totm nov 2023 SpaceX Discussion Thread

[Shpaget]

33 minutes ago, RCgothic said:

In Flight Abort pics:

 

Is there a failure mode where main engines can't be shut down? I suppose there is a conceivable scenario, but if the computer that is supposed to turn off the engines locks up, can they still be shut down? If not, can Dragon still get away if abort needs to happen near the end of the first stage burn (max acceleration)?

[mikegarrison]

2 minutes ago, Shpaget said:

Is there a failure mode where main engines can't be shut down? I suppose there is a conceivable scenario, but if the computer that is supposed to turn off the engines locks up, can they still be shut down? If not, can Dragon still get away if abort needs to happen near the end of the first stage burn (max acceleration)?

IIRC, they said something during the video stream to the effect that the capsule is able to safely LES even if the booster engine does not shut down.

[CatastrophicFailure]

4 hours ago, tater said:

Pad area:

https://p3d.in/dGEWg

Wow. Really puts in perspective how close the launch site is to the tank farm.  Yeesh. 

Edited May 14, 2020 by CatastrophicFailure

[sevenperforce]

Just now, RCgothic said:

Shared RCS and abort propellant is efficient, I like! This would have been awkward for landing burns though.

Yes, it's pretty efficient. An escape tower is wasted mass; using the same propellant for abort as for maneuvering means you can take your LES to orbit for nothing more than the weight of the SuperDracos. Note that this is also what Starliner does, although its liquid-fueled abort and maneuvering system are in its service module so it drops that before re-entry. Disadvantage to both systems is that liquid engines are more complex and fault-prone, and if something goes wrong the crew are trapped with it (for example, the capsule that blew up). 

The original design had enough propellant to do all on-orbit maneuvers and still execute a powered landing, with chutes for abort or for landing backup.

Just now, RCgothic said:

Ok, so 300s ISP and 1290kg propellant is 235 to 375m/s. Should be sufficient for all docking manoeuvres on a lunar mission.

*BUT* not enough for NRHO injection or TEI. Dragon would have to devote up to 2.2t of its 6t payload to get to TEI from NRHO. How much DV for NRHOI?

As I noted above, there's more props than we thought. Around 450 m/s of dV.

Getting in or out of NRHO on a short transit costs 410 m/s dV. In both cases you do a powered lunar flyby in addition to your entry/exit burn at NRHO. 

4 minutes ago, mikegarrison said:

9 minutes ago, Shpaget said:

Is there a failure mode where main engines can't be shut down? I suppose there is a conceivable scenario, but if the computer that is supposed to turn off the engines locks up, can they still be shut down? If not, can Dragon still get away if abort needs to happen near the end of the first stage burn (max acceleration)?

IIRC, they said something during the video stream to the effect that the capsule is able to safely LES even if the booster engine does not shut down.

I think the peak loading of the first stage is something like 2.5 gees and the abort pushes 5-6 gees, so plenty of margin. 

[sevenperforce]

@RCgothic

If you gave Crew Dragon an aux prop pack in the trunk with 4-6 Dracos and the same propellant tanks it carries internally, it would increase takeoff mass to 12.97 tonnes and give the whole system 827 m/s of dV. That's assuming 6:1 ratios on the propellant tank system. More than enough to get from NRHO back to Earth but not enough to get there and back again. Triple the prop tanks in the trunk and you get 1,112 m/s of dV, which is enough to go there and back again if launched onto TLI by FH with the center core expended (would require man-rating FH).

Tripling the prop tanks in the trunk would make the liftoff mass just shy of 15 tonnes, which is more than FH can throw to TLI with full reuse but easily within margins for side-core reuse.

[magnemoe]

37 minutes ago, RCgothic said:

Shared RCS and abort propellant is efficient, I like! This would have been awkward for landing burns though.

Ok, so 300s ISP and 1290kg propellant is 235 to 375m/s. Should be sufficient for all docking manoeuvres on a lunar mission.

*BUT* not enough for NRHO injection or TEI. Dragon would have to devote up to 2.2t of its 6t payload to get to TEI from NRHO. How much DV for NRHOI?

Think superdrako is currently not set up for restarting. That was the issue with the dragon 2 who blew up so they switched to burst disc. 
Even if they planned to land with the superdrako doing an parachute landing, either splashdown or perhaps parachutes and short landing burn if low on fuel because say you had an bad launch and had to use more propelant. 

[RCgothic]

Argh! Wonder what the hold up is?

 

[tater]

5 minutes ago, RCgothic said:

Argh! Wonder what the hold up is?

They have a few days in a row lined up. Better to do it right.

[RCgothic]

Testing may be cancelled today, but work continues:

 

[RCgothic]

I'm actually amazed by how few Falcon cores seem to be active right now! A complete list of known Falcon 9 cores:

B1049 4 Flights, prepping for Starlink-7 on May17th. Joint flight leader.

B1051 4 Flights, in refurbishment. Joint flight leader.

B1058 New, planned for Crew Dragon Demo-2.

B1059 2 RTLS CRS flights. In refurbishment.

B1060 New, planned for GPS-III (Columbus).

