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General Discussion / Best mobile app to track satellites
« Last post by raf22 on Today at 08:57 pm »
What is the best mobile app for android or any website to track satellites that are visible with unaided eyes.
I would like see alert before a satellite will appear in the night sky and info where to look for it.
This is very heavy modification which means it'd be appropriately costly.

Moreover you want to use capsule shaped for hypersonic re-entry for subsonic or at most low supersonic operations.  That's a kludge at best.

It's the cheapest kludge I could think of, reusing as much tech as possible.  Yeah, it's fairly costly.  But the alternative is to wait for enough empirical data to prove, probably at a 95% confidence level (or a 95% credible interval, as the bayesian cool kids say), that Starship has a pLOC<1/1000 on both ascent and EDL, and therefore doesn't need an abort system for those regimes.  It only takes a couple of failures deep into the program to make that take a long time,¹ and time is money. 

Really, use zero-zero ejection seats instead.

You could seat 12 people in Starship in 2 lines and 6 rows or 4 lines and 3 rows (or asymmetric 3 lines and 4 rows). And while one poster claimed that those ejecting later in ejection sequence would be fried, they missed the obvious fact that every next person would be protected inside the hull while waiting (fraction of a second) for their ejection turn. The sequence for each line would be: blow hull panel, eject occupant from the rear, blow away the next pane, eject the next up occupant, and so on. And the sequence could alternate between the lines for extra clearance.

It's an already solved problem. So less development cost, sooner readiness for use, and better capacity.

You'll have to explain how this helps in a pad abort, where the ejection path is horizontal, not vertical, and you're ejecting the crew into an environment that's quite likely to be flamey and/or explodey. Ejection seats are just barely steerable, and their purpose is to get the occupant into the slipstream safely, not to blow them clear of an explosion.  And if you're on or near the ground, the assumption is that they're pointed more-or-less up.

¹This is why PRA is good.  If you have late-program failures but your PRA model can account for the failures, you can certify faster than a purely empirical approach.  But your PRA model has to be trustworthy, which means that your spacecraft has to look a lot like previous spacecraft.  That's not going to be true for Starship without a lot of flight heritage.
Advanced Concepts / Medusa concept using chemical explosives
« Last post by Beratnyi on Today at 08:32 pm »
Hello everyone! While studying the concept of the Medusa spacecraft the idea came up to use chemical explosives instead of nuclear bombs. This idea, in my opinion, has a number of advantages over traditional rockets:
1) C4 can be used as an example, when it is detonated, the speed of the outflow of gases is 8 km / s. If we achieve the efficiency of transferring the energy of the explosion into the kinetic energy of the spacecraft in the region of 70%, then the specific impulse will be 570 s, which is more than that of the best hydrogen rocket engines
2) Specific impulse increases rather than decreases when operating in an atmosphere, since air is used as a reaction mass
3) Fuel stored in solid form at room temperature with high density
4) Spacecraft materials work in tension, not compression, so the dry mass of the structure can be reduced even despite the additional mass of the sail
5) In flight, you can get electrical energy for the spacecraft by detonating bombs and withdrawing part of the energy to recharge the batteries
What do you think about this idea? I would love your feedback in the comments

MegaBay Stablemates.

Booster 7 (left). Booster 9 (right).

Retired pals in the Rocket Garden.
And from Nomadd's photo above, looks like it's traversing the entire berm top.
Orbit at epoch Dec 3, 09:52 UTC:
2022-163A/54381 in 898 x 912 km x 67.14°
and Object 54383 (Kosmos 2566?) at epoch Dec 3, 02:45 UTC
2022-163C/54383 in 896 x 911 km x 67.14°
Well... Looks like I was right.
Photos taken yesterday and posted today by NASA Johnson
Blowout panels are at the bottom. Rate of fill of the tank is controlled by controlling the flow of gas out the top valves. This is like the ballast tanks on a submarine. Yes, I know you compute your EDL to end up with almost empty tanks. I'm proposing a brief hover about a meter above the surface to empty the LOX tank all the way. If you blow the blowout panels while they are still at or just above the sea surface (or within a foot of the surface from below) the final bit if LOX will blow out before the water begins to flow in. The only remaining cooling in capacity in the system is in the stainless steel, and cannot create an ice plug if the blowout panel is big enough.

Blowouts anywhere pretty much imply pyros to blow them, don't they?  Pyros aren't necessarily bad, especially if the number of crewed flights is fairly modest compared to the number of robotic ones (a good assumption).  But pyros in a LOX tank don't sound wonderful, especially if the probability of an uncommanded blow-out is >0.01%.

You can't run the engines until the lines go dry; it'll make the turbopumps explode, which is a bad property during a landing--even a crash-landing.  The question is whether the sump holds 100-200kg of LOX, or whether it holds 1-2t.  The former isn't a big problem, the latter is.

Blow-out while still in the air might work, but you have to have the engine turbopumps shut down (i.e. preburners off) before you can depressurize the tank, and that doesn't leave much time for LOX to drain out away from the blow-out inlets.  Also, you want the tank pressurized on impact, even from a meter or two, because you don't want it to crumple or break open.

So now we have our ship vertical with the engines just in the water, engines off, and just beginning to fall by gravity into the water. The panels blow and the last LOX blows out across the surface and the panels become submerged, so water begins to flow in. As gravity accelerates the drop into the water, the remaining O2 begins to compress (and heat) as water flows in, and the rate of drop eventually decreases as buoyancy counteracts gravity. The magical control system regulates the flow of gas out of the top valves to achieve the correct amount of bouyancy, bringing the whole system to a halt just before it would begin to rebound toward the surface.

I think you want an uncontrolled vent that pops at the same time as blow-out, because the goal is to get seawater in as quickly as possible.

If at this point we are still topheavy, we are still being held vertical by the reaction wheel and RCS, and we can begin dumping methane since we are no longer spewing O2 all over the place.

Is the issue that you need to flood the methane tanks as well?  Because dumping methane into an atmosphere with oxygen in it, at what's more-or-less a crash site, doesn't sound like a great plan, LOX or no LOX.

However, don't put heavy payloads on crewed flights.  I haven't done the math, but I suspect that your CoG is now underwater if the crew module is the only payload and weighs <20t, the LOX tanks are flooded and the thrust structure and engines are dangling down.

So:  Not to give you a hard time, but how does this help pad abort?  For that matter, how does it help survive a failed flip maneuver?  You have to cover all the survivable abort contingencies, or it's not worth it.
Or you sacrifice some performance to do the flip early.

Separating the crew every mission sounds like a recipe for cost and unreliability.

Technically some might be crew, but really, they are all just passengers sort of like Paratroopers are passengers in a C130.
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