totm nov 2023 SpaceX Discussion Thread

[Ultimate Steve]

Just now, CatastrophicFailure said:

Y'all sure about that? The thing's already got 8 engines, another four would be a lot of extra weight. Seems more reasonable to just use one pair of the SuperDrakes, maybe throttled down, for orbital meanuevers...

Okay, I'm sort of confused as to what you mean here...

Note: This post may sound slightly rude, but I promise I do not mean for it to be rude.

 

I'm not sure what you mean by the four additional engines. I meant using the existing Draco thrusters, I never said anything about adding engines.

In case confusion between the Dracos is the issue:

Spoiler

Draco = attitude control thruster, RCS. 18 of them are used on normal Dragon V1 for docking and orbital maneuvers. Some version of these will be used on Dragon V2.

 

Superdraco = larger engine (not an RCS engine) used by Dragon V2 as an LES. Dragon V2 Crew will have 8.

 

 

Both versions of Dragon V2 will use some form of Dracos for docking and orbital maneuvering. The SuperDracos will only be used as an LES on the Crew version of Dragon V2 (I think they also decided to drop the SuperDracos on the cargo version because you don't really need an LES there).

 

 

 

 

[CatastrophicFailure]

23 minutes ago, StupidAndy said:

SES-10 and Iridium-L3 are going to be only 2 days apart, granted they ARE on the opposite side of the country, but still important

It's been done.  Just back in July, IIRC, I forget the sat names but there was a launch from Vandy like 24-48hrs after one at the Cape. 

25 minutes ago, StupidAndy said:

EDIT: ALSO WE ARE ONLY 4 FLIGHTS AND 2 MONTHS AWAY FROM FALCON HEAVY LAUNCH (I hope)

We hope. 

 

@Ultimate Steve heh, my bad, I thought the Dracos were separate from the RCS thrusters.  

 

[Ultimate Steve]

Just now, CatastrophicFailure said:

@Ultimate Steve heh, my bad, I thought the Dracos were separate from the RCS thrusters.  

Oh, well. Everyone makes dumb mistakes sometimes!

I mean, seriously. A while ago I made a mistake in a mission report I was writing and somebody pointed it out to me. I responded by fixing the problem, quoting him, and saying:

Quote

Everyone makes dub mistakes!

...Misspelling "dumb," accidentally proving my own point...

[kerbiloid]

53 minutes ago, CatastrophicFailure said:

Seems more reasonable to just use one pair of the SuperDrakes, maybe throttled down, for orbital meanuevers...

Draco = 400 N, SupeDraco = 70 000 N.
So, this would be throttled down to 6%, i.e. down to the observational error value. Unlikely it's even possible.
SupeDracos are 175 times overpowered as a maneuvering engine.

53 minutes ago, CatastrophicFailure said:

The thing's already got 8 engines, another four would be a lot of extra weight.

As SuperDracos are no longer mentioned as a landing thruster, Dragon-with-Superdracos = landing all this by parachutes:
 

Spoiler

Just LES tower is implanted into the capsule and liquid-fueled.

On the one hand, this will save LES tower.
On another hand - is that relatively small powder rocket really so dear to their heart to sacrifice several tonnes of payload and to make the parachutes be larger and heavier?
_{("Parachutes are too heavy! Rocket landing is necessary!!1oneone")}

On the one hand, _{("terrible-toxic-ecokilling-never-never")} hydrazine LES engines eat less and share fuel with the orbital engine.
On another hand, a powder LES unlikely can fail, while the liquid LES uses 8 engines.
(Exactly 8, because even with 8 it has just 6 g to escape from the fireball. A pair of them gets down - no escape.)

They still have some time to admit their mistake, repent and throw out these superdracos, using Dragon v1 with a normal, powder, single-use LES tower.

Edited September 10, 2017 by kerbiloid

[CatastrophicFailure]

17 minutes ago, kerbiloid said:

They still have some time to admit their mistake, repent and throw out these superdracos, using Dragon v1 with a normal, powder, single-use LES tower.

