[HN Gopher] Pangea Aerospace successfully hot fire tests the fir...
___________________________________________________________________
Pangea Aerospace successfully hot fire tests the first MethaLox
aerospike engine
Author : rbanffy
Score : 185 points
Date : 2021-11-19 13:09 UTC (9 hours ago)
(HTM) web link (www.satellite-evolution.com)
(TXT) w3m dump (www.satellite-evolution.com)
| ChrisMarshallNY wrote:
| Cool stuff.
|
| In a meta note, that article seems to have been translated by
| Google.
| its_bbq wrote:
| From someone who knows little about this -- what is the advantage
| of this kind of engine? And have we scrapped the idea of space
| elevators?
| zardo wrote:
| > And have we scrapped the idea of space elevators?
|
| If you're looking at sci-fi fixed infrastructure for access to
| space, the orbital ring looks more plausible.
|
| It's out there, but unlike a space elevator it doesn't require
| gigatons of unobtanium cable.
| Tuna-Fish wrote:
| Space elevators are still pretty far out there. And if we ever
| do end up building one, we're going to need pretty damn good
| rockets to do that.
|
| To reach maximum theoretical performance, a rocket engine
| nozzle needs to expand the exhaust to be of equal pressure as
| the ambient air. Being too underexpanded can actually destroy
| the engine, and even well before that being over- or
| underexpanded saps efficiency, so you can improve performance
| by specializing for the pressure you target. But of course, as
| a rocket ascends, pressure falls. This means that the expansion
| ratios of traditional engines are compromises over the pressure
| range they are expected to operate in.
|
| Aerospike engines use a neat hack to make a "virtual nozzle",
| where the pressure of outside air is used to push on the
| exhaust stream. This makes it slightly less efficient than a
| traditional de Laval nozzle that is specialized for the exact
| pressure, but it can maintain that not-perfect but high level
| of efficiency for the whole ascent, from atmospheric to vacuum.
|
| When everyone was trying to build single stage to orbit
| vehicles, aerospikes sounded very promising as they would allow
| a single engine to be used from the launch pad to vacuum with
| reasonable efficiency. However, now that first stages are
| routinely returning to the launch site and landing on their
| own, SSTOs are not nearly as attractive, and with a two-stage
| architecture, you want to give the second stage a proper vacuum
| engine, and then the first stage won't lose that much if it's
| optimized for near-sealevel conditions. I'm not sure aerospikes
| make that much sense anymore.
| avmich wrote:
| The space elevators problems include not only finding a good
| cable material, but also solving the problem of collision with
| satellites, so I'm not holding my breath.
|
| Aerospike nozzles are spike nozzles where the spike is cut
| short and "replaced by air". They are shorter and usually
| lighter than equivalent bell-shaped nozzles, but they have
| bigger surface area in the critical section - most heat-loaded
| part of the engine - so cooling them is harder. For small
| engines the problem is cooling, and for big engines there is a
| problem of area where to put those engines (for large rockets
| length and weight of nozzle isn't a problem, but cross-section
| of the rocket, where the engines have to be installed, is), so
| aerospikes have different trade-off than bell-shaped nozzles.
| patrickwalton wrote:
| Beyond all the theoretical implementation complexities of space
| elevators, we don't even know of a single material with the
| required tensile strength. Graphene was thought to be strong
| enough, but recent research found practical graphene had
| defects that significantly reduces its strength below that
| required for a space elevator.
|
| Space elevators aren't scrapped, just on the shelf until we
| even have a material that let's us think they might be
| feasible. That said, Lunar space elevators could be done with
| lower-strength materials, like Kevlar, and there are some
| people working on them.
|
| For Earth orbit, I think the centrifuge concept (e.g.
| SpinLaunch) has some promise. Still some huge implementation
| hurdles, but could be a huge step forward to put all of the
| energy for the first stage on the ground.
| Ajedi32 wrote:
| Spinlaunch is potentially okay for cargo, assuming they can
| overcome limitations imposed by atmospheric drag, and scale
| up sufficiently to make it practical; but the G forces
| involved make it impossible to use for human spaceflight.
|
| IMO the closest thing to a space elevator realistically
| achievable with today's technology would be a Skyhoook:
| https://en.wikipedia.org/wiki/Skyhook_(structure)
| jhgb wrote:
| Is something like spinlaunch (centrifugal force) even
| better than a hydrogen gun (linear acceleration) from the
| perspective of g forces? For example Quicklaunch (6 km/s
| speed, 1100 m barrel) would require ~1700g of acceleration.
| Spinlaunch appears to be significantly more demanding while
| providing even smaller initial velocity. Even if it's just
| cargo applications, surely there's still a difference
| between 1000g and 10000g.
| Ajedi32 wrote:
| The main advantages of spin launch's approach over a more
| conventional mass driver are that it takes up less space
| (Quicklaunch's proposed driver is over 1km long), and
| that it requires less peak power to get up to speed
| (Spinlaunch accelerates over a period of one and half
| hours).
| jhgb wrote:
| One could argue that Quicklaunch doesn't _practically_
| require much peak power either since you have means to
| store hydrogen and oxygen in tanks over time if you
| generate them in trickles. The fact that firing it
| generates high peak power is no more relevant for
| practicality than the fact that firing a handgun
| generates high peak power. It 's just combustion.
