Can someone explain what the nominal "velocity" counter means? I thought it made sense going up (although I wasn't sure why its rate of change---which would be the acceleration---seemed to increase a bit), but then I was totally baffled after the separation. It goes down from 2900 to 2500, then back up to 2920, then it plummets to around 300, then gently lowers down to the 50 or so that it's at for splashdown; there is no discernible change in acceleration when the chutes blow around 190.
Here's what I would have expected: numbers increasing at a relatively constant rate until separation, then a rapid decrease to zero (and since 1mph ~~ .5m/s, expected decrease at about 20mph/s), then increasing again (maybe with a negative sign) until atmosphere, then a decrease to terminal velocity, then another big decrease when the chutes blow.
So aside from the fact that there is no direction (not even a minus sign), so it's at best a speed counter, there still is something I really don't understand about that number. But... what?
The velocity counter means airspeed. The reason you aren't seeing the results you expect is that the shuttle launches in a ballistic arc to enter orbit. The boosters also follow that same trajectory, but lack orbital velocity. So what you see is them losing speed until they reach the peak of that arc, then gaining speed as they are drawn back towards the earth.
The shuttle isn't going straight upward at separation. It's actually going mostly eastward, so when the boosters separate they retain most of their speed, and even regain a bit as they drop through the ultra-thin upper atmosphere.
You're right about the rest -- a decrease to terminal velocity and then a big decrease as the chutes take effect.
But there wasn't a big decrease when the chutes deployed. It took a while. I found that odd. I expected an immediate decrease in speed the second the chutes deployed. Maybe the counter wasn't synched with the video?
> "there wasn't a big decrease when the chutes deployed. It took a while."
They take some time to completely expand. They're actually deployed in a constricted ("reefed") configuration, and then after several seconds they're allowed to fully open.
They're also trying to slow down a large piece of metal -- the booster rockets are about 150 feet long and weigh about 200,000 pounds (empty weight) each. The chutes produce a lot of force, but they're pulling on a lot of mass too (acceleration = force/mass.)
The rocket engine was still running after separation and we could not see when it stopped propelling the rocket so it is difficult to really understand its motion by just using its interaction with gravity and the athmosphere as our only variables affecting its behavior.
My guess on why accelerating is increasing is that both air resistance and gravity is decreasing the higher you go (the former much more than the latter). So with constant force, the acceleration would increase.
Agreed on the audio track - it does an excellent job of reflecting the extremely inhospitable conditions to which the boosters are subjected. I'm also curious about the cameras, although I wish they had been running at fixed sensitivity rather than constantly trying to balance between black space and a very reflective Earth.
I wonder how much the audio was post processed (it says at the end of the video that Skywalker Sound worked on it). I also wonder how much information can be derived about the internal structure of the boosters based on the harmonics of the vibrations picked up by the microphones while outside the atmosphere.
I was wondering what that buildup of cloud was and then I saw the velocity breaking 760 MPH and realized it was breaking the sound barrier. Pretty awesome stuff!
I'm surprised they landed so close together. amazing. Also, can anyone tell me why they are slowing down as they fall towards earth (before the parachutes deploy)? Shouldn't they be speeding up by 9.8m/s as they fall?
Ahh, got it. I expected more of a speedup as they dropped the last mile or so. I guess they didn't slowdown very fast right away because there wasn't much air up in the upper atmosphere.
this doesnt make sense to me. On the orbit they look like they gaining a distance between each other. Any distance on that altitude would be 150-fold back on earth. How come they landed less than 20m from each other, no idea. Anyone?
Once they hit the atmosphere, their lateral motion (groundspeed) is probably greatly reduced by air resistance, while theory downward motion is maintained by gravity. So shortly after reentry, they probably mostly stop diverging.
Still, though, I feel like I would be hard-pressed to throw two objects from space and have them land within sight of each other.
The 150-fold figure might apply if they actually took divergent paths back to Earth by a degree or two, but that doesn't seem to be the case--they took very nearly parallel tracks, with a few meteres of random jostling one way or the other. I'm not sure how much effect the explosive detachment from the shuttle+main tank has though / which way those forces are directed.
Where do you get the figure of 150? I reason that if they are nearly identical pieces, and falling near each other, wind and other atmospheric forces would shift them about equivalently. Even if they veered hundreds of miles, it seems reasonable that they would do so together.
