The U.S. Air Force’s budget request, which calls for spending $9.8 million on unclassified space-related activities next year — $500 million more than this year — is about as good as could be expected under the circumstances.

At 5 percent, the proposed growth rate for space falls below the 7-percent spending increase being sought for the U.S. Department of Defense overall. But given the military’s problems with budget-busting space programs in the last several years, a more ambitious plan likely would have been dead on arrival at Capitol Hill.

Congress has been preaching conservatism in space, and that seems to be the overriding theme of the Air Force’s spending plan. The service continues to push hard for the two development programs about which lawmakers have voiced some of their strongest reservations — the Transformational Satellite (T-Sat) Communications System and Space Radar — but has taken what officials say is a less-risky technology tack on both.

No major programs have been dropped, and the budget even includes funds for a brand new one: the Alternate Infrared Satellite System, the successor to the hopelessly fouled-up Space Based Infrared System missile warning effort.

One source of disappointment in the budget is the Air Force’s $36 million request for Operationally Responsive Space, a decrease of nearly $3 million from the current-year funding level. Perhaps this was done in anticipation that Congress will add money to that account. As drawbacks go, this is a minor one, especially since the Operationally Response Space effort has demonstrated little so far other than that it remains as difficult as ever to field a new launcher capability.

There is a broader question, however, which lawmakers and staffers need to keep in the front of their minds as they kick the tires on the budget request: is the Air Force sacrificing too much in terms of system capabilities to make its numbers add up?

The service has pledged to front-load its space programs with the systems engineering work that experts agree is necessary to prevent costly surprises from springing up after a design is complete. In addition, it has adopted a supposedly more-reliable standard for estimating program costs. This so-called 80-20 standard means there is an 80-percent likelihood that cost estimates for a program are accurate.

The change was long overdue — the previous 50-50 standard was essentially useless as a program- and portfolio-management tool, not to mention comically mislabeled given the Air Force’s terrible recent track record on meeting cost projections.

Common sense says that better design-phase systems engineering and more realistic cost estimates would tend to inflate the budgets of new satellite development programs. This is not reflected in the 2007 spending plan, however, suggesting that the Air Force is counting on its so-called spiral development strategy to keep design costs in check.

Spiral development is military procurement-speak for deploying new system capabilities and technologies incrementally, rather than all at once. On one hand, it has a certain appeal — one of Congress’ main concerns with the T-Sat program, for example, was that the Air Force was courting trouble by attempting to achieve too many technological breakthroughs at once.

But taken to its logical extreme, budget- and schedule-driven spiral development leads to the fielding of new systems that differ from their predecessors in name only. One could envision the initial T-Sat satellites, for example, devolving to the point where they offer little qualitative improvement over the Advanced Extremely High Frequency satellites.

On Space Radar, plans now call for an initial batch of satellites whose ability to operate over areas obscured by darkness — a key attribute of radar sensors — would be limited to save the costs of qualifying advanced battery and solar-cell technologies for space.

That approach makes sense only if the initial satellites represent a step up from current capabilities; and if the Air Force can outline a credible, funded plan for qualifying the new technologies and getting them aboard the next round of satellites. Otherwise, the case for Space Radar as a moving-target surveillance tool — a truly new capability that has long been the program’s biggest selling point — is substantially diluted.

The Pentagon’s poster child for spiral development is, of course, the Ground-based Midcourse Defense System, the U.S. territorial missile shield now being deployed in Alaska and California. Critics of the program have argued that spiral development is not so much a strategy as it is a boilerplate justification for deploying a system that is not yet ready for operational use. Recent test failures suggest that this criticism is not without merit. The latest test, whose success was trumpeted by the Missile Defense Agency and its contractors, was little more than a basic rocket launch, an illustration of how lowered expectations can warp one’s sense of progress.

The Air Force’s newfound sense of caution on space development was adopted largely in response to the warning signals flashed from Capitol Hill. It is now up to Congress to make sure that caution does not become the enemy of progress in space.