I don't think the capsule has the right aerodynamic properties to allow it to work as a proper lifting body in the 0.01 ATM Martian atmosphere. We don't really have any experience about lifting bodies on Mars, even less than we have about huge supersonic parachutes.
You can't land on Mars with just a parachute anyway, not with a 900 kg payload. The main problem with Mars is that its atmosphere is just dense enough that it complicates things but not dense enough that it's really helpful.
Apparently according to this video [1] (about half way through) the capsule is a lifting body however I was thinking of something like a simple guided arrow, perhaps some fins that are extended on a telescopic shaft. You could possibly then put a tractor rocket at the end of this shaft to slow descent and keep the rocket plumes away from the main body and the ground.
Regarding parachutes, is it not the case that if you need more performance, that you simply increase their size?
Unless the atmosphere is so thin that the added weight of the parachute and it's support hurts more than it helps. 0.6 kPa is really that bad.
The effectiveness of a parachute grows at a square of your airspeed. This means that every planet has a minimum speed you can successfully slow down to using parachutes with a given system. For realistic loads and conventional materials, on Mars that is about 50m/s. Which is just too fast.
> I was thinking of something like a simple guided arrow, perhaps some fins that are extended on a telescopic shaft
It's one thing to say it, it's another to design it such it has a chance of working. Telescoping mechanisms with deployable aerodynamic structures sounds very complicated to me, compared to the thrusters they're using.
> You could possibly then put a tractor rocket at the end of this shaft to slow descent and keep the rocket plumes away from the main body and the ground.
The sky crane already does this.
> Regarding parachutes, is it not the case that if you need more performance, that you simply increase their size?
'Performance' is lots of things, presumably you mean drag. Increasing the diameter does increase the drag, but it also increases the opening forces, which requires a stronger structure, which means more mass. You don't have the luxury of much margin when every gram in your landing system has cost the us taxpayer thousands of dollars and is a gram that you can't use for science.
You can't land on Mars with just a parachute anyway, not with a 900 kg payload. The main problem with Mars is that its atmosphere is just dense enough that it complicates things but not dense enough that it's really helpful.