Realistically, what is the feasibility of a space catapult? I mean, the speed at ground level to be able to reach orbit must be insanely high, no? This high speed in a thick atmosphere would cause all kind of heating problem on the catapult itself and the "rocket". I wonder what would be the actual numbers.
Not to mention the acceleration needed to achieve orbital velocity with a catapult. Seems like insanely high forces on the payload. I’d love to see how they solve this.
At around 50km radius you get 3g. That would be a pretty big centrifuge! Humans will probably never use this but maybe some types of satellites can handle the load.
Yes, the centripetal acceleration only starts to get reasonable (ie less than 10g) with a 20km radius centrifuge. The only practical way to do that would be an evacuated circular tunnel equipped with a maglev. Maybe that's their solution?
Launch from near the equator, high in the mountains? Chimborazo, Ecuador? At 6000 feet, its half the air pressure of sea level, and 1/4 the atmosphere to travel through. And accessible. A good start?
Going to space is not entirely about being high. It's about going sideways, fast.
And if, at 6,000 feet, air pressure were half that of sea level, nobody would live in Denver and most Tibetans would be dead. Half is more like 6,000 meters.
Getting high quickly is important, which is why launch vehicles go up first, then do a gravity turn in thinner air, reducing drag and aerodynamic pressures on the vehicle. It's hard to go horizontally fast when you're fighting thick atmosphere.
Air density at the top of Everest is 1/3 of sea level, and because of the Earth's shape, Chimborazo's 20,000 feet (6,000 meters)
is actually further from the Earth's center than Everest, so half pressure sounds pretty reasonable: https://www.npr.org/templates/story/story.php?storyId=942816...
What you're forgetting is that the same mechanics that make Chimborazo the furthest from the earth's center (the oblate spheroid shape due to spin) also applies to the atmosphere (though probably to a different degree). So over Chimborazo, the atmosphere is also thicker, I'd imagine (could be more, could be less). I haven't looked at the actual measurements, but you might want to before you compare different latitudes. Also, see my other comment for non-engineering difficulties.
Ok the troposphere is 4 miles up at the poles, and 12 miles up at the equator. So 6000m (about 3.6 miles) is not even half of 12. Still, its half-pressure. But you have 8 miles to go to get out of it. So maybe somewhere halfway? Seattle? There the troposphere is 6 miles up; Mt Rainier is 2 miles high. Maybe a better deal?
Chimborazo is >6000m above sea level tbf and not 6000ft as the OP suggested. It's actually the furthest point from the Earth's centre (the earth's shape gives it a boost over mountains which are higher above sea level but further from the equator)
For related reasons, its difficult-to-reach, low oxygen, snow-covered summit is not ideally suited for building and maintaining a space launch site.
"Not ideal" may overlap with 'tremendously cheap' if the SpinLaunch 10-100x cost factor is true. So a few oxygen masks may be worth the trouble. And a highway goes within a few miles of the peak right now.
I've been on that highway. Trouble is you're still a few thousand metres of relatively technical climbing or a helicopter ride away from the top. I mean, people can work in some pretty inhospitable conditions if the cost advantages are real, and the payloads you've got to get up there have to be relatively comfortable with being moved to get fired into space anyway, but it's hard to imagine anything on a Cape Carnaveral scale happening there even if Ecuador decides the dollars from supporting space programmes are worth more than the scenery and symbolism
I came across the idea of launches from Ecuador while reading about spaeflight. IIRC, I assumed 3,000m launch (assumed a suitable site near Quito exists), and calculated a disappointing, less-than 10% increase in payload, assuming a BFR as the launch vehicle. However, for a kinetic energy launcher, or small rocket like the new record-settinf Japanese SS-520, that improvement would be a lot larger (and more importantly, the logistics a lot easier!).
The thing is, with rocket size increasing, payload increases cubically while air resistance is squared. So for the really big rockets, altitude is not as big of a factor as being near the equator.
If I am not wrong, propulsive landing on drone ships uses another roughly 10% fuel (depends on launch trajectory, etc).
As fossil fuels are non-renewable, and Hydrogen expensive, I am very sure (and even hope to be correct) that in the future we will see launches from high-altitude equatorial regions, using booster-capture technologies and perhaps even terestial-power-assisted launches. Those things may reduce the fuel-cost of escape velocity by 30+%, and when we're sending enough stuff into orbit that this is too advantageous to ignore, we will do it.
But for now, the best way to go is to get really good at building bigger rockets.
I came to mention this as well. I wish more people would look at all the factors before saying "X elevation and Y latitude is what we need, therefore this place fits the bill." Given the active volcanoes and weather in Ecuador, you'd be lucky to find a road and suitable launch complex site over 4000m.
And then there is this whole science and tech imperialism. Maybe Ecuadorans don't want roads and launch complexes cut out of their high mountains. Hawaii is going through this issue right now with new telescopes on Mauna Kea, and Ecuador has a strong indigenous rights movement, including the party in power at times.
I mean, sort of. That's less than 6% of the dv you need to get to LEO. If this thing can only add another 3k mph we're still at less than a quarter of the dv needed to get to space today. It might make a reasonable 'first stage' if they can work though the tech needed to get to that 3k without destroying the payload, but it doesn't sounds like it's capable of anything resembling a complete 'launch system' for things wanting to go to space.
They give only 'hypersonic speeds' as a metric. That's 4000-8000mph approximately. So not there yet. But don't knock a free 1000mph! Launching to the west means you have to add 1000mph to be standing still, orbit-wise.
>All that momentum is then harnessed to catapult a payload into space at speeds one source said could be around 3,000 miles per hour.
So that's what I was working off of. Admittedly, it's unclear who that source is. And 8k is still less than half of LEO.
And right, I'm familiar with orbital mechanics and would never turn down free dv, but you get ~90% of that even out of somewhere as far off the equator as CCAFS. The bigger benefit would be if you're looking to launch into a low inclination (equatorial) orbit you can avoid the dv required for the plane change, but that would work just as well out of CSG.
The altitude itself would be the only advantage I could see over somewhere like CSG.
if we assume our desired orbit to be at an altitude of 320 kilometers and our orbital velocity to be 7 kilometers per second; and we assume that air resistance decreases as a proportion of the cube of velocity inside the troposphere, proportional to the square of velocity inside the stratosphere, proportional to velocity inside the mesosphere, and discount air resistance above the mesosphere, we can begin to set up a differential equation to solve the problem.