|
| As for size, honestly, that doesn't seem to be much of a
| problem. You still have exclusion zones, and I'd argue
| that the exclusion zone around a spinning device like
| Spinlaunch proposes would have to be fairly large in all
| directions. Quicklaunch doesn't have a failure mode where
| the payload goes sideways at its full speed. Even if
| Quicklaunch were on land (which it wasn't planned to be),
| it would still probably require a smaller exclusion
| _area_.
| Ajedi32 wrote:
| Ah, I hadn't read up on Quicklaunch and assumed it was a
| railgun. Light gas does seem better in that respect.
| jhgb wrote:
| Well, I _did_ specifically say "hydrogen gun". ;)
| jjk166 wrote:
| > The fact that firing it generates high peak power is no
| more relevant for practicality than the fact that firing
| a handgun generates high peak power. It's just
| combustion.
|
| This is not a trivial engineering problem. And in the
| case of a light gas gun, not only do you need to dump all
| this energy into a driver to compress the light gas
| extremely quickly, you also then must bring that driver
| to a halt extremely quickly without destroying
| everything.
| jhgb wrote:
| I'm not saying that a space gun is simple. But I'm not
| convinced that it's that much more complicated than a
| hypersonic centrifuge that provides smaller benefits to
| begin with.
|
| BTW did Quicklaunch even have a driver/piston? I'm not
| quite sure that it had.
| jjk166 wrote:
| Yeah, quicklaunch actually uses methane combustion to
| drive the piston, the hydrogen is just the working gas.
| The whole advantage of light gas guns is that since you
| don't need your working fluid to do the combustion, you
| can use gasses with much higher speeds of sound which can
| thus produce much higher velocities, such as superheated
| pure hydrogen.
|
| I am in total agreement though that spinlaunch is a much
| worse system though.
| jhgb wrote:
| I checked on the Quicklaunch design
| (https://vimeo.com/29822477) and the only solid moving
| mass in the gun is the projectile. So apparently you
| don't need to "bring [...] driver/piston to a halt
| extremely quickly" since there is none. They _did_
| propose to recover most of the gas by closing the muzzle
| just after the projectile exit, though. That might be
| complicated.
| jjk166 wrote:
| There is a piston. At 2:07 they show a close up of the
| first stage which they are referring to as the "pump
| tube", that larger diameter section, where the piston is
| driven up to speed, pumping the hydrogen into the second
| stage barrel at high pressure.
| moron4hire wrote:
| SpinLaunch is easily the dumbest thing I've seen this year,
| and I got to become aware of NFTs this year. It's going to
| end up in the long list of grifts designed to bleed
| investors.
| spanktheuser wrote:
| Curious about your reasoning. I immediately wondered what
| type of cargo would be suitable for this sort of launch
| system. I came up with a fairly short list.
| Fuel/water/perhaps food for interplanetary spacecraft
| destined for Luna or Mars. I imagine one could design some
| types of cubesats to withstand the tremendous acceleration
| forces. That was about it.
|
| Is your skepticism based on cargo suitability or other
| factors.
| NikolaeVarius wrote:
| Who the fuck cares about cargo before trying to figure
| out if any second stage rocket that isn't a rock can
| reasonably survive the extended application of high
| G-forces
| robszumski wrote:
| They have some data that indicates most off the shelf
| electronics survive or need very minor modifications to
| withstand the G forces. That's better than no data at all
| but they do have a ways to go.
| jjk166 wrote:
| The cargo isn't the issue, it's the design.
|
| First, you're making a giant spinning thing that contains
| a ridiculous amount of energy. If the release of the
| projectile is off by a millisecond, instead of flying
| through the outlet it's instead flying into the wall of
| the launcher where it will deliver all of its kinetic
| energy in the form of an explosion with the energy of
| about a half ton of TNT, which sounds bad but really
| isn't compared to the arm its exploding next to that
| would release the energy of a small nuke if it gets
| damaged. This isn't a failure mode that can be monitored
| and avoided; eventually you're going to have a component
| fail or a software glitch and before the system can even
| register that something is wrong the launcher will be a
| crater.
|
| You're launching bulk material into orbit where no one
| cares if the occasional launch fails so long as it's
| cheap, and you're wasting that on a launch system where
| the most minor failure results in not just the loss of
| the launch vehicle but the entire infrastructure for
| launching.
|
| But even if everything works exactly as intended there
| are still issues. Your giant centrifuge spins up in a
| vacuum because at those speeds air resistance would be
| extremely damaging. Unfortunately, after you release the
| payload, it breaches the seal on the outlet and now you
| have a giant inrush of air into your vacuum chamber.
| Unfortunately, the giant arm is still spinning at 8000
| kph. The surface of the arm is going to ablate as it
| moves through sea level air at hypersonic speeds, and its
| going to generate massive shock waves which are going to
| reverberate in the chamber. All those precision
| components for releasing your payload with extreme
| precision are going to be exposed to these hellish
| conditions. You're going to need extensive repairs or
| replacements after every launch.
|
| You're doing all this and you still need a launch vehicle
| with its own rocket engine and propellant, flight control
| surfaces and surface protection for its own hypersonic
| journey through the lower atmosphere. Everything needs to
| survive ridiculous g forces. All this to deliver a few
| kilograms of low value cargo?
