jambooger
Defender of the Stupid
What should I know about Planet atmospheres and gravities so that when I approach I know what my minimum Pea can be? I also need this info so I know if I can land.
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General Question Planet Atmospheres & Gravities for Pea
- Thread starter jambooger
- Start date
Izack
Non sequitur
All you need to know is how far up the atmosphere goes, basically. The only part gravity has is making your orbit follow Kepler's laws.
jambooger
Defender of the Stupid
Ok, but what do I need to know about the atmosphere so I know how to enter it. Example: Earth and Moon.
Izack
Non sequitur
Oh, are you going for aerocapture? I thought you just meant 'how low can I go without hitting the atmosphere?'
To be honest, I don't know a lick about proper aerocapture/braking... :embarrassed:
To be honest, I don't know a lick about proper aerocapture/braking... :embarrassed:
jambooger
Defender of the Stupid
Well I guess my question was sort of two parts. "Aerocapture" is a new term for me, but yes there must be some chart that would give me some info on the planet or moon so reentry would not be trial and error.
Tommy
Well-known member
Aerocapture is the process of using aerodynamic drag to reduce or eliminate an orbit insertion burn. For instance, if you are going from Mars to Earth, normally you would need a retrograde (relative to the Earth) burn when you reach Earth in order to avoid flying away from the Earth. Aerobraking can be used in place of this retrograde burn.
The altitude used for the aerocapture (or even just a regular re-entry) varies depending on the velocity of your vessel, and with the type of vessel. For instance, with an XR-2, 50k is a good Pea for re-entry, 70k is good for a lunar return, and 74k is about right for the Mars - Earth trip.
Aerocapture requires that you stay in the atmosphere longer than a regular re-entry, and often the vessel's wings are used to generate "downward" lift (by flying inverted) to prevent the vessel from gaining altitude after the periapsis is reached - velocities are often still at or above orbital velocity for a few minutes after Pe.
Aerocapture is tricky, and can be dangerous in vessels which model hull heating, but it's a very useful way to save fuel. Not only do you save the fuel you would have used for the retro burn, you can carry less fuel to begin with - thus lowering the vessel's mass and saving the fuel used to accelerate that extra mass.
The altitude used for the aerocapture (or even just a regular re-entry) varies depending on the velocity of your vessel, and with the type of vessel. For instance, with an XR-2, 50k is a good Pea for re-entry, 70k is good for a lunar return, and 74k is about right for the Mars - Earth trip.
Aerocapture requires that you stay in the atmosphere longer than a regular re-entry, and often the vessel's wings are used to generate "downward" lift (by flying inverted) to prevent the vessel from gaining altitude after the periapsis is reached - velocities are often still at or above orbital velocity for a few minutes after Pe.
Aerocapture is tricky, and can be dangerous in vessels which model hull heating, but it's a very useful way to save fuel. Not only do you save the fuel you would have used for the retro burn, you can carry less fuel to begin with - thus lowering the vessel's mass and saving the fuel used to accelerate that extra mass.
jambooger
Defender of the Stupid
Great explanation of aerocapture, I understand that much better, especially for Earth, Moon and Mars. Now my question is... how do I know how much atmosphere a different planet or moon will have,,, before I reach it?
Pyromaniac605
Toast! :D
jambooger
Defender of the Stupid
Holy smoke, thats alot of information. Good find Darren, I just added that to my favs. Guess I need to read now. Read, Read, Read, lol Thanks :thumbup:
Pyromaniac605
Toast! :D
Tommy
Well-known member
Wikipedia is darn handy, and provides a wealth of information. It won't tell you what the entry interface altitude is for a particular planet, at least not in a way that is directly usable in Orbiter. It will, at best, give you a "starting point" for further investigation.
In Real Life nothing is launched into space without rigorous testing in a computer simulation. Why should things be different in Orbiter?
It's not that hard to test things in Orbiter. Just pretend that you are doing "pre-flight simulations".
Try to use scientific principles in your tests - make them repeatable, and try to have a "control" to compare them against. For example, when I designed my ascent and re-entry profiles for the DGIV i followed the following steps.
