Atlas V - NROL-35 Launch Updates
Launch Vehicle Overview, Countdown Timeline, ULA Archive, Live Launch Coverage
Atlas V Launch of classified NROL-35 wows Observers in California & Europe
December 13, 2014
Photo: William Stewart
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The launch of an Atlas V rocket from Vandenberg Air Force Base in the evening hours on Friday, local time, did not only startle unsuspecting witnesses in Hollywood from where UFO reports came in. In Europe, observers reported seeing a bright comet-like object in the early hours on Saturday that turned out to be the Centaur Upper Stage going through its post-separation maneuvering to achieve a safe state before deorbit.
Atlas V carrying the classified NROL-35 satellite made a thundering blastoff from Space Launch Complex 3E at 3:19 UTC on Saturday after an uneventful countdown that was extended by six minutes during its final hold for reasons that are unknown. Racing into the dark skies over California, Atlas V 541 was powered by its massive RD-180 main engine and four Solid Rocket Motors - making it the most powerful Atlas ever to launch from the west coast with a total liftoff thrust of 1,080 metric tons. After launch, the Atlas turned to the south, flying a slight dogleg maneuver of just a few degrees taking the launcher south-east, heading for a Molniya orbit 63.5 degrees in inclination. |
The target orbit was known prior to launch given the public navigational warnings that confirmed the south-easterly flight path leading to a Molniya orbit and ruling out Polar Orbit and any useful Low Earth Orbit such as retrograde orbits that can be targeted from Vandenberg. Knowing the orbital destination, satellite trackers prepared their predictions on where to find the classified satellite after its journey to orbit.
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Atlas V headed onwards as its boosters burned out after 95 seconds, falling away from the launcher a short time later. Only powered by the RD-180, Atlas V continued flying south, passing about 170 Kilometers west of Los Angeles where a number of surprised observers stared at the sky following a bright object unknown to them.
The launch vehicle headed into the usual news blackout after payload fairing separation occurring three and a half minutes into the flight. From there, the RD-180 continued to burn for about one more minute before the Common Core Booster separated from the trusted Centaur Upper Stage which ignited its RL-10C engine on the first burn to boost the stack into a slightly elliptical orbit with an apogee on the order of 2,200 Kilometers. There, the stack was set for a relatively short coast phase before the Centaur upper stage conducted its second burn. The coast allowed the proper placement of the apogee passage and also allowed the stack to gain altitude so that the second burn could raise the perigee of the orbit. According to analysis performed by well-respected satellite tracker and space analyst Ted Molczan, the NROL-35 payload was expected to be inserted into an orbit of 1,120 by 37,560 Kilometers at an inclination of 63.5 degrees. Spacecraft separation would have taken place less than 50 minutes after launch. The declaration of mission success from the NRO came at T+75 minutes, confirming the short duration of the ascent mission. With the satellite sent on its way, Centaur performed a standard Contamination and Collision Avoidance Maneuver to move away from the payload before, about two hours after launch, a short retrograde RL-10C burn was performed to place the vehicle onto a path for re-entry after one orbit, over a safe zone over the Ocean, south of Australia. Completing its third burn, Centaur was planned to complete passivation by venting its pressurant and propellant tanks as re-entry was still about ten hours away at that point. |
Photo: United Launch Alliance
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In a previous NRO launch to Molniya Orbit, Centaur could be seen over a large stretch of Europe and into Asia as a bright cloud of vented propellant enveloped the upper stage at that point in the flight.
Image: Spaceflight101/JSatTrak
Photo: Sören Petersen
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This was again the case on Saturday morning when observers saw the phenomenon from the United Kingdom, Germany and a number of other places that had the luck of getting a break in clouds.
