Classic British Flight Sim

Very interesting stuff, Kevin! Really good to hear it from someone who was involved with the design process.

Thanks, Ed. It wasn't just a job, it was one of those times in your life when you're doing something you feel 'matters', and you believe in it.

What was very disappointing was that NASA dropped the ball: we (Martin, plus Rockwell & occasionally Boeing) proposed all sorts of simple upgrades to Shuttle which would gain performance (+50% payload), raise safety (a lot) and lower the operations cost dramatically, but nothing significant was ever really implemented, due to lack of interest in Washington. NASA always was looking for new R&D funding, and much preferred 'R' over 'D', because it feeds the NASA Field Centers.

I also did a lot of work on Advanced Programs during that time (Space Station in the early days, new launch vehicles, lifting bodies, all sorts of things) but eventually decided to quit the manned program because nothing of consequence was likely to be built. Fifteen years on, we've gone backwards.

I don't really blame the politicians for this - I blame them for lots of other things, but not this. It's NASA, which has become simply another self-serving bureaucracy and has lost any get-up-and-go it had.

Cheers,

Kevin

Hi Kevin,
I have a quick question for you, I don't know if you'll be able to answer it, though. I have a paper on a re-usable space bomber designed by McDonnell Douglas called the GRM-29A, which is an acronym for Global Range Mach 29. In the article it makes reference to a water wick TPS.

One of the diagrams shows the weight of the water wick TPS being almost only 50% of another sytem it calls "Advanced RSI." I'm just curious if you have ever worked with a water wick system. If so, how do they work? Does the water litterly "leach" through the bottom of the vehicle and evaporate in a form of active cooling or does it circulate just under the skin, in the same manner that fuel systems are used as heat sinks on high speed and stealthy aircraft to regulate heat? Also, do you know what the RSI stands for? I haven't figured that one out yet.

I preferred SRM's back in school. The calculations were so much simpler.

Kevin,

Thanks for the corrections.

As I said in my first post, the foam loss had been happening since the first launches, but my understanding from the released papers on the subject was that the size was closer to what we saw during this latest launch and less like what we saw on the previous 2 launches and that the larger size of the chunks was due to the new foam and the afore mentioned issues with the underlying skin/foam interface while fueled.

As for the fueling of the tank, the report on the Challenger accident states that the ET was continuously topped off and never fully defueled for the entire period it stayed on the pad. The information from NASA during this launch indicated the same that they did not fully defuel the ET during the first two launch days.

As for defueling procedures, it's always dangerous. It may be mainly safe, but if something breaks, LOX and LH2 can cause a lot of problems to anything they touch. There is a good chance that if a line breaks that there can bo structural damage to the surrounding Launch Support Structure, something that NASA has always been worried about since the Saturn launches (which were the first manned launches to have a fixed LSS). Fueling and defueling the STS has about the same amount of risk as fueling or defueling a 777 when you break it down. It's safe as long as nothing breaks. But when it does break, it gets extremely dangerous, as a co-worker of mine found out as he was killed when a bayonett (the thing on the airplane you hook the fuel nozzle to) on a BA 777 broke and the fuel that rushed out of the fuel hoze caught fire on something (never been determined for sure what the ignition source was). You take precautions, but as long as you're working with a hazardous substance, it's always dangerous.

Sundog wrote:I'm just curious if you have ever worked with a water wick system. If so, how do they work? Does the water litterly "leach" through the bottom of the vehicle and evaporate in a form of active cooling or does it circulate just under the skin, in the same manner that fuel systems are used as heat sinks on high speed and stealthy aircraft to regulate heat? Also, do you know what the RSI stands for? I haven't figured that one out yet.

I preferred SRM's back in school. The calculations were so much simpler.

No, I haven't analysed a water wick system - the obvious trade study issue is the benefit from the high latent heat of vaporisation versus the mass of water that has to be carried. I would think that evaporation would have to be the method - simple circulation wouldn't do much - just move the heat around, whereas it has to be removed from the vehicle.

Actually, Douglas Aircraft (as was) devised what I think was the best cryogenic insulation system for a launch vehicle. It consisted of internal foam panels with open-celled foam and sat immersed in the propellant. The propellant next to the outer skin naturally boiled, providing a trapped gas layer with 100 times the insulating properties of the liquid, and therefore preventing any more significant heat transfer. This system flew operationally on the S-IVB stage of Saturn IB & Saturn V.

