United Launch Alliance’s Atlas V rocket has completed the US Navy’s Mobile User Objective System (MUOS) constellation Friday, following the launch of the fifth and final first-generation satellite from Cape Canaveral. The launch occurred at the start of a 44-minute window that opened at 10:30 Eastern Daylight Time (14:30 UTC).
The Mobile User Objective System, or MUOS, is a constellation of geostationary communications satellites operated by the US Navy.
Consisting of five spacecraft – of which Friday’s launch lofted the fifth – MUOS is a replacement for the earlier UHF Follow-On (UFO) programme and will provide video, voice and data communications to mobile terminals with near-global coverage.
The satellites provide two services, a legacy UHF communications system to provide continuity for users of the UFO satellites and a new, more advanced service: Wideband Code Division Multiple Access (WCDMA).
MUOS’ WCDMA capabilities only require four of the five satellites, so in this role MUOS-5 will serve as a reserve satellite; however its UHF payload will be fully operational.
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MUOS replaces the eleven UFO satellites that launched between 1993 and 2003, ten of which were successfully placed into service. UFO was itself a replacement for the Navy’s earlier constellation of FLTSATCOM satellites, and the five Leasat spacecraft deployed from early Space Shuttle missions.
Each MUOS satellite has a mass of approximately 6,740 kilograms (14,900 lb) fully fuelled, and is designed for fifteen years of service.
They were built by Lockheed Martin, based around the A2100M bus, with an IHI Corporation BT-4 engine to provide propulsion for orbit-raising and manoeuvring.
The first satellite, MUOS-1, was launched in February 2012 with subsequent launches in July 2013 and January and September 2015.
Although the satellite aboard Friday’s launch is the fifth to fly, it is actually the third-production MUOS satellite, MUOS SV-3, which was found during tests ahead of its planned launch as MUOS-3 to have defective soldering.
As the satellite required repairs, its place on the MUOS-3 mission was taken by the SV-4 vehicle that was to have flown next. It was originally reported that SV-3 has been launched as MUOS-4, however it now appears that the final satellite to be built, MUOS SV-5, was used instead for that flight.
Although MUOS-5 completes the constellation, a sixth satellite could possibly be launched between 2018 and 2020. This satellite, if launched, would be funded by contributions from international partners in exchange for access to the constellation.
Two satellites of the US Air Force’s Wideband Global Satcom (WGS) programme were funded by similar agreements.
Friday’s launch was the third Atlas launch of the year, and the first since the deployment of the OA-6 Cygnus mission in March.
During the Cygnus launch a problem with a Mixture Ratio Control Valve (MRCV) resulted in the rocket’s first stage using a higher ratio of oxidiser to fuel than intended.
Due to this incorrect ratio, the vehicle depleted its supply of liquid oxygen earlier than had been planned, causing the first stage to cut off a little under six seconds ahead of schedule.
Due to the relatively low mass of its Cygnus payload, the Centaur second stage was able to correct for the shortfall, automatically adjusting its burn time and firing for over a minute longer than it would have on a nominal mission.
The extended Centaur burn was able to ensure Cygnus still made it to its correct deployment orbit, although the upper stage itself ran out of fuel during a disposal burn following separation.
Despite the Cygnus launch ultimately being successful, subsequent launches – including that of MUOS-5 which was then scheduled for early May – were delayed pending an investigation into the first stage problem – which could easily have caused a failure had the rocket been carrying a heavier payload or targeting a higher orbit.
The Atlas V has not yet suffered a launch failure; the most recent failure of any Atlas vehicle occurred in March 1993 with an Atlas I carrying the first UHF Follow-On (UFO) satellite, a direct predecessor of MUOS – and both the Atlas II and Atlas III completed their entire service lives without failing once.
Despite this a 2007 Atlas V launch did result in a partial failure – in that the rocket reached a lower-than-planned orbit but its payload was able to compensate using its own propulsion system and propellant supply – when a faulty valve allowed propellant to leak from the Centaur upper stage during a coast phase causing the subsequent burn to end a few seconds early.
The launch of MUOS-5 was conducted by United Launch Alliance, a company formed in 2006 to provide launch services to the US Government using Atlas and Delta rockets.
It currently operates the Atlas V, Delta II and Delta IV rockets, however it is in the process of phasing out the Delta series. Ultimately the company plans to introduce a new rocket, Vulcan, to replace both Atlas and Delta with a maiden flight expected towards the end of the decade.
For Friday’s mission the Atlas V flew in its 551 configuration, which consists of a Common Core Booster (CCB) first stage, a single-engine Centaur upper stage and five Aerojet Rocketdyne AJ-60A solid rocket motors clustered around the first stage.
