JR,
Is there any particular reason why something like the Delta IV Heavy can't be man-rated?
FC
Originally right after the CAIB and the announcement of the VSE by Bush Jr., back when Sean O'keefe and Admiral Steidle were coming up with the "spiral development" plan to meet the goals of the "moon, Mars, and beyond", manrating Delta IV Heavy was a central part of the plan-- it was to be the booster for the CEV, which later became known as "Orion".
Problem was, Delta IV Heavy wasn't the shuttle... the problems were more political than anything. D-IV-H didn't keep the shuttle folks employed and the money flowing into the correct political districts, plain and simple... too many "space state" contractors were going to lose BIGTIME if the EELV based spiral development plan went ahead... and we couldn't have that... hence they pressured Bush to get rid of O'keefe and Steidle and replace them with Mike Griffin, who never met a monster rocket he didn't like... and who would ride the "shuttle derived" train just like Congress and the shuttle contractors wanted... right up until it went over a cliff...
NASA studies and ESAS found "problems" with D-IV-H like "black zones", points in which the trajectory made escape via a LES tower "impossible"... of course, they were using a stacked deck-- EELV trajectories that were modeled to maximize UNMANNED CARGO launches, NOT safety for MANNED launches... the EELV's fly "highly lofted" trajectories that ascend quickly and then turn horizontal to pick up speed to reach orbit, to maximize cargo capability to orbit. For manned trajectories, one would fly a flatter, gentler trajectory to minimize gee forces and make escape easier if the rocket malfunctioned, but which would also reduce payload capability-- which D-IVH had to spare anyway... So it wasn't a hard problem to solve, but the PTB didn't WANT it solved, and therefore claimed it ruled out D-IVH for human launches (despite it being the preferred launcher for the Orbital Space Plane, which preceded the CEV before the Columbia disaster).
The decision was taken quite early to consciously make Orion "too big" to fit on Delta IV Heavy... that's why ORIGINALLY the Orion was to be 5.5 meters in diameter. This was back when CEV was to have a methane SPS engine and all sorts of other things like that for Mars missions using ISRU fuels (methane made on Mars from hydrogen brought from Earth, or electrolyzed from Martian water). Of course it was quickly found that the 5.5 meter Orion (CEV) was too big to be lifted by Ares I as well, so it was quickly downsized to 5 meters, where it stands today.
The subject of manrating D-IVH has come up several times, and the main problems are 1) the NASA manrating standards require a 1.4 factor of safety-- this means every part must be designed to fail at NO LESS than 140% of the design load... and not ever part of D-IVH is designed this way-- quite a bit is designed to a more standard 120% of rated load standard... and beefing up the parts would cut into performance and cost a lot of money for redesign/ recertification... according to NASA it would cost MORE to "modify" and manrate D-IVH than it was supposed to cost to design, develop, test, and evaluate an ENTIRELY FRIGGIN NEW ROCKET, Ares I... course we ALL know how THAT turned out! We also know how accurate NASA cost estimates are...
The second factor is, the RS-68 engines... they weren't designed with manrating in mind-- they were designed as cheap, throwaway CARGO ROCKET engines... and again, the "redesign" of them for a crewed vehicle was deemed "too expensive". RS-68 is actually based on the Space Transportation Main Engine, or STME, which was a proposed engine derived from the shuttle SSME, to be an uprated, cheaper, expendable version of the SSME... a first stage engine burning hydrogen and oxygen to power such rockets as the proposed but never approved National Launch System and Advanced Launch System. Some versions of "Shuttle-C" type vehicles also proposed using the STME. Of course with none of these plans ever approved or funded for development, STME basically went on the shelf as one of those neat "what if" engines on "what if" boosters that I end up summarizing over in the scale section for interested readers or future/fantasy scale builders... until, that is, the EELV competition came along to replace Titan IV, which cost as much per flight as the shuttle (which was entirely TOO MUCH), with something cheaper. The plans for STME were dusted off and revamped and what emerged was the RS-68.
Unfortunately, due to RS-68's pedigree as a cheap transportation engine, it was never designed with expensive manrating modifications in mind-- purely costs... it doesn't have the level of instrumentation and "mission assurance" hardware necessary for manrating as-is, and again, NASA determined that it would be "too expensive" to modify RS-68 and install the necessary "health monitoring" systems to enable an abort if necessary... this wasn't considered a problem on the Ares V because ORIGINALLY Ares V was to launch UNMANNED-- CARGO ONLY. Crew were only supposed to ride on "the safest rocket ever built", that being Ares I... (yeah, right, but I digress). Of course, as Ares I performance flagged and Orion still remained too heavy, and more and more of the mission mass was switched over to Ares V, eventually the plans started to change... Ares I wasn't even capable of lifting a fully-fueled lunar-capable Orion-- in fact, it burned out suborbitally-- and not just a little suborbitally, requiring a circularization burn like shuttle-- we're talking "burn the SPS service module engine for SIX MINUTES to reach orbit" kind of 'suborbitally'... of course this would SO much fuel that the SPS tanks wouldn't have enough propellant left to perform a lunar mission! SO, the plan that was flirted with was "Ares IV"-- basically slapping an Ares I upper stage on the Ares V, with Orion atop it, and launching the lunar capable Orion, along with more of the mission mass (cargo) on the Ares IV, to meet up with an Ares V-launched Altair/EDS stage in orbit, ready to go to the moon... I don't think it ever became "official", but it floated around for a good, long while... of course, the core of Ares V, which was also the first stage core of Ares IV, was powered by a cluster of RS-68's, and how they planned to deal with the "manrating issues" of the RS-68 cluster was something "to be determined" later... (TBD). Not that I ever read anything on how it was, or proposed to be, other than doing an extensive redesign of RS-68 to make it "manratable"...