I'll be back, if anyone wants to follow along at home, post your answers when you are ready.
But the heat load due to atmospheric friction would be immense and immediate.
The US built an antiballistic missile system that included a missile called Sprint [1]. It accelerated at 100G and developed temperatures of over 3000°C less than 5 seconds after launch. A video here [2].
It's a formidible engineering challenge to make a vehicle and payload that will survive such a difficult flight regime with commercially attractive economics. At this point, I don't understand SpinLaunch's advantage over earlier projectile systems (Gerald Bull) or current launchers like SpaceX. This will be interesting to follow.
Worst case scenario the missile blows up on launch leveling the surroundings before the enemy missiles arrive, thus stealing the sense of achievement from them ;)
They mention in the article of being able to launch objects at 3,000 MPH. That's a tad short of the typical 17,500 MPH used for low earth orbit, and that's not counting the extra Delta-V required to resist atmospheric drag.
I'm very glad that this company exists, but this article doesn't help its case very much other than "Hey look, they got a load of funding".
Just a wild guess here, maybe they’re using a variant of a ramjet, skipping the inefficient speeds, and then propelling it to LEO speed once it’s launched.
Ramjet would still require atmosphere. If you look at the Japanese SS-520 or the RocketLab's Electron, you don't need a giant rocket to get a small payload to orbit from a standing start. If you give your payload a Mach 5 kick you can eliminate a lot of the propellant mass and get by with smaller rocket motors optimized for high altitude operation.
Elon Musk wants to put 12,000 satellites into orbit. It would be very strange to me if he doesn't have someone looking into the feasibility of a giant subterranean launch tube to do something similar. Get the payload up to Mach 10 on terrestrial power and complete the orbit with a small single stage.
The Hyperloop is a rehashed vacuum-train idea originally from the 1800s (reduce air and rolling resistance as the primary forces counteracting speed). [1]
A launch tube would be very different, if for no other reason then the fact that you need to actually jettison the payload at one end at high speed.
so to put something in orbit you have to do 2 things:
- get it high out of the atmosphere
- give it a sideways kick so that it's going fast enough as it falls back that it misses the earth
Going straight up minimises the velocity lost by drag, but means you have to pull a right angled turn, going straight sideways grossly increases drag but makes the energy for insertion less
A railgun can only put one velocity vector on a launch, you still need a rocket of some sort to pull that turn
All unthrusted orbits eventually return to their starting points - so without a rocket on the payload there would be absolutely no way for a railgun to orbit anything. (Even if the railgun was on a tower on the moon, the satellite would eventually hit the back of the railgun.)
Agreed the articles leaves technical information to be desired.
On the point of 3,000 MPH. One of the comments on the TechCrunch article maybe provides some insight on why they aren't targeting 17,500 MPH.
"even if they need to supplement with rocket propulsion (after exiting the rotational acceleration phase), the amount of rocket energy needed will be way less. could see a huge increase in payload mass fraction as a result. maybe closer to 20 or 30% instead of 1 or 2%"
IF they are flying beyond Mach 1, drag coefficient will actually drop as Mach number increases. [1] Gravity loss will play an interesting roll as well for a system launching with a high initial velocity. There will be a balance between aerodynamic drag and gravity drag losses. The lower the angle launched, the higher the aerodynamic drag but the low the gravity drag loss. [2] Typically launch vehicles actually need more than 9.5 km/s of delta-v even though the orbital velocity for low earth orbit is only 7.8 km/s. This is due to predominantly to account for the large drag forces the velocity experiences during the vertical portion of ascent at sub, trans, and lower super sonic speeds prior to exiting the atmosphere. Some allocation will need to be made for drag loss, but I suspect it is less than a traditional launch vehicle. I would also suspect there is a balance between launch speed, fuel fraction reduction, and difficulty of implementation. The sweet spot between those three things will be important to hone in on.
> SEC documents show that Yaney raised $1 million in equity in 2014, the year SpinLaunch was founded, $2.9 million in equity in 2015, $2.2 million in debt in mid-2017 and another $2 million in debt in late 2017. Now Yaney confirms SpinLaunch has raised a total of $10 million to date, and that he’s personally an investor... “The current status of our Series A raise is that we are still taking meetings with potential investors and have not yet received an executed offer.”
This reminds me of the "Supergun" that Gerald Bull [2] was trying to build with Saddam Hussein [1].
One of my professors, that worked with Bull at the University of Toronto, told me all about his arms dealing/designing escapades. Bull was ultimately assassinated outside his home in Brussels.
Before he was working with Iraq, he worked on Project HARP, which was funded by the USA and Canada.
They did managed to get a projectile to space. They had plans to try and get one to orbit, using a rocket as a second stage, but the project was cancelled before that came to fruition.
> Two sources say physicists who’ve looked into the company said a potential challenge could be air resistance on the cargo when the catapult fires. Earth’s atmosphere is so dense that it could be like the cargo was hitting a brick wall upon ejection.
Reminds me of the calculation that shows Santa Claus and his reindeer, if they ever existed would have vaporized instantly at the beginning of first Christmas delivery:
...353,000 tons traveling at 650 miles per second creates enormous air resistance — this will heat the reindeer up in the same fashion as spacecraft reentering Earth’s atmosphere. The lead pair of reindeer will absorb 14.3 QUINTILLION joules of energy. Per second. Each. In short, they will burst into flame almost instantaneously, exposing the reindeer behind them, and create deafening sonic booms in their wake. The entire reindeer team will be vaporized within 4.26 thousandths of a second. Santa, meanwhile, will be subjected to centrifugal forces 17,500 times greater than gravity. A 250-pound Santa (which seems ludicrously slim) would be pinned to the back of his sleigh by 4,315,015 pounds of force. In conclusion — If Santa ever DID deliver presents on Christmas Eve, he’s dead now.
Even ignoring air resistance, if your hypothetical spacecraft centrifuge had a radius of one mile, then the spacecraft would still experience 114 g at 3000 miles per hour. If you more realistically spun up Apple's new headquarter with a diameter of 461 meters [1] to one revolution per second, that makes 3240 miles per hour, the spacecraft and the outer wall of your centrifuge would experience a centripetal acceleration of 928 g. Not going to happen. And 3000 miles per hour is also pretty slow, about half the speed in a geostationary orbit, for a low earth orbit you need about 17,500 miles per hour [2] which is almost 6 times faster and would increase the forces 36 times.
