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I really love the out-in-the-open development process. It doesn't cost SpaceX anything, yet they attract lots of internet media where people set up streams, dis
by martythemaniak 6y ago
I really love the out-in-the-open development process. It doesn't cost SpaceX anything, yet they attract lots of internet media where people set up streams, discuss progress etc.
The next year should be pretty exciting as they develop things further. Starship has a number of big innovations, which are:
- the raptor engine. This was developed behind closed doors and is sort of finished. We won't see much of it, but it is the most advanced rocket engine ever made and I'm not aware of any upcoming engine that can compete with it.
- Stainless steel construction. What we're seeing with SN5 is the basic tank structure of the second stage. The hopper that flew last year was a neat demo, but SN5 was pressurized and the design is way closer to what the actual starship will end up having. The first stage tanks will also be a stretched version of these tanks, so that's why you see them focus on this so much right now.
- belly-flop landing. To land, starship will be coming downhorizontal until a few hundred meters above ground when it'll make itself vertical to land. SN5 won't have the fins and cone to perform this, but SN6 will. It might be possible to see this before the end of the year - SN6 (with 3 engines) goes up 20km, goes horizontal to burn off speed, then lands vertically.
- belly-first re-entry. Instead of a heatshielf that withstands a high temperature, Starship will burn off speed with its belly, but do it over a longer time period of time so that while the total heat is the same, the max temperature doesn't rise too much. The stainless steel can't take the temperatures ablative heatshields on capsules can. Don't know if Starhip will be able to perform this meaningfully without a booster.
- in-orbit refueling. Starship is big and heavy and basically can't get anywhere unless it's re-fueled in orbit. I don't think this has been done before, definitely gonna need 2+ starhips and boosters to show this.
- superheavy booster. This might be the simplest part of the whole system - a first stage with 31 raptor engines.
Lots of stuff coming in the next few years.
- dgritsko 6y ago> the most advanced rocket engine ever made Would love to learn more about this, can you expand? What makes Raptor so unique?
- codeulike 6y agoFull flow staged combustion cycle, never been flown* before, explained here: https://everydayastronaut.com/raptor-engine/ https://everydayastronaut.com/raptor-engine/ * The Russians built one in the 60s but it never got past static fire tests
- chriswarbo 6y agoThe raptor is a "full flow staged combustion engine" https://en.wikipedia.org/wiki/Staged_combustion_cycle#Full-flow_staged_combustion_cycle https://en.wikipedia.org/wiki/Staged_combustion_cycle#Full-f... AFAIK it's the only flying, non-research example of such an engine.
- martythemaniak 6y agoTim Dodd explains it very well: https://everydayastronaut.com/raptor-engine/ https://everydayastronaut.com/raptor-engine/ It's basically a sweet-spot between being very powerful, very efficient, cheap and easy to operate and highly reusable. To get all these, they implemented a design that never got past the basic demo stage before, which included independently working out the secret sauce of the best Russian-made engine.
- phkahler 6y ago>> which included independently working out the secret sauce of the best Russian-made engine. Another hurdle was that there was no material available for some of the parts. SpaceX - so we'll get some materials science people to develop a new alloy that does what we need. Not an easy sub-task but one that needed a solution, so they found one.
- Already__Taken 6y agoThis might be the way to go - https://www.youtube.com/watch?v=Sdwy9fzQzl4 https://www.youtube.com/watch?v=Sdwy9fzQzl4
- cplex_go_nogo 6y agoThe raptor uses a full flow staged combustion cycle. This makes a very efficient engine but increase the complexity. Everyday astronaut and Scott Manly on youtube do an excellent job explaining this in more detail
- njarboe 6y agoI am not a rocket scientist, but one of the main reasons it is so unique is that it will be the first full-flow staged combustion rocket engines to successfully be used on rockets. Rocket engines have powerful turbo pumps to move large amounts of fuel quickly to the combustion chamber to create thrust. Usually these pumps are powered by burning some of the propellant in a turbine and exhausting the resulting gas on the side of the engine. A full-flow engine mixes this turbo pump exhaust gas back into the main combustion chamber. This makes the engine more fuel efficient but it is a difficult engineering problem. All previous types of these engines blew up too often to be used on spacecraft. Check out the Wikipedia page for more info [1]. [1]https://en.wikipedia.org/wiki/SpaceX_Raptor https://en.wikipedia.org/wiki/SpaceX_Raptor
- xcskier56 6y agoTo add on, one of the biggest challenges with a full flow staged combustion engine is that the exhaust gas from the oxidizer rich turbopump is almost pure gaseous oxygen at very very high temperature. This combination likes to corrode and eat away any thing, metal included. To solve this, SpaceX had to develop special metal alloys that could withstand this incredibly corrosive environment for long durations.
