I still think the BFR/MCT diameter will not exceed 10m. There are many reasons for this. I also think this version would be more economical in the long run. A 3 core heavy for MCT launch. Say 5.5m-8m for a single core for launching deep space probes, filling a fuel depot and other cash making activities. The single core would be able to launch 80-100 tons. A 3 core heavy version 250 tons. A fully reusable 80 ton launcher might eliminate Falcon Heavy. Say it had 9 engines at 550k lbs thrust or slightly more for a 5 million lb thrust reusable rocket. This rocket can put up a lot of stuff to make money from the Air Force, NASA or others to help pay for MCT. A single core could also be adapted to have two Falcon 9 cores attached for boosting slightly over 100 tons to LEO and could still launch from the cape. This size also would greatly expand locations for manufacturing and shipping via cheap barge and launch locations. Otherwise if too wide it would have to be built at a shipyard and transported via ocean to various launch locations. River and intercoastal barge widths in America are 36', or 10m maybe 11m. This may make MCT cylindrical which might mean horizontal landing. A try at using the vacuum Raptor in a reusable upper stage would be a good test for MCT cylinder design.
I still think the BFR/MCT diameter will not exceed 10m. There are many reasons for this. I also think this version would be more economical in the long run. A 3 core heavy for MCT launch. Say 5.5m-8m for a single core for launching deep space probes, filling a fuel depot and other cash making activities. The single core would be able to launch 80-100 tons. A 3 core heavy version 250 tons.
Quote from: Impaler on 01/21/2016 02:35 amWith ~30 engines you probably don't need gimbaling, or at least not on most of the engines. Some variable thrust and a few engines along the edge that gimbal on just one axis should be sufficient and is the Russian way of doing it.That worked sooo great for the N1. I know that was failure of testing, but using variable thrust for control is a truly *terrible* idea. That's when you need more power, not less of it.A few central engines may be fixed, but most should fully gimbal for general control authority and engine out capability. Having all the engines be identical (including their gimbal setups) also simplifies mass production and testing procedures, as SpaceX illustrate whenever their F9 rocket launches. (it seems to be a VERY common misconception that some F9 engines are fixed, they are NOT)
With ~30 engines you probably don't need gimbaling, or at least not on most of the engines. Some variable thrust and a few engines along the edge that gimbal on just one axis should be sufficient and is the Russian way of doing it.
Lars you seem to have mentally dropped half of the proposal in your responses so that you can rail against throttling, I said gimbaled engines on the outer perimeter of the vehicle would be used and a vehicle so equipped would only need to vary thrust if these gimbaled engines are insufficient, just as ANY rocket with multiple engines can and would vary thrust beyond what it's gimbaling provides.
Quote from: Robotbeat on 01/16/2016 04:10 amIf you were to have an abort system on MCT, it'd have to work for Mars ascent (as well as Earth), and probably even terminal landing as well. No, this is not impossible. Hard, but not impossible.Or just not have an abort system."Work" would be subjective. ejecting and landing on mars with no supplies would leave you just as dead.
If you were to have an abort system on MCT, it'd have to work for Mars ascent (as well as Earth), and probably even terminal landing as well. No, this is not impossible. Hard, but not impossible.Or just not have an abort system.
Quote from: Lars-J on 01/21/2016 04:08 amQuote from: Impaler on 01/21/2016 02:35 amWith ~30 engines you probably don't need gimbaling, or at least not on most of the engines. Some variable thrust and a few engines along the edge that gimbal on just one axis should be sufficient and is the Russian way of doing it.That worked sooo great for the N1. I know that was failure of testing, but using variable thrust for control is a truly *terrible* idea. That's when you need more power, not less of it.A few central engines may be fixed, but most should fully gimbal for general control authority and engine out capability. Having all the engines be identical (including their gimbal setups) also simplifies mass production and testing procedures, as SpaceX illustrate whenever their F9 rocket launches. (it seems to be a VERY common misconception that some F9 engines are fixed, they are NOT)Lars you seem to have mentally dropped half of the proposal in your responses so that you can rail against throttling, I said gimbaled engines on the outer perimeter of the vehicle would be used and a vehicle so equipped would only need to vary thrust if these gimbaled engines are insufficient, just as ANY rocket with multiple engines can and would vary thrust beyond what it's gimbaling provides.
