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Just thinking this through, because I'm more familiar with airplanes than manned rockets: The design has 4 parachutes, likely for packaging and design constrai

Just thinking this through, because I'm more familiar with airplanes than manned rockets: The design has 4 parachutes, likely for packaging and design constraints, but also provide some level of redundancy. My comment wasn't clear now that I re-read it, but if you use a propulsive landing after a propulsive abort, you'd need additional fuel. If you remove the parachutes, that weight could then be used for landing fuel, but fuel weight may still exceed that. I haven't run the numbers. The aborted dragon, after leaving Falcon, is now a self-contained vehicle carrying multiple people. It is a redundant and failsafe safety part of the entire system, but it's hard for me to believe it would be designed with everything having to work perfectly after an abort in order to safely return the occupants. Guidance and Control, life support, propulsion... I'm mainly wondering if you were aware of the systems they would have in place on a propulsive return. It seems that the amount of fuel to return all the way downrange back to land on a propulsive abort would be more than the parachute weight, which forces a water landing. And since you already design the capsule for carrying those parachutes, you might as well use them on a normal landing as well. That cuts down on additional weight for an abort return. I also don't know that if you have a successful launch, that you have enough reserve from un-used launch abort fuel to then land the capsule without chutes. Seems unlikely, especially with needing failsafe/redundancy.

lutorm 7y ago
The Superdracos are powerful engines but they don't have anything near the delta-v to always return to land after an abort even if you fill the entire Dragon with propellant. So you'd always need the chutes anyway. One additional issue with propulsive lsnding is that you need legs, and they need to penetrate the heat shield. This significantly complicates and weakens an absolutely critical part.
- speedplane 7y ago
  > The Superdracos are powerful engines but they don't have anything near the delta-v to always return to land after an abort even if you fill the entire Dragon with propellant. So you'd always need the chutes anyway. Not sure that's true. The chutes bring the speed of the capsule down quite a bit, just a short burst of the dracos at the last few feet could allow it to softly land and wouldn't require much propellant. This is exactly what the Soyuz does. My guess is that this approach was rejected by NASA (not SpaceX) due to complexity rather than feasibility.
  - hadlock 7y ago
    This is what's referred to in some circles as a "suicide burn"; in that you wait until the absolute last second, then ignite the engines at full throttle to zero out velocity. Assuming the engines work, it's very efficent as you're not accruing what's called "gravity drag" as the velocity goes to zero very rapidly and you're not fighting 9.8m/s acceleration. If the engines don't start, or you don't get the predicted thrust out of them, well, that's why it's called a suicide burn.
    - speedplane 7y ago
      > If the engines don't start, or you don't get the predicted thrust out of them, well, that's why it's called a suicide burn. Fair enough, but this is exactly what the Soyuz has done for decades, and NASA (as well as Roscosmos) found the approach to be acceptable for human spaceflight. It may introduce complications, but it's clear that it's doable.

lutorm 7y ago

The Superdracos are powerful engines but they don't have anything near the delta-v to always return to land after an abort even if you fill the entire Dragon with propellant. So you'd always need the chutes anyway. One additional issue with propulsive lsnding is that you need legs, and they need to penetrate the heat shield. This significantly complicates and weakens an absolutely critical part.

speedplane 7y ago
> The Superdracos are powerful engines but they don't have anything near the delta-v to always return to land after an abort even if you fill the entire Dragon with propellant. So you'd always need the chutes anyway. Not sure that's true. The chutes bring the speed of the capsule down quite a bit, just a short burst of the dracos at the last few feet could allow it to softly land and wouldn't require much propellant. This is exactly what the Soyuz does. My guess is that this approach was rejected by NASA (not SpaceX) due to complexity rather than feasibility.
- hadlock 7y ago
  This is what's referred to in some circles as a "suicide burn"; in that you wait until the absolute last second, then ignite the engines at full throttle to zero out velocity. Assuming the engines work, it's very efficent as you're not accruing what's called "gravity drag" as the velocity goes to zero very rapidly and you're not fighting 9.8m/s acceleration. If the engines don't start, or you don't get the predicted thrust out of them, well, that's why it's called a suicide burn.
  - speedplane 7y ago
    > If the engines don't start, or you don't get the predicted thrust out of them, well, that's why it's called a suicide burn. Fair enough, but this is exactly what the Soyuz has done for decades, and NASA (as well as Roscosmos) found the approach to be acceptable for human spaceflight. It may introduce complications, but it's clear that it's doable.