratories. NASA has budgeted $941 million for the X-33 program through 1999. Lockheed Martin will invest at least $212 million in its X-33 design.
Specific technology objectives of the X-33 space vehicle include:
demonstrate a reusable cryogenic tank system, including the tanks for liquid hydrogen (LH2) and liquid oxygen (LOX), cryogenic insulation, and an integrated thermal protection system (TPS)
verify TPS durability, low maintenance, and performance at both low and high temperatures
demonstrate guidance, navigation, and control systems, including autonomous flight control of checkout, takeoff, ascent, flight, reentry, and landing for an autonomously controlled space vehicle
achieve hypersonic flight speeds (speeds up to Mach 15 or 18,000 km/hr(11,000 mph))
demonstrate composite primary space vehicle structures integrated with the TPS
demonstrate ability to perform 7-day turnarounds between three consecutive flights (a turnaround is the amount of time required from a takeoff and flight until the vehicle is serviced, refueled, and ready to fly again)
demonstrate ability to perform a 2-day turnaround between two consecutive flights
demonstrate that a maximum of 50 personnel performing hands-on vehicle operations, maintenance, and refueling can successfully accomplish flight readiness for two flights.
Specific test flight objectives would include demonstration of:
successful interaction of the engines, airframe, and launch (also referred to as takeoff) facility
engine performance, thrust, and throttling capability meets specifications
operability and control of the X-33's flight control surfaces (canted fins, flaps, ailerons, etc.)
durability of the metallic thermal protection system during repeated flights
performance of the guidance, navigation, and control system
performance of primary operations facilities, including takeoff infrastructure
automated landing at a designated point on the runway
verification of tasks required to service the vehicle on landing and prepare it for next flight in minimal time.
The reusable, wedge-shaped X-33, called VentureStar, will be about half the size of a full-scale RLV. The X-33 will not take payloads into space; it will be used only to demonstrate the vehicle's design and simulate flight characteristics of the full-scale RLV. Lockheed Martin plans to conduct the first flight test in March 1999 and achieve at least 15 flights by December 1999. NASA has budgeted $941 million for the project through 1999. Lockheed Martin will invest $220 million in its X-33 design. After the test program, government and industry will decide whether or not to continue with a full-scale RLV.
The RLV will fly much like the Space Shuttle. It will take off vertically and land on a runway. However, there are differences between the two vehicles. The RLV will be a means of transport only. It will not be used as a science platform like the current Space Shuttle.
Also, the RLV will be a single-stage-to-orbit spacecraft it does not drop off components on its way to orbit. It will rely totally on its own built-in engines to reach orbit, omitting the need for additional boosters. Unlike the shuttle, the RLV will use a new linear aerospike engine, which looks and runs much differently than the bell-shaped Space Shuttle Main Engine. NASA considered the aerospike engine for the Space Shuttle 25 years ago, but opted to use the Space Shuttle Main Engine, also built by Rocketdyne. The aerospike has been revived and enhanced to power the RLV. The aerospike nozzle is shaped like an inverted bell nozzle. Where a bell nozzle begins small and widens toward the opening of the nozzle like a cone, the aerospike decreases in width toward the opening of the nozzle. The aerospike is 75 percent shorter than an equivalent bell nozzle engine. It is also lighter, and its form blends well with the RLV's lifting body airframe for lower drag during flight. The shape spreads thrust loads evenly at the base of the vehicle, causing less structural weight.
The half-scale X-33 test vehicle will use two smaller test versions of the aerospike, whilet the full-scale RLV will use seven aerospike engines. The X-33 main propulsion system (full system of engines and propellant tanks) consists of two J-2S aerospike engines, one aluminum LOX tank in the front, and two LH2 tanks in the rear for short- and mid-range flights. The vehicle could sustain one engine out at liftoff and still have sufficient power from the remaining engine to continue acceleration and make a safe landing at the intended runway or an abort landing area depending on where the engine out occurred during flight. For the long- range flights an engine out situation could be tolerated approximately 30 seconds after liftoff.
