United Launch Alliance (ULA) launched an Atlas V rocket on Saturday evening, carrying out the classified NROL-42 mission for the United States National Reconnaissance Office. Atlas – delayed two days via the requirement to changeout a battery on the booster – lifted off from California’s Vandenberg Air Force Base at 22:49 Pacific Time (05:49 UTC on Sunday).
Atlas V Launch:
Saturday’s launch – the fifth Atlas V launch of the year and the seventy-third overall for United Launch Alliance’s workhorse rocket – came a little over a month after Atlas orbited NASA’s TDRS-M satellite and achieved its seventy-first launch success from seventy-two attempts.
First flown in August 2002, Atlas V was developed by Lockheed Martin under the US Air Force’s Evolved Expendable Launch Vehicle (EELV) program, in competition with Boeing’s Delta IV.
The Air Force opted to fund two rockets in order to provide assured access to space should one fail. Since December 2006 both rockets, along with the older Delta II vehicle, have been constructed and operated by United Launch Alliance (ULA), a joint venture between Boeing and Lockheed Martin.
As well as being used for military launches, Atlas V and to a lesser extent Delta IV are also used to launch missions for NASA and commercial satellites. Both rockets can fly in several different configurations, with increasing numbers of solid rocket motors to allow heavier payloads to be carried.
The Delta IV also has its Heavy configuration, with two additional cores strapped to either side of its first stage to allow it to deploy the heaviest payloads and to reach higher orbits. A similar Atlas V Heavy configuration was planned, but never flew.
As it looks to America’s future launch needs – and to compete with new companies such as SpaceX entering the launch market – ULA has begun discontinuing its Delta IV line, retiring all configurations except the Heavy as they fly out their remaining launches. A new rocket, Vulcan, is expected to replace both the Atlas and Delta lines in the next decade.
The launch saw Atlas carry out NRO Launch 42 (NROL-42) for the National Reconnaissance Office. Although the NRO does not publish details about most of its spacecraft many aspects of NROL-42 and the mission of the spacecraft to be deployed can be inferred from what is known about previous launches and other spacecraft, airspace and nautical hazard areas announced ahead of the launch, Atlas V’s capabilities and classified information that has leaked from the NRO over the years.
The Atlas V lifted off from Space Launch Complex 3E (SLC-3E) at the Vandenberg Air Force Base in California. Formerly part of the Naval Missile Facility at Point Arguello, the launch complex became part of Vandenberg when the two adjacent launch sites were merged in 1964 and has supported Atlas rockets since July 1961 and the Atlas-Agena vehicle.
SLC-3E is the Atlas’ only West Coast launch pad, providing access to high-inclination trajectories such as polar and sun-synchronous orbits useful for optical imaging and the retrograde orbits used by some radar imaging spacecraft.
In contrast, launches from Cape Canaveral on the East coast can reach lower-inclination trajectories like geostationary orbit. Orbits with intermediate inclination, such as elliptical Molniya orbits that are used by signals intelligence satellites, can be reached from either coast.
For this mission, Atlas V flew in its 541 configuration with four solid rocket motors, the second-most-powerful version of the rocket. This suggests the NROL-42 payload is fairly heavy, targeting a high orbit, or both.
The 541 configuration has made only four flights prior to NROL-42, with two of these in support of NRO missions and only one launching from Vandenberg. The Vandenberg launch, December 2014’s NROL-35, deployed the USA-259 satellite into Molniya orbit. The other NRO launch to use the 541 configuration, from Cape Canaveral, deployed NROL-67 or USA-250 into a high-perigee geostationary transfer orbit earlier the same year.
The use of a Molniya orbit for the NROL-35 mission suggest that the spacecraft was the first member of a new series of highly elliptical orbit (HEO) signals intelligence (SIGINT) satellites, a series that began with the Jumpseat satellites launched aboard Titan IIIB rockets in the 1970s and 1980s.
A second generation of these satellites, believed to have been named Trumpet, were flown in the 1990s aboard Titan IV(401)A rockets. Two spacecraft identified as a third-generation, USA-184 (NROL-22) and USA-200 (NROL-28) were launched aboard Delta IV-M+(4,2) and Atlas V 411 rockets in 2006 and 2008 respectively.
As no codenames have leaked for the third-generation satellite, observers identify them as “Advanced Trumpet”, “Improved Trumpet” or “Trumpet Follow-on”.
NROL-35 and – likely – NROL-42 appear to be the fourth generation, a “Further Improved Trumpet”, although it is unclear whether the geostationary NROL-67 forms part of the same series.
A Molniya orbit for this launch is borne out by notices to airmen, or NOTAMS, issued to ensure flight safety along the launch corridor. These show that the rocket flew along a south-south-easterly azimuth along the Pacific coasts of California and Mexico, consistent with the approximately-63-degree Molniya orbit. The NOTAMS for NROL-42 resemble those issued ahead of the NROL-35 launch.
The Molniya orbit is a special class of highly elliptical Earth orbit, with an orbital period of approximately twelve hours and inclination of about 63.4 degrees.
