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  #11  
Old 09-11-2017, 09:46 AM
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Originally Posted by BigRIJoe
So why the launch vehicle switch for the X-37B?


They want multiple launch vehicles for a couple of reasons.

1. Competition drives the cost down a little.

2. Redundancy. If one launch vehicle gets grounded, the other can be used in its place. I haven't kept up and don't know if it has been replaced yet, but the Atlas V was using an NPO Energomash RD-180 main engine from Russia. That supply could be cut off at any time.


https://spaceflightnow.com/2017/06/...eplane-mission/



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  #12  
Old 09-11-2017, 06:04 PM
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Originally Posted by BigRIJoe
So why the launch vehicle switch for the X-37B?


"Guaranteed access to space"... IOW, if the Atlas it usually launches on blew up due to faulty Russian engines or something, they have a ready backup.

Plus, it's a reusable unmanned spaceplane. Just makes sense to launch it on a (mostly) reusable rocket... IOW, it's what NASA SHOULD have done 10-15 years ago...

If/when SpaceX decides to recover the second stage, this combination would be a fully reusable orbital vehicle. How cool is that??

Later! OL J R
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  #13  
Old 09-11-2017, 06:11 PM
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Originally Posted by tbzep
They want multiple launch vehicles for a couple of reasons.

1. Competition drives the cost down a little.

2. Redundancy. If one launch vehicle gets grounded, the other can be used in its place. I haven't kept up and don't know if it has been replaced yet, but the Atlas V was using an NPO Energomash RD-180 main engine from Russia. That supply could be cut off at any time.


https://spaceflightnow.com/2017/06/...eplane-mission/



.


Not replaced YET, but Bezos is developing the BE-4 methane/LOX engine to replace the Russian RD-180's...

I'm not sure they'll incorporate it into the existing design of the Atlas V... the methane/LOX propellant combination would have somewhat different tank volume requirements from the present LOX/RP-1 combination used with the RD-180's.

I think (last I read) the present plan is to basically fly out the Atlas V's and when the BE-4 is ready, come out with a larger Atlas V replacement designed around the BE-4's, for methane and LOX. Basically it's a re-engined version of the Atlas V Phase II proposals that would have enlarged Atlas V by using the larger Delta IV diameter tanks feeding a pair (4 chambers) of RD-180's... Part of that plan is to develop the ACES upper stage as a larger, more capable replacement for the current Centaur upper stage (IIRC).

Later! OL J R : )
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  #14  
Old 09-11-2017, 06:56 PM
BigRIJoe BigRIJoe is online now
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Quote:
Originally Posted by luke strawwalker
"Guaranteed access to space"... IOW, if the Atlas it usually launches on blew up due to faulty Russian engines or something, they have a ready backup.

Plus, it's a reusable unmanned spaceplane. Just makes sense to launch it on a (mostly) reusable rocket... IOW, it's what NASA SHOULD have done 10-15 years ago...

If/when SpaceX decides to recover the second stage, this combination would be a fully reusable orbital vehicle. How cool is that??

Later! OL J R

IMHO your second opinion is a bit of a stretch. And if Space X does decide to recover the second stage won't the technology to do that lead to a performance hit for the launch vehicle?
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  #15  
Old 09-11-2017, 09:25 PM
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Quote:
Originally Posted by luke strawwalker
Not replaced YET, but Bezos is developing the BE-4 methane/LOX engine to replace the Russian RD-180's...

I'm not sure they'll incorporate it into the existing design of the Atlas V... the methane/LOX propellant combination would have somewhat different tank volume requirements from the present LOX/RP-1 combination used with the RD-180's.

I think (last I read) the present plan is to basically fly out the Atlas V's and when the BE-4 is ready, come out with a larger Atlas V replacement designed around the BE-4's, for methane and LOX. Basically it's a re-engined version of the Atlas V Phase II proposals that would have enlarged Atlas V by using the larger Delta IV diameter tanks feeding a pair (4 chambers) of RD-180's... Part of that plan is to develop the ACES upper stage as a larger, more capable replacement for the current Centaur upper stage (IIRC).

