sevenperforce

I see what you did there.

From everything I've seen, S1 sep always comes before LES jettison. Glad the crew is ok.

Looks to be a 70-75 second test fire, by my count. Mach diamonds not nearly as pronounced as on the devscale engine. Suggests that they really are going all-out with sea level engines, rather than designing a compromise nozzle with a converging-diverging-converging bell like the SSMEs. The fact that they expect to be able to do a lunar free return (roughly 2.8 km/s out of LEO) without refueling, combined with the fact that they expect upwards of 100 tonnes to LEO in cargo configuration, can provide some degree of guesstimate as to how much "payload" they expect to comprise in a dozen passengers and their cabins, etc.. The mechanics of that flip are going to be challenging. Makes more sense now than it did before, though.

Ugh. I agree with you and disagree with the article. "...astronaut David Scott intentionally left a simple plaque the size of a beer coaster with the names of astronauts and cosmonauts that perished in the space race on the lunar surface. Charles Duke left a family portrait encased in plastic. Astronaut Alan Shepard decided to drive a pair of golf balls across the surface of the moon. Apparently for kicks, astronaut Edgar Mitchell hurled one of the support rods of a solar wind collector like a javelin through the lunar atmosphere. All these astronauts peed into sacks called urine bags then discarded them on the moon. (It reminds me of guys at a bachelor party in New Orleans.) Twelve men have walked on the moon, and zero women. It shows. The moon has become the solar system’s largest bro playground." Moralizing, self-aggrandized, self-righteous claptrap.

I did test the biconic, four-brake entry in KSP. It works quite well for how much limited control I was able to exercise. KSP's SAS engine doesn't understand what's happening, so the surfaces don't really work via SAS. I had to bind each control surface to an action group and toggle that way, and this meant no fine control authority. Forward and aft flaps are both elevons set perpendicular to the axis of the vehicle. Execute deorbit burn, then use RCS to rotate around to prograde, then SAS hold. Pitch up to radial-out as you cross 70 km. Set all flaps to maximum lateral extension (launch position for forward flaps; ~45 degree deflection from landing position for aft flaps). During descent, hold AoA at approximately 75 degrees and damp roll. Use the following controls: To pitch up, feather the aft flaps dorsally, away from landing position, and feather the forward flaps ventrally to maximum lateral extension. To pitch down, feather the forward flaps dorsally and feather the aft flaps ventrally to max lat ext. To cancel clockwise roll, feather both port flaps dorsally and hold both starboard flaps at max lat ext. To cancel counterclockwise roll, feather both starboard flaps dorsally and hold both port flaps and max lat ext. Care should be taken to avoid dropping AoA below 40 degrees. At roughly 40 degrees, the aft flaps come out of stall and begin to develop lift, kicking the tail up and turning the whole vehicle into a lawn dart. You have NO differential braking authority without a high AoA. Entry works best if you maintain forward flaps at maximum lateral extension and use the aft flaps for primary pitch control. This allows some degree of combined pitch/roll authority, because you can control pitch with the aft flaps while damping roll with the forward flaps. Yaw authority is possible if you lower AoA to around 50 degrees, so that the aft flaps develop stall lift (still no laminar flow) and then brake differentially. For port yaw, maintain lateral extension on the port forward and starboard aft flaps but feather the other two dorsally; this will point the small control surface lift vectors in the direction you want. For starboard yaw, reverse. With four differential braking surfaces, the landing flip is a breeze. Extend the forward flaps and feather the aft flaps to full dorsal position, which pitches you up into a body-lift stall and orients the engines retrograde. Throttle up, and all control surfaces stop interacting with the airstream as you complete the landing burn. Rotate the aft flaps forward into landing position and land.

Work has been nuts so I just now got a chance to come here and comment on the presentation (which I was lucky enough to view live).... WOWWWWWW AHHHH! Okay, got that out of my system. I must say I was completely sure that those trapezoidal panels were something fancy to protect the engines or act as a collective nozzle or something...and no, it's aft cargo. SMH. Aft cargo is neat, though. Competes neatly with Blue Moon, if you think about it. "Hey, we can deliver up to 4.5 tonnes to the lunar surface!" "Oh, that's nice. We can deliver 5 tonnes to the lunar surface. Twelve times. In twelve different places. Reusably. While carrying tourists." Also teases the possibility of a separate abort assist motor if NASA is hesitant about abort TWR; you could replace several of the pallets with solid motors to give the initial kick away from a RUDing first stage. On to the control surfaces. This makes a LOT of sense, and it explains why I was never able to get my BFS clones to re-enter properly. The four flaps do NOT have laminar flow over their surfaces during entry, so they do not provide any meaningful lift. Rather, they function as airbrakes. Elon made several comparisons to a skydiver, and that's exactly how it will work. A skydiver falls prone, with all four limbs extended to act as brakes. By pulling in or extending limbs in pairs, the diver can induce pitch and roll, and if skillful, yaw. I didn't see how the BFS could have three-axis control with only two control surfaces, but with four differential braking surfaces, it's fairly straightforward. It sounded a little odd when Elon made statements about "yeah it is riskier but I like the aesthetics," but on review I think that's looking more holistically. The risk is development risk, not operational risk; it's risky to force landing gear and control surfaces to develop as a single unit because if you can't do it then you've wasted a lot of time. And the aesthetics probably include stuff like simplicity, functionality, and so forth.