This orbit allows a satellite to spend most of its time over the northern hemisphere – useful for communications or observations at high latitudes that cannot be served by a geostationary satellite orbiting above the equator – without perturbations changing its argument of perigee over time.
The orbital regime is named after the Soviet Union’s Molniya communications satellites which were among the first spacecraft to use it. The NRO has used Molniya orbits for Jumpseat and Trumpet-series SIGINT spacecraft and Quasar communications satellites, although no Molniya-orbit Quasars have been launched since 2007.
The “Improved” and “Further Improved” Trumpet satellites carry an additional payload unrelated to their reconnaissance mission. The NROL-22, 28 and 35 payloads each carried a SBIRS-HEO, as part of the Space-Based Infrared System (SBIRS), a missile defense program of the US Air Force.
The replacement for the long-serving Defense Support Program (DSP), SBIRS consists primarily of dedicated geostationary satellites with infrared sensors to detect and track missile launches. The 240-kilogram (530 lb) SBIRS-HEO packages aboard NRO satellites in Molniya orbit provide additional capabilities and enable missiles to be observed at higher latitudes than the geostationary element of the system can accommodate.
Lockheed Martin, the prime contractor for the SBIRS program, announced in June 2015 that it had shipped the fourth and final SBIRS-HEO sensor, SBIRS HEO-4, for integration with its parent spacecraft. This timeline would be consistent with previous launches for the sensor to be aboard the NROL-42 payload. No other compatible payload appears to be scheduled for launch in the foreseeable future.
The NRO’s mission patch for NROL-42 depicts a grizzly bear, a stylised impression of the Atlas V ascending to orbit and ten stars. Four stars form a pattern that has appeared on patches associated with the last three Trumpet-series launches. A second patch, for the launcher, carries a Douglas Adams theme, playing on the number 42 being the answer to the Ultimate Question of Life, the Universe and Everything in his Hitchhiker’s Guide to the Galaxy novels.
The NROL-42 mission was conducted by Atlas V AV-072. AV-072 flew in the 541 configuration with a five-meter payload fairing, four Aerojet Rocketdyne AJ-60A solid rocket motors and a single-engine Centaur upper stage.
The fairing, which is manufactured by RUAG of Switzerland, comes in three different lengths, with this launch using the shortest of these. This measures 20.7 meters (68 feet) in length, while the exact diameter is 5.4 meters (17.7 feet). As well as encapsulating the payload, the five-meter fairing also encloses the rocket’s second stage, Centaur.
About 2.7 seconds before the countdown reached zero, Atlas ignited its RD-180 first stage engine. At T+1.1 seconds the rocket’s solid rocket motors ignited and the vehicle began its climb away from the launch pad, reaching a speed of Mach 1 within 35 seconds and passing through the area of maximum dynamic pressure, or Max-Q, twelve seconds later.
Atlas’ first stage, or Common Core Booster (CCB), is powered by a single RD-180 – manufactured by Russia’s NPO Energomash and derived from the RD-170 series used by the Zenit and Energia rockets. It burns RP-1 propellant, oxidized by liquid oxygen.
The AJ-60A motors burned for 98 seconds. After burnout, the spent motors remained attached for another thirteen seconds before separating in pairs a second and a half apart.
Payload fairing separation took place towards the end of first stage flight, at three minutes and 24 seconds after liftoff, followed five seconds later by the forward load reactor – a device attached at the top of the Centaur to reduce vibrations within the fairing.
Once the fairing separates, the mission entered a news blackout, with the only further announcement coming via press release confirming a successful launch following spacecraft separation. The RD-180 continued to fire until a little over four minutes after liftoff, around which time Booster Engine Cutoff (BECO) occurred, with the engine shutting down.
Six seconds after BECO, the spent Common Core Booster was jettisoned, with the Centaur upper stage began its prestart sequence. Centaur’s single RL10C-1 engine ignited ten seconds after stage separation, beginning its first burn of the mission. Trumpet-series satellites are typically deployed directly into Molniya orbit. After separating the NROL-42 payload, Centaur will perform a deorbit burn, propelling itself to a destructive reentry to the south of Australia.
The launch of NROL-42 was the twenty-fifth that United Launch Alliance has conducted on behalf of the National Reconnaissance Office, a partnership which stretches back to ULA’s inaugural mission in December 2006.
This saw a Delta II rocket carry out the NROL-21 mission, deploying a satellite that became known as USA-193. Despite a successful launch, USA-193 failed within minutes of deployment and was subsequently destroyed by a US Navy missile to prevent debris reaching the ground when it reentered.
NROL-42 was the third NRO payload to launch this year. In January an Atlas V 401 flying from Vandenberg deployed NROL-79, a pair of Intruder naval signals intelligence satellites. In April SpaceX conducted its first dedicated mission for the NRO, deploying the NROL-76 payload via a Falcon 9 rocket.
Two further NRO missions are expected to launch this year, with the next being NROL-52 atop an Atlas V from Cape Canaveral. This is currently expected to lift off on 5 October, and is also the next launch for both United Launch Alliance and its Atlas V rocket.
(Images via ULA, NRO and L2/NSF Philip Sloss).
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