_Augustus_

NASA SLS/Orion/Payloads

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22 hours ago, Bill Phil said:

But you're trading an increase in the occurrence of failures for an increase in redundancy for those failures. More things will go wrong, but the system as a whole is more capable of handling those events than a heavy lift architecture.

Oh?  And where does that redundancy and capability come from?  No program funds flight ready spares anymore.  Certainly you have the theoretical capability to delay a flight for years to decades while the next flight's unit is hurried through the process, but at the end of the day that's not significantly different from a heavy lift architecture.

What do you think would have happened to ISS if (say) Destiny had been lost in a launch accident?

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@DerekL1963 makes a really good observation. Unless the mission plan is to send multiples, and is funded such that the mission 2 craft is ready at the same time as mission 1, then any LOM failure of any component, assembled on orbit, or launched all up (or merely fewer, larger pieces) is equivalent in terms of outcome---you are waiting for the next launch window at the very least. If you do the multiple, smaller pieces modality, then you need the spares good to go, and LVs to put them up. You also need to have them assembled far enough in advance that your schedule can deal with loss of flight issues.

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22 hours ago, DerekL1963 said:

Oh?  And where does that redundancy and capability come from?  No program funds flight ready spares anymore.  Certainly you have the theoretical capability to delay a flight for years to decades while the next flight's unit is hurried through the process, but at the end of the day that's not significantly different from a heavy lift architecture.

What do you think would have happened to ISS if (say) Destiny had been lost in a launch accident?

I suspect that NASA figured that US manned flight wouldn't survive such a loss and there was no justification for other plans.

As long as congress (or whoever else controls the spending) insists on micromanaging things you will get cases like this.  I'm fairly certain it would make a lot more sense to have split the shuttle program into manned and unmanned [cargo] missions, but that would let Congress simply cancel the manned missions so NASA never gave them the option.

Don't underestimate Blue Origin.  Bezos may not have [personally] the engineering chops to micromanage the program like Elon Musk, but at least that is the only space program that isn't ultimately answerable to politics.

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On 6/22/2017 at 0:18 PM, wumpus said:

Don't underestimate Blue Origin.  Bezos may not have [personally] the engineering chops to micromanage the program like Elon Musk, but at least that is the only space program that isn't ultimately answerable to politics.

Their Moon lander is entirely banking on POTUS wanting a moonbase instead of a Mars mission.......

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On 6/21/2017 at 0:14 PM, DerekL1963 said:

Oh?  And where does that redundancy and capability come from?  No program funds flight ready spares anymore.  Certainly you have the theoretical capability to delay a flight for years to decades while the next flight's unit is hurried through the process, but at the end of the day that's not significantly different from a heavy lift architecture.

What do you think would have happened to ISS if (say) Destiny had been lost in a launch accident?

The extra redundancy comes from the fact that two thirds of the launches are bulk materials. Launch failure on propellant? No problem. We were building 20 or more of those modules regardless.

What would happen to any potential Mars mission if the return vehicle fails? It has to be there years in advance and must be in place and in perfect operation millions of kilometers away with no one nearby to maintain it.

So that program would have even more risk than the ISS. It has to rely on a launcher which hasn't flown even once, and the equipment has to work perfectly with no hope of fixing it if anything breaks. 

Using Earth orbit rendezvous allows the crew to have everything they need and potentially fix it if and when something goes wrong. And if you want extra redundancy, build multiple Mars ships. And build extras. 

Actually, there were some spare modules for the ISS. Albeit not for Destiny.

If Destiny was lost in a launch accident, I don't know what would happen. Considering that it flew on a shuttle, there'd be quite a few other issues that NASA would face besides losing a station module. But Atlas V has an amazing launch record.

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@Bill Phil, you literally need a spare for everything. If the architecture uses fueling, then you indeed just need a tanker, but that implies stage reuse, otherwise it requires excess tanks. If the spacecraft is 4 modules, then you need at least 2 of all of them, which really tends to mean 3, as NASA likes to keep a flight article around for Apollo 13 moments.

Assume that you build the craft well in advance to avoid delay problems, and provide some scheduling room for a LOM event on a component,  You still need the spares ready to go, because the lead time on those almost certainly exceeds a launch synod to Mars.

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3 hours ago, tater said:

@Bill Phil, you literally need a spare for everything. If the architecture uses fueling, then you indeed just need a tanker, but that implies stage reuse, otherwise it requires excess tanks. If the spacecraft is 4 modules, then you need at least 2 of all of them, which really tends to mean 3, as NASA likes to keep a flight article around for Apollo 13 moments.

Assume that you build the craft well in advance to avoid delay problems, and provide some scheduling room for a LOM event on a component,  You still need the spares ready to go, because the lead time on those almost certainly exceeds a launch synod to Mars.

