25

It would be possible to design a check valve chain of high reliability of closing, but it would restrict flow and start to increase the risk of one valve sticking shut. You would probably also need pressure sensors between the valves to determine system state, so you end up with a large number of pipe to fitting joints that are potential leaks and a bunch of ...


12

Dragon V2 (Crew Dragon) uses 8 SuperDraco engines with maximum of 73,000 N thrust each. So, in theory, it could produce enough thrust to lift about 50,000 kg off the pad at thrust-to-weight ratio (T/W) of ~ 1.19. You need T/W larger than 1 to lift off the ground, and some more. T/W of ~ 1.2 is low for a launch vehicle and is usually closer to ~ 1.5, but let'...


9

That's 1,388 kg of propellant for the whole vehicle, not per engine. Reading the original document referred to by Wikipedia, it says 3,060 pounds of propellant for the Crew Dragon capsule. (It's on page 8. The fuels are NTO and MMH and the combined weight of both is given.)


8

The thrust of the engines (for any launcher or spacecraft, really) is nowhere near as important as the amount of fuel feeding them. It takes about 9400-10000m/s of ∆v, depending on trajectory, to reach stable orbit from Earth's surface. The second stage of a Falcon 9 1.1, depending on payload, is responsible for the majority of that speed: 6200-6700 m/s. ...


8

In this photo, the exhaust doesn't expand so much. The nozzle looks to be a bit longer. So they've played with various nozzles. (cropped and adjusted for visibility) And the Ars Technica article has this mosaic, which shows variations in the exhaust (maybe due to throttling?). It also shows how little room there is. The exhaust impinges on the shielding. ...


6

PearsonArtPhoto answers why it isn't done - generally NASA's very conservative approach to spacecraft safety, and hurdles it would set to get it implemented. But assuming a miraculous change in NASA management and organizational culture, it would be fairly simple. The engines have enough thrust to provide 4g of acceleration and are angled outwards and ...


5

Firstly, available space for engines isn’t really a problem. A spacecraft can be made exactly as big as the needed cargo space plus engines. Capsules only look tiny because you usually see them next to an absolutely enormous launch vehicle. Secondly, landing doesn’t require that much fuel. Even the apollo capsules returning from a very fast orbit had slowed ...


5

Like any good descent engine, SuperDraco throttles deeply; Wikipedia says down to 20%. Various speculative sources put the thrust angle anywhere between 25º and 35º, which determines cosine losses. The sidewall angle is 15º, and the thrust angle is greater than that. Split the difference and assume it's 30º for 0.87 cosine. I can't find a solid reference ...


5

The critical number for rocket engines is their specific impulse (Isp, a measure of how efficient the engine is). The Merlin has an Isp of 311 s. The SuperDraco Isp is estimated to be around 225 s (which is in line with other hydrazine engines). This means an upper stage that uses SuperDracos would need to be much heavier than a Merlin-powered upper ...


4

There was discussion on using the Super Draco design to land the second stage, but SpaceX has mostly given up on second stage recovery for Falcon. (NOT for the BFR booster that will be the vehicle to Mars). Super Dracos do not gimble, so using them for directional control would not help that much. Except perhaps differential throttling. The major ...


4

Dragon 2 (Crew Dragon) has two separate types of engines: the powerful SuperDraco thrusters (currently planned only for use in launch escape) and the much smaller Draco thrusters used for attitude control and orbital adjustment (including de-orbit). Draco thrusters are also used on Dragon 1. As for why the SuperDracos are still integrated with the capsule ...


4

There is no plan to do this, nor has there ever been an extensively studied plan. In theory it could be done, but NASA would want to certify it, and it is just better to spend more effort to make sure the primary mode works every time.


4

Theoretically, it could, but why use the larger, more expensive rocket engines when you could just use a less expensive, smaller draco engines? Super Dracos are off axis, meaning that any thrust from them will be less efficient than if they were directly in the desired direction. They burn real quick, which means more force that the station has to absorb, ...


