JEL
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Pioneer anomaly
- Thread starter agentgonzo
- Start date
jedidia
shoemaker without legs
Not exactly. If I understood the article correctly, then the dish is the main reason why the radiation is anisotropic (that is, not regular to all sides). Photons don't have mass, but they have momentum, so whenever a photon is radiated away, or reflected, they impart an equal and opposite reaction on whatever they have been radiated or reflected off of.
If that radiaton is regular to all sides, the effects cancel each other out, but due to the dish deflecting a lot of the radiation into a specific direction the effect became measurable (over long periods of time).
As said before, a powerplant does get rid of its heat by thermal conduction. Of course there's quite a bit of IR radiation, but that is usually not directed to one side. Also, the pressure of the sun burning down on it would probably be larger than the pressure by its own radiation, but not even that is really noticable...
Quick_Nick
Passed the Turing Test
That's what I meant with my last post but I think I made it far from clear.
JEL
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@jedidia; thanks
Would you say, that if we made a vehicle with the shape of a large dish-antenna, or a bowl, with a strong radiating device placed underneath it, that it might theoretically be possible to make this vehicle levitate by the radiation-pressure coming from it's radiative 'pod' at the bottom? Theoretically at least
Would you say, that if we made a vehicle with the shape of a large dish-antenna, or a bowl, with a strong radiating device placed underneath it, that it might theoretically be possible to make this vehicle levitate by the radiation-pressure coming from it's radiative 'pod' at the bottom? Theoretically at least
jedidia
shoemaker without legs
Theoretically, sure, if you can build a power source and a dish with almost zero mass. Although the dish size only has a secondary influence. The more focused the light is, the more thrust you generate (but the 300 MW/N stated above are a (approximation of a) theoretical maximum, based on the plank constant).
So what you need is a laser, and a larger dish generally would mean a better focused laser, but there's a point when increasing dish size will lead to dropping thrust to mass ratio and it will hit pretty quickly I guess.
The hole you burn in the ground when levitating the contraption would likely be the bigger problem, though. TBH, a photon drive with a thrust to mass ratio bigger than one (needed to overcome earths gravity) is about as impossible a thing as I've ever heard although the general concept is researched for laser assisted launch by some people, where you'd have the whole powersource and laser dish on the ground and push the vehicle from there (successfully done with lightweight objects to an altitude of something like 40 meters, if memory serves me right, but I also think there was ablation involved to produce additional thrust).
So what you need is a laser, and a larger dish generally would mean a better focused laser, but there's a point when increasing dish size will lead to dropping thrust to mass ratio and it will hit pretty quickly I guess.
The hole you burn in the ground when levitating the contraption would likely be the bigger problem, though. TBH, a photon drive with a thrust to mass ratio bigger than one (needed to overcome earths gravity) is about as impossible a thing as I've ever heard although the general concept is researched for laser assisted launch by some people, where you'd have the whole powersource and laser dish on the ground and push the vehicle from there (successfully done with lightweight objects to an altitude of something like 40 meters, if memory serves me right, but I also think there was ablation involved to produce additional thrust).
Last edited:
JEL
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...as a search-term on google gave me this:
[ame="http://en.wikipedia.org/wiki/Nuclear_photonic_rocket"]http://en.wikipedia.org/wiki/Nuclear_photonic_rocket[/ame]
Fascinating stuff, even if still mostly theoretical
For something to impart a reaction (during an impact) It needs to have mass. A massless sub-atomic particle isn't going to affect anything (in the newtonian sense of push and push back) regardless of the momentum.
Zatnikitelman
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Then how do solar sails work?
Mattyv
Rocket Scientist in Training
Not exactly. Einstein postulated and was later proven correct that photons have do have momentum equivalent to p = E/c.
Edit: Whoops. Never mind I misread your post.:facepalm:
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RisingFury
OBSP developer
I think I know what you're referring to. I once saw video of a laser hitting a ...disk-ish rocket thingy... but as far as I remember, the laser served to heat the air, which expanded and produced thrust that way...
jedidia
shoemaker without legs
Ah yes, that was it!
Linguofreak
Well-known member
Utter poppycock. [ame="http://en.wikipedia.org/wiki/Radiation_pressure"]Radiation pressure[/ame] is a very real effect that has been observed to occur.
Furthermore, if your claim were correct, conservation of momentum would be violated. (Since photons would have their momentum vectors reversed when they reflected off of surfaces, but the momentum vector of whatever they hit would not change).
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NASA JPL:
Study Finds Heat is Source of 'Pioneer Anomaly'
July 17, 2012
The unexpected slowing of NASA's Pioneer 10 and 11 spacecraft - the so-called "Pioneer Anomaly" - turns out to be due to the slight, but detectable effect of heat pushing back on the spacecraft, according to a recent paper. The heat emanates from electrical current flowing through instruments and the thermoelectric power supply. The results were published on June 12 in the journal Physical Review Letters.
"The effect is something like when you're driving a car and the photons from your headlights are pushing you backward," said Slava Turyshev, the paper's lead author at NASA's Jet Propulsion Laboratory, Pasadena, Calif. "It is very subtle."
Launched in 1972 and 1973 respectively, Pioneer 10 and 11 are on an outward trajectory from our sun. In the early 1980s, navigators saw a deceleration on the two spacecraft, in the direction back toward the sun, as the spacecraft were approaching Saturn. They dismissed it as the effect of dribbles of leftover propellant still in the fuel lines after controllers had cut off the propellant. But by 1998, as the spacecraft kept traveling on their journey and were over 8 billion miles (13 billion kilometers) away from the sun, a group of scientists led by John Anderson of JPL realized there was an actual deceleration of about 300 inches per day squared (0.9 nanometers per second squared). They raised the possibility that this could be some new type of physics that contradicted Einstein's general theory of relativity.