A plot of the expected orbit of NROL-35 shows the large visibility footprint of the Centaur Upper Stage showcasing the benefit of Molniya orbits for use by communications and reconnaissance satellites, but also showing the visibility zone for Centaur's venting. The event was visible from across the nighttime portion of Europe and the north-western portion of Africa. Photos published in various web forums (1, 2) and Social Media show the bright cloud of expanding propellant around the Centaur Upper Stage that completed two separate venting events of its propellant components to achieve a safe state that avoids an in-orbit explosion. Some observers concluded what they saw was a comet, but the location of the object and its characteristic appearance confirmed that it was the Centaur upper stage of NROL-35. With confirmation of NROL-35 going into the expected orbit, satellite observers will continue tracking the vehicle to determine its exact orbital parameters that will be monitored as the spacecraft enters its commissioning phase that will likely include fine-tuning of the orbit to achieve the expected period, matching the duration of half a sidereal day. NROL-35 is most likely an electronics intelligence satellite outfitted with a large deployable antenna to pick to radio signatures from ground-based facilities, military or otherwise, to track foreign activity. The NROL-35 spacecraft is potentially hosting the SBIRS-HEO-3 payload for the Space-Based Infrared System that consists of satellites in Geostationary Orbit and hosted payloads in Molniya orbit to ensure proper coverage of the high-latitude regions as part of an Early Warning System that can detect and track infrared signatures of missiles and other objects. |
Identifying the secret NROL-35 Satellite
Image: NRO
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As one in a long line of National Reconnaissance Office Launches, NROL-35 follows the normal secrecy routine of NRO launches - no details on the identity of the payload or its target orbit are released, the exact launch window duration is kept secret and the live launch broadcast will end at the point of payload fairing separation when Atlas V will head into the customary news blackout.
Clues on the identity of the payload can be provided through the mission patches, but more substantial data is available through analysis of the targeted launch time, the launch vehicle that is being used and navigational warnings that are issued prior to flight and allow insight into the target orbit. For NROL-35, the navigational warnings clearly confirm that the payload is headed to a Molniya Orbit which is a highly elliptical orbit at an inclination of 63.4 (in this case) or 116.6 degrees with a period of half a sidereal day (~12 hours) and a high apogee around 40,000 Kilometers. This type of orbit was first used by a series of Russian military communications satellites known as Molniya (Lightning). |
Choosing an inclination of 63.3 or 116.6 degrees allows the satellite to have a constant argument of perigee of 90 or 270 degrees because the orbits are not perturbed by the gravitational field of Earth (J2 term of the Geopotential Model). This allows the satellite to have a constant perigee and apogee location on Earth over the course of its mission - for Molniya orbits, apogee is located above the northern hemisphere.
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Relative to Earth, the satellite's speed is slowest at higher altitudes, meaning that the spacecraft spends the majority of its time around apogee. Communication satellites in Molniya orbits operate for eight hours per orbit centered around the apogee passage. Reconnaissance spacecraft take advantage of the long apogee passage to observe target locations at virtually any point in the northern hemisphere.
The major benefit of a Molniya orbit despite being less energetic than GEO is the coverage of the polar regions which is in many cases not possible from Geosynchronous Orbit due to low elevation angles. Current NRO programs using Molniya Orbits are the Trumpet electronic intelligence satellites and the HEO Segment of the Satellite Data System which includes spacecraft in Geostationary Orbit and satellites in Molniya Orbits. Since the Geostationary Satellite Data System spacecraft only require Atlas V 401 rockets it seems unlikely that a 541 would be required to send an SDS craft of any modification to a Molniya orbit. Another clue of NROL-35 being a Trumpet satellite is the SBIRS-HEO-3 payload for the Space-Based Infrared System that includes dedicated satellites in Geostationary Orbits and hosted payloads on satellites in Highly Elliptical Orbits (HEO). The HEO-3 payload was shipped for integration with its classified host spacecraft in mid-2013, making a perfect fit for the NROL-35 timetable. Both SBIRS HEO payloads that have previously flown were hosted on Improved Trumpet Satellites (NROL-22 and NROL-28 in 2006 and 2008). The Trumpet satellites started operations in the 1990s as a successor to the Jumpseat spacecraft that started deployment in 1971 using Titan III(33)B launch vehicles. |
Molniya Orbit Design
Image: Google Earth/Spaceflight101
NROL-35 Departure from California towards 63.4° Orbit
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A total of seven Jumpseat signals intelligence satellites were launched until 1983, six of them achieved orbit. Three Trumpet satellites were launched by Titan IV rockets in 1994, 1995 and 1997 featuring a number of differences to the Jumpseat satellites - first and foremost their mass since Trumpet satellites are estimated to weigh a little over five metric tons while Jumpseat satellites had a mass of around 700 Kilograms which can also serve as an indicator of the satellite's capabilities.
