CAPE CANAVERAL, Fla. — The selection of the Delta 4 rocket’s upper stage for use on two test flights of NASA’s planned heavy-lift Space Launch System (SLS) could position the Delta 4 as an astronaut-launching vehicle.
Currently, the Delta 4 is used only for unmanned launches of U.S. government satellites, but under the proposed NASA contract a modified version of its Boeing-built upper stage would be used on an astronaut-carrying SLS demonstration mission in 2021.
NASA’s SLS, designed to carry the Orion crew capsule on missions beyond low Earth orbit, ultimately will incorporate the Apollo-heritage J-2X engine, currently in development. But the first two demonstration flights of the shuttle-derived heavy lifter, slated for 2017 and 2021, will use a commercially provided upper stage because the J-2X will not be ready by then.
NASA announced May 3 its intent to contract with Boeing Defense, Space and Security of St. Louis for an interim upper stage, referred to as the Delta Cryogenic Second Stage (DCSS), for the second and third Orion capsule test flights, both of which will use the SLS.
A heavy-lift version of the Delta 4 will loft Orion in its scheduled 2014 debut, an unmanned mission in which the capsule will simulate atmospheric re-entry from a lunar orbit. Orion’s second and third flights are expected to circle the Moon; the first will be unmanned, the second will be piloted.
“As a result of internal market research that looked at available in-space propulsion capabilities in the United States, Europe, and Japan, NASA determined that the DCSS, with minor modifications, was capable of fulfilling the SLS needs,” NASA wrote on its procurement website at the Marshall Space Flight Center in Huntsville, Ala.
The market research was validated by the results of a sources-sought synopsis published Jan. 9, NASA added.
Based on the responses, NASA determined that the DCSS is “the only means available to support the immediate in-space propulsion needs of the SLS within the SLS manifest schedule constraints.”
NASA said the DCSS meets all requirements except human-rating and the ability to achieve a velocity change of 3,050 meters per second with three engine burns.
“With minor modifications it can be human-rated by the second flight unit,” NASA noted.
“No other in-space propulsion stage, either existing with proven flight performance, or planned, requires such relatively minor modifications to be made fully compliant with the SLS requirements,” the agency said.
NASA received three responses to its January solicitation, agency spokeswoman Jennifer Stanfield said.
The deadline for any additional organizations to submit options to NASA is May 18.
Denver-based United Launch Alliance (ULA), the Boeing-Lockheed Martin joint venture that manufactures the Delta 4 along with the Atlas 5 rocket, says it has no firm plans to human-rate the Delta 4 system.
“We have studied it in the past,” ULA spokeswoman Jessica Rye told Space News.
ULA has an unfunded partnership agreement with NASA to human-rate the two-stage Atlas 5, the launcher of choice for several of the firms vying for NASA contracts to ferry astronaut crews to and from the international space station on a commercial basis. Currently the only means of space station crew transport is the Russian Soyuz vehicle.
“If the Delta 4 upper stage is used within the SLS system to launch humans, we will work with NASA and Boeing to determine what, if any, modifications are required,” ULA’s Rye wrote in an email.
“This assessment depends on the overall approach taken by NASA to human rate the SLS/Orion system. It is meaningless to speak of ‘human-rating’ the stage without that overarching context,” she said.
In an interview in March, George Sowers, ULA’s vice president of business development, said the company has considered Delta 4 for human launches and “was certainly open to the idea.”
“Almost all the work that we’re doing to human-rate Atlas would be applicable to Delta 4,” Sowers said.
Boeing said it would not discuss the use of the Delta 4 upper stage on SLS until after its contract with NASA is signed.