[X] My Assistant

[Bart]

Hi, I’ve been lurking here for a while, but this is my first post. The recent talk on the Uranus & Neptune orbiter forums about Galileo- vs. Cassini-style tours of the moons of the outer planets reminded me of an idea that I had a while ago.

Would it be possible to arrange a Cassini-style trajectory in the Earth-Moon system that would allow periodic visits of NEOs as they passed by? If you limited yourself to visits within 2-3 million km, you would have about one opportunity per year.

Lunar gravity assists should provide enough delta-v for the necessary plane changes, and the flyby orbits would have periods of ~100 days, allowing for a few assists between flybys.

If you could do close flybys of 5 different NEOs over 5 years without going more than 3 million km from Earth, that would seem like an ideal candidate for a Discovery mission.

The potential problem I see with this idea is that Earth’s Hill sphere is only ~1.5 million km, so you’d be spending a good part of each rev orbiting the Sun instead of the Earth. Would it be prohibitive either in terms of time or delta-v to get a spacecraft from a solar orbit 3 million km from Earth to a lunar return trajectory?

[Phil Stooke]

I looked into this lunar gravity assist question. The communication satellite was Asiasat 3, named HGS 1 after it was salvaged by Hughes. Its lunar flybys were on 13 May 1998 and 7 June 1998.

I didn't find anything about Genesis doing a lunar flyby to set up its re-entry - it did an Earth flyby, certainly. Possibly it did a lunar flyby initially to get out to L1?

That idea of using lunar flybys to get to a Lagrange point was used by WMAP on 30 July 2001. It was done in reverse by ISEE-3 (later renamed ICE, the comet probe) on five occasions, the last on 22 December 1983, to transition from an L1 halo orbit to its comet trajectory. Also, Geotail and Wind, two solar wind probes, used repeated lunar flybys to keep their apogees on the desired side of Earth throughout the year (Geotail on the night side, Wind on the day side).

Phil

[Bob Shaw]

More on the Asiasat 3/HGS 1 Lunar flyby:

http://www.spacedaily.com/news/Book_Reveal...at_In_1997.html

Bob Shaw