> With a fully reusable rocket (as SpaceX is going to use)
This is the sort of thing where you need to be careful with what you infer, the the sort of thing that often causes engineers to be overconfident in performance and reliability estimates.In reality, they're doing some very initial experiments in vertical landing with a view towards exploring reusability. That is different to your implication that reusability is a done deal.
> They come from extensive simulations and tests, which are then extrapolated. It's not the same guarantee as running thousands of end-to-end missions, but it's better than you imply.
And that's the problem. Notice you're talking about man rated 'parts' and I'm very deliberately not. Many of the mission failures or anomalies in launch vehicles so far have come from parts that work fine on the bench as individual subsystems. It's the lack of full-scale, realistic tests of complete systems that cause problems. There's just not the money for it nowadays. For example, Orion's crew vehicle had budgeted 2 aeroplane parachute drop tests. Apollo's landing module had over 230. Interestingly, they recorded anomalies on over 210 of those.
As for simulations, well one of the catch-phrases in the rocket engine business is 'plumbing never leaks in simulations'.
As for extrapolation, as a datapoint related to a field I have worked in (parachutes for space systems), quite a few of the high profile parachute failures were colloquially summarised as 'they extrapolated without a license'. All the Mars landers the USA have landed so far have used disc-gap-band parachutes of the same design and size that were explored in a set of very expensive and extensive tests performed at high altitudes for the 70s Viking Lander. It's called the 'viking box' and people at JPL know you do not just 'extrapolate' out of it because they've seen what happens when smart, well intentioned engineers do. That's why they called it a box :)
Going back to simulation for a moment, I am familiar with the state of the art of parachute simulation (and fluid-structure interaction simulation in general), and so are they people in charge of the space missions, and that's why they stick to the Viking box. We can barely match that viking data in sims, let alone start wondering out of it into unexplored territory.
Finally a little anecdote from Charles 'Chuck' Lowry, the guy who designed the apollo landing systems, about testing. On Apollo 15 reentry, one of the 3 parachutes failed, the first and only recorded failure of an apollo chute during operations. It was traced back to being because the landing module thrusters had vented their fuel out before landing, but this had ignited on the still hot nozzles on the way out, causing a load of burning fuel to go fly up into the chute and destroy it. Thank god, he said, that it only caught the one and not a second one, else it could have ended very badly.
The parachute system tested perfectly, and the thrusters performed admirably during their entire qualification program and all previous flights. But the combination of these two systems, under real conditions, interacted in such that the consequences were a significant risk to life. 'You ain't tested it till you've tested it', he said.
HN is full of similar examples of outages of things like AWS due to an interaction of failures of parts, systems, and bob the technician not putting the circuit breaks back in exactly the right place after routine maintenance. The space of possible failures rises exponentially with the number of parts, when you consider all the ways they can interact. It's a hard problem to solve and the people at the top are under no illusions about the reliability numbers, they're made for congress and journalists.
> The whole point of these two adages is that reusing an existing design is better than a new one.
Yes, and that's put in doubt. Starship aims to improve on previous designs - in terms of affordability, that is, making human flights cheaper. This cheapness can't be realized with existing designs, so a new design becomes better in that regard.
> SpaceX's REUSABLE rockets are great for a number of reasons yes, but by definition, those are not NEW launch vehicles.
I don't know how good definition can exclude reusable rockets from being new. Was Shuttle ever new? Delta Clipper? Reusable Falcon-9? Falcon Heavy? I think this is not a good definition, if, according to it, reusable rockets can't be new.
> And when they were new, well, lots of delays and setbacks and costs as they kept accidentallying rockets trying to land them.
Do you know the difference between designing and using? In software it's rather clear, and nobody would expect a half-written program to function according to specs. Neither it's the case in aerospace - while Falcon reusability was being designed and tested, nobody should expect it to perform flawlessly as when used "in production". Not cheap, agree (actually, quite cheap by aerospace standards, but still not some typical household-sized money), but I'd argue that was rather quick - just a few years to put reusable first stage into production starting from announcing the idea and building the first "Grasshopper". So, while 39[a] may stand here, your comment doesn't provide a good justification to it.
> If anything, SpaceX's entire business model is EMBRACING that adage, not disproving it or an exception to it.
SpaceX benefited immensely from using proven solutions, but the results they are showing are still disproving the idea of this law. The ambitions of SpaceX are high compared to the rest of the world launching industry, but so are the results, and we also have genuine "firsts", like putting the reusable first stage into production, or flying reusable spacecrafts to space station, TKSes and Shuttles notwithstanding.
