21

SpaceX Falcon Missions Section / Re: SpaceX F9 : Transporter-14 Rideshare : Jun 2025

« Last post by StraumliBlight on 12/02/2024 09:39 pm »

Care Weather Technologies' 1U Veery-0G cubesat will be carried on an Exolaunch Exopod dispenser. (1110-EX-CN-2024) [Dec 2]

Altitude: 590 km
Inclination: 97°
Mass: 0.95 kg

22

SpaceX Starship Program / Re: Catching Starship's upper stage

« Last post by OTV Booster on 12/02/2024 09:38 pm »

This is probably a good place to cross-link the "catch-only towers" discussion...

To get an idea of what SpaceX means by "rapid reuse", here's a quote from Elon.
I'm not sure SpaceX could meet these goals with catch-only towers.

Starship needs to be fully and completely reusable, and rapidly so.
It's being designed to be relaunched an hour after landing, with zero nominal work.

Like you could have scheduled maintenance, or you could have something like a squawk issue just like commercial aircraft. But the only thing you expect to change on a regular basis is propellant. And it's got to be fast.

Now for the ship, unless you're launching due East from the equator, you've got to figure out some way to get the ship orbital ground track to pass over the landing site. Otherwise you're too far away. So the ship might take 3 orbits, 4 orbits maybe to get back over the launch site.

But I think we want to aim for a capability of 3 flights a day for the ship, most of which is taken up with getting the orbital ground track to come over the launch site. And then an hour for everything else.

It takes 12 hours (8 orbits) for the orbit to match up assuming both ascending and descending nodes are useful. Being one orbit off is an offset of 2400km. I've no idea of the dV requirements needed for this much cross range on ascent but I doubt it's trivial.

Tankers are the easiest. No payload handling other than the normal but extended propellant handling. Are they gonna load dry cargo while stacked? It's safer and easier on the ground.

All ships (depot & LSS excluded) have a heat shield that is delicate and no alternatives or supplements other than transpiration cooling have been flight tested. The tiles and the ship in general can be checked while the cargo is loaded.

ISTM the 1 hour turnaround can be reached for the pad and booster eventually but the ship is not so easy. Elons quote above calls for 3 uses per day which means an 8 hour turnaround. This tempo fits in well with a separate ship landing pad. If the launch pad is rockin and rolling every hour the last thing it needs is a ship coming in for a landing.

Booster lands. While it's being checked and serviced a ship is brought up for stacking. Stack, load propellant, final check and go. An hour turnaround will be a difficult target but not impossible. Interrupt the cycle, landing a ship that will not stack on the booster that's already on the table, and it only makes the turnaround more difficult.

As a side note, I doubt the one hour turnaround is anything more than an inspirational aspiration. Ninety minutes from landing to launch would work well for high tempo ops like a fleet to mars, then 90 minutes to check and prep the pad before the next landing.

Most of the launches will be tankers en route to a LEO depot. One traffic pattern would be one depot in each of 8 orbits separated by 120 180 minutes. Or two or four depots in each orbit.


Edit: changed numbers and cleanup

23

SpaceX Starship Program / Re: Larger Starships

« Last post by meekGee on 12/02/2024 09:24 pm »

Size comparison between Saturn V, Starship, Starship V3, and a theoretical 200x18m Super-Starship.

Super Starship,

~35,000t GTOW
~1,000t to LEO

Eat your heart out Sea Dragon!

Tanker version could basically fully fuel V3 Starship in 2 launches, and probably enough to go to mars in one launch, and a depot version could fill several. This would probably be the main reason to build such a monster.

Size comparison between Saturn V, Starship, Starship V3, and a theoretical 200x18m Super-Starship.

Super Starship,

~35,000t GTOW
~1,000t to LEO

Eat your heart out Sea Dragon!

Tanker version could basically fully fuel V3 Starship in 2 launches, and probably enough to go to mars in one launch, and a depot version could fill several. This would probably be the main reason to build such a monster.

