As Elon Musk prepares for one of the biggest moments in SpaceX’s history, the billionaire entrepreneur reflected over the weekend on one of the company’s past milestones.

In 2015, SpaceX successfully launched and then landed on Earth its Falcon 9 rocket for the first time. Musk’s reaction to that event was captured on video by National Geographic.

On Saturday, I shared the video, which had previously been posted on Twitter. Musk responded to the post by tweeting: “5 years ago. We need to accelerate progress towards fully reusable rockets. Cost per ton to orbit needs to improve by >1000% from where Falcon is today for there to be a self-sustaining city on Mars.”

On Wednesday, SpaceX will attempt to launch its Crew Dragon spacecraft with two NASA astronauts on board to the International Space Station — a first for a private company and the first launch of humans to orbit from U.S. soil since NASA’s shuttle program ended in 2011.

While SpaceX has been working towards this moment for 18 years, Musk’s tweet highlights his desire to go well beyond what is possible today.

It’s no secret he has long dreamed of building a human colony on Mars — one of many subjects he often discusses on Twitter.

Musk is juggling SpaceX’s high profile launch while steering his other company, Tesla Inc., through the COVID-19 pandemic.

“It’s pretty intense days,” Musk told Bloomberg Businessweek earlier this month.

“SpaceX has been working this entire time because we have a national security exemption. We’ve had 8,000 people working full time through the whole pandemic.  We’ve had zero serious illnesses or deaths despite working in L.A., Washington, Texas and Florida.”

In his Bloomberg Businessweek interview, Musk acknowledged his tweets — and in particular, his anti-lockdown views — are not without controversy.

“It’s hard to make everyone happy, especially on Twitter,” Musk said in the interview. “Look, you can either say things that are not controversial at all, and then you’re boring, and nobody cares.”