On Friday, the Navy quietly released a "market survey" asking the big defense contractors for their "candidate[s]" for "strike fighter aircraft" in the decades to come. Which is a little weird, considering the Pentagon is currently spending a trillion dollars on just such an aircraft: the troubled Joint Strike Fighter.

The stealthy F-35 Joint Strike Fighter (JSF) is supposed to one day make up 90 percent or more of America's combat aviation power. But the program has been hit with all kinds of expensive technical glitches and delays. So the Navy has long hedged against the giant JSF bet by buying more of its beloved F/A-18 Super Hornet; that way, the Navy can keep flying modern fighters, even if the JSFs slip. With this "market survey," the Navy appears to be making a second hedge: a Son of the Super Hornet – one that would come online after the F/A-18s are retired in the 2030s – just in case the JSF flames out entirely.

"That's absolutely not the right interpretation," says Capt. Frank Morley, the Navy's program manager for the Super Hornet and its cousin, the EA-18 jamming Growler. But if the Son of the Super Hornet isn't a hedge against the JSF becoming too expensive for the cash-strapped military, then the aircraft carrier decks of the future may be stocked with redundant planes.

After the Super Hornets retire, the Navy wants "a multi-role strike capability" that can fly from a carrier, according to the "market survey" that the Navy released Friday. Some of its primary missions: "air warfare (AW), strike warfare (STW), surface warfare (SUW), and close air support (CAS)."

And that sounds suspiciously like the role that the Navy's version of the JSF is supposed to play. That plane, already the most expensive weapons program in the history of mankind, is in serious budget trouble. In addition to newly discovered design flaws, the Government Accountability Office last month found additional problems with its software and safety systems. The military wants the F-35 to ultimately replace nearly every tactical fixed-wing aircraft the Navy, Marines and Air Force fly, but the admiral in charge of the program has backed off the 2018 estimate for when the plane is expected to enter the air fleet.

So the Navy has bought more Super Hornets as delays plague the JSF. At the Navy's annual Sea Air Space convention, Morley self-congratulated by noting that the Super Hornet is "on time, on cost, and on schedule."

But the Son of the Super Hornet, the Navy's survey swears, isn't supposed to be a backup in case the JSF fails. Instead, it will be a "complementary ... asset to the F-35C and an unmanned persistent intelligence, surveillance, and reconnaissance (ISR) vehicle with precision strike capability." In other words, it'll fly in a carrier air wing alongside the JSF and the Navy's future carrier-based drone, currently known as the X-47B.

But if so, that raises a question of redundancy. Both the JSF and the post-Super Hornet plane would be performing very similar manned strike missions. (Although the survey doesn't suggest the post-Super Hornet will need to be stealthy, a central asset of the JSF.)

Morley strongly denies that the Son of the Super Hornet poses a threat to the JSF or will replicate its missions. "We are an all-F-18 fleet today," Morley tells Danger Room. "In that 2020-2030 time frame, those decades, we intend to be a Super Hornet-JSF fleet. And then those Super Hornets are going to be aging out, those earlier ones, and we need to be a JSF-and-something-else fleet."

But then what will the something else be? What will keep the Son of Super Hornet from redundancy with the JSF?

"Don't know," Morley concedes. "That's the point of the whole analysis. What do we need it to do? What will the threat be then? What will JSF be able to cover? What additional capabilities might we need? That's all the stuff we're starting to look at now."

Other Navy officials are just as emphatic. "This is prudent planning on the Navy's part," argues Rob Koon, a spokesman for the Navy's tactical aircraft program. "Every airframe needs to have a follow-on replacement." His boss, Marcia Hart, adds, "There has to be something after the Super Hornet."

There's a sense in which that's correct. The program for the Super Hornet replacement, officially called the FA-XX and announced last week in the Pentagon's 30-year aviation plan, might not necessarily yield a new aircraft. It could. But as the program goes on, the brass might decide that the JSF in fact does what the Navy needs a post-Super Hornet plane to do. Or it might even decide that the post-X-47B is a better substitute.

Put another way, it might be best to think of the FA-XX as a placeholder constant, like in physics or math, necessary for making a formula operate, rather than a definite thing on its own.

But there's also a chance that the post-Super Hornet will turn out to be exactly what it sounds like: another strike jet, designed for the seaborne attack missions that the Navy's F-35 variant is supposed to perform. Even 20 years from now, Super Hornet's son could be picking up the JSF's slack.