I don't think they are targeting 17,500mph. Guessing they are trying to do something sub Mach 10 for aero reasons to reduce fuel and increase structural margins that are held tight by the rocket equation. Reduced delta v = improved margins.
That's ~1000mph less delta-v needed to reach orbit. But note that the air is also moving in the same rotating frame, so there is no difference in air resistance upon exit from the launcher whether you are going east or west.
Even ignoring air resistance, if your hypothetical spacecraft centrifuge had a radius of one mile, then the spacecraft would still experience 114 g at 3000 miles per hour
We can build electronic components that are rated for 100000 g's. I think craft that can withstand 10's of g's are within our capability to build. Why not make the circle the size of the LHC? Why not larger?
Anything like this should be assumed to be launching bulk payloads or hardened payloads. For machines 10's of g's is not that big a deal. It's challenging, but quite doable. For lots of kinds of bulk cargo, it's not a big deal.
Those orbital numbers are sobering, but there may still be plenty of reason to investigate a launch mechanism where the "fuel" comes from an external source.
I haven't run the numbers, but a quick look at typical delta-V budgets [1] (which calculate atmospheric losses as 1.5 to 2 km/s of delta-v), if one could accelerate something fast enough that it escapes most of Earth's atmosphere (and only then burn for orbital velocity), you'd be saving ~17 to 20% on the delta-v requirements. Due to the nature of the Tsiolkovsky equation, that could be a very substantial saving.
That said, I'm also wondering why a centrifuge would be better than say, some kind of low pressure tube / rail, but I'm sure these guys have done their maths and believe in it.
I wonder how much it would help to have multiple projectiles firing in close succession with the payload last. Centrifuges seem like an ideal launcher for such a strategy, since you could finely tune the timing of successive releases.
If you can do that, and design a booster to round out the orbit that can withstand the acceleration you're golden. You have a system for cheaply delivering raw materials to LEO. Does a block of aluminum have sufficient tensile strength to be spun up to the required energy at reasonable diameter?
Is there a calculation to determine a max spin speed of an object? Can an object spin infinitely faster and faster if it had unlimited energy and force spinning it? Is there a name for where centrifugal force is so high that an object rips itself apart? Picturing hand tossing pizza dough as a simple example, but what about massive structures?
Could you lift the whole catapult setup to a higher altitude with a greatly reduced atmosphere before firing?
Or create a tunnel ahead of the projectile? You could use a laser to facilitate a artificial lightning strike- and fire the projectile up the thunder-tunnel of the lightning.
The idea of launching objects into space using a catapult interests me if only because my physics profs in high school and university all have at one point or another shot down the idea of space catapults. Since I don't remember exactly what their beef with space catapults was about, I figured I'd have a go and see if I could get an estimation of feasibility myself.
I am also not an aeronautical engineer (or even close to being one), but I do have some free time and I have a notepad.
According to Wiki[1], ∆V to LEO is ~8km/s plus 1.5km/s to account for drag (so a total of 9.5km/s total). The article claims that the craft exits the launch device at ~1.3km/s which leaves 8.2km/s to be accounted for. For the purposes of our math, let us assume that the craft has an alternate way to get up to speed. We'll note that SpinLaunch is not throwing their spacecraft into space at all; in fact, they're barely getting their spacecraft off the ground (relative to LEO).
Even with the significantly reduced launch speed, getting the craft spun up to speed is no small task. The equation for relating linear speed to angular speed is:
[Linear Speed] = [Rotational Speed]*[Radius]
Since we have a linear speed in mind, we can make assumptions for rotational speed or for the radius of the launching arm and solve for the other. I think revolutions per second is easier to imagine, so we'll just Fermi this out.
If your maximum angular speed is one revolution per second (~6.3rad/s), then your launching arm will need to be ~213m long. To put that in perspective, the centrifuge would need to be about four football fields in diameter. Not only that, but it would be hurling a spacecraft around the circumference once every second! Because the relationship is linear, if you want to halve the angular speed, then you'd have to double the radius. Just building a structure that can not only support the weight of a spacecraft at the tip, have a diameter of 450m, and complete full revolution every second seems like a challenge already.
Additionally, unlike a regular centrifuge, this launch structure would likely not be parallel to the ground either; you want to launch your craft into space after all. Which means that you'll have to deal with unequal forces and accelerations as you spin.
To really put things into perspective, the largest centrifuge in the world is the TsF-18 in Russia and it has a radius of 18m and can only manage 0.65 rotations per second at maximum speed[2].
But hey, I'm no mechanical engineer either, so maybe that's no big deal. Maybe introducing a vacuum in the launch structure makes such a huge difference that getting up to speed is easy enough.
How does one exactly create such a big vacuum chamber though? Even if the height of the chamber is only 5m tall, the total volume is ~710,000m3. The largest vacuum chamber is the Space Power Center and it has a maximum volume of 22,653 m3[3].
You'll need to build something that outspins the largest centrifuge in the world (by more than an order of magnitude) and outsucks the largest vacuum in the world (by more than an order of magnitude). If somehow SpinLaunch can build the most spinniest and suckiest structure ever built, you're still only 13% of the way into space.
Really puts into perspective how outrageous SpinLaunch's claims are.
I have a bit of background on rotor systems. That TsF-18 is puny compared to other rotational systems. See below.
Largest Centrifuge:
Regarding the largest centrifuge in the world, perhaps the TsF-18 in Russia has a large diameter but the JET Tokamak [1] flywheel spun a 775 TON rotor at a speed nearly 6 times what is cited for the TsF-18. The Tokamak's centrifuge's provided over 3.8 gigajoules of energy. To provide a more intuitive sense of that energy, 3GJ is equivalent to a 100kg mass traveling at 7.7km/s [2].
Fast Flywheels:
OakRidge National Laboratory [3] achieved over a 1.4 km/s tip speed and that was back in 1985.
Large Vacuum Chambers:
The Large Hadron Collider[4] is a vacuum system over 5 miles in diameter although toroidal in nature.
What sort of launch vehicle or payload is going to tolerate the Gs of being spun at such a high rate. How on earth does this even raise a dollar of funding?
