Shuttle fuel burn

[riff_raff]

If you're referring to around T-7, that's the sound suppression system, which is a water blanket designed to protect the shuttle stack from damage due to noise reflecting from the concrete.

No, I wasn't referring to the blast of water below the engines used to dampen engine noise. Take a look at the engine nozzle on the left in this image. The light colored plume just right of the nozzle centerline is propellants dumping out of the combustion chamber that have not yet ignited.

[bratschewurst]

History was rather more complex than usually made out. See, for example http://history.nasa.gov/SP-4221/ch9.htm

While I'm not clear precisely what point you are trying to make, I agree that the document you cite is well worth reading. As a case study on decision-making about pushing the limits of engineering in a complex political environment, with serious financial constraints, it is unsurpassed by anything else I've read.

[bratschewurst]

Have a look at this superb footage of a launch. The Shuttle main engines start first - to make sure they are all healthy - before the boosters are started. You can see (and hear) the whole STS angle over with the force, and then the boosters are lit.
https://m.youtube.com/watch?v=Lq_shHu4lAs

Another revealing look at a shuttle launch is here: https://www.youtube.com/watch?v=C0OmJFFQp50

If you look at 5:07, you will see just how violent the ignition of the solid rocket boosters was.

Also extremely interesting is this video, which is part 2 of about 30 minutes of 400 fps video of the launch from various engineering cameras: https://www.youtube.com/watch?v=M0L5CBrqE2U

Go to 9:20 to see just how rough was the thrust that the SRBs produced; essentially the thrust pulsed about around 7 hz. SRBs were not an elegant technology.

[bratschewurst]

Originally posted by JOEMA:

Quote:
Originally Posted by MG23
"It was basically designed to minimize the risk of failure, rather than to have backups if it did fail. The ascent stage engine, for example, was about as simple as you can make a rocket engine; if I remember correctly, it was pressure-fed and hypergolic, so just a couple of tanks, a couple of valves, and a rocket nozzle."

That is correct, and I would not describe the LM as lacking contingencies. The design philosophy was extreme reliability through simplicity -- even at a significant cost of performance.

One of the most interesting things I learned from reading about Apollo 13 was that NASA's design philosophy assumed that structures didn't - or wouldn't - fail. So structures, unlike systems, generally did not have backups or much redundancy. The reason was simple - the weight penalty would have been prohibitive. So they designed the structures and non-redundant systems to be a simple as possible.

There were multiple navigation systems on both the CSM and the LM, and multiple sources of electrical power on both as well. But there was only one SPS engine (albeit with two sets of valves for the hypergolic fuels) and only one descent engine and ascent engine on the LM.

They also tried to design the systems so that they could use what redundancy was inherent - being able to use the LM engine to power the entire stack, for example, as was done in Apollo 13, or more broadly being able to use the LM as a lifeboat for those portions of the mission when it was attached. But that fell well short of full redundancy. If the O2 tank on Apollo 13 had exploded when the LM was on the moon, or on return to earth, it would have caused the loss of the crew.

[Amadis of Gaul]

Originally Posted by tdracer

My personal vision has long been for a two stage shuttle - horizontal takeoff, the first stage being air breathing using hydrocarbon liquid fuel and some combination of turbojets/ramjets/scramjets, and a pure rocket H2/O2 orbiter. Of course it would cost a large fortune to develop, but per launch costs would basically be fuel and maintenance. Sadly it won't happen in my lifetime. Neither the money or the technology are there to make something like that viable.

Perhaps that's because such a setup is not viable period. To me, the whole idea of trying to combine more than one type of vehicle in one (e.g. a "spaceplane", a tilt-rotor, a "flying car", a half-track etc) is that you end up with something that combines most of the DISadvantages of both with only a few of the advantages. In this example the "orbiter" still has wings, some kind of landing gear, some sort of an aerodynamic control system for re-entry, none of which it needs at any time OTHER than re-entry. It also has to carry all the "spaceship stuff" which it does not need during the re-entry. In other words, at any given time in the mission, good half the mass of the vehicle is dead weight that's sitting there doing nothing, but still has to be carried. Is this not the very definition of inefficiency? It's hard enough to build a good airplane or a good spaceship, but to build something that's both is, in my opinion, well-nigh impossible.

All this is before we even get to your first stage vehicle which will ostensibly be this fairly large, cumbersome, expensive airplane that will only be good for one thing.

