Starting around 50 years ago, astronomy began a winning streak of amazing discoveries. We found the cosmic microwave radiation left over from the big bang back in the 1960s, for instance, and in recent years we have identified thousands of planets orbiting distant stars. But the good times may be about to stop rolling. There is reason to fear that astronomy is ending its long run of lifting the veil on cosmic wonders.

Our early successes came from looking through new windows across a vast range of wavelengths invisible to the naked eye. The first radio, x-ray, ultraviolet and infrared telescopes were small, but everything we saw through them was new and mysterious. The next generation of telescopes leaped forward in capabilities, leading to the discoveries of neutron stars, black holes, dark matter, dark energy—the list goes on.

But this greater power came at a cost. Each new generation of telescopes carried a price tag several times higher than that of the one before. Today a single telescope can take almost a full decade's worth of NASA's budget for “big astronomy.” A case in point is the James Webb Space Telescope, now scheduled for launch in 2020. Webb's price tag ballooned from what was originally supposed to be just about $1 billion to nearly $9 billion, crowding out nearly everything else. Without other major missions to fall back on, the only response to technical problems with Webb was to keep throwing more money at them.

The glory of our golden age has been that we can access the entire electromagnetic spectrum at a single point in time from various instruments. The discovery of gravitational waves from the merger of two neutron stars is a perfect example: ground-based detectors spotted these ripples in spacetime, but follow-up observations with gamma-ray, x-ray and visible-light telescopes gave us a far better understanding of how the event unfolded. Ideally we need several comparably sensitive “flagship” telescopes, on a par with Webb—and they need to be flying at the same time.

Yet such flagships are designed to last only about five years (although that can often be stretched to 10). When the infrared-sensitive Webb flies, it will be 10 to 100 times more powerful than its predecessors, the Hubble and Spitzer space telescopes. But if new flagships cost as much as Webb, it will be a decade before even one of them can be launched. By then, Webb itself will likely be on its last legs. Every discovery it makes will take more than 10 years to follow up. At that point, we will have forgotten what it was that we wanted to know in the first place.

But it does not have to be this way. Once a decade astronomers set priorities about what new space telescopes to build, and the next time we do so, in the “Astro2020” survey, we should require multiple new missions. There are at least half a dozen ideas for much cheaper telescopes—not as powerful as Webb-scale flagship telescopes but dramatically better than their predecessors. These range from gamma-ray telescopes that can detect merging neutron stars to x-ray and ultraviolet telescopes for probing intergalactic space and more to a far-infrared telescope we can use to understand how stars and planets form. And unlike Webb, they are not just affordable; all of them can be completed within 10 years.

The downside of this approach is that highly desirable but extremely expensive flagship telescopes along the lines of Webb must be postponed until the commercial space industry comes fully of age. SpaceX, for example, already launches satellites at one third of the traditional cost, and soon, maybe, that will drop to as little as one fifth. That is a sizable saving by itself.

Cheaper launch services also take the pressure off engineers to relentlessly shave mass from the telescopes themselves by using the lightest and most expensive possible components. Without such a restriction, costs could plausibly be cut by two thirds. Shrinking costs makes a doubling of flagship launch rates feasible.

As this commercial revolution continues, an even higher rate of flagship missions could come about. If we embrace such a strategy, the good times needn't stop rolling, and the golden age of astronomy doesn't have to end.