NASA insists it is making progress on its often-repeated “Journey to Mars,” but Administrator Charles Bolden won’t tell you how much it will cost.

At a Peter Huessy breakfast series event on Capitol Hill Monday, Bolden gave a variety of reasons for why he doesn’t know how much getting to Mars will cost. He said any price tag on the journey to Mars would be under the assumption that the agency would go in today’s systems with today’s processes. Bolden also said that NASA doesn’t know which type of booster, liquid or solid, would be used as the Space Launch System’s (SLS) advanced booster.

But a veteran NASA observer said Monday Bolden’s reluctance to say how much the “Journey to Mars” will cost isn’t necessarily his fault. Commercial space advocate and industry consultant Rand Simberg said Bolden won’t say how much it will cost to get to Mars because the civil space agency knows any “actual, realistic technical plan” it presents to Congress to get to Mars that utilizes the lawmaker-directed SLS will be “dead on arrival,” because it would require much more funding than Congress has been willing to appropriate since Apollo. Simberg said Apollo cost about $25 billion, in then-year 1967 dollars, and over $100 billion in current-year dollars.

Congress wants to fund SLS, Simberg said, but always cuts the technology budget to develop things that are actually necessary to get to Mars. This, he said, is because some lawmakers, many who represent NASA districts like the Space Coast of Florida or NASA Johnson Space Center, Texas, don’t actually care whether NASA gets to Mars, as long as it’s building a big rocket. Simberg said SLS was designed to be expensive using the Shuttle/Saturn infrastructure. This, he said, maximizes job creation while minimizing actual space exploration.

The Government Accountability Office (GAO) said in 2015 that SLS, NASA’s congressionally-directed choice of transportation for getting to Mars, and its Orion multi-purpose crew vehicle would cost nearly $23 billion to demonstrate initial capabilities. This includes the first SLS flight, ground systems and first two Orion flights.

Simberg said since NASA is afraid to present a plan to Congress that involves using SLS to get to Mars, the agency hasn’t produced a well-thought-out plan to get to the fourth planet from the sun and, thus, doesn’t truly know how much it will cost. Does NASA want to ultimately set up a base and settlements, does it want to send astronauts to the red planet or does it want to simply re-do Apollo, which Simberg described as taking everything necessary to reach Mars in one single launch in the 2030s. Simberg said taking everything necessary to get to Mars in one single launch is not physically possible. NASA wants to send a human to an asteroid by 2025 and Mars in the 2030s.

“They have several plans, and they’re doing trade studies, which they should,” Simberg said. “But they haven’t clearly articulated why they’re doing this and if you don’t know why you’re doing this, then it makes it impossible to figure out the best way to do it.”

Congress insisting on NASA developing its own rocket to get to deep space is the antithesis of the modern way the agency uses rockets. For example, NASA has embraced a new world of procuring services from companies like Space Exploration Technologies Corp. (SpaceX) and Orbital ATK [OA]. NASA buys launch services from these two companies to deliver cargo and food to astronauts on the International Space Station (ISS). Simberg believes buying launch services from industry would be a better way to get to Mars as industry’s resources would be focused on getting to Mars, as opposed to building a “big rocket” in SLS.

Mary Lynn Dittmar, the head of the prime contractor advocacy group Coalition for Deep Space Exploration, said Monday she supports NASA’s approach to getting to Mars. Dittmar said there are so many unknowns in how to get to Mars due to the extreme distance required to get to the planet, NASA is treading in new territory. Dittmar said NASA doesn’t know how to put astronauts “in a can” for six months nor know how to deal with the harsh environment of Mars. She added that just a fraction of robotic missions planned for Mars have been successful.

Dittmar also said NASA’s approach is much like how the first ocean explorers discovered new continents. These people, Ditmar said, didn’t have road maps or milestones, they just learned as they went, which she said is NASA’s current approach for Journey to Mars.

Dittmar agreed with Simberg’s assertion that NASA doesn’t have a plan for Mars because it doesn’t know exactly what it wants to accomplish. This, she said, will be driven by the architecture it selects. Dittmar said NASA could put forward a simple plan to get to Mars, but it would be only for getting “boots” on the planet. But if NASA wanted to put forth an ambitious plan for Mars like getting humans off earth and get them into space on a sustainable basis, it can’t just lay out steps. She said NASA would need to take enough time to figure out “what we don’t know.”

The Coalition for Deep Space Exploration, Dittmar’s group, is supported by prime contractors Lockheed Martin [LMT], Boeing [BA], Northrop Grumman [NOC], Orbital ATK and Aerojet Rocketdyne [AJRD].