[tdracer]

Perhaps that's because such a setup is not viable period. To me, the whole idea of trying to combine more than one type of vehicle in one (e.g. a "spaceplane", a tilt-rotor, a "flying car", a half-track etc) is that you end up with something that combines most of the DISadvantages of both with only a few of the advantages. In this example the "orbiter" still has wings, some kind of landing gear, some sort of an aerodynamic control system for re-entry, none of which it needs at any time OTHER than re-entry. It also has to carry all the "spaceship stuff" which it does not need during the re-entry. In other words, at any given time in the mission, good half the mass of the vehicle is dead weight that's sitting there doing nothing, but still has to be carried. Is this not the very definition of inefficiency? It's hard enough to build a good airplane or a good spaceship, but to build something that's both is, in my opinion, well-nigh impossible.

Not sure what you're getting at - all vehicles contain some level of compromise to maximize their usefulness. A commercial jetliner carries around landing gear, flaps, brakes, etc. which make up a significant portion of the aircraft mass but are worthless for 95% of the flight. But the aircraft itself is worthless if it can't takeoff or land.
A spacecraft that can't re-enter and slow for landing is similarly of very limited value.
The Space X landable booster has to carry considerable extra weight for the landing struts and fuel in order to soft land - but the alternative is for the entire booster to be disposable. Isn't a single use spacecraft the real definition of inefficiency?

[Jonno_aus]

A good read

Space Shuttle Systems 101 - More Than You Ever Needed To Know About The Space Shuttle Main Engines


Some interesting stuff. Couple things caught my untrained and knowledge-less eye :

The power settings during flight are controlled automatically but if necessary the pilot can manually throttle the engines with a thrust lever located to the left of his seat, this is the same lever used to operate the speed brake during landing. The commander also has a similar lever for the speed brake but it is not capable of throttling the engines.

Wonder what fancy program was written to stop the throttles from also operating the speed brake if the pilot had to manually take over after launch? Obviously not a problem later on on approach if no rockets attached. And limiting having too many levers etc on the flight deck. Interesting nontheless.

At this point the vehicle will begin a roll, pitch and yaw maneuver that places it on its back (crew heads down) as it tracks the appropriate flight path for the desired orbit

From what I've read that lasts just over 5 mins in that position until it rolls back with the crew then 'heads up'. Must be a disconcerting feeling with the g-forces, vibrations, noise and I guess some blood draining to the head for some of that time.


Couldn't pay me enough to be an astronaut. I guess they get paid well..

[Amadis of Gaul]

Originally Posted by tdracer

Not sure what you're getting at - all vehicles contain some level of compromise to maximize their usefulness.

Indeed. It's exactly the level of compromise that's the issue. Landing gear, flaps and brakes comprise only a very small percentage of an airline's weight, unlike what we're talking about here.

[MG23]

Originally Posted by Jonno_aus

Wonder what fancy program was written to stop the throttles from also operating the speed brake if the pilot had to manually take over after launch?

There were separate programs (or program modes) for launch and landing, so, with the throttle lever in auto mode, I guess it would depend on which program you were running.

Looks like there was also a manual override to switch between throttle and speed brake:

HSF - The Shuttle

From what I've read that lasts just over 5 mins in that position until it rolls back with the crew then 'heads up'. Must be a disconcerting feeling with the g-forces, vibrations, noise and I guess some blood draining to the head for some of that time.

Gravity will affect the shuttle and crew at the same rate, so it shouldn't matter. Most of the effects the crew felt would come from thrust and drag.

And most of the vibration went away when the SRBs separated.

Couldn't pay me enough to be an astronaut. I guess they get paid well..

I think the astronauts who gave a talk I went to in the 90s said it was in the region of $40-50,000 a year at that time. So decently middle-class, but not exactly City banker levels. I don't think anyone did it for the money!

[Peter47]

I think that US Apollo astronauts were on service pay - the typical rank was Colonel or Naval Captain and they probably got less than half what a long haul airline captain got. Then again they could retire after twenty years.

You could earn rather more from being an astronaut. I understand that at some stage during the Apollo (or It may have been the Gemini) programme astronauts shared the proceeds of a very lucrative contract with, I think, Time magazine. Many went on to front advertising campaigns (Armstrong Chrysler, Shepard beer, etc.)

I also saw that Buzz Aldrin was charging a five figure sum for a public speaking engagement around ten years ago. The trouble is that whilst the man in the street might be able to name the Apollo 11 astronauts, how many could name those who flew the later missions. I don't know how much Tim Peake could get as a public speaker but he won't be making a fortune as an Army major.

