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Author
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Topic: Shuttle now safest manned spacecraft ever?
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dom
Member Posts: 855
From:
Registered: Aug 2001
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posted 08-09-2007 02:15 PM
   
For those of us who remember the Challenger disaster vividly, yesterday's launch was a tense lift-off indeed but am I right in saying that the Space Shuttle it now officially the safest manned space vehicle ever?Although the technological marvel of the Shuttle is tainted by the realisation that it can all go tragically wrong, very quickly, after over 100 flights it has had only two crew loses verus Soyuz's record of two crew loses in 90 odd flights. Please correct me if I'm wrong on the stats... |
Blackarrow
Member Posts: 3120
From: Belfast, United Kingdom
Registered: Feb 2002
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posted 08-09-2007 04:22 PM
What about Mercury (100%), Gemini (100%) and particularly Apollo/Skylab/ASTP (100%)? |
Robert Pearlman
Editor Posts: 42988
From: Houston, TX
Registered: Nov 1999
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posted 08-09-2007 05:21 PM
Perhaps a more balanced comparison would be the flight records of Redstone, Atlas, Titan and Saturn (with the shuttle and Soyuz). The latter (Saturn) in particular came no where close to flying 100 times and thus drawing conclusions between it and the shuttle in regards to their success rates is probably impossible. |
mjanovec
Member Posts: 3811
From: Midwest, USA
Registered: Jul 2005
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posted 08-09-2007 05:59 PM
To consider safety and what vehical is the "safest," you must also consider your options for escape if and when things go wrong. Mercury and Apollo has launch escape towers. Granted, they were never used, but their availability greatly increased the crew's chances of surviving a launch mishap. Challenger had no such system. If it had, the crew could have likely survived.Also, previous programs kept their thermal protection systems covered until the spacecraft were ready for re-entry. With the Shuttle, the large and complex thermal protection system is exposed to the elements the whole time...which makes it particularly vulnerable during launch (as was witnessed by the Columbia disaster). If a one of thousands of key tiles is damaged, it could spell disaster. To me, these are two design shortcomings that cannot be fixed with the present Shuttle design...and therefore they still represent two factors that put the crew at greater risk. As such, I cannot accept that the Shuttle is the safest manned space vehical. The risks are deemed acceptible for the moment, but after 2010 I would be surprised if another manned spacecraft is designed with these two key shortcomings. Having said that, the Atlas was probably the most unreliable launch vehical to ever carry a manned spacecraft. If the Atlas had been launched 100 times, my guess is that the launch escape system would have had a few opportunities to be utilized. |
John Youskauskas
Member Posts: 126
From:
Registered: Jan 2004
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posted 08-10-2007 02:43 PM
Comparisons of this type can be futile, since a single occurrence can skew statistics widely, and there are so many ways to measure any aircraft's safety record.The Concorde, for instance, went from being the world's safest aircraft (statistically) to the worst with one crash. This was because the plane flew less than 1000 hours per year on long trips with fewer than 800 total takeoffs and landings. The Boeing 737, considered to be one of the world's safest airliners flying, has had many more crashes but flies 100,000's hours per year worldwide. Mercury, Gemini, and Apollo had no in-flight fatal accidents(0%), but were exposed to the risk of one, i.e. not parked in the VAB, far less than the shuttle has been over it's 118 flights. But with 0%, it's impossible to compare the two. As far as system redundancy goes, I'm certain the shuttle, with it's many upgrades over the years, far surpasses MGA. It doesn't stray far from home, rely on a single engine for any critical maneuver, or re-enter nearly as fast as Apollo did, so it is inherently "safer" just by virtue of the role it performs. But that is all circumstantial...it does not explain how you lose two of five orbiters in 118 flights(and however many flight hours). Like they say...there are Lies, Damn Lies, and Statistics. |
mjanovec
Member Posts: 3811
From: Midwest, USA
Registered: Jul 2005
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posted 08-10-2007 03:39 PM
quote:
Originally posted by John Youskauskas:
As far as system redundancy goes, I'm certain the shuttle, with it's many upgrades over the years, far surpasses MGA. It doesn't stray far from home, rely on a single engine for any critical maneuver
