totm nov 2023 SpaceX Discussion Thread

[Grand Ship Builder]

Second stage re-usability anyone?

[CastleKSide]

6 minutes ago, Grand Ship Builder said:

Second stage re-usability anyone?

I wish... needs a LOT more problem solving however

[Grand Ship Builder]

Just now, CastleKSide said:

I wish... needs a LOT more problem solving however

Simple. Optimize Merlin to work in atmosphere/add atmosphere engines, heatshield, and landing legs, plus more fuel. Maybe not with Falcon 9, but Falcon Heavy surely.

 

[CastleKSide]

With FH it might be doable however they would basically need to completely redesign the upper stage.

[Grand Ship Builder]

9 minutes ago, CastleKSide said:

With FH it might be doable however they would basically need to completely redesign the upper stage.

Spoiler

 

 

[KSK]

4 hours ago, Grand Ship Builder said:

Simple.

You use this word. I do not think it means what you think it means.

Falcon Heavy was going to be simple. Strapping three boosters together - how hard could it be. Especially when it's been done before on a number of other rockets. Ask Elon how easy it turned out to be in practice.  

I'm sure SpaceX have plans and I look forward to seeing how they work. Some of them might even resemble that video.

[Elthy]

A picture of the spacesuit:

It looks just like the mockups from ages ago...

[kerbiloid]

Pressurized tunic from StarTrek?

These pleats make me to facepalm.

Imagine 1 atm inflating this... thing... from inside.

Where are shoulder joints to rotate arms when the suit is pressurized?
(The pleats definitely show that this is not a "tight" suit).

Edited August 23, 2017 by kerbiloid

[Nibb31]

Why do you want joints? It's not a EVA suit. It's strictly for IVA to survive a depressurization event. Nothing more, nothing less.

[Nikolai]

1 hour ago, kerbiloid said:

Imagine 1 atm inflating this... thing... from inside.

Luckily, spacesuits aren't pressurized to a full atmosphere.

[IncongruousGoat]

7 hours ago, Grand Ship Builder said:

Simple. Optimize Merlin to work in atmosphere/add atmosphere engines, heatshield, and landing legs, plus more fuel. Maybe not with Falcon 9, but Falcon Heavy surely.

Using a SL-optimized Merlin on the second stage would be simple-but pointless. You'd lose ~50 seconds of Isp, and the penalty that would incur to dV and payload capacity just isn't worth it.

The other things are anything but simple. Remember, real life is not KSP. Adding a heatshield and landing legs is a non-trivial challenge, especially since the heat shield would change the load upon the stage significantly. As for adding engines? They actually do have a SL-optimized appropriately-sized hypergolic engine: SuperDraco. But this doesn't make just adding it easy. You'd need new fuel tanks, more control systems, probably different materials engineering due to the... colorful chemistries of the propellants used (MMH/NTO)... all of which are complicated, difficult to engineer into an already built stage, and heavy (in that they cut directly into payload capacity).

I highly doubt SpaceX is going to go for second-stage reuse with the Falcon family. It makes much more sense for them to go for it with mini-ITS, since there second-stage reuse is an integral part of the design. Whether they'll succeed is a whole nother matter entirely...

[tater]

Yeah, I have no idea if that is TPS burning, bells heating, or what.

 

Edited August 23, 2017 by tater

[Nefrums]

33 minutes ago, IncongruousGoat said:

I highly doubt SpaceX is going to go for second-stage reuse with the Falcon family. It makes much more sense for them to go for it with mini-ITS, since there second-stage reuse is an integral part of the design. Whether they'll succeed is a whole nother matter entirely...

This is exactly the reason that i believe that they will try to make the second stage of falcon reusable.  To be able to develop and test the technology on "free" launches.

It will cut into the payload, so it will not be used on all missions, just like the first stage is not reusable for all missions. 

I also believe that they will use the vacuum optimized engine for the landings,  the ISP will not be good, but the twr on a almost empty second stage should not be a problem.

Edited August 23, 2017 by Nefrums

[tater]

I think the most we will see from F9 S2 reuse is testing to aid in mini-ITS. Entry burns, perhaps some materials testing, etc.

Edited August 23, 2017 by tater

[magnemoe]

45 minutes ago, Nefrums said:

This is exactly the reason that i believe that they will try to make the second stage of falcon reusable.  To be able to develop and test the technology on "free" launches.

It will cut into the payload, so it will not be used on all missions, just like the first stage is not reusable for all missions. 

I also believe that they will use the vacuum optimized engine for the landings,  the ISP will not be good, but the twr on a almost empty second stage should not be a problem.

Will it work at all? Will it not be an major issue with back pressure? Having an extendable one could solve this, you would still get the issue with very high twr. 

[wumpus]

10 hours ago, Grand Ship Builder said:

Simple. Optimize Merlin to work in atmosphere/add atmosphere engines, heatshield, and landing legs, plus more fuel. Maybe not with Falcon 9, but Falcon Heavy surely.

As KSK mentioned,  nothing in rocket science is ever simple.

Second, there already exists a Merlin to work in the atmosphere.  They are on stage 1.  You really can't afford to use one for stage 2 power.  If you meant Draco engines, that is possible if painful.  The catch is that adding dry mass to stage 2 is wildly more painful than in stage 1.

