This might also explain why we've got fewer "UFO" sightings than we used to even 20-30 years ago, in spite of all of us carrying cameras in our pockets (apart from the fact that many of these were hoaxes to begin with).
SpaceX has best in class hypersonic combustion CFD capability that runs on a GPU. Written in-house.
I'm sure one can speculate. In the video they do talk about all the possible intermediate species, so one might have to add air molecules (which can break apart and add to the reactants) to the mix. But yeah, lots of unknowns. Doing experiments and comparing to the simulations should help figure it out. The problem has traditionally been an inability to do the simulations, but that's possible now.
Compare SpaceX and SLS / Ares.
there are still places which put models into chambers. (I know, I used to work behind this one, and we have a steel membrane punched through by the airblast to make the shockwave from the dumpster out back)
the part called "primary diaphragm"
It's also much easier to ignore these things, since most of them are just ordinary things that the person who took the video doesn't know how to identify. If you made a great UFO hoax now, chances are nobody would ever see it who was the least interested in looking at it skeptically, because it would be lost in the noise of people seeing trash bags blowing in the wind.
So I think that https://xkcd.com/1235/ is premature about UFOs, though I think it's pretty conclusive about lake monsters and bigfoot (although if you look around, people see a lot of strange looking mangy bears that people think are bigfoot).
At night, though, we can still see a lot better than the cameras in our phones.
For instance, I saw something weird one night. It was big enough and bright enough that I had no trouble seeing it, but my iPhone 6 plus camera just got a vague blob. This was not a UFO, since among other things it was on the ground, but it illustrates the limits of the cameras.
(In case anyone is curious, I'll describe what I saw at the end of this comment).
The most interesting current UFO reports I've seen (interesting in the sense that they are probably something real--not aliens or supernatural stuff of course, just either an unknown natural phenomenon or some manmade thing that is not well known) are where people see what looks like a star, but moving in a straight line (sometimes pausing now and then), that then suddenly changes direction and zooms off over the horizon very suddenly. No way is a phone camera going to capture that.
The weird thing I saw: this was the night before the 2017 total solar eclipse in the US. I was parked in a big field that had been turned into a car camping area for the eclipse and the day/night before.
A few rows down and a couple dozen spots to the left I saw what looked like two copies of a movie or TV show side by side, kind of wavy and translucent. It looked like either they had hung up a sheet and were projecting video onto it, or they had a couple of flat panel displays and there was a sheet between them and me.
Then what looked like an arm poked up. If they had been in a tent I would have said it looked like someone in the tent was pushing up on the top, stretching the tent--but tents were not allowed. (There were some trucks and vans that had tent-like extensions on top, so they may have had something like that). The arm moved back and forth a while, and then was apparently pulled down.
Then what looked like a leg replaced it...but it was a huge leg. It looked to be about 2 meters long. The "leg" started moving rapidly back and forth along what would be the length of the vehicle. After it had done this a few times, it disappeared. (There may have also been an arm or two mixed in here).
Then a light rose up from the middle of the vehicle. I though it might be a flashlight. It then stopped rising, and started turning. It continued turning until it was pointing right at my car, and then it stopped turning for about 10 seconds. Finally, it resumed turning until it went all the way around, and then it descended, and things were dark, with no activity at that other vehicle.
I thought "what the hell was all that?".
Then the images came back, and the whole thing repeated!
The third time it happened I had my phone out and the camera recording. Unfortunately, all the recording shows is that there was some lights moving around in that direction.
It's called you were on mushrooms bro.
There was an annual organized trip to Disneyland at my school, and a large fraction of the student body went. I decided not to go that year, and picked that night to try mushrooms because the campus would be sparsely populated. I figured that the fewer people there were around, the fewer chances there were for something to go wrong.
I had done a lot of reading, and talked to a lot of people who had used them, so that I knew what to expect on a mushroom trip. I was seeing and feeling the effects I expected, and having a good time.
Then several people I did not recognize walked by, speaking Chinese! Then more Chinese speaking people walked by. That was weird. I started wandering around campus, and kept running into people I did not recognize who were speaking Chinese.
This was very unusual. My school (Caltech) was small enough that every student could normally recognize every other student by sight, so seeing so many strangers was odd enough...but that they were all speaking Chinese was just freaky.