Which would require a complete redesign of the capsule, more delays, etc, etc. I don't think they've giving up on powered landing entirely, they're shelving it because of the regs involved in getting it past NASA. Presumably, they might look at it again in the future, like for non-NASA flights, once the rest of the D2 system is verified and operational.

19 minutes ago, kerbiloid said:

A pair of them gets down - no escape.)

No, they've designed the whole thing from the get-go to tolerate a failed engine, even during an abort. For comparison, Boeing's Starliner only has 4 liquid-fueled abort motors, so if one of those fails, they're really boned.

 

23 minutes ago, kerbiloid said:

Draco = 400 N, SupeDraco = 70 000 N.
So, this would be throttled down to 6%, i.e. down to the observational error value. Unlikely it's even possible.
SupeDracos are 175 times overpowered as a maneuvering engine.

Just for comparison, if I'm mathing right (and I rarely am), 2 Superdracos @ 20% (minimum) throttle = 28.4 kN, and the Space Shuttle OMS engine (being used for Orion's maneuvering engine) is 26.7 kN.

[kerbiloid]

1 minute ago, CatastrophicFailure said:

No, they've designed the whole thing from the get-go to tolerate a failed engine, even during an abort.

On landing - of course. But you can watch that combined video of fireball+abort_test, and see that even if the capsule starts without a second delay, with all 8 engines on, it stays right on the surface of the fireball.
With 6 engines it has onlt 3/4*6 = 4.5 g T/W, while regular LES make 12-20 g.
So, Boeing just accepts the inevitable.

11 minutes ago, CatastrophicFailure said:

Which would require a complete redesign of the capsule, more delays, etc, etc.

Which would require putting the internals of D2 into D1, with no changes of the systems already tested in flights.
(Btw we still know nothing about the actual readiness of these internals).

[KSK]

I have a couple of thoughts on this although admittedly, I don't really know enough to say whether my thoughts are worth much.

1.  About riding on the edge of a fireball. Isn't this more or less what the capsule is designed to do on the way back down from space? I don't see why it would necessarily be a problem in the event of an abort.

2.  We've already had a live abort test of sorts with CRS-7. General opinion afterwards seemed to be that the capsule might have been recovered if the parachutes had been deployed. There's a big difference between 'recovered' and 'recovered with live astronauts in' of course but CRS-7 does suggest that the capsule is pretty rugged.  Which is good because as per  point 1 above, I'd be more concerned about debris hitting the capsule than riding the edge of a fireball.

3.  For whatever reason, SpaceX have already abandoned the idea of propulsive landing for NASA flights but as far as we know are sticking with their pusher mode LES. To me that suggests that NASA is OK with that plan or at the least, considers the risks of a lower acceleration SuperDraco powered abort to be acceptable. After all, a traditional high-G launch escape system is hardly risk free - it's just better than no escape option.

Edited September 10, 2017 by KSK

[Nibb31]

4 hours ago, CatastrophicFailure said:

Which would require a complete redesign of the capsule, more delays, etc, etc. I don't think they've giving up on powered landing entirely, they're shelving it because of the regs involved in getting it past NASA. Presumably, they might look at it again in the future, like for non-NASA flights, once the rest of the D2 system is verified and operational.

There won't be many non-NASA flights. CRS and CCrew are  only about a dozen flights before the ISS is decommissioned and customers aren't exactly queueing up to buy tickets for orbital joyrides. There might be a couple of lunar flybys, if they get that far, but it won't be worth certifying the propulsive landing.

After CRS and CC, SpaceX will be concentrating on ITS. Dragon 2 is a dead end and a waste of R&D resources if they want to fly ITS one day.

 

27 minutes ago, KSK said:

I have a couple of thoughts on this although admittedly, I don't really know enough to say whether my thoughts are worth much.

1.  About riding on the edge of a fireball. Isn't this more or less what the capsule is designed to do on the way back down from space? I don't see why it would necessarily be a problem in the event of an abort.

A booster blowing up isn't just a fireball. It's also a lot of debris and a huge shockwave. You really want to get away faster than the debris and the shock wave.

