Flight Question decaying orbit

[coffeene]

Hello, this is my first post so go easy on me please.

Problem: My orbit constantly decays while trying to align to ISS, EVERYTIME. Not sure what is going on, no matter what I have my alt it always seems to decay to less than 150 and I get reentry. Stable orbit (at least I thought) at 350k, align to ISS, check orbit and its at 401ap 190 per. I use the DG from fresh install and used interplanitary to get stable orbit.

Question: why does my orbit decay so much and what factors cause it, and how do I prevent them. I have watched tutorial videos but they do not have the same problems of dacaying orbits as much as I do.

2nd Question, not related, why doesnt the scram work on the DV? when I get to 10k and manually raise the throttle to full nothing happens, I have to use hover to get orbit. Checked for a port or an intake but I cant find one.


Thanks in advance.

 

[jthill]

Stable orbit (at least I thought) at 350k, align to ISS, check orbit and its at 401ap 190 per.

If you're not burning directly normal or antinormal to your orbit plane you'll change the orbit shape as well as alignment.

It's easy to unintentionally light the hover engines on the dg, that can hurt.

Scram only works on the DG-S, see the docs.

 

[dbeachy1]

If you're interested in a good tutorial, check out Bruce Irving's Go Play In Space -- it walks you through ascent and docking with the ISS. :thumbup:

 

[coffeene]

If you're not burning directly normal or antinormal to your orbit plane you'll change the orbit shape as well as alignment.

It's easy to unintentionally light the hover engines on the dg, that can hurt.

Scram only works on the DG-S, see the docs.

I'm burning normal+ or normal - is needed, no more no less

I've done that, now I make sure the hover is off at all times.

I'm currently on the DV-S, shows scram fuel at max

---------- Post added at 11:11 PM ---------- Previous post was at 09:59 PM ----------

ok, restarting the whole process over again. Somehow I got a file changed as something happened to the earth. Restarting orbiter from the "ready to launch to ISS" senario I noticed the iss didnt move (it orbited but the orbit lines did not), and nither did the earth. Time changed but not the earth, such as, at midnight it was still dawning at cape caneveral.

Uninstalled orbiter and reinstalled and trying to dock again. Hopefully I'll be able to dock now. Will reply when I dock, (or get completly frusterated and quit).


Only been using Orbiter for about a week, I'm 39 years old. I should figure this out eventually.

 

[cymrych]

That is a weird one, the time not propogating properly. Don't think I've heard of that one before. Hope that reinstall works.

And definitely try to stick with it until you get your hard-dock! For a lot of us on this forum, that first successful docking, when you finally see that proverbial lightbulb over your head as the process becomes clear as a bell, is one of the most rewarding milestones in our Orbiter experience. (Followed closely by first moon landing on target, then first successful interplanetary trip, then first successful sling-shot, etc.) Stick with it, you'll get there! And then you'll be hooked, and find yourself reading these threads 3 or 4 times a day, lol.

Welcome to the Forum!

 

[Urwumpe]

I'm currently on the DV-S, shows scram fuel at max

You use hover, that is already a problem. The Scram jet engine needs a high enough Mach number to produce enough compression, as the name of the engine type already suggests: Supersonic combustion Ramjet.

Use the main engines, not the hover engines and keep AOA low, as long as you are below 60 km. higher AOA means higher drag.

Also, you can decay in Orbiter now, because the atmosphere model supports exosphere drag. But I suspect from your description, that this is not the case. It also takes a little more time, a few weeks from 200 km altitude.

 

[coffeene]

Reinstall worked:thumbup:. Took me three tries but I finally met up with the ISS, if you can call it that. I got to about 10k, I think, and it flew by me like a bullet. I'll have to work on that, but its the closest I've got so far. Silly me retrograded when I saw it approching so fast, lost orbit real quick, wound up landing in Aulstralia.:rofl:


Gonna try again tommorow. let me dock this time.

