The J-2 engines (using cryogenic H2/O2) were a huge advance over anything that had been done before using H2 as a fuel; even so, they only generated 110,000 lbs of thrust vs 1.5 million for the F-1. The SSMEs were, in turn, a huge advance over the J-2s, and even they only produced 400K lbs or so. If Apollo had needed H2/O2 engines for the first stage, it likely never would have made it to the moon.

If I understand matters correctly, it's also true that the specific thrust advantage of H2/O2 engines mattered less at lower speeds and denser atmospheres.

The shuttle SRB's provided most of the thrust at launch. But the RS-25 liquid engines were used because they could be throttled. The RS-25 liquid engines were started about 3 seconds prior to igniting the solid boosters. This allowed the liquid engine turbopumps to spool up and produce thrust. If you watch a video of the RS-25 engines starting up, you'll see an initial spray of liquid propellants just before the engines ignite.

And the engines needed to be throttled down soon after launch to avoid exceeding max Q or max structural dynamic pressure loads on the STS.

To do this, they took the shuttle main engines down to 67% thrust in the lower atmosphere and then back up to 104% when the atmospheric density reduced sufficiently.

The solid boosters were more sophisticated than I imagined. They each had an APU and vectored thrust nozzle.

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.

Awesome !!

https://m.youtube.com/watch?v=Lq_shHu4lAs

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.

The SRBs also 'throttled down' at that point by a change in the shape of the propellant at that stage of the burn.

Pedantically, the boosters were lit when the shuttle returned to the vertical after the SSME ignition pushed the stack forward and it swung back.

Also check out this film, also available as an iPad app (NASA Ascent), 45 minutes of gorgeous slow motion launch photography from the numerous cameras on and around the pad narrated by two guys who ran the operation.

https://www.youtube.com/watch?v=vFwqZ4qAUkE

One great geeky detail of the SSME start process was that the engine bell vibrated quite markedly as the engine lights up. The flight position of the two lower engines (no. 2 and 3) placed the bells very close together and there was a chance they could collide during the start so they were held apart during light up and then gimballed back into position once they are up and running. Easily visible on close ups of engines during launch.

Another vote for Riding Rockets by Mike Mullane, great behind scenes look at the operation, warts and all. One thing that is very clear from the book is that the astronauts themselves were under no illusions about how dangerous and marginal the vehicle was and the risks they were taking with every launch.

Disconnect?
 

I think GordonR missed his boat or flight. Space Cadet?
The original question said NOTHING about the Saturn V. Not a single word. Focus, please...:p

:)

Invoice for keyboard on its way.

Somewhere I found that the last check before the SRB's are lite off all three of the main engines test their gimbaling and only after being successful on all three engines do they fire the SRB's or do an abort if any one fails.

The whole American space program was mind blowing. I have visited KSC twice, and I spent ages just looking at the Saturn V and all the engines in awe.

Another awesome fact is that the Shuttle's rate of climb is 2000 feet per second. I will write that again, 2000 feet per second.

The Airbus I fly can climb at 2000 - 2300 per minute with normal loading........

The more rapid liftoff for the shuttle was due to higher initial thrust-to-weight ratio, but this changed vs the Saturn V during the ascent.

From a thrust standpoint, the Saturn V sea-level liftoff thrust on Apollo 15 was 7.823 million lbf (34.8 MN), which increased with altitude to a peak of 9.18 million lbf (40.8 MN) at T+135 seconds. The engines were not throttled; this was due to increasing nozzle efficiency as ambient pressure dropped:

Image:SaturnVThrust2.jpg - from the Schools Wikipedia

The shuttle liftoff thrust was about 6.78 million lbf (30.16 MN). The SRBs underwent significant throttling over their approx. 120 sec firing time, as can be seen in this graph. This throttling was not dynamic but designed in by controlling propellant surface area:https://en.wikipedia.org/wiki/Space_...Srbthrust2.svg

Like the Saturn V, the shuttle SRB and SSME engines improved with altitude, but they both throttled back around Max Q, roughly T+60 sec. Despite improving nozzle efficiency with altitude, the SRB throttle schedule probably meant the peak vehicle thrust was at liftoff not at altitude like the Saturn V. So comparing peak thrust to peak thrust, it was about 6.78 million lbf vs about 9.18 million lbf.

Despite the slower start, at higher altitudes the Saturn V accelerated more rapidly, reaching a peak of 3.8 g just before 1st stage cutoff.

Of course the ultimate goal is delivering a payload. On Apollo 15 the Saturn V delivered a payload of 140,930 kg (310,697 lbs) to low earth orbit. The heaviest shuttle payload was about 23,586 kg (52,000 lbs).

It would have taken six shuttle launches to deliver to LEO the same useful payload as a single Saturn V.

Getting the desired time/thrust curve is quite the science for solid rockets. Unlike the simple 'end burning' black powder rockets, most AP based solid rocket motors are 'core burning' and are ignited at the front. The shape of that core cavity determines the time/thrust relationship. IIRC, the Shuttle boosters had a 'star' shaped core to get the desired characteristics.

The shuttle was a tremendous technological achievement, but it failed miserably at it's primary goal of reducing the cost of inserting payload into orbit by at least an order of magnitude. By most measures, even accounting for inflation, the cost of placing a pound of payload into orbit was not meaningfully different between the Space Shuttle and Saturn V. About the only meaningful capability we gained with the shuttle was the ability to bring large objects back from orbit.

