SpaceX, Elon Musk’s rocket and satellite internet company, has received billions of dollars in federal contracts over its more than two-decade existence.

But SpaceX has most likely paid little to no federal income taxes since its founding in 2002 and has privately told investors that it may never have to pay any, according to internal company documents reviewed by The New York Times.

The rocket maker’s finances have long been secret because the company is privately held. But the documents reviewed by The Times show that SpaceX can seize on a legal tax benefit that allows it to use the more than $5 billion in losses it racked up by late 2021 to offset paying future taxable income. President Trump made a change in 2017, during his first term, that eliminated the tax benefit’s expiration date for all companies. For SpaceX, that means that nearly $3 billion of its losses can be indefinitely applied against future taxable income.

Tax experts consulted by The Times said that not having to pay $5 billion in federal income taxes was substantial and notable for a company that has relied on contracts with the U.S. government to an unusual degree. SpaceX works closely with the Pentagon, NASA and other agencies, giving it a vital role in national security. In 2020, federal contracts generated almost 84 percent of the rocket maker’s revenue, according to the documents, a figure that had not been previously reported.

Larger tech companies — including some that have taken advantage of the tax benefit — often pay billions in federal income taxes. Microsoft, for one, said it expected to pay $14.1 billion in federal income taxes in its last fiscal year.

SpaceX can use the tax benefit even if its business thrives. By one measure of corporate profitability, the company had roughly $5 billion in earnings from its core operations last year, up from $2.6 billion in 2023, according to what the company has privately told some stakeholders.

Danielle Brian, the executive director of the Project on Government Oversight, a group that investigates corruption and waste in the government, said the tax benefit had historically been aimed at encouraging companies to stay in business during difficult times.

It was “quaint” that SpaceX was using it, she said, as it “was clearly not intended for a company doing so well.”

Mr. Musk has built SpaceX into one of the world’s most influential companies, which dominates the space industry through its rockets and its Starlink satellite internet service. It has been a jewel in the crown of his business empire and an essential source of his wealth and power, along with his electric vehicle company, Tesla. It has also given Mr. Musk a perch on the world stage, allowing him to weigh in on geopolitics.

Like many tech start-ups, SpaceX lost money as it plowed billions of dollars into building its business. Uber, Amazon, Tesla and other tech firms were also not profitable for years. As SpaceX has grown, the firm has been valued at more than $350 billion, crowning it one of the world’s most valuable private companies, according to the start-up tracker PitchBook.

Several news organizations have reported on aspects of SpaceX’s finances, which the company discloses to its investors and other stakeholders. But the documents reviewed by The Times — including income statements and balance sheets covering 23 years — offered new insight into SpaceX’s revenue sources, investors and taxes.

SpaceX appears to have paid some income taxes over the years, though likely not to the federal government, according to the documents. In one document, the company said it expected to pay $483,000 in income tax to foreign governments and $78,000 in state income tax in 2021. Separately, it reported paying $6,000 for income taxes in 2020 and 2021, but did not disclose if the payments were for federal, state or local governments.

SpaceX and Mr. Musk did not respond to requests for comment. Mr. Musk has often trumpeted SpaceX’s role in carrying out missions for NASA and other agencies. In June, he proudly posted on social media that the company had reached a milestone, as its “commercial revenue from space will exceed the entire budget of @NASA next year.”

Mr. Musk, who left his role as a close adviser to Mr. Trump in late May, founded SpaceX with the goal of shuttling humans to Mars and colonizing the Red Planet. He owned 44 percent of the company as of 2022, according to the documents.

Getting to Mars is an expensive endeavor, and SpaceX’s losses piled up from the start. In its first year of operation in 2002, the company lost about $4 million, the documents show. The next year, it lost $14.5 million. Those losses ballooned in subsequent years, reaching $341 million in 2020. In 2021, it lost $968 million.

All the while, Mr. Musk and Gwynne Shotwell, the president of SpaceX, pushed the company to grow. It began developing and testing Starship, a reusable rocket that Mr. Musk hopes will one day reach Mars.