Quote

2.  We've already had a live abort test of sorts with CRS-7. General opinion afterwards seemed to be that the capsule might have been recovered if the parachutes had been deployed. There's a big difference between 'recovered' and 'recovered with live astronauts in' of course but CRS-7 does suggest that the capsule is pretty rugged.  Which is good because as per  point 1 above, I'd be more concerned about debris hitting the capsule than riding the edge of a fireball.

That the capsule survived in one piece doesn't mean that the astronauts inside wouldn't have been beaten pulp. CRS-7 was not an abort test.

Quote

3.  For whatever reason, SpaceX have already abandoned the idea of propulsive landing for NASA flights but as far as we know are sticking with their pusher mode LES. To me that suggests that NASA is OK with that plan or at the least, considers the risks of a lower acceleration SuperDraco powered abort to be acceptable. After all, a traditional high-G launch escape system is hardly risk free - it's just better than no escape option.

Contrary to powered landing, the actual abort tests are milestones in the CCDev plan approved by NASA, including a Max Q abort test on a live F9. There were no planned reentry-propulsive landing tests for Crew Dragon, and if there were, they would be expensive because they would have to be full-on $60M test flights with a very high chance of failure.

Edited September 10, 2017 by Nibb31

[Nibb31]

3 hours ago, kerbiloid said:

Which would require putting the internals of D2 into D1, with no changes of the systems already tested in flights.
(Btw we still know nothing about the actual readiness of these internals).

How do you know that D2 systems are compatible with D1 ? D1 has a CBM, not a docking system. They are two completely different vehicles, with different moldlines, tanks, systems, interfaces, and pressure vessels. You'd also need to design a whole new solid LES. Removing the SDs on D2 would be a complete redesign of the spacecraft, back to square one.

Edited September 10, 2017 by Nibb31

[KSK]

49 minutes ago, Nibb31 said:

A booster blowing up isn't just a fireball. It's also a lot of debris and a huge shockwave. You really want to get away faster than the debris and the shock wave.

That the capsule survived in one piece doesn't mean that the astronauts inside wouldn't have been beaten pulp. CRS-7 was not an abort test.

Contrary to powered landing, the actual abort tests are milestones in the CCDev plan approved by NASA, including a Max Q abort test on a live F9. There were no planned reentry-propulsive landing tests for Crew Dragon, and if there were, they would be expensive because they would have to be full-on $60M test flights with a very high chance of failure.

Right - which is why I called it an abort test of sorts, mentioned that I was concerned about debris and specifically pointed out that there was a difference between a recovered capsule and a recovered capsule with live astronauts inside.

And I'm aware that the abort tests are milestones in the NASA approved CCDev plan. Amongst many other milestones, which you probably know more about than me but quite a few of which appear to involve the launch abort system. My point was that so far NASA has approved the SuperDraco abort system (contingent on successful testing of course),  so, unlike @kerbiloid, presumably doesn't have a problem with the concept. And I can't imagine that something as basic as the acceleration imparted by the system would have escaped their notice.

[kerbiloid]

2 hours ago, Nibb31 said:

How do you know that D2 systems are compatible with D1 ?

I don't know that. But:
1. Wasn't compatibility one of SpaceX's key features?
2. Probably, they develop two variants of a ship, not two incompatible ships.

2 hours ago, Nibb31 said:

D1 has a CBM, not a docking system.

D1 has at least a berthing mechanism, while D2 - mostly 3d animations and strange exhibition pieces which are never described, nor visible from the top.
So, I presume, that things at least won't get worse.

2 hours ago, Nibb31 said:

They are two completely different vehicles, with different moldlines, tanks, systems, interfaces, and pressure vessels.

Probably, there is some description of all this? SpaceX site still has only a splitted animation of Dragon v1. Would be glad to read and feel wrong.

2 hours ago, Nibb31 said:

You'd also need to design a whole new solid LES.

After 60 years of LES towers, it is a problem to develop one more powder rocket, rather than the octo-pack of liquid engines inside a capsule?

2 hours ago, Nibb31 said:

Removing the SDs on D2 would be a complete redesign of the spacecraft, back to square one.

Are you sure that the circle is not the square with four rounded segments aside?

