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?
JRP3
Hyperactive Member
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.
Brass Guy
Active Member
You people are too funny - designing Space-X's SH booster catcher for them! I hope Elon's paying attention here.
Ben W
P85 #61, Roadster #108
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.
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.
Watts_Up
Active Member
What not using existing buildings to have StarShipPorts similar to HeliPorts !!!!
UkNorthampton
TSLA - 12+ startups in 1
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.
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).
You're thinking 50m of motion!?!?
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?
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...
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.You're thinking 50m of motion!?!?
No abort at that point, same phase of launch as releasing the hold down clamps.
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
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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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:
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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JRP3
Hyperactive Member
Scott Manley did some Kerbal modeling
Xepa777
Member
So, what's the under/over for when Bezos is going to say that the New Glenn was always going to be caught, and that landing on barges is so last decade?
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...
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
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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