Ok, the idea behind this is as follows:It would not be clever to build a full up BFR with 10 Raptor engines (or more) without first having tested Raptor engines in a real space environment. If I was in charge of building something like BFR, I'd insist on first building something that is easy, predictable and cheap ... and only has a single Raptor engine to take care of.My first thoughts revolved around improving what they have or building another rocket. Something that might be useful.1) A 200t, two stage rocket. First stage powered by a Raptor (150t fuel, 7t empty mass), second stage is a Merlin Vac (40t fuel, 3t empty mass), which results in a performance roughly comparable to a Soyuz rocket. (roughly 8t LEO, 3t GTO) Disadvantages: Non-reusable, redundant (a Falcon 9 can do this with reusable 1st stage)2) An improved Falcon Heavy upper stage, using a vacuum Raptor - this should result in roughly 30% higher GTO payloads in fully expendable flights. More in reusable flights. This has a chance of working if it is true that it can be throttled down deeply (supposedly from 100% to 30% if memory serves - which would be in line with similar engines). This actually seems like it might be a good idea in the long run. But - Disadvantages: Requires an expensive Falcon Heavy just to test Raptor (plus: payloads would be hard to come by or without much profit). Raptor cannot be safely started on the ground.2*) A combination of 1) and 2) - build the rocket of the first suggestion, test it, use it a few times, put it on top of a Falcon Heavy. Because, secretly, we all know that rockets are LEGOs. 3) Forget about all that. Build a single Falcon9-derived stage with 200t of mass and a single Raptor engine. Empty mass should be no more than 8t (including some residual fuel). This stage could single-handedly deliver a 4t payload into LEO. Disadvantage: Non-reusable. No further economic usefulness.
There is absolutely no reason for this. Ground testing is sufficient to iron out combustion and do thorough testing. If there was no need to mount the F-1 on a tiny rocket before launching the Saturn V, there it sure isn't needed for Raptor.Keep in mind that if the vehicle is reusable, it can be tested like Grasshopper as well. Test as you fly. Fly as you test.
Quote from: Lars-J on 01/10/2015 02:04 amThere is absolutely no reason for this. Ground testing is sufficient to iron out combustion and do thorough testing. If there was no need to mount the F-1 on a tiny rocket before launching the Saturn V, there it sure isn't needed for Raptor.Keep in mind that if the vehicle is reusable, it can be tested like Grasshopper as well. Test as you fly. Fly as you test.So what you're saying is that testing the engine itself only needs the test stand. After stand testing is done, they are testing the rocket instead of the engine ?
Quote from: macpacheco on 01/14/2015 05:33 pmQuote from: Lars-J on 01/10/2015 02:04 amThere is absolutely no reason for this. Ground testing is sufficient to iron out combustion and do thorough testing. If there was no need to mount the F-1 on a tiny rocket before launching the Saturn V, there it sure isn't needed for Raptor.Keep in mind that if the vehicle is reusable, it can be tested like Grasshopper as well. Test as you fly. Fly as you test.So what you're saying is that testing the engine itself only needs the test stand. After stand testing is done, they are testing the rocket instead of the engine ?Basically, yes. The engine won't be flown on a rocket until it has been qualified through testing.
What if they start with an equivalent of Grasshopper first? Instead of building a full blown BFR, just start with one engine and make sure you can land with it. Then add more engines, fix problems as they arise, and when everything is working with full number of engines, add the second stage.
For M1D, that was flight qualification of the design (exhaustive testing regime) followed by testing each flight engine individually at McGregor and then the set of nine at McGregor for full duration. Of course, there is also the static fire on the pad before launch which is more about the full launch system readiness...The testing approach not broken, so why fix it.
Quote from: Lars-J on 01/10/2015 02:04 amThere is absolutely no reason for this. Ground testing is sufficient to iron out combustion and do thorough testing. If there was no need to mount the F-1 on a tiny rocket before launching the Saturn V, there it sure isn't needed for Raptor.Keep in mind that if the vehicle is reusable, it can be tested like Grasshopper as well. Test as you fly. Fly as you test.Lars, you may have just posted one the most jaw dropping things I've ever read. The purpose of "testing" is to show that a design can deliver to the requirements (or... "the operational objectives"). Testing may also be performed to show that a risk is not as significant as may have been subjectively thought prior to its first usage. But one should not simply define tests for testing sake (which is quite common).Yes, everyone already knows the system will function like a rocket... but there is a lot more to rocket science that really drives the need for testing. Aim a Raptor vertically at a floating autonomous barge and impinge the surface with LOX/methane combustion products (or other) similar to the CONOPS. Or just do things the hard way. The world is full of money.
Given that F9 cores are already being mass produced, bulding a test article from one of those should be straight-forward. It wouldn't add much work to the test program.
Quote from: tp1024 on 01/15/2015 03:28 pmGiven that F9 cores are already being mass produced, bulding a test article from one of those should be straight-forward. It wouldn't add much work to the test program.I don't agree. It's a methane engine versus a stage built to store kerosene. I think you'd need a very different stage for a Raptor engine.
IMHO, the second stage raptor (Raptor Vac) is the one that might need some creative testing methods (conventional ground testing should suffice for the first stage engines). The issue I'm concerned about for the Raptor Vac is ignition.
Quote from: CJ on 01/16/2015 02:56 amIMHO, the second stage raptor (Raptor Vac) is the one that might need some creative testing methods (conventional ground testing should suffice for the first stage engines). The issue I'm concerned about for the Raptor Vac is ignition.Why? Not a single SpaceX upper stage engine has failed to start.Re-start? Yes, there has been one (or two?) occurrence. But starting an upper stage engine is NOT cutting edge science.
