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joel Leleux · 21st May 2020 at 4:17 pm

Why Don’t you use directly N2 bottles to pressurize your tanks. You don’t need that much pressure, 4 or 5 – 200 bar bottles would fit, no?

    Sarunas Kazlauskas · 21st May 2020 at 7:54 pm

    Hello Joel,

    We actually have a couple of detailed blogs on the subject and reasoning behind this design:

    But the tl;dr is that we would need to bring approx. 67,000 standard liters of gaseous nitrogen on board for the flight, which equates to eleven 20 liter, 300bar COPV’s. That becomes a fairly large mass fraction of the whole rocket and probably the most expensive single system on Spica. The LN2 burner saves us a lot of weight and money in exchange for a bit more complexity.

    Ad Astra,
    Sarunas K.

    Steven Kasow · 27th May 2020 at 1:46 am

    Test like you want to fly, fly like you have tested.
    The heat exchangers and hardware are lighter than more nitrogen bottles, which makes for a more effective rocket.

Jānis · 12th June 2020 at 12:59 pm

How about tap-off cycle? Or enginering to make it work would have almost no impact to performance?

    Sarunas Kazlauskas · 12th June 2020 at 7:02 pm

    Hello Jānis,

    That would complicate the engine’s design and manufacturing, which we would like to avoid.

Serjoscha Evci · 13th June 2020 at 2:14 am

How high would the Apogee of Spica be if you would for whatever reason stop the burn, let’s say for example one and a half seconds later than planned?
i would love to know that, because sometimes timing precision isn’t perfectly exact and i have no idea how big of an impact a small change in burn time has on apogee.

disclaimer: if you find spelling or grammar mistakes you can keep them, and it’s 2:13 A.M. here in switzerland right now so i’m a bit tired

    Sarunas Kazlauskas · 13th June 2020 at 9:06 am

    Hello Serjoscha,

    The engine shutting off 1.5s later would not have a big effect on apogee, as you would still have utilized all the energy stored in the propellants. You, of course, would see a bigger (negative) impact if the engine shut off 1.5s early and did not use all of it’s propellants for some reason. But there you have a lot of variables to account for before coming to a clear answer.

    We have members who volunteer in an organization that teaches kids coding and computer skills here in Denmark. So for one of their exercises they developed a fairly realistic Spica flight simulator where you can time your engine shut off, throttle the engine down before MECO or during MaxQ and see how all that affects G loads on the astronaut as well as the maximum apogee. The goal of the game is to keep the astronaut at “comfortable” G loads and maximize apogee. So if you have some spare time, you can experiment with these scenarios a bit, and hopefully it can give you a clearer understanding of the effect of these variables. You can find the simulator here:

Rune · 31st July 2020 at 3:54 pm

Really hope the engine thrust support structure is massively overdimensioned, otherwise I Guess you may see a rocket engine flying straight through both fuel and LOX tanks. Wishing all the best for you guys, please be sure you are all safe!

    Sarunas · 31st July 2020 at 4:41 pm

    Hello Rune,

    Thank you for your concern! This is just a conceptualization, as Thomas mentioned in the video.

    There will be more than two tons of heavy steel support pillars transferring the load of the engine to the corners of the shipping container in the actual design.

    Ad Astra,
    Sarunas K.

Richard von Brecht · 6th January 2021 at 3:37 am

I’m very impressed with the simplicity of your rocket design. It should result in a reliable thruster. The cryogenic metering valves are the weak link. As a controls engineer I’d be interested in seeing how you are approaching this problem.

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