Hello hitchhikers and tinkerers!

Nasa wants now short trips to and from Mars for a manned mission to minimize the radiation dose on the crew since some shields have shown impractical. Also, I had wanted to lower the trip's perihelion to stay shortly on Mars, but with short leg durations, this looks compromised even with the Isp=1267s of my Solar thermal engine
http://www.scienceforums.net/topic/76627-solar-thermal-rocket/

So here's my spreadsheet that estimates travel times and speed increments, without nearing to the Sun between the planets - this v5 lets orient the departure from the planet, and is bidirectional.
NonHoMarsRadiusSlice5.zip

Some speed increment examples for 80-days legs with my Solar thermal engine in mind (but are 80 days necessary?):

• Add 7337m/s to low-Mars-orbit (120m/s over the optimum), with 60° angle, brake 17643m/s in Earth's atmosphere (saved 840m/s).
• Add 6346m/s to low-Earth-orbit, with 33° angle, brake 14084m/s in Mars' atmosphere.
• Between locations above planets' gravity, for instance Lagrange points, add 10308m/s near Mars and 11575m/s near Earth.

The departure angle can be tuned a lot to spread the speed increment among Earth and Mars, or to widen the launch window. When aerobraking, the smallest departure speed is favoured, but little more linders much the brutal aerobraking.

Marc Schaefer, aka Enthalpy

An interesting option is to go nearer to the Sun between Earth and Mars. On this portion, the vessel has a higher angular speed than both Earth and Mars; properly done, it permits to lead Earth when arriving at Mars, and then the crew can stay shortly on Mars during the planets' opposition, instead of waiting two years there.

 

 

Because this option adds a portion to the Earth-Mars trip, the travel is longer. The necessary performance would also be much for chemical engines.

 

This spreadsheet for Excel, Gnumeric... is to evaluate such a trip - sorry for the mess. Here one shall choose the perihelion and the speed there; the spreadsheet determines the speeds at Earth and Mars, and the travel and stay times.

 

NonHoMarsInwardsOpposition2.zip

 

Marc Schaefer, aka Enthalpy

The lowered perihelion transfer for a "short stay mission" is long known, also as "opposition-class" mission type. It is considered for instance in 2009 in Nasa's NASA/SP–2009–566
"Human Exploration of Mars, Design Reference Architecture 5.0"
https://www.nasa.gov/pdf/373665main_NASA-SP-2009-566.pdf

Because a short stay gathers less science and needs too long transfers (rays, microgravity) in wasn't favoured in 2009. Meanwhile, sensors on Mars' surface have shown that rays are rather benign there, and the astronauts can shield their house anyway
http://www.scienceforums.net/topic/83289-manned-mars-mission/?do=findComment&comment=895610
so the long stay is a clear choice now. My corresponding spreadsheet here is NonHoMarsRadiusSlice5.

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And because the Xls are lost here, I upload them again.

NonHoMarsRadiusSlice5.xls

NonHoMarsInwardsOpposition2.xls

Edited October 11, 20178 yr by Enthalpy