# Could a Mars return mission go directly back to the ISS?

I was reading a FAQ on Mars missions when I came across the following snippet:

NASA does have the rocket technology to get humans to Mars. However, current technology is not advanced enough to get us there efficiently. We are continuing to develop technologies to improve that efficiency. Another challenge we are actively working to overcome is the heat shield that will be needed to protect the returning capsule as it passes through Earth's atmosphere.

The last sentence is what gets me the most. I know the atmosphere is the most effective way we have to shed excess velocity, and if something made it back to Earth from Mars it would have to be going pretty darned fast. But are there other alternatives? Could a Mars mission instead shed its velocity with an anti-gravity-assist on the Moon or some other means and proceed to dock up with the ISS? Or is that simply too much excess velocity to shed given mission constraints...

• An entry heat shield is not that much of a challenge. It would be far greater challenge to do something different. – Mark Adler Feb 8 '16 at 19:47

• Doesn't help. Basically, you can't fall towards the Earth from outside its Hill sphere with your speed being less than ~ 10.8 km/s at ISS orbital altitude, even if you've removed all hyperbolic excess velocity first. There's a couple of ways to get to that same number, one is simply using escape velocity $v_e=\sqrt{2GM/r}$ at target orbital altitude. You'll still have to remove at a bare minimum of about 3,173 m/s and then circularize from eccentricity of ~ 0.02 to basically 0 (about 0.0005 for ISS). First part can be done with aerobraking, second with a not too delta-v heavy impulse burn. – TildalWave Feb 8 '16 at 21:25