Yeah. Even so, heavy launchers also suffer similar issues, if not worse, as the hardware has to be en route to Mars as well as on Mars and perfectly operational. So unless we launch two habs, two return vehicles, and two landers per mission for redundancy, then we can easily have astronauts stranded or worse, dead. No infrastructure to support the mission makes it an enormous risk. 

Of course, we can still do EOR with heavy lift. Direct-style missions have some big fallback issues.

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I suppose the question is the chance of failure. If each LV has a standard of 1:200 LOM failure, then the more launches, the more chance of failure.

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1 hour ago, tater said:

I suppose the question is the chance of failure. If each LV has a standard of 1:200 LOM failure, then the more launches, the more chance of failure.

OTOH the more times you launch, presumably the better the data you get on LOM probabilities and more opportunities to iron out problems which ultimately should help prevent future lost vehicles.

Consider the chances of an airplane crashing due to mechanical conditions now with say 50 and a 100 years ago.  A lot of planes went down in the process of improving safety but things were learned along the way which improved safety going forward.

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5 hours ago, Bill Phil said:

The extra redundancy comes from the fact that two thirds of the launches are bulk materials. Launch failure on propellant? No problem. We were building 20 or more of those modules regardless.


Which part of "nobody builds flight ready spares" was too difficult to grasp?  That's true for boths numbers and schedule.  If the mission calls for four tanker modules, then there's going to be four tanker modules.  Period.  If there's another mission in the next window, they're going to be somewhere in the pipeline - not sitting around waiting to be used in this window.
 

5 hours ago, Bill Phil said:

If Destiny was lost in a launch accident, I don't know what would happen.


Yet you're blithely certain that losing a part of your Mars craft won't be a problem.  This does not compute.
 

5 hours ago, Bill Phil said:

Using Earth orbit rendezvous allows the crew to have everything they need and potentially fix it if and when something goes wrong.

0.o  Everything they need to potentially fix any problem?  No way in a very hot place.   EOR or heavy lift, you're still weight limited by your transfer stage, by how accurately your engineers calculated what spares you'll need, and by budget.  (Trust me, from bitter experience I assure you that the engineers get it wrong sometimes - even for mature systems with decades of operational experience.)  You also presume the vehicle is designed to be extensively maintained in flight.
 

5 hours ago, Bill Phil said:

But Atlas V has an amazing launch record.


So far.  But with only seventy odd launches so far, a loss in the next ten or fifteen would immediately move it from "very amazing" to "among the worst of currently operational vehicles".  (Worse than the Shuttle!)

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Also remember that it need not be a catastrophic failure, it could simply end up in the wrong orbit, for example. 

You could mitigate problems by sending up something like the crew transfer vehicle as a single large part, then schedule such that the transfer stages have one complete ahead of the mission for the next transfer. For example you use 3 propulsion stages that are identical. 1 for TEI, and 2 for TMI (I recall seeing something like this in a DRA, though the TEI might have varied). Make sure you have one built ahead for the next mission and you can deal with a single launch issue.

This would be smart, but very atypical.

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4 hours ago, tater said:

This would be smart, but very atypical.


And it would also make incorporating any "lessons learned" or variability due to mission more expensive and difficult.  It's pretty much always so for changes of any significance, more difficult and expensive to modify than to make the changes during production.

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If they could use all of their budget, it'd happen. But they're not allowed to do that, and for good reason.

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On ‎6‎/‎27‎/‎2017 at 8:02 PM, DerekL1963 said:


Which part of "nobody builds flight ready spares" was too difficult to grasp?  That's true for boths numbers and schedule.  If the mission calls for four tanker modules, then there's going to be four tanker modules.  Period.  If there's another mission in the next window, they're going to be somewhere in the pipeline - not sitting around waiting to be used in this window.
 


Yet you're blithely certain that losing a part of your Mars craft won't be a problem.  This does not compute.
 

0.o  Everything they need to potentially fix any problem?  No way in a very hot place.   EOR or heavy lift, you're still weight limited by your transfer stage, by how accurately your engineers calculated what spares you'll need, and by budget.  (Trust me, from bitter experience I assure you that the engineers get it wrong sometimes - even for mature systems with decades of operational experience.)  You also presume the vehicle is designed to be extensively maintained in flight.
 


So far.  But with only seventy odd launches so far, a loss in the next ten or fifteen would immediately move it from "very amazing" to "among the worst of currently operational vehicles".  (Worse than the Shuttle!)

Nobody builds flight spares at the moment. And actually, there are flight spares. Just not for every piece of hardware.

The mission I'm referring to calls for more than four. It calls for the spares, as well. That's kind of the point. Redundancy. You make the assumption that something will break, so you build spares.

I'm not saying that losing part of the Mars craft won't be a problem, I'm saying that it would be a far smaller problem than losing a part of a heavy lifter mission profile, each and every part is absolutely key to mission success. Part of the Mars craft built using EOR can break, but if it breaks in LEO, then it's not doomed to die. If it breaks en route to Mars, then the other vehicles can support the crew. Sending multiple transfer vehicles.

