United Launch Alliance (ULA) launched its Atlas V with the labeled NROL-107 Silent Barker mission set on Sunday, following a number of days, together with a rollback as a result of a hurricane risk.
For this demanding mission, sending the payload to a near-geosynchronous orbit, Atlas V flew in its strongest lively configuration: Atlas V 551.
NROL-107 Silent Barker launch
Silent Barker is a joint mission of the Nationwide Reconnaissance Workplace (NRO) and america House Pressure that has been in improvement for roughly three years. In response to revealed price range evaluations, “SILENTBARKER will present the aptitude to look, detect, and observe objects from a space-based sensor for well timed custody and occasion detection.”
This basically implies that Silent Barker will kind a “watchdog” constellation of satellites used for monitoring different nations’ actions in geostationary orbit. This departs from the present methodology of geostationary monitoring utilizing ground-based belongings, which might observe objects all the way down to the dimensions of a basketball — relying on the climate on the bottom. Silent Barker can observe smaller objects and repeatedly observe their place and motion.
This launch, anticipated to be one among two in whole for the preliminary constellation, may have a number of satellites onboard — though the precise quantity is classed. NRO will function the constellation, which ought to be operational by 2026.
From the publicized launch necessities, the Silent Barker payload might be launched right into a 41,849 by 42,479-kilometer orbit with zero inclination, positioned on the 105-degree East slot. This locations the satellites round 7,000 kilometers above a correct geosynchronous orbit. It’s unknown the place the satellites will maneuver themselves following deployment.
However earlier than any on-orbit actions happen, Silent Barker should first launch.
The payload’s Atlas V launcher started stacking in early August. The primary stage booster was first put in on the cell launcher, adopted by the 5 GEM-63 strong rocket motors (SRMs) and the Centaur higher stage — located inside the bottom of the five-meter payload fairing.
On Aug. 11, the whole stack — minus the payload — was rolled out to the launch pad at SLC-41. There, the automobile carried out a moist costume rehearsal (WDR). Because the identify suggests, this occasion is a whole rehearsal of launch day actions, from propellant loading till simply earlier than engine ignition. This helps work out any potential points within the built-in launch automobile and floor assist techniques previous to launch day.
Many ULA launches don’t embrace a pre-flight WDR. Nonetheless, clients can request them for extra necessary or costly payloads. Missions equivalent to Boeing Starliner flights, NASA science missions, and NRO payloads have generally utilized such exams.
An exploded view of the Atlas V 551 configuration – probably the most highly effective flown model of Atlas V. This rocket will carry NROL-107 to orbit. (Credit score: United Launch Alliance)
After finishing the WDR, Atlas V was rolled again into the vertical integration facility to have the payload put in. Though the cryogenic liquid oxygen and liquid hydrogen propellants had been drained from the automobile earlier than the rollback, the first-stage RP-1 gas was not. It is because RP-1, a refined type of kerosene, is steady at room temperatures and might stay contained in the automobile long-term in comparison with cryogenic propellants.
NROL-107, located inside its five-meter-wide payload fairing, was lifted onto the remainder of the launch automobile earlier than the now-complete rocket returned to the launch pad.
On launch day, Atlas V was loaded with its remaining, cryogenic propellants — liquid oxygen and liquid hydrogen. The primary stage RD-180 engine burns RP-1 and liquid oxygen, whereas the Centaur second stage’s RL-10C-1-1 engine burns liquid hydrogen and liquid oxygen.
Each the RD-180 engine and Centaur higher stage can hint their roots again to earlier Atlas automobiles. Centaur has been flying as a second stage for Atlas rockets since Could 1962 on Atlas-Centaur, the rocket that launched the Surveyor lunar probes, a number of Mariner missions to Mars, and Pioneer 10 & 11 to Jupiter and Saturn. The RD-180, nonetheless, is way more fashionable, starting its service life on the short-lived Atlas III in 2000. Whereas the RD-180 might be retired alongside Atlas V later this decade, Centaur has been additional developed for ULA’s upcoming Vulcan rocket.
The countdown entered a deliberate maintain at T-4 minutes, throughout which Atlas mission management performs a remaining go/no-go ballot of all flight controllers to make sure the automobile is protected and prepared for launch. Ought to all controllers reply with “go,” the maintain is launched shortly afterward.
Through the remaining 4 minutes of the countdown, the propellants had been topped off and the tanks pressurized for flight. At T-2.7 seconds, the RD-180 engine ignited, and the flight computer systems autonomously examine all engine and automobile techniques.
The computer systems command the simultaneous ignition of the 5 SRMs and the discharge of the launch clamps, permitting the automobile to carry off from the launch pad at T+1 second.
Because of the excessive thrust of the 5 GEM-63 SRMs, Atlas V goes supersonic simply over 35 seconds after liftoff. Solely 11 seconds later, the automobile reaches max-Q, which is the interval of most dynamic stress on the automobile. After this level, aerodynamic loading on the automobile decreases till it reaches near-zero because the rocket enters the vacuum of area.
Onboard view from the Centaur second stage on a earlier Atlas V launch, exhibiting the booster stage falling away. (Credit score: United Launch Alliance)
At one minute and 44 seconds after launch, the SRMs burn out and are jettisoned. They separate in a single group of two and one group of three, with a spot of two seconds in between.
The following occasion is payload fairing jettison at T+3 minutes and 5 seconds, which exposes Centaur and the Silent Barker payload to area. This eliminates some lifeless mass; the protecting fairing is not wanted because the automobile might be within the vacuum of area. The 2 Centaur ahead load reactors jettison a couple of seconds later. These items of {hardware} redirect some structural load from the payload adapter to the perimeters of the fairing, decreasing the general stresses on the skinny tank partitions of Centaur throughout the preliminary high-acceleration parts of the flight.
Given the labeled nature of this mission, the revealed launch timeline doesn’t element any additional mission occasions. Nonetheless, primarily based on earlier Atlas V 551 flights, it may be inferred that the Atlas booster — or first stage — ought to burn out and separate round 4 and a half minutes into the flight. Centaur will then start its first of possible three or 4 burns, bringing the payload right into a low-Earth parking orbit. The RL-10 engine will then shut down and the stage will coast.
After coasting for some time period, the RL-10 will ignite for a second time, sending the stack right into a geostationary switch orbit. As soon as once more, the stage will enter a coast part, this time for roughly 5 to 6 hours.
Close to apogee, the very best level within the geostationary switch orbit, Centaur will ignite its RL-10 engine for the third time, boosting Silent Barker right into a near-geosynchronous orbit. The satellites will then deploy, and Centaur will both vent the remaining propellants or ignite its engine for a remaining time, getting into a graveyard orbit for disposal.
This mission was the 98th for Atlas V, and the second this 12 months for United Launch Alliance. It additionally closes a chapter in Atlas V’s historical past. NROL-107 would be the final NRO payload to launch on the Atlas V, as all additional ULA-launched reconnaissance missions will fly on their upcoming Vulcan rocket.
(Lead picture: Atlas V rolling out to the launch pad at SLC-41 forward of the AEHF-6 mission in March 2020. Credit score: Sawyer Rosenstien)