Let me try to explain again my main point: SpaceX aims to make human spaceflight significantly cheaper, and the opinion is that it can't be done without radical redesign from scratch. It was attempted several times in the past, with e.g. Shuttle and Energiya, and it still isn't done today, but if you want to risk being put on the "you're currently here" list of SpaceX achievements(1), which were doubted and then happened, I'd at least propose you to think from the basic assumptions and find out why SpaceX won't actually achieve cheaper human spaceflight this time.
>It pains me to think what NASA could be doing with 10x more money.
Me too, but pretty much it all ends going to Lockheed anyway whether it comes via the DoD or Nasa. I don't mean that conspiratorially either, even JPL people joke that JPL stands for "Just Procure Lockheed". The subcontractors rarely get mentioned in Nasa PR, but Nasa is really a whole bunch of different project offices spread over a few campuses with an enormous ecosystem of subcontractors.
I expect a vertical, strongly-led skunkworks style structure with guaranteed funding for several continuous years (vs "start working on this now but we can't promise we won't change our minds in 12 months" which causes a lot of subcontractors to not properly commit to new hires or other big capital commitments, and having to spread all the work evenly among different states) would probably yield 10x as much for exactly the same money.
Regardless of all that organizational arm-chairing (though I work in this space, hoho), Curiosity is bloody fantastic and I am very excited to follow its progress over the next year at least.
Camera chat: fewer bigger pixels = less ccd noise - remember Mars further away from the Sun than Earth, and so it's generally darker. Take an Iphone 1 photo of things at twilight to appreciate some of the difference!
> Everytime I read news like this it just furthers the impression in my mind that Congress's SLS (and that rocket program is truly owned by Congress, not NASA) is an incredible waste of money that makes your average military recruitment contract red-faced with embarrassment.
Welcome to alt-space point of view of a few decades. Looking at NASA contracts - and Congress mandates for them - you can easily guess that the goal of them isn't space related, but something else - maybe politics related, when you have a fell-good agency, lots of work contracts distributed across many states and producing jobs for same old ways of doing things. If one would care about space exploration, one should definitely use modern opportunities for faster, better and cheaper technology. And even if, as in case of SpaceX, you have more mission failures for unmanned missions, you still have net savings and tremendous advantage in the speed of development.
> Add to that the fuel for the launch vehicle; and fuel for the the cruise stage.
What you've just said is the equivalent of someone witnessing a Ferrari crash into a tree and destroy itself, and saying 'Ouch, that's an expensive tank of fuel he's just wasted'.
In fact the costs of fuel for these things are trivially small, basically inconsequential, compared to the cost of the things that are using the fuel - the rocket and the cruise stage. You don't get them back, they're single use, expended as part of the mission, and they're expensive.
> Landing still requires a lot of fuel, which needs fuel to be carried up.
That's true, and that reduces the payload of the returning stage. To have it working, you either have to reduce the payload or to increase the size of the stage. In both cases the payload weight to liftoff weight decreases.
> It was a waste and still is.
That's false, as in exchange the operator gets the stage back to be reused on the next flight. That's usually a huge saving in costs. Fuel is relatively cheap, and to make a rocket somewhat bigger or a payload somewhat smaller does relatively small change to the price of a kilogram to LEO comparing to the opportunity not to pay for the stage hardware on the next flight.
Overall SpaceX made a huge improvement in costs and moved the world launch industry quite a bit forward.
Quite incorrect. If we rewind to the golden age in the 60s, the US's Saturn V had 5 F-1 engines on the first stage. The UK's Black Arrow had 8 identical engines in 4 pairs. Russia's Soyuz has 20.
Similarly, if you ask anyone at SpaceX they would tell you it's difficult to underestimate how much they owe to the old grey-beards from NASA who are still around and who helped them get up to speed quickly, avoiding many hundreds of thousands, indeed millions of dollars of blind alleys and reinventing the wheel.
SpaceX is a wonderful example of good engineers - old nasa ones and fresh graduates, united by a common mindset, with enlightened (for which private is often but not strictly a prerequisite) management. That's where they succeed, I think. They look at where they are now, where they want to be, and keep the string taught between the two. But don't think SpaceX could have done this in a vacuum (hohoho). Of the several SpaceXers I've met, including Elon Musk himself back when he had time to give talks at SEDS conferences, none would make such a claim, certainly.
That's a pretty hard problem. F-1 took unimaginable efforts to make right - event though the only unusual, untested parameter for this engine is its size. RD-170 took all the genius of Glushko - including his previous somewhat successful experience with RD-270, which deserves a whole story for itself - to get working properly. With all hindsight, only the forth Merlin of SpaceX is actually pushing technical limits - and that's in XXI century. Then, there is the issue of time - to build an engine from scratch is easy to delay a rocket for a year - if you're lucky and do that right from the first attempt.
So Orbital words can be taken seriously and for the face value. NK-33 is a pretty good engine.
