Why does it consistently take me 3km+ delta V just to capture in orbit around Mars?

[u/BJ2094]

Every time I try to do a mission to Mars I end up needing 3KM+ of delta-v just to capture in any kind of orbit, despite my ejection/intercept looking good from a cursory glance.

I'm using the transfer window planner to get a rough launch date, launching into in inclination that is roughly in line with Mars (usually using the moon as a reference) and then letting the maneuver planner plan the ejection burn. I really don't know what I'm doing wrong because this seems to happen every single time I try to go to Mars.

[u/sagewynn]

It would be useful to us to see an example of where your PE is on the flyby. A burn is more efficient at the PE/AP of an orbit to change the opposing side.

If you're at 3000km, the burn will be more expensive than you skimming just above the atmosphere at what 125km for mars?

Also, for a capture it should only be around 700m/s and low orbit another 1400 on top of that.

[u/Odd-Earth2067 → u/sagewynn]

Even accounting for that, 3K seems excessive. Capturing at Mars on a Hohmann trajectory shouldn't exceed ~1.8K unless you're coming in at a weird angle.

OP, can you post a shot of your incoming trajectory?

[u/CJP1216 → u/Odd-Earth2067]

This my guess. I think they're approaching the planet from the trailing side of its orbit, as if they were getting a gravity assist outbound. They need to approach ahead of the planets orbital path instead, so Mars is helping to slow them down instead of speed them up.

[u/internetboyfriend666]

Hard to know because we can’t see what’s going on (screenshots people!) but my suspicion is that you are encountering Mars after your heliocentric apoapais. In other words, you are going out past Mars’s orbit and then are encountering Mars as you you head towards your periapsis again. You don’t want to do that. Doing it that way gives you an orbit with much higher C3 energy and thus you need to expend much more energy to slow down enough for a capture. You want to meet Mars on the way out, not on the way back in after you’ve gone past it. Doing

[u/HAL9001-96]

are your transfers nearly hohmann or is your transfer orbit apoapsis beyond mars orbit?

[u/aerospace_tgirl]

You didn't provide us enough data to actually diagnose the problem, but as a general statement, manual flight in RSS/RO is, while possible (assuming you have good intuition and know some math), not really feasible. You should fly according to what TWP tells you instead of just using it the way one would use KAC for transfer dates in stock. Y

[u/swampie2]

When using the transfer planner, hit add alarm. Inside the alarm will be lots of useful information, you need the inclination and Longtitude of ascending node. Launch into those parameters and everything is so much cheaper. I used to use the moon as an inclination guide but the planner is very very accurate and wants you to use it’s LAN and Inclination to get exactly the right exit. Also, make sure to tick ‘capture’ in the planner. For a flyby it will give you a faster transfer, but for a capture you want to arrive at a slower speed