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What are Black Holes?
The Basics
A Black Hole is a Celestial Object that has a very strong gravitational pull that not even light can escape.
This happens because Black Holes have an astronimically large mass.
The lowest-mass known black hole belongs to a binary system named XTE J1650-500.
The black hole has about 3.8 times the mass of our sun.
How do they form?
Black holes are formed when a massive star reaches the end of its life and implodes, collapsing in on itself.
Now you might be thinking our sun could become a black hole, but that is wrong.
It’s way to small for that, The sun would have to be about 20 times as massive to become a black hole at the end of it’s life.
Different Parts of a Black Hole
This illustration of a black holes show us all the different parts.
The Singularity is the core of a black hole, this is where all the matter has collapsed into, making a tiny, infinitely dense point.
The Event Horizon is the part of the black hole that is actually black, if anything is at this point it will not be able to escape.
Relativistic jets are the jets of particles and radiation being produced when a black hole feeds on stars, gas or dust, this results in the jets of particles and radiation blasting out from the black holes poles at near light speed.
They can extend for thousands of light-years into space.
The Accretion disc is a disc of superheated gas and dust which whirls around a black hole at very fast speeds, producing electromagnetic radiation that reveal the black holes location.
The Innermost stable orbit is the inner edge of an accretion disc, it is the last point where an object can orbit safely without falling past the point of no return
This has been an MIS Blog Post.
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How to receive images directly off of Satellites
General Understanding
Getting Images off of Satellites is pretty easy, all you need is a simple antenna, a Software Defined Radio (SDR) and a computer or even android mobile device.
The Satellites that are most used for this hobby are the American NOAA Satellites and the Russian Meteor M2 Satellites.
Both of them are in a low sun-synchronous and almost polar orbit, meaning the countries they fly over will vary.
They constantly transmit “images” of the surface of the earth, however they are not captured like typical images.
They are being captured by a sort of “scanner” capturing one line of pixels at a time and instantly transmitting them.
Differences
There are a few differences between NOAA and Meteor M2.
The most obvious one is that NOAA uses analogue tones to transmit the images while Meteor M2 uses digital signals.
They transmit different “types” of images, most commonly theres APT, LRPT and HRPT.
APT (Automatic Picture Transmission) is an analog signal with 2 analog channels, the image resolution is also quite low. [Used by NOAA]
LRPT (Low Rate Picture Transmission) is a digital signal with 3 digital channels, it is also a higher resolution than APT. [Used by Meteor M2]
HRPT (High Rate Picture Transmission) has a greater bandwidth than APT and LRPT, meaning you can get more channels and a higher resolution. [Used by both]
Meteor M2 Satellites also break more often or undergo maintinance.
Receiving
Hardware
Receiving these images is quite simple, the most basic setup you could have consists of a V-Diapole antenna, something like an RTL-SDR dongle as an SDR and an old laptop.
You can get a kit with the RTL-SDR BLOG V4 and RTL-SDR V-Diapole for as low as 50€ on a website like amazon.
Where is the Satellite?
To know where the satellite currently is and when it next passes over your location you can use websites like N2YO or an app like Look4Sat
If you are using a V-Diapole Antenna for receiving, it might be smart to orient it to where the satellite is, which is easy when looking something like Look4Sat but might be harder when using N2YO.
Software for Receiving
You need something like SDR++ to actually use the SDR.
If you have a pass coming up soon, position yourself in a relatively free area where you can maintain line of sight with the satellite.
Plug your SDR into your laptop and start up your software, if you are using SDR++ then the process is quite simple.
Simply select your SDR using the Source menu from the side
Put the gain up to max
Now the process varies between NOAA and Meteor
NOAA
For NOAA, you should scroll down to recording settings and select audio
As soon as you see a signal like this you should press record, when it dissapears you should wait a bit and then stop recording, after this go to the decoding step.
METEOR M2
For Meteor M2, you should select Baseband and scroll back up to select “IQ Correction”
As soon as you see a signal like this you should press record, when it dissapears you should wait a bit and then stop recording, after this go to the decoding step.
Decoding
For decoding, the best option would be SatDump
In SatDump, select the Satellite you just recorded and import your file, then simply press on decode and watch the images flow in.
Example Images
NOAA
METEOR
This has been an MIS Blog Post.
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What is Thrust to Weight Ratio (TWR) in Rockets?
Thrust to Weight Ratio (TWR) is a dimensionless ratio of thrust to weight of a rocket, jet engine, propeller engine, or a vehicle propelled by such an engine that is an indicator of the performance of the engine or vehicle.
In rockets, it indicates how fast you can go with the weight and thrust of your rocket.
A higher TWR means that you can go faster, while a lower TWR means you go slower.
On Earth
During liftoff you need a TWR of atleast 1.00 to overcome the atmosphere and gravitational forces.
In Space
While in space, TWR doesn’t really matter due to there not being an atmosphere and gravitational forces being much lower or in some cases even nonexistant.
A low TWR in space just means that you will go slow, which in many use cases does not matter at all.
Even if you cannot execute a burn due to your vessel being way to slow, you can still, in most cases like changing apoapsis or periapsis, break up the burn into many different burns.
How to Calculate TWR
Thrust to Weight Ratio
TWR is calculated by dividing the Thrust by the Weight (TWR=T/W)
Weight
Weight is calcuated by multiplying Mass and Acceleration due to Gravity (W=m⋅g)
For Earth, The Acceleration due to Gravity would be 9.81 m/s²
Thrust
Thrust is usually indicated by the Rocket Engines Manufacturer, it is usually measured in Newtons (N)
It can be calculated, but calculating it requires some more advanced math that I’m not gonna go into detail with.
Here is an article from NASA on how to calculate thrust.
Example
Here is a generic example of a TWR calculation:
TWR= 735,750N/800,000N ≈ 1.09
(Note: To have a TWR > 1.00, thrust must be greater than the weight, so double-check the numbers to ensure accuracy)
This has been an MIS Blog Post.
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