It has crossed my mind in the past why we don't use something like a linear electric motor to help get rockets going off the pad, even just a hundred yards or so of acceleration assist might save a good chunk of fuel. But the rockets aren't exactly designed to have acceleration applied anywhere other than at the engine, so maybe you end up having to add the weight you'd save in fuel back in structure for the ancillary acceleration source.
At its face it does sound pretty crazy but I found some analogs of previous and ongoing projects that provide some reason to suspend disbelief.
Here's what I can find on high G launch vehicle's and payloads:
Breakthrough Starshot: Backed by physicist and VC Yuri Milner and lead by former director of NASA Ames, Peter Worden. 10,000 G's. Project Ongoing. [1]
Hiller Hornet: US Army helicopter, powered by jet turbines located at the tips of the helicopter blades. The turbines operated under 14,000 Gs. Project Completed [2]
HARP Project: Joint US Army & Canadian effort. Successfully launched electronics (radios, control systems, etc) and solid fueled rockets. 10,000+ Shock G's. Project Completed. [3]
A variety of documents come up while researching g-hardening electronics. The US Army Research Lab a a few papers. Linked one of them. 30,000 + Shock G's. Various Projects Completed and Ongoing[4]
The Hiller Hornet is likely the most applicable given it is a propulsion system operating at over 10,000 G's. I wonder how they designed the Hornet's turbine given Finite Element Analysis wasn't really a thing in 1950.
The fact that this seems demonstrably impossible on its face, and yet he is raising money, always makes me curious.
During the 'Star Wars' period in the US when the military was going to buy up thousands and thousands of launches to low earth orbit there were probably 1/2 dozen companies pursuing a single stage to orbit (SSTO) type solution. Gary Hudson, the CEO of Rotary Rocket (one of the SSTO companies at the time), gave a great example that showed that because the atmosphere was thick at ground level and thin at altitude you wanted a velocity that proportional to altitude. As he explained it, everything you do to a rocket to reinforce it adds weight, and every pound you add is another 90lbs of fuel (or what ever your mass fraction is). In that way your rocket could be as delicate as a feather if you went very slowly down near the ground and hypersonic near the edge of the atmosphere.
But systems that attempt to impart enough kinetic energy at altitude zero to allow the rocket to coast to orbit require a rocket that is structurally extremely rigid because it withstands both the force of acceleration and the atmospheric drag at its worst. That is astonishingly hard to pull off.
I a serious challenge, first you have to actually start at higher than orbital velocity because you're going to exchange a lot of energy with the air around the air frame. Volcanoes are currently the champions at throwing things up into the air, Mt St. Helens through ash over 100,000 feet up. But if you start your orbit going straight up you won't be able to miss hitting the planet post apogee. The more angled you make your initial shot, the more air you have to go through before you are in space, the more energy you're going to dump in the atmosphere, and the faster you'll have to start.
And all of that makes me really wonder about an engineering solution that fits within all those constraints. What ever it is, it will be super amazing.
The "Lazy Kerbal" approach: go straight up to get out of the atmosphere as soon as possible (stupid drag) and turn right once you pass the Kármán... Err, Kerman Line (at 70km). Start burning near apoapsis until your periapsis is >=70km as well. If your initial apoapsis was high enough, you'll make it to orbit before re-entry. If not, revert to launch. Efficient? Not at all, but certainly effective and simple.
Any viehicle of useful size de-orbiting, even from a low orbit, needs a heat shield to reach the surface intact, right? And this thing needs to be going faster than orbital speed at the surface - I don't see how that could work out without it becoming a fireball.
At one point, I was thinking that perhaps a de-orbiting vehicle needs a heat shield only because it has to fall several tens of miles before it encounters enough atmosphere to matter, during which time it accelerates, but that cannot make a difference, because at that altitude, a ballistic vehicle being launched needs to be going at least as fast as the re-entering vehicle in order to end up in the same orbit.
I wonder if you could sink a very buoyant rocket to the bottom of the ocean with a weight, and then fire up the rocket engine as it breaks through the surface of the ocean with a positive upward velocity.
Presumably drag in water is the biggest issue, which would be somewhat mitigated by the aerodynamic shape of the rocket. I wonder what is the maximum theoretical exit velocity from the ocean, using only buoyancy as propulsion.
Since we're talking about space, I am wondering when some nation can build a rotating space station.
Null-gravity is nice to play in, and some null-g research is necessary. But to work, and operate normally, null-g sucks. Especially if you need to handle fluids.
And if you need to do an emergency surgery in space, then dealing with floating blood is disgusting and biologically hazardous. As well as dealing with used surgical tools that can float around.
I would rather live in a centrifuge space station, and go to the null-g zone to conduct my work research.
It's interesting how in all scifi movies, all the spacecraft have an artificial gravity.
It's too bad China's proposed space station, will not break new ground, and have a rotating space station. They would need to spend much more money on designing and building it, than what they are willing to spend.
I've actually been posting about this a bit recently on various threads. I think a permanent rotating space station with 1G artificial gravity in low earth orbit could be the next stepping stone to opening access into outer space. Facilities with gravity would enable permanent habitation without bone and muscle loss, and manufacturing could be done with existing processes.
As to why we haven't built one already, the main reason is because early research indicated that such structures would have to be prohibitively large to avoid nausea (300+ meter diameter) and require thousands of tons of shielding. The Space Shuttle's lift capacity was also limited (only 25T of payload) and expensive ($450M/launch).
This paper suggests that humans are more tolerant of a rotating environment than early studies led us to believe, and that shielding is unnecessary for some low-Earth orbits: http://www.nss.org/settlement/space/GlobusRotationPaper.pdf (In particular, see pages 19-23)
The figures it suggests are ~600 tons of mass, 25m to 60m radius for the station. Falcon Heavy can launch 63T for $95M, and the BFR is aiming for 150T for $7M.
You might be able to get by with even less if your goal is to provide a consistent up/down and not have to velcro everything down. I don't have any sourcing for it and obviously it's from a Sci-Fi book, even if it's one that is rather well-researched, but in the Expanse series they use accelerations of around 0.3g a lot (both for stations and ship drives). Would be nice to know if they pulled that number from thin air or what the thought process behind it is.
I played enough KSP to know that this sort of thing is somewhere halfway up on the list of "things that you might think go to space but don't".
