simcosmos - 14/9/2005 5:56 AM
SRBseparama - 14/9/2005 5:18 AM
So the Magnum would be for the moon and the Longfellow for Mars?
Hello,
Maybe this discussion would be better on the SDLV forum section. Anyway, for what I understood, Magnum and Longfellow are just the name for two vehicles with the same payload capability but using different engines, etc configurations (SSME vs RS-68…). Please someone correct if I'm wrong.
The Magnum name originated with a design which came out back in the mid 1980's, around the same time as Shuttle-C. It was the in-line alternative of that time, the only version I've ever seen from that time included Liquid Flyback Boosters powered by multiple SSME's too.
Today though, it appears that Magnum has been redefined a little, hence the confusion.
Chris posted this image elsewhere on this forum which defines the current differences between the 'new' Magnum and LongFellow:
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I'm a little confused about several aspects. Those confusions will only be dissipated when we all know more precise news from NASA.
From what I read in the latest times, it seems that NASA might be preparing to completely stop using the 4 segment SRB once the Space Shuttle is retired. This in favour of the exclusive use of the 5 segment SRB for the new launchers (both SRB launcher and SDHLV), if not from start, as soon as possible… Again this is just a supposition.
The 5-segment SRB has only ever been test-fired once, so there isn't a lot of real-world data on it. It also has not yet been man-rated - a very costly process. The 4-seg version is already man-rated and could be flown unchanged right now for no extra development cost.
The SDLV though is planned to use the 5-segment versions from the get-go. The development time will be much longer for the SDLV than for the CEV LV, and won't need to ever be man-rated, so 5-segments can be used there far cheaper.
I would expect that once the 5-segs have flown successfully a few times, then they will be man-rated without time pressures and then CEV LV will be 'upgraded' to 5-seg.
Translating the hypothesis to the heavy lifter this means that we may be more or less "sure" about many of its components:
- longer ET (around 8m to 10m more?),
- powered by 4 x SSME (named Magnum?; if using 4 x RS-68 it is called Longfellow?, these names may not be the definitive ones)
- 2 x 5 segment SRB
- and a payload fairing with dimensions around the +/- 40m x 10m (35m x 9m in many references)
The major question mark is about the second stage: maybe there will be two different second stages (powered by J-2S? another kind of engine? just one engine? multiple?).
It seems that NASA is aiming for a LEO payload of 125tons (instead of the 110 of early news) and that the heavy lifter may be taller than 111m… However it may not be too much taller, given the VAB doors… I would say (rough estimative) that the maximum height would be… say… 121m.
The gap from the top of the MLP Deck to the top of the highbay door is 124.6m. Say that 0.6m is your clearance, then the rocket can be 124m tall.
- 2 x 5 segment SRB
- 10m stretch to the main ET is what I'm hearing
- Engine choice is still to be decided:
RS-68 has more thrust and is cheaper ($8m each), SSME is more efficient and has higher impulse but is over twice the price ($20m). There are pro's and con's for each, and the choice will be made on cost/performance for the specific detailed vehicle configuration they need - which still has not been finalized yet. I know SSME offered significant extra perfomance for Magnum, but with the additional capacity of the second stage on Longfellow, the higher thrust of RS-68 might get an advantage early on in the flight. I'll run some numbers and get back to you.
- Payload fairing seems decided: 9m x 35m body, plus aero cone ~7m tall.
Stage 2 - I think I may have figured out what's going on there. I think that by using SSME instead of J2-S the performance advantage may help to account for the 110MT to 125MT upgrade. You'll need about 70MT of fuel onboard the 2nd stage after LEO insertion to use as propellant to get 125MT (inc. the fuel) plus 25MT CEV to lunar orbit.
I am hearing that there will probably be a mini-stage developed, basically similar to the OMS Pods.
The ET/SRB combo can put 100+ tons into LEO without any upper stage. You do need some sort of OMS pod for circularizing the orbit at apogee though. That vehicle configuration could fly a lot sooner and cheaper than the full one and might be great for completing the ISS. Later, when the upper stage is finished and fully validated, it can be used to upgrade the whole system AND provide the Earth Departure Stage (EDS) for lunar missions at the same time.
Looking at the 3D model I made for the heavy lifter (based on released pictures, please see above) I ended up with a total height of +/- 109m (using 5 segment SRB and 4xSSME powered ET having around 56m height + 40mx10m fairing... this gives 109m-56m-40m=13m for interstage + second stage). All these numbers seem to suggest that the second stage may have more length / fuel / performance than what was initially being considered (that bigger second stage also seen in some other pictures).
So, forgetting dubious names, that's why I'm thinking about the possibility of that heavy launcher to be equipped with two different kinds of second stages… One more for LEO, another for Moon missions… That "Moon second stage" would also be used for Mars missions… Please have in mind that there is the possibility of NASA considering LEO assembly for such missions instead directly sending stuff to red planet.
Of course that my point of view is very limited… If only I could have more free time I would do another crude Orbiter implementation (this time for the heavy lifter) and "test" a few stuff around…
Summing up: I have the impression (possibly very wrong one) that the heavy lifter will have at least a choice between two different upper stages, both having the same diameter, but different lengths (perhaps 8m to 10m difference, making the Moon stage to have the double of the lenght of the LEO stage) and possibly different engine setup, all that depending of the type of mission being planned.
However, this is just me talking to the air… I'm no engineer 
(looking forward for more details about the 60 day study…)
António
I think you're basically right.
However, I can see a logical progression of development for both the CEV launcher and the SDLV, starting with a smaller variant and upgrading to the full specifications. I think that's sensible and economical too.
I'll try running more numbers as soon as I can and confirm some of this.
