common sense

Space, Space Programs, Manned and Unmanned Missions
blackirishkarma
Joined: 09 Aug 2013, 03:20

29 Oct 2014, 03:28 #1

It seems to be lacking in a lot of decisions we make as a nation these days. There is an oft repeated mantra amongst a large segment of the population that the government cannot do anything efficiently. We hear it repeated so often that people who should know better are beginning to believe it is irrefutable. The truth is that private industry does some things very well but there are a LOT of things that private industry does not do well. There are very few such homilies that apply across the board and this is NOT one of those that do.

Space travel, even lower earth orbit space travel, is one of the things that private industry does not do well. There are a mulititude of reasons for this, not the least of which it is an incredibly dangerous and incredibly risky business. Orbital Sciences has now lost three major vehicles to catastrophic failure since they started into this business just a few years ago. That is not to say that NASA never lost a vehicle either as the early days of the program saw a LOT of failures. Even the Shuttle program had two terrible disasters when a lot of the lessons learned from earlier problems were ignored. 

However, there is a common thread in all such disasters; schedule pressure which overrides technical expertise. Every NASA failure, most noticeably the two shuttle disasters, were directly attributable to this one cause. When you put a private industry company in this position there is simply no counterbalance to schedule pressure as meeting schedules equals profit and there is NO other incentive for a private industry outside of profit. 

Private industry is astronomically and inherently more reckless than NASA when it comes to such decision making processes. I personally know of numerous decisions already that NASA would never have made that private industry companies in competition for space contracts routinely make. NASA's own investigations into previous accidents all point out that schedule pressures for budget approval in Congress are their worst enemy as far as vehicle safety. Mulitiply that by a factor of ten in the numerous startups competing for federal money in the nascent private space race and you get a notion of what we are likely to face in the near future. 

Faster, better, and cheaper are not the best guiding principles in aeronautical engineering. They are the sure and certain causes of numerous disasters to come in the space industry unless we wake up and change our understanding of the complex but necessary obstacle that space travel presents. 

blackirish
The increase of misery in the present state of society is parallel and equal to the increase of wealth..... Unknown member of Parliament 1840's
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blackirishkarma
Joined: 09 Aug 2013, 03:20

30 Oct 2014, 03:37 #2

http://news.yahoo.com/decades-old-sovie ... 46633.html

more to come... This is the kind of accident that people look back on and say, "Why did anyone think that was a good idea?"

The truth is... no one did except the people responsible for pushing the schedule and minimizing the costs...
The increase of misery in the present state of society is parallel and equal to the increase of wealth..... Unknown member of Parliament 1840's
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blackirishkarma
Joined: 09 Aug 2013, 03:20

30 Oct 2014, 04:53 #3

Suppose for a moment that someone offers you a lot of money to build a rocket that will carry supplies to the international space station. You might say this sounds like a very expensive thing to do with a large learning curve and lots of research and development needed and who knows how much that might cost. Don't worry... they say... we will pay you for all your research and development. We will call it a private space initiative and simply ignore the fact the the government is paying for it. It's a for profit project funded by the bottomless pockets of the US government. What could go wrong?

Also suppose that they give you access to forty Soviet style rocket engines designed and built to carry cosmonauts to the moon. Sounds great? Of course these rocket engines were assembled in Soviet Russia about the time the Space program there was running completely out of money with little or no real quality control over parts, soft goods, or design build requirements. Not to worry... they are very powerful engines, built to go all the way to the moon. What could go wrong?

Also suppose that during the design and build of your new vehicle you decide you need to at least take the precaution of test firing a couple of these engines to get an idea of the thrust, vibration, and harmonics issues involved with using them to power your vehicle and a couple of them self destruct on the test stand. Not a good thing you might say. Naturally, since you just burned up a couple of very expensive engines on a NASA test stand there are going to be questions. 

Also suppose that NASA appoints teams of people to find out what just happened. As it turns out; it is not a good idea to take a forty year old experimental and untested engine with incomplete and/or nonexistent build paperwork and try to live fire it. Corroded fittings turn loose under pressure. Forty year old soft goods with a shelf life of ten years fail and thrust measurements go through the roof because throttling orifices in parts of the engine were simply never installed. 

Also suppose that this team of NASA experts in view of these findings suggests that as a minimum all engines should be torn down and gone through to replace out of date soft goods, corroded fittings, and non-existent orifices that control thrust levels. This all sounds expensive and time consuming and you have a schedule to meet. After all, your competition for getting an even larger chunk of the gravy train you find yourself on is already sending supplies to the Space Station on their new vehicle. Besides, every one knows NASA is notorious for finding fault with vehicles, just look at all the delays they experienced with Shuttle programs. Besides, you have plenty more engines and you will pre-fire them on NASA's test stands to make sure they work correctly. What could go wrong?

blackirish
The increase of misery in the present state of society is parallel and equal to the increase of wealth..... Unknown member of Parliament 1840's
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blackirishkarma
Joined: 09 Aug 2013, 03:20

09 Dec 2014, 02:03 #4

The prime consideration in launching payloads into space is weight. Weight of the vehicle vs. weight of payload is always at the center of such discussions. Every pound of payload costs somewhere near a million dollars to get up into space. Therefore, every pound that can be saved on the vehicle is worth the same amount of money. On pressure systems in common usage throughout industry there is a 4-1 safety factor margin built into every design. In other words, if a system is going to see a maximum operating pressure of 100 PSIG it is designed to withstand 400 PSIG. For space vehicles the margin is routinely reduced to 1.5-1 because of the high costs associated with launching payloads discussed above. 

