totm nov 2023 SpaceX Discussion Thread

[HebaruSan]

Just now, Brotoro said:

No... but the Falcon 9 upper stage IS going to be put into a heliocentric orbit.

Ahh, gotcha.

[tater]

 

[XB-70A]

Got the occasion to take some pictures too (a bit better than usual).

Taken from Playalinda Beach, about 13 km/8 miles North-West from the SLC-40.

 

Spoiler

 

 

 

From my photos I took of some Falcon 9 launches, these are the ones I like the most for now 

Edited April 19, 2018 by XB-70A

[Rakaydos]

6 hours ago, HebaruSan said:

How long till the new exoplanet discoveries start rolling in?

50+ days before Tess is in the final orbit and can start actual science. So call it 2 and a half months for the first science return.

[Delay]

46 minutes ago, Rakaydos said:

first science return.

First potential science return. How likely is it that TESS will find an exoplanet during the first few days of actual operation?

Edited April 19, 2018 by Delay

[Rakaydos]

Just now, Delay said:

First potential science return. How likely is it that TESS will find an exoplanet during the first few days of actual operation?

First two weeks of operation. TESS only transmits once an orbit, at periapse.

And tess doesnt analyses it's own recordings- that will happen on the ground after first transmission.

[Josh IN SPACE]

Another exciting launch! I was watching a terrible feed though from work. No HUD, no telemetry, no POV from first stage as it's coming in. Just a shot from the drone ship before the feed cut out as the rocket approached. For all I knew, the thing hit the deck at full speed. Seeing the cheers on here told me otherwise and I looked up a better feed.

Thinking about the second stage, could they alter it as a sort of hybrid rocket that contains of course the usual Merlin, but also a sort of air skimming mechanism that would collect very small trace amounts of passing atmosphere (at relatively low altitude) to give a small retrograde burn through a second specialized engine placed alongside the Merlin?

 There could be panels that open next to the engine and the energy converted to a small thrust to the special engine. The Merlin could perform a preliminary burn after delivering the payload already, which puts periapsis at a close enough altitude for the special engine to gather a tiny amount of atmosphere each pass to drive a small burn from the special engine and lower apoapsis over a long period of successive orbits. This could then bring the rocket's orbit and velocity down to something more manageable for the Merlin to burn for re-entry/landing without having to expend as much of it's own fuel reserves in the process.

I admit my understanding of the subject is quite limited and I'm happy for any corrections to such assumptions above. Just like to see the discussion.

[RCgothic]

The main problem is that the MVac is too fragile to be exposed to the airflow whether it's doing the final burn or not.

[KSK]

It's an interesting idea for sure. I can think of a number of issues though, apart from the MVac nozzle point that @RCgothic raised. For example:

1. Booster lifetime on orbit. You'd need to provide enough batteries to keep the booster systems running for those extra atmosphere skimming orbits. More batteries = more weight - see point 2 below. I'm choosing batteries as the simplest solution here - I'm sure you can imagine other options but they have their own drawbacks.

Edit - for an easy demonstration of how flimsy the MVac nozzle is, just pick any SpaceX launch video and watch out for the upper stage shutting down. The nozzle wobbles quite visibly. 

2. Added mass and complexity of the extra engine. The delta-V requirement for deorbiting is not high (the Shuttle Orbital Maneuvering System could put out around 300m/s if I recall correctly, which covered everything from External Tank Separation to deorbit burn.) Instead of that airscoop system and extra engine, the boring solution might be to just leave a bit of extra propellant in the tank because the mass of propellant required might not be much more than the mass of your airscoop system.

Edited April 19, 2018 by KSK

[sevenperforce]

Beautiful launch and landing!

Flew this a few days ago but I'm just uploading it now:

 

5 hours ago, Josh IN SPACE said:

Thinking about the second stage, could they alter it as a sort of hybrid rocket that contains of course the usual Merlin, but also a sort of air skimming mechanism that would collect very small trace amounts of passing atmosphere (at relatively low altitude) to give a small retrograde burn through a second specialized engine placed alongside the Merlin?

 There could be panels that open next to the engine and the energy converted to a small thrust to the special engine. The Merlin could perform a preliminary burn after delivering the payload already, which puts periapsis at a close enough altitude for the special engine to gather a tiny amount of atmosphere each pass to drive a small burn from the special engine and lower apoapsis over a long period of successive orbits. This could then bring the rocket's orbit and velocity down to something more manageable for the Merlin to burn for re-entry/landing without having to expend as much of it's own fuel reserves in the process.

The dry mass increase of adding this system would be prohibitive. If the system masses, say, one tonne...well, if you don't have it, then there's one extra tonne of fuel you'd have left over instead. So just burn the one tonne of fuel.

The biggest problem with MVac recovery is that the engine bell is too fragile to be exposed to the hypersonic airstream during entry, and it is too over-expanded to fire at sea level (even if not for the major TWR problem). 

 

[tater]

1 hour ago, sevenperforce said:

The biggest problem with MVac recovery is that the engine bell is too fragile to be exposed to the hypersonic airstream during entry, and it is too over-expanded to fire at sea level (even if not for the major TWR problem). 

The party balloon comment by Musk, and the "bouncy castle" as well---which in reality has become something like a trapeze artist's net on Mr. Steven---implies two things to me. One, that while they've not caught a fairing yet, they're getting more confident they can solve the problem, and two, I can imagine a solution to the fragile engine bell issue that is pretty straightforward. Make a balloon that is a hollow cylinder when inflated that surrounds the bell. To visualize imagine a small engine in KSP with a toroidal tank just above it---the tank in this case would really be a balloon that when inflated would make a kind of engine shroud that cushions the bell by touching it on all sides (assuming that the bell cools enough for this to happen by the time it deploys).

