SpaceX Starship/Super Heavy Engineering General Thread 2

[Chris Bergin]

New thread (Thread 2 as it's a follow-on thread, but more specific to avoid wandering of the specific subject).

Follows on from this thread:
Starship (BFS) Engineering Thread (#dearMoon edition + Musk Stainless Update)
https://forum.nasaspaceflight.com/index.php?topic=46395.0

Feel free to post a few major highlights into this thread from the previous thread, which I'll keep open for a day to allow quoting etc.

[AC in NC]

An informative picture.

This is an important post for this new thread with the picture originally provided in Oli's post

[Jcc]

Some thoughts about landing system design and landing on unprepared surfaces:

Assuming the Tin-Tin design with landing legs below the fins, I think there should be a way to adjust the leg length to self-level the ship on uneven surfaces. Some sort of hydraulic system. Then, the landing radar/Ladar/lidar can be enhanced to provide a 3D model of the landing area in real time to reveal any obstacles that need to be avoided and measure slope so leg lengths can be determined.

[Slarty1080]

Some thoughts about landing system design and landing on unprepared surfaces:

Assuming the Tin-Tin design with landing legs below the fins, I think there should be a way to adjust the leg length to self-level the ship on uneven surfaces. Some sort of hydraulic system. Then, the landing radar/Ladar/lidar can be enhanced to provide a 3D model of the landing area in real time to reveal any obstacles that need to be avoided and measure slope so leg lengths can be determined.

I would have thought from low orbit they would be able to get super high definition images of the landing site down to a resolution where they can see boulders of a size sufficient to be a problem and avoid those areas.

Concerning the greater issue of debris, I think debris damage is a major challenge. Not having massive flimsy vacuum raptors aboard helps a bit but they will still need to take measures to prevent damage. Not sure if the three tubular structures at the end of the flippers would contain extendable legs? If so this would put the engines a bit further from the surface. They could probably also cut the engines a metre or so above the ground and they might be able to use RCS and engine gambolling and throttling, but not sure if this would be enough? There will be one hell of a lot of debris ranging in size from silt particles to small boulders flying about in all directions.

[AC in NC]

I would have thought from low orbit they would be able to get super high definition images of the landing site down to a resolution where they can see boulders of a size sufficient to be a problem and avoid those areas.

Concerning the greater issue of debris, I think debris damage is a major challenge. Not having massive flimsy vacuum raptors aboard helps a bit but they will still need to take measures to prevent damage. Not sure if the three tubular structures at the end of the flippers would contain extendable legs? If so this would put the engines a bit further from the surface. They could probably also cut the engines a metre or so above the ground and they might be able to use RCS and engine gambolling and throttling, but not sure if this would be enough? There will be one hell of a lot of debris ranging in size from silt particles to small boulders flying about in all directions.

Will it not be the case that the landing burn effectively clears the landing site.  As you say, I'd imagine they can pick a place that only has loose debris rather than fixed outcroppings.  Anything that isn't avoided in site-selection should be cleared.  I suppose there is a risk of something like a boulder buried that gets exposed toward the end of landing and causes problems.

747 vs. a Truck is pretty dramatic:



747:  ~300kn x 4 = ~1200kn (and I doubt the video above was at full power)
SS:   ~1700kn x 3 = ~5100kn (using what are likely outdated numbers)

I only half jokingly quip that they might end up landing on bedrock. 

Of course that would result in all sorts of debris damage issues like you rightly point out.  The tail-end debris issues are serious.

[jak Kennedy]

While thinking about the problem of cooling during re-entry I came up with an idea (after reading on here the shock wave pressure is only about 20 bar)of magnetism to deflect the ionized gas. A quick search though shows I am not the first, damn it.
Could this be used at least in the hottest areas to at least spread the heat over a larger area?

https://phys.org/news/2009-11-superconductor-magnet-spacecraft-shield.html

Edit - corrected psi to bar.

[ThomasGadd]

I have some comments about the manufacturing differences between the booster and ship.

The ship, whatever form for cooling it ends up with, will be more complex and heavier than the booster.
The booster skin will be thinner the tanks simpler. 
The engines will be the same.
The air frames are different enough for separate flight testing.

While the construction materials and techniques are the same how much accurately overlaps?
Are my above assumptions correct?

[HVM]

While thinking about the problem of cooling during re-entry I came up with an idea (after reading on here the shock wave pressure is only about 20 psi) of magnetism to deflect the ionized gas. A quick search though shows I am not the first, damn it.
Could this be used at least in the hottest areas to at least spread the heat over a larger area?

https://phys.org/news/2009-11-superconductor-magnet-spacecraft-shield.html

Where did you find that? Apollo test max pressure was 20 bar = 290 psi and shuttle at mach 8 was 150 -250 psi.

Edit Google "apollo dynamic pressure data" for actual data.