Alas there's as cube law fighting a square law, and as a general rule the cube law wins.

The cube law is the volume, which means mass which means GTOW

The square law is the surface area that can be populated by Raptor 3 engines, whose thrust needs to be 1.5x that of the GTOW.

the 18m Super Starship stack has 5 times the GTOW but only 4x the surface area for Raptor3 thrust, leaving you 4/5 the thrust/weight ratio of Stack V3.  It'll spend a large amount of its fuel just getting 1km into the air.

Then there's a launch mount that can handle 35kt GTOW.  Not to mention the exhaust plume putting 52.5kt of force on top of pilings that are on top of sand.  There's a limit has to how much a rocket can weigh when you are building on sand.

Then there's transporting 18m wide sections down the road from the factory to the launch mount.  A top of the line US standard roadway is 11.6m wide.

I can see maybe going with 12m wide if the height becomes too much for various factors such as center of mass or other considerations, but 18m wide just isn't useful enough to counter the huge downsides.

In other words, for a given engine/frame technology, height is fixed, and so volume grows with R^2  and everything cancels out just fine.

(The constant is different for cylindrical, skirted, or conical rockets - but just relative to R, the relation holds)

A big rocket, in theory, is just like a bunch of small ones in parallel.

That's the end of the theory section.

I practice, large rockets, airplanes ships and trucks benefit from size until at some point they don't.

Since 9 m is a tad small for interplanetary travel, I expect something 12 and up to be the nextGen (I'd have guessed 15) and tankers have to match.

All this, until we get high ISP engines and everything will change.

24

SpaceX Starship Program / Re: Larger Starships

« Last post by RobLynn on 12/02/2024 09:12 pm »

The rational way to design a follow on would be to figure out what is optimal in terms of booster nozzle expansion ratios for whatever chamber pressure they can achieve to minimize payload cost to orbit (nozzles can grow significantly to increase Isp, likely up to Ø2m range at 40MPa chamber pressure up from current Ø1.3m for a 5-10s increase in average Isp), and then perhaps do a separate optimization of length/diameter of starship to maximize payload mass fraction given heat shield and landed payload COG constraints - and use a conical diameter adaptor..  Most likely the stack will end up significantly shorter than block 3 Starship/superheavy.

A more squat starship would obviously help for stability landing on Mars etc.

25

Space Science Coverage / Re: NASA - SDO updates

« Last post by ccdengr on 12/02/2024 08:55 pm »

Keith is on a bit of a hair trigger.  "Really bad news" would be losing the spacecraft, not a water leak in a server room

26

SpaceX Starship Program / Re: Safe Intantaneous Impact Point Tracks for Starship Recovery

« Last post by TheRadicalModerate on 12/02/2024 08:55 pm »

Wow, that does seem grim.

How then will the SpaceX magician comply with FAA public safety regulations?  At first glance there doesn't appear to be a rabbit hidden anywhere in that hat.

Oh but wait. Essentially at whim, the Secretary of Transportation can waive any or all of those regulations, simply by deciding that doing so "will not jeopardize the public health and safety." Title 51 U.S.C. 50905(b)(3).

The key there is that the law doesn't say the Secretary must determine public safety isn't jeopardized. The Secretary must simply decide that is the case. Having made that decision, the Secretary can waive any requirement, including the requirement to obtain a license.

The most obvious way to comply is to demonstrate entry and descent reliability that's high enough that overflying the populated areas doesn't exceed the 1E-04 expected value for injuries to the public.  However, that requires a fairly deep set of successful EDLs.  As usual, there has to be some point where empirical data gives way to probabilistic risk analysis, so it likely doesn't require more than... 20 EDLs?  15?

I have no clue what the Trump Whisperer and King of DOGE will be able to get through in terms of regulatory reform.  However, relaxing the expected value--or waiving it--is a bad look if something bad happens.  "Keep things from falling on people" should be a pretty non-controversial goal for the FAA.

(OT note:  I do think it's now highly likely that the FAA won't hold up a license for Starship missions to land on Mars, effectively pulling the teeth on any planetary protection restrictions.)