[sevenperforce]

8 minutes ago, tater said:

The party balloon comment by Musk, and the "bouncy castle" as well---which in reality has become something like a trapeze artist's net on Mr. Steven---implies two things to me. One, that while they've not caught a fairing yet, they're getting more confident they can solve the problem, and two, I can imagine a solution to the fragile engine bell issue that is pretty straightforward. Make a balloon that is a hollow cylinder when inflated that surrounds the bell. To visualize imagine a small engine in KSP with a toroidal tank just above it---the tank in this case would really be a balloon that when inflated would make a kind of engine shroud that cushions the bell by touching it on all sides (assuming that the bell cools enough for this to happen by the time it deploys).

Musk said "party balloon" but I'm thinking something more like a rigid inflatable, like HIAD. Toroidal inflatable ballute with individual inflatable ribs, tight-packed around the engine area and plumbed to the same helium lines that go into the engine bell for regenerative cooling and tank pressurization. Wouldn't have the ablative coating of HIAD though.

 

 

[YNM]

12 minutes ago, tater said:

Make a balloon that is a hollow cylinder when inflated that surrounds the bell.

Like an airbag ?

 

I don't know, perhaps Elon could look at airplane evacuation slides.

 

Then land retropropulsively, somehow after getting rid of the engine-bell-stiffener.

[sevenperforce]

3 minutes ago, YNM said:

Like an airbag ?

I don't know, perhaps Elon could look at airplane evacuation slides.

Then land retropropulsively, somehow after getting rid of the engine-bell-stiffener.

Similar to an airbag, yes, but comprising a series of inflatable tubes connected lengthwise to create a secure, stiff cylinder.

Retropropulsive landing is a non-starter, though. He's already said he'd do a bouncy castle (that is, a big-ass net). The MVac can't fire retropropulsively in-atmo, and auxiliary landing engines would be too large a mass penalty.

[sevenperforce]

I was thinking of something like this for the rigid central cushion:

All the tubes inflate at once using leftover helium from the pressurant system. The tube walls are joined and so, when stiffened, the tapering cylinder becomes rigid enough to protect the MVac, both from the airstream and from any impacts on landing.

The larger ballute (not shown above) is attached to the lower region of the ring and comprises some sort of sturdy canvas or polymer sheeting that would expand either via inflatable ribs like the individual tube sections, or via an inflated ring:

[tater]

^^^^exaxtly what I was thinking for the curtain airbag around the Mvac

[Wjolcz]

That is something amazing I've never thought of. Wouldn't that mean the second stage has to reenter nose (front?) first tho? Unless the CoG moves down far enough to keep it stable during the engine-first reentry.

18 hours ago, Brotoro said:

No... but the Falcon 9 upper stage IS going to be put into a heliocentric orbit.

Why though? To test stuff (fuel boil off naybe) or just because that way there's less debris floating around Earth?

[sevenperforce]

19 minutes ago, Wjolcz said:

That is something amazing I've never thought of. Wouldn't that mean the second stage has to reenter nose (front?) first tho? Unless the CoG moves down far enough to keep it stable during the engine-first reentry.

Second stage would definitely need to enter nose-first. Gotta protect the MVac.

19 minutes ago, Wjolcz said:

Why though? To test stuff (fuel boil off naybe) or just because that way there's less debris floating around Earth?

After separation, the stage was in EEO, so it was probably less of a dV cost to get out of the Earth-Moon system entirely than it would be to brake all the way back down to a certain entry location.

With a really high orbit like that, the entry trajectory uncertainty is super high. And the MVac will be dead after a couple of days so there's no way to perform any sort of correction later on.

[sevenperforce]

An interesting whitepaper on proposed use of a towed ballute to perform cislunar Earth entry without a heat shield:

https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20060018288.pdf

[Ultimate Steve]

I'm starting to think that Elon announced this just to copy any proposals the KSP forum came up with...

[kerbinorbiter]

4 minutes ago, Ultimate Steve said:

I'm starting to think that Elon announced this just to copy any proposals the KSP forum came up with...

which begs the question, which user is Elon if he even has an account...right?

but the balloon is actually logical Elon being Elon could have came up with it

[sevenperforce]

8 minutes ago, kerbinorbiter said:

which begs the question, which user is Elon if he even has an account...right?

but the balloon is actually logical Elon being Elon could have came up with it

I am Elon.

Spoiler

 

Edited April 19, 2018 by sevenperforce
you shouldn't believe this

[Ultimate Steve]

9 minutes ago, kerbinorbiter said:

which begs the question, which user is Elon if he even has an account...right?

Without pinging people, here are a bunch of potential accounts:

Elon, Elon Kerman Jr, Elon Musk, Elon's Musk, ElonMusk, Elonmuskrat, ElonMusksFinancialAdvisor, ElonsMusk, Falcon 9, Falcon H, Falcon_1e, SpaceX, spacex_falconhevy, spacex34, SpaceX666666, SpaceXPotatoGuineaPig, SpaceXray, SpaceXRules, StarMan, starman001, Starman10, Starman245, starman338, Starman4308, Starman78, Starman8000, StarmanGhost, BFRenthusiast.

Edited April 19, 2018 by Ultimate Steve

[CatastrophicFailure]

Oh come now, it’s so obvious. Elon is really@Just Jim, since they’re both clearly trying to take over the world.  

[tater]

Such ballutes were modded into KSP a long time ago...