Starting Point
Initially there was a significant difference in the sizes and inclinations of the two orbits. Intelsat was following a circular orbit around the Earth's equator but MEV-1 was in an inclined and much more eccentric orbit.
The illustrations above and below show the relative locations of the two satellites on 2019 October 9 at noon UTC, the day after MEV-1 reached orbit. The view below shows the fifferences in the shapes of the two orbits.
Orbital Manoeuvres
Following confirmation that MEV-1 had reached space safely and was alive and well, Intelsat began to switch off 901's services and on 2019 Dec 1 its station keeping seemed to come to an end. It started to drift very slowly westwards (<0.2° per day) and increased its inclination slightly from 1°.3 to 1°.45. Commencing December 11, a series of gentle thruster firings were used to push it higher. By January 18 of the new year it was at 35,996 x 36,008 km and still rising although the rate slowed noticeably January 20.
Simultaneously, MEV-1 commenced an operation to lower its orbit to a point where it can be guided to a rendezvous with Intelsat 901. It will latch itself on and its thrusters will be used to return to the geosynchronous belt and guide Intelsat to its new operating slot.
The effects of near-continuous operation of MEV-1's electric thruster system has been to simultaneously raise perigee and lower apogee. At the same time it has been reducing its orbital inclination and moving the Right Ascension of the orbit Ascending Node to match Intelsat's. When both sets of orbital parameters have the same values, it will be in a position to rendezvous with its target and capture it.
By 2020 January 18, again at noon, the comparative orbits were distinctly different from those on day one.
Late on January 28, MEV-1's electric thruster was turned off indicating it had arrived at a point where rendezvous could be initiated. At the time, Intelsat 901 was in a 36,073 km circular orbit. MEV-1 was 225 km higher and in a slightly eccentric orbit, causing it to oscillate between about 500 and 2,000 km from Intelsat. By virtue of its slighly greater orbit period MEV-1 continued slowly to 'catch up' with Intelsat.
Orbit data issued by Space-Track Jan 30 showed MEV-1 again on the move, approaching even closer to Intelsat.
Orbit Heights
This plot shows how apogee and perigee of MEV-1's orbit converged on Intelsat 901. The MEV's target was a 36,000 kilometre circular orbit to match Intelsat. On January 31, the two satellites were matched in orbit height but with a minor difference in orbital eccentricity..
Orbit Inclination
MEV-1 had also slowly been lowering its inclination. It started at 13°.4 but by mid-January the inclination was down to 1°.7, almost matching Intelsat's 1°.4. On January 22, MEV-1's inclination ceased to change and stabilised at 1°.56, probably the desired inclination for the time of rendezvous.
In parallel, the inclination of the Intelsat orbit had been increasing slowly since the time it left its geosynchronous location and, on January 31, it matched MEV-1's 1°.58.
GEO Convergence
The two orbits' values of Right Ascension were also converging. They too fell into alignment on January 31
By mid-January, MEV-1's orbit was dropping into the region that could be considered near-geosynchronous. It was above the western Atlantic Ocean and moving further west. In the meantime, Intelsat was on the equator, in line with the eastern States and also travelling westward. They were converging on a get together in the region of longitude 130° west around the end of January.
Rendezvous
February 1, all major manoeuvres had ceased. The satellites were within tens of kilometres of each other. Any further orbit changes would be part of what might be termed 'terminal manoeuvres' aimed eventually at a docking. The Northrop Grumman image on the right is of Intelsat 901 with the Earth as a backdrop as MEV-1 approached.
Docking and Next Moves
2020, late January, in response to being questioned about plans now the two satellites had come together, Northrop Grumman indicated a careful approach with an indication that rendezvous and capture would occur "early February". In the event, it was a little later, February 25, when docking occurred. Before that MEV-1 had been manoeuvering within a two kilometre radius of Intelsat for several days, lining up for final capture and perhaps rehearsing its approach.
MEV-1 latched itself on to Intelsat using a 'stinger' grappling device designed to connect with the conical nozzle of the thruster used to raise Intelsat 901 from its original transfer orbit. Both can be seen in the image below, taken by MEV-1 and released by Northrop Grumman.
One week later, on March 2, activity resumed. MEV-1's orbit adjustment thruster was used to raise the pair's orbit by 150 km. It had the effect of speeding up their westward drift slightly. At the time, their location was 102° east and the manoeuvre increased the drift rate from 4° per day to 5°.7 per day.
The expected new station for Intelsat 901 was 27°.5 west longitude. The pair arrived there March 29 and dropped into the slot alongside Intelsat 907.
Intelsat 907 was launched early 2003 about 17 months after Intelsat 901. Like Intelsat 901, it had a planned life of 15 years and has now passed the end of that period. Whether the plan is to retire intelsat 907 or operate the two satellites in parallel remains to be seen. In reality, Intelsat 901 will have returned to almost the same location (29°.4 west) that it departed 2019 December 1 in order to meet MEV-1.
The manoeuvres of both satellites can be viewed in the orbit tables further up this page.
Northrop Grumman Announces Successful Mission
2020 April 17, Northrop Grumman issued a press release to confirm that the mission to relocate Intelsat 901 had been a success and the satellite was back in service, and that Intelsat 1 was again fully operational:
"Intelsat today announced that Intelsat 901 has returned to service following the successful docking with the first Mission Extension Vehicle (MEV-1) from Northrop Grumman Corporation and the company’s wholly-owned subsidiary, SpaceLogistics LLC, on February 25 – the first time that two commercial spacecraft docked in geostationary orbit.
"Since the February rendezvous, MEV-1 has assumed navigation of the combined spacecraft stack reducing its inclination by 1.6° and relocating IS-901 to its new orbital location. Intelsat then transitioned roughly 30 of its commercial and government customers to the satellite on April 2. The transition of service took approximately six hours. IS-901 is now operating at the 332.5°E orbital slot and providing full service to Intelsat customers."
