America's airspace is crossed with invisible tracks, lanes with designated entrance and exit points that warplanes use for aerial refueling. Our track is No. 16, heading east.

I'm sitting next to pilot Capt. Timothy "Scar" Sullivan inside the cockpit of a B-2 Spirit stealth bomber 27,000 feet over mid-Missouri. We're en route to meet the KC-135 Stratotankers that will top off our fuel tanks in a 450-mph hookup. "In 6 minutes we'll see tankers," Scar says through the headphones in my helmet; without an intercom, his words would be drowned out by the whine of the engines of the bomber, the Spirit of Georgia.

Nearly as many people have been to space as have flown in a B-2. More than 530 people have traveled off-planet; as of my flight in late 2012 only 543 people have been airborne in the cockpit of a Spirit. Upon landing I'll become No. 544.

The cockpit of a stealth bomber is built for two pilots, sitting side by side. The dashboard's digital graphics were state-of-the-art in the 1980s, when Northrop Grumman designed the aircraft. There's a crude toilet—a stainless-steel bowl, no walls or dividers—behind the right seat, not too far from a bank of classified communications servers. Also behind the two seats is a 6-foot flat space where pilots can set up a cot to sleep, although many just stretch out on the floor. Missions in the B-2 often stretch into double-digit flight hours. "I can fall right to sleep anywhere," Scar says. "Except, for some reason, the cockpit of a B-2."

Only 543 people have been airborne in the cockpit of a Spirit. Upon landing I'll become No. 544.

At 10 miles, 136-foot-long Stratotankers are just specks. The outlines of the aircraft, operated by the National Guard's 128th Air Refueling Wing, become more distinct as we close.

What follows is a coordinated dance routine. The airplane in need of fuel flies directly behind and just below the tanker. The KC-135 extends a telescoping fueling boom; the fuel nozzle at the end fits into a small hole in the receiving bomber. The fuel pumps as the conjoined aircraft fly in harmony.

This seemed like a rational plan when I heard it during the preflight briefing. But as we creep closer, the KC-135 looming through the windshield, the whole operation reveals itself to be crazy. There is something totally illogical about edging to within 12 feet of another airplane and then holding that position for minute after minute. It makes your brain freeze up.

I can see every slight adjustment as Scar steadies the Spirit of Georgia, edging to within spitting distance of the Stratotanker. The face of the boom operator is staring at us from a small window in the rear of the KC-135. Happily, the air gets less choppy as we close the gap. We're near enough that the B-2 is sharing the bubble of displaced air, the bow wave, that envelops the Stratotanker.

The B-2's fuel port is on top of the fuselage, so Scar can't tell how close the boom is to the bomber's receptacle. He's watching lights under the tanker plane's fuselage that tell him in which direction to move. The frame of the windows is another indicator—he knows what the correct position looks like from his vantage point. Once the connection is made, a dashboard screen says LATCH and thousands of gallons of fuel flow.

The B-2 can fly more than 6000 miles on a full tank, but a trip from Missouri to the Middle East still requires several aerial refuels each way. I ask Scar what they do when they have to connect to tankers in turbulence or foul weather. "We just have to do it," he says, with more resignation than bravado. "I mean, we need the gas."

The B-2 is rightly regarded as the most advanced bomber in the world, but there is plenty of room for improvement. I ask Scar over the cockpit headset what he'd like to see in a new bomber. "Longer legs," he says. "More time between refueling."

New engines and lighter materials could give future pilots the extended range Scar is seeking—but that kind of retrofit can't easily be installed in the B-2's old bones. The cat-and-mouse world of military aviation never stands still, and the B-2 is not getting any younger.

Once and Future Bomber

No one knows more about operating a stealth-bomber fleet than the personnel at Whiteman Air Force Base in Missouri, which makes them de facto experts on the future of long-range strike aircraft. The topic is not hypothetical: Last year the Obama administration budgeted more than $6 billion through 2017 to develop a new long-range strike aircraft. The effort to build America's next stealth bomber, due for delivery around 2025, has already begun.

