totm nov 2023 SpaceX Discussion Thread

[JoeSchmuckatelli]

8 hours ago, AckSed said:

*reads* Much as I actually want to talk about it in the correct thread... I will not be sticking my face in to that crossfire of dogma. Then they moved on to just comparing SS/SH with other approaches. I'll be good.

Mein Gott - someone who respects his own time and sanity!

GG.

Well played.

Just now, tater said:

Oil rigs sold. Still interested, but want to fly SS first before committing to particular rigs.

 

Quite interesting.

I'm wondering if it is because of how slow it is to move rigs and given the broad range of potential orbit/launch paths whether they decided that the size was good - but not efficient for other reasons.

[AckSed]

Awww. Though I get it. Even if it would have provided a sort of emergency landing site, it would have been a money pit (oil rig workers need to be paid well, and so do rocket engineers) and not used much otherwise.

[Nuke]

curious about rp flip or something like it. supposedly a lot easier to move and very stable when deployed. i doubt there is enough space there for a launchpad or mechazilla, and its not self propelled so you need a tug. perhaps with substantial retrofitting or a completely new design (potentially self propelled to keep costs down). one advantage is once you catch the starship/superheavy, you could just flip the boat and store it horizontally. 

Edited February 14, 2023 by Nuke

[sevenperforce]

10 hours ago, Nuke said:

curious about rp flip or something like it. supposedly a lot easier to move and very stable when deployed. i doubt there is enough space there for a launchpad or mechazilla, and its not self propelled so you need a tug. perhaps with substantial retrofitting or a completely new design (potentially self propelled to keep costs down). one advantage is once you catch the starship/superheavy, you could just flip the boat and store it horizontally. 

I can't imagine RP being able to flip while holding a 200-tonne empty booster out in front of it.

I guess I can see, however, how something like that would have the advantage of high stability with a high "tower" section poking out of the water that could potentially allow the booster to be caught off to one side. Not sure that there's any advantage to storing Superheavy on its side, though. They've always been upright; that's how they are strongest.

[darthgently]

13 hours ago, JoeSchmuckatelli said:

Mein Gott - someone who respects his own time and sanity!

GG.

Well played.

Quite interesting.

I'm wondering if it is because of how slow it is to move rigs and given the broad range of potential orbit/launch paths whether they decided that the size was good - but not efficient for other reasons.

Consider that when they purchased them it was before stage 0 with catch arms.  Maybe they think they may need a bigger rig.  And want a few flights in to test the booster, stage 0, etc to get some real data for what the real requirement would be.

I could imagine a scenario where after a lot of flights and data are accumulated they end up going back to raw landings without stage 0 and catch arms.  But it would be at the cost of payload given landing leg mass and such

[sevenperforce]

One of the challenges for any ocean vessel platform for Starship is that when fully fueled, Starship+Superheavy comes in at nearly 5000 tonnes, more than ten times the mass of small oil rigs. That weight needs to rest on a launch mount, and if that launch mount isn't positioned over the center of mass of the platform, it's going to cause the platform to list or pitch. Even if the launch mount IS perfectly over the center of mass, it's going to result in the center of mass of the entire platform coming up higher relative to the center of buoyancy, which makes the whole thing less stable to minor rolling/pitching from wave action.

Plus, to take maximal advantage of being out on the ocean, you want your "flame trench" to be open to the water, which means the ship needs to have an open center at its center of mass. That's not impossible, but it does cause some structural concerns. And it also means you have to catch over the launch mount, rather than off to one side as envisioned for the fixed launch facilities.

[RCgothic]

The Troll A platform weighs over a million tonnes with ballast and was mobile prior to installation, so stability with a mere 5000 is not necessarily an insurmountable issue (admittedly that's for a sea floor supported structure). I use it as an example as I was part of its expat community when I was younger.

[sevenperforce]

57 minutes ago, RCgothic said:

The Troll A platform weighs over a million tonnes with ballast and was mobile prior to installation, so stability with a mere 5000 is not necessarily an insurmountable issue (admittedly that's for a sea floor supported structure). I use it as an example as I was part of its expat community when I was younger.

I'm assuming SpaceX would not want a seafloor-supported structure. A single-spar floating structure doesn't work either, given the need for an open center. But a tension-leg floating platform like Mars or Magnolia could work:

Mars, pictured above, has a gross displacement of 53,000 short tons, around ten times the weight of a fully loaded Starship + Superheavy. It is typically secured to the ocean floor and tensioned down to reduce vertical wave movement, but it can pull up its securing members and be towed around. It cost the oil company a billion dollars to build.