Hitting the atmosphere after accelerating will probably cause most materials outside of reentry heatshield to immediately melt, ignite and explode without particular order of these events. After turning into a molten blob of lava or a spent heatshield, it would still be nowhere close to orbital velocity and would have to fire an engine that somehow survived A) the heat and B) the intense G-forces involved.
I'll probably file this under "solar freaking roadways" and hope they don't try to fire a human in this.
And yet, also in KSP, if you can find a cheap and efficient way to cross the first hundred meter upwards, you've already saved a load of fuel. I had a setup once where my first booster was a lot of plane engines; seemed to work all right.
The last half of the atmosphere is an easy flight; drag is reduced to the point that it barely matters and most of the bigger engines have reached almost peak efficiency. Due to lack of drag you will also barely loose any velocity anymore.
The first half is hard because drag is so high but if you can sustain atleast 150m/s (or Mach 0.5) until you reach about 15km altitude and then sustain atleast 1.5G until 35km you can make it easily into space. If necessary you can try to gain some vertical velocity and abuse body-lift to drag you up higher despite not having sufficient lifting power in your boosters (if you have between 1.02 and 1.1 TWR)
Most rockets burn 80% of their fuel to get out of the atmosphere, the remaining 20% are usually good enough to get into orbit, insert into any transfer orbit you like and fly off into empty space.
Eh, I'm going to give them the benefit of the doubt, mostly because they appear to be able to attract large amounts of VC funding.
When it comes to orbital mechanics, the idea works. You just need to make your starting velocity high enough after it has decelerated though our atmosphere slows down to orbital velocity. Then you just design your ascent capsule to "deal" with the extreme declaration and heating, which isn't a huge problem: Heat shields exist, and so do g-force hardened electronics. Nobody should be under the impression that this will be used to launched anything other than small specially designed g-force hardened satellites.
It's not like "solar freaking roadways" which has blearlying obvious economic and efficiency flaws, the designs for catapult based launchers have been well studied and there is nothing physically stopping them. It's more of a engineering problem.
Honestly, I'm more concerned about the engineering practicalities of building an extremely large centrifuge spinning at some absurdly high RPM (presumably at the top of a mountain, so it bypasses some of our atmosphere)
>Eh, I'm going to give them the benefit of the doubt, mostly because they appear to be able to attract large amounts of VC funding.
Just because someone is giving them money doesn't mean they can do it.
>When it comes to orbital mechanics, the idea works.
Of course it does, similar systems have been suggested for lunar transfers to earth (IIRC). Without atmosphere these systems are trivial to implement and use. (Comparatively)
> Heat shields exist, and so do g-force hardened electronics.
Heatshields are rather large and expensive. There is also a difference between heatshields for reentry and heatshields you'd need for leaving the atmosphere efficiently.
At the moment, heatshields are basically ramming through the air and compressing it in front of the aircraft, this is most efficient in reducing velocity and can reduce the temperature at the shield somewhat.
When you fire something through the atmosphere with the goal to get it into a suborbital trajectory you need a different solution; your aircraft becomes a spike/spear, generating friction with air instead of compression. Friction is harder to deal with if I recall correctly from various pages on the topic.
you could have a covered (hyperloop) train go round and round in the antarctic (against the earth's spin) until in reached escape velocity and segment of the loop would detach and point the train up the space.
A second idea would be to create a bridge from the closest points of africa and south america, use it as a standard bridge between launches, the launches would only have to do 2g to get to escape velocity.
Would it help to catapult the cargo at high altitude where the air is rarefied? That way you have to deal with less atmosphere and the initial energy required for the catapult is smaller. Idk where, maybe the Andes?
There was a video of a marble cyclotron, that basically had a spiral like the above, but instead of tilting, the whole disk moved along the z axis (as we look at it, x up, y left and right) it was about 1 meter wide, and was oscillating at about 2hz, that was capable of ejecting marble sized objects at about 500 mph or something similar.
So I can see the method, but I doubt how payloads will survive that level of G.
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[ 3.1 ms ] story [ 178 ms ] threadCheck your own numbers at: http://www.calctool.org/CALC/phys/newtonian/centrifugal
Hyperloop, magnets, battery arrays, solar, boring company, etc sounds pretty cool.
That's reasonable _for humans_. No one's going to launch a human by this thing, though, I hope.
https://www.google.com/maps/place/Chimborazo/@-1.4685873,-79...
And if, at 6,000 feet, air pressure were half that of sea level, nobody would live in Denver and most Tibetans would be dead. Half is more like 6,000 meters.
Air density at the top of Everest is 1/3 of sea level, and because of the Earth's shape, Chimborazo's 20,000 feet (6,000 meters) is actually further from the Earth's center than Everest, so half pressure sounds pretty reasonable: https://www.npr.org/templates/story/story.php?storyId=942816...
Total impulse required to blow through drag forces is a nasty nasty power law.
It wouldn't be that difficult to make a linear rail launcher in a vacuum, or on the moon. Air resistance really is the whole problem.
If you can put the launcher above the atmosphere, it's 100% worth the effort.
I'm aware. That's the math I did in my comment, solving for 0.5 atm.
For related reasons, its difficult-to-reach, low oxygen, snow-covered summit is not ideally suited for building and maintaining a space launch site.
The thing is, with rocket size increasing, payload increases cubically while air resistance is squared. So for the really big rockets, altitude is not as big of a factor as being near the equator.
If I am not wrong, propulsive landing on drone ships uses another roughly 10% fuel (depends on launch trajectory, etc).
As fossil fuels are non-renewable, and Hydrogen expensive, I am very sure (and even hope to be correct) that in the future we will see launches from high-altitude equatorial regions, using booster-capture technologies and perhaps even terestial-power-assisted launches. Those things may reduce the fuel-cost of escape velocity by 30+%, and when we're sending enough stuff into orbit that this is too advantageous to ignore, we will do it.
But for now, the best way to go is to get really good at building bigger rockets.
And then there is this whole science and tech imperialism. Maybe Ecuadorans don't want roads and launch complexes cut out of their high mountains. Hawaii is going through this issue right now with new telescopes on Mauna Kea, and Ecuador has a strong indigenous rights movement, including the party in power at times.
>All that momentum is then harnessed to catapult a payload into space at speeds one source said could be around 3,000 miles per hour.
So that's what I was working off of. Admittedly, it's unclear who that source is. And 8k is still less than half of LEO.