It's not really mentioned in the article but as a starting point they received all the work done for Fastrac [1], a NASA program to build small, cheap, expendable rockets - something like the Falcon 1. That got cancelled as NASA projects are wont to do but it made sense to use that design as a baseline. A clean sheet engine design is very complicated indeed - it's a very high dimensional, highly coupled optimisation problem, so a known good starting point is a very valuable thing to have.
Indeed the turbopump, which is one of the hardest bits of a rocket engine, is made by Barber Nichols, who made the turbopump for Fastrac and who make the turbopumps for the Merlin engines [2]. I've heard rocket engineers describe rocket engines as turbopumps with some extra plumbing. Perhaps a slight exaggeration but not far off, especially since their design is so tightly coupled and dependent upon overall engine parameters. The degree of coupling depends on the topology of the plumbing, or the 'cycle' of the engine, which I'll try and explain:
There are three kinds of rocket engine cycle (well, there are maybe more but these are the three that have been flown historically). The Expander Cycle, the Staged Combustion Cycle, and the Gas Generator cycle. I'll mention the last two.
Merlin, as the article mentions, is an example of a Gas Generator cycle [3]. In this cycle, you take off a little bit of fuel and oxidiser to burn outside the main combustion chamber, to generate some hot energetic gases that you can exhaust over a turbine. This spins the turbine up, which is connected to a shaft with a compressor on the other end. The compressor increases the pressure of the propellents so that they can be injected into the main combustion chamber. This assembly (turbine, shaft, compressor) is called the turbopump. It's necessary because the engines require very high flow rates to get the thrust they need, and that has to be at a high pressure - higher than the pressure of the combusting gases inside the combustion chamber, else you wouldn't be able to inject it!
Back to the bleed-off to drive the turbine. You usually don't want a perfect stoichiometric mix of fuel and oxidiser for this, or even close, because it generates extraordinary hot gases that no turbine would last long in (The turbines are spinning at many tens of thousands of RPM usually so would be subject to much higher forces than the actively cooled walls of the main combustion chamber). For this reason you usually have a large imbalance of one propellent to the other to keep the temperature down. Usually you run with excess fuel, or 'fuel-rich', as the opposite - oxidiser rich - means you have hot oxidising gases which are harder on the metallurgy. I do know of some russian exceptions to this, though, where fuel rich would have left sooty deposits in the plumbing (The materials science employed in the turbines was apparently so witchcraft that when the US got intelligence of oxidiser-rich turbine precombustors, they thought is was deliberate counterintelligence from the russians to get them to waste billions researching the impossible). The gas generator cycle, as the article mentions, dumps this turbine exhaust overboard separately. The problem with this is that there's a load of uncombusted fuel in this exhaust, which you're just wasting, and this hits your rocket performance - the Specific Impulse ( I_{sp} ), as you're not getting as much bang out of a given mass of fuel as you could.
The answer to this is the Staged Combustion Cycle [4], where you also inject the exhaust of the turbine into the combustion chamber to finish off combustion. The performance of these engines is higher but the thermodynamic balance to design a working system is a greater challenge, and some of the engineering is a bit harder too. Staged Combustion engines are mostly russian, although the Space Shuttle Main Engines are a US-design example of Staged combustion.
SpaceX have been gradually and incrementally improving the Merlin's away from their simpler beginnings, and it's been pleasing to watch as an interested outsider. To bring it back to the OP question, "are all engines of that caliber that size or is this one special?", Merlin didn't particularly stand out in terms of power density in the early days, although it's been improving and improving. Now there is the Merlin 1D [5], which claims to have the highest thrust to weight of any rocket engine every made. One should take these claims with a pinch of salt as what counts as 'engine' and what counts as 'plumbing' and what counts as fuel tank is sort of open to debate and you can do some creative accounting to make your numbers look better. However, it's an impressive achievement regardless.
The metric that doesn't lie, from a performance point of view, is the mass fraction of the rocket - that is the fraction of the all-up, fuelled-up mass of the rocket on the pad that makes it into orbit. The higher the better - i.e. you can take bigger payloads for a given size rocket. Note this is just from a performance point of view, not an economics point of view.
However, increasing mass fraction will be important to SpaceXs staged aim of re-usable rockets. That's because as well as the payload, each rocket stage as to also carry the fuel it needs to land. I believe Falcon 9 can launch about 2% of its pad mass into orbit (i.e. the payload can be 2% of the total mass), and Musk reckons if that could be increased to about 4 or 5%, there's be enough margin to carry enough landing fuel and extra landing hardware like legs.
