Landmark launch in rocketry: Centaur set for Flight 200
BY JUSTIN RAY
Posted: February 9, 2012
The venerable U.S. upper stage rocket -- the Centaur -- that created the pathway to the Moon and every planet across the solar system will be making its 200th flight next Thursday in a milestone mission to boost the U.S. Navy's sophisticated new mobile communications satellite to orbit.
"Centaur makes it possible for the U.S. to launch spacecraft of much greater size and weight then ever before," NASA said on the eve of the first launch in 1962. "Hydrogen offers more pounds of thrust per pound of propellant consumed per second than any other fuel possible in chemical rockets."
The stage was at the forefront of advancing rocket technology by conquering cryogenic fuels, a key accomplishment that benefited a host of different space boosters to follow.
"Centaur has been pioneering space launch for the last 50 years. The first launches in the early 1960s demonstrated the extremely high performance that can be achieved with a liquid hydrogen/liquid oxygen rocket stage. LH2/LO2 stages were subsequently used for the Saturn I, Saturn V, Space Shuttle, Titan and Delta programs," said Jim Sponnick, United Launch Alliance's vice president for mission operations.
"Centaur developed and flight demonstrated in-flight restarts for LH2/LO2 engines -- a technology that was critical for the Apollo programs and also for enabling a wide variety of flexible mission designs."
Success came on the second launch in November 1963, injecting the Centaur into Earth orbit where it continues to loop today in an elliptical perch ranging from 290 to 840 miles. The NASA press kit from the second mission is online too.
The project had a difficult development. Insulating the Centaur to preserve the supercold liquid hydrogen propellant at -423 degrees F was a major challenge and keeping the fuel "bottomed" in the tank for in-space relighting of the engine proved temperamental.
Several of the early launches failed due to a variety of issues including a steering problem on flight three and the inability to get the engines restarted on flights four and seven as the ullage thruster design was worked out.
Successful single-burn missions were repeated over and over, then a good restart of the engine in orbit occurred on flight ten as the Centaur moved closer toward perfection.
To the Moon, Mars and beyond
"Centaur has delivered scientific missions to explore the sun, our Moon, and every planet in our solar system," said Sponnick.
Other notable early spacecraft that successfully reached orbit aboard Centaurs were the Orbiting Astronomical Observatory ultraviolet telescope, Mariners 6 and 7 that performed photo reconnaissance flybys of Mars in 1969 and Mariner 9 that became the first spacecraft to enter orbit around another planet -- Mars -- in 1971.
Then came Pioneers 10 and 11 on mankind's first journey to explore the outer solar system, launching from Complex 36 at the Cape in March 1972 and April 1973, respectively. Pioneer 10 made the first-ever close encounter with Jupiter in December 1973 before being flung out on an escape trajectory from our planetary neighborhood. Pioneer 11 also visited Jupiter before continuing on to make the first flyby of Saturn and getting sent on its own escape path.
At the end of 1973, Mariner 10 took off to cruise by Venus and use that planet's gravity as a sling shot to venture further inward in the solar system to become the first craft to visit Mercury.
Besides NASA scientific probes, Centaurs were flying in the early days on communications spacecraft deployment flights for Intelsat, the International Telecommunications Satellite Organization.
Further exploits to the outer solar system -- Voyagers 1 and 2 -- also rode Centaurs atop their Titan rockets from Cape Canaveral in the summer of 1977. Both visited Jupiter and Saturn, then Voyager 2 continued on a grand tour to fly by Uranus and Neptune.
The planetary legacy of Atlas-Centaur included more Pioneer missions -- 12 and 13 -- that went to orbit Venus in 1978.
Also in 1978, the Navy's first Fleet Satellite Communications System spacecraft -- FLTSATCOM 1 -- was lofted to orbit. That military communications constellation was assembled by Atlas-Centaur vehicles through 1989, becoming the initial generation that eventually would be replaced by the UHF Follow-On program in the 1990s and now the MUOS mobile communications craft beginning with next Thursday's launch.
In more recent years, high-profile missions like Cassini to Saturn, Mars Reconnaissance Orbiter and the Mars Science Laboratory, New Horizons to Pluto and Juno to Jupiter have gotten successful starts on Centaur.
The rocket stage even went to the Moon on a crashing experiment to hit a crater in the South Pole to search for evidence of water ice.