It seems odd that the Pentagon is launching an expensive project to build a new stealth warplane as the federal government grapples with defense budget cuts. Air Force leadership concedes that dwindling funds will certainly delay the new aircraft, but it is standing by its intention to move forward. "Long term, we're committed to the long-range strike bomber," Air Force Secretary Michael Donley said early this year.

"I would venture to say that B-2s keep a lot of people awake at night."

A $6 billion investment might seem like a lot, but experienced aerospace analysts like Richard Aboulafia, vice president at Teal Group, say it won't get a bomber program too far. "Somehow we have to have the sustained strategic need and political will to shell out $120 billion over a dozen years," he says. "It's $50 billion just for showing up. And that's for a prototype or two."

But such incremental funding is a popular Pentagon strategy for advancing expensive programs. "You start funding a research and development program, but you don't move forward too aggressively," Aboulafia says. "You fund it a billion or two a year so that you can get a running start as the strategic situation evolves."

As the war in Afghanistan winds down, America is indeed shifting its strategic posture. Instead of preparing for immediate conflict against low-tech enemies like insurgents, the Pentagon is again focusing on facing nation-states with sophisticated hardware. Strategists call these enemies peer or near-peer adversaries. The Obama administration announced in 2011 that the Pentagon would focus more attention on Asia, a "pivot to the Pacific" that pits U.S. strategy against China, the most potent near-peer adversary in the world.

This strategic shift breathed new life into the stealth bomber program, which Secretary of Defense Robert Gates canceled in 2009. A long-range strike bomber can take off far outside the range of China's cruise and ballistic missiles, and a stealthy one can defeat that nation's increasingly advanced radar and antiaircraft weapons. Also, a bomber can fly home to rearm in less time than it takes a submarine or surface vessel to return to port to reload, making it more useful in long military campaigns.

The struggle between China's (and others') air-defense weaponeers and the U.S. Air Force is fought in aircraft hangars. To the untrained eye, the surface of a B-2 looks black. But Staff Sgt. Jesse Phillips, a young airman who has spent his whole career on B-2 maintenance at Whiteman, sees a complex pattern. Some materials absorb radar waves, while others are designed to direct the returns across the fuselage and toward the back of the jet so the enemy sees no signal. "We are in constant contact with engineers at Tinker Air Force Base [home of a major air logistics center in Oklahoma] to get new procedures or changes in tech data," Phillips says. "We have to be one step ahead since someone is always trying to defeat our radar-beating capabilities." The longer the B-2 remains in the fleet, the harder it will be for Phillips to stay ahead of an opponent.

The peer-adversary rationale for a new bomber is lost on many critics, especially among the disarmament community. William Hartung, director, Arms and Security Project at the Center for International Policy, summed up many detractors' attitudes in February when he called for "eliminating or scaling back projects, like a new nuclear bomber … whose capabilities are better attuned to cold war."

The risk of an overwhelming, surprise nuclear missile attack is now almost zero, making a nuclear-capable bomber less of a priority. However, having nukes at the ready could prevent a conventional war from escalating, says Eli Jacobs, a program coordinator for the Center for Strategic and International Studies. "The side that is losing may feel compelled to initiate limited nuclear strikes in order to terminate the conflict," he wrote on CSIS's website in 2012. Having a nuclear retaliation at the ready makes this catastrophic choice less likely, he argues.

But the key demand of America's new bomber is not an ability to drop nukes, but the delivery of other weapons. The Air Force indicated this priority last year when officials announced that the new aircraft will first be readied for nonnuclear missions. In contrast, the Pentagon readied the B-2 for nuclear bombs years before conventional munitions.

Brig. Gen. Thomas Bussiere, commander of the 509th Bomb Wing at Whiteman, knows his fleet of 20 airplanes is the tool of choice to influence—i.e., threaten—rogue regimes. "I would venture to say that B-2s keep a lot of people awake at night," he says.

My six-foot-five frame is too tall to safely fit int the cockpit, so the wing commander gives me a waiver to fly. However, if forced to eject, my legs would hit the console.

