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The Space Shuttle had the benefit of having some lift and some controlability via control surfaces (elevons and a rudder). While it had a famously terrible gli
by _verandaguy 2y ago
The Space Shuttle had the benefit of having some lift and some controlability via control surfaces (elevons and a rudder).
While it had a famously terrible glide ratio, it did glide, and this meant that it could use these control surfaces to steer without needing to carry or burn extra fuel -- which is very important in a weight-critical field like spacecraft design.
Capsules don't produce any lift, for all practical purposes. They can't be steered using control surfaces, at least not in the same way as the Shuttle orbiter; their best means of slowing down are either a chute or soft-landing boosters, or both.
Chutes are subject to the wind, while soft-landing boosters fire only a few feet above the ground, and neither give any real steering ability. Between this and trajectory variations on re-entry caused by wind throughout the atmosphere, you can't achieve the same level of precision when landing a capsule compared to the Shuttle orbiter.
- fouronnes3 2y agoCapsules do generate lift by having a slightly offset center of mass and control its orientation by rolling the entire capsule. This is used since the Apollo days to steer to the landing site. Even mars rovers use capsule lift during mars entry to steer.
- accrual 2y agoIndeed, there's some neat old school diagrams showing how the capsule lift worked. It's a bit unintuitive at first, but if you have a blunt/rounded object traversing the atmosphere at a few times the speed of sound, slightly shifting the CoM around and tilting/rolling the capsule can dramatically affect the landing site.