Visually, we see little evidence of such effect in the Falcon 9 launches. Then again, inward gimbal on skirt engines is very limited so they may not be able to gimbal inward enough. As far as I understand the fluid dynamics...which is not much, admittedly, but probably about as much as anybody here...it's a valid approach. Might squeeze out an extra 2-3% more thrust. Keep in mind that a full-size engine bell is only 5% more thrust and carries with it a bunch of extra dry mass. That's something completely different.

Such a configuration would really decrease the maximum thrust of the stage. Dev Raptor, SL nozzle, SL: 567 kN Dev Raptor, SL nozzle, space: 612 kN Dev Raptor, Vac nozzle, space: 633 kN Raptor, SL nozzle, SL: 1,700 kN Raptor, SL nozzle, space: 1,834 kN Raptor, Vac nozzle, space: 1,900 kN You know, looking at this, I don't think they need vacuum nozzles at all. The Raptor has such a ridiculously high chamber pressure that its SL pressure losses are really small, and it's only about 5% underexpanded in vacuum.

Nah, you misunderstand. The Raptor they've shown tests for was a scaled-down Raptor: So the development scale Raptor is a third the thrust of the full-size Raptor. Presumably, then, you could connect a dev scale Raptor to a full-size Raptor's engine bell assembly and you'd end up with a vacuum-optimized dev scale Raptor.

The dev scale Raptor is about the size of a Merlin, albeit heavier with much higher thrust. An MVac is roughly the size of a SL full-size Raptor. I wonder if they decided to mix 3 SL full-size raptors with 4 dev scale Vacuum Raptors and use the same engine bells for everything.

So, little-known fact: "aerospike" actually refers to a "plug" nozzle, the point being that you do not need a full-length spike because gases entrained at the base of the plug act as a stagnation zone which generate a spike effect. The spike is made of "air" (gases), thus aero-spike. If the outer engines are all gimbaled inward, then perhaps the same effect is possible, with the exhaust plume of the core engine acting as the virtual aerospike. Extensible nozzles a la RL-10 save length but not diameter. The BFS is diameter-limited.

They don't want a complete engine redesign.

Agreed. Getting even an empty rocket stage to orbit one time (and being able to confirm it) is enough.

I'd be happy with 4-10 grams, too -- anything big enough to transmit. The issue is that when we start to do extreme miniaturization, the benefits start to drop off considerably. Once the payload is less than half the dry mass of your terminal stage, decreasing the mass of the payload is really no longer necessary because it only adds a tiny amount of extra dV, since the dry mass of the terminal stage dominates the rocket equation. The other solution is to add yet another stage...but below a certain size, mass-efficient solid-fueled stages are simply not a thing, due to square-cube losses. So, Ignition! is a fantastic book, but I do think some of the danger is exaggerated for comedic and dramatic effect. HTP isn't very nice, to be sure, but it's doable. This guy synthesizes his own HTP to build monoprop jetpacks and he hasn't exploded yet. More to the point, HTP is the only dense, non-toxic, non-cryogenic liquid oxidizer available, period. Would have to build at least 4x as many cores if we don't do recoverable test. Recovery of side boosters is still on the table for the orbital flight if our margins are good enough. Sorry, I mean vetoing the expendability of the side boosters. See above.

If you count pixels you can see that the depicted engine bells are exactly 1.3 meters, so they are standard SL engines. I imagine the depiction of a burn in cislunar space is probably just artistic license. You'd need a lot of refueling trips to do an orbital mission. While the original reusable Falcon 9 upper stage was designed with a translatable engine, the complexity is far too great. Thrust structure concerns alone would make it utterly unmanageable. I like going back to three landing points. Four landing points means instability if you land on a surface that isn't completely flat. And those big fins look Those petals are curious. I can see them folding down to act as debris impingement protection for the engine bells. One really unlikely (but exciting) possibility is that they protrude to act as an inside-out aerospike nozzle and the six engines in the ring gimbal outward to make that happen. Getting the wings to fold and unfold correctly is a problem. If they don't fold out properly after entry, you can't land. Though perhaps with those new forward canards, the vehicle would have enough pitch control to do a survivable unpowered belly-first splashdown in the event of a critical failure.

Wall thickness and fineness ratio are becoming major questions in estimating mass ratios. I wonder if a small electric pump for the HTP would be helpful. If we run into propellant mass fraction issues, it might be useful to consider a kerosene+HTP electric-impeller-fed liquid engine with concentric tanks for strength.