Penetration Mode

B-2 pilots don't drop ordnance with bombsights and trigger pulls, but with buttons and keystrokes. The bomber calculates the time of release at the particular airspeed, and automatically opens the bomb-bay doors to release the weapons from either a rotary launcher or a bomb rack. Published reports say the B-2 can deliver 80 unguided bombs to within 500 feet of their target. The B-2 can also carry up to 16 Joint Direct Attack Munitions, 2000-pound bombs converted into guided weapons by adding strakes and fins that adjust the weapons' course. Explosive bolts detonate during a JDAM release. "You can feel the jet punch them out," Scar says.

The B-2's abilities were on display during the one-night attack on Libya in March 2011. "We struck 45 of the 48 planned targets with precision munitions," Lt. Gen. James Kowalski, head of the Air Force's Global Strike Command, tells PM. "The targets were all hardened aircraft shelters. And that's where [Muammar] Gaddafi found out that his shelters were not hardened and they weren't really shelters."

There's a button on the B-2 console, just larger than a laptop key, that says PEN. It stands for Penetration. When a B-2 pilot pushes it, the airplane readies itself to enter defended airspace by retracting protruding antennas, restricting communications emissions, and reducing other telltales of the bomber's presence.

Being a stealth warplane means more than having the right shape and radar-baffling materials. It's also a strategy. For example, the B-2 can be more easily spotted on radar from the sides but is a lot harder to detect head-on. So B-2 pilots plan an attack that keeps the angles in their favor, and that means jagged flight paths. Scar calls this spike management.

The lesson is clear: No airplane is truly invisible on a radar screen, so the less time spent in defended airspace, the better. But the B-2 isn't capable of great bursts of speed. The next stealth bombers will have engines that operate in two modes: one for fuel economy and another for high-speed acceleration. (See "Inside the Future Engine," opposite.)

While in the air, Scar demonstrates how the B-2 can capture an image of the ground below by reflecting a radar pulse off the ground. When I say that this ability makes the bomber a de facto reconnaissance airplane, he shoots me a disgusted look. I've hit the nerve of a larger issue.

A bomber that can defeat enemy radar, Pentagon planners reason, could also loiter in hostile airspace and gather video, intercept communications, and serve as a radio relay for troops below. But this idea is inherently distasteful to the airmen of Whiteman. When I ask Scar what he thinks about using the future bomber to collect intelligence, he offers a politely skeptical question about Air Force planners: "Do they want a jack-of-all-trades, master of none?"

It's a great question—and the Pentagon has not come up with the answer. "That remains classified," says Kowalski. "And some of that, frankly, is not quite fleshed out yet."

The author inside the B-2

Spirit 544 on the Stick

Out of nowhere, Scar asks me over the intercom, "Ready to fly?" I hesitate before saying yes. There's a second B-2 flying formation with us and looking like a flying saucer as it slices through clouds a scant 4 miles ahead. With some exceptionally bad luck, I could endanger one-tenth of America's long-range strike fleet and cause a subtle but real rebalance of global military power. It's a reminder of the vital national security niche these warplanes fill, and the high stakes involved in creating their replacement.

"Okay, you have the jet."

But Scar isn't worried. The B-2 pilot has confidence in his ability to recover from anything I can possibly do at this altitude. He's also rated as an instructor, so he's one of the few in the Air Force trained to operate the B-2 Spirit alone.

"Okay, you have the jet," he says, relinquishing control. I place one suddenly damp left hand on the throttle and the right on the stick. "Take her to the other side," Scar says, wanting me to steer the Spirit of Georgia so it crosses behind the leading B-2.

I gingerly push the stick left and the horizon tilts. "You can be more aggressive," the pilot says. "You're not gonna break her." This time I push the stick firmly and the bomber casually edges left. Maneuvers in an aircraft built for endurance happen slowly and deliberately. The Spirit of Georgia is responsive and has a top speed of 600 mph, but it's not what you'd call peppy.

We smoothly swing behind the other B-2. The turn complete, I straighten the Spirit so it's flying even with the horizon and increase speed to catch up with the other bomber. My adrenaline levels off. For this fleeting moment, it's true. I have the jet.