And right, I'm familiar with orbital mechanics and would never turn down free dv, but you get ~90% of that even out of somewhere as far off the equator as CCAFS. The bigger benefit would be if you're looking to launch into a low inclination (equatorial) orbit you can avoid the dv required for the plane change, but that would work just as well out of CSG.
The altitude itself would be the only advantage I could see over somewhere like CSG.
I'll be back, if anyone wants to follow along at home, post your answers when you are ready.
But the heat load due to atmospheric friction would be immense and immediate.
The US built an antiballistic missile system that included a missile called Sprint [1]. It accelerated at 100G and developed temperatures of over 3000°C less than 5 seconds after launch. A video here [2].
It's a formidible engineering challenge to make a vehicle and payload that will survive such a difficult flight regime with commercially attractive economics. At this point, I don't understand SpinLaunch's advantage over earlier projectile systems (Gerald Bull) or current launchers like SpaceX. This will be interesting to follow.
[1] https://en.wikipedia.org/wiki/Sprint_(missile) [2] https://www.youtube.com/watch?v=msXtgTVMcuA
I'm very glad that this company exists, but this article doesn't help its case very much other than "Hey look, they got a load of funding".
Elon Musk wants to put 12,000 satellites into orbit. It would be very strange to me if he doesn't have someone looking into the feasibility of a giant subterranean launch tube to do something similar. Get the payload up to Mach 10 on terrestrial power and complete the orbit with a small single stage.
Hyperloop?
A launch tube would be very different, if for no other reason then the fact that you need to actually jettison the payload at one end at high speed.
1. https://en.wikipedia.org/wiki/Vactrain
"Tom Swift and his Subterranean Launch Tube"
- get it high out of the atmosphere - give it a sideways kick so that it's going fast enough as it falls back that it misses the earth
Going straight up minimises the velocity lost by drag, but means you have to pull a right angled turn, going straight sideways grossly increases drag but makes the energy for insertion less
A railgun can only put one velocity vector on a launch, you still need a rocket of some sort to pull that turn
On the point of 3,000 MPH. One of the comments on the TechCrunch article maybe provides some insight on why they aren't targeting 17,500 MPH.
"even if they need to supplement with rocket propulsion (after exiting the rotational acceleration phase), the amount of rocket energy needed will be way less. could see a huge increase in payload mass fraction as a result. maybe closer to 20 or 30% instead of 1 or 2%"
IF they are flying beyond Mach 1, drag coefficient will actually drop as Mach number increases. [1] Gravity loss will play an interesting roll as well for a system launching with a high initial velocity. There will be a balance between aerodynamic drag and gravity drag losses. The lower the angle launched, the higher the aerodynamic drag but the low the gravity drag loss. [2] Typically launch vehicles actually need more than 9.5 km/s of delta-v even though the orbital velocity for low earth orbit is only 7.8 km/s. This is due to predominantly to account for the large drag forces the velocity experiences during the vertical portion of ascent at sub, trans, and lower super sonic speeds prior to exiting the atmosphere. Some allocation will need to be made for drag loss, but I suspect it is less than a traditional launch vehicle. I would also suspect there is a balance between launch speed, fuel fraction reduction, and difficulty of implementation. The sweet spot between those three things will be important to hone in on.
[1] https://en.wikipedia.org/wiki/Drag_(physics)#/media/File:Qua... [2] https://en.wikipedia.org/wiki/Gravity_drag
Do I not understand how series of funding works?
One of my professors, that worked with Bull at the University of Toronto, told me all about his arms dealing/designing escapades. Bull was ultimately assassinated outside his home in Brussels.
[1] https://en.wikipedia.org/wiki/Project_Babylon [2] https://en.wikipedia.org/wiki/Gerald_Bull
[0] https://smbc-comics.com/soonish/
They did managed to get a projectile to space. They had plans to try and get one to orbit, using a rocket as a second stage, but the project was cancelled before that came to fruition.
Reminds me of the calculation that shows Santa Claus and his reindeer, if they ever existed would have vaporized instantly at the beginning of first Christmas delivery:
...353,000 tons traveling at 650 miles per second creates enormous air resistance — this will heat the reindeer up in the same fashion as spacecraft reentering Earth’s atmosphere. The lead pair of reindeer will absorb 14.3 QUINTILLION joules of energy. Per second. Each. In short, they will burst into flame almost instantaneously, exposing the reindeer behind them, and create deafening sonic booms in their wake. The entire reindeer team will be vaporized within 4.26 thousandths of a second. Santa, meanwhile, will be subjected to centrifugal forces 17,500 times greater than gravity. A 250-pound Santa (which seems ludicrously slim) would be pinned to the back of his sleigh by 4,315,015 pounds of force. In conclusion — If Santa ever DID deliver presents on Christmas Eve, he’s dead now.
[1] https://en.wikipedia.org/wiki/Apple_Park
[2] https://en.wikipedia.org/wiki/Orbital_speed
https://en.wikipedia.org/wiki/Turbofan
I don't think they are targeting 17,500mph. Guessing they are trying to do something sub Mach 10 for aero reasons to reduce fuel and increase structural margins that are held tight by the rocket equation. Reduced delta v = improved margins.
https://en.wikipedia.org/wiki/Tsiolkovsky_rocket_equation#/m...
That's ~1000mph less delta-v needed to reach orbit. But note that the air is also moving in the same rotating frame, so there is no difference in air resistance upon exit from the launcher whether you are going east or west.
We can build electronic components that are rated for 100000 g's. I think craft that can withstand 10's of g's are within our capability to build. Why not make the circle the size of the LHC? Why not larger?
I haven't run the numbers, but a quick look at typical delta-V budgets [1] (which calculate atmospheric losses as 1.5 to 2 km/s of delta-v), if one could accelerate something fast enough that it escapes most of Earth's atmosphere (and only then burn for orbital velocity), you'd be saving ~17 to 20% on the delta-v requirements. Due to the nature of the Tsiolkovsky equation, that could be a very substantial saving.
That said, I'm also wondering why a centrifuge would be better than say, some kind of low pressure tube / rail, but I'm sure these guys have done their maths and believe in it.
[1] https://en.wikipedia.org/wiki/Delta-v_budget
If you can do that, and design a booster to round out the orbit that can withstand the acceleration you're golden. You have a system for cheaply delivering raw materials to LEO. Does a block of aluminum have sufficient tensile strength to be spun up to the required energy at reasonable diameter?
you get a degree of wind resistance reduction there.
http://thothx.com https://en.wikipedia.org/wiki/ThothX_Tower
Nope. Eventually the centrifugal force exceeds inter-molecular forces.