So my bet, just for fun (I'm not connected with SpaceX, this is just sideline speculation for the sake of interest) is that you might start to see development of a Staged combustion engine instead of gas generator, and a switch to methane fuel which, with LOX, has a slightly higher specific impulse than Lox/Kerosene which they currently use. Maybe 20 seconds extra (seconds being the unit of specific impulse), which is maybe 5-7% more than they might be seeing now, which is worth having. Methane is nice because it has a similar density to kerosene. Lox/LH2 has almost 50% better performance than LOX/Kerosene in theory but LH2 is of a very much lower density, so the tanks must be much bigger (the illustrates my earlier point about the slipperyness of engine-only thrust to weight as a metric - how much bigger and heavier are the tanks?).
[Edit: of course instead of building a higher performance engine you could just built a much bigger rocket with the same mass fraction and have the cargo be a smaller percentage of launch mass. probably cheaper than developing a staged combustion engine. I suspect the rocket science equivalent of more servers vs a rewrite in C]
This post has ended up being a bit longer than I thought it would. Hopefully of some interest if you're new to the subject.
> Don't actually think you can iterate from Merlin to Raptor.
In some sense Earth science had practically do that - from Goddard's 1926 pressure-fed/piston pumps feed via von Braun's open loop of 1944, via Isayev-Melnikov staged combustion of 1949-1959 to Glushko's full-flow combustion of 1967.
Slow, and engines were designed from scratch. But still some iterations and evolution.
No, this is all just wrong. The efficiency is because you dont throw a load of enthalpy overboard as in a gas generator. The phase is _exremely_ second order by comparison.
You’re all over this thread being wrong and confused.
> The real efficiencies come when you use like an expander cycle or a staged combustion cycle or you feed the gas generator exhaust back into the nozzle like Merlin Vacuum or F-1.
If I remember correctly, with F-1 the gas generator exhaust was sent to the nozzle to cool the nozzle, not to add efficiency to the engine main cycle.
We're still trying to get more efficiency from isochoric combustion, but the expected wins aren't too big. It's good that full-flow combustion becomes more of a norm.
This is the sort of thing where you need to be careful with what you infer, the the sort of thing that often causes engineers to be overconfident in performance and reliability estimates.In reality, they're doing some very initial experiments in vertical landing with a view towards exploring reusability. That is different to your implication that reusability is a done deal.
> They come from extensive simulations and tests, which are then extrapolated. It's not the same guarantee as running thousands of end-to-end missions, but it's better than you imply.
And that's the problem. Notice you're talking about man rated 'parts' and I'm very deliberately not. Many of the mission failures or anomalies in launch vehicles so far have come from parts that work fine on the bench as individual subsystems. It's the lack of full-scale, realistic tests of complete systems that cause problems. There's just not the money for it nowadays. For example, Orion's crew vehicle had budgeted 2 aeroplane parachute drop tests. Apollo's landing module had over 230. Interestingly, they recorded anomalies on over 210 of those.
As for simulations, well one of the catch-phrases in the rocket engine business is 'plumbing never leaks in simulations'.
As for extrapolation, as a datapoint related to a field I have worked in (parachutes for space systems), quite a few of the high profile parachute failures were colloquially summarised as 'they extrapolated without a license'. All the Mars landers the USA have landed so far have used disc-gap-band parachutes of the same design and size that were explored in a set of very expensive and extensive tests performed at high altitudes for the 70s Viking Lander. It's called the 'viking box' and people at JPL know you do not just 'extrapolate' out of it because they've seen what happens when smart, well intentioned engineers do. That's why they called it a box :)
Going back to simulation for a moment, I am familiar with the state of the art of parachute simulation (and fluid-structure interaction simulation in general), and so are they people in charge of the space missions, and that's why they stick to the Viking box. We can barely match that viking data in sims, let alone start wondering out of it into unexplored territory.
Finally a little anecdote from Charles 'Chuck' Lowry, the guy who designed the apollo landing systems, about testing. On Apollo 15 reentry, one of the 3 parachutes failed, the first and only recorded failure of an apollo chute during operations. It was traced back to being because the landing module thrusters had vented their fuel out before landing, but this had ignited on the still hot nozzles on the way out, causing a load of burning fuel to go fly up into the chute and destroy it. Thank god, he said, that it only caught the one and not a second one, else it could have ended very badly.
The parachute system tested perfectly, and the thrusters performed admirably during their entire qualification program and all previous flights. But the combination of these two systems, under real conditions, interacted in such that the consequences were a significant risk to life. 'You ain't tested it till you've tested it', he said.
HN is full of similar examples of outages of things like AWS due to an interaction of failures of parts, systems, and bob the technician not putting the circuit breaks back in exactly the right place after routine maintenance. The space of possible failures rises exponentially with the number of parts, when you consider all the ways they can interact. It's a hard problem to solve and the people at the top are under no illusions about the reliability numbers, they're made for congress and journalists.
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