AFAIKR, orbital velocity is something like 5.1 km/s, or about 26,100 ft/s, significantly in excess of the 6,000 ft/s exhaust velocity of LH2/LOX. While you are braking, you are initially giving your exhaust a 6,000 ft/sec boost over your velocity, it quickly loses that as it hits ionospheric plasma: the hydrogen ions that make up the microvacuum of LEO (LEO is not a perfect vacuum by any stretch). The lower your orbit, the more there is, the atmosphere just doesn't stop at a defined boundary. Being in orbit is merely being high enough that you can't measure an indicated air speed, which is different from there being no gas at all. A spacecraft stays in orbit because it is dense and has a lot of momentum. Exhaust gasses are not dense and cannot maintain momentum against gas of equal or slightly lesser density.<br /><br />As your exhaust plume expands after it leaves your nozzle, in accordance to the gas law, it eventually drops to near the ambient pressure of your surrounding space, at which point its momentum is totally cancelled by space plasma, and it becomes a contribution to the space plasma that, if it is in your trajectory, is going to heat you up when you hit it. While it is far far less dense than atmosphere would be at reentry, you spend a lot more time passing through this lower density hot plasma.<br /><br />If you are high enough in orbit, this isn't an issue, but in LEO its an issue that is highly dependent upon your altitude.<br /><br />My proposed alternative is like that used by GE in my prior post: very shallow reentry with large surface area, to slowly skip-dive multiple times. The shuttle comes in hot and heavy cause its a brick with stripes. JP Aerospace's proposals are in line with my own ideas on this.