The U.S. Air Force will use a Minotaur 4 rocket (pictured above) from Orbital ATK to launch the ORS-5 satellite.

NASA could save millions of dollars by using Minotaur rockets to launch the Soil Moisture Active-Passive (SMAP) spacecraft and several other medium-class science missions planned through 2020, according to a Feb. 17 report by the NASA Office of Inspector General.

“Our analysis shows that use of the Minotaur for certain NASA science missions offers significant savings compared to the available commercially provided intermediate-launch vehicles,” said the report, dubbed “Review of NASA’s Acquisition of Commercial Launch Services.” These commercial vehicles include the Space Exploration Technologies (SpaceX) Falcon 9, “which is still under development and not yet certified to carry NASA science missions,” the report said.

While the SMAP satellite is small enough to fly aboard a United Launch Alliance Delta 2 rocket, that longtime workhorse vehicle is no longer in production and the remaining Delta 2s in inventory are 7920 heavy configurations that can only be launched from Cape Canaveral Air Force Station in Florida, according to the report. SMAP, like most NASA Earth science missions, needs to launch from Vandenberg Air Force Base, Calif., in order to reach polar orbit.

Launching SMAP on a Minotaur 4, which utilizes excess Peacekeeper missile stages, would save NASA between $61 million and $156 million compared with using Falcon 9 or an intermediate-class Atlas 5, according to the report. Those savings are based on a projected 2012 cost of $50 million for a Minotaur, $111 million for a Falcon 9 and $205 million for an Atlas 5.

After reviewing the report, NASA said it would consider the Minotaur for some of the 13 medium-class science missions the agency plans to launch through 2020. However, NASA officials “expressed concern that using the Minotaur for multiple missions would threaten the viability of commercial providers of small- and medium-class launch services and may increase the number of bid protests on contract awards because commercial companies would argue that U.S. law and space transportation policy requires NASA to use U.S. commercial vendors to the maximum extent practicable,” the report said.

That is what happened in 2009 when then-NASA Administrator Mike Griffin approved launching the Lunar Atmosphere and Dust Environment Explorer spacecraft on a Minotaur, which is assembled by Orbital Sciences Corp. SpaceX protested the award to the U.S. Government Accountability Office, which upheld NASA’s decision on the grounds that cost-effective commercial alternatives were not available for the mission, which is slated to launch in May 2013.

NASA launch service officials, the report says, estimate the soonest Falcon 9 could complete NASA certification for launching science payloads is between late 2013 and early 2014.

While NASA could award SpaceX a launch service task order for SMAP before certification is completed, “the Agency would need to accept a significantly higher degree of risk and determine how to address potential cost increases and schedule delays that could result if technical issues were identified during the certification process,” the report says.