At first glance, SLS looks awesome. A core stage flanked by two boosters on top of which sits a small kick stage or a larger second stage that can send cargo or an Orion manned spacecraft to Mars and beyond (pictured top). It's versatile and more powerful than anything that has preceded it. But it's expendable and far from completion.

Former flight director Chris Kraft is adding his to the growing number of dissenting voices decrying SLS as deeply flawed. It's destroying jobs and killing NASA, he says, and there are cheaper ways to undertake missions to the moon and asteroids.

NASA's Space Launch System (SLS) is a bit of a mixed bag. Promising a return to Saturn V-type strength, the rocket is a congressional camel reflecting the self interested agendas of the congressmen responsible for its funding.

It's also really expensive. From inception to first unmanned launch currently planned for 2017, it's expected to cost around $10 billion. Once operational, it will launch once every year with a price tag between $1.3 billion and $2.45 billion every time. That's not including the money put towards research, development, and building the payload and all the associated systems. And that's what Chris Kraft has a problem with.

Kraft was NASA's first flight director. He was the one calling the shots in mission control during the Mercury program in an era when they were writing procedures and handbooks during missions and finding creative solutions to problems as they occurred. He was there when mission control moved to the Johnson Spacecraft Centre (JSC) in 1961 as the Manned Spacecraft Centre. Since then, it's been the nerve center of mission operations.

Now, says Kraft, SLS is threatening the kill the JSC and destroy the 50 year legacy of innovation that has come out of the center.

In NASA's current situation of severe fiscal constraints, the $4 billion to $5 billion annual cost for the SLS program isn't something the agency can afford. Neither is the proposed human exploration program built on the rocket's capacity. The cost of SLS is crowding out the technology of these long-term missions like lunar landers and deep space capable multi-mission vehicles. At the current rate, manned missions beyond Earth orbit aren't likely before the 2030s.

Kraft points to JSC's most famous role - mission control - as the crown jewel under threat. "JSC's world class engineering and development capability created the concepts, designs and development for every American human spacecraft that has flown to space," he says. Its multi-disciplinary systems engineering and technical expertise, which has been built up over five decades "is the envy of the world's space agencies and aerospace industries."

Now, with the shuttle program ended, construction on the ISS complete, and no funding behind a deep space vehicle or a multi-mission vehicles, there is less for JSC to do. All that's left is support for ongoing missions, support of commercial crew missions, and support to see Orion to completion.

These roles demand a staff of hundreds, he says, not the 2,500 that are currently employed. He calls the decrease in personnel need and lack of clear goals a an "going-out-of-business" strategy. From there it's a domino effect. The demise of human space exploration will destroy the job market in Texas, and the strength and stability of NASA won't be far behind.

The kicker is that there are other options for NASA's planned return to the moon and missions to asteroids. A multi-center team completed a study on how these missions might be done with existing launch vehicles within the existing budget.

A presentation from July 2011 titled "Propellant Depot Requirements Study Status Report" compares SLS mission architecture to those that use commercial vehicles and use fuel depots - filling stations in orbit so spacecraft could be lighter at launch. The report shows that fuel depot missions fit within NASA's current budgetary restrictions and can facilitate a return to the moon a decade sooner than an SLS mission.

Moreover, commercial launch vehicles could carry out these missions for a fraction of the cost. The presentation repeatedly praises commercial vehicles for "breaking costs into smaller, less-monolithic amounts allows great flexibility in meeting smaller and changing budget profiles."

The report does, however, admit that reliance on one commercial provider is an undesirable arrangement and one NASA is unlikely to consider even if this does cut mission costs by tens of billions. As for congressional support, it isn't hard to see why cutting SLS and switching to commercial vehicles is an unpopular move. It doesn't help that NASA is trying to hide the data that supports SLS's cancellation, according to Kraft.

He urges congressmen, particularly in Texas, to look at the numbers and back the plan for space exploration that's right for NASA and the country rather for themselves. A move away from SLS could create jobs and reinvigorate NASA, providing it happens before its too late and NASA has suffered irreparable damage.