Jump to content

SpaceX Discussion Thread


Skylon

Recommended Posts

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:

14ipea8.jpg

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

Link to comment
Share on other sites

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. 

Link to comment
Share on other sites

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

Link to comment
Share on other sites

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:

14ipea8.jpg

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?

Link to comment
Share on other sites

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.

Link to comment
Share on other sites

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.

Link to comment
Share on other sites

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

Link to comment
Share on other sites

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.

Link to comment
Share on other sites

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?

Link to comment
Share on other sites

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.

 

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...