Quote from: RanulfC on 04/17/2015 07:14 pmQuote from: Eerie on 04/17/2015 06:56 pmQuote from: Impaler on 04/17/2015 02:43 am But for the full blown system you clearly need to be using this vehicle as a crewed launch vehicle and it is impossible to see how you can put people in this vehicle and rescue them when a launch failure happens.Ehm, you know airplanes, right? They transport hundreds of people without a rescue systems. When they fail, everyone on board dies. It just happens rarely enough for the society to accept the risk.How old are you? If you're over 25 you should be aware that crashes were MUCH more common even 20 years ago than today and MUCH higher before that. Society "accepted" it (but complained a lot anyway) because air travel was fast and relatively "safe" and people were more concerned with "time" than safety.(The math did show that you were more likely to die in a car crash than a plane crash but cars rarely carried over 70 passengers so "individually" the odds were on your side )Rockets are inherently more dangerous than aircraft. They are put under more stress and perform across a much greater envelope than any aircraft and it is NOT that hard to design in sufficient safety to mitigate almost all the dangers involved so why NOT do so?Wow. Not hard? What planet are you from... This has to be one of the most stunning proclamations I have read on this forum. There will always be mass penalties and engineering compromises. Making the Shuttle as safe as you seem to want it would have crippled it.Accept the risk and move on. You yourself wrote "Rockets are inherently more dangerous than aircraft", so more risks will be expected and accepted. If this bothers you, others will gladly take your place in line.Here's the ultimate safe vehicle for you: One that doesn't go anywhere.
Quote from: Eerie on 04/17/2015 06:56 pmQuote from: Impaler on 04/17/2015 02:43 am But for the full blown system you clearly need to be using this vehicle as a crewed launch vehicle and it is impossible to see how you can put people in this vehicle and rescue them when a launch failure happens.Ehm, you know airplanes, right? They transport hundreds of people without a rescue systems. When they fail, everyone on board dies. It just happens rarely enough for the society to accept the risk.How old are you? If you're over 25 you should be aware that crashes were MUCH more common even 20 years ago than today and MUCH higher before that. Society "accepted" it (but complained a lot anyway) because air travel was fast and relatively "safe" and people were more concerned with "time" than safety.(The math did show that you were more likely to die in a car crash than a plane crash but cars rarely carried over 70 passengers so "individually" the odds were on your side )Rockets are inherently more dangerous than aircraft. They are put under more stress and perform across a much greater envelope than any aircraft and it is NOT that hard to design in sufficient safety to mitigate almost all the dangers involved so why NOT do so?
Quote from: Impaler on 04/17/2015 02:43 am But for the full blown system you clearly need to be using this vehicle as a crewed launch vehicle and it is impossible to see how you can put people in this vehicle and rescue them when a launch failure happens.Ehm, you know airplanes, right? They transport hundreds of people without a rescue systems. When they fail, everyone on board dies. It just happens rarely enough for the society to accept the risk.
But for the full blown system you clearly need to be using this vehicle as a crewed launch vehicle and it is impossible to see how you can put people in this vehicle and rescue them when a launch failure happens.
Quote from: Lars-J on 04/17/2015 07:44 pmHere's the ultimate safe vehicle for you: One that doesn't go anywhere.If SpaceX loses an MCT or BFR full of paying customers, they will face a bigger risk of bankruptcy than the passengers themselves risked prior to buying tickets. It's in SpaceX's interest to make those craft as safe as possible.
Here's the ultimate safe vehicle for you: One that doesn't go anywhere.
Impaler. Good comments. A few additional ones in response.Quote from: Impaler on 04/17/2015 02:43 amThese integrated 2nd stage concepts have some unavoidable problems.* No possible abort during launch, the propellent mass is simply too high for the large vehicle to have any appreciable acceleration away from an exploding 1st stage. For our early missions when crews are just a handful of explorers it's easy enough to put them on F9 to rendezvous with the MCT that launches un-manned. But for the full blown system you clearly need to be using this vehicle as a crewed launch vehicle and it is impossible to see how you can put people in this vehicle and rescue them when a launch failure happens.The MCT going to MArs would launch first, and be uncrewed. Several subsecquent launches would come up bringing propellant and other provisions. Lastly would come up the crew and probably the LH2 feedstock for making the methalox on the surface.So the Mars-MCT doesn't need an LAS system. The other LEO-MCT could have one, as it could withstand the mass penalty of it. It would just then take more launches to get the adequate propellant, provisions, and crew to the Mars-MCT prior to departure. However, we need to really ask ourselves, what would the LAS on the LEO-MCT need to be? If the 2nd stage -is- the Spacecraft, then really the only "abort" scenario is if the booster is failing during the first 2-2.5 minutes of ascent. Once staging has occured and the upper stage lit, there's really no abort option. If it blows up, there's a LOC. If there's some other issue, it can actually divert to an alternate landing area and come back down and land before reaching orbit.If the MCT spacecraft where to have landing thrusters like Dragon, the LEO-MCT could be built with enough of them to do an emergency separation from the booster and much the spacecraft away from the booster.So you really need to look at what and how you are aborting. MCT landing engines should be able to do an emergency separation in any condition but a catestrophic booster explostion....and those would be pretty rare. If you feel you need to be able to abort during a full booster explostion, more landing thrusters could be added, or a large tractor down, or something else. Again, that wouldn't be needed for the Mars MCT as that would launch unmanned.And as you say, earlier flights where the system doesn't have a lot of flights under it's belt, they may launch the crews on Dragon. I can't imagine early Mars missions would have more than like 14 people anyway. Two Dragons can do that. Quote from: Impaler on 04/17/2015 02:43 am* Highly unstable landing on Mars, with is extreme height your in great danger of toppling over. Even if cargo hold is in the bottom as Lobo's sketch indicates the tanks above are going to have residual propellent, and center of mass will be higher above the ground then the leg base is wide. We have seen how difficult it is to keep F9 first stage strait on landing and that is on a flat surface. On Mars your surface can be both rocky AND it can give-way during landing or even after, say if subsurface ice sublimates you end up like the Leaning tower of Pisa.Both these problems make the system more dangerous then I think is acceptable.Hard to know if the cargo would be on the bottom, or on top and use a swing out crane or something. This stability issue will be the issue with any vertical lander, and I don't know if SpaceX is looking at anything but a a vertical lander. So issues of landing will be inherrent whether my integrated stage concept, or a separate dedicated spacecraft.Remember, whatever that spacecraft looks like, it will need to carry enough propellant on board to get itself back to Earth. So it will be tall no matter what, unless they switch to a horizontal lander or something.
