totm nov 2023 SpaceX Discussion Thread

[magnemoe]

17 hours ago, kerbiloid said:

But the Big Dumb Boosters were using Big Dumb Engines.

Who is correct, however as was disposable it was critical to keep the cost down. 
SpaceX does not have this constrain because of reuse. 

16 hours ago, mikegarrison said:

This is totally not true.

Musk has declared that he *intends* to do this, but it's thermodynamically crazy. Even though there is too much CO2 in the air right now, it's still only 400 parts per million. Just collecting it from the air is quite difficult. And then turning it into fuel NECESSARILY requires more energy than burning that fuel (second law, entropy), so it takes a crazy amount of energy to turn large quantities of CO2 into a hydrocarbon fuel.

And all that energy has to come from somewhere. Even if Musk has a huge solar plant that creates enough energy to make rocket fuel with, that's still energy that's not being used to avoid emissions in other places. Low-carbon energy should be used preferentially to replace high-carbon energy, not wastefully to try to turn CO2 back into methane.

This,  now having an test plant to create methane from co2 and water makes sense, but I guess they would use low pressure co2 with some other gases like nitrogen, argon and traces of oxygen. rather than our atmosphere there the main problem is separating out the co2. Yes you will get some if you try to make lots of LOX

 

[RealKerbal3x]

A new FCC document gives us an idea of how the first Starship orbital flight test will proceed:

Quote

The Starship Orbital test flight will originate from Starbase, TX. The Booster stage will separate approximately 170 seconds into flight. The Booster will then perform a partial return and land in the Gulf of Mexico approximately 20 miles from the shore. The Orbital Starship will continue on flying between the Florida Straits. It will achieve orbit until performing a powered, targeted landing approximately 100km (~62 miles) off the northwest coast of Kauai in a soft ocean landing.

I guess they're going to be attempting booster ocean landings until the 'catch it with the tower' system is ready to go.

Landing Starship in the middle of the Pacific also seems sensible given that the chance of RUD on this first re-entry is quite high, though I'm not sure how or even if they plan to recover it.

[tater]

 

(I assume it's Kauai and a typo)

[RealKerbal3x]

1 minute ago, tater said:

(I assume it's Kauai and a typo)

Yeah, the document I posted above says Kauai.

[RCgothic]

Same thing with some images from Michael Baylor

 

 

[sevenperforce]

Just now, RCgothic said:

Same thing with some images from Michael Baylor

Literally came here to post that.

It makes a lot of sense. Avoids overflight of land during the scary parts. And they definitely need to be able to demonstrate boostback and landing burns for the booster before attempting to drop it onto land. This allows them to validate the heat shield and aerodynamic re-entry management even if they haven't worked out all the kinks in the landing sequence yet. 

[tater]

 

 

[YNM]

1 minute ago, sevenperforce said:

It makes a lot of sense. Avoids overflight of land during the scary parts. And they definitely need to be able to demonstrate boostback and landing burns for the booster before attempting to drop it onto land. This allows them to validate the heat shield and aerodynamic re-entry management even if they haven't worked out all the kinks in the landing sequence yet. 

Actually interesting to note that in the Boca Chica EIS the role that Boca Chica can play is to "Allow SpaceX to launch the Falcon 9 and Falcon Heavy orbital launch vehicles, and a variety of reusable suborbital launch vehicles".

Not sure if this has since been changed to allow for experimental orbital launch vehicles (ie. Starship / Superheavy completing one full orbit) but I think the less-than-one-orbit situation still fits the planning description...

[tater]

As expected, soft water landings.

It's actually not impossible that they could still recover the vehicles.

(for study)

[RealKerbal3x]

Just now, tater said:

As expected, soft water landings.

It's actually not impossible that they could still recover the vehicles.

Maybe they could bring OCISLY or JRTI out to SN20's mid-Pacific landing zone and use it to transport it back after it's been fished out of the water.

