Were you wondering what the last remaining sticking point was inside the U.S.-Russian negotiations over a START follow-on treaty? Well, as it turns out, the issue is ... rocket science, and, more specifically, telemetry data.

What's telemetry, you ask? In this context, it's the assurance that if either side tests a missile, the detailed data about the test would be instantly available in real time to the other side. That assurance was part of the original START treaty, which expired in December, and the Obama administration wants similar language in the new treaty but the Russians are resisting.

Many insiders see the telemetry issue as somewhat of a red herring. New verification and tracking technologies, most of them classified, can provide the same capability without the Russians directly providing the data. But a lack of a provision on telemetry could complicate Senate ratification of START.

"For the United States, the politics matter because certain senators will go nuts without access to the data," said Travis Sharp, a nonproliferation expert at the Center for a New American Security. "Substantively, however, the United States may not need the same level of information as negotiated under START I, particularly because ‘New START' will likely have streamlined counting and verification rules and technological advancements allow us to get the data in other ways. On the other hand, Russia politically doesn't want our noses in their business and substantively is hesitant to give up too much information."

A diplomatic source told The Cable that the Russians are bargaining for access to telemetry data for U.S. missile defense tests in exchange for giving America telemetry data on their offensive missile tests. That's only their latest attempt to link START and missile defense, another potential problem for Senate ratification.

"Everybody knows that telemetry is bullshit [substantively], but it's become an issue nonetheless," the source explained. Russian Prime Minister Vladimir Putin has been trying to link missile defense to START recently and this is one example.

"If we want to retain the balance, we have to establish an exchange of information: Let the U.S. partners provide us information on [their] missile defense while we will give them information on [our] offensive weapons," Mr. Putin said last month. The Russians are also pushing to have an acknowledgment of the relationship of missile defense to offensive weapons in the main body of the START agreement text, while the U.S. wants it in the preamble, the source said.

A very carefully worded acknowledgement of the link was included in the joint understanding Obama and Russian President Dmitry Medvedev signed in July.

Under Secretary of State Ellen Tauscher talked about the telemetry issue Wednesday morning and said that the "expectation has always been" that telemetry, which is very important to the Pentagon, would be included in the new treaty as "part of confidence building and to reassure both sides there won't be any sort of surprises."

She confirmed that telemetry was among the final issues on the table but portrayed it as not a major substantive issue.

"Telemetry is one of the last things to be done, but it's not a big issue or the most important thing," she said, adding that sometimes the fact that certain provisions were in a previous treaty creates the expectation that they will remain in the next treaty.

She implied, but didn't state explicitly, that the U.S. was not going to agree to share missile-defense data in exchange for the Russians agreeing to share their offensive telemetry data.

"This agreement is about strategic offensive systems. Missile defense is a defense system," she said.

One GOP Senate aide disputed Tauscher's assertion that telemetry isn't a major issue. The U.S. technologies that are said to compensate for a lack of telemetry data aren't necessarily 100 percent effective, the aide said, adding that not having access to Russia's data would add burden to the U.S. defense community that it didn't have before. "Why should we spend our resources on this when telemetry data gives us that capability for free?," he asked.

Assistant Secretary of State Rose Gottemoeller is in Moscow now and could head back to Geneva later this month with her team to try to complete the agreement. Jan. 25 is the date being bandied about for the resumption of talks, but the Russians have yet to agree to return to the table.

The administration needs to get it ratified by the time the Non-Proliferation Treaty review conference begins in May.