I agree with all that you said except for this statement. The Shuttle relies on both SRBs to work flawlessly for the first 2.5 minutes of flight. There is no redundancy to account for SRB failure. If an SRB fails, the crew is dead. There really is no way around that fact. Mercury and Apollo (and to some extent, Gemini) had systems in place to get the crew out in the event of failure of their boosters during flight. |
Robert Pearlman
Editor Posts: 42988
From: Houston, TX
Registered: Nov 1999
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posted 08-10-2007 04:01 PM
Regardless of what emergency systems were in place, there has never been a manned rocket launched that hasn't put the crews' lives in direct and unavoidable risk of being killed. So if you are going to compare rockets based on their ability to manage that risk, you need to take into consideration all their abort modes.The launch escape towers and ejection seats on earlier vehicles carried their own set of health risks to the crew. The shuttle is the only vehicle that has the ability to return its crew to its launch site or land elsewhere under pilot control if required in an abort. The losses of Challenger and Columbia were avoidable and were based on the decision of management to overlook flight rules. Neither accident were the result of poor engineering, which cannot be said for the losses of Redstones, Atlas and Titans, nor near misses such as Gemini 8 or Apollo 13. Had any of the earlier vehicles flown as long as the shuttle program, they would have been equally susceptible to similar problems as raised by management decisions during the shuttle-era. |
mjanovec
Member Posts: 3811
From: Midwest, USA
Registered: Jul 2005
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posted 08-10-2007 04:52 PM
quote:
Originally posted by Robert Pearlman:
The launch escape towers and ejection seats on earlier vehicles carried their own set of health risks to the crew. The shuttle is the only vehicle that has the ability to return its crew to its launch site or land elsewhere under pilot control if required in an abort.
The shuttle, however, has NO options for abort in the first 2.5 minutes of flight. None whatsoever. In my opinion, that is the riskiest portion of the flight, because it includes liftoff, tower clearance, and max Q. Given the choice between an abort on the Shuttle (RTLS or abort to another site) or risking riding the launch escape tower and coming down into the ocean in a capsule under parachute, I'll take the later. An RTLS, under the best of circumstances, is a pretty difficult proposition. Not that I doubt the crew's ability to perform such an abort if needed, but it would still require the orbiter to be in good enough condition to perform the manuever. If not, jumping from the orbiter and coming down in the ocean under a personal parachute is a less-than-desirable alternative. I would also say that one cannot tie down failures of either the Shuttle or the previous programs to be either management or engineering errors. I firmly believe all launch and recovery failures were a combination of each. In most instances, faulty engineering or a design flaw led to the disaster becoming possible, then bad management decisions allowed the disaster to take place without intervention.
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dom
Member Posts: 855
From:
Registered: Aug 2001
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posted 08-10-2007 04:57 PM
Although everyone is absolutley paranoid about a shuttle failure (and considering there are very few escape options I don't knock them), my point is that statistically the Shuttle is now the safest mannned spacecraft ever...Personally. I would rather be on a Soyuz because of the escape tower but I only want to point out that although the Shuttle is a fantastically conplex technological system it has worked more often than the simpler Soyuz system. Think about it again! If the shuttle goes wrong, it goes wrong in a big way. The shuttle, something which many people think is a very flawed system, has managed over 100 successful flights! A unique record... |
Robert Pearlman
Editor Posts: 42988
From: Houston, TX
Registered: Nov 1999
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posted 08-10-2007 06:09 PM
quote:
Originally posted by mjanovec:
The shuttle, however, has NO options for abort in the first 2.5 minutes of flight.
And why is that? Because once the SRBs are lit, they cannot turn off, unlike say, a cluster of engines. And in that regard, the SRBs are very reliable. Even on STS-51L, the SRBs continued to fly — the break up of the stack was due to the external tank. Nor has an SRB exploded (on its own), whereas boosters, such as the Atlas, have.That's not to say that the shuttle wouldn't be an even safer vehicle with an LES, but given a choice, I would pick the shuttle each time. quote:
In most instances, faulty engineering or a design flaw led to the disaster becoming possible, then bad management decisions allowed the disaster to take place without intervention.