B1061 New, planned for Crew-1.

That's two fairly used boosters and just one other that's flown!

For Falcon Heavy we have:

B1052 Side core, 2 flights. Presumed for upcoming USSF-44.

B1053 Side core, 2 flights. Presumed for upcoming USSF-44.

Presumably a new centre core is in production for USSF-44 but it won't survive that Side-ASDS Core-expended mission.

 

[Hannu2]

10 minutes ago, RCgothic said:

I'm actually amazed by how few Falcon cores seem to be active right now! A complete list of known Falcon 9 cores:

 

I am actually amazed how one company can have 8 working rocket stages simultaneously and half of them are used and to be used again. If someone had predicted this decade ago I would have thought he is crazy and maybe need medical help. Actually I think Musk is crazy but in very creative and positive way and does not need doctor but billions of funding for his crazy ideas. SpaceX has made impossible to obvious in a decade, even all those manned Mars things are not realistic.

[RCgothic]

It's not very many vs a stated aim of 35-38 falcon launches for 2020 though. Either they've got a few more in production or they're expecting those 6 cores to each fly 5 times this year! Of course demand may be a little lower due to events.

Block 5 has had attrition of 13 to 5 cores over 35 core flights. That's an average of 2.7 flights per core, and a core lost or expended every 5 missions.

In fact, put that way it doesn't sound half bad! 80% of missions recovered, including those where no attempt was even made!

 

Edited May 15, 2020 by RCgothic

[Hannu2]

36 minutes ago, RCgothic said:

It's not very many vs a stated aim of 35-38 falcon launches for 2020 though. Either they've got a few more in production or they're expecting those 6 cores to each fly 5 times this year! Of course demand may be a little lower due to events.

Those numbers are typically quite optimistic. Probably they can also manufacture few new ones during end of the year. As far as I know they have relatively fast production line.

 

[zolotiyeruki]

One thing to keep in mind is that F9 first stages are rather large.  Having many just sitting around would take up a LOT of space.  And it's not like they're cheap to make, either.  Having a large inventory is not efficient, business-wise, especially since launches are scheduled far in advance.  Unlike with some commodities, you're not going to see any panic-buying of rocket launches, barring some sort of cataclysmic world-ending event

[RealKerbal3x]

Eventually, when Starship is in operation, I envisage that Falcon 9/Falcon Heavy's only remaining customer will be NASA, for crew missions to the ISS and cargo to Gateway in NRHO. It remains to be seen whether NASA will warm up to SpaceX using flight-proven boosters on crewed missions, and SpaceX's future inventory size hinges around that. It's possible that they may continue to produce F9 boosters at a reduced rate, or just stop the F9 production line entirely and simply fly a number of flight-proven boosters repeatedly, periodically refurbishing them to keep them going.

ISS will probably remain in operation until 2030, and by then NASA may have already decided to crew-rate Starship, meaning bye bye Falcon and Dragon. Though before NASA flies crew on Starship/Super Heavy, I imagine NASA will want it to have some kind of launch escape system. I've been thinking about possible Starship LES configurations for a while and I feel that since Starship is designed to be a fully reusable system, meaning that the LES can't just be jettisoned when it is no longer deemed necessary, that anything designed into the vehicle as part of a launch escape system must also serve another useful purpose post-launch. Perhaps a set of throttleable liquid fuel LES engines draining propellant from the header tanks could later act as auxiliary thrusters for final landing on the Moon/Mars, similar to the 9 auxiliary engines planned for Starship HLS.

[RCgothic]

LES doesn't work on Mars or the Moon. The goal for starship is to just be reliable enough that it's not required. 

[RealKerbal3x]

Just now, RCgothic said:

LES doesn't work on Mars or the Moon. The goal for starship is to just be reliable enough that it's not required. 

That's what NASA said about the Space Shuttle, and 14 people died. I think at least initially NASA is going to require an LES if they ever fly their astronauts on Starship, because they don't want to make that same mistake again.

Besides, my point is to make the LES useful later as a set of auxiliary engines for landing (to avoid plume-regolith interaction) rather than it being dead weight - or worse, jettisoned - after it is no longer useful as an escape system. Essentially, it's similar to the original plans for Crew Dragon - as long as there isn't a launch abort, the LES is put to a different use later for assisting in the landing of the vehicle.

[RCgothic]

Starship just doesn't work with an LES, and if that means NASA won't use it then so be it.

You don't just bring along auxiliary thrusters capable of blasting 1500t free from Superheavy at MaxQ, and Starship isn't capable of controlled flight in part.

[RealKerbal3x]

10 minutes ago, RCgothic said:

Starship just doesn't work with an LES, and if that means NASA won't use it then so be it.

You don't just bring along auxiliary thrusters capable of blasting 1500t free from Superheavy at MaxQ, and Starship isn't capable of controlled flight in part.

Well, then we'll just have to see how reliable Starship can be made. LES or not, I think crew Starship is still some years off, giving them some time to get it right. The fact that it's being built by a single company with a single vision, rather than a country-spanning network of contractors, will mean it avoids the fate of the Shuttle, hopefully.

