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MEV-1 and Intelsat 901

Tyneside, UK
2024 Jul 24
Wednesday, Day 206

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Breathing Life Into an Ageing Satellite

2019 October 9, Russia's Khrunichev company launched Northrop Grumman's MEV-1. The Mission Extension Vehicle has been designed to chase down another satellite, dock with it and then take over its steering, pointing and orbit adjustment work. It is a relatively simple task and is a service for the future.

Northrop Grumman is not alone in its approach to spaceborne maintenance. Effective Space Solutions is waiting to get a lift to orbit for a pair of its Space Drone satellites that will perform similar tasks but with extended capabilities including satellite repair using manipulator arms. China, Russia and the US have all been observed conducting missions that hint at using manipulator systems to grapple and release other satellites. The ISS uses manipulator systems to grab and dock visiting spacecraft..

A contract between Intelsat and Northrop Grumman is for MEV-1 to provide its Intelsat 901 satellite with pointing and station-keeping for five years. At that point, the contract could be extended or MEV-1 will move Intelsat to a graveyard orbit and then move itself on to rendezvous and capture of another satellite.

One Mission Ends, Another Begins

After successfully chasing down and locking itself on to Intelsat 901 on 2020 Feb 5, some four months after launch, MEV-1 spent a few days of health checks before starting the job of moving Intelsat to its new location. 2020 March 2, its thrusters were fired to start the pair on a relatively fast track to Intelsat 901's new station at 27°.5 west longitude.

Before the manoeuvre, that happened when the pair were in near-geosynchronous orbit above 102° east, they had been moving westwards at about 4° per day. This speeded up to nearly 6° per day suggesting that they would reach their destination before the end of March.

Around March 25, MEV-1 started a short series of thruster firings to slow down the approach then, on March 29, the pair stopped at 27°.5 west. Intelsat 901 was at it's new station.

Intelsat 901 was then checked out and brought back into operation, sitting less than 10 kilometres from Intelsat 907, the satellite that it will supplement and (probably) eventually replace.

As of 2020 April 2, neither Intelsat nor Northrop Grumman had made any announcements concerning the arrival on station. In fact, Intelsat's website was still showing Intelsat 901 as being active at its original 29°.5 west station, as it had done throughout the whole of the repositioning manoeuvre.

April 2 was actually the date that Intelsat 901 was recommissioned and the services of about 30 Intelsat customers were transferred across from Intelsat 907. It was, however, another two weeks before either Intelsat or Northrop Grumman formally acknowledged it.

What follows is a summary of how the mission unfolded.

Intelsat 901

Intelsat 901 was launched 2011 June 9 by an Ariane 4 flying out of French Guiana. Since 2018 April it had been residing at 29°.5 west longitude in geosynchronous orbit. Prior to that it had been operating at 18° west following a brief period of testing after launch. Orbit measurements are based on Twoline Element Sets published by Space-Track.

NOTE - 2020 Feb 25, Intelsat docked with MEV-1 so subsequent entries apply to the combined pair.

Ariane 44L (V-141)
Centre Spatiale Guyanaise, French Guiana
2001 Jun 9, 06:45
Intelsat 901
in space
Commercial comsat.

epoch (UTC)         
s-m axis
( km )
ecc    perigee
( km )
( km )
( min )
( ° )
( ° )
2001 Jun 11, 16:48243440.730518235751630.027.05180
2001 Jun 11, 19:26279240.5089733535757773.993.03178
2001 Jun 12, 18:36381310.103527806356981235.010.62175
2001 Jun 14, 13:41399050.055031332357221322.220.36157
2001 Jun 16, 04:47421380.001035717358021434.710.1325070° west
2001 Jun 19, 04:16421310.001235703358041434.390.1524368° west
2001 Jun 23, 03:26421630.000035784357871436.030.1420967° west
2001 Oct 17, 14:23420380.000035660356611429.640.032843° west
2001 Nov 02, 19:34421070.001635662357971433.170.0129718° west
2001 Nov 04, 13:31421640.000435770358021436.070.017118° west
2018 Mar 25, 05:37421650.000235776357961436.090.0632318° west
2018 Mar 29, 09:48421990.000335809358331437.870.0727920° west
2018 Apr 21, 20:56421630.000335772357981436.010.1221729° west
2019 Dec 01, 20:24421650.000235779357951436.101.448829° west
2019 Dec 14, 09:53421960.000135814358221437.711.4713631° west
2020 Jan 20, 10:34423940.000136010360221447.831.5628893° west
2020 Jan 31, 09:00424600.000136079360851451.221.5886131° west
2020 Feb 23, 11:07424670.000236080360981451.581.64347140° east
2020 Feb 25, 11:23424680.000236080360981451.591.64345132° east
2020 Mar 02, 14:24426160.000336227362491459.221.51339102° east
2020 Mar 12, 14:01426160.000336227362501459.220.8635845° east
2020 Mar 18, 15:24426190.000436225362561459.350.5635410° east
2020 Mar 26, 00:00422720.001135847359421441.600.32724° west
2020 Mar 26, 04:48422300.000135848358571439.450.175525° west
2020 Mar 29, 07:39422310.000135849358571439.490.064327° west
2020 Mar 30, 11:16421650.000135781357931436.110.0611327° west