1; Design a test procedure that gives usable information. I decided that what I needed to know was:
A; the minimum velocity required to maintain level flight at any given altitude,
B; the maximum velocity I could attain at a given altitude without overheating,
C; the velocity where, at a given altitude, drag forces (in m/s) became more than gravitational forces (also in m/s)
2; Establish a "control". To establish a "heat" control, I flew a DGIV straight up, and cut the thrust when I vessel had an ApA at the altitude I was testing (I decided to test for every 5k altitude). This resulted in a "stall", an instant where my vertical and horizontal velocities were very close to zero - and I noted the external and hull temps (note that I kept the velocity under 100 m/s during the climb to help prevent the hull temps from reading too high as a result of friction during the climb) at that point.
3; Data Gathering. First, for every 5k altitude, I did test flights to determine what the minimum velocity was that would allow me to maintain altitude using the wings, using only elevator trim to maintain attitude. Next, I accelerated at that altitude until the hull temps hit the red. I recorded every flight so I could watch the replay and get data without being distracted by having to fly the vessel. I watched the recording in external view with "visual helpers" enabled so I could see the actual thrust, lift, gravity, and drag forces.
In the end, the data I gathered led to some conclusions. One was that it doesn't pay to break the sound barrier until you are over 10k altitude. Another was that a DGIV will NOT burn up (at normal re-entry velocities of under 8km/s) until you are under 64k altitude (at least in Orbiter 2006P1, and some preliminary testing shows this seems to be the same in 2010P1).
In short, some flights I "pretend" are done in a simulator to gather data, and some flights I "pretend" are For Real. After all, that's how real spaceflight is done - they just don't have to "pretend".
I'm not a math wiz, so I tend to use methods that are a bit on the crude side. The important thing is to use the scientific process - Gather Data, Make Hypothesis, Test Hypothesis. Tests should be designed to be repeatable (make each test several times, and if you get notably different result each time it means your testing method is flawed), and to exclude the "interference" of conditions not being tested for (ie, control the environment as much as possible).
I don't know of any chart that gives you this info, as it applies to Orbiter. You'll have to test it for yourself (and maybe you could be the one who creates the chart)!
In Real Life nothing is launched into space without rigorous testing in a computer simulation. Why should things be different in Orbiter?
It's not that hard to test things in Orbiter. Just pretend that you are doing "pre-flight simulations".
Try to use scientific principles in your tests - make them repeatable, and try to have a "control" to compare them against. For example, when I designed my ascent and re-entry profiles for the DGIV i followed the following steps.
1; Design a test procedure that gives usable information. I decided that what I needed to know was:
A; the minimum velocity required to maintain level flight at any given altitude,
B; the maximum velocity I could attain at a given altitude without overheating,
C; the velocity where, at a given altitude, drag forces (in m/s) became more than gravitational forces (also in m/s)
2; Establish a "control". To establish a "heat" control, I flew a DGIV straight up, and cut the thrust when I vessel had an ApA at the altitude I was testing (I decided to test for every 5k altitude). This resulted in a "stall", an instant where my vertical and horizontal velocities were very close to zero - and I noted the external and hull temps (note that I kept the velocity under 100 m/s during the climb to help prevent the hull temps from reading too high as a result of friction during the climb) at that point.
3; Data Gathering. First, for every 5k altitude, I did test flights to determine what the minimum velocity was that would allow me to maintain altitude using the wings, using only elevator trim to maintain attitude. Next, I accelerated at that altitude until the hull temps hit the red. I recorded every flight so I could watch the replay and get data without being distracted by having to fly the vessel. I watched the recording in external view with "visual helpers" enabled so I could see the actual thrust, lift, gravity, and drag forces.
In the end, the data I gathered led to some conclusions. One was that it doesn't pay to break the sound barrier until you are over 10k altitude. Another was that a DGIV will NOT burn up (at normal re-entry velocities of under 8km/s) until you are under 64k altitude (at least in Orbiter 2006P1, and some preliminary testing shows this seems to be the same in 2010P1).
In short, some flights I "pretend" are done in a simulator to gather data, and some flights I "pretend" are For Real. After all, that's how real spaceflight is done - they just don't have to "pretend".
I'm not a math wiz, so I tend to use methods that are a bit on the crude side. The important thing is to use the scientific process - Gather Data, Make Hypothesis, Test Hypothesis. Tests should be designed to be repeatable (make each test several times, and if you get notably different result each time it means your testing method is flawed), and to exclude the "interference" of conditions not being tested for (ie, control the environment as much as possible).
I don't know of any chart that gives you this info, as it applies to Orbiter. You'll have to test it for yourself (and maybe you could be the one who creates the chart)!
Last edited:
Pyromaniac605
Toast! :D
Tommy
Well-known member
"Launched", yes. "Into Space" NOT.
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