Edited September 10, 2017 by kerbiloid

[Grand Ship Builder]

10 hours ago, Ultimate Steve said:

(I think they also decided to drop the SuperDracos on the cargo version because you don't really need an LES there).

While not completely necessary, an launch escape system for a Dragon full of cargo would be nice to have, because nobody wants to lose all that expensive cargo. Could also increase SpaceX's reputation a bit.

[Nibb31]

3 hours ago, kerbiloid said:

I don't know that. But:
1. Wasn't compatibility one of SpaceX's key features?

Why ? Compatibility is usually at the expense of innovation. SpaceX is more into innovation that in maintaining compatibility with old hardware.

3 hours ago, kerbiloid said:

2. Probably, they develop two variants of a ship, not two incompatible ships.

Because D2 is not an evolution of D1. Just by looking at them side by side, you can see they they have practically zero in common. They are completely different vehicles.

3 hours ago, kerbiloid said:

D1 has at least a berthing mechanism, while D2 - mostly 3d animations and strange exhibition pieces which are never described, nor visible from the top.
So, I presume, that things at least won't get worse.

My point was that the access tunnel is a different diameter. Portholes are at different locations. The hatch is a different shape. The whole pressure vessel is a different shape with different interfaces, different attachment points, and different holes in different places. Propellant tanks are different sizes, located in different positions and attached differently with different plumbing for the thrusters that are also fitted in different locations. The parachutes are different, and so are the deployment systems and lines.

D2 is 90% finished, so there is no reason to start all over on a D1 design that is not suitable for crew anyway (because it doesn't have an ECLSS and it can't dock and therefore can't be used for emergency evacuation). Adapting a docking system, new parachutes, ECLSS, and LES into D1 would be a whole new design starting from scratch. It's not going to happen.

3 hours ago, kerbiloid said:

After 60 years of LES towers, it is a problem to develop one more powder rocket, rather than the octo-pack of liquid engines inside a capsule?

For a vehicle that is supposed to fly next year, yes. There's much more to LES that simply a solid rocket.

 

[Nefrums]

Why are LES required anyway?  The shuttle did for obvious reasons not have LES.   And the total lives saved by LES through out history  is -1   (2 saved and 3 killed).   

[CatastrophicFailure]

3 minutes ago, Nefrums said:

Why are LES required anyway?  The shuttle did for obvious reasons not have LES.   And the total lives saved by LES through out history  is -1   (2 saved and 3 killed).   

The shuttles lack of ANY kind of abort procedure in the first two-ish minutes of flight directly resulted in the death of 7 people, yo. I'm not sure where you're getting that "3" number, Soyuz 10a (crew of 2) was directly saved by their LES. Soyuz 1 and 10 did not lose their crews during launch but landing. And Apollo 12 almost needed it after getting struck by lightning. Every crewed vehicle except the shuttle and Voskhod has had some sort of launch escape system  

And back to the earlier discussion, that big thick heat shield should add a lot of protection during a pad or other low-altitude abort. Once you get above 50k feet or so, an actual explosion (with its shock wave and debris flying past the capsule) is no longer a concern, there's not enough oxygen to support one. A catastrophic failure would result in a breakup instead, IF they don't simply shut the engines down, THEN fire the abort motors, which is the likely procedure. 

[Grand Ship Builder]

This is how hard it is to actually re-use a rocket:

Spoiler

Just a normal day of re-using a rocket, right?

 

 

Spoiler

Wrong

Spoiler

When math class is over

 

[Nefrums]

12 minutes ago, CatastrophicFailure said:

I'm not sure where you're getting that "3" number, Soyuz 10a (crew of 2) was directly saved by their LES.

I mean people killed because there was a LES.

[CatastrophicFailure]

3 minutes ago, Nefrums said:

I mean people killed because there was a LES.

Which was whom?

 

[Nefrums]

5 minutes ago, CatastrophicFailure said:

Which was whom?

 

https://en.wikipedia.org/wiki/Soyuz_7K-OK_No.1

[TheEpicSquared]

9 minutes ago, Nefrums said:

https://en.wikipedia.org/wiki/Soyuz_7K-OK_No.1

1. Those 3 people killed weren't crew, they were ground personnel. This is like saying the presence of a seat belt is unnecessary because one snapped and killed someone back in the factory. 

