Wikipedia:Reference desk/Archives/Science/2019 March 30

= March 30 =

SETI jamming?
Have any studies been performed to determine whether ETIs' radio signals that SETI would otherwise detect are being jammed by other ETIs, as e.g. two warring alien species might do to prevent each other from allying with humans? Neon Merlin  20:25, 30 March 2019 (UTC)
 * Do you mean scientific studies? And would the answer be no? SpinningSpark 21:57, 30 March 2019 (UTC)
 * How would one even study that? If someone is actively and successfully trying to block us from picking up a signal, then we won't have picked up a signal. --OuroborosCobra (talk) 23:28, 30 March 2019 (UTC)


 * If they are fighting over something, it won't be about us as we're insignificant to ET. Count Iblis (talk) 00:51, 31 March 2019 (UTC)


 * Jamming usually does not work by literally blocking a signal (except for very specific types of receiving equipment), but by overriding it with a stronger one. Thus any ET's jamming would be more easily detectable than the other ET's original signal – we wouldn't be able to decipher it, but we'd surely be able to tell that it was artificial. {The poster formerly known as 87.81.230.195} 90.200.138.194 (talk) 10:01, 31 March 2019 (UTC)
 * Covert Radio jamming works by transmitting a Pseudorandom noise signal that degrades to unusability the Signal-to-noise ratio experienced at receiver(s). Studies of the CMB do not disprove a conjecture that it has origins in intentional extraterrestrial transmissions. DroneB (talk) 14:03, 31 March 2019 (UTC)


 * It is also said that the best encoded signal is indistinguishable from noise. Maybe they just are saying too much... Wnt (talk) 19:31, 31 March 2019 (UTC)

How far could the Space Shuttle go if?
you made it go as far as it can without ever reaching orbit velocity, the Karman line or whatever the exact Karman line for the Space Shuttle would be? (<100km since the wings are small to save weight?) How much more range could it get launching from the highest point on the equator instead of the equator at sea level? Would max-g forces or landing harshness be higher than usual? If there was an extremely long runway where it can't glide no more that is. Sagittarian Milky Way (talk) 22:02, 30 March 2019 (UTC)


 * The shuttle launched straight upwards and I'm pretty sure it would have been well past the Karman line by the time it reached max velocity. I don't know what the highest altitude on the equator is, but if you can find it, you can calculate the delta-vee straightforwardly (h=&frac12;gt2).  As for issues of landing in case of not reaching orbit, see the novel Shuttle Down, which was scientifically accurate enough that NASA used it when working on contingency planning. 67.164.113.165 (talk) 23:19, 30 March 2019 (UTC)
 * The shuttle launched in no way straight upwards, except to the smallest initial part of the trajectory. Does this look straight up to you?. See gravity turn. Fgf10 (talk) 15:41, 31 March 2019 (UTC)
 * As I recall, the 1960s-1970s NASA missions also launched straight up at the start (obviously) and then also quickly veered away from the vertical. ←Baseball Bugs What's up, Doc? carrots→ 21:10, 31 March 2019 (UTC)
 * Yes, it's all the same physics. You need to get up to about 8 meters/second perpendicular to the Earth's surface for low Earth orbit, and you also want to get out over the ocean and away from people in case things go wrong. --47.146.63.87 (talk) 02:24, 1 April 2019 (UTC)
 * Er, parallel, not perpendicular. Brain fart. --47.146.63.87 (talk) 06:04, 1 April 2019 (UTC)
 * 8 km/s... Fgf10 (talk) 07:50, 1 April 2019 (UTC)
 * I was thinking of using it as an airplane instead of a spacecraft. A pointless waste of fuel but what ferry range could you get? Would you want to level off at a cruising altitude of almost 100km and speed of almost orbital velocity and use only enough throttle to maintain speed then dump the tank and glide? I think they throttle down the engines when fuel loss lowers the mass:thrust ratio enough for full power to reach 3-5 G's, would max range require increasing this G force? Sagittarian Milky Way (talk) 01:20, 31 March 2019 (UTC)


 * As for altitude limit I've heard the empty orbiter could reach geostationary transfer orbit but the service ceiling is ~960km for some reason. GTO might be too much radiation for its shielding but what's wrong with 1,000?Sagittarian Milky Way (talk) 01:26, 31 March 2019 (UTC)


 * It seems like the Shuttle ought to be able to follow a course that stops short of the Karman line and ends in as stable an orbit as can be accomplished at that height. Beyond that point, I think you could guesstimate how rapidly its orbit decays from that height (though a very advanced simulation would be need to determine the exact atmospheric drag) and how much extra fuel it could have on board (especially if no payload is needed) then figure out how long you can keep boosting the orbit?  Not very useful to know, of course, unless the Earth has been taking over by giant bureacratic cockroaches from outer space and their police are shooting anybody flying over 100 km in self-defense. Wnt (talk) 03:18, 31 March 2019 (UTC)


 * A pointless waste of fuel but what ferry range could you get? The vessel you want is called an ICBM ;). I believe Shuttle missions would completely exhaust the main engine's fuel getting to orbit, then use the orbital maneuvering system (different set of smaller engines) for orbit adjustments and reentry.  As for getting the orbiter to GTO, I doubt it was capable of that, and even if it was, you'd need equally much delta-v to get it back down.  And why would you want it there to begin with?  There were various proposals to tow the external tank into orbit and then use it as staging materials of various sorts, but I think the idea was to build a second transport system (space tug) that only travelled between low and high orbits, to be used in conjunction with the Shuttle which got stuff from earth to LEO. 67.164.113.165 (talk) 04:51, 31 March 2019 (UTC)
 * The Main engines were not burned to exhaustion, the OMS burn was to so the external tank didn't enter a stable orbit and to target it to a safe oceanic disposal area (intially Indian Ocean, latterly Pacific) Fgf10 (talk) 15:41, 31 March 2019 (UTC)
 * Is it true something bad would've happened if it ran dry with the fuel pumps still running? Sagittarian Milky Way (talk) 00:16, 1 April 2019 (UTC)
 * This is true, but, the broader point the poster was making is that you'd need a lot more fuel to get to GTO. The main engines were never normally re-ignited after main engine cutoff during ascent. There was only a small amount of remaining fuel/oxidizer for the main engines after this. Also, here's a neat lecture about how to land the Shuttle, which also touches on launch and maneuvering. --47.146.63.87 (talk) 02:20, 1 April 2019 (UTC)
 * Not only where the engines never re-ignited, they couldn't be. The SSME needs the head pressure of the external tank and a tons of ground support equipment to start. This was a major issue when the plan was to use an SSME as an upper stage engine on the Ares I as originally proposed. Fgf10 (talk) 07:50, 1 April 2019 (UTC)
 * Yes, the Shuttle was just one component of the proposed Space Transportation System which was intended to follow Apollo with an eye towards eventual manned Mars missions. (That article needs lots of work, but it has some links to more info.) Space Shuttle and Space Shuttle program have some more details. NASA's budget was slashed after Apollo, and they decided to go ahead with just the Shuttle. --47.146.63.87 (talk) 02:20, 1 April 2019 (UTC)