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Falcon Super Heavy/Starship - General Development Discussion

JRP3

Hyperactive Member
Aug 20, 2007
19,577
43,139
Central New York
I did some sophisticated modeling

Catchy Mc Catchtface.jpg
 

mongo

Well-Known Member
May 3, 2017
12,904
38,113
Michigan
I did some sophisticated modeling

View attachment 622916
Nice :)
The thing I don't like about that setup is the arms push the top of the rocket into the valley which messes up the control dynamics. Also need sone level of movement to track the ship. Without enough standoff, the rocket needs to slot the gap.
Can work with less gap if the cradle rotates around the tower to surround the booster as it moves by.

Two towers playing double dutch with cables?
:D
 
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JRP3

Hyperactive Member
Aug 20, 2007
19,577
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Central New York
Yeah I thought about straps/cables to allow some flex and cushion the forces, though the arms could have a swivel point and be spring loaded to provide some flex.
 

Ben W

P85 #61, Roadster #108
Feb 27, 2009
622
491
Santa Barbara, CA
I would imagine that catching all four grid fins at once (rather than two) would be much better for load-balancing. I'm envisioning two semicircular arms that start wide and pinch inward as the rocket descends, catching two grid fins each.

FWIW, I don't think it's realistic that the fully-fueled rocket could be held in midair by its grid fins on launch; all that fuel (plus Starship) is HEAVY! (Hence the name.) But who knows, maybe the arms could still attach and provide a slight upward push on launch? Might increase max payload by a ton or so, but I doubt it's worth the added complexity.
 
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UkNorthampton

TSLA - 12+ startups in 1
Jun 15, 2019
580
4,925
Northampton, England
I'm not thinking a cradle, that would be one arm.
I'm envisioning two independent arms that each pivot and cover a near 180 degree region extending out their length. (90 degrees to tower being ideal).
They track the booster's entry and swing into position as it passes by.
Black: tower
Blue: arms
Orange: capture area
View attachment 622895
Not really any tolerances, critcal parameters are arm manuvering speed and accuracy versus booster lateral speed.
Optionally, the fins can move to an angled downward position to grab the arms and tuck them in. Other pair should be folded for clearance.

For fun, imagine holding the rocket by all four points for launch. Can then be high off the ground, and the base never needs to support a fully fueled rocket stack. The vertical actuators can even add delta-v at launch.

Elon has been practicing THROWING the baby up & then CATCHING. A small initial vertical throw upwards seems like a good idea, just getting the mass moving. Very mild catapult (aircraft carrier) launch.
 
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bxr140

Active Member
Nov 18, 2014
2,680
3,575
Bay Area
A small initial vertical throw upwards seems like a good idea, just getting the mass moving.

FWIW I think the KISS approach probably rules out ground based motion. Providing any appreciable external energy into a fully fueled launcher seems a complicated proposition. I think this one is analogous to SpaceX using Starship as a moon/mars lander instead of adding complication with additional vehicles.
 
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mongo

Well-Known Member
May 3, 2017
12,904
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Michigan
FWIW I think the KISS approach probably rules out ground based motion. Providing any appreciable external energy into a fully fueled launcher seems a complicated proposition. I think this one is analogous to SpaceX using Starship as a moon/mars lander instead of adding complication with additional vehicles.
Yeah, it's added complexity, but if the arms already have the actuators due to the landing system, it would boost payload. The rocket is least efficent on a fuel to delta-v metric at launch.
The travel is a limiting factor, but with 50m of motion, at 1G (same as static loading, engines provide net acceleration, so could be as simple as a counter weight) it would provide 31m/s of boost or 112 kph.

I've had the mind game of using a pully and counter weight system to lanuch rockets with >1G acceleration using a tunnel in/ on a tall mountain for launch rail support. A counterweight 8x the rocket mass and a 2:1 mechanical (dis)advantage (so pulley output of 4x) gives a 3 G acceleration (I think). But I digress (even further).
 

bxr140

Active Member
Nov 18, 2014
2,680
3,575
Bay Area
Yeah, it's added complexity, but if the arms already have the actuators due to the landing system, it would boost payload. The rocket is least efficent on a fuel to delta-v metric at launch.
The travel is a limiting factor, but with 50m of motion, at 1G (same as static loading, engines provide net acceleration, so could be as simple as a counter weight) it would provide 31m/s of boost or 112 kph.

You're thinking 50m of motion!?!? :eek:

So you're thinking a mostly/fully passive thing? Interesting...that would be a little less complicated. I guess the major factor would be designing the thing to abort a big ass rocket moving at 112kph?

Given my extreme laziness what's the benefit of 31m/s in vertical velocity? I guess one would wag the nominal energy required to get to orbit and then 1/2mv2 a 0th order fractional energy offset from the huck-o-gizmo?

I've had the mind game of using a pully and counter weight system to lanuch rockets with >1G acceleration using a tunnel in/ on a tall mountain for launch rail support. A counterweight 8x the rocket mass and a 2:1 mechanical (dis)advantage (so pulley output of 4x) gives a 3 G acceleration (I think). But I digress (even further).

