What is "Man rated"?

[dwightlooi]

What exactly makes a launch vehicle man rated? NASA keeps pulling this term out of the hat as an excuse to retain the Shuttle infrastructure, but what exactly does it mean? NASA has never been specific about it and always appear to be dodging the question. Is it the mission success rate of the booster system? Is it benign failure modes? Is it the probability of successful crew salvage in the event of a catastrophic failure during launch and/or ascent? The truth is we don’t know and the more one think about it the more it sounds like a completely meaningless term whose purpose is none other than a tool for BS.<br /><br />If being man rated means benign failure modes, crew survivability and safety record, the shuttle should not be man rated at all! SRBs by definition do not have benign failure modes – they either work as advertised or they kill you. They are simple and generally very reliable, not to easily mention storable, but when they fail they generally do one of two things – they blow up or they get madly out of control., Even if you detect an impending failure, such as a failing gimbal mechanism or a case rupture, there is nothing you can do about it but accept your fate and die. Once lit solids cannot be turned off, throttled or have anything done to them. Even though the SSMEs have not failed in flight, they are one the most complex and highly stressed liquid engine design. And when the first shuttle went up with a human crew, they had less flight hours than the RS-68. Records aside, RS-68 being a much less complex gas generator cycle engine by design, with lower chamber and line pressures, should be more reliable and predictable. Yet, NASA insists that they consider the SSME “man-rated” but not the RS-68 (or the RD-180 for that matter). In terms of the ability to get the crew to safety in the event of a launch failure, the shuttle has NO launch escape system period. There is no way for the crew to bail out once the shuttle leaves the pad and no way for the shu

 

[pathfinder_01]

The EELV although very reliable are built with the idea of caring cargo. At a minimum the EELV would need some sort of system to warn the CEV of impending disaster so that the crew can get out. In addition what will the g-forces and accelerations are like on the crew? An EELV does not have to have a smooth ride. It is much easier to beef up cargo to withstand a rough ride than people. Also the shuttle’s launch record at the moment is about equal to any EELV. <br /><br /> Also frankly I don’t think that manned space flight can be done for 80 million at the moment. I am no accountant, but a shuttle launch cost $600 mill or so, the delta heavy comes is estimated to come in at $170 mil or so (just for cargo). There are some cheap launches but they started at $40 mil and I doubt they have the performance to launch crew, a couple of day’s worth of supplies, a life support system, and a reentrylanding system. <br /><br />Also I think the way to reduce costs is to keep infrastructure intact for as long as it makes sense. What I dislike greatly about NASA has been its inability to create multiple manned launch systems based on common elements. Or use the same booster for many years like the Russians. The keep incurring development costs and development risks which have a tendency to eat up any gain. I sort of semi lean towards splitting Nasa into two programs one which focuses more on the r/d of spaceflight and the other that focuses on actually getting there. <br />

 

[gunsandrockets]

"[man rating is] a completely meaningless term whose purpose is none other than a tool for BS."<br /><br />There is more than a little truth to that. In fact recent statements by Griffin against using EELV because of "man rating" issues contradict his earlier testimony to Congress on the very same issue!<br /><br /><br />http://www.spaceref.ca/news/viewsr.html?pid=9138<br /><br />"What challenges may NASA face in using an Expendable Launch Vehicle (ELV) as the boost vehicle for the OSP? Does the use of an ELV for human spaceflight pose an unacceptable risk?<br /><br /> In the 1950s and 1960s, the term "man rating" was coined to describe the process of converting the military Redstone, Atlas, and Titan II vehicles to the requirements of manned spaceflight. This involved a number of factors such as pogo suppression, structural stiffening, and other details not particularly germane to today's expendable vehicles. The concept of "man rating" in this sense is, I believe, no longer very relevant." <br /><br /><br /><br /><br />I have to admit I have lost a little respect for Griffin because of this. Perhaps the raw data for the SRB really do favor it over the EELV for use as a manned launcher. But I can't help but think the real reason for favoring the SRB is because use of a manned SRB supports Griffin's major objective which is development of a shuttle derived heavy lift vehicle. <br /><br /><br /><br /><br />

 

[gunsandrockets]