Later! OL J R : )


There are no plans for an Atlas V variant that uses Delta IV tooling feeding two RD-180s. The Vulcan does, however, use the Delta IV tooling for the LOX/Methane combo - because the volume requirements are not "somewhat" different, they are vastly different.
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  #16  
Old 09-12-2017, 12:03 AM
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Quote:
Originally Posted by BigRIJoe
So why the launch vehicle switch for the X-37B?
In the SpaceX video (in the first posting above), there is a brief presentation by Boeing about the X-37B. In it, they mention that they wanted to demonstrate the X-37B's compatibility with a different launch vehicle. I don't know if that's the only reason (a few years ago SpaceX had taken legal action to be able to bid on defense-related government satellite launches, though not specifically the X-37B). Aside from (I presume) winning the bid for this latest X-37B mission, Boeing (and probably also the USAF) probably like having a second launch vehicle option, just in case the Atlas V might be temporarily unavailable due to a "launch queue bottleneck," or because the vehicle was out of service due to a launch failure (and its review period), which might also--depending on the nature of the anomaly--involve a damaged and unusable launch pad. (I'm not prognosticating an Atlas V failure, but at some point such a failure is statistically inevitable.)
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  #17  
Old 09-14-2017, 11:04 AM
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Originally Posted by BigRIJoe
IMHO your second opinion is a bit of a stretch. And if Space X does decide to recover the second stage won't the technology to do that lead to a performance hit for the launch vehicle?


Well, you're welcome to your opinion, though I don't share it. What NASA has been doing since the shuttle demonstrated its outdated and increasingly fragile nature and was eventually retired is basically outdated and absolutely monstrously expensive and slow, and it will be obsolete by the time it ever flies. In short, SLS won't exist long as an operational system, and if it does, it will basically kill the space program because it's so freakin' expensive.

If Elon Musk, a commercial "outsider" could build something like Falcon 9, you can bet your boots that NASA could have built something like it (same functionality) 10-15 years ago, HAD THEY WANTED TO. That's the REAL problem... lack of vision, lack of will.

Yes, it's all about tradeoffs. Recovery of the first stage has a price, an impact on payload capability. Thing is, due to the rocket equation and the way rocketry works, the cost is much lower for first stages than subsequent stages. When the Saturn V was being developed, weight savings was an important issue, to maximize payload performance. Taking weight out of the first stage had little effect-- Weight on the third stage, which performed the final ascent and escape burn, was absolutely the most critical-- every extra pound of weight in the third stage was a pound less payload that could be carried, so minimizing it's weight was of paramount importance. Removing weight from the first stage had little effect-- one had to shave 11 pounds off the first stage to gain 1 pound of additional payload performance from the stack. The first stage design and the S-IVB third stage were already well advanced and mostly optimized, and little weight savings could be accomplished, so most of the weight savings measures were applied to the second stage, which was in an earlier stage of design and therefore changes could be accommodated easier. Saving weight in the second stage was harder in that basically 2 pounds of weight had to be saved to gain 1 pound of payload capacity, (IIRC-- read or saw the details on this years ago) but it was a priority and put a lot of pressure on the design and development of the second stage, since the payoff was considerable in additional performance, almost as good as shaving weight out of the S-IVB, and much more payoff than shaving weight out of the S-IC. Because of this pressure to shave weight out of the S-II stage, it created a lot of problems for the development of the S-II stage at North American...

SO what does all this mean?? Adding weight (in additional fuel for boost-back burns, reentry burns, landing gear, grid fins, additional avionics, etc) for recovery and landing of the stage to the FIRST STAGE, has the LEAST impact on payload performance. Because the first stage is the most massive, because it had to lift the payload, all the other stages, itself, and it's own fuel from a standing start from the bottom of the atmosphere and gravity well. Thrust is the most important parameter, even more important than specific impulse (fuel efficiency) which is why kerosene/oxygen is a better first stage fuel than hydrogen, which is more efficient but requires an ENORMOUS tank to store it, making the first stage much larger. (the S-IC would have had to be about double the size had it been fueled by hydrogen rather than kerosene).

