Stratolaunch, the launch venture created by Microsoft co-founder Paul Allen, took the world’s biggest airplane out of its hangar this weekend at California’s Mojave Air and Space Port and revved up its engines in preparation for the next step toward shooting rockets into space from midair.

The rocket-launching part is still a year or two away, but Stratolaunch is aiming to put the 385-foot-wide, twin-fuselage plane through its first test flight within the next couple of months.

In order to do that, the test program calls for flying five on-the-ground runway taxi tests at increasing speeds. Two of those tests have been done already, and in a tweet on Friday, Stratolaunch CEO Jean Floyd hinted that the third runway race might be run this weekend:

We are rolling out this morning for Taxi Test #3. We plan to conduct 5 Taxi Tests prior to First Flight. pic.twitter.com/kEXAiIIGOx — Jean Floyd (@WJeanFloyd) August 10, 2018

The taxi test didn’t end up happening this weekend, but Stratolaunch’s team did put the plane through a couple of days’ worth of fueling operations. full-power engine tests and communication tests. And folks in Mojave got a good look at the monster plane (which has carried the nickname “Roc” in honor of the giant bird of Eastern mythology). Here’s aTwitter sampler:

Weekend aircraft testing continues as we wrap up a full day of fueling operations and engine runs. All engines successfully tested to max power settings. pic.twitter.com/XsXI3nLKGW — Jean Floyd (@WJeanFloyd) August 11, 2018

#Stratolaunch is crazy big. Jaw dropping when you see it just on the other side of the fence. Yesterday I caught sight of it miles away coming up from Lancaster on the 14. Just sitting outside hangar looking massive miles away. Impressive. #carbongoose #compositegoose #BIRDZILLA — Parabolicarc.com (@spacecom) August 12, 2018

The Stratolaunch aircraft is back in the hanger tonight. We didn’t make it to the main runway for taxi testing this weekend. Successfully completed fueling ops, engine runs, and communications testing. We’ll be outside again very soon. pic.twitter.com/JkSHDv6SPc — Jean Floyd (@WJeanFloyd) August 13, 2018

Exclusive: Check Out These Incredible Photos Taken Last Week of the Massive Stratolaunch Space Plane https://t.co/FoT3uRXf4k pic.twitter.com/2ErHDxx3l7 — The Aviationist (@TheAviationist) August 13, 2018

Stratolaunch executives laid out the test schedule for the plane, which was built by Mojave-based Scaled Composites, during a space conference in April. The company plans to follow up on the first two taxi tests (at runway speeds of 15 mph and 40 knots) with three more at speeds of 70, 85 and 120 knots.

The last speed is roughly what’s needed for takeoff.

After the fifth taxi test, Stratolaunch would put the plane into the air for a series of flight tests over the course of what’s expected to be 18 to 24 months. In April, executives said they were targeting the first flight test for this summer (which technically runs until Sept. 23).

Once the plane is certified by the Federal Aviation Administration, Stratolaunch would ramp up its system for carrying rockets on Roc. Orbital ATK (which was recently acquired by Northrop Grumman) has already agreed to provide a version of its Pegasus XL rocket for air launch.

The company hasn’t yet announced that it has signed up customers, but it intends to put commercial payloads on its first launches — perhaps at a discounted rate.

Stratolaunch’s air-launch system is a super-sized version of the setup being developed by Virgin Orbit, one of billionaire Richard Branson’s space ventures. As it happens, Virgin Orbit is gearing up for a new round of flight tests as well.

The company has converted a Boeing 747 to carry LauncherOne rockets, and the first captive-carry test of the system (which won’t involve lighting up the rocket engine) is thought to be just around the corner.

Virgin Orbit’s rocket-carrying test flights will also be flown out of Mojave, so if you happen to be in the area … watch the skies.