- paulsutter 6y agoIn addition to being full-flow, Raptor runs on methane (CH4, the simplest hydrocarbon), which already exists many places in the solar system (including Mars), and is easier to manufacture than kerosene or liquid hydrogen. SpaceX developed an incredibly advanced simulator to make it happen: https://www.youtube.com/watch?v=vYA0f6R5KAI https://www.youtube.com/watch?v=vYA0f6R5KAI
- apendleton 6y agoSlight clarification: while there have been traces of methane detected on Mars, there's probably not enough to be able to easily use it as fuel. Methane is still beneficial for refueling on Mars, though, because you can make it in place out of water (which is plentiful on Mars as water ice) and CO2 (also plentiful, in the atmosphere) using the Sabatier process. So it remains the case that methane as fuel lets you avoid needing to bring enough fuel for a round trip.
- SEJeff 6y agoExactly. Elon has explicitly mentioned manufacturing metholox (the raptor engine fuel) using a really beefy ISRU factory. It would be feasible, but is still a lot of work required.
- ba2plus 6y agoMars could be the key to opening up the entire solar system. It's close enough to the sun for solar power to be practical, it's proven to have the mass amounts of subsurface ice and atmospheric CO2 needed for Sabatier-process methane/oxygen production, and it has a very shallow gravity well that would make it easy to lift huge propellant loads into orbit. I don't think it's a stretch to imagine that Mars-based tankers supplying propellants and breathing oxygen would be commonplace through the solar system by the end of the century.
- bryanlarsen 6y agoThere are two main metrics of rockets and rocket engines. Specific Impulse (ISP), and the Thrust to Weight Ratio (TWR). ISP is essentially a measure of the fuel efficiency. And since there are no gas stations in space, the further you can go per kg of fuel, the further you can go, period.[1] TWR is the measure of useful power. TWR is the key measure for the first stage because a ton of power is required to escape Earth's gravity and atmosphere. For subsequent stages ISP is the main metric. The Space Shuttle Main engines have an excellent ISP but because hydrogen needs massive tanks, it has a crappy TWR. Which is why the shuttle had a couple of strap on solids with a high TWR. But instead of specialized engines, SpaceX designs engines that are good at everything. The ISP isn't as high as an advanced hydrogen engine and the TWR isn't as good as a solid, but both numbers are quite respectable and they bring other advantages such as the ability to relight and to be reused without refurbishment, they don't need use ablative cooling. 1: Although SpaceX is relying on in flight refueling for it's Moon and Mars plans. Nobody's done it before, but that doesn't stop SpaceX.
- sandworm101 6y ago>> - in-orbit refueling. Starship is big and heavy and basically can't get anywhere unless it's re-fueled in orbit. This is one of those "let's see" things that SpaceX has talked about but never actually explained. Their current rocket tech offers no hint as to how this is might happen. They aren't running internal bladders in their tanks. So the physical act of moving fuel from one tank to another is an open question. The options are really limited. Either you use an internal bladder, something never done with cryogenic fuels, or some sort of maneuver to shift all the fuel over towards the pump. Maybe they plan on docking the two ships and then spinning the entire rig to create sufficient G to stabilize the fuel on one side of the tank? The entire operation seems more kerbal than reality atm.
- balfirevic 6y agoSome rockets have already used small acceleration prior to engine ignition to settle the propellant in zero gravity situations: https://en.wikipedia.org/wiki/Ullage_motor https://en.wikipedia.org/wiki/Ullage_motor
- skykooler 6y agoAt the last presentation on Starship, Elon said they planned to do the refueling by applying a small amount of thrust during the procedure, giving a small g-force that's enough to drive the fuel from one ship to the other.
- Robotbeat 6y agoIt's not particularly hard. Just like with regular rocket upper stages that require multiple burns to complete the mission, you can use small ullage thrusters to settle the propellant and make sure liquid (instead of pressurant gas) is transferred from one tank to another. The physics is exactly the same as making sure the engine receives fuel. Just need the thrusters to be fired longer. SpaceX has done experiments with how much thrust is necessary for ensuring propellant settling. That's one reason you often see a video feed of inside the upper stage liquid oxygen tank during a Falcon 9 mission. It doesn't take much thrust to ensure propellant settling. Not at all an open question. This always struck me as one of the least questionable new things in SpaceX's architecture. Much less Kerbal than most Mars architectures which require assembling a massive craft in LEO or whatever. (One would be remiss to not mention the history of refueling... SpaceX's competitor ULA had been pushing refueling and orbital depots, which it called "distributed launch", since its formation, but has only been able to do small experiments since one of its parent companies, Boeing, sees orbital refueling as a threat to NASA's SLS rocket, which Boeing is the main contractor for. That's a huge reason for a lot of the "skepticism" about orbital refueling you sometimes see in aerospace circles, besides the usual pathologically conservative mindset of many grey beards...)
