For its second launch of the year, the Atlas V rocket marked its 70th mission to space on Wednesday as the veteran rocket lofted the National Reconnaissance Office’s NROL-79 spacecraft to Low Earth Orbit (LEO). Liftoff took place from SLC-3E at Vandenberg Air Force Base, California, at 0950 PST (1750 UTC), the opening of a 40 minute launch window. The mission has been declared a success.
Atlas V’s 70th mission:
After entering service in 2002, the Atlas V rocket quickly became the go-to vehicle for the US military and various customers for whom launch success was critical for multibillion-dollar interplanetary payloads.
Over the course of its previous 69 missions to date, the Atlas V has launched satellites for various US military outfits, including the Air Force and the Navy, the National Reconnaissance Office (NRO), NASA, various commercial entities, and another commercial launch provider: Orbital ATK and their Cygnus resupply spacecraft for the International Space Station.
For its 70th mission, the Atlas V made use of the 68th produced Atlas V core stage – known as AV-068 – and flew in its most common configuration: the 401, with a four meter payload fairing, no solid rocket motors, and a single-engine Centaur upper-stage.
In fact, this was the 35th flight of the Atlas V and its 401 configuration – marking its use in exactly 50% of all Atlas V missions.
Additionally, this was the 14th time that the NRO selected the Atlas V for launch of one of its spacecraft.
To date, the mission has already seen years of preparation, including two unforeseen, late campaign setbacks.
Originally, launch of NROL-79 was scheduled for 1 December 2016 but was postponed into late January 2017 following a period of protracted wildfires and subsequent rebuilding operations at Vandenberg Air Force Base.
The fires and recovery previously postponed the launch of the commercial WorldView 4 mission – also aboard an Atlas V 401 rocket – late last year.
Moreover, an issue was then discovered within the Centaur that necessitated an additional one month slip to the launch date.
Pointedly though, the mission is still – to the day – occurring within three months of the original launch date selected more than two years ago by the NRO, with two-thirds of that total delay owing to wildfires and not to the Atlas-Centaur system itself.
The Atlas V sported the name of a firefighter who lost his life fighting the fire.
Final preparations and launch:
Following the recovery of Vandenberg Air Force Base assets and the resumption of launch operations from the West Coast with the WorldView 4 mission, this mission’s Atlas core stage was actually delivered to the base during the wildfire threat last year.
After the WorldView 4 launch, the NROL-79’s Atlas V booster stage and Centaur upper stage were stacked together on SLC-3E in late 2016 and prepared for a Wet Dress Rehearsal (WDR) countdown – which occurred on 10 January 2017.
Following the WDR, a standard data review led to the discovery of an issue with the Centaur upper stage.
Technicians and engineers designed a plan to return the rocket to optimal health, and United Launch Alliance (ULA) CEO Tony Bruno confirmed that the issue was specific to the launch vehicle itself and was not a family issue with the Centaurs.
A second WDR subsequently proved the fix and corrective actions taken with the Centaur, and by 9 February, ULA booked assets on the Western Range for a 1 March 2017 launch.
On 15 February, the classified NROL-79 spacecraft was transported to SLC-3E and hoisted atop its Atlas-Centaur booster.
With launch day fast approaching, teams at Vandenberg Air Force Base spent the weekend performing final close out operations on the Atlas V rocket while preparing the various systems and Western Range assets required to support a successful liftoff Wednesday morning.
Monday was then spent performing a series of flight readiness reviews from both the customer and the rocket provider sides, which culminated with clearance to proceed into launch operations.
Based on the scheduled opening of the launch window, the launch team spent most of Tuesday off duty, adjusting their sleep cycles so that all personnel would be ready to support the start of the 8-hour countdown at 0150 PST Wednesday morning.
Once the countdown began, the first six hours were spent conditioning the pad’s environmental control systems, powering up various systems aboard the Atlas and Centaur, performing final spacecraft checks, and ensuring that all propellant loading equipment is ready to support fueling operations.
Communication checks with the rocket then occurred prior to the pad being cleared of all personnel approximately three hours prior to liftoff.
