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8 hours ago, mikegarrison said:

This is not how these things work.

You submit a plan for how you are going to certify your product. After review and negotiation, the plan is approved. It does not have to be the same plan as anybody else. You have to meet the same rules, but you are allowed to come up with your own way to demonstrate that, as long as your way of doing it is approved.

Then you execute the plan. Once the plan is approved, you don't just start dropping parts of it.

Interesting.

1 hour ago, RealKerbal3x said:

I’m just sad that they don’t plan to reuse the capsules. The design just screams ‘REUSE MEEEEEE’.

They won't? I must've been out of the loop recently. Is safety the reason behind it?

1 hour ago, Motokid600 said:

Yep. Its a shame. SpaceX could've ditched the super dracos, taken them out of the Dragon2 design and developed a reusable escape tower.

Doing it with SuperDracos is probably the simplest and cheapest way anyway. I'm really not sure how a reusable escape tower could be better than this.

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2 minutes ago, Wjolcz said:

Interesting.

It protects everybody involved. This way, nobody changes the requirements at the last minute. SpaceX can't just drop a test, but NASA can't just arbitrarily come up with a new one they have to pass. Since everybody agreed to the plan, as long as you do everything in the plan, then you get qualified.*

*Really unusual events can force changes to the plan despite that it was all agreed in advance.

10 minutes ago, Wjolcz said:

I must've been out of the loop recently. Is safety the reason behind it?

SpaceX gave up the idea of reusing the Crew Dragon when they decided to land them in the ocean. They have said they hope to reuse them as cargo-only flights.

CST-100 is planning to reuse their capsules, but they are not doing ocean landings.

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5 hours ago, Wjolcz said:

 

Doing it with SuperDracos is probably the simplest and cheapest way anyway. I'm really not sure how a reusable escape tower could be better than this.

Are throttling liquid rocket engines usually cheaper and simpler then solid fuel? They're hypergolic, but still the original design intention is a thing of the past. Couldve saved all the headaches and extra weight of the engines with a classic escape tower. 

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10 minutes ago, Motokid600 said:

Are throttling liquid rocket engines usually cheaper and simpler then solid fuel? They're hypergolic, but still the original design intention is a thing of the past. Couldve saved all the headaches and extra weight of the engines with a classic escape tower. 

Throttling liquid engines are vastly MORE complicated than solid fuel. But, the current design can offer full envelop of escape (from zero-zero abort to abort-to-orbit). Yet, Superdracos are made with 3D printing, which I suspect to be quite cheap.

Plus the original design probably expected using those engines for abort too. Also note that traditional escape towers are heavy.

Edited by Xd the great
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8 minutes ago, Motokid600 said:

Are throttling liquid rocket engines usually cheaper and simpler then solid fuel? They're hypergolic, but still the original design intention is a thing of the past. Couldve saved all the headaches and extra weight of the engines with a classic escape tower. 

Given the current margin on F9, this is true. At the time they started with Dragon, and the concept of Crew Dragon they might not have had the margin for an escape tower on top of wanting reuse as part of the initial idea.

Escape towers are also not as good in many ways, they don't offer aborts in all flight regimes---notably after they are jettisoned ;)

Knowing what they do now, maybe they would have put it in the trunk...

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Just now, Xd the great said:

Throttling liquid engines are vastly MORE complicated than solid fuel. But, the current design can offer full envelop of escape (from zero-zero abort to abort-to-orbit). Yet, Superdracos are made with 3D printing, which i suspect to be quite cheap.

Plus the original design probably expected using those engines for abort too.

I assume the super drakos and the RCS system share fuel reducing the weight for the system. 

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5 hours ago, mikegarrison said:

It protects everybody involved. This way, nobody changes the requirements at the last minute. SpaceX can't just drop a test, but NASA can't just arbitrarily come up with a new one they have to pass. Since everybody agreed to the plan, as long as you do everything in the plan, then you get qualified.*

*Really unusual events can force changes to the plan despite that it was all agreed in advance.

 

This ^ 

Government projects are NOTORIOUS for scope creep and going over budget. Changing the plan in the planning stage is fast, cheap, and relatively painless. Changing the plan just before delivery causes delays, budget overruns, and is generally just horrible.

Scope creep is the bane of engineering.

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4 hours ago, tater said:

Escape towers are also not as good in many ways, they don't offer aborts in all flight regimes---notably after they are jettisoned ;)

In all fairness, once you’re more or less “in space” a full-up LES isn’t really necessary, things generally happen slowly enough to shut a malfunctioning booster down and abort with the spacecraft’s orbital engines. Soyuz did this after a staging failure a long while back, and even the most recent abort only used small motors on the fairing, the main tower had already been discarded.   

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23 minutes ago, CatastrophicFailure said:

In all fairness, once you’re more or less “in space” a full-up LES isn’t really necessary, things generally happen slowly enough to shut a malfunctioning booster down and abort with the spacecraft’s orbital engines. Soyuz did this after a staging failure a long while back, and even the most recent abort only used small motors on the fairing, the main tower had already been discarded.   

What about an exploding booster?

