Gone to the moon, BRB(Destination Moon)
Posted: Mon Nov 09, 2009 9:35 am
Thought this might tickle a few brains here. 1950 movie.
http://www.youtube.com/watch?v=DsisGSBlQqo
http://www.youtube.com/watch?v=DsisGSBlQqo
a discussion forum for Polywell fusion
https://talk-polywell.org/bb/
Try this. Four trailers inside.kunkmiester wrote:Thought this might tickle a few brains here. 1950 movie.
http://www.youtube.com/watch?v=DsisGSBlQqo
Isp is best thought of as the measure of rocket efficiency. Technically it is the velocity of the rocket exhaust products divided by gravitational acceleration. For example, H2/LOX has an exhaust velocity of ~4500m/s, and a theoretical max Isp of just over 450 seconds ((4500m/s)/(9.80665m/s^2)).taniwha wrote:I don't know about ISP (I don't grok it yet),
Closer to 16,000m/s. Both the Moon and Mars oddly require almost the same dv to land on, Earth surface to alien surface.taniwha wrote:but the other day I worked out that you need at least about 12km/s delta V to get to lunar orbit (ie, to get into a similar orbit to the moon, not orbit around the moon (eg, leading/trailing trojan): that will be a little extra).
You also need to add in gravitational drag, the Earth's gravitational field trying to drag you back down. Both atmo and grav drag together add a penalty of about 2000m/s to the baseline LEO orbital velocity. The average design dv to reach LEO is between 9500 and 10,000m/s, depending on where you launch from and what altitude of "LEO" you want to achieve.taniwha wrote:Orbital velocity in LEO (150km) is about 7821m/s.
"Orbit" at 10km is about 7907m/s (yes, I know very well you can't orbit at 10km).
Transfer orbit from 10km is 7949m/s@10km and 7779m/s@150km. Since orbit is impossible at 10km, just use its velocity as delta v to get to LEO (plus some, thus the "at least"), and the circularization delta v is about 42m/s, so about 8000m/s (rounding) + atmospheric drag
http://en.wikipedia.org/wiki/File:Deltavs.svgtaniwha wrote:So total delta V to get to Lunar orbit is 8000 (+ drag losses) + 4000 = 12000m/s + drag losses.
Hohmann.taniwha wrote:This ignores any effects of the moon on the orbit and Earth-LEO transfer is very sloppy. Transfer orbits are Holman (sp?)
As I thought, Isp alone isn't enough to answer kunkmiester's question. I just didn't have the confidence.djolds1 wrote:Isp is best thought of as the measure of rocket efficiency. Technically it is the velocity of the rocket exhaust products divided by gravitational acceleration. For example, H2/LOX has an exhaust velocity of ~4500m/s, and a theoretical max Isp of just over 450 seconds ((4500m/s)/(9.80665m/s^2)).taniwha wrote:I don't know about ISP (I don't grok it yet),
The Rocket Equation:
dv = Isp*(G)*ln(Mo/Mf)
Very interesting, and a little surprising, though it agrees with the figures quoted in Apollo 13 (just watched it for the 3rd time, Japanese subs mentioned 17000+m/s on re-entry). Note, however, my figures aren't for landing on the moon, or even going into orbit around it.djolds1 wrote:Closer to 16,000m/s. Both the Moon and Mars oddly require almost the same dv to land on, Earth surface to alien surface.
Does using the parameters of an elliptical orbit from ground not take gravitational drag into account? Indeed, it doesn't take the atmospheric drag into account.djolds1 wrote:You also need to add in gravitational drag, the Earth's gravitational field trying to drag you back down. Both atmo and grav drag together add a penalty of about 2000m/s to the baseline LEO orbital velocity. The average design dv to reach LEO is between 9500 and 10,000m/s, depending on where you launch from and what altitude of "LEO" you want to achieve.
Thanks for that.djolds1 wrote:Hohmann.
That is a sig worthy line.Rocket science is easy. Rocket engineering is... not.
Blogged at the usual places with attribution.kunkmiester wrote:That is a sig worthy line. :lol:Rocket science is easy. Rocket engineering is... not.
Read up on Bob Truax's '60s concept called "Sea Dragon."taniwha wrote:Rocket science is easy. Rocket engineering is... not.
In part. In rocket engineering, mass expended on the way from "Mo" to "Mf" includes not only fuel burned, but also the mass of rocket stages that have been discarded during flight. Also, the usual rule is lower Isp = higher thrust engines; usual but not always. Orions and Nuclear Salt Water Rockets are dirty mothers that deliver the best of both worlds.kunkmiester wrote:ISP tells you how much fuel you need though, for a given time/thrust, right? And that's what you need to know to get all that delta V. Right?