|
Post by ubique on Jan 13, 2012 23:58:41 GMT -4
Hello all, first post here! Others have covered main parts of the post below while I waited for the account to be approved, but I'll still add a couple of points: so an astronaut going to the moon would experience a concentrated dose of radiation as he traveled thru the belts followed by continual doses from then on. There would be virtually no space devoid of radiation. so to say that the only danger is the van Allen belt is not valid, in space there would be continuous radiation exposure. Correct, but you'll need to note that the absorbed dose rate is much lower in the cislunar space than during the VARB transit. It's not a problem for a short trip, though it's high enough to cause real trouble for any voyage to Mars, for example. No, it can't be, because solar wind is captured in Earth's magnetic field (and other processes also produce trapped particles). This is not true. Free neutrons will decay to a proton, an electron, and an antineutrino, with a half-life of about 15 min. A proton can absorb an electron and turn into a neutrino, in a process called electron capture.
|
|
|
Post by PhantomWolf on Jan 14, 2012 5:25:30 GMT -4
This is not true. Free neutrons will decay to a proton, an electron, and an antineutrino, with a half-life of about 15 min. A proton can absorb an electron and turn into a neutrino, in a process called electron capture. Sure on this? The sources I have seen say that neutrons decay into a proton, an electron, and a neutrino, while electrons colliding with protons can create a neutrino/anti-neutrino pair, absorb the neutrino and form a neutron.
|
|
|
Post by ubique on Jan 14, 2012 9:23:21 GMT -4
Sure on this? The sources I have seen say that neutrons decay into a proton, an electron, and a neutrino, I'm a physicist by training, which included particle physics, so yes, I'm quite sure. It's an antineutrino, to preserve the lepton count. As there are no leptons before the decay, the lepton number is 0. The number has to be the same after the decay. Electron gives +1 to lepton number, so the other lepton created must be an antiparticle for it to have -1 as the lepton number. Electron capture is a well-known process for decay of certain elements. Yes, there's a neutrino produced too, again to preserve the lepton number; I left it out as it's not really meaningful for the discussion. I'm not sure where the neutrino-antineutrino pair would come from. Rather, if you go to a detailed level, an up-quark in the proton turns into a down-quark by emitting a W-boson (and thus the proton transmutes into a neutron), which interacts with the electron, turning it into a neutrino. Beta decays, closely related to electron capture, are other well-known examples where the weak force transmutes protons and neutrons.
|
|
|
Post by ka9q on Jan 15, 2012 0:09:19 GMT -4
how is the radiation held in the belts? or what force could hold it, is is by electrical charge or magnetic? Basic electromagnetism says that when a charged particle moves through a magnetic field, it experiences a force at right angles to both the direction of the field and the motion of the particle. This same principle is used in CRT-type TVs to deflect the electron beam so that it repeatedly scans the screen. This force deflects the particle at an angle, so the direction of the force continually changes to remain at right angles to the particle's new direction. If the magnetic field covers a large volume, as the earth's field does, the particle now moves in a closed circle. It is trapped in the field. The diameter of the circle depends on the mass of the particle, its velocity and the strength of the field. Because the earth's magnetic field strength and direction varies with location, other factors come into play. The charged particles spiral around the magnetic field lines. Because they're repelled by increasing field gradients, they tend to bounce back and forth between the north and south magnetic poles, occasionally hitting the atmosphere where they produce auroras. All this has been extensively studied and published since Van Allen's original discovery in 1958. The radiation exposures to the Apollo astronauts were carefully measured and those figures too are public.
|
|
raven
Jupiter
That ain't Earth, kiddies.
Posts: 509
|
Post by raven on Jan 15, 2012 0:35:32 GMT -4
As an addendum, I would like to point something else out as well., something likely already pointed out but that bears repeating. Electronics is also affected by radiation. Not in the same way as us meatbags, but it is definitely affected. Let's say NASA was lying through it's teeth about the radiation levels of the Van Allen Belts. Now, many satellites are owned by private companies, such as many communications satellites, including those used for satellite TV, radio and internet services. These companies are insured by companies whose livelihood depends on knowing when things will fail. If NASA was lying about the radiation levels, these satellites would fail that much sooner. Which means who ever owns for example, the DirectTV satellites and, for example, Lloyds of London, would lose a lot of money. Is there evidence of this happening? It would have to happen if NASA was lying about the radiation levels.
