Jump to content

SpaceX Discussion Thread


Recommended Posts

23 minutes ago, mikegarrison said:

I wonder what the volume limit is? And of course there will be a door-passing size limit, probably.

The PDF posted earlier has the diagram for the internal dimensions and the image which implies no door passing size limit.

Link to post
Share on other sites
46 minutes ago, mikegarrison said:

Every cargo vessel is both weight and volume limited. We're only seeing the weight limit here, but I wonder what the volume limit is? And of course there will be a door-passing size limit, probably.

Screenshot-20200331-183936-Drive.jpgFeel free to do some maths. Extra-long 22m version also available apparently.

Link to post
Share on other sites
2 hours ago, RCgothic said:

Screenshot-20200331-183936-Drive.jpgFeel free to do some maths. Extra-long 22m version also available apparently.

The trapezoidal volume of revolution of the given points is 678m3, or 917.5m3 for the 22m version assuming it's the 8m section that's stretched not the curve.

Space shuttle had a cargo volume of 10600cuft or 300m3.

SLS Block 1 cargo has 286m3.

SLS Block 1b cargo has 537m3

SLS Block 2 cargo has 988m3 assuming an 8.4m fairing.

So SLS Block 2 cargo has more volume than even a stretched starship and could potentially be larger still with a 10m fairing, but let's not start pretending SLS Block 2 isn't anything more than a paper rocket, lol.

6 minutes ago, RealKerbal3x said:

I love how Starship can get more payload to the lunar surface than SLS can get to LEO :P

With refuelling.

Edited by RCgothic
Link to post
Share on other sites

Spadre's 4K stream is alive. The nose cone looks stacked?

That might be the old one. The camera is at such an angle you can barely see the fins.

Edited by Wjolcz
Link to post
Share on other sites

Some more maths - at 2MN and a sea level ISP of 330s a single raptor has a specific propellant consumption of approx 620kg/s.

A single raptor can lift about 165t at a TWR of 1.2. If the dry mass is 120t+ then the propellant mass is <45t. That's 72s of full throttle or less.

Technically the acceleration is an inverse function of thrust divided by time-variant mass, but as the mass fraction is low for an estimate I save myself a lot of trouble by assuming acceleration varies linearly between ignition (0.2g) and burnout (0.7g). This overestimates the acceleration mid-flight by about 2.5%.

a = 2.1 + 0.061*t   m/s/s

v = 2.1t + 0.031*t^2 m/s

Velocity at burnout (72s) is 312m/s. Coasts to 0m/s in a further 32s.

The altitude at burnout is:

s = 1.1t^2 + 0.01t^3 m

Or approx 9.4km. From 312m/s it'd coast another 5.0km before gravity brings it to a stop.

That's an absolute flight ceiling of 15km expendable on a single raptor, ignoring air resistance and being really generous with the dry mass. Spitballing I'd guess 5km max altitude including reserves for landing.

Link to post
Share on other sites
13 minutes ago, cubinator said:

I suppose they'll eventually do hop tests with the Superheavy booster as well.

Given how much data they must have from 50 Falcon 9 landings, I'm not so sure. Obviously they'll need to do static fires to make sure a vehicle with 37 Raptors doesn't tear itself apart, but Superheavy is basically a bigger Falcon 9 with more engines, which should make it easier.

Link to post
Share on other sites
7 minutes ago, sevenperforce said:

Seems like a LOT of torque on those hinges. With Falcon 9 the force is distributed between the hinge and the piston.

Yeah, the second animation seems more likely. Still, the narrow spread seems... scary.

Of course for a lunar variant, 1/6g...

Link to post
Share on other sites
13 minutes ago, MinimumSky5 said:

Maybe not, the weight on the legs seems to be transmitted through the final bulkhead directly onto the legs, without the hinge taking any strain. 

Yeah, that was the impression I got

Link to post
Share on other sites
6 minutes ago, StrandedonEarth said:
21 minutes ago, MinimumSky5 said:

Maybe not, the weight on the legs seems to be transmitted through the final bulkhead directly onto the legs, without the hinge taking any strain.

Yeah, that was the impression I got

It seems like it could put a lot of torque on the joint/hinge, but I suppose if you can make it work under tension then that's a positive anyway.

I wonder how to get larger spread.

Link to post
Share on other sites
3 minutes ago, sevenperforce said:

It seems like it could put a lot of torque on the joint/hinge, but I suppose if you can make it work under tension then that's a positive anyway.

I wonder how to get larger spread.

If the legs go straight down, then the weight shouldn't strain the hinges (discounting lateral motion). If the legs spread out, then yeah,  that would put strain on the hinges. OTOH, lots of heavy machinery (excavators and such) have some heavy-duty pivot points. The trick is making it beefy enough without being too heavy..

Link to post
Share on other sites
5 hours ago, StrandedonEarth said:

If the legs go straight down, then the weight shouldn't strain the hinges (discounting lateral motion). If the legs spread out, then yeah,  that would put strain on the hinges. OTOH, lots of heavy machinery (excavators and such) have some heavy-duty pivot points. The trick is making it beefy enough without being too heavy..

If you have multiple locking points you can reduce the stress on the hinge, but yes you will still try to twist the frame, 

Link to post
Share on other sites

I wonder how the auto levelling will work, specifically. Perhaps the ship will have downward-facing radar to enable it to deploy each leg in the correct extension before touchdown, to avoid any tippage.

Link to post
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...