No existing rocket has tried to perform either the "belly flop" or the "Landing flip manouver" that SpaceX is trying to do.
The failures are due to complex issues (fuel tanks, valves, engine reliability under complex forces) not simple control system issues (choosing wrong thrust, not able to orient using thrusters, etc)
I don't understand the term belly flop or rapidly reusable. Do You mean that it is becoming horizontal to reduce the falling speed rate to land on its belly?
shuttle was reused and landed on wheels parallel to its belly.
Rapidly reusable means the goal is to have Starship (or at the very least the Super Heavy booster) fly multiple times a day. The Space Shuttle needed a new external fuel tank each flight, and the SRBs required significant refurbishment, to say nothing of the orbiter's own refurbishment.
Also important to note that Starship is going to be an interplanetary vehicle. And that means it needs to be able to land in places with little to no atmosphere on a surface with no runway.
The Space Shuttle was an impressive engineering marvel, especially for the time, but even if it could leave low earth orbit, there was no way it could land anywhere other than Earth.
Rapidly reusable - You can land it directly on (or next to) a launch platform, refuel it and launch it again the same day. Same as a regular aircraft.
The Space shuttle had a disposable tank (which was lost on launch), recovered but basically destroyed solid rocket boosters (ditched into ocean) and finally on landing it had (potentially) damaged heat tiles which all needed inspection and which were all fragile and different.
SpaceX Starship boosters are refueled after they land themselves using a pump.
Shuttle solid rocket boosters have their shells fished out of the ocean by a boat. Then they return to the factory to be broken into sections and filled with a solid propellent.
1. People doing analysis and hoping to check everything through engineering rigor and (hopefully) good assumptions
2. Test early and often, learning along the way until many positive tests have proven the system
I'd prefer 2. Look at systems like SLS to see the schedule results of (1).
No people were put on Falcon launches until almost 100 successful launches. I imagine a similar situation for StarShip. For example NASA is funding in orbit refuelling experiments (unmanned) and also a StarShip moon landing (unmanned) which will help prove the system prior to human flight.
Don't worry, plenty of people will carefully do analysis (1) later on. But the data they will review will include telemetry from real flights rather than just hopeful simulation / analysis results.
Don't get your hopes up. Since it is rotating on an axis while moving and twice, it has a huge degree of freedom for failure.
Even if successfully returns 100 times, any untested change to its payload can change the parameters which are apparently unknown because they have not used any fancy simulation.
Good luck. I will be watching and ready to say I told you so. The staff could be absolute geniuses by they will not be able to foresee all the unexpected results.
The failures so far relate to the pressurization of the header tanks and the engine performance on re-light (hard problems). I imagine these will be well solved after 100 flights.
The assumption that shifting payload is going to boggle the flight computers leading to loss of craft sounds unlikely. Both because the payload will be secured and the flight computers are more dynamic than that.
Finally, the forces on the cargo shift from 1G towards the belly during the belly flop to a mix of gravity and pressure from the engines during the flip. While the view from the window would be "interesting" - the actual forces on the payload will remain a summed ~2G from these two axes (mostly from "down") during landing. This is similar to how the lift vector while rolling in an aircraft keeps you safely stuck to the floor (and not the walls) during jet flight.
Anyone flying an aircraft or space vehicle who doesn't secure their loads is going to experience some shifting of cargo. Of course that's why you have a small cargo compartment which physically restricts the movement of potential cargo. See how 747s secure cargo in large bins within a dedicated cargo hold for reference.
747 can not flip like that; it would stall and crash. The narrow bodied 737s crashed for less. Their fancy flight computer miscalculated because of center of gravity miscalculations. They crashed after 100s of flights.
I like your optimism. Good luck. I mean it. I would not fly in that thing even if they paid me a million.
Big airliners do parabolic arcs - "vomit comet", so it's not a huge problem. 737 MAX crashed for different reasons. E.g. Soyuz capsule returns safely despite different loads and different distributions of mass - control systems, even relatively modest ones, can compensate. It's failures which provide most useful information about shortcomings of the system at some point, so they are welcome during testing - if you think that at this point they shouldn't explode, you'd better bring good arguments. Shuttle had much better aerodynamic shape than Starship, and their landing modes are different.
737-max crashed because they never went through full blown simulation and acceptance procedures for it. They just made the body longer and compensated for differentials in flight control software parameters but they had a blind spot in their assumptions. Those aircrafts have decades of air flight simulation behind them and yet ....
Shuttle is a much finer craft but these guys may have different objectives and that is their prerogative. The fact that there are errors in there that can lead to explosion is troubling to me.
The claim that the explosions will lead towards a better design is an assumption.
737-Max crashed because of the "lets analyse this rather than test it" thinking that you described earlier. That and an overly cosy relationship with the FCC and a culture of silencing cautious engineering voices.
