“In the modern era,” Dr. Mountain said, “only space scientists are this patient.”

But the cost of the Webb telescope swelled from an initial budget in 1996 of $1.6 billion to nearly $9 billion, acting like a wrecking ball to the rest of NASA’s space science budget. To avoid retracing that trail of tears, the AURA astronomers said NASA should start investing now in the critical technologies needed to make future telescopes work.

So the High Definition telescope is not destined to be the next item on NASA’s list, or even next to next. After Webb in the pipeline is the ungainly named Wfirst-Afta (don’t ask) designed to investigate dark energy, the mysterious something that is speeding the expansion of the cosmos. That mission was the first priority of the 2010 survey, and it could lift off in 2024 if all goes well.

The High Definition Space Telescope stands at the end of an exciting line of exoplanet research. Thanks to the Kepler spacecraft, astronomers think they now know that roughly 10 percent of the stars in our galaxy have Earth-size planets at the so-called Goldilocks distance suitable for liquid water and life. But the planets Kepler has discovered are too far away — hundreds of light-years — to study closely.

There is already one rocket, the Delta IV Heavy, that could launch this telescope, and the Space Launch System that NASA is developing to send astronauts to deep space would be even better. Packed into a rocket, the telescope would unfold in space like a butterfly spreading its wings, a technique NASA hopes it has perfected with the Webb.

Moreover, even a million miles from Earth, it could be serviceable by robots or even astronauts. “It would be crazy not to do it,” said Neil deGrasse Tyson, the director of the museum’s Hayden Planetarium, who moderated a discussion of the telescope report. He noted that a million miles would be by far the farthest a human had ever been from Earth, smashing the record set when the Apollo 13 astronauts swung around the moon and reached a distance of 249,000 miles in 1970.