sevenperforce

Speculation over on NSF.... They are moving the fairing recovery ship, with its new fancy fairing-catchin', net-holdin' arms, to the West Coast. ZUMA was postponed due to unspecified fairing issues with the next fairing-equipped flight...which would be Iridium-4. The Iridium exec said, in a very cagey way, that the Iridium-4 booster wouldn't be recovered but he couldn't say why. The original placement of JRTI was MUCH farther downrange than would have been expected. So the most likely explanation is that the Iridium-4 launch will test new, final hardware for Block 5 fairing recovery, hardware which was under review during the Zuma launch window and resulted in Zuma being postponed. The new hardware likely adds non-negligible dry mass, so the Block 3 booster would have difficulty lofting it while flying recoverable, leading them to strip off the landing legs and other first-stage recovery hardware and burn to completion instead of reserving propellant for boostback and landing. This will also improve the final orbit for the Iridium sats, essentially thanking Iridium for trusting them to use a flight-proven (and, in this case, multiple-flight-proven) booster. Test as you fly. That's what SpaceX has always done.

The rope will not hang perpendicular to the ship, because both the rope and the ship are in free-fall. Gravity is not pulling the rope toward the center of the Earth any differently than it is pulling the ship toward the center of the Earth. In reality, there will be tiny tidal effects which would tend to pull the entire ship into a radial orientation relative to the ground, but there is no source of differential gravitational force which would "tug" on the rope. Again, the rope will not fall. The rope is already falling, and it is falling along with the spacecraft. No, it will not hang in any sense whatsoever. The average temperature of the diffuse gas in the thermosphere is around 2500 degrees, but the air pressure is so negligible that there is no meaningful heat transfer between objects and the air around them. Even though the temperature is technically very high, you are almost perfectly insulated by a vacuum and so it's effectively very cold. Counter-intuitive, I know, but it's the same principle as someone dipping his hand in water and then dunking it in molten lead. The water boils and expands so fast that it holds the molten lead away from your hand, so the heat cannot be transferred to you. Similarly, the gas molecules in the thermosphere have a LOT of kinetic energy due to solar radiation, but there is so much space between molecules that very little of that kinetic energy is transferred to objects as heat. Of course, the lack of heat transfer goes both ways. We say it's "cold" in space because objects lose thermal energy by blackbody radiation faster than they gain thermal energy by collisions with gas molecules, but it isn't cold in the sense that objects in space instantly freeze. If you step into a freezer, you feel cold because your body begins losing thermal energy to the frigid air, but there aren't enough molecules in space to lose energy to, so you don't gain energy or lose energy. Objects that produce their own internal heat, like the ISS and the astronauts it contains, are so well-insulated by vacuum that they will rapidly overheat if radiators are not used to radiate away that thermal energy in the form of blackbody radiation. The rate of heat transfer by blackbody radiation depends on the emissivity of the material and the material's surface area, which is why big thin metal panels are so great at radiating away heat. Slightly pedantic, I suppose, but ships heat up not due to friction but due to compression. When you compress an ideal gas, its temperature increases, because you have the same amount of thermal energy packed into a smaller volume. A re-entering spacecraft is traveling so fast that the air cannot get out of the way, so it is compressed. The air is compressed so rapidly and thoroughly that the kinetic energy of the molecules exceeds their ionization energies, causing them to flash into plasma. As tongues of plasma come into contact with the surface, they transfer their heat to that surface by a combination of conduction and radiation, eating away at it. Modern heat shields are typically phenol-impregnated carbon. Phenol is a volatile organic compound (responsible, incidentally, for the unique flavor present in Islay scotch) that is stable to reasonably high temperatures and then rapidly evaporates. The heat transferred by the re-entry plasma causes the phenol to evaporate, bleeding into a boundary layer that insulates the shield, not unlike the water on a person's hand boils away and insulates them from the molten lead in the example above. The carbon shield underneath doesn't really burn as much as it just slowly bakes in the radiated heat from the plasma.

Surely they can still dog-leg to the ISS, with enough margin. And GTO is a big part of the launch market. The original planned position for JRTI was REALLY far south, presumably because of the trajectory requirements on the planned launch date, so it may be that the booster simply doesn't have enough margin to target JRTI in boostback.

Unless I miss my guess, this is the first time a reused booster will be expended. Wonder if this has anything to do with testing for FH.

I dunno. With nine engines burning and a full fuel tank, the F9 should be able to hover for quite a while. Though you're right; the landing legs would not be happy.

HOLY MOTHER OF

http://www.projectrho.com/public_html/rocket/spacewartactic.php

If there is anything that SpaceX has robustly programmed for, you better believe it's single-engine-out. I daresay the F9S1 has a specific routine for each engine-out at every possible point of the flight envelope. I do not know whether the two edge return engines can fire without the center engine, though. So center-engine-out may FUBAR recovery. If not, then the landing might be two-engine, which we haven't seen. Engine-outs aren't a problem, even with RUD, because of the Octaweb. But the stage can still have structural failures. I wonder -- if a major problem happened in the first few seconds after launch, is there a contingency to simply fly over to LZ-1 and land?

