Screenshot from ULA Webcast of the launch of NROL-52. Note the green poll from mission control
Mission Rundown: ULA - Atlas V 421 - NROL-52
Written: December 14, 2022
Telephone exchange in the Sky
United Launch Alliance’s clandestine Atlas V launch in support of NRO the US National Reconnaissance Office finally departed SLC-41 on Sunday, after previously failing to dodge bad weather and then suffering a telemetry transmitter issue. Liftoff of NROL-52 from the Cape Canaveral Air Force Station occurred on October 15, 2017 at 07:28 EDT.
Notam: NROL-52 will drop of two SRB’s, two fairings and its first stage booster in the red zones
The launch – which is only broadcast to fairing jettison – is carrying out the NROL-52 mission for the National Reconnaissance Office (NRO), deploying an unspecified payload into Earth orbit. The sixth flight of Atlas this year, this launch followed the successful deployment of the NROL-42 mission – whose payload is now designated USA-278 – from Vandenberg Air Force Base in late September.
The NROL-52 Payload
NROL-52 is a classified mission being conducted in the interests of national security. Despite this secrecy, experts and amateur observers are often able to identify different classes of spacecraft, track the satellites in orbit and make deductions about their missions and some of their capabilities.
The use of the more powerful Atlas V 421 over the Atlas V 401 for the NROL-61 and NROL-52 launches suggests a new fourth-generation satellite that is heavier than its predecessors, while the use of the extra-extended fairing instead of the Long Payload Fairing that was used for third-generation Quasars, indicates that the new spacecraft are also physically larger or carry bigger antennae.
Satellite Data System (SDS) ‘Quasar’ spacecrafts are communication relay satellites for transmitting real-time data from US reconnaissance satellites (e.g. KH-11, Onyx, Topaz). They are also used for communications to USAF aircraft and connect the various ground stations of the Air Force Satellite Control Network (AFSCN). The spacecraft relayed the downlinked data to a ground station at Fort Belvoir, Virginia.
These satellites are the fourth generation of the system, the SDS-4, which appears to use only the geostationary orbit and no longer the earlier highly elliptical Molniya orbits.
Quasar 21 is the second satellite launched of this class of communication satellites.
The Atlas V 421 Launch
The Atlas V that launched NROL-52 had tail number AV-075. Flying in the 421 configuration it consists of a Common Core Booster (CCB) first stage, two Aerojet Rocketdyne AJ-60A solid rocket motors, a single-engine Centaur upper stage and the four by fourteen meter Extra-Extended Payload Fairing (XEPF).
The Common Core Booster burns RP-1 kerosene propellant, oxidized by liquid oxygen. Centaur burns liquid hydrogen and liquid oxygen.
About 2.7 seconds before Atlas’ launch time the first stage’s single RD-180 engine ignited.
Ignition of the solid rocket motors and liftoff of the rocket followed at about 1.1 seconds after the zero mark in the countdown. AV-075 lifted off from SLC-41 and began her ascent towards orbit, beginning a series of pitch, roll and yaw maneuvers to attain the planned launch trajectory shortly after liftoff.
About 47 seconds into the flight Atlas reached Mach 1 – the speed of sound – passing through the area of maximum dynamic pressure – or Max-Q – five seconds later.
The boosters burned for the first 91 seconds of flight before depleting their propellant and burning out. The spent motors jettisoned 38 seconds later, two minutes and nine seconds into the flight.
Following burnout of the boosters, the CCB’s RD-180 engine continued to power Atlas towards orbit. RD-180 cutoff came four minutes and ten seconds after liftoff, with the Common Core Booster separating six seconds later.
Ten seconds after stage separation, Centaur ignited its RL10C-1 engine to begin its first burn of the mission. Eight seconds later the payload fairing separated from the nose of the rocket. At this point, official coverage of the mission entered a news blackout, except for confirmation of a successful launch following spacecraft separation.
Centaur will likely make two burns prior to spacecraft separation, with its first lasting about eleven minutes to establish an initial parking orbit. Following a coast of about ten minutes, Centaur will restart its engine for a second burn of about four minutes to reach geostationary transfer orbit.
Shortly after this burn concludes, the NROL-52 payload will separate from Centaur. The deployment orbit is expected to be around 1,100 by 35,800 kilometers (680 by 22,200 miles, 590 by 19,300 nautical miles), with inclination of about 18.7 degrees.
From this transfer orbit NROL-52 will under its own power raise itself into a full circular geostationary orbit, where it will join its ‘brothers in arms’.
Following spacecraft separation, Centaur will make a further burn at 08:33 UTC to deorbit itself, with reentry expected to occur over the Pacific Ocean, to the south of Hawaii.