Image: United Launch Alliance
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Details on the Trumpet Electronic Intelligence Satellites are not available. Speculative information claims that the satellites host large deployable mesh antennas with a diameter of over 100 meters to pick up even faint radio signals over foreign territory to allow insight into activity at military installations and other sites of interest. It is speculated that the Trumpet satellites were manufactured by Boeing.
Starting in 2006 a second generation, known as Improved Trumpet, started deployment beginning with a Delta IV M+(4,2) launch and followed in 2008 with the launch of an Atlas V 411 that sent the satellite into Molniya orbit. NROL-35 is using the more powerful Atlas V 541 with the larger 5-meter payload fairing which would indicate that the launch is likely carrying another version of the Trumpet Satellite, potentially starting the deployment of the third generation of spacecraft. It still remains possible that NROL-35 is a one-off spacecraft or a new type of HEO spacecraft series which can only be confirmed by tracking the satellite's orbit and potential activities after launch. Satellite trackers around the world are eager to pin-point the satellite's orbit and help confirm is identity. The mission's patch, like most NRO patches in the past, showcases plenty of symbolism and insignia to keep analysts busy. The mission poster includes the elemental symbols of fire, air and Earth while the mission patch prominently features a female figure with glowing eyes and purple hair holding a trident - possible references to Nisus and Poseidon in Greek Mythology. The trident is also the US Navy Special Warfare insignia worn by the SEALs and representing three aspects of SEAL operations on land, at sea and in the air. One interpretation of these 'clues' is that NROL-35 is a type of surveillance satellite that can monitor activity across the globe. |
This flight marked the fist time the new RL-10C engine flew on the Centaur Upper Stage which will become the future engine of both, the Atlas V and Delta IV fleets to increase the amount of common parts used on both launchers in an effort to reduce overall cost and increase efficiency while also introducing improvements in engine design.
Following a nominal mission profile, Centaur would inject the satellite into Molniya orbit about 40 minutes after launch, likely with a perigee over 1,100 Kilometers and an apogee around 37,500 Kilometers at an inclination of 63.5 degrees. Centaur is planned to conduct a deorbit maneuver to set up for a re-entry south-west of Australia after its first orbit. Update: The National Reconnaissance Office declared Saturday's launch a success - indicating that the NROL-35 had been released into the target orbit. The confirmation of mission success came around 75 minutes after launch, further underlining the short duration of this mission into a Molniya Orbit.
The hold also included the Go/No Go Poll for cryogenic tanking which brought positive results as all stations reported a GO for fueling on time. As soon as clocks started ticking at T-2-hours, the complex Propellant Loading sequence was started.
Only cryogenics had to be loaded as the Atlas Common Core Booster already had 94,600 liters of Rocket Propellant-1 loaded earlier. As clocks started ticking again, the RP-1 tank was pressurized to an intermediate pressure to provide additional stability to the launch vehicle. The tanking procedure started with with Ground Support Systems & Transfer Lines Chilldown and Atlas/Centaur Tank Chilldown before propellants started actually flowing inside the vehicle’s tanks. The first tank to begin fueling was the Centaur LOX tank that entered slow fill at L-2 hours and 8 minutes before quickly entering fast fill to load the tank with 15,700 liters of the -183°C oxidizer. Next was the oxidizer tank of the Common Core Booster that completed chilldown before LOX started flowing in slow fill and switching to fast fill in order to eventually reach topping when 185,500 liters were loaded.
As part of final countdown operations, Atlas V was put through Flight Termination System checks to make sure the system was ready to destroy the launcher in the unlikely event of a major malfunction. As countdown clocks ticked down, teams loaded new flight software into the launch vehicle’s computers based on the latest weather data. The RD-180 engine completed its Fuel Fill Sequence and teams verified that all tanks had reached flight level.