[50_Caliber]

Some thoughts about landing system design and landing on unprepared surfaces:

Assuming the Tin-Tin design with landing legs below the fins, I think there should be a way to adjust the leg length to self-level the ship on uneven surfaces. Some sort of hydraulic system. Then, the landing radar/Ladar/lidar can be enhanced to provide a 3D model of the landing area in real time to reveal any obstacles that need to be avoided and measure slope so leg lengths can be determined.

I think there is a considerable amount of engineering to be done on this problem. One concern I would have is if there is ice or loose dirt in the spot where they land, it could shift when the weight of the BFS touches down and potentially cause it to topple. Would ground penetrating radar be able to determine if the surface is solid enough to sustain the weight of the BFS?

Would SpaceX want an adaptive system for landing that reads the surface on the fly? Or would they be ok with getting high-res pics of their landing spot and basing their landing on the pics? I wouldn't think they would want to depend on static pics when an adaptive system would be far more versatile in an unknown environment.

This is a case where having a car company that is making self-driving cars can be really beneficial in supplying a lot of useful info into engineering an adaptive AI landing system.

[Jcc]

To deal with the possible condition where one side of the landing area is soft enough for a leg to sink in significantly, and also potential errors in measurement of the terrain before landing, I think the "self-leveling system" should be able to respond to tilt by extending the leg that's low.

[AC in NC]

I'm of the opinion that the terrain issues are insignificant enough that the notion of leveling systems will not gain much traction.

[jak Kennedy]

While thinking about the problem of cooling during re-entry I came up with an idea (after reading on here the shock wave pressure is only about 20 psi) of magnetism to deflect the ionized gas. A quick search though shows I am not the first, damn it.
Could this be used at least in the hottest areas to at least spread the heat over a larger area?

https://phys.org/news/2009-11-superconductor-magnet-spacecraft-shield.html

Where did you find that? Apollo test max pressure was 20 bar = 290 psi and shuttle at mach 8 was 150 -250 psi.

Sorry, I may have gotten bar and psi mixed up in my memory.

[Oersted]

Very hard to simulate Starship landings on unprepared terrain... Which is of course why they're building the Hopper.

I think the landing legs will compress real-time reactively to the eventual slope they encounter on landing. Maybe that's over-complicating things, though. The Hopper will tell.

[Slarty1080]

I'm of the opinion that the terrain issues are insignificant enough that the notion of leveling systems will not gain much traction.

Leveling terrain issues might not be a problrm, but what abut sand blasting and stone catapulting effects of all that engine power just a few metres from a nice dusty unstable surface?

[AC in NC]

Leveling terrain issues might not be a problrm, but what abut sand blasting and stone catapulting effects of all that engine power just a few metres from a nice dusty unstable surface?

Very significant area of concern.  From my chair it seems like one biggest unknowns in the transport hardware

[Mongo62]

I hope that this is the correct thread.

I have not seen a timeline based on Elon Musk's tweets (or other sources) of when milestones on the Starship/Super Heavy development pathway are planned to be reached. In which case, this might be a start:

Hopper:
Under construction in Boca Chica: now (December) -- per observations and per Elon Musk tweet
First flights: before March/April -- per Elon Musk tweet

Starship, Mk 1
Under construction at subsection level in San Pedro: now (December) -- per Elon Musk tweet
First suborbital flights: second half of 2019 -- per Gwynne Shotwell tweet (NOTE: information might be superseded by later design changes)
First orbital flights: 60% chance of 2020 -- per Elon Musk tweet

Super Heavy:
Beginning of construction: spring 2019 -- per Elon Musk tweet

Raptor:
"Radically redesigned" Raptor first firing: January 2019 -- per Elon Musk tweet

[CuddlyRocket]

Regarding landing the Starship on Mars: If you intend to deploy for use the ship's onboard solar panels whilst on the surface, then you need to ensure their correct orientation towards the Sun, which requires you control the ship's rotation round the vertical axis.

[su27k]

Attached is a slideshow about using reflective material for TPS, the tech itself is very low TRL but the first 10 or so slides give a primer about shock layer radiation which is very interesting. It looks like shock layer radiation falls off quickly if your reentry speed is less than 10km/s (return from the Moon), so I'm not sure how much it matters for LEO reentry, probably little. But for returning from the Moon/Mars, it's a major factor, so this reflective layer could be an optimization for BLEO missions.

[Slarty1080]

Leveling terrain issues might not be a problrm, but what abut sand blasting and stone catapulting effects of all that engine power just a few metres from a nice dusty unstable surface?

Very significant area of concern.  From my chair it seems like one biggest unknowns in the transport hardware

Yes and at 20% min throttle I don't think they can land with all 7 engines running

[DJPledger]

While thinking about the problem of cooling during re-entry I came up with an idea (after reading on here the shock wave pressure is only about 20 psi) of magnetism to deflect the ionized gas. A quick search though shows I am not the first, damn it.
Could this be used at least in the hottest areas to at least spread the heat over a larger area?

https://phys.org/news/2009-11-superconductor-magnet-spacecraft-shield.html

Where did you find that? Apollo test max pressure was 20 bar = 290 psi and shuttle at mach 8 was 150 -250 psi.

Please state the pressures in Pa to avoid confusion.