I've been playing around with some speculation and head canon about how to Justify a HUMAN component to a multi species ARK project within the timeframe of the Reapers discovery and invasion.
Using an On Screen perspective of the game world in ME. I believe is almost impossible to justify that the Alliance could build an ARK without some major retcons of the series that could be perceived as breach the integrity of the previous games in story, character and lore. ME3 directly shown the Alliance were totally unprepared for the Reapers Invasion and the strategic high command were fighting too many fires, committing all resources available to them to the Citadel project. Running the 2 projects in parallel is problematic and makes major characters dialogue scripts look foolish or totally wrong.
So How could humans contribute? Time to look beyond the on screen Military perspective and look at a far bigger picture of human civilization in space; The commercial and civilian world that we only saw glimpses of. I'll try and put some form of perspective on this in an extended timeline.
The Mass Effect Human time line starts in 2069 with the establishment of human colonies on Luna. The next entry is for 2070 and the departure of the Maxwell Expedition to colonize another star sector. This indicates a pretty advanced level of capability in engineering solutions to allow human colonization had been achieved in the previous few decades. Military exploitation of space is prohibited by treaties and there is not enough political will to jump start space exploration in an economic crisis like 2016, so how did we get started for real?
How that could have happened from today's perspective of space exploration is through corporate interests that had made space exploitation profitable and sustainable. Currently there are 2 leading companies that target different forms of exploiting the potential in Near Earth Asteroid mining. This is a massive resource pool and relatively easy to access with current technologies that the companies have developed.
The figures are astronomical in current economic values. A 500mtr Silica asteroid is forecast with a yield potential of aqueous silicate of around $5 Trillion; this is the target of the company Planetary Resources. Their technological system is called “Asteroid Perspiration Systems” and it would be ESSENTIAL in the MEU. Humans need to unfreeze the Mass Relay and this tech is designed to exploit water and ice for rocket propulsion and supporting organic life.
The second company, Deep Space Industries targets metallic asteroids for rare minerals and space construction purposes. They value a 500mtr platinum asteroid at around $3 Trillion. Their process of exploitation is more long term investment, their “Bacterial Decomposition Process” takes several years to work efficiently, but they have developed major advances in manufacturing and construction processes using vacuum 3D printing.
If these pay out; the next gold rush begins and a technological uplift would follow, but it would pay out most for the first movers if they also controlled the supply tech chain. Essentially they would control the means to exploit space. Any colonization or exploration effort would be under their, near total control.
How this refers to MEU is that it is uncannily similar monster as Eldfell-Ashland Energy's wiki entry:
In 2137, the Ashland Energy Corporation successfully extracted helium-3 from Saturn's atmosphere, beginning a new era of fusion research. On the wave of this success, they merged with Eldfell Construction to vertically integrate the two companies' strengths. Ashland would recover the raw materials for energy production, and Eldfell would build power plants, refineries, and pipelines on nearby worlds to distribute Ashland's products to the consumer. Eldfell-Ashland Energy was born.
As EAE's reach extended, they absorbed companies to create a "cradle-to-grave corporate experience" for their employees. Today, subsidiaries such as Second Star Living recruit colonists to staff EAE facilities, and the education group Excelsior provides job-related education opportunities to provide EAE stations with a qualified incoming workforce. Water, power, food, shipping -- EAE provides them all. If EAE wants to put a colony on a garden world, they are able to do so and keep 90% of services performed completely in-house, creating consumers out of its own employees. Its primary revenue stream, however, continues to come from mining base elements like hydrogen, helium-3, and eezo and trading in their futures.
Forget the Alliance, they were simply a police force and political arm of a far larger entity that was already exploring and colonizing space successfully for decades and was their major tech supplier. The Alliance built NOTHING, they contracted out to those who already did that work for commercial purposes.
Possibly one of the places most capable of constructing ARK components in humanity is Caleston and Eldfell Ashland are named interest. This is the supply planet of Alliance drive cores etc, best equipped facility in humanity to develop ME technologies into practical applications and possibly the place that Cerberus stole the Normandy SR2 drive design from in period after ME1. This was developed into a practical, highly efficient design by a team with relatively limited resources. What could be under R and D on a world like Caleston?
The Alliance also are not the major exploration, colonization or exploitation presence in the human timeline; again most likely this was EAE flexing its muscles and reach in the shark pool of interstellar commerce, growing into a Megalodon capable of taken sizable chunks out the Asari Blue whales, and hold its own against other species corporate sharks. The galactic economy had been in stasis since the Rachni wars, but was stimulated by the introduction of a capitalist monster that grew to hold around a 20% stake in the total galactic economy. And that monster was Jonah Ashland most probably The Asari certainly respect him enough to consider doing serious business with.
If you want to see who moves people, builds the colonies and keeps them alive. Has a successful track record of return on high risk exploration ventures of several decades, and the capacity to do cutting edge Mass Effect engineering, Bioware wrote in Eldfell Ashland in a way I hope to have shown to have the most plausible capability for an ARK that features humans.