|
alexSA
|
|
« Reply #2775 on: 10/25/2009 09:12 PM » |
|
280mT for a lunar mission? Total crap. Completely unnecessary.
Whether it's necessary or not is irrelevant. The point the Augustine report was making is that if you have Ares V Lite, only a dual launch scenario makes sense, as a 1.5 launch scenario with Ares V Lite doesn't work. But if you account for 2 Ares V Lite per crewed mission, you need to start comparing this scenario to something comparable with J-241 or J-246. 2 J-241 evidently would mean a crewed mission that falls short of the capability and margins of a 2-launch Ares V Lite mission. All that being said, of course you could also try to compare a scenario of 6 Ares V Lite vs. 6 J-246 which results in about comparable engine costs. But 6 J-246 per year is a much more limited architecture than a 6 Ares V Lite per year architecture.
|
|
|
|
Downix
|
|
« Reply #2776 on: 10/25/2009 09:28 PM » |
|
As long as there has been no reduction in thrust the higher Isp (435s/418s vs 414s) will automatically give greater performance.
To take advantage they'd have to re-design the Delta IV into a new Delta V design, as you'd run out of fuel before you took full advantage of the added isp.
Higher Isp means you use less fuel to get the same performance. Your statement is wrong.
You are assuming that the RS-68 Regen will get more isp than the RS-68A however. But you post the isp for the RS-68A here. So, again, what is the advantage of a longer burn time between two engines of the same isp, assuming that the RS-68 Regen has the same isp as the RS-68A. Now, if the Regen can get a further performance improvement, well, then you can get the DoD interested. So far, however, I have not heard of that.
|
|
|
|
robertross
|
|
« Reply #2777 on: 10/25/2009 09:32 PM » |
|
280mT for a lunar mission? Total crap. Completely unnecessary.
Whether it's necessary or not is irrelevant.
It is TOTALLY relevant! The whole reason we have the choices before us are based around the required mass to orbit, TLI, and beyond. It's the one reason why PD makes so much sense going forward: develop a base architecture that can be scaled up over time to launch the necessary mass in sizable chunks that are affordable over the long term. That's the beauty of Direct: it is 100% scalable, and one of the most affordable options out there.
|
|
|
|
kraisee
|
|
« Reply #2778 on: 10/25/2009 09:33 PM » |
|
You always need to start with your REQUIREMENTS if you are ever to have any chance of realistically assessing any architecture at all.
Failing to define any REQUIREMENTs at all is the #1 Category A mistake which the Committee made.
The entire comparison of this 280mT pseudo-requirement completely breaks down when you factor in the additional cost of the larger lander which can utilize the 280mT of lift performance.
The total mass in LEO has never been an official REQUIREMENT. It's the total mass heading towards the moon which is the only real REQUIREMENT.
For CxP, the 45mT lander currently being designed is expected to be a $4-5bn per year program -- and we can't even afford that!
A lander 50% larger simply isn't an affordable proposition.
The *underlying premise* of this particular comparison is therefore a completely BROKEN one.
What the committee should have done is find out what it takes for each architecture to accomplish the mission REQUIREMENTs.
The current mission requirement are defined by CxP 70000 Constellation Architecture Requirements Document (CARD) Rev 3 Change 001, March 2009 (available on L2).
That document currently specifies that at the time of a TLI, the lander must mass no more than 45,000kg, Orion mass 20,185kg, ASE mass 890kg and there is 5,000kg of Manager's Margin included for safety. That's a grand total of 71,075kg or 71.1mT of total spacecraft mass being pushed thru TLI.
71.1mT thru TLI is the official NASA CARD REQUIREMENT as it stands today.
If they had done their job properly, the Committee should have spent their time studying how much each option costs to accomplish the ACTUAL REQUIREMENTS.
If they had done the job properly, they would have found that the current Ares-I + Ares-V architecture can simply not meet the performance REQUIREMENT at all.
If they had done the job properly, they would have found that while Dual Ares-V Lite can exceed that performance, there is no cost profile which allows that excess performance to be utilized, so the vehicles would have been overly expensive for the actual REQUIREMENT.
If they had done the job properly, they would have found that 4 Advanced EELV's could have done the job, but the cost for four launchers is quite high to meet the REQUIREMENT.
If they had done the job properly, they would have found that Side-Mount SDLV could not actually deliver the required masses of those specific spacecraft & associated propellant in just two flights, so would have required a third -- which is similarly too high to meet the REQUIREMENT.
If they had done the job properly, they would have found that an In-Line solution can deliver the correct REQUIREMENT masses to both LEO and to TLI in just two launches. Further, it costs no more to develop & operate than the Sidemount option -- and costs considerably less than any Ares configuration.
IF they had done the job properly.