[sevenperforce]

9 minutes ago, tater said:

I wonder whether Starship will do a deorbit burn or if it will just boost to what is effectively a very, very long suborbital trajectory and come down that way. It definitely saves propellant reserves. They might even be able to get away with a smaller prop load and only sacrifice three Raptors...although that seems unlikely.

This also means they don't have to worry about solving the landing leg problem yet.

[tater]

3 minutes ago, sevenperforce said:

I wonder whether Starship will do a deorbit burn or if it will just boost to what is effectively a very, very long suborbital trajectory and come down that way. It definitely saves propellant reserves. They might even be able to get away with a smaller prop load and only sacrifice three Raptors...although that seems unlikely.

This also means they don't have to worry about solving the landing leg problem yet.

The flight time is just over 90 minutes (5420s).

The only reason to technically achieve orbit, then deorbit is for the right to say they went to orbit. So I bet they do that.

[RealKerbal3x]

12 minutes ago, sevenperforce said:

This also means they don't have to worry about solving the landing leg problem yet.

The current landing legs aren't a problem for landing on prepared surfaces like the landing pad. They only really need to solve that problem once they're landing on the Moon or Mars, but I expect they'll have some better legs ready before then.

[sevenperforce]

4 minutes ago, tater said:

The flight time is just over 90 minutes (5420s).

The only reason to technically achieve orbit, then deorbit is for the right to say they went to orbit. So I bet they do that.

Hawaii is 3700 miles from Boca Chica. 90 minutes is a lot of flight time to only go 85% of the way around the world. Granted, part of that is ascent and descent but most of it is not. Seems more likely that they would say "we placed Starship in an orbit which intentionally crossed Earth's atmosphere to ensure safe disposal if there was a problem." It would be a bad, bad day if you ended up with another CZ-5B R/B situation but with a vehicle ten times larger.

19 minutes ago, sevenperforce said:

They might even be able to get away with a smaller prop load and only sacrifice three Raptors...although that seems unlikely.

And to answer my own question -- no, they can't do this, three SL Raptors would limit it to a prop load of about 550 tonnes which only gives 4.9 km/s, not nearly enough for orbit.

[tater]

https://twitter.com/SpaceX/status/1392926112540364807?s=20

 

6 minutes ago, sevenperforce said:

Hawaii is 3700 miles from Boca Chica. 90 minutes is a lot of flight time to only go 85% of the way around the world. Granted, part of that is ascent and descent but most of it is not. Seems more likely that they would say "we placed Starship in an orbit which intentionally crossed Earth's atmosphere to ensure safe disposal if there was a problem." It would be a bad, bad day if you ended up with another CZ-5B R/B situation but with a vehicle ten times larger.

Yeah, what is the min nominal alt for orbit? Anything below 200km is coming down in the next couple orbits for sure, if not the current one. Maybe a small burn to land by Kauai, with the hazard area still before S. Am. over the Pacific if the burn fails. Whatever they do, high enough to claim orbit, low enough for certain safe disposal.

[Beccab]

9 minutes ago, tater said:

https://twitter.com/SpaceX/status/1392926112540364807?s=20

Damn, I hoped it would have been the full flight without the interruptions because of the signal at least the landing is beautiful there

[tater]

Yeah, waiting on the youtube version. Their cameras aboard MUST buffer the data, right?

[CatastrophicFailure]

45 minutes ago, RealKerbal3x said:

Maybe they could bring OCISLY or JRTI out to SN20's mid-Pacific landing zone and use it to transport it back after it's been fished out of the water.

They’ve been planning this for a while, I would think they’d have a recovery ship of suitable capacity to fish it out of the water, given prior experience. 
Tho more than likely it will just become marine habitat for some fish who have NO idea how cool their new home is. 

[RealKerbal3x]

I still want more Flap Cam.

[tater]

BTW, the FCC filing is interesting in that they are perfectly happy to throw away a rocket as big as Nova for data.

Substantially more powerful than SLS. Their "Green Run" will be to orbit.

Remember when Musk said he saw a path to building Starship for less than Falcon 9? No one knew if he meant the dev costs, the actual vehicle, or what. 30-something million on engines, and some metal tubes.

