Billions of dollars in defense funding hang in the balance for big-ticket items such as the F-35 fighter, the size of the Army and missile defense as armed services committee members convene a conference to hammer out a final version for the National Defense Authorization Act this month.

The talks will determine the final number of troops, aircraft, and ships, as well as an even more controversial question — whether a new Space Corps will take over military operations in space.

Each chamber has overwhelmingly passed its version of the NDAA along with its own vision for the military over the next year. Committee chairmen Sen. John McCain, R-Ariz., and Rep. Mac Thornberry, R-Texas, and the top two House and Senate Armed Services Democrats will be tasked with reconciling the differences and sending up a final bill for Congress to pass.

The good news for negotiators: Those two visions for defense are significantly similar.

"Versus other years there is not as many issues, so I think we can [reach agreement] but it just takes some time to work through it," Thornberry told the Washington Examiner.

This year, both include a $30-40 billion hike over President Trump's requested budget. The House NDAA calls for $632 billion for base defense spending and $65 billion in war funding, while the Senate version top line is $640 billion with $60 billion for the war fund, called overseas contingency operations.

"The question is how do we resolve that and what is the top line" dollar amount, Sen. Jack Reed, D-R.I., the Armed Services ranking member, told the Washington Examiner.

But the two bills are also divided on crucial specifics such as the total number of F-35s to buy, the size of the Army, how much to pump into missile defense in the face of North Korea, and whether to wrest control of space from the Air Force.

Thornberry's committee wrote the House-passed NDAA and proposed buying 87 Lockheed Martin F-35s, which is 17 more than what Trump has requested.

But the Senate Armed Services Committee under McCain went higher and budgeted 94 of the aircraft, about two thirds of which would go to the Air Force. The high-tech fighters cost $95-123 million each, depending on the variant.

The size of the Army is also a big point of difference in the two bills. The House is eager to start adding 17,000 soldiers to the current force of just over 1 million active-duty, National Guard, and reserve soldiers.

But the Senate was more skeptical that the service would be able to grow that much after already adding about 28,000 soldiers this year. Its NDAA calls for an increase of 6,000.

Meanwhile, there were new calls for boosts to missile defense as North Korea has ramped up its ballistic missile and nuclear weapons testing. Defense Secretary Jim Mattis confirmed last week that the Pentagon wants to shift more than $400 million of its budget toward the effort.

The House NDAA proposes a $2.5 billion increase for missile defense, which includes buying more Raytheon Standard Missile-3 Block IB ship-based interceptors as well as Lockheed Martin's Terminal High Altitude Area Defense and Raytheon Patriot missile interceptor systems.

The Senate plan, spearheaded by Sen. Dan Sullivan, R-Alaska, is a $630 million boost for the Missile Defense Agency above what Trump requested. It is aimed at strengthening homeland, regional, and space missile defenses, and would add up to 28 ground-based interceptors as well as put $28 million into developing space-based missile sensors.

McCain, in his gruff way, appeared optimistic about working out the differences in the House-Senate conference. Staff in both chambers have been working informally on the negotiations, and formal talks were expected to begin soon.

"We've got a lot of concerns, and I'm sure we'll get them resolved. We do every year," McCain told the Washington Examiner. "There [are] always differences; we always work them out."

Still, Space Corps is one NDAA issue in particular causing deep divisions between the House and Senate and is most likely to start a political tangle during the conference.

The House added a controversial measure to its bill this summer that would create a separate military service within the Air Force Department to oversee space operations in what is fast becoming an important and competitive domain for warfare.

The Air Force handles the lion's share of such work, but an Armed Services subcommittee chaired by Rep. Mike Rogers, R-Ala., added the legislation over concerns it is mismanaging space while the U.S. is falling behind.

But the Senate unanimously agreed in September to add a NDAA amendment barring the creation of a Space Corps. The Air Force has also strongly opposed the move, saying it would create unneeded bureaucracy.

"They really have not immersed themselves in this issue as we have, as they come to learn more about it they are going to arrive at the same place we are," Rogers told the Washington Examiner. "It's going to be a little period of education to make sure they get up to speed on the stuff the House has been focused on, but I'm optimistic that we'll get there."

Sen. Bill Nelson, D-Fla., an Armed Services Committee member who flew on the Space Shuttle in the 1980s, sponsored the amendment barring a Space Corps and said the House's idea will wash out during conference negotiations.

"There will be no Space Corps," Nelson told the Washington Examiner. "Why change something that is working? It is doing very well right now with the U.S. Air Force leading it."

The conference committee is expected to wrap up negotiations and produce a final NDAA bill by December, when the current stopgap federal budget ends and Congress is faced with passing the 2018 annual budget.

Once the dust has settled on the NDAA, a major budgetary hurdle still remains for the House and Senate plans for a hike in military funding. The Budget Control Act limits 2018 base defense spending to $549 billion, as well as imposing caps on non-defense spending important to many Democrats.

Any final NDAA could be in danger unless a deeply divided Congress can reach some agreement to lift the spending caps and pass appropriations bills to fund the bill's defense priorities before Christmas.

"I think the [NDAA] bills overall are fine. I think the biggest priority is resolving the money, I mean it's $91 billion over the caps with no proposal to raise the caps, so we've got to figure out the money," Rep. Adam Smith, D-Wash., the Armed Services ranking member, told the Washington Examiner.