27

Space Science Coverage / Re: NASA - SDO updates

« Last post by StraumliBlight on 12/02/2024 08:53 pm »

JSOC Emergency Resources Page

Status:
 • All resources from the Stanford JSOC website and data system are unavailable until repairs and recovery are completed
 • IRIS Level 2 data through November 22, 2024 remain available at iris.lmsal.com/search/
 • The Virtual Solar Observatory is the best location to find historical AIA and HMI science data through November 26, 2024,  • though not all dates and products are available
 • SDO EVE data products are not impacted by this outage

28

SpaceX Starship Program / Re: Safe Intantaneous Impact Point Tracks for Starship Recovery

« Last post by TheRadicalModerate on 12/02/2024 08:46 pm »

Starship flies a lifting entry so you would generally expect debris following a ballistic trajectory to come up shorter. Having them overshoot requires a breakup before the onset of significant aerodynamic forces and extremely high ballistic coefficients.

Yeah, this is really the big insight from this exercise.  (Like many "insights", it's more of a "duh!" once you think about it.)  It isn't really surprising that an intact vehicle would have a higher BC than its debris field.

what is the equivalent BC of Starship following a lifting entry?

Just doing the most brain-dead estimation possible:

m = 120t + 20t for EDL (could be a little heavy)
Cd = short cylinder with streamlined nose and flaps =... 1.0?
A = 50m x 9m @ 60º AoA (assume flaps and reduced nose area roughly cancel) = 450 * .87 = 390 (fixed sin(60) value)
BC = m/(ACd) = ~360kg/m², maybe up to 400 around max q, as AoA comes down a bit.

29

Space Science Coverage / Re: NASA - SDO updates

« Last post by Targeteer on 12/02/2024 08:41 pm »

https://twitter.com/NASAWatch/status/1863545758441513410/photo/1

30

SpaceX Starship Program / Re: Larger Starships

« Last post by ZachF on 12/02/2024 08:39 pm »

Size comparison between Saturn V, Starship, Starship V3, and a theoretical 200x18m Super-Starship.

Super Starship,

~35,000t GTOW
~1,000t to LEO

Eat your heart out Sea Dragon!

Tanker version could basically fully fuel V3 Starship in 2 launches, and probably enough to go to mars in one launch, and a depot version could fill several. This would probably be the main reason to build such a monster.

Size comparison between Saturn V, Starship, Starship V3, and a theoretical 200x18m Super-Starship.

Super Starship,

~35,000t GTOW
~1,000t to LEO

Eat your heart out Sea Dragon!

Tanker version could basically fully fuel V3 Starship in 2 launches, and probably enough to go to mars in one launch, and a depot version could fill several. This would probably be the main reason to build such a monster.

Alas there's as cube law fighting a square law, and as a general rule the cube law wins.

The cube law is the volume, which means mass which means GTOW

The square law is the surface area that can be populated by Raptor 3 engines, whose thrust needs to be 1.5x that of the GTOW.

the 18m Super Starship stack has 5 times the GTOW but only 4x the surface area for Raptor3 thrust, leaving you 4/5 the thrust/weight ratio of Stack V3.  It'll spend a large amount of its fuel just getting 1km into the air.

Then there's a launch mount that can handle 35kt GTOW.  Not to mention the exhaust plume putting 52.5kt of force on top of pilings that are on top of sand.  There's a limit has to how much a rocket can weigh when you are building on sand.

Then there's transporting 18m wide sections down the road from the factory to the launch mount.  A top of the line US standard roadway is 11.6m wide.

I can see maybe going with 12m wide if the height becomes too much for various factors such as center of mass or other considerations, but 18m wide just isn't useful enough to counter the huge downsides.

Scaling law also works in the favor of larger turbines, the larger turbines get, the more efficient they get.

A ~5x larger ~15,000kN Super-Raptor could probably get 450 bar pretty easy if they are already getting 350+ bar with Raptor 3.