[Beccab]

If everything goes fine with BN3 and soft water landing, I could see them attempt an actual landing or even booster catching with BN4

[sevenperforce]

20 minutes ago, RealKerbal3x said:

The current landing legs aren't a problem for landing on prepared surfaces like the landing pad. They only really need to solve that problem once they're landing on the Moon or Mars, but I expect they'll have some better legs ready before then.

The current landing legs are single-use crushables. 

Spoiler

12 minutes ago, tater said:

Yeah, what is the min nominal alt for orbit? Anything below 200km is coming down in the next couple orbits for sure, if not the current one. Maybe a small burn to land by Kauai, with the hazard area still before S. Am. over the Pacific if the burn fails. Whatever they do, high enough to claim orbit, low enough for certain safe disposal.

Let's see here.

The burn to orbit lasts 345 seconds (there's not much we can figure out from this; burning all six engines at full throttle for that long would consume 1,413 tonnes of propellant which is much more than Starship's capacity but we know they will throttle down or shut off the SL Raptors at some point). I don't feel like doing the integration to estimate the distance covered by a vehicle with variable thrust over this regime, so I'm going to cheat and use Falcon 9 as a rough guide. A quick glance at the last RTLS launch with a good webcast suggests that SECO-1 occurs about 1400 km downrange from the pad.

So in the 4900 seconds between SECO and splashdown, Starship will travel 7450 km less than the circumference of the Earth, about 81% of a full orbit. We do have to shave off some time for the descent, of course. It took SN15 about two minutes to go from 10 km to the ground. If we guesstimate that SN20 will reach terminal velocity about 20 km above the Pacific (based on the Shuttle's speed-to-altitude regime), that's about four minutes total of non-horizontal motion.  So we reduce that 4900 seconds to 4660 seconds. By the power of basic math, a full orbit would be 5,750 seconds or about 96 minutes. For a circular orbit that would be an orbital altitude of 568 km ASL which seems wildly high.

Even if we increase the drop time and allow six minutes of non-horizontal motion, that's still 471 km. It doesn't make sense to allow any more drop time than that because terminal velocity will be higher where it's higher up, decreasing drop time. No way is SpaceX putting a 150-tonne chunk of metal into a circular orbit HIGHER than the ISS, not on its first go-round. If anything goes wrong that would be disastrous.

On the other hand, if the targeted periapsis is ~30 km ASL then the apoapsis can be a nice merry 970 km, you get an toasty entry interface at 8 km/s, and you are assured of a safe disposal if anything goes wrong. And you can still say it's a proper orbit.

[Beccab]

4 minutes ago, sevenperforce said:

So in the 4900 seconds between SECO and splashdown, Starship will travel 7450 km less than the circumference of the Earth, about 81% of a full orbit. We do have to shave off some time for the descent, of course. It took SN15 about two minutes to go from 10 km to the ground. If we guesstimate that SN20 will reach terminal velocity about 20 km above the Pacific (based on the Shuttle's speed-to-altitude regime), that's about four minutes total of non-horizontal motion.  So we reduce that 4900 seconds to 4660 seconds. By the power of basic math, a full orbit would be 5,750 seconds or about 96 minutes. For a circular orbit that would be an orbital altitude of 568 km ASL which seems wildly high.

I am probably missing something obvious, but would it be possible to make starship do a full orbit and then the 81% or would that reduce altitude too much?

[tater]

A full orbit has the failure mode of not restarting, and an uncontrolled reentry a la cz-5b.

Bad idea.

[sevenperforce]

5 minutes ago, Beccab said:

I am probably missing something obvious, but would it be possible to make starship do a full orbit and then the 81% or would that reduce altitude too much?

Definitely not possible. 1.8 full orbits at exactly 100 km would take 156 minutes. 

Deimos is currently undergoing retrofit at Brownsville. The FCC filing doesn't specifically say that the booster will splash down. I wonder if they try to land it on Deimos if only to recover the engines.