02 – Aerodynamic flight principals & establishing orbit
This lesson doesn’t require any additional addons.
We will now get ready to take our first flight in Orbiter. If you have experience with flight simulators, that will help, but if not, then we’ll quickly jump into it now and learn the basics. Start up Orbiter and select the scenario Mission 1 – DG to ISS which can be found under Checklists. We wont actually be flying to the ISS today but we’ll use this scenario because it starts us out with everything we want. For this first flight, you can disable the Limited fuel option in the Parameters tab.
Once the simulation begins, you should find yourself in the cockpit of the Delta Glider on the runway of Kennedy Space Center at Cape Canaveral, Florida.
Before we take off, we need to establish some basics on how to look around. First, lets start out with the F1 key. This alternates between the external and internal views. Switch to the external view, now use the right mouse button on the screen while moving your mouse around. This allows you to rotate your view around your vehicle, and the mouse wheel will allow you to zoom in and out. You can zoom out quite a ways and see your situation from the perspective of the whole solar system and anywhere in between.
Switch back to the internal view with F1. Now press F8, F8 will cycle through the different internal views, and depending on the spacecraft you are in, there will be up to three different views available. They are the 2D cockpit view, the 3D cockpit view and the glass cockpit view. “Glass cockpit” is a term that refers to displays or digital instruments taking place of dials and indicators of traditional aircraft. In any of the internal views, you can use the right mouse button to look around, though this is probably most relevant in the 3D cockpit view. Looking around in the 3D cockpit view gives you a pretty good immersive sense of what your spacecraft is like. If at any time you want to go immediately back to your forward view, press the Home button on your keyboard.
Using the metric system
It is essential to understand your instruments in order to fly effectively. Before we go any further, however, I want to point out that Orbiter is a purely metric system based simulator (although certain addons bring in imperial measurements of their own). If you are used to reading your airspeed in knots or your altitude in feet, then this will certainly be a shift for you, but in the end I think its worth it. After all, space exploration is a scientific and international endeavor which makes the metric system more fitting. In any case, the conversion is pretty simple.
|Meters / sec||Knots||Meters||Feet|
Heads up display (HUD)
The HUD provides most of the information you will need in order to fly effectively. Go ahead and switch to the glass cockpit view by pressing F8 (if you need to). This view is taken up mainly by the HUD. Pressing the H key will cycle the HUD through three different modes, surface, orbit, and docking. CTRL-H will turn the HUD off and on, and ALT-H will cycle through HUD colors. For this portion, set the HUD to surface mode. You can verify the mode by the words “SRFCE EARTH” at the top of the screen. We will go over the other HUD modes later.
The image above highlights most of the HUD elements, I will go through them one by one here.
Engine, Fuel, RCS, and Trim
These are only shown in the glass cockpit view, the other views typically contain this same information in some other way. MAIN PROP indicates your current fuel level, MAIN ENG indicates the current thrust being applied from your main engines, HOVER ENG indicates the current thrust being applied from your hover engines (if available).
The RCS mode can be selected here, RCS stands for reaction control system which is what your spacecraft uses to maneuver in zero atmosphere. For atmospheric flight however, RCS should be set to OFF. We will visit the two RCS modes a bit later.
Your trim controls how your elevators on your aircraft (or spacecraft during atmospheric flight) behave. Your craft may naturally dip its nose up or down on its own due to its aerodynamic properties, as well as air speed and air pressure, you can use the trim control to compensate for this effect.
Shows your current true airspeed in meters per second (or simply m/s). It is important to note there are different methods for determining airspeed, but for now, we’ll keep it simple and just use this one.
This shows you which direction the nose of your craft is currently pointed, in relation to the cardinal directions, north being 000 degrees, east being 090 degrees, south being 180 degrees and west being 270 degrees.
Displays your current altitude in meters (or kilometers).
Shows how high or low your craft is pitched up or down. The numbers represent degrees, so the +10 line represents 10 degrees, and the long solid line represents the horizon. In the picture above there is a carrot symbol like this, -^- that represents the nose of the craft shows you where you are headed in relation to the pitch elevator.
The three boxes indicate that your landing gear is currently deployed, other symbols or messages regarding the status of your craft may also appear as they are relevant to your situation.