Nothing I had read or heard said that mushrooms could make one have that kind of hallucination, so I was starting to get seriously worried that I was on more than just mushrooms.
It turned out that I was not hallucinating. I had not been the only one who decided to take advantage of most Caltech students going to Disneyland that night. The Chinese Students Association picked that night to throw a party and invite the Chinese students from UCLA and USC and nearly every other college in the Los Angeles area.
If you every watched a jet moving at ~600mph then I think we can agree something going 10 times as fast would still be easy to notice.
Jets cross out of view in a couple minutes and are big (and probably flying lower). So a little thing in ~20 seconds.
Even with the tiny size the speed is still a big factor because the opportunity to sight the object from a given location will be pretty short.
If you're a fan of the SR-71, this hilarious interview with pilot Brian Shul is definitely worth watching:
Such limited manoeuvring also requires planning and 90 minutes between passes. Lots of opportunity for bad guys to push their missile back into a hangar.
An atmospheric aircraft can follow an arbitrary course to take in as many targets as required, can be rerouted on a moment's notice and can approach from unexpected vectors to catch the target out in the open.
Judging by the publicly-released payload specs for the DoD-operated Boeing X-37 spaceplane, it should be able to deliver about 2000+ L of hydrazine, compressed Xenon, or other suitable fuel in a single launch.
Edit: It looks like DARPA has been experimenting with "space gas station" experiments since at least 2007.
A LOT of fuel. So much so that even if lifetime wasn't an issue, it makes more sense to launch additional satellites in the proper inclination, rather than moving one.
I know that, in one instance, a company wanted to use the moon's gravity to change a satellite's inclination, as it was cheaper to all the way to the moon and back (and then circularize again). That maneuver seems to be patented, though.
The high altitude spy planes (U2, SR-71) were mostly to prevent being shot down; surviving to return the film to base.
Drones don't need to bring film back, and it's not such a big deal if a few of them are lost.
- There is no real need for SR-72 to be manned on all flights;
- Hypersonic plane would be very good for small (2m wingspan) drone delivery behind the enemy lines fast (in half an hour). This was already a concept with M-21/D-21, but now the drone part can be much smaller and one plane could carry more than 4 of those.
Satellites are quite limited when you need to make fast decisions. Hypersonic plane will move about 7 times slower than an optical recce satellite, yet it can maneuver very fast if you need to relocate the imaging area and can get at least 10 times closer to the target. Instruments can be selected/improved even after the first flight of the plane -- not true for the satellites.
Though I suppose that you could try to make your drones so cheap and in such volume that shooting them down becomes logistically and economically infeasible, but that's another strategy entirely.
The whole idea of the SR-71 was that it went so fast that SAMs could just barely not catch up to it before they ran out of fuel. Any other plane couldn't outrun them, but the Blackbird? Well, Mach 3.4 will give you some breathing room.
Missiles and radar tend to operate in a "bubble". Even with the Russian S200 system at 190 miles range, the time you spend in that "bubble" when you're at 70k ft is not often long enough to do anything. That also assumes the aircraft directly overflies the battery. You can play games like pointing the camera sideways and observing from an angle if you know there are going to be angry people with guns nearby.
I imagine thought a little snake left/right might compromise getting the images that was the point of the mission.
The "Misty" satellites came up on HN last week related to the SpaceX launch and failure.
"A week after launch, reports were released from the Soviets that six bits of debris had been detected suggesting an explosion had occurred. The Pentagon announced that any debris would decay after six weeks. The amateur astronomers and observers that were tracking this object only catalogued five out of the six pieces. Six months later an unidentified satellite was discovered in orbit on a similar trajectory to that of the classified payload was released, leading the satellite spotters to suspect it was the missing piece, nick-named Misty. However a couple of noticeable manoeuvres later, Misty disappeared again. Perhaps the ‘explosion’ was a decoy to put Misty into place unbeknownst to the Russians."
Here's a diagram of their style orbit: https://www.planet.com/docs/spec-sheets/spacecraft-ops/monit...
2. The Space Shuttle suffered from many costly design compromises due to its excessively large hangar bay.
Given #1 and #2, there are four likely kinds of classified missions that the Space Shuttle undertook.