It's seemed cheaper to tack larger engines and new software onto the old air-frame than to redesign the aircraft to be mechanically stable and update the cockpit.
Not surprising that the same company (Boeing) that campaigned for analysis over testing in spaceship design (they claimed SpaceX couldn't do commercial crew) also failed to design a working and stable aircraft.
I'd argue that the bureaucracy involved in "signing off" an new aircraft design contributed to these problems. Designing a aircraft or spacecraft from first principles and then refining through testing does have its advantages.
My point about aircraft was that the lift vector is perpendicular to the wings, even if the aircraft flips (rolls) upside-down there is still a force that pushes you toward the deck if you are inside the plane. In the StarShip there is a similar upwards force from the engines (when lit) towards the nose regardless of which direction the ship is oriented with respect to the Earth.
The reason why flying a plane in clouds is so dangerous is that your sense of up and down in a plane is invalid. You'll always think the deck is down without the aid of either a view of the horizon or the correct use of functioning instrumentation.
The bureaucracy had nothing to do with it. They did not want to spend the money to create a new craft. The long bodies aircraft was not airworthy physically speaking and so the software was designed to limit its pitch to prevent it from stalling.
All aircrafts can stall and some angle of attack but a long+narrow aircraft is way more sensitive.
Design of an aircraft from scratch would have flagged it as poor design right away.
As pointed out in some other comments, SpaceX do extensive simulations, they almost certainly have the best rocket simulations in the world (see some of the published talks on youtube to see the state of their research).
We know that their simulations/calculations were excellent for these last couple of Starship tests because the tests themselves were excellent. There were a number of things being tested, including things like flying multiple Raptor engines, turning those engines off, switching between different fuel tanks for launching and landing, the bellyflop maneauver, the landing flip maneauver, engine relight from the header tank, and finally landing. Almost all of these were perfect, from what information we have.
There have been two failures, and from what we know these were not related to simulations at all - they seem to be system/integration issues, though we don't really know much about the engine failing to relight this test.
On SN8 they had a pressure issue feeding the engines from the header tanks. It may have been possible to anticipate this or test it independently, but it was probably the least important of all the things being tested. Given that they have multiple new (and updated!) test articles rolling off the production line they clearly made the choice to conduct the test without spending years trying to validate every single component. Again, they obviously did a lot of excellent engineering despite not undertaking a long pre-flight validation, as the test was so succesful.
Both you and I agree that aerospace companies should do large scale vehicle simulations, which they do.
In addition SpaceX does complex fluid dynamics simulations to design and test their engines. That's likely part of why they have successfully made the "holy grail" of Full-Flow staged combustion work in the Raptor. [0]
None of the failures so far could have been detected through simulation since they were complex integration issues. At some point the cost of simulation is vastly larger than the cost of just creating a test article.
Components like drogue chutes, explosive bolts, failsafe valves and abort systems are typically validated both analytically (by reviewing designs) and are often hard to fully validate by testing.
Since validating components is so expensive, it leads companies that rely on analyitical validation (like Boeing) to become overly attached to previously analysed and working components because analysis is so time consuming and expensive. You end up with modern rockets built with space-shuttle engines as components (SLS) and old jets with new engines tacked on (747 Max).
When you talk about explosive deconstruction of a test article after something new was learnt you fail to realise the learning (not the landing) was the goal. If SN9 had landed correctly, it is very likely they would have deconstructed it anyway. They just deconstructed SN12, 13 and 14 to make way for SN15 which has a very improved design.
Pedantic trolling noted; I’ll engage just to hone my thoughts.
Every production rocket is fully expendable. Launch, expect discard of 100%* of launch system. Starship is designed for 100% reusable, with same-day fly/land/refuel/repeat. That’s obviously a huge difference.
* - exceptions:
Space Shuttle discarded most of the launch system, acting as glider to return crew/cargo and some engines. Reuse turnaround was months, with extensive repairs expected. Boosters required prolonged recovery and refurbishing, with high likelihood of loss.
Falcon 9 is only one remotely viable for same day return to pad and reuse of first stage. Second stage is discarded.
SN# is a fast-reuse second stage. Landing involves leveraging the terminal velocity physics of a brick (not gentle glide of Shuttle), followed by effectively flipping a 16-story building ~90° in free fall with powered deceleration to 0m/s in less than 2km vertical.
