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X-37B Secret Space Plane To Land Soon
Phoghat writes "The highly classified X-37B Space Plane is scheduled to land soon. It was launched from Cape Canaveral in Florida on April 22 atop an Atlas 5 rocket, and the Air Force is still being very secretive on all aspects of the flight. We do know that it's set to touch down at Vandenberg Air Force Base's 15,000-foot runway, originally built for the Space Shuttle program. In many ways, the craft resembles a Shuttle with stubby wings, landing gear and a powerful engine that allows the craft to alter its orbit (much to the dismay of many observers on the ground). Its success has apparently given new life to its predecessor, the X-34, which had been mothballed."
The direction of that fall is mainly controlled by the forward motion of the craft and the centrifugal effect by that speed allows it to stay in orbit above the atmosphere.
So once you start breaking this forward speed, usually by firing rockets, the gravity starts to win from the centrifugal force and the craft starts to come down.
When you brake carefully the craft will slowly enter the atmosphere and now be slowed down when encountering the high altitude atmosphere, the problem is the speed at that time is still extremely high causing a lot of friction heat.
Would you brake hard with the rockets the craft would fall out of orbit much quicker and enter the denser parts of our atmosphere much sooner causing extreme friction braking and heat, basically the craft would burn up like a meteorite.
So the trick is to brake in a sensible way and have a craft that can withstand the inevitable friction heat long enough to slow down and enter navigable levels of the atmosphere where the wings can take over.
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Black items will ABSORB more light. When light (i.e. the energy contained in a photon) is absorbed by a molecule, there are a certain number of likely fates for this energy. Remember, 'what goes up, must come down'
Yes, remember that. Black items will absorb more light, and also radiate exactly that much more heat.
The perfect absorber is also the perfect transmitter. Anything else would be a violation of the first law of thermodynamics, and we can't go around breaking them laws, now can we?
Yes, remember that. Black items will absorb more light, and also radiate exactly that much more heat.
Yeah but for a heat shield some heat comes from conduction and that is the same regardless of the albedo of the surface.
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I was looking at the photos and was thinking about the wing size. "That's because they fly very fast because they re-enter the asmosphere really fast." But then I thought "why do they need to re-enter that fast? Surely they could use the atmosphere to slow themselves down, and enter at a much slower, cooler and more relaxed pace." Then I thought "well maybe the gravity has a fair amount of time to act on the craft before the atmosphere really begins, therefore giving plenty of opportunity for speed, well before a viable way to slow down"
Am I right? Does someone have a better explaination?
Here's a link with the basics: Nasa's Landing 101
When the shuttle de-orbits, it fires it's engines in the opposite direction to it's orbit's travel to slow it's forward velocity, which is several magnitudes faster than ground speed (17239.2MPH for the ISS). At this point, the shuttle's inertia stops counteracting the pull of gravity, and the shuttle starts "Falling", like swinging a bucket full of water around on a string, then slowing down the rotation.
Given that there is no atmosphere at this height, the shuttle can accelerate (at 9.81m/s^2) to speeds well in excess of "terminal velocity" as there is no drag to slow it. It typically hits the atmosphere (80 miles up) after 30 minutes of freefall, travelling at speeds of at least twice the speed of sound.
The orbiter then uses it's aerodynamic profile to control its descent, making a series of sharply banking turns to brake it's speed as it descends through the atmosphere, the friction of the air moving against the underside of the orbiter heating the heatproof ceramic tiles up to white hot.
So, here's the answer to you question is "Because gravity has been pulling them down for half an hour before they even hit the atmosphere". In theory, they could use retro thrusters to brake their descent before they hit the atmosphere (Like the Apollo missions did with their lunar landers), but as that would take immense amounts of fuel (close to that required for blast-off) it would make the orbiter's payload capacity virtually nil. Therefore it is easier for them to take the descent into the atmosphere with the best high-speed aerodynamics they can, using the friction of wind resistance to slough off the excess speed, trading it for heat that can be dealt with as they aerodynamically slow their descent and approach the ground at a safe speed.
It's about +3.5 average (2.2 - 4.5) magnitude. It's orbital inclination is 40 degrees making it visible in the twilight sky when conditions are right anywhere between about 45N and 45S latitudes. It's orbital altitude is getting lower and it is maneuvering, both of which make predictions of where to look less precise, but http://www.heavens-above.com has predictions. It travels west to east.