RSI - could be any one of a number of things - there's no control on the generation of new acronyms! My guess would be 'reusable surface insulation', but it's the duty of the papar's author to define it.

Thermal insulation for space vehicles is a very big subject - sometimes you are trying to keep heat out, sometimes keep it in and, depending on whether the vehicle is in the atmosphere or in space, the heat transfer mechanisms can change dramatically (convection vs conduction vs radiation, for example).

It's not only external heating - on the ET, the liquid oxygen can 'stratify', with different layers at different temperatures (and therefore densities). If uncorrected, this would lead to (i) not getting sufficient mass in the tank to make the mission - (yes, it's that precise: [fixed volume x variable density] = variable mass; the LO2 mass is about 1.3 million lb, the total payload to a given orbit is around 35 to 50 thousand lb and you gain or lose lb for lb), and (ii) feeding the engines with LO2 at a temperature they couldn't accept - too warm and the propellant will boil in the turbopump inlet and blow up the engine, too cold is also bad. What we do to break down the stratification is (i) to bubble a small trickle of cold helium gas into the bottom of the tank to remove heat and (ii) recirculate the LO2 using a pump.

SRMs: I could write a lot about these, not much of it good, but I will say, in relation to calculations, that you should try analysing the chemical species generated by combustion and how they change as they transit the convergent-divergent nozzle. There are about 150 different chemical compounds in a typical SRM plume - and the mix is continuously variable. Since this directly affects thrust and specific impulse, it matters - and it'll make your head spin!

Chris:

Foam loss is essentially random. We understand what causes it: it's the variability in the physical and underlying chemical properties of the material itself. The trouble is that there isn't a lot that can be done about it as long as we continue to use the present design. What would be needed is a completely new ET design which used (for example) an internal insulation system of the kind I outlined above. However, with the planned abandonment of the STS in a few years, this won't happen, so it's been patched.

Just so you know the extent of the problem, the foam is a 2-part sprayed material which forms in the air as it leaves the spraygun on its way to the tank, continues to react as it forms on the surface and sets in seconds, curing all the time. The basic leading physical properties can vary by up to a factor of SIX! Processes have been improved over the many years, and some of the best engineers I have ever worked with have spent a large part of their careers on this very subject, but it is still a weak point.

Defuelling: I assume that you meant 'Columbia', not 'Challenger'? There isn't enough propellant at LC-39 to keep an ET 'topped-off' for more than a few days; the storage capacity is about two tanks' worth before more LH2 & LO2 has to be sent from Louisiana (LH2 from Air Products at Michoud, LO2 from Lake Charles): it takes about 40 truckloads of each to replace one tanking, 80 to replenish dry tanks. That's why they don't ususally try to keep the tank loaded for a launch attempt more than 24 hours out.

Sorry to hear about your co-worker, but I must emphasise that there is little or no similarity between Shuttle propellant loading/offloading and the aircraft equivalent. Once the decision to detank has been made, the flight crew are removed from the cockpit, the pad is evacuated and the detanking begins. No lines are connected/disconnected (except the LO2 tank 'beanie cap', which is remotely activated. No personnel are normally allowed within the pad perimeter during this operation. It is an entirely normal procedure, remotely operated, with no personnel exposed to hazard.

When I left the program, we had done around 60 of these, without significant incident. The main hazard (don't laugh, it's true) is people falling asleep at their consoles in the firing room or in the support operation in Huntsville, due to the resulting long work day: typically, for a 7am launch, they will have come on duty at 9 pm the previous night, then loaded the tank from midnight to 4 am ready for the launch. If the launch is scrubbed, 'drainback' (ofloading propellants) starts about 9 am and finishes about 5 pm. For a 24 hr turnaround, these same people will be coming on duty in another 4 hr to do it all over again. That's the real reason that sometimes we leave the propellants to boil off and accept the cost of providing more.

However, I say again that there is no known correlation between TPS damage and the use or non-use of 'drainback'.

