sevenperforce

Further speculation suggests that one possible reason for keeping the grid fins on S1 is to control the descent and make sure the plummeting empty stage avoids the fairing recovery boats that will be out there. EDIT: Doesn't explain why the mission patch shows a bare S1 with its engines firing, though. Maybe they will still do the entry burn to ensure structural integrity is maintained through entry? Not super sexy, but makes sense. Also, related -- Mr. Steven has left the harbor and is pushing south as fast as it can go. From NSF article: Has SpaceX ever actually come right out and stated that Block 3 stages can only be reflown a single time?

The rest of the rocket is metal that they want to protect. The interstage is composite and doesn't need a protective coating.

Same reason as the Shuttle ET, I suppose?

It's my understanding that the Block 5 interstage is unpainted composite -- dark grey or black.

Maybe it's just the lighting, but it looks like a Block 5 interstage. Perhaps the grid fins are to test the new interstage?

Wait what

Mr Steven in still in harbor, last we checked, but one of the support boats (a Go Searcher, I think) is on its way out to the NOTAM. Of course, Mr Steven is quite fast so that's no surprise.

The bird is out on the TEL! And sure enough, there are fins but no legs. Curiosuer and curiouser. Thought they said RCS wasn't yet good enough for stability just before landing. Also, no clamp slots.

That is very odd. And clearly intentional. It's not like they could "accidentally" draw fins but no legs. I wonder if they are going to use this as a test of maximum survivable entry speed, using a booster they're expending anyway? Or perhaps they are testing entry without an entry burn, to see if it can be managed?

The going theory is that they’re simply out of space for used boosters, and being a Block 3 there’s not much utility in recovering it anyway. #1stworldproblems Along with some speculation that they want additional margin because they're testing the Block 5 fairing recovery system, which makes the fairings a bit heavier than Block 3 boosters can safely lift AND land WITH recovery hardware.

I think the initial separation kick will be during the boostback burn; from there on, they'll be gliding back toward each other.

Ti fins also give the returning boosters more control authority and a higher glide ratio, meaning they don't have to reserve as much propellant for boostback because they can glide crossrange. The core doesn't need crossrange capability, so aluminum fins are fine. Of course, the aluminum fins on the core will get torched since it's a high-energy entry, but what else are they good for?

Flying expendable, Falcon Heavy can send 3.5 tonnes to a Pluto Hohmann transfer, which is 390 m/s short of solar escape with a hyperbolic excess velocity of zero. Oumuamua is trucking along with a hyperbolic excess velocity of 26 km/s. So if you can fit more than 26.39 km/s of dV into a 3.5-tonne package on Falcon Heavy, you can catch up to Oumuamua. At launch, the Dawn spacecraft packed three ion thrusters and 425 kg of xenon with a dry mass of 792.7 kg, for a total of about 10 km/s of dV (avg isp = 2000 seconds). Let's suppose we add 2.28 tonnes of xenon (ignoring tankage mass, as that dry mass can probably be reduced since we don't need all the same things Dawn has), bringing total mass up to 3.5 tonnes. With the same average isp, that gives us 30.8 km/s of dV. Not an early catch, but a catch. We can improve that if we strip down the mass of our spacecraft a bit. New Horizons had a dry mass of only 401 kg; optimistically, this would give us a whopping 42.6 km/s of dV. Very doable.

Since AMOS-6, they don't encapsulate or integrate until after the static fire.

They'll encapsulate and then integrate.

TEA-TEB.

Oh. Well, that explains that. Makes sense. The nose cone has lower drag than the bare interstage, lowering the center of pressure, so they'd want to increase the drag on the fore end of the rocket to help with stability. This suggests that they'd like to burn through all of the aluminum grid fins, but they can't do so with the side boosters.

Tidal forces will have an effect on the ship as a whole. Unless there's some magical station-keeping force (KSP-style infinite reaction wheels and an RTG) keeping the spacecraft oriented prograde, then tidal forces will tend to pull the whole thing into a single equilibrium position as it orbits.

Someone, ahem, me. Poring over the image of the octaweb mating at the bottom. Looks like clasps at the nearest attachment points, plus two pneumatic pushers on each side. Also looks like those pneumatic pushers will rotate up after the separation. This is really quite complicated.

Also, FWIW, hypergolics are bipropellant just like LO/LF. Given the infinite restartability of kerbal engines, hypergols are a closer analogue to kerbal fuel than cryos.

HELLS TO THE YESSSSSSS (excuses himself while the adrenaline rush passes) Grid fin setup is exactly as I thought, based on the one little image we got all ready. It's an odd choice. The Block 5 grid fins have more control surface area and can provide a better L/D ratio for the returning stages, which would presumably give the side boosters a better shot at returning. Aluminum grid fins can be used for high-energy entries, like what the core will have, but they are single-use. Maybe they are less-than-optimistic about the core recovery chances and so they are going to use up the aluminum grid fins that way? Also, WOW at the insides of those reused Merlins. Another note -- the two boosters are oriented to the reverse of each other. This suggests the design for the side boosters is singular (e.g., they only mount one way) and are oriented appropriately, as needed. Smart.

In stock, build a reusable launch system capable of assembling, erecting, de-erecting, and fueling an orbital launch vehicle with at least two stages.

I don't think it's nearly so simple as that. Note that the pricing for F9 is for "up to 5.5 mT to GTO" and the pricing for FH is "up to 8.0 mT to GTO", even though the theoretical maximum GTO performance of the two rockets is 8.3 mT and 26.7 mT to GTO, respectively. So the current pricing is for new boosters, but assumes that they will reserve enough performance for recovery. This performance reservation allows SpaceX to stockpile boosters which it can offer at a reduced price, thus making money hand over fist while vastly undercutting all competing launch providers. So the $14M/booster upcharge for FH should not be taken as an indicator of manufacture cost, but of manufacture cost amortized over the expected lifespan of reused boosters at the not-listed-above reused booster price.

I wonder what delta-v is required for what is, in essence, an ICBM launch from the east coast to the west coast. The lowest-energy transfer probably has a really high apoapse, which makes entry...challenging. Could be the start of a nice challenge, over on the challenges subforum. "Using fully-recoverable rocket stages, take a boat from KSC to the water on the west coat of the KSC continent."

If you have to get a ship from FL to Vandy at short notice, just strap F9S1s to those four arms and to the prow, and rocket it over!