|
| These problems don't go away as you refine the
| technology, they are fundamental. You will always need
| precision release mechanisms to avoid catastrophic
| failure, you will always be exposed to hypersonic
| conditions, you will always experience ridiculous g
| forces, you will always need rockets for orbital
| insertion, you will always be restricted to low value
| cargo.
|
| It's an interesting engineering problem; they might learn
| some cool lessons along the way, maybe some valuable
| patents will come out of it, but there is no hope for
| developing a practical space launch method competitive
| with existing methods.
| an9n wrote:
| > that would release the energy of a small nuke if it
| gets damaged
|
| All we need to do now is containerise it for easy
| transportation across borders! Err..
|
| My first thought on seeing the prototype was whether
| they've taken a map and drawn an arc in line with the
| rotation to see the areas that might be impacted when
| this thing RUDs. Perhaps they'll put it on a turntable?
|
| Nonetheless I'd suggest it's probably safest to build
| this thing in a concrete pit such that failure results in
| a big hole, and not hot and spicy hypersonic plasma flung
| across the continental USA.
| Yizahi wrote:
| I don't think that even Rh(null) blood, unicorn tears or
| HP color ink liquids are commercially viable to launch at
| prices around 10-50k$ per liter. And that if that whole
| assembly will work at all at prices they are advertising
| today (1/20 of comparable commercial rockets, but it will
| have very small payload).
|
| PS: I don't have numbers, but I'm guessing that F9
| hitchhike Transporter missions cost less per kilogram,
| compared to the imaginary numbers for non-existing full
| scale Spinlauch.
| avmich wrote:
| Some classification considers 3 types of cargo - bulk
| materials (metals, fuel); complex electronics; humans.
| The majority of weight is in the 1st type. Unless first
| two types have complex mechanical structure, where loads
| can't be distributed into supports - which is an
| important issue - the first two groups are candidates.
| jhgb wrote:
| But this launch system still needs the projectile itself
| to be a fairly complex rocket capable of delivering
| several km/s of delta V and of steering the payload onto
| a desired orbit. That still implies electronics and
| mechanical systems onboard even if you're carrying only
| bulk cargo.
| avmich wrote:
| Electronic chips themselves are rather good to withstand
| acceleration - can be packaged well. Mechanical systems
| for simple rockets could also be, well, simple - e.g.
| first orbital launcher of France used pressure-fed
| engine.
| moron4hire wrote:
| Skepticism? I'm not "skeptical" about SpinLaunch. I'm
| _incredulous_ about SpinLaunch. Skeptical implies that I
| think there might be a chance, if certain criticisms are
| addressed. No, I am certain there is no chance SpinLaunch
| will end up being a thing.
|
| First of all, putting aside the _several_ red-flags for
| why this looks like a scam, and assuming it 's actually
| do-able, it's still not going to happen. The global space
| industry is built on rockets. At best, stuff like this--
| even if it does work--gets a "cute project, kid" pat on
| the back and then ignored. When was the last time any
| fundamental redesign of an existing technology take over
| an industry? It just doesn't happen.
|
| And I think everyone involved probably knows that. You're
| not going to compete against Google as a scrappy startup
| trying to make a search engine. You're not going to
| compete against SpaceX as a scrappy startup trying to
| make alternative launch systems. Somebody, somewhere, has
| to understand that. So they have to be in on the scam.
|
| Now, as for the actual idea, there are several problems.
| First and foremost is: energy is energy. If this thing
| fails, it blows up just as bad as a chemical rocket on
| the platform.
|
| At least chemical rockets are based on decades-old
| materials science. This spinning arm malarky expects us
| to believe that they can support 10,000x their payload on
| the arm and be able to release it on a hair trigger? I
| suppose next they're going to tell us the arm is made of
| carbon nanotubes or some other unobtanium.
|
| So they want to spin the object in a vacuum. How are they
| going to seal the spin chamber in such a way that they
| can generate a significant vacuum while also allowing the
| payload to escape? They show a paper or some other thin
| membrane door over the escape hatch that the payload
| punches through. OK, that means that door needs to be
| able to support 13.75 _pounds per square inch_ of
| atmosphere. A 2m x 2m door needs to be able to hold up
| over 40 tons of atmosphere. The payload needs to punch
| through a door that is holding up over 40 tons of
| atmosphere. That payload needs to punch _into_ a 40 ton
| column of atmosphere. At ~5,000 mph?!
|
| So what I expect to happen is that the payload hits the
| column of air, creates a mach shockwave that destroys all
| of the windows in a 5 mile radius, while the rush of air
| into the chamber and clapping back around the tunnel of
| vaccum the payload creates blinding spike of plasma (not
| unlike lightning), that ends up destroying the launch
| chamber.
|
| Oh, yes, there are "challenges" to "figure out". From
| their launch command center that was clearly designed for
| aesthetics more than functionality. Lots of problem
| solving gonna happen there.
| h2odragon wrote:
| Agreed, but the year ain't over yet.
| Valgrim wrote:
| A similar but somewhat more physicaly sound idea is the
| Slingatron: a launch track several kilometers long in a
| spiral shape, on stilts that rotate in synchronization. The
| g-forces are much more reasonable because of the increasing
| track diameter.
