This static test fire of one of SpaceX’s Falcon Heavy booster may not actually be sending any rockets to space, but it does put off a lot of exhaust. The bulk of that is actually steam, as SpaceX founder and CEO Elon Musk pointed out on Twitter following the release of the test fire footage – and there will be three times as much of it when the Falcon Heavy actually launches, since it’ll use three of these boosters to propel its considerable bulk into orbit.

The side booster test actually happened last week in McGregor, Texas, where SpaceX has a testing and development facility. It’s a key step as SpaceX prepares to launch the Falcon Heavy for the first time late this year, with a tentative timeframe of summer provided the Cape Canaveral LC-40 launch site is fully repaired and operational in time.

Static fire test of a Falcon Heavy side booster completed in McGregor, TX last week. This booster previously launched Thaicom 8. pic.twitter.com/nWrNCXtu13 — SpaceX (@SpaceX) May 25, 2017

Falcon Heavy will be able to carry up to 46,700 lbs of cargo to geostationary transfer orbit when it’s ready to roll, and up to 140,700 lbs to low-earth orbit, though its max capacity will require configuring the rocket in an expandable configuration that won’t allow for reuse. As with Falcon 9, SpaceX will aim to reuse Falcon Heavy first stage rockes where possible in order to minimize the cost of launches.

If all goes to plan, Falcon Heavy will have the highest cargo capacity of any operational rocket today, which will put SpaceX in a very good position when it comes to its Mars ambitions and to being able to offer something unique to prospective commercial customers.