[magnemoe]

43 minutes ago, RealKerbal3x said:

That's what NASA said about the Space Shuttle, and 14 people died. I think at least initially NASA is going to require an LES if they ever fly their astronauts on Starship, because they don't want to make that same mistake again.

Besides, my point is to make the LES useful later as a set of auxiliary engines for landing (to avoid plume-regolith interaction) rather than it being dead weight - or worse, jettisoned - after it is no longer useful as an escape system. Essentially, it's similar to the original plans for Crew Dragon - as long as there isn't a launch abort, the LES is put to a different use later for assisting in the landing of the vehicle.

You has the idea of mine of putting both header tanks in the nose. Have 9? small engines and decouple the top one or two decks and let this fly off or land separate. Extra weight will be the escape engines, piping to them and the extra bulkhead or two at the bottom of the escape module. 
You has to move some stuff like hot gas tanks for pressurizing the header tank and flight system up in the nose and have extra systems to let you fly the escape module independent. 
Technically you can use this on a Moon or mars base too, if you figure out how to land on the escape engines but it would only be useful during the final part of landing or at start of takeoff as you would end up too far downrange, however with just the top decks you probably get some dV with the header tank. 

The moon starship top engines most belive are methane and oxygen gas engine who would be capable of hover starship on moon but not on earth. 

 

[CatastrophicFailure]

3 hours ago, RealKerbal3x said:

That's what NASA said about the Space Shuttle, and 14 people died. I think at least initially NASA is going to require an LES if they ever fly their astronauts on Starship, because they don't want to make that same mistake again.

The space shuttle had a number of failure modes during launch that were not survivable purely because of its bizarre design. That design itself made it impossible to ever be “reliable enough.” Firstly, Starship won’t suffer those same flaws (tho it may have different ones), it can shrug off multiple engine failures, even, ahem, catastrophic ones. It has no finicky solids to worry about. It can’t have a repeat of the two Falcon failures since it won’t have pressurant tanks within the fuel tanks. 

But more importantly, what really gives Starship the possibility of eventually becoming “reliable enough” is its flight rate. The shuttle flew, what, 135 times? Once up and going, SS could conceivably exceed that in less than a year, even a few months. An average of one flight a day is well within SpaceX’s plans, and that is a lot of flight hours to get all the bugs out, though it will take time. We don’t plan these days for the wings simply falling off an airplane, in the early days of aviation this was a very real threat. Crew rating Starship based on “reliable enough” will take a lot of launches, but with the planned flight rates this actually becomes plausible. 

[Barzon]

11 minutes ago, CatastrophicFailure said:

Once up and going, SS could conceivably exceed that in less than a year, even a few months. An average of one flight a day

why would it be launching that often? what would it be launching? the space market cannot support even 3 or 4 M/HLVs, so why would it have enough demand to enable Starship to fly hundreds of times a year? It won't be flying hundreds of starlink batchs, because I've heard that it takes about a month to make a batch of 60 sats, which limits it to 12 Starlink launches a year and I don't think SpaceX would want to launch each sat one at a time, no matter how cheap Starship launch costs are.

And no matter how reliable Starship gets, NASA will never accept the risk of not having a LAS on crewed spacecraft.

Edited May 15, 2020 by Barzon

[tater]

They should delay the Starlink, why trash a booster?

[magnemoe]

9 minutes ago, CatastrophicFailure said:

The space shuttle had a number of failure modes during launch that were not survivable purely because of its bizarre design. That design itself made it impossible to ever be “reliable enough.” Firstly, Starship won’t suffer those same flaws (tho it may have different ones), it can shrug off multiple engine failures, even, ahem, catastrophic ones. It has no finicky solids to worry about. It can’t have a repeat of the two Falcon failures since it won’t have pressurant tanks within the fuel tanks. 

But more importantly, what really gives Starship the possibility of eventually becoming “reliable enough” is its flight rate. The shuttle flew, what, 135 times? Once up and going, SS could conceivably exceed that in less than a year, even a few months. An average of one flight a day is well within SpaceX’s plans, and that is a lot of flight hours to get all the bugs out, though it will take time. We don’t plan these days for the wings simply falling off an airplane, in the early days of aviation this was a very real threat. Crew rating Starship based on “reliable enough” will take a lot of launches, but with the planned flight rates this actually becomes plausible. 

True Shuttle has multiple design flaws, SRB is one, yes they work for Dreamliner and Orion simply as it has an escape system and is high above the SRB so you can simply shred them to terminate.
Reentry is another, here Starship is better but not fail safe. Abort during high stress phase of reentry is very very hard, you could perhaps manage it with an top escape pod on Starship, leading has tiles and you could use flaps to keep the tiles forward during reentry but this will probably require multiple orbital drops. Luckily cargo starship can do them while deploying satellites  

[StrandedonEarth]

19 minutes ago, Barzon said:

why would it be launching that often? what would it be launching?

Tankers. IIRC it takes at least three or four tanker launches to refill a Starship. Then boost to high elliptic and refill again. It can take quite a few tanker launches to refill a heavily laden Starship bound for BLEO