In 2004, Turyshev decided to start gathering records stored all over the country and analyze the data to see if he could definitively figure out the source of the deceleration. In part, he and colleagues were contemplating a deep space physics mission to investigate the anomaly, and he wanted to be sure there was one before asking NASA for a spacecraft.
He and colleagues went searching for Doppler data, the pattern of data communicated back to Earth from the spacecraft, and telemetry data, the housekeeping data sent back from the spacecraft. At the time these two Pioneers were launched, data were still being stored on punch cards. But Turyshev and colleagues were able to copy digitized files from the computer of JPL navigators who have helped steer the Pioneer spacecraft since the 1970s. They also found over a dozen of boxes of magnetic tapes stored under a staircase at JPL and received files from the National Space Science Data Center at NASA Goddard Space Flight Center, Greenbelt, Md., and worked with NASA Ames Research Center, Moffett Field, Calif., to save some of their boxes of magnetic optical tapes. He collected more than 43 gigabytes of data, which may not seem like a lot now, but is quite a lot of data for the 1970s. He also managed to save a vintage tape machine that was about to be discarded, so he could play the magnetic tapes.
The effort was a labor of love for Turyshev and others. The Planetary Society sent out appeals to its members to help fund the data recovery effort. NASA later also provided funding. In the process, a programmer in Canada, Viktor Toth, heard about the effort and contacted Turyshev. He helped Turyshev create a program that could read the telemetry tapes and clean up the old data.
They saw that what was happening to Pioneer wasn't happening to other spacecraft, mostly because of the way the spacecraft were built. For example, the Voyager spacecraft are less sensitive to the effect seen on Pioneer, because its thrusters align it along three axes, whereas the Pioneer spacecraft rely on spinning to stay stable.
With all the data newly available, Turyshev and colleagues were able to calculate the heat put out by the electrical subsystems and the decay of plutonium in the Pioneer power sources, which matched the anomalous acceleration seen on both Pioneers.
"The story is finding its conclusion because it turns out that standard physics prevail," Turyshev said. "While of course it would've been exciting to discover a new kind of physics, we did solve a mystery."
{...}
Study Finds Heat is Source of 'Pioneer Anomaly'
July 17, 2012
The unexpected slowing of NASA's Pioneer 10 and 11 spacecraft - the so-called "Pioneer Anomaly" - turns out to be due to the slight, but detectable effect of heat pushing back on the spacecraft, according to a recent paper. The heat emanates from electrical current flowing through instruments and the thermoelectric power supply. The results were published on June 12 in the journal Physical Review Letters.
"The effect is something like when you're driving a car and the photons from your headlights are pushing you backward," said Slava Turyshev, the paper's lead author at NASA's Jet Propulsion Laboratory, Pasadena, Calif. "It is very subtle."
Launched in 1972 and 1973 respectively, Pioneer 10 and 11 are on an outward trajectory from our sun. In the early 1980s, navigators saw a deceleration on the two spacecraft, in the direction back toward the sun, as the spacecraft were approaching Saturn. They dismissed it as the effect of dribbles of leftover propellant still in the fuel lines after controllers had cut off the propellant. But by 1998, as the spacecraft kept traveling on their journey and were over 8 billion miles (13 billion kilometers) away from the sun, a group of scientists led by John Anderson of JPL realized there was an actual deceleration of about 300 inches per day squared (0.9 nanometers per second squared). They raised the possibility that this could be some new type of physics that contradicted Einstein's general theory of relativity.
In 2004, Turyshev decided to start gathering records stored all over the country and analyze the data to see if he could definitively figure out the source of the deceleration. In part, he and colleagues were contemplating a deep space physics mission to investigate the anomaly, and he wanted to be sure there was one before asking NASA for a spacecraft.
He and colleagues went searching for Doppler data, the pattern of data communicated back to Earth from the spacecraft, and telemetry data, the housekeeping data sent back from the spacecraft. At the time these two Pioneers were launched, data were still being stored on punch cards. But Turyshev and colleagues were able to copy digitized files from the computer of JPL navigators who have helped steer the Pioneer spacecraft since the 1970s. They also found over a dozen of boxes of magnetic tapes stored under a staircase at JPL and received files from the National Space Science Data Center at NASA Goddard Space Flight Center, Greenbelt, Md., and worked with NASA Ames Research Center, Moffett Field, Calif., to save some of their boxes of magnetic optical tapes. He collected more than 43 gigabytes of data, which may not seem like a lot now, but is quite a lot of data for the 1970s. He also managed to save a vintage tape machine that was about to be discarded, so he could play the magnetic tapes.
The effort was a labor of love for Turyshev and others. The Planetary Society sent out appeals to its members to help fund the data recovery effort. NASA later also provided funding. In the process, a programmer in Canada, Viktor Toth, heard about the effort and contacted Turyshev. He helped Turyshev create a program that could read the telemetry tapes and clean up the old data.
They saw that what was happening to Pioneer wasn't happening to other spacecraft, mostly because of the way the spacecraft were built. For example, the Voyager spacecraft are less sensitive to the effect seen on Pioneer, because its thrusters align it along three axes, whereas the Pioneer spacecraft rely on spinning to stay stable.
With all the data newly available, Turyshev and colleagues were able to calculate the heat put out by the electrical subsystems and the decay of plutonium in the Pioneer power sources, which matched the anomalous acceleration seen on both Pioneers.
"The story is finding its conclusion because it turns out that standard physics prevail," Turyshev said. "While of course it would've been exciting to discover a new kind of physics, we did solve a mystery."
{...}