On a two stage vehicle, adding weight to the upper stage has a MUCH larger impact on payload performance, because it delivers the payload into orbit. Because the speed is SO much greater at second stage shutdown (17,500 mph versus about 4,000 mph for the first stage, depending on the rocket) recovery is much more difficult, requiring a heat shield of some sort, and a deorbit burn to initiate a controlled reentry. The additional weight of the heatshield, avionics, and whatever landing gear or other recovery devices (depending on the methodology chosen for recovery-- be it splashdown, land-landing via parachute/airbag, rocket thrust hover to landing like Falcon 9 first stage, or mid-air parachute capture like the Discoverer film buckets, which has been proposed for larger stages, including S-IC at one point, but never implemented). All this additional recovery weight SUBTRACTS POUND-FOR-POUND from payload capacity. IOW, if you add 1,000 lbs of recovery system weight to the second stage, you reduce payload to orbit by 1,000 lbs. Due to the higher speeds, altitudes, etc. the recovery of the second stage is much more difficult, meaning more weight for systems to recover it, and that weight has a MUCH higher price on the payload than the same equipment in the first stage. Due to the fact that the first stage is the largest, most powerful, and is the most expensive component of the rocket stack, the highest payoff in savings comes from recovery of the first stage, and since it comes at the lowest cost in payload performance, it's the most logical to accomplish, and the "easiest" to accomplish. Recovery of the second (upper) stages is more difficult, more costly in terms of payload performance hit, and the second stage is much smaller and built lighter (again to maximize payload) and usually has only one engine (or fewer, smaller engines, depending on the rocket) and therefore not only is recovery of the second (upper) stages more difficult, more costly, more impacting upon payload capability, but it has a lower payoff in savings on the ultimate cost of the rocket. That is why there hasn't been as much effort (thus far) put into recovery of the upper stage of Falcon 9, or any other rocket.

Not to say it's not feasible... it is. With a suitable "hot structures" type heat shield, a sufficiently "fluffy" design (like the original Faget shuttle design with stubby straight wings would have been) and perhaps an inflatable heat shield (if needed) or a plug nozzle engine capable of acting as it's own heat shield (similar to the ROOSTER S-IVB fully reusable SSTO design), perhaps augmented with fluid film cooling from propellant pumped out the nozzle during reentry (which has been proposed, I remember reading about it somewhere) and minimal landing/recovery gear weight (mid-air capture? Other methods?) then second (upper) stage recovery would certainly be feasible... but again, a much higher cost to the vehicle's payload to orbit performance capability.

Later! OL J R
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  #18  
Old 09-14-2017, 11:06 AM
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Quote:
Originally Posted by frognbuff
There are no plans for an Atlas V variant that uses Delta IV tooling feeding two RD-180s. The Vulcan does, however, use the Delta IV tooling for the LOX/Methane combo - because the volume requirements are not "somewhat" different, they are vastly different.


Yes... thanks for restating what I already said. Better choice of adjective. Good for you.

So it's called "Vulcan" instead of "Atlas- *whatever*". Thanks for the correction.

The idea started out as "Atlas V Phase 2".

Later! OL J R
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  #19  
Old 09-14-2017, 11:03 PM
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Quote:
Originally Posted by luke strawwalker
Yes... thanks for restating what I already said. Better choice of adjective. Good for you.

So it's called "Vulcan" instead of "Atlas- *whatever*". Thanks for the correction.

The idea started out as "Atlas V Phase 2".

Later! OL J R


It was never called "Atlas V Phase 2" within ULA. It has gone by a number of acronyms like "Next Generation Launch Vehicle." Vulcan was the name selected via Internet voting.
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  #20  
Old 09-14-2017, 11:40 PM
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Quote:
Originally Posted by frognbuff
It was never called "Atlas V Phase 2" within ULA. It has gone by a number of acronyms like "Next Generation Launch Vehicle." Vulcan was the name selected via Internet voting.


I was referring to the design using Delta IV size tanks with Atlas kerosene engines. Goes back a long way.

Vulcan is just the latest iteration of the idea...

Later! OL J R
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