By the end of 2021, SpaceX had accumulated almost $5.4 billion in tax losses, according to the most recent figure in the documents. Those losses generated the tax benefit, known as a net operating loss carryforward. It enables SpaceX to avoid federal income taxes on an equivalent amount of future taxable income. The benefit is available to all companies, including start-ups that lose money for years before turning a profit.

In one document, SpaceX told investors that it was “more likely than not that some portion or all of the deferred tax assets will not be realized,” meaning it might never pay taxes. The company cited, among other things, its past losses. Such language can be common for companies with a history of losses, and this outlook can be revised if their finances improve, said Robert Willens, an accounting analyst who runs his own firm.

SpaceX also benefited from a sweeping package of tax cuts that Mr. Trump signed in 2017. One change was eliminating a 20-year limit on the use of tax-loss carryforwards, meaning that losses generated after 2017 no longer expired. That change allows SpaceX to apply nearly $3 billion in carryforwards indefinitely.

In addition, the company had $227 million in carryforwards that could offset state income taxes, the documents show. It had more than $1.1 billion in other federal and state tax credits.

“Given the size of its net operating loss, the company almost surely didn’t pay any federal tax for years,” said Gregg Polsky, who teaches tax law at New York University School of Law. “And it’s so large, it’s unlikely it has paid taxes even if it has had positive taxable income in recent years.”

The tax benefits may have come in handy in recent years as SpaceX’s finances have improved, at least by one measure. The company has privately said its earnings before interest, taxes, depreciation and amortization nearly doubled to roughly $5 billion last year from 2023. That figure, known as EBITDA, is one way of measuring corporate profits but is not the same as the bottom line and does not mean that SpaceX is paying taxes.

Starting in the mid-2000s, SpaceX began landing hundreds of federal contracts, including one with NASA to deliver cargo to the International Space Station and another with a U.S. intelligence agency for $1.8 billion to provide spy satellites. Some contracts are expected to generate substantial revenue for years, according to the documents.

The documents, reviewed by The Times, provide the first insights into how heavily SpaceX depends on federal contracts. In 2020, they generated about $1.4 billion, or 83.8 percent, of the company’s total revenue that year. The next year, federal contracts brought in about $1.7 billion, or 76 percent, of the total revenue, the documents show.

Mr. Musk said in June that he expected SpaceX’s revenue to reach $15.5 billion this year. That is up from about $7.4 billion in 2023, the documents show. (Revenue includes sales of the company’s products.)

A big part of that growth stems from Starlink, which has six million subscribers, according to the company. The documents showed that SpaceX told investors that Starlink had 2.5 million users in 2023 and generated roughly $8 billion in revenue last year, more than double the previous year’s revenue and outpacing SpaceX’s rocket division in both years.

The documents do not include SpaceX’s net profits or losses for the past two years. The Wall Street Journal reported that the company generated $55 million in profit on $1.5 billion in revenue in the first quarter of 2023. Companies can simultaneously report profits to shareholders and tax losses to the I.R.S. in any given year because of the differences in how certain items are treated.

To fund SpaceX, Mr. Musk has relied on longtime investors like Fidelity and Google and friends like Antonio Gracias, who is also a SpaceX board member. The documents reviewed by The Times identified others who had not been publicly associated with the company.

A company called AI RT SPX Holdings is listed as an investor on a 2020 document. It appears to be affiliated with Access Industries, an investment firm founded by Len Blavatnik, the billionaire investor who was born in Ukraine and raised in Moscow and made his fortune in the privatization era in the 1990s after the Soviet Union collapsed. Now a British and American citizen, he has become a prolific philanthropist and investor in American and European companies.

The document was signed by two Access executives, including Mr. Blavatnik’s brother Alex Blavatnik. It is unclear whether Access Industries remains a SpaceX investor. Through a spokeswoman, Mr. Blavatnik declined to comment.

Chris Anderson, the entrepreneur who is the head of the organization behind TED Talks, appears to have invested in SpaceX through a company called Excalbians. He did not respond to requests for comment. Mr. Musk has delivered several TED Talks in the past.