Thread by @11K25_Energia

Buran vs Space Shuttle 🧵🧵🧵

In this thread I'll outline some of the similarities and differences between the Space Shuttle with Energia-Buran, from the basics like size and vehicle configuration to capabilities and subsystems.

I hope you enjoy!

The Shuttle uses two Solid Rocket Boosters and 3 main hydrolox engines (RS-25) mounted to the orbiter, Energia-Buran has 4 kerolox boosters (with RD-170 engines) and 4 main hydrolox engines (RD-1020) mounted to the core stage.

The RD-0120 achieves a slightly higher Isp (455 v 452s) and chamber pressure (21.9 v 20.6 MPa) than the RS-25, is less complex, cheaper to manuf. and has a wider throttle range (45-100% v 67-104%) but it's not reusable, produces less thrust (1.96 v 2.28 MN) and is heavier.

The Space Shuttle stack is 56.1m tall and masses 2030t on liftoff. The Shuttle Orbiter is 37.2m long, 17.9m tall, with a wingspan of 23.8m. Energia-Buran is 58.8m tall and masses 2375t and Buran-class orbiters are 36.4m long, 16.4m tall with a 23.9m wingspan.

Both orbiters look similar from afar; this was mostly due to the need for Buran to match the Shuttle's capabilities. Copying the Shuttle provided a safety net for the engineers - in case of failure they couldn't be blamed for doing things differently than the Americans

Both orbiters have a wing surface of 250m², but Buran's wings are "positioned slightly more forward than the Shuttle's to adjust the center of mass in the absence of heavy main engines". The outer leading edges are swept by 45° in both, the inner by 79° on Buran, 81° on Shuttle.

The Shuttle orbiter masses 78t dry and 110t fueled with a 25t capacity to a 200km 28° orbit. Buran-class orbiters mass 65t dry and 105t fueled with a 30t capacity to a 200km 51° orbit. Both have ~18 x 4.5m payload bays.

(Note that for low altitudes (<380km) the Shuttle's deploy capability was downmass-limited; the lack of SSMEs on Buran allows for a much wider payload CoM envelope. Also, Shuttle could launch to inclinations as low as 28.5°, Buran had to fly to at least 51°)

Buran has a slightly better subsonic lift-to-drag ratio than the Shuttle (5.6 vs 4.5). Both orbiters have very similar control surfaces but the max. deflection angles are slightly different (e.g. Buran's elevons could move 35° up and 20° down vs 40° and 25° on the Shuttle).

Both orbiters have conventionally arranged landing gear, although Buran's nose gear is positioned significantly further aft than on the Shuttle. Upon landing, Buran deployed three drag chutes - early Shuttle flights did not carry a drag chute but NASA started using them in 1992.

The TPS config is very similar on both orbiters: black and white silica tiles and felt blankets on most of the orbiter, 22 reinforced carbon-carbon panels on each wing leading edge and a RCC nosecap, although Buran had more silica tiles than Shuttle (38,800 vs 31,000 for STS-1).

Another notable difference in TPS is the layout of the silica tiles. Buran's engineers tried to keep the long edges between rows of tiles perpendicular to the airflow, resulting in a fan pattern.

(Left: Shuttle, Right: Buran)

The crew modules of both orbiters have a very similar layout; up to 4 seats in the flight deck and up to 6 seats in the mid-deck (the Shuttle never flew with a crew larger than 8, but theoretically two extra seats could be installed in place of sleep stations in the mid-deck)

Both orbiters have similar nose RCS clusters, but the Shuttle's OMS engines and aft RCS thrusters are located in two large pods either side of the fuselage, while Buran only has the RCS clusters outside of the fuselage and the OMS base unit (ODU) is housed inside the fuselage.

Both had 38 primary RCS thrusters. Buran had 4 verniers per aft RCS cluster and none in the nose (8 total), while Shuttle had 2 per OMS pod and 2 in the nose (6 total).

Perhaps the most significant difference between Shuttle and Buran (other than main engine placement) is the propellant combination used in the RCS and OMS systems. Shuttle uses the hypergolic N2O4/MMH for both OMS and RCS while Buran uses a (semi)cryogenic mix of LOX and sintin.

In addition to being safer to handle, the use of cryo props made Buran's orbital man. engines' performance higher than Shuttle's and allowed for LOX crossfeed to the fuel cells and indirectly to the life support system.

The Shuttle can crossfeed propellant between the two OMS pods and between OMS and RCS tanks therein, Buran can transfer both between the primary and auxilliary ODU tanks (akin to OMS-RCS tank crossfeed) and between the ODU tanks and the nose RCS cluster.

Buran was designed to use two robotic arms to allow for more flexibility in payload manipulation and back-up capability, both could be operated from mission control. The Shuttle used one robotic arm and (on later flights) the OBSS extension, which had to be operated by the crew.

The Shuttle's Solid Rocket Boosters were reusable; after a parachute splashdown and refurbishment their components could be reused many times. Buran's Block A boosters were designed with reuse in mind but flew without recovery hardware on both launches and were expended

Energia's core stage is very similar to the Shuttle ET (with the exception of the engine compartment of course), but has a smaller diameter (7.75m vs 8.4m). The Shutte ET's LOX feed line was placed on the outside of the tank while Energia's ran inside at a 7° angle.

Both the ET and Energia's core used a combination of polyurethane-based spray-on foam insulation and ablative material. Energia's propellants were loaded at lower temp. than Shuttle (-255°C vs -253°C for LH2 and -195°C vs -182°C for LOX); this reduced boiloff losses.

The Shuttle program used an unpowered glider released from a 747, Enterprise, to train pilots and rehearse landings. Since the USSR didn't have a plane large enough, the Buran program used OK-GLI, which had 4 turbojets and could take off on its own.

Each Shuttle flight was controlled by the guidance systems in the Orbiter, while Energia (due to being a standalone LV) had its own guidance. Also, Buran could fly uncrewed from its first flight, a capability the Shuttle got late in the program and which was never demonstrated.

The Energia-Buran stack was integrated horizontally and used "grasshopper" transporter-erectors inherited from the N1 program. The Space Shuttle stack was integrated vertically (for reasons), which is slower and more expensive but allowed it to launch some DoD payloads.

Buran's use of liquid boosters instead of SRBs offered more rescue options than Shuttle. Both systems did (or were planned to) fly early missions w/ crews of 2 and ejections seats in the flight deck; the seats have similar speed/alt specs (24km/Mach 2.7 Shuttle vs 30km/M 3 Buran)

Since the seats work for the first ~100s of flight, ejecting on Shuttle would mean descending through the SRBs' (spicy) plume, Buran crews could eject (relatively) safely throughout the 100s period.

In case of a forced shutdown of all engines above the max ejection seat use altitude, Buran could use its 4 emergency separation motors to separate from the Energia stack, although this would be a tricky and risky maneuver.

The Shuttle orbiter could not separate during SRB flight, meaning that it'd have to wait until SRB sep to initiate the RTLS abort, TAL, Abort Once Around, or Abort to Orbit. Failure of one SSME could be compensated for by a longer burn.

In case of a failure of the RD-170 in one of the boosters, the engine on the opposite side would be shut down to ensure symmetrical thrust. Failure of one the core engines could also be compensated for by a longer burn. Post-booster-sep abort modes are equivalent to the Shuttle's

Thanks for coming to my Ted Talk

If I forgot about something, please let me know and I'll add it below

The main source for all of this is of course Hendrickx' and Vis' "Energiya Buran, The Soviet Space Shuttle" and buran.ru

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