U.S. Navy communication satellite MUOS-5 finally reached its designated orbit after prolonged maneuver.
Extended time necessary for reaching orbital position was caused by previous problems with main propulsion of MUOS-5. Engineers from Lockheed Martin (main contractor for MUOS-5) and U.S. Navy decided to use instead main IHI BT-4, additional thrusters used for attitude control system. It caused extensive consumption of fuel – secondary thrusters were designed to burn only Monomethylhydrazine fuel without Nitrogen Tetroxide oxidizer. During prolonged use they consumed most of fuel providing much less thrust (144 N instead 450 N generated by BT-4). Finally after over three months, MUOS-5 reached specified orbit on October 22. Now it remains on Geostationary Orbit with apogee at 36764 km, perigee at 34810 km and with inclination of 9.6745° on 105°W slot. Since then, satellite managed to deploy its antennas and performed tests of solar arrays. According to official statement given by U.S. Navy it will start test procedures to confirm, that it is able to operate just as other four MUOS satellites. MUOS-5 will probably enter service in the end of December 2016 or in the early 2017.
Problems with MUOS-5 started on early July, when satellite failed to finish second part of orbit raise maneuver. After performing series of self-tests and taking pictures of exterior of MUOS by one of Geosynchronous Space Situational Awareness Program satellites, it was decided to use onboard attitude control system thrusters to raise the orbit. These thrusters, made by Aerojet Rocketdyne, were designed to be used for course correction and performing precision maneuvers. Twelve MR-103G are generating 1N of thrust along with six stronger MR-106L 22 N thrusters are fueled with Monomethylhydrazine without additional oxidizer. These thrusters are fueled only with single component propellant and used in ACS due their small dimensions and simplified construction comparing two bi-fuel thrusters; as they are used for short burns their fuel consumption level is less important factor, just as their relatively low thrust. IHI BT-4 was design to provide 450 N of thrust and consume much more oxidizer then fuel, in case of using attitude control thrusters we have reversed situation. During prolonged burn, ACS thrusters used most of fuel from tanks. Now MUOS-5, which was launched as backup satellite for operating over Indian Ocean MUOS-4, probably is not meeting basic demands of its missions. Even if there is any amount of fuel in tanks, probably it will not be enough to perform any orbital maneuver, not to mention about operating for planned 15 years. Most possible solution in this situation is swapping MUOS-5 with MUOS-2 remaining on 100° W slot. It could serve as backup without interrupting whole constellation, while MUOS-5 would operate as regular MUOS satellite. Probably U.S. Navy will not have any other option and will be forced to use older MUOS-2 launched in 2013 (which still for sure has more fuel than MUOS-5). Leaving MUOS-5 close to libration point will help in reducing number of burns necessary to keep correct course, but still predicted operational life of it is reduced comparing to original plan. Most possible is keeping satellites in described configuration and sending refueling satellite to MUOS-5 as soon as possible.