[Space, Spaceships] Mars Semi-Cycler?

[DaltonS]

Originally Posted by DaltonS

I've come to prefer the idea of the free-return semi-cycler. Instead of using an orbit based on the Earth-Mars synodic period (780 days), the ship would use a free-return orbit of exactly 2 years (730.5 days) which would require two 3.16 mps burns to leave and re-enter Earth orbit, where it stay for 49.5 days being refueled and refurbished for the next mission. According to my calculations, the taxis would require a ∆V of 5.68 mps between the cycler and Mars orbit each way because the transfer orbit crosses that of Mars at an angle of 21.6 degrees.

I've come to a bit of a quandary. According to my calculations based on these formulas, the time of flight from Earth to Mars orbit should be 127 days. However, according to GURPS Mars

With a delta-V of 3.2 miles per second (11,520 mph), the crew can follow a free-return path which will get them to Mars in 180 days; this speed is still low enough to make aerobraking at Mars practical.

Trajectories sidebar, p.32

That's almost 8 weeks difference. Have I missed something?

Dalton “who is proud of his "One-Tangent Burn" spreadsheet” Spence