Two hours 40 minutes before liftoff, the countdown entered a 10-minute hold, at which point the launch director conducted the GO/NO GO for tanking poll.
The with the vehicle, range, and weather green, the countdown emerged from its 10-minute hold 2 hours 30 minutes prior to lift off, at which point LOX (Liquid Oxygen) chilldown began.
Fueling began with Centaur LOX tanking operations 2 hours 13 minutes prior to liftoff.
Then, 34 minutes prior to liftoff, the count entered a 30-minute hold at the T-4 minute mark.
During this final hold, the final weather briefing occurred, the range confirmed that it is clear and ready to proceed into the terminal count, and the spacecraft received a final go/no-go poll for liftoff and deployment.
Also during this final hold, Centaur LOX and LH2 propellant loads were brought to flight levels.
The Launch Director performed a final poll to exit the hold and commence the 4-minute terminal count sequence 7 minutes prior to liftoff – a process required whether that liftoff was timed to the opening of the launch window or sometime within.
The launch window was understood to have run from 0950-1030 PST (1750-1830 UTC).
Once the hold was released, the Atlas-Centaur entered a highly choreographed final 4-minute terminal count sequence that saw the termination of LOX replenishment to the Atlas booster at the T-4 minute mark.
The Atlas tanks were brought to flight pressure at T-3 minutes, and the Atlas-Center launch vehicle were switched to internal power at the T-2 minute mark.
Center propellant topping was completed at T-1 minute 50 seconds, with the launch control system taken to “enable” 90 seconds prior to liftoff.
A final launch verification took place at T-16 seconds, leading to the start sequence of the RD-180 engine at the base of the Atlas V core at T-2.7 seconds.
After ramping up to full thrust and a series of health checks, the hold down clamps released and the Atlas V lifted off at T+ 1.1 seconds.
While the exact orbital destination for NROL-79 has not been revealed, all previous NROL missions from Vandenberg have been non-GTO (Geostationary Transfer Orbit) missions to either LEO or Molniya orbits (highly elliptical, high inclination orbits with arguments of perigee of -90 degrees and an orbital period of one half of a sidereal day).
Given this, the NROL-79 Atlas V 401 can be expected to follow an LEO ascent profile, with the RD-180 engine producing 860,000 lbf at liftoff, a level of thrust that will gradually increase to 933,000 lbf as the vehicle breaks through Earth’s atmosphere and enters the vacuum of space.
In its 401 configuration, the Atlas V reached Max Q – the moment of maximum dynamic pressure and mechanical stress on the vehicle – 88 seconds after liftoff at an altitude of 11.6 km (37,970 ft) with a total Max Q of 490 psf.
Throughout the first 100 seconds of flight, the RD-180 engine thrusted at 100% of total throttle, stepping down to 95% of rated thrust from 100 seconds through 210 seconds, at which point a throttle drop off occurred as the booster maintained a 5G acceleration limit in preparation for Booster Engine Cutoff (BECO).
BECO occurred just prior to Atlas/Centaur separation at the T+ 246 second mark at an altitude of ~157.6 km (~517,015 ft).
Ten seconds after Atlas core stage separation, the Centaur single-engine upper stage ignited at the T+ 256 second mark.
Payload fairing jettison followed at T+ 264 seconds at an altitude of 193. km (633,100 ft).
Once payload fairing jettison occurs, per the NRO’s usual request to ULA, the live webcast ceased, and the final portion of launch operations and placement of the satellite into orbit will not be seen live.
However, the US Air Force later confirmed a successful deployment.
Launch of NROL-79 marks the first of three launch campaigns within 19 days for ULA.
The next mission is the scheduled 8 March launch of WGS-9 on a Delta IV M+ rocket from the Cape Canaveral Air Force Station, FL (launch window: 18:48-19:53 EST).
This is to be followed by the 22:56-23:16 EDT launch of an Atlas V 401 rocket on 19 March with the Orbital ATK Cygnus OA-7 mission to the International Space Station.
(Images: Philip Sloss, ULA; National Reconnaissance Office)