Add to that the complexity of systems performing with Liquid Hydrogen and Liquid Oxygen (LOX) at high pressure and extreme flow rates and you begin to see the complicated nature involved in succesfully launching payloads into space. Historically, both the US and the Soviet Union used RP1 (Rocket Propellant 1 which is basically refined Kerosene) or Liquid Hydrogen as a fuel and pure Liquid Oxygen as an oxidizer. RP1 has a little more energy than Liquid Hydrogen but it is also much heavier per gallon so the tradeoff is very close. At lower altitudes RP1 outperforms Liquid Hydrogen per weight but at higher altitudes the scale shifts the other way. Ideally, one would use RP1 for first stage engines and Liquid Hydrogen for second stage engines. Liquid Hydrogen has the added complexity of existing in liquid form only at extremely cold temperatures. Around -420 Degrees F Liquid Hydrogen begins to boil and turn into gas with around a 850-1 expansion rate. All components that will be exposed to Liquid Hydrogen must be extremely strong (read expensive and hard to work with) metals. Provisions must be made to avoid trapping Liquid Hydrogen in between valves where it can warm up and expand enough to rupture the lines. 

Shuttle engines were Liquid Hydrogen and LOX. The larger Apollo main engines were RP1 and LOX. Almost all Soviet made engines are RP1 and LOX. LOX is now and always has been the hardest part of rocket engines. There are numerous reasons for this. The first is that it is also a cryogen and begins to boil and build pressure at any temperature above it boiling point of -297 degrees F with an expansion rate of 856-1. These properties make the usage of LOX in a system problematic at the start but it gets worse. LOX has a violent reaction to hydrocarbons. The precludes the usage of almost all lubricants and demands a cleanliness level on all parts that is in the parts per million range. Turbo pumps that feed LOX into rocket engines often rotate in the 15000- 45000 RPM range to get the amount of LOX needed to the engine. 

In other words, a natural cryogen with has the tendency to shrink metal parts so that they bind against each other has to be fed by pumps spinning at extremely high rates of speed without any lubricant beyond the LOX itself. Add to that the the parts themselves have to first be completely degreased before assembly. Stainless steels have a marked tendency to gall or friction weld themselves together when they are degreased to this level. I have seen fittings gall after LOX cleaning while they are being hand tightened. 

The final piece of bad news in dealing with LOX is that it is the perfect oxidizer. LOX itself will not burn but it will make everything else burn readily. When I say everything else... I mean literally everything else. Stainless steel, aluminum, and virtually all other metals that are good for the temperatures of LOX readily become fuel in LOX fires. This is a hard thing to get your mind to process but the reality is that LOX containment systems become the fuel for LOX fires when they start. 

The infamous fire triangle that every child learns when young contains everything needed for a fire. You basically need three things, fuel, and oxidizer, and an ignition source. In a LOX system you start out with two of the three and are never able to do anything to remove either of them. The containment system is the fuel, the LOX is the oxidizer so all you really need is an ignition source and your system consumes itself. I have seen numerous oxygen fires and even more numerous results of oxygen fires and they almost always involve loss of large systems as everything burns in an oxygen fire. 

Many years ago, I was taking an oxygen design class from the group within NASA who do destructive testing on LOX systems. This group is based at White Sands, New Mexico and they are the experts on LOX fires. Since two of the three legs of the fire triangle are always present in oxygen systems they have become experts on ignition sources. Small amounts of metal shavings and high velocity systems are a deadly combination. The metal shaving produced by screwing a fitting into a system can be enough to start a LOX fire when they collide with an elbow at high velocity. There are numerous other ignition sources in LOX systems but I won't go into those right now. 

What struck me in that class and what I still carry with me in dealing with LOX systems was an offhand comment the instructor made after class one day. He was discussing how they could often tell by examining burn points and source component parts after a LOX fire what the ignition mechanism had been. In recreating such fires he said they often had to introduce the ignition mechanism and run the test 30-50 times before they could successfully recreate the incident. In other words, they know the ignition source is there. They know it will inevitably lead to a catastrophic fire wherein the system will violently consume itself. Still.... it may take up to 50 times before it happens. 

I think of that comment whenever I hear of a group saying they are running one full up system test before launch. Unfortunately, as more and more people get into this industry that voice of wisom is absolutely ignored in the rush to compete for funds in launch systems. If it is ever raised at all, a series of 2 or 3 tests is run and then the speaker is forevermore labeled an alarmist. At least until the inevitability factor catches up and by then... it is a very large disaster indeed. 

blackirish
The increase of misery in the present state of society is parallel and equal to the increase of wealth..... Unknown member of Parliament 1840's
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