He wanted the ability to land at any point on the moon and did not want to use L1/l2 staging to do so. The drives some requirements delta V and time it takes to return home.

The 6 months unmanned and undocked was due to ability to support a moon base (i.e. leave Orion in a parking orbit and return). This however causes an interesting problem because fuel cells are not a good trade over this amount of time. So instead of fuel cells, Orion would use solar panel and battery plus water tank for crew.

The capsule was also sized to support 6 to LEO and 4 to the moon. But the mass of the capsule is too much for the parachute system to handle loaded with 6 people and thus the crew is stuck at 4.

It is the radiant heat from the burning aluminum in the deflagrating and raining solid propellant elements that is most likely to melt the plastics in a capsule’s parachute and cause a failure. In the event that the range safety officer has to activate the shape charge on an SRB and rupture it — or the SRB detonates/deflagrates on its own — this is the biggest risk to the capsule. The likelihood of actual pieces of solid propellant from a deflagrating SRB making contact with the parachute and directly burning holes in it is less.

“The argument could be made for a ruptured propellant tank.”

No, it couldn’t. Unlike a solid rocket motor, liquid propellant in a tank is not burning or even rapidly expanding when it is ruptured. You have to introduce an external flame or high heat source in the right environment, like the flame from an SRB o-ring burn-through as happened on Challenger, for example. In the absence of an external flame/heat source, a mere ruptured liquid propellant tank will just vent propellant.

“The escape system is designed to pull the capsule away, vertically and laterally.”

Of course.

But that means nothing if the escape system can’t pull you away faster than a high-thrust SRB is chasing you.

And it means nothing if you have two high-thrust SRBs chasing you from different angles, giving you a very narrow or no escape trajectory.

And it means nothing if the thermal environment from a deflagrating SRB is too large to navigate your capsule and its parachute around.

“The hazards are no different.”

They are qualitatively the same but quantitatively they are very, very different. Shuttle SRBs contain an order of magnitude more energy than Atlas V SRBs, they’re firing for 30% longer, and there’s two of them.

“I can see you have not done FMEA before.”

I can see that you know nothing about FMEA.

In FMEA, you analyze both the severity _and_ likelihood of an event.

In this case, the Shuttle SRBs have a greater likelihood of colliding with a capsule than the Atlas V SRB because they burn longer, they’re faster, and there’s two of them.

Also in this case, the much greater energies involved in two, big Shuttle SRBs creates a much larger thermal environment for a capsule to navigate around than one, small, Atlas V SRB, again increasing the likelihood that the plastics in the capsule’s parachute will be compromised and the capsule will plummet to the ground.

“You are one of the yahoos speaking in extremes about SRBs in manned applications.”

It’s not extreme to state that two SRBs that fire for ~30% more time and possess 10x more energy pose a much greater risk to a safe crew abort than one SRB that fires for 30% less time and possesses 10x less energy.

Given these numbers, only an idiot would claim that the Shuttle and Atlas SRBs pose comparable risks to a safe crew abort.

It’s like claiming that two M-80 firecrackers pose the same risk as one little Black Cat firecracker. Or that two .44 Magnums pose the same risk as a BB gun. All are dangerous to a degree, but only an idiot would say that the former examples are as dangerous as the latter examples.

“I was just trying to point out the fallacy of your thinking,”

All you’ve done is put your own utter ignorance on display about FMEA fundamentals, the differences between various SRB designs, and the differences between qualitative and quantitative analysis.

What a total idiot you are.

“My source is one of the SpaceX executives in negotiations with NASA for LC-39A.” ROFLMAO you’ll have to do better than that… consider the source– quite unreliable. Tick-tock, tick-tock.

It is not ‘radiant heat’ that is the hazard. It is uncontained burning chemicals! The argument could be made for a ruptured propellant tank. The escape system is designed to pull the capsule away, vertically and laterally. The hazards are no different. I can see you have not done FMEA before.

The threat posed by the Atlas V SRB to a CST-100 abort is not comparable the threat posed by the Shuttle SRBs to an MPCV abort.

You are one of the yahoos speaking in extremes about SRBs in manned applications. I was just trying to point out the fallacy of your thinking, and I think I’ve done that.

The point is that the Shuttle SRBs on SLS pose a crew abort risk for about 30% longer than the Atlas 412 SRB. That’s significant.

“The hazards are similar.”

The hazards are not quantitatively “similar”.

A Shuttle SRB has a thrust level an order of magnitude higher (10x) than the Atlas V SRB. And there are two Shuttle SRBs compared to the one Atlas V SRB. That makes it much harder for MPCV to get away from and avoid a collision with the Shuttle SRBs in the event of an abort during the first 90-odd seconds of flight.

If the SRBs have to be ripped open during the abort, the radiant heat from the burning propellant on the two, big Shuttle SRBs is also going to extend over a much larger volume than the one, small, Atlas V SRB. This is going to make it much more difficult for the MPCV to navigate a landing without its parachute burning up and dropping the crew to their death in the event of an abort during the first 90-odd seconds of flight.

On top of all that, the two Shuttle SRBs fire for 120-odd seconds, and thus expose the crew to these abort risks for 30% longer than the Atlas V SRB.

Put it this way — if you’re in a car, which is much more difficult to get away from? A kamikaze driver in a Honda carrying a black powder bomb and only enough gas for 90 seconds of driving? Or two kamikaze drivers in two Ferraris, each packed with C4 and enough gas for 120 seconds of driving?

“Thank you are acknowledging my point”

I did not acknowledge your point. The threat posed by the Atlas V SRB to a CST-100 abort is not comparable the threat posed by the Shuttle SRBs to an MPCV abort.

I’m not the only one who thinks so. The Air Force has raised serious concerns about the Shuttle SRBs in a capsule abort, but has raised no such concerns about the Atlas V SRB.

http://www.physorg.com/news167210662.html

“, and thanks for your opinion. Boeing engineers think otherwise.”

I never questioned the judgement of the Boeing engineers. I questioned your assertion that the threat posed by the Atlas V SRB to a CST-100 abort is comparable the threat posed by the Shuttle SRBs to an MPCV abort. It’s not.

Nonsense. They are responsible for much more than that (e.g., ensuring no damage to uninvolved third parties, no EMI interference with other systems, environmental issues, payload compliance with national security requirements, all issues relating to the OST and Liability Convention, etc.), though they do not currently have statutory authority to regulate passenger safety. No one does.

Also as a quick addition. There is no such thing as a 100% risk free rocket. All we can do is to reduce risk to the best of our ability and insure that there is an abort system that has the capability to detect as many of the probable failures that it can, and safely remove the crew from harms way. If, as a nation, we demand no failures then there is no point in continuing the space program.

“All of you lost the SRB argument long ago.”

See my point above about large grain stand alone combustion oscillations.

How this slipped through NASA safety early in the Ares 1 design process really needs to be looked at. They’re supposed to be rocket scientists, ya know.

pathfinder – What the hell kinds of architectures was Griffin thinking about?

No commercial entity is going to use LC-39. That has been stated by the few commercial entities that exist Spacex is looking to LC-40 for both F9 and FH.

Wrong. My source is one of the SpaceX executives in negotiations with NASA for LC-39A. Your source is …?