These controls wont be necessary right now, just be aware that they are there, we’ll discuss what they’re for later.
Throughout your experience with Orbiter, you will end up using many different MFDs, or multi-functional display modules. MFDs are small displays that, as the name suggests, are able to function in different modes, displaying different information, etc. We will use the surface MFD to demonstrate how MFDs integrate with Orbiter. From the glass cockpit view, you have two MFD panels that you can use (the 2D and 3D views also have two panels). All around your MFD are several buttons. Click the button labeled PWR on either the left or right MFD. This turns the MFD on and off. Turing an MFD display off doesn’t really serve much other than to remove a distraction from your view. Make sure at least one MFD is on and then click SEL. This brings up the MODE SELECT screen, from here you should see several options of MFD modules available. Select Surface.
The view for your MFD should now look like this (the scenario starts out with this MFD on the left side, so you probably saw it anyway). Since we already discussed the elements of the HUD, you’ll see much of the same information laid out here as well. The pitch elevator now comes with a virtual horizon (the HUD doesn’t need one because there’s a real horizon instead). You can also see information about your acceleration and vertical speed and acceleration.
Now that we’ve got a feel for our instruments, its time to push the throttle and take off.
Now that you have endured all of the boring stuff, lets get your craft off of the ground. If you have a joystick with a throttle (and you’ve configured Orbiter to use your throttle), go ahead and push your throttle to full now. If you’re on the keyboard, hold down the CTRL and + keys on your number pad until you see that your MAIN ENG indicator reads full power. You will start moving forward very quickly.
Watch your TAS (airspeed) as you move forward, it will climb rapidly. When your speed hits 150m/s, pull back on your joystick, or use the down arrow key on your number pad until your craft’s nose starts to move upward. You may not actually take off until about 160m/s or 170m/s, but once you’re up, you’ll notice your altitude increasing. After a moment or two, hit the G key to retract your landing gear, you’ll fly smoother this way. Your engines provide an enormous amount of thrust, so back them off in the lower atmosphere to about 80% (use the – key on your number pad for keyboard users), your crafts airframe will get stressed out otherwise.
Now that you’re in the air, give yourself a good amount of altitude, you don’t want to hit the ground while you’re learning. Keep your nose pitched up to gain altitude, but don’t be too aggressive about it or you’ll end up stalling. Keep your TAS between 200 and 400 m/s, adjust your throttle as necessary. Once you’ve reached around 1500 to 3000 or so meters, you can start playing around. Bank right and left by moving your joystick right or left, or using the right and left arrow keys on your number pad. This is how your craft turns in atmospheric flight, just like an airplane. Try to find a comfortable angle to turn at, you can bank all the way to 90 degrees with your wingtip pointing at the ground, then pull up on your craft to turn faster. Be careful turning like this however, you can easily over stress the frame of your vehicle.
Give yourself a few minutes, restart the scenario as often as you need to. Get to a point where you feel comfortable maneuvering your craft in the atmosphere, because the next step, you’re graduating as a pilot and becoming an astronaut.
Getting to space
The FAI considers the edge of space to be 100km, otherwise known as the Karman line. This is the point you need to cross for the international community to consider you an astronaut. Today, we will discuss two basic types of space flights, orbital, and sub-orbital.
An orbital flight contains two main elements, sufficient altitude (>100km) and sufficient velocity, whereas a sub-orbital flight is of sufficient altitude, but not of sufficient velocity to sustain a flight path around an body in space (in this case, the Earth). Lets quickly describe an orbit in more detail.
Basic Orbital Mechanics
Without air resistance, an object will travel in whatever direction is heading at whatever speed its going at until another force is acted upon it. In the vicinity of a planet, there’s gravity, and lots of it, so the path of an object is going to be affected by that gravity, depending on how close it gets to it and how fast its going. Considering this, there are two basic forces, working in two different directions. The initial trajectory of the object, which is in whatever direction it was traveling, and the gravity from the planet, which is pulling the object directly towards it. What will happen is the object will go in neither direction exactly, but in a direction somewhere between the two, depending on the distribution of the two forces. Then it becomes a little more complicated as time goes on, because gravity is a constant force, so moment by moment, as the gravity influences the object in space, it pulls its trajectory more towards its barycenter, the focal point of the gravitation force.
