NASA-funded R&D engineers are working on plans for future spaceships to enter orbit around Mars using a doughnut shaped, steerable balloon-chute to slow down by flying through the Red Planet's atmosphere.
Global Aerospace is a Californian firm founded by ex-NASA engineers and in this case funded with NASA Small Business Innovation Research (SBIR) money. The company announced yesterday that it would start modelling work aimed at developing what it calls a "lifting-towed-toroidal-ballute" for use by spacecraft approaching planets with a view to entering orbit around them, or perhaps subsequently landing on them.
More: http://www.theregister.co.uk/2009/04/17/doughnut_ballutes_go_to_mars/