The heat shield is a major part of the space shuttle, it protects it during the re-entry in the dense layers of the atmosphere, because the temperature could grow up to 1200☌. Then a parachute slow them down until they reach the Ocean where they sea land. For STS the boosters are ejected after 2 min burn. Finally to slow down near touch down retro-rockets are turned on and landing gears are deployed to land them safe. A small parachute is deployed to them down, once the atmosphere is more dense a bigger one is deployed. Once they burn all their propellant they are ejected from Energia in pair (to avoid damaging the shuttle), then they are separated. The boosters of Energia are also reusable but they use a totally different scheme. The dimensions of the launcher are nearly the same (the Energia's boosters are smaller), but because Energia uses liquid propellant it is more powerful than STS. This is a major difference in design because liquid propellants are more powerful that solid (chemical), and the engines can be easily controlled (increase or decrease the power, or cutting off), so in case of emergency they can be cut-off and prevent the launcher from explosion. The 1st stage is made of 4 boosters which are burning fuel and oxygen instead of solid propellant. A central block (2nd stage) with strap on boosters on its side (1st stage). The scheme of Energia is nearly the same of STS. So the engines are on the Energia launcher. This difference lead to another one, Buran needed a launch vehicle whereas the STS Shuttle is its own launcher.

The STS Shuttle has powerful engines because they are used for the putting into orbit, but once there they are useless. Buran was only a payload of the Energia LV so its engines was only for the orbit trajectories.

This due to an important difference in the design process. The major difference is the rear of the shuttles, STS have 3 powerful engines SSME for the lift-off whereas Buran has no.

But Buran is a little bit lighter than the STS orbiter (62 tons instead of 68 tons). As a whole the 2 shuttles have the same dimensions, mainly because Buran was made to be a counterpart of the STS Shuttle.

Buran shuttle rf syste