The white rectangle is the NOTAM hazard zone. Hawaii is just visible on the horizon, 750 km to the north. The re-entry impact zone was an approximately 160 x 600 km rectangular region, centered near 11.87 N, 154.63 W.
The depicted re-entry trajectory begins at about 1000 km altitude. The alternating red and white line segments span 5 seconds of flight.
The TLE propagated to theoretical impact within the NOTAM boundaries, near 11.92 N, 155.62 W, at about 15:57 UTC - 12 min. after the start of the NOTAM period.
The Centaur reached a maximum velocity of nearly 10.2 km/s inertia (not far below escape velocity), 9.7 km/s relative to the atmosphere. Maximum deceleration of about 44 G occurred at about 49 km altitude. Nearly all horizontal velocity had been lost by 30 km altitude, following which any surviving debris would have fallen almost vertically.
The final vertical descent is clearly depicted in the above graphic.
The Atlas V 421 rocket
The Atlas V is an expendable medium lift launch system and member of the Atlas rocket family. The rocket is one of the most reliable in the world, having more than 76 launches with no complete failures.
The Atlas V 421 rocket, tail no. AV-075 is standing 59.1 meters - 194 feet tall on SLC-41.
The rocket has two stages. The first is a Common Core Booster (CCB), which is powered by an RD-180 engine with two bells and burns kerosene (RP-1) and liquid oxygen (LOX). This is accompanied by up to five strap-on solid rocket boosters. The second stage is the Centaur upper stage, which is powered by one or two RL10 engines and burns liquid hydrogen (LH2) and liquid oxygen (LOX).
Atlas V rocket is filled with 344 472 liter - 91 000 gallons of RP-1, liquid oxygen and liquid hydrogen. Question is now how much goes to fill each stage and the four tanks. Together they can contain 344,47 m3 RP-1, cryogenic oxygen and cryogenic hydrogen.
Atlas V 421 split in its major parts. This is a generic non mission specific graphic configuration
The Common Core Booster holds 184 728 liter - 48 800 gallon liquid oxygen chilled to below -182,96 0C Celsius or -297,33 0F Fahrenheit that can fit in a 184,73 m3 oxygen tank.
The Common Core Booster holds 94 635 liter - 25 000 gallon RP-1 highly refined kerosine at room temperature that can fit in a 94,64 m3 fuel tank.
The Centaur upper stage holds about 49 400 liter - 13 050 gallons of liquid hydrogen chilled to -252,8 0C Celsius or -423 0F Fahrenheit that can fit in a 49,40 m3 hydrogen tank.
The Centaur upper stage holds about 15 709 liter - 4 150 gallons of liquid oxygen chilled to below -182,96 0C Celsius or -297,33 0F Fahrenheit that can fit in a 15,71 m3 fuel tank.
Still to find is data on Helium gas, pressures used and number of COPV to store it. And are there tanks to store propellant used to maneuver during ascent and in orbit.
HAZ GAS operations are completed when the hydrazine is loaded. The RCS thrusters on the Centaur stage are using hydrazine as a monopropellant during orbit insertion.
The reaction control system (RCS) includes the ullage pressure thrust from the tanks and consists of twenty hydrazine monopropellant engines located around the stage in two 2-thruster pods and four 4-thruster pods. For propellant, 150 kg (340 lb) of Hydrazine is stored in a pair of bladder tanks and fed to the RCS engines with pressurized helium gas, which is also used to accomplish some main engine start up functions.
In the 421 configuration, the Atlas V is capable of carrying up to 14,067 kg to Low Earth Orbit (LEO), and 6,890 kg to Geostationary Transfer Orbit (GTO).
The Atlas V 421 rocket has a three number configuration code.
The first number represents the fairing diameter size in 4 or 5 meters, so in this instance there is a 4 meter fairing. This launch will use the 14-meter-long (46 ft) XEPF.
The standard four-meter fairing, named the Long Payload Fairing (LPF), measures 12.2 meters (40 feet) in length and was first introduced as an optional larger fairing for the Atlas I rocket in 1990.
One or two 90-centimeter (3-foot) cylindrical segments can be added to the fairing to form an Extended Payload Fairing (EPF - 43 feet tall) or Extra-Extended Payload Fairing (XEPF - 46 feet tall) respectively for payloads that require a little additional space.
The second number denotes the number of solid rocket boosters (SRBs), which attach to the base of the rocket. The number of SRBs for a 4 meter fairing can range from 0 – 3. In this case there will be 2 SRBs attached to the center core.
The third number shows the number of engines on the Centaur Upper Stage, which is 1 in this configuration. So this means that this rocket will have a 4 meter faring, 2 solid rocket boosters, and 1 engine bell on the Centaur Upper Stage.
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