Shuttle circular de-orbiting ?

Right now, for de-orbit, they make one big burn, putting the shuttle
into an elliptical orbit whose perigee brings the shuttle low enough to
hit "dense" atmosphere for re-entry interface.

What if they lowered the Shuttle's orbit in a more circular fashion
(multiple smaller burns) ? The shuttle would still lose the same amount
of energy from the de-orbit burns, but it would not hit dense atmosphere
right away and be able to bleed more energy from orbiting through light
atmosphere, and this would also gradually lower its orbit, giving a much
more gradual deceleration, and by the time it his dense atmosphere,
wouldn't it have bled much more energy than the current scenario, hence
less heat load on the heat shield ?


If de-orbiting in a circular fashion would not bring teh shuttle low
enough to hit sufficient atmosphere to slow it down, perhaps a hybrid
solution could be use with just a slightly eliptical orbit where
multiple passes through atmosphere at the perigee would bleed more still
slow the shuttle down before it actually get low enough to really start
to heat up ?

Has this ever been studied before ?