[JoeSchmuckatelli]

1 hour ago, sevenperforce said:

One of the challenges for any ocean vessel platform for Starship is that when fully fueled, Starship+Superheavy comes in at nearly 5000 tonnes, more than ten times the mass of small oil rigs. That weight needs to rest on a launch mount, and if that launch mount isn't positioned over the center of mass of the platform, it's going to cause the platform to list or pitch. Even if the launch mount IS perfectly over the center of mass, it's going to result in the center of mass of the entire platform coming up higher relative to the center of buoyancy, which makes the whole thing less stable to minor rolling/pitching from wave action.

Plus, to take maximal advantage of being out on the ocean, you want your "flame trench" to be open to the water, which means the ship needs to have an open center at its center of mass. That's not impossible, but it does cause some structural concerns. And it also means you have to catch over the launch mount, rather than off to one side as envisioned for the fixed launch facilities.

So for the moment they are left with expendable or RTLS.  But if they want to go for down range recovery I'd assume most of the fuel will be expended by the launch, boost back and landing burns - leaving mostly dry mass, correct? 

I think that the structure of a oil rig (having the ability to ballast and quite a bit of it being under water) is definitely better than a barge (given not only the weight but also the height of the booster) - but then I look at F9 and think maybe a large barge could work. 

[AckSed]

Sea launch makes me think of Sea Dragon, and while I don't think they'd go for underwater launch, I'm thinking of them ditching the 1st stage in the sea. Would the booster be strong enough to be refurbished after soft-landing in the sea?

To do it on the regular, or in an emergency, you'd certainly have to do waterproofing of any electronics or access holes, maybe find some way of keeping the rocket end out of the water. Or just drop a test Raptor in the sea, fire it up and see what explodes. If the smaller electric-pump-fed Electron can survive, I wonder how the more corrosion-resistant alloys in the Raptor turbines and injector would fare. Perhaps it's as simple as sending a 'pintle injector close' command before it hits the water?

Edited February 14, 2023 by AckSed

[sevenperforce]

Just now, JoeSchmuckatelli said:

So for the moment they are left with expendable or RTLS.  But if they want to go for down range recovery I'd assume most of the fuel will be expended by the launch, boost back and landing burns - leaving mostly dry mass, correct? 

I think that the structure of a oil rig (having the ability to ballast and quite a bit of it being under water) is definitely better than a barge (given not only the weight but also the height of the booster) - but then I look at F9 and think maybe a large barge could work. 

AFAIK, there has never been any serious plan to do downrange recovery with the booster being caught and then brought back to the launch site. Superheavy was never designed to be transported horizontally, and it is far too large to be transported by ordinary road in any event. Even if it could be caught on a barge and towed back to Boca Chica, there is no port at Boca Chica where it could be offloaded. Boca Chica Bay averages four feet deep and the adjoining beach isn't much better.

So the plan has generally been to have a quasi-fixed offshore launch-and-landing installation, not a "catch-and-return" installation.

It's possible that SpaceX could do catch-and-return to the Cape, though. The Pegasus Barge which brought Space Shuttle external tanks to the VAB had a 15' draft and was able to reach the VAB by going through Port Canaveral and heading up the Banana River, so presumably they could build something similar. The current landing barge/droneships SpaceX uses for Falcon 9 have a draft of 19', which is comparable to the Pegasus, but a barge suitable for catching Superheavy would have to be significantly larger (even setting aside the need for a catch tower).

One possibility (if they were going to catch-and-return) would be a semi-fixed mobile platform with a catch tower that would catch the booster, then transfer it to a secure mount on a dedicated barge. This eliminates the need for landing legs on the booster or a catch tower on the transport barge. Once back at the Cape, the barge could head up the Banana River and have the booster craned off onto a mobile transporter. They might be able to get away with a <25' draft on a barge like that.

2 minutes ago, AckSed said:

Sea launch makes me think of Sea Dragon, and while I don't think they'd go for underwater launch, I'm thinking of them ditching the 1st stage in the sea. Would the booster be strong enough to be refurbished after soft-landing in the sea?

There have been a number of calculations on this. Saltwater is not good for engines generally, so that's considered to be problematic...Raptor is not designed to be submerged in water.

And the tipover, while slowed by the booster's aft section descending into the waves, would still subject the top of the booster to around 16 gees at impact, which is likely more than it can handle.