Also could use fans to minimize the air column in a tunnel...though...maybe the impact of hitting the atmosphere at the end of the tunnel would cause some problems...
 
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mongo

Well-Known Member
May 3, 2017
12,904
38,113
Michigan
You're thinking 50m of motion!?!? :eek:
Yeah, because I'm also thinking of the arms traversing that far on the landing catch. Basically make contact early and then lock at 0 velocity.

So you're thinking a mostly/fully passive thing? Interesting...that would be a little less complicated. I guess the major factor would be designing the thing to abort a big ass rocket moving at 112kph?

No abort at that point, same phase of launch as releasing the hold down clamps.

Also could use fans to minimize the air column in a tunnel...though...maybe the impact of hitting the atmosphere at the end of the tunnel would cause some problems.

If it's a really tall mountain, then we could get lower pressure. Or for most worst case failure, vacuum doors at the end
 

Ben W

P85 #61, Roadster #108
Feb 27, 2009
622
491
Santa Barbara, CA
Given my extreme laziness what's the benefit of 31m/s in vertical velocity? I guess one would wag the nominal energy required to get to orbit and then 1/2mv2 a 0th order fractional energy offset from the huck-o-gizmo?

The rocket equation is cruel, particularly when combined with gravity losses. Saturn V used up 8% of its fuel just clearing the tower. So a little boost at launch can go a long way. It still may not be worth the added complexity, but I bet they've done the math. If the arms are reliable enough to catch the booster, they're probably reliable enough to throw it (or rather, to give it some assist on launch; even a 10% effective weight reduction is huge during the first few seconds).
 
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mongo

Well-Known Member
May 3, 2017
12,904
38,113
Michigan
Given my extreme laziness what's the benefit of 31m/s in vertical velocity? I guess one would wag the nominal energy required to get to orbit and then 1/2mv2 a 0th order fractional energy offset from the huck-o-gizmo?

The rocket equation is cruel, particularly when combined with gravity losses. Saturn V used up 8% of its fuel just clearing the tower. So a little boost at launch can go a long way. It still may not be worth the added complexity, but I bet they've done the math. If the arms are reliable enough to catch the booster, they're probably reliable enough to throw it (or rather, to give it some assist on launch; even a 10% effective weight reduction is huge during the first few seconds).

My go to for the rocket equation: Rocket Equation Calculator

If the full stack is 5,000 mT and the isp is 330, then the first 31m/s would require burning off 48mT of fuel. 38m/s takes 53mT.
However, that is the in-orbit calculation (ideal). Since the rocket is fighting gravity, the acceleration and fuel burn depends instead on total engine thrust and burn rate.
Number of engines: 28
Full stack mass of around 5,000 mT (metric tons)=5,000,000 kg = 5Mkg
Total thrust: Raptor is 2,200 kN * 28 engines = 61.6 MN. (Might be 65MN)
Force due to Gravity is 5Mkg * 9.8 = 49 MN.
Net force 12.6 MN.
Acceleration = 12.6 MN / 5Mkg = 2.52 m/s or about a quarter of a G.
Assuming mass stays relatively constant for ease of calculation:
Fuel consumption: 565kg/s

Note that using a straight 1:1 counterweight approach would result in only 9.8 m/s acceleration until the rocket hit a thrust to weight ratio of >1. Anything higher would out accelerate and unload the counterweight.

Edit: need mechanical advantage in addition to the mass: Using a 1.25x mass counterweight would provide the acceleration calculated here.

With a 1G addition: 9.8m/s + 2.52m/s = 12.32m/s
50 m travel: t=sqrt(50*2/12.32) = 2.85s
Speed at end of boost: 2.85 * 12.32 = 35.1m/s
Time to speed without boost: 35.1/2.52 = 13.93s
Time saved: 13.93 - 2.85 = 11.08s
Fuel saved: 11.08 * 565 * 28 = 175Mkg or 175mT
This does not correspond directly to payload, and they would not rely on the boost to get to orbit, but it would increase the amount of fuel Starship or Tanker have once they get there which is the critical factor for refueling trips needed.
 
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HVM

Savolainen
Oct 30, 2012
1,005
1,724
Finland
There was talk about how sea launch and landing platform would cost up hundred millions of dollars to build. SpaceX subsidiary has acquired two oil rigs just $3.5 million apiece. What was the thread "Shorting Oil, Hedging Tesla"? There could be lot of semi free sea platforms for sale in future...

rigs1.jpg

https://twitter.com/thejackbeyer/status/1351331758084661252

NSF thread about rigs:
Deimos and Phobos - offshore Starship launch platforms

"Following up on thejackbeyer's find, I can confirm that Deimos and Phobos are the names of two oil rigs purchased by SpaceX – likely for conversion to support Starship operations. ENSCO 8500 and ENSCO 8501 were the previous names of the rigs. They are nearly identical twins."
https://twitter.com/nextspaceflight/status/1351442201134264321
 
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