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How to start a rocket engine

everydayastronaut.com

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Re: How to start a rocket engine

#31

Post by chriswarbo »

sbradford26 wrote: post #19
EvanAnderson wrote: post #13

Earlier quoted context omitted.

All the imperial units in this PDF hurt my head. I'm an American, so I'm used to them, but seeing them in the context of precision aerospace hardware is so jarring. As a student it seemed like math re: chemistry and physics was so much easier (read: less error-prone) with metric units than with imperial. Mars Climate Orbiter indeed.

The biggest lessons learned on the Mars Climate Orbiter wasn't exactly that everything should be metric. It was the unit conversion is dangerous and needs to be handled very carefully. Just saying everything will be metric doesn't avoid unit conversion. You might have one thing measuring fuel burn rate in grams/second and another in kg/second. That conversion can still lead to issues if not handled correctly. In the…

> You might have one thing measuring fuel burn rate in grams/second and another in kg/second

This sort of redundancy is a big problem with metric (e.g. hours, litres, tonnes, etc.); and why it's better to stick to the SI subset. http://www.chriswarbo.net/projects/units/improving_our_units...

In particular, SI is "coherent" https://en.wikipedia.org/wiki/Coherence_(units_of_measuremen...

- There is only one unit for each dimension. In your example, "grams/second" would not be a valid unit; SI only has kilograms/second (yes, it's annoying that the unit of mass has a name beginning "kilo" :( )

- The conversion factor between different dimensions is exactly 1 (by definition). In your example, the rate R is related to mass M and time T via M = TR (i.e. kilograms = seconds × kilograms/second). There are no conversion factors, since the unit of rate is derived from the units of time and mass (unlike, say, measuring energy as calories OR pound-feet OR coulomb-volts OR ounce-miles OR slug-acres-per-squared-hour OR ...)

See also http://www.chriswarbo.net/projects/units/metric_red_herring....

Re: How to start a rocket engine

#32

Post by pasiaj »

chasd00 wrote: post #28

I think there was a russian engine that literally had 2x4's on fire stuck in the combustion chamber in place of torch ignitors or TEAB. If anyone's interested the experimental high-power rocketry hobby is pretty fun, there's a lot to learn and hack on. A lot of people focus on propulsion and formulating, profiling, and flying various solid fuels they develop themselves. This guy is highly regarded https://www.nakka-r…

> literally had 2x4's on fire stuck in the combustion chamber

I REALLY wouldn't want to be the person tasked with starting that fire.

Re: How to start a rocket engine

#33

Post by h2odragon »

MS90 wrote: post #18
Koshkin wrote: post #16

Starting the engine(s) even in a propeller-driven airplane used to be a big deal, too. Hell, I'm sure that even starting a car engine back in the day was a much more complex affair (than simply pushing a button like it is today).

Yes, early cars had to be started with a crank handle that stuck out of the front of the grill, similar to how early propeller engines had to be hand-spun to get going. Apparently if you didn't crank it quite hard enough the handle could snap back at you rather violently, one of my great-grandmothers had her arm broken this way.

> the handle could snap back at you rather violently

If it backfired. I got thrown over a Studebaker that way when I was like 8; I wasn't big enough to turn the handle by hand so I was jumping on it. It usually worked tho.

Re: How to start a rocket engine

#34

Post by chriswarbo »

perilunar wrote: post #30
Koshkin wrote: post #15

Earlier quoted context omitted.

I mean, sure, converting grams to kilograms is easier (for a human) than converting ounces to pounds, but how often do we have to do that in our heads? Computers, on the other hand, do not care (and they "prefer" the binary system anyway).

Converting grams to kilograms not so much, but mm to m, mL to L, even g to mL and L to kg (of water) — all the time, and of course in our heads — it's so easy you barely need to think about it.

I don't even consider those to be "conversions" at all; in the same way that "two dozen metres" and "twenty four metres" and are both just some number of metres (not a conversion from a separate "dozen-metre" unit).