[JoeSchmuckatelli]

13 minutes ago, sevenperforce said:

transported horizontally

Derp!  Should have thought about this, given the 14-16 foot average height for overpass bridges in the US... It would make no sense for them to reinforce it for road travel anyway. 

RTLS it is. 

Which now makes me question the entire purpose of buying the two rigs in the first place.  Customers would have to ship payloads, etc and then transfer at sea (I know sea transport isn't entirely problematic - but transfer at sea is something I know about and would not recommend for delicate things). 

Which now brings up an entirely new issue... Let's say that SX is successful - and SS becomes the new standard.  Even if you step down to a 7m or 5m diameter payload - getting the rocks we want to throw at space to the launch site is problematic... Meaning what?  Build on site? 

[sevenperforce]

5 minutes ago, JoeSchmuckatelli said:

Derp!  Should have thought about this, given the 14-16 foot average height for overpass bridges in the US... It would make no sense for them to reinforce it for road travel anyway. 

RTLS it is. 

They can ship it back to the launch site if they have a port large enough to allow the catching vessel (or the transfer vessel) to pass in, come up to a dock, and offload to a crane. Then the crane can put it on a crawler and they can transport it to the launch site or inspection site vertically, provided that there is a clear road between the crane location and the destination.

They can likely do this at the Cape, but not at Boca Chica.

5 minutes ago, JoeSchmuckatelli said:

Which now makes me question the entire purpose of buying the two rigs in the first place.  Customers would have to ship payloads, etc and then transfer at sea (I know sea transport isn't entirely problematic - but transfer at sea is something I know about and would not recommend for delicate things). 

That's a relatively minor problem, I think. The launch site just needs to have a clean, protected integration space.

5 minutes ago, JoeSchmuckatelli said:

Which now brings up an entirely new issue... Let's say that SX is successful - and SS becomes the new standard.  Even if you step down to a 7m or 5m diameter payload - getting the rocks we want to throw at space to the launch site is problematic... Meaning what?  Build on site? 

The big flagship things like JWST are already transported over water due to their size. The "suitcase" used to enclose JWST was 5.5 meters high, 4.5 meters wide, and twice as long as a semi-trailer.

[RCgothic]

Of course one option is to catch offshore, refill, and then *fly* back to the launch site.

[sevenperforce]

21 minutes ago, RCgothic said:

Of course one option is to catch offshore, refill, and then *fly* back to the launch site.

Yes, but since the catch arms can't hold a fully-fueled (or really even partially-fueled) booster, you'd still need a whole launch mount for that. At which point, why not just use it for launch as well?

Unsure whether Superheavy can fly on its own without a fairing on the front. That front end with those protruding grid fins has got to be draggy as all hell. Of course the Raptors have great gimbal authority, but still.

[Nuke]

4 hours ago, sevenperforce said:

I can't imagine RP being able to flip while holding a 200-tonne empty booster out in front of it.

I guess I can see, however, how something like that would have the advantage of high stability with a high "tower" section poking out of the water that could potentially allow the booster to be caught off to one side. Not sure that there's any advantage to storing Superheavy on its side, though. They've always been upright; that's how they are strongest.

keeping it in the vertical seems like it would pose a transport problem. the barges seem to work well but keeping the rocket in the vertical probibly limits transport speed by quite a bit. other than being a barge. but being able to ship the booster back to the launch site promptly, and being able to re-deploy the flip boats in a hurry for the next launch seems like a serious solution to the problem of launch cadence.

there are lots of things you can do at sea by moving ballast around to keep the vessel in trim. however you cant just put a mechazilla on a ship and expect that to work, wave action will keep that from happening. immobility is probibly what killed the platforms as a solution, even though its possibly the most stable. barge stability mostly comes from being a flat bottom with a lot of deck space, but that doesnt work if you can burn through the deck. so whatever solution works the best, has yet to be determined. out of box thinking required. 

[magnemoe]

18 hours ago, AckSed said:

Awww. Though I get it. Even if it would have provided a sort of emergency landing site, it would have been a money pit (oil rig workers need to be paid well, and so do rocket engineers) and not used much otherwise.

One use I saw for it was to land Starship on then hopping back to starbase. Most orbits landing at the Texas launch site would be overflying Mexico. You could avoid this launching 45 degree south however. 

