braddock - 9/6/2006 1:11 PMWhat is the smallest theoretical rocket that can make orbit? What factor causes the limit?
As far as I can tell, the Tsiolkovsky rocket equation doesn't seem to address the problem of scale. If I wanted to launch a paper clip into orbit, and I had a 350 Isp micro-machined thimble engine, then I just plug that in and get the same mass fraction that the big boys use. But this seems intuitively wrong.
So is the problem just building a teeny tiny engine of some exotic type? Or possibly carrying a very high muzzle-velocity gun up on a balloon to shoot my pea into orbit?
braddock - 9/6/2006 7:48 PMOkay, so far it seems like the show stoppers are:1) Volume doesn't scale linearly with Surface Area (even if 1/10th the mass may need only 1/10th the fuel, but the scaled rocket will only have ~1/5th the surface area). Larger relative surface area = larger relative air friction resistance. 2) Also larger relative surface area MAY require larger proportion of weight to be structural (although lower pressures and smaller stresses could mitigate that)3) Larger relative air viscosity (air is "thicker"). This is what the Micro UAV folks have run into as well (often to their advantage, although probably not to ours)I'm still rather interested in the case of a balloon or otherwise boosted start at 100k ft where the atmosphere density is a fraction of ground level. There must be some reason amateur rocketeers haven't taken a shot at orbit from a balloon (the likes of JP Aerospace and others have done balloon launches)?What _IS_ the smallest rocket to have ever made orbit?
Jim - 10/6/2006 9:01 AMCost of the aircraft
braddock - 10/6/2006 8:04 AMVery interesting. I found an article on Project Pilot that suggests that it actually achieved orbit twice, although the telemetry reports were ify. Only source of this article seems to be in an old mailing list archive: http://www.uoregon.edu/~stevev/sd-archive/raw/sd1998-3.txt (search for NOTSNIK)So a 16' x 2' air-launched solid (Caleb) can at least theoretically get a 15 lb payload to orbit, with a payload-to-mass ratio of .5%. Can't find altitude info on Caleb, but Project Pilot was launched at 41k feet. http://www.astronautix.com/graphics/n/nots.jpg">Interesting lower limit example. And I spent a couple hours last night reading about Dr. Bull's Project HARP gun-launched rockets, which was also fascinating. Astronautix has an excellent series of articles on that. http://www.astronautix.com/articles/abroject.htmI still don't have a good idea of what defines the lower limit for an air-launched orbital launch vehicle, however. Caleb seems to have a reasonable payload mass fraction for a solid (although by my figures Pegasus is closer to 2%, but is also much more refined).
Zachstar - 10/6/2006 4:40 PMMight find this interesting http://www.microlaunchers.com/home.htm
mlorrey - 11/6/2006 3:59 PMQuoteZachstar - 10/6/2006 4:40 PMMight find this interesting http://www.microlaunchers.com/home.htmIt is interesting what micromachinery is being made. Just the other day I was chatting with a fellow at a company that produces MEMS chip liquid cooling devices, made by diffusion bonding hundreds of leaves of 1-3 mil metal, each with their own micro cut patterns.
Jim - 11/6/2006 6:20 PMQuotemlorrey - 11/6/2006 3:59 PMQuoteZachstar - 10/6/2006 4:40 PMMight find this interesting http://www.microlaunchers.com/home.htmIt is interesting what micromachinery is being made. Just the other day I was chatting with a fellow at a company that produces MEMS chip liquid cooling devices, made by diffusion bonding hundreds of leaves of 1-3 mil metal, each with their own micro cut patterns.The problem is micromachinery doesn't work very well with fluids. The same reasons that there are no small jst engines, would be the same for turbo pumps. Reynolds numbers don't scale.
As far as I can tell, the Tsiolkovsky rocket equation doesn't seem to address the problem of scale.
Reynolds numbers don't scale.