> Interestingly, (from a standpoint of trying to avoid the waste of > fuel-eating trajectory corrections) GS orbits need not be circular. > Even with a circular orbit, it still appears doable via a Hohmann > transfer.
If you meant "equatorial period of exactly one day," then OK. I was wrong to imply that Earth can't be used for slingshot trajectories, since we get probe flybys of Earth for precisely this purpose. However, starting from Earth's inertial framework ... I have trouble seeing any slingshot potential except for using the Moon. > Equatorial mountain candidates for drilling the gun boreholes include > Chimborazo in Ecuador at 20,700, Kenya's Mt Kenya at 17000 + and another > in Sumatra at 12400 +. 12,000 feet is getting a little low, but altitude still helps. Drilling stratovolcanoes, though ... can that be very easy? Of course, I like the idea, in part because it helps quell environmental objections. Volcanoes are already environmental disaster areas. > An example of the non-linear thinking which can be easily applied to the > gun method is that with many cargoes, the entire projectile could be > deep frozen (Say in liquid N or He) prior to launch, thereby extending > the heat tolerance. But also increasing the brittleness of whatever you immerse. One idea I've doodled around with, not too seriously, is some scheme where you take advantage of the strong deceleration through the atmosphere (about 20% I've read) to push cryogenic fluid to the nose cone for cooling, then recycle some of the heat gain as propellant - superheated gas. If you could hold onto some of the gas for a few minutes after leaving the atmosphere, you might even use it for the apogee kick stage. (500 m/s delta V, according to some calculations.) But this would probably only work (if it all) after some amount of ablation down to the metal layers of the nose cone. An empty tank plus nose cone plus kick stage rockets might be engineered for intact re-entry, and be reused. > I was of course backward with the orientation - the bore hole would > actually be pointed a little eastward. GS (circular) orbital velocity > is about 3440 mph, eastward, so there is a little delta V (about 1400 > mph) to make up. Some portion of this would come from the vectored > rocket firing in the Hohmann transfer maneuver. > > Jack > > > -----Original Message----- > From: Michael Turner [mailto:[EMAIL PROTECTED] > Sent: Thursday 08 April 2004 11:48 > To: [EMAIL PROTECTED] > Subject: Re: The gun thing again > > > > Joe Latrell writes: > > Having done some experiments in gun launching (nothing to orbit mind > > you) there are a lot of factors involved that make it very > > unattractive. Heat is a really big issue. > > I've read papers that suggest a dead-mass burden of about 15% for > ablative shielding. I.e., in the same ballpark as reentry capsules. No > showstopper, at least for the optimist. Launching from higher altitudes > definitely helps, since even 14,000 feet gets you above over 25% of the > atmosphere. > > > However, the geosync inflatable station is a great idea. Using a > > transhab type design, you can launch a really big space station with > > only a few launches, assemble it (self assembly?) and then get to work > > > building probes to wherever you want to send them. > > Engineering inflatables for gun launch is an interesting idea. There > may be some kinks in it (as it were), but it seems ideal for solving > many construction problems. If you perfected rendezvous, one approach > that I think would be kinda cool is: > > 1. launch an inflatable > 2. inflate it > 3. launch another > 4. rendezvous at some orifice > 5. inflate the new one *inside* the current one > (vent residual gas to a pressure tank, and > reuse the gas for future inflation) > 6. repeat from 3 until you have enough layers > for whatever purpose desired. > > This is nice because it means you can build structures of considerable > mass within small payload limitations, and because it's fault tolerant > -- blow a launch or miss a rendezvous, and the relative cheapness of gun > launch (amortized over many launches, anyway) means just planning for a > few more launches than the absolute minimum. > > To Jack's questions: > > > > Sundry clever primates around the world .... > > Having met me recently, Jack, you know just how ridged a brow and > prognathous a jaw you're dealing with, in talking to me. (Thanks for > the back-shaving tips, by the way. ;-) > > > > OK, OK, I know. The gun thing won't work for orbital delivery of > > > stuff to build Europan probes because one can't shave the big bump > > > off of the resultant wobbling orbit ... or +- something like that. > > "The big bump"? If you mean that it starts out very elliptical, shaving > the big bumps (which I'm better at now; my back isn't as red and sore as > it used to be) amounts to circularizing the orbit. If you launch enough > fuel into the same orbit as the original projectile, you can use it to > circularize the orbit at perigee pretty efficiently, or even just head > right on out of Earth orbit, I would think. (Joe? You're the guy who > most recently did the orbital dynamics stuff, right?) > > > > However if one were to cant the trajectory of an equatorial gun back > > > > a little to the west, a projectile could be delivered which would > > > "die" into a geosynchronous orbit. Granted, you'd only get one shot > > > > per gun per day, but at say a ton per shot ... > > Um. Hm. I did some rough calculations a while back, looking at > shooting straight up and using the Earth's rotation as free vector, and > I remember coming up with an orbit out past the moon. But you're > proposing something else, I realize. Still, I don't think you can get > GEO without a burn, no matter what. > > Everything I've looked at suggests that you need a kick stage at the top > just to avoid grazing the atmosphere on the backswing. Of course, it's > also possible to coast up to a libration point, I suppose. But that's a > lo-oo-ong way out there. And means a bigger gun. How much bigger? > Haven't figured it out. Probably not too much smaller than what you'd > need for Earth escape velocity. > > > > Then from this orbit, a finished product could be dropped and > > > sling-shotted with Earth gravity assist to wherever. > > "Dropped"? In some sense (a sense that drove Newton crazy until the > light bulb went on in his head) GEO is *already* "dropping" - in a > circle. > > My impression is that slingshotting works with moons planets. > "Dropping" > *does* sort of make sense if you talk about the Sun-facing Sun-Earth > libration point: drop it toward Venus, or rather give it a little shove > at just the right time. Not sure where that point is in relation to the > Van Allen belts, but if you're already rad-hardened for near Jupiter, > maybe the Van Allen belts are negligible anyway. > > Joe! Help! I'm talking barely-informed nonsense, right? > > > >>From another of my cerebral railroad sidings - an inflatable Mylar > > > geosynchronous space station would be a pretty handy toy too - at > > > say 95% gun delivered. > > Reasonable enough, to my mind. Some guy is working on slabs of plastic > for shielding, good on the cosmic ray aspect because of their high > hydrogen content. The stuff seems to perform as well or better than > aluminum by almost every measure. My laminate-in-space inflatable > scheme would seem to amount to the same thing, just different > fabrication technique. > > > > I await the group's scorn. > > I say you get an I (Incomplete) on orbital dynamics, A for thinking > creatively, D- minus for being so narrowly on-topic. But my GPA isn't > much better on this list. What say the other committee members? > > -michael turner > [EMAIL PROTECTED] > > == > You are subscribed to the Europa Icepick mailing list: [EMAIL PROTECTED] > Project information and list (un)subscribe info: http://klx.com/europa/ > > > == > You are subscribed to the Europa Icepick mailing list: [EMAIL PROTECTED] > Project information and list (un)subscribe info: http://klx.com/europa/ > > == You are subscribed to the Europa Icepick mailing list: [EMAIL PROTECTED] Project information and list (un)subscribe info: http://klx.com/europa/