1. Stealing Russian military satellites.
2. Returning American military satellites to Earth.
3. Launching American military satellites into unpredictable orbits.
4. Refueling American military satellites, which allowed them to change to a new, unpredictable orbit.
It's entirely possible that the Space Shuttle only engaged in some of these tasks... But it's difficult to conclude that given the very odd design of the space shuttle, and the very lengthy missions that it undertook, that no satellite servicing/orbital shenanigans took place.
Yes, satellites can change orbits using on-board fuel reserves, but due to the tyranny of the rocket equation, those reserves are limited - and are unlikely to allow a very large inclination change (Inclination changes are incredibly fuel-expensive.)
Likewise there is no such thing as an unpredictable orbit. Orbits are predictable, by definition. Any country with a good set of radars, telescopes, and IR sensors can find the exact orbit of every single satellite.
The Space Shuttle was certainly used for launching American military satellites into regular predictable orbits. They might have done a refueling mission at some point as a proof-of-concept but even that seems unlikely considering that it's always cheaper to just build and launch a new satellite.
If SpaceX succeeds at lowering launch costs then it would be easier to launch many small and disposable spy satellites than ever to bother refueling one.
Nonetheless, the point is that satellites are limited as to opportunities due to limited availability and limited time windows. This does argue that there ought to be a role for an SR-71. I'm not sure there's much of a role for an SR-72, but certainly for the SR-71 there ought to be.
stealthy or speedy aircraft could work over more hostile places and add to the satellite capabilities. Maybe there are things you can sense from 10 miles up that you can't at 100mi. And maybe there's some brand new gear that you don't have in space yet. And maybe you want to time your picture with some unpredictable events on short notice. there are a ton of reasons to have this variety of capabilities.
When you control the sky’s you don’t need to fly at 6000 mph.
We have bases in Pakistan and Afghanistan, for example.
Which mission profiles are you describing that are actually needed to fly at hypersonic speed? A lot of these countries are quite small for that speed. A 100 miles a minute.
Mission profiles better suited to a plane than a satellite: anything that requires loitering, returning to a target, anything that requires a curved path that a satellite cannot fly or anything that requires close up - optics on satellites are good, but fundamental physics limits the achievable resolution. Hypersonic speed might not be required to fulfill the actual mission, but it allows shorter response times on all spots. It also would allow evading most intercept attempts.
So, technically and at least according to ICAO, these birds flew/fly above a nation's sovereign airspace. That doesn't stop a nation-state from attempting to down one of these birds, of course.
I think the general rule is that sovereign airspace covers air-breathing planes but not spacecraft. From your link:
> There is no international agreement on the vertical extent of sovereign airspace, with suggestions ranging from about 30 km (19 mi)—the extent of the highest aircraft and balloons—to about 160 km (99 mi)—the lowest extent of short-term stable orbits. The Fédération Aéronautique Internationale has established the Kármán line—at an altitude of 100 km (62 mi)—as the boundary between the Earth's atmosphere and outer space, while the United States considers anyone who has flown above 80 kilometres (50 mi) to be an astronaut.
I could see utility in being able to rapidly deploy a team of special ops, or specialized unanticipated equipment, to a faraway location. That it can do things a missile can without being a missile is also useful. (Suppose you need a bunch of drones over a random location. You could launch a missile and risk (a) breaking your birds in launch and (b) someone thinking you're flying nukes. Or, you could use this plane.)
This won't be landing on any improvised airstrips, and a hypersonic configuration won't be able to go slow enough to drop paratroopers.
The more interesting impact would be on the design of the plane doing the drop. While I think you could keep the paratroopers alive, I'm skeptical there's any way you can go that fast and drop a large container. I would expect the process to destroy the plane by making it too unstable.
The Osprey is probably the fastest troop carrier, so you would need to identify some use cases it can’t do then figure out if the cost is worth it. Traditionally SF get there by jumping in and then hiking cross-country, is there a use case for getting them on the ground in a couple of hours?
Galus, what do you base your claim on that a hypersonic config can't go "slow enough"?
2. Higher resolution imaging could still be quite useful. For example, if we could possibly find all of the Chinese DF-21B anti-ship ballistic missile launchers, this erodes the deterrent effect of that weapon, which then increases the value of the US aircraft carrier groups.
Missiles are generally powered by rocket motors - they don't need air intake.