Again, sorry about the long post: I hope it doesn't bore too many, but I want to get across the complexity of this thing and the fact that a lot of thought has gone into it over the years. We at the Martin company always tried to persuade NASA to go for a 'Shuttle II' rather than the all-new exotic 'aerospace plane' SSTO concepts they were obsessed with. As engineers, we knew what could be built and operated, whereas they were looking too far ahead. There is a lot on Shuttle that works very well, as well as much that doesn't: it doesn't take a genius to figure out that we could build a pretty effective second-generation Shuttle based on judicious development from what we have now.

Cheers,

Kevin

I'm comparing the human danger of airplane fueling (which is, for the most part, a remote operation as many airplanes we can fuel from 10-15 feet away due to automatic fueling systems where we set the fuel load desired into the computer, hook up the hose, and then stand clear, watching the gauges we must monitor on the truck from a safe distance and the flight crew watching the quantity gauges and stopping the process if needed or alerting the fueler to stop the process. I was specific in stating that the danger from the de-tanking operation on the Shuttle was dangerous due to the possible interaction of the propellants and the structure of the LSS if there was ever to be a crack or complete separation of one of the feed lines on the LSS. The analogy (and was stated as such) was that while it might be mainly safe, it isn't always and that airplane fueling is something that is similarly safe most of the time, but when it isn't, it can have disasterous consequences. NASA has long worried about what might happen should there be a LH2 or LOX release on the LSS and the possibility of the structure failing and destroying the Saturn V (initially), then later the SIB, and finally the Shuttle. While it hasn't happened (thankfully) there is that risk. My co-worker who was killed was the first to have been in close to 30 years in the United States. So, such fueling fires are very rare, but they do happen.

Anyways, it appears CEV is the way we're going, so I guess we have to hope that the initial un-manned launches coming around 2010 and the first manned missions in 2014 or earlier to cover the gap between the end of STS in 2010 and the start of serious CEV lunar missions around 2018.

I only hope that the next President of the US and other world leaders continue the push for a serious return to spaceflight and interplanetary exploration as it's our best way forward to create major leaps in technology as Apollo bore out in the late 1960s.

Chris,

I don't want to beat this to death, but if anyone is worried about the structural failure of a (fixed, frequently-inspected-and tested and with enormous margins) propellant line while the STS vehicle is quiescent on the pad perhaps they would be better off in another line of work. It is the safest cryogenic operation I know. In ten years on the STS Program I never heard any safety concern uttered over our operation.

The trouble is, this is the attitude which stopped the Space Station being of any use whatsoever: in the early days ('84 to '87 or so) we were planning to have vehicles based at the Station. In other words, it would have had a facility to berth and service vehicles with both storable and cryogenic propellants. These vehicles would have carried the payloads (brought up by Shuttle) to higher orbits or to the Moon and planets.

Gradually, NASA strangled the Station by banning one activity after another to 'free-flying platforms' which would have been in effect unmanned Space Stations. These platforms would have handled any hazardous operations (including propellant transfer) and were of course never funded as they would have made the Station itself become visibly pointless. As it is, it is still pointless, but less-visibly so.

These NASA actions also came close to banning all EVA activity until it was pointed out that you then can't assemble or operate in space at all. It was very similar in its paralysing effect to the UK's obsessive 'Health-n-Safety' culture.

I was closely involved in a strong, last-ditch effort in the Spring of 1991 to save the OMV (Orbital Maneuvering Vehicle) and we assisted TRW in preparing their last proposal. When NASA cancelled even that, there were no more space-based vehicles in prospect and I (and a lot of experienced people) chose to leave the manned program.

The NASA leopard hasn't changed its spots, there is much less hands-on development experience in the program today and there is virtually no public support for it.

I wish it were otherwise, but I don't think the US will be capable of continuing serious manned spaceflight in another 5 - 10 years. No President will want to be the one to kill it, but it's being allowed to decay gradually. Speeches and studies are cheap, action is not.

The solution may be to break up and remake NASA from the ground up.

Kevin

Thanks Kevin,
I was wondering whatever happened to the OMV. I've also wondered how many of these programs have become classified USAF missions.

Yeah, when I was in school, we just did the basics, with regard to the chemical reactions for liquid propellants. All I remember was when balancing the equations one of the by-products was water. I also remember being awed by the turbopumps and what they have to do. I've never thought about the different strata in the LOx tank, that was quite interesting. Did we ever consider going over to Kerosene? Or do you take too much of an Isp hit with it compared to LOx/LH?