| jjk166 wrote:
| Space elevators don't work on the moon. While gravity is
| weaker, the moon's rotation period is also much lower. To
| build a space elevator, its center of mass must be in a
| stationary orbit over the body. A geostationary orbit around
| the moon (selenostationary) would be about 88,000 km. The
| moon's Hill sphere, the region where its gravity dominates
| and thus things can stay in stable orbit around it, is only
| about 58,000 km. Basically a lunar space elevator would be so
| tall that Earth's gravity would yoink it off the moon.
|
| You could potentially build a skyhook on the moon, which a
| space elevator is merely a special case of, but you lose a
| lot of the advantages of a space elevator - namely you still
| need something to blast off the surface to reach the skyhook,
| and you have to carefully time it because everything's moving
| at extremely high speed. Saves a lot of fuel though.
| Valgrim wrote:
| On the moon, you'd need a mass driver in conjunction with a
| skyhook.
| jhgb wrote:
| But why not _just_ build a mass driver, then? It 's a
| somewhat large horizontal structure, compared to a space
| elevator which is an absolutely humongous vertical
| structure. If you can reach 2 km/s on magnetic rails, you
| don't need anything else to launch from the Moon -- or
| even land on it.
| sobellian wrote:
| What if you position the counterweight of the space
| elevator at the L1 lagrange point of Earth/Moon? Since the
| moon is tidally locked, it should always stay about the
| same spot relative to the lunar surface.
| hoffspot wrote:
| Excellent use of "Yoink"
| wombatpm wrote:
| Spin Launch for cargo. Can't imagine being a passenger
| qayxc wrote:
| At about 10,000Gs of acceleration (as per their claims1
| ~2200m/s in a 100m vacuum chamber, e.g. a=v2/r [?]
| 97,000m/s2 or roughly 10,000Gs) any human passenger would
| be liquified and form a nice smooth film on the inner
| surfaces of the vehicle.
|
| 1https://www.spinlaunch.com/orbital#p2
| klodolph wrote:
| > From someone who knows little about this -- what is the
| advantage of this kind of engine?
|
| Take a traditional bell nozzle engine. The shape of the bell is
| designed to redirect the exhaust in the correct direction, but
| one of the design parameters for the shape is the ambient air
| pressure. If you design it to work at a specific altitude, it
| will be less efficient at other altitudes.
|
| The aerospike is more efficient over a broader range of
| altitudes. (That is, if you take the average efficiency over a
| wider range of altitudes, the aerospike wins. If you pick one
| altitude or a narrow range of altitudes, the traditional nozzle
| wins.)
| reasonabl_human wrote:
| Piggy backing off of this- the real net benefit is unblocking
| an SSTO design (Single Stage to Orbit).
|
| Instead of having a lift stage and an orbital stage,
| aerospikes can theoretically do both, meaning one cohesive
| vehicle from launch through orbit.
|
| The weight savings and reusability factors are huge if SSTO
| setups become feasible.
| ashtonkem wrote:
| Piggybacking off this too, if you look at rocket
| specifications, they'll often mention the same motor on
| different stages with a (VAC) behind it. This denotes the
| different bell shape required to make the motor efficient in
| vacuum as compared to sea level.
|
| The issue with an aero spike is that the benefits just aren't
| there for a multi stage rocket. We do multi stage rockets to
| balance the needs of high thrust at the launch pad with the
| need to minimize our final non-payload weight in orbit.
| Varying the bell design to match flight profile naturally
| plays well with this approach. If you're going to ditch parts
| of your rocket for weight saving during ascent, you might as
| well tune each stage for the altitude it will actually work
| at. Motors that need to work at all altitudes are pretty
| rare, the only ones I can think of are SSTOs in theory, and
| the space shuttle main engines.
|
| If we could get a falcon 9 with aero spikes it would
| theoretically be an improvement, but not a huge one. All the
| gains would be in the edges of various stages where say, the
| stage 1 motors are flying above their designed altitude. The
| efficiency gains are there, but they might be completely
| offset by increased weight, cost, cooling concerns, etc.
| the_cramer wrote:
| We haven't. We just can't produce enough carbon nanotubes
| cheaply to build a space elevator. Amongst other technical
| issues.
|
| One limiting factor of a rocket engine is the exhaust cone.
| This big dome-shaped piece of internally cooled structure tries
| to make the burning of fuel most efficient by controlling the
| shape of the exhaust reaction. In atmosphere you need a
| different size than in orbit to burn optimal, that's one reason
| why staging is done and the second stage is much different in
| cone size.
|
| Since in aerospike the direction and shape of the exhaust
| gasses is different, air pressure is used as a "dynamic cone"
| making single-stage to orbit" rockets much more feasable. I'm
| not sure if we want that at all, though.
| oconnor663 wrote:
| My naive understanding: The appeal of a space elevator is that
| all you need to get to space is the energy to climb the
| elevator. But if Starship is able to hit its "fully and rapidly
| reusable" goals, it will have basically achieved the same
| thing: You can go to space on Starship for not much more than
| the cost of fuel to get there.
|
| The next question is which version is more energy efficient.