Your N-1 comparison is completely disingenuous by your own admission, the failure were not the result of insufficient control authority provided by fixed engines, the Russians knew this and continued to use fixed engines for decades because they are mechanically simpler. And when engines do gimbal they generally do so on only one axis outward to provide maximum leverage again simplifying all the mechanics. All engines being provided with 2 axis gimbaling is just an American excess not worth the cost and complexity much like Hydrogen fuel.
A 30 engine booster will have around a dozen engines on the out perimeter that can all gimbal on one axis. Only the center engine would need 2 axis gimbaling for landing. That leaves some ~18 engines that can be fixed and packed closer together for maximum thrust density. This is very similar to the configuration the Soyuz uses 4 fixed nozzles and 4 small single axis vernier nozzles, and as we all know the Soyuz is the most successful Russian vehicle and one SpaceX would be wise to copy.
Quote from: Burninate on 01/21/2016 04:34 amWith that said, I don't have any good reason to think non-gimballing engines are going to be a thing on BFR. With MCT, on the other hand, there may be value in fixing the combustion chambers as well as the massive engine bells rigidly to the spacecraft; Those gimbals are a source of potential failure with a few years of vacuum between uses, and whether the odds of that are greater than the odds of some other steering system failing, is a bit more of an open question than with BFR.I strongly disagree with that. I consider fixed engines more likely on a BFR booster than a MCT. First, the fewer engines you have, the more critical it is that they all gimbal. Otherwise you really have no engine out capability at all, a *long* way from home. Yes, your gimbal actuators need to be VERY reliable, but I think they need to be there to provider multiple levels of redundancy.
With that said, I don't have any good reason to think non-gimballing engines are going to be a thing on BFR. With MCT, on the other hand, there may be value in fixing the combustion chambers as well as the massive engine bells rigidly to the spacecraft; Those gimbals are a source of potential failure with a few years of vacuum between uses, and whether the odds of that are greater than the odds of some other steering system failing, is a bit more of an open question than with BFR.
Quote from: RoboGoofers on 01/21/2016 05:20 pm"Work" would be subjective. ejecting and landing on mars with no supplies would leave you just as dead.After a couple synods of crewed missions (assuming the number of BFSes each synod grows), there will be a sizable presence on Mars, and it would soon be cheap to have a "launch on need" BFS available (that would be used for a cargo flight back if not used for rescue during that synod, so doesn't use any resources other than space near the pad).
"Work" would be subjective. ejecting and landing on mars with no supplies would leave you just as dead.
It's been suggested before that a small number of the very first BFS's (formerly MCT) landers on Mars will not return to Earth. It shouldn't be hard to modify one or two into a point-to-point planetary hopper. It's a useful tool to have, and serves as a rescue vehicle.
Quote from: Paul451 on 01/22/2016 05:54 pmIt's been suggested before that a small number of the very first BFS's (formerly MCT) landers on Mars will not return to Earth. It shouldn't be hard to modify one or two into a point-to-point planetary hopper. It's a useful tool to have, and serves as a rescue vehicle.If they can do such hops, they can probably return to earth as well.
Depends on the size of the hops Paul was going for, and... mathematically that doesn't seem logical. What's your reasoning, Guckyfan? Whilst I agree with you all BFSs will RTE, the margins to hop and the margins for Earth return are considerably far apart from each other.
Quote from: The Amazing Catstronaut on 01/22/2016 11:29 pmDepends on the size of the hops Paul was going for, and... mathematically that doesn't seem logical. What's your reasoning, Guckyfan? Whilst I agree with you all BFSs will RTE, the margins to hop and the margins for Earth return are considerably far apart from each other.My reasoning. BFS are capable of return to earth when functioning. They need to be functioning to make the hops.
Quote from: guckyfan on 01/23/2016 08:47 amQuote from: The Amazing Catstronaut on 01/22/2016 11:29 pmDepends on the size of the hops Paul was going for, and... mathematically that doesn't seem logical. What's your reasoning, Guckyfan? Whilst I agree with you all BFSs will RTE, the margins to hop and the margins for Earth return are considerably far apart from each other.My reasoning. BFS are capable of return to earth when functioning. They need to be functioning to make the hops.Being functioning and being supplied by an active ISRU facility is a wholly separate thing. Without propellant it doesn't matter.
Or ISRU methane production is built into the early BFS's, or maybe all of them for redundancy. How large would the device be?