Instead of a heatshield you might do a more powerful backboost.  This should be effective as the payload is missing and your delta-v should be much higher.  Note that light heatshields are ablative and limited use, something that Spacex historically shys away from (although they may think it worthwhile like the landing legs/crush zones).  Last I heard, the plan involved a relatively high glide ratio to kill most of the velocity, but actual landing methods weren't released (note that stage 1 is not a place you want heavy parachutes, and I'm not sure that extra draco engines are any lighter).

Stage 2 recovery has always seemed like a wild dream.  Most of the reason Falcon 9 appears to be more reusable that the Space Shuttle is that 90% of the thing doesn't go past Mach 6 or so (at least the ones to be recovered don't), so the booster has far less wear and tear.  The upper stage will suffer all the damage the Shuttle orbiter did, has to kill all the velocity somehow on the way down, all to recover the final 10% of the spacecraft.  Spacex probably expects this to be more like Falcon 1 recovery plans: try to test the first idea for ITS before it goes into final design.  Failure is likely expected and only means more data for the next design (this might mean that there is no "final landing" system like parachutes or landing engines: they just want to see a good terminal velocity near Earth's surface.  Everything else just uses up the customer's payload capacity).

One quick and dirty means of making stage 2 recovery easier would be to add a third stage.  Since the dragon capsule already has draco thrusters, the idea would be that adding an expendable drop tank to dragon would allow stage 2 to max out at a lower velocity and have an easier recovery.  The biggest issue is is that even with zero-mass fuel tanks (I suspect they are vacuum fed, which might throw off the calculations at even this lousy wet/dry ratio), the difference between CRS mass and maximum mass to LEO with recovery nets about ~2km/s with draco's Isp of 300.  While this would presumably mean considerably less fuel in stage 2 (and could presumably trade a bit more), it isn't clear if this is enough to make a difference in recovery.  Oh, and expect a lot of paperwork when increasing your hazardous materials (dracos use hypergolics) by a factor of 3-4.

Edited August 23, 2017 by wumpus

[tater]

Yeah, I think that they decided that biconic was the way to go on large craft propulsive landings from orbital velocity (or higher), and it makes no sense to bust their chops retrofitting S2, which is not really fit for purpose in that regard.

Better to jump straight to mini ITS.

I think elements of reentry can be studied on F9 S2, but as data gathering, not actually trying to land the thing.

[sevenperforce]

6 hours ago, Elthy said:

A picture of the spacesuit:

It looks just like the mockups from ages ago...

omigod omigod yessssssssssssss

[CatastrophicFailure]

52 minutes ago, sevenperforce said:

omigod omigod yessssssssssssss

Bad-S=True. Awwwwwww yiiiihhhh. 

[KSK]

1 hour ago, CatastrophicFailure said:

Bad-S=True. Awwwwwww yiiiihhhh. 

Yeah - that suit looks like something out of Elite: Dangerous. Very nice indeed.

 

[DVDRW]

Val Kilmer inside? 

https://www.youtube.com/watch?v=26uff6SDu88

 

[Shpaget]

Quote

 Already tested to double vacuum pressure. 

What does that mean?

Double pressure of vacuum? Double of diddly squat is still not much more than diddly squat.
Or is that double vacuum, as in doubly more vacuumy than vacuum itself?

It does look cool, though.

[sevenperforce]

32 minutes ago, Shpaget said:

What does that mean?

Double pressure of vacuum? Double of diddly squat is still not much more than diddly squat.
Or is that double vacuum, as in doubly more vacuumy than vacuum itself?

It does look cool, though.

It probably means they tested it to three atmospheres of internal pressure.

The stress on a pressure vessel (or, in this case, a pressure suit) is a function of differential pressure, not absolute pressure. In other words, if the inside has one atmosphere of pressure and the outside has zero atmospheres of pressure, that's one atmosphere of differential pressure. If the inside has two atmospheres of pressure and the outside has one atmosphere of pressure, that's still just one atmosphere of differential pressure.

Elon meant that the difference between the internal and external pressure, during the test, was twice as much of a pressure differential as being in a hard vacuum. So they probably just pumped up the inside of the suit to three atmospheres; that's the easiest way to do it. Of course, they could have pumped the inside to 2.5 atmospheres and then pumped the outside down to 0.5 atmospheres. Same difference.

[Bill Phil]

43 minutes ago, sevenperforce said:

It probably means they tested it to three atmospheres of internal pressure.

The stress on a pressure vessel (or, in this case, a pressure suit) is a function of differential pressure, not absolute pressure. In other words, if the inside has one atmosphere of pressure and the outside has zero atmospheres of pressure, that's one atmosphere of differential pressure. If the inside has two atmospheres of pressure and the outside has one atmosphere of pressure, that's still just one atmosphere of differential pressure.

Elon meant that the difference between the internal and external pressure, during the test, was twice as much of a pressure differential as being in a hard vacuum. So they probably just pumped up the inside of the suit to three atmospheres; that's the easiest way to do it. Of course, they could have pumped the inside to 2.5 atmospheres and then pumped the outside down to 0.5 atmospheres. Same difference.

That's probably the only time saying "same difference" makes any kind of sense. 

[sevenperforce]

29 minutes ago, Bill Phil said:

That's probably the only time saying "same difference" makes any kind of sense. 

Precisely.