|
|
|
Post by trebor on Jan 16, 2012 11:17:15 GMT -4
playdor, I know you've been busy searching for promotional videos you can say have something to do with the documented Apollo record, so in case you missed it: Neil Armstrong says you can see stars:Also, I still want to know exactly what you mean by claiming to have "mulitple degrees in science". sts60 what changed that the stars could now be seen? What changed is that they passed into the shadow of the moon, so that it was blocking all sunlight. As astronaut Mike Fossum also very recently pointed out when asked about seeing stars : “The key is to be in a place where you can dark adapt – any sunlight overpowers night vision.”
|
|
|
Post by Jason Thompson on Jan 16, 2012 12:37:59 GMT -4
what changed that the stars could now be seen? You're really not paying attention, are you?
|
|
|
Post by gillianren on Jan 16, 2012 17:12:08 GMT -4
You're really not paying attention, are you? Why should he start now?
|
|
|
Post by echnaton on Jan 16, 2012 21:58:59 GMT -4
You're really not paying attention, are you? Why should he start now? He is too busy reading those van Allen papers.
|
|
|
Post by tedward on Jan 17, 2012 3:09:17 GMT -4
Too busy finding qualifications?
|
|
|
Post by sts60 on Jan 18, 2012 21:07:52 GMT -4
sts60 what changed that the stars could now be seen? What happened is that they were in the shadow of the Moon, and their spacecraft was not brightly illuminated by the Sun, nor was there a large brilliant object (Moon or Earth) occupying much of their field of view. This should be obvious from the many explanations offered to you thus far. This demonstrates clearly - again - that astronauts saw stars under appropriate circumstances. Now that I have answered your question, I still want to know exactly what you mean by claiming to have "multiple degrees in science".
|
|
|
Post by twik on Jan 28, 2012 13:42:00 GMT -4
playdor ... what exactly is your point with all these numbers? It would be very good of you to state what you're driving at.
Have you been taking lessons from Patrick1K?
|
|
|
Post by ka9q on Jan 28, 2012 13:42:06 GMT -4
Note ->ka9q (post #364) "In a vacuum, a rocket plume expands so quickly..." ... how quickly does it expand? Watch any rocket launch: Shuttle, Delta, Atlas, Falcon, Ariane, whatever, preferably one with solid rocket boosters producing a very visible plume. The first stage typically operates from sea level to almost a pure vacuum, and you can see the plume steadily broaden as it climbs. Some of the gases even begin to wrap around the base of the launcher. Depending on the camera angle you may not be able to fully appreciate just how much the plume broadens. The effect is especially visible in downward-looking cameras mounted on the side of the rocket. Most recent Deltas have carried cameras, as have most recent Shuttle SRBs. The nozzle design also affects the size and shape of the plume. Upper stage rocket engines, like those on the LM, generally have longer nozzles designed to operate in a pure vacuum. First stage engine nozzles lit on the ground are smaller. They're always a compromise since they have to operate all the way from the surface to a vacuum. The Shuttle SRBs are lit on the ground so they have relatively short nozzles. The Delta II is especially interesting. In its 9-SRB version, 6 are ignited at launch and the other 3 are ignited at altitude a minute after launch. A close look at those SRBs before launch shows that the ground-lit solids have short nozzles while the air-lit solids have much longer nozzles optimized for vacuum operation. With so many SRBs it's especially easy to see the plume-broadening effect on the Delta II.
|
|
|
Post by ka9q on Jan 28, 2012 13:49:56 GMT -4
playdor ... what exactly is your point with all these numbers? Yes, what's your point? The lunar surface is covered with very fine dust that is easily lifted and blown away to great distances by the LM descent engines below about 100 feet. But that dust layer is very thin, and below it the regolith rapidly gets harder and denser. That's why you don't see (and shouldn't expect to see) a deep crater in the ground under a landed LM. Instead you see a "scouring" effect over a fairly wide area. It's especially visible in the pictures returned by Apollo 11 since the Eagle's descent engine operated all the way to the ground.
|
|
|
Post by tedward on Jan 28, 2012 14:16:18 GMT -4
One of the lift off videos from the moon is quite telling when the gold coloured material is shifted away from the lander.
Playdor, what are your qualifications that you have alluded to?
|
|