For Questions That Don't Merit Their Own Thread

[ProtoJeb21]

14 hours ago, Silavite said:

(Paging @ProtoJeb21)

I'm working on a very simple model for the atmosphere of an exoplanet, and I'm a bit stuck. I understand that it is possible to find scale height and the composition of an exoplanet's atmosphere. It should be possible to roughly find the planet's average temperature from the parent star's irradiance at the distance of the exoplanet. Is it possible to get an absolute value for density or pressure at an altitude from direct observation and thus create a rudimentary atmospheric model? (Assuming a very simplistic single layer atmosphere).

Sorry, I’m not good with atmospheric modeling, but I can help you find the equilibrium temperature and insolation of an exoplanet. 

If the planet’s star does not have a determined luminosity already, you can calculate through (Rs/1)^2 • (Ts/5778)^4, where Rs is the star’s radius in solar units, and Ts is its temperature in Kelvin. You will also need the planet’s semi-major axis in AU, which is found through the cube root of ((P/365.25)^2 • Ms), where P is the planet’s orbital period in days, and Ms is the star’s mass in solar units. Put this information into (Ls/1) • (1/a)^2, where Ls is the luminosity of the star, and a is the planet’s semi-major axis. Your answer will be the planet’s insolation in Earth units. For equilibrium temperature, plug in luminosity and semi-major axis into the PHL’s planetary calculator: http://phl.upr.edu/projects/habitable-exoplanets-catalog/calculators

I hope this at least helps in some way, and again, I apologize that I can’t help you with atmospheric modeling. 

[DDE]

What is Russia’s NRO? I’m pretty sure the 821st Center doesn’t just monopolize and process all of military satellite data.

[Mad Rocket Scientist]

Anyone have any good data on the LEROS engine, as used by the Beresheet lander? Someone asked me about the long transfer time, and it has somewhat to do with low TWR forcing the burn to be split up. But I don't know which variant of the engine is being used, and news articles have said that it was modified by increasing thrust and decreasing Isp.

This is the data on the "stock" LEROS engine:

https://www.moog.com/literature/Space_Defense/Spacecraft/Propulsion/Upper_Stage_Engines_Rev_0913.pdf

Also, it looks like Beresheet will be waiting more than one orbit between each periapsis kick, any idea what that's about?

[kerbiloid]

7 hours ago, Mad Rocket Scientist said:

Also, it looks like Beresheet will be waiting more than one orbit between each periapsis kick, any idea what that's about?

I guess, the engine is weak to stay light, while the most effective apoapsis change is in periapsis.
So, they save tthe fuel by splitting one big deltaV into several small deltaVs to perform the acceleration only in periapsis.

The same with lunar orbit.

[Guest]

It's me again, back with another question. This time about fluid dynamics.

The de Laval nozzle accelerates a gas while reducing its pressure, correct? If I reverse its orientation, will the result be a gas with a slower velocity, but higher pressure?

If not, is there any other device that increases fluid pressure without moving parts?

 

[Gargamel]

46 minutes ago, Aperture Science said:

If not, is there any other device that increases fluid pressure without moving parts?

Gravity, but that probably won't be practical for your application, whatever it is. 

[Mad Rocket Scientist]

15 hours ago, kerbiloid said:

I guess, the engine is weak to stay light, while the most effective apoapsis change is in periapsis.
So, they save tthe fuel by splitting one big deltaV into several small deltaVs to perform the acceleration only in periapsis.

The same with lunar orbit.

That was my guess too, but the engine is strong enough for a powered landing on the moon, so I have trouble imagining it being so low acceleration that it couldn't do a TLI from GTO in one burn.

Also, in this official simulation it waits multiple orbits between each periapsis burn: http://spaceil.com/live/

[Guest]

3 minutes ago, Gargamel said:

Gravity. 

I'm sorry, but what I'm looking for is a device that can do it. A nozzle, perhaps, or some other kind of structure.

Unless, you know, that's the only one available. I did, however, read that when going to a pipe with greater diameter than the previous one, the fluid's tendency is to gain pressure and lose velocity. Is that the only way, or is there some kind of structure that does that with greater efficiency?

[magnemoe]

4 hours ago, Mad Rocket Scientist said:

That was my guess too, but the engine is strong enough for a powered landing on the moon, so I have trouble imagining it being so low acceleration that it couldn't do a TLI from GTO in one burn.

Also, in this official simulation it waits multiple orbits between each periapsis burn: http://spaceil.com/live/

Tanks will be almost empty on touchdown but is full now. 

[kerbiloid]

10 hours ago, Gargamel said:

10 hours ago, Aperture Science said:

If not, is there any other device that increases fluid pressure without moving parts?

Gravity, but that probably won't be practical for your application, whatever it is. 

It can even increase its temperature and cause local hurricanes.

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

10 hours ago, Mad Rocket Scientist said:

That was my guess too, but the engine is strong enough for a powered landing on the moon

Earth-to-Moon delta-V ~ 3 km/s
The Moon landing requires less.

Also it can decelerate for minutes on landing keeping the craft retrograde, but the orbit insertion impulses should be as short as possible because it passes the periapsis quickly.

10 hours ago, Mad Rocket Scientist said:

Also, in this official simulation it waits multiple orbits between each periapsis burn

Maybe it awaits the proper phase angle.

5 hours ago, magnemoe said:

Tanks will be almost empty on touchdown but is full now. 

+1

[Green Baron]

3 hours ago, kerbiloid said:

It can even increase its temperature and cause local hurricanes.

