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The big one off the top of my head: Dream Chaser flies in a fairing for aerodynamic reasons. In order to fly crew (so that the vehicle could have a working lau

The big one off the top of my head: Dream Chaser flies in a fairing for aerodynamic reasons. In order to fly crew (so that the vehicle could have a working launch abort system), they'd need to figure out how to fly without a fairing.

SJC_Hacker 2y ago
Can't they blow the fairing as part of launch abort?
- nordsieck 2y ago
  > Can't they blow the fairing as part of launch abort? I'm not a rocket scientist, so I don't really know the answer. But I have some questions: * How reliable will the "blow the fairing" system be? If it's only used in emergencies (instead of the regular fairing separation mechanism) than it'll suffer from the same problem as emergency generators - they're rarely tested and fail very often when needed. * How easy is it to get the fairing out of the way once it's opened? Normally, regular aerodynamic forces slough the fairing halves off, but an LES/LAS doesn't have time for that - it's escaping a potentially exploding rocket. And those fairings will act like sails - huge surface area:volume ratio means they're just not going to move fast. * What happens if DreamChaser hits one of the fairings on the wing? Would it damage it enough that it'd have trouble landing? Is it enough to cause it to foul the escape trajectory? Or even put it in a spin? It seems like a lot of work to get it to work with or without a fairing.
- giantrobot 2y ago
  That's one more thing to go wrong. In a LES scenario something(s) has gone wrong in an unrecoverable way. Very few systems can be relied upon to exist let alone work correctly. A LES on a crewed capsule is supposed to be able to pull itself from the vehicle all under its own power. It can't assume explosive fasteners on the fairing are functional or actual all function correctly. You don't want the LES to activate, seem to be working correctly, and then blast the crew into a fairing panel that did not fully separate. The crew doesn't have time to roll down the window and kick it loose.
- m4rtink 2y ago
  Soyuz launches with the crew capsule under fairung and even stacked under the orbital module - it still has a LES[0], that pulls off the whole fairing away & then drops the capsule once clear of the rocket. A bit complicated but was already used in emergency and worked. [0] https://en.wikipedia.org/wiki/Soyuz_abort_modes#Jettisonable_emergency_escape_head_section https://en.wikipedia.org/wiki/Soyuz_abort_modes#Jettisonable...
enragedcacti 2y ago
From some quick reading it seems like the crewed Dream Chaser is intended to fly without a fairing. The cargo version's ability to fold the wings and fly within a fairing seems to be for 1) compliance with NASAs CRS-2 requirements, 2) wide compatibility with existing boosters that weren't designed for the forces that flying without a fairing would create. Could be spin from Sierra but that's what they were saying to the press as of 2015 when they announced the cargo variant. https://spacenews.com/sierra-nevada-hopes-dream-chaser-finds-sweet-spot-of-iss-cargo-competition/ https://spacenews.com/sierra-nevada-hopes-dream-chaser-finds...
- NotSammyHagar 2y ago
  The problem with the wings is they generate lift during launch and that will screw up the rocket, thus the fairing. I thought there was no known solution for that.
  - NortySpock 2y ago
    Fold the wings up? Seems like Starship fins and Falcon 9 grid fins did that trick as well.
  - enragedcacti 2y ago
    It seems like you could mitigate that by designing the wing such that when mounted the angle of attack is 0 and thus no lift is generated. Obviously the wing would still have an effect when the booster changes orientation or in cases of high winds. I'm not remotely qualified to calculate the scale of those forces but I don't see why any of that would be a guaranteed showstopper given a booster with enough thrust vectoring capability.
  - adastra22 2y ago
    Not any different than shuttle or energia. Lift can be accounted for. It’s not as easy as launching in a fairing, but it’s certainly not impossible.
oooyay 2y ago
Naive question: Planes and helicopters do not have the ability to safely eject passengers mid-flight. We largely accept these conditions as a risk of those modes of travel. Why is LES/LAS a unique requirement for space shuttles?
- JoeCortopassi 2y ago
  planes/helicopters have a fuel source that is orders of magnitude less volatile, and are also able to safely land without power
  - philwelch 2y ago
    What fuels do you mean in particular? If you’re talking about hypergolic propellants, those aren’t commonly used as a main propellant on manned rockets. Most planes and helicopters use kerosene, which is also the primary fuel used by the launch stages of manned rockets.
- nordsieck 2y ago
  > Planes and helicopters do not have the ability to safely eject passengers mid-flight. We largely accept these conditions as a risk of those modes of travel. Why is LES/LAS a unique requirement for space shuttles? That's a fair point, although my understanding is that parachute systems for small planes are becoming more common. My view is that flight rate is the fundamental issue at hand. Airplanes and helicoptors fly many orders of magnitude more than these capsules, which means we know they are many orders of magnitude more reliable. They've also generally been through a long process of refinement - the original airplanes were extremely dangerous compared to modern variants. Additionally, aircraft can afford to have a lot higher margin of safety baked in to them. Because of how high gravity is on Earth and the nature of the Rocket Equation[1], it's just not possible to have a lot of margin in rockets of capsules. They need to be extremely svelt to launch at all. And lastly, we have experience with human spacecraft without an LES/LAS - it was the Space Shuttle. And it killed 14 people - easily the most dangerous spacecraft ever created. No one has any desire to build on that particular legacy. --- 1. https://en.wikipedia.org/wiki/Tsiolkovsky_rocket_equation https://en.wikipedia.org/wiki/Tsiolkovsky_rocket_equation