Ross.
|
|
|
|
Downix
|
|
« Reply #2779 on: 10/25/2009 09:34 PM » |
|
280mT for a lunar mission? Total crap. Completely unnecessary.
Whether it's necessary or not is irrelevant.
It is TOTALLY relevant!
The whole reason we have the choices before us are based around the required mass to orbit, TLI, and beyond. It's the one reason why PD makes so much sense going forward: develop a base architecture that can be scaled up over time to launch the necessary mass in sizable chunks that are affordable over the long term.
That's the beauty of Direct: it is 100% scalable, and one of the most affordable options out there.
Ok, so they want 280mT to LEO, you take the Jupiter, stretch the tank, add a 5th SSME, use 5-seg SRB.... oh wait, you now have an Ares V Classic don't you? You'd actually be beating the Ares V Lite in total lift if my estimation is right, yes?
|
|
|
|
alexSA
|
|
« Reply #2780 on: 10/25/2009 09:40 PM » |
|
280mT for a lunar mission? Total crap. Completely unnecessary.
Whether it's necessary or not is irrelevant.
It is TOTALLY relevant!
The whole reason we have the choices before us are based around the required mass to orbit, TLI, and beyond. It's the one reason why PD makes so much sense going forward: develop a base architecture that can be scaled up over time to launch the necessary mass in sizable chunks that are affordable over the long term.
That's the beauty of Direct: it is 100% scalable, and one of the most affordable options out there.
Ok, so they want 280mT to LEO, you take the Jupiter, stretch the tank, add a 5th SSME, use 5-seg SRB.... oh wait, you now have an Ares V Classic don't you? You'd actually be beating the Ares V Lite in total lift if my estimation is right, yes?
The Ares V Classic is more expensive than the Ares V Lite (engine costs). Whether Ares V Classic would be able to lift more with 5 SSMEs than Ares V Lite with 5 RS68As is very much up to debate.
|
|
|
|
kraisee
|
|
« Reply #2781 on: 10/25/2009 09:43 PM » |
|
Ok, so they want 280mT to LEO, you take the Jupiter, stretch the tank, add a 5th SSME, use 5-seg SRB.... oh wait, you now have an Ares V Classic don't you? You'd actually be beating the Ares V Lite in total lift if my estimation is right, yes?
+/- 2mT difference between them. Ross.
|
|
|
|
Downix
|
|
« Reply #2782 on: 10/25/2009 09:51 PM » |
|
Ok, so they want 280mT to LEO, you take the Jupiter, stretch the tank, add a 5th SSME, use 5-seg SRB.... oh wait, you now have an Ares V Classic don't you? You'd actually be beating the Ares V Lite in total lift if my estimation is right, yes?
+/- 2mT difference between them.
Ross.
Right. Now, for this, under any estimate, would cost more than Ares V Lite. *however* With Ares V Lite, you *MUST* be spending that much on every launch, even when the lifting capacity of the vehicle is overkill. Say we need to lift a SuperHubble, in the 60mT range. Well, Ares V lite can do it, but you're wasting part of it's capability. Jupiter, by comparison, you scale it down, to a J130. Now, the Jupiter costs a *lot* less than the Ares V Lite. If you have the same profile for the mission, always lifting 140mT, and can guarantee that you will be lifting the same regularly for a long time, then the Ares V Lite does have a good case. But, this is the real world, things change, we often times come up with newer missions, with alternative ideas, which may or may not fill up an Ares V Lite lift, but will eat it up volume-wise. With DIRECTs approach, we can cut the cost to operate by tailoring the rockets capability to the missions needs. Only need 60mT, great, you only need a rocket of that range. Need 140mT, well, they can do that too. Ares V Lite comes off as a one-trick pony, DIRECT more like a toolkit. We have enough one-trick ponys out there, what we need is a system, not just a rocket, that can be tailored to meet our needs, now and in the future.
|
|
|
|
kraisee
|
|
« Reply #2783 on: 10/25/2009 09:54 PM » |
|
The Ares V Classic is more expensive than the Ares V Lite (engine costs). Whether Ares V Classic would be able to lift more with 5 SSMEs than Ares V Lite with 5 RS68As is very much up to debate.
I might agree with you if it weren't for the fact that J-2X isn't the only upper stage engine choice for the SSME variants. While the low velocity of staging using the RS-68 Core requires the extra thrust of the J-2X to make orbit successfully, the SSME vehicles stage *much* later in the ascent profile, so they don't require the same levels of thrust from their Upper Stages. This allows for alternative engine option on the SSME vehicle which are just not viable on the RS-68 vehicles. An "Ares-V Classic" using 6 RL-10's powering the Upper Stage (JS-256 Heavy) would be significantly lower cost total vehicle package than the Ares-V Lite. But the key issue is that WE CAN'T AFFORD TO BUILD A 75mT LANDER ANYWAY -- SO ALL THIS TALK ABOUT TRYING TO SUPPORT THIS ARBITRARY 280mT TARGET IS JUST PLAIN *STUPID*. Ross.
|
|
|
|
|
|
alexSA
|
|
« Reply #2785 on: 10/25/2009 10:02 PM » |
|
But the key issue is that WE CAN'T AFFORD TO BUILD A 75mT LANDER ANYWAY -- SO ALL THIS TALK ABOUT TRYING TO SUPPORT THIS ARBITRARY 280mT TARGET IS JUST PLAIN *STUPID*.