The X-33 was scheduled to complete its first flight by March of 1999. As of early 1999 the projected date for the X-33 rollout was May 1999, with its first flight planned for that July. The program is scheduled to be completed by the year 2000. The baseline test program would include a combined total of approximately 15 flights beginning in July 1999 and concluding in December 1999. The baseline test flight plan includes three short-range, seven mid-range, and five long-range test flights. Actual numbers of test flights to any range may vary due to changing plans and/or actual test flight data evaluation.
Test flights involve: (1) launching the X-33 from a vertical position like a conventional space launch vehicle梩his reduces the weight of the landing gear and wheels to only that required to support an unfueled vehicle (baseline dry weight of vehicle is approximately 29,500 kg (65,000 lb) and fueled weight of X-33 is approximately 123,800 kg (273,000 lb)); (2) accelerating the vehicle to top speeds of Mach 15 (15 times the speed of sound or approximately 18,000 km/hr (11,000 mph) and reaching high altitudes up to approximately 75,800 m (250,000 ft); (3) shutting down the engines; gliding over long distances up to 1,530 km (950 mi) downrange of the launch site followed by conducting terminal area energy maneuvers to reduce speed and altitude; and (4) landing like a conventional airplane.
Optimally, the flight test plan to meet Program objectives would involve flights of approximately 160, 720, or 1,530 km (100, 450, and 950 mi). Landing sites meeting the above criteria and providing 3,050 m (10,000 ft) of hard surface are referred to as short-, mid-, and long-range landing sites, respectively. The X-33 Program prefers to land the vehicle on a dry lake bed at least for its first flight in order to have a wider and slightly safer landing area than conventional runways offer. The same philosophy was used for the Orbiter's and most X-planes' first landings.
The launch site is located within Edwards Air Force Base, California. A total of fifteen launches are scheduled over a period of approximately one year. The X-33 will blast off from the site near Haystack Butte, located at the eastern edge of the Base near the AFRL/PR. Predominantly local NASA and USAF tracking and command assets will be utilized to support this phase of flight. Construction of the X-33 launch site at was completed in December 1998, just a little more than 12 months after groundbreaking.
Once the X-33 is readied for flight, the engines will be fired two times on the launch pad, with the second firing having a duration of 20 seconds. The longest flight will be approximately 20 minutes at an altitude of about 55 miles. The plan is to demonstrate a 2-day turnaround for the vehicle. Landing sites include Silurian Dry Lake Bed, Michael Army Air Field and Malmstrom Air Force Base. One of NASA's 747s will be used to carry the X-33 from its landing destinations back to Edwards.
Silurian Dry Lake Bed near Baker, California is approximately 3000 feet wide and 12000 feet long. The lake bed will be the site of the first landing attempts for the X-33 vehicle. Three flights are scheduled to Silurian Lake that will include vehicle speeds in excess of Mach 3. The flights are scheduled to start in mid 1999.
Michael Army Airfield will be the second landing site for the X-33. This will also be the first downrange runway landing. Michael Army Airfield is part of the Utah Test and Training Range, located south of Salt Lake City. This airfield is located on the eastern boundary of Dugway. The airfield has a 3,960 m (13,000 ft) long by 61 m (200 ft) wide hard surfaced runway. Immediate surrounding terrain is relatively flat. It is a secure facility with a long history of flight operations. The airspace above Dugway Proving Ground is restricted military airspace controlled by Hill Air Force Base which manages and approves use of the Utah Test and Training Range (UTTR). Seven flights are scheduled to Michael with vehicle speeds in excess of Mach 10. Flights are scheduled to start in the latter part of 1999.
Malmstrom Air Force Base will be the third and final landing site for the X-33. The airfield was closed on Decmeber 31, 1996, except for the area used by helicopters of the Malmstrom's Air Rescue Flight. The airfield has a hard surface runway approximately 3,500 m (11,500 ft) long and 61 m (200 ft) wide with a 305 m (1,000 ft) overrun at each end. Since closure of the airfield, the USAF has no plans or budget to operate the runway. Five flights are scheduled to the Malmstrom runway with vehicle speeds in excess of Mach 15. Flights are scheduled to start in the spring of 2000. |
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