Then and now: The evolution of Centaur
Centaurs have come in dual-engine and single-engine versions, serving multiple variants of Atlas and Titan, flying 176 times on Atlas and 23 times on Titan, and even was envisioned for use aboard the space shuttle starting in 1986 for planetary probes, but that plan was scrapped after Challenger.
The first RL10 engine was designed to generate about 15,000 pounds of thrust. Upgrades and advancements to today's RL10A-4-2 used on the Atlas 5 produces 22,300 pounds of thrust to push payloads to Earth orbit and beyond.
The Pratt & Whitney Rocketdyne fact sheet has more details on the venerable powerplant.
"The overall Centaur stage architecture (today) is fundamentally the same as the versions flown in the early 60s -- with a thin-walled, less than the thickness of a dime -- stainless steel pressure-stabilized structure that provides the most weight-efficient stage possible, and also the Centaur is still powered by the very reliable and proven RL10 engine," said Sponnick.
"The Centaur avionics have evolved through numerous generations, with the current system based on an extremely capable 8-processor, fault tolerant, ring laser gyro navigation system and flight computer.
"The Centaur has grown in size, now carrying 50 percent more propellant than the early Centaur vehicles.
"These evolutionary changes over the 5-decade history of the Centaur have made for an increasingly flexible and reliable upper stage that has triple the performance capabilities of the first Centaurs developed and flown by rocket pioneers in the early 1960s," said Sponnick.
Remarkable success rate
After surviving the bumpy road of development in the early days, Centaur has proven to be a dependable booster for space. In the 199 launches over the past 50 years, only 11 Centaurs have failed, and over half of those malfunctions occurred in the 1960s and 70s.
The last outright failure happened on a Titan-Centaur in 1999 when a software error caused the stage to misfire and ruined the mission of an Air Force MILSTAR communications satellite.
"I and many of my coworkers clearly recall the 100th flight of the Centaur in April of 1995. It took 33 years for Centaur to accomplish those first 100 flights. The next 100 Centaur launches have been accomplished in 17 years," said Sponnick.
A big payload for No. 200
Roaring off the launch pad at Cape Canaveral's Complex 41 next Thursday, the Centaur will be shrouded inside the bulbous nose cone of the Atlas 5 rocket for the climb through Earth's atmosphere.
Its chance to perform begins four-and-a-half minutes into flight when the first stage drops away and the RL10 engine fires to life for the first of three burns needed to heave the massive MUOS 1 spacecraft into the proper orbit for the U.S. Navy.
At nearly 15,000 pounds, the satellite is the heaviest payload ever launched by an Atlas rocket. Filled with state-of-the-art 3G cellular telephone technology, MUOS 1 will provide an unprecedented level of capacity for mobile communications to U.S. and allied warfighters on the move.
"The 200th flight of the Centaur is a very big milestone for the ULA team," said Sponnick.
Initially firing for almost 8 minutes, the Centaur will reach a preliminary low-Earth orbit of 90 by 337 nautical miles in altitude, tilted 28 degrees to the equator, to begin the three-step process of achieving the desired orbit.
The rocket will coast briefly while crossing the Atlantic before igniting the main engine a second time just over 20 minutes after liftoff for a six-minute firing to propel MUOS into a highly elliptical transfer orbit of 104 by 18,600 nautical miles inclined 26 degrees.
Then begins a lengthy coast away from the planet in this new orbit for two-and-a-half hours.
Previous Atlas 5 launches to geosynchronous transfer orbit have used just two burns, but MUOS will feature three firings.
"The three burn mission design for MUOS provides 1,000 pounds greater lift capability than a conventional 2-burn geosynchronous transfer orbit," said Sponnick.
"The MUOS 1 mission represents an excellent example of the performance and mission design capabilities of the Centaur," said Sponnick.
"Our customers for this mission asked for a mission design that would launch this very heavy and capable satellite in a manner that would minimize the amount of energy (and propellant) that the satellite would have to consume to position itself into the final geosynchronous orbit. Considering all of the commodities and capabilities of the Centaur, our mission design team developed this three-burn mission profile to provide an optimal solution for the MUOS customer."
MUOS separates from the Centaur three hours and one minute after leaving Cape Canaveral, beginning its 15-year life for the Defense Department. Controllers will spend about three months getting the craft maneuvered into a circular geosynchronous orbit over the equator and checked out before putting it into service.
You can follow Thursday's launch in our Mission Status Center with live journal updates and streaming video.
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