These integrated 2nd stage concepts have some unavoidable problems.* No possible abort during launch, the propellent mass is simply too high for the large vehicle to have any appreciable acceleration away from an exploding 1st stage. For our early missions when crews are just a handful of explorers it's easy enough to put them on F9 to rendezvous with the MCT that launches un-manned. But for the full blown system you clearly need to be using this vehicle as a crewed launch vehicle and it is impossible to see how you can put people in this vehicle and rescue them when a launch failure happens.
* Highly unstable landing on Mars, with is extreme height your in great danger of toppling over. Even if cargo hold is in the bottom as Lobo's sketch indicates the tanks above are going to have residual propellent, and center of mass will be higher above the ground then the leg base is wide. We have seen how difficult it is to keep F9 first stage strait on landing and that is on a flat surface. On Mars your surface can be both rocky AND it can give-way during landing or even after, say if subsurface ice sublimates you end up like the Leaning tower of Pisa.Both these problems make the system more dangerous then I think is acceptable.
If SpaceX loses an MCT or BFR full of paying customers, they will face a bigger risk of bankruptcy than the passengers themselves risked prior to buying tickets. It's in SpaceX's interest to make those craft as safe as possible.
The obsession with avoiding risk in our society is pathological.
What's pathological is this belief by Space-Cadets that all the problems with our space program be be boiled down to 'timidness' and 'spinelessness', and taking greater risks with human life will magically yield the glory they seek.It is a simplistic, self-gratifying message that conforms to the general anti-government ideology and 'nanny state' bogyman of the political right-wing. But it bears no resemblance to reality, NASA engineers when faced with envelope pushing performance demands and inadequate funding (both the fault of Congress) have in fact sacrificed safety REPEATEDLY and become quite cavalier in doing so.SpaceX success has been based on internally NOT making the mistakes Congress cripples NASA with, Musk adequately funded the company and it's internal development and he dose not make absurd performance demands. This gives them the engineering headroom to make their system SAFER then NASA equivalents. Elon is smart, he knows this is what space travel needs to be if it has any chance of succeeding as a means of colonization. People with large amounts of disposable income (and very good earning potential if they stay on Earth) are not going to accept 1-2% chances of dieing in a fireball on the launch pad to go to Mars, Mars is not THAT attractive of a place. This is not 1620 in which religious dissidents and peasants in Europe consider a leaky boat to America better then wars and plagues in their home land, and even then the death rate in crossing the Atlantic was only 2% on the Mayflower, people are going to rightfully demand better then that after 500 years of improved living standards and technology development.
How many times have we had this discussion on aborts with no definite conclusion again?
Nobody is somehow blaming this on the "nanny state". Decades down the line, launch may very well be the part of a journey to Mars least likely to fail. At some point it doesn't make sense to make design compromises in a low-margin system to catch every failure mode. It's not likely to be feasible to build a launch escape system that works on Mars, and not every abort from a failing booster on Earth is going to require a high-g escape.
What's pathological is this belief by Space-Cadets that all the problems with our space program be be boiled down to 'timidness' and 'spinelessness', and taking greater risks with human life will magically yield the glory they seek....NASA engineers when faced with envelope pushing performance demands
If you don't think MCT will land back on Earth or even on Mars, then you are saying SpaceX will need to develop 2 additional large vehicles to do so. Dragon certainly isn't cheap enough to do this. Sounds like a very complicated and expensive architecture.
This Space-Cadet (actually, I'm a scientist and space enthusiast for 50+ years) never referred to NASA...But if you choose to wear it, it's your shoe.The point I was making is that the SpaceX Mars goals are not compatible with zero risk tolerance. Having the trip to Mars always decades in the future is the only zero risk strategy.Note: What is pathological, in my thinking, is our society's (in US of A) aversion to perceived risk, based in part on our lack of technical education to judge actual risk.
As to MCT's LAS, I think it will have none. This is because I'm one of the small minority here that think MCT will not take off from Earth with crew aboard. Cargo, yes. Provisions, yes. Heat shield for Earth re entry, no. Fuel for TMI, no. I don't think the 'fleet' of MCTs will ever return to Earth's surface. Not sure about Mars surface either... after all, 'land the whole thing' is only four words. And those words were in reference to the Mars end of the trip.
The only way a complete MCT would be capable of launch abort would be if it was launched with a minimal fuel load relative to its large capacity. Full tanks don't work for high-G abort at max Q, there just isn't enough thrust.This would require:1) That crew is not onboard, because it will take months/years to fill those tanks and crew won't want to spend all that time waiting in orbit2) That the MCT not be used to achieve orbit. This means that there need to be two or more likely 3 stages *below* the MCT.Better to just send the crew up at a later date, after the MCT is fueled in orbit.-----A nosecone capsule has been a repetitive conclusion in my designs. I keep trying to remove it and finding it's congruent with some other purpose.