I find it both amusing and pathetic that NASA is now spending billions of dollars to recreate the capability we already had 45 years ago with the Saturn V :ugh:

Wow.

So does that mean that the Shuttle and its fuel tank could have used the Saturn V first stage instead of the boosters?

I presume the boosters were much easier and vastly cheaper to manufacture?

I didn't know the booster thrust varied during the launch - very clever.

Indeed. The amount of expertise around here is truly overwhelming at times.

The Saturn V S-IC first stage was considered as a shuttle booster:

https://joema.smugmug.com/Aerospace/...er/i-TmrdjpS/A

However the initial goal was a fully-reusable two-stage vehicle. Unfortunately the optimum staging velocity for lowest total mass is around Mach 12, which means a reusable first stage would essentially be a hypersonic transport in the 3-4 million pound gross weight class. This would have entailed extremely high development cost and risk. Former shuttle program manager Robert F. Thompson said even had they been given the money, he didn't think it would have been possible.

This iteratively drove the design process to an expendable booster (the above Saturn S-IC was one of many concepts), which then led to an orbiter with external propellant, which then led to an expendable tank with semi-reusable solid rocket boosters.

See "The Space Shuttle Decision": The Space Shuttle Decision: Chapter 6

It was understood early on the shuttle would likely not be economical to operate. This was covered in the 1972 GAO report to Congress: http://archive.gao.gov/f0302/096542.pdf

There was also a RAND study in that period which had similar statements about projected per-flight cost, also reviewed in the Jenkins book, "Space Shuttle: History of the National Space Transportation System", p. 173. It was known in the early 1970s even at 60 (!) flights per year, the shuttle payload cost per pound would only be about 38% cheaper than expendable boosters. If that flight rate could not be achieved it would be (and was) more expensive.

The vehicle was never designed to reach that flight rate, e.g, the maximum production rate of external tanks using three shifts at the Michoud facility was only 24 tanks per year.

The shuttle was an amazing vehicle but in hindsight there was no possible design in the early 1970s that would have permitted achieving the conflicting performance, safety, cost and flight rate goals.

I get the sense everybody knew this was a bad idea, but did it anyway. Gotta love the government.

Not so much a bad idea as ahead of its time - the technology just wasn't ready yet. I was only a teenager when NASA abandoned the fully reusable 'two stage' shuttle concept - but even then I knew that basically meant throwing out the baby with the bathwater.

NASA has long been accused of being more interested in "sexy" than in functionality, and the shuttle was "sexy". There have long been advocates of "Big Dumb Rockets" - simple, (relatively) cheap, not man rated so reliability was not as critical. One proposal was for a Saturn 1B sized rocket based around a single F-1 engine, million plus pound launch weight that could put the same payload as the shuttle into orbit but for much lower cost (there was even talk of recovery and reuse of the F-1 engines but I don't know how viable it was). But that NASA wasn't interested because such a rocket was boring and the shuttle was sexy :rolleyes: Although to be fair, boring doesn't get as much funding as sexy :E

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.

It still seriously ticks me off that all that engineering that went into the Saturn V was lost - I still consider the Saturn V/Apollo (along with the associated moon landings) to be the greatest technological achievement of the 20th century and we literally threw that away.

One way of thinking of the acceleration the crew of the orbiter experience is to imagine doing 0-60 in just under two seconds. But continuously for 8.5 minutes...

The fundamental problem with the space shuttle program was the same basic problem that NASA had post-Apollo 11; there simply was no appetite on the part of either the public nor the political leadership for any potential follow-on missions that would justify the kind of funding required for successful completion of those programs.

As the document referenced in post #57 made clear, the design of the shuttle system - a re-usable vehicle with a pretty small payload, launched with the aid of two massive solid-rocket boosters and a disposable tank - was chosen because it was the cheapest to develop at a time when NASA budgets were being pared back significantly in real terms. They knew at the time it wouldn't be the cheapest to operate, but they weren't given the money to develop a better or more sustainable program.

To give one example of the choices forced on NASA after Apollo 11, the last three moon missions were cancelled, even though the hardware was built, and even though the cost of launching those missions was a tiny fraction of what had been spent on the space program, which had been driven entirely by the goal of getting to the moon. Yet NASA cancelled almost 1/3 of the moon missions - although hundreds of billions in current dollars had been spent to develop the capability to launch those missions - simply to free up some cash for shuttle development, because they weren't allocated the money to do both.

The ultimate irony of the shuttle program was that it was most designed to build, service and re-supply a space station - which was, due to budgetary constraints, abandoned pretty early on in shuttle development. It became a machine with the sole mission of flying people into space to do - what?

No doubt NASA made some bad decisions post-Apollo. But the fundamental decision that crippled the space program was the decision by the political leadership and the American people not to have an Apollo-scale space program at all.

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

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.

http://www.spaceflightnowplus.com/hd...ilm_ssmeHD.jpg

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.

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.

Originally posted by JOEMA:
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.

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.

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?

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 :


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.



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..

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.

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

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.

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!

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.

Thanks MG23
 

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


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

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

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.

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:

https://upload.wikimedia.org/wikiped...bort_panel.jpg

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

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

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. :eek:

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 :eek:)

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.

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.

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.

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.

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.

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


Rockets seem to accomplish that.