Missiles are also generally one-time-use - you send it somewhere and don't expect to reuse it (also it usually explodes)
I suppose it might be possible to increase payload per fuel efficiency, but the only reason the military would probably care about that is cost, and the rocket engineering is already paid for and proven.
https://en.wikipedia.org/wiki/AGM-86_ALCM - "All variants of the AGM-86 missile are powered by a Williams F107 turbofan jet engine"
https://en.wikipedia.org/wiki/Tomahawk_(missile) - "After achieving flight, the missile's wings are unfolded for lift, the airscoop is exposed and the turbofan engine is employed for cruise flight."
https://en.wikipedia.org/wiki/Harpoon_(missile) - "Power plant: Teledyne CAE J402 turbojet, 660 lb (300 kg)-force (2.9 kN) thrust, and a solid-propellant booster for surface and submarine launches"
https://en.wikipedia.org/wiki/Kh-55 - "It is powered by a single 400 kgf Ukrainian-made, Motor Sich JSC R95-300 turbofan engine, with pop-out wings for cruising efficiency."
The hypersonic missiles use a rocket to get up to speed, like:
https://en.wikipedia.org/wiki/Zircon_(missile) - "A booster stage with solid-fuel engines accelerates it to supersonic speeds, after which a scramjet motor in the second stage accelerates it to hypersonic speeds."
It’s also not entirely true, tomahawk cruise missiles for example use turbofan engines with a solid state booster.
USGS on seismographs and sonic booms generally:
The "digital transformation" part alone gives this up as vaporware...
Even back then, supersonic, let alone hypersonic, aviation was such a pipe dream for civilian aviation. Not saying it can’t be done, but I can’t imagine the breakthroughs that need to be made would be made outside of any context short of a World War.
Let me list the problems:
1. Materials Science. Very hard to design materials
that survive those kind of stresses, and that you know will last 30+ years. Airplanes routinely have 60 year life cycles, so 30 years of material survival is the minimum. The stresses on these things are huge. The Concorde would actually expand 10 inches from head-to-tail during flight because of the heat.
2. Overpromising dating back 40 years. My favorite example is Ronald Reagan promising an “Orient Express” that would be 90 minutes New York to Tokyo. That was in his 1986 “State of the Union”.
3. Acceleration. Flying Mach 6 is one thing. Having a plane that can accelerate up to that speed fast enough that the flight doesn’t already end, AND THEN slow down an equal amount, is another thing.
4. Sound. This sounds like a nuisance thing, until you hear one of these aircrafts in action. THEY ARE SO DAMN LOUD. It’s a health and safety issue almost. I would compare it to being around artillery fire, maybe worse. It stays with you for days.
The Japanese and Australians from time to time do some good work on this kind of aviation. Boeing had a civilian supersonic project in the 70’s, but it’s all been given up except for the occasional private jet or military experiment.
One word: Concorde.
Makes one wonder how much the mainstream hacker news threads are suffering from similar problems that I just can't perceive.
This is a path which once you start down, you're somewhat committed to in perpetuity.
Is England under duress? Is France under duress? Are the Dutch under duress? Is Spain under duress?
Most importantly, at what point do we ask ourselves what it is that we are even defending? 50% of the population making less than 5 richest people?
Those countries were under duress for years during the Cold War, and were protected by the U.S.'s massive military spending during that time. And given that Russia recently annexed part of a sovereign country, those times may be back.
A useful perspective to look at the military budget through is: consider that outspending by multiples every other military power averts wars (because a WW2-scale war with the US would be suicidal). What's the price you would put on avoiding a war at that scale?
In other words China and Russia may contemplate fighting WW3 now rather than waiting to be leap frogged. Fun.
The US and China are now spending $1+ trillion per year on their militaries. The combined sum will likely eclipse the entire value of Russia's annual economic output in the next 15-20 years.
US spending one trillion dollars, and China spending one trillion dollars, it doesn't guarantee that they will be technologically matched.
It does not have to be symmetric. You only have to spend as much as you need to nullify an adversary's capability. Ex, one does not need to manufacture an aircraft carrier to counter one, you just need to take it out of action.
Well, by definition, since half the components probably originate there.
They made a computer model that wouldn't immediately destroy itself. Let's calm down a bit.
"Digitally print" is used as a synonym for "3D print" or "additively manufacture."