In the early days, satellites didn’t stick around for very long. After it was launched by the Soviet Union in 1957, it only took about three months for Sputnik 1 to renter the atmosphere and burn up. But the constant drive to push ever further into space meant that soon satellites would remain in orbit for years at a time. Not that they always functioned for that long; America’s Explorer 1 remained in orbit for more than twelve years, but its batteries died after just four months.
Of course back then, nobody was too worried about that sort of thing. When you can count the number of spacecraft in Earth orbit on one hand, what does it matter if one of them stays up there for more than a decade? The chances of a collision were so low as to essentially be impossible, and if the satellite was dead and wasn’t interfering with communication to its functional peers, all the better.
The likelihood of a collision steadily increased over the years as more and more spacecraft were launched, but the cavalier approach to space stewardship continued more or less unchanged into the modern era. In fact, it might have endured a few more decades if companies like SpaceX weren’t planning on mega-constellations comprised of thousands of individual satellites. Concerned over jamming up valuable near-Earth orbits with so much “space junk”, modern satellites are increasingly being designed with automatic disposal systems that help make sure they are safely deorbited even in the event of a system failure.
That’s good news for the future, but it doesn’t help us with the current situation. Thousands of satellites are in orbit above the planet, and they’ll need to be dealt with in the coming years. The good news is that many of them are at a low enough altitude that they’ll burn up on their own eventually, and methods are being developed to speed up the process should it be necessary to hasten their demise.
Unfortunately, the situation is slightly more complex with communications satellites in geosynchronous orbits. At an altitude of 35,786 kilometers (22,236 miles), deorbiting these spacecraft simply isn’t practical. It’s actually far easier to maneuver them farther out into space where they’ll never return. But what if the satellite fails or runs out of propellant before the decision to retire it can be made?
That’s precisely the sort of scenario the Mission Extension Vehicle (MEV) was developed for, and after a historic real-world test in February, it looks like this “Space Tow Truck” might be exactly what we need to make sure invaluable geosynchronous orbits are protected in the coming decades.
On paper, the idea behind the Mission Extension Vehicle is simple. It flies up to a satellite, attaches itself securely to it, and very literally drags it to where it needs to go. In the case of a completely defunct satellite, the destination would be a so-called “graveyard orbit” that will never intersect with another vehicle. If the satellite is just out of propellant but otherwise functional, then the MEV could remain attached to it for the remainder of its mission; taking over the maneuvering and propulsion tasks that the spacecraft could no longer perform on its own.
There’s only one problem with this concept: these satellites were never designed to dock with another spacecraft. In fact, they were never even supposed to come within a 100 kilometers of another vehicle. Between unfurled solar panels and extended antenna arrays, approaching a large communication satellite and trying to capture it is not entirely unlike trying to grab a cactus. The result of anything but the most delicate and accurate handhold is going to be immediately and exceptionally unpleasant.
So where do you even attempt to snag such a satellite? There won’t be a formal docking port or dedicated capture point. Again, this is a vehicle that was launched into space with the assumption that it would operate in total isolation until such time that it was pushed into deep space for all eternity. A convenient carrying handle wasn’t exactly on anyone’s mind while it was being designed.
A Lesson in Satellite Anatomy
With so many different satellite designs in use, and precious few of them being well suited to mid-mission servicing attempts, the engineers behind the MEV had to find some kind of common structural component that could be used as a makeshift grapple fixture. Attaining compatibility with 100% of the spacecraft currently in orbit wouldn’t be possible, but if they could at least make sure MEV was able to snag the majority of targets it ran up against, it would be a step in the right direction.
Somewhat ironically, the perfect grapple point ended up being the part of the satellite that at this point would be otherwise useless: the engine. Nearly every geostationary satellite will have what’s known as an “apogee motor”, a liquid propellant thruster that’s used to put the spacecraft into a circular geostationary orbit after it has separated from the booster rocket that carried it into space.
Not only does the nozzle of this engine make an ideal visual detail to search for on the surface of the target, but the area where it’s mounted to the satellite would have obviously been designed to handle considerable structural loads. In short, the best place to push a satellite is the exact spot where the engineers originally designed it to be pushed.
To firmly attach itself to the engine of the target satellite, the MEV uses an expandable probe not unlike an anchor used to secure a screw into a hollow wall. The probe is carefully inserted down the “throat” of the engine, and then expanded inside of the combustion chamber so that it’s too large to come back out. Damage to the engine seems inevitable with this method, but again, at this point the satellite would have either failed entirely or expended all of its propellants. In either event, the engine was doomed before MEV ever paid it a visit.
All In a Decade’s Work
The MEV is designed to operate for at least 15 years, which Northrop Grumman hopes will allow it to service multiple satellites during its lifetime. In theory it could spend 10 years proving auxiliary propulsion for an elder communications satellite, send it off towards deep space once its replacement was ready, and still have a few good years left in it should another satellite require its services. With a fleet of MEVs, the company could provide orbital “Roadside Assistance” for an entire industry.
To that end, Northrop Grumman chose an excellent candidate for the first mission. Intelsat 901 is a Ku-band satellite launched back in June of 2001 that had recently run low on propellant and moved itself into a graveyard orbit as a precaution. On February 25th, Mission Extension Vehicle 1 (MEV-1) met Intelsat 901 in this orbit and commenced docking operations. The event not only marked the first docking of two commercial spacecraft, but the first time a docking has ever been performed with a spacecraft that wasn’t originally designed with the capability.
Soon, MEV-1 will tow Intelsat 901 back into a standard orbit where it will resume normal operations for five more years. After which, the satellite will be returned to the graveyard orbit and MEV-1 will detach with at least a decade left on the clock. With the ability to extend the lifetime of multiple expensive geosynchronous communications satellites on each mission, the Mission Extension Vehicle promises to be very lucrative endeavor for both Northrop Grumman and its future customers.