[Jonno_aus]

Thanks MG23

Fascinating stuff. Also found this from Canadian astronaut Commander Chris Hadfield :

Launch is immensely powerful, and you can truly feel yourself in the centre of it, like riding an enormous wave, or being pushed and lifted by a huge hand, or shaken in the jaws of a gigantic dog. The vehicle shakes and vibrates, and you are pinned hard down into your seat by the acceleration. As one set of engines finishes and the next starts, you are thrown forward and then shoved back. The weight of over 4 Gs for many minutes is oppressive, like an enormous fat person lying on you, until suddenly, after 9 minutes, the engine shut off and you are instantly weightless. Magic. Like a gorilla was squishing you and then threw you off a cliff. Quite a ride

He also noted that it’s not possible to pass out during the launch, because you are being pushed into space while lying on your back, so your blood doesn’t end up draining out of your brain. Also, he said it takes about 15 seconds to go from a sunny day to complete darkness.

Brave indeed. And I'll happily admit now I'm not that brave and I'd only do it for the money.

[chksix]

John Young who has ridden almost all vehicles to space: "-Smooth as glass"

[joema]

Originally Posted by tdracer

"My personal vision has long been for a two stage shuttle - horizontal takeoff, the first stage being air breathing using hydrocarbon liquid fuel and some combination of turbojets/ramjets/scramjets, and a pure rocket H2/O2 orbiter. Of course it would cost a large fortune to develop, but per launch costs would basically be fuel and maintenance."

Winged HTOL air breathing shuttles (esp SSTO) have long been the ultimate dream. Superficially it's an alluring concept: just make it like an airliner. The U.S. spent billions of $ on the National Aerospace Plane (NASP) with this goal, and the UK is still backing Skylon.

Unfortunately the ugly reality is orbital velocity requires gigantically higher kinetic energy -- KE = 1/2*m*v^2, and every element in the design hinges on this. An air breathing first stage doesn't provide much performance advantage, yet entails huge financial cost and development risk.

When you calculate what kind of mothership is needed to launch an orbiter having a meaningful useful payload, it's something like a ramjet-powered XB-70 with 4x the gross weight. Then on top of that you need a self-powered orbiter capable of accelerating from Mach 5 to Mach 25.

NASP required multiple breakthroughs on many levels -- unobtanium materials, active cooling of the structure, scramjet propulsion which no wind tunnel can test, etc. A detailed account of this development is in the on-line publication "The Hypersonic Revolution": http://tinyurl.com/h8advzk

Getting into orbit via airbreathing propulsion has been called "getting to space the hard way". Unlike the casino game of craps, you don't get extra payoff for getting there "the hard way". Rather you want to get there the easiest, simplest way possible. Given current technology, that's probably some kind of a rocket.

[riff_raff]

Here's a very interesting document from NASA describing the Transoceanic Abort Landing (TAL) sites for the Shuttle. It was a big effort preparing all of the emergency landing sites for each Shuttle launch.

A TAL could be declared at T+2:30. But neither a Return To Launch Site (RTLS) or TAL could begin until the SRB's were jettisoned. This chart shows the abort conditions for loss of one or more SSMEs.

A RTLS abort procedure was interesting since it could require a hair-raising maneuver called a Powered Pitch Around (PPA). A PPA involved pitching the Orbiter 180deg at an altitude of >400kft so that the SSME thrust could be used to propel it back to the launch site for landing.

Here is an image of the Shuttle's abort mode selector switch:

[joema]

Originally Posted by riff_raff

"A TAL could be declared at T+2:30. But neither a Return To Launch Site (RTLS) or TAL could begin until the SRB's were jettisoned. This chart shows the abort conditions for loss of one or more SSMEs."

That chart only applies before the 1986 Challenger accident. Afterward there were many enhancements which enabled intact aborts or at least bailout aborts. For higher-inclination launches (e.g, ISS missions) these also included East Coast Abort Landings (ECAL) at various sites along the U.S. east coast.

The abort improvments can be seen by comparing figure 7 and 8 in the 2011 AIAA document "Space Shuttle Abort Evolution": http://tinyurl.com/jm8zelv

[chksix]

It was said somewhere that had a TAL happened it would have set an unbeatable record for quickest crossing of the Atlantic.

[Jonno_aus]

Smooth as silk indeed!

I see they're given a couple intructions along the way for 'abort boundaries' at 3:30. Guess they change pretty quickly too as it accelerates at ridicules speeds.

[tdracer]

Originally Posted by joema

Getting into orbit via airbreathing propulsion has been called "getting to space the hard way". Unlike the casino game of craps, you don't get extra payoff for getting there "the hard way". Rather you want to get there the easiest, simplest way possible. Given current technology, that's probably some kind of a rocket.

