Aucbvax.6294 fa.space utcsrgv!utzoo!decvax!ucbvax!space Thu Feb 25 03:57:12 1982 SPACE Digest V2 #115 >From OTA@S1-A Thu Feb 25 03:47:02 1982 SPACE Digest Volume 2 : Issue 115 Today's Topics: re: giant mass driver to colonize other galazies by accelerating to c/2 re: giant mass driver to colonize other galazies by accelerating to c/2 Re: Quasars re: giant mass driver to colonize other galazies by accelerating to c/2 Laser & Hydrogen What a million Gs?!? Re: Quasars ---------------------------------------------------------------------- Date: Wednesday, 24 February 1982 08:09-PST From: KING at KESTREL Subject: re: giant mass driver to colonize other galazies by accelerating to c/2 To: dietz at usc-ecl, space at mit-mc cc: King at KESTREL How do you decelerate when you get there? ------------------------------ Date: 24 Feb 1982 1027-PST From: Paul Dietz Subject: re: giant mass driver to colonize other galazies by accelerating to c/2 To: KING at KESTREL, space at MIT-MC cc: DIETZ at USC-ECL Deceleration: Presumably with rockets, stellar sails, pressure of the interstellar gas against magnetic fields (you'd have to ionize it first). Steering when you get to the other galaxy is no problem: just put a large electric charge on the ship and let the galactic magnetic field move you around. You could throw away most of the ship, or use it for fuel. Length of the Mass Driver: c = 3.0E8 m/sec (m=meters), and g = 10 m/sec^2, so it takes 1.5E8 / 1.0E4 = 1.5E4 seconds to reach .5c at 1000g's (ignoring relativity). During that time you travel .5at^2 = (.5)(1.0E4)(2.25E8) = 1.125E12 meters, or 1.125 billion kilometers. (darn arithmetic errors!) One millon g's: Lest this figure seem ridiculous, let me note that railguns have already achieved accelerations of over 1E6g's. So it's just engineering to design a railgun 1.1E6 km long. The big advantage of linear accelerators is that energy is used much more efficiently than in a rocket, where you have to use exponentially increasing amount of energy to accelerate a payload to higher and higher velocities. The energy used in a mass driver grows more slowly. Also, the mass driver can be used repeatedly. ------------------------------ Date: 24 Feb 1982 11:22 PST From: Lynn.ES at PARC-MAXC Subject: Re: Quasars In-reply-to: Reed.ES's message of 23-Feb-82 8:52:52 PST To: Space-Enthusiasts at MIT-MC cc: Reed.ES, Lynn.es Halton Arp was the astronomer mentioned in the article. Everyone agrees that all quasars show huge redshifts. Essentially all normal galaxies are receding from us, causing a red-direction Doppler shift (redshift) in their spectra. The bigger the redshift, the faster the recessional velocity. The fact that the universe (on the galactic scale) is expanding requires that distance and speed of recession be directly related; that is, the faster the recession, the farther the galaxy is from us. Now we have two choices in explaining quasars: 1) they follow the rules of galaxies, and the huge redshifts mean huge recession velocities and huge distances, or 2) there is some physical means (what means is not clear) that redshifts quasar light, and they are not so distant nor receding. Arp is apparently the only astronomer of international note that believes the second choice. His contention is that some quasars show physical links with normal galaxies that have small redshifts and are therefore nearby. Most other astronomers believe that the apparent physical connections have to be coincidence of wispy objects nearby happening to lie in a line of sight with the distant quasars and some nearby galaxy. That seems easier to believe since no one, after years of trying, has come up with a decent explanation of a non-Doppler way to create huge redshifts in quasars. Arp wants to continue looking for physical connections to quasars to show that there are too many for it to be line-of-sight coincidences, while other astronomers want a physical explanation of the redshifts before spending much on the connections search. A few years ago, several astronomers were listening to Arp with interest, but apparently from the Times article and a few others elsewhere on quasars, few now give Arp much chance of being right. /Don Lynn ------------------------------ Date: Wednesday, 24 February 1982 11:26-PST From: KING at KESTREL To: Paul Dietz cc: space at MIT-MC, King at KESTREL Subject: re: giant mass driver to colonize other galazies by accelerating to c/2 The ship has a momentum of 1.5e17 newton-seconds. I suspect it would be necessary to shoot a dummy load through the mass driver backwards to avoid losing the mass driver after a couple of shots. I would design it as a series of separate modules "attached" by station-keeping hardware. Each module would have its own energy storage system (and probably its own power plant). However, one wonders whether something analogous to a traveling wave tube could be used. Send your energy pulse down a non-uniform helical superconducting cable wound in such a manner that the spiraling electrical pulse's velocity matches the ship. The mechanism is simple, but now the energy has to be supplied all at once. I'd rather use a laser and have frozen Hydrogen on the tail of the ship, to be heated within an inch of its life and sent back at .99c. Anyone have any thoughts on this? Sorry about the lack of detail - I'm pressed for time right now. Dick ------------------------------ Date: 24 Feb 1982 1200-PST From: Paul Dietz Subject: Laser & Hydrogen To: king at KESTREL cc: space at MIT-MC The problem with this scheme is that you have to accelerate your fuel, along with the ship. So, the amount of fuel increases exponentially with the final velocity of the payload. The mass driver avoids this problem. Also, I imagine that heating the hydrogen to such high temperatures will roast the ship in a bath of x-rays and gamma-rays. Recoil can be minimized by making the launcher very massive. If it weighs 1.0E12 tons the velocity increment is 150 m/sec. By launching when the launcher is on opposite sides of the sun the delta-v's will cancel out. Thumbnail calculations indicate that a trillion tons is bout the mass of an asteroid 5-10 km in diameter, so materials are no problem. The biggest problem is the energy source. It can be massive, though, because you don't have to accelerate it. ------------------------------ Date: 24 Feb 1982 1502-PST From: Ted Anderson Subject: What a million Gs?!? To: space at MIT-MC, Dietz at USC-ECL In support of Paul's claim that a million Gs is "reasonable", consider this: I understand that experiencing an acceleration of 100,000 Gs is not uncommon for an artillary shell. Now I don't know that this is the same type of artillary pieces but I know of at least two fairly sophisticated devices that live in artillary shells. On is a nuclear warhead, the other is a frob which actually looks for tanks in some fashion. I don't know any of the details, however. At any rate, I'd be surprised if something interesting like an intergalactic probe couldn't be built to withstand 1 million Gs. Ted Anderson ------------------------------ Date: 24-Feb-82 15:17:52 PST (Wednesday) From: Reed.ES at PARC-MAXC Subject: Re: Quasars In-reply-to: Lynn's message of 24 Feb 1982 11:22 PST To: Lynn cc: Space-Enthusiasts at MIT-MC, Reed If I remember correctly, a large gravitational potential can also cause a redshift. Is it not possible that a quasar's redshift could be at least partially gravitational in nature, thus reducing the recession velocity (and therefore distance) for a given redshift? On a scifi tack, what would a spaceship travelling away from us at an appreciable fraction of the speed of light (say .5c) look like to an observer on earth? Would we see a light source with a redshift? Could a quasar be such a light source? -- Larry -- ------------------------------ End of SPACE Digest ******************* ----------------------------------------------------------------- gopher://quux.org/ conversion by John Goerzen of http://communication.ucsd.edu/A-News/ This Usenet Oldnews Archive article may be copied and distributed freely, provided: 1. There is no money collected for the text(s) of the articles. 2. The following notice remains appended to each copy: The Usenet Oldnews Archive: Compilation Copyright (C) 1981, 1996 Bruce Jones, Henry Spencer, David Wiseman.