Yes they have everything they need to fix any problem. Or at least continue the mission even if a large portion of the hardware has been destroyed. Again, that is the entire point.

I presume the vehicle is designed to be maintained in flight because that's just common sense. Again, we're talking hypotheticals here. If it came down to a small flotilla of multiple ships, spreading the risk around so that the mission has a higher chance of success, and letting us find problems with the spacecraft in cis-lunar space (before we send people to their doom), we can reduce the risk significantly. Compared to just sending people out there on a transfer habitat and hoping that everything works, with very little actual flight certification (we did this with Apollo, that's why 13 happened, with EOR, it may have never occurred, or even if it did, the issue would have been much smaller and less deadly), that's much safer. If we're going to send people millions of kilometers away on voyages lasting years, we should not, under any circumstances, half-cheeks it. If we do, people will be exposed to unnecessary risks.

What I'm talking about here is a mission profile that is designed to not get astronauts killed by testing and repairing hardware close to home for a long time, and hammering out the big issues. But, accepting that that is not enough to ensure success and survival, we should also send multiple vehicles for redundancy. That way, when something goes wrong with one of them (as it is guaranteed, Murphy's Law), the others can provide assistance. Heavy lift is not necessary, but even with heavy lift, it would be a very good idea to use EOR, so that we can do a large amount of hardware testing in our backyard.

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2 hours ago, _Augustus_ said:

Seeing as NASA just admitted that it can't afford putting humans on Mars or even the Moon I think SLS/Orion will soon be cancelled by POTUS, Congress, or both.

https://arstechnica.com/science/2017/07/nasa-finally-admits-it-doesnt-have-the-funding-to-land-humans-on-mars/

In general, I'd considering it a losing bet that congress would do anything because it is logical... and don't get me started on the POTUS.

 

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13 hours ago, Bill Phil said:

And actually, there are flight spares. Just not for every piece of hardware.

Well, since we're talking about "every piece of hardware" (I.E. entire mission modules)...  My statement "Nobody builds flight spares" holds.
 

13 hours ago, Bill Phil said:

I'm not saying that losing part of the Mars craft won't be a problem, I'm saying that it would be a far smaller problem than losing a part of a heavy lifter mission profile, each and every part is absolutely key to mission success.


0.o  No offense, but this statement makes zero sense whatsoever - because regardless of the mode (EOR or Heavy Lift), each and every part is going to be absolutely key to mission success.

 

13 hours ago, Bill Phil said:

What I'm talking about here


Is a fantasy mission where what real world concerns aren't addressed by vast increases in budget are simple airily hand waved away.

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Yeah, you are either prepared to quickly relaunch any lost mission component, or you are not. NASA will not be prepared in that way, it's too expensive.

Even one part/module missing means you're not going.

Alternate architectures are plausible in emergency situations (think Apollo 13), but NASA is not leaving Earth with pieces missing.

Edited by tater

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23 minutes ago, DerekL1963 said:

Well, since we're talking about "every piece of hardware" (I.E. entire mission modules)...  My statement "Nobody builds flight spares" holds.

NASA used to launch their "spares".  Think Voyage 1 and Voyager 2, various pioneer and viking pairs.  This made a lot of sense since the second article build cost a fraction of the first.  Presumably cost and computer modeling effectively obsoleted this practice, but I still think it was a good one (and I think essentially used in Opportunity/Spirit Mars rovers).

"Use the spares" works great if you have need of more than one type of similar part (and the unique parts are rare and not overly expensive to duplicate) and is a standard means of engineering reliability.  Can't say there are obvious ways to use it going to Mars (and it certainly was never designed into SLS) beyond basics such as engines and fuel/oxidizer tanks.

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In the case of what we are talking about, you'd need spares of all mission modules, and LVs for them as well.

I suppose the calculus could be (assuming identical LVs for the components) to have module spares, and one excess LV. It would. It be a 100% mitigation of risk, but would allow for one LOM failure out of X required launches.

Still won't happen, though :) . Too expensive.

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11 hours ago, wumpus said:

NASA used to launch their "spares".  Think Voyage 1 and Voyager 2, various pioneer and viking pairs.  This made a lot of sense since the second article build cost a fraction of the first.  Presumably cost and computer modeling effectively obsoleted this practice, but I still think it was a good one (and I think essentially used in Opportunity/Spirit Mars rovers).

Don't forgot Curiosity and M2020. The instrumentation is different but the build, RTG, etc. are the same.

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9 hours ago, _Augustus_ said:

Don't forgot Curiosity and M2020. The instrumentation is different but the build, RTG, etc. are the same.

Building upon a proven design is a far cry from building a spare.

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Interesting.

Using already flow vehicles? That pretty much means a Centaur based lander, which is not that far-fetched.

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