How to not build a two stage model rocket | Hacker News Reader

How to not build a two stage model rocket

knowone08.gitbook.io

126 pointsKMJ-00746 comments

It is great that people are going out doing stuff, having fun and learning. But this project seems like a disaster in the making.

-Making your own fuel.

-Using inappropriate materials (e.g. PVC)

-Poor storage of motors.

-People are standing quite close to the rocket when it launches.

-There seem to be buildings quite close to the launch in one of the videos.

-Night launches. How are you going to get out of the way, if you can't see the rocket?

2 stage rockets are particularly dangerous, because as the second stage can launch horizontally or downward if the first stage tilts (as shown in one of the videos).

I think they are being irresponsible with the safety of themselves and anyone nearby. I would strongly recommend they learn a bit of safe practices and make a single stage rocket that works reliably, before even attempting 2 stage.

As opposed to the way SpaceX does it?

Let huge rockets blow up over active airspace?

This looks like a bunch of college kids building small little rockets. I'm probably taking a much bigger risk walking on the street, where I live in India.

It's a little risky. But do the stuff far enough away from people and they'll be fine.

SpaceX's rockets launch with downrange areas carefully considered; launches have been aborted because of boats wandering into these areas.

Twice now Starship has exploded over the Gulf of Mexico and caused massive and dangerous disruptions to commercial passenger air travel. Flights were delayed and some diverted because of fuel limitations.

I get the impression that SpaceX's attitude is that it is cheaper to learn by blowing stuff up, than it is to meticulously plan everything (as NASA is famous for). However, SpaceX don't have to pay for the externalities (such as disrupted air travel). I don't see SpaceX attitude changing now that Musk seems to be running[1] a sizeable chunk of the US government.

[1] into the ground.

> Starship has exploded over the Gulf of Mexico and caused massive and dangerous disruptions to commercial passenger air travel

Disruptive, yes. Dangerous, no. (They’re disruptive because the planes avoid the debris field. Launches are also scheduled such that no plane should be pinned down by debris.)

I’d also note that, apart from two deaths in 2014, SpaceX’s track record with human lives is pristine.

>It's a little risky.

Everything in life involves risks. And there are cultural differences in attitude to risk. But some of these risks are quite unnecessary.

Also, I would consider making your own fuel (without sufficient expertise), as more than 'a little risky'. Especially if they move on to bigger rockets.

> making your own fuel (without sufficient expertise), as more than 'a little risky'

It seems like just the classic smoke bomb recipe with KNO3 and sugar. I would be comfortable preparing this even indoors, let alone outside.

My friends and I made far riskier stuff as teens based on our high school chemistry knowledge. It was fun but in retrospect not particularly safe.

I get the sense that the team represented here are going it alone e.g. there aren't amateur rocketry organizations around that they can work with and gain knowledge and working practices from.

Maybe someone on here who is in amateur rocketry can reach out and forge some connections between their group and more established ones? That's the true beauty of the Internet, right?

Yes, for context: this appears to be a group at Vishwakarma Government Engineering College in Ahmedabad, India. A quick search suggest that there might not really be any regulation or much of a community for model rocketry in India in general.

If you want to build a two-stage water rocket, Air Command Rockets has detailed build series over on YouTube[1], from simple soda bottle setups to a custom rocket that they got[2] to over 1600m (5000 ft).

That's air and water propelling a rocket a mile up!

[1]: https://www.youtube.com/@AirCommandRockets

[2]: https://www.youtube.com/watch?v=GCaiK3Zqs4M

> Turns out, PVC was never the move. It’s lightweight, yes, but also has the structural integrity of a soggy biscuit under pressure.

I believe that PVC is not considered safe for model rockets, as it turns into shrapnel if it ruptures. Happy to be corrected, if that isn't right.

so does the steel they replaced it with ductile metals like aluminium are required by HPR rocket safety codes

Yes, you want something that tears (like aluminium) rather than fragments.

When I was a kid I was into Estes model rockets and it always amazed me the preferred/documented way of glomming the multiple stages of engines together was a single strip of scotch tape.

My memory is that two-stage rockets had a few more points of failure but were harder to retrieve, so not really worth the effort. The Estes engines solved most of the technical challenges, but I lived in an area with lots of trees and no huge expanses of open space.

