Donald Trump would like to see Americans walk on Mars during his presidency. Nasa would love to get there that quickly, too. The reality of space travel is slightly more complicated, however. From a report: On Monday, during a call with astronaut Peggy Whitson, who was aboard the International Space Station, Trump pressed her for a timeline on a crewed mission to Mars, one of Nasa's longest standing and most daunting goals. "Tell me, Mars," he asked her from the Oval Office, "what do you see a timing for actually sending humans to Mars? Is there a schedule and when would you see that happening?" Whitson answered by pointing out that Trump, by signing a Nasa funding bill last month, had already approved a timeline for a mission in the 2030s. She added that Nasa was building a new heavy-launch rocket, which would need testing. "Unfortunately space flight takes a lot of time and money," she said. "But it is so worthwhile doing." Trump replied: "Well, we want to try and do it during my first term or, at worst, during my second term, so we'll have to speed that up a little bit, OK?" It was not clear whether the president meant the remark as a quip or something more serious.