"Also frankly I don’t think that manned space flight can be done for 80 million at the moment. I am no accountant, but a shuttle launch cost $600 mill or so, the delta heavy comes is estimated to come in at $170 mil or so (just for cargo). There are some cheap launches but they started at $40 mil and I doubt they have the performance to launch crew, a couple of day’s worth of supplies, a life support system, and a reentrylanding system."<br /><br />Hmmm...well the Russians will sell you a seat on Soyuz for 20 million. That adds up to 60 million per 3 man Soyuz mission. The Space Shuttle, at a cost of 1 billion per flight with a crew of seven, comes out to 142 million per seat or seven times the cost of the Soyuz. <br /><br />

 

[dwightlooi]

<i>The EELV although very reliable are built with the idea of caring cargo. At a minimum the EELV would need some sort of system to warn the CEV of impending disaster so that the crew can get out. In addition what will the g-forces and accelerations are like on the crew? An EELV does not have to have a smooth ride. It is much easier to beef up cargo to withstand a rough ride than people. Also the shuttle’s launch record at the moment is about equal to any EELV.</i><br /><br />The EELVs have very smooth rides. The Delta IV medium or Heavy without SRBs are especially gentle. It is the Shuttle which shakes and vibrates during the first minute and a half of launch -- due to the pair of 2.6 million pound thrust SRBs. If ride quality is a concern, a CEV launched atop a SRB as it's first stage will be the worst!<br /><br />As far as not having a launch escape system on the EELV, that is not really a problem. The launch escape system is generally designed into the capsule system (CEV in this case) not the booster. Whether it comes in form of an escape tower tip atop the CEV or in form of a solid rocket at the vehicle's base, it'll integrate into the EELV just fine. As a matter of fact, the shuttle is the only existing human booster that doesn't have any launch escape mechanism.

 

[no_way]

Here's the long answer: <br />http://www.transterrestrial.com/archives/000991.html<br /><br /><i>There is another factor that drives this decision. It's called "man rating." This is a concept that everyone who is familiar with space programs thinks they understand, and that very few, in fact, do. The myth here is that vehicles designed to carry people are intrinsically more expensive to design, build and operate, because they are "man rated." Now in the case of the next-generation Shuttle envisioned by NASA, even without a crew, the vehicle will still have to be "man rated," because it's meant to carry passengers in a separate module in the payload bay, so they won't get the cost savings that conventional thinking would indicate by not "man rating" it.<br /><br />But the very notion that a space transport, even one that carries pilots and passengers must be "man rated", or that it will cost more than one that doesn't carry crew or passengers, is yet another myth.</i><br /><br />Read on from the article.<br /><br />

 

[najab]

><i>The launch escape system is generally designed into the capsule system (CEV in this case) not the booster.</i><p>True, but the vehicle health monitoring has to be built into the booster to know <i>when</i> to activate the LES.</p>

 

[cuddlyrocket]

'Man rated' simply means that the probabililty of death and/or injury to the crew is below an acceptable level. For obvious reasons, this acceptable level is quite low!<br /><br />The EELVs were designed to carry cargo. The probability of failure of a cargo rocket is set at the level where the expense of obtaining further reliability is greater than the cost of building new rockets and cargo.<br /><br />For instance, suppose you have a cargo rocket that with its payload costs $200 million per flight with a (very high) 98% reliability. Then on average you'd lose 2 rockets per hundred flights - cost $400 million. Say you could improve the reliability to 99% at the cost of $3 million per rocket. This would save you one rocket, or £203 million per 100 flights, or $2.03 million per flight. The increased gain in reliability is not worth the expense. It's cheaper to replace the ones that fail.<br /><br />This economical failure rate is invariably much greater than the acceptable failure rate for crew survivability (astronauts are not considered to be simply replaceable). So man-rating a cargo rocket is expensive, as it usually involves detailed re-designs. And it's the last tenths of a percentage point that cost the most.<br /><br />Shuttle hardware is already man-rated. Not sufficiently, but at least it shows the expense in trying to make it acceptably safe - and this is a rocket that was designed from the beginning to be man rated. The SRBs are actually the most reliable component, having never failed to my knowledge.

 

[najab]

Well, technically (and this is getting <i>really</i> pedantic) the SRB was still producing a substantial proportion of rated thrust when it was destroyed by the RSO.

