Mars halo mirror for terraforming?

Leaving aside the debates about Mars' desirability etc ........

Zubrin and McKay have proposed statite reflectors for heating Mars.
http://www.users.globalnet.co.uk/~mfogg/zubrin.htm

This concept has some problems with the stability of mirrors, and also
the fact that not all of the sun is visible to the mirror, because
Mars blocks the sun. Stability needs to be maintained in three
dimensions, and the mirror needs to be kept flat, or at least have a
controlled curvature.

How about an alternative: A halo mirror. This would be a ~10,000km
diameter halo shaped mirror, placed behind Mars where the
gravitational and light forces balance. (This would be in a bit from
the Sun / Mars L2 point). The halo width would vary according to how
much heating is required, but about 30km width would give 1 million
km2. Solar power reflected is about 500TW, and the solar force is
about 35KN.

The halo would be angled in to illuminate the night side of Mars. The
angled reflection of light pushes the mirror outward, but given the
angle, the hoop stress would be around 5KN. This maintains the shape
of the ring. If additional hoop stress is needed, the system can be
slowly rotated.

In effect this creates a rigid tensional structure. A few heavy steel
cables, made on Diemos, maintain the structures rigidity. (Carbon
tubes could also be used, but I suspect steel is easier). If the outer
steel cable is heavier than the inner cable, then this one will always
be in front (nearer to Mars and the Sun), thereby maintaining the
reflection angle. (The inner hoop has a small net force towards Mars,
the outer hoop has no force, and the reflector has a small net force
away)

This concept seems easily scalable to a halo width of hundreds of
kilometres. The forces are small enough to make the engineering
straightforward - at least for the scale that is.