Unfolded again.

51 tonnes is way too big. Falcon 1 was 85 tonnes. Smallest orbital rocket ever launched was the SS-520 at just under 3 tonnes. Individual rocket components need to be transportable by road w/o difficulty, so any unfueled component over half a tonne is right out. The specification above uses 5 cores that are each 300 kg empty and 2.3 tonnes fully-fueled, with a 60-kg upper stage, and a liftoff TWR of 1.8:1 on a GLOW of under 12 tonnes. Total combined takeoff thrust of 210 kN is about three times that of a SuperDraco and only 17% higher than the Stratos II+, but with a lower TWR than the Stratos II+ you might need a flame trench.

Some preliminary calculations... We can put a 4-10 kg payload into LEO (120x120 km, 0 degrees from sea launch at the equator) with a 12-tonne 2.5-stage launch vehicle if we can manage the following: HTP+jellied petrol first stage and boosters Propellant mass fraction of 85% Vacuum Isp of 240s Dry TWR of 15:1 Solid-fueled second stage Propellant mass fraction of 80% Vacuum Isp of 200s Dry TWR of 20:1 Propellant mass fraction on the hybrid is going to be the biggest challenge. For reference, the extremely well-designed Stratos II+ hybrid rocket built by DARE students in the Netherlands has a propellant mass fraction of roughly 50%. HTP has a much better density than nitrous, of course, but it's still a big challenge.

Something like the GIRD rocket first built by the Soviets is a mixture of liquid and hybrid tech and is VERY easy to build and test: http://www.russianspaceweb.com/gird09.html

Ablative paint on the inside of the nozzle (can probably be sprayed on) makes the nozzle reusable. No need for regenerative cooling. Parachute recovery of a true bipropellant stage is a complete non-starter. A hybrid motor is, by design, tough enough to land via chute.

I wonder if they can do a partial prop load on S1 for the P2P hops. BFS can almost make an antipodal P2P flight with no first stage at all, so it could get away with a much lower separation speed. Saves wear on the booster, reduces propellant costs. The bulk of the propellant cost is on the first stage.

I believe the Merlin 1D gimbals only the nozzle, not the chamber. The pusher is in contact with the throat of the chamber. Yes, stage 2 absolutely needs gimbal. Gimbal is far more dV-efficient than RCS for attitude control. RCS is only for roll control, and when the deorbit the stage, they do so by venting through the nozzle, not with RCS. Draco engines are already used as OMS engines, if you mean orbital maneuvering in general. If you mean "can Draco engines be used to circularize a barely-suborbital orbit" then the answer is no, not really. They have enough thrust, clustered (after all, the Shuttle's OMS only produced about 0.04 gees of acceleration during circularization), but thrust pod tanks are not large enough to give it significant dV.

A few major points: Veto on recovery of the upper stage or payload. Minimum possible payload. Veto on expendable side boosters. The point is to be able to do this on the cheap and so we need to do non-destructive testing. We can test-fire the boosters as sounding rockets and recover as chutes. Maybe do test suborbital spaceflights using a single solid motor on top of a recovered booster. Veto on any air-started liquid rocket. Ignition is a tough enough problem on the ground, and true hypergolics are far beyond what we could pull off. The only way we could conceivably manage an air-started hybrid motor is that decomposed HTP is hypergolic with hydrocarbons. Along with many other advantages, parallel staging allows us to use differential throttling in place of gimbal for in-atmosphere and exoatmospheric attitude control. It is the only way to do attitude control without drag or cosine losses, and it is essentially "free" because we need fine throttleability of our boosters already. Boosters can either have fixed fins (to help hold prograde) or controllable fins for roll control. Additional hybrid advantage is venting steam from the pressure chamber as automatic RCS for attitude control of the core. If we can get away with fixed fins, then ideally the only moving parts on the rocket are little valves actuated by a small controller. It will save money if every single valve is identical. It may be cheaper to synthesize HTP than it would be to try and source it.

I was the OP and yeah I'm still a little active active. Sometimes threads stay active for a while, sometimes not. This was def an interesting discussion. I don't like HTP rocketry either but it beats the heck out of nitrous in both thrust and Isp, and it can be self-pressurizing with the right setup, and you can vent the pressure chamber as RCS. I think that was the assumption that started this thread. The first ever "bipropellant" rocket used jellied petrol inside a mesh with pressure-fed GOX, which was basically a hybrid rocket. My thought, though others questioned it, is that properly-jellied petrol may be able to "flow" from a non-burning region into a combustion region, which means you need lower amounts of inert binder and also allows for finer control. Never heard of pressure-fed LOX? Err...the Kestrel? You can even autogenously pressurize LOX if you heat it properly, though that gets into "hot oxygen gas" which is nasty on the best of days.