At least in the cases of Challenger and Columbia, the cause of failure was well understood prior to the loss. In both cases, engineers issued warnings in advance, and in both cases, management decisions led to those warnings being dismissed. Post-Columbia, the shuttle has become the safest vehicle that has ever flown, in my opinion. No vehicle has had more opportunity for inspection, precaution and rescue than the orbiter. |
mjanovec
Member Posts: 3811
From: Midwest, USA
Registered: Jul 2005
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posted 08-10-2007 06:32 PM
quote:
Originally posted by Robert Pearlman:
And why is that? Because once the SRBs are lit, they cannot turn off, unlike say, a cluster of engines. And in that regard, the SRBs are very reliable. Even on STS-51L, the SRBs continued to fly — the break up of the stack was due to the external tank.
I've never heard of anyone citing that as a factor for reliability...unless you want something to reliably kill you if something goes wrong with them.  Think of a possible scenario where the Shuttle is launched and shortly after clearing the tower, a flame is seen coming out of SRB field joint. Under the current scenario, even knowledge of such a breach leaves little option other than riding the stack to one's near-certain death. Now if you could shut down the boosters and jettison them, you have some options to bail out or perhaps bring the orbiter in for the a landing, given that you have some altitude at the time of shutdown. In my opinion, the use of solid fueled rocket boosters necessitates the inclusion of the launch escape system. Luckily, the design for Ares appears to include a LES at this time. Hopefully that won't be something that ends up being cut due to weight considerations. quote:
Originally posted by Robert Pearlman:
Even on STS-51L, the SRBs continued to fly — the break up of the stack was due to the external tank.
What caused the breakup of the external tank, however? Failure of the SRBs! Just because they continued to fly does not mean they did not fail. |
Robert Pearlman
Editor Posts: 42988
From: Houston, TX
Registered: Nov 1999
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posted 08-10-2007 06:45 PM
quote:
Originally posted by mjanovec:
What caused the breakup of the external tank, however? Failure of the SRBs! Just because they continued to fly does not mean they did not fail.
What caused the failure of the SRB, however? Flying outside the limits of its known safety margins. If you use something improperly, it's bound to break... |
Lunatiki
Member Posts: 237
From: Amarillo, TX, USA
Registered: Dec 2006
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posted 08-10-2007 06:47 PM
And why is that? Because once the SRBs are lit, they cannot turn off, unlike say, a cluster of engines.Its all about altitude. You can be 30 feet off the ground and if something goes wrong, the Apollo crews could abort and hopefully parachute to an ocean landing, or even land. The shuttle crew, however, MUST have altitude if they are to have a chance at returning if something should occur in the early stage of launch. That is why airliners don't waste time with gaining altitude at take off. They need to build altitude, quickly, incase something goes wrong and they need to maneuver. Anyone know what the minimum altitude is for the shuttle to abort should something go wrong? |
mjanovec
Member Posts: 3811
From: Midwest, USA
Registered: Jul 2005
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posted 08-10-2007 11:39 PM
quote:
Originally posted by Lunatiki:
Anyone know what the minimum altitude is for the shuttle to abort should something go wrong?
Any time after SRB sep. |
dom
Member Posts: 855
From:
Registered: Aug 2001
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posted 08-11-2007 05:44 AM
I've often heard the prediction that if both SRBs don't light-up within milli-seconds of each other the whole vehicle would disintegrate on the pad there and then...Although this is purely speculation, is it possible for the shuttle system to get off the ground with only one SRB working to get some height for an abort? Around the time of Challenger there was talk that if the crew knew they could have separated from the stack before SRB separation but surely the shuttle would have broken up from the stress? Is it even possible for the shuttle to stay on the pad until a solo SRB burned out? |
Lunatiki
Member Posts: 237
From: Amarillo, TX, USA
Registered: Dec 2006
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posted 08-11-2007 09:38 AM
Can the SRBs be jettisoned early? |
Blackarrow
Member Posts: 3120
From: Belfast, United Kingdom
Registered: Feb 2002
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posted 08-11-2007 09:39 AM
I assume the ignition of only one SRB would cause the whole stack to cartwheel, resulting in crew death, shuttle destruction and pad facility destruction. |
Lunar rock nut
Member Posts: 911
From: Oklahoma city, Oklahoma U.S.A.