| Again, my very naive understanding is that they seem to be kind
| of similar. The space elevator is less efficient than you might
| think, because you can't just run electrical wires up and down
| it. The weight would be a problem, and resistance losses over
| such a long cable would be high. Instead, you might send power
| through the air with a big laser, but that also comes with
| efficiency losses, in the same ballpark as rocket engines.
|
| And of course, Starship has the obvious advantage that it seems
| like it actually might work with current technology. I think
| this comparison is an interesting way to highlight what a big
| deal it will be, if Starship does work.
| mercutio2 wrote:
| I agree that space elevators are very unlikely in the next
| few centuries.
|
| But arguing that Starship achieves basically the same thing
| seems wrong to me.
|
| Starship is subject to the rocket equation. That means all
| but a few percent of its launch mass is rocket fuel.
|
| Space hooks of all sorts require _some_ transfer of energy,
| but the idea is it 's on the order of magnitude of the actual
| potential energy gained.
|
| Edit: It strikes me as implausible that we'll get unobtainium
| with sufficient material strength to build a space elevator
| without accompanying superconductors run through the elevator
| structure, but when I ran the numbers, current lithium ion
| batteries are about 1/60th of the energy density of mass
| moved from the highest equatorial point on earth to geosync
| orbit.
|
| Not so very different from the rocket equation, you're right,
| if we decide there's no way to convey energy through the
| space elevator.
|
| It's all sci-fi anyway!
| orbital-decay wrote:
| Spike engines aren't that great not because of cost, but because
| their supposed benefit is largely eaten by added weight and
| cooling complexity in most designs, so the entire thing isn't
| worth it, usually. Meanwhile, things like nozzle extensions can
| provide 80% of their benefits for 20% effort. The article is
| light on information on whether they solved typical issues, and
| what exactly they traded for the efficiency.
| isaiahg wrote:
| The article hints that this design may be less complex.
|
| > The engine is extremely low cost to produce, as it is
| completely additively manufactured (metallic 3D printing) in
| only two pieces.
| baybal2 wrote:
| 3D printing is likely not to do a single thing about the
| cost.
| NikolaeVarius wrote:
| wut. 3D printing allows extremely complex geometries that
| doesn't require a 30 year experience machinist to
| manufacture.
|
| The F9 and Electron both aggressively drove down costs
| using 3D printing
| baybal2 wrote:
| 3D printing is expensive
| NikolaeVarius wrote:
| A master machinist is also expensive and probably doesn't
| like working 24/7
|
| Also 3D printing has the advantage of not throwing out
| 75%+ of the metal stock
| baybal2 wrote:
| Even without a machinist, 3D printing is still very
| expensive, which makes it even worse comparatively.
| wolfram74 wrote:
| I am with you on 3D printing being over hyped often. But
| keep in mind you are arguing that
|
| COST_3D-(COST_CONVENTIONAL+SALARY_MACHINIST) = SAVINGS
|
| is more than the literally unreproducible parts 3D
| printing can achieve. These are not comparable
| quantities.
| baybal2 wrote:
| You don't need these unreproducible parts for a rocket
| switchbak wrote:
| And there are designs that are simply impossible to build
| with traditional machining. This is most certainly a
| valuable technology.
| Valgrim wrote:
| Why? Even if a additive manufacturing is slower than
| traditional manufacturing, 3d printers can be mass-produced
| (unlike assembly lines and skilled engineers).
| kabdib wrote:
| I assume that all of the support gear (turbopumps, etc.)
| are not 3D printed. I'd be super impressed if the fuel
| and oxidizer injectors were printed.
|
| Anyway, there's a bunch of stuff they're not including in
| this statement; it's like "we can print your car's engine
| block" but glosses over the additional whirly-sparky
| stuff that turns a lump of metal -- even if it is in the
| right _shape_ -- into a functional engine.
| Gravityloss wrote:
| A favorite of mine is Thrust Augmented Nozzle or TAN, where, at
| low altitudes, extra propellant is injected into the nozzle
| (not the chamber) to prevent flow separation and to increase
| thrust, albeit at lower specific impulse. Think of it as a bit
| of an afterburner for a rocket engine.
|
| https://www.aerodefensetech.com/component/content/article/ad...
|
| More thrust even at lower specific impulse at the start of the
| flight can save you a significant amount of gravity loss,
| engine mass etc.
| jhgb wrote:
| A similar, but much more useful thing for the future seems to
| be LANTR, a.k.a. the only _practical_ nuclear rocket engine
| we know of. At the very least it doesn 't waste all oxygen
| from water mined on other bodies of our solar system like
| traditional pure-hydrogen NTRs do. And its average impulse
| density of propellant is way higher, of course.
| kurthr wrote:
| I had to look that up. This was the nicest explanation I
| found, but if you recommend a different one, please post. I
| also found stuff on Kerbal, but I'm not clear how real that
| is.
|
| http://www.astronautix.com/l/lantrmoonbase.html
| jhgb wrote:
| There's a NASA TR about it:
| https://ntrs.nasa.gov/citations/19950005290
| credit_guy wrote:
| This is solving a different issue. Aerospike engines deal
| with the fact that rocket engines need to be different in
| an atmosphere vs in vacuum. Nuclear thermal rockets (NTRs)
| are not really envisioned for being used in the atmosphere,
| the risk of a blowup is too high. I consider them a
| wonderful technology which could really open up new
| possibilities, but we first need to nail down the challenge
| of affordably getting to orbit.
