totm nov 2023 SpaceX Discussion Thread

[Nibb31]

50 minutes ago, _Augustus_ said:

Meanwhile Boeing gets away with their detachable heat shield and airbags, which is also an unproven concept.

Do I smell favoritism?

As I said (I'm getting a bit tired of saying the same thing 20 times), it's not about proving the technology works, it's about calculating the reliability, which is a function of how complex a system is.

• Propulsive landing requires guidance systems, sensors, engines, software, all of which are complex with many failure modes.
• Jettisonning a heatshield and deploying airbags requires a series of aerospace-grade pyro devices, which are standard off-the-shelf parts with known stats and very high reliability rates.

[Nibb31]

2 hours ago, magnemoe said:

They could do drop tests from planes and will for the parachutes anyway. This has been done with all capsules. One Apollo boilerplate for drop tests was lost and found by Soviet who returned it. 
Now they could probably do 100 drop tests from planes but it would not simulate reentry heat damage on engines and systems like attitude radar.
 

There aren't any planes that could drop a Dragon 2. It won't fit in any existing rear-loading cargo plane and you couldn't really carry it in any other configuration. You could do helicopter drops, but that won't be a very useful test of guidance systems or the actual reentry or high altitude attitude control.

You might be better off doing suborbital tests by launching it straight from a reusable F9, without the upper stage, but that would require a lot of engineering work.

The only option for testing it, and (hopefully) bringing up the reliability figures, is to test propulsive landings on actual cargo flights. NASA doesn't want this, which is understandable, because downmass cargo is typically considered valuable.

[Silavite]

20 minutes ago, Nibb31 said:

There aren't any planes that could drop a Dragon 2. It won't fit in any existing rear-loading cargo plane and you couldn't really carry it in any other configuration. You could do helicopter drops, but that won't be a very useful test of guidance systems or the actual reentry or high altitude attitude control.

You might be better off doing suborbital tests by launching it straight from a reusable F9, without the upper stage, but that would require a lot of engineering work.

The only option for testing it, and (hopefully) bringing up the reliability figures, is to test propulsive landings on actual cargo flights. NASA doesn't want this, which is understandable, because downmass cargo is typically considered valuable.

The An-225 could carry it internally (just looking at dimensions and masses), but, uh, good luck on obtaining the thing...

It might be possible to mount it on top of an aircraft and release it in a negative G push down, but that seems a bit risky, since the Dragon 2 has a much worse L/D than, say, the Space Shuttle Enterprise.

[HebaruSan]

9 hours ago, Nibb31 said:

It's about probability calculations.

They have a global failure rate for LOC and LOM. The global failure rates are calculated from the failure rates of each system combined with the failure rates for redundancies. The failure rates for each of those systems are calculated from the failure rates of each component, and so on. With that methodology, and no proven track record, it's simply too hard to meet the target requirements based on calculations only.

Wouldn't they have known this at the outset (since it can all be done on paper)? Why announce a design in defiance of those standards, only to later cancel it because of them?

[Nibb31]

16 minutes ago, HebaruSan said:

Wouldn't they have known this at the outset (since it can all be done on paper)? Why announce a design in defiance of those standards, only to later cancel it because of them?

Just because it can be done on paper doesn't mean that there isn't a lot of work involved. Determining reliability stats for a complex system isn't exactly instantaneous. And once they got those numbers, maybe they thought they could engineer the numbers they wanted and slowly realized that they couldn't.

Maybe they also had the plan to test propulsive landing on the cargo flights, which is something that NASA has ruled out.

Don't forget that Musk has a reality distortion field. SpaceX has a long history of making spectacular announcements based on their Dear Leader's vision and changing their plans when reality finally kicks in.

28 minutes ago, Silavite said:

The An-225 could carry it internally (just looking at dimensions and masses), but, uh, good luck on obtaining the thing...

It's actually available for charter service to anyone who is willing to pay for it. But it's a front loader, so it can't do airdrops.

 

Edited August 6, 2017 by Nibb31

[Silavite]

5 minutes ago, Nibb31 said:

It's actually available for charter service to anyone who is willing to pay for it. But it's a front loader, so it can't do airdrops.

Dang, thought it was rear loaded... oh well, shows what I know.

[CastleKSide]

Wow, I guess I didnt realize how big the D2 actually was.

[DerekL1963]

2 hours ago, HebaruSan said:

Wouldn't they have known this at the outset (since it can all be done on paper)? Why announce a design in defiance of those standards, only to later cancel it because of them?

How could they have known it at the outset?  The design wasn't complete then and relevant calculations almost certainly weren't even started.  I wouldn't be surprised to learn the relevant equipment and systems weren't much more than a high level block diagram, a few sketches, and a couple of pages of rough calculations at that point (almost six years ago now).

Design and qualification are complex, lengthy, and iterative processes.  I'd be surprised if there weren't any surprises along the way.  There's probably been more, which we'll never hear about until some SpaceX engineer writes his memoirs in 2050 or so.

[magnemoe]

6 hours ago, Nibb31 said:

Don't forget that Musk has a reality distortion field. SpaceX has a long history of making spectacular announcements based on their Dear Leader's vision and changing their plans when reality finally kicks in.

It's actually available for charter service to anyone who is willing to pay for it. But it's a front loader, so it can't do airdrops.