4

Yes, fuel is still carried. Only 600 m before splashdown (2:12 in this video), "Dragon has safed all propulsion systems on board." https://www.space.com/spacex-crew-dragon-demo-2-splashdown.html So propulsion must be useful in some contingency even that close to splashdown. But I won't speculate on what contingencies were considered. Edit: On ...


3

To begin with, SpaceX bid Starship as their lunar lander. Starship used methalox as their propellant for their Raptor engines. However, Starship does need landing engines higher up on the hull for the moon landing to avoid digging a crater in the moon surface with the Raptor exhaust. So why don't they use SuperDracos here? Well, SuperDracos uses as ...


3

The Merlin Engine is a gas generator cycle engine which uses liquid Oxygen(LOX) and refined Kerosene(RP1) as its propellants. The SuperDraco engine is a pressure fed cycle engine which uses mono-methyl hydrazine (MMH) and dinitrogen tetroxide (N2O4) as their propellants. The key differences of the engine are the size of the engine, the way the propellants ...


3

I think its clear the lack of a nozzle is the cause. As to the "why" I can think of a few reasons that might be partly responsible (other than it's just testing): They are not designed to be used for long durations. Mass and TWR are more important relative to ISP than for 'main' engines. They need to tuck in for minimum impact on the aero-dynamic profile of ...


2

The SuperDraco engines themselves are quite compact. Liquid rocket engines consist of a relatively small combustion chamber and a nozzle which may be large or small in proportion depending on the ambient air pressure where it's intended to be used. Vacuum engines work best with very large nozzles, but for an engine that is only intended to work at low ...


2

First of all, the SuperDracos were designed from the start primarily as a launch escape system. Although using them for propulsive landing was explored extensively, it was never implemented. For landing on Earth or Mars, the atmosphere is used to lose most of the craft's speed, with the thrusters (and/or parachute) used only after that. The moon has no ...


1

Yes, the fuel for the launch abort system is kept during the duration of the flight, however it is not wasted. The SuperDraco abort thrusters use the same combination of propellants (NTO and N2O2) that the Draco maneuvering thrusters use. In fact, they use the same propellant storage tanks, with different pressurization lines and fuel valve systems. Dumping ...


1

I believe these are the flaps that open and close to reveal the openings for the SuperDracos. The SuperDracos allow Dragon 2 to separate from the rocket during aborts. I think they swivel so the ones on the side go inward and the ones on top drop down to cover the holes made by the parts swiveling inwards. https://www.teslarati.com/spacex-fires-redesigned-...


1

The abort test was done several years ago. Quite a few changes have been made since. The covers on the Super Draco nozzles are quite recent, from what I've seen. The entire pod area now has a silver-colored surface, the same coating used at the edge of the heat shield where it joins the capsule. The silver-colored surface was used previously on Cargo Dragon, ...


1

The Super Dracos are used for two purposes in the initial design. Launch Abort System, and powered landing. For LAS usage, they need to get away from an exploding booster, faster than the explosion wavefront. For powered landing the ultimate goal is to let the capsule hits its aerodynamic terminal velocity and then finally brake in the last few seconds ...


1

We've seen how high a Dragon can reach with its superdraco engines on its pad abort test, and it was about 5000 feet. If you filled it with propellant instead of cargo and passengers it might get a bit higher, but not that much. If you hooked up a big fuel tank to it the engines would not be powerful enough to lift it. It's not going to get anywhere near ...


1

Think of it like this: how would you test the vehicle without a crane? They are testing out the powered landing capabilities so the idea is to work with slow, smooth trajectories that may be mostly vertical but will obviously incorporate some lateral movement too. If anything were to go wrong the vehicle could diverge wildly off-course and probably ...


1

As we saw in the last few launches, cold gas thrusters (the F9 first stage uses nitrogen for recovery maneuvers) seem to be sufficient to maneuver the stage before fins engage. But yes, Superdracos could be used to help land the first stage but are not needed since the center engine can throttle down far enough to allow landing (and that's already with a ...


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