SJC_Hacker 2y ago

Can't they blow the fairing as part of launch abort?

nordsieck 2y ago
> Can't they blow the fairing as part of launch abort? I'm not a rocket scientist, so I don't really know the answer. But I have some questions: * How reliable will the "blow the fairing" system be? If it's only used in emergencies (instead of the regular fairing separation mechanism) than it'll suffer from the same problem as emergency generators - they're rarely tested and fail very often when needed. * How easy is it to get the fairing out of the way once it's opened? Normally, regular aerodynamic forces slough the fairing halves off, but an LES/LAS doesn't have time for that - it's escaping a potentially exploding rocket. And those fairings will act like sails - huge surface area:volume ratio means they're just not going to move fast. * What happens if DreamChaser hits one of the fairings on the wing? Would it damage it enough that it'd have trouble landing? Is it enough to cause it to foul the escape trajectory? Or even put it in a spin? It seems like a lot of work to get it to work with or without a fairing.
giantrobot 2y ago
That's one more thing to go wrong. In a LES scenario something(s) has gone wrong in an unrecoverable way. Very few systems can be relied upon to exist let alone work correctly. A LES on a crewed capsule is supposed to be able to pull itself from the vehicle all under its own power. It can't assume explosive fasteners on the fairing are functional or actual all function correctly. You don't want the LES to activate, seem to be working correctly, and then blast the crew into a fairing panel that did not fully separate. The crew doesn't have time to roll down the window and kick it loose.
m4rtink 2y ago
Soyuz launches with the crew capsule under fairung and even stacked under the orbital module - it still has a LES[0], that pulls off the whole fairing away & then drops the capsule once clear of the rocket. A bit complicated but was already used in emergency and worked. [0] https://en.wikipedia.org/wiki/Soyuz_abort_modes#Jettisonable_emergency_escape_head_section https://en.wikipedia.org/wiki/Soyuz_abort_modes#Jettisonable...

enragedcacti 2y ago

From some quick reading it seems like the crewed Dream Chaser is intended to fly without a fairing. The cargo version's ability to fold the wings and fly within a fairing seems to be for 1) compliance with NASAs CRS-2 requirements, 2) wide compatibility with existing boosters that weren't designed for the forces that flying without a fairing would create. Could be spin from Sierra but that's what they were saying to the press as of 2015 when they announced the cargo variant. https://spacenews.com/sierra-nevada-hopes-dream-chaser-finds-sweet-spot-of-iss-cargo-competition/ https://spacenews.com/sierra-nevada-hopes-dream-chaser-finds...

NotSammyHagar 2y ago
The problem with the wings is they generate lift during launch and that will screw up the rocket, thus the fairing. I thought there was no known solution for that.
- NortySpock 2y ago
  Fold the wings up? Seems like Starship fins and Falcon 9 grid fins did that trick as well.
- enragedcacti 2y ago
  It seems like you could mitigate that by designing the wing such that when mounted the angle of attack is 0 and thus no lift is generated. Obviously the wing would still have an effect when the booster changes orientation or in cases of high winds. I'm not remotely qualified to calculate the scale of those forces but I don't see why any of that would be a guaranteed showstopper given a booster with enough thrust vectoring capability.
- adastra22 2y ago
  Not any different than shuttle or energia. Lift can be accounted for. It’s not as easy as launching in a fairing, but it’s certainly not impossible.

oooyay 2y ago

Naive question: Planes and helicopters do not have the ability to safely eject passengers mid-flight. We largely accept these conditions as a risk of those modes of travel. Why is LES/LAS a unique requirement for space shuttles?

JoeCortopassi 2y ago
planes/helicopters have a fuel source that is orders of magnitude less volatile, and are also able to safely land without power
- philwelch 2y ago
  What fuels do you mean in particular? If you’re talking about hypergolic propellants, those aren’t commonly used as a main propellant on manned rockets. Most planes and helicopters use kerosene, which is also the primary fuel used by the launch stages of manned rockets.
nordsieck 2y ago
> Planes and helicopters do not have the ability to safely eject passengers mid-flight. We largely accept these conditions as a risk of those modes of travel. Why is LES/LAS a unique requirement for space shuttles? That's a fair point, although my understanding is that parachute systems for small planes are becoming more common. My view is that flight rate is the fundamental issue at hand. Airplanes and helicoptors fly many orders of magnitude more than these capsules, which means we know they are many orders of magnitude more reliable. They've also generally been through a long process of refinement - the original airplanes were extremely dangerous compared to modern variants. Additionally, aircraft can afford to have a lot higher margin of safety baked in to them. Because of how high gravity is on Earth and the nature of the Rocket Equation[1], it's just not possible to have a lot of margin in rockets of capsules. They need to be extremely svelt to launch at all. And lastly, we have experience with human spacecraft without an LES/LAS - it was the Space Shuttle. And it killed 14 people - easily the most dangerous spacecraft ever created. No one has any desire to build on that particular legacy. --- 1. https://en.wikipedia.org/wiki/Tsiolkovsky_rocket_equation https://en.wikipedia.org/wiki/Tsiolkovsky_rocket_equation