NASA past performance ratings higher for cost plus contracts than fixed price, FIerceGovernment
"The more a company has a contractually risky relationship with NASA, the more likely it is that the agency will rate that contractor well during past performance evaluations, according to new research from INPUT, a Reston, Va.-based intelligence and analysis firm. INPUT obtained information on NASA past performance evaluations through Freedom of Information Act requests, releasing a proprietary August 16 report supplied by the firm to FierceGovernmentIT."



I have managed both cost plus (CP) and firm fixed price (FFP) contracts at one NASA center. The idea that an FFP contract results in lower overall cost is incorrect in this business.
When negotiating an FFP, NASA has little or no insight into the cost rackup or profit margin. Also, since the supplier assumes all the risk, they will pump up the price proportional to the risk. Suppliers love it, because they can negotiate high and then squeeze their own costs down to make big profits. Also, every change that comes in is justification for another contract mod and cost increase (and more fee!).
On a CP contract, NASA gets full insight into the cost basis and controls the fee (typically 8-10%). Consequently, the initial cost of the CP contract can easily be much lower than an FFP for the same effort. Visibility into the cost breakdown helps a lot with managing (and avoiding) those costs.
Finally, I have seen several cases where FFP contracts ran into major technical issues and NASA or one of its partners needed to pay extra to complete the work. Often its a choice between pay and launch on time or don't pay, go to court, and maybe many years from now you can launch....
FFP might works great when the risk is low, the product is well defined, and the supplier has experience doing the job. This is not typically the case for NASA products, and CP contracts are not why NASA is so expensive....