You'll note that I did specify that the technology isn't there yet. But as long as we continue to throw away a significant portion (or all) of a rocket every time we use it, space access will remain insanely expensive (currently between $2,600 and $10,000 per pound - and the shuttle was ~ $24,000/lb )

Something around 75% of the liftoff weight of an orbital capable rocket is oxidizer - get rid of that for the first stage and you can add a whole bunch of hardware to make the thing reusable while still reducing the overall vehicle size and weight. True, the current state of the art for Ramjet/Scramjets is no where near making this viable, but technology marches on. An air breathing launch vehicle that could carry an orbiter to ~120,000 ft./Mach 7 (or better) would mean the orbiter wouldn't need to be huge to carry the fuel to get into orbit.

As I noted, it's not going to happen in my lifetime - the money and technology are not there. Worse, the will to do things like going to the moon is long gone. But if we're ever going to get to the stage where traveling into space is as routine and commonplace as traveling cross country, that's what it's going to take.

[joema]

Originally Posted by tdracer

"as long as we continue to throw away a significant portion (or all) of a rocket every time we use it, space access will remain insanely expensive (currently between $2,600 and $10,000 per pound - and the shuttle was ~ $24,000/lb )

This is the standard argument; it has some validity but is misleading. A good example is the reusable shuttle cost about $10,000-$25,000 per lb to LEO. The expendable SpaceX Falcon Heavy currently costs under $1,000 per pound, and that was achieved with no reusability, no exotic airbreathing, no wings, etc.

In his presentation to the Augustine Commission, shuttle program manager John Shannon called reusability a myth. He explained when a vehicle is made in very small numbers, you cannot just shut down all manufacturing capacity after it's built. The vehicle and subsystems require ongoing R&D, fixes, testing, etc. Parts wear out, you have failures, design issues become apparent during use. You essentially have to keep the production line available, even if nothing is being manufactured, along with much of the associated industrial infrastructure. Then you must buy "one of" pieces to fix things which is expensive.

Airliners achieve lower costs through mass production, not just reuse. They also benefit from a smaller "standing army" of support personnel relative to the fleet size.

Any envisionable air breathing SSTO would be far more complex and expensive than the space shuttle. If built in small numbers, there's no mass production. It would be costly to operate, regardless of having wings and airbreathing propulsion.

Originally Posted by tdracer

"Something around 75% of the liftoff weight of an orbital capable rocket is oxidizer - get rid of that for the first stage and you can add a whole bunch of hardware to make the thing reusable while still reducing the overall vehicle size and weight."

An air breathing design would save oxidizer. However LOX costs about $0.01 (one penny) per pound. The LOX for a shuttle launch cost only about $14,000. You are right much of the liftoff mass of an orbital rocket is oxidizer. On the shuttle the tankage cost for that was maybe about 1/2 of the total $50 million ET, so eliminating the LOX would enable smaller, cheaper tankage.

OTOH the additional cost and mass of a hypersonic airbreathing design offsets the gain from losing the oxidizer. An air breather must fly a depressed ascent trajectory, like a shuttle reentry in reverse. You must have active cooling of the vehicle skin and wings, multiple propulsion systems, fuel, structure and thermal protection for those systems, etc. Since scramjets cannot reach orbit, conventional rocket propulsion must be used for the final ascent. All the mass, structure and thermal protection for that must be hauled to and from orbit.

Originally Posted by tdracer

...True, the current state of the art for Ramjet/Scramjets is no where near making this viable, but technology marches on.

This is true so there is always hope. The NASP research made significant progress in various areas. With today's more advanced CFD and material science it might be more achievable.

Originally Posted by tdracer

An air breathing launch vehicle that could carry an orbiter to ~120,000 ft./Mach 7 (or better) would mean the orbiter wouldn't need to be huge to carry the fuel to get into orbit."

This is not quite like it seems because of the v^2 term. Mach 7 is only 7.8% of orbital kinetic energy. Being at 120,000 ft actually helps relatively little since gravity and air drag losses to reach that altitude are not severe. If launched at that altitude and velocity the orbiter would still have to do over 80% of the work to reach orbit, yet a Mach 7 mother vehicle would be fantastically heavy and expensive. Optimum staging velocity for lowest total vehicle mass on a two-stage launcher is about Mach 10, and the total vehicle mass curve is very steep around that minimum. IOW deviate much from Mach 10 staging and the whole stack get a lot heavier, quickly.

A lot of smart people have worked on airbreathing launchers for many years. It is a compelling concept but in the real world it is much more difficult than first appears. The current trend is that optimization of conventional rocket technology through lean production and partial re-use are a more effective way forward.

[Amadis of Gaul]

It seems to me the words often attribute to Ed Henneman are very applicable here. Simplicate and add lightness.


Rockets seem to accomplish that.