Two months ago, an Orbital Sciences (NYSE:OA) rocket launch to resupply the International Space Station ended with a fireball lighting up the skies over Wallops Island, Virginia.

The explosion spread wreckage over nearly half the island. It cost NASA a payload of supplies, cost Orbital Sciences credibility with investors, and improved rival SpaceX's chances of winning future NASA supply contracts.

But Orbital promised quick action, outlining last month a "go forward" plan consisting of:

"one or two non-Antares launches of the company's Cygnus cargo spacecraft to the ISS in 2015-2016,"

"early introduction of its previously selected Antares propulsion system upgrade in 2016," and

"repairs to the Mid-Atlantic Regional Spaceport (MARS) launch complex at NASA's Wallops Flight Facility."

One year from now, Orbital Sciences should have a new engine for its Antares rockets. The question is: Whose rocket will it be?

Questions answered

Or rather, that was the question. Two weeks ago, Orbital confirmed it had picked the new replacement engine for Antares. And last week, we learned who the lucky winner is: Russia.

In the short term, Orbital Sciences will contract with rivals at the United Launch Alliance, or ULA, to send its next one or two ISS supply missions into orbit atop Lockheed Martin (NYSE:LMT) Atlas V rockets. (Lockheed owns one half of the ULA joint venture. Boeing (NYSE:BA) owns the other.) The first Cygnus cargo capsule is scheduled to go up in the fourth quarter of 2015. A second launch might go up on an Atlas V in 2016.

Or not. Orbital plans to have Antares ready in time to make three ISS supply runs in 2016, launching in the first, second, and fourth quarters. What's more, Orbital said "the upgraded Antares will permit Cygnus spacecraft on each of these missions to deliver over 20% more cargo than in prior plans."

This is because, as now confirmed by Russia's Izvestia, Orbital has agreed to pay at least $1 billion for 20 to 60 new RD-181 rocket engines from Russian manufacturer Energomash.

Heading back to the Russian well

Derived from the RD-191 "Angara" engine, the kerosene/liquid oxygen-fueled RD-181 puts out 432,000 foot-pounds of thrust at sea level. Two engines power each rocket, which combined makes for 28% more thrust than a pair of NK-33/AJ-26 engines -- the type Orbital used in its October launch -- produce. This tallies with Orbital's promise of the ability to lift "over 20% more cargo."

What it means to investors

Here at The Motley Fool, we love reading about cutting-edge space tech -- but what we really enjoy is translating defense news into cold, hard profits in our portfolios. With that end in mind, let's take a quick look at what this news could mean for defense investors.

The RD-181 might prove to be safer than Orbital's old NK-33s. It is built at the same Russian factory that builds ULA's preferred RD-180 engines, for one thing, and (a reduced-strength version of) it has been successfully used by South Korea's space program, for another. Orbital Sciences Executive Vice President Ron Grabe says it's got the best combination of any rocket of "availability, technical performance and cost" for use on Antares.

Grabe also confirmed that the RD-181 won't be subject to the congressional ban on use of Russian RD-180 rocket engines in national security space launches, noting: "Our application is in civil space. There's a long history of U.S.-Russian cooperation in civil space."

That's reassuring. Orbital rival ULA, for example, has cited Congressional moves to ban use of the Russian RD-180 rocket engine in national security space launches as having the potential to lock it out of this important market, and give SpaceX a de facto monopoly. If Orbital can dodge that bullet in the civilian market, maybe its shareholders can breathe easy.

But even so, ULA has responded to Congress's threat by promising to build a made-in-America engine for its rockets going forward. And SpaceX already builds its engines here. Given the choices, when NASA is handing out contract awards for future missions, Orbital Sciences may increasingly look like the odd man out.