Nothing in the industry resembles the fast launch/fall/relight/reorientate/decelerate/land/refuel/repeat sequence, of SN#. There is no established industry specifications addressing such operation. And as the history of rocketry shows, establishing such specifications practically involves lots of crashes. [cue How Not To Land A Booster]
It’s been a few days and other people above have already put you through the ringer on this, but funny enough the 1960’s work style, of the soviets specifically, is ideal for rapidly advancing rocket tech. Or any tech, for that matter! They iterated and flight tested early and often. The soviets only lost the space race because they ran out of resources, as this is an expensive approach, but SpaceX is back-stopped by Elon + the US gov via contracts + they already have production flight revenue and wildly successful products.
I won’t be able to do the explanation much justice in a paragraph here but Google around about how the Soviet approach to rocketry was far superior than that of the US and you’ll uncover plenty on the topic. SpaceX is executing that same style of engineering development, marrying the ‘move fast and break things’ tech company ethos with aerospace engineering.
That’s why they’re so revolutionary: aero is typically riddled with red tape and risk aversion... they take the Silicon Valley approach of moving fast and breaking things, along with keeping as much engineering in-house as possible to cut down on expenditure, lead time, quality control etc. etc.
Source: used to work on SpaceX’s only commercial crew capsule competitor, Boeing’s Starliner, down at the Kennedy Space Center.
You can choose to develop rockets - especially of such size - this way instead of putting (much) more efforts in calculating how it would behave and prepare for all cases.
Nasa did the calculation with with ancient computers and these guys are speculating and not using proper technology to achieve success. It makes no sense in 2021.
They should not be experimenting. Their simulations should be been solid before this stage.
They're developing this thing in stages; they've developed and tested the engines, they've developed and are testing launching the thing, they've developed and are testing the re-entry flop. They have partially developed the whole "landing" thing and if you're going to be testing the belly flop, you might as well put whatever you have with regards to landing through its paces as well.
By having a small team develop and test individual parts in stages, you avoid needing a giant team, and you avoid needing to have all of the schedules line up to be ready to go all at once. And it's the engineers who develop the rocket that is expensive, not the manufacturing.
IMHO the benefits of having a completely flexible schedule greatly outweigh the expensive of assuming failure.
You are so confident in your opinion and you are so incredibly wrong.
Pretty much every NASA engineer that has worked with SpaceX has been incredibly impressed by their methods. Literally every single one of their competitors, including nation states have started to change their who launch strategy because they saw no other way to compete with Spacex (and they are still failing) all of them have expressed how impressed they are with SpaceX.
You also seem to have a very trivial understanding of what SpaceX is doing and how it is different then what has been done before.
SpaceX is not just developing a the biggest rocket ever (double Satrun V lift-off thrust), or just the most advanced rocket engine ever, or just a new method of landing (very different from Shuttle), or a new type of heat shield (again different from Shuttle or SpaceX Pica), or a method of mass producing rockets. They are fully vertically integrated and they build and work on all of these and many other things at the same time.
Having one prototype explode is fine, because they are not just testing the prototype, they are testing the production of the rocket and optimizing the operations and everything mentioned above. The goal is to have the most advanced rocket of all time by a long margin, and be able to produce it cheaper then a current generation rocket, and operating it as cheaply as a airliner.
You can not simulate or plan anything so complex and get it right the first time. They are constantly learning and improving every single aspect. The engine team uses every test fire for new inputs and adjust their simulation and improve the design, the engine manufacturing team is trying to improve the cost per engine and the production quality, the rocket manufacturing engineers are constantly improving the way the rocket is built and later prototypes have these improvements, the materials team invents new materials and is measuring their performance on the prototypes, the operations team is trying to reduce the amount of work it takes set up a launch and I could go on and on like that.
Literally every prototype coming of the manufacturing line is a incrementally improved and usually cheaper then the one that came before it. The current SN8, SN9, SN10, SN11 are only small differences and with them they want to test the landing. They will be museum pieces once the landing is done, them blowing up generates real world data that can then improve their simulations. One of SpaceX core believe with this project is that the manufacturing system is 10-100x more difficult then the design of the rocket itself, and that their goals can only be achieved if these two things are co-designed. A test of a prototype is not just testing the design but also the manufacturing and quality control.
When you try to design something that has never been done before and is incredibly complex, and you have the requirement that it must be incredibly cheap and incredibly reliable there is no way you can simply design it on a white sheet of paper, simulate it and then simply have a mass production system of that vehicle. That is simply impossible.
And your claim that this is just 'cash burn' for no reason is equally wrong. SpaceX approach to engineering has routinely beat everybody in every single competition and usually by quite a lot. Nobody knows better how to develop something with a small budget compared to SpaceX. The whole Starship program so far, including new revolutionary engines, has cost less half of the much smaller Ariane 6, or less then a single year of the SLS program.
SpaceX is simply universally acknowledged as the most advanced rocket company in the world, and its not close. They are doing it this way for a reason, and they are a lot smarter then you.
