Aug09
Mars Spreadsheet Update
on August 9, 2012 at 8:41 amFor anyone interested, I’ve got a new, improved version up. It’s basically more organized, with the constants grouped together, and with no references to rows below the formula.
For anyone interested, I’ve got a new, improved version up. It’s basically more organized, with the constants grouped together, and with no references to rows below the formula.
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Line 56 you’re evidently leaving directly from EML to the transfer orbit.
A .7 km/s burn can drop you from EML1 to a 300 km perigee. At this perigee you’d be moving 10.8 km/s, just a hair under escape (10.9 km/s).
sqrt(10.9^2+1.65^2) = 11.05 km/s.
11.04 – 10.81 = .23. .23 km/s at perigee will send you on your way.
Between .7 km/s to drop to a deep perigee and .23 insertion burn, total is about .93 km/s.
Your 1.47 km/s is a needlessly high delta V that ignores possible Oberth benefits that can be had from dropping from high orbit to a perigee deep in earth’s gravity well.
Yes, this was discussed previously. It’s actually been a long time since I’ve done any serious orbital mechanics. I was just doing a quick-n-dirty to demonstrate the concept. There is a lot of refinement to do, and a lot of trade space to explore.
I agree with John Schilling that heliocentric depots between Mars and earth aren’t a good idea.
But depots at EML1 or EML2 could be a huge help. EML1 has about a 2.4 km/s advantage over LEO. There’s a 8 day route from EML2 where you can drop to a deep perigee for virtually no delta V. EML2 can have a 3.1 km/s advantage over LEO.
If PR is successful in getting propellant to EML1 or 2 this could make travel to deep space destinations (NEOs, Mars, etc) much less difficult. It could also help with travel about cislunar space
I agree with John Schilling that heliocentric depots between Mars and earth aren’t a good idea.
Yeah, an SML1/2 depot would be more useful and once you have it the remaining hops are very small, so you don’t need additional staging along the way. It’s a mere 2 km/s from EML1/2 to SML1/2.
That said, I have wondered whether a set of gateway stations and communication / navigation satellites at the Sun Earth or Sun Mars Lagrange points or both could be useful. I think it would allow you to launch prepositioned rescue craft from at least one such location at any time without phasing difficulties. And the communication and navigation network in the inner solar system could also be very useful.
A .7 km/s burn can drop you from EML1 to a 300 km perigee.
And with a lunar flyby before the Earth flyby you can reduce the cost even more. This is the reverse of the approach to getting to the moon that Kirk Sorensen has been evangelising.
Ah, I see you mentioned that 8 day route already.
Hop David is too modest to mention it himself, but over the years he has made many illuminating drawings of concepts and problems in orbital mechanics.
I still need to buy his book, and so probably should all of you:
Conic Sections & Celestial Mechanics Coloring Book
Thank you, Martijn.