NASA's Ares V cargo launch vehicle (CLV), named after its five first-stage cryogenic powerplants, could have six engines, be taller than the Apollo programme's Saturn V and diminish the space agency's common element approach to its new transportation system.
For missions to the Moon, Ares V will launch the Earth departure stage (EDS) and Altair lunar lander that will dock with the manned Orion crew exploration vehicle. The EDS carries out trans-lunar injection the Altair handles lunar orbit injection.
The ongoing changes to the CLV are to provide more performance margin to help with possible future mass growth in the US space agency's Altair and Orion, according to NASA's exploration launch project office's advanced planning manager and former Apollo programme rocket engineer John "Phil" Sumrall.
Since the 2005 Exploration Systems Architecture Study that set out NASA's plans for returning to the Moon by 2020, the Ares V has changed from having five Space Shuttle main engines at its 10m (33ft)-wide core-stage's base and two Apollo era J-2S+ engines for its slimmer upper stage/EDS.
In some of the latest design deliberations it has up to six Pratt & Whitney Rocketdyne RS-68 engines at the core-stage's base and solid rocket boosters (SRB) with a spacer to lengthen its five-segment SRB versions of the Space Shuttle's four-segment SRBs. With an EDS as wide as the core - with one Pratt & Whitney Rocketdyne J-2X engine - and a longer first-stage for more propellant, the whole vehicle's height could reach 113m the Saturn V was 111m tall.
Ares V's height is dictated by the length of the SRBs, as they act as load-bearing structures and allow the lengthened core-stage. But the final height is limited to 118m, the height of Kennedy Space Center's vehicle assembly building where Ares V's elements will be stacked.
"The [core stage] engines' arrangement could be one in the centre with the other five around the periphery or two in the centre and the other four around them. We would have to manifold the exhaust ducts. We haven't decided how many exit nozzles six engines could have," says Sumrall, admitting that Ares V could have fewer than five nozzle cones.
Another design change could see the Ares V abandon the metal segment casings and PBAN solid fuel as used by the Shuttle and Ares I crew launch vehicle SRBs, opting instead for filament-wound casings with a higher internal combustion pressure using the solid fuel HTPB.
This approach would run counter to the notion of reducing development and life cycle costs for the Ares I and V rockets by using common elements.
For the Ares rockets, Kennedy Space Center's launch complex pads 39A and 39B will become "clean pads" after Shuttle is retired. This means that it is the mobile launch platform that is specific to the rocket and not the pad itself, allowing Ares V or I to launch from either pad.
The Shuttle launch pads' flame trenches are not wide enough for the combined width of the Ares V's 10m wide core and SRBs, but Sumrall says that could be overcome by positioning the launcher at an angle.