 

[vogon13]

It was a weird aspect of the Challenger accident. TVC was still attempting to steer SRB on correct flightpath. <br /><br />I do suspect though, at point of RSO command, SRB was probably within seconds of case rupture due to growing hole from burn through. Hoop stresses had to be really extreme on booster casing immediately fore and aft of the burn thru.<br /><br /> <div class="Discussion_UserSignature"> <p><font color="#ff0000"><strong>TPTB went to Dallas and all I got was Plucked !!</strong></font></p><p><font color="#339966"><strong>So many people, so few recipes !!</strong></font></p><p><font color="#0000ff"><strong>Let's clean up this stinkhole !!</strong></font> </p> </div>

 

[drwayne]

I found it amamzing that some of the last commands seen on telemetry were SSME shutdowns due to low pressure in the feed lines.<br /><br />Wayne <div class="Discussion_UserSignature"> <p>"1) Give no quarter; 2) Take no prisoners; 3) Sink everything."  Admiral Jackie Fisher</p> </div>

 

[najab]

Yeah, it probably would have ruptured before burnout, but we'll never know.

 

[radarredux]

I think "man rated" is one of those slippery definitions that can be thrown out to justify a particular need. Goal posts can be moved as needed.<br /><br />Should SpaceX put a capsule on a Falcon V or t/Space pursue the CXV, what guarantees would they have that NASA would certify it for carrying passengers to the ISS? If after years of development could NASA simply say: "The <spacecraft /> isn't as rigid as ours, so it cannot be certified as human rated."<br /><br />If this important criteria isn't well defined on well-founded principals, how can you expect investors to pony up money if a capricious employee (perhaps with a conflict of interest ("Marshall"?)) can block an independently developed system from the market?

 

[the_ten]

I always assumed "man-rated" had to do with systems that enable a human presence... Pressurization, temperature, air, protection from radiation, water, waste, food, etc... Basically everything that would be a human necessity to survive a flight.<br /><br />I'm sure Shuttle_Guy can tell us exactly what it means.

 

[frodo1008]

If we were to go for a really tight definition as some advocate on these boards it would have to go something like this. "Using actual data a vehicle would be man-rated if its actual failure rate was less than 1%."<br /><br />I am certain that the astronauts themselves would be willing to accept this level of risk. Of course, I am not certain that any human rocket system has achieved this yet but you people seem to want something hard and fast and condemn Griffen for advocating less.<br /><br />THis would mean that we would have to have at least 100 ACTUAL launches of the EELV Heavy configurations. This will, of course take well over 10 years. As for the Falcon V, Musk and company haven't even flown the Falcon I yet. The Falcon V is still just a paper study.<br /><br />Heck, even the STS system with 2 actual failures in 114 flights would not qualify!<br /><br />Do you kind of get the picture here? Obviously what I have just pointed out is both an over-simplification and an impossibility. While I was just kidding it does illustrate the level of the problem here. It IS going to take at least some actual (successful) flights of these various vehicles to establich any kind of reasonable failure rate. The only two systems currently that can say this are the Soyus and the Space Transportation System (the shuttle). However, I do hope to see other systems on line by the time the shuttle is retired. What Griffen is saying is that using shuttle hardware in a new configuration is better tested than using relatively untested launch systems like the EELV and the Falcon. If you were to ask the astronauts and cosmonauts they would tell you this also, as they are the ones laying their lives on the line!

 

[dwightlooi]

