It doesn’t even have to be that big! Even in 1969, you could design a simple, “open-top” personal ascent rocket the size of an easy chair:
Not totally inconsistent with what was said before. They have several things they need to take care of before the next flight:
- Repair and upgrade of the ground systems
- Polishing off the vehicles themselves, doing static fires, etc.
- Fixing and requalifying the Flight Termination System (which proved to be less than fully effective in the last flight)
- Resolving the lawsuit against the FAA and getting approval for the next flight
Some of these will take longer than others.
SpaceX switching to hot staging instead of the flip maneuver:
There have been hints for a while, as people spotted a ring piece with strange cutouts that was hard to explain otherwise:
Supposedly, it gets them 10% mass to orbit. The original flip maneuver fits with Musk’s philosophy of “the best part is no part”, and hot staging will require something more than that (if only thermal protection for the upper part of the booster). But it’s still pretty simple compared to the usual approach of pneumatic pushers and the like.
It also potentially adds escape capability. If the upper stage can separate like this, there’s a possibility it could do so under more adverse conditions.
I assume you mean the frowny faces. What are the grid fins (if that’s the word) for?
They’re for steering the booster on its way back down.
(ninjaed, but anyway)
The grid fins serve the same purpose as on the Falcon 9: they give the booster aerodynamic maneuverability as it descends through the atmosphere. Importantly, they also enable giving the booster a significant angle of attack vs. the airstream, which gives them some degree of lift. That means they can use less propellant to get the booster back to the launch site, which means more mass to orbit.
And yeah, the frowny faces are the new thing. They’re vents for the engine exhaust. I’m a little surprised they’re sufficient, and that it’s possible to build in sufficient thermal protection that the booster isn’t destroyed, but we’ll see what happens.
They might be lighting a subset of Starships engines to stage and then the rest after there’s some distance to the booster? That would minimize the need for venting and heat protection.
Oh, I should probably explain “hot staging” for people who don’t want to read the whole article.
Staging is when the vehicle drops off the booster stage and switches to the upper stage engines. Normally, there is some kind of pusher system to separate the two parts. The booster engines shut off, then there is some kind of device (like a pneumatic ram) that pushes them apart, and then the upper stage engines ignite. The upper stage engines are pointed directly at the booster at that point, but usually it’s ok because it’s a little ways away by the time they ignite. And also because on every rocket except the Falcon 9, they don’t reuse the booster anyway, so it doesn’t matter if it gets a little fried.
Starship was going to use something a little different, where they impart a spin on the stack and then fling the two stages apart. The only hardware required are some clamps that get released at the right moment. However, it has some drawbacks, namely that it’s a tricky maneuver, and that the time it spends spinning is time lost to gravity. So it costs performance.
Normal staging also costs some performance, in that there’s a several-second gap between the first stage shutoff and the second stage igniting. There’s also the problem that the second stage needs some means of settling the propellant at the bottom of the tanks so that the engines can pump it properly.
Hot staging is another alternative. Basically, ignite the upper stage engines before the first stage has shut down. Advantages are that it requires no extra pusher hardware, there’s no propellant settling problem, and that there’s no gap where there’s no thrust.
But, the disadvantage is that you fry the first stage with the exhaust. Obviously, you don’t want to cause an explosion under you as the rocket burns through the propellant tanks. And Starship is supposed to be reusable, so even if it only gets mildly fried, it’s still damage that has to be repaired.
But I guess SpaceX has figured that they can solve these problems. It’ll be exciting!
Cool thanks. Why are they deployed in boost phase (if they are)?
Agreed; that came to mind as well. They don’t need full thrust right away. The booster can be reduced to just one engine, so it’ll be pushing at much less than 1 G. Then, a single upper stage engine should be enough to pull it away.
Ideal would be one of the vacuum engines, since their thrust is spread out over a larger area, but they don’t gimbal, and they’re on the edge of the craft. So I think those are a no-go. But one of the center engines should be ok.
They are deployed in the boost phase–this is different than the Falcon 9, where they fold out only after separation. I think it’s just simplicity. They don’t cause much drag on their own, and can be steered in a way that they don’t interfere with flight. Eliminating the folding mechanism is just one less thing to go wrong, and also one less step to prepare the vehicle for the next flight.
Are we talking moving up/down against the fuselage? Or rotating about the mounting axis? Not sure if I’m being clear?
The fins can only be rotated on an axis perpendicular to the fuselage. They can’t be tilted up and down. Just one degree of freedom each. But since there are four of them, they get yaw/pitch/roll control out of that.
You might notice that they aren’t mounted symmetrically. Basically, they are spaced at either 60 or 120 degrees (i.e., 60+120+60+120=360). That give them more control authority for pitch than for yaw. But that’s generally what they want.
Thanks! Yeah, I did notice they’re mounted more like an X than a cross. I’m trying to picture that locating, plus 1 degree rotation doing anything useful and I really can’t, but I believe the picture you’re painting. Thanks again.
Yep, sure thing.
Consider the Falcon 9 version where the fins are spaced symmetrically. And imagine that they are oriented in a + relative to the flow.
To get pitch, leave the vertical fins alone and rotate the horizontal ones in the same direction. It’s symmetrical left-right, but the horizontal fins are pushing either up or down. The same principle for yaw, except with the vertical fins instead of horizontal.
Finally, to get roll, rotate the fins so that they’re like the blades of a fan. The vehicle rotates clockwise or counterclockwise depending on the orientation. You can blend these together to get a combination of effects.
Now consider Starship, with a squashed X shape. Roll works the same way, with the fins working like fan blades.
Pitch works with all fins in combination. Just make all of them point down or up (looking from one end). Importantly, since they’re at an angle, they also have an outward, horizontal push–but the pairs cancel each other out. It gets pushed left as much as it is pushed right. There’s a little waste here, but it’s not that much (about 13%).
Yaw is the same, but you can see that it’s much weaker. There’s more waste because so much of the flow is going up and down (that just gets canceled out). And the net flow left or right is less due to the shallow angle. Still, it’s enough for their purposes. They need yaw for steering, not to control angle-of-attack.
And again, these things can be blended together. But they’re easier to think of one at a time.
I mean, that’s how I’d do it in Kerbal!
That’s extra-hot staging. Why bother with a stack decoupler at all when you can just explode the stage below you?
I seem to recall using this trick to get to orbit even before the decoupler was accessible.
Ha! Yes. To orbit with only solid rocket motors and a capsule. De-orbit not an option unless you save a stage, but more likely you’re rescuing the unfortunate crew with a later rocket with more amenities.
Can Kerbals hibernate?
And I’ve got to say, when I see that design, my first thought is that it looks like it’s designed to fry the lower stage, and to separate it by burning through. I don’t know if that’s practical, but it’s sure what it looks like.
Without mods, in KSP your kerbals have zero life support requirements and are immortal barring explosions or high speed collisions. A kerbal in a space capsule will survive indefinitely. You could theoretically strand someone in a comet-like orbit around the sun with a ten thousand year orbital period, and pick him up three or four orbits later no worse for wear.