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Astronauts say riding Falcon 9 rocket was different from space shuttle
- userbinator 6y agoI wonder if it's more similar to a Soyuz.
- excalibur 6y agoYou would think it would be. Strange that they don't mention that.
- mhandley 6y agoThe Merlin 1-D Vacuum on the Falcon upper stage is much more powerful than the RD-0124 used on the Soyuz third stage (934 kN vs 294 kN), but uses a single huge engine bell, whereas the Soyuz has four smaller engine bells. I would imagine this might make the Soyuz a bit smoother. The Falcon also stages really early (this allows you to land the first stage), so the 2nd stage MVac engine is more powerful than is really ideal. As fuel burns away, I understand the MVac has to throttle down a lot to keep g-loads under control. I believe it can throttle down to something like 35%. Rocket combustion tends to get less stable at lower throttle settings, so this probably is part of what they're feeling.
- sandworm101 6y agoIirc, Soyuz also hot stages. So no dramatic zero-g cutoffs between stages.
- KuiN 6y agoYou're right. The first stage (4 conical shaped boosters hanging off the sides) and the second stage (central core booster) all fire together to lift-off. When the side-boosters are depleted they jettison (and perform the Korolev cross) while the second stage keeps firing. The third stage also starts before the second stage is completely depleted; this is why there's an "open grate" visible in photos of the rocket (about half way down the stack, see [1]), gives the exhaust somewhere to go before the previous stage is jettisoned. Hot staging is advantageous as you don't need extra ullage motors to deal with propellant being in the wrong place inside the tanks in microgravity. The Soyuz (and other R-7 variants) are brilliantly engineered; There's a reason they're still flying nearly 70 years on. [1] https://upload.wikimedia.org/wikipedia/commons/thumb/9/9a/Soyuz_TMA-9_launch.jpg/1200px-Soyuz_TMA-9_launch.jpg https://upload.wikimedia.org/wikipedia/commons/thumb/9/9a/So...
- Already__Taken 6y agoYou see a lot of that whole-system level engineering in Russian things imo.
- Udik 6y agoWhy is there a G buildup? I would love imagine acceleration to be fairly constant, not to increase with time (at least once out of the atmosphere).
- torpfactory 6y agoSame thrust but less mass as the fuel burns up.
- Udik 6y agoAh, right!
- m4rtink 6y agoAlso rocket engines are (IIRC) generally less efficient at lower than full thrust, so you want to keep firing them at max as long as possible. On the other hand you also don't want to turn your crew into pancakes or even make your upper stage look like a squashed can. You have a couple options: - throttle the engine - design payload weight, propellant load and trajectory to make g loads bearable till burnout And one more thing related to stage 2 burnout - precise orbit insertion. Rocket engines used to be pretty imprecise at shutdown, delivering a slightly lower/higher impulse at shutdown at random. Due to this many older rockets have also some small & precise engines to correct the orbit insertion once the main one shuts down - many Chinese rockets have that. As far as I know, the Falcon 9 upper stage engine (Merlin 1D Vacuum) is precise enough so this is not needed.
- samcheng 6y agoI don't believe either test astronaut had ever ridden a Soyuz, so they don't have any way to make that comparison. We'll have to wait for the next mission, which will have an astronaut who has also ridden a Soyuz (and a Shuttle).
- artemisyna 6y agoThis is a nice summary of commentary the astronauts have given since arriving at the space station, but I wish this article would cite the original events. =/ Iirc, this is some combination of a the “SpaceX press event” that they did as well as some words exchanged upon arrival. (I’m not 100% on that, though I do feel like all the quotes came from videos from their first two days in the shuttle.)
- DudeInBasement 6y agoWho can sum it up with the least amount of words: Liquid smoother ride than solid rockets
- sandworm101 6y agoDon't forget aerodynamics. Shuttle suffered from all sorts of buffeting that a smooth cylindrical rocket would not. The complex shape also meant more unpredictable asymmetric vibrations. A liquid-fueled shuttle would still have been a rough ride. And shuttle took a much more aggressive path. SpaceX rockets aim very high for longer burn times (more up, less sideways on first stage). It is technically a less efficient approach but allows for the recovery trickery.
- nikofeyn 6y agoi'm not for sure what you're addressing. the astronauts described the falcon 9 as much more rough than the space shuttle.
- dredmorbius 6y agoAccording to the briefing video above, smoother than the Shuttle off the pad (for Falcon), which is the lower-atmosphere phase with more aerodynamic interactions, rougher following Falcon MECO, under the single-engine second stage. During the equivalent flight phase the Shuttle has shed its solid rocket boosters and consists of the three space-shuttle main engines (SSME), and the external tank. Still not a vertical stack (so subject to greater structural dynamics), though the thought occurs that three engines might be smoother than one. There can be other effects as well --- the Saturn V had significant issues with "pogo oscillations", which are just what they sound like: strong periodic variations in vertical acceleration. Falcon 2nd stage issues might be similar. https://en.wikipedia.org/wiki/Pogo_oscillation https://en.wikipedia.org/wiki/Pogo_oscillation
- deleted 6y ago[deleted]
- manicdee 6y ago
- dilandau 6y agoFuck that's so cool. Imagine being strapped to that thing. Love hearing the astronauts candid experience.
- wiradikusuma 6y agoSo it's like driving a convertible car with the roof opened? (Of course not literally)
- jacoblambda 6y agoThe third-hand description that I've found best describing the single engine burn is that it is comparable to driving fast on a gravel road. It's bumpy as hell of a ride due to all the vibration from the engine placement but otherwise it's not too bad.
- uselesswaste 6y agoYour meme is retarded fucking shit, and you suck. Please kill yourself upon seeing this auto-banned comment.
- sebazzz 6y agoAnd now we wait for Boeing.
- mclightning 6y agoAre they comparing their Falcon 9 experience to Space Shuttle which flew almost a decade ago last time?
- sidcool 6y agoWhat is the difference in weight carrying capacities of the space shuttle vs Falcon 9?
- dredmorbius 6y agoLEO payload mass for the Falcon 9 heavy, fully-expended (no booster recovery) is 63,800 kg. With booster recovery, 30,000–57,000 kg. For the Space Shuttle it was 24,400 kg. The total mass boosted by the shuttle was higher, but much of that was the orbiter itself, not usable payload.
- ncrmro 6y agoI wonder if people will ride the Soyuz one day for that classic vintage experience. Seems like such a vital part of our history.