| jhgb wrote:
| Except LANTR solves a very similar problem, which is the
| requirement for different performance parameters at the
| beginning and at the end of a rocket flight (high thrust
| and propellant density in first stage, low thrust and
| high Isp in the second stage) in a single stage vehicle.
| And I mentioned it because its way of operation is very
| similar to the thing describe above, i.e., injecting
| something extra into the nozzle, so it reminded me of it.
| Not because I consider it comparable to using aerospikes
| on Earth (I'm not convinced that's useful at all) but
| because this is one of the few such variable Isp options
| that appears to provide any useful benefits at least
| _somewhere_ (even if it 's not on Earth).
| fudged71 wrote:
| NextAero in Australia was working on an additive manufactured
| Aerospike https://nextaero.com.au/index.php/engine-
| progress/projectx/
| avmich wrote:
| Nadir Bagaveev got YC investment after showing such a thing -
| https://www.youtube.com/watch?v=JqWVWBkPAtg .
| 8bitsrule wrote:
| >The aerospike engine has been the saint grail for rocket
| scientists since its was first theorized in the 50's.
|
| 'saint grail' ...
| lcrz wrote:
| The automated translation is pretty noticeable.
| 8bitsrule wrote:
| Turns out that was actually a thing:
|
| 'the line of messianic descent was defined by the French word
| Sangreal.... In English translation, the definition, Sangreal,
| became "San Greal", as in "San" Francisco. When written more
| fully it was written "Saint Grail", "Saint", of course,
| relating to "Holy"; and by a natural linguistic process came
| the more romantically familiar name, "Holy Grail".'
| dylan604 wrote:
| Nice to see Dan Brown in our midst.
| taneq wrote:
| And here was me thinking Wheel of Time and their
| "sa'angreals".
| ryzvonusef wrote:
| episodes are out!
| tsimionescu wrote:
| That's just bad etymology. The word/expression Saint Graal in
| Old French. Saint was translated into English directly as
| Holy, while Graal was adopted as is morphing into grail. It
| seems the etymology for graal is likely ultimately Ancient
| Greek krater, a type of wine bowl.
|
| The 'sang real' (royal bloodline) nonsense was a much later
| invention (15th century).
| kleton wrote:
| Santo Grial in Spanish, I suspect neural machine translate
| would have translated their press release into more idiomatic
| English.
| roveo wrote:
| In many languages "saint" and "holy" are the same word.
| TruthWillHurt wrote:
| Honorable mention: an aerospike engine has been flown by Arca
| space.
|
| Well, kind off.. it's a spike, but they're using water steam as
| propellent, I'm guessing to "solve" the cooling problem. So not
| sure if it counts (and how successful their rocket will be).
|
| But still.. https://www.youtube.com/watch?v=QsKE_SBY-kE
| CarVac wrote:
| If that counts, then my flight of a demo Aerotech aerospike HPR
| reload counts.
| bryanlarsen wrote:
| I don't think ARCA's tea kettle is technically a rocket engine,
| since there's no combustion.
| avmich wrote:
| Hydrazine or hydrogen peroxide can be used as monopropellant,
| and it's still rocket engines, even without combustion.
| bryanlarsen wrote:
| True, but it's still a highly exothermic decomposition, the
| energy comes from a chemical reaction, unlike ARCA's
| silliness.
| avmich wrote:
| But it's not combustion. I guess you meant something
| else. Now you label they approach; do you think laying
| boundary line this way looks obviously correct? Say,
| nuclear rocket engines heat up gases - also without
| chemical reaction; resistor jets also have reasonable
| history in rocketry - why ARCA's approach is wrong?
| bernulli wrote:
| I don't see that as a reasonable constraint - nuclear
| propulsion does not need combustion, thermo electric does not
| need combustion, and there's also things like cold gas
| thrusters, laser ablation etc. etc. etc.
| bryanlarsen wrote:
| Usually those are called thrusters rather than rocket
| engines.
| p_l wrote:
| There's no combustion requirement for a reaction drive ;-)
| SonicScrub wrote:
| Ah yes, ARCA Space. That company founded by a guy who faced 13
| counts of fraud, 5 counts of embezzlement, and one count of
| forgery. I'm not surprised that company has so many "buzzword"
| technologies that it's supposedly developing. What better way
| to scam... err I mean... provide opportunities for bold
| investors.
|
| What's the ISP on a water rocket? 90?
| rbanffy wrote:
| Well... If you have a hydrolox aerospike engine, what comes out
| of the exhaust is just very hot water... ;-)
| BenjiWiebe wrote:
| And MethaLox is just very hot soda water. :)
| rbanffy wrote:
| Sparkly!
| noisy_boy wrote:
| For those who want to see it in action:
| https://www.youtube.com/watch?v=CombVB48ziY
| ortusdux wrote:
| Thanks for this. I wonder if they do spectroscopy on the
| exhaust plume. You can tell that it is burning a little engine
| rich at the start.
| dtgriscom wrote:
| My reaction to the greenish tinge of the flame was "I wonder
| what part of the engine is melting away?"