[magnemoe]

4 hours ago, RCgothic said:

The Troll A platform weighs over a million tonnes with ballast and was mobile prior to installation, so stability with a mere 5000 is not necessarily an insurmountable issue (admittedly that's for a sea floor supported structure). I use it as an example as I was part of its expat community when I was younger.

Troll A is the heaviest single object moved. Now its an skyscraper higher than the Eiffel tower put on the sea floor, with an platform on top, The bottom has an benefit as you can use it to separate out water so you don't need to pump it 300 meter up. 
I think an platform who is pulled down by anchors would work well because of the sudden weight shift launching. You will also need to store enough oxygen and methane for launches, launches create some safety issues on an oil rig, yes they are designed to manage fire but not an 5.000 ton fuel air bomb, if things go worst possible you could release more energy than the Hiroshima bomb. 
Perhaps some sort of underwater storm shelter at the base of the legs? If the thing blows up you are pretty safe far below the water and if the platform sink you separates and float up slowly unless you drop ballast. 
 

[zolotiyeruki]

What's the status of SpaceX's R&D for producing fuel on Mars?  An offshore launch pad, with nearby floating solar/wind farm (free real estate!) might be an interesting test bed.

[Beccab]

32 minutes ago, magnemoe said:

Troll A is the heaviest single object moved. Now its an skyscraper higher than the Eiffel tower put on the sea floor, with an platform on top, The bottom has an benefit as you can use it to separate out water so you don't need to pump it 300 meter up. 
I think an platform who is pulled down by anchors would work well because of the sudden weight shift launching. You will also need to store enough oxygen and methane for launches, launches create some safety issues on an oil rig, yes they are designed to manage fire but not an 5.000 ton fuel air bomb, if things go worst possible you could release more energy than the Hiroshima bomb. 
Perhaps some sort of underwater storm shelter at the base of the legs? If the thing blows up you are pretty safe far below the water and if the platform sink you separates and float up slowly unless you drop ballast. 
 

It's actually the tallest object ever moved, the heaviest is Gullfacks C. I believe the Troll A is the second tho

[darthgently]

Ultimately, a series of land and water based static launch and landing sites encircling the planet near the equator might become viable.  Boosters would not RTLS, but return to the next site down range.  Then take off from there next eastward launch

Edited February 14, 2023 by darthgently

[CBase]

3 hours ago, sevenperforce said:

Yes, but since the catch arms can't hold a fully-fueled (or really even partially-fueled) booster, you'd still need a whole launch mount for that. At which point, why not just use it for launch as well?

I guess dv loss is too big for ping pong between a land and offshore site as at least launch would be against earth rotation.

And then there is of course the logistic challenge to deliver payloads to the offshore site, additional crew for integration etc. Oh and of course SH and SS would need to land at the offshore plattform to actually use it for orbital launches.

Actually I like the SH refill and fly back story: it provides quite some additional payload over RTLS with minimal requirements for the offshore platform.

30 minutes ago, darthgently said:

Ultimately, a series of land and water based static launch and landing sites encircling the planet near the equator might become viable.

Again I doubt it for the logistics reasons and costs to maintain so many ground based facilities.

[darthgently]

13 minutes ago, CBase said:

I guess dv loss is too big for ping pong between a land and offshore site as at least launch would be against earth rotation.

And then there is of course the logistic challenge to deliver payloads to the offshore site, additional crew for integration etc. Oh and of course SH and SS would need to land at the offshore plattform to actually use it for orbital launches.

Actually I like the SH refill and fly back story: it provides quite some additional payload over RTLS with minimal requirements for the offshore platform.

Again I doubt it for the logistics reasons and costs to maintain so many ground based facilities.

When the eventual goal is thousands of launches per year to Mars and elsewhere  with an additional suborbital hop industry (I'm skeptical on that last, but not the first)  that infrastructure isn't that far out. 

I imagine by that point it would be more an international project with lots of  nations having skin in the game than merely an Elon project.  I mean not even the Wright Bros imagined the current worldwide airport infrastructure and ATC network

Edited February 14, 2023 by darthgently

[mikegarrison]

5 hours ago, JoeSchmuckatelli said:

Which now makes me question the entire purpose of buying the two rigs in the first place.

Have you considered that maybe it was just a bad idea that they finally got around to accepting as a bad idea?

[RCgothic]

On consideration, I would have thought 700t-750t wet would have enough DV to fly superheavy back to the launch site from the offshore landing platform with zero payload, so an offshore Mechzilla wouldn't need to hold the full 5000t.

Edited February 14, 2023 by RCgothic