From the blog post: "Pro tip: just take your time and design the O-ring system properly. Trust us — you don’t want to gamble with hot gases and bad seals."

I think NASA may have learnt that lesson in '86.

Note that making your own fuel is:

a) Very dangerous, if you don't know what you are doing.

b) Illegal without a licence in some countries (such as the UK).

What's the fun of buying ready made parts and just assembling it? At least the authors probably learned something new in the process.

Besides, the fuel "hacking" they seem to be doing seems relatively simple, isn't it what is commonly called "Rocket Candy" or something like that? In that case, it's a fairly common propellant made by amateur's. We're on Hacker News after all, as long as they're not hurting other people, if it's illegal or not should matter less.

What's the fun of doing a bunch of work but not getting a successful launch (best case) or blowing your hand off or burning the house down (worst case)?

For the same reason that it's generally illegal to make your own fireworks: you have a pretty good chance of killing yourself or more importantly kill someone nearby.

The risk of letting random people blow themselves up is one thing, but having innocent bystanders get killed or maimed is totally different.

Most fully developed adults agree that putting yourself at risk in the pursuit of your hobbies is fine, with limits. Putting others in danger who are unaware of the risk to life and limb is not acceptable. You, a private citizen, simply do not have the right to produce bombs as a hobby because of the undue risk to everyone around you.

So, basically a longer and reworded version of "as long as they're not hurting other people"?

As long as they can prove that they are not risking hurting other people. Suppose that I fire a gun in a randomly chosen direction and don't hurt anyone, should I be allowed to repeat the process?

Some say yes, others say no. The Internet will never be able to solve this issue.

Yes but what do you say? Don't dodge the question.

I don't know that my personal opinion is all that important but I fully admit to driving in excess of the speed limit in very specific places where I deem it safe and others do not. I don't know anything about shooting guns, unfortunately.

I had a lot of fun building rockets in a similar way as a kid. We also tried PVC but discovered that it fails in a dangerous way, after which we used only copper. I had fun programming a PIC16 in assembler to read from the accelerometer and fire the home made igniters of black powder, nitrocellulose laquer, and nichrome wire.

reminds me of the BPS Space youtube channel, he makes rockets too:

https://www.youtube.com/@BPSspace

https://bps.space/pages/about

That guy is amazing in not just his accomplishments but his determination and resolve over the year (And I'm surprised the authorities haven't shut him down over ITAR type regulations).

He does mention ITAR in some of his videos and is clearly aware of the issue.

Except that he launches them from a proper launching site whilst hiding in a bunker/shelter, rather than standing around the thing in flip flops.

I would be warry about doing this, no matter what country you are in. Using commercial motors is one thing, baking your own very much another. There is a very fine line between cooking up some rocket propellant and operating a bomb factory. Imagine getting discovered with a few pounds of homemade explosives and box of electronics. I wouldn't want to have that conversation with the police.

>There is a very fine line between cooking up some rocket propellant and operating a bomb factory.

Indeed. A solid rocket motor is pretty much just a bomb with a hole+nozzle at one end.

I didn't know about OpenRocket! Great that there are open source solutions for this stuff

OpenRocket is great. But it obviously isn't doing a full CFD simulation, so take the apogee (max altitude) estimates with a pinch of salt. It estimated our apogee about 15% higher than we actually got.

A few years back I built a dual stage model rocket using regular rocket motors:

https://youtu.be/zPtFv-cwcfQ?si=mjy6hg9YPARpTkRV

https://www.youtube.com/bpsspace Does some pretty informative work with amateur rockets.

I hoped for some kind of postmortem to understand what went wrong and what was learned from the failure.

The second and especially third pages have some of that.

oh, it looked like link to another post

Here’s the direct link to the 3rd page if anyone wants :

https://knowone08.gitbook.io/vgecrocketry/subsystem-survival...

I’d recommend reading the earlier 2 pages for context though.

I don't get why it was bad to name the rocket Vanessa.

I was wondering the same. I’m not in this industry, but perhaps rockets are not typically given human names, so it’s a joke? Also, it’s spelled Venessa rather than Vanessa, so maybe it’s humorous because of the misspelling.

I think the author was pointing at the fact that "Venessa" looks like a typo.

Reply on news.ycombinator.com