Soft landing on the moon discussion

[DougF]

I thought you might like to see some diagrams, so here you are, I'll put my two cents in where I can.

Project Apollo Diagrams
Apollo Lunar Module
Apollo Lunar Module - Wikipedia, the free encyclopedia

[Qfwfq]

Originally Posted by Janus

Starting at an orbital altitude 100km. First you do a 230m/s burn to put you in a moon grazing elliptical orbit. At perigee, your speed will be 1704m/sec, which is the velocity you need to shed. total delta v = 1934 m/sec, more than the value above.

That certainly isn't the only way and sure isn't the easiest.

[Roadam]

Apollo lander has designated delta v of 2470m/s as a descent with rockets, go get figure.

[Pyrotex]

Informational presentation at :

Idaho National Laboratory - Nuclear Energy

Click on "Space Nuclear" in the frame at far left, about 4 inches down.

Various types and sizes of Radioactive Thermoelectric Generators (RTGs).

Useful for Lunar missions -- when you don't wanna hafta go to sleep when the Sun goes down!!

[Roadam]

Various types and sizes of Radioactive Thermoelectric Generators (RTGs).

Useful for Lunar missions -- when you don't wanna hafta go to sleep when the Sun goes down!!

Usefull, but not really needed, maybe on lander. Those things have low power output compared to their weight, although they last long.

Recently I looked into the three default rockets and it turned out that only rockot has reignitable upper stage. Also it has the best isp of all three, 310 in vacuum. Surely its third stage could be extended and maybe even used as a lander...

[Janus]

Originally Posted by Roadam

Recently I looked into the three default rockets and it turned out that only rockot has reignitable upper stage. Also it has the best isp of all three, 310 in vacuum. Surely its third stage could be extended and maybe even used as a lander...

Checking the specs, the net mass of the upper stage is 1820 kg. Even if the entire payload (1850 kg) was extra fuel, you wouldn't have enough to reach a translunar trajectory.

Gotta dump that last stage, it represents too much dead weight.

One draw back for the Eurockot that hasn't been mentioned yet is that the payload value given is for an orbit with an inclination of 63 degrees. That's going to increase the delta v needed to make a proper moon intercept, as it involves an additional course correction.

[Roadam]

Originally Posted by Janus

Gotta dump that last stage, it represents too much dead weight.

One draw back for the Eurockot that hasn't been mentioned yet is that the payload value given is for an orbit with an inclination of 63 degrees. That's going to increase the delta v needed to make a proper moon intercept, as it involves an additional course correction.

You are right of course. Smaller engine would be better. As for inclination problem: Does inclination really needs to be zero if one wants to make ideal moon approach? If I am not mistaken there are some companies that launch from equator, or close to it at least. Maybe even a ride on one of the Arianes?

Quick thought: Maybe the whole 1.6tonnes could still be one last stage, if we could find an engine with thrust that just still allow earth departure, and also strong enough to kill orbital velocity and make gravity turn landing on the moon. Combine it with fuel tanks that can be dumped in transit...

On the hunt

[Janus]

Originally Posted by Roadam

You are right of course. Smaller engine would be better. As for inclination problem: Does inclination really needs to be zero if one wants to make ideal moon approach? If I am not mistaken there are some companies that launch from equator, or close to it at least. Maybe even a ride on one of the Arianes?

Here's the thing, a 1° difference in inclination at the Moon's distance equals a distance of 6700 km or over 3 times the radius of the Moon. The minumum difference in inclination between the Eurockot LEO orbit and the Moon's orbit is 34°.
If you don't match inclinations, it really limits your launch windows. you can only make the translunar trajectory burn when you are at a point when the orbits cross, and the Moon is in the right position in its orbit to be at the opposite node when the craft arrives. And when you arrive, the Moon and probe will be traveling along different vectors, so it will take a little extra delta v to match velocities for a landing. It might only be a difference of a few meters per second, but every bit of extra delta v is a little less useful payload we can deliver to the surface.

[Qfwfq]

Looks like the Chinese are beating you to it! Launched shortly after noon CET today, Chang'e One is planned to orbit the moon for a year examining its surface. No doubt they'll be putting something on the surface in a near future mission and perhaps even taikonauts.

[TheBigDog]

Originally Posted by Qfwfq

Looks like the Chinese are beating you to it! Launched shortly after noon CET today, Chang'e One is planned to orbit the moon for a year examining its surface. No doubt they'll be putting something on the surface in a near future mission and perhaps even taikonauts.

The pressure is clearly on them. They don't want to be upstaged by a group of hobbyists. I wish them all the success they can get. I can only hope that they intend to share their research.

Bill