Ross.
Ross, to be honest, the development of a 75mt lander isn't that much different from the development of a 45mt lander - speaking about the development project itself. However, one thing is really clear, 2 cargo landers launched by 2 Ares V Lite per year are less expensive than 3 cargo landers launched by 3 J-241 or J-246 per year.
|
|
|
|
robertross
|
|
« Reply #2786 on: 10/25/2009 10:07 PM » |
|
But the key issue is that WE CAN'T AFFORD TO BUILD A 75mT LANDER ANYWAY -- SO ALL THIS TALK ABOUT TRYING TO SUPPORT THIS ARBITRARY 280mT TARGET IS JUST PLAIN *STUPID*.
Ross.
Thanks for filling in for me there...had something on the go here. Umm, can you humour me for a second Ross? I had an idea. Do you think 280mt would be sufficient for a Mars architecture? Maybe you can see where I'm going with that.
|
|
|
|
marsavian
|
|
« Reply #2787 on: 10/25/2009 10:14 PM » |
|
280mT for a lunar mission? Total crap. Completely unnecessary.
Whether it's necessary or not is irrelevant.
It is TOTALLY relevant!
The whole reason we have the choices before us are based around the required mass to orbit, TLI, and beyond. It's the one reason why PD makes so much sense going forward: develop a base architecture that can be scaled up over time to launch the necessary mass in sizable chunks that are affordable over the long term.
That's the beauty of Direct: it is 100% scalable, and one of the most affordable options out there.
Ok, so they want 280mT to LEO, you take the Jupiter, stretch the tank, add a 5th SSME, use 5-seg SRB.... oh wait, you now have an Ares V Classic don't you? You'd actually be beating the Ares V Lite in total lift if my estimation is right, yes?
The Ares V Classic is more expensive than the Ares V Lite (engine costs). Whether Ares V Classic would be able to lift more with 5 SSMEs than Ares V Lite with 5 RS68As is very much up to debate.
Not according to NASA, it was the reason they chose to go that RS-68 route in the first place. p13-14 http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20070002798_2007001569.pdf
|
|
|
|
alexSA
|
|
« Reply #2788 on: 10/25/2009 10:15 PM » |
|
Just to follow up on what the Committee is getting at in their report when comparing Ares V Lite to other options:
- on page 67 they say Ares V Lite Dual architecture gets 7mt of cargo to the lunar surface on a crewed mission and 14mt of cargo on a single Ares V Lite cargo flight. This compares favorably with only 2mt of cargo to the lunar surface on a crewed mission of Ares I/V and 15mt for Ares V in a single-cargo launch. For a Lunar First architecture Ares V Lite is thus quite impressive. It allows long sortie missions with a crew of 4 and for 180 day missions with an additional cargo launch.
- on the same page, they say that the Directly Shuttle Derived HLVs with a 3-launch scenario only land about 5mt of cargo on a crewed mission. They also say that a single cargo launcher would get less than 5mt of actual cargo to the lunar surface.
Of course it's hard to say that any of these numbers are correct. What we can say is that they are vetted numbers. They would not have made it into the report without any back-up. Thus we can assume that the analysis of the Committee did provide them with these numbers and that they at least are in the ballpark.
All that being said, from a programmatic viewpoint it is understandable that NASA would rather want Ares V Lite than J-246 given the less complex and more capable (in terms of cargo to lunar surface) architecture.
|
|
|
|
marsavian
|
|
« Reply #2789 on: 10/25/2009 10:16 PM » |
|
280mT for a lunar mission? Total crap. Completely unnecessary.
Whether it's necessary or not is irrelevant.
It is TOTALLY relevant!
The whole reason we have the choices before us are based around the required mass to orbit, TLI, and beyond. It's the one reason why PD makes so much sense going forward: develop a base architecture that can be scaled up over time to launch the necessary mass in sizable chunks that are affordable over the long term.
That's the beauty of Direct: it is 100% scalable, and one of the most affordable options out there.
Ok, so they want 280mT to LEO, you take the Jupiter, stretch the tank, add a 5th SSME, use 5-seg SRB.... oh wait, you now have an Ares V Classic don't you? You'd actually be beating the Ares V Lite in total lift if my estimation is right, yes?
Don't you bother to read the links posted in replies ?
|
|
|
|
