Many in the space community are still beaming over last week’s launch of Orion, the historic unmanned test flight that NASA said touched off a “new era” in human space exploration.

But at a congressional hearing Tuesday, a government watchdog report and some skeptical members of Congress brought some of the grandiose talk of a trip to Mars down to Earth, saying that the program still faces daunting challenges that NASA has struggled to overcome.

The Government Accountability Office’s Cristina Chaplain said in testimony that the agency’s human exploration program is plagued by “inconsistent and unrealistic schedule goals,” as well as “significant technical and funding issues.”

And while members of Congress were quick to congratulate NASA officials for Friday’s test flight — a 41/2-hour mission that sent a spacecraft designed for humans farther than any has gone in more than 40 years — they also took aim at a program to build a new heavy rocket.

Known as the Space Launch System (SLS), the rocket NASA plans for its future deep space missions is still being built and isn’t expected to have its first test flight for another four years. (Friday’s mission was aboard a Delta IV Heavy rocket built by the United Launch Alliance.)

After its first test flight in 2018 — originally planned for 2017 but delayed because of funding issues — SLS is then expected to perform its first manned flight in 2021.

But after that flight, “future mission destinations remain uncertain,” the GAO said.

Orion’s maiden flight Friday was a long-awaited triumph for an agency that has been unable to fly humans into space since the retirement of the space shuttle three years ago. American astronauts have been hitching rides to the International Space Station aboard a Russian spacecraft at more than $70 million a seat.

The test flight — seen by thousands — was a huge step in advancing human exploration, NASA said, and ultimately landing a person on Mars.

After the SLS test flights, NASA plans to capture an asteroid with a robotic spacecraft and then drag it to the moon’s orbit, where it would connect with Orion. Astronauts would then take samples from the asteroid.

But that wouldn’t happen until sometime in the 2020s, NASA has said. And its next mission — Mars — wouldn’t happen until the following decade.

The lack of specificity and the long times in between flights frustrated some members of the House Committee on Science, Space and Technology.

NASA has scheduled the launch of an uncrewed Orion spacecraft for a 4 ½-hour mission.

“It took us less than a decade not only to go around the moon but to land on the moon under Apollo,” said Rep. Mo Brooks (R-Ala.).

Rep. Dana Rohrabacher (R-Calif.) said it could cost at least $10 billion to develop “this monstrous rocket project.” Even then, he said, it “won’t have a real mission until we go to Mars, which could be two decades or three decades from now, depending on if we can ever get over the technological hurdles we haven’t gotten over yet.”

Meanwhile, the program would continue to eat up much of the budget and take away from other endeavors, Rohrabacher said.

“We made a wrong decision when we went down this road,” he said.

But William H. Gerstenmaier, NASA’s associate administrator for human exploration and operations, said that despite the funding challenges, the agency has made significant progress and that each development gets NASA closer to its ultimate mission: Mars.

“The results of the test flight show that we’re making significant and substantial progress as we move forward,” he said, adding that Orion’s flight went “flawlessly.”