Technically, the SI standard does consider millimetres, centimentres, kilometres, etc. to be separate ("derived") units from the base unit of "metre". That matters when we have multiple interacting multiples, e.g. "one cubic centimetre" is not the same as "one centi cubic metre"; but of course, that's avoided if we stick to base units like cubic metre. (see http://www.chriswarbo.net/projects/units/improving_our_units... )

Re: How to start a rocket engine

#35

Post by AshleyGrant »

localplume wrote: post #5
ragebol wrote: post #2

I could watch stuff like this all day. Tim's stuff is so great. Easy to be jealous of, since being YouTuber seems easy, but to make quality content, it really can't be. And then he's going around the moon, it's really mind blowing to see the success he's had. His interviews with Musk are a treasure trove as well, whatever you think of Musk.

He, like most big Youtubers, probably have a large crew of people working with them. The article was written by Trevor Sesnic, the video was likely edited by others, I don't know if he did the graphics, but Tim still did a lot (and arguably did the most fun stuff). Smaller Youtubers need to do all of that, and from what I've heard editing is the absolute worst given how time consuming it is. Many Youtubers struggle w…

I support Tim on Patreon. He also utilizes a cadre of Patreon donors who provide commentary on early cuts of videos and even drafts of scripts. I personally have never understood why people would pay to do work for him, but they must get satisfaction from it, and the final product is better because of it.

Re: How to start a rocket engine

#36

Post by nordsieck »

ragebol wrote: post #9
samwillis wrote: post #3

Earlier quoted context omitted.

> His interviews with Musk are a treasure trove as well, whatever you think of Musk. My main take away from those interviews is just how knowledgable Tim is, he's able to engage in low level and in depth conversations about how these engines work. It's not just superficial high level knowledge from making videos, he is thinking himself how to optimise and improve these things, and leading that conversation. The passi…

Absolutely. Imagine if all journalists had this level of depth in all of the topic they covered? I don't think that's possible though.

> Imagine if all journalists had this level of depth in all of the topic they covered? I don't think that's possible though.

It helps a lot that Youtube seems to have become the home of long form video. Not really something that fits into traditional media. But for the people that really want to dive deep into a topic, it's great that there are now often high quality creators that cater to those tastes.

Re: How to start a rocket engine

#38

Post by sbradford26 »

fnordpiglet wrote: post #21
sbradford26 wrote: post #19

Earlier quoted context omitted.

The biggest lessons learned on the Mars Climate Orbiter wasn't exactly that everything should be metric. It was the unit conversion is dangerous and needs to be handled very carefully. Just saying everything will be metric doesn't avoid unit conversion. You might have one thing measuring fuel burn rate in grams/second and another in kg/second. That conversion can still lead to issues if not handled correctly. In the…

I mean what issues would power of 10 fractions have in floating point after all?

If I have data going out on a data bus in grams/second, but someone reading that data in a different sub system reads it and thinks it is kilograms/second because that is the default unit they use then you have an issue. The actual conversion of the bits isn't the issue it is that certain systems might use different units internally and making sure those conversions are done correctly. It is much more an engineering design/human interaction issue than a computation issue.

Re: How to start a rocket engine

#39

Post by lsllc »

Koshkin wrote: post #16

Starting the engine(s) even in a propeller-driven airplane used to be a big deal, too. Hell, I'm sure that even starting a car engine back in the day was a much more complex affair (than simply pushing a button like it is today).

They used to use what were basically shotgun shells with no pellets to start airplane engines -- it was called a Coffman engine starter (it was actually used as a plot device in the movie Flight of the Phoenix).

https://en.wikipedia.org/wiki/Coffman_engine_starter

Re: How to start a rocket engine

#40

Post by martythemaniak »

ivankirigin wrote: post #37

This makes me want to go back to school and major in aero/astro engineering.

Yeah, I think atoms are just so cool. After almost two decades of many different kinds of software, it all starts to looks the same and kinda boring. Even LLMs, which are super exciting, can barely hold my interested.

All my startup and side-project ideas are now robot or machine based. Feels like the combo of LLMs (or rather large multi-modal models) and cheap robots will yield tons of interesting results over the next decade.

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