Reaching T-4 minutes, the countdown entered a planned 20-minute built-in hold to facilitate the transfer of the spacecraft to internal power and final polling that was performed by the launch team. After an extension of the hold by five minutes, all stations were able to provide a GO for launch as Atlas V was a well-behaved vehicle during the countdown and the weather took at favorable trend. Pressing into the Automated Countdown Sequence at 3:15 UTC, Atlas V began the final computer-controlled steps to transition to its launch configuration. The launch vehicle and ground ordnances were armed and at T-3 minutes, the Common Core Booster started propellant tank pressurization to ‘Step 3 Pressure’ or flight pressure after LOX Topping was terminated. The FTS went on internal power at T-2 minutes 45 seconds and the Atlas/Centaur stack transferred to internal at T-1:58. At T-1:55, the Countdown Auto Sequencer assumed control of the vehicle as its health was closely monitored by computers as well as the launch team. Next, LOX and LH2 topping on the Centaur was terminated and the upper stage began to pressurize its two tanks. At T-1 minute and 20 seconds, a final verification of the hydraulic system was performed and the Flight Termination System began its Terminal Countdown Sequence. All tanks were stable at flight pressure and during the final status check, the familiar words ‘GO Atlas! GO Centaur!’ were heard on the voice loops, confirming that all systems were ready for launch.
The pyrotechnic valve of the Reaction Control System pressurization bottles was fired to fully pressurize the Hydrazine tanks to feed the 12 attitude control thrusters mounted on Centaur. Also, the boost-phase chilldown of the RL-10 engine of Centaur was started to condition it for ignition.
Just before hitting the T+3 minute and 30-second mark, Atlas V started throttling back its RD-180 engine to limit stress on the vehicle during payload fairing separation. The fairing was jettisoned a short time later by pyrotechnics that separated the two halves of the fairing and pushed them outward to rotate clear of the satellite before falling away. Separation of the fairing occurred at a point in the flight when exposing the NROL-35 spacecraft was safe, having exited the dense layers of Earth's atmosphere.
RL-10C delivers a vacuum thrust of 106 Kilonewtons, slightly more than the RL-10A-4-2 and a little less than the RL-10B-2 with its huge nozzle. The engine achieves a specific impulse of 448.5 seconds. RL-10C measures 1.44 meters in diameter and 2.22 meters in length with a total mass of 190 Kilograms.
The second burn of the Centaur Upper Stage will significantly raise the apogee of the orbit and also put a few Kilometers on the perigee to achieve a Molniya orbit with a duration of nearly 12 hours. Orbital insertion is calculated to take place before T+40 minutes and the NROL-35 satellite is expected to be found in an orbit around 1,120 by 37,500 Kilometers at an initial inclination of 63.5 degrees. Over the course of the satellites' initial operations, this orbit will be fine-tuned to achieve a duration of exactly half a sidereal day to ensure a stable apogee passage over the northern hemisphere. To conclude its mission, Centaur will make a Collision and Contamination avoidance maneuver before re-igniting its RL-10C engine to make a deorbit burn that places it on a path to re-entry at its first perigee passage, about 12 hours after launch for entry south-west of Australia. This marked the 55th launch of the Atlas V launcher family, the third of the 541 specification and the ninth launch of Atlas V in 2014, setting a new record. |
Atlas V Launch with NROL-35 delayed by unfavorable Weather |
December 11, 2014 |
Photo: United Launch Alliance
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The launch of a United Launch Alliance Atlas V rocket carrying the classified NROL-35 payload for the U.S. National Reconnaissance Office had to be postponed on Thursday due to unfavorable weather conditions at Vandenberg Air Force Base in California. With rain showers and disturbed weather moving through the area Thursday evening and into the night, the launch team decided to back out of the countdown in its initial hours and return on Friday when conditions are looking more favorable.
Bad weather was on the forecast all week for this first launch attempt of the NROL-35 mission and teams headed into Thursday's launch countdown with only a 10% chance of favorable conditions during the classified launch window opening at 3:17 UTC on Friday. Entering the launch countdown at L-7 hours and 50 minutes, Atlas V and its Centaur Upper Stage were powered up for initial testing activities. Before the removal of the Mobile Service Tower at Space Launch Complex 3E, teams received a weather briefing that re-affirmed the bad forecast with virtually no chance of launching and persisting weather rule violations for MST rollback. As a result, the decision was made to keep the Service Tower in place and delay the launch one day to Friday night. This broke a streak of two years scrub-free countdowns for Atlas V since all of the vehicle's flights since the NROL-36 mission in 2012 left the pad on the first attempt. Through no fault of its own, Atlas V will stay on the ground for another day as teams prepare to re-initiate countdown operations on Friday. Forecasters issued a 40% chance of favorable weather conditions for the next attempt that is set for 3:13 UTC on Saturday. Ahead of the countdown, technicians will already be busy at the pad, completing final hands-on work and closing out the service structure, umbilical tower and the Atlas V launcher. At T-7 Hours, the ULA launch team and Air Force personnel will report to console to start working the pre-launch checklist. Following the activation of the launcher, teams begin a series of checkouts of the electrical system of the rocket. |
The Mobile Service Structure of Space Launch Complex 3E at Vandenberg Air Force Base will be retracted about 4.5 hours prior to launch. It will be placed at a safe distance to the Launch Pad. Subsequently, initial checks of the Atlas Launcher will be made and the Launch Area will be cleared of all personnel.