2. That was back in 1966. Technology wasn't as advanced then. I highly doubt anything like that could ever happen again.

[CatastrophicFailure]

23 minutes ago, TheEpicSquared said:

1. Those 3 people killed weren't crew, they were ground personnel. This is like saying the presence of a seat belt is unnecessary because one snapped and killed someone back in the factory. 

2. That was back in 1966. Technology wasn't as advanced then. I highly doubt anything like that could ever happen again.

This. It wasn't the LES that caused the explosion, if anything it was the bad igniter. Or switching to internal power. Or the severed coolant lines. Or the fully-fueled third stage. One link in a chain of failures.

[Tullius]

1 hour ago, Nefrums said:

Why are LES required anyway?

Because safety.

If both the rocket and the LES only have 97% reliability each (which is quite low for a modern rocket), it gives the crew a chance of about 99.9% of surviving the launch, i.e. very very safe. On the other hand, to achieve this survivability solely with the reliability of the rocket, the rocket needs to be 99.9% reliable, which is ridiculously high.

[magnemoe]

 

15 hours ago, kerbiloid said:

Draco = 400 N, SupeDraco = 70 000 N.
So, this would be throttled down to 6%, i.e. down to the observational error value. Unlikely it's even possible.
SupeDracos are 175 times overpowered as a maneuvering engine.

As SuperDracos are no longer mentioned as a landing thruster, Dragon-with-Superdracos = landing all this by parachutes:
 

  Hide contents

Just LES tower is implanted into the capsule and liquid-fueled.

On the one hand, this will save LES tower.
On another hand - is that relatively small powder rocket really so dear to their heart to sacrifice several tonnes of payload and to make the parachutes be larger and heavier?
_{("Parachutes are too heavy! Rocket landing is necessary!!1oneone")}

On the one hand, _{("terrible-toxic-ecokilling-never-never")} hydrazine LES engines eat less and share fuel with the orbital engine.
On another hand, a powder LES unlikely can fail, while the liquid LES uses 8 engines.
(Exactly 8, because even with 8 it has just 6 g to escape from the fireball. A pair of them gets down - no escape.)

They still have some time to admit their mistake, repent and throw out these superdracos, using Dragon v1 with a normal, powder, single-use LES tower.

You save the LES tower, you share fuel with the orbital trusters, yes it might be overkill with fuel for this but it give you an option to save an launch with issues like the first dragon launch. Dragon 2 is lightweight for Falcon 9 FT as in return to pad mission, no reason to reduce weight, its volume rather than weight limited for cargo.

As the superdrako are reusable they can be tested before launch, testing of an solid fuel rocket is destructive.  Old military joke about old questionable ammo, officer tell sergeant to check it its still good, sergeant takes his men to the range, come back and say they tested all the ammo and all but 5 rounds worked 

6g is also an safety margin, you want belt and suspenders. 3g would saved you from both the two falcon 9 fails. the dragon 1 was intact after second stage explosion with no LES. Probably also in the pad explosion before static test. 

Edited September 10, 2017 by magnemoe

[wumpus]

5 hours ago, Tullius said:

Because safety.

If both the rocket and the LES only have 97% reliability each (which is quite low for a modern rocket), it gives the crew a chance of about 99.9% of surviving the launch, i.e. very very safe. On the other hand, to achieve this survivability solely with the reliability of the rocket, the rocket needs to be 99.9% reliable, which is ridiculously high.

That only works if the failure modes are completely independent.  Testing the LES at maxQ mostly confirms that this should be true, but there are always possible failures that could destroy the LES.

[Grand Ship Builder]

9 hours ago, Grand Ship Builder said:

This is how hard it is to actually re-use a rocket:

  Reveal hidden contents

Just a normal day of re-using a rocket, right?

 

 

  Reveal hidden contents

Wrong

  Reveal hidden contents

When math class is over

 

After an endless amount of tries, I finally got the second stage on the first stage. It's not stable so, i'm just gonna scrap it, and re-design a new, better one, which I am right now.