The way I look at….<br /><br />(1) The EELVs are reliable enough both in terms of design fundamentals and launch records to carry human payloads. They are have a launch record and a basic design that is a hell lot safer than the Redstone, Atlas and Titan missiles. They are less complex and less “stressed” systems compared to the Shuttle and the Saturn V. The EELV as they are today, with no modifications, is inherently safer than the shuttle – no side mounted orbiter, no tank to orbiter fuel transfer, available no SRB configuration, simpler less stressed engine, less engines, etc. The arguments that the shuttle orbiter itself hasn’t failed (yet), the SSMEs hasn’t failed (yet) and that the two shuttle disasters are due to non-orbiter systems – the SRB in the case of the challenger and fuel tank foam insulation in the case of Columbia – is invalid because the reliability of the shuttle itself is irrelevant. The only thing that matters is the reliability of the entire launch system.<br /><br />(2) As far as vehicle health monitors are concerned, EELVs already have an abundance of engine, tank, and telemetry sensors. The only need is for a system capable of processing these readings and using them to initiate launch abort and/or launch escape. This has to be done for shuttle derived designs such as a shuttle SRB based CEV launcher or a shuttle main tank based Heavy Lift Vehicle anyway.<br /><br />(3) Re-engineering a shuttle main tank to accept a heavy payload on top and engines below practical entails redesigning the entire tank structure and the fuel feed system. This will be just as costly as designing a new fuel tank from a clean sheet. In terms of utilizing the existing launch infrastructure, a vertically stack shuttle derivative will still need a new launch tower and substantial changes to the infrastructure – if anything just because the crew loading/unloading location will be very different. The NASA proposal to use 6 SSMEs, a shuttle derived tank and two SRBs, promise

 

[najab]

><i>The EELVs are reliable enough both in terms of design fundamentals and launch records to carry human payloads.</i><p>I suppose one (almost) successful launch out of a total of one attempts is an enviable service record - 100% (almost) success, for the EELV heavy.<p>><i>As far as vehicle health monitors are concerned, EELVs already have an abundance of engine, tank, and telemetry sensors.</i><p>Do they? I suppose so.<p>><i>Re-engineering a shuttle main tank to accept a heavy payload on top and engines below....</i><p>Is irrelevant, as they don't intend to launch that configuration manned.<p>><i>The SRB based launch system is scarily unsafe theoretically and promises very high acceleration loads and low payload efficiency. </i><p>Why is it unsafe? The failure modes of large solid motors are well known and are rarely catastrophic. They are very reliable (no moving parts). The acceleration loads are easily controlled by (a) having a large upperstage/payload (the figure S_G throws around is ~400,000lbs); and (b) changing the shape of the motor grain and/or applying more burn inhibitor to slow burn rate late in flight.</p></p></p></p></p></p></p>

 

[radarredux]

> <i><font color="yellow">Is irrelevant, as they don't intend to launch that configuration manned.</font>/i><br /><br />I was under the impression that the not-yet-announced architecure (Lunar Surface Rendezvous) would require humans on the SDHLV and that the single stick SRB solution was only for CEV to LEO/ISS. Is this not correct?</i>

 

[mikejz]

I am somewhat intrested in knowing what failure modes for a EELV would result in the likely loss of crew.

 

[radarredux]

> <i><font color="yellow">Any humans would dock with it and go to the Moon.</font>/i><br /><br />So the not-yet-announced plan is an Earth Orbit Rendezvous architecture?<br /><br />What portion of a human-mission spacecraft would be taken into orbit on the SRB stick, what portion would be taken on the SDHLV, what would return to Earth?<br /><br />Part of the reason I ask is the t/Space plan was an Earth Orbit Rendezvous architecture (although for <i>both</i> to the moon and back from the moon), but I thought this architecture was dismissed.</i>

 

[dwightlooi]

I am all for a safe manned orbital flights. But at some point we have to be realistic. Human life is not as priceless as some people make it up to be. The astronauts are aware of the risks of their vocation. If they cannot live with some degree of risk, they should not be in the business. There is no shortage of over qualified applicants so NASA will have no recruiting problems. At some point one has to ask, is reducing failure rate from 5% (not always fatal) to (0.5%) worth trippling the launch costs? I think that it will be helpful if NASA put a dollar value on a human life -- insurance companies do that -- and use it as a measure for writing up what is acceptable risks.

 

[vogon13]

Another point though is wasting the man-centuries of effort in designing testing and building the vehicle.<br /><br />Without a reasonable probability of success, the waste of resources is not justified in an expensive unreliable craft.<br /><br /> <div class="Discussion_UserSignature"> <p><font color="#ff0000"><strong>TPTB went to Dallas and all I got was Plucked !!</strong></font></p><p><font color="#339966"><strong>So many people, so few recipes !!</strong></font></p><p><font color="#0000ff"><strong>Let's clean up this stinkhole !!</strong></font> </p> </div>

 

[frodo1008]

