A United Launch Alliance (ULA) Delta IV Heavy rocket beat the weather and launched a top secret payload into space for the US National Reconnaissance Office (NROL-37) on Saturday. Launch from Space Launch Complex 37 (SLC-37) at Cape Canaveral was on schedule at the start of the window that opened at 1:51pm Eastern (17:51 UTC).
Delta IV-Heavy Mission:
The flight, designated NRO Launch 37 – or NROL-37 – is the second of the year for the National Reconnaissance Office (NRO), following February’s NROL-45 mission which flew from Vandenberg Air Force Base, also atop a Delta IV. It is also the second Delta launch of the year.
Flying in its Heavy configuration, the Delta IV is the largest and most powerful rocket currently in service with the United States. NROL-37 will be the thirty-second Delta IV mission and the ninth for the Heavy version of the rocket.
As is usual for an NRO mission, details of the NROL-37 payload are kept classified by the US Government, as are specifics of the Delta IV’s mission profile. Typically launch broadcasts and official coverage of NRO missions will end shortly after separation of the payload fairing from around the satellite.
Despite this, most NRO spacecraft can be identified long before launch from an analysis of information that has been made public, previous missions and past leaks. In the case of NROL-37, the use of a Delta IV Heavy indicates that significant performance is required.
Launching from Cape Canaveral, the rocket will be unable to reach high-inclination trajectories – such as polar, sun-synchronous and retrograde orbits – used by optical and radar imaging satellites.
Notices to airmen and mariners show the rocket will fly East after lifting off, towards geosynchronous orbit.
The Delta IV Heavy is capable of placing a payload of 6,750 kilograms (14,900 lb) directly into geosynchronous orbit or upwards of 14,000 kg (31,000 lb) into a geosynchronous transfer orbit.
Few satellites are large enough to require a Delta IV Heavy to reach geosynchronous transfer orbit; past NRO launches to use the vehicle from the Cape have all gone directly to geosynchronous orbit.
This suggests that the payload will be an Orion electronic signals intelligence (ELINT) satellite.
NROL-37 will be the ninth launch of an Orion satellite, part of a series of spacecraft introduced in the mid-1980s to replace the earlier Aquacade satellites.
The first two satellites were deployed from Space Shuttle Discovery during the 1985 and 1989 STS-51C and STS-33 missions, with the aid of Inertial Upper Stages. Also known as Magnum, these two spacecraft appear to have been a first-generation form of Orion, with subsequent satellites being known unofficially as “Advanced Orion”.
The later spacecraft had previously been rumoured to be called “Mentor”. However, documents leaked by Edward Snowden to the Washington Post refer to all of the vehicles as just Orion.
The third Orion was carried to orbit by a Titan IV(401)A rocket with a Centaur-T upper stage in May 1995, while the next two in May 1998 and September 2003 used Titan IV(401)B core vehicles.
With the Titan IV’s retirement in 2005, Orion launches switched to the Delta IV. The first such mission was NROL-26, which lifted off in January 2009; since then NROL-32 and NROL-15 were launched in November 2010 and June 2012 respectively.
Due to performance enhancements introduced to the Delta IV ahead of the NROL-15 launch, combined with unconfirmed reports that the increase in the rocket’s performance was necessary for the mission, it has been speculated that NROL-15 may be the first satellite of a third-generation Orion constellation. However, this remains to be verified.
The modifications made ahead of NROL-15 – including RS-68A engines on the first stage and boosters in place of the earlier RS-68 – are now standard across the Delta IV fleet including Delta 374, which will make the launch.
Delta’s first stage is a Common Booster Core (CBC), powered by a single RS-68A which burns liquid hydrogen oxidised by liquid oxygen. In the Heavy configuration two further Common Booster Cores are attached at the side of the first stage, providing additional thrust during the early stages of flight.
All three ignited five and a half seconds before liftoff, building up to full thrust by T-0, when launch occurred.
After lifting off, the rocket pitched and yawed to attain its planned easterly trajectory. About fifty seconds after launch the centre Common Booster Core’s engine throttled back to limit acceleration and conserve fuel.
Flying downrange over the Atlantic Ocean, Delta 374 passed through the area of maximum dynamic pressure around eighty seconds into flight. Shortly afterwards it achieved a speed of Mach 1, equal to the speed of sound.
Two and a half minutes into flight the vehicle rolled to an attitude at which the three CBCs were level, in preparation for staging. About 230 seconds after lifting off, the outboard boosters began to throttle down before burnout fifteen seconds later. Separation of the two spent boosters took place place three seconds after cutoff, with the core engine throttling back up to increase thrust.