Flight Termination System testing is also completed and the Nitrogen Purge flow on the vehicle is initiated. L-4 Hour commanding is performed by teams. By L-3 hours, the launch pad is cleared by all personnel.
At T-2 Hours, the countdown enters a 30-minute built-in hold during which teams perform the fueling pre-task briefing and the GO/No GO Poll for propellant loading. As soon as the countdown resumes at T-2 Hours, propellant loading operations start. The complex procedure to load the two stages of the rocket with cryogenics begins with the chilldown of ground support equipment and transfer lines, and tank chilldown on the Liquid Oxygen side.
Liquid Oxygen starts flowing into the Centaur upper stage tanks shortly thereafter. Centaur LOX loading takes about 40 minutes as 15,700 liters of –183-degree Celsius oxidizer are filled into the upper stage. Once Centaur is into propellant loading, the large Liquid Oxygen tank of the Common Core Booster also starts fueling. LOX load on the CCB also moves through the three steps, slow-fill, fast-fill and topping. The Common Core Booster is loaded with Rocket Propellant 1 (refined Kerosene) ahead of the launch countdown. The large Common Core Booster that stands 32.46 meters tall with a diameter of 3.81m and a fuel load of 185,500 liters of LOX and 94,600 liters of RP-1.
The final tank to be loaded during the countdown is the Liquid Hydrogen Tank of the upper stage that also goes through the usual steps. Centaur is loaded with a total of 48,100 liters of -253-degree Celsius LH2 fuel. Centaur is 12.68 meters tall and 3.05 meters in diameter.
>>>Atlas V 541 Overview
Flight Termination System testing is also completed and the Nitrogen Purge flow on the vehicle is initiated. L-4 Hour commanding is performed by teams. By L-3 hours, the launch pad is cleared by all personnel.
At T-2 Hours, the countdown enters a 30-minute built-in hold during which teams perform the fueling pre-task briefing and the GO/No GO Poll for propellant loading. As soon as the countdown resumes at T-2 Hours, propellant loading operations start. The complex procedure to load the two stages of the rocket with cryogenics begins with the chilldown of ground support equipment and transfer lines, and tank chilldown on the Liquid Oxygen side.
Liquid Oxygen starts flowing into the Centaur upper stage tanks shortly thereafter. Centaur LOX loading takes about 40 minutes as 15,700 liters of –183-degree Celsius oxidizer are filled into the upper stage. Once Centaur is into propellant loading, the large Liquid Oxygen tank of the Common Core Booster also starts fueling. LOX load on the CCB also moves through the three steps, slow-fill, fast-fill and topping. The Common Core Booster is loaded with Rocket Propellant 1 (refined Kerosene) ahead of the launch countdown. The large Common Core Booster that stands 32.46 meters tall with a diameter of 3.81m and a fuel load of 185,500 liters of LOX and 94,600 liters of RP-1.
The final tank to be loaded during the countdown is the Liquid Hydrogen Tank of the upper stage that also goes through the usual steps. Centaur is loaded with a total of 48,100 liters of -253-degree Celsius LH2 fuel. Centaur is 12.68 meters tall and 3.05 meters in diameter.
>>>Atlas V 541 Overview
Image: United Launch Alliance
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When clocks reach T-4 Minutes, the countdown enters its final built-in hold. This hold can be extended in case of technical issues or uncooperative weather. During the hold, the launch team receives a final weather briefing and performs the GO/No GO Poll for Terminal Countdown.