 

[Wishbone]

From your descriptions: are you getting to a stable orbit with periapsis well above 150 km?

 

[Ripley]

...(or get completly frusterated and quit)...

NEVER do that!!
The Probe will eventually pop-in and drive your mind.

 

[Tex]

Hi coffeene, welcome! If video would help, you can check out my tutorial here:

http://www.orbiter-forum.com/showthread.php?t=2055

Although I use the DeltaGliderIV addon, you can still get the basic concepts behind the PlaneAlign and OrbitSync maneuvers from the video. :thumbup:

 

[deltawing777]

I'm burning normal+ or normal - is needed, no more no less

I've done that, now I make sure the hover is off at all times.

I'm currently on the DV-S, shows scram fuel at max

---------- Post added at 11:11 PM ---------- Previous post was at 09:59 PM ----------

ok, restarting the whole process over again. Somehow I got a file changed as something happened to the earth. Restarting orbiter from the "ready to launch to ISS" senario I noticed the iss didnt move (it orbited but the orbit lines did not), and nither did the earth. Time changed but not the earth, such as, at midnight it was still dawning at cape caneveral.

Uninstalled orbiter and reinstalled and trying to dock again. Hopefully I'll be able to dock now. Will reply when I dock, (or get completly frusterated and quit).


Only been using Orbiter for about a week, I'm 39 years old. I should figure this out eventually.

Humm kinda sounds like you maybe you installed orbiter multiplayer. If you did then the earth don't rotate as it does in regular orbiter. And also welcome to the forums and orbiter

 

[coffeene]

Thanks for the help everyone, I have now made several successfly dockings with the ISS (DG-4 on auto, but I'm watching it do its thing and will try it solo when I feel comfortable). I did install the "multiplayer addon" so I will not install it on this setup, I only installed it to check it out, couldnt connect anyways.


Thanks again


Quick question if I may. How do you determine the place and/or time to deorbit to land? Say I'm at the ISS and want to land at cape can. on the DG-4.

 

[Urwumpe]

Quick question if I may. How do you determine the place and/or time to deorbit to land? Say I'm at the ISS and want to land at cape can. on the DG-4.

The usual way is to wait until your ground track is a tiny bit east of the base you want to land, and you are a fixed distance away from the base, when you do your de-orbit burn and "drop out" of orbit that way. About halfway around Earth isn't a bad guess there.

Personally, I prefer using IMFD for deorbit planning, then I can place the entry interface (The waypoint that you use in spaceflight for controlling your initial reentry conditions) precisely at 45° angular distance to the base, 120 km altitude, and aim for a 1.5° reentry angle.

If you hit this entry interface, you keep AOA constant and use bank alone for controlling how fast you decelerate. If you descent with a higher rate, your deceleration will increase, if you descent at a more shallow angle, your deceleration will drop. Constant 16 m/s² is the goal until you are close to the base. This always gets me home with enough energy left for a nice steep unpowered landing approach.

Don't try to land like an airliner. you can pass the base in 8 km altitude and then do a steep spiral for lining up with the runway, if you do all right, you will be in 2.5-3 km altitude right in front of the runway, dropping at pretty high speed towards the runway at around 17° glide angle. Aim your velocity vector marker at the beginning of the lights in front of the runway, and intercept the ILS glideslope of the runway.

Pulling up for following the 3° glideslope gives you a great preflare, makes you loose velocity at the right rate, permit you to lower landing gear at low enough speeds still just as high above ground as possible. Flare, touchdown, step on the brakes, applause, power down, get out.

Any landing after that you can still walk away from your spacecraft, is a good landing.

 

[Tommy]

You may also want to check out AerobrakeMFD, available at OrbitHangar. This will help you pinpoint your re-entry so that you end up where you want to be.

If I remember correctly, after you enter the target, you want to hit the <MOD> and <PRJ> buttons - you want the page that shows a little map. AerobrakeMFD will predict where you will end up if you keep your current AoA and bank - but you need to under 200k altitude for it to be accurate.