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31

The engines themselves were identical within manufacturing tolerances, but there were some installation differences, mostly due to "packaging" constraints in the crowded aft compartment of the shuttle. The propellant feedlines were not identical in shape and this resulted in some minor performance differences. For example, the left SSME LH2 line had a ...


26

The lines that exited at the end of the nozzle were drain lines carrying leakage from seals, output of hydraulic actuator drain lines, etc. The following schematic shows the various systems attached to these drain lines. Source: Rockwell SSME Pocket Data Book, R/RD87-142. This graphic differentiates between the transfer ducts (which carried the hydrogen ...


23

1) Can someone provide an overview of the crossfeed system - in particular the detachable joint that fed LOX to to the shuttle from the tank? The buzzwords to use for googling this topic are "ET Umbilical". The system as implemented on Shuttle was complicated but caused major problems only once in the program (see below). There were two umbilical areas ...


19

tl;dr The first mission to run the engines normally at above 100% of nominal maximum thrust: STS-6 The changes to the engine made that thrust increase possible: the 147 design changes implemented between the FMOF and FPL versions of the SSME. Details The SSME had five major versions over the life of the program. The definition of 100% Rated Power Level ...


17

I wouldn't recommend it, and there's several reasons why. First, even if we assumed you'd get chemically pure water out of the exhaust plume, in essence distilled water, it would lack any dissolved minerals and cause you to lose electrolytes. If that was all that was wrong with it, then small quantities wouldn't hurt you, but you'd have to substitute lost ...


17

The crossfeed seen in KSP works by pumping fuel from one fuel tank to another, i.e. against tank pressure. To do this, you need pumps (independent of the engine turbopumps). Pumping large amounts of fuel quickly is not easy. You need to stop pumping cleanly when the tank is empty (or risk a pump explosion when the pump runs dry), this is difficult: you ...


16

The space shuttle throttled down its main engines from the normal setting of approximately 104% to around 67% as it was passing through the region of max dynamic pressure ("max q"), to make sure that the certified dynamic pressure limit was not exceeded. Once the threat had passed, the engines throttled back up. If you plotted throttle level vs time on a ...


15

I wouldn't draw any conclusions based on diagrams alone, SSME is very well-known to the public, so we have a more detailed diagram. That doesn't mean that the actual engine is more or less complex, because many things are omitted from diagrams. To prove my point, here is a newer Raptor diagram drawn by a propulsion engineer Elisei Maslov, who's ...


12

The 3 engines were identical. Of the 46 SSME engines produced, at least 3 were installed in 3 different positions on various flights: engine 2012 on OV-103 Discovery engine 2019 on OV-104 Atlantis engine 2054 on OV-105 Endeavour If you really want to know which engine flew where, there's a chart that tracks the flight history of each engine. Engine ...


11

The engine controller is a computer mounted on the SSME which monitors and controls the engine. It, for example, takes throttle commands as a % of power level from the vehicle and translates them into control commands for the engine valve control loops. The SLS engine controller is a new hardware device and presumably new software as well. The pogo ...


11

The biggest risk I foresee is nitric acid. A hot open flame in the atmosphere will cause N2 and O2 to react, creating a number of different molecules such as NO and NO2. These dissolve reasonably well in water and will form acids.


11

The SSME is a staged-combustion rocket engine, which means that some small fraction of the propellant flow into the main combustion chamber is first diverted into a small pre-burner (two actually). These preburners combust (relatively) small amounts of fuel and oxidizer to produce hot exhaust gas which is expanded through a turbine, which is mechanically ...


11

A lot of questions here, let's tackle these two first: 4.And last but not least, what's SpaceX's solution for the oxygen-rich environment at 377bar, 748K injector and 546bar, 811K pre-burner? 2.The Raptor's oxygen pump sits directly on top of the main combustion chamber, while the SSME's two pumps are on the opposite sides of the main combustion ...


10

They do use sparklers: the Radially Outward Firing Initiators (ROFI), derived from the Shuttle system, are started at T-15 seconds. Note that a hydrogen fire is the expected result of this system; they just didn't expect it to be this extensive. On the NasaSpaceflight forum, someone suggested that the scorching of the insulation is caused by the hydrogen not ...


10

This is complicated, but here is the gist: Thrust is generated by flowing high pressure gas into a lower pressure environment. This flow is supersonic, so what goes on downstream of the throat (top of the the nozzle) cannot be sensed by what is going on in the combustion chamber (sound is just a pressure wave). The nozzle is supersonic, the combustion ...


10

Some changes appear to be under consideration for future production of SLS RS-25s: From Wikipedia's SSME page, about the SLS plan: Once the remaining RS-25Ds are used up, they are to be replaced with a cheaper, expendable version, currently designated the RS-25E ('E' for expendable). This engine may be based on one or both of two single-use ...