I think part of the problem with NASA is they are risk averse, but more because of the politicians who don't want to tolerate failure. I always get into arguments with people who think we spend too much money on NASA, but when I tell them the money we spend on NASA is usually less than the cost of over-runs on many weapons systems they just shrug their shoulders. I think many people in this country (The U.S.) think most of the technology they use just "magically" happened.

Sundog,

It wouldn't surprise me at all if TRW found another customer for the OMV's capabilities, but it isn't available to the manned program, and that's a big loss. It was already being built, with over $700m spent when NASA pulled the plug. They did it in a sneaky way, too, by arbitrarily changing the basic design requirements after metal was cut, then declaring that the OMV wouldn't meet the requirements. When TRW, with some assistance from other interested parties, such as ourselves at the Martin Company, proved that they could meet them, NASA cancelled it anyway.

Nasa pulled the same kind of dishonest stunt on the Liquid Rocket Booster (LRB) program: this was the (Congressionally-mandated) study to replace the Solid Rocket Booster on Shuttle, after the Challenger accident in 1986:

I was the lead propulsion engineer for Martin, who won the study contract. After we proved initially to NASA that a practical, safe LRB could be developed cheaply, and even gave them a safe engine-out capability for a failure straight off the pad, they came back with the most ludicrous set of specification changes I have come across in my entire career.

What they did was (i) rule out the use of storable propellants on spurious environmental grounds and (ii) specify that the LRB must be pressure-fed, not pump-fed. We could deal with the first change, but no-one on Earth could deal with the second.

To cut a long explanation short, small liquid-fuelled rockets are pressure-fed - their propellant tanks are pressurised to feed the engine directly. If you want a big rocket, bigger than about 20 - 50 k lb of thrust, this gets a bit heavy, and you consider keeping the tanks at low pressure (lighter pressure vessel) while providing pumps on the engine to feed it. As you get to Shuttle size (2 m lb of thrust) the mass penalty is around 100 000 lb per booster, versus a pump the size and mass of a desk! Oh, and you also need a large heat exchanger to pressurise the tank to the 1000 to 2000 psi needed, in a 2-minute period.

If you work the numbers you will find you need a FIVE MEGAWATT heat exchanger, which is an extraordinary item and the size and weight of a bus. Nasa simply said that they would pay us to develop this as a technology item!

It was clear to us all that NASA had no intention of complying with the Presidential Comission's recommendation, and the resulting Congressional mandate and was determined to use dishonest means to keep their damned SRB, because it was their own design. [Although Thiokol took the rap for the accident they were only partly to blame as the SRM contractor and overall responsibility for the SRB lay with NASA Marshall Space Flight Center: they were in the unique position of being their own Prime Contractor!]

Back to your questions!

That's a very perceptive observation about Kerosene. Specific impulse is so often used as the only figure of merit that people forget that propellant density matters, too. Liquid hydrogen is about 4.4 lb/cu ft, LO2 is about 70 lb/cu ft (close to the density of water) and kerosene & liquid methane are around 35 lb/cu ft (ballpark figures).

There are lots of different fuels but only a few viable oxidisers for heavy launch vehicles. For practical purposes there are only two - oxygen and the various oxides of nitrogen. Once you've settled on LO2, you look for a fuel. Hydrogen is very attractive if all-out specific impulse is vital, but it leads to a very big vehicle. It is best to use it in upper stages (because of the 'Rocket Equation') and use a hydrocarbon in the first stage. You save stage tank mass that way. Saturn used lox/kerosene (well, it was actually RP-1 which is a special kerosene) in its first stages for that very reason.

However, we have since found that, if you want a high chamber pressure (smaller, lighter engine & higher Isp) - around 2000 psi - kerosene deposits carbon as 'coke' in the combustion chamber which leads to uneven combustion. Liquid methane is OK in that respect, so that's what we'd use today.

I agree wholeheartedly with your observation that people think technology 'magically' happened. This is in part why they don't realise how easily it can slip away. I was fortunate to work early in my career with a number of experienced people who had worked on Apollo from start to finish. Much of the knowledge I have absorbed from them has been re-applied into other projects. However, there are very few people now working in the space business who have participated in the development of a new vehicle which has actually been built. This practical understanding and knowledge doesn't appear in papers, but is learned on the job. When they go, so does the knowledge and we have to start all over again.

Cheers,

Kevin