The core booster burned at full power for about seventy seconds, before throttling down again ahead of its own burnout and separation. At five minutes and thirty-three seconds mission elapsed time the RS-68A shut down and seven seconds later the spent first stage was jettisoned.
The Delta IV’s second stage, a five-metre Delta Cryogenic Second Stage (DCSS), is powered by a single RL10B-2 engine also burning liquid hydrogen and liquid oxygen.
The engine has an extendible nozzle which will be deployed following first stage separation; the RL10 will ignite about 13.5 seconds after staging has been completed.
Ten seconds into second-stage flight, the payload fairing separated from the nose of the rocket.
Delta IV launches of Orion satellites make use of a modified Titan IV metallic payload fairing, in place of the Delta’s usual composite fairing.
This has a trisector design, meaning that it separates into three segments instead of two pieces like the fairings of most modern rockets.
Once the fairing separates, it was not expected that any further updates would be given on the status of the launch, other than to confirm whether it was successful or not. This is currently pending.
Following fairing separation Delta 374 will likely follow a similar flight plan to Delta 310 – the first Delta IV launch – which attempted to carry a demonstration payload to geosynchronous orbit. Although Delta 310 failed to achieve its planned orbit, details of its mission profile were published ahead of the launch and it is rumoured that the mission was specifically simulating the launch of an Orion satellite.
The DCSS will need to make three burns; the first to achieve a low Earth parking orbit – requiring about seven minutes burn time – followed by a coast phase of about seven minutes, 40 seconds. An eight-minute second burn will then be used to achieve geosynchronous transfer orbit.
Once the transfer orbit has been established, Delta 374 will coast to the apogee of its orbit, which will take around five hours, before making a three-and-a-quarter minute circularisation burn to raise its perigee and establish geosynchronous orbit.
After deploying the NROL-37 payload into this orbit, the stage will manoeuvre itself away from the geosynchronous belt as best as remaining propellant allows to limit the chances of colliding with an operational satellite.
ULA confirmed the successful conclusion to the mission around seven hours after launch.
East Coast Delta IV launches are made from Space Launch Complex 37 (SLC-37) at Cape Canaveral.
Originally built as a test and backup launch site for the Apollo programme, the facility was used by Saturn I and IB rockets between 1964 and 1967; including for the launch of Apollo 5, the first test of the Lunar Module in low Earth orbit.
After Apollo 5 the complex was mothballed and subsequently demolished in the 1970s. One of the site’s two launch pads, SLC-37B, was rebuilt ahead of the Delta IV’s 2002 debut and now serves as one of the rocket’s two available launch pads, alongside Space Launch Complex 6 at Vandenberg Air Force Base in California.
The launch was the second of the year for the Delta IV, and for the NRO. It was conducted by United Launch Alliance (ULA), a company formed in 2006 from Boeing and Lockheed Martin’s space launch divisions.
ULA manufactures and operates the Delta II, Delta IV and Atlas V rockets and provides launch services to the US Government. Lockheed Martin continues to market the Atlas for commercial launches, which are subcontracted to ULA. The Delta IV is no longer offered for commercial missions and the Delta II is out of production and expected to make its final flight next year.
United Launch Alliance is currently in the process of developing a new rocket, Vulcan, which is expected to replace both the Delta IV and Atlas V.
The Medium and Medium+ versions of the Delta IV are expected to be retired by the end of the decade; although additional Heavies will be manufactured and placed into storage to serve as a stopgap to launch payloads too heavy for the Atlas V – typically just Orion satellites and Improved Crystal imaging spacecraft.
There have been some reports that the US government may consider using the European Ariane 5 rocket as an interim. However, the Ariane would not be able to launch an Orion because in its heavy-lift ECA configuration the upper stage is not restartable and the more versatile Ariane 5ES configuration would not have sufficient payload capacity.
United Launch Alliance will next be in action on 24 June, using an Atlas V to deploy a fifth MUOS communications satellite for the US Navy. The NRO’s next launch will come in late July, with an Atlas V deploying NROL-61.
The Delta IV is next expected to launch in early August with a payload for the US Air Force Space Command, including a pair of GSSAP space surveillance satellites, flying atop a Medium+(4,2) vehicle. The next Heavy mission is not expected for over two years; NASA’s Solar Probe Plus spacecraft is slated for launch in late July 2018.
(Images via ULA, NASA.)