Published by Rasmus Agdestein on


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:

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