Of course, not TOO long after that, Ares V started having problems-- the RS-68's, which are designed as ablatively-cooled engines, and not regeneratively cooled engines that circulate propellant through the nozzle and combustion chamber walls to cool them down and prevent them from melting, wasn't designed to be operated under a 33 foot diameter core vehicle in large clusters of 5 or 6 engines in close proximity, flanked by a pair of volcanically burning SRB's, with thier extremely hot and particle-dense exhaust plumes... The huge core would have an enormous base plume recirculation zone (much like Saturn V, which had SO much exhaust plume recirculation that flames licked some 70 feet up the sides of the rocket during parts of the flight, once it had gone supersonic, and the shock wave from the interstages/transitions created a low pressure zone around the sides of the first stage, which "sucked" the exhaust flames up alongside the rocket half the length of the first stage! (readily visible in some Saturn V launch videos). Besides the enormous vortex in it's 33 foot wide base wake, which would suck hot flames back up in/around the RS-68 engines, the SRB's created intensively radiant-heat exhaust plumes, since they're full of white-hot droplets and particles of alumina slag from the solid propellant... the RS-68's rely on radiative cooling of their nozzles as well as the ablative cooling of the inner layers burning and charring away while the engine is operating... and basically the SRB's plume radiation was going to throw more heat onto the nozzles than they could radiate away of their own internal heat. This, coupled with the exhaust gas plume impingement and base recirculation would cause the RS-68 nozzles to melt in flight before the first stage burned out...
Hence the switch back from the 'cheap' RS-68 to the "expensive" SSME... (RS-25). The SSME, being regeneratively cooled, could handle the exhaust plume impingement and thermal radiation environment next to the SRB's, and the base recirculation heating... and it was *miraculously* found that actually the "cheap" RS-68 wasn't that much cheaper than SSME anyway-- in fact, in "bulk buys" at higher production rates, the two engines were supposed to be broadly "comparable" in price... (ya right). Of course, SSME is already manrated, and thus eliminated the problem... but all this happened basically right before Constellation was canceled....
Now, it's a shame that D-IV can't use the SSME. The RS-68 is a powerful engine-- around 750,000 lbs of thrust, versus around 500,000 for the SSME, BUT, the SSME beats it ALL TO PIECES on ISP... the RS-68 is a thirty buggar, with a LOW ISP, compared with the highly efficient fuel-sipping SSME. Course, most of that is due to the SSME's more complex (more expensive) combined cycle engine which is much more complex and hard to tame, versus the RS-68's simpler gas-generator design... But a PAIR of SSME's on a Delta IV would be a BIG improvement in thrust AND performance, for the same propellant load... but it would require too many changes to the D-IV to justify it... the thrust structure being chief among them, as well as many others...
SO, can Delta IV-Heavy be manrated... depends on who you ask... the EELV proponents who've ALWAYS stuck to their position that the EELV's can be uprated and modified to do whatever task is necessary to perform the "moon, Mars, and beyond" mission (or whatever you think the mission is/should be/will be/might be/hopefully will be now that the VSE is canceled along with Constellation) say that it IS capable of being manrated, and for FAR less money than NASA has spent on things like the five-segment SRB...
Those who claim that only a "shuttle derived" heavy lift vehicle can meet NASA's needs say no, D-IVH can't be manrated without spending as much money to do that as it would cost to build their preferred HLV, or a big chunk of it... and it would be money poorly spent, because D-IVH is NOT an HLV as they define it (Saturn V-ish). Therefore it would be a foolish waste of money, time, and resources to manrate D-IVH or complete Atlas V Heavy, which using the already manrated RD-180 engines from Russia, would be far easier to manrate, or doing something like an Atlas V Phase II booster rocket, putting a pair of RD-180's on a Delta-IV size core designed for liquid oxygen and kerosene propellants for those engines rather than the liquid hydrogen/liquid oxygen burned by the RS-68...
In the end, it all comes down to who's ox is getting gored... it's not a technical decision, but a political one... in fact, the EELV companies were told by Griffin to "shut up" about EELV solutions or risk getting further NASA contracts... so there's your answer...
Later! OL JR