| lquist wrote:
| Is this a threat (or boon) to SpaceX?
| [deleted]
| irjustin wrote:
| Super cool!
|
| I'm still dubious of the benefits of the aerospike but I'm happy
| to see the pursuit.
| rbanffy wrote:
| They'd be most useful in single-stage-to-orbit craft, but, if
| they can increase efficiency of reusable boosters and orbit-to-
| ground propulsive landings, that's still great - an aerospike-
| based Starship wouldn't need both vacuum and sea-level engines
| and could use the same engines in space as it would use to
| land.
| PaulHoule wrote:
| In principle the SSTO is better for reuse because you can
| refuel a single vehicle and send it out again, compared to a
| Starship-class vehicle which has two stages that need to be
| stacked each time.
|
| The trouble is that SSTO is on the margin of the possible and
| mastering reuse of a 2 stage system is a certain win whereas
| the SSTO is risky. You have to perfect quite a few
| technologies such as the aerospike engine, very lightweight
| tanks and thermal management system and get them to all work
| together and really be able to reuse them without tearing it
| down each time like the old STS.
| rbanffy wrote:
| For SSTO to be worth for a Starship-Superheavy class
| vehicle, the aerospike engines would need to be as
| efficient as the Merlin ones at the same weight and the
| removal of the Starship engines would need to account for
| added thermal protection of the lower part.
|
| The napkin math seems workable, but rockets require a lot
| more than napkin math.
|
| Having said that, Shuttles were almost SSTOs in the sense
| that the fuel tank could be placed in orbit (and reused as
| pressurized habitation space, with some extra work). Maybe
| some SLS-derived work can add some very large volumes able
| to dock into a future space station.
| PaulHoule wrote:
| The Shuttle still dropped the two solid rocket boosters.
|
| Still it performed better than Tsiolkovsky and everyone
| else thought a chemical rocket could perform because
| running rich with extra H2 lets you get a better ISP
| since it lowers the molecular weight of the exhaust even
| if it does lower the temperature a little.
| pbronez wrote:
| > Shuttles were almost SSTOs in the sense that the fuel
| tank could be placed in orbit (and reused as pressurized
| habitation space, with some extra work).
|
| That is super cool! I gotta dig into that.. pity they
| never did that. It would be neat to have an ISS module
| that was a re-purposed shuttle external fuel tank.
| Tuna-Fish wrote:
| > an aerospike-based Starship wouldn't need both vacuum and
| sea-level engines and could use the same engines in space as
| it would use to land.
|
| In vacuum, an aerospike will not be as efficient as a
| maximally expanded traditional nozzle. If you could conjure
| an aerospike raptor from thin air, you'd still probably want
| the vacuum engines there, but you'd of course want to replace
| the sea-level ones with the spikes for higher efficiency
| immediately after stage sep (when all 6 are firing).
| gameswithgo wrote:
| Yeah but saying "This is useful for SSO" is like saying "This
| is a better way to get to orbit a bad way"
| rbanffy wrote:
| SSTO is not great, but when you add full reusability to the
| mix, it becomes attractive. You spend more in propellant
| but makes operations so much easier.
| everyone wrote:
| Everyday Astronaut has a great video on Aerospikes.
|
| .
|
| https://youtu.be/D4SaofKCYwo
|
| .
|
| Basically everything a layman would want to know imo.
| yummybear wrote:
| I understand atmospheric pressure has an impact on the exhaust
| shape, but why aren't the nozzles that feed onto the aerospike
| affected just like a traditional engine?
|
| I.e. in their illustration on the page, the two nozzles next to
| the spike itself?
| FourHand451 wrote:
| It seems that the nozzles feeding onto the aerospike are
| sufficiently small to operate safely at sea level air pressure.
| That kind of nozzle can operate safely at lower air pressure as
| well, but is inefficient. The aerospike gives you back your
| efficiency at lower atmospheric pressures, so you end up with
| something that's both safe and efficient at all altitudes,
| relative to a traditional bell nozzle.
|
| At least that's my understanding - I just like to learn about
| rockets.
| techdragon wrote:
| They are affected by air pressure, but it doesn't actually
| hurt, it actually helps! because of the way an aerospike engine
| works it actually relies on that pressure change behaviour on
| the "outside" edge. The expansion of the exhaust on the
| atmospheric side of the aerospike is actually part of how it
| obtains its efficiency.... That expansion pushes the expanding
| exhaust plume back towards the nozzle wall in proportion to the
| normal expansion with outside pressure and that drives the
| physics that make aerospike nozzles work at all altitudes. It's
| a clever feedback loop if you want a computer analogy, but it's
| really just a clever arrangement that maximises system
| efficiency in that lovely "continuous" way that
| mechanical/physical systems work.
| kevin_nisbet wrote:
| You may want to check out the video / text from everyday
| astronaut pointed to elsewhere in this post, which goes through
| a much deeper research and explanation on the topic.
|
| The TLDR as I remember it, is physical nozzles on the aerospike
| don't work the same way as they do on a traditional rocket.
| It's more like like just an exit from the combustion chamber.
|
| The appeal of an aerospike is by having lots of exhaust port
| aligned around a spike, is it creates a sort of virtual nozzle
| that is the right size for the atmospheric pressure. And as
| such acts sort of like a nozzle that changes shape and size as
| the rocket goes through the thinner and thinner atmosphere.