150 was a wild guess. I think there is so many variables when they orbit in space and drop to Earth, that I don't see it that simple to land one next to another. Its like taking two peppercorns and throwing them at the same time, very close to each other from the Empire State building.
well they are similar objects, undergoing the same forces, and they were released from nearly the same spot (from which they were both traveling in the same direction) the difference is mostly from the forces due to slight differences in tumbling motion when interacting with the atmosphere. just try thinking about conducting the same situation with out an atmosphere. the objects would follow the same trajectory from the moment they were released back to the ground. I'm sure nasa has to try to calculate the specifics/landing location, you dont want SRB's falling on property.
I think you can see ships in the background of the video, presumably for recovery. So maybe they know pretty close to where they land, close enough that they don't have to worry about hitting the ships. That's impressive.
you can't imagine a simple physics problem? i understand that they DID travel through an atmosphere, but the basic mechanics involved can be understood just using projectile motion equation without taking the effects of air drag.
I think you're forgetting to take air resistance and other factors into account? Google terminal velocity.
Edit: If you meant prior to re-entry of Earth's atmosphere, the force of gravity is changing the objects course, thereby affecting acceleration, speed, velocity, etc
Specifically, direction as well as speed. But yes, that would have self-answered my question about what the numbers mean (by showing the "sideways" component).
they should be speeding up but not until infinity of course. At some point (here around 300mph) their size with "glide" in the atmosphere causing it to slow down.
It was interesting to watch how they gained speed on the orbit while being sucked by Earth gravity, and then quickly hit the breaks when atmosphere/air got thicker... awesome! Must be amazing feeling, given you would have 3000mph-withstand material, to actually "drop" yourself from space to Earth :)
well they were released from the same point in space, and since they are similar objects traveling nearly at the same velocity, its not that surprising. im sure nasa calculated for it, and towards the end of the video there looked like a ship on the horizon for pick up.
Did nobody bother watching the credits at the end? The sound design credits mention Ben Burtt, the sound designer for Star Wars (think: Darth Vader's breathing, that lightsaber fwoom noise, etc.).
Sort of makes me wonder how much of the sound in that video was real. I really want to believe that's what space sounds like. :)
Edit: Oh, I guess that's his son! A splendid lineage.
One of the reasons the Concorde never really succeeded was due to the nature of faster than sound travel. A sonic boom doesn't just happen as you pass the sound barrier, but rather trails behind an aircraft the entire time it is traveling over that critical speed. This resulted in the Concorde only being able to travel faster than the speed of sound when it was over water (hence it's primary use for travel between New York and Paris or London).
But what if you could travel where there is no air?
Suborbital space flight means that any place on the globe is a 2 hour flight away. This will happen, and I am confident that I will travel in space before I die.
One of the other reasons Concorde never really succeeded was due to the other part of the nature of faster than sound travel: it uses a huge amount of fuel, which is a major expense. For comparison, the 747-100 (which made its first flight just before Concorde's) used perhaps 1.1 times more fuel to cross the Atlantic but carried about 4 times as many passengers.
Suborbital space flight means any place on the globe is a 2 hour flight away, but the fuel costs are pretty high. I expect such a service to one day exist, but I don't expect to be able to afford it.
yeah we need a new way of powering our ships. for it to be affordable. the only cheap and responsible way i think would be to use solar thermal power and use molten salt storage onboard.
I hear what you saying, but is there anything else than an issue of material being burnt in atmosphere due to speed lost/air friction? Gravity will make sure you will get back on Earth so its not like you have to spend another million bucks to get on earth. Given you have a heat/damage-proof can and know when to open parachutes (I know its more complicated than that), you should be good to go (I mean - come back).
I would guess that just getting from the ground into space requires more fuel than traveling by plane 180 degrees around the world (the longest possible great circle route for air travel). And it's not just a maturer of waiting for improved efficiency. Reaching a given altitude will always require energy proportional to mass and desired altitude (until we build a space elevator and can offset that by dropping a counterweight down shaft number 2).
The big fuel tank has significant foam insulation because its two major fuel components are kept very cold (liquid oxygen at -300F/-180C; liquid hydrogen at -420F/-250C) and the external surface gets fairly hot at the speeds the shuttle travels.