Registered: Feb 2007
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posted 08-11-2007 09:55 AM
Here are answers to the mentioned scenarios.Terry |
mjanovec
Member Posts: 3811
From: Midwest, USA
Registered: Jul 2005
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posted 08-11-2007 02:07 PM
quote:
Originally posted by dom:
Is it even possible for the shuttle to stay on the pad until a solo SRB burned out?
No, because they blow the hold-down bolts BEFORE the SRBs ignite. Besides, even if the bolts could hold the shuttle in place while the SRBs burned, the force of the blast would tear apart the Shuttle. Also, separation of the SRBs before burnout isn't possible. The SRBs would outrun the stack and destroy the orbiter.
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Jay Chladek
Member Posts: 2272
From: Bellevue, NE, USA
Registered: Aug 2007
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posted 08-12-2007 01:19 AM
I am pretty sure they don't blow the holddown bolts before the SRBs ignite based on what I have read. The bolts blow when the SRBs reach a certain chamber pressure, which is a few milliseconds after ignition. But yes, I am pretty sure the bolts would blow both boosters in the event of a failure, although the igniters on the SRBs are a very reliable system.Now concerning other space programs, all have critical single point failure items, some more visible then others. With Mercury and Gemini (and Soyuz) it was a single main parachute. If that doesn't open, you get the result of what happened to Vladamir Kamarov. Apollo was the heat shield for lunar return entry. Apollo 13 was thankful that didn't fail. Even with the Saturn there has been some discussion that a possible catastrophic detonation of the fully fueled vehicle might happen too fast for the abort handle to get pulled, igniting the LES system. It does indeed boil down to how one interprets the numbers. Shuttle has indeed racked up quite a lot of successes, although a lot of critical items need to work for each shuttle mission to succeed and bring the crews home. Soyuz by comparison might be considered safer in some aspects in that it can operate to a certain extent in some failure modes and still bring the crew back (it just gives them a rougher ride in the process). So for every space vehicle that one classifies as the "safest" there need to be a few asterisks or other symbols near those clasifications. |
John Charles
Member Posts: 339
From: Houston, Texas, USA
Registered: Jun 2004
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posted 08-12-2007 07:07 PM
quote:
Originally posted by Jay Chladek:
...With Mercury and Gemini (and Soyuz) it was a single main parachute. If that doesn't open, you get the result of what happened to Vladamir Kamarov....
No argument that spaceflight is risky, and there are a few failures in the systems of every spacecraft that can prove fatal. Other examples of potential single point failures have included the LM ascent engine,and the CSM main engine. However, the Mercury, Gemini and Soyuz parachutes have not been single point failures. (Maybe Voskhod--I just don't recall...) Mercury and Soyuz had (and/or have) a reserve main parachute. Gemini did not, but that function was served by the personal parachutes and ejection seats for the two pilots. ------------------
John Charles
Houston, Texas |
Jay Chladek
Member Posts: 2272
From: Bellevue, NE, USA
Registered: Aug 2007
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posted 08-13-2007 12:19 AM
I stand corrected, thanks!  |
Lou Chinal
Member Posts: 1306
From: Staten Island, NY
Registered: Jun 2007
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posted 08-22-2007 03:27 AM
Mercury carried a reserve parachute that was also 63 feet in diameter. Shepard & Grissom had chest style personal canopies on there sub-orbital flights. I tried to get out of the McDonnell mock-up with a chest pack, it wasn,t easy. -Lou |
Cliff Lentz
Member Posts: 655
From: Philadelphia, PA USA
Registered: Mar 2002
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posted 08-22-2007 07:53 AM
I don't have the actual numbers, but most of the astronauts I talked to said that the chances of survival from an ejection seat is very low. I asked Wally Schirra about this since he was the closest to pulling the "D" ring as anyone in the Gemini program. He told me to look at an actual spacecraft and hoew tight the fit is for the crew. The chances of the hatches opening, the seat ejecting properly, and the emergency chute performing up to it's billing were not good. He also said that once you eject from Gemini you probably move yourself right out of the rotation in the flight line. For most pilots, that's usually the last option. |
Lou Chinal
Member Posts: 1306
From: Staten Island, NY
Registered: Jun 2007
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posted 08-22-2007 08:13 AM
Not to mention the G loading on your spine is ENORMOUS. -Don't try this at home boys and girls. | |
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