- napier 6y ago> any upcoming engine that can compete with it. There's the criminally underfunded SABRE engine, an a air-hydrogen mix breathing-rocket hybrid design from Reaction Engines that rated to reach speeds of Mach 25 (roughly 35,000 miles per hour). As modelled, it's more efficient than any other current or proposed chemical propulsion technology, and the proposed single-stage runway launchable system would be capable of delivering around 11 tons of cargo to the ISS. The costs to go to orbit and beyond using this engine could be less than half that of current best in class technology; even less after development cost amortization. Not sure why SpaceX haven't invested in it yet. Perhaps it doesn't fit in with their current vertical integration philosophy, but it seems like a game changing technology.
- mabbo 6y ago> Not sure why SpaceX haven't invested in it yet > an a air-hydrogen mix breathing-rocket hybrid design Tough to use a breathing rocket anywhere but Earth. And SpaceX's goal is to use this to land on the Moon, Mars, everywhere.
- Ajedi32 6y agoThat's true for Starship (the second stage) but AFAIK Super Heavy (the first stage) will only ever be used on Earth. Seems like an air-breathing rocket engine could potentially be good for that use-case.
- shdh 6y agoThen you have to introduce another system (SABRE) and integrate it with your system instead of just using the same Raptor engines being used in the second stage vehicle.
- yazaddaruvala 6y agoOne benefit of Raptor is that its designed to be mass produced. Achieving cost efficiencies with scale. Adding another engine means, one more production line each with less production volume (i.e. less efficiency of scale).
- jcun4128 6y ago> 31 raptor engines That'll be something to see haha N1
- nkoren 6y agoThe Falcon Heavy uses 27 engines and has a perfect track record ,so they've got some credibility here.
- shdh 6y agoJust to add clarification, Falcon Heavy uses the Merlin engine, not the Raptor engine.
- jcun4128 6y agoYeah looks like 3 for 3 so far. It seems like a big number... as opposed to just 5 (Saturn V). What is the rationale for more smaller engines(other than offset/greater forces/new R&D)?
- NikolaeVarius 6y agoLosing one means less affect on the overall mission
- koalala 6y agoi suppose 2 could blow up, no problem :)
- SEJeff 6y agoWhy only turn it up to 11 when you can turn it up to 31? See the Starship dial goes all the way to 31.
- HPsquared 6y agoThings have different scaling laws. Very large rocket engines might not be practical for a range of reasons: wall thickness required to contain the high pressures (this is probably a big one) combined with the temperatures, combustion instability, controllability, and general ability to manufacture. Why are elephants and ants differently shaped? Another example is piston engines: large ones generally have lots of (relatively small compared to the overall displacement) cylinders rather than a couple of massive ones. If a small number of rocket engines was required they would probably have a completely different design, perhaps an aerospike. Or maybe resurrecting Project Orion?
- SEJeff 6y ago> - the raptor engine. This was developed behind closed doors and is sort of finished. We won't see much of it, but it is the most advanced rocket engine ever made and I'm not aware of any upcoming engine that can compete with it. I believe the Raptor is the first actually working full flow staged combustion engine. It is sort of a holy-grail of engine for liquid rockets. Tim Dodd has a lot more info on it here: https://everydayastronaut.com/raptor-engine/ https://everydayastronaut.com/raptor-engine/ However please call it what it really is. It isn't a belly flop so much as it is a skydiver maneuver. Just like how a skydiver splays out their arms and legs to maintain stability and slow down a bit, starship will do the same. Also like a skydiver, it will upright itself before landing as a belly flop would almost guarantee a RUD.
- DannyB2 6y agoLettuce not forget Raptor runs on Oxygen and Methane. Both of which might be produced on Mars.
- fastball 6y agoI mean we know for a fact that there is already (in small amounts) methane and plenty of CO2 on Mars. Obviously if we find lots of H2O this all becomes even easier as we can just combine the abundant CO2 with the H2O to get loads of CH4 and O2.
- anticensor 6y agoYou mean, by unburning the fuel?
- fastball 6y agoYep, effectively! That is what is great about these fuels (H2 and CH4) vs something like RP-1. First you get hydrogen by electrolyzing water. Then you can go H2 + CO2 → CH4 via the Sabatier process[1]. [1] https://en.wikipedia.org/wiki/Sabatier_reaction https://en.wikipedia.org/wiki/Sabatier_reaction
- peter303 6y agoSpaceX using $3.6 billion investors money to build Starship. It will probably circle the Moon before NASA SLS.