Not quite what you were asking, but related https://www.wikiwand.com/en/Roche_limit
That being said I had trouble believing you could land two rocket boosters simultaneously so at worst I'm not surprised, at best it works
Or create a tunnel ahead of the projectile? You could use a laser to facilitate a artificial lightning strike- and fire the projectile up the thunder-tunnel of the lightning.
I am also not an aeronautical engineer (or even close to being one), but I do have some free time and I have a notepad.
According to Wiki[1], ∆V to LEO is ~8km/s plus 1.5km/s to account for drag (so a total of 9.5km/s total). The article claims that the craft exits the launch device at ~1.3km/s which leaves 8.2km/s to be accounted for. For the purposes of our math, let us assume that the craft has an alternate way to get up to speed. We'll note that SpinLaunch is not throwing their spacecraft into space at all; in fact, they're barely getting their spacecraft off the ground (relative to LEO).
Even with the significantly reduced launch speed, getting the craft spun up to speed is no small task. The equation for relating linear speed to angular speed is:
Since we have a linear speed in mind, we can make assumptions for rotational speed or for the radius of the launching arm and solve for the other. I think revolutions per second is easier to imagine, so we'll just Fermi this out.If your maximum angular speed is one revolution per second (~6.3rad/s), then your launching arm will need to be ~213m long. To put that in perspective, the centrifuge would need to be about four football fields in diameter. Not only that, but it would be hurling a spacecraft around the circumference once every second! Because the relationship is linear, if you want to halve the angular speed, then you'd have to double the radius. Just building a structure that can not only support the weight of a spacecraft at the tip, have a diameter of 450m, and complete full revolution every second seems like a challenge already.
Additionally, unlike a regular centrifuge, this launch structure would likely not be parallel to the ground either; you want to launch your craft into space after all. Which means that you'll have to deal with unequal forces and accelerations as you spin.
To really put things into perspective, the largest centrifuge in the world is the TsF-18 in Russia and it has a radius of 18m and can only manage 0.65 rotations per second at maximum speed[2].
But hey, I'm no mechanical engineer either, so maybe that's no big deal. Maybe introducing a vacuum in the launch structure makes such a huge difference that getting up to speed is easy enough.
How does one exactly create such a big vacuum chamber though? Even if the height of the chamber is only 5m tall, the total volume is ~710,000m3. The largest vacuum chamber is the Space Power Center and it has a maximum volume of 22,653 m3[3].
You'll need to build something that outspins the largest centrifuge in the world (by more than an order of magnitude) and outsucks the largest vacuum in the world (by more than an order of magnitude). If somehow SpinLaunch can build the most spinniest and suckiest structure ever built, you're still only 13% of the way into space.
Really puts into perspective how outrageous SpinLaunch's claims are.
1: https://en.wikipedia.org/wiki/Delta-v_budget
2: http://www.rusadventures.com/tour35.shtml
3: https://www1.grc.nasa.gov/facilities/spf/
Largest Centrifuge: Regarding the largest centrifuge in the world, perhaps the TsF-18 in Russia has a large diameter but the JET Tokamak [1] flywheel spun a 775 TON rotor at a speed nearly 6 times what is cited for the TsF-18. The Tokamak's centrifuge's provided over 3.8 gigajoules of energy. To provide a more intuitive sense of that energy, 3GJ is equivalent to a 100kg mass traveling at 7.7km/s [2].
Fast Flywheels: OakRidge National Laboratory [3] achieved over a 1.4 km/s tip speed and that was back in 1985.
Large Vacuum Chambers: The Large Hadron Collider[4] is a vacuum system over 5 miles in diameter although toroidal in nature.
1: https://www.euro-fusion.org/fusion/jet-tech/jets-flywheels/ 2: https://www.calculatorsoup.com/calculators/physics/kinetic.p... 3: http://www.guinnessworldrecords.com/world-records/fastest-ro... 4: https://en.wikipedia.org/wiki/Large_Hadron_Collider
So it does seem like it is possible to get a spacecraft spinning up to speed. It'll just require a lot of effort and even more capital.
What sort of launch vehicle or payload is going to tolerate the Gs of being spun at such a high rate. How on earth does this even raise a dollar of funding?
It has crossed my mind in the past why we don't use something like a linear electric motor to help get rockets going off the pad, even just a hundred yards or so of acceleration assist might save a good chunk of fuel. But the rockets aren't exactly designed to have acceleration applied anywhere other than at the engine, so maybe you end up having to add the weight you'd save in fuel back in structure for the ancillary acceleration source.
Here's what I can find on high G launch vehicle's and payloads:
Breakthrough Starshot: Backed by physicist and VC Yuri Milner and lead by former director of NASA Ames, Peter Worden. 10,000 G's. Project Ongoing. [1]
Hiller Hornet: US Army helicopter, powered by jet turbines located at the tips of the helicopter blades. The turbines operated under 14,000 Gs. Project Completed [2]
HARP Project: Joint US Army & Canadian effort. Successfully launched electronics (radios, control systems, etc) and solid fueled rockets. 10,000+ Shock G's. Project Completed. [3]
A variety of documents come up while researching g-hardening electronics. The US Army Research Lab a a few papers. Linked one of them. 30,000 + Shock G's. Various Projects Completed and Ongoing[4]
The Hiller Hornet is likely the most applicable given it is a propulsion system operating at over 10,000 G's. I wonder how they designed the Hornet's turbine given Finite Element Analysis wasn't really a thing in 1950.
[1] https://en.wikipedia.org/wiki/Breakthrough_Starshot [2] http://www.aviastar.org/helicopters_eng/hiller_hoe-1.php [3] http://www.astronautix.com/a/abriefhistoheharpproject.html [4] http://www.arl.army.mil/arlreports/2006/ARL-TR-3705.pdf
During the 'Star Wars' period in the US when the military was going to buy up thousands and thousands of launches to low earth orbit there were probably 1/2 dozen companies pursuing a single stage to orbit (SSTO) type solution. Gary Hudson, the CEO of Rotary Rocket (one of the SSTO companies at the time), gave a great example that showed that because the atmosphere was thick at ground level and thin at altitude you wanted a velocity that proportional to altitude. As he explained it, everything you do to a rocket to reinforce it adds weight, and every pound you add is another 90lbs of fuel (or what ever your mass fraction is). In that way your rocket could be as delicate as a feather if you went very slowly down near the ground and hypersonic near the edge of the atmosphere.
