After first emerging from its hangar in the middle of 2017, the Stratolaunch aircraft has been slowly but surely edging towards takeoff with a series of increasingly rapid taxi tests. Its latest outing has seen the team clock the gargantuan dual-fuselage plane at speeds approaching those typically needed for regular aircraft to lift-off on the runway.

With a massive wingspan of 385 ft (117 m), the Stratolaunch plane tips the scales at 500,000 lb (226,000 kg) and is built to accommodate payloads up to 550,000 lb (249,476 kg). If it does eventually take flight it will be the largest plane ever to do so, and its creators hope it can become the first commercial air-launch vehicle capable of delivering small payloads to various Earth orbits.

This would work in a similar way to Virgin Orbit's Cosmic Girl aircraft, which is also making promising strides, heading upward to a designated altitude before firing a separate launch vehicle into orbit and then returning to the runway for another mission.

Stratolaunch first rolled down the runway in March last year reaching a speed of 46 mph (74 km/h), and then upped the ante with a 90-mph (145-km/h) outing in October. In the latest round of testing, the team reports the aircraft has reached a speed of 136 mph (218 km/h). What's more, its front wheels lifted into the air momentarily, another promising step in demonstrating its capacity to get off the ground.

While the company hasn't made clear the exact speeds the Stratolaunch will need to hit on the runway in order to takeoff, it does say it takes off just like any other aircraft, which typically lift off in the 150-180 mph range (240 to 285 km/h).

Given its size, its entirely possible the Stratolaunch will need greater momentum than this to get off the ground. Officials told reporters last April that this third taxi test is expected to be the final one before the maiden flight, and that it expected it to reach around (136 mph) 220 km/h during the test, according to SpaceNews. Back in October the company also stated it hopes to conduct the maiden flight sometime in the next 12 to 18 months, so we shouldn't have long to wait.

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