Flight Question achieving orbit

[porterguy]

I feel stupid asking this, but how does one achieve orbit and stay there?

I already know the first answer, take off! But whenever I'm in a ship ad I've reached space, by v/s goes into the negatives. I'm not talking -50 or -60, I'm talking -1000 - -3000. It's frustrating because I've never flown a mission longer than half an hour from takeoff to splashdown because I can't stay in orbit. I've read on the wiki how to get orbit but every time I try to do that stuff I get confused and reenter the earth sooner or begin spinning uncotrolably

 

[Mythos]

Where do you launch from, earth? What spacecraft do you use? Try a Deltaglider on Moon first to get a feeling.

Like the wikis and tutorials say... Take off with not 90° angle, but about 70°. Reduce that angle the higher you are. When high enough, you'll have to thrust at 0° angle quite a while to get orbital speed. Watch "Orbit" MFD until it looks good.

If you fall down after burning and burning all the time, maybe your fuel is out!?

 

[Jarvitä]

Orbiting is about horizontal velocity, not vertical velocity. In a perfectly circular orbit, your vertical velocity will always be 0, and the horizontal velocity will remain constant (around 7800 m/s for a low Earth orbit). So, to reach orbit, don't just launch straight up, but, once you're out of the dense atmosphere, pitch down and start gaining horizontal velocity as fast as possible.

 

[PhantomCruiser]

Someone here on the forum had a "rule-of-thumb" for rocket launches, of having a pitch angle of 40 degrees at 20,000 altitude, 30 degrees at 30k and 20 degrees at 40k. Then hold 20 degrees pitch while watching the surface mfd for your vertical speed and tailor your pitch as required. It's not always pretty, but it works for me. I'd like to give a big "thanks!" to whoever posted that advice (years ago).

If you are flying the (most excellent) DGIV, it comes with some very good autopilots, one of which is a climb to circular orbit. After watching it (the auto pilot), you can then try a manual ascent mimicking what the autopilot had done.

There is also the Universal AutoPilot by Artlav. It has a few good sample launch programs in the scenarios (but you may need a few extra add-ons). But it works pretty good for vertical launches. And again, just kind of do-what-it-does for a manual launch.

In both cases; don't forget to read the manual :thumbup:

http://www.orbiter-forum.com/showthread.php?t=22753&highlight=UAP

 

[N_Molson]

And there is [ame="http://www.orbithangar.com/searchid.php?ID=5030"]another way[/ame] to put a DeltaGlider in Earth Orbit the easy way...

 

[Cras]

And there is another way to put a DeltaGlider in Earth Orbit the easy way...

That is my ride into orbit (heavily modified).

I would hesitate on following the DGIV's ascent autopilot too much, because it does take a strange route up there. I would say take a look at how the Space Shuttle gets into orbit. Try using the lua script for Atlantis ,or grab a copy of Shuttle Fleet, and watch how it gets into orbit, how it pitches down as it gains altitude, much like Phantom described, and gets itself both high, and fast, in the shortest and most fuel efficient manner.

 

[Spacethingy]

LaunchMFD is also pretty good - it has a target indicator that shows you which way you have to point your ship to get to a certain orbit (and an autopilot that can follow the indicator too).

 

[Cras]

LaunchMFD is very very very good.

 

[porterguy]

I usually fly vehicles that are "real" i.e. Space Shuttle, Soyuz, Apollo. Those three mainly. Sometimes I fly on the Ares I with the Orion capsule on it. I'll try the 70 degrees thing. Is that immediately after takeoff or at a certain amount of km above the surface?

 

[Rareth]

I've found the "Go Play in Space" guide to be very informative for the basics. it is written for learning on the Delta Glider, but I've used the steps to get the shuttle-A from earth to LEO (unloaded) before the tanks go dry.

 

[insanity]

As said above, Go Play in Space is the must-read here. Getting to orbit means more than reaching a couple hundred km above the surface of the planet. You need a lot of horizontal speed so much so that your lowest point in the orbit gives you enough speed to reach the highest point of your orbit (basically a continuous free-fall where your momentum keeps you going around and around).
This is a gross oversimplification, but you're going to have a bad time without a lot of manual reading and trial/error.

 

[EndeavourCmdr]

My contribution (not mine, but I provided the link hehe)

 

[KuatYards]

Try the UAP MFD, to can help with establishing orbit, docking with other ships/stations, landing flight to the moon, and a lot more

 

[Gothmog]

Porterguy, I think it's safe to say that most of the spacecraft you are attempting to use are minimal low-earth-orbit launch vehicles, meaning that there's only marginal room for maneuvering errors. What I have noticed about vehicles of this type is that, once the lower atmosphere is cleared, you need to pitch down towards a nearly horizontal attitude early on and start building your horizontal velocity. This means incurring a significant angle of attack, on the order of 15% or more, which is counterintuitive--we tend to imagine that the most efficient way to reach orbit is to continue applying thrust in the direction of flight.

