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How do you power a rocket engine?

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Re: How do you power a rocket engine?

#81

Post by trhway »

phkahler wrote: post #57
panick21_ wrote: post #46

Earlier quoted context omitted.

Yes. See: https://en.wikipedia.org/wiki/SABRE_(rocket_engine) https://en.wikipedia.org/wiki/Skylon_(spacecraft) But there are lot of problems with this and it adds a huge amount of complexity.

Maybe too small an effect, but what if they put 8 NACA scoops on the sides of Falcon 9 and just fed the air in between the center and outer engines. It would get accelerated out with all the regular exhaust, and I suppose would cause a small back pressure on the center engine in particular, but they could throttle it slightly if that were a problem.

That was the approach on a USSR N1 Moon rocket. And also on a small air-defense missile Gnom.

Re: How do you power a rocket engine?

#82

Post by MertsA »

hydrogen7800 wrote: post #19
jacksonkmarley wrote: post #2

Wouldn't the pressurant/backfill gas dilute the propellant as it was added?

Expert here. I'm a longtime lurker on HN, but registered just for this comment. I design aerospace pressure vessels for a living. As showerst alluded to, there are often things called "propellant management devices" or PMDs. There are a few reasons these might be used. In zero G, you need the propellant sump to remain wetted with propellant; it would be bad to ingest the pressurant/ullage gas into your engines. Some…

Neat, that's one subject that's always bugged me as every article or video out there just handwaves away settling of propellant tanks in orbit with "ullage thrusters". No one ever mentions how you get a nice continuous feed to your ullage thrusters though.

Re: How do you power a rocket engine?

#83

Post by hydrogen7800 »

MertsA wrote: post #82
hydrogen7800 wrote: post #19

Earlier quoted context omitted.

Expert here. I'm a longtime lurker on HN, but registered just for this comment. I design aerospace pressure vessels for a living. As showerst alluded to, there are often things called "propellant management devices" or PMDs. There are a few reasons these might be used. In zero G, you need the propellant sump to remain wetted with propellant; it would be bad to ingest the pressurant/ullage gas into your engines. Some…

Neat, that's one subject that's always bugged me as every article or video out there just handwaves away settling of propellant tanks in orbit with "ullage thrusters". No one ever mentions how you get a nice continuous feed to your ullage thrusters though.

Ullage thrusters are used exactly as you described, for tanks that do not have PMDs. For example, the large second or third stage main propellant tanks which need to be lit in zero G. On Saturn V, the ullage motors themselves were solid rocket boosters mounted to the aft end of the stage, and thus did not themselves need PMDs, nor access to the main liquid propellants. On some videos of stage separation, you can see these solids firing from the point of view of the jettisoned stage facing forward. (In fact, I think there were also retrograde solid thrusters at the fore end of the stages to aid in separation.) I suppose you could call ullage solid motors PMDs, too.

For an excellent deep dive into the systems, operations, and functions of the Saturn V, get a copy of "How Apollo Flew to the Moon" by W. David Woods.

Re: How do you power a rocket engine?

#84

Post by WalterBright »

panick21_ wrote: post #77
WalterBright wrote: post #70

Earlier quoted context omitted.

Different cycle type? I'm interested - what's different?

I mean one uses the main propellant to drive the turbine the other has a sodium permanganate/hydrogen peroxide. That seems to me a pretty significant difference in how the engine works. To be fair, technically one could call both gas generators but its still significantly different.

I'm sorry, but picking a different source of hot gas to drive the turbopump is not a conceptual difference. Just like adding nitrous injection to your car doesn't make it a conceptually different engine.

Re: How do you power a rocket engine?

#85

Post by simne »

wumpus wrote: post #64
simne wrote: post #44

Very good article, but have few shortcomings. 1. Only first generations of "Soyuz" used H2O2 propellant, because it have very limited time before use (for "Soyuz", guaranteed 6 months), and because it have relatively high melting temperature. First chose H2O2, because "Soyuz" planned as independent ship, to fly relatively short missions around Moon (it is near impossible to withstand even 6 months in so small volume)…

I've frequently read in news articles that the lifetime of the Soyuz spacecraft on orbit is limited by H2O2. You appear to be saying that's false. A while ago I looked at Wikipedia and saw that the Soyuz spacecraft article didn't mention what the reaction control system uses for propellant. Perhaps you can point at a source?

> I've frequently read in news articles that the lifetime of the Soyuz spacecraft on orbit is limited by H2O2. You appear to be saying that's false

May be I misunderstood, what said by insiders. As I remember, first "Soyuz" spacecrafts was maid with H2O2 system, but than they made lot of changes, including new reaction control system.

But looks logically, system used in space separated from system used on atmosphere. And because "Soyuz" landing on dry land, and because accuracy of landing is its weak side, it is also logical to not use toxic components.

I think you remember, how long astronauts stay inside "Dragon" once, because sensors shown hydrazine fuel vapor near ship.

- American ships

> Perhaps you can point at a source?

Sorry, it is not easy now.

It is not secret. Before approximately 2005 I talked a lot on Russian forums, and there was specialists from Russian space industry, and they shared extremely interest info, and I even considered to go work there. Plus books, mostly from Russian authors.

After ~2005, appeared serious tension in talks, so I avoid them, to save my own psychic health.

I cannot be sure, but looks like, it was another step in preparing for big war.

And you are right, that open information on Russian technologies is very limited. This is partially, because they considered nearly all space technologies as semi-military, so some information just classified. Other part is that Russians extremely conservative in business behaviors, and one thing, they inherit form Soviets - very big love to close nearly all information, even harmless and useless, just to show only good info, to look better, to look winner.

What I mean about Soviets - typically, they made launches without announces, and only talk about them if success.

Because of this exists "kosmos" satellites, some of which was planned to flight with this designation, but mostly these are unsuccessful satellites, which reach orbit (and appeared in NORAD list) but does not function from beginning.

If satellite not reached orbit (for example because of malfunction of rocket), and NORAD don't catch it, nothing said at all. If reached some orbit, but malfunction - appears new "kosmos". Because of this behavior, in late USSR was about 1500 "kosmos" sats, and now this number more than 2000.

Re: How do you power a rocket engine?

#86

Post by namibj »

Toutouxc wrote: post #38
Cerium wrote: post #31

Earlier quoted context omitted.

I have never really looked into it before myself, but this explanation seems to make sense: https://www.grc.nasa.gov/www/k-12/airplane/nozzled.html Quote: On the other hand, if the converging section is small enough so that the flow chokes in the throat, then a slight increase in area causes the flow to go supersonic. For a supersonic flow (M > 1) the term multiplying velocity change is negative (1 - M^2 0) produces…

That's why I was asking for an ELI5 explanation. I know that the equation holds and that compressibility turns everything upside down, I just haven't been able to figure out an intuitive explanation. I have this idea that in supersonic flow, a pressure wave can't move backwards against the flow, right? Which would mean that any single molecule inside the flow has no way of knowing what's in front of it (because the i…

Well, the slow-down won't happen until after it exits the nozzle (c.f. Mach diamonds in rocket exhaust... they are the shocks where the supersonic flow interacts with the ambient air).

Re: How do you power a rocket engine?

#87

Post by bumlebi »

panick21_ wrote: post #8

One thing I always wanted to see was a close expander cycle areospike. The reason is that expander cycles are heat limited. Areospikes biggest negative is that they require more cooling but if you are heat limited that is an advantage. You could make the highest possible thrust expander cycle and it would be high efficiency upper stage for early staging as you don't lose efficiency by staging early. ------- Another t…

Did you ever look into this? I've been wondering the same now for a couple of years.
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