America’s space scientists are entitled to a period of mourning after the Cassini spacecraft burns up in Saturn’s atmosphere on Friday. After all, 20 years after its launch, the most expensive spacecraft ever sent to the outer planets has produced 3,948 science papers (and counting), 453,048 photographs (and counting), and a cohort of young scientists who earned their Ph.D.s and other training thanks to the mission.

Accomplishments like that don’t come cheap, and in today’s climate of tight budgets and more immediate needs, a proposal with a $3.26 billion price tag like Cassini’s almost certainly wouldn’t fly. But the U.S. can’t afford to lose the long-term economic, diplomatic and prestige benefits that large-scale missions bring. For NASA, that presents a complicated challenge: How does the agency ensure that we have more Cassinis — for less money?

For decades, NASA’s reputation has been defined by human exploration and what the agency calls its “large strategic missions” like Cassini, the Mars Curiosity rover and the Hubble space telescope. Such missions generally require more than a decade to plan, and support and sustain large teams of space scientists and students for years. As a rule, they cost more than $1 billion.

Sometimes far more.

These missions have become known for huge cost overruns that place them in political as well as technical trouble. The most notable example is the James Webb space telescope, the yet-to-launch successor to Hubble. Since it was proposed in the 1990s, the cost has grown from under $1 billion to $8.8 billion, while the launch date has stretched out a decade, to 2018. A 2012 NASA report identified several factors for the agency’s cost overruns, including a belief that “projects that fail to meet cost and schedule goals will receive additional funding and that subsequent scientific and technological success will overshadow any budgetary and schedule problems.”

NASA is trying to change its reputation so Congress won’t tighten the purse strings. Because of the James Webb debacle, for example, the agency has taken steps like increasing budget reserves to meet unexpected funding needs for complicated missions.

But as helpful as those changes have been, they probably aren’t enough to guarantee a planned mission to Europa, the moon of Jupiter which many scientists believe harbors the ingredients for life, or an even more ambitious decade-plus trek out to Uranus or Neptune. Indeed, like other federal agencies that are pressed to justify their size and cost, NASA may face fiscal challenges in coming years. The U.S. should ensure that ambitious missions continue to have a chance.

First, there needs to be a change in how NASA is led. In 2015, Representative John Culberson of Texas noted that NASA had spent more than $20 billion on cancelled programs over the last 20 years — enough for almost six Cassini missions! — thanks to the changing priorities of new presidential administrations and Congress. To fix the problem, he proposed giving the NASA administrator a politically insulated 10-year term and the authority to contract space missions over years, rather than through the annual contracts that Congress currently allows. The stability associated with such long-term planning would preserve complicated programs and offer significant savings. Representative James Bridenstine, President Trump’s nominee for NASA administrator, has offered up some similar proposals, and they deserve serious consideration.

Meanwhile, NASA’s planning process — historically dominated by science — must become more sensitive to budget concerns. In an August report, the National Academies of Sciences, Engineering, and Medicine recommended that NASA’s long-term mission planning identify what specific scientific objectives are most desirable and feasible at specific levels of funding. If and when budgets shrink, such options can provide mission planners flexibility to “de-scope” a mission — aiming for a more modest approach, rather than scrapping the project entirely. NASA and its supporters should heed the academies’ advice.

These tiers of ambition would not only prepare NASA to scale back when needed, but also would keep the agency ready to scale up when possible. In recent years new technologies like low-cost satellites the size of a Rubik’s cube — known as CubeSats — have opened up new modes of budget-conscious exploration. For example, in August NASA approved funding to study a CubeSat mission to Venus’s atmosphere. Such a mission would be cheaper and less ambitious than a large-scale mission to the outer solar system, but it would help resolve scientific questions and possibly point the way to doing expensive large-scale missions more cheaply.

Indeed, scientists recently proposed using a CubeSat as a low-cost probe to sense dust and radiation during NASA’s planned, likely multi-billion-dollar, Europa mission. Such a probe could cut costs or — by virtue of its low cost — expand the mission’s scope. Either way, the flexibility improves the odds that NASA can get to where it wants to go.

Of course these measures won’t eliminate all of the financial risks associated with exploration, especially when the budgets are already big and the goals are billions of miles away. But they can help NASA control costs while ensuring that future generations will benefit from their own Cassinis.

Adam Minter is a Bloomberg View columnist. He is the author of “Junkyard Planet: Travels in the Billion-Dollar Trash Trade.”