Lockheed designed the tank with insulation outside the main shell, and it's never held together very well. I've spoken to retired engineers from another company who designed a competing tank with internal insulation; they're still upset their version didn't get picked. I've never heard a clear explanation as to the specific reasoning for Lockheed or NASA's decisions.
Of particular note, the Columbia disaster was caused by one of those foam pieces breaking off during takeoff and damaging the thermal protective tiles on the shuttle's wing. During re-entry, the edge of the wings reaches a temperature of around 3000 F; damage to the protective tiles basically allowed hot air to burn through the wing.
This is an appropriate place as any. WE have an ambitious start up idea to launch loaves of bread into space so that they will re-enter as toast, perfectly cooked to perfection and delivered right to your door.
Running the numbers, you need at least 1 MJ/kg to get past the 100km limit into what's officially considered "outer space". That's only factoring in Earth's gravity.
If we could do it with purely electrical motors, then assuming you pay 10 cents per kilowatt hour and only have a conversion efficiency of 75% into actual lifting power, it would only cost you $0.04/kg energy-wise to get up there. Assuming that you'd need to take an environment of, say, 10,000 kg with you, the marginal cost would still only be about $400. That's something of an ideal case, the "space elevator" proposal. Actually there might even be a possibility to use counterweights somehow to make it even cheaper.
Solid rocket fuel, the numbers are a little harder to come by. It sounds like the active ingredient is usually aluminum. One page on Wikipedia suggests that aluminum has an energy density of 31 MJ/kg (and my calculations based on Wikipedia's "aluminum oxide" page agree) and that only 16% of solid rocket fuel is aluminum. So that's 5 MJ/kg. However, this is a little smaller because it basically needs to push itself up along with you -- it's 1 MJ/kg to bring anything up to space, remember, so 1 kg can lift roughly 5 kg of stuff, but the 1kg of fuel is itself part of that 5 kg. So we're at roughly 4 MJ/kg if you take into account that the fuel more or less has to push its own way up with you. (Not all the way, of course, but I'm too lazy to do the calculation properly and there's wind resistance anyway.)
The first rocketry site on Google says that they'll sell you 20 pounds of rocket fuel (9 kg) for something like 200 bucks, or $22/kg. With the conversion factor of 4 kg lifted / kg fuel, the equivalent number is about 550 times higher -- $5.50 per kg that you want to send into space, and the marginal cost for our 10,000 kg environment is presumably then something like $55,000.
Can we do better by bulk? Google says people sell the main ingredient -- ammonium perchlorate -- at $3,000 per metric ton. Aluminum is a bit pricier, but I can find people selling large chunks at about $500/50kg, adding about $1,500 to the above. Adding in the cost of the plastic binding, the raw fuel components might cost $5/kg. So you're not going to get cheaper with rocket fuel than around $15,000 per flight.
Of course, the spacecraft is going to be the more expensive bit, I'm sure. But that's more complicated because maybe you can amortize that cost over many successful runs. I'm just saying that, even without that, based on fuel alone, it's still going to be an order of magnitude more expensive than a trip to a far-off land. If we had a space elevator we could fix that, maybe -- but not without a massive cord going from us to outer space.
I will add that you can make these numbers cheaper if you don't go into the 'official' outer space region, but just content yourself to fly really high up. People who fly weather balloons can get them to a height where you'd need closer to 0.3 MJ/kg to get to, so you could divide those costs by ~3.
Using my numbers above, getting up to 100 km requires u = 1 MJ/kg of energy. For the trebuchet model, this number is u = ½ v² and you're presumably going to be flying in a circular arc before you are released, where your acceleration is a = v²/r, or r = 2 u / a.
If we want to keep the maximum acceleration beneath 4g's or so, so that it's uncomfortable in the roller-coaster-thrill-ride sense, not in the 'crap I'm going to die' sense, we'd still need a trebuchet of radius 50,000 m. Even the LHC isn't that long across. :P
I mean, you can in principle get those sorts of speeds, but don't expect a human to easily survive it.
Here's what I would have expected: numbers increasing at a relatively constant rate until separation, then a rapid decrease to zero (and since 1mph ~~ .5m/s, expected decrease at about 20mph/s), then increasing again (maybe with a negative sign) until atmosphere, then a decrease to terminal velocity, then another big decrease when the chutes blow.
So aside from the fact that there is no direction (not even a minus sign), so it's at best a speed counter, there still is something I really don't understand about that number. But... what?
(Edit: fixed dumb math error)