totm nov 2023 SpaceX Discussion Thread

[Ultimate Steve]

Later down the line, they could save some Delta-v by not bringing the lox for the ascent, just getting it from the moon. This would make descent abort impossible, but they also don't have descent abort for Mars.

[tater]

One of the talks regarding BFR suggested that for lunar missions they'd do the refilling ops in an elliptical orbit, so that the vehicle would have the dv to land, then return.

[Ultimate Steve]

This managed to slip through, from the SSTO article:

Quote

The teams are now pressing ahead with an untethered test campaign which is expected to see a hop as high as 20 meters in the coming weeks.

 

[tater]

There is a Boca Chica road closure the 28th and 29th, so that's gonna be a hop.

[cubinator]

44 minutes ago, Ultimate Steve said:

This managed to slip through, from the SSTO article:

 

Baby steps - first 20 meters, soon 200 billion meters

[Exoscientist]

9 hours ago, sh1pman said:

“multiple sources”, though. I'll wait for official confirmation. 

How much dv does it need to pull it off? 10k? (Launch + landing)

Theoretically possible with 10k m/s dV, Isp of 380s, 75t dry, 1100t wet mass.

 

 You get 400 m/s for free by launching near the equator, such as from Cape Canaveral. Taking this into account, the delta-v to LEO is often taken to be about 9,100 m/s or 30,000 ft/s:

From Modern Engineering for Design of Liquid-Propellant Rocket Engines, p. 12.
https://books.google.com/books?id=TKdIbLX51NQC&pg=PA12&source=gbs_toc_r&cad=4#v=onepage&q&f=false
 

 Because of the exponential nature of the rocket equation that 900 m/s difference between 10 km/s and 9.1 km/s accounts for a significant amount of payload.

   Bob Clark

[magnemoe]

8 hours ago, Ultimate Steve said:

If Starship has SSTO capability, then it has the Delta-v, if refueled in LEO, to go to the Moon and back with no payload. 3 for TLI, 1 for LLO, 4 for landing and ascent, 1 for transfer, and 1 for landing, heat shielding, and boiloff. That's 10, close to the same as an SSTO. It's a useless capability, but an interesting one.

SSTO will leave little payload capacity, Might be an option for Falcon 9 type launches to LEO, anything higher and you would need an booster stage making an full stack cheaper. 
Nice for testing however. 

[Exoscientist]

4 hours ago, AVaughan said:

Well if they can refuel in LEO, then they should be able to refuel in a highly elliptical orbit (once they have enough operational tankers).  

From a 250 km LEO lunar transfer is about 3120 m/s, capture to low orbit about 820 m/s, landing 1720 m/s, ascent another 1720 m/s, then Earth return and landing should be another 820 m/s plus around 400 m/s to land. So they need around 8600 m/s.  

So assuming a fully refuelled Starship in LEO, and another fully refuel Starship as tanker (also starting from LEO).   1100 tons fully fueled mass and 75 tons dry mass for both ships.   ISP of 380.  (So the tanker version has 1025 tons of fuel and 10 km/s dV at this point.  The other ship has less because it has a payload).

...

 

 The delta-v to orbit is commonly taken to be 9.1 km/s for equatorial orbits because you get a 400 m/s boost by the Earth’s rotation for free.

 Also the dry mass for the BFS upper stage is given as 85 tons by wiki. But this is the version with the passenger quarters for 100 Mars colonists. The tanker version would weigh much less without the passenger quarters, perhaps only in the 50 ton range.

  Bob Clark

[Xd the great]

46 minutes ago, Exoscientist said:

 

 You get 400 m/s for free by launching near the equator, such as from Cape Canaveral. Taking this into account, the delta-v to LEO is often taken to be about 9,100 m/s or 30,000 ft/s:

From Modern Engineering for Design of Liquid-Propellant Rocket Engines, p. 12.
https://books.google.com/books?id=TKdIbLX51NQC&pg=PA12&source=gbs_toc_r&cad=4#v=onepage&q&f=false
 

 Because of the exponential nature of the rocket equation that 900 m/s difference between 10 km/s and 9.1 km/s accounts for a significant amount of payload.