As clocks start ticking down from T-4 Minutes, final vehicle configurations such as ordnance arming, flight termination system arming, propellant tank pressurization, transfer to internal power, and flight control system reconfigurations will be made as part of the Automated Sequence to place the vehicle in its launch configuration. >>>Atlas V Countdown Timeline At T-2.7 seconds, the massive two-chamber RD-180 main engine of the Common Core Booster ignites and soars up to its full liftoff thrust of 390,250 Kilograms. As the four boosters ignite, Atlas V will jump off the pad with a liftoff thrust of 1.08 Million Kilogram-force creating an initial thrust to weight ratio of 2.0. Less than ten seconds after liftoff, Atlas V will start its roll program to align itself with its precise ascent path, heading south. Atlas V will pass Mach 1 just 35 seconds after blastoff and encounter Maximum Dynamic Pressure just after passing 45 seconds into the flight. Burning out after 94 seconds, the four SRMs will have completed their job of providing that extra push needed to boost NROL-35 into orbit. The vehicle will hold onto the SRMs for several more seconds before separating them in a staggered fashion. |
Powered
by the RD-180 engine alone, Atlas V will continue its flight, burning
1,150 Kilograms of propellant each second. Approximately three and a
half minutes into the flight, the protective payload fairing will be
jettisoned, exposing the NROL-35 spacecraft.
At that point, the mission will head into the usual news blackout of NROL flights. No more updates on mission progress will be provided except for the confirmation of successful orbital insertion well after the event.
As the first stage passes the 4-minute mark into the flight, it will start throttling down its RD-180 engine to maintain a maximum acceleration of 5 Gs. During first stage flight, the Centaur Upper Stage initiates Reaction Control System pressurization and boost-phase chilldown. The Common Core Booster will burn until just before T+4.5 minutes. Shutdown is followed six seconds later by Stage Separation initiated by pyrotechnics and eight retrorockets that push the spent first stage away. It is then up to the Centaur Upper Stage and its new RL-10C-1 engine to perform the necessary maneuvers to place NROL-35 into its classified orbit, which, through analysis of navigational warnings, can be identified as a Molniya Orbit, a type of highly elliptical orbit.
At that point, the mission will head into the usual news blackout of NROL flights. No more updates on mission progress will be provided except for the confirmation of successful orbital insertion well after the event.
As the first stage passes the 4-minute mark into the flight, it will start throttling down its RD-180 engine to maintain a maximum acceleration of 5 Gs. During first stage flight, the Centaur Upper Stage initiates Reaction Control System pressurization and boost-phase chilldown. The Common Core Booster will burn until just before T+4.5 minutes. Shutdown is followed six seconds later by Stage Separation initiated by pyrotechnics and eight retrorockets that push the spent first stage away. It is then up to the Centaur Upper Stage and its new RL-10C-1 engine to perform the necessary maneuvers to place NROL-35 into its classified orbit, which, through analysis of navigational warnings, can be identified as a Molniya Orbit, a type of highly elliptical orbit.
Secret NRO Satellite ready for Launch atop Atlas V, challenged by Weather
December 10, 2014
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A United Launch Alliance Atlas V 541 rocket is ready for launch from Space Launch Complex 3E at Vandenberg Air Force Base in the evening hours local time on Thursday to embark on a classified mission to deliver a clandestine satellite to orbit for the U.S. National Reconnaissance Office. Becoming the most powerful Atlas rocket ever flown from the U.S. West Coast, the vehicle will also debut a new version of the trusted RL-10 engine used of the launcher's Centaur Upper Stage.
The NROL-35 launch is planned at 3:17 UTC on Friday, the opening of a classified launch window, but the mission is facing a pessimistic weather forecast showing only a 10% chance of favorable weather for the launch attempt. Atlas V 541 is the most powerful Atlas to launch from the West Coast to date in a program that saw its first Vandenberg launch back in 1959 using the original Atlas booster based on the SM-65 missile. In its 541 configuration, Atlas V uses its Common Core Booster with four AJ-60A Solid Rocket Motors attached to it. |
Photo: United Launch Alliance
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Sitting atop the Common Core Booster is the trusted Centaur Upper Stage that itself can look back at a five-decade long career, but the NROL-35 launch will be its first using the RL-10C-1 engine, a close relative to the previously used RL-10A-4-2 engine.