There will be no need to test the BFR like grasshopper. That was/is to evaluate and push the envelope on the concepts. They can be adapted to a larger vehicle which can then be dropped into the ocean enough times until it can be recovered, just like F9. You'll see a single engine tested, then the core tested and then a full up launch - just like S-V and SLS.
Quote from: newpylong on 01/16/2015 12:42 amThere will be no need to test the BFR like grasshopper. That was/is to evaluate and push the envelope on the concepts. They can be adapted to a larger vehicle which can then be dropped into the ocean enough times until it can be recovered, just like F9. You'll see a single engine tested, then the core tested and then a full up launch - just like S-V and SLS.I used the grasshopper above, even though I should have used BFR-dev1. In my opinion the reason to start development with small hops isn't technological difficulties (not that there wouldn't be enough of those), but economical. AFAIK there aren't any payloads that need the capability of BFR and a rocket of that size won't be cheap. That means that dropping first stages to the drink until all the details are ironed out is going to be expensive. Very expensive.With dev vehicle there is still a chance of blowing it up, but the risk is much smaller. Also remember that BFR is supposed to be reusable, so why not start with that in the test program. From operations point of view it's more like developing a plane than a traditional rocket, isn't it?
Quote from: Lars-J on 01/16/2015 03:20 amQuote from: CJ on 01/16/2015 02:56 amIMHO, the second stage raptor (Raptor Vac) is the one that might need some creative testing methods (conventional ground testing should suffice for the first stage engines). The issue I'm concerned about for the Raptor Vac is ignition.Why? Not a single SpaceX upper stage engine has failed to start.Re-start? Yes, there has been one (or two?) occurrence. But starting an upper stage engine is NOT cutting edge science.I do see your point, but what's confusing me is this; the J2X was based on the already-proven J2 engine, which was also vac start. The J2 apparently didn't need an enormous vacuum-chamber test stand, but for some reason, the J2x would, and badly enough that they spent $350 million on a vacuum test stand. So, seeing as how no one has ever vac started a staged combustion methlox engine, can we be sure that whatever required a vacuum chamber test stand for the J2X doesn't apply to the Raptor vac? I certainly hope it doesn't, for things would be far simpler without any need for vac testing, but do we actually know?
Quote from: ChrisWilson68 on 01/16/2015 01:48 amQuote from: tp1024 on 01/15/2015 03:28 pmGiven that F9 cores are already being mass produced, bulding a test article from one of those should be straight-forward. It wouldn't add much work to the test program.I don't agree. It's a methane engine versus a stage built to store kerosene. I think you'd need a very different stage for a Raptor engine.F9 does carry LOX which is colder then liquid methane.A test rocket built with F9 tooling could pretty much use construction similar to the lox tank for the methane tank.
Quote from: Lars-J on 01/16/2015 03:20 amQuote from: CJ on 01/16/2015 02:56 amIMHO, the second stage raptor (Raptor Vac) is the one that might need some creative testing methods (conventional ground testing should suffice for the first stage engines). The issue I'm concerned about for the Raptor Vac is ignition.Why? Not a single SpaceX upper stage engine has failed to start.Re-start? Yes, there has been one (or two?) occurrence. But starting an upper stage engine is NOT cutting edge science.I do see your point, but what's confusing me is this; the J2X was based on the already-proven J2 engine, which was also vac start. The J2 apparently didn't need an enormous vacuum-chamber test stand, but for some reason, the J2x would, and badly enough that they spent $350 million on a vacuum test stand.
So, seeing as how no one has ever vac started a staged combustion methlox engine, can we be sure that whatever required a vacuum chamber test stand for the J2X doesn't apply to the Raptor vac? I certainly hope it doesn't, for things would be far simpler without any need for vac testing, but do we actually know?
Quote from: CJ on 01/16/2015 04:51 amQuote from: Lars-J on 01/16/2015 03:20 amQuote from: CJ on 01/16/2015 02:56 amIMHO, the second stage raptor (Raptor Vac) is the one that might need some creative testing methods (conventional ground testing should suffice for the first stage engines). The issue I'm concerned about for the Raptor Vac is ignition.Why? Not a single SpaceX upper stage engine has failed to start.Re-start? Yes, there has been one (or two?) occurrence. But starting an upper stage engine is NOT cutting edge science.I do see your point, but what's confusing me is this; the J2X was based on the already-proven J2 engine, which was also vac start. The J2 apparently didn't need an enormous vacuum-chamber test stand, but for some reason, the J2x would, and badly enough that they spent $350 million on a vacuum test stand. AFAIK they had built a gigantic test stand for J-2 in the sixties. And they could have used the same old test chamber with very slight/cheap modifications/reparations also to test J-2X, but pork senators won and instead of repairing/modifying the old chamber, they built a totally new one to get jobs to some senator's district.QuoteSo, seeing as how no one has ever vac started a staged combustion methlox engine, can we be sure that whatever required a vacuum chamber test stand for the J2X doesn't apply to the Raptor vac? I certainly hope it doesn't, for things would be far simpler without any need for vac testing, but do we actually know?Spacex can launch _many_ first stages for the price of 350 million. NASA cannot. Or it's against their philosophy.For SpaceX, it's cheaper to "test" the upper stages in real flights than construct a very expensive test stand for the testing.