ETA: If you are set up to run historic flights, meaning you have Earth 1962 textures installed, you can try installing the [ame="http://www.orbithangar.com/searchid.php?ID=1882"]Saturn Single Stage To Orbit[/ame] concept vehicle. Press "O" to start the autopilot. Set one of the MFDs to "Surface" and watch how the flight progresses. I'm not sure this will run in Orbiter 2010, I run this in Orbiter 2006 which is where I keep all of my historic scenarios and vehicles, like Mercury, Gemini, and so on.

 

[Mikeol1987]

Orbital Mechanics are incredibly confusing at first, I'm no mathematic genius, I also casually play Orbiter to enjoy the views and performing parts of missions in AMSO/Shuttle Fleet, AMSO helped me visualize a route into flying deep space by showing the angles of braking phase and descent phase, attack the orbit at a breaking angle (or Polar opposite depending on position) and you should be able to escape the orbit, its probably advised to do one orbit of the earth before you attempt to leave the LEO.

As for help with MFDs, I'm only just learning myself.. it takes a long time to understand spaceflight

 

[Urwumpe]

Actually, the basic orbital mechanics are just applied geometry in the form of Keplers laws of planetary motion. Until you get to flights to other celestial bodies, Keplers laws will serve you well enough.

And Keplers laws are just three.

http://en.wikipedia.org/wiki/Kepler's_laws_of_planetary_motion

They are not accurate today and especially not for interplanetary missions, but for the beginning, they are all you really need.

 

[ADSWNJ]

PorterGuy - lots of good advice above, but here's a couple more things to think about.

Have Orbit up on one of your MFD's, and have the surface HUD up in the main window. You are looking to fly East ideally, to gain the maximum benefit of the spin of the Earth. (If you are going to a specific place - e.g. Mir or ISS - then your heading may vary, but just to get into a free orbit, then head east). If you are on a fuel budget (read: realistic flight in one of the vehicles you mentioned), then you want to get up above 10km on quite a sharp angle (e.g. 70 degrees), then gradually flatten it out to horizontal by say 50km.

On the orbit display - click DSP so the left side says PeA and ApA (altitudes) rather than PeR and ApR (radius distance from center of Earth). Watch how Altitude (ALT) goes up relative to ApA (your Apoapsis Altitude - i.e. top of the curve of your ballistic trajectory or orbit). As your speed picks up past 6500 m/s you'll start to see ApA grow bigger than ALT. This means you are starting to overcome gravity with the centrifugal force from your horizontal velocity (i.e. stone on a rope starting to pull the rope taught as it picks up speed around the circle). When you hit the magic speed (around 7500 m/s, you will see ApA rapidly increase to say 200-250 km, despite your Alt being say 80 km). This is a perfect time for Main Engine Cut Off (MECO), and let the ship cruise up to the Apoapsis (watch ApT trend down to zero on Orbit MFD).

At this point, you need to do one more thing to complete your objective of getting to orbit. At ApT = 100-200 secs (e.g. 180), hit Prograde autopilot. At ApT of a few seconds (depending on your rocket power - you need to figure this out, but say 10-15 secs for a realistic engine and 5 secs for a DGIV or XR-series ship), hit the throttle again for a short burn of say 10-30 secs, to raise your Periapsis up to your Apoapsis. (Watch PeA coming up to the same value as ApA, and Eccentricity (Ecc) going down to 0.000). As you get close, you can use your forward and reverse translation thrusters to get to the elusive Ecc = 0.000, or perfect circular orbit.

Hit F1 and admire your handiwork! You'll be in orbit.

p.s. Don't feel shy about using a DG or DGIV or an XR-2 to try this stuff out. The overpowered engines are ideal to get a feel for the orbital mechanics first, and give you much more performance margin to play around than say the Shuttle's engines.

 

[Mikeol1987]

See I'm at the same level with Orbiter I think, its these kinds of breakdowns, knowing keplars law and ADSWNJ's Info will help me also. thanks alot guys, it takes stages of learning

 

[C3PO]

A good source: http://www.braeunig.us/space/index.htm

 

[ADSWNJ]

See I'm at the same level with Orbiter I think, its these kinds of breakdowns, knowing keplars law and ADSWNJ's Info will help me also. thanks alot guys, it takes stages of learning

You are very welcome. One thing I have seen consistently on this board is more experienced Orbitnauts never hesitating to help with advice for those on the learning curve. It's always great to know that whatever level you get to, there are people reading this board that have degrees in astrophysics or have worked for NASA, or simply have the time and patience to create the most awesome addons and ships for us all to fly.

I did my first trip to Mercury the other day. How cool is that?! I just wished that the sun had been 50x bigger and the ship temperature was burning up on the sunny side! Oh well!