So, if the object has a tangential velocity in relation to the influence of gravity (that is the two forces roughly share a 90 degree angle to one another), then the object will follow a pretty nice curve around the barycenter. However, planets are very big, so there’s a very good chance that the curve the object follows will intersect the planet. When that happens, you have a sub-orbital path. If however, the object has sufficient velocity, then the curved path it follows will avoid the planet itself and will eventually return to its original position around the planet, completing an orbit.
This is a very basic look at the mechanics of an orbit, if you are intrigued but don’t feel like the explanation quite makes sense (apart from the description being brief) this is actually a good thing. This was one of the motivations that got Einstein to question Newtonian mechanics and develop the theory of general relativity. In any case, I encourage you to explore and look into it more, wikipedia’s article on orbit is a good place to start.
So, back to the simulation. As before, lets start with the Mission 1 – DG to ISS scenario. Get your Delta Glider in the air, and point yourself at a heading of 090 degrees, east. Spacecraft typically use a little trick to get a rotational boost from the Earth by taking off in an easterly heading, the Delta Glider however, has enough fuel and thrust to establish an orbit in any direction with ease, but we’ll make this a practice anyway.
Once you’ve established your heading, pitch up to gain altitude. You want to bypass the densest parts of the atmosphere as fast as you can, from altitudes of around 500 to 3000 meters, try pitching somewhere between 30 and 50 degrees. At about 10,000 meters, keep your 090 degree heading and you can maintain a pitch angle between 20 and 40 degrees, depending on whatever is most comfortable to you, your craft will pitch down on its own as it increases altitude, compensate with the trim if you need to.
You’ve got the surface MFD open in either the left or right display, open the Orbit MFD in the other one. Press CTRL-P if you have to pause the simulation.
Immediately the Orbit MFD has a lot of information and options on it. For now, look at the top where it says Prj, see if it says ECL or SHP. If it says ECL then click the PRJ button to the right of the MFD display to switch modes. This changes the perspective of the orbital projection as displayed here, form ecliptic to ship.
Next look at the left portion and see if it says PeR, ApR and Rad or if it says PeA, ApA and Alt. The first set is a measurement of orbital radius, the latter is of altitude. Radius is useful for knowing your distance to the barycenter, which is effectively the center of the Earth, whereas altitude tells you how far you are from the ground. If it appears to be in radius mode, click the DST button to switch modes, lets stick with altitude for today.
All of these numbers will update throughout our flight, and you will also notice a large grey circle and a oblong green shape. The grey circle represents the Earth, and the oblong green shape is your orbital path. It doesn’t resemble anything useful yet because you’re not in orbit, so keep gaining altitude.
At about 30km in altitude, we don’t have to climb as dramatically anymore. You can sit between 10 to 15 degrees, again whatever is most comfortable to you. At this stage, we still want to steadily gain altitude, but we also want to focus hard on speed. To establish an orbit with Earth (at lower orbit), you’ll need somewhere around 7800 m/s of speed. As I mentioned before, we’re heading east to get a boost from the rotation of the Earth, click the OS button on the surface MFD to switch to orbital speed measurement. You may notice the speed indicator in the surface MFD (but not in your HUD) change quite a bit, that’s because you’re now counting that rotation boost as well, and this is the number we’re going to watch as it approaches 7800 m/s.
Between 30km and 70km, the flight characteristic starts to become difficult, use the trim to your advantage to help keep your nose pitched appropriately. Somewhere around 50km, it gets a little ridiculous and its time to switch to your RCS systems. Set it to ROT which is your rotational mode, and in this mode, your RCS behaves similarly to your aerodynamic flight surfaces.
As you approach 60km, take a look at your orbit MFD. Look at the number for ApA, that is your apogee altitude, or the highest point of your current flight. Since space is at 100km, we want that number to be above that somewhere, lets shoot for 150km for now, a good comfortable distance outside the atmosphere. The ApA number increases as you gain altitude, and also as you gain vertical speed, or VS m/s in your surface MFD. If you feel like you’re doing pretty good with your orbital velocity, pitch your nose up some more to gain more vertical speed and increase your ApA a bit. Don’t go too far though, you’ll make your orbital insertion fairly awkward if you’ve got a big ApA but not a lot of orbital speed.