MEV-1 was placed into a 12,000 x 65,000 km, 13°.4 inclined super-synchronous GEO transfer orbit by a Proton rocket along with Eutelsat 5 West B. Once it had been checked out on orbit, MEV-1 started up its low thrust electric engine for near-continuous operation. Its aim was to reach the GEO belt by 2020 February. As of 2020 Jan 29, MEV-1's orbit was close to being geosynchronous.

Zarya.info's launch list for 2019 chronicles the results of its manoeuvres.

NOTE - 2020 Feb 25, MEV-1 docked with Intelsat 901 and became part of that satellite.

Proton-M + Briz-M
Baikonur Cosmodrome, Kazakhstan
2019 Oct 9, 10:17
MEV-1 (Mission Extension Vehicle)
in space
Northrop Grumman spacecraft - launched to rendezvous and attach itself to the Intelsat 901 GEO comsat (28624/2001-024A), and take over its pointing and station-keeping functions in order to extend its on-orbit life by five years. May then move to another satellite. Precise launch time 10:17:56 UTC. Released from the launch vehicle Oct 10 at 02:11 UTC into super-synchronous orbit then pushed towards Intelsat rendezvous by onboard electric thruster system, arriving 2020 Jan 31. Intelsat 901 had departed its station at 27°.5 east 2019 Dec 11 and moved to GEO graveyard orbit. MEV-1 then docked with Intelsat 901 on 2020 Feb 25 at 07:15 UTC so all subsequent listed orbits are for the combined objects. Arrived at Intelsat 901 new location of 27°.5 west 2020 Mar 29.

epoch (UTC)         
s-m axis
( km )
ecc    perigee
( km )
( km )
( min )
( ° )
( ° )
2019 Oct 10, 15:18448420.590611979649481575.0113.39179
2019 Oct 14, 11:02460210.547914429648571637.579.81179
2019 Nov 22, 20:00454250.386221505565891605.845.20188
2019 Nov 26, 11:14454390.386321510566131606.605.21189
2019 Dec 29, 03:25441860.217228209474071540.592.74207
2020 Jan 03, 05:00441900.217328212474131540.812.75207
2020 Jan 23, 03:30429820.054234272389351478.031.63251
2020 Jan 29, 00:22426670.020835401371751461.811.57266118° west
2020 Jan 31, 17:34424850.003535956362581452.501.56294132° west
2020 Feb 25, 13:28424670.000236081360981451.591.64351132° east
2020 Mar 03, 13:33426160.000236228362471459.221.4234097° east
2020 Mar 12, 14:01426160.000336227362501459.220.8635845° east
2020 Mar 17, 16:11426190.000336227362551459.380.5635316° east
2020 Mar 22, 07:05426220.000336229362581459.500.2234211° west
2020 Mar 26, 00:00422720.001135847359421441.600.32724° west
2020 Mar 26, 04:48422300.000135848358571439.450.175525° west
2020 Mar 29, 07:39422310.000135849358571439.490.064327° west
2020 Mar 30, 11:16421650.000135781357931436.110.0611327° west

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.


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."

Page Date: 2020 Jan 20
Updated: 2020 Jan 23
Updated: 2020 Jan 29
Updated: 2020 Jan 30
Updated: 2020 Jan 31
Updated: 2020 Mar 10
Updated: 2020 Mar 31
Updated: 2020 Apr 2
Updated: 2020 Apr 19
Orbits updated: real time
Charts updated: 2020 Feb 1

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