I just want to know how you know that "you" are incredibly right in this. You are just speculating like everybody else here. There is no quality or quantitative measurement available here for you to make these absolute statements. The only thing that I can gather from your text is that a lot can go wrong in fact.
Having the prototype that is exploding is NOT fine at this stage and that is "my" opinion. Your opinion is yours alone.
You are basically claiming your analysis is indisputable and that it has to be accepted and your belief in people's intelligence makes it so and I am stupid because you believe that they are smarter.
It is not matter of getting it right the first time and improvements in parts and efficiency. It is about having it never explode after the first round.
I don't care who you believe they are beating in the market place and how magnificent you believe this rocket is.
Good luck if you are associated with this venture. If so you are allowed to pump it.
I know that because that is what Elon Musk and other SpaceX engineers and have said. They have explained this in multiple presentations and interviews over the last 5 years. This is not a mystery. I am not speculating.
There is a whole community that has been following this project since day 1. There are people filming the production site every day. The analyze every part they see and try to figure out what changed. Some people in the community can get questions to Elon Musk and others.
The reason you are getting down-voted is that you seem to have not studied it at all what SpaceX is actually doing, and simply jump into the comments and make strong statements that what SpaceX is doing is wrong.
And your justification for this opinion is totally unconvincing for anybody that has actually studied the problem.
> I don't care who you believe they are beating in the market place and how magnificent you believe this rocket is.
Its really not about believe. Its a simple fact that everybody has acknowledged.
> I just want to know how you know that "you" are incredibly right in this. You are just speculating like everybody else here.
Sure, and the same goes for you. Empirically, though, we know that when the US/NASA throws a ton of money at something and has a good engineering culture, we can get brilliant things like Apollo. When that culture erodes and the appetite for burning cash fades, we get things like the Space Shuttle. Yes, amazing, but mediocre when compared to the achievements of the Apollo program, and ultimately ending in failure and decommissioning.
Empirically, we have SpaceX, which has basically invented the "reusable rocket" category, using a hybrid development method that includes simulations and building and testing prototypes early and often.
Empirically, we (still) have Boeing, which has stuck with the old model, overengineering from the start. What do we have? A development process that is years behind SpaceX's, for a lot more money.
Learning from failure is fine when the only cost is money and materials. SpaceX's progress so far seems to have proven their development model, even before Starship.
I do find it really funny that you start out by deriding everyone for just speculating, but then finish your post loudly denouncing everyone who supports SpaceX as some sort of idiot... which is exactly the same sort of speculation... speculation which is not supported by the facts on the ground.
Simulations of certain things are still a problem today, even though less than it was in 1960-s. For example, trans-sonic aerodynamics is still hard. I'd imagine a good simulation of Raptor's inner flow when Starship does active maneuring can be a problem, especially if you also need to take into account material properties under dynamic loads.
That is where they should spend their cash to produce something of real value that can be reused. Simulation close to perfection is the end game. Not sending something chunky into space.
Falcon 9 now flies and lands with no crashes, especially comparing to expendable rockets. Of course a modification big enough will require changing control parameters, but that's a routine task for engineering.
Some day we'll have good enough models for air flows in all necessary modes and good enough computers to run those models; we aren't there yet. Testing is still required.
Honest question: Have you worked with fluid simulations before?
We cannot fully predict turbulent flow from first principles. I mean, we can, but when constrained by real-world computing hardware, we can only do it in very tiny domains. Turbulence requires way too many orders of magnitude in spatial resolution to fully resolve it in "real world" problems.
Therefore, any practical simulation for engineering purposes involves some way of modelling (read: approximating) turbulent behavior at sub-grid scales. There are tons of these models suitable for all kinds of different applications, domains, flows, etc. - but they are all just models. Part of the engineering effort is finding the right model for the task on hand, and for that you need experimental data.
This of course doesn't apply only to fluid dynamics (but also e.g. the overall dynamic behavior of the entire assembled rocket and rocket engine, which could interact with the fluid flows in a nontrivial manner), but the point is that simulations aren't automatically accurate because you do more of them or throw more money or compute at them (that is also a good way to burn cash) - they are still approximations of unknown accuracy until you actually compare them with data from reality to confirm whatever modeling assumptions you made. The "least cash expenditure" approach will thus involve both simulations and experiments, and you will eventually reach the point where putting money into making rockets (potentially) crash will give you better lessons than running yet another simulation with (unbeknownst to you) subtly flawed assumptions.
SpaceX does do simulations, and tons of it. SN8 and 9 wouldn't have performed that well during the descent stage without amazing guidance software, which could only have been developed through extensive simulations.
Simulations are always going to be "assume a spherical cow in a vacuum" to a degree, as the real world is unbelievably complex, and you have to use models at some point. These models _can_ be wrong, and the only way to test them is through experimentation.