10

Engines at the size and performance of an SSME are very difficult to develop. The SSME has one of the highest ISP's ever attained in a production engine. (Not some crazy Fluorine involving demo). It is anything but a simple, or even 'old' engine. Its re-manufacture would likely benefit from modern techniques, like the people examining starting F-1 engine ...


10

Please refer to this (modified) schematic diagram from the crew's Ascent Pocket Checklist for this discussion. The blue shows the parts of the plumbing still filled with LOX after MECO. The green is the helium pressurization line. Two minutes after MECO the onboard computers start the dump by opening the LO2 Manifold Pressurization Valve (1), the LO2 ...


10

Let's take the second image for the F1 engine - the situation is similar for SSME, though everything is 'upside-down' in its pictures. The 'seat', 'body' and 'block' are three parts that turn against each other. The block can turn around the shaft in X axis. The body can turn around the block in the Y axis. The Z axis remains fixed, as the block can't ...


10

They are provided to help damp out combustion instabilities. The main injector uses cooled baffle elements, developed at Glenn in the 1960s to control pressure waves that could destroy the engine. Pressure waves in the space shuttle main engine combustion chamber are also controlled by acoustic cavities. Testing by Glenn engineers determined the ...


9

Stealing the mass-at-MECO number from this answer, and using the 104.5% thrust numbers for 3 SSMEs from here, I get (3 x (490,000) lbf / 308650 lbm ) = ~ 4.75 g's Sanity check (3 x (.65 x 490,000) lbf / 308650 lbm ) = ~ 3.1 g's Using the approximate 65% power level at shutdown, assuming that the thrust varies linearly with throttle percent (and ignoring ...


8

The SRB's were ground tested, as were the SSME's. Consider for a moment the scale/scope of a test stand that can hold an SRB full fire test. (The SRB's put out 2.8 million lbs of thrust. To compare, even an F-1 engine was only 1.5 Mlbs). Ironically the only real standalone launch of an SRB was the Ares-1X launch, well after the Shuttle was ready to be ...


7

The containment pond at the Stennis Space center, Test Stand A-1, is used to hold runoff from contact-cooling water (where water comes into contact with something other than the insides of a clean pipe). You can see it's not particularly deep and does not itself runoff or drain anywhere (except to groundwater and the nearby river). Google Map view of the ...


7

It varied throughout the program - the SSMEs changed a lot over its course. Columbia's original FMOF engines were only marginally OK for flight. Until the Pratt turbopump redesign, the high pressure turbopumps had to be overhauled after every mission. By the end, overhaul requirements were somewhat reduced. Here is overview information on SSME ground ...


6

The obvious way to test the SRBs and SSME would be to fly an unmanned Shuttle mission. Any alternative meant developing a one-off rocket just for the tests. NASA considered doing unmanned Shuttle flights from the beginning. STS-1 pilot John Young, discussing the topic, in his 2006 interview with collectSPACE: They wanted to fly the thing unmanned. I ...


6

There are reasons why this wouldn't have worked at all. I'll explain at the end, but first the numbers you ask for. Liquid mass in Orbiter plumbing: Common feedline (between external tank disconnect valve and engine prevalve): 4000 lbm LO2, 250 lbm LH2 Engine feedline (between engine prevalve and SSME): 298 lbm/line LO2, 22 lbm/line LH2 Using the engine ...


5

SSME wouldn't have been insane. RL-10 is used on relatively lightweight upper stages: Centaur and DCSS plus their payloads are in the 20-40 ton range, and the thrust-to-weight ratio winds up being in the ballpark of 0.3:1 -- not enough to lift off, but reasonable for circularizing your orbit once the first stage gets you most of the way to altitude. If you'...


5

SSME & Merlin use hydraulic actuators. For instance, The engine is gimballed through two planes by hydraulic actuators for vehicle pitch, yaw, and roll control. - Space Transportation System, Space Shuttle Main Engine Orientation, pg 4 (PDF) and Engine failure modes are minimized by eliminating separate subsystems where appropriate. For ...


5

A good assumption is that the startup sequence is very similar to the SSME. Here is some SSME startup data showing the time you asked about from the Rocketdyne Pocket Data Book. Eventually the SLS will be using RS-25Es which are somewhat different from the SSME, but my guess is that the start sequence won't change much if at all. The hashed field is test ...


5

(This is all for shuttle, not SLS) Running the engine out of propellant was a Big Bad Thing. There were sensors in the External Tank (for hydrogen) and in the orbiter feedlines (for oxygen) that would trigger a shutdown if the sensor registered dry. The placement of the sensors was such that the engine should shut down before they ran out of prop. ...


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