 

AN-124 can handle 4.4 meter high cargo, think the height and with of hold is the same on AN-225 but its longer and can take heavier cargo. 
C-5 has 4 meter max height. 
dragon 2 diameter is 3.7 meter. 

They did an test of the dragon 2 parachutes but with an smaller boilerplate 

[Nibb31]

1 hour ago, magnemoe said:

AN-124 can handle 4.4 meter high cargo, think the height and with of hold is the same on AN-225 but its longer and can take heavier cargo. 
C-5 has 4 meter max height. 
dragon 2 diameter is 3.7 meter.

Those planes are also front loaders. You'd need a C-17, but a Dragon with an airdrop palette won't fit, besides...

1 hour ago, magnemoe said:

They did an test of the dragon 2 parachutes but with an smaller boilerplate 

...an airdrop test is relevant for a full parachute test, because there are less parameters. All you need is enough altitude for the chutes to deploy. Propulsive landing requires firing into a supersonic airflow, guidance, and attitude control, none of which can be properly tested in a simple airdrop environment.

[magnemoe]

8 minutes ago, Nibb31 said:

Those planes are also front loaders. You'd need a C-17, but a Dragon with an airdrop palette won't fit, besides...

...an airdrop test is relevant for a full parachute test, because there are less parameters. All you need is enough altitude for the chutes to deploy. Propulsive landing requires firing into a supersonic airflow, guidance, and attitude control, none of which can be properly tested in a simple airdrop environment.

AN-124 is both rear and front loaded, tail door was dropped on AN-225 to save weight. Tail door is most relevant for air drop or fast turnabout, C-5 is larger than C-17.

See the issues with firing while supersonic, this is anyway the less critical time as you can fall back to parachutes. Its the actual landing who is dangerous as you would be to low for parachutes and if you loose stability you crash. 

[Nibb31]

Guidance and attitude control throughout the descent are even more critical. Parachutes will always keep the capsule upright, whereas Dragon  needs to be pointing in the right direction before it can fire its engines. All engines need to be working properly in order to maintain attitude and to control de descent rate and trajectory. It's much more complicated than parachutes and it is very different from an F9 landing.

But as I said, technical problems can be solved with good engineering. That's the easy part.

The hard part is proving on paper that the solution is going to work with 99.99% reliability instead of only 99.9%.

Edited August 7, 2017 by Nibb31

[TheEpicSquared]

A bit off-topic, but wasn't there a half-built version of the An-225 that had a rear cargo door, but was scrapped?

[hms_warrior]

3 hours ago, Nibb31 said:

Guidance and attitude control throughout the descent are even more critical. Parachutes will always keep the capsule upright, whereas Dragon  needs to be pointing in the right direction before it can fire its engines.

Not entirely true. If the chute opens while pointing straight ahead it will most likely just wrap around the capsule... but that's an extreme case. Just wanted to point out that a parachute-capsule still needs SOME control too ^^

[magnemoe]

1 hour ago, TheEpicSquared said:

A bit off-topic, but wasn't there a half-built version of the An-225 that had a rear cargo door, but was scrapped?

Its an half build version of AN-225, you could probably fit it with an rear door if the bottom of tail is simlar enough to the AN-124, the problem is that rear doors are heavy and not that useful outside of military use. 
The rear door let you air drop and it is its own ramp who is nice the landing on remote places, lower the ramp and drive of. 

[Grand Ship Builder]

I think a SpaceX designed plane would be cool. Sure. probably not worth the cost, but reuse! Heck, even a kerbal spaceplane designed by SpaceX, with grid fins hidden under airbrakes, which retract and extend to maintain speed that could carry a Dragon would be cool enough, and proves how independent SpaceX really could be on spending money.

 

 

Of course, they probably won't build a spaceplane, but, hey, there's always a possibility!

[Jaff]

Definitely won’t build a space plane.

 

musk has made his opinion on wings in space and their uselessness previously 

[rudi1291]

 

[Skylon]

I feel like every delay just pushes the Falcon Heavy launch date back further

[linuxgurugamer]

8 minutes ago, Skylon said:

I feel like every delay just pushes the Falcon Heavy launch date back further

Ummmm, you know, it IS rocket science.

[Racescort666]

1 hour ago, Skylon said:

I feel like every delay just pushes the Falcon Heavy launch date back further

I would hazard a guess that FH launch will be at the very end of November if it doesn't get pushed into December. Although from a timing standpoint, OTV-5 is the last launch from LC-39A according to Spaceflight Now and if it launches on schedule (reasonably, it might not), 60 days after that (the amount of time that SpaceX has said they need) is November 6th. So I think that delays to Falcon Heavy would probably be more related to Falcon Heavy itself rather than other SpaceX flights or the pad modifications, assuming that November 30th is the latest non-delayed date.

[tater]

https://twitter.com/NASASpaceflight/status/895634329891622912

 

Once again, twitter not embedding. Static fire.

Edited August 10, 2017 by tater

[tater]

https://twitter.com/SpaceX/status/895646473869705216

 

Give us the ability to edit the forum code already. This randomly embedding or not nonsense stinks.

[CatastrophicFailure]

@tater if you're on a PC and using Chrome, try pasting as plain text, that seemed to get it to work for me the other day. If you're on mobile, then, well... 

[tater]

I'm on a  mac, but I'll try that...

 

Wow.

That worked.