The engine builds on the heritage of the RL-10 engine family that can look back at a history of several decades having completed its first test in 1959 after being developed by Pratt & Whitney. Over the years, the engine underwent a number of modifications, going through several generations and being used on different launch vehicles. The RL-10A versions of the engine were used by the trusted Centaur Upper Stage, most recently in the RL-10A-4-2 variant while previous RL-10A versions were also in use aboard the Saturn I and DC-X vehicles. RL-10B-2 is used on the Delta Cryogenic Upper Stage fitted on all launchers of the Delta IV rocket family.
The engine builds on the heritage of the RL-10 engine family that can look back at a history of several decades having completed its first test in 1959 after being developed by Pratt & Whitney. Over the years, the engine underwent a number of modifications, going through several generations and being used on different launch vehicles. The RL-10A versions of the engine were used by the trusted Centaur Upper Stage, most recently in the RL-10A-4-2 variant while previous RL-10A versions were also in use aboard the Saturn I and DC-X vehicles. RL-10B-2 is used on the Delta Cryogenic Upper Stage fitted on all launchers of the Delta IV rocket family.
Photo: NASA Kennedy
Centaur Upper Stage with RL-10A-4-2 Engine
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RL-10C uses existing RL-10B-2 engines that are part of the inventory of United Launch Alliance while RL-10A-4-2 engines had to be ordered as newly-built units from Aerojet-Rocketdyne. It is more economic to modify existing RL-10B engines with hardware adopted from the 10A version to create the RL-10C-1. Overall, the RL-10C engine has a larger operating margin than any previous RL-10 engine taking advantage of flight experience of the earlier models and a comprehensive test campaign performed by the RL-10C that demonstrated extremely long burn times and operation outside of set operating parameters.
To modify existing RL-10B-2 engines to become RL-10C-1, a number of changes are necessary such as the substitution of the extendable nozzle of the RL-10B-2 with a shorter radiatively-cooled carbon-carbon nozzle extension. Also, the RL-10B-2 needs to be outfitted with a Propellant Utilization avionics unit that controls the mixture ratio of propellant supplied to the engine for optimized propellant consumption – a feature of the Centaur’s RL-10A but not the RL-10B of the DCSS. It also includes the installation of a redundant spark ignition system that is standard on the Centaur upper stage. Aside from these changes, RL-10C employs the common turbopump and plumbing of both, RL-10A and B, but uses the chamber and injector of the RL-10B instead of the RL-10A’s unique design. Overall, RL-10C delivers a vacuum thrust of 106 Kilonewtons, slightly more than the RL-10A-4-2 and a little less than the RL-10B-2 with its huge nozzle. The engine achieves a specific impulse of 448.5 seconds. RL-10C measures 1.44 meters in diameter and 2.22 meters in length with a total mass of 190 Kilograms. The nozzle of the RL-10C creates an expansion ratio of 130 and the engine operates at a chamber pressure of 24 bar. |
To accommodate the Atlas V and its four Solid Rocket Motors, a number of changes were made to the Mobile Service Structure of SLC-3E that does not feature a clean-pad approach like SLC-41 at Cape Canaveral. Instead, SLC-3E features a Fixed Umbilical Tower and Mobile Service Structure that allows technicians access to the launch vehicle during assembly and testing.
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The Atlas V for the NROL-35 mission began stacking in September, beginning with the installation of the Common Core Booster atop the launch table before the four Solid Rocket Motors were attached to the CCB over a period of weeks. Next was the installation of the Interstage Adapter before Centaur was mated atop the CCB. Testing of the assembled launcher was performed before the NROL-35 payload, encapsulated in the short 5-meter fairing of Atlas V, was rolled to the launch pad to be hoisted atop the launch vehicle in late November.
A detailed set of integrated testing followed and Atlas V was awarded a clean bill of health in the Launch Readiness Review held earlier this week to clear the vehicle for flight. Although Atlas V is ready for launch, chances are high that the vehicle will stay on the ground for a little longer due to bad weather conditions that are expected for Friday's launch attempt due to a front passing through the area right around the planned time of liftoff. Unsettled weather with rain, cumulus clouds, thick clouds, strong winds and lightning are on the forecast for Thursday night creating only a 10% chance of acceptable weather conditions. The Launch Team has multiple decision points at which they can decide to back out of the countdown and come back one day later. One of those decision points is the Go/No Go for propellant loading coming during the T-2-Hour hold during which teams will decide whether to press to T-4 minutes and holding at which point weather has to be GREEN to allow the Automated Countdown to commence. |
Photo: United Launch Alliance
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