The scramjet engine must take in atmospheric air as an oxidizer and burn it with a fuel. This results in significant drag. In fact, the net thrust of a scramjet (or any airbreathing engine) is the difference between the product of exhaust mass flow and exhaust velocity and the product of intake mass flow and forward velocity, in keeping with the following equation: Fthrust_net = MFexhaust * vexhaust - MFintake * vvehicle Looks complex, but it's intuitive if you think about it. What's providing forward impulse? Well, it's the momentum of whatever you're pushing out of the back end of the engine. But what are you pushing out of the back end of the engine? Fuel, yes, but also all the air you pulled into your intake to mix and burn with your fuel. And that air entered your engine at the forward airspeed of your vehicle, so you have to subtract the momentum it already had in order to find out what your actual effective net thrust is. All that to say -- a scramjet, or any other airbreather, has to deal not only with drag on the vehicle, but also with intake drag. If the handwavium engine has the same total thrust as the scramjet, then the handwavium aircraft will have far superior drag performance because you don't have to deal with an intake. If the handwavium engine has the same net thrust as your scramjet, the scramjet will have lower total drag because net thrust factors in intake drag losses, and the intake of a scramjet is typically a large component of your vehicle body. Another thing to deal with is mass. The scramjet will lose mass as it flies while the handwavium engine will not. However, the scramjet will also lose thrust as it accelerates, due to that vvehicle value increasing, so that needs to be taken into account as well. But none of these differences have anything to do with the mechanical transference of force/acceleration. One can presume the scramjet's airframe is rigid enough that force on the engine mount is transferred to the rest of the craft as well as if each component were being accelerated together.

Tanks were definitely only partially full at takeoff. Lower liftoff mass meant lower takeoff speed. The KC-135 did have to be physically modified (into the KC-135Q) to segregate the JP-7 from the JP-4. I also thought there were modifications to the tanker to allow higher cruise speed (usual refueling speed was below the Blackbird's stall vmin), but it may have just been a different flight profile rather than physical modifications. And the limiting factor on the SR-71's endurance was the amount of TEA-TEB carried onboard to fire the afterburners...which is the same stuff used to ignite Merlin 1D engines.

And let's not forget that an SR-71 had to launch with half-full fuel tanks in order to get airborne, by design, and thus required a top-off refuel by a specially-designed high-airspeed tanker, just to START missions.

And of course they've never had a launch failure on a flight-proven booster. Wonder how long that will last. I also wonder if the failure rate for new boosters (as in, all orbital launches from October 4, 1957 through the present, apart from the three reflown ones) will ever be lower than the failure rate for flight-proven boosters.

Probably around 35-40 tonnes to LEO, with the two boosters returning to the landing pads and the core landing on the ASDS. Fully-reusable throw to GTO is around 8 tonnes, though I think that's for all three boosters RTLS. There is a huge gulf between FH's LEO performance and its GTO performance, because LEO can make better use of its low-isp, high-thrust upper stage than GTO. Anything going beyond LEO really either needs a low-mass kick stage or a very high-energy propellant, for maximum mass efficiency. According to the experts over at NSF, that camera is rotated 90 degrees so it was a normal flip. It does get me thinking, though. Ideally, they'd want as much separation between the two side boosters as possible, to prevent any possible interactions. Flipping horizontally and firing up the three boostback engines mid-flip would push the boosters as far away from each other as possible; then they'd be following a trajectory such that their closest approach would be the landing burn itself.

Sure. Or you can just do it the way I do, and stick a pod to the side of the LV and then blow it off after you jump into the seat, before launch. Won't count against total mass.

Was it just an odd angle, or did the first stage do a horizontal-plane flip? It looked very different. In all prior flips I've seen, it looked like the first stage fired the nitrogen thruster pointing at the ground, causing the nose to head up toward radial and then back toward retrograde. In this flip, it looked like one of the lateral forward thrusters fired, causing the nose to yaw toward normal (or perhaps antinormal?) before rotating around toward retrograde. Is this really a change? If so, why? One possible reason, if this is a new change, might be that they are going to do horizontal-plane flips for the side boosters on Falcon Heavy rather than vertical-plane flips, to put more distance between the two boosters, and so this was an early practice run.

The OP specified "make an all-liquid SSTO" and I suggested we score it based on either "lowest mass/kerbal to LKO" or "lowest part count" or "lowest part count, with ties broken by lowest mass".

Loving pics like these from today's launch: Looking longingly at the old Falcon Heavy animation. All the official SpaceX imagery still has the black landing legs. Any word on whether the Block V legs will have special TPS or something similar, or will they be white too?

IIRC, aluminum fins can be repainted and reused after RTLS landings but not after ASDS landings. The highest-energy ASDS landings burn up the aluminum grid fins so badly that they may start to lose control authority. Titanium grid fins have more control surface area and are thus better for all flights, but particularly for high-energy flights because they give the booster an enhanced glide ratio so it can use less propellant for guidance. You're slightly less likely to lose a booster if it has titanium fins than if it has aluminum ones.

Challenge: Send the doomed Kerbal of your choice on a one-way ride to the destination world, and land him (or her) successfully to plant a flag. Your Kerbal need not return. Lowest launch mass wins. I'll create a separate leaderboard for each destination as they are submitted, but the initial suggestions are Minmus, the Mun, and Duna. All parts must be stock.

They are just much darker than the underlying paint. Oddly, I don't see the same for the core. Doesn't make much sense to use titanium fins on the lower-stress side boosters and aluminum ones on the hot-entry core...but idk. Maybe they are running short on aluminum grid fins and so they decided to put their last four on the core because it has the lowest chance of recovery. Or maybe they just hadn't installed grid fins on the core booster when this screengrab was caught.

I'm going to go out on a limb and say those ARE titanium grid fins, at least on the side boosters.

Clearly I should have read earlier pages of the thread.

As I understand it, the trickiest part of dealing with comet trajectories is that comets lose mass and experience significant braking at perihelion, which really screws up estimates. For something with a perihelion at 1 AU, it should be much more predictable.

And terra firma!

Grid fins out.