   Bob Clark

Can that book be found on NTRS server?

[Exoscientist]

 Not the recent version from the 90’s. But the 70’s version can be downloaded from the NASA technical reports server:

Design of Liquid Propellant Rocket Engines Second Edition.

https://ntrs.nasa.gov/search.jsp?print=yes&R=19710019929

  Bob Clark

 

Edited May 18, 2019 by Exoscientist

[tater]

 

[tater]

 

So the best they could do is suborbital if they want to test entry and landing downrange.

[CatastrophicFailure]

Off the chain. 

[sh1pman]

I remember the NSF article stating that

Quote

at present multiple sources have indicated that the company is hoping to perform orbital test flights of the Starship prototypes through Single Stage to Orbit (SSTO) launches.

And then there’s that latest tweet by Elon. NSF changed their article after that, and now it doesn’t say anything about the “multiple sources” and their info about SSTO launches. So... why did NSF choose to publish unreliable information from some unknown sources? Not a good look.

[Rakaydos]

15 minutes ago, sh1pman said:

I remember the NSF article stating that

And then there’s that latest tweet by Elon. NSF changed their article after that, and now it doesn’t say anything about the “multiple sources” and their info about SSTO launches. So... why did NSF choose to publish unreliable information from some unknown sources? Not a good look.

The theory I heard is that Elon is managing expectations. The rebuttal to SSTO was in reply to something about starlink launches on starship. even if it can test SSTO (or close enough to SSTO to return to launch site) it's borderline enough that it wont be the miracle SSTO that SSTO fanatics hype up.

[tater]

LOL:

 

[tater]

 

[Exoscientist]

13 hours ago, tater said:

 

So the best they could do is suborbital if they want to test entry and landing downrange.

 Expendable SSTO would also be useful to test. Remember all rockets including the F9 were tested in an expendable mode.

  Bob Clark

[tater]

17 minutes ago, Exoscientist said:

 Expendable SSTO would also be useful to test. Remember all rockets including the F9 were tested in an expendable mode.

  Bob Clark

They know they can go up, they need the EDL part, at least the ED part (skydiver descent). I can see a full up orbital test with a booster, not expecting Starship to survive, perhaps many of those.

[MinimumSky5]

9 hours ago, tater said:

LOL:

 

While SpaceX can be many things, discrete is not one of them! 

[CatastrophicFailure]

40 minutes ago, MinimumSky5 said:

While SpaceX can be many things, discrete is not one of them! 

[magnemoe]

4 hours ago, tater said:

 They know they can go up, they need the EDL part, at least the ED part (skydiver descent). I can see a full up orbital test with a booster, not expecting Starship to survive, perhaps many of those.

Don't think they will launch assuming fail, that is the first orbital reentry will be very high risk.

They obviously start with small jumps followed by actual flights there they brake with the fins, probably with far more safety margins than on later flights, things like going to powered flight far higher. 
Next up will be real suborbital trajectories, later might use the superheavy. 
As landing downrange is a bit impractical they will have to do an falcon 9 first stage style boost back, this will also give some temperature data as in who parts get most heated so they can compare this to simulations. 
Finally the first orbit. 

One issue with landing is that you obviously will have to overfly land unless you land on the US west coast and then you have to move it trough the panama canal on ship anyway.
Any ideas here?

[Kergarin]

On 4/4/2019 at 11:04 PM, sevenperforce said:

Hey all...

Just finished my draft whitepaper/open letter to NASA Administrator Bridenstine. I think it's decent. Sharing a draft link here before I publish.

https://medium.com/@davidstarlingm/back-to-the-moon-61a47c60f78d

Here is a little preview visualization of this.

Please correct if I got something wrong.

 

[tater]

 

[tater]