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

A little addition: a foehn is something different than a hurricane. Tropical cyclones are low pressure areas and form over warm water surfaces. They receives their energy from outside, the warm water. A foehn is (mostly) the result of air containing high moisture that crosses a mountain ridge, where it is forced upwards, raining out, and falls down again on a lee ward side. It is an adiabatic process, there is no or little energy exchange. The dry air from high levels, when it crosses the ridge towards the lee side is denser than the surrounding, beginning to sink, being compressed, sinking faster ... and so on. It is usually a local effect, channeled in valleys and limited to the immediate forelands, and with limited duration until circulation changes. In the Alps they occur frequently "pre-frontal" and die down when the front passes through.

Just for completeness :-)

Edited February 24, 2019 by Green Baron

[ARS]

How long nuclear fuel lasts? Like, if for some reason, a nuclear power plant was shut down and abandoned, but there's still spare unused nuclear fuel and all of the necessary stuff to reactivate the reactor, how long it will last until it's considered "expired"?

[kerbiloid]

Fuel reload:
fast-neutron reactor: 1..2 years,
thermal-neutron reactor: 2..4 years.

Then 3..7 years in a pool, then utilization.

37 minutes ago, ARS said:

if for some reason, a nuclear power plant was shut down and abandoned, but there's still spare unused nuclear fuel and all of the necessary stuff to reactivate the reactor, how long it will last until it's considered "expired"?

I guess, 0.
Once you have started the reactor, its fuel composition starts changing, its neutron field distribution starts changing, different rods start having different composition of their fuel.
Also it's radioactive, so requires cooling.

So, unlikely anybody would play a roulette.
Even if so, probably he would face an unproper neutron field distribution, some rods getting hotter than required, some rods still not reacting, and the reactor will automatically shurdown.

Edited February 25, 2019 by kerbiloid

[Racescort666]

On 2/23/2019 at 4:03 PM, Aperture Science said:

I'm sorry, but what I'm looking for is a device that can do it. A nozzle, perhaps, or some other kind of structure.

Unless, you know, that's the only one available. I did, however, read that when going to a pipe with greater diameter than the previous one, the fluid's tendency is to gain pressure and lose velocity. Is that the only way, or is there some kind of structure that does that with greater efficiency?

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

The air intake section might be the most relevant to your question. The phenomena at work is Bernoulli's principle which comes from the law of conservation of energy. 

[DDE]

On 2/25/2019 at 3:59 PM, ARS said:

How long nuclear fuel lasts? Like, if for some reason, a nuclear power plant was shut down and abandoned, but there's still spare unused nuclear fuel and all of the necessary stuff to reactivate the reactor, how long it will last until it's considered "expired"?

Tens of thousands of years for U-233 fuel bred from thorium; somewhat less if you’re burning plutonium. Hundreds of millions of years for classical U-235.

The nuclear fuel is not the limiting factor, obviously.

[DDE]

Alright, let’s go there.

We know that Burevestnik is going to be hosted at Plesetsk.

We know, thanks to Bart Hendrickx, that it uses the tank and thrusters from Nivelir, so it’s probably of comparable size and mass - ~100 kg.

Let’s take aim at the holy grail. Assuming Angara-A5 with the recently added ground processing capability for Block D, how many Burevestniks would it be capable of dropping into the orbital region of GPS? And would it be possible to use a bielliptical transfer to scatter payloads from one launch into different GPS planes? What would the payload penalty be then?

 

Edited March 2, 2019 by DDE

[TheDestroyer111]

On 3/2/2019 at 10:12 AM, DDE said:

Burevestnik

You mean you want to place some nuclear-powered missiles (that aren't even designed for spaceflight AFAIK?) with nuclear warheads into orbit and then blow them up on GPS sats? There are probably better ways to disable GPS without violating the Outer Space Treaty, but if you want to...

 

Using an LV performance calculator, quick data from Wikipedia, and guessimation where I didn't immediately find required data, I pressed the data in (assuming the rocket is equipped with a Briz-M third stage) and got results:

https://imgur.com/a/jKpoAum

So using my Mostly Unreliable Data™ you can launch about 1700 kg into a GPS orbit with an Angara. To be taken with a handful of salt.

Edited March 4, 2019 by TheDestroyer111

[DDE]

1 hour ago, TheDestroyer111 said:

You mean you want to place some nuclear-powered missiles (that aren't even designed for spaceflight AFAIK?) with nuclear warheads into orbit and then blow them up on GPS sats?

Welcome to the very confusing world of naming conventions of Soviet/Russian military hardware.

https://forum.nasaspaceflight.com/index.php?topic=45734.0

[kerbiloid]

Spoiler

I will never put my important sats into a circular orbit.
I will never put my important sats into a circular orbit.
I will never put my important sats into a circular orbit.
I will never put my important sats into a circular orbit.
I will never put my important sats into a circular orbit.
I will never put my important sats into a circular orbit.
.....

 

[tater]

 

 

(click that then open the original sized one)

[tater]

Youtube just recommended this:

 

[Green Baron]

I like sepia images :-)

Seriously, it is time that somebody gets out again to Moon or Mars. Just to look if everything is ok.

 

[DDE]

1 hour ago, Green Baron said:

Seriously, it is time that somebody gets out again to Moon or Mars. Just to look if everything is ok.

Genau.

[kerbiloid]

Helium-3 tanks look so helium-3...

Interesting facts.
Do you know that if inflate a lunar balloon with the mined helium-3, then it falls, not flies?
You need to extract oxygen and fill with it the lunar atmosphere before you can fly in a helium-3 lunar balloon.

But to extract the lunar oxygen, you first need the lunar helium-3 as a fuel.

Very strange is your Moon.

Edited March 6, 2019 by kerbiloid

[DDE]

2 minutes ago, kerbiloid said:

Helium-3 tanks look so helium-3...

Could be simple gaseous storage. Could be something else entirely.