Orbital Sciences and Space Exploration Technologies are to benefit from millions of dollars more than originally agreed under their NASA-funded Commercial Transportation Space Act agreements.
NASA is spending $24 million on launch and test infrastructure, including at its Wallops flight facility where Orbital will launch its Taurus II rocket and Kennedy Space Center, where SpaceX will operate its Falcon 9 booster.
NASA declines to say how much investment the two companies' launch sites are getting because it "may be procurement sensitive information".
The funding comes from the American Recovery and Reinvestment Act (ARRA) and some of the $24 million is being spent on John C Stennis Center testing facilities.
Orbital could not provide investment figures for its site and construction company RS&H, which has won a Wallops contract, is prohibited from giving details. However, sources close to SpaceX say that Kennedy will get around $1 million of ARRA funds and that company's complex will gain improvements.
The two companies are the leading lights in NASA's commercial programme that seeks to change how the agency procures space transport and use privately supplied services to fill the transport gap that will follow the retirement of the Space Shuttle fleet next year.
Out is a traditional NASA-centered approach with cost-plus payments. Instead, SpaceX and Orbital matched their own funds against the agency's commercial orbital transport services programme Space Act agreement awards, worth $278 million and $170 million respectively.
This was to develop rockets and spacecraft that deliver International Space Station cargo. In December 2008 the companies were competitively awarded contracts worth $3.5 billion for ISS resupply from 2010 to 2015.