Once your ApA is around 100km or so, you can start to pitch down. 12 or 15 degrees is a good pitch angle to steadily gain altitude. Once your altitude approaches 90km, the atmosphere starts to play very little in your aircraft performance, and you’ll start to notice your RCS controls really taking effect. Now will be a good time to introduce the KILL ROT auto pilot function. Although with experience, you can learn to control the momentum of your space craft in a vacuum, its nice to be able to get the rotation of your craft under control and the KILL ROT function helps facilitate that. When you engage it, the auto pilot immediately takes over your RCS and tries to nullify the rotational forces on your craft. Normally the auto pilot will automatically turn itself off once the rotation has been killed, however, if you’re still within the atmosphere, there will be a little bit of influence from it and you’ll see the KILL ROT light stay on, click it again to disengage the auto pilot (AP). Use the KILL ROT function from time to time in small dosages to help keep your flight under control.
As you ascend and your ApA grows larger than 100km, you’ll notice the green oblong now resembling more and more of a circle, your orbital path is beginning to take shape. You should also notice a few features of the green oblong and I’ll point them out to you now. The solid line connecting to the curve points to your current position along the orbital path. The small hollow circle represents your apogee, and the small solid circle represents your perigee, the low point in your orbit. There is also a dotted line the intersects the green curve and has two boxes attached to it, one hollow, one solid. That line represents the intersection to the ecliptical plane, and the boxes represent the ascending (solid) and descending (hollow) nodes corresponding to that intersection. But don’t worry too much about that now, that will become important later.
Once your ApA hits 150km or so (you can go over, no need to worry if you hit 200, or 350km, etc), and your orbital speed is above 6000 m/s, shut down your engine. This is called MECO, or main engine cut off, but we’re not in orbit yet. You can see that your orbital path is still not all the way around the Earth, and if you were to follow your current trajectory, you’d hit your apogee and then descend back into the atmosphere; a sub-orbital flight. In the orbit MFD, look for ApT, this is the number of seconds until you reach your apogee. The apogee, or rather, shortly before it, we’re going to initiate the final orbital injection burn, building up the necessary velocity in order to circularize our orbit around the planet. In the orbit MFD, click the HUD button, this switches your HUD view from surface, to orbit. Now everything is different and your pitch elevator is sideways, etc. Click the PRO GRD autopilot button, and you’ll notice your craft automatically turn and pitch, lining up your nose indicator with the flight path indicator (the circle with a cross inside of it).
The flight path indicator was also there when the HUD was on surface mode, you may have noticed it jumping around as you were ascending. It simply shows you where your current trajectory is taking you, and in orbit mode, represents your pro grade direction, or the direction you’re currently heading in your orbit.
To circularize your orbit, you want to raise your PeA (perigee altitude) above 100km or ideally, as close as possible to your ApA. The first orbital mechanic you’re going to learn is simple, burning your engine pro grade at apogee increases perigee altitude, and burning at perigee affects your apogee altitude. The opposite is also true, burning retro grade at either one will decrease the altitude of the other. If you remember from your surface MFD what your ACC m/s² was when you were ascending to orbit, it was probably around 15 m/s². Look at your current orbital speed now and realize you need to get to ~7800 m/s. If you are at 6000 m/s now, you need to increase your speed by 1800 m/s, by the way, this difference in speed is called Delta-V, or literally, change in velocity. You will burn up fuel as you fire your engine, so your acceleration will increase, but if you just count on it being 15 m/s², then you should give yourself 120 seconds to achieve your Delta-V. You want to perform this maneuver around your apogee, so watch the ApT in your orbit MFD and when it says 60 seconds, begin your burn, that way, your burn evens out around the apogee. If you don’t have enough time with your ApT, don’t worry, begin your burn anyway, it wont be perfect, but it will be good enough.
Watch your PeA as you burn, and slow your throttle down a bit when it approaches the value you’re shooting for, then when you’ve got it, cut it off. Congratulations, you’re in orbit.
Now that you’ve gone through this process, you may find quite a bit of appreciation for this video, SpaceX’s December 2010 launch of the Dragon spacecraft.