There is a consequence that many on these boards may not be aware of. I was a machined parts inspector working on the SSME's at Rocketdyne. In quite a few instances some of the blueprint dimensions and their tolerances were found to be far too tight. Tolerance for clearances of parts that would miss each other by far more than the standards that NASA itself gave us would frequently come up. Engineers always design far more conservatively for far more than where inexpensive manufacturing processes could be used to make the hardware, sometimes this is necessary and other times not. We could have avoided many Material Review conditions if these print tolerances could have just been relaxed. However, as the entire engine would have to be retested to recirtify man rated levels this was more often impossible than not. This would then necessitate far more expensive manufacturing processes (grinding a tight diameter instead of relaxing the tolerance so that a simple lathe operation could be used).<br /><br />However, this flexibility was allowed for the engines to be used for commercial launch vehicles such as the delta. And when it came to designing the RS68 for the Delta IV vehicles even the engineering itself was heavily based on making the engine as inexpensive as possible without compromising either safety or reliability. With the SSME, weight and performance, were the absolute guide for design and manufacturing. I think we were finally able to get the 430 K lbs of thrust (at sea level) SSME down to a total cost of less then $20 million for one complete engine system. Whereas the total cost of the 665 K RS68 I believe was to be less than $6 million for one engine system. Yes, high thrust liquid rocket engines aren't cheap! <br /><br />However, in defense of the SSME it has a couple of features that no other engine system had. One, was its throttle ability, in other words the thrust could be changed during flight. And the other was its reusability, which makes

 

[radarredux]

> <i><font color="yellow">The "60 day team" that Griffin formed is to report it's findings July 12th. That will also reccomend an architecture.</font>/i><br /><br />Cool! Speculation can be fun, but it can also be frustrating. Looking forward to next Tuesday!<br /><br />Last speculation until then:<br /><ol type="1"><li> SRB booster with capsule to LEO (LEO CEV), operational by 2010.<li> SDHLV for cargo and Lunar CEV "back end"<li> For Lunar mission, capsule launches to LEO, SDHLV launches CEV "back end", Capsule docks with "back end" to form complete Lunar CEV. That is: Lunar CEV == LEO CEV + "back end".<li> Lunar CEV goes directly to the Lunar surface.<li> Returning from the Moon there are two options: (a) the Lunar CEV can go into LEO, capsule separates from "back end", LEO CEV returns to earth and "back end" remains in orbit (possibly for reuse); or (b) following Apollo profile the capsule separates during return and plunges directly into the atmosphere.<br /></li></li></li></li></li></ol><br />In short, it is similar to the t/Space architecture but using much of the space shuttle system technology (politically acceptable, limited risks from new technology, etc.) and supports abort to Earth at each stage. But the architecture also lets others play (SpaceX, t/Space, ...) if they build a compliant capsule.<br /><br />Until next week...</i>

 

[dwightlooi]

<i>However, this flexibility was allowed for the engines to be used for commercial launch vehicles such as the delta. And when it came to designing the RS68 for the Delta IV vehicles even the engineering itself was heavily based on making the engine as inexpensive as possible without compromising either safety or reliability. With the SSME, weight and performance, were the absolute guide for design and manufacturing. I think we were finally able to get the 430 K lbs of thrust (at sea level) SSME down to a total cost of less then $20 million for one complete engine system. Whereas the total cost of the 665 K RS68 I believe was to be less than $6 million for one engine system. Yes, high thrust liquid rocket engines aren't cheap!<br /><br />However, in defense of the SSME it has a couple of features that no other engine system had. One, was its throttle ability, in other words the thrust could be changed during flight. And the other was its reusability, which makes the cost per flight of these magnificent engines comparable to the engines used on the EELV. Which when used up, are just discarded into the ocean. </i><br /><br />Well... the current reports seems to indicate that NASA plans to use 6 x SSMEs in the throw away shuttle derived heavy booster. These wil be clustered at the base of a shuttle main tank. The tank and SSME engines will burn up on re-entry. In this scenario the SSMEs will not be cost effective because they will not be reused at all.<br /><br />The SSMEs are also not the only engine that can be throttled in flight. The RS-68 for example can be throttled from 60% to about 110% of it's rated thrust in flight. In the Delta IV heavy, the central booster's RS-68 engine is throttled back to roughly 60% shortly after lift-off and stays throttled back for the rest of the flight.