The vehicle is topped with a five-metre payload fairing which encapsulates both the Centaur and the payload. For MUOS launches the medium-length version of this fairing is used, which is 23.4 metres (76.8 feet) in length. The rocket had tail number AV-063.
The Atlas V flew from Space Launch Complex 41 (SLC-41) at the Cape Canaveral Air Force Station, one of two launch pads it uses along with Space Launch Complex 3E at Vandenberg Air Force Base.
SLC-41 was originally built in the 1960s for the Titan IIIC rocket, and has also served the Titan IIIE and Titan IV rockets prior to its conversion to an Atlas launch complex ahead of the Atlas V’s maiden flight in 2002. SLC-41 replaced Space Launch Complex 36, a two-pad complex that had served the Atlas II and III, as well as earlier Atlas-Centaur vehicles.
Atlas rockets launched from SLC-41 are assembled vertically atop a mobile launch platform in the complex’s Vertical Integration Facility (VIF), to the southeast of the launch pad. Shortly before launch the fully-integrated rocket is rolled to the launch pad atop this mobile platform, which moves along rail tracks to the centre of the pad.
The Atlas V was originally conceived to use a clean-pad approach, with the only towers at the launch pad the four lightning masts that formed part of the original Titan complex.
Recently a fixed tower has been constructed to support future manned launches from the pad by Boeing’s CST-100 Starliner spacecraft, however this was not used for Friday’s launch and all umbilical connections to the rocket are still made via the tower atop the mobile platform.
AV-063’s flight began with ignition of the RD-180 engine, at the minus 2.7-second mark in the countdown. The engine built up thrust, reaching readiness to launch at the zero mark in the countdown. This was followed by ignition of the five solid rocket motors, with the rocket lifting off at 1.1 seconds elapsed time.
With five solids burning the Atlas cleared the pad quickly, before beginning a series of pitch and yaw manoeuvres to attain its prescribed trajectory, 3.9 seconds after liftoff. The Atlas flew East from Cape Canaveral over the Atlantic Ocean, along an azimuth of 94.58 degrees.
The vehicle encountered the area of maximum dynamic pressure, or max-Q, 49.3 seconds into the mission.
The solid rocket motors burned for about ninety seconds after liftoff before tailing off. To ensure a clean separation they were kept attached for a few seconds after burnout, with the first pair separating 108.7 seconds into the flight. The remaining three were jettisoned a second and a half later.
The RD-180 engine continued to power the mission, burning RP-1 propellant oxidised by liquid oxygen, as Atlas climbs towards orbit.
The payload fairing separated from the nose of AV-063 at 207.8 seconds after liftoff.
Five seconds later the Forward Load Reactor, which attaches to the forward end of the Centaur and is used to dampen vibrations within the fairing, was also jettisoned.
First stage flight concluded with booster engine cutoff, or BECO, four minutes and 25.6 seconds into the mission. The spent Common Core Booster separated six seconds later.
Following stage separation, the Centaur began its prestart sequence. Its single RL10C-1 engine ignited ten seconds after staging, beginning the first of three planned burns.
This lasted seven minutes and 46.9 seconds, establishing an initial parking orbit.
Seven minutes and 59.2 seconds after the first burn ends, a second burn began lasting five minutes and 46.9 seconds, raising the apogee of the orbit towards geosynchronous altitude.
After the second burn the mission entered a lengthy coast phase, with a third burn occurring two hours, 48 minutes and 40.4 seconds after launch and last for 58.3 seconds. This raised the perigee and reduce the inclination of the vehicle’s orbit.
Three minutes and 39 seconds after the end of the third burn, MUOS-5 separated from the Centaur.
The target geosynchronous transfer orbit for spacecraft separation is 3,841.75 by 35,706.86 kilometres (2,283.15 by 22,187.21 miles; 2,074.38 by 19,280.16 nautical miles) at an inclination to the equator of 19.10 degrees. The spacecraft will use its own propulsion system to achieve its operational geostationary orbit.
The third Atlas launch of the year, Friday’s launch was the fifth for United Launch Alliance, which has also conducted two missions with its Delta IV rocket.
ULA’s next launch is currently scheduled for the end of July, with an Atlas V deploying the NROL-61 mission for the National Reconnaissance Office. A few days later a Delta IV is expected to launch the AFSPC-6 payload for the US Air Force Space Command – which is believed to be a second pair of Geosynchronous Space Situational Awareness Program (GSSAP) space surveillance satellites.
(Images via ULA).