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2 minutes ago, CatastrophicFailure said:

In all fairness, once you’re more or less “in space” a full-up LES isn’t really necessary, things generally happen slowly enough to shut a malfunctioning booster down and abort with the spacecraft’s orbital engines. Soyuz did this after a staging failure a long while back, and even the most recent abort only used small motors on the fairing, the main tower had already been discarded.   

In a propulsion-integrated, reusable capsule, this can be trickier. You need a heat shield on the back end, so the spacecraft's orbital engines (which would be on a service module if they were expendable) do not necessarily point backward. Dragon 2's major burns (deorbit particularly) use four Draco thrusters grouped around the docking port, pointing forward, and are covered by the nose cone during ascent. 

If you use the same propellant for abort as you use for orbital maneuvers and deorbit, as is the case with Dragon 2 and Starliner, then the only "extra" thing you're carrying to orbit is the weight of the abort engines themselves, and those are not terribly heavy to begin with. 

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Just now, Geonovast said:

What about an exploding booster?

Liquid rocket stages do a surprisingly poor job of exploding in flight, and particularly out of the atmosphere. Even in Challenger, when the entire external tank ruptured, mixed, and then ignited, the fireball produced only 4-5 psi of overpressure, which did no significant damage to the orbiter. The orbiter broke apart from aerodynamic loads. In order to have an explosion with overpressure, you need to thoroughly mix the reactants, then contain the ignition long enough to form a supersonic propagating wavefront, which results in a detonation.

CRS-7, which was more or less the worst-case scenario for an in-flight failure of a liquid-propellant two-stage booster, had an extremely benign failure with respect to the capsule.

Super Heavy may be problematic in this regard. If a leak formed in the common bulkhead on the pad, the liquid methane and LOX could mix, forming an explosive gel. Its inevitable ignition would be constrained by the cryosteel walls long enough to produce a massive detonation, larger than some tactical nukes. 

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48 minutes ago, sevenperforce said:

Liquid rocket stages do a surprisingly poor job of exploding in flight, and particularly out of the atmosphere. Even in Challenger, when the entire external tank ruptured, mixed, and then ignited, the fireball produced only 4-5 psi of overpressure, which did no significant damage to the orbiter. The orbiter broke apart from aerodynamic loads. In order to have an explosion with overpressure, you need to thoroughly mix the reactants, then contain the ignition long enough to form a supersonic propagating wavefront, which results in a detonation.

If parallel universes are real, then there is one where the orbiter managed to stay facing forward through the breakup suffering only minor damage. From there it could have glided down to a ditching in the ocean.

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It's worse than that chart shows. The footnote on the per seat is a couple pages up. It's the price of the 6 flights divided by the 24 available seats. If they do nominal ISS missions of just 3 seats (or 2 for the SpaceX DM-2 test flight) we get different values.

If they use 3 seats per vehicle, the cost per seat for Boeing is 120 M$/seat. That's 148% the price of Soyuz.

For SpaceX doing the same it's 73.3 M$/seat (77.6M$/seat given the first mission is just 2 seats). That's 96% the price of Soyuz.

 

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25 minutes ago, Ultimate Steve said:

If parallel universes are real, then there is one where the orbiter managed to stay facing forward through the breakup suffering only minor damage. From there it could have glided down to a ditching in the ocean.

There was no probability of the orbiter surviving an SRB failure during the SRB burn.

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22 minutes ago, sevenperforce said:

There was no probability of the orbiter surviving an SRB failure during the SRB burn.

If I remember correctly the srbs never ruptured beyond the small opening that caused the strut and tank burn through. If, when the whole thing broke up, the srbs didn't strike the orbiter (they had struck the tank so idk how likely that is) it may have been fine. Granted the shuttle would be exposed to the sides of the srb plumes for a short period of time, but likely not the full on force of an srb firing or exploding.

I think the srbs continued to fly afterwards, only blowing up after range safety told them to.

Another tantalizing thought is if the srb leak had been on the other side of the srb. It wouldn't have burned through anything, it would have just looked alarming and reduced thrust slightly.

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14 minutes ago, Ultimate Steve said:

Another tantalizing thought is if the srb leak had been on the other side of the srb. It wouldn't have burned through anything, it would have just looked alarming and reduced thrust slightly.

And led to a thermal curtain failure due to a differing burn time. ;) And with no mischievous spherical robot to help, either. 
 

The orbiter crew surviving ditching is probably impossible too. The space shuttle truly was a flying brick, touchdown speed was on the order of 220mph, almost twice what Sully’s famous ditch was at, and a 737 is actually designed for such, too. The crew had no way to bail out, either. 
 

Even if the stack had only failed after SRB sep, outside of the atmosphere, there’s no way the orbiter could have survived, there were HUGE “black zones” in the flight profile where LOCV was guaranteed after a major failure. The updated procedures after Challenger didn’t entirely eliminate them, either. 

2 hours ago, Geonovast said:

What about an exploding booster?

What @sevenperforce said. 
Also, in that recent Soyuz abort, the booster actually struck the core and caused it to depressurize and go off course, yet the capsule was fine with only tiny separation motors. 

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