|
| This in theory gains efficiency over a rocket that has a set
| shape for it's nozzle, and isn't always operating at optimal
| efficiency due to the size of the nozzle.
|
| * Not an expert on these things, just going off of memory
| tnorthcutt wrote:
| For anyone curious about aerospike engines, Tim Dodd has a great
| in depth video on them: https://youtu.be/D4SaofKCYwo
| loudmax wrote:
| If you'd rather read Tim Dodd than watch his video, here's the
| text version: https://everydayastronaut.com/aerospikes/
| airstrike wrote:
| Alternatively you can watch the video on mute with captions
| turned on, which is my favorite approach
| vultour wrote:
| But... why? Having to read the captions prevents you from
| watching the video.
| ErneX wrote:
| People have been watching subtitled movies for decades.
| FullyFunctional wrote:
| Indeed, people outside of USA (and France, Germany, and a
| few others that dub everything) have lived with this
| their entire lives. Even today my wife and I watch with
| subtitles as it's not always easy to hear all of the
| dialogue over the other noises in movies/shows.
| Narretz wrote:
| To me, that's like the worst of both worlds. You have text,
| but you can't read it at your own chosen speed.
| airstrike wrote:
| You can always pick a faster / slower playback speed in
| YT
|
| And you get to keep the images, which are not there for
| the text-only version
| NikolaeVarius wrote:
| YT maxes out at 2x, which is extremely slow
| gibolt wrote:
| If you're on desktop:
| https://chrome.google.com/webstore/detail/youtube-
| playback-s...
|
| Go beyond 2x!
| devoutsalsa wrote:
| You can also play the YouTube video with your eyes closed
| to get the audiobook version.
| Ajedi32 wrote:
| In Tim's interview with Elon Musk, Elon mentioned[1] low
| combustion efficiency as one of the major disadvantages of
| aerospike engines compared to the more traditional bell nozzles
| used on Raptor.
|
| I wonder if Pangea has done anything in an attempt to solve
| that problem.
|
| [1]: https://youtu.be/cIQ36Kt7UVg?t=408
| phkahler wrote:
| >> Elon mentioned low combustion efficiency as one of the
| major disadvantages of aerospike engines
|
| If you haven't seen the SpaceX presentation on their
| combustion CFD software, it's a must see. They have state of
| the art simulation capability in this area - better than any
| commercial offerings.
| aero-glide2 wrote:
| Everyone keeps posting this, but there's no update on that
| video.
| taneq wrote:
| They seem kinda busy over there, maybe they have higher
| priorities?
| bernulli wrote:
| That was 6 years ago, hard to say what remained of that
| ambitious goal. Also, these guys aren't with SpaceX
| anymore.
| baq wrote:
| Raptor has since exceeded its target performance, maybe
| they ran out of frontiers to explore?
| dokem wrote:
| From what little i've seen of this guy; he appears to have no
| actual technical understand or depth to anything he reports on
| and basically just echos pop science and press releases. Scott
| Manley, Curious Mark and Periscope archival footage comes to
| mind for high quality content to learn about rocketry and
| related technology.
| aero-glide2 wrote:
| I like him a lot, but recently in his tweet he didn't even
| know how pressure varies with area in a nozzle. I do think he
| should learn a bit more.
| NikolaeVarius wrote:
| I have no idea why people recommend this guy. Such bad 40
| seconds wiki article reading with a annoying way of talking.
|
| A personality driven channel versus engineering
| mc32 wrote:
| If he just stepped back and kept his personality out of it
| would be much more tolerable.
| datameta wrote:
| His target audience is not the highly technical, but the
| public at large - including children. He's a space
| ambassador in that he wants to get the current and upcoming
| generation excited and learning about space.
|
| With that said, he has been able to get in-situ interviews
| with rocket company CEOs including his amazing 2 hour
| almost single take video tour with Elon Musk [0] where I
| was able see Elon comfortable in speaking much more deeply,
| candidly, and enjoyably than with any interviewer/reporter
| prior. Tim Dodd is no professional engineer but he really
| knows his stuff. His personality helps bridge the gap
| between the highly technical and the layman.
|
| [0] https://youtu.be/t705r8ICkRw
| tnorthcutt wrote:
| Well put.
|
| Personally I love that Tim's personality shines through
| in his videos. His enthusiasm is infectious and just
| plain nice to see, IMO.
| NikolaeVarius wrote:
| Why. The personality removes so much information density.
| kataklasm wrote:
| Well, after spending eight hours working demanding jobs,
| be it physical or mentally, everyday people usually like
| to spend their free time with something a little more
| relaxing, and for most people that isn't reading
| documentation or reading highky technical engineering
| papers but rather watching a highly enthusiastic guy try
| and share his joy of rocket science.
| baq wrote:
| Content can be also be entertaining to watch. Not
| everyone wants to superoptimize their time.
| an9n wrote:
| Well sure, but there are moments where Elon just flat out
| ignores him, so idk.
| mc32 wrote:
| That's a good point. I'm not an engineer yet I prefer
| there be more description and less personality shining
| through; but you make a good point about target audience.
| And as you say he prepares for the material and does well
| to understand the experts.
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