But systems that attempt to impart enough kinetic energy at altitude zero to allow the rocket to coast to orbit require a rocket that is structurally extremely rigid because it withstands both the force of acceleration and the atmospheric drag at its worst. That is astonishingly hard to pull off.
I a serious challenge, first you have to actually start at higher than orbital velocity because you're going to exchange a lot of energy with the air around the air frame. Volcanoes are currently the champions at throwing things up into the air, Mt St. Helens through ash over 100,000 feet up. But if you start your orbit going straight up you won't be able to miss hitting the planet post apogee. The more angled you make your initial shot, the more air you have to go through before you are in space, the more energy you're going to dump in the atmosphere, and the faster you'll have to start.
And all of that makes me really wonder about an engineering solution that fits within all those constraints. What ever it is, it will be super amazing.
Not to mention that the payload must also be able to survive these high accelerations.
At one point, I was thinking that perhaps a de-orbiting vehicle needs a heat shield only because it has to fall several tens of miles before it encounters enough atmosphere to matter, during which time it accelerates, but that cannot make a difference, because at that altitude, a ballistic vehicle being launched needs to be going at least as fast as the re-entering vehicle in order to end up in the same orbit.
Presumably drag in water is the biggest issue, which would be somewhat mitigated by the aerodynamic shape of the rocket. I wonder what is the maximum theoretical exit velocity from the ocean, using only buoyancy as propulsion.
https://www.quora.com/Why-dont-we-launch-spaceships-from-und...
Null-gravity is nice to play in, and some null-g research is necessary. But to work, and operate normally, null-g sucks. Especially if you need to handle fluids.
And if you need to do an emergency surgery in space, then dealing with floating blood is disgusting and biologically hazardous. As well as dealing with used surgical tools that can float around.
I would rather live in a centrifuge space station, and go to the null-g zone to conduct my work research.
It's interesting how in all scifi movies, all the spacecraft have an artificial gravity.
It's too bad China's proposed space station, will not break new ground, and have a rotating space station. They would need to spend much more money on designing and building it, than what they are willing to spend.
Possibly related to the fact that all film studios are subject to gravity.
As to why we haven't built one already, the main reason is because early research indicated that such structures would have to be prohibitively large to avoid nausea (300+ meter diameter) and require thousands of tons of shielding. The Space Shuttle's lift capacity was also limited (only 25T of payload) and expensive ($450M/launch).
This paper suggests that humans are more tolerant of a rotating environment than early studies led us to believe, and that shielding is unnecessary for some low-Earth orbits: http://www.nss.org/settlement/space/GlobusRotationPaper.pdf (In particular, see pages 19-23)
The figures it suggests are ~600 tons of mass, 25m to 60m radius for the station. Falcon Heavy can launch 63T for $95M, and the BFR is aiming for 150T for $7M.
It's unlikely a full g is necessary, anyway. A half would do well.
Hitting the atmosphere after accelerating will probably cause most materials outside of reentry heatshield to immediately melt, ignite and explode without particular order of these events. After turning into a molten blob of lava or a spent heatshield, it would still be nowhere close to orbital velocity and would have to fire an engine that somehow survived A) the heat and B) the intense G-forces involved.
I'll probably file this under "solar freaking roadways" and hope they don't try to fire a human in this.
The first half is hard because drag is so high but if you can sustain atleast 150m/s (or Mach 0.5) until you reach about 15km altitude and then sustain atleast 1.5G until 35km you can make it easily into space. If necessary you can try to gain some vertical velocity and abuse body-lift to drag you up higher despite not having sufficient lifting power in your boosters (if you have between 1.02 and 1.1 TWR)
Most rockets burn 80% of their fuel to get out of the atmosphere, the remaining 20% are usually good enough to get into orbit, insert into any transfer orbit you like and fly off into empty space.
When it comes to orbital mechanics, the idea works. You just need to make your starting velocity high enough after it has decelerated though our atmosphere slows down to orbital velocity. Then you just design your ascent capsule to "deal" with the extreme declaration and heating, which isn't a huge problem: Heat shields exist, and so do g-force hardened electronics. Nobody should be under the impression that this will be used to launched anything other than small specially designed g-force hardened satellites.
It's not like "solar freaking roadways" which has blearlying obvious economic and efficiency flaws, the designs for catapult based launchers have been well studied and there is nothing physically stopping them. It's more of a engineering problem.
Honestly, I'm more concerned about the engineering practicalities of building an extremely large centrifuge spinning at some absurdly high RPM (presumably at the top of a mountain, so it bypasses some of our atmosphere)
Just because someone is giving them money doesn't mean they can do it.
>When it comes to orbital mechanics, the idea works.
Of course it does, similar systems have been suggested for lunar transfers to earth (IIRC). Without atmosphere these systems are trivial to implement and use. (Comparatively)
> Heat shields exist, and so do g-force hardened electronics.
Heatshields are rather large and expensive. There is also a difference between heatshields for reentry and heatshields you'd need for leaving the atmosphere efficiently.
At the moment, heatshields are basically ramming through the air and compressing it in front of the aircraft, this is most efficient in reducing velocity and can reduce the temperature at the shield somewhat.
When you fire something through the atmosphere with the goal to get it into a suborbital trajectory you need a different solution; your aircraft becomes a spike/spear, generating friction with air instead of compression. Friction is harder to deal with if I recall correctly from various pages on the topic.
A second idea would be to create a bridge from the closest points of africa and south america, use it as a standard bridge between launches, the launches would only have to do 2g to get to escape velocity.
Basically its a large disk with a spiral track on the inside. The disk is then oscillated in along its flat plane, like this: https://www.youtube.com/watch?v=OPLzsRojo_A
There was a video of a marble cyclotron, that basically had a spiral like the above, but instead of tilting, the whole disk moved along the z axis (as we look at it, x up, y left and right) it was about 1 meter wide, and was oscillating at about 2hz, that was capable of ejecting marble sized objects at about 500 mph or something